JP2005202321A - Deflection mirror, optical scanning device, and image forming apparatus - Google Patents

Abstract

Disclosed is a deflection mirror (vibrating mirror) that can be driven at a predetermined scanning frequency regardless of the resonance frequency.
The present invention relates to a movable mirror 202 for deflecting a light beam, a torsion beam 208 connected to the movable mirror and defining a rotational axis, and a mirror swinging means for generating a rotational torque on the movable mirror, The mirror oscillating means includes a first torque generating means (first and second fixed electrodes) capable of generating a rotational torque in a first angle range in accordance with a swing angle of the movable mirror 202. 203, 204, etc.) and second torque generating means (third, fourth fixed electrodes 211, 212, etc.) capable of generating rotational torque in the second angle range, and pulses in each angle range described above A driving force is generated in a shape, and the movable mirror is amplitude driven in a frequency region deviating from its resonance frequency.
[Selection] Figure 1

Description

  The present invention relates to a deflection mirror (vibration mirror) that can be applied to an optical scanning device, an optical scanning display device, an in-vehicle laser radar device, and the like, an optical scanning device using the deflection mirror, and light thereof. The present invention relates to an image forming apparatus such as a digital copying machine, a printer, a plotter, and a facsimile using a scanning device.

In a conventional optical scanning device, a polygon mirror or a galvanometer mirror is used as a deflector for scanning a light beam. However, in order to achieve a higher-resolution image and high-speed printing, this rotation must be further increased. However, the durability of the bearing, heat generation due to windage damage, and noise are problems, and there is a limit to high-speed scanning.
On the other hand, in recent years, research on optical deflectors using silicon micromachining has been conducted, and as disclosed in Patent Document 1 and Patent Document 2, a vibrating mirror and a pivotal support using a silicon (Si) substrate are provided. A method of integrally forming a torsion beam is proposed. According to this method, since reciprocal vibration is performed using resonance, high-speed operation is possible, but noise is low and driving force for rotating the vibrating mirror is small, so that power consumption can be kept low, and Si Since a plurality of vibrating mirrors are laid out on a wafer and a plurality of wafers are simultaneously processed by batch processing, there is an advantage that the productivity is excellent.

  However, these oscillating mirrors cannot scan a wide area like conventional polygon mirrors, and as disclosed in Patent Document 3, a plurality of optical scanning devices using the oscillating mirrors as deflectors are used in the scanning direction. Are arranged and the image area is divided into main scans to perform image recording. When a plurality of oscillating mirrors are used in this way, if the scanning frequencies are not aligned, the scanning lines are not connected at adjacent boundary portions and the image quality deteriorates, so it is necessary to set the scanning frequency to a common one.

  On the other hand, the resonance frequency of the oscillating mirror is determined by the finished dimensions of the torsion beam and mirror, and if the resonance frequency is deviated, the deflection angle becomes extremely small. Therefore, in general, the scanning frequency is driven according to the resonance frequency. . Therefore, it is necessary to produce resonance mirrors with a uniform resonance frequency by using a plurality of vibration mirrors, in other words, without variation in resonance frequencies. An example in which a body is attached and the resonance frequency is driven to a target value by adjusting the mass thereof is disclosed in Patent Document 5, and an example in which processing is performed while oscillating a vibrating mirror is disclosed. Further, Patent Document 6 discloses an example in which the resonance frequency is adjusted by changing the temperature of the torsion beam and changing the spring constant.

Japanese Patent No. 2924200 Japanese Patent No. 30111144 JP 2002-258183 A JP-A-8-75475 JP 2002-40355 A JP-A-9-197334

  As described above, in the method of recording an image by dividing an image area into main scans, the optical scanning device can be downsized by reducing the scanning width and the optical path length, and using a minute vibrating mirror or the like. In addition, there is an advantage that an image forming apparatus with low noise and power saving can be provided by performing optical scanning with a low load. However, in order to match the predetermined resonance frequency as described above, the finished dimensions of the torsion beam and mirror are increased. It is necessary to process to accuracy.

However, since a plurality of vibrating mirrors are etched from one Si wafer, there is a slight difference in the etching progress speed within the surface, and there is a limit to increasing the processing accuracy. Therefore, after dividing each oscillating mirror, the mass of the oscillating mirror was individually adjusted by trimming or the like to drive the resonance frequency to the target value, or by selecting a oscillating mirror having a resonance frequency close to the target value, etc. .
For this reason, there is a problem in that the production efficiency is poor, and the resonance frequency fluctuates with a change in temperature of the spring constant, so that measures for stabilizing the resonance frequency must be taken.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a deflection mirror (vibration mirror) that can be driven at a predetermined scanning frequency regardless of the resonance frequency even if there is a variation in the resonance frequency as described above. And
More specifically, the present invention avoids the vicinity of the resonance frequency where the change in the deflection angle with respect to the scanning frequency is large, sets the scanning frequency in a frequency region outside the resonance frequency where the change is relatively small, It is an object of the present invention to obtain a deflection mirror (vibration mirror) that can improve the stability of the deflection angle with respect to a change in the resonance frequency by ensuring a predetermined deflection angle. In addition to the above object, in the present invention, productivity is improved by simultaneously processing a plurality of deflecting mirrors (vibrating mirrors) by batch processing by Si micromachining using an Si wafer substrate stacked through an insulating layer. The purpose is to improve, and furthermore, by allowing the frequency range for setting the scanning frequency to be as far as possible from the resonance frequency, the allowable range for processing variations of Si micromachining is expanded, and the productivity is further improved. For the purpose.
Furthermore, in the present invention, an optical scanning device that uses the above-described deflection mirror (vibration mirror) by Si micromachining and can perform high-quality image recording even if each deflection mirror (vibration mirror) has a variation in resonance frequency. The purpose is to provide.
Furthermore, an object of the present invention is to provide a small-sized and power-saving image forming apparatus by using the optical scanning device using the deflection mirror (vibrating mirror) by the Si micromachining.

As means for achieving the above object, a deflection mirror (vibration mirror), an optical scanning device, and an image forming apparatus according to the present invention have the following characteristics.
(1): a deflection mirror having a movable mirror that deflects a light beam, a torsion beam that is connected to the movable mirror and defines a rotation axis, and mirror swinging means that generates rotational torque in the movable mirror; The mirror swinging means includes a first torque generating means capable of generating a rotational torque in a first angle range according to a swing angle of the movable mirror, and a second torque generating a rotational torque in a second angle range. Torque generating means, generating a driving force in the form of pulses in each of the angular ranges, and driving the amplitude of the movable mirror in a frequency region outside the resonance frequency.
(2): In the deflection mirror described in (1), the mirror oscillating means generates a rotational torque in a direction in which the torsion beam is twisted at the time of activation, and a rotational torque in a direction in which the torsion beam returns after the activation. It is characterized by doing.
(3): In the deflection mirror according to (1), the mirror swinging means includes the following steps: The movable mirror is swung at or near the resonance frequency by the first and second torque generating means.
2. The drive frequency is swept from the resonance frequency and set to a predetermined scanning frequency.
Then, the movable mirror is amplitude driven.
(4): In the deflecting mirror according to (1), the mirror swinging means includes gain adjusting means for changing the gain of the driving pulse in at least one of the first and second torque generating means, The maximum deflection angle θ of the movable mirror is adjusted.
(5): In the deflection mirror described in (1), the mirror swinging means includes at least one of the first and second torque generating means, and a phase adjusting means for changing the phase of the drive pulse, It is characterized by adjusting the phase with respect to the amplitude.
(6): In the deflection mirror described in (1), the mirror swinging means generates the drive pulses of the first and second torque generating means in time series when the movable mirror rotates in any one direction. It is characterized by doing.
(7): In the deflection mirror described in (6), an overlap region is provided in an angle range of the first and second torque generating means.
(8): In the deflecting mirror described in (1), the first substrate formed by being connected to the movable mirror via the torsion beam, and the movable substrate joined to the first substrate via an insulating layer. And a second substrate forming a mirror oscillating space, wherein the first torque generating means is formed on the first substrate, and the second torque generating means is formed on the second substrate. .
(9): In the deflecting mirror described in (8), the first and second substrates are sealed in a state where the pressure is reduced at least below atmospheric pressure, and a transmission window for a light beam entering and exiting the movable mirror is provided. And a terminal means connected to the torque generating means and penetrating inside and outside for sealing.
(10): In the deflection mirror described in (1), the mirror swinging unit includes a third torque generating unit capable of generating a rotational torque in a third angle range, and according to a rotation direction of the movable mirror. Thus, the drive pulse is generated by switching to the first or second torque generating means.
(11): An optical scanning device of the present invention includes the deflection mirror according to any one of (1) to (10) above, a light source unit that emits a light beam that is reciprocally scanned by the deflection mirror, and Imaging means for forming an image of the scanned light beam on the surface to be scanned.
(12): As another configuration of the optical scanning device of the present invention, a plurality of optical scanning devices according to (11) are provided, and the scanned areas scanned by the respective optical scanning devices are connected in the scanning direction to form an image. It is characterized by forming.
(13): An image forming apparatus according to the present invention includes the optical scanning device according to (11) or (12), an image carrier that forms an electrostatic latent image with the optical scanning device, and the latent image using toner. The image forming apparatus includes a developing unit that makes a visible image and a transfer unit that transfers the toner image to a recording medium.

The deflection mirror described in the above (1) includes: a movable mirror that deflects a light beam; a torsion beam that is connected to the movable mirror and defines a rotation axis; and a mirror oscillating means that generates rotational torque in the movable mirror. In the deflection mirror, the mirror oscillating means generates the first torque generating means capable of generating the rotational torque in the first angle range according to the swing angle of the movable mirror, and generates the rotational torque in the second angle range. A second torque generating means capable of generating a driving force in a pulsed manner in each of the angular ranges described above, and driving the movable mirror in an amplitude range that is out of the resonance frequency, thereby changing the resonance frequency. Even if there is a variation in processing, the change in the deflection angle can be suppressed to a small value at a specific scanning frequency, so that the productivity is excellent and the scanning characteristics can be stably ensured until lapse of time.
Note that the present invention is not limited to the first and second angular ranges, and can provide an effect as long as it includes a plurality of torque generating means capable of generating rotational torque in different angular ranges. As the number increases, the rotational torque can be stably maintained regardless of the rotation angle, and a great effect can be expected.

  In the deflection mirror according to (2), in addition to the configuration of (1), the mirror swinging means generates a rotational torque in the direction of twisting the torsion beam at the time of activation, and after the activation, the torsion beam By switching so as to generate rotational torque in the direction of return, it is possible to generate rotational torque in an angular range close to the maximum deflection angle during driving and to act to boost the return force of the torsion beam As a result, the amplitude can be maintained even in a frequency region outside the resonance frequency.

In the deflection mirror described in (3), in addition to the configuration of (1), the mirror swinging unit includes:
1. The movable mirror is swung at or near the resonance frequency by the first and second torque generating means.
2. The drive frequency is swept from the resonance frequency and set to a predetermined scanning frequency.
By driving the movable mirror with the amplitude through the above steps, it is possible to drive the amplitude with a swing angle that exceeds the angular range in which the rotational torque of each torque generating means can be generated at the time of startup, so each angular range can be used effectively. Rotational torque can be generated, and amplitude driving can be performed with a larger deflection angle than when starting in a frequency region deviating from the resonance frequency.

  In the deflection mirror described in (4) above, in addition to the configuration in (1), the mirror swinging means varies the gain of the drive pulse to at least one of the first and second torque generating means. Equipped with gain adjustment means, and by adjusting the maximum deflection angle θ of the movable mirror, the amplitude can be made uniform at a specific scanning frequency even if there is a variation in resonance frequency between solids, which is excellent in productivity and scans over time The characteristics can be secured stably.

  In the deflecting mirror described in (5), in addition to the configuration of (1), the mirror swinging means varies the phase of the drive pulse to at least one of the first and second torque generating means. By providing phase adjustment means and adjusting the phase with respect to the amplitude, the timing of each drive pulse can be adjusted in each angle range, and rotational torque can be applied efficiently, so that the deflection angle can be maintained stably. it can.

In the deflection mirror described in (6), in addition to the configuration of (1), the mirror oscillating means is configured to drive the driving pulses of the first and second torque generating means when the movable mirror rotates in one direction. Is generated in time series so that the direction of the rotational torque can be aligned in each angular range and can be efficiently applied to the amplitude of the movable mirror, so that the deflection angle can be stably maintained.
In addition to the configuration of (6), the deflection mirror described in (7) is provided with an overlap region in the angular range of the first and second torque generating means, so that each torque generating means An angular range in which the rotational torque can be generated can be continuously provided, and the rotational torque can be efficiently applied to the amplitude of the movable mirror, so that the deflection angle can be stably maintained.

In addition to the configuration of (1), the deflection mirror described in (8) includes a first substrate formed by being connected to a movable mirror via a torsion beam, and insulated from the first substrate. And a second substrate that forms a swinging space for the movable mirror. The first torque generating means is the first substrate, and the second torque generating means is the second substrate. By forming each of them, it becomes possible to perform simultaneous processing by etching using a substrate on which the first and second substrates are bonded, so that the first and second torque generating means can be accurately applied to the amplitude of the movable mirror. It can be positioned and has excellent productivity.
In addition to the configuration of (8), the deflecting mirror described in (9) is configured such that the first and second substrates are sealed at a pressure lower than at least atmospheric pressure, and enters and exits the movable mirror. By providing sealing means having a light beam transmission window and terminal means connected to the torque generating means and penetrating inside and outside, the viscous resistance applied to the movable mirror can be reduced, and the influence of disturbance Therefore, the deflection angle can be stably maintained until lapse of time.

  In the deflection mirror described in (10), in addition to the configuration of (1), the mirror swinging means includes third torque generating means capable of generating rotational torque in a third angle range, and a movable mirror By switching to the first or second torque generating means according to the rotation direction of the motor and generating a drive pulse, the angular range in which the rotational torque can be generated can be further expanded, and the first substrate is sandwiched. By arranging the second and third substrates in this way, each drive pulse can be efficiently applied in either direction with respect to the reciprocation of the movable mirror, so that the deflection angle can be stably maintained. it can.

The optical scanning device according to (11) above includes a deflection mirror according to any one of (1) to (10) above, a light source unit that emits a light beam reciprocally scanned by the deflection mirror, By forming the scanned light beam with an image forming unit that forms an image on the surface to be scanned, the entire optical system can be miniaturized and an optical scanning device with low power consumption can be provided.
The optical scanning device according to (12) includes a plurality of optical scanning devices according to (11), and forms an image by joining the scanned areas scanned by the respective optical scanning devices in the scanning direction. Thus, the scanning width of each optical system can be reduced, so that the optical path length can be shortened and the size can be further reduced.

  The image forming apparatus described in (13) includes the optical scanning device described in (11) or (12), an image carrier that forms an electrostatic latent image by the optical scanning device, and the latent image that is developed with toner. By comprising the developing means for forming an image and the transfer means for transferring the toner image to a recording medium, the entire optical system can be made compact and the power consumption is small, so that a compact and power-saving image forming apparatus can be provided. .

  Hereinafter, the best mode for carrying out the present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 is an explanatory diagram showing the details of a deflection mirror module (vibration mirror module) used in the optical scanning device according to the present embodiment. The vibrating mirror substrate is configured by joining two Si substrates 206 and 207 via an insulating film such as an oxide film. The first Si substrate 206 is made of a Si substrate having a thickness of 60 μm, and a movable mirror 202 and a torsion beam 208 pivotally supported on the same straight line are formed by etching and separated from the fixed frame 210 by etching. The torsion beam 208 is formed in a Y shape, and is connected to the movable mirror 202 at two ends eccentric from the rotational axis by a branch branch 246. The movable mirror 202 is formed symmetrically with respect to the torsion beam 208, and has comb-like irregularities formed on the edges of both ends and the inner side of the fixed frame 210 facing each other with a gap of several μm so as to alternately engage with each other. ing. A metal film such as gold (Au) is sputtered on the surface of the movable mirror 202 to form a reflecting surface. In addition, the first and second substrates 206 and 207 as shown in FIGS. 1B and 1C are joined via an insulating layer, and etching is stopped around the electrodes from the fixed frame 210 by etching. The substrate itself is formed as an electrode by penetrating up to an insulating layer (oxide film) as a layer and separating it individually.

In this embodiment, the concave and convex portions at both ends of the movable mirror are the first and second movable electrodes (separated for convenience, but the same potential), and the concave and convex portions of the opposing fixed frame are the first and second fixed electrodes 203, 204, the island portion 221 having the movable mirror, the torsion beam, and the base portion of the torsion beam, and the island portions 222 and 223 having the respective fixed electrodes are separated from the fixed frame 210 with a separation groove gap of about 5 μm. .
The second substrate 207 is made of an 80 μm Si substrate, penetrates through the central portion by etching, and has an inner side overlapping the concave and convex portions formed on the fixed frame 210. In the same manner, the third and fourth fixed electrodes 211 and 212 are formed, and the island portions 224 and 225 are separated from the fixed frame. At this time, the separation groove is formed so as not to overlap with the separation groove in the first substrate, so that the joined state can be maintained even if the periphery is penetrated in an island shape. The third and fourth fixed electrodes 211 and 212 pass through the movable mirror 202 so that the first and second movable electrodes are engaged with each other.
In this embodiment, a voltage pulse having the same phase is applied to the first and second fixed electrodes 203 and 204 constituting the first torque generating means, and the third fixed electrode constituting the second torque generating means. A voltage pulse having a phase more advanced than a voltage pulse applied to the first and second fixed electrodes 203 and 204 is applied to 211, and a voltage pulse applied to the first and second fixed electrodes 203 and 204 is applied to the fourth fixed electrode 212. A voltage pulse having a phase delayed from the voltage pulse is applied.

  FIG. 2 is a diagram showing a state of electrostatic torque generated between the electrodes corresponding to the deflection angle of the movable mirror. Depending on whether the fixed electrode is ahead or behind with respect to the rotation direction of the movable mirror 202, the positive / negative of the electrostatic torque distribution is switched, so that a voltage pulse is applied in accordance with the amplitude and timing of the movable mirror. The range of the deflection angle where the electrostatic torque is generated is provided with an overlap region, and the second substrate is provided so that the movable mirror can secure the torque from the horizontal state (the deflection angle of 0) to the angle close to the maximum deflection angle θ. A thickness of 207 is set. The first and second fixed electrodes 203 and 204 constituting the first torque generating means and the third and fourth fixed electrodes 211 and 212 constituting the second torque generating means each have electrostatic torque. A voltage is applied in the form of a pulse within the range of the generated deflection angle, and the movable mirror 202 is driven.

  FIG. 3 shows a cross section of the electrode. In the figure, the electrostatic torque in the counterclockwise rotation direction is positive. Although the movable mirror 202 is horizontal in the initial state, when a voltage pulse is applied to the third fixed electrode 211 or the fourth fixed electrode 212, an electrostatic force in a negative or positive direction is generated between the movable mirror 202 and the opposite movable electrode. When the torsion beam 208 is twisted and rotated to tilt to a deflection angle that balances with the return force of the torsion beam, and the voltage pulse is released, the movable mirror 202 is temporarily moved to the initial state beyond the horizontal by inertia due to the return force of the torsion beam. However, it is possible to oscillate back and forth by applying voltage pulses to the first and second fixed electrodes 203 and 204 immediately before returning to the horizontal direction and continuously generating an electrostatic force in the positive or negative direction. it can.

  At this time, the moment of inertia of the movable mirror 202 and the width and length of the torsion beam 208 are designed to be applied to the band of the primary resonance mode with the torsion beam 208 as the rotation axis at a frequency close to the desired scanning frequency to be scanned. Thus, when the repetition frequency of the voltage pulse is adjusted to the resonance frequency, the amplitude is greatly increased by excitation, and the swing angle through which the movable electrodes at both ends of the movable mirror are opposed to the third and fourth fixed electrodes 211 and 212 is opposed. Expand to.

  Here, at the moment when the timing of applying the voltage pulse to the third and fourth fixed electrodes 211 and 212 exceeds the maximum deflection angle and returns to the horizontal, the third fixed electrode 211 has a positive direction, and the fourth fixed electrode 212. Then, the phase of the voltage pulse with the first and second fixed electrodes 203 and 204 is adjusted so as to generate an electrostatic force in the negative direction, and the third time-series with respect to the rotation direction of the movable mirror 202 is performed. Positive electrostatic force due to the fixed electrode 211 of the first electrode → positive electrostatic force due to the first and second fixed electrodes 203 and 204 → negative electrostatic force due to the fourth fixed electrode 212 → first and second fixed electrodes 203 and 204 Are generated in the order of negative electrostatic forces due to the above, and in both cases, the process of returning from the maximum deflection angle θ to the deflection angle 0, that is, boosting the return force of the torsion beam, The deflection angle passing through the fixed electrodes 211 and 212 can be maintained.

FIG. 4 is a diagram showing the timing of pulses applied to each fixed electrode with respect to the amplitude of the movable mirror 202. In this embodiment, writing is performed only in one of the reciprocating scans, By applying voltage pulses at optimal timing, the phase between applied pulses is set so that electrostatic torque works efficiently. The conditions are shown below.
Now, the thickness of the third and fourth fixed electrodes 211 and 212, in other words, the thickness of the second substrate 207 is t, the maximum deflection angle of the movable mirror 202 is θ (= 5 °), and the width is 2L (= 4 mm), when the thickness of the first substrate 206 is t0 (= 60 μm),
t0 <t <L · sinθ
Set the relationship to be
θ0 = arcsin ((t0 + t) / L)
Then, the first and second fixed electrodes 203 and 204 have
-θ0 <α1 <θ0
The third fixed electrode 211 includes
θ0 <α2 <θ
The fourth fixed electrode 212 includes
−θ <α3 <−θ0
A voltage pulse is applied in the range of the swing angle of the movable mirror.

In this way, by allowing the electrostatic force to work to a swing angle as close as possible to the maximum swing angle, the momentum of the amplitude can be maintained even at a scanning frequency that deviates from the resonance frequency, and the swing angle can be secured and applied to each fixed electrode. While maintaining the timing of the voltage pulse, the repetition frequency is swept from the resonance frequency and set to a desired scanning frequency.
As will be described later, the amplitude is detected by measuring the scanning time of the light beam on the scanning start side and the scanning end side, and the gain of the voltage pulse is adjusted so that the amplitude has a desired maximum deflection angle. The gain adjustment may be performed by any one of the fixed electrodes, for example, the third and fourth fixed electrodes 211 and 212. It is not necessary to perform the gain adjustment for all the fixed electrodes.

FIG. 5 is a diagram showing an example in which fifth and sixth fixed electrodes 231 and 232 are provided symmetrically to the third and fourth fixed electrodes 211 and 212 with respect to the first and second fixed electrodes 203 and 204. However, in the same manner as in FIG. 3, the positive electrostatic force by the third and sixth fixed electrodes → the positive electrostatic force by the first and second fixed electrodes in time series with respect to the rotation direction of the movable mirror 202. → Negative electrostatic force by the fourth and fifth fixed electrodes → Negative electrostatic force by the first and second fixed electrodes are generated in this order, and in the above example, the third and fourth fixed electrodes are Although the electrostatic force is applied only to one end of the movable electrode alone, that is, the electrostatic force can be applied to both ends of the movable electrode by setting the fixed electrode in three stages, even at a scanning frequency far from the resonance frequency. An electrostatic torque that secures the deflection angle is obtained. FIG. 6 shows the distribution of electrostatic torque.
The shape and thickness of the Si substrate having the fifth and sixth fixed electrodes are the same as those of the second substrate 207, and an insulating layer is provided on the first substrate opposite to the bonding surface of the second substrate. It may be joined via.

  FIG. 7 is a graph showing the characteristic of the deflection angle with respect to the driving frequency. If the scanning frequency is made to coincide with the resonance frequency, the deflection angle can be maximized, but the deflection angle changes sharply in the vicinity of the resonance frequency. . Therefore, even if the scanning frequency applied to the fixed electrode is initially set to match the resonance frequency in the drive control unit of the movable mirror, the deflection angle drastically decreases when the resonance frequency fluctuates due to a temperature change or the like. As a result, the stability over time is poor.

  FIG. 8 is a diagram showing fluctuations in resonance frequency with respect to temperature. As described above, in the case of having a plurality of movable mirrors, it is necessary to drive at a common scanning frequency, and in this embodiment, the driving frequency is in the vicinity of the resonance frequency unique to the vibrating portion composed of the movable mirror and the torsion beam. The frequency band is set to a frequency band that deviates from the resonance frequency with relatively little fluctuation of the deflection angle. The scanning frequency is 2.5 kHz with respect to the resonance frequency of 2 kHz, and the maximum deflection angle is ± 5 ° by adjusting the gain of the applied voltage. It is matched. At this time, if the resonance frequency variation (300 Hz in the present embodiment) due to the processing error of the movable mirror and the variation of the resonance frequency due to temperature (3 Hz in the present embodiment) are taken into account, even if there are these, the scanning frequency is any resonance. It is desirable to set the frequency band that does not affect the frequency, that is, sweep to 2.303 Hz or more.

Now, assuming that the dimensions of the movable mirror are length 2a, width 2b, thickness d, torsion beam length L, width c, and using the Si density ρ and material constant G, the moment of inertia I is
I = (4abρd / 3) · a ^ 2
The spring constant K is
K = (G / 2L) · {cd (c ^ 2 + d ^ 2) / 12}
And the resonant frequency f is
f = (1 / 2π) · (K / I) ^ 1/2
= (1 / 2π) · {Gcd (c ^ 2 + d ^ 2) / 24LI} ^ 1/2
It becomes.
Here, since the beam length L and the deflection angle θ are in a proportional relationship,
θ = A / If ^ 2 (A is a constant)
The deflection angle θ is inversely proportional to the moment of inertia I, and the deflection angle θ is reduced unless the moment of inertia is reduced in order to increase the resonance frequency f.

Therefore, in this embodiment, the substrate thickness d on the back side 219 of the reflecting surface of the movable mirror is left in a lattice shape, and the other portions are etched to a thickness of d / 10 or less by etching, so that the moment of inertia I is about 1/5. Has been reduced.
These parameters that are useful for the moment of inertia, dimensional errors of the torsion beam, and the like cause variations in the resonance frequency.

On the other hand, when the dielectric constant ε of air, the electrode length H, the applied voltage V, and the inter-electrode distance δ, the electrostatic force F between the electrodes is
F = εHV ^ 2 / 2δ
And the deflection angle θ is
θ = B · F / I (B is a constant)
The deflection angle θ increases as the electrode length H is longer, and a driving torque of 2n times the number of comb teeth n is obtained by using a comb-teeth shape.
In this way, consideration is given to obtaining a larger electrostatic torque at a low voltage by increasing the outer peripheral length as much as possible to increase the electrode length.

By the way, with respect to the speed υ and area E of the movable mirror, if the density of air is η, the viscous resistance P of air is
P = C ・ ηυ ^ 2 ・ E ^ 3 (C is a constant)
This viscous resistance P works against the rotation of the movable mirror. Therefore, it is desirable to seal the movable mirror and keep it in a reduced pressure state.

In this embodiment, as shown in FIG. 1, a vibrating mirror substrate formed by bonding first and second substrates 206 and 207 is bonded to a ceramic plate 213 penetrating the central portion, and is formed on a substrate 241 of a CAN package. Then, with the reflecting surface facing upward, the rotating shaft is mounted on a straight line connecting a pair of V-grooves formed on the outer edge of the substrate.
A lead terminal 216 is integrated with the base body 241 through the base body, an electrode pad of a vibrating mirror is removed on the upper surface of the second substrate, and an insulating film is removed from the separated island portions 224 and 225. In addition, the islands 221, 222, and 223 are formed by filling the through holes 226, 227, and 228 formed in the second substrate to the surface with a metal paste through an insulating film. Are connected by wire bond. Then, the step 243 of the base 241 is covered with a cap 242 and joined through a sealing material under a reduced pressure environment so that the space in the cap is sealed to 1 torr or less. At this time, the non-evaporable getter may be enclosed and activated by heating from the outside to reduce the pressure after sealing. The light beam enters and exits through a transmission window 245 joined to the inside of the cap upper opening.

  In this embodiment, the opposing mirror 215 is integrally joined to the upper surface of the second substrate 207 so as to face the movable mirror 202 in a direction perpendicular to the torsion beam. The opposing mirror 215 is formed of resin, and a metal coating is applied to a pair of inclined surfaces inclined by 9 ° and 26.3 ° from the substrate surface so as to form a roof-like angle of 144.7 ° across the slit opening 213, respectively. The structure is such that the reflective surfaces 217 and 218 are deployed in pairs by vapor deposition. The bottom surface of the counter mirror 215 is formed in parallel with the movable mirror surface and is in contact with and joined to the upper surface of the frame portion of the second substrate 207. At this time, the second substrate 207 is positioned to position the counter mirror. The mating holes 214 are formed on both sides by etching, and the pins 241 protruding from the lower surface of the opposing mirror are inserted into the mating holes 214 so that the mating holes 214 can be accurately arranged perpendicular to the rotation axis.

Conventionally, in such a vibrating mirror module, as shown in FIGS. 9A and 9B, a torsion beam 302 is formed so as to be aligned with the rotational axis of the movable mirror 301 and directly connected thereto. As described above, the inertial force Fs of the movable mirror 301 is distributed according to the distance from the rotation axis and works against the torsion beam 302, in other words, the torsional force Ft acting in the vicinity of the rotation axis. A bending stress distribution having a peak at an intermediate portion between the rotation axis and the mirror end occurs, and the surface undulates in a sine wave shape. For example, if the mirror width (both blades) is A, the maximum displacement occurs at a position about A / 6 away from the rotation axis, and the surface accuracy reaches 0.5 μm in PV.
On the other hand, in the present embodiment, the torsion beam 208 is formed in a Y shape and is connected to the movable mirror 202 at both ends of the branch branch portion 246. In addition, the width | variety of the trunk part of a torsion beam and a branch branch part is the same. By bringing the coupling position closer to the mirror end in this way, the torsional force Ft transmitted from the torsion beam 208 is dispersed, the bending stress of the mirror region surrounded by the coupling of the branch branches is reduced, and planarity can be improved.

  FIG. 10 shows the distribution of the bending stress generated in the movable mirror substrate. To counter this bending stress, the area of the thinned portion 310 is reduced in the region where the bending stress is large, and the region where the bending stress is small. It is desirable to achieve a balance between rigidity and inertial force Fs by increasing the area for removal. FIG. 11 shows an example of this. The number of ribs 309 perpendicular to the rotation axis formed on the back side of the mirror substrate is set to the mirror end, and the number of ribs is varied in a plurality of stages, and is separated from the rotation axis with a large bending stress by about A / 6. The design is such that the number of ribs in the region is increased, and the number of ribs in the region around the rotating shaft with a small bending stress and around the movable mirror is reduced. In addition, it is not limited to such a rib, it is the same even if you open a plurality of bag holes and remove the meat, or even if you change the depth with the same area of the meat removal part, arrange in any way it can.

  FIG. 12 is a diagram showing a sub-scanning section of the optical scanning device showing an embodiment of the present invention. The light beam emitted from the semiconductor laser 101 is incident through a coupling window 110 and an incident prism 136 through a transmission window 245 above the cap 242 of the vibrating mirror module 130 as will be described later. When a light beam is incident on the movable mirror 202 through the slit opening 213 of the counter mirror 215 at an angle of about 20 ° with respect to the normal in the sub-scan section including the torsion beam, the light is reflected by the movable mirror 202. The light beam is incident on the first reflecting surface 217 of the counter mirror 215 and returned to the movable mirror 202. Further, the reflected light beam passes through the slit opening 213 and is incident on the second reflecting surface 218 of the counter mirror 215 and is moved in the sub-scanning direction while reciprocating between the movable mirror 202 and the movable mirror 202. After a total of five reflections at 202, the light is again emitted through the slit opening 213.

  In this embodiment, the reflection is repeated a plurality of times in this manner, so that a large scanning angle can be obtained even if the deflection angle of the movable mirror 202 is small, and the optical path length is shortened. Now, assuming that the total number of reflections is N and the deflection angle α, the scanning angle θ can be expressed by 2Nα. In this embodiment, since N = 5 and α = 5 °, the maximum scanning angle is 50 °, of which 35 ° is an image recording area. By using resonance, the applied voltage is very small and little heat is generated. However, as is clear from the above equation, it is necessary to increase the spring constant K of the torsion beam as the recording speed, that is, the resonance frequency increases, and the deflection angle cannot be obtained. End up. Therefore, by providing the counter mirror 215 as described above, the scanning angle is expanded so that a necessary and sufficient scanning angle can be obtained regardless of the recording speed. In addition, a reflecting surface is formed facing the roof, and the incident angle in the sub-scanning direction to the movable mirror is repeatedly positive and negative for each reflection, in other words, the traveling direction accompanying reflection is distributed to the right and left. Therefore, the bending of the scanning line on the scanned surface due to the oblique incidence is suppressed, the linearity is maintained, and the rotation of the light beam in the plane orthogonal to the optical axis returns to the original posture at the time of emission. Consideration is given to avoid degradation of image performance.

  FIG. 13 is an exploded perspective view of the optical scanning device in the present embodiment, and FIG. 14 is a diagram showing the arrangement of optical elements. The semiconductor laser 101, which is a light source, has two light emitting sources formed monolithically at a pitch of 50 μm in the sub-scanning direction, and the outer periphery of the stem from the opposite side to the stepped through hole 103 provided on the wall standing on the frame member 102 , The optical axis direction is positioned by abutting the flange surface against the stepped portion, and is pressed and fixed from the back by the presser plate 1141 as shown in FIG.

  As shown in detail in FIG. 15, a pair of presser plate protrusions 1142 are engaged with notches formed on the outer periphery of the stem and rotated around the central axis of the through hole 103 to cut and raise the outer peripheral portion. The leaf spring 1143 is engaged with a hook-shaped protrusion 1144 formed on the frame member 102 to press the semiconductor laser 101, and the arrangement direction of the light emitting sources is adjusted so as to be inclined from the main scanning direction by a predetermined amount. A rotation stop is made. In addition, the U-shaped concave portion 105 has a light emitting point so that the optical axis of the coupling lens 110 is aligned with the emission axis from the semiconductor laser 101 via the UV adhesive, and the emitted light beam is a parallel light beam. Then, the UV adhesive in the gap between the recess and the coupling lens is cured and fixed.

  The coupling lens 110 can be adjusted even when the vibration mirror module and cylinder lens described later are attached, and the surface accuracy of the movable mirror and the focal line misalignment of the cylinder lens can be invalidated. There is a merit that you can. In the case of the present embodiment, there are three light source units, but all have the same configuration.

  As shown in FIG. 12, the two parallel light beams emitted from the semiconductor laser 101 and passed through the coupling lens 110 are joined to the exit window of the vibrating mirror module and have a positive curvature in the sub-scanning direction. 109 enters the incident prism 136 affixed to the incident surface, is reflected obliquely downward on the inclined surface, and is incident on the oscillating mirror module 130 as a focused light beam that is focused on the movable mirror surface in the sub-scanning direction. Then, as described above, a light beam is incident from the slit opening 213 of the counter mirror 215, and after being repeatedly reflected a plurality of times between the movable mirror 202 and the counter mirror 215, is again emitted through the slit opening 213. The

FIG. 16 is a diagram showing an array of beam spots on the surface to be scanned. As described above, the beam spot interval P in the sub-scanning direction is set by mounting the semiconductor laser 101 at an angle. The beam spot interval P is determined by using the sub-scan magnification β of the entire system from the light source to the scanned surface including the first and second scanning lenses 116 and 117 described later, and the pitch p between the two light sources.
P = β ・ p ・ sinφ
As will be described later, the pitch P is adjusted according to the inclination correction amount of the line formed on the transfer belt.

  The vibrating mirror module 130 is positioned with reference to the outer edge of the base 241 from the back side of the stepped square hole 104 provided on the bottom surface side of the frame so that the direction of the torsion beam is aligned with the optical axis direction. In this embodiment, three vibrating mirror modules 130 are positioned by a single frame member 102 at equal intervals. Each vibrating mirror module 130 is fixed to the printed circuit board 112 by abutting and fixing the upper surface of the board so as to close the lower opening of the frame member 102 by inserting the lead terminals protruding from the bottom surface of the base body into the through holes and soldering them. Circuit connection is made. A printed circuit board 112 is mounted with a semiconductor laser drive circuit, electronic components constituting a movable mirror drive circuit, and a synchronization detection sensor 113, and wiring with external circuits is made in a lump. A cable 115 having one end connected to a printed circuit board is connected to a lead terminal of the semiconductor laser 101.

  The upper surface of the frame member 102 is a surface parallel to the abutting surface in the mirror normal direction of each vibrating mirror module 130 provided on the back side of the square hole 104, and two protruding from the bottom surface of the housing 106 that houses the scanning lens. The projection 135 is inserted into the engagement hole of the frame member 102 for positioning on the same surface, and the four corners are fixed with screws. In the embodiment, the screw 137 is screwed to the printed circuit board 112 through the through hole of the frame member 102, and is integrally joined to sandwich the frame member 102, and then the soldering is performed.

  In the housing 106, a first scanning lens 116 and a second scanning lens 117 constituting an image forming unit are arranged in the main scanning direction, and are positioned and integrally held so that the respective scanning regions slightly overlap. . The first scanning lens 116 has a projection 120 that protrudes in the center of the reference surface in the sub-scanning direction and performs positioning in the main scanning direction, and a flat pressing surface 119 that engages both ends to perform positioning in the optical axis direction, The projections 120 are engaged with grooves 122 integrally formed in the housing 106 and provided on the exit surface side, and flat push surfaces 119 at each end are inserted into each of the pair of notches 121, and the corrugated springs 143 are provided on the entrance surface side. By maintaining the posture in the same plane, the relative arrangement of the scanning lenses is aligned with the same plane orthogonal to the optical axis, and the reference plane in the sub-scanning direction is aligned with the tips of the projections 142 protruding from the housing 106. By abutting, positioning in the plane orthogonal to the optical axis is performed, the installation height in the sub-scanning direction is determined, and the plate spring 141 integrally formed with the cover 138 is pressed and supported.

  On the other hand, the second scanning lens 117 is similarly provided with a protrusion 123 that projects in the center of the reference surface in the sub-scanning direction and performs positioning in the main scanning direction, and a flat pressing surface 144 that performs positioning in the optical axis direction at both ends. The protrusion 123 is engaged with the integrally formed groove 122, the flat pressing surface 144 is inserted into the notch 121, the pressing posture is held on the emitting surface side by the corrugated spring 143, and the reference surface in the sub-scanning direction protrudes from the housing 106 The installation height is positioned by abutting against the tips of the projections 145 and 146, and is pressed and supported by a leaf spring 141 integrally formed with the cover 138. Reference numeral 147 denotes a screw for fixing the cover 138.

  The synchronous detection sensor 113 (pin photodiode) is arranged at an intermediate position and both end positions shared by the adjacent oscillating mirror modules 130 so that a beam can be detected on the scanning start side and the scanning end side of each oscillating mirror module. Implemented in place. On the exit surface side of the second scanning lens 117, a mirror receiving portion 128 for attaching a V-shaped high-luminance aluminum thin plate 127 between the scanning areas of the respective lenses is formed in the housing, and the light beam reflected by the high-luminance aluminum thin plate 127 is formed. Reflecting surfaces corresponding to the scanning start side and the scanning end side of the adjacent optical scanning means so as to be guided to the respective synchronization detection sensors 113 through the openings 129 formed between the scanning regions and the rectangular holes of the frame member 102. Are placed facing each other. An opening 139 through which the light beam passes is formed in the cover 138. The cover 138 is screwed to seal the upper surface of the housing 106, and presses the scanning lens with the plate spring 141 so as to surely abut each contact portion as described above.

  FIG. 17 is a diagram illustrating a positioning method with respect to the photosensitive drum. The frame member 102 and the housing 106 of the above-described optical scanning device are formed of glass fiber reinforced resin, aluminum die cast, or the like that is secured to some degree. As shown in FIG. A pin 131 and a screw hole 133 are formed. In FIG. 17, the side plates 632 and 633 are formed of sheet metal and are arranged facing each other in the main scanning direction. Each is formed with a notch 635 for positioning the bearings 636 of the photosensitive drums 620, 621, 622, and 623, and can be engaged and supported while maintaining the arrangement accuracy of the photosensitive drums. In this embodiment, when the interval between the shaft centers is an integral multiple of the circumferential length of the photosensitive drum and the drum diameter is r, they are arranged at equal intervals so as to be k · πr. Each of the optical scanning devices 640, 641, 642, 643 inserts the positioning pin 131 into the fitting hole 637, positions the side wall of the housing in contact with the inside of the side plates, bridges the side plates, and places the screws 634 on the outside. Secure through.

FIG. 18 is a diagram showing a seam correction method for line images in adjacent optical scanning means. In this embodiment, the difference between the respective writing positions is adjusted to be zero. Assume that the recording position of the adjacent optical scanning means is shifted by D. The correction may be performed so that D = 0, but the correction unit first corrects the writing timing of the scanning line in units of line pitch p.
Specifically, the timing is shifted every k times (k · T) of one cycle T by selecting a synchronization detection signal for reading image data. Here, k is a natural number, and k with L−k · p closest to 0 is selected. Next, the remaining portion is corrected in p / n units by shifting the amplitude phase of the vibrating mirror every 1 / n times (T / n) of one cycle T. Here, n is a natural number and L- (k + 1 / n) · p may be selected as n closest to 0. In this way, line images recorded in adjacent areas on the transfer belt 638 can be joined together.

  FIG. 19 is a diagram showing the intensity distribution of each beam spot in the sub-scanning direction and the potential distribution of the electrostatic latent image formed thereby. In the drawing, the left and right are the sub-scanning direction, and a plan view and a cross-sectional view corresponding to dots for one pixel are shown. The left is the potential distribution by the beam from the first light source, and the right is the potential distribution by the beam from the second light source. In this way, in the state where the beam spots are close to each other, the potential distribution formed thereby is reproduced as a uniform distribution in which the profile (light quantity) of each beam spot is synthesized, and FIG. If the light quantity of each beam spot is the same as shown in FIG. Further, as shown in FIG. 19B, when the light amounts of the respective beam spots are different, two distributions having different latent image diameters are combined to obtain a distribution in which the center of gravity is shifted toward the higher light amount from the intermediate position. . The charged toner is attracted and adhered to a portion of the potential distribution formed in this way, which is higher than the developing bias potential, to form dots, and by balancing each light quantity, a uniform dot diameter d0 with respect to an arbitrary center of gravity position. It can be. Therefore, if the center of gravity position of the latent image is moved across the lines by changing the ratio of the light amount of each beam spot, a line having the same width as when scanning with one beam is tilted by the pitch P from the scanning direction. It can be formed. Thereby, even if the scanning line is inclined, the inclination can be corrected without using a mechanical mechanism.

The diagram shown in FIG. 20 shows an example in which the inclination of the recorded line is corrected to the lower right with respect to the scanning line as an example. The line inclination correction amount Δθ is obtained by detecting the reflected light of the beam projected from the light emitting diode 630 as shown in FIG. 17 from the detection pattern (toner image) formed on the transfer belt by the optical scanning device corresponding to each color. By disposing registration deviation detecting means 629 that receives light at the diode 631 at both ends of the transfer belt 638, it is detected as a relative deviation with respect to the reference color. Based on the detection result, the first and second beam pitches P are determined using the scanning width L according to the line inclination correction amount Δθ,
P = L · tanΔθ
The amount of the second beam is set to the maximum at the scanning start end, the first beam is set to 0, and at the scanning end, the first beam is set to the maximum and the second beam is set to 0. The light quantity of the second beam is varied so as to monotonously increase, and the light quantity of the second beam is monotonously decreased, and each sum is made constant at each position in the scanning direction. Thus, as shown by the thick line in the figure, the locus of the center of gravity of the latent image is formed obliquely to the right with respect to the scanning line with respect to the scanning direction. By correcting the adjacent areas in the same manner, the lines to be recorded are aligned in parallel, and are obliquely connected on the transfer belt to form inclined lines.

By the way, the light quantity is represented by the product of the beam intensity and the lighting time, and in order to form a latent image as described above, any of the following methods may be used.
1. Variable beam intensity.
2. The pulse width of the beam is varied.
Details will be described in drive control of a semiconductor laser, which will be described later. In this embodiment, the amount of light is varied to approximate a step shape.
The registration deviation detection means 629 can detect registration deviation (parallel shift amount) simultaneously with the inclination deviation between the respective colors. This is a method of correcting the seam correction of the line image in the adjacent optical scanning means, as described above. What is necessary is just to apply between, and it can correct | amend similarly.

  FIG. 21 is a schematic configuration diagram of an image forming apparatus showing an embodiment of the present invention. In this embodiment, tandem images are formed one color at a time on the corresponding photosensitive drum (image carrier) 504 by the four optical scanning devices 500, and the colors are superimposed as the transfer belt (intermediate transfer member) 501 rotates. Each of the optical scanning devices 500 (corresponding to the optical scanning devices 640, 641, 642, and 643 of FIG. 17 and having the configuration using the vibrating mirror module) is an example in which the present invention is applied to a color laser printer of the type. It is arranged so that the light beam emission direction is downward (the arrangement in which the optical scanning device in FIG. 12 is turned upside down). A transfer belt (intermediate transfer member) 501 constituting a transfer unit is supported by a driving roller and two driven rollers, and the photosensitive drums 504 are arranged at equal intervals along the moving direction. Around the photosensitive drum, a developing unit having a developing roller 502 and a toner hopper unit 503 for replenishing toner corresponding to each color of yellow, magenta, cyan, and black, and scraping and storing the transferred residual toner with a blade or the like A cleaning unit 508 and the like are integrally provided. Each color image is statically detected by each optical scanning device 500 by shifting the writing timing in the sub-scanning direction using a signal from a sensor 505 (registration deviation detecting means 629 in FIG. 17) for detecting a registration mark formed at the end of the transfer belt 501 as a trigger. An electrostatic latent image is formed, toner is attached to the electrostatic latent image at the developing unit, and the images are sequentially superimposed on the transfer belt 501. Paper as a recording medium is supplied from a paper feed tray 507 by a paper feed roller 506, sent out by a registration roller 510 in synchronization with image formation of the fourth color, and simultaneously transferred from a transfer belt 501 by a transfer unit 511 to four colors. Then, the toner image is sent to the fixing device by the conveying belt 515 with the toner image placed thereon. The toner image transferred to the paper is fixed by the fixing roller 512, and the paper after the fixing is discharged to the paper discharge tray 514.

  As described above, each optical scanning device 500 connects the scanning lines of a plurality of optical scanning units to form one line. The total number of dots L per line is divided into three and 1 to L1, L1 + 1 to L2, and L2 + 1 to L dots are assigned and printed from the beginning of the image. In this embodiment, the scanning areas overlap several mm on the photosensitive member. An overlap area is provided in each pixel so that the number of allocated pixels L1 and L2 is not fixed and is different for each color, so that the seams of the scan lines of each color constituting the same line do not overlap so that the boundary of the scan area becomes more conspicuous It is difficult.

  As described above, the image data is divided into three in the main scanning direction, stored in the bitmap memory of the writing control unit (not shown) for each optical scanning unit, raster-expanded for each vibrating mirror module, and buffered as line data. Saved in. The stored line data is read using each synchronization detection signal as a trigger, and image recording is performed individually. Further, as will be described later, by setting each writing start timing, registration of the writing start end is adjusted.

  In this embodiment, even if the resonance peaks of the respective vibrating mirrors are different, scanning is performed with a common driving frequency by matching the deflection angles in a predetermined band by changing the gain of the applied voltage. The spring constant changes due to changes in the environmental temperature and the resonance band shifts uniformly. Even when the drive frequency is selected again, a common drive frequency is given and the scanning frequency is shared by each oscillating mirror module. By doing so, the resist of each line can be matched up to the end of each region.

FIG. 22 is a block diagram showing a drive control system for a semiconductor laser and a movable mirror. The drive pulse generator 601 divides the reference clock by a programmable frequency divider, generates a pulse train so that a voltage pulse is applied at a timing that matches the amplitude of the movable mirror as described above, and each oscillating mirror is generated by a PLL circuit. A voltage is applied to each of the electrodes given to the driving unit 602 of each movable mirror with a predetermined phase delay δ between the modules.
Here, the relative phase delay δ between the oscillating mirrors is expressed by using one scanning line pitch p,
δ = (1 / fd) · {(Δy / p) −n}
(Where n is a natural number satisfying (Δy / p) −n <1)
The positional deviation at the joint is an integer multiple of one scanning line pitch, and the registration deviation Δy in the sub-scanning direction is reduced by correcting the writing timing every other period of the oscillating mirror, that is, by shifting by n line periods. It can be invalidated, and a high-quality image with no seam misalignment can be obtained.

In the present embodiment, the synchronization detection sensor 604 and the end detection sensor 605 are arranged on a printed circuit board, but the detection surface is arranged at a position equal to the optical path length reaching the scanned surface. In detail, the photodiode 801 and the non-vertical photodiode 802 are arranged perpendicular to the main scanning direction. When the light beam passes through the edge of the photodiode 801, a synchronization detection signal or a termination detection signal is output. By measuring the time difference Δt generated from the photodiode 801 to the photodiode 802, the scanning position deviation Δy in the sub-scanning direction, which is the main cause of the registration deviation, is measured corresponding to the photoconductor as the surface to be scanned. Can be detected as
Δy is the tilt angle γ of the sensor unit 802 and the scanning speed v of the light beam,
Δy = (v / tanγ) · Δt
If Δt is constant, there is no scan position deviation. In the present embodiment, this time difference is monitored by the scanning position deviation calculation unit 610 to detect the scanning position deviation, and the phase between the oscillating mirrors can be constantly varied and corrected so as to meet the Δt reference value.

In the main scanning direction, as will be described later, the deviation of the scanning speed in each image region is
1) Adjust the swing angle (amplitude) to a predetermined value by adjusting the gain of the voltage pulse applied to each vibrating mirror.
Also, the seam position shift between adjacent image areas is
2) The magnification of the image width is varied by shifting the pixel clock in accordance with the drive frequency of the movable mirror, and the joint between the scanning end and the scanning start end of the adjacent optical scanning device is matched.
This can be corrected.

Basically, no drive voltage is applied to the oscillating mirror except for image recording and its preparation period. When turning on the power and starting from the standby state, the drive frequency fd is varied from the high frequency side by continuously changing the frequency division ratio with a programmable frequency divider, and the output from the amplitude detector 609 is implemented. In the example, the beam is detected by the synchronization detection sensor 604 and the end detection sensor 605 disposed in the vicinity of the scanning angle −θ0, and the time difference T between the synchronization detection signal and the end detection signal is measured by the amplitude calculation unit 609. Then, the deflection angle (amplitude θ0) of the movable mirror is detected.
Now, if the scanning angle of the light beam detected by the sensor is θd, the scanning time from the center of the image is t, and the driving frequency of the movable mirror is fd,
θd / θ0 = sin2π · fd · t, t = T / 2
Given in.

The deflection angle is corrected by varying the gain of the applied voltage pulse until the time difference T reaches a predetermined reference value T0. This correction is performed periodically under each environment, for example, between jobs. If this correction is performed during image recording, the main scanning end of the image fluctuates, so that the same value is maintained during recording. In this embodiment, a plurality of oscillating mirrors are provided. However, when a common drive frequency is selected and the reference values of the gains are aligned, the deflection angles between the oscillating mirrors are made to coincide.
The above correction is performed in each of the vibrating mirror modules, and in this embodiment, it is composed of three optical scanning means, so that the printing operation can be performed after all the corrections are completed.

Next, drive control of the semiconductor laser will be described. As described above, in order to make the line pitch of the latent image uniform by reciprocating scanning, it is necessary to change the beam intensity or the pulse width of the beam. Therefore, in the first embodiment, a method for changing the beam intensity will be described.
FIG. 24 shows the beam intensity with respect to the applied current to the semiconductor laser. When the beam intensity exceeds the threshold current, the beam intensity increases in proportion to the applied current. Therefore, the difference Im-Ith from the threshold current Ith to the maximum current Im for obtaining a predetermined beam intensity is divided into n, in this embodiment, 255, and the drive current may be varied stepwise based on variable data. .
As described above, in one light source, Im is gradually decreased from the start of writing in the main scanning direction to the end of writing using the synchronization detection signal as a trigger, and in the other light source, writing is performed. Im is gradually increased from Ith from the beginning to the end of writing.

By the way, in general, the LD drive unit 606 performs feedback control to increase or decrease the drive current so that the beam intensity becomes constant by the monitor signal from the semiconductor laser. This is because Ith and Im that emits the same beam intensity change as the case temperature changes, and unless this control is performed, the beam intensity changes between the low temperature state and the high temperature state, and the image density differs. A malfunction occurs.
Therefore, in this embodiment, a change in the drive current Im ′ that provides a predetermined monitor signal output value is uniformly added to the drive current as a bias current ΔIth of the threshold current.

Next, a method for changing the pulse width (pixel clock fm) of the beam in the second embodiment will be described. The clock pulse generator 607 counts the frequency-divided clock obtained by dividing the reference clock f0 by the programmable frequency divider based on the variable data to form a PLL reference signal fa having a pulse width as long as k clocks. The phase of the reference clock f0 is selected in the PLL circuit, and the pixel clock fk is generated. Of course, the longer the pulse width, the larger the diameter of the latent image formed, and the shorter the pulse width, the smaller. Therefore, a latent image having an arbitrary diameter based on variable data can be formed by switching the pulse width stepwise along the main scan.
As described above, one light source is reduced from the latent image diameter corresponding to one pixel from the start of writing in the main scanning direction to the end of writing using the synchronization detection signal as a trigger, and the other light source is written. The latent image diameter corresponding to one pixel is increased from the start to the writing end.

By the way, since the movable mirror is resonantly oscillated, the scanning angle θ changes like a sine wave. On the other hand, it is necessary to print main scanning dots at a uniform interval on the photosensitive drum surface that is the surface to be scanned, and the imaging characteristics of the scanning lens described above are such that the scanning distance dH / dθ per unit scanning angle is sin ⁻¹ θ /. It is necessary to correct the direction of the light beam so that it is proportional to θ0, that is, in the middle of the image, it becomes faster and faster as it goes to the periphery, and the power is distributed so that the imaging point moves away from the center to the periphery. However, in order to obtain a uniform beam spot, there is a limit in expanding the effective scanning area θs with respect to the maximum amplitude θ0.

  Therefore, in the present embodiment, as shown in FIG. 25, the phase difference corresponding to each pixel is delayed in a stepwise manner from the state in which it progresses from the start of writing to the end of writing, against the change in scanning speed due to the amplitude. At the same time, the pixel clock fm is driven by LD so that the pulse width of each pixel is gradually reduced from a long state in the region from the start of writing to the center of the image, and becomes longer in the region from the center of the image to the end of writing. By applying the electrical correction to the unit 606, the burden on the scanning lens is reduced and the scanning efficiency is improved. Such control is to set the pulse width and its phase difference so that the dot diameter corresponding to each pixel is uniform, so a pulse is generated by proportionally distributing the pulse width corresponding to one pixel set here. Thus, even if the latent image diameter is changed as described above, it can be easily handled without adding a new control circuit.

  In the embodiment described above, the semiconductor laser is a semiconductor laser array having two light emitting sources. However, the present invention is not limited to this. The above light emission sources may be used.

  The deflection mirror (vibration mirror) of the present invention described above can be suitably used for an optical scanning device. Further, it can be applied to an optical scanning display device, an in-vehicle laser radar device, and the like. The optical scanning device using the deflection mirror can be suitably used as an optical writing device for an image forming apparatus such as a digital copying machine, a printer, a plotter, and a facsimile, and a compact and power-saving image forming apparatus can be used. realizable.

FIG. 2 is a configuration explanatory diagram of a deflecting mirror (vibrating mirror) module according to an embodiment of the present invention. It is a figure which shows the mode of the electrostatic torque which generate | occur | produces between each electrode corresponding to the deflection angle of the movable mirror of the deflection | deviation mirror (vibration mirror) module shown in FIG. FIG. 2 is a schematic cross-sectional view of an essential part showing an example of a cross section of an electrode of the deflection mirror (vibration mirror) module shown in FIG. 1. It is a figure which shows the timing of the application pulse to each fixed electrode with respect to the amplitude of a movable mirror. It is a schematic principal part sectional drawing which shows another example of the cross section of the electrode of the deflection | deviation mirror (vibration mirror) module shown in FIG. It is a figure which shows the mode of the electrostatic torque which generate | occur | produces between each electrode corresponding to the deflection angle of a movable mirror at the time of providing the 5th, 6th fixed electrode. It is a figure which shows the characteristic of the deflection angle with respect to a drive frequency. It is a figure which shows the fluctuation | variation of the resonant frequency with respect to temperature. It is explanatory drawing of the bending stress which arises in the movable mirror board | substrate of the conventional vibration mirror module. It is a figure which shows distribution of the bending stress which arises in a movable mirror board | substrate. It is a figure which shows the example of the rib formed in the back side of the mirror substrate of a movable mirror. It is sectional drawing of the subscanning direction of the optical scanning device which shows one Example of this invention. It is a disassembled perspective view of the optical scanning device which shows one Example of this invention. It is a figure which shows arrangement | positioning of the optical element of the optical scanning device shown in FIG. It is a figure which shows the detail of the fixing | fixed part of a semiconductor laser. It is a figure which shows the arrangement | sequence of the beam spot in a to-be-scanned surface. FIG. 4 is an exploded perspective view of a main part of the image forming apparatus showing a positioning method between the optical scanning device and the photosensitive drum. It is a figure showing the joint correction method of the line image in an adjacent optical scanning means. It is a figure which shows the intensity distribution of each beam spot in a subscanning direction, and the electric potential distribution of the electrostatic latent image formed by this. It is a figure which shows the example which correct | amends the inclination of the line recorded on the right side with respect to a scanning line. 1 is a schematic configuration diagram of an image forming apparatus showing an embodiment of the present invention. It is a block diagram showing the drive control system of a semiconductor laser and a movable mirror. It is a figure which shows an example of the detection part of a synchronous detection sensor or a termination | terminus detection sensor. It is a figure which shows the beam intensity with respect to the electric current applied to a semiconductor laser. It is a figure which shows the change of the pulse width and phase difference in the area | region from the write start to the write end.

Explanation of symbols

101: Semiconductor laser
102: Frame member
106: Housing
109: Cylinder lens
110: Coupling lens
113: Synchronous detection sensor
116: First scanning lens
117: Second scanning lens
130: Vibration mirror module
136: Incident prism
138: Cover
202: Movable mirror
203: First fixed electrode
204: Second fixed electrode
206: First substrate
207: Second substrate
208: Torsion beam
210: Fixed frame
211: Third fixed electrode
212: Fourth fixed electrode
213: Slit opening
215: Opposite mirror
241: Base
242: Cap
500, 640, 641, 642, 643: Optical scanning device
501, 638: Transfer belt (transfer means)
504, 620, 621, 622, 623: Photosensitive drum (image carrier)

Claims (13)

In a deflection mirror having a movable mirror for deflecting a light beam, a torsion beam connected to the movable mirror and defining a rotational axis, and a mirror swinging means for generating a rotational torque in the movable mirror,
The mirror swinging means includes a first torque generating means capable of generating a rotational torque in a first angle range according to a swing angle of the movable mirror, and a second torque generating a rotational torque in a second angle range. And a torque generating means for generating a driving force in a pulsed manner in each angle range, and driving the movable mirror in the frequency region deviating from its resonance frequency. The deflection mirror according to claim 1.
The deflection mirror according to claim 1, wherein the mirror swinging means generates a rotational torque in a direction in which the torsion beam is twisted at the time of activation, and a rotational torque in a direction in which the torsion beam returns after the activation. The deflection mirror according to claim 1.
The mirror swinging means includes the following steps:
1. The movable mirror is swung at or near the resonance frequency by the first and second torque generating means.
2. The drive frequency is swept from the resonance frequency and set to a predetermined scanning frequency.
A deflection mirror characterized in that the movable mirror is amplitude driven via The deflection mirror according to claim 1.
The mirror oscillating means includes gain adjusting means for changing the gain of the drive pulse in at least one of the first and second torque generating means, and adjusts the maximum deflection angle θ of the movable mirror. And a deflection mirror. The deflection mirror according to claim 1.
The mirror oscillating means includes a phase adjusting means for changing the phase of the drive pulse in at least one of the first and second torque generating means, and adjusts the phase with respect to the amplitude. The deflection mirror according to claim 1.
The deflection mirror characterized in that the mirror swinging means generates the drive pulses of the first and second torque generating means in time series when the movable mirror rotates in any one direction. The deflection mirror according to claim 6,
A deflection mirror characterized in that an overlap region is provided in an angle range of the first and second torque generating means. The deflection mirror according to claim 1.
A first substrate connected to the movable mirror via the torsion beam, and a second substrate joined to the first substrate via an insulating layer to form a swinging space of the movable mirror. And a first mirror generating means on the first substrate and a second torque generating means on the second substrate, respectively. The deflection mirror according to claim 8.
The first and second substrates are sealed in a state at least depressurized below atmospheric pressure, and are connected to a sealing means having a transmission window for a light beam entering and exiting the movable mirror, and the torque generating means, A deflecting mirror comprising terminal means penetrating inside and outside to be sealed. The deflection mirror according to claim 1.
The mirror swinging means includes third torque generating means capable of generating rotational torque in a third angle range, and is switched to the first or second torque generating means according to the rotation direction of the movable mirror. A deflection mirror that generates a driving pulse.   11. A deflection mirror according to claim 1, a light source means for emitting a light beam reciprocally scanned by the deflection mirror, and an imaging means for forming an image of the scanned light beam on a surface to be scanned. And an optical scanning device.   12. An optical scanning device comprising a plurality of optical scanning devices according to claim 11 and forming an image by joining scanned regions scanned by the respective optical scanning devices in a scanning direction. 13. The optical scanning device according to claim 11 or 12, an image carrier for forming an electrostatic latent image by the optical scanning device, developing means for developing the latent image with toner, and recording the toner image on a recording medium. An image forming apparatus comprising: a transfer unit that transfers the image to the image forming apparatus.

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