Method of measuring position error of a feed system

Abstract

The application discloses a method for measuring position error of a feeding system, which is characterized in that the feeding system comprises a shaft bed, a long shaft member and a moving body, at least one pattern label is arranged on a working surface of the shaft bed, the moving body is provided with an optical sensor, and the method for measuring the position error of the feeding system comprises the following steps: controlling the moving body to move along the long shaft member, and controlling the optical sensor to take two photos of the pattern label respectively in the process of moving of the moving body, so as to obtain a first image and a second image respectively; selecting an image feature from the first image, and searching for the image feature from the second image; and comparing the position of the image feature in the first image and the second image, so as to estimate the position error. In this way, whether the position error occurs can be known in real time in the feeding process.

Description

TECHNICAL FIELD

[0001] The present application relates to a feeding system, in particular to a method for measuring position error of a feeding system. BACKGROUND

[0002] Taiwanese Patent No. I539143 discloses a linear device non-parallel detection system. The system sets a feature pattern on a screw rod and uses a camera unit to directly measure whether the feature pattern changes based on the characteristic that the deformation of the screw rod at the location of the feature pattern will cause the feature pattern to deform. Thus, it is inferred whether the screw rod deforms. Since the camera unit is set at a fixed position outside the linear device, and one camera unit corresponds to one feature pattern, if different positions on the screw rod are to be observed for deformation, multiple feature patterns need to be set on the screw rod, and corresponding camera units need to be set for each feature pattern. In addition, a strain gauge is needed to help detect the non-parallel degree. Therefore, the system requires a high cost, and cannot detect other types of errors. SUMMARY

[0003] Therefore, the main purpose of the present application is to provide a method for measuring position error of a feeding system, which aims to detect position error in multiple axes (different types) in real time.

[0004] According to an embodiment of the present application, a method for measuring position error of a feeding system is provided. The feeding system comprises a spindle bed, a long shaft and a moving body. The long shaft is fixed to the spindle bed, and the moving body is movably arranged on the long shaft. A working surface of the spindle bed is provided with at least one first pattern label. The moving body is provided with a first optical sensor corresponding to the at least one first pattern label. The method comprises the following steps:

[0005] Step A: controlling the moving body to move along the long shaft, and controlling the first optical sensor to take two pictures of the first pattern label respectively during the movement of the moving body, so as to obtain a first image and a second image respectively;

[0006] Step B: selecting a first image feature from the first image and the second image; and

[0007] Step C: comparing the position of the first image feature in the first image and the second image to estimate the position error.

[0008] In another embodiment, the step A comprises:

[0009] Step A1: controlling the moving body to move along the long shaft in a first direction of travel;

[0010] Step A2: controlling the first optical sensor to capture the first graphical tag to obtain the first image when the mobile body moves toward the first travel direction;

[0011] Step A3: controlling the mobile body to move along the long axis member toward a second travel direction, the second travel direction being opposite to the first travel direction; and

[0012] Step A4: controlling the first optical sensor to capture the first graphical tag to obtain the second image when the mobile body moves toward the second travel direction.

[0013] In yet another embodiment, the step C comprises:

[0014] Step C1: calculating a difference between the position of the first image feature in the first image and the position of the first image feature in the second image in at least one axial direction to obtain a displacement in the axial direction as part of the position error.

[0015] In yet another embodiment, in the step A, the mobile body moves along the long axis member toward a travel direction, and the first optical sensor captures the first graphical tag twice consecutively to obtain the first image and the second image respectively when the mobile body moves toward the travel direction.

[0016] In yet another embodiment, the step C comprises:

[0017] Step C2: calculating a difference between the position of the first image feature in the first image and the position of the first image feature in the second image in a first axial direction to obtain a first displacement in the first axial direction as part of the position error; and

[0018] Step C3: calculating a difference between the position of the first image feature in the first image and the position of the first image feature in the second image in a second axial direction to obtain a second displacement in the second axial direction as another part of the position error, the first axial direction being perpendicular to the second axial direction.

[0019] In yet another embodiment, at least one second graphical tag is disposed on a lateral surface of the axis bed, the lateral surface being angled with respect to the working surface by an angle greater than 0 degree and less than 180 degree, and the mobile body is further equipped with a second optical sensor corresponding to the at least one second graphical tag, and the method for measuring the position error of the feeding system further comprises:

[0020] Step D: controlling the second optical sensor to capture the second graphical tag twice respectively to obtain a third image and a fourth image during the movement of the mobile body;

[0021] Step E: selecting a second image feature from the third image and the fourth image; and

[0022] Step F: comparing the second image feature with the positions in the third image and the fourth image to estimate the position error.

[0023] In yet another embodiment, the step F comprises:

[0024] Step F1: calculating the difference between the position of the second image feature in the third image and the position of the second image feature in the fourth image in a first axial direction to obtain a third displacement in the first axial direction as a part of the position error; and

[0025] Step F2: calculating the difference between the position of the second image feature in the third image and the position of the second image feature in the fourth image in a third axial direction to obtain a third displacement in the third axial direction as another part of the position error, the second axial direction being perpendicular to the third axial direction.

[0026] In yet another embodiment, the step D comprises:

[0027] Step D1: controlling the mobile body to move along the long member in a first travel direction;

[0028] Step D2: controlling the second optical sensor to capture the second graphical tag to obtain the third image when the mobile body moves toward the first travel direction;

[0029] Step D3: controlling the mobile body to move along the long member toward a second travel direction, the second travel direction being opposite to the first travel direction; and

[0030] Step D4: controlling the second optical sensor to capture the second graphical tag to obtain the fourth image when the mobile body moves toward the second travel direction.

[0031] In yet another embodiment, the step B is performed by using a digital image correlation algorithm and the following conditions:

[0032] ,

[0033] wherein γ ij is a correlation coefficient representing the first image and the second image, is an average value representing gray scale values of all pixels in the first image; is an average value representing gray scale values of all pixels in the second image; m represents an x-coordinate of a pixel in the first image or the second image; and n represents a y-coordinate of a pixel in the first image or the second image.

[0034] In yet another embodiment, the step C is performed using the following condition:

[0035] ,

[0036] wherein the displacement amount refers to an offset of the second image relative to the first image in an axial direction; the movement distance refers to a distance between a current position of the second image and a starting position of the second image in the axial direction when the correlation coefficient reaches a maximum degree; the image size refers to a length of the second image in the axial direction; and the pixel size refers to a size of one pixel.

[0037] Therefore, the method for measuring the position error of the feeding system provided by the present application measures the position error of each graphic label by setting a sensor on a moving body and taking pictures of the graphic labels on the movement path as the moving body moves. In addition, the present application also uses an optical sensor in combination with an image analysis technique (such as a digital image correlation (DIC) algorithm) to achieve the purpose of simultaneously measuring the position deviation in multiple axial directions. BRIEF DESCRIPTION OF DRAWINGS

[0038] Other aspects of the present application and many of its advantages will be further appreciated from the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0039] Figure 1 A schematic diagram of a feeding system to be measured according to an embodiment of the present application;

[0040] Figure 2 A block diagram of a feeding system to be measured according to an embodiment of the present application;

[0041] Figure 3 A schematic diagram of a part of a feeding system from a perspective; Figure 1

[0042] Figure 4 A flowchart of a method for measuring the position error of a feeding system according to an embodiment of the present application;

[0043] Figure 5A A schematic diagram of image analysis of a first image of gray scale according to an embodiment of the present application, showing the position of a label image of a graphic label and the position of an image feature thereof;​

[0044] Figure 5B A schematic diagram for image analysis of a second image according to an embodiment of the present application, showing the positions of label images of graphic labels and the positions of image features thereof;

[0045] Figure 6 A flowchart of a method for measuring position error of a feeding system according to an embodiment of the present application, applied to measuring back lash of a ball screw;

[0046] Figure 7A A schematic diagram for measuring position error of a feeding system according to an embodiment of the present application, showing a state in which a moving body moves in a direction from a front end of an elongated member, and an optical sensor takes a first shot of graphic labels during the movement;

[0047] Figure 7B A schematic diagram for measuring position error of a feeding system according to an embodiment of the present application, showing a state in which the moving body moves to an end of the elongated member, and the optical sensor has taken the first shot of all the graphic labels during the movement;

[0048] Figure 7C A schematic diagram for measuring position error of a feeding system according to an embodiment of the present application, showing a state in which the moving body moves in an opposite direction, and the optical sensor takes a second shot of the graphic labels during the movement;

[0049] Figure 8 A flowchart of a method for measuring position error of a feeding system according to an embodiment of the present application, applied to measuring whether two linear slides are parallel;

[0050] Figure 9A A schematic diagram for measuring position error of a feeding system according to an embodiment of the present application, showing a state in which a moving body moves in a direction, and an optical sensor takes a first shot of graphic labels during the movement;

[0051] Figure 9B A schematic diagram for measuring position error of a feeding system according to an embodiment of the present application, showing a state in which the moving body moves in the same direction, and the optical sensor takes a second shot of the same graphic labels during the movement;

[0052] Figure 10 A schematic diagram for a feeding system according to another embodiment of the present application, when the feeding system is to be measured;

[0053] Figure 11 A block diagram for a feeding system according to another embodiment of the present application, when the feeding system is to be measured;

[0054] Figure 12A flowchart for applying the method of measuring the position error of the feed drive system according to an embodiment of the present application to measuring whether the respective linear slide is skewed;

[0055] Figure 13A A schematic diagram for image analysis of the fourth image of the gray scale according to an embodiment of the present application, for presenting the position of the label image of the graphic label and the position of the image feature thereof; and

[0056] Figure 13B A schematic diagram for image analysis of the fourth image of the gray scale according to an embodiment of the present application, for presenting the position of the label image of the graphic label and the position of the image feature thereof; and

[0057] Figure 14 A flowchart for applying the method of measuring the position error of the feed drive system according to another embodiment of the present application to measuring whether the respective linear slide is skewed.

[0058] Wherein, 1-axis bed; 11-body part; 12-protruding part; 13-working surface; 14-lateral surface; 2-moving body; 3-linear slide; 31-slide rail; 32-slide block; 4-bearing; 5-roller screw; 51-screw; 52-nut; 53-flange; 6-coupling; 7-motor; 8-servo end; 81-processor; D1-first axial direction; D2-second axial direction; D3-third axial direction; FI1, FI2-image feature; IM1-first image of the gray scale; IM2-second image of the gray scale; IM3-third image of the gray scale; IM4-fourth image of the gray scale; OT1-first optical sensor; OT2-second optical sensor; PI1-first label image; PI2-second label image; TP1-first graphic label; TP2-second graphic label; V1-first travel direction; V2-second travel direction. DETAILED DESCRIPTION

[0059] A method of measuring the position error of a feed drive system is provided. Please refer to Figures 1 to 3As shown, the feeding system comprises a shaft bed 1, a worktable 2 (moving body), two linear slides 3, two bearings 4, a ball screw 5, a coupling 6, a motor 7 and a servo end 8. The shaft bed 1 extends along an axial direction D1 (first axial direction) and comprises a seat portion 11 and two protrusions 12. The two protrusions 12 extend from the seat portion 11 along an axial direction D3 (third axial direction) and are respectively located on opposite sides of the seat portion 11 along an axial direction D2 (second axial direction). The axial directions D1, D2 and D3 are perpendicular to each other. The two linear slides 3 are respectively arranged on opposite sides of the shaft bed 1, for example but not limited to being arranged on the two protrusions 12 respectively. In the present embodiment, each linear slide 3 comprises a slide rail 31 (long axis member) and two slide blocks 32 (moving body). The slide blocks 32 are sleeved on the slide rail 31 and can move back and forth along the slide rail 31, but the present application is not limited thereto; in fact, the number of slide blocks 32 can be increased or decreased as needed, so the number of slide blocks 32 can be one or more than two. The two bearings 4 are respectively assembled on opposite ends of the shaft bed 1 along the axial direction D1. The ball screw 5 comprises a screw rod 51 (long axis member) and a nut 52 (moving body). One end of the screw rod 51 is connected to one of the bearings 4, and the opposite end of the screw rod 51 is connected to the motor 7 through the other bearing 4 and the coupling 6. The nut 52 is sleeved on the screw rod 51 and can move back and forth along the screw rod 51. The worktable 2 (moving body) is assembled on the slide blocks 32 and the nut 52. The motor 7 is connected to and controlled by the servo end 8. When the servo end 8 controls the motor 7 to rotate, the motor 7 can drive the screw rod 51 to rotate, thereby driving the worktable 2 to move along the slide rail 31 and the screw rod 51.

[0060] To measure the position error of the feeding system, an optical sensor OT1 (first optical sensor) can be installed on the worktable 2, and a plurality of pattern tags TP1 (first pattern tags) can be arranged on the working surface 13 of the seat portion 11 along the axial direction D1, as shown in Figure 1 and Figure 3 . The optical sensor OT1 can be, for example but not limited to, a Charge Coupled Device (CCD) image sensor or a Complementary Metal-Oxide-Semiconductor (CMOS) image sensor. The installation position of the optical sensor OT1 can be selected according to requirements, as long as the sensing range of the optical sensor OT1 can cover (or partially cover) the entire pattern tags TP1, and is not limited to the position shown in Figure 1 and Figure 3 . The optical sensor OT1 can be connected to and controlled by the servo end 8 in a wired or wireless manner.

[0061] The servo end 8 can be, for example, one or more computer devices, and at least comprises a processor 81. The processor 81 is used to control the operation of the motor 7 and the operation of the optical sensor OT1, thereby executing the method for measuring the position error of the feeding system provided by the present application.

[0062] Referring to FIG. 1, a measurement system 1 is shown. The measurement system 1 includes a processor 81, a motor 7, an optical sensor OT1, a long shaft member 3, and a workpiece 2. The processor 81 is connected to the motor 7 and the optical sensor OT1. The motor 7 is connected to the long shaft member 3. The long shaft member 3 is connected to the workpiece 2. The workpiece 2 includes a pattern tag TP1. The motor 7 is configured to rotate and drive the long shaft member 3 to move the workpiece 2. The optical sensor OT1 is configured to capture an image of the pattern tag TP1. Figure 4 Referring to FIG. 2, a flowchart of a method for measuring a position error of a feed system is shown. First, as shown in step S10, the processor 81 controls the motor 7 to rotate and drive the moving body (e.g., the workpiece 2, the nut 52, and the slider 32) to move along the long shaft member (e.g., the slide rail 31 and the screw rod 51). According to the progress information (e.g., the encoder signal of the motor 7) generated by the operation of the motor 7, the processor 81 can estimate the distance that the moving body has moved, and determine whether to control the optical sensor OT1 to capture an image. Next, as shown in step S11, during the movement of the moving body, when the sensing range of the optical sensor OT1 reaches a position that can completely cover (or partially cover) the pattern tag TP1, the processor 81 controls the optical sensor OT1 to capture two images (e.g., still images) of the pattern tag TP1, respectively.

[0063] Then, as shown in step S12, the processor 81 performs grayscale processing on the image (hereinafter referred to as the first image) obtained by the first capturing, and selects an image feature from the grayscale first image by, for example but not limited to, a DIC algorithm. For example, as shown in FIG. 3, an image feature FI1 (first image feature) that matches a default template is found in the image (hereinafter referred to as the tag image PI1 (first tag image)) of the pattern tag TP1 presented in the grayscale first image IM1. Figure 5A Similarly, as shown in step S13, the processor 81 also performs grayscale processing on the image (hereinafter referred to as the second image) obtained by the second capturing, and searches for a portion that is the same as the image feature of the first image from the grayscale second image by, for example but not limited to, a digital image correlation algorithm. Specifically, as shown in FIG. 4, the same image feature FI1 is found in the tag image PI1 presented in the grayscale second image IM2. Figure 5B

[0064] Finally, as shown in step S14, the processor 81 compares the positions of the above-mentioned image features in the two images by, for example but not limited to, a DIC algorithm with convolution operation, i.e., calculates the difference in the position of the image feature FI1 in the first image IM1 and the second image IM2 in at least one axial direction, to obtain the displacement in the at least one axial direction, and estimates the position error of the long shaft member at the position of the above-mentioned pattern tag TP1. Specifically, the grayscale values of the same positions in the grayscale first image IM1 and the second image IM2 are multiplied, and then integrated, as shown in the following formula (1):

[0065] ,

[0066] ​Where f(τ) and g(t-τ) represent the grayscale values ​​at the same position on the first image IM1 and the second image IM2, respectively. Next, the correlation coefficient γ between the first image IM1 and the second image IM2 is calculated using the following formula (2). ij :

[0067] .

[0068] in It represents the average grayscale value of all pixels in the first image; is the average grayscale value of all pixels in the second image; m is the x-coordinate of an individual pixel in the image; and n is the y-coordinate of an individual pixel in the image. When the calculated correlation coefficient γ... ij When the similarity reaches its maximum, the corresponding position is the position where the similarity between the two images is the greatest, which is the position of image feature FI1. At this time, the displacement along one axis can be calculated using the following formula (3):

[0069] ,

[0070] The displacement refers to the offset of the second image IM2 relative to the first image IM1 on this axis; the movement distance refers to the distance on this axis between the current position of the second image IM2 and its starting position when the correlation coefficient reaches its maximum, in pixels; the image size refers to the length of the second image IM2 on this axis, in pixels; and the pixel size refers to the size of a pixel, in units such as micrometers (μm).

[0071] In this way, users can use the above measurement results to determine whether the long shaft is bent, and then consider whether to repair or replace the long shaft.

[0072] The method for measuring the position error of a feed system provided by this invention can be applied to measuring position errors in multiple axes (different types), such as, but not limited to, whether two linear guides 3 are parallel in the horizontal plane (e.g., composed of axes D1 and D2), whether the ball screw 5 has backlash, and whether individual linear guides 3 are skewed in the vertical plane (e.g., composed of axes D1 and D3). Examples will be given below to illustrate these applications.

[0073] Please refer to Figure 6 and 7AAs shown in Figure 7C, in one embodiment of the present invention, the method for measuring the position error of the feed system provided by the present invention is applied to measuring whether there is backlash in the ball screw 5. Generally, when taking two separate photos of the same graphic label TP1, the photos are taken from the same position, so the two images obtained from the previous and subsequent photos should be similar. However, once backlash occurs in the ball screw 5, due to the backlash difference, the positions of the two photos will be separated by a distance, causing the positional offset of the image features in the previous and subsequent photos to exceed the allowable range. Therefore, the measurement method provided in this embodiment first performs step S20, which is the same as step S10, to control the worktable 2 to move along the slide rail 31 and the screw 51 in the travel direction V1 (first travel direction). Figure 7A As shown, whenever the optical sensor OT1 moves in the direction of travel V1 to a position where its sensing range can completely (or partially) cover an individual graphic tag TP1, step S21 is executed to control the optical sensor OT1 to take a first picture of the graphic tag TP1 to obtain a first image of the graphic tag TP1.

[0074] Next, as Figure 7B As shown, after each graphic label TP1 has been photographed for the first time, step S22 is executed to control the worktable 2 to move along the slide rail 31 and screw 51 in the travel direction V2 (second travel direction). The travel direction V2 is opposite to the travel direction V1. Figure 7C As shown, whenever the optical sensor OT1 moves in the direction of travel V2 to a position where its sensing range can completely (or partially) cover the individual graphic tag TP1, step S23 is executed to control the optical sensor OT1 to take a second picture of the graphic tag TP1 to obtain a second image of the graphic tag TP1.

[0075] After acquiring each first image, step S24, identical to step S12 above, is executed to select specified image features in the grayscale first image. Similarly, after acquiring each second image, step S25, identical to step S13 above, is executed to search for specified image features in the grayscale second image. The image features in the first and second images corresponding to the same graphic label TP1 are identical.

[0076] Then, step S26, which is the same as step S14 above, is performed to compare the position of the image feature in the corresponding first and second images, thereby estimating the first displacement of the image feature in axis D1 and / or the second displacement in axis D2, and further estimating the degree of deviation of the motion path of the optical sensor OT1 (or the feed path of the table 2) at the position of the corresponding graphic label TP1. When the degree of deviation exceeds a preset range, it indicates that backlash has occurred in the ball screw 5.

[0077] Referring to Figure 8 , 9A and 9B, the method of measuring the position error of the feeding system according to the present application is applied to measure whether the two linear slides 3 are parallel. First, the same step S20 as step S10 is performed to control the movement of the worktable 2 along the slides 31 and the screw 51 in the direction of travel VI. As shown in Figure 9A , whenever the optical sensor OT1 moves to a position where its sensing range can completely cover (or partially cover) a graphic tag TP1 in the direction of travel VI, the step S31 is performed to control the optical sensor OT1 to continuously take two images of the graphic tag TP1 during the movement to obtain a first image and a second image.

[0078] After each first image is obtained, the same step S32 as step S12 is performed to select the specified image feature in the gray-scale first image. Similarly, after each second image is obtained, the same step S33 as step S13 is performed to search for the specified image feature in the gray-scale second image. The image features in the first image and the second image corresponding to the same graphic tag TP1 are the same.

[0079] Finally, the same step S34 as step S14 is performed to compare the image features in the above-mentioned first image and second image to estimate the position of the image feature in the graphic tag TP1, the first displacement in the axial direction D1 and the second displacement in the axial direction D2, and further estimate the deviation of the respective linear slide 3 at the position of the corresponding graphic tag TP1. In this way, it can be determined whether the two slides 31 are parallel in the plane space formed by the axial direction D1 and the axial direction D2.

[0080] In another embodiment of the present application for measuring whether the two linear slides 3 are parallel, the method for measuring whether the ball screw 5 has backlash can also be used, that is, the steps shown in Figures 6 to 7C are used to estimate the deviation of the respective linear slide 3 at the position of the corresponding graphic tag TP1. In this way, it can be determined whether the two slides 31 are parallel in the plane space formed by the axial direction D1 and the axial direction D2.

[0081] To measure whether the respective linear slide 3 is tilted up or down, reference can be made to Figure 10 and 11As shown, a plurality of pattern tags TP2 (second pattern tags) can be provided on the lateral surface 14 of the convex portion 12 of the shaft bed 1, and an optical sensor OT2 (second optical sensor) corresponding to the pattern tags TP2 can be provided on the moving body (e.g., the worktable 2). The angle between the lateral surface 14 and the working surface 13 is greater than 0 degrees and less than 180 degrees. The manner of measuring whether the respective linear slide rails 3 are tilted up and down is similar to the manner of measuring whether the two linear slide rails 3 are parallel, as shown in Figure 12 As shown. First, the same step S50 as step S10 is performed, and the same step S51 as step S31 is performed to obtain a third image and a fourth image. Then, after each third image is obtained, the same step S52 as step S12 is performed to find the specified image feature in the gray-scale third image, as shown in Figure 13A As shown. First, the same step S50 as step S10 is performed, and the same step S51 as step S31 is performed to obtain a third image and a fourth image. Then, after each third image is obtained, the same step S52 as step S12 is performed to find the specified image feature in the gray-scale third image, as shown in Figure 13B As shown. First, the same step S50 as step S10 is performed, and the same step S51 as step S31 is performed to obtain a third image and a fourth image. Then, after each third image is obtained, the same step S52 as step S12 is performed to find the specified image feature in the gray-scale third image, as shown in

[0082] Finally, the same step S54 as step S14 is performed to compare the positions of the image features in the gray-scale third image and the fourth image, thereby estimating the position of the image feature at the position of the pattern tag TP2, the third displacement amount in the axial direction D1, and the fourth displacement amount in the axial direction D3, and further estimating the degree of deviation of the respective linear slide rails 3 in the plane formed by the axial directions D1 and D3 at the position of the corresponding pattern tag TP2.

[0083] Similarly, another embodiment of measuring whether the respective linear slide rails 3 are tilted up and down can also be implemented in a manner similar to Figure 6 As shown. First, the same step S50 as step S10 is performed, and the same step S51 as step S31 is performed to obtain a third image and a fourth image. Then, after each third image is obtained, the same step S52 as step S12 is performed to find the specified image feature in the gray-scale third image, as shown in Figure 10 As shown. First, the same step S50 as step S10 is performed, and the same step S51 as step S31 is performed to obtain a third image and a fourth image. Then, after each third image is obtained, the same step S52 as step S12 is performed to find the specified image feature in the gray-scale third image, as shown in 14 As shown. First, the same step S50 as step S10 is performed, and the same step S51 as step S31 is performed to obtain a third image and a fourth image. Then, after each third image is obtained, the same step S52 as step S12 is performed to find the specified image feature in the gray-scale third image, as shown in

[0084] After the third image is obtained, the step S52 is performed to find the specified image feature in the third grayscale image; and after the fourth image is obtained, the step S53 is performed to find the specified image feature in the fourth grayscale image. The image features in the third image and the fourth image corresponding to the same graphic tag TP2 are the same.

[0085] Finally, the step S54 is performed to compare the positions of the image features in the third grayscale image and the fourth grayscale image, so as to estimate the position of the graphic tag TP2, the third displacement amount in the axial direction D2, and the fourth displacement amount in the axial direction D3, and further estimate the deviation of the individual linear slide 3 in the plane formed by the axial direction D2 and the axial direction D3 at the position corresponding to the graphic tag TP2.

[0086] Although the above Figure 4 , 6 , 8, 12, and 14 are each embodiments in which the first image and the second image corresponding to the same graphic tag are obtained first, and then the image processing and feature searching are performed on the two images, the present application is not limited thereto. In other embodiments, the image processing and feature searching can be performed on each image immediately after the image is obtained.

[0087] Although the above Figure 6 and Figure 14 are each embodiments in which the first shooting is performed on all the graphic tags at one time, and then the second shooting is performed on all the graphic tags at one time, the present application is not limited thereto. In other embodiments, the optical sensor can be controlled to perform the first shooting on the current graphic tag while moving in the first direction of travel, and then perform the second shooting on the graphic tag while moving in a second direction of travel opposite to the first direction of travel; and then, the optical sensor can be controlled to perform the first shooting on the next graphic tag while moving in the first direction of travel, and then perform the second shooting on the graphic tag while moving in the second direction of travel.

[0088] In the present application, the number of optical sensors can be determined according to the application requirements, and is not limited to the number used in the above embodiments.

[0089] Although the above Figure 1 , 3 , 7A to 7C, 9A to 9B, and 10 are each embodiments in which the optical sensor OT1 / OT2 is arranged on the workbench 2, the present application is not limited thereto. In other embodiments, the optical sensor OT1 / OT2 can also be arranged on the slider 32 or the nut 52 (e.g., the flange 53 of the nut 52) according to requirements.

[0090] Furthermore, although the above embodiments regarding measuring whether the two linear slides 3 are parallel in the horizontal plane, whether the ball screw 5 has a back lash, and whether the individual linear slides 3 are skewed in the vertical plane are described separately, in fact, at least two of the above applications can be performed simultaneously, such as measuring whether the two linear slides 3 are parallel in the horizontal plane and measuring whether the individual linear slides 3 are skewed in the vertical plane simultaneously.

[0091] Although the present application has been disclosed with reference to the foregoing embodiments, these embodiments are not intended to limit the present application. Any modification, improvement, equivalent replacement, etc. made without departing from the spirit and scope of the present application shall fall within the scope of the present application. The present application shall be defined by the scope of the claims.

Claims

1. A method for measuring position error of a feeding system, the feeding system comprising a shaft bed, a long shaft member and a moving body, the long shaft member being fixed to the shaft bed, the moving body being movably arranged on the long shaft member, at least one first pattern label being arranged on a working surface of the shaft bed, the moving body being provided with a first optical sensor corresponding to the at least one first pattern label, characterized in that, The method for measuring the position error of the feeding system comprises: Step A: controlling the moving body to move along the long-axis member, and controlling the first optical sensor to take two shots of the first graphic label respectively during the movement of the moving body, so as to obtain a first image and a second image respectively; Step B: selecting a first image feature from the first image and the second image, wherein the first image feature refers to a part of the image of the first graphic label that matches a default template; and Step C: comparing the positions of the first image feature in the first image and the second image to estimate the position error; In the step A, the moving body moves along the long-axis member towards a moving direction, and the first optical sensor takes two continuous shots of the first graphic label to obtain the first image and the second image respectively when the moving body moves towards the moving direction.

2. The method of claim 1, wherein, The step C comprises: Step C1: calculating the difference between the position of the first image feature in the first image and the position of the first image feature in the second image in at least one axial direction, so as to obtain a displacement in the axial direction as at least part of the position error.

3. The method of claim 1, wherein, The step C comprises: Step C2: calculating the difference between the position of the first image feature in the first image and the position of the first image feature in the second image in a first axial direction, so as to obtain a first displacement in the first axial direction as part of the position error; and Step C3: calculating the difference between the position of the first image feature in the first image and the position of the first image feature in the second image in a second axial direction, so as to obtain a second displacement in the second axial direction as another part of the position error, wherein the first axial direction is perpendicular to the second axial direction.

4. The method of claim 1, wherein, The step B is performed by using a digital image correlation algorithm and the following conditions: ， wherein γ ij is a correlation coefficient representing the first image and the second image, is an average value of gray scale values of all pixels in the first image; is an average value of gray scale values of all pixels in the second image; m is an x coordinate corresponding to a pixel in the first image or the second image; and n is a y coordinate corresponding to a pixel in the first image or the second image.

5. The method of claim 4, wherein, The step C is performed by using the following conditions: ， Wherein, the displacement refers to the offset of the second image relative to the first image in an axial direction; the moving distance refers to the distance between the current position of the second image and the starting position of the second image in the axial direction when the correlation coefficient reaches the maximum degree; the image size refers to the length of the second image in the axial direction; and the pixel size refers to the size of one pixel.

6. A method for measuring position error of a feed system, the feed system comprising a shaft bed, a long shaft member and a moving body, the long shaft member being fixed to the shaft bed, the moving body being movably arranged on the long shaft member, at least one first pattern mark being arranged on a working surface of the shaft bed, the moving body being provided with a first optical sensor corresponding to the at least one first pattern mark, characterized in that, The method for measuring the position error of the feeding system comprises: Step A: controlling the moving body to move along the long-axis member, and controlling the first optical sensor to take two shots of the first graphic label respectively during the movement of the moving body, so as to obtain a first image and a second image respectively; Step B: selecting a first image feature from the first image and the second image, wherein the first image feature refers to a part of the image of the first graphic label that matches a default template; and Step C: comparing the positions of the first image feature in the first image and the second image to estimate the position error in multiple axial directions; In the step A, the moving body moves along the long-axis member towards a moving direction, and the first optical sensor takes two continuous shots of the first graphic label to obtain the first image and the second image respectively when the moving body moves towards the moving direction. Wherein, in the step A, the moving body is moving along the long axis member towards a moving direction, and when the moving body is moving towards the moving direction, the first optical sensor continuously takes two pictures of the first graphic label to obtain the first image and the second image respectively; and The lateral surface of the spindle bed is provided with at least one second graphic label, the angle between the lateral surface and the working surface is greater than 0 degrees and less than 180 degrees, the moving body is also provided with a second optical sensor corresponding to the at least one second graphic label, and the method for measuring the position error of the feeding system further comprises: Step D: controlling the second optical sensor to take two pictures of the second graphic label respectively to obtain a third image and a fourth image during the movement of the moving body; Step E: selecting a second image feature from the third image and the fourth image; and Step F: comparing the position of the second image feature in the third image and the fourth image to estimate the position error.

7. The method of claim 6, wherein, The step C comprises: Step C1: calculating the difference between the position of the first image feature in the first image and the position in the second image in at least one axial direction to obtain a displacement in the axial direction as part of the position error.

8. The method of claim 6, wherein, The step C comprises: Step C2: calculating the difference between the position of the first image feature in the first image and the position in the second image in a first axial direction to obtain a first displacement in the first axial direction as part of the position error; and Step C3: calculating the difference between the position of the first image feature in the first image and the position in the second image in a second axial direction to obtain a second displacement in the second axial direction as another part of the position error, the first axial direction being perpendicular to the second axial direction.

9. The method of claim 6, wherein, The step F comprises: Step F1: calculating the difference between the position of the second image feature in the third image and the position in the fourth image in a first axial direction to obtain a third displacement in the first axial direction as part of the position error; and Step F2: calculating the difference between the position of the second image feature in the third image and the position in the fourth image in a third axial direction to obtain a third displacement in the third axial direction as another part of the position error, the first axial direction being perpendicular to the third axial direction.

10. The method of claim 6, wherein, The step B is performed using a digital image correlation algorithm and the following conditions: ， wherein γ ij is a correlation coefficient representing the first image and the second image, is an average value of gray scale values of all pixels in the first image; is an average value of gray scale values of all pixels in the second image; m is an x coordinate corresponding to a pixel in the first image or the second image; and n is a y coordinate corresponding to a pixel in the first image or the second image.

11. The method of claim 10, wherein, The step C is performed using the following conditions: ， The displacement is an offset of the second image relative to the first image in an axial direction; the movement distance is a distance between a current position of the second image and a starting position of the second image in the axial direction when the correlation coefficient reaches a maximum degree; the image size is a length of the second image in the axial direction; and the pixel size is a size of one pixel. The displacement is an offset of the second image relative to the first image in an axial direction; the movement distance is a distance between a current position of the second image and a starting position of the second image in the axial direction when the correlation coefficient reaches a maximum degree; the image size is a length of the second image in the axial direction; and the pixel size is a size of one pixel. The displacement is an offset of the second image relative to the first image in an axial direction; the movement distance is a distance between a current position of the second image and a starting position of the second image in the axial direction when the correlation coefficient reaches a maximum degree; the image size is a length of the

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