A circular grating self-calibration method based on fixed reading head and variable position reading head

Abstract

The present invention provides a circular grating self-calibration method based on a fixed readhead and a variable-position readhead. The method utilizes both fixed and variable-position readheads to self-calibrate the measurement error of a circular grating encoder. The fixed readhead determines the zero position of the error compensation data. By changing the position of the variable-position readhead, interference is determined to confirm whether the readhead needs to be changed. The recorded data is then processed to simulate multiple readheads and self-calibrate the circular grating's angle measurement error. The method is relatively simple and low-cost, addressing the shortcomings of conventional methods. It enables circular grating self-calibration without the need for external high-precision measuring instruments and eliminates higher-order harmonic errors in the circular grating encoder's measurement error.

Description

Technical Field

[0001] The present invention belongs to the field of precision measurement technology, and relates to a circular grating self-calibration method, and more specifically to a circular grating self-calibration method based on a fixed reading head and a variable position reading head. Background Art

[0002] Circular encoders are commonly used for angle measurement. They offer advantages such as high resolution, compact size, easy installation, and fast response speed. They are widely used in aerospace, intelligent robotics, high-end CNC machine tools, high-precision coordinate measuring machines, and other fields. However, with technological advancements, various instruments and equipment are demanding increasingly higher angular measurement accuracy, placing even higher demands on the angular measurement accuracy of circular encoders.

[0003] A circular grating system typically consists of a circular grating and a readhead. Angular measurement errors in a circular grating system primarily stem from circular grating errors and installation errors, including eccentricity, tilt, and circular grating ring deformation. Calibration is a common and effective method for improving circular grating measurement accuracy.

[0004] At present, there are many studies on circular grating self-calibration methods, and various circular grating self-calibration methods have been proposed. There are two common methods: (1) using multiple reading heads evenly distributed around the circular grating, using the principle of average reading of multiple reading heads, can partially eliminate the effects of installation eccentricity, scale line error, etc. on reading accuracy; (2) using the method of optimizing the layout of sensors such as 2x3, 3x4 and 3x4x7, and reasonably placing the reading heads, can increase the order of harmonic error that can be eliminated without increasing the number of reading heads, thereby improving the effect of circular grating self-calibration.

[0005] The above circular grating self-calibration method also has certain shortcomings: (1) When the size of the circular grating is determined, the number of read heads that can be installed is always limited due to the constraints of the circular grating diameter and the size of the read head, so the influence of higher-frequency harmonic errors cannot be eliminated; (2) The number of read heads used is relatively large, usually more than 2, and the cost of the read heads of high-precision circular gratings is relatively high. The more read heads there are, the higher the cost of the self-calibration system. Summary of the Invention

[0006] In order to solve the problems existing in the prior art, the present invention proposes a circular grating self-calibration method based on a fixed reading head and a variable position reading head. The principle is that the fixed reading head determines the zero position of the error compensation data, and by changing the position of the variable position reading head, the two reading heads are used to simulate multiple reading heads to perform self-calibration of the circular grating angular measurement error.

[0007] The present invention is achieved through the following technical solutions:

[0008] A circular grating self-calibration method based on a fixed reading head and a variable position reading head, the method comprising the following steps:

[0009] Step 1: Select one of the two readheads as a fixed readhead and the other as a variable readhead. Based on the actual dimensions of the circular grating and readhead and the pre-determined readhead mounting locations, select two readhead mounting locations from the list that will not interfere with each other. Install the fixed readhead in one of the two selected mounting locations and the variable readhead in the remaining location. Mark all locations in the mounting location list as unmeasured.

[0010] Step 2: The circular grating rotates k revolutions, where k ≥ 1, and the data collected by the two readheads are recorded synchronously. After recording is completed, the current installation positions of the two readheads are marked as the positions where measurements have been taken in the readhead installation position list.

[0011] Step 3: Determine whether all positions in the reading head installation position list have been measured;

[0012] If all positions in the reading head installation position list have been measured, that is, there is no position that has not been measured, go to step 4;

[0013] Otherwise, if there is a position that has not been measured in the reading head installation position list and installing the variable position reading head at this position will not interfere with the fixed reading head, then install the variable position reading head at this position and then go to step 2;

[0014] Otherwise, if there are any unmeasured positions in the readhead installation position list and installing the variable position readhead at this position will interfere with the fixed readhead, then switch the identities of the fixed readhead and the variable position readhead, that is, change the fixed readhead to the variable position readhead, and change the variable position readhead to the fixed readhead. Then, select a position that has not been measured and where installing the variable position readhead at this position will not interfere with the fixed readhead, and install the variable position readhead there, then go to step 2.

[0015] Step 4: After completing all data acquisition work, process the recorded data to achieve self-calibration of the circular grating.

[0016] Furthermore, in step 2 of the method, the recorded data is used to calculate the actual angle between the installation positions of the two reading heads, including the following steps:

[0017] Step 2-1: Extract the readings of the two reading heads at the moment when the zero line of the circular grating passes through the two reading heads from the recorded data. The reading of the fixed reading head when the zero line of the circular grating passes through the fixed reading head is recorded as F1, and the reading of the variable position reading head is recorded as V1; the reading of the fixed reading head when the zero line of the circular grating passes through the variable position reading head is recorded as F2, and the reading of the variable position reading head is recorded as V2;

[0018] Step 2-2: The actual angle A between the two reading heads is ((F2-F1)+(V2-V1)) / 2;

[0019] Step 2-3: If the calculated angle A is greater than 180 degrees, convert it to an angle less than 180 degrees using the formula A=360-A.

[0020] Furthermore, when installing the readhead to a predetermined installation position, it is necessary to ensure that the installation position is accurate, which specifically includes the following steps:

[0021] Use the method in step 2 to calculate the actual angle between the two reading head installation positions, and determine whether the angle error of the actual installation position of the reading head exceeds the predetermined threshold. If the position error is too large, readjust the installation position and check again until the position angle error is less than the predetermined threshold. Only then can the adjustment process of the reading head be ended and data collection can be started.

[0022] Furthermore, after completing all data collection work in step 4, the data is processed to reduce the impact of random errors, specifically including the following steps:

[0023] Step 4-1: First determine the number of revolutions k of the circular grating. If k>1, perform mean processing on the data of each revolution to reduce the influence of random errors. If k=1, no mean processing is required.

[0024] Furthermore, after recording the data once in step 2, data processing begins before all data collection work is completed, thereby improving data processing efficiency.

[0025] The beneficial effects of the present invention are as follows:

[0026] The above technical solution demonstrates that the method of the present invention utilizes a fixed readhead and a variable-position readhead to achieve self-calibration of the measurement error of a circular grating encoder. This method aims to simulate multiple readheads, and the number of readheads that can be simulated is not limited by their size; theoretically, an unlimited number of readheads can be simulated. This method can eliminate higher-order harmonic errors in the measurement error of a circular grating encoder. This method achieves circular grating self-calibration without the need for external high-precision measuring instruments, requires fewer readheads, and is relatively inexpensive. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 It is a schematic flow chart of the method of the present invention;

[0029] Figure 2 1 is a flow chart of a method for calculating the actual angle between the installation positions of two reading heads in the method of the present invention;

[0030] Figure 3 is a flow chart of a method for determining whether an installation position is accurate in the method of the present invention;

[0031] Figure 4 This is a diagram showing the uniform distribution position of the reading heads of the present invention;

[0032] Figure 5 This is a diagram of the optimized layout position of the reading head 2×3 of the present invention;

[0033] Figure 6 Schematic diagram of the installation position of the reading head in Example 1;

[0034] Figure 7 is a curve diagram showing the difference between the data of the displacement reading head after alignment and the data of the fixed reading head in Example 1;

[0035] Figure 8 is a graph showing the angle measurement error of the circular grating in Example 1;

[0036] Figure 9 is a comparison diagram of the difference curves between the position 2 data and the position 1 data before and after error compensation in Example 1;

[0037] Figure 10 Schematic diagram of the installation position of the reading head of the second embodiment;

[0038] Figure 11 is a curve diagram showing the difference between the data of the displacement reading head after alignment and the data of the fixed reading head in Example 2;

[0039] Figure 12 is a graph showing the angle measurement error of the circular grating in the second embodiment;

[0040] Figure 13 1 is a comparison diagram of the difference curves between the position 2 data and the position 1 data before and after error compensation in Example 2;

[0041] The figures are marked as follows: 1. Fixed reading head, 2. Variable position reading head, 3. Circular grating. DETAILED DESCRIPTION

[0042] The advantages, features and specific embodiments of the present invention are further described below in conjunction with the accompanying drawings. These embodiments are given as examples with reference to the accompanying drawings only, and are non-limiting descriptions, illustrations and explanations of the present invention. The scope of protection of the present invention is not limited to the following embodiments.

[0043] The present invention proposes a circular grating self-calibration method based on a fixed reading head and a variable position reading head; the principle is that the fixed reading head 1 determines the zero position of the error compensation data, and by repeatedly changing the position of the variable position reading head 2, the two reading heads are used to simulate multiple reading heads to self-calibrate the circular grating angle measurement error.

[0044] The specific implementation is as follows:

[0045] Example 1 (no interference between adjacent position reading heads):

[0046] like Figure 1 As shown, a circular grating self-calibration method based on a fixed reading head and a variable position reading head includes the following steps:

[0047] Step 1: Select one of the two readheads, called fixed readhead 1, and the other, called variable readhead 2. Based on the actual dimensions of the circular grating and readheads and the pre-determined readhead mounting position list, select two readhead mounting positions from the list that will not interfere with each other. Install fixed readhead 1 in one of the two selected mounting positions, and variable readhead 2 in the remaining position. Mark all positions in the mounting position list as unmeasured.

[0048] In this embodiment, one of the reading heads is designated as fixed reading head 1, and the other reading head is designated as variable position reading head 2. In this embodiment, the reading head installation method is predetermined to be evenly distributed in 6 reading head positions, i.e., the number of reading head positions n in the installation position list is 6;

[0049] Each predetermined position is numbered as P1, P2, ..., P6. The predetermined installation positions of the reading head are shown in Figure 4 , the angle between two adjacent reading heads is α=360° / n=60°.

[0050] In this embodiment, it is assumed that the size of the reading head is small and the two reading heads at adjacent installation positions will not interfere with each other. Let P1 and P2 be the two selected reading head installation positions that will not interfere with each other. Figure 4 Position P1, install the variable position reading head 2 to Figure 4The middle position P2 is selected, and the six positions P1, P2, ..., P6 are marked as positions that have not been measured.

[0051] Step 2: The circular grating rotates k revolutions, where k ≥ 1, and the data collected by the two read heads are recorded synchronously during this period. After recording is completed, the current installation positions of the two read heads are marked as the positions where measurements have been taken in the read head installation position list.

[0052] In this embodiment, the two reading heads are fixed after installation, and the moment when the zero mark of the circular grating passes through the fixed reading head 1 is captured during rotation, and counting starts from this moment;

[0053] After the counting starts, the circular grating rotates k=2 revolutions, during which the data collected by the two reading heads are synchronously recorded, as shown in Table 1 below, where m is the number of times the reading head reads the measurement data during one revolution of the circular grating. In this embodiment, m=36.

[0054] The data to be recorded should include the measurement data when the zero line of the circular grating passes through each readhead. After the recording is completed, the current installation positions of the two readheads are marked as the positions where measurements have been taken in the readhead installation position list, as shown in Table 1.

[0055] Table 1 Measurement data of each time in Example 1

[0056]

[0057] Step 3: Determine whether all positions in the reading head installation position list have been measured;

[0058] If all positions in the reading head installation position list have been measured, that is, there is no position that has not been measured, go to step 4;

[0059] Otherwise, if there is a position that has not been measured in the reading head installation position list and installing the variable position reading head 2 at this position will not interfere with the fixed reading head 1, then install the variable position reading head 2 at this position and then go to step 2;

[0060] Otherwise, if there are any unmeasured positions in the readhead installation position list and installing the variable position readhead 2 at this position will interfere with the fixed readhead 1, then switch the identities of the fixed readhead 1 and the variable position readhead 2, that is, change the fixed readhead 1 to the variable position readhead 2, and change the variable position readhead 2 to the fixed readhead 1. Then, select a position that has not been measured and where installing the variable position readhead 2 at this position will not interfere with the fixed readhead 1, and install the variable position readhead 2 there, then go to step 2.

[0061] In this embodiment, the installation positions of the two reading heads are as follows Figure 6As shown, Figure 6 In (a), the fixed reading head 1 is at position P1, and the variable position reading head 2 is at position P2; Figure 6 In (b), the fixed reading head 1 is at position P1, and the variable position reading head 2 is at position P3; Figure 6 In (c), the fixed reading head 1 is at position P1, and the variable position reading head 2 is at position P4; Figure 6 In (d), the fixed reading head 1 is at position P1, and the variable position reading head 2 is at position P5; Figure 6 In (e), the fixed reading head 1 is at position P1 and the variable position reading head 2 is at position P6.

[0062] Following the above steps, multiple measurements were completed. The readhead installation positions and measurement results for each measurement are shown in Table 1. After five measurements, all installation positions were marked as measured. This means that there were no unmeasured positions in the readhead installation position list. Therefore, proceed to Step 4.

[0063] Step 4: After completing all data collection work, process the data to achieve self-calibration of the circular grating.

[0064] Furthermore, the data processing method that can be used in step 4 of the first embodiment of this patent is as follows:

[0065] Each time sampling, the number of rotations k = 2, so the data of each circle can be averaged to reduce the influence of random errors; the idea of ​​average processing is to take the average value of the corresponding data of each cycle, and each cycle has a total of m data; for the measured data P in Table 1 above 1,1 , the processing method is:

[0066]

[0067] Processed data P′ 1,1 ={p′ 1,1,1 , p′ 1,1,2 ,……,p′ 1,1,m}; Other data (P 1,2 、P 2,1 ,……,P 5,6 The processing method of (etc.) is similar to this, and after processing, P′ is obtained 1,2 , P′ 2,1 ,……,P′ 5,6 , the specific process will not be repeated here.

[0068] Then align the data, that is, make the data in each curve have a unified starting point, or place the curves in the same coordinate system. To do this, subtract some specific value from the vertical coordinate of each curve point. The specific process is as follows:

[0069] In the first measurement, find the values ​​recorded by the two reading heads when the fixed reading head 1 passes the zero scale line of the circular grating for the first time from the collected data, and call them p and 1,1,0 and p 1,2,0 , and then the data is aligned through the following calculations:

[0070]

[0071]

[0072] The aligned data is:

[0073] P″ 1,1 ={p″ 1,1,1 , p″ 1,1,2 ,……,p″ 1,1,m}

[0074] P″ 1,2 ={p1″ ,2,1 , p1″ ,2,2 ,……,p1″ ,2,m}

[0075] Other data (P' 2,1 , P′ 2,3 ,……,P′ 5,6 The processing method of the above data is similar to this, and the aligned data P″ is obtained after processing. 2,1 , P″ 2,3 ,……,P″ 5,6 The specific process will not be described in detail

[0076] Next, the aligned data is subjected to difference processing, that is, the data at the corresponding positions in each array are subtracted. The difference curve after subtraction is as follows Figure 7 As shown, the formula is as follows:

[0077]

[0078] Then find the average of the above ΔP1~ΔP6 The formula is as follows:

[0079]

[0080] The above calculations This is the angle measurement error curve of the circular grating obtained by self-calibration using the method of the present invention, as shown in Figure 8 As shown, the data on the curve can be used to correct the angular measurement error of the circular grating.

[0081] In order to illustrate the effect of the circular grating self-calibration of this patent, two difference curves of the measurement data of position 2 and position 1 before and after compensation are drawn, as shown in the figure below: Figure 9As shown in the figure, it can be clearly seen from the comparison of the difference curves before and after error compensation that the effect of circular grating self-calibration is very significant.

[0082] It should be noted that in this embodiment:

[0083] 1) In step 3 of Example 1, when installing the variable position reading head 2 to the next position, it is necessary to determine whether the installation position is correct:

[0084] First, measure the actual angle between the two reading heads to obtain the actual angle A. Then, subtract the actual angle A from the theoretical angle α between the two reading heads at this time. When |A-α| is less than 0.1, the installation position can be considered accurate. To avoid calculation errors, the actual angle A and the theoretical angle α should both be less than 180°.

[0085] 2) The number of variable position reading heads 2 in the first embodiment can be increased. The measurement method and data processing principles are the same as when there is only one variable position reading head 2. That is, one reading head is fixed at a time, and the remaining reading heads are rotated and shifted. This can improve the efficiency of self-calibration.

[0086] 3) The installation order of the variable reading head in the first embodiment is not unique. In theory, any order is acceptable. In practice, any installation and measurement order can be selected arbitrarily.

[0087] Example 2 (interference between adjacent reading heads):

[0088] like Figure 1 As shown, a circular grating self-calibration method based on a fixed reading head and a variable position reading head includes the following steps:

[0089] Step 1: Select one of the two readheads, called fixed readhead 1, and the other, called variable readhead 2. Based on the actual dimensions of the circular grating and readheads and the pre-determined readhead mounting position list, select two readhead mounting positions from the list that will not interfere with each other. Install fixed readhead 1 in one of the two selected mounting positions, and variable readhead 2 in the remaining position. Mark all positions in the mounting position list as unmeasured.

[0090] In this embodiment, one of the reading heads is designated as fixed reading head 1, and the other reading head is designated as variable position reading head 2. In this embodiment, the reading head installation method is predetermined to be evenly distributed in 6 reading head positions, i.e., the number of reading head positions n in the installation position list is 6. Each predetermined position is numbered and recorded as P1, P2, ..., P6. The predetermined installation positions of the reading heads are shown in FIG. Figure 4 , the angle between two adjacent reading heads is α=360° / n=60°.

[0091] In this embodiment, it is assumed that the size of the reading head is small and the two reading heads at adjacent installation positions will not interfere with each other. Let P1 and P2 be the two selected reading head installation positions that will not interfere with each other; install the fixed reading head 1 at position P1, and install the variable position reading head 2 at position P2, and then mark the six positions P1, P2, ..., P6 in the table as positions that have not been measured.

[0092] Step 2: The circular grating rotates k revolutions, where k ≥ 1, and the data collected by the two readheads are recorded synchronously. After recording is completed, the current installation positions of the two readheads are marked as the positions where measurements have been taken in the readhead installation position list.

[0093] In this embodiment, the two reading heads are fixed after installation, and the moment when the zero mark of the circular grating passes through the fixed reading head 1 is captured during rotation, and counting starts from this moment;

[0094] After the counting starts, the circular grating rotates k=2 revolutions, during which the data collected by the two reading heads are synchronously recorded, as shown in Table 2, where m is the number of times the reading head measurement data is read during one revolution of the circular grating. In this embodiment, m=36;

[0095] The data to be recorded should include the measurement data when the zero position line of the circular grating passes through each reading head;

[0096] After the recording is completed, the current installation positions of the two reading heads are marked as the positions where measurements have been taken in the reading head installation position list, as shown in Table 2.

[0097] Table 2 Measurement data in Example 2

[0098]

[0099] Step 3: Determine whether all positions in the reading head installation position list have been measured;

[0100] If all positions in the reading head installation position list have been measured, that is, there is no position that has not been measured, go to step 4;

[0101] Otherwise, if there is a position that has not been measured in the reading head installation position list and installing the variable position reading head 2 at this position will not interfere with the fixed reading head 1, then install the variable position reading head 2 at this position and then go to step 2;

[0102] Otherwise, if there are any unmeasured positions in the readhead installation position list and installing the variable position readhead 2 at this position will interfere with the fixed readhead 1, then switch the identities of the fixed readhead 1 and the variable position readhead 2, that is, change the fixed readhead 1 to the variable position readhead 2, and change the variable position readhead 2 to the fixed readhead 1. Then, select a position that has not been measured and where installing the variable position readhead 2 at this position will not interfere with the fixed readhead 1, and install the variable position readhead 2 there, then go to step 2.

[0103] In this embodiment, the installation positions of the two reading heads are as follows Figure 10 As shown, Figure 10 In (a), the fixed reading head 1 is at position P1, and the variable position reading head 2 is at position P3; Figure 10 In (b), the fixed reading head 1 is at position P1, and the variable position reading head 2 is at position P5; Figure 10 In (c), the fixed reading head 1 is at position P1, and the variable position reading head 2 is at position P4; Figure 10 In (d), the fixed reading head 1 is at position P4, and the variable position reading head 2 is at position P1. Here, the positions of the two reading heads are swapped. Figure 10 In (e), the fixed reading head 1 is at position P4, and the variable position reading head 2 is at position P2; Figure 10 In (f), the fixed reading head 1 is at position P4 and the variable position reading head 2 is at position P6.

[0104] Following the above steps, multiple measurements were completed. The readhead installation positions and measurement results for each measurement are shown in Table 2. After five measurements, all installation positions were marked as measured. This means that there were no unmeasured positions in the readhead installation position list, so we proceeded to Step 4.

[0105] After the third measurement, P 3,1 and P 3,4 After the data is obtained, the variable position reading head 2 will interfere with the fixed reading head 1, and the identities of the fixed reading head 1 and the variable position reading head 2 are switched, that is, the fixed reading head 1 is renamed the variable position reading head 2, and the variable position reading head 2 is renamed the fixed reading head 1. Then, let P2 be the selected one that has not been measured and the variable position reading head 2 is installed at this position without interfering with the fixed reading head 1, and the new variable position reading head 2 is installed.

[0106] Step 4: After completing all data collection work, process the data to achieve self-calibration of the circular grating.

[0107] The data processing method used in step 4 of the second embodiment of this patent is as follows:

[0108] Each time sampling, the number of rotations k = 2, so the data of each circle can be averaged to reduce the influence of random errors; the idea of ​​average processing is to take the average value of the corresponding data of each cycle, and each cycle has a total of m data; for the measured data P in Table 1 above 1,1 , the processing method is:

[0109]

[0110] Processed data P′ 1,1 ={p′ 1,1,1 , p′ 1,1,2 ,……,p′ 1,1,m}; Other data (P 1,3 、P 2,1 ,……,P 5,6 The processing method of (etc.) is similar to this, and after processing, P′ is obtained 1,3 , P′ 2,1 ,……,P′ 5,6 , the specific process will not be repeated here.

[0111] Then align the data, that is, make the data in each curve have a unified starting point, or place the curves in the same coordinate system. To do this, subtract some specific value from the vertical coordinate of each curve point. The specific process is as follows:

[0112] For the data before the identity swap, for example, in the first measurement, find the value recorded when the fixed reading head 1 passes the zero scale line of the circular grating for the first time from the collected data, and refer to them as p 1,1,0 and p 1,3,0 , and then the data is aligned through the following calculations:

[0113]

[0114]

[0115] The aligned data is:

[0116] P″ 1,1 ={p″ 1,1,1 , p″ 1,1,2 ,……,p″ 1,1,m}

[0117] P″ 1,3 ={p″ 1,3,1 , p″ 1,3,2 ,……,p″ 1,3,m};

[0118] Other data (P' 2,1 , P′ 2,5 , P′ 3,1 , P′3,4 ) is processed in a similar way, and the aligned data P″ is obtained after processing 2,1 , P″ 2,5 , P″ 3,1 , P″ 3,4 , the specific process will not be repeated here.

[0119] For the data after identity swap, in this embodiment, the position of the fixed reading head 1 changes from P1 to P4, and the angle between the two reading head positions P1 and P4 is θ. For example, in the fourth measurement, the values ​​recorded by the fixed reading head 1 and the variable position reading head 2 when the fixed reading head 1 passes the zero scale line of the circular grating for the first time are found from the collected data, and they are called p 4,4,0 and p 4,2,0 , and then the data is aligned through the following calculations:

[0120]

[0121]

[0122] The aligned data is:

[0123] P″ 4,4 ={p″ 4,4,1 , p″ 4,4,2 ,……,p″ 4,4,m}

[0124] P″ 4,2 ={p″ 4,2,1 , p″ 4,2,2 ,……,p″ 4,2,m};

[0125] Other data (P' 5,4 , P′ 5,6 ) is processed in a similar way, and the aligned data P″ is obtained after processing 5,4 , P″ 5,6 , the specific process will not be repeated here.

[0126] Next, the above data is processed by difference, that is, the data at the corresponding position in each array is subtracted, and the difference curve after subtraction is as follows Figure 11 As shown, the formula is as follows:

[0127]

[0128] Then find the average of the above ΔP1~ΔP6 The formula is as follows:

[0129]

[0130] The above calculations This is the angle measurement error curve of the circular grating obtained by self-calibration using the method of the present invention, as shown in Figure 12 As shown, the data on the curve can be used to correct the angular measurement error of the circular grating.

[0131] In order to illustrate the effect of the circular grating self-calibration of this patent, two difference curves of the measurement data of position 2 and position 1 before and after compensation are drawn, as shown in the figure below: Figure 13 As shown in the figure, it can be clearly seen from the comparison of the difference curves before and after error compensation that the effect of circular grating self-calibration is very significant.

[0132] It should be noted that in this embodiment:

[0133] 1) In step 3 of the second embodiment, when installing the variable position reading head 2 to the next position, it is necessary to determine whether the installation position is correct:

[0134] First, measure the actual angle between the two reading heads to obtain the actual angle A. Then, subtract the actual angle A from the theoretical angle α between the two reading heads at this time. When |A-α| is less than 0.1, the installation position can be considered accurate. To avoid calculation errors, the actual angle A and the theoretical angle α should both be less than 180°.

[0135] 2) The number of variable position reading heads 2 in the second embodiment can be increased. The measurement method and data processing principles are the same as when there is only one variable position reading head 2. That is, one reading head is fixed at a time, and the remaining reading heads are rotated and shifted. This can improve the efficiency of self-calibration.

[0136] 3) The installation order of the variable reading head in the second embodiment is not unique. In theory, any order is acceptable. In practice, any installation and measurement order can be selected arbitrarily.

[0137] Further, such as Figure 2 As shown, the method for calculating the actual angle between the installation positions of the two reading heads used in the first and second embodiments includes the following steps:

[0138] Step 1: Extract the reading values ​​of the two reading heads at the moment when the zero line of the circular grating passes through the two reading heads respectively from the recorded data. Among them, when the zero line of the circular grating passes through the fixed reading head 1, the reading of the fixed reading head 1 is recorded as F1, and the reading of the variable position reading head 2 is recorded as V1; when the zero line of the circular grating passes through the variable position reading head 2, the reading of the fixed reading head 1 is recorded as F2, and the reading of the variable position reading head 2 is recorded as V2;

[0139] Step 2: The actual angle A between the two reading heads is ((F2-F1)+(V2-V1)) / 2;

[0140] Step 3: If the calculated angle A is greater than 180 degrees, convert it to an angle less than 180 degrees using the formula A=360-A.

[0141] Further, such as Figure 3 As shown, in the first and second embodiments, a method for ensuring the accuracy of the installation position when the reading head is installed in a predetermined installation position includes the following steps:

[0142] Calculating the actual angle between the two installation positions of the reading heads using the method of claim 2, and determining whether the angle error between the two installation positions of the reading heads exceeds a predetermined threshold;

[0143] If the position error is too large, readjust the installation position and check again until the position angle error is less than the predetermined threshold; then the adjustment process of the reading head can be ended and data collection can be started.

[0144] Figure 5 This is a 2×3 optimized layout position diagram of the reading heads of the present invention. Compared with the uniform distribution of the reading heads in Examples 1 and 2, the use of a 2×3 optimized layout of the reading heads can further improve the efficiency of the self-calibration in the present invention.

[0145] Figure 8 and Figure 12 They are respectively the angular measurement error curve diagrams of the circular gratings in the two embodiments, which are the average value curve diagrams of the differences between the measurement data of each position and the measurement data of position one. The origin of this diagram corresponds to the zero scale position of the circular grating.

[0146] In summary, the method of the present invention adopts a fixed reading head 1 and a variable position reading head 2 to realize self-calibration of the measurement error of the circular grating encoder. The method can eliminate higher-order harmonic errors in the measurement error of the circular grating encoder; circular grating self-calibration can be achieved without the aid of external high-precision measuring instruments. The method is simple, improves measurement efficiency, requires fewer reading heads, and has low cost, which is conducive to application in actual production.

[0147] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A circular grating self-calibration method based on a fixed reading head and a variable position reading head, characterized in that: The method comprises the following steps: Step 1: Select one of the two readheads as a fixed readhead and the other as a variable readhead. Based on the actual dimensions of the circular grating and readhead and the pre-determined readhead mounting locations, select two readhead mounting locations from the list that will not interfere with each other. Install the fixed readhead in one of the two selected mounting locations and the variable readhead in the remaining location. Mark all locations in the mounting location list as unmeasured. Step 2: The circular grating rotates k revolutions, where k ≥ 1, and the data collected by the two readheads are recorded synchronously. After recording is completed, the current installation positions of the two readheads are marked as the positions where measurements have been taken in the readhead installation position list. Step 3: Determine whether all positions in the reading head installation position list have been measured; If all positions in the reading head installation position list have been measured, that is, there is no position that has not been measured, go to step 4; Otherwise, if there is a position that has not been measured in the reading head installation position list and installing the variable position reading head at this position will not interfere with the fixed reading head, then install the variable position reading head at this position and then go to step 2; Otherwise, if there are any unmeasured positions in the readhead installation position list and installing the variable position readhead at this position will interfere with the fixed readhead, then switch the identities of the fixed readhead and the variable position readhead, that is, change the fixed readhead to the variable position readhead, and change the variable position readhead to the fixed readhead. Then, select a position that has not been measured and where installing the variable position readhead at this position will not interfere with the fixed readhead, and install the variable position readhead there, then go to step 2. Step 4: After completing all data acquisition work, process the recorded data to achieve self-calibration of the circular grating.

2. A circular grating self-calibration method based on a fixed reading head and a variable position reading head according to claim 1, characterized in that: In step 2 of the method, the recorded data is used to calculate the actual angle between the installation positions of the two reading heads, including the following steps: Step 2-1: Extract the readings of the two reading heads at the moment when the zero line of the circular grating passes through the two reading heads from the recorded data. The reading of the fixed reading head when the zero line of the circular grating passes through the fixed reading head is recorded as F1, and the reading of the variable position reading head is recorded as V1; the reading of the fixed reading head when the zero line of the circular grating passes through the variable position reading head is recorded as F2, and the reading of the variable position reading head is recorded as V2; Step 2-2: The actual angle A between the two reading heads is ((F2-F1)+(V2-V1)) / 2; Step 2-3: If the calculated angle A is greater than 180 degrees, convert it to an angle less than 180 degrees using the formula A=360-A.

3. The circular grating self-calibration method based on a fixed reading head and a variable position reading head according to claim 2, characterized in that: When installing the readhead into a predetermined mounting position, it is necessary to ensure that the mounting position is accurate. This involves the following steps: Use the method in step 2 to calculate the actual angle between the two reading head installation positions, and determine whether the angle error of the actual installation position of the reading head exceeds the predetermined threshold; if the position error is greater than the predetermined threshold, readjust the installation position and check again until the position angle error is less than the predetermined threshold; then end the adjustment process of the reading head and start data collection.

4. The circular grating self-calibration method based on a fixed reading head and a variable position reading head according to claim 1, characterized in that: After completing all data collection work in step 4, the data is processed to reduce the impact of random errors, which specifically includes the following steps: Step 4-1: First determine the number of revolutions k of the circular grating. If k>1, perform mean processing on the data of each revolution to reduce the influence of random errors. If k=1, no mean processing is required.

5. A circular grating self-calibration method based on a fixed reading head and a variable position reading head according to any one of claims 1 to 4, characterized in that: After recording the data once in step 2, data processing begins before all data collection work is completed, thereby improving data processing efficiency.

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