Device and method for angle measurement

Abstract

The invention relates to a device and a method for angle measurement. The device in the form of a protractor (10) comprises: a scale frame (20, 200) having a code channel (25) arranged concentrically to its center; at least two detection units (30-33) for determining the angle value of the scale frame (20, 200) by detecting the code channel (25); a control unit (40) having an instrument interface (42) for communicating with a subsequent electronic device (100) and at least one interface (45-48) for communicating with an interface (35-38) of the detection unit (30-33), wherein the control unit (40) comprises a processing unit (41), which can request the angle value of the detection unit (30-33) via at least one interface (45-48) and can process it into a corrected angle value, and the corrected angle value can be transmitted to the subsequent electronic device (100) via the instrument interface (42).

Description

Technical Field

[0001] The invention relates to a device according to the invention for angle measurement and a method according to the invention for angle measurement. The device according to the invention or the method for angle measurement can significantly improve the accuracy, in particular, when measuring the angular position of shafts with larger diameters, in circular tables and in telescopic applications. Background Art

[0002] High-precision protractors for measuring the angular position of shafts (e.g., rotary tables) are known. Variants with a shaft on the measuring system side and self-supporting (Eigenlagerung) are described, for example, in the book "Digitale Laengen- und Winkelmesstechnik", A. Ernst, Moderne Industrie, 3rd edition 1998, pages 61-64. In order to achieve higher accuracy, on the one hand, very precise and therefore very expensive precision bearings must be used in the measuring system, and on the other hand, a high cost must be used to connect the shaft of the measuring system (which carries a graduated disk with radial measuring scale) to the shaft to be measured by means of a suitable clutch.

[0003] Furthermore, from the aforementioned book, pages 64-70, protractors without self-supporting are known in which a rotationally symmetrical measuring scale or a corresponding graduated disk is arranged directly on the axis to be measured. The corresponding detection unit for detecting the measuring scale is arranged stationary relative to the rotating graduated disk.

[0004] Incremental scales with up to 36,000 radial graduations are used as measuring scales in these protractors, the angular resolution being further increased by interpolation.

[0005] In an ideal case, the accuracy of the angle measurement for such a protractor now depends only on the accuracy with which the measuring scale is applied to the graduated disk and on the measuring errors of the detection unit. In practice, however, the rotary motion of the graduated disk and therefore the measuring scale is always subject to eccentricity errors and wobble errors due to manufacturing tolerances. This is due, on the one hand, to the fact that the center of the graduated disk can never be exactly on the axis of rotation of the shaft to be measured, and on the other hand, the axis of rotation of the graduated disk and the shaft to be measured cannot be arranged in exact alignment. As a result of this, the distance and position of the measuring scale relative to the detection unit change within the rotation of the shaft to be measured, which results in measuring errors during angle measurement.

[0006] In order to reduce the higher costs for precision bearings and precision clutches and for mechanical adjustment, in particular for larger protractors for shafts with larger diameters, rotary tables or telescopic applications, the applicant's document DE 199 07326 A1 proposes detecting the measuring scale at a plurality of detection positions distributed on the circumference of the graduated disk and evaluating the sinusoidal signals generated thereby and correcting eccentricity errors or wobble errors.

[0007] However, instead of an incremental track, modern protractors preferably use an absolutely coded code track. This code track is, for example, a multi-track code (e.g. Gray code) or a single-track chain code, a so-called "pseudo-random code" (PRC). This has the advantage that the absolute angular position can be determined directly at any time by detecting the code track. However, the signal processing proposed in DE 199 07 326 A1 cannot be used for absolutely coded code tracks. Summary of the invention

[0008] It is therefore the object of the invention to specify an absolute protractor with improved accuracy.

[0009] This object is achieved by the device according to the invention.

[0010] A device for angle measurement in the form of a protractor is now proposed, comprising:

[0011] a graduated frame with code tracks arranged concentrically in its center,

[0012] at least two detection units for determining the angle value of the scale frame by detecting the code track,

[0013] a control unit with a device interface for communication with subsequent electronics and at least one interface for communication with an interface of a detection unit,

[0014] Therein, the control unit comprises a processing unit, from which the angle value of the detection unit can be requested via at least one interface and processed into a corrected angle value, and the corrected angle value can be transmitted to a subsequent electronic device via a device interface.

[0015] Furthermore, it is an object of the invention to specify a method with which the accuracy of such an absolute protractor can be improved.

[0016] This object is achieved by a method according to the invention.

[0017] A method for measuring an angle with a protractor according to the invention is now proposed, which method comprises the following steps:

[0018] Requesting angle values ​​of the at least two detection units,

[0019] Process the angle value into a corrected angle value and

[0020] Transmit the corrected angle value to the subsequent electronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Further advantages and details of the invention will be found in the following description based on the accompanying drawings, in which:

[0022] Figure 1 shows a block diagram of a first embodiment of a protractor according to the present invention,

[0023] Figure 2 shows a block diagram of a first embodiment of a control unit of a protractor according to the invention,

[0024] Figure 3 shows a block diagram of a second embodiment of a control unit of a protractor according to the invention,

[0025] Figure 4 shows a block diagram of a third embodiment of a control unit of a protractor according to the invention,

[0026] Figure 5 A block diagram of another embodiment of a protractor according to the present invention is shown. DETAILED DESCRIPTION

[0027] Figure 1 The block diagram of a first embodiment of a protractor 10 according to the invention is shown. It comprises a circular or annular code disc 20 as a scale frame with code tracks 25 arranged radially around the center M of the code disc 20, four detection units 30, 31, 32, 33 and a control unit 40.

[0028] For the operation of the protractor 10, a code disc 20 is connected to the shaft to be measured in a rotationally fixed manner so that it rotates about its center M together with the axis of rotation of the shaft to be measured. The code disc 20 carries a code track 25 which can be detected photoelectrically, magnetically, capacitively or inductively. According to the invention, the code track 25 comprises an absolutely coded scale, for example in the form of a multi-track code (for example Gray code) or a single-track chain code (pseudo-random code, PRC). In order to increase the resolution of the protractor 10, a further track (not shown) with an incremental scale can be arranged in addition parallel to the absolutely coded scale.

[0029] As explained at the outset, eccentricity errors and wobble errors occur due to unavoidable tolerances when the shaft to be measured is mechanically connected to the code disc 20. This applies both to non-self-supporting goniometers 10, in which the code disc 20 is arranged directly on the shaft to be measured, and to self-supporting goniometers 10, which themselves include a shaft, to which the code disc 20 is fixed in a rotationally fixed manner and which in turn is connected to the shaft to be measured via a coupling.

[0030] The detection units 30, 31, 32, 33 are suitably designed to detect the code track 25 and determine the absolute angle value of the code disk 20 and thus the axis to be measured from the detection signal. The physical detection principle is not important for the present invention. In this example, the detection units 30, 31, 32, 33 are arranged in a fixed position on the circumference of the code disk 20 with a defined angular spacing, and the angular spacing between the detection units 30, 31, 32, 33 is, for example, 90° each. The deviations thus obtained when determining the absolute angle values ​​of the detection units 30, 31, 32, 33 can already be taken into account in the detection units 30, 31, 32, 33 or can also be taken into account in the control unit 40 when determining the corrected angle value.

[0031] Despite Figure 1 In the embodiment of FIG. 4 , four detection units 30 - 33 are used, but the invention is not limited to this number. It is important that at least two detection units are present for determining the corrected angle value.

[0032] In order to output the absolute angle values, the detection units 30, 31, 32, 33 have digital interfaces 35, 36, 37, 38. Both parallel interfaces with a preferred data width of 4 bits (half a byte), 8 bits (a byte) or 16 bits (a word) and serial interfaces can be used. Particularly suitable serial interfaces are the known standard interfaces for position measuring devices (for example EnDat or SSI). However, field bus systems (for example CAN bus, Interbus-S, SERCOS) or interfaces that can be summarized under the general term "real-time Ethernet" can also be used. Accordingly, these interface connections (such as in Figure 1 ) can be a point-to-point connection, but there may also be a bus connection with a line structure or a ring structure.

[0033] For communication between the control unit 40 and the detection units 30-33, interfaces 45-48 are provided in the control unit 40, which are connected to the interfaces 35-38 of the detection units 30-33 via corresponding signal lines. The signal lines can be conventional electrical wires, but in the case of large spatial distances between the control unit 40 and the detection units 30-33, it can be advantageous to use optical waveguides as signal lines and optical interfaces as interfaces 45-48 of the control unit 40 or interfaces 35-38 of the detection units 30-33. The absolute angle values ​​determined in the detection units 30-33 can be transmitted to the control unit 40 via the interface connection in the instrument.

[0034] Furthermore, the control unit 40 comprises a device interface 42 for communication with the subsequent electronic device 100. This is advantageously also a serial data transmission interface, prominent examples of which are once again EnDat, SSI or a real-time Ethernet interface.

[0035] Furthermore, a processing unit 41 is provided in the control unit 40 . It is used to request angle values ​​from the detection units 30 - 33 via corresponding interface connections, to form corrected angle values ​​using the requested angle values, and to transmit the corrected angle values ​​to the subsequent electronic device 100 via the device interface 42 .

[0036] Furthermore, processing unit 41 can check the angular values ​​received from detection units 30 - 33 for plausibility and, in the event of deviations exceeding certain tolerance thresholds, send a warning or error message to subsequent electronic device 100 via device interface 42 .

[0037] For applications that are relevant to reliability, it is advantageous to design the processing unit 41 in such a way that at least two corrected angle values, which are based on the angle values ​​of the different detection units 30-33, can be generated and transmitted to the subsequent electronic device 100. In this way, errors in the generation or transmission of the corrected angle values ​​can be reliably revealed by comparison in the subsequent electronic device 100.

[0038] Especially for very large protractors 10 (in which the code disk 20, the detection units 30-33 and the control unit 40 are not arranged together in the housing, but are assembled separately as individual components), the control unit 40 and one of the detection units 30-33 (in Figure 1 It is advantageous to combine the intermediate detection unit 30) into the main detection unit 50. This facilitates the assembly of the protractor 10 on the one hand and the interface connection of the corresponding interfaces 35, 45 on the other hand can be implemented more simply.

[0039] A particular advantage of the protractor 10 according to the invention is that, from the perspective of the subsequent electronics 100, no difference can be detected with respect to the communication with the instrument interface 42 compared to the communication with a protractor as known from the prior art, but a significantly improved measurement accuracy is nevertheless achieved. Thus, existing devices can also be retrofitted with the protractor 10 according to the invention and their accuracy improved without having to be integrated into the subsequent electronics 100.

[0040] Figure 2 FIG. 4 shows a block diagram of a control unit 40 of a first embodiment of a protractor 10 according to the invention. Figure 1 Functional blocks that have already been described in connection herewith are provided with the same reference numerals.

[0041] In order to determine the corrected angle value, the processing unit 41 includes an extrapolation unit 410 , a clock generator 420 , a time measurement unit 430 and a correction unit 440 .

[0042] The extrapolation unit 410 requests the current angle value from the detection unit 30-33 via the interface 45-48 in the time interval determined by the clock signal of the clock generator 420. If the position request command from the subsequent electronic device 100 now arrives via the instrument interface 42, the extrapolation unit 410 determines the extrapolated angle value from at least the two latest angle values ​​of each detection unit 30-33. The time measurement unit 430 measures the time between the request for the last angle value of each detection unit 30-33 required for the extrapolation and the time when the position request command arrives. The extrapolated angle value is supplied to the correction unit 440, which processes them into a corrected angle value, for example, by forming an average value from the extrapolated angle values. This value is sent to the subsequent electronic device 100 via the instrument interface 42.

[0043] Figure 3 FIG. 4 shows a block diagram of a control unit 40 of another embodiment of the protractor 10 according to the present invention. Figure 1 Functional blocks already described in this connection also carry the same reference numerals here.

[0044] In this embodiment, the processing unit 41 includes a correction unit 510 and a correction value determination unit 520. Optionally, the processing unit 41 may further include a rhythm generator 530.

[0045] If a position request instruction arrives from the subsequent electronic device 100, the correction value determination unit 520 requests the current angle value of the detection unit 30-33 via the interface 45-48 and determines a correction value suitable for correcting the angle value currently arriving from the leading detection unit 33. The correction value determination unit 520 is advantageously designed in this way so that the request for the current angle value is made with as little time delay as possible and for all detection units 30-33 at the same time. The determined correction value is supplied to the correction unit 510, which corrects the angle value currently arriving from the leading detection unit 33 and sends it to the subsequent electronic device 100 via the device interface 42.

[0046] With regard to the reaction time of the protractor 10 (that is to say the time between the arrival of the position request command and the issuance of the current corrected angle value), it has proven to be advantageous when, instead of using the correction value determined from the currently arriving angle value, the correction value determined when the previous position request command arrived is used as the correction value transmitted to the correction unit 510 for determining the corrected angle value. Since eccentricity errors or sway errors are long-term errors, it is possible that the correction value changes only insignificantly in the case of small angle changes. Furthermore, the protractor 10 is usually interrogated periodically at short time intervals (that is to say at a high interrogation frequency) during the operation of the subsequent electronic device 100. In this way, in particular in the case of a slow rotation speed of the shaft to be measured or in the case of a high interrogation frequency of the subsequent electronic device 100, an improved reaction time is achieved without a significant reduction in the measuring accuracy, because the correction value is already available at the time of the arrival of the position request command.

[0047] In a further development, the request for the current angle value of the detection unit 30-33 and the determination of the correction value in the correction value determination unit 520 can be controlled by an optional clock generator 530. This ensures that new correction values ​​are continuously determined and that very recent correction values ​​are always available when a position request command arrives.

[0048] In order to avoid time conflicts between the internal request for the current angle value in the master detection unit 33, which is controlled by the clock generator 530, and the external request for the current angle value, which arrives via the device interface 42, the master detection unit 33 can be excluded from determining the new correction value. In this case, the new correction value is determined only using the angle values ​​of the remaining detection units 30-32.

[0049] Figure 4 FIG. 4 shows a block diagram of a control unit 40 of another embodiment of the protractor 10 according to the present invention. Figure 1 Functional blocks already described in this connection also carry the same reference numerals here.

[0050] This embodiment is based on the recognition that the time intervals at which position request instructions arrive from the subsequent electronic device 100 via the instrument interface 42 during the periodic operation of the protractor 10 are known. In addition to the correction unit 610, a trigger unit 620 is now provided, which controls the request for new angle values ​​of the detection units 30-33 and the determination of the corrected angle values. The trigger unit 620 sends a trigger signal to the correction unit for this. The timing of the trigger signal is determined in such a way that it is generated at a specified time after the last arrival of the position request instruction of the subsequent electronic device 100, but before the arrival of the current position request instruction. This results in that the current corrected angle value can be sent immediately to the subsequent electronic device during the periodic operation of the position request instruction. The information when the trigger unit 620 must send the trigger signal to the correction unit 610 can be informed to the trigger unit 620, for example, via the instrument interface 420.

[0051] Figure 5 FIG. 2 shows a block diagram of another embodiment of a protractor 10 according to the present invention. Figure 1 In the embodiment of the invention, the protractor 10 comprises a ring 200 as a scale frame, on whose cylindrical outer surface a code track 25 is arranged. In this embodiment, the code track 25 comprises an absolutely coded scale 125 and an incremental scale 126. The ring 200 is made of steel, for example, and is also referred to as a "drum" in professional circles. Advantageously, the length of the scale lines 125, 126 transverse to the measuring direction is implemented in such a way that it is greater than the detection length required by the detection units 30-33, so that an axial movement of the ring 200 relative to the detection units 30-33 does not cause a distortion of the measured value.

[0052] Especially when the outer diameter of the ring 200 is large, the absolutely coded scale 125 and the incremental scale 126 are not applied directly to the ring 200, but in the form of a steel strip which carries the scale tracks 125, 126 and is inserted into a groove in the outer diameter of the ring and is tensioned with a turnbuckle. Figure 5 As shown in section A of FIG. 4 , a collision point S is generated. When driving over the collision point S with the detection units 30 - 33, a jump can occur in the angle values ​​read out. In order to minimize their influence on the formation of the corrected angle value, it is advantageous if the processing unit 41 selects the angle values ​​of the detection units 30 - 33 in the area of ​​the collision point S and does not use them to determine the corrected angle value.

[0053] It should also be noted that in the implementation of the control unit 40, in particular according to Figure 2-4In the described embodiment, it is not absolutely necessary to completely transmit the angle values ​​of all detection units 30-33 to the control unit 40 for determining the correction value. Deviations in the angle values ​​caused by sway errors and / or eccentricity errors occur in a relatively small angular range. Therefore, it is sufficient in most cases to completely transmit only the current angle value of the dominant detection unit 30-33 and to transmit so many low-order bits of the reserved detection unit 30-33 for its correction that the largest errors can be reliably corrected.

[0054] It is usually advantageous if the control unit 40 is designed so that the detection units 30-33 can also be individually responded to by the subsequent electronic device 100 via the device interface 42. For this purpose, for example, special interface commands can be provided, which enable the selection, description or reading of the individual detection units 30-33. In principle, however, other selection or switching mechanisms are also possible.

[0055] Furthermore, it is advantageous to implement the control unit 40 in such a way that individual detection units 30-33 can be disabled or their angle values ​​are not taken into account for determining the corrected angle value. In this case, the protractor 10 can also continue to operate with reduced accuracy if a detection unit 30-33 fails or supplies erroneous values. Figure 3 In conjunction with the exemplary embodiment described in , it is advantageous to optionally implement a dominant detection unit 33 .

[0056] The invention is of course not restricted to the exemplary embodiments described, but rather further embodiments common to a person skilled in the art exist within the scope of the idea according to the invention.

Claims

1. A device for angle measurement in the form of a protractor (10), comprising: a scale frame (20, 200) having a code track (25) arranged concentrically in its center, said code track (25) comprising absolutely coded graduations, at least two detection units (30-33) for determining the absolute angle value of the scale frame (20, 200) by detecting the code track (25), a control unit (40) having an instrument interface (42) for communicating with a subsequent electronic device (100) and at least one digital interface (45-48) for communicating with an interface (35-38) of the detection unit (30-33), The control unit (40) comprises a processing unit (41), which can request the angle value of the detection unit (30-33) via the at least one interface (45-48) and can process it into a corrected angle value, and the corrected angle value can be transmitted to the subsequent electronic device (100) via the instrument interface (42). The processing unit (41) further comprises a clock generator (420, 530) and the request for the angle value can be controlled by the clock generator (420, 530), Wherein, the processing unit (41) further comprises: a time measurement unit (430) by means of which the time between the last request for an angle value and the arrival of a position request command at the device interface (42) can be measured, a correction value determination unit (520) for determining a correction value from the angle value of the leading probe unit, wherein the angle value requested before the arrival of the position request command is used to determine the correction value, and A correction unit (440) with which a corrected angle value can be calculated from the current angle value of the leading detection unit and the correction value.

2. A device for angle measurement in the form of a protractor (10), comprising: a scale frame (20, 200) having a code track (25) arranged concentrically in its center, said code track (25) comprising absolutely coded graduations, at least two detection units (30-33) for determining the absolute angle value of the scale frame (20, 200) by detecting the code track (25), a control unit (40) having an instrument interface (42) for communicating with a subsequent electronic device (100) and at least one digital interface (45-48) for communicating with an interface (35-38) of the detection unit (30-33), The control unit (40) comprises a processing unit (41), which can request the angle value of the detection unit (30-33) via the at least one interface (45-48) and can process it into a corrected angle value, and the corrected angle value can be transmitted to the subsequent electronic device (100) via the instrument interface (42). The processing unit (41) further comprises a clock generator (420, 530) and the request for the angle value can be controlled by the clock generator (420, 530), Wherein, the processing unit (41) further comprises: a correction value determination unit (520) for determining a correction value from the angle values, wherein the dominant detection unit can be excluded from determining a new correction value, the new correction value being determined only using the angle values ​​of the remaining detection units, and A correction unit (440) with which a corrected angle value can be calculated from the stored current angle value of the detection unit and the correction value.

3. The device according to claim 1 or 2, characterized in that: One of the detection units (30-33) and the control unit (40) are combined into a main detection unit (50).

4. The device according to claim 1 or 2, characterized in that: The code track (25) includes an absolute coded scale (125) and an incremental scale (126).

5. A method for measuring angles with a device according to claim 1 or 3 or 4, comprising the following steps: Request the angle values ​​of at least two detection units (30-33), Processing the angle value into a corrected angle value and · transmitting the corrected angle value to a subsequent electronic device (100), in, The request for the angle value is controlled by a clock generator (420, 530), in, determining in a correction value determination unit (520) a correction value from the angle value for correcting the angle value of the leading detection unit (30) to a corrected angle value, wherein the angle value requested before the position request command arrives is used to determine the correction value, and · Calculating the corrected angle value in the correction unit (510).

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