A method for correcting the eccentricity of a circular grating encoder

Abstract

The present invention relates to the field of circular grating encoder correction technology, and specifically provides a circular grating encoder eccentricity correction method, which aims to solve the problem that the existing adjustment method cannot perform fine-tuning on the local part of the grating code disk. To this end, the present invention provides a circular grating encoder eccentricity correction method, the correction method comprising: rotating the grating code disk in a set manner, determining the angle error values ​​of a plurality of set eccentric angles; determining the angle error value to be adjusted according to the angle error values ​​of the plurality of eccentric angles; calculating the eccentricity according to the angle error value to be adjusted; and locally correcting the grating code disk according to the eccentricity angle corresponding to the angle error value to be adjusted and the eccentricity.

Description

Technical Field

[0001] The invention relates to the technical field of circular grating encoder correction, and specifically provides an eccentricity correction method for a circular grating encoder. Background Art

[0002] Circular grating encoders are measuring tools for precise angle measurement and are widely used in CNC machine tools, articulated coordinate measuring machines, robots and other equipment.

[0003] The core components of the circular grating encoder are the grating code disk and the reading head. The grating code disk is fixed on the encoder shaft to keep synchronous rotation, and the reading head is fixed on the encoder fixed component. The two components can perform relative rotational motion. Due to the limitations of the encoder installation process, the optical center of the grating code disk and the rotation axis of the encoder shaft system do not coincide during the installation process, resulting in installation eccentricity errors. Therefore, before using the circular grating encoder, it is necessary to debug the installation error of the grating code disk to control it within a preset range. Existing circular grating encoders usually adjust the installation position accuracy of the grating code disk and the shaft by adjusting the size of the radial runout.

[0004] However, the above adjustment method is to adjust the entire grating code disk as a whole, and it is impossible to fine-tune the grating code disk locally. Summary of the invention

[0005] The present invention aims to solve the above technical problem, that is, to solve the problem that the existing adjustment method cannot perform fine adjustment on the part of the grating code disk.

[0006] The present invention provides an eccentricity correction method for a circular grating encoder, the correction method comprising: rotating a grating code disk in a set manner to determine angle error values ​​of a plurality of set eccentricity angles; determining an angle error value to be adjusted according to the angle error values ​​of the plurality of eccentricity angles; calculating an eccentricity distance according to the angle error value to be adjusted; and locally correcting the grating code disk according to the eccentricity angle corresponding to the angle error value to be adjusted and the eccentricity distance.

[0007] As a preferred technical solution of the above-mentioned eccentricity correction method provided by the present invention, the "determining the angle error value to be adjusted based on the angle error values ​​of multiple eccentricity angles" includes: determining an angle error curve based on the angle error values ​​of multiple eccentricity angles; determining the angle error value to be adjusted based on the angle error curve.

[0008] As a preferred technical solution of the eccentricity correction method of the circular grating encoder provided by the present invention, the "determining the angle error curve based on the angle error values ​​of multiple eccentricity angles" includes: the angle error curve is formed by fitting through the least squares method or Lagrange interpolation method.

[0009] As a preferred technical solution of the eccentricity correction method of the circular grating encoder provided by the present invention, the "determining the angle error value to be adjusted based on the angle error curve" includes: obtaining the maximum and minimum values ​​of the angle error values ​​on the angle error curve; determining the angle error value to be adjusted based on the maximum and minimum values.

[0010] As a preferred technical solution of the eccentricity correction method of the circular grating encoder provided by the present invention, the "determining the angle error value to be adjusted based on the maximum value and the minimum value" includes: calculating the average value of the maximum value and the minimum value and using the average value as the angle error value to be adjusted.

[0011] As a preferred technical solution of the eccentricity correction method of the circular grating encoder provided by the present invention, the "calculating the eccentricity according to the angle error value to be adjusted"

[0012] The arc length e corresponding to the angle error value to be adjusted is calculated according to the following formula (1), and the eccentricity X is calculated according to e:

[0013]

[0014] In formula (1), D is the diameter of the grating code disk, and θ is the angle error value to be adjusted.

[0015] As a preferred technical solution of the eccentricity correction method of the above-mentioned circular grating encoder provided by the present invention, the circular grating encoder includes a grating code disk and a reading head, and the grating code disk is fixed on the rotating shaft of the corresponding turntable through a plurality of fasteners, and the "locally correcting the grating code disk according to the eccentricity angle corresponding to the eccentricity" includes: determining at least one fastener near the eccentricity angle corresponding to the angle error value to be adjusted, and locally correcting the grating code disk by adjusting one or more of the at least one fastener.

[0016] As a preferred technical solution of the eccentricity correction method of the circular grating encoder provided by the present invention, the "determining at least one fastener near the eccentricity angle corresponding to the eccentricity to be adjusted, and locally correcting the grating code disk by adjusting one or more of the at least one fastener" includes: determining a first fastener near the eccentricity angle closest to the angular error value to be adjusted; determining at least one second fastener adjacent to the first fastener; and locally correcting the grating code disk by adjusting the first fastener and the second fastener.

[0017] As a preferred technical solution of the eccentricity correction method of the circular grating encoder provided by the present invention, the "determining at least one second fastener adjacent to the first fastener" includes: determining at least one second fastener on both sides of the first fastener.

[0018] As a preferred technical solution of the eccentricity correction method of the circular grating encoder provided by the present invention, the adjustment force of the first fastener is greater than the adjustment force of the second fastener.

[0019] When the above technical solution is adopted, the eccentricity correction method of the circular grating encoder of the present invention has the following technical effects:

[0020] By determining the angle error value to be adjusted according to the angle error values ​​of multiple eccentric angles; calculating the eccentricity according to the angle error value to be adjusted; and locally correcting the grating code disk according to the eccentricity angle and the eccentricity corresponding to the angle error value to be adjusted. In this way, the eccentricity angle and the eccentricity of the angle error value to be adjusted can be located to locally correct the grating code disk. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The preferred implementation of the eccentricity correction method of the circular grating encoder of the present invention is described below in conjunction with the accompanying drawings, in which:

[0022] Figure 1 Schematic diagram of the main process of the eccentricity correction method of the circular grating encoder of the present embodiment;

[0023] Figure 2 Schematic diagram of an angle error curve of a circular grating encoder of this embodiment. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0025] It should be noted that, in the description of the present invention, the terms "first", "second" and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0026] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0027] It should be noted that the circular grating encoder is first fitted on the mounting surface of the rotating shaft, and the corresponding threaded mounting holes are tightened with a torque wrench; then the rotary axis calibration device is positioned on the rotating shaft and the alignment of the laser device installed on the outside of the rotating shaft is adjusted, that is, the rotary axis calibration device is installed on the rotating shaft, the angle beam splitter is fixed between the laser device and the rotary axis calibration device, and the laser head, beam splitter and rotary axis calibration device are adjusted to be in a straight line; the laser device is reset to zero at the starting position of the shaft, and data collection and CNC program running on the computer are started; when the shaft reaches the starting target position, the actual rotation angle data of the grating code disk and the encoder reading head are recorded. The grating code disk rotates in the set manner, and the rotary axis calibration device obtains the actual rotation angle data of multiple grating code disks. At the same time, the eccentric rotation angle data of multiple grating code disks when they rotate one circle can be obtained through the reading head.

[0028] In order to solve the above problems in the prior art, that is, to solve the problem that the existing adjustment method cannot fine-tune the grating code disk locally, please refer to Figure 1 The present embodiment provides an eccentricity correction method for a circular grating encoder, the correction method comprising: S1, rotating the grating code disk in a set manner, and determining angle error values ​​of a plurality of set eccentricity angles; S2, determining an angle error value to be adjusted according to the angle error values ​​of a plurality of eccentricity angles; S3, calculating an eccentricity distance according to the angle error value to be adjusted; S4, locally correcting the grating code disk according to the eccentricity angle and the eccentricity distance corresponding to the angle error value to be adjusted.

[0029] S1. Rotate the grating code disk in a set manner to determine angle error values ​​of a plurality of set eccentric angles.

[0030] Specifically, the grating code disk rotates one circle at a set interval angle, and the actual rotation angle data of the grating code disk is obtained by a laser device and a rotating axis calibration device. The eccentric rotation angle of the grating code disk at the same rotation angle is obtained by a reading head, and the angle error value of the eccentric angle is obtained by subtracting the actual rotation angle data of the grating code disk from the eccentric rotation angle of the grating code disk.

[0031] S2. Determine an angle error value to be adjusted according to angle error values ​​of multiple eccentric angles.

[0032] Specifically, an angle error curve is determined according to angle error values ​​of a plurality of eccentric angles; and based on the angle error curve, an angle error value to be adjusted is determined.

[0033] The horizontal coordinate of the angle error curve is the actual rotation angle of the grating code disk, and the vertical coordinate of the angle error curve is the angle error value of the eccentric angle corresponding to the actual rotation angle of the grating code disk.

[0034] It can be understood that the more actual rotation angle data of the grating code disk and the eccentric rotation angle data of the grating code disk are obtained, the more accurate the angle error curve is, but the more data, the longer the calculation time is. Therefore, in this embodiment, while ensuring both accuracy and reducing calculation time, the grating code disk is selected to rotate at an interval of 5°, and 72 sets of actual rotation angle data of the grating code disk and the eccentric rotation angle data of the grating code disk are obtained. In this way, the accuracy can be ensured and the calculation time can be reduced, and the eccentricity error curve can be drawn by fitting the 72 sets of data.

[0035] In this embodiment, the actual rotation angle of the grating code disk and the rotation angle data of the eccentricity of the grating code disk can be fitted by the least square method or by the Lagrange interpolation method.

[0036] It is understandable that the above-mentioned interval angle values ​​are schematic, and other methods can be used in other embodiments. For example, the interval angle is selected to be 3°, 8°, 10°, etc. At the same time, the above-mentioned least square method and Lagrange interpolation method are schematic for fitting the actual rotation angle of the grating code disk and the rotation angle data of the eccentricity of the grating code disk. In other embodiments, other methods can also be used. For example, the weighted least square method can be selected for fitting, or the weighted Lagrange interpolation method can be selected for fitting. Of course, other functions that can fit the curve can also be selected, as long as it can fit multiple sets of data into a smooth curve.

[0037] In a preferred implementation manner of the eccentricity correction method of the circular grating encoder provided in this embodiment, the maximum value and the minimum value of the angle error values ​​on the angle error curve are obtained; and the angle error value to be adjusted is determined based on the maximum value and the minimum value.

[0038] The actual rotation angle of the grating code disk and the eccentric rotation angle data of the grating code disk are fitted into an angle error curve through the least squares method, thereby obtaining the corresponding curve function. The maximum and minimum values ​​of the angle error value are obtained through the curve function, and the angle error value to be adjusted is determined based on the maximum and minimum values.

[0039] In a preferred implementation of the eccentricity correction method of the circular grating encoder provided in this embodiment, the angle error value can be obtained by calculating the average value of the maximum value and the minimum value.

[0040] It should be noted that, because the grating code disk is eccentrically installed with the rotating shaft, the obtained angle error curve is wavy. Thus, from the graphical point of view, the error curve includes a rising stage and a falling stage. When the error curve is in the rising stage, that is, it rises from the minimum position of the eccentric angle error value in the error curve to the maximum position of the eccentric angle error value. At this time, the actual rotation angle of the grating code disk is greater than the eccentric rotation angle of the grating code disk, and the grating code disk gradually moves away from the detection head of the laser device relative to the turntable position. The average value of the maximum and minimum values ​​of the eccentric angle error is used to determine the angle error value to be adjusted. At this time, the detection head of the laser device, the center of the grating code disk and the center of the turntable shaft are collinear. Therefore, it is necessary to find the rising stage of the angle error curve, so as to calculate the average value of the maximum and minimum values ​​of the eccentric angle error according to the maximum and minimum values ​​of the eccentric angle error in the rising stage, so as to obtain the actual rotation angle of the grating code disk corresponding to the average value according to the angle error curve, so as to determine the angle error value to be adjusted and the corresponding actual rotation angle position of the grating code disk.

[0041] It can be understood that the above-mentioned method for obtaining and determining the angle error value to be adjusted is illustrative, and other methods may also be used in other embodiments.

[0042] S3. Calculate the eccentricity according to the angle error value to be adjusted.

[0043] Specifically,

[0044] The arc length e corresponding to the angle error value to be adjusted is calculated according to the following formula (1), and the eccentricity X is calculated according to e:

[0045]

[0046] In formula (1), D is the diameter of the grating code disk, and θ is the angle error value to be adjusted. For the same grating code disk, the relationship between the angle error value to be adjusted and the corresponding arc length exists in the following formula (2):

[0047]

[0048] When the corresponding arc length is very small, the eccentricity corresponding to the angle error value is approximately equal to the arc length corresponding to the angle error value to be adjusted, that is, X≈e. Therefore, formula (1) and formula (2) can be arranged into the following formula (3):

[0049]

[0050] Therefore, the eccentricity X can be calculated according to formula (3).

[0051] S4. Perform local correction on the grating code disk according to the eccentricity angle and eccentricity distance corresponding to the angle error value to be adjusted.

[0052] Specifically, at least one fastener near the eccentric angle corresponding to the angle error value to be adjusted is determined, and the grating code disk is locally corrected by adjusting one or more of the at least one fastener.

[0053] For example, it is determined that the eccentric angle corresponding to the angle error value to be adjusted just corresponds to a fastener, and then only the fastener is adjusted according to the eccentricity corresponding to the angle error value to be adjusted to complete the local correction. Of course, when adjusting the fastener, in order to protect the grating code disk from being damaged by excessive locking force, the eccentricity needs to be locked in multiple times, for example, the eccentricity needs to be locked in three times.

[0054] Of course, the first fastener closest to the eccentric angle corresponding to the angle error value to be adjusted is determined; at least one second fastener adjacent to the first fastener is determined; and the grating code disk is locally corrected by adjusting the first fastener and the second fastener.

[0055] For example, the grating code disk is fixedly connected to the rotating shaft through multiple fasteners. At this time, there is no fastener facing the eccentric angle value of the angle error value to be adjusted. Then, the fastener closest to the eccentric angle value of the angle error value to be adjusted is preferentially selected as the first fastener, and the second fastener adjacent to the first fastener, wherein the angle range formed by the first fastener and the second fastener includes the eccentric angle of the angle error to be adjusted. At this time, because the first fastener is the main fastener to be adjusted, its adjustment force is greater than the second fasteners on both sides, thereby completing the local correction of the grating code disk. Of course, when adjusting the first fastener and the second fastener, in order to protect the grating code disk from being damaged by excessive locking force, it is necessary to lock the eccentricity in multiple times. For example, the first fastener can be locked three times and the second fastener can be locked twice. In this way, the local adjustment of the grating code disk is completed by adjusting the first fastener and the second fastener respectively.

[0056] In addition, the first fastener is the eccentric angle closest to the angle error value to be adjusted, so the adjustment force of the first fastener is greater than the adjustment force of the second fastener.

[0057] Of course, at least one second fastener can also be determined on both sides of the first fastener. At this time, there is a first fastener facing the eccentric angle value of the angle error value to be adjusted, and two adjacent second fasteners are symmetrically arranged on both sides of the first fastener. At this time, because the first fastener is the main fastener to be adjusted, its adjustment force is greater than the second fasteners on both sides, thereby completing the local correction of the grating code disk. Of course, when adjusting the first fastener and the second fastener, in order to protect the grating code disk from being damaged by excessive locking force, it is necessary to divide the eccentricity into multiple times for locking. For example, the first fastener can be locked three times and the second fastener can be locked twice. In this way, the local adjustment of the grating code disk is completed by adjusting the first fastener and the second fastener respectively.

[0058] It can be understood that the above-mentioned method of performing local correction on the grating code disk is illustrative, and other methods can be used in other embodiments as long as they can satisfy the local correction of the grating code disk.

[0059] In a preferred implementation of the eccentricity correction method of the circular grating encoder provided in this embodiment, the step S4 further includes: if the angle error value to be adjusted is greater than a preset value, repeating the above process to continue correcting the grating code disk.

[0060] Among them, the preset value is the maximum acceptable value of the grating code disk installation error. In this way, the positioning accuracy is re-measured, and after repeated measurements and corrections, the positioning accuracy meets the requirements, thereby achieving the purpose of improving the encoder position accuracy.

[0061] In this embodiment, the mounting surface of the rotating shaft and the grating code disk is a conical surface. In this way, even if the grating code disk is mounted on the rotating shaft, it is also convenient to adjust the grating code disk to the fastener on the grating code disk. The inclination angle of the conical surface of the grating code disk is 15°±0.2°.

[0062] A preferred implementation of the eccentricity correction method of the circular grating encoder provided in this embodiment further includes displaying the angle error curve, the maximum and minimum values ​​of the angle error values, the angle error value to be adjusted, the angle corresponding to the angle error value to be adjusted, and the eccentricity. In this way, a more intuitive display is provided, which facilitates technicians to make local adjustments to the grating code disk.

[0063] The laser device, the rotary axis calibration device and the reading head are all connected to the computer via wireless signals. For example, the data processing module can communicate with the laser device and the rotary axis calibration device via Bluetooth or WIFI. In addition, the computer receives the actual rotation angle data of the grating code disk and the eccentric rotation angle of the grating code disk, fits the received data into an angle error curve through the least square method, and displays it on the display.

[0064] Take the calibration of Renishaw's 75mm diameter circular grating encoder as an example. Specifically, the 75mm diameter circular grating encoder is calibrated using the R20-W rotary axis calibration device and the XL-80 laser device.

[0065] First, fit the circular grating encoder to the mounting surface of the rotating shaft, and tighten the screws of the corresponding threaded mounting holes with a torque wrench; then position the R20-W rotary axis calibration device on the rotating shaft and adjust the alignment of the XL-80 laser device installed on the outside of the rotating shaft, that is, install the R20-W rotary axis calibration device on the rotating shaft, fix the angle beam splitter between the XL-80 laser device and the R20-W rotary axis calibration device, and adjust the laser head, beam splitter and R20-W rotary axis calibration device to be in a straight line; reset the XL-80 laser device to zero at the starting position of the shaft, and start collecting data and running the CNC program on the computer; when the shaft reaches the starting target position, start recording the actual rotation angle data of the grating code disk and the eccentric rotation angle of the grating code disk through the R20-W rotary axis calibration device. The grating code disk starts to rotate with a step of 5° until it stops after one circle. The R20-W rotary axis calibration device obtains 72 actual rotation angles of the grating code disk. At the same time, the eccentric rotation angles of the grating code disk can be obtained through the reading head. The data processing module that receives the actual rotation angle of the grating code disk and the eccentric rotation angle of the grating code disk draws an angle error curve according to the 72 sets of data and the set program, as shown in Figure 2 As shown, the angle error curve, the maximum and minimum values ​​of the angle error value, the angle error value to be adjusted, the angle corresponding to the angle error value to be adjusted, and the eccentricity are displayed. The corresponding minimum angle error value is -15", the maximum angle error value is 19", the angle error value to be adjusted is 17", the angle corresponding to the angle error value to be adjusted is 240°, and the eccentricity is 3.1μm.

[0066] The specific calculation process of the eccentric distance is as follows: According to the above formula (3), the eccentric distance X is obtained,

[0067]

[0068] The calculated eccentric distance is 3.1μm. According to the maximum eccentric position corresponding to the 240° position of the grating code disk, the micrometer is fixed at the 240° position, and the corresponding fasteners are tightened with a torque wrench, 1μm at a time, and tightened three times to move the center of the grating code disk upward by 3μm. The grating code disk is partially corrected, and the positioning accuracy is then remeasured until the positioning accuracy meets the requirements.

[0069] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A method for correcting the eccentricity of a circular grating encoder, characterized in that: The correction method comprises: The grating code disk is rotated in a set manner to determine the angle error values ​​of the set multiple eccentric angles; Determining an angle error value to be adjusted according to angle error values ​​of multiple eccentric angles; Calculating the eccentricity according to the angle error value to be adjusted; Performing local correction on the grating code disk according to the eccentric angle and the eccentric distance corresponding to the angular error value to be adjusted; The "calculating the eccentricity according to the angle error value to be adjusted" includes: The arc length e corresponding to the angle error value to be adjusted is calculated according to the following formula (1), and the eccentricity X is calculated according to e: In formula (1), D is the diameter of the grating code disk, and θ is the angle error value to be adjusted; The circular grating encoder includes a grating code disk and a reading head, wherein the grating code disk is fixed on a rotating shaft of a corresponding turntable through a plurality of fasteners, and the “locally correcting the grating code disk according to an eccentric angle corresponding to the eccentricity” includes: At least one fastener near the eccentric angle corresponding to the angle error value to be adjusted is determined, and the grating code disk is locally corrected by adjusting one or more of the at least one fastener.

2. The eccentricity correction method according to claim 1, characterized in that: The “determining the angle error value to be adjusted according to the angle error values ​​of multiple eccentric angles” includes: According to the angle error values ​​of multiple eccentric angles, an angle error curve is determined; Based on the angle error curve, an angle error value to be adjusted is determined.

3. The eccentricity correction method according to claim 2, characterized in that: The “determining an angle error curve according to angle error values ​​of multiple eccentric angles” includes: The angle error curve is formed by fitting through the least square method or the Lagrange interpolation method.

4. The eccentricity correction method according to claim 2, characterized in that: The “determining the angle error value to be adjusted based on the angle error curve” includes: Obtaining the maximum and minimum values ​​of the angle error values ​​on the angle error curve; An angle error value to be adjusted is determined according to the maximum value and the minimum value.

5. The eccentricity correction method according to claim 4, characterized in that: The “determining the angle error value to be adjusted according to the maximum value and the minimum value” includes: An average value of the maximum value and the minimum value is calculated and used as the angle error value to be adjusted.

6. The eccentricity correction method according to claim 1, characterized in that: The "determining at least one fastener near the eccentric angle corresponding to the eccentricity to be adjusted, and locally correcting the grating code disk by adjusting one or more of the at least one fastener" includes: Determine a first fastener that is closest to the eccentric angle corresponding to the angle error value to be adjusted; determining at least one second fastener adjacent to the first fastener; The grating code disk is locally corrected by adjusting the first fastener and the second fastener.

7. The eccentricity correction method according to claim 6, characterized in that: The “determining at least one second fastener adjacent to the first fastener” includes: At least one second fastening member is respectively defined on both sides of the first fastening member.

8. The eccentricity correction method according to claim 6 or 7, characterized in that: The adjustment force of the first fastener is greater than the adjustment force of the second fastener.

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