DEVICE 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. The first part is fitted with an absolute code consisting of a plurality of consecutive code segments of the first and second type. The second part is fitted with a readout device for acquiring the code, 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, which determines a relative position between the first and second parts based on the measured values ​​acquired by the readout device. The specific shape and sequence of contiguous areas of code segments of the first and second type constitute the absolute code.All code segments of the first type are themselves formed from at least, and in particular exactly, two adjacent subsegments of different types. Furthermore, a method for forming a corresponding code is described.

Description

[0001] The present invention relates to a device for determining position, length, or angle. 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, 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 and motor feedback systems.

[0003] Conventionally, such a device comprises a first and a second part, wherein the first and second parts 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 second parts based on these measured values.

[0004] Such devices make it possible to determine, at least roughly, the relative position between the two parts. To improve the resolution of the relative position, an incremental track with an associated additional readout device is usually provided in addition to the aforementioned 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 device for accurately determining the relative position of the two parts, which does not require an additional incremental track with associated readout device.

[0006] This object is achieved in that the code sections of the first type, which together with the code sections of the second type form the absolute coding, are each formed from at least, in particular exactly, two adjacent subsections of different types.

[0007] In other words, the higher-level structure of the absolute coding, which is defined by the shape and sequence of contiguous areas consisting of code sections of the first and second type, is supplemented by a fine structuring of the code sections of the first type. The evaluation of this fine structuring enables not only the rough determination of the relative position based on the higher-level structure, but also fine adjustment of the determination of the relative position, similar to the incremental track. For this purpose, it is not necessary to resort to a separately provided coding, for example in the form of an incremental track, and an associated readout device. Against this background, it should also be noted that it is also possible to design the code sections of the second type with a corresponding fine structuring with subsections.However, it is essential that the code sections of the second type still differ from the code sections of the first type.

[0008] Preferably, a number of 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. Each code word is preferably present only once in the coding, resulting in an absolute code or absolute coding. 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 an individual code section, in particular when the code section is located exactly at the two sensors. In particular, the device comprises at least twice as many sensors as bits per code word, preferably four times as many sensors as bits per code word.

[0009] Preferably, the subsections divide the respective code sections into equal parts.

[0010] In other words, the subsections are all the same length and evenly arranged along the respective code segment. Such a symmetrical fine structure of the code segments is comparatively easy to evaluate.

[0011] Preferably, the type of at least one subsection of each code section of the first type corresponds in type to that of the code sections of the second type. In this case, the type of at least one subsection of each code section of the first type is different in type from that of the code sections of the second type.

[0012] This makes particular sense if only the code sections of the first type have a fine structure. With regard to a configuration in which the code sections of the second type are also formed by corresponding subsections, the entirety of the subsections preferably consists of subsections of two different types. This means that both the code sections of the first type and the code sections of the second type are then formed from only two types of subsections. Such a configuration allows a comparatively simple evaluation of the measured values ​​from the sensors and thus a reliable and precise determination of the relative position. The types of code sections or subsections can differ from one another, for example, with regard to brightness, color, transmissivity, electrical charge or magnetization.

[0013] According to the invention, two adjacent sensors are coupled via a differential circuit, which is designed to output a corresponding differential signal to the evaluation unit. The evaluation unit is designed to determine the relative position between the first and second parts, taking these differential signals into account.

[0014] Such a differential signal enables a rapid and reliable determination of the positions of transitions between contiguous areas of code sections of the first type and the second type within the detection range of the sensors. Taking this information into account, a more precise determination of the relative position between the first and second parts is possible without having to resort to additional coding, for example, in the form of an incremental track with an associated readout device.

[0015] Specifically, 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, for example, "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.

[0016] 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.

[0017] 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.

[0018] Preferably, the detection range of each sensor on the coding is half as wide as the individual code sections and / or exactly as wide as the individual subsections.

[0019] This results in an oversampling of the coding by the sensors of the reading device, which ultimately enables a more precise determination of the relative position between the first and the second part.

[0020] Preferably, at least one sensor is designed as a position-sensitive device.

[0021] This enables even more precise scanning of the coding and thus a more precise determination of the relative position between the first and second part.

[0022] The sensors are preferably optical sensors, in particular photodiodes, magnetic sensors, capacitive sensors or inductive sensors.

[0023] Such sensors are particularly sophisticated and cost-effective. Optical sensors can be designed, in particular, to absorb light reflected from the coding or light transmitted through the coding. Hall sensors are also particularly suitable. The types of code sections or subsections are selected in such a way that they can be distinguished by the sensors used. With optical sensors, the sections of different types can differ, for example, in terms of color, brightness, or transmissivity. With magnetic sensors, the sections of different types differ, in particular, in terms of their magnetization.

[0024] Preferably, the first part and the second part are movable relative to each other purely in a translational or purely rotational manner. The sensors are arranged next to each other, parallel to the coding.

[0025] The evaluation of purely translational and purely rotational movements is particularly easy. The parallel arrangement of the sensors eliminates the need for correction of the measured values ​​prior to analysis, which would be necessary due to the variable distance between the sensors and the coding.

[0026] Preferably, the code sections each have the same size and / or the same offset from one another.

[0027] This makes it much easier to evaluate the measured values ​​and thus to determine the relative position between the first and second parts.

[0028] To form the coding for a device described above, an absolute coding is first formed from a plurality of code sections of the first and second type using a conventional method. Subsequently, all code sections of the first type are replaced by code sections that themselves are formed from at least, in particular exactly, two adjacent subsections of different types.

[0029] Additionally or alternatively, all code sections of the second type can also be replaced by code sections which themselves are formed from at least, in particular exactly, two adjacent subsections of a different type. If both the code sections of the first type and the code sections of the second type are replaced by code sections from corresponding subsections, care must be taken to ensure that the code sections of the first type are still different from the code sections of the second type. As already described above, this fine structuring of the code sections enables a more precise determination of the relative position between the first part and the second part. In this case, additional coding, for example in the form of an incremental track, with the associated readout device, can be dispensed with.

[0030] The above explanations regarding the device according to the invention apply accordingly to the method according to the invention, and vice versa. This applies in particular to advantages and embodiments.

[0031] The invention is described below by way of example with reference to the drawings, in which: Fig. 1 a schematic view of the basic structure of an exemplary device for determining position or length, which is to be further developed according to the invention; Fig. 2 a schematic view of a further development of the device from Fig. 1; and Fig. 3 shows an example of a conventionally formed 4-bit long absolute code and two examples of inventive modifications of this absolute code.

[0032] In the figures, the same reference symbols denote the same or similar features.

[0033] 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).

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] The sensors 20-1 to 20-8 are followed by differential circuits 26-1 to 26-7 and an evaluation unit 24.

[0040] 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).

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] In the following, with reference to Fig. 3 the present invention is discussed in detail.

[0048] Fig. Figure 3 shows in the top line an example of a conventionally generated 4-bit long absolute coding from a large number of equally long code sections of the first and second type (each shown in white or black).

[0049] Based on this, and analogous to the above description, the code sections shown in white can be understood as code sections of the first type and the code sections shown in black as code sections of the second type. According to the invention, the code sections of the first type shown in white are each replaced by code sections which themselves are formed from at least, in particular exactly two adjacent subsections of different types. Specifically, for example, each code section of the first type originally shown in pure white can be replaced by a code section in the form of a first subsection (left-hand side) of the first type (shown in white) and a second subsection (right-hand side) of the second type (shown in black). This results in a modified coding corresponding to the second line in Fig. 3. According to the invention, this modified coding replaces the one in Fig. 1 shown coding 12.

[0050] Alternatively, in contrast to the above description, the code sections shown in black can be understood as code sections of the first type and the code sections shown in white as code sections of the second type. According to the invention, the code sections of the first type shown in black are each replaced by code sections which themselves are formed from at least, in particular exactly two adjacent subsections of different types. Specifically, for example, each code section of the first type originally shown in pure black can be replaced by a code section in the form of a first subsection (left-hand side) of the first type (shown in black) and a second subsection (right-hand side) of the second type (shown in white). This results in a modified coding corresponding to the third line in Fig. 3. According to the invention, this second modified coding can also be Fig. Replace coding 12 shown in figure 1.

[0051] As can be seen from a comparison of the three codings from Fig. 3, the modification of the coding according to the invention results in contiguous areas of code sections of the first type receiving a fine structure which, in analogy to a separately provided incremental track, enables a finer determination of the relative position between the first part 14 and the second part 18.

[0052] It should be noted that it is also possible to replace both types of code sections of the original coding with code sections consisting of subsections. However, it is important that the code sections of the original first type remain distinguishable from the code sections of the original second type. It is also possible to replace the respective code sections with code sections consisting of more than two subsections. The subsections can be of two different types or comprise several different types. As shown, the individual subsections can preferably divide the respective code section into equal parts. There are virtually no limits to the possibilities of the person skilled in the art in this regard.However, it should be noted that a finer structuring of the code sections also requires a finer sampling of the coding (in particular by more sensors, each with a smaller detection range) and / or more detailed evaluation of the measured values ​​(for example by the difference formation described above and / or the comparators described above) in order to be able to resolve the fine structure formed and to take it into account when determining the relative position between the first and the second part. 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 (22-1 to 22-8) 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 (22-1 to 22-8) and output a corresponding measured value, and - an evaluation unit (24) which determines a relative position between the first and the second part (14, 18) on the basis of said measured values, wherein the specific shape and sequence of contiguous areas of code sections (22-1 to 22-8) of the first and second type forms the absolute coding (12), wherein all code sections (22-1 to 22-8) of the first type are themselves formed from at least, in particular exactly, two adjacent subsections of different types characterized by , that two adjacent sensors (20-1 to 20-8) are coupled via a differential circuit which is designed to output a corresponding differential signal to the evaluation unit (24), wherein the evaluation unit (24) is designed to determine the relative position between the first and the second part (14, 18) taking these difference signals into account. [2] Device (10) according to the preceding claim 1, characterized by that the subsections divide the respective code sections (22-1 to 22-8) into equal parts. [3] Device (10) according to one of the preceding claims, characterized by that the type of at least one subsection of each code section (22-1 to 22-8) of the first type corresponds in type to that of the code sections (22-1 to 22-8) of the second type, and the type of at least one subsection of each code section (22-1, 22-2, 22-3) of the first type is different in type from that of the code sections (22-1 to 22-8) of the second type. [4] Device (10) according to one of the preceding claims, characterized by that the detection range of each sensor (20-1 to 20-8) on the coding (12) is half as wide as the individual code sections (22-1 to 22-8), and / or exactly as wide as the individual subsections. [5] Device (10) according to one of the preceding claims, characterized by that at least one sensor (20-1 to 20-8) is designed as a position-sensitive device. [6] Device (10) according to one of the preceding claims, characterized by that the sensors are optical sensors, in particular photodiodes, magnetic sensors, capacitive sensors or inductive sensors. [7] Device (10) according to one of the preceding claims, characterized by that the first and the second part (14, 18) are movable purely translationally or purely rotationally relative to one another, wherein the sensors (20-1 to 20-8) are arranged next to one another parallel to the coding (12). [8] Device (10) according to one of the preceding claims, characterized by that the code sections (22-1 to 22-8) each have the same size and / or the same offset from one another.

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