DE19932965A1 - Optical rotational moment sensor for a rotating shaft, comprises a scale unit, a detection unit, and an evaluation unit. - Google Patents

Abstract

An optical rotational moment sensor for a rotating shaft, comprises a scale unit (30) with a primary double scale (31), a detection unit (40) for the optical determination of a Moire region, and an evaluation unit. The scale unit consists of primary and secondary scales located about the shaft, which have a carrier (33,34). The detection unit is used on a stationary shaft, and the evaluation unit produces an image.

Description

The invention relates to an optical torque sensor for a shaft rotatable about an axis of rotation, the at least one Scale unit with a first double scale from a first and a second arranged in the circumferential direction of the shaft Line scale, which is mechanically fixed over a carrier and axially from each other by a predetermined measuring distance spaced connected to the shaft and so adjacent to each other are arranged that a superimposition of both stroke scale a of the torque acting on the measuring section dependent first moiré pattern generated, includes. Such a optical torque sensor is from GB 2 162 309 A knows.

In the "Manual of Sensor Technology - Measuring Mechanical Sizes ", Verlag Moderne Industrie, Landsberg / Lech, 1989, Chapter 6.6, pages 419 to 443, contains a general one Compilation of currently common and well-known designs tion forms of a torque sensor. The torque of one rotating shaft or a rotating rod is ins especially about a twisting (= torsion) of the shaft averages. The twist is namely proportional to the rotation moment and the length of the shaft section concerned and inversely proportional to the wave cross section and a mate rial-specific torsional stiffness. Except for the twist these are parameters that are known before the start of the measurement. Therefore, the torque can then be determined the wave torsion in a certain wave section determine.

In the manual mentioned, among other things, an optoelectro described torque sensor with coding / perforated disks ben, with a detection of the torsion optically and thus be  done without contact. Another disclosed torque sensor uses an eddy current effect between two ge slotted sleeves or washers due to the torsion conditional twist to a detectable change in impedance to lead. This sensor also works without contact. Farther there is a torque sensor that detects the detuning a resonance frequency of a resonant structure e.g. B. one Vibrating string works. The disclosed torque sensors are always more or less depending on the embodiment susceptible to interference and / or they are very complex Construction.

In the book "Sensors - A Comprehensive Survey", Vol. 6, Optical Sensors, VCH Verlagsgesellschaft mbH, Weinheim, 1992, Chapter 22.4.4, pages 570 to 585, and in the book "Grund sensor technology - An instrumental science for surveying engineers ", Wichmann, 1996, pages 113 to 118, pages 292 to 294 and pages 442 to 447, the so-called Moiré-Ver drive described in connection with the sensor technology. On An evaluable moiré pattern is created by an overlay two line scales, with light and dark maxima form that have a significantly larger period interval as a lattice period (= period between the bars of the Line scale) of the underlying line scales. Thereby Detection is considerably simplified since one is used te detector unit with a lower cutoff frequency can be driven.

A distinction is made between two basic moiré ver drive. In the first procedure, the two line scales twisted against each other. That is why this procedure also works referred to as the twist moiré method. In the second ver driving, the two line scales are slightly apart other deviating grating period. This results in a Moiré pattern, which is influenced by a measured variable, e.g. B. leads to an expansion of one of the two line scales, ver changes. This second method is also called the division moiré  Process called. Generally you can reach with a sol Chen Moiré process a simple and inexpensive acquisition mechanical stretching or mechanical deformity tion.

GB 2 162 309 A1 is an optical torque sensor disclosed, the torsion in a training as a measuring section section of a rotating shaft over a moiré pattern detected. The two line scales overlaid are mechanically firmly against each other by means of a carrier overlying ends of the measuring section with the rotating shaft connected. If it comes to the measuring section as a result of a torque to torsion, an op table-detectable change in the moiré pattern. The revealed Torque sensor only works with a rotating one Wave because only one at a sampling point of an input light signals passing moire pattern can be detected. In contrast, when the waves are at a standstill, it is impossible to determine which area of the moiré pattern is at the sampling point det. But since the zero point of the Torque is present, therefore no zero point adjustment.

In the case of a torque sensor, in particular with a high Ge However, accuracy is generally required a calibrability. This allows the necessary Significantly reduce precision during installation as such Sensor also calibrated to its zero point afterwards can be. It may also be him required a high-precision torque sensor in the course calibrate again and again in order to avoid aging eliminate conditional influences. In particular one in the Torque sensor used in automotive engineering should therefore the possibility of zero adjustment at the quietest wave.  

It is now the object of the invention to make an optical rotation to specify the moment sensor of the type described at the beginning, with the a zero point adjustment is possible when the shaft is at a standstill. The Optical torque sensor should also be simple and inexpensive to be manufactured.

An optical torque sensor is used to solve this task according to the features of the independent claim specified.

The optical torque sensor according to the invention for a shaft rotatable about an axis of rotation comprises at least

• - A scale unit with a first double scale from one first and a second in the circumferential direction of the shaft ordered line scale, each over a carrier mechanically fixed and axially through a given measuring section spaced from each other connected to the shaft and so to are arranged adjacent to each other that an overlay both line scales one of which acts on the measuring section generates a torque-dependent first moiré pattern,
• - Detection means for optical detection of a first one Moiré pattern portion of the first moiré pattern stationary wave over at least one at first Moiré pattern partial area directed input light signal and
• - An evaluation unit for generating a first image at least one period of the first moiré pattern from the optically captured first moiré pattern part area and Assignment of the first image to that of a stationary one Shaft present zero point of torque.

The invention is based on the knowledge that a optical torque sensor that the torque in simple Way via an optical detection of a moiré pattern with a few additional resources, even for a zero point adjustment or calibration when the shaft is stationary can be strengthened. All that is required is simple and inexpensive Detection means are required, which are able to  first moiré pattern portion of the first moiré pattern to detect a standing wave. The at least one for Input light signal used by optical detection is from the first moiré pattern section, especially in its Intensity affected. Then in an evaluation unit the optically recorded first moiré pattern partial area complete period of the wave stop Reconstruct the first moiré pattern in the form of the first image iert. Since there is no torque when the shaft stops are before the actual sensor operation begins all information required for a current zero point adjustment mations before.

In particular, the evaluation unit can refer to this The current positions of light and dark areas (Light and dark maxima) in the first moiré pattern and thus also the current position of a sample point of the input light signal relative to these extreme values of the first moiré Determine patterns. The light and dark maximum of the first Moire patterns are namely immediately in a maximum or minimum intensity value in an output light signal pictured. The one aimed at the first moiré pattern aisle light signal is experienced when passing the first moiré Pattern or when reflecting on the first moiré pattern a corresponding variation in light intensity. To An exit light passes through the first moiré pattern signal with an intensity modulation that the light / Dark variation in the first moiré pattern corresponds.

Since the intensity of the input light signal is a measured variable are subject to independent age-related variation and also the current position of the first moiré pattern in relation to the angle of rotation z. B. may vary due to temperature a current, the current light / dark distribution of the intensity distribution in the first moiré pattern Output light signal an important variable for the zero point adjustment. The most important parameters are the  current light and dark areas of the first moiré pattern assigned extreme intensity values.

The most important for the zero point adjustment to obtain extreme values, it is favorable if in the Evaluation unit an image of at least one complete period of the first moiré pattern. This first image can then for example one over a complete period of first Moiré pattern determined intensity distribution of the Display output light signal. The determination can either by optically scanning a correspondingly large one Detail of the first moiré pattern or by optical Scanning a smaller section with the following Signal reconstruction takes place in the evaluation unit.

For signal reconstruction, one can also have knowledge of use the basic course of the first moiré pattern. The brightness distribution of the first moiré pattern has näm Lich always an essentially sinusoidal course. The Signal reconstruction can therefore z. B. correspond to one Correlation method or a sine fit serve.

The optically recorded first moiré pattern partial area can thus both larger and smaller than a period of the first Be a moire pattern. He doesn't have to be from one contiguous section of the first moiré pattern be stand. However, it is always larger than one, Ver compared with the period of the first moiré pattern smaller Sampling point of a z. B. focused by an LED (Lumines zenzdiode) generated input light signal. Crucial for the size of the first moiré pattern part to be optically detected area is the reconstructibility of a complete period of the first moiré pattern in the evaluation unit, whereby also Additional knowledge can be included.  

It is now possible to either have the complete first image in Form that over a period of the first moiré pattern intensity distribution of the output light signal or even only the extreme intensity values of this intensity ver division in a z. B. electronic memory of the evaluations deposit unit. This information is then available in addition to the possibly also stored in each case rotation angle positions for calibration, d. H. the zero point matching, available.

Under a "superimposition of the two line scales" through which the first moiré pattern is in this together to understand a real local "stacking". Likewise, however, the more general case should also be included be standing, in which the input light signal the two Line scales run through one after the other or one after the other two line scales is reflected. A combination of Transmission through a line scale and reflection at the other line scale is also possible.

Special configurations of the optical torque sensor result from the dependent claims.

A simple adjustment mechanism for one is preferred optical sampling point of the input light signal on the first Moiré pattern is provided so that the sample point by the length of the first moiré pattern partial area to be optically detected can be moved on the first moiré pattern. At a Displacement length of z. B. at least half a period The scanning point sweeps the length of the first moiré pattern all possible brightness levels within the first Moire pattern.

In a first embodiment, the sampling point can be by positioning means in the circumferential direction of the shaft move the first moire pattern. This offers particularly then advantages if the light and dark areas of the first  Moire pattern ver substantially parallel to the axis of rotation run because the sampling point is then essentially perpendicular to shifted in a main direction of the first moiré pattern can be. All necessary for the zero point adjustment Information can then be easily determined.

A second embodiment is designed so that the Positioning means a displacement of a sampling point in Direction of the axis of rotation, d. H. in the axial direction, possible chen. This embodiment then offers in particular divide when the first moiré pattern is light and dark includes the ver at a certain angle to the axis of rotation to run. Viewed in the circumferential direction, one results oblique arrangement of the light and dark areas. Then it will be also with an axial displacement of the sampling point corresponding section of the first moiré pattern chen, so that all information necessary for calibration tion can be determined.

An advantageous embodiment is characterized by that the positioning means a mechanically displaceable Detector unit include. Depending on the training chosen This detector unit can rotate the first moiré pattern be rotatably mounted on the shaft or along the axis Axis of rotation can be arranged so that either one Shift in the circumferential direction or a shift in axial direction is possible. An embodiment with Ver possibility of sliding both in the circumferential direction and in axial direction is also possible. About one Detector unit, the sampling point is particularly easy move on the first moire pattern. In addition, the sliding detector unit a very inexpensive solution because no complex components are required.

The detector unit advantageously contains electro-optics cal transmission means, for example in the form of a laser diode or a luminescent diode (LED) to send out the on  gangslichtsignals and also optoelectric reception medium, for example in the form of one or more photos diodes or a CCD line (Charge Coupled Device) to Receiving the at least one output light signal.

Another embodiment is advantageous, in which one Positioning unit the exact mechanical positioning of the slidable detector unit controls. This positioning unit represents the current position of the sampling point on the first moiré pattern and at the same time also delivers Position information that is saved and then for the Calibration can be used. The positioning unit can a mechanical slide, e.g. B. in the form of a Magnetic slide or a piezo actuator, for positioning the sliding detector unit included. Other mechanical Sliders are also conceivable.

In an advantageous embodiment, the optically settles first moiré pattern partial area to be recorded from at least two independent segments of the first moiré Patterns together. All segments are then over each separate input light signals optically detected. Through the Using multiple input light signals, i. H. also several Sampling points, can be used to determine the first Image required displacement length of the movable Reduce detector unit.

A variant is also favorable in which the optically capturing first moiré pattern partial area from two segments composed of a quarter period of the first Moire pattern are arranged. Because of this convenient distance it is achieved that there are never two associated sampling points at the same time in one place of the first moiré pattern, which have a low contrast, i.e. H. a low local Gradients of the brightness distribution. This is a further reduction in the required displacement length of the movable detector unit possible.  

Another favorable embodiment is with lighting equipped with complete lighting, at least of the first moiré pattern partial area to be optically detected enable. The lighting can e.g. B. over a large area towards the light point, that for the zero point adjustment optically detectable first moiré pattern partial area com recorded in full. From the first moiré pattern section then practically an image comparable to a photograph created, the evaluation of which for the zero point adjustment provides the required information. A suitable one for this Light source can e.g. B. also a simple light bulb with downstream pinhole. A lot is also possible number of individual LEDs. To record the reflected back Light is used, for example, by a CCD line. With this out the section of the first moiré pattern becomes pure recorded electronically. In particular, there is no mechanical ver shift provided.

In a further preferred embodiment, lighting is provided means provided that several separate input light emit signals. Sampling points of these input light signals cover the optically for the zero point adjustment the first moiré pattern section. To do this are the individual Sampling points alongside each other along the optically detecting first moiré pattern portion. The separate input light signals are e.g. B. from an ent speaking number, in particular individually controllable light sources in the form of laser diodes or LEDs. The one Individual light sources can also form a single unit be summarized. According to the desired coverage of the entire section to be evaluated by the individual Sampling points are also the focus of the individual light sources a little bit laterally compared to the respective neighboring focus puts. The individual light sources can be simultaneously or can also be controlled successively. Accordingly it follows the image to be created of the first to be optically recorded  Moiré pattern subarea immediately or only after composed in the evaluation unit.

Differentiate in an advantageous embodiment the line counts of the two line scales only slightly from each other. A relative difference between the prime len of at most 10% leads to a first moiré Patterns with a long period, so that a ver strengthening of the measuring effect results. Under the influence of a spin moments, the first moiré pattern becomes a large one Angular range shifted, whereas the line scales even a small shift even due to the torsion Experienced. Since also the light and dark areas are one much larger spatial extension than the individual Detection can have dashes of the two line scales with a much lower cutoff frequency than one Detection of the individual lines of the two line scales respectively.

A configuration is also favorable in which the scales unit a second double scale with a third and fourth Line scale contains. From an overlay of the third and fourth line scale results in a second moiré pattern, the analogous to the first moiré pattern, measurement information about the includes torque acting on the measuring section. The second moiré pattern can both have the same input light signal like the first moiré pattern as well as over a separate second input light signal can be detected. However, there are always two separate output light signals - one for the first and the other for the second moiré Template. Analogous to the first moiré pattern, the Detection means also from the second moiré pattern when still standing wave a second moiré pattern sub-area optically to capture. The evaluation unit then generates optically captured a second image in the second moiré pattern partial area for at least one period of the second moiré pattern. The the second image is then also in the evaluation unit  with the shaft at a standstill zero point of rotation assigned to moments. With the then in the evaluation unit lying, independent measurement information from the The two moiré patterns can then be used, for example Increase signal dynamics or a disturbance variable compensation carry out. All of the above for evaluating the first Moiré pattern described embodiments, Ausgestaltun conditions or variants can also be used to evaluate the use a second moire pattern.

An embodiment variant in which the first line scale of the first double scale and the fourth Line scale of the second double scale an identical first Have lines. Also have the second line scale the first double scale and the third scale scale of the second Double scale also has an identical second number of lines. This means that the two moiré patterns are on them rotating shaft in the opposite direction around the rotation revolve axis. If you then evaluate the difference between the two moiré patterns, you get a larger signal dynamic than when evaluating only one moiré pattern. Moreover is not used as additional information for the evaluation more the current angle of rotation, but only a time between the two moiré patterns.

A configuration is advantageous in which all surfaces, which are passed by or at which a light signal Light signal is reflected, dirt-resistant are. In addition, these surfaces have a self-cleaning Nanostructure. This accumulates dirt Surfaces under the influence of ambient humidity such as the washed off. This configuration is therefore special in an environment that is heavily polluted, e.g. B. in the engine compartment of a motor vehicle, is subject to cheap. A in a further embodiment for preventing unwanted pollution at least within the range between the detection means and the scale unit  seen filling with a liquid can when off there is no need to design with the nanostructured surfaces.

The configurations and principles described above can also be used analogously if the individual line scales not with constant, but with variable periods length between the individual lines are formed.

Preferred embodiments of the opti according to the invention cal torque sensor are now based on the drawing explained in more detail. The drawing is not for clarification made to scale, and certain features are schematic represented. In detail show:

Fig. 1 cut an optical torque sensor, in a longitudinal,

Fig. 2, the scale unit of the optical torque sensor of Fig. 1,

Fig. 3 shows the optical torque sensor of Fig. 1 in a cross section,

Fig. 4 shows two bar scales a double scale,

Fig. 5 moiré patterns at three different relative posi tions of the two stroke scale of Fig. 4,

Fig. 6 shows an intensity profile of the output light over the angle of rotation,

7 intensity curves of two output light signals over time,

Fig. 8 a moire pattern with parallel to the rotational axis of ordered light and dark areas,

Fig. 9 shows a moire pattern with obliquely to the axis of rotation angeord Neten light and dark areas,

Fig. 10 shows a moire pattern with two spaced a quarter period of the moiré pattern th arranged Abtastpunk,

Fig. 11 an optical torque sensor disposed on two support plates stroke scale,

Fig. 12 shows a torque sensor with ° to 45 phases of support tubes arranged Line scales and

Fig. 13 an optical torque sensor having means for illuminating a portion of the moiré pattern.

Corresponding parts are provided with the same reference numerals in FIGS. 1 to 13.

In Fig. 1, an optical torque sensor 100 is provided, which detects the torque that acts on a rotatable shaft 20 within a measuring section 35 . The shaft 20 rotates at an angular velocity ω about an axis of rotation 21st An initial angular position of the shaft 20 is denoted by α0 and the current angle of rotation by α. The shaft 20 can also rotate at a variable angular velocity ω. In particular, the shaft 20 can also stand still, in which case no torque acts on the measuring section 35 .

The optical torque sensor 100 is for a high accuracy in a harsh environmental condition such. B. designed for use in the engine compartment of a motor vehicle. The properties of the optical torque sensor 100 are retained over a period of several years. For this purpose, it is possible to calibrate (= calibrate) a zero point of the optical torque sensor 100 . When used in a motor vehicle, such a zero-point calibration is favorable, since at the moment of zero torque a smooth and gear-saving shifting is possible. In order to reliably detect a torque zero point in the normal operating state, that is to say when the shaft 20 is rotating, the optical torque sensor 100 is adjusted to the torque zero point which is also present when the shaft 20 is stationary. For this purpose, the optical torque sensor 100 includes additional, but very simple and therefore inexpensive means.

The optical torque sensor 100 is located in a sensor housing 44 which is rotatably mounted on the shaft 20 . For zero point adjustment when the shaft is at a standstill, a small rotary movement of the shaft 20 is in principle formed by moving the housing 44 instead of the shaft 20 a small distance in the circumferential direction around the stationary shaft 20 . The measurement information obtained in this way is then used for zero point adjustment.

The optical torque sensor 100 detects the torque via a torsion measurement. This is done with the help of two moiré patterns 330 a and 330 b, which each result from a superimposition of two line scales of a first and a second double scale 31 and 32 , respectively. Both double scales 31 and 32 are part of a scale unit 30 .

The two double scales 31 and 32 are arranged on two supports 33 and 34 , which are mechanically fixed to the shaft 20 axially spaced apart from one another by the measuring section 35 . If torsion now occurs on the measuring section 35 due to an applied torque, the relative position of the carrier 33 also shifts to that of the carrier 34 . This also results in a change in the two moiré patterns 330 a and 330 b formed by the two double scales 31 and 32 , which are optically detected and used to determine the underlying torque.

The supports 33 and 34 each contain a support tube 331 and 341, respectively. The carrier 34 also includes a transparent end portion 340 at one end of the carrier tube 341 . This transparent end portion 340 is pushed over the end of the support tube 331 facing it, so that in an overlap pungsbereich an inside of the transparent end portion 341 and an outside of the support tube 331 are closely adjacent but still arranged without contact.

The two double scales 31 and 32 of the scale unit 30 are arranged in this overlap region, which is shown enlarged in FIG. 2. The first double scale 31 comprises a first scale scale 311 and a second scale scale 312 . The second double scale 32 comprises a third scale 321 and a fourth scale 322 . In the overlap region, the first and third line scales 311 and 321 are arranged on the inside of the transparent end section 340 and the second and fourth line scales 312 and 322 are arranged on the outside of the carrier tube 331 in such a way that the first and second line scales 311 and 321 312 and the third and fourth line scales 321 and 322 are each opposite one another.

By overlaying the first and second line scales 311 and 312 of the first double scale 31 and by overlaying the third and fourth line scales 321 and 322 of the second double scale 32 , the first and second moiré patterns 330 a and 330 are formed b. In the present case, the first and fourth line scales 311 and 322 have a line number of 100, whereas the second and third line scales 312 and 321 each have a line number of 101. The A dashes are arranged with an axial orientation in the circumferential direction around the shaft 20 . Due to the small difference in the number of lines, the two moiré patterns 330 a and 330 b are formed with light and dark areas, which have a much greater extent than the single lines of the underlying line scales 311 , 312 , 321 and 322 .

In embodiments of the optical torque sensor 100 that are not shown, other values for the number of lines and for the deviation between the number of lines are also provided. In addition, the lines of a line scale can also be arranged at a certain angle to the axis of rotation 21 , ie obliquely.

As shown in Fig. 1, the first and second moiré patterns 330 a and 330 b are optically scanned via a common input light signal LS0. The light signal LS0 generated in a detector unit 40 by means of a light source 41 , in the present case by means of an LED, passes through the transparent end section 340 and the two line scales 311 and 321 , in order then to be reflected back at the other two line scales 312 and 322 to the detector unit 40 . After passing through both double scales 31 and 32 , a first and a second output light signal LS1 and LS2 are available. The first output light signal LS1 is influenced by the first moiré pattern 330 a and the second output light signal LS2 is influenced by the second moiré pattern 330 b in intensity. Light and dark areas of the two moiré patterns 330 a and 330 b, which move below a sampling point of the input light signal LS0 due to the rotational movement of the shaft 20 , cause a corresponding intensity modulation in the two output light signals LS1 and LS2. This can then be evaluated as a measure of the torsion of the measuring section 25 and thus as a measure of the torque sought.

In the detector unit 40 , the two output light signals LS1 and LS2 are received by a first and a second light receiver 42 and 43 and each converted into an associated electrical signal. The light receivers 42 and 43 are simple photodiodes here. In another embodiment, not shown, the light receivers 42 and 43 can also be formed as a CCD line.

An interior 46 of the sensor housing 44 is filled with a silicone oil 47 in order to prevent contamination of the upper surfaces in particular, which are passed by a light signal or at which a light signal is reflected. In another embodiment, another optically transparent liquid can be used instead of the silicone oil 47 .

In the area of the detector unit 40 , the sensor housing 44 has a projection 45 , which is used for the mechanical displacement of the rotatably mounted sensor housing 44, in particular during the zero point adjustment when the shaft 20 is stationary.

A cross section of the optical torque sensor 100 is shown in FIG. 3, the illustration additionally comprising a positioning unit 50 and an evaluation unit 60 . The positioning unit 50 controls the displacement of the sensor housing 44 in the circumferential direction about the axis of rotation 21 . It holds a magnetic slide 51 which engages the projection 45 of the sensor housing 44 and the sensor housing 44 can change its position in the circumferential direction around the axis of rotation 21 . The positioning unit 50 also contains a stop 52 against which the projection 45 is pressed by a spring 43 . The restoring force of the spring 53 then also causes the sensor housing 44 to be turned back when the magnetic slide 51 is repositioned. A displacement path of the magnetic slide 51 is now designed so that the sensor housing 44 can be rotated so far about the stationary shaft 20 that the input light signal LS0 on the first moiré pattern 330 a and a first moiré pattern area and on the second moiré pattern 330 b sweeps over a second moiré pattern section and is visually detected.

The first and the second moiré pattern partial areas are then used in the evaluation unit 60 , which is electrically connected both to the detector unit 40 and to the positioning unit 50, to produce a first or a second image of a period of the first moiré pattern 330 a or of the second moiré pattern 330 b. The evaluation unit 60 contains all the information required for the zero point adjustment.

The current positions of the respective sampling point of the input light signal LS0 on the two moiré patterns 330 a and 330 b can be determined from the current displacement path of the magnetic slide 51 . The current intensity distributions of the two output light signals LS1 and LS2, which result from optical scanning of one period each of the two moiré patterns 330 a and 330 b, are known. The intensity distributions of both output light signals LS1 and LS2 are assigned to the respective brightness distributions of both moiré patterns 330 a and 330 b. In particular, the intensity extreme values assigned to the respective light and dark areas of both moiré patterns 330 a and 330 b can also be determined in the two output light signals LS1 and LS2. These parameters are stored electronically in the evaluation unit 60 and used for the zero point adjustment.

The formation of a moire pattern will be explained by a superposition of two stroke scale on when the game of the first Moire pattern 330 a reference to FIGS. 4 and 5. The starting point is the first line scale 311 shown in FIG. 4 here with a total of 41 individual lines and the second line scale 312 here with a total of 40 individual lines.

The first and the second scale scale 311 and 312 are arranged according to the embodiment of FIGS. 1 to 3 in the optical torque sensor 100 as closed circular rings in the circumferential direction around the shaft 20 . For the sake of better clarity, an uncurved form of representation has been chosen for FIGS . 4 and 5, in which the ring-shaped line scales 311 and 312 are fictitiously separated at any point and are just bent.

The first moiré pattern 330 a shown in FIG. 5 results from the superimposition of both line scales 311 and 312 . In the present example, this has a light area 336 and a dark area 337 . The period length of the first moiré pattern 330 a thus corresponds to the complete circumferential length of the shaft 20 . In the first moiré pattern 330 a of FIG. 5, it is assumed that the overlap has taken place in the relative position of both line scales 311 and 312 shown in FIG. 4. If the relative position of the line scales 311 and 312 shifts due to a torsion of the measuring section 35 , this also results in a change in the first moiré pattern 330 a.

If, for example, the two line scales 311 and 312 are shifted against each other by approximately 0.33 times a single line width, the result is a modified first moiré pattern 331 a. A shift of 0.66 times a single stroke width results in a further modified first moiré pattern 332 a.

The change in the first two moiré patterns 331 a and 332 a compared to the original first moiré pattern 330 a manifests itself in a shift in the light and dark areas 336 and 337, respectively. With increasing relative displacement of the two line scales 311 and 312 , the first moiré pattern 330 a thus moves in the circumferential direction about the axis of rotation 21 .

In Figs. 4 and 5 can be clearly seen that the bright or the dark portion 336 and 337 each having a local we sentlich greater dimension than the interstices or the individual strokes of both scales 311 and 312 bar. This results in easier detectability, since a significantly lower cut-off frequency can be provided for optical scanning. In addition, a slight shift due to torsion leads to a significantly larger shift of the light and dark areas 336 and 337 in the first moiré pattern 330 a. The measuring effect is enhanced and is also easier to detect optically.

In contrast to the exemplary embodiment in FIGS . 4 and 5, the line scales 311 and 312 can also each comprise a different number of individual lines. The total number and difference of the individual lines of both line scales 311 and 312 then determine the position and number of light and dark areas 336 and 337 , respectively, which the first moiré pattern 330 a has in the circumferential direction. In particular, the first moiré pattern 330 a can then also contain several periods over a circumferential length.

In Figs. 6 and 7 is the determination of a measured value M for the torsion of the measuring section 35, and thus also shown for the actually searched torque. The measured value M is determined from intensities I1 and I2 of the first and second output light signals LS1 and LS2. Both output light signals LS1 and LS2 have namely a modulation in their intensities I1 and I2, which is substantially in FIG. 5 shown distribution of bright and dark areas 336 and 337 sampled at the associated first or second moire pattern 330 or a 330 b corresponds. This intensity modulation can be seen both in a representation of the local curve according to FIG. 6, in which the intensity I1 is plotted over the current angle of rotation α, and in the representation of the temporal curve in accordance with FIG. 7, in which the two intensities I1 ( solid line) and I2 (dashed line) are plotted over time t.

FIG. 6 illustrates the determination of the measured value M using a single moiré pattern, ie using a single output light signal LS1 with the intensity I1. In addition to measuring the intensity I1, which carries the measurement information about how far the first moiré pattern 330 a has moved in the circumferential direction, the detection of the current angle of rotation α is also necessary. In the case of zero point adjustment, for example, the angular position of the bright area 336 , which leads to a maximum intensity I1, is defined as the starting position α0. The displacement of this bright area 336 in the circumferential direction, expressed as the angle of rotation α0 related to the starting angle position α0, then serves as a measured value.

With detection of two moiré patterns, for example the two moiré patterns 330 a and 330 b, via the two output light signals LS1 and LS2 with the respective associated intensities I1 and I2, a measured value acquisition takes place according to the representation of FIG. 7 without one additional determination of the angle of rotation α. An important parameter for determining the measured value M is a time offset Δt between the two intensities I1 and I2, which is a measure of the relative shift between the two moiré patterns 330 a and 330 b. The time offset Δt is therefore also proportional to the torque to be determined.

From FIGS. 6 and 7 it is seen that an important parameter for the Meßgrößenermittlung the extreme values of the intensities of I1 and I2 and, optionally, also the position of the corresponding light and dark areas 336 and 337 of the two moiré patterns 330 a and 330 b serve . This information is now newly determined before the start of the measurement as part of the zero point adjustment, so that a variation of the intensity of the input light signal LS0, for example due to aging, does not falsify the measured value M determined.

In FIG. 8 is shown in perspective and in plan view, such as a sampling point 334 of the input light signal is moved away when the shaft 20 in the circumferential direction over the first moire pattern 330 a LS0. The scanning point 334 can be moved away during the zero point adjustment over at least an entire period of the first moiré pattern 330 a, ie over at least one light area 336 and one dark area 337 . In the embodiment of the optical torque sensor 100 according to FIGS . 1 to 3, this is easily possible thanks to the rotatably mounted on the shaft 20 housing 44 . But there are also other embodiments in which the sampling point 334 only over a smaller part of both moiré patterns 330 a and 330 b, z. B. is only moved over half a period. An image of an entire period of the first or second moiré pattern 330 a or 330 b is then generated in the evaluation unit 60 by appropriate measures for signal reconstruction.

In an alternative embodiment according to FIG. 9, however, a zero point adjustment can also be carried out by moving a sampling point 335 not in the circumferential direction but in the axial direction over a first moiré pattern 333 a. For this purpose, the first moiré pattern 333 a has light and dark areas 338 and 339 , which run obliquely with respect to the axis of rotation 21 . This also makes it possible to move over a period of the first moiré pattern 333 a by axially shifting the sampling point 335 and thus determining the information required for the zero point adjustment.

In the exemplary embodiment of FIG. 10, a particularly small displacement path of the displaceable sensor housing 44 can be provided without questioning the possibility of adjusting the zero point. In this embodiment, the first moiré pattern 330 a is optically detected in addition to the sampling point 334 via a further sampling point 334 'of a further input light signal, not shown. The information required for the zero point adjustment can thus be acquired over a considerably shorter displacement path than in the exemplary embodiments with only a single sampling point 334 . The two sampling points 334 and 334 'are arranged at a distance 36 from one another on the first moiré pattern 330 a. It is particularly favorable if the distance 36 is approximately as large as a quarter period of the first moiré pattern 330 a. Then it is ensured that both sampling points 334 and 334 'are never simultaneously at a low-contrast location of the first moiré pattern 330 a.

In Figs. 11 and 12 alternative embodiments for an optical torque sensor 101 and 102 are Darge provides. The optical torque sensor 101 of FIG. 11 differs from the optical torque sensor 100 only in that the scale unit 30 is arranged instead of within an overlap area of two stacked carrier tubes 331 and 341 on two carrier plates 332 and 342 . Both carrier plates 332 and 342 are perpendicular to the axis of rotation 21 . Both are illuminated by the input light signal LS0. In the area of the scale unit 30 , the carrier plates 332 and 342 are optically transparent. The optical torque sensor 101 has a purely trans missive optical detection.

In contrast, the optical torque sensor 102 of FIG. 12 is designed with a purely reflective optical detection. Both carrier tubes 331 and 341 each have a 45 ° phase 333 and 343 at the mutually facing ends. The double scales 31 and 32 are arranged on these 45 ° phases 333 and 343 . The input light signal LS0 then first strikes the second and fourth line scales 312 and 322 and is deflected by 90 ° due to the 45 ° phase 343 and directed to the first and third line scales 311 and 321 . Here, due to the 45 ° phase 333, a further 90 ° deflection takes place, so that the two output light signals LS1 and LS2 return to unit 40 .

Instead of filling the interior 46 with a silicone oil 47 in accordance with the embodiment of the optical sensor 100 from FIGS. 1 and 2, the optical torque sensor 102 from FIG. 12 has one on all surfaces 48 that are affected by the light signals LS0, LS1 and LS2 Nanostructure. The interior 46 , not shown, can then be filled with air. Dirt that may accumulate on the surface 48 is then washed off by the natural moisture and due to the special nanostructure. The optical torque sensor 102 is consequently equipped with self-cleaning on the surfaces 48 that are important for optical detection.

The optical torque sensors 101 and 102 of FIGS. 11 and 12 also include means for zero-point adjustment analogous to the optical torque sensor 100 of FIGS. 1 and 2. For reasons of clarity, however, these means are not shown in FIGS. 11 and 12.

FIG. 13 shows a further optical torque sensor 103 , in which the information for the zero point ab is determined immediately by illuminating a corresponding partial area of the first moiré pattern 330 a, which is only shown here. In Fig. 13 this illuminated first Moire pattern portion is about as large as a period of the first Moire pattern 330 a.

The optical torque sensor 103 includes illuminating means 410 which have a plurality of input light signals LS0, LS0 ', LS0'',. , , via separately controllable light sources 41 , 41 ', 41 '',. , , produce. The light sources 41 , 41 ', 41 '',. , , are designed as LEDs and integrated into a single structural unit. Because of the separate control option, the illumination of the first moiré sample partial area can take place both simultaneously and successively.

Associated sampling points 334 , 334 ', 334 '',. , ., the input light signals LS0, LS0 ', LS0'',. , ., are distributed on the first moiré pattern 330 a in such a way that the first moiré pattern partial area that can be optically detected is completely covered by the scanning points 334 , 334 ', 334 '',. , , is covered. The input light signals LS0, LS0 ', LS0'',. , , experience an intensity modulation corresponding to that at the location of the associated sampling point 334 , 334 ', 334 '',. , , present brightness value of the first moiré pattern 330 a.

After reflection on the first moiré pattern 330 a, output light signals LS1, LS1 ',. , , detected by means of a CCD line 420 . The CCD line 420 is arranged adjacent to the lighting means 410 . Optionally, a second CCD line (not shown) can also be arranged on the side of the lighting means 410 facing away from the CCD line 420 shown . A first image of the scanned moiré pattern partial area is generated from the electrical output signals of the CCD line 420 ( not shown) in an evaluation unit (also not shown). The first image is saved and used to determine the information required for the zero point adjustment.

With the optical torque sensor 103 , the zero point adjustment takes place in a purely electronic way. No mechanically moving parts are provided for zero point adjustment.

The optical torque sensors 100 , 101 , 102 and 103 can each be used as an intermediate part in the shaft 20 or as an optionally stabilized plug-on part on the shaft 20 .

Claims (18)

1. Optical torque sensor for a shaft ( 20 ) rotatable about an axis of rotation ( 21 ) comprising at least one

• - A scale unit ( 30 ) with a first double scale ( 31 ) from a first and a second in the circumferential direction of the shaft ( 20 ) arranged scale scale ( 311 , 312 ), each mechanically fixed and axially by a carrier ( 33 , 34 ) by a Predetermined measuring section ( 35 ) spaced from one another is connected to the shaft ( 20 ) and is arranged adjacent to one another in such a way that a superimposition of both line scales ( 311 , 312 ) is a first moiré pattern ( 330 that depends on the torque acting on the measuring section ( 35 ) a, 331 a, 332 a, 333 a) generated,

marked by

• - Detection means ( 40 , 50 , 410 ) for the optical detection of a first moiré pattern partial area of the first moiré pattern ( 330 a, 331 a, 332 a, 333 a) with the shaft ( 20 ) at a standstill via at least one of the first moiré pattern part range directional input light signal (LS0) and
• - An evaluation unit ( 60 ) for generating a first image from at least one period of the first moiré pattern ( 330 a, 331 a, 332 a, 333 a) from the optically detected first moiré pattern partial area and for assigning the first image to that with the shaft ( 20 ) at a standstill, the zero point of the torque.

2. Optical torque sensor according to claim 1, characterized by means ( 40 , 50 ) for the changeable in the circumferential direction of positioning a sampling point ( 334 ) of the input light signal (LS0) on the optically detectable first moiré pattern partial area. 3. Optical torque sensor according to claim 1 or 2, characterized by means ( 40 , 50 ) for axially changeable positioning of a sampling point ( 335 ) of the input light signal (LS0) on the first Moiré pattern portion to be optically detected. 4. Optical torque sensor according to claim 2 or 3, characterized by a changeable in position detector unit ( 40 ) with electro-optical transmission means ( 41 ) for the at least one input light signal (LS0) and optoelectric receiving means ( 42 , 43 ) for at least one output light signal (LS1, LS2), which results from influencing the at least one input light signal (LS0) on the first moiré pattern ( 330 a, 331 a, 332 a, 333 a). 5. Optical torque sensor according to claim 4, characterized by a positioning unit ( 50 ), via which the mechanical position of the detector unit ( 40 ) can be controlled. 6. Optical torque sensor according to claim 4 or 5, there characterized in that the first moiré pattern section consisting of at least two segments composed, each separately for optical detection dered input light signals (LS0, LS0 ') are assigned. 7. Optical torque sensor according to claim 6, characterized in that the optically to be detected first moiré pattern partial area is composed of two segments which are at a quarter-period interval of the first moiré pattern ( 330 a, 331 a, 332 a, 333 a) are arranged. 8. Optical torque sensor according to claim 1, characterized by marked lighting means ( 410 ) with which the entire optically detectable first moiré pattern part can be illuminated. 9. Optical torque sensor according to claim 8, characterized in that the lighting means ( 410 ) are designed to emit a plurality of input light signals (LS0, LSO ', LS0 ",...), Each of which has associated sampling points ( 334 , 334 ' , 334 ″, ... ) On the first moiré pattern ( 330 a, 331 a, 332 a, 333 a) are arranged next to one another along the optically detectable first moiré pattern partial area. 10. Optical torque sensor according to one of the preceding claims, characterized in that the first and the second scale scale ( 311 , 312 ) differ slightly in their number of lines, in particular by less than 10%. 11. Optical torque sensor according to one of the preceding claims, characterized in that the scale unit ( 30 ) comprises a second double scale ( 32 ) from a third and fourth scale scale ( 321 , 322 ), the superimposition of which one on the measuring section ( 35 ) acting torque-dependent second moiré pattern ( 330 b), where

• - The detection means ( 40 , 50 , 410 ) for the optical detection of a second moiré pattern portion of the second moiré pattern ( 330 b) when the shaft ( 20 ) and
• - The evaluation unit ( 60 ) for generating a second image from at least one period of the second moiré pattern ( 330 b) from the optically detected second moiré pattern part area and for assigning the second image to the zero point of the standing wave ( 20 ) Turn moments

are designed. 12. Optical torque sensor according to claim 11, characterized in that the first and fourth line scales ( 311 , 322 ) have a matching first number of lines and the second and third line scales ( 312 , 321 ) have a matching second number of lines. 13. Optical torque sensor according to one of the preceding claims, characterized in that the two carriers ( 33 , 34 ) each contain a carrier plate ( 332 , 342 ) arranged perpendicular to the axis of rotation ( 21 ), on which the respective line scales ( 311 , 312 , 321 , 322 ) are arranged. 14. Optical torque sensor according to one of claims 1 to 12, characterized in that the two supports ( 33 , 34 ) each contain a support tube ( 331 , 341 ) arranged concentrically to the axis of rotation ( 21 ), 15. Optical torque sensor according to claim 14, characterized in that one of the two support tubes ( 331 , 341 ) has an optically transparent end portion ( 340 ) which is pushed over the other of the two support tubes ( 331 , 341 ), so that one Overlap area between the two support tubes ( 331 , 341 ) results, the line scales ( 311 , 312 , 321 , 322 ) being arranged in the overlap area. 16. Optical torque sensor according to claim 14, characterized in that the two carrier tubes ( 331 , 341 ) each have a 45 ° phase ( 333 , 343 ) at the facing ends and the line scales ( 311 , 312 , 321 , 322 ) are arranged on the 45 ° phases ( 333 , 343 ). 17. Optical torque sensor according to one of the preceding claims, characterized in that an interior ( 46 ) between the detection means ( 40 , 410 ) and the scale unit ( 30 ) is filled with liquid, in particular with silicone oil ( 47 ). 18. Optical torque sensor according to one of the preceding claims, characterized in that all surfaces ( 48 ) through which a light signal (LS0, LS1, LS2) passes or on which a light signal (LS0, LS1, LS2) is reflected, a dirt-repellent nano have structure.