GB2199266A - Automatic density control in electrostatographic copiers - Google Patents

Abstract

A bar code scanner or reader 106 is used for automatic density control in electrostatographic copiers. A test patch composed of a succession of different voltage levels on a photoreceptor 104, (corresponding to lines of a bar code), are arranged in order that the number of lines developed to a visible state are used to produce proper development control. As an example, assuming five lines, the first three would be developed to visibility when toner concentration (developability) is normal, and only two lines developed to visibility if a standard addition of toner is needed. The presence of only one line might call for a larger-than-normal toner addition, and a count of zero or more than three lines trigger appropriate signals to the operator. The lines of various voltages could be generated in several ways, such as a small transparency or slitted screen 100 with a separate light source 102, a transparency intermittently introduced into the path of the exposure light, an opaque test patch adjacent the document area for exposure through a lens, or a small charging device intermittently energized to various voltages. <IMAGE>

Description

Reproduction ApParatus This invention relates to toner dispensing devices and in particular to the automatic control of these devices.

In electrophotographic apparatus, an electrostatic image, formed on the surface of a drum or web, is developed by the application of finely-divided toner particles to form a toner image. In certain electrophotographic apparatus, toner images are formed from electrostatic images by Drushlng a developer mixture of ferromagnetic carrier particles and smaller toner particles across the electrostatic images. The contact of the ferromagnetic particles with the toner oarticles charges the toner particles by triboelectrification to a polarity needed in order that the toner particles are attracted to the electrostatic images for toning.

In this process, toner particles are depleted from the developer mixture, requiring replenishment to avoid a gradual reduction In density of the toner images. Toner replenishment is accomplished by several different types of apparatus. in one type, a given amount of toner Is added to the mixture after a given number of copies is made. This approach is acceptable if the amount of toner used for each copy is reasonably predictable. In some apparatus, however, the amount of toner used in any copy or group of copies can vary substantially. For this reason, toner concentration monitors have been designed which automatically add toner according to the results of a monitoring process.

US-A- 2,956,487 generally shows the use of control signals to activate a vibrator to add developer particle powders from a reservoir to a magnetic brush trough. US-A- 3,348,522, 3,348,523 and 3,376,853 disclose a reflective type sensor for use in closed loop automatic development control. A ciean drum signal is compared to a signal reflected from a test pattern formed on the drum. Separate sensors are utilized for detecting each signal. The outputs of the sensors are compared by a bridge circuit to provide an error signal, and a toner dispenser is operated in response to the error signal. In these systems,the degree of development is measured directly from a developed test stripe on the photoreceptor drum extending along the peripheral edge of the drum.

In systems such as shown in US-A- 3,873,002 and 4,065,031, an electrically-biased transparent electrode disposed on the photoreceptor surface is conveyed past the development station to attract toner particles. Light is transmitted from within the photoreceptor through the transparent electrode and detected by a photosensor located near the photoreceptor surface.

The photosensor provides a signal indicative of the density of toner particles on the transparent electrode. A disadvantage with systems of this type is the relative cost because of the complexity and number of components required.

Other systems control toner dispensers by measuring toner concentration in the developer mixture contained in a developer housing or reservoir. For example, US-A- 3,233,781 discloses reflecting a light beam from the developer mixture. The measure of the reflectivity of the mixture manifests the proportion of toner to carrier concentration In the mixture.

Disadvantages with Systems of this type are due in part to "noise" generated in the system, to the fact that the system is only an analog of the amount of toner actually applied to the photoreceptor surface, and to the dependence of the system on the constituents of the developer mixture.

Other examples of analog control are the use OT a funnel in tne developer apparatus to collect developing material An induction coil is wound about the funnei and connected to the motor of a toner disperser Ihrougn a bridge circuit.The reactance nf the snciuctlor coil varies In accordance W!'t DrODOr4!Oo oi toner cor.tained in tre aeveloD n? maKev,a; Other systems, sucn as disclosed In u'S-A- 3,719. 16;;, control a toner reDlenisher Dj' measuring ne eieciric ootential of a magnetic developing brusn In US-A- 3,876,106, light is reflected from a aeveiopment brush to measure the concentration of toner in the developer housing The reflected signal Is fed to a computer and the computer determines whether or not toner should be added, and controls a toner replenishment device accordingly. In other approaches to Improve toning, often 'referred to as "Auto-bias," the potential of an electrode In the development station Is adjusted as a function of the charge density of the electrostatic image.See, for example, US-A- 3,779,204 teaching the use of an electrometer probe disposed near a photoreceptor belt to provide "Autobias" and also to produce a signal to actuate a toner dispenser through threshold circuitry.

It is also known as disclosed in US-A- 3,529,546, to replenish the supply of printing substance in relation to the number of print signals sensed, i.e. the pixel count. US-A- 4,587,411 discloses a method for printing, evaluating, and checking a printing image such as a bar code in an electrically-activated thermal printer. The method involves the printing image scanning and sensing the resulting bar code, comparing the sensed portion with predetermined data, and rejecting inadequate printing images. US-A- 4,589,762 discloses a method and device for dispensing toner in a xerographic printer. An electrostatic image is produced by exposing each line of a photoconductor by the activation of discrete sources of radiation spaced along the line.

The toner dispensing operation Is controlled by counting the number of operative radiation sources during exposure of the photoconductor, and dispensing additional toner when a preset number of operative radiation sources is obtained.

The difficulty with many of the forementioned development control systems is often the cost and complexity. In addition, it is often difficult to compensate for a variety of changing characteristics, such as the changing characteristics of a photoreceptor surface, the changing characteristics of the documents to be copied, and even the changing characteristics of the toner dispenser Itself. Another difficulty with prior art systems Is often the inability to control low densitv, or narrow-line, copies It is an object of the present invention, therefore, to provide a new and improved automatic toner density control.

Briefly, the present invention is based on the use of a bar code scanner or reader for automatic density control. A test patch, composed of a succession of different voltage levels on a photoreceptor (corresponding to lines of a bar code), is arranged in order that the number of lines developed to a visible state are used to produce proper development control. As an example, assuming five lines, the first three would be developed to visibility when toner concentration (developability) is normal. and only two lines developed to visibility if a standard addition of toner is needed. The oresence of only one line might call for a larger-than-normal toner addition. and a count ot zero, or more rnan three !ines, trigger appropriate signals to the operator.The lines of various voitages could be generated In severai ways, such as a small transparency with a flashing light, a transparency intermittently introduced into the path of the exposure light, an opaque test patch adjacent the document area for exposure through a lens, or a small charging device intermittently energized to various voltages.

For a better understanding ofthe present invention, reference may be had to the accompanying drawings wherein the same reference numerals have been applied to like parts and wherein: Figure 1 is a front view of a reproduction machine incorporating the present invention; Figure 2 is a schematic-block diagram illustrating the bar code reader development control system in accordance with the present invention; Figure 3 illustrates a toner dispenser mechanism of Figure 1; and Figure 4 illustrates another embodiment of a bar code projector and reader.

Referring to Figure 1, there is shown a typical reproducing machine 10 employing an image-recording drum 12 having the outer periphery coated with a suitable photoconductive material providing an image-bearing surface 13. The drum 12 is suitably journaled for rotation within a machine frame (not shown) by means of a shaft and rotates in the clockwise direction to bring the image-bearing surface past a plurality of machine components or xerographic processing station. Suitable drive means (not shown are provided to power and coordinate the motion of various machine components to produce a faithful reproduction 0T image of an original document upon a sheet of final support material.

Initially, the drum 12 moves the surface 13 through a charging station 17 for placing an electrostatic charge over the surface 13 in known manner preparatory to imaging. Thereafter, the drum 12 is rotated to exposure station 18 and the charged surface 13 is exposed to a light image of an original document supported at platen P. The document image selectively dissipates charged surface 13 to form an electrostatic latent Image. After exposure, drum 12 rotates the electrostatic latent image recorded on the surface 13 to development station 19 and a conventional developer mix including toner and carrier particles is supplied to the surface 13, rendering the latent Image visible.

Sheets 15 of the final support material are supported in a stack arranged on an elevating stack support tray 20. With the stack at its elevated position, a sheet separator 21 feeds Individual sheets to a registration device 22. The sheet Is then forwarded from registration device 22 to a transfer station 23 In proper registration with the Image on the drum.The developed Image on the surface 13 Is brought into contact with the sheet of final support material within the transfer station 23 and the developed Image Is transferred from the surface 13 to the contacting side of the support sheet after the oeveiooea :mage has beer transferred to the sheet of final suDport maternal 15. the sheet with the developed image Is advanced to a suitable fuser 24. The fuser 24 coaiesces tne transferred image to the final support sheet 15 After the fusing process, the final support sheet is advanced to a suitable output device, such as a tray 25.

although a preponderance ot the toner particles are transferred to the final support material, invariably some residual particles remain on the surface 13 after transfer. The' residual particles remaining on the surface 13 are removed form the drum 12 by a cleaning station 26. The particles may be mechanically cleaned from the surface 13 by any conventional means as, for example, by the use of a cleaning blade.

Documents are manually presented for exposure on platen P or automatically presented by a document handler 30 including an Input transport comprised of input pinch rolls 31 and 32, selectively disengageable in order that a document may be readily placed between them. The document handler 30 also includes a wait station 33 and a (not shown) pivotallysupported registration gate for pre-registrating the document, and also a platen belt transport 35 and registration gate 37 provided at the distal end of platen P. After imaging, the document is advanced off the platen P to output tray 38 by means of the belt transport 35.

A document positioned on platen P is scanned by a lamp 40 moving from left to right (as viewed) together with a full-rate mirror 41 and half-rate mirror 42. The image of the scanned document is projected from full-rate mirror 41 to half-rate mirror 42 to lens 43. The image is projected from a lens reflection mirror 44 back through the lens 43 to stationary mirror 45 to drum surface 13.

Still referring to Figure 1, a copy output station generally shown at 47 is arranged adjacent the output of the fuser 24. As a sheet 15 leaves fuser 24, it is carried by output rolls along a sorter transport 49 A deflection gate or pivoting chute 48 is arranged to deflect the sheet 16 selectively from the sorter transport 49 into the output tray 25, or allows its continued advancement along the horizontal transport. When the chute 48 is in the 'up' position, the sheet 15 falls into the output tray 25 When the chute is in the 'down' position, the sheet 15 is directed forward along the sorter transport 49 to the sorter bins via vertical transport 51.

With reference to Figure 2, in accordance with the piesent invention, a bar code transoarency 50, upon excitation of lamp 52 by controller 54, projects a bar code onto a portion of the drum surface 13 in the interdocument space. The interdocument space is defined as that portion of the drum surface 13 separating successive document images projected onto surface 13.

For a more complete description of controller 54, reference is made to US-A- 4,326,646.

During projection of a document image onto the drum surface 13, portions of the surface will be dischargea corresponding to the Image. The bar code area (not drawn to Scale, for illustration porposes) on the surface 13 is discharged by the projection of light from lamp 52 through transparency 50.

t should be noted that the scooe of this invention contemplates any suitable method for projecting a bar code image onto the surface 13 of the photoreceptor. For example, another method would be to secure an opaque bar code target at the end of the platen P. This bar code target or image is preferably placed on the underside of the platen P outside the image area of the platen as illustrated at 52. The scanning mechanism Is then adjusted to continue to scan under the target in order to project the bar code image onto surface 13 immediately before or after the image.

Both the areas of the surface 13, corresponding to document imaging and the portion of interdocument space exposed to the bar code platen rotate to the development station 19 and receive toner from magnetic brush developer 55 in combination with dispenser roll or toner dispenser 56. A suitable bar code sensor 58 located near drum 12 between development station 19.and transfer station 23 senses the number of bars developed on the surface 13.

A typical sensor might include a housing having a light-emitting diode (LED) 60, receiving an activating pulse from the controller 54. The light from LED 60 is reflected from the bar code sample area on the surface 13 and received by a detector 62. The signal from the detector 62, manifesting the number of developed lines of the bar code, is amplified in preamplifier 64 and enters the signal-processing circuits 66 which may be a simple digital counter.

The output signal from the signal processing circuits 66 is conveyed to controller 54 for appropriate response depending upon the number of bars that have been sensed.

As illustrated in Figure 2, an automatic development control loop comprising sensor 58 provides an input signal to processing circuits, and an energizing signal provided by controller 54 to vary the time period of activation of toner dispenser 56. In a preferred embodiment, the time period is duty cycle related. That is, the time of activation is a predetermined percentage of the machine copy cycle time.

Responsive to sensor 58 the controller 54 produces a signal to activate solenoid 74 to control toner dispenser 56. The toner dispenser 56 adds toner to the magnetic brush developer 56 to change the quantity of toner particles added to drum surface 13.

Referring to Figure 3, the magnetic brush developer 55 is provided in a developer housing 75 at the developing station 19. The rear of the housing 75 forms a sump containing a supply of developing material. A passive cross-mixer (not shown) In the sump area serves to mix the developing material, and a transport roll 77 lifts the material to the top of the housing 75.

As will be understood by those skilled in the art, the electrostatically-attractable developer material commonly used in magnetic brush developing apparatus comprises a pigmented resinous powder, referred to as toner. and larger granular beads referred to as carrier.

To provide the necessary magnetic proDerties. the carrier Is comorised of a magnetizable material such SS stee' By virtue of the magnetic fieíd established bv the magnetic brush develooer 55. a Slarc-et of oeveiooing mater a! ::s formed along tne surTace ox tne magnetic Drusn developer 55 aaiacent tne drum surtace 13 oner is attracted to the electrostatic latent Image from the carrier deans to produce a visible powder image on the drum surface 13 Magnetic brush oeveioper 55 comprises a rotatale exterior sleeve and a relatively stationary magnet disposed within tne interior of the exteriOr sleeve. The sleeve Is rotated with respect to the drum surface 13 by the housing drive 78 In a preferred embodiment, housing drive 78 is a gear connected to the machine 10 main drive through a suitable clutch.To regulate development of the latent electrostatic image on the drum surface 13, the exterior sleeve is electrically biased by a suitable power supply (not shown).

In accordance with another aspect of the present invention,the optimum proportion of toner to carrier material is provided by sensing the developed bar code by sensor 58 and producing a bar code signal for signal processing circuits 66. The signal generated by processing circuits 66 determines the time period of activation of the dispenser roll or toner dispenser 56 through dispenser solenoid 74 to control the amount of toner to be added to the developer housing 75 from a toner supply hopper 80. To discharge toner from the toner supply hopper 80, rotatable toner dispenser 56 is provided at the lower or dispensing end of the toner supply hops 80, at the inlet to the developer housing 75.Toner supply hopper 80 can be any suitable container for toner that provides toner to a toner dispenser for replenishing the supply of toner in the developer housing.

Preferably, toner dispenser 56 is a foam roll driven by a cam follower 81 integral with lever arm 82. The cam follower 81 pivots about dispenser roll point 84 responsive to the housing drive 78 driving dispenser drive cam 86. As illustrated in Figure 3, this motion is prevented by the action of pin 88 of interrupt mechanism 90 engaging lever arm 82. To release pin 88 from engagement with lever arm 82, dispenser solenoid 74 is energized to retract interrupt mechanism 90. This disengages pin 88 from engagement with surface 92 of lever arm 82. The energization of dispenser solenoid 74 retracts interrupt mechanism 90 from right to left, and thus pin 88, to the position shown In phantom. The retraction of pin 88 releases lever arm 82 for pivoting motion about dispenser roll point 84.The release of lever arm 82 enables cam follower 81 engaging the toner dispenser 56 to move in response to the surface of cam 86. The motion of cam follower 81 rotates the toner dispenser 56, causing toner to be deposited from the supply hopper 80 to the developer housing 75 Preferably, the toner dispenser roll 56 is comprised of a relatively porous, sponge-like material and rotates to carry toner particles adhering to the sponge-like material for depositing into the developer housing 75. Any other suitable toner dispenser may be used.

With reference to Figure 3, the machine 10 preferably includes a controller logic board 94 incorporating the controller 54 with related memory and a driver board 96 electrically connected to the controller logic board 94 and the sensor 58 ne sensor 58 can pe anv standard commercial bar coae reader sucn as used ,n suDermarKets and other out!et stores. Suitablv, the test patch or bar code is composed of a succession oi lines of varying voltage arranged so that the number of lines developed to a visible state Decomes the criterion or standard of adeauate development.In one embodiment, a number ot lines, for exampie, five, each about 0.5 mm wide 6 mm long and 2.5 mm apart, extend across the photoreceptor perpendicular to the direction of motion. After development, these lines would come into the field of view of the bar code sensor in succession. At the beginning of the test pattern or bar code, and if desired again at the end of the test pattern, there would be two or more lines that would identify the pattern and to Initiate counting the lines between.

Other variations, such as different line widths and spacing, could be used.

Various control responses can be implemented. For example, assume five lines in the bar code pattern. A suitable control response could be that the first first three lines would be developed to visibility when toner concentration (developability) is normal. Two lines would be developed for an indication of a normal addition of toner. The presence of only one line developed would indicate a larger-than-normal toner addition, and count of zero or four lines might trigger appropriate instructions or signals to the key operator.

In response to a reading of three lines, the dispenser solenoid 74 might be activated for 0.5 seconds. A sensing or measurement of only two lines might result in a energization of the dispenser solenoid for two seconds. On the other-hand, if the fourth line starts to become visible, indicating a more-than-normal density, the dispenser solenoid 74 might not be activated at all. It should be understood that there are various embodiments and variations of the bar code in response to the sensed lines to provide a wide range of development control. For example, Figure 4 illustrates another embodiment. A slitted screen 100 is placed in front of an LED array, shown at 102, and during the interdocument period, the LEDs are illuminated, generating a latent image of the array on the photoreceptor 104. The image is then developed creating an imperfect image of the original which is then read by the bar code reader 106. It should also be noted that the use of a simple bar code reader as a detector device provides a digital control responding to the number of image elements counted rather than an analog control responding to the density of the image

Claims (6)

1. CLAIMS: 1. A reproduction machine including: a photoreceptor, means for projecting a document image onto the photoreceptor, a test target to form a bar image on the photoreceptor, a clue; eloper for applying toner to the bar image, a toner dispenser for providing toner to the developer, a control electrically connected to the developer.

   a par cooe reaaer resDona!ng to -ne oar image no proouc.ng control signals reDresentat!re of ne developed bar Image. a first control signal representative OT a first number of bars In the developed bar Image, a secono control signal representative of a second number of bars in the developed bar image, and means responsive to the control signals to activate the toner aispenser for given periods.
2. 2. The. reproduction machine of Claim 1, wherein the number of developed bars represents a low or a high development condition.
3. 3. The reproduction machine of Claim 1 or 2, wherein the test target is a bar code transparency disposed near the photoreceptor and exposed by a flash lamp.
4. 4. The reproduction machine of Claim 1 or 2, wherein the test target is an opaque bar code selectively disposed in path swept by the projection means.
5. 5. A reproduction machine including: a photoreceptor, means to form a bar code latent image on the photoreceptor, a developer station for applying toner to the bar code image, a bar code reader producing a control signal representative of the developed bar code, and means to control the developer station in response to the control signal, including a toner dispenser coupled to the bar code reader.
6. 6. A reproduction machine including: a photoreceptor.

   means to form a bar code image on the photoreceptor, a developer station for applying toner to the bar image, a toner dispenser for providing toner to the developer station, a bar code reader producing a code signal representative of the developed bar Image, and means to activate the toner dispenser for predetermined time periods in response to the code signal 'he reorpouction machine of anv preceding Claim, wherein the activation of the oner oisoenser Is n Incremenl!na time period S he reproduction machine of Claim 6 or 7, wherein the code signal represents low- zoner concentration or high-toner concentration, ana wherein The means to activate the toner dispenser s responsive to successive signals representing low-aevelopea toner mass 9. The reproduction machine of any preceding Claim, wherein the means to activate the toner dispenser responds to the number of developed bars of the bar code image.