Feed system-specific position deviation measurement method

Abstract

Feed system-specific position deviation measurement method, wherein the feed system consists of an axis bed (1), a long shaft part (31) and a sliding part (2), wherein the long shaft part (31) is mounted on the axis bed (1) and the sliding part (2) is movably attached to the long shaft part (31), wherein the running surface (13) of the axis bed (1) is provided with at least one graphic volume label (TP1) and the sliding part (2) is provided with a first optical sensor (OT1), wherein the method comprises the following steps: (A) Generating two images, namely the first image (IM1) and the second image (IM2), by recording twice through the first optical sensor (OT1) of the first graphic volume label (TP1) during a controlled displacement of the sliding part (2) along the long-wave part (31), (B) Selecting a first image feature (FI1) from both the first image (IM1) and the second image (IM2), and (C) Determining the positional deviation by comparing a position of the first image feature (FI1) in the first image (IM1) with a position of the first image feature (FI1) in the second image (IM2).

Description

[0001] The invention relates to a feed system, in particular a feed system-specific position deviation measuring method.

[0002] In the prior art, Taiwanese patent application TW I539143 B discloses a non-parallel detection system for linear feeds. Its camera units are each mounted at a fixed location outside a linear feed or remain complementary to a characteristic pattern. Therefore, to monitor possible deformation at various points on a screw, not only must several characteristic patterns be attached to the screw, but several camera units must also be used. Furthermore, a strain gauge is required to measure non-parallelism. Consequently, this system not only entails higher manufacturing costs but also cannot detect other deviations.

[0003] US 2005 / 0225788 A1 describes an exposure device in which a light beam is irradiated from a recording head onto a recording medium mounted on a recording stage, and the recording stage and the recording head are moved relatively.

[0004] From US 2003 / 0057229 A1 a feeding device for electronic components is known with a component conveying device which conveys an electronic component to a component receiving opening.

[0005] In view of the shortcomings of the conventional design, the object of the invention is to provide a feed system-specific position deviation measuring method which can detect position deviations in several axis directions (in different ways).

[0006] To achieve the object, an embodiment according to the invention provides a feed system-specific position deviation measuring method, wherein the feed system consists of an axle bed, a long shaft part and a sliding part, wherein the long shaft part is mounted on the axle bed and the sliding part is movably mounted on the long shaft part, the running surface of the axle bed is provided with at least one graphic volume label and the sliding part is provided with a first optical sensor corresponding to the first graphic volume label, wherein the method comprises the following steps: I. Generating two images, namely the first and the second image by recording twice by the first optical sensor on the first graphic volume label during a controlled displacement of the sliding part along the long shaft part, II. Selecting a first image feature from the first and the second image, III.Detecting the positional deviation by comparing the positions of the first image features in the first and second images.

[0007] With such a configuration, the sensor system attached to the sliding part can record data on at least one graphic volume label arranged in the running surface during the displacement of the sliding part in order to detect the positional deviation relative to the individual graphic volume label in real time. Furthermore, in the embodiment according to the invention, the optical sensor system is combined with an image analysis technique (e.g., digital image correlation - DIC algorithm) to detect the positional deviations in multiple axial directions.

[0008] Further objects, advantages, features and possible applications of the present invention will become apparent from the following description of the embodiments with reference to the drawings. Fig. 1 View of the feed system provided for measuring according to an embodiment of the invention. Fig. 2 Block diagram of the feed system provided for measuring according to an embodiment of the invention. Fig. 3 View from a viewing angle for a part of the feed system in relation to Fig. 1. Fig. 4 Flowchart of the position deviation measuring method according to an embodiment of the invention. Fig. 5A Schematic representation of the image analysis of a grayscale-related first image according to an embodiment of the invention, for illustrating the positions of the label image and the image feature of a graphic volume label. Fig. 5B Schematic representation of the image analysis of a grayscale-related second image according to an embodiment of the invention, for illustrating the positions of the label image and the image feature of a graphic volume label. Fig. 6 Flowchart of the backlash measurement of the ball screw according to an embodiment of the position deviation measuring method according to the invention. Fig. 7A Schematic representation of the position deviation measurement of the feed system according to an embodiment of the invention, for illustrating the moving sliding part from the front end of the long-wave part in one direction, wherein the optical sensor makes a first recording to a graphic volume label. Fig. 7B Schematic representation of the position deviation measurement of the feed system according to an embodiment of the invention, showing the sliding part moved to the end of the long-wave part, wherein the optical sensor has made a first recording to all graphic volume labels respectively. Fig. 7C Schematic representation of the position deviation measurement of the feed system according to an embodiment of the invention, for indicating the sliding part moved in the opposite direction, wherein the optical sensor makes a second recording to a graphic volume label. Fig. 8 Flowchart of the position deviation measuring method according to an embodiment of the invention for checking the parallelism of two linear sliding guides. Fig. 9A Schematic representation of the position deviation measurement of the feed system according to an embodiment of the invention, for illustrating the moving sliding part in one direction, wherein the optical sensor makes a first recording on a graphic volume label. Fig. 9B Schematic representation of the position deviation measurement of the feed system according to an embodiment of the invention, for indicating the sliding part moved in the same direction, wherein the optical sensor makes a second recording to the same graphic volume label. Fig. 10 View of the feed system provided for measuring according to another embodiment of the invention. Fig. 11 Block diagram of the feed system provided for measuring according to another embodiment of the invention. Fig. 12 Flowchart of the position deviation measuring method according to an embodiment of the invention for measuring the offset of two linear sliding guides. Fig. 13A Schematic representation of the image analysis of a grayscale-related third image according to an embodiment of the invention, for illustrating the positions of the label image and the image feature of a graphic volume label. Fig. 13B Schematic representation of the image analysis of a grayscale-related fourth image according to an embodiment of the invention, for illustrating the positions of the label image and the image feature of a graphic volume label. Fig. 14 Flowchart of the position deviation measuring method according to another embodiment of the invention for measuring the offset of the individual linear sliding guides.

[0009] The position deviation measuring method according to the invention is intended for a feed system. As can be seen from the Fig. As can be seen from Figures 1 to 3, the feed system comprises an axis bed 1, a workbench 2 (sliding part), two linear slide guides 3, two bearings 4, a ball screw 5, a coupling 6, a motor 7, and a servo side 8. The axis bed 1, which has a pedestal 11 and two shoulders 12, extends in an axial direction D1 (first axial direction). The two shoulders 12 protrude from the pedestal 11 in an axial direction D3 (third axial direction) and are located on two opposite sides of the pedestal 11 in an axial direction D2 (second axial direction). The axial directions D1, D2, and D3 are perpendicular to each other. The two linear slide guides 3 are mounted on two opposite sides of the axis bed 1, such as, for example, on the two shoulders 12, but without limitation.In the present embodiment, each linear guide 3 includes a slide rail 31 (long shaft portion) and two sliders 32 (sliding portion), with the two sliders 32 being mounted on the slide rail 31 for reciprocating sliding movement. However, the present embodiment is not limited to this. The number of sliders 32 can be determined as needed, for example, one or more than two sliders. The two bearings 4 are mounted on two opposite ends of the axis bed 1 in the axial direction D1. The ball screw 5 includes a worm gear 51 (long shaft portion) and a cap 52 (sliding portion). One end of the worm gear 51 is coupled to one bearing 4, while the opposite end is coupled to the motor 7 through the other bearing 4 and the coupling 6. The cap 52 is mounted on the worm gear 51 and can reciprocate along the worm gear 51.The workbench 2 (sliding part) is connected to the two carriages 32 and the closure cap 52. The motor 7 is connected to the servo side 8 and is controlled by it. When the motor 7 rotates, controlled by the servo side 8, the worm 51 is driven to rotate, so that the workbench 2 moves along the slide rail 31 and the worm 51.

[0010] To measure the positional deviation of the feed system, the optical sensor OT1 (first optical sensor) can be attached to the workbench 2 and several graphic volume labels TP1 (first graphic volume labels) can be attached in the axis direction D1 to the running surface 13 of the trestle 11 (see Fig. 1 and Fig. 3). The optical sensor OT1 can be a light-sensitive CCD (charge-coupled device) or CMOS (complementary metal-oxide-semiconductor field-effect) transistor image sensor, but is not limited to these. The mounting location of the optical sensor OT1 should be selected as required, i.e., not limited to the Fig. 1 and Fig. 3, provided that the scanning area of ​​the optical sensor OT1 completely or partially covers the entire graphic volume label TP1. The optical sensor OT1 can be connected to the servo side 8 either wired or wirelessly to be controlled by the servo side 8.

[0011] The servo side 8 can, for example, comprise one or more computing devices, each with at least one evaluation unit 81. The evaluation unit 81 controls, among other things, the operation of the motor 7 and the optical sensor OT1 in order to implement the position deviation measurement method according to the invention.

[0012] As can be seen from the flow chart of the position deviation measurement procedure in Fig. 4, in step S10, the evaluation unit 81 causes the motor 7 to rotate in order to drive the sliding part (e.g., the workbench 2, the closure cap 52, and the carriage 32) to move along the long-shaft part (e.g., the slide rail 31 and the worm 51). The evaluation unit 81 then determines the travel path of the sliding part based on the process data resulting from the rotation of the motor 7 (e.g., the rotary encoder signal of the motor 7) and then decides whether the optical sensor OT1 should make a recording. In the subsequent step S11, the evaluation unit 81 causes the optical sensor OT1 to make two recordings to the graphic volume label TP1 in order to obtain two images (e.g., static images), provided that the scanning range of the optical sensor OT1 completely or partially covers the entire graphic volume label TP1 during the movement of the sliding part.

[0013] In the subsequent step S12, the evaluation unit 81 implements a grayscale evaluation of the image resulting from the first recording (hereinafter referred to as the first image) and selects an image feature from the grayscale-related first image using, for example, a DIC algorithm, but without limitation. As can be seen from Fig. 5A, an image feature FI1 (first image feature) corresponding to a standard template is found from an image (hereinafter referred to as label image PI1 (first label image)) of the graphic volume label TP1, which is represented in the grayscale-related first image IM1. In the subsequent step S13, the evaluation unit 81 implements a grayscale evaluation on the image resulting from the second recording (hereinafter referred to as the second image) and selects a portion identical to the image feature of the first image from the grayscale-dependent second image using, for example, a DIC algorithm, but without limitation. As can be seen from Fig. 5B, an identical image feature FI1 is found from the label image PI1 shown in the grayscale-related second image IM2.

[0014] As can be seen from step S14, the evaluation unit 81 finally compares the positions of the aforementioned image features in the two images using, for example, a DIC algorithm, but without limitation, in conjunction with a convolution operation, thus calculating a positional difference value between the image feature FI1 in the first image IM1 and the image feature FI1 in the second image IM2 in at least one axial direction in order to determine a displacement amount in this axial direction and then to detect the positional deviation of the long-wave part from the graphic volume label TP1. This means that the grayscale values ​​complementary to the same position from the first image IM1 and the second image IM2 are multiplied, and then an integral calculation is implemented using the following formula (1): (f×g)(t)≜∫−∞∞f(τ)g(t−τ)dτ

[0015] Here, f(τ) is a grayscale value of a position in the first image IM1, and g(t-τ) is a grayscale value of the same position in the second image IM2. The coefficients γij of the first image IM1 and the second image IM2 are then calculated using the following formula (2): γij=∑m∑n[f(m+i,n+j)−f¯]×[g(m,n)−g¯]∑m∑n[f(m,n)−f¯]2×∑m∑n[g(m,n)−g¯]2

[0016] Where f is the average of the grayscale values ​​of all pixels in the first image, g is the average of the grayscale values ​​of all pixels in the second image, "m" is the x-coordinate of the individual pixel in the image, and "n" is the y-coordinate of the individual pixel in the image. When the calculated coefficients γij have reached their maximum, the corresponding positions refer to the maximum similarity between the two images, i.e., to the positions of the image features FI1. The displacement in one axis direction can now be calculated using the following formula (3): Displacement dimension = (distance − image size) × pixel size

[0017] The displacement measure is understood as the offset of the second image IM2 relative to the first image IM1 in this axial direction, the travel distance as the distance (unit: pixel) with respect to this axial direction between the actual position and the starting position of the second image IM2 at the maximum coefficients reached, the image size as the width (unit: pixel) of the second image IM2 in this axial direction, and the pixel size as the size (unit: for example µm) of the individual pixel.

[0018] Based on the above measurement results, you can judge whether the long wave part is bent and then consider repairing or replacing the long wave part if necessary.

[0019] The position deviation measurement method according to the invention can be used to measure position deviations in several (different) axial directions, for example, to check the parallelism of two linear guides 3 in a horizontal plane (for example, designed with the axial directions D1 and D2), to assess any backlash of the ball screw 5, or to measure the offset of individual linear guides 3 in a vertical plane (for example, designed with the axial directions D1 and D3). The application is explained below using the exemplary embodiments.

[0020] In relation to Fig. 6 and the Fig. 7A to 7C illustrate an embodiment of the positional deviation measuring method according to the invention for measuring any backlash of the ball screw 5. When recordings are made twice, each time to the same graphic volume label TP1, the recordings are made at predetermined, identical positions, so that the two resulting images from the recordings remain almost identical. It should be noted that the offset of the individual image feature from the two recordings may exceed a tolerance range, since backlash occurring on the ball screw 5, due to the differential recoil, results in the positions of the two recordings being spaced apart by a certain distance. In this case, the positional deviation measuring method according to the invention first implements a step S20 identical to step S10, so that the workbench 2 moves in a running direction V1 (first running direction) along the slide rail 31 and the worm 51. As can be seen from Fig. 7A, whenever the scanning area of ​​the optical sensor OT1 moved in the travel direction V1 completely or partially covers the single graphic volume label TP1, step S21 is implemented so that the optical sensor OT1 makes an initial recording to the graphic volume label TP1 and then delivers a first image.

[0021] If each graphic volume label TP1 is subject to initial recording (see Fig. 7B), step S22 is executed so that the workbench 2 moves in a running direction V2 (second running direction) along the slide rail 31 and the worm 51. The running direction V2 remains opposite to the running direction V1. As can be seen from Fig. 7C, whenever the scanning area of ​​the optical sensor OT1 moved in the travel direction V2 completely or partially covers the single graphic volume label TP1, step S23 is implemented so that the optical sensor OT1 makes a second recording to the graphic volume label TP1 and then delivers a second image.

[0022] For the obtained first images, step S24, identical to step S12, is implemented to select the image features from the grayscale-related first images. Also for the obtained second images, step S25, identical to step S13, is implemented to select the image features from the grayscale-related second images. For the same graphic volume label TP1, the image feature of the first image is identical to that of the second image.

[0023] Subsequently, a step S26, identical to step S14, is initiated to compare the positions of said image features in the first image and the second image, and then to determine a first displacement amount of said image features in the axis direction D1 and / or a second displacement amount in the axis direction D2, and finally to detect a deviation amount of the movement path of the optical sensor OT1 (or the feed path of the workbench 2) from the graphic volume label TP1. If the deviation amount exceeds a specified range, backlash has occurred on the ball screw 5.

[0024] In relation to Fig. 8, Fig. 9A and Fig. 9B shows the position deviation measuring method according to the invention for checking the parallelism of two linear guides 3. First, a step S20 identical to step S10 is implemented so that the workbench 2 moves in a running direction V1 along the slide rail 31 and the worm 51. As can be seen from Fig. 9A, whenever the scanning area of ​​the optical sensor OT1 moved in the travel direction V1 completely or partially covers a graphic volume label TP1, step S31 is implemented so that the optical sensor OT1 makes two consecutive recordings to the graphic volume label TP1 and then delivers a first image and a second image.

[0025] For the obtained first images, step S32, identical to step S12, is implemented to select the image features from the grayscale-related first images. Also for the obtained second images, step S33, identical to step S13, is implemented to select the image features from the grayscale-related second images. For the same graphic volume label TP1, the image feature of the first image is identical to that of the second image.

[0026] Subsequently, a step S34, identical to step S14, is initiated to compare the positions of said image features in the grayscale-related first image and second image, and then to determine a first displacement amount in the axial direction D1 and / or a second displacement amount in the axial direction D2 of said image features in the graphic volume label TP1, and finally to detect a deviation amount of the individual linear slide guide 3 from the graphic volume label TP1. This makes it possible to assess any non-parallelism of the two slide rails 31 in a plane formed with the axial directions D1 and D2.

[0027] In a further embodiment, the parallelism test of two linear guides 3 can also be carried out by a backlash measurement on the ball screw 5, i.e. by detecting a deviation measure of the individual linear guide 3 from the graphic volume label TP1 (see Fig. 6 to Fig. 7C). In this way, one can possibly assess a non-parallelism of the two slide rails 31 in a plane formed with the axis directions D1 and D2.

[0028] For offset measurement of the individual linear guides 3 in a vertical plane, Fig. 10 and Fig. 11 several graphic volume labels TP2 (second graphic volume labels) are attached to a flank 14 of the respective shoulder 12 of the axle bed 1. Accordingly, an optical sensor OT2 (second optical sensor) complementary to these graphic volume labels TP2 can be attached to the sliding part (for example, on the workbench 2). The included angle between the flank 14 and the running surface 13 is greater than 0 degrees and less than 180 degrees. The offset measurement on the individual linear guides 3 in a vertical plane is carried out similarly to the parallelism test of two linear guides 3 with respect to Fig. 12. First, a step S50 identical to step S10 and a step S51 identical to step S31 are implemented to obtain a third image and a fourth image, respectively. For the obtained third images, a step S52 identical to step S12 is implemented to select a specific image feature from the grayscale-related third image. Fig. Figure 13A shows an image feature FI2 (second image feature) of the label image PI2 (second label image) from the grayscale-related third image IM3. For the fourth images obtained, a step S53 identical to step S13 is implemented to select a specific image feature from the grayscale-related fourth image. Fig. Figure 13B shows an image feature FI2 of the label image PI2 from the grayscale-related fourth image IM4. For the same graphic volume label TP2, the image feature of the third image is identical to that of the fourth image.

[0029] Thereafter, a step S54 identical to step S14 is initiated to compare the positions of said image features in the grayscale-related third image and fourth image, and then to determine a third displacement amount in the axial direction D1 and / or a fourth displacement amount in the axial direction D3 of said image features in the graphic volume label TP2, and finally to detect a deviation amount of the individual linear sliding guide 3 from the graphic volume label TP2 in a plane formed with the axial directions D1 and D3.

[0030] Analogously, the offset measurement on the linear sliding guides 3 in a vertical plane can be carried out in a similar way to the parallelism test of two linear sliding guides 3 with respect to Fig. 6. As described in the Fig. As shown in Figures 10 to 14, first, a step S50 identical to step S10 and a step S61 identical to step S21 are implemented to obtain a third image. Subsequently, a step S62 analogous to step S22 and a step S63 analogous to step S23 are implemented to obtain a fourth image.

[0031] For the obtained third image, step S52 is executed to select a specific image feature from the grayscale-related third image. For the obtained fourth image, step S53 is implemented to select a specific image feature from the grayscale-related fourth image. For the same graphic volume label TP2, the image feature of the third image is identical to that of the fourth image.

[0032] Thereafter, step S54 is initiated to compare the positions of said image features in the grayscale-related third image and fourth image, and then to determine a third displacement amount in the axial direction D2 and / or a fourth displacement amount in the axial direction D3 of said image features in the graphic volume label TP2, and finally to detect a deviation amount of the individual linear sliding guide 3 from the graphic volume label TP2 in a plane formed with the axial directions D2 and D3.

[0033] In the respective embodiment with regard to Fig. 4, Fig. 6, Fig. 8, Fig. 12, Fig. 14, a first image and a second image are first obtained from the same graphic volume label, and then image processing and feature search are performed on the two images. However, the embodiment of the invention is not limited to this. In another embodiment, each obtained image can be directly subjected to image processing and feature search.

[0034] In the respective embodiment with regard to Fig. 6 and Fig. 14, a second recording to all graphic volume labels only follows a first recording to all graphic volume labels, but the embodiment according to the invention is not limited thereto. In a further embodiment, the optical sensor can be caused to make a first recording to a graphic volume label when moving in a first direction, and then to make a second recording to the same graphic volume label when moving in the second direction opposite to the first direction, and then to make another first recording to a next graphic volume label when moving in the first direction, and then to make another second recording to this next graphic volume label when moving in the second direction.

[0035] In the embodiment according to the invention, the number of optical sensors can be determined as required and is therefore not limited to the number mentioned in each embodiment above.

[0036] In the embodiments relating to Fig. 1, Fig. 3, Fig. 7A to 7C, Fig. 9A to 9B and Fig. 10, the respective optical sensors OT1 / OT2 are mounted on the workbench 2. However, the embodiment of the invention is not limited thereto. In a further embodiment, the optical sensors OT1 / OT2 can also be mounted on the carriage 32 or the closure cap 52 (for example, on the flank 53 of the closure cap 52), as needed.

[0037] Although the parallelism check of two linear guides 3 in a horizontal plane, the assessment of possible back play of the ball screw 5 and the offset measurement on individual linear guides 3 in a vertical plane are explained separately in the above-mentioned embodiments, in practice at least two applications can be implemented simultaneously, for example the parallelism check of two linear guides 3 in a horizontal plane simultaneously with the offset measurement on individual linear guides 3 in a vertical plane.

Claims

[1] Feed system-specific position deviation measuring method, wherein the feed system consists of an axle bed (1), a long shaft part (31) and a sliding part (2), wherein the long shaft part (31) is mounted on the axle bed (1) and the sliding part (2) is movably mounted on the long shaft part (31), wherein the running surface (13) of the axle bed (1) is provided with at least one graphic volume label (TP1) and the sliding part (2) is provided with a first optical sensor (OT1), the method comprising the following steps: (A) generating two images, namely the first image (IM1) and the second image (IM2) by recording twice by the first optical sensor (OT1) of the first graphic volume label (TP1) during a controlled displacement of the sliding part (2) along the long-wave part (31), (B) selecting a first image feature (FI1) from each of the first image (IM1) and the second image (IM2), and (C) detecting the positional deviation by comparing a position of the first image feature (FI1) in the first image (IM1) with a position of the first image feature (FI1) in the second image (IM2). [2] Positional deviation measuring method according to claim 1, characterized by that step (A) comprises the following operations: (A1) Causing the sliding part (2) to move along the long shaft part (31) in a first running direction (V1), (A2) Causing the first optical sensor (OT1) to record the first graphic volume label (TP1) when the sliding part (2) is moved in the first travel direction (V1) and then to obtain a first image (IM1), (A3) causing the sliding part (2) to move along the long shaft part (31) in a second running direction (V2) opposite to the first running direction (V1), and (A4) Causing the first optical sensor (OT1) to record the first graphic volume label (TP1) when moving the sliding part (2) in the second travel direction (V2) and then to obtain a second image (IM2). [3] Positional deviation measuring method according to claim 2, characterized by that step (C) comprises the following operations: (C1) Calculating a positional difference value between the first image feature (FI1) in the first image (IM1) and the first image feature (FI1) in the second image (IM2) in at least one axial direction (D1, D2) in order to determine a displacement amount in this axial direction (D1, D2) as at least one part of the positional deviation. [4] Positional deviation measuring method according to claim 1, characterized byin that the sliding part (2) moves in step (A) along the long-wave part (31) in a running direction (V1), wherein the first optical sensor (OT1) makes two successive recordings of the first graphic volume label (TP1) and then obtains a first image (IM1) and a second image (IM2). [5] Positional deviation measuring method according to claim 2 or 4, characterized by that step (C) comprises the following operations: (C2) calculating a positional difference value between the first image feature (FI1) in the first image (IM1) and the first image feature (FI1) in the second image (IM2) in a first axial direction (D1) to determine a first displacement amount in this axial direction (D1) as a portion of the positional deviation, and (C3) Calculating a positional difference value between the first image feature (FI1) in the first image (IM1) and the first image feature (FI1) in the second image (IM2) in a second axial direction (D2) to determine a second displacement amount in this axial direction (D2) as the other part of the positional deviation, wherein the first axial direction (D1) remains perpendicular to the second axial direction (D2). [6] Positional deviation measuring method according to claim 1, characterized by that a flank (14) of the axle bed (1) is provided with at least one second graphic volume label (TP2), wherein the included angle between the flank and the running surface (13) is greater than 0 degrees and less than 180 degrees, the sliding part (2) is equipped with a second optical sensor (OT2), wherein the second optical sensor (OT2) is complementary to this second graphic volume label (TP2), the method comprising the following steps: (D) causing the second optical sensor (OT2) to make two recordings of the second graphic volume label (TP2) when moving the sliding part (2) and then to obtain a third image (IM3) and a fourth image (IM4), (E) selecting a second image feature (FI2) from each of the third (IM3) and the fourth image (IM4), and (F) detecting the positional deviation by comparing a position of the second image feature (FI2) in the third image (IM3) with a position of the second image feature (FI2) in the fourth image (IM4). [7] Positional deviation measuring method according to claim 6, characterized by that step (F) comprises the following operations: (F1) Calculating a positional difference value between the second image feature (FI2) in the third image (IM3) and the second image feature (FI2) in the fourth image (IM4) in a first axial direction (D1) to determine a third displacement amount in this axial direction (D1) as a portion of the positional deviation, and (F2) Calculating a positional difference value between the second image feature (FI2) in the third image (IM3) and the second image feature (FI2) in the fourth image (IM4) in a third axial direction (D3) to determine a fourth displacement amount in this third axial direction as the other part of the positional deviation, wherein the first axial direction (D1) remains perpendicular to the third axial direction (D3). [8] Positional deviation measuring method according to claim 6, characterized by that step (D) comprises the following operations: (D1) Causing the sliding part (2) to move along the long shaft part (31) in a first running direction (V1), (D2) causing the second optical sensor (OT2) to record the second graphic volume label (TP2) when the sliding part (2) is moved in the first direction (V1) and then to obtain a third image (IM3), (D3) causing the sliding part (2) to move along the long shaft part (31) in a second direction (V2) opposite to the first direction (V1), and (D4) Causing the second optical sensor (OT2) to record the second graphic volume label (TP2) when the sliding part (2) is moved in the second travel direction (V2) and then to obtain a fourth image (IM4). [9] Positional deviation measuring method according to claim 1, characterized by that step (B) is implemented using a digital image algorithm or conditionally by the following: γij=∑m∑n[f(m+i,n+i)−f¯]×[(m,n)−g¯]∑m∑n[f(m,n)−f]2×∑m∑n[g(m,n)−g¯]2, • where γij are the coefficients of the first image (IM1) and the second image (IM2), f is an average of the grayscale values ​​of all pixels in the first image (IM1), g is an average of the grayscale values ​​of all pixels in the second image (IM2), “m” and “n” are the x-coordinate and the y-coordinate of a single pixel in the first image (IM1) or the second image (IM2), respectively. [10] Positional deviation measuring method according to claim 9, characterized by that step (C) is implemented conditionally by the following: Displacement dimension=(distance−image size)×pixel size, • wherein the displacement amount is the offset of the second image (IM2) relative to the first image (IM1) in an axial direction (D1), the travel distance is the distance with respect to this axial direction (D1) between the actual position and the starting position of the second image (IM2) at which the coefficients have reached the maximum, the image size is the width of the second image (IM2) in this axial direction (D1) and the pixel size is the size of a single pixel.

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