DEVICE AND METHOD FOR DETERMINING POSITION, LENGTH OR ANGLE

Abstract

A device for determining position, length, or angle, comprising a first and a second part which are movable relative to each other. An absolute code consisting of a plurality of consecutive code segments of the first and second type is attached to the first part. A readout device for detecting the code is attached to the second part, the readout device comprising several sensors, each configured to detect the code segments and output a corresponding measured value. Furthermore, the device includes an evaluation unit configured to determine a relative position between the first and second parts. The readout device comprises at least one, and preferably several, differential circuits, preferably analog ones. These differential circuits are configured to calculate the difference between the measured values ​​of two adjacent sensors and output it as a differential signal.The evaluation unit is designed to determine the relative position between the first and second parts, taking these difference signals into account. Furthermore, a corresponding procedure for determining position, length, or angle is described.

Description

[0001] The present invention relates to a device for determining position, length, or angle, as well as a corresponding method. Reference is made to DE 10 2008 022 027 A1, DE 102 01 496 A1, US 2015 / 0 069 225 A1, DE 692 18 376 T2, DE 11 2012 005 836 B4, DE 10 2020 107 230 A1, and EP 4 242 595 A1 as prior art.

[0002] Devices for determining position, length, or angle, also known as encoders, and corresponding methods can be used in a wide variety of technical fields. For example, such devices can be used in machine tools, enabling the position or angle measurement of a tool relative to the workpiece. Other areas of application include rotary angle sensors, for example, for motor feedback systems.

[0003] Conventionally, a corresponding device comprises a first and a second part, wherein the first and the second part are movable relative to one another. An absolute code comprising a plurality of consecutive code sections of the first type and of the second type is attached to the first part. A readout device for detecting the code is attached to the second part. The readout device comprises a plurality of sensors, each of which is designed to detect the code sections and output a corresponding measured value. Furthermore, such devices comprise an evaluation unit designed to determine a relative position between the first and the second part based on these measured values.

[0004] Such devices make it possible to at least roughly determine the relative position between the two parts. To improve the resolution of the relative position, an additional coding, for example in the form of an incremental track, with an associated additional readout device is usually provided in addition to the absolute coding. Based on the measured values ​​from the additional readout device, a subsequent correction or refinement of the relative position determination is then carried out. However, this incremental track and additional readout device require additional installation space and are associated with additional costs.

[0005] Against this background, it is an object of the present invention to provide a possibility which enables a high-resolution determination of the relative position between the first part and the second part without having to rely on the evaluation of the relative position on the basis of a further coding, in particular in the form of an incremental track.

[0006] This object is achieved in that the readout device comprises at least one, in particular several, preferably analog, differential circuits. These differential circuits are designed to calculate the difference between the measured values ​​of two adjacent sensors of the readout device and output it as a differential signal. The evaluation unit is designed to determine the relative position between the first and second parts, taking into account the obtained differential signals.

[0007] In other words, the known determination of the relative position between the first and second parts is not carried out solely based directly on the measured values ​​of the sensors, but rather by taking into account the difference values ​​of the signals of two adjacent sensors. The differential circuits provided according to the invention make it possible to reliably identify the signal edges in the temporal progression of the measured values ​​of the sensors and, based on this, to infer the associated transitions between regions of consecutive code sections of the first type and regions of consecutive code sections of the second type. Based on the identified transitions, it is then possible to deduce exactly where the identified section of the absolute coding lies within the detection range of the sensors.From this, the respective relative position between the first and second parts can be determined very precisely without having to resort to a second coding, for example, in the form of an incremental track. The preferred analog subtraction method prevents distortion of the measurement results that could result from prior digitization. Analog subtraction is also faster and more resource-efficient (in terms of computing power) than digital subtraction.

[0008] In this context, it should be noted that the difference signals obtained in the sense of the present invention do not have to be used directly to determine the relative position. As will be explained below with reference to Fig. As described in section 2, the differential signals can be further processed and / or digitized, for example, via comparators, before being evaluated by the evaluation unit. This does not change the fact that the relative position is determined taking the differential signals into account.

[0009] Preferably, several code sections each form a code word. For example, code words can each consist of 4, 8, or 10 individual code sections, resulting in a 4-, 8-, or 10-bit code. Preferably, each code word is present only once in the encoding, resulting in an absolute code or absolute encoding.

[0010] In particular, the size of the code sections and the size of the area of ​​the coding detected by individual sensors are selected such that exactly two sensors or at least two sensors detect a single code section, in particular if the code section lies exactly at the two sensors.

[0011] In particular, the device comprises at least twice as many sensors as bits per codeword, preferably four times as many sensors as bits per codeword.

[0012] During operation, the device can initially read the absolute code in a conventional manner, in particular without the aforementioned subtraction, and in this way already detect a coarse position of the relative position. In addition, according to the invention, a fine position of the relative position can also be detected via subtraction. If, for example, it is determined during detection of the coarse position that a code section of the first type (e.g., a light area) lies "opposite" two sensors, the position of the code section can be detected even more precisely via subtraction. If, for example, an adjacent code section of the second type (e.g., a dark area) already extends into the detection range of one of the two sensors, the signal generated by this sensor is attenuated. Instead of a signal of, for example, "1", this sensor can then only deliver a signal of "0.8".As a result, the result of the differential circuit is not zero, but "0.2." The "position" of the edge, or more precisely, the transition between the different code sections, can therefore be determined more precisely. This makes it possible to determine that the relative position of the first and second parts does not exactly correspond to the coarse position, but should be corrected, for example, by 20% of the length of the area detected by a sensor. This can increase the accuracy of the position measurement.

[0013] Another advantage is that offset errors, which can be caused by thermal effects, for example, are minimized. The offset error usually affects both sensors connected to the differential circuit, thus eliminating the offset error during the difference calculation.

[0014] Another advantage is that for many positions of the coding, a higher amplitude is obtained after the difference calculation than when evaluating only one sensor. For example, with only one sensor and half of the area covered by a dark area, a signal with an amplitude of 50% would be present, whereas with the difference calculation, one sensor would deliver 100% amplitude and the other sensor 0%, resulting in an amplitude of 100% after the difference calculation.

[0015] Preferably, each differential circuit is coupled via a first input to a first sensor of the readout device and via a second input to a second sensor of the readout device, which is arranged adjacent to the first sensor.

[0016] According to the invention, a comparator is connected between at least one, in particular each, of the differential circuits and the evaluation unit. Each of these comparators is designed to compare the differential signal, in particular its current or voltage, from the upstream differential circuit with a reference signal, in particular its current or voltage, from a reference unit and to output a corresponding comparison signal to the evaluation unit.

[0017] In other words, the differential signal from the differential circuits is not transmitted directly to the evaluation unit to be binarized based on a fixed threshold value. Rather, the differential signal is first related to a reference signal. The reference signal effectively defines a variable threshold value. By varying the threshold value for binarization, it is possible to determine the signal edges and thus the transitions between contiguous areas of code sections of the same type within the detection range of the sensors even more precisely. This enables an even more precise resolution of the relative position between the first part and the second part. A clear separation of these comparators from the evaluation unit is neither necessary nor technically sensible. In other words, the comparators, possibly together with the reference unit, can (unlike in Fig. 2) can also be understood as components of the evaluation unit.

[0018] Preferably, the reference unit (REF) is designed to output a time-varying, in particular periodically repeating, reference signal to the provided comparators, which then compare these with the respective measured values.

[0019] In particular, the variation of the reference signal occurs relatively quickly compared to the fastest expected change in the measured values ​​(i.e., for sensors that output a continuous measured value, compared to the maximum intended speed of the relative movement; and for sensors that output pulsed measured values, compared to the output frequency of the sensors). Specifically, the reference signal is generated in such a way that the comparators effectively compare each individual difference value with at least two, preferably more than two, different reference values. This enables multiple binarization of the difference values ​​and thus even more precise resolution of the transitions between the contiguous areas of code sections of the same type and thus of the relative position between the first and second parts.

[0020] Preferably, an output of each differential circuit is coupled to a first input of an associated comparator and the reference unit is coupled to a second input of each of the provided comparators.

[0021] This ensures that the same reference signal is compared with the respective difference signal in each comparator. This facilitates comparison of the reference signals from the different comparators in the evaluation unit without the need for complex corrections.

[0022] Preferably, each sensor is coupled to at least one differential circuit. In particular, for n sensors, n-1 differential circuits are provided, with n-2 sensors each coupled to two differential circuits and two sensors each coupled to only one differential circuit.

[0023] By coupling each sensor to at least one, preferably two, differential circuits, a particularly precise determination of the relative position between the first and second parts can be achieved. In a device for angle measurement, the sensors can be arranged evenly along a circular ring. Each sensor then has two direct neighbors, which makes it possible to provide n differential circuits for n sensors, with each sensor being coupled to exactly two differential circuits.

[0024] The sensors are preferably optical sensors, in particular in the form of photodiodes, magnetic sensors, capacitive sensors or inductive sensors.

[0025] Such sensors are particularly sophisticated and inexpensive to obtain. For example, the sensors can also be designed as Hall sensors.

[0026] Preferably, the first and second parts are movable relative to each other either purely translationally or purely rotationally. The sensors are arranged next to each other, parallel to the coding.

[0027] Purely translational or purely rotational relative movement is relatively easy to implement and evaluate. The parallel arrangement of the sensors to the coding eliminates the need for correction of the measured values, which would be necessary due to a variable distance between the sensors and the coding.

[0028] Preferably, the code sections each have the same size and / or the same offset from one another.

[0029] This makes it much easier to evaluate the measured values ​​and thus to determine the relative position between the first and second parts.

[0030] Finally, the present invention also relates to a method for determining position, length, or angle using the device described above. In this method, the first and second parts are moved relative to each other. The readout device attached to the second part detects the coding. Finally, at least one differential signal is generated from the measured values ​​of two adjacent sensors, and an absolute relative position between the first and second parts is determined based on this difference.

[0031] In particular, several differential signals from neighboring sensors are generated and used to determine the relative position. The inventive generation of differential signals enables a reliable and precise determination of signal edges in the course of the measured values ​​from the sensors and thus a particularly precise determination of transitions between contiguous areas of code sections of the same type. This enables a more precise resolution of the relative position than would be possible simply by determining which section of the absolute code is currently within the detection range of the sensors.

[0032] The above explanations regarding the device according to the invention apply accordingly to the method according to the invention. This applies in particular to advantages and embodiments.

[0033] The invention is described below by way of example with reference to the drawings, in which: Fig. 1 is a schematic view of the structure of an exemplary device according to the invention for determining position or length; and Fig. 2 a schematic view of a further development of the device from Fig. 1.

[0034] In the figures, the same reference symbols denote the same or similar features.

[0035] Fig. Figure 1 schematically shows the structure of a device 10 according to the invention for determining position or length. The device 10 shown serves as an encoder, for example, in a motor feedback system (not shown).

[0036] The device 10 comprises a first part 14, to which an absolute coding 12 is attached. The device 10 further comprises a second part 18, to which a readout device 16 is attached. The coding 12 and the readout device 16 are fastened to the first part 14 and the second part 18 in such a way that they move relative to one another together with the two parts 14 and 18. In the present example, the first part 14 and the second part 18—and thus the coding 12 and the readout device 16—are movable relative to one another purely in a translational manner (see the double arrow B). Purely rotational relative movements can also be easily implemented by a person skilled in the art.

[0037] The coding 12 is formed by a plurality of consecutive code sections 22-0 to 22-9 of the first type (shown in white) and the second type (shown in black). Fig. 1, only ten such code sections 22-0 to 22-9 are depicted. The coding 12 can comprise additional code sections to the left and / or right of the depicted code sections 22-0 to 22-9. This would allow the relative position between the two parts 14 and 18 to be determined over a larger range than would be possible with the ten depicted code sections 22-0 to 22-9.

[0038] The reading device 16 comprises eight sensors 20-1 to 20-8, for example in the form of photodiodes, wherein the sensors 20-1 to 20-8 are arranged side by side parallel to the coding 12. The sensors 20-1 to 20-8 are aligned with the coding 12 and are designed to detect the different code sections 22-0 to 22-9 of the coding 12.

[0039] For uniform illumination of the code sections 22-0 to 22-9, a light source (not shown) can be provided, which illuminates at least those code sections 22-0 to 22-9 that lie within the detection range of the sensors 20-1 to 20-8 (the area between the two dashed-double-dotted arrows). Each of the sensors 20-1 to 20-8 receives – depending on the type of code sections 22-0 to 22-9 in its detection range – a specific amount of light reflected or transmitted by the respective code sections 22-0 to 22-9. The sensors 20-1 to 20-8 then output a corresponding measured value, for example in the form of a voltage or current value.

[0040] To facilitate the evaluation of the measured values ​​of sensors 20-1 to 20-8, the code sections 22-0 to 22-9 are spatially identical to each other. It is assumed here that the detection range of each sensor 20-1 to 20-8 is half as wide as the individual code sections 22-0 to 22-9 are long. The sensors 20-1 to 20-8 are aligned with the coding 12 in such a way that they form a continuous detection range (see the area between the dashed-double-dotted arrows in Fig. 1) on the coding 12, the length of which corresponds exactly to the length of a code word of the coding 12. In other words, each code section 22-4 to 22-6, which lies entirely within the detection range of the sensors 20-1 to 20-8, is located within the detection range of at least two, in particular three, adjacent sensors 20-1 to 20-8. This enables particularly fine scanning of the coding 12 and thus a particularly precise resolution of the relative position between the first part 14 and the second part 18.

[0041] The sensors 20-1 to 20-8 are followed by differential circuits 26-1 to 26-7 and an evaluation unit 24.

[0042] In this case, these differential circuits 26-1 to 26-7 are preferably each designed analogously and are coupled on the input side to two adjacent sensors 20-1 to 20-8, which output analog measured values ​​to the differential circuits 26-1 to 26-7 (see also the illustration in Fig. 2).

[0043] Each of the differential circuits 26-1 to 26-7 is configured to calculate a difference between the obtained measured values ​​and output it as a differential signal to the evaluation unit 24. Based on these differential signals, the evaluation unit 24 can reliably and precisely identify and locate the position of the transitions between regions of consecutive code sections of the first type 22-0, 22-2, 22-4, 22-5, and 22-9, and consecutive code sections of the second type 22-1, 22-3, and 22-6 to 22-8. Specifically, the differential signal of two adjacent sensors exhibits a peak whenever a transition between regions of code sections 22-0 to 22-9 of different types moves from the detection range of one sensor into the detection range of the adjacent second sensor.Consequently, it is possible to determine precisely, in a relatively simple and reliable manner, the location of the transitions between the contiguous areas of code sections of the same type in relation to the detection ranges of the sensors. From this, the relative position between the first part and the second part can be determined very precisely, taking into account the type of the respective areas of the code sections. This eliminates the need for additional coding, for example, in the form of a separate incremental track with an associated readout device.

[0044] As in Fig.2, each of the differential circuits 26-1 to 26-7 can further be followed by a comparator 28-1, 28-2, or 28-3. Each of these comparators 28-1 to 28-3 can further be connected on the input side to a reference unit REF and can be designed to compare the differential signal received from the associated differential circuit 26-1 to 26-7 with a reference signal received from the reference unit REF. A comparison signal generated therefrom, in particular a binary one, is then output to the evaluation unit 24 for analysis. In other words, the differential values ​​are not digitized based on a single fixed threshold value, as is usual, but rather based on a varying threshold value. If the reference signal varies sufficiently quickly, each differential value is effectively binarized based on a plurality of different threshold values.The evaluation unit 24 can then more precisely reconstruct the specific form of the difference signal based on the corresponding comparison signal and thus more precisely determine the positions of the transitions in the detection range of the sensors 20-1 to 20-8 as well as the corresponding relative position between the first part and the second part. In doing so, the reference unit generates, in particular, a time-varying, preferably periodically repeating, reference signal.

[0045] To put it figuratively, in the first comparator 28-1, an analog difference value from the first difference circuit 26-1 can be compared with, for example, three different reference values ​​specified by the reference signal. Assume a first difference value is 80% and the three reference values ​​defined by the reference signal are 25%, 50%, and 75%. The comparator 28-1 then outputs a "111" to the evaluation unit 24 as a binarized comparison signal for the first difference value, since the first difference value is higher than all three reference values. From this, the evaluation unit 24 can conclude that the difference value and thus the associated coverage is at least 75%. In the case of a second difference value of, for example, 60%, the binarized comparison signal would correspond to a "110."From this, the evaluation unit 24 can conclude that the second difference value and thus the corresponding coverage lies between 50% and 75%. This allows the evaluation unit 24 to distinguish between the situations of the two exemplary difference or coverage values ​​of 80% and 60%. Based on this, the evaluation unit can more precisely determine the positions of the transitions and thus the relative position between the first and second parts. In a conventional design with a fixed comparison value of, for example, 50%, this distinction would not be possible, since the evaluation unit 24 cannot resolve any difference in the binarized signal. The binarized signal would simply display a "1" for both difference values.

[0046] As an alternative to discrete comparison signals, the comparison signal can also be changed continuously, whereby the currently applied comparison signal is determined when the comparator is switched.

[0047] It is possible to use a predefined periodic reference signal or to have the evaluation unit 24 specify the exact shape of the reference signal in order to be able to determine the positions of the transitions with particular precision, particularly iteratively. Specifically, if the reference signal is controlled by the evaluation unit 24, the evaluation unit 24 could increase the reference value for a binarized value of 1 and decrease the reference value for a binarized value of 0 until the exact difference value is determined with sufficient accuracy. Of course, with such a functionality, it is also conceivable to supply the different comparators with specific reference signals. This makes the evaluation of the difference values ​​more complicated, but also more efficient and accurate.

[0048] It is understood that the device 10 described here can also be replaced by magnetic, capacitive, or inductive sensors and a corresponding coding 12 as an alternative to optical sensors 20-1 to 20-8 and an optical coding 12. A person skilled in the art will also be able to devise numerous modifications and deviations from the described embodiments, which are probably not explicitly described here but nevertheless fall within the scope of the claims.

[0049] Finally, it should be noted that the present invention also relates to a corresponding method for determining position, length, or angle. According to the invention, such a method comprises the relative movement of a first part 14 with an absolute coding 12 consisting of a plurality of code sections 22-0 to 22-9 of the first and second type relative to a second part 18 with a readout device 14, which comprises a plurality of sensors 20-1 to 20-8 for detecting the code sections 22-0 to 22-9. The relative position between the first part 14 and the second part 18 is then determined taking into account at least one difference signal from the measured values ​​of two adjacent sensors 20-1 to 20-8. List of reference symbols 10 Device for determining position, length or angle 12 Coding 14 first part 16 Reading device 18 second part 20-1 to 20-8 sensors 22-0 to 22-9 code sections 24 evaluation unit 26-1 to 26-7 differential circuits 28-1 to 28-3 Comparators REF Reference Unit

Claims

[1] Device (10) for determining position, length or angle, comprising: - a first and a second part (14, 18) which are movable relative to each other, - an absolute coding (12) attached to the first part (14) consisting of a plurality of successive code sections (22-0 to 22-9) of the first type and of the second type, - a reading device (16) attached to the second part (18) for detecting the coding (12), wherein the reading device (16) comprises a plurality of sensors (20-1 to 20-8), each of which is designed to detect the code sections (22-0 to 22-9) and output a corresponding measured value, and - an evaluation unit (24) which is designed to determine a relative position between the first and the second part (14, 18), wherein the readout device (16) comprises at least one, in particular several, preferably analog, differential circuits (26-1, 26-2), wherein the differential circuits (26-1, 26-2) are designed to form a difference between the measured values ​​of two mutually adjacent sensors of the readout device (16) and to output it as a difference signal, wherein the evaluation unit (24) is designed to determine the relative position between the first and the second part (14, 18) taking into account these difference signals, characterized by , that a comparator (28-1, 28-2, 28-3) is connected between at least one, in particular each, of the differential circuits (26-1, 26-2) and the evaluation unit (24), wherein the at least one comparator (28-1, 28-2, 28-3) is designed to compare the difference signal, in particular its current intensity or voltage, from the upstream differential circuit (26-1, 26-2) with a reference signal, in particular its current intensity or voltage, of a reference unit (REF) and to output a corresponding comparison signal to the evaluation unit (24). [2] Device (10) according to the preceding claim 1, characterized by that each differential circuit (26-1, 26-2) is coupled via a first input to a first sensor (20-1, 20-2) of the readout device (16) and via a second input to a second sensor (20-2, 20-3) of the readout device (16), which second sensor is adjacent to the first sensor (20-1, 20-2). [3] Device (10) according to one of the preceding claims, characterized bythat the reference unit (REF) is designed to output a, in particular periodically repeating, time-varying reference signal to the provided comparators (28-1, 28-2, 28-3), which then compare them with the respective measured values. [4] Device (10) according to one of the preceding claims, characterized by that an output of each differential circuit (26-1, 26-2) is coupled to a first input of an associated comparator (28-1, 28-2, 28-3) and the reference unit (REF) is coupled to a second input of each of the provided comparators (28-1, 28-2, 28-3). [5] Device (10) according to one of the preceding claims, characterized bythat each sensor (20-1 to 20-8) is coupled to at least one differential circuit (26-1, 26-2), preferably to two differential circuits (26-1, 26-2), wherein in particular n sensors (20-1 to 20-8) and n-1 differential circuits (26-1, 26-2) are provided, wherein n-2 sensors (20-1 to 20-8) are each coupled to two differential circuits (26-1, 26-2) and two sensors (20-1 to 20-8) are each coupled to only one differential circuit (26-1, 26-2). [6] Device (10) according to one of the preceding claims, characterized by that the sensors (20-1 to 20-8) are optical sensors, in particular in the form of photodiodes, magnetic sensors, capacitive sensors or inductive sensors. [7] Device (10) according to one of the preceding claims, characterized by , that the first and second parts (14, 18) are movable relative to each other either purely translationally or purely rotationally, wherein the sensors (20-1 to 20-8) are arranged next to each other parallel to the coding (12) [8] Device (10) according to one of the preceding claims, characterized by that the code sections (22-0 to 22-9) each have the same size and / or the same offset from one another. [9] Method (100) for determining position, length or angle by means of a device according to one of the preceding claims, wherein in the method (100): - the first and second parts (14, 18) are moved relative to each other, - the reading device (16) attached to the second part (18) detects the coding (12), and - at least one difference signal of measured values ​​of two adjacent sensors (20.1 to 20.8) is generated and, taking this difference signal into account, an absolute relative position between the first and the second part (14, 18) is determined.

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