System and method for measuring spatial posture of reference points

Abstract

The present invention provides a system and method for measuring the spatial posture of a reference point, comprising: a robot, an end effector, and a control module. The end effector includes a normal presser foot and a vision module. Under the control of the control module, the end effector measures the normal direction of a workpiece surface. The vision module identifies the center coordinates of a reference point on the workpiece, obtains the positional deviation between the reference point and the axis of the normal presser foot, and the robot drives the end effector to compensate for the positional deviation until the positional deviation between the reference point and the axis of the normal presser foot is within a preset threshold. The normal presser foot then extends and presses against the workpiece. The present invention solves the problem of aligning reference points on a workpiece, enabling accurate measurement of the spatial coordinates of the reference points and the surface normal direction.

Description

Technical Field

[0001] The present invention relates to the field of mechanical processing technology, and in particular to a system and method for measuring the spatial posture of a reference point. Background Art

[0002] In aviation automatic drilling and riveting applications, due to the pre-assembly error of the processing object, there is a deviation between the actual processing position and the theoretical position of the digital model. In order to improve the accuracy of the final drilling and riveting position, the equipment needs to have the ability to align the pre-installed reference holes or nails on the processing object.

[0003] The existing related technologies are measurement solutions using vision or laser line scanners, which focus on the position coordinate measurement of reference holes or nails, and lack attention to the actual normal vector of the reference point surface.

[0004] Patent publication number CN111912335B discloses a method for identifying reference holes on an aircraft surface suitable for a robotic drilling and riveting system. The method comprises the following steps: 1) setting a laser line scanner and calibrating its initial installation position and direction of motion; 2) using the laser line scanner to scan the aircraft surface where the reference hole is located, obtaining point cloud data of the reference hole and its surrounding area; 3) due to the smoothness of the aircraft surface, a threshold exists in the difference between the longitudinal coordinates of two adjacent points in the area near the reference hole in the point cloud data of the aircraft surface. When the longitudinal distance between the two adjacent points exceeds the threshold, it indicates that one of the points is within the reference hole. The point with the larger longitudinal coordinate height value is then taken as the boundary point of the reference hole; 4) fitting the point cloud data of the reference hole boundary to obtain the coordinates of the center of the reference hole. The disadvantages of this method are: the high cost of the line laser, the limited number of reference types that can be identified, and the poor integration of the automated drilling and riveting system. Summary of the Invention

[0005] In view of the defects in the prior art, the present invention provides a system and method for measuring the spatial posture of a reference point.

[0006] According to a system and method for measuring the spatial posture of a reference point provided by the present invention, the scheme is as follows:

[0007] In a first aspect, the present invention provides a spatial posture measurement system for a reference point, the system comprising: a robot, an end effector, and a control module, the end effector comprising a normal pressure foot and a vision module;

[0008] Under the control of the control module, the end effector measures the normal direction of the workpiece surface, the vision module identifies the center coordinates of the reference point on the workpiece, and obtains the position deviation between the reference point and the normal presser foot axis. The robot drives the end effector to move and compensate for the position deviation until the position deviation between the reference point and the normal presser foot axis is within a preset threshold range, and the normal presser foot extends to press the workpiece.

[0009] Preferably, the end effector further includes: a distance measuring unit, an end base plate, a guide rail and a cylinder; the end base plate is mounted on the robot, and the guide rail and the cylinder are both mounted on the end base plate; the normal pressure foot is mounted on the guide rail and driven by the cylinder, and the distance measuring unit measures the linear displacement of the normal pressure foot.

[0010] Preferably, the distance measuring unit comprises: a grating ruler, a reading head and a bracket thereof;

[0011] The grating ruler is installed on the end base plate in parallel with the guide rail, and the reading head and its bracket are fixedly connected to the normal pressure foot. When the normal pressure foot moves, the reading head and its bracket combine with the grating ruler to measure the extended position of the normal pressure foot.

[0012] Preferably, the vision module comprises: a light source, a lens and a camera, the light source provides lighting for visual measurement, and the lens focuses reflected light from the workpiece surface onto the camera.

[0013] Preferably, the system comprises a tool coordinate system and a base coordinate system;

[0014] The tool coordinate system is located at the front end face of the normal presser foot when the distance measuring unit reading is zero; the base coordinate system is located at the center of the robot base;

[0015] The pose of the reference point includes the spatial position coordinates of the hole and the surface normal direction. Through the feedback of the vision module and the sensor built into the normal pressure foot, the system aligns the center of the normal pressure foot with the center of the reference point and ensures that the axis of the normal pressure foot is perpendicular to the workpiece surface.

[0016] Preferably, aligning the normal presser foot center with the reference point center specifically includes:

[0017] Obtain theoretical coordinates through offline programming, and position the end effector to the reference point according to the theoretical coordinates;

[0018] After the workpiece is pressed by the normal presser foot, normal measurement and adjustment are performed to make the normal presser foot axis and the camera axis perpendicular to the workpiece surface;

[0019] Adjust the distance between the end effector and the workpiece so that the distance between the camera and the workpiece remains consistent with the calibration state;

[0020] The center coordinates of the reference point fed back by the vision module are used to perform closed-loop position adjustment in the tool coordinate system to achieve alignment between the normal presser foot axis and the center of the reference point.

[0021] Preferably, the normal measurement and adjustment are specifically as follows:

[0022] Step a: The normal direction of the workpiece surface is measured by the displacement sensor built into the normal presser foot, and the deflection angle between the normal direction and the presser foot axis is calculated;

[0023] Step b: If the deflection angle is less than the set threshold, stop adjusting; otherwise, proceed to the next step;

[0024] Step c: After the robot drives the end effector to deflect around the hole point and measure the deflection angle, execute step a.

[0025] Preferably, the closed-loop position adjustment is specifically as follows:

[0026] Step A: After the vision module measures the center coordinates of the reference point, it calculates the position deviation δy, δz between it and the normal presser foot axis in the tool coordinate system {TCS};

[0027] Step B: If both δy and δz are less than the set threshold, stop adjusting; otherwise, proceed to the next step;

[0028] Step C: The robot drives the end effector to move δy, δz in the tool coordinate system {TCS}, and after achieving one position compensation, execute step A.

[0029] Preferably, determining the spatial coordinates of the final reference point includes:

[0030] The spatial coordinates of the reference point are obtained using the following formula:

[0031]

[0032] Among them, c α 、c β 、c γ 、s α 、s β 、s γ Represent cos(α D ), cos(β D ), cos(γ D )、sin(α D ), sin(β D ), sin(γ D );x D 、y D 、z D , α D , β D , γD Represents the pose coordinates of the tool coordinate system {TCS} in the control system under the base coordinate system {BCS}; δ l Represents the extension of the pressure foot; δ y ,δ z Represents the residual deviation of the reference point measured by the camera after the reference point is aligned; i N 、j N and k N Represents the normal vector coordinates measured by the sensor built into the normal pressure foot after precise positioning is completed.

[0033] In a second aspect, the present invention provides a method for measuring the spatial posture of a reference point, the method comprising:

[0034] Step S1: Position the end effector to the reference point;

[0035] Step S2: Make the normal presser foot axis and the camera axis perpendicular to the workpiece surface;

[0036] Step S3: Keep the distance between the camera and the workpiece consistent with the calibration state;

[0037] Step S4: using the center coordinates of the reference point fed back by the vision module, performing closed-loop position adjustment in the tool coordinate system to achieve alignment between the normal presser foot axis and the center of the reference point;

[0038] Step S5: The normal presser foot extends and presses the workpiece, and finally obtains the position of the reference point.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] By combining the normal pressure foot on the end effector and the visual system, the problem of aligning the reference point on the workpiece is solved, and the precise measurement of the spatial coordinates of the reference point and the surface normal direction is achieved.

[0041] Other beneficial effects of the present invention will be explained through the introduction of specific technical features and technical solutions in the specific implementation methods. Those skilled in the art should be able to understand the beneficial technical effects brought about by the introduction of these technical features and technical solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0043] Figure 1 It is a schematic diagram of the structure of the present invention;

[0044] Figure 2 Schematic diagram of reference hole posture measurement.

[0045] Figure numerals: 1. end base plate; 2. grating scale; 3. reading head and its bracket; 4. guide rail; 5. cylinder; 6. normal pressure foot; 7. light source; 8. lens; 9. camera; 10. robot; 11. workpiece. DETAILED DESCRIPTION

[0046] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0047] An embodiment of the present invention provides a spatial posture measurement system for a reference point, which specifically includes: a robot, an end effector and a control module, wherein the end effector includes a normal pressure foot and a vision module.

[0048] Under the control of the control module, the end effector measures the normal direction of the workpiece surface, the vision module identifies the center coordinates of the reference point on the workpiece, and obtains the position deviation between the reference point and the axis of the normal presser foot. The robot drives the end effector to move and compensate for the position deviation until the position deviation between the reference point and the axis of the normal presser foot is within a preset threshold range, and the normal presser foot extends to press the workpiece. The reference point in this embodiment includes but is not limited to a reference hole or a nail.

[0049] Specifically, the end effector also includes: a distance measuring unit, an end base plate, a guide rail and a cylinder; the end base plate is installed on the robot, and the guide rail and the cylinder are both installed on the end base plate; the normal pressure foot is installed on the guide rail and driven by the cylinder, and the distance measuring unit measures the linear displacement of the normal pressure foot.

[0050] Among them, the distance measuring unit includes: a grating scale, a reading head and its bracket; the grating scale is installed on the end base plate parallel to the guide rail, and the reading head and its bracket are fixedly connected to the normal pressure foot. When the normal pressure foot moves, the reading head and its bracket combine with the grating scale to measure the extended position of the normal pressure foot.

[0051] Specifically, the system includes a tool coordinate system and a base coordinate system;

[0052] The tool coordinate system is located at the front end of the normal pressure foot when the distance measuring unit reading is zero; the base coordinate system is located at the center of the robot base;

[0053] The pose of the reference point includes the spatial position coordinates of the hole and the surface normal direction. Through the feedback of the vision module and the sensor built into the normal pressure foot, the system aligns the center of the normal pressure foot with the center of the reference point and ensures that the axis of the normal pressure foot is perpendicular to the workpiece surface.

[0054] The vision module includes: a light source, a lens, and a camera. The light source provides illumination for visual measurement, and the lens focuses the reflected light from the workpiece surface onto the camera.

[0055] Aligning the normal presser foot center with the reference point center specifically includes:

[0056] 1) Obtain theoretical coordinates through offline programming and position the end effector to the reference point according to the theoretical coordinates;

[0057] 2) After the workpiece is pressed by the normal pressure foot, normal measurement and adjustment are performed so that the axis of the normal pressure foot and the axis of the camera are perpendicular to the workpiece surface;

[0058] 3) Based on the workpiece distance obtained from the normal pressure foot and the grating ruler feedback, adjust the distance between the end effector and the workpiece so that the distance between the camera and the workpiece remains consistent with the calibration state; wherein the calibration state is to keep it constant;

[0059] 4) Using the center coordinates of the reference point fed back by the vision module, perform closed-loop position adjustment in the tool coordinate system to align the normal presser foot axis with the center of the reference point.

[0060] The normal measurement and adjustment are as follows:

[0061] Step a: The normal direction of the workpiece surface is measured by the displacement sensor built into the normal presser foot, and the deflection angle between the normal direction and the presser foot axis is calculated;

[0062] Step b: If the deflection angle is less than the set threshold, stop adjusting; otherwise, proceed to the next step;

[0063] Step c: The robot drives the end effector to deflect the hole point to measure the deflection angle, and then executes step a.

[0064] The center coordinates of the reference points fed back by the vision module are specifically as follows: In the vision module, the light source provides illumination for visual measurement, and the lens focuses the reflected light from the workpiece surface onto the photosensitive chip in the camera, ultimately obtaining a planar image of the workpiece surface. The characteristics of the reference points are identified through the machine vision algorithm, and their center coordinates are calculated.

[0065] The closed-loop position adjustment is as follows:

[0066] Step A: After the vision module measures the center coordinates of the reference point, it calculates the position deviation δy, δz between it and the normal presser foot axis in the tool coordinate system {TCS};

[0067] Step B: If both δy and δz are less than the set threshold, stop adjusting; otherwise, proceed to the next step;

[0068] Step C: The robot drives the end effector to move δy, δz in the tool coordinate system {TCS} to achieve a position compensation, and then execute step A.

[0069] The spatial coordinates of the reference point are obtained using the following formula:

[0070]

[0071] Among them, c α 、c β 、c γ 、s α 、s β 、s γ Represent cos(α D ), cos(β D ), cos(γ D )、sin(α D ), sin(β D ), sin(γ D );x D 、y D 、z D , α D , β D , γ D Represents the pose coordinates of the tool coordinate system {TCS} in the control system under the base coordinate system {BCS}; δ l Represents the extension of the pressure foot; δ y ,δ z Represents the residual deviation of the reference point measured by the camera after the reference point is aligned; i N 、j N and k N Represents the normal vector coordinates measured by the sensor built into the normal pressure foot after precise positioning is completed.

[0072] The present invention also provides a method for measuring the spatial posture of a reference point, which specifically includes:

[0073] Step S1: Position the end effector to the reference point;

[0074] Step S2: Make the normal presser foot axis and the camera axis perpendicular to the workpiece surface;

[0075] Step S3: Keep the distance between the camera and the workpiece consistent with the calibration state;

[0076] Step S4: Using the center coordinates of the reference point fed back by the vision module, a closed-loop position adjustment is performed in the tool coordinate system to align the normal presser foot axis with the center of the reference point;

[0077] Step S5: The normal presser foot extends and presses the workpiece, and finally obtains the position of the reference point.

[0078] Next, the present invention will be described in more detail.

[0079] The present invention provides a reference point spatial posture measurement system, which uses the normal pressure foot 6 and camera 9 on the end effector and the robot 10 system to realize the alignment of the spatial position and normal direction of the reference hole or reference pin. At the same time, combined with the coordinates of the robot 10 system, the spatial posture of the reference hole or reference pin can be accurately measured. Figure 1 As shown, the system specifically includes: a robot 10, an end base plate 1, a grating ruler 2, a reading head and its bracket 3, a guide rail 4, a cylinder 5, a normal pressure foot 6 and a vision module;

[0080] The end base plate 1 is mounted on the robot 10, and the guide rail 4, the cylinder 5 and the grating ruler 2 are all mounted on the end base plate 1;

[0081] The normal presser foot 6 is mounted on the guide rail 4 and driven by the cylinder 5. The reading head and its bracket 3 are fixed to the normal presser foot 6 and are used in conjunction with the grating ruler 2 to measure the extended position of the normal presser foot 6. The normal presser foot 6 has a built-in sensor that can measure the normal direction of the surface of the workpiece 11.

[0082] The light source 7, lens 8 and camera 9 constitute the vision module. The light source 7 is close to the normal pressure foot 6, and the lens 8 and camera 9 are connected to the light source 7 in sequence. The components installed on the end flange of the robot are collectively referred to as the end effector. The vision module is installed as a whole on the end effector, and the axis of the vision module is adjusted to be coaxial with the axis of the normal pressure foot 6 during measurement, so that the center coordinates of the reference hole or reference pin on the workpiece 11 can be identified. In the vision module, the light source can provide illumination for visual measurement, and the lens focuses the reflected light from the workpiece surface onto the photosensitive chip in the camera, ultimately obtaining a planar image of the workpiece surface. The characteristics of the reference point are identified through the machine vision algorithm, and the calculation of its center coordinates is then realized.

[0083] like Figure 2 As shown, the robot system tool coordinate system {TCS} is located at the front end of the normal pressure foot 6 when the grating ruler 2 reads zero, and the robot base coordinate system {BCS} is located at the center of the robot base. The position of the reference point includes the spatial position coordinates P of the hole M and the surface normal direction n M Through the feedback of the vision module and the sensor built into the normal presser foot, the system can align the center of the presser foot with the center of the reference point and ensure that the axis of the presser foot is perpendicular to the surface of the workpiece 11.

[0084] The specific steps for measuring the reference hole posture are as follows:

[0085] Step S1: Obtain theoretical coordinates through offline programming, and position the end effector to the reference point according to the theoretical coordinates;

[0086] Step S2: After the workpiece 11 is pressed by the presser foot, normal measurement and adjustment are performed so that the axis of the camera 9 is perpendicular to the surface of the workpiece 11. The process of normal measurement and adjustment is as follows:

[0087] (1) The normal direction of the workpiece surface is measured by the displacement sensor built into the normal presser foot, and the deflection angle between it and the axis of the presser foot is calculated.

[0088] (2) If the deflection angle is less than the set threshold, stop adjusting; otherwise, execute step (3).

[0089] (3) The robot drives the end effector to deflect the hole point and measure the deflection angle. Then, execute step (1).

[0090] Step S3: Based on the distance of the workpiece 11 obtained by the feedback from the pressure foot and the grating ruler 2, the distance between the end effector and the workpiece 11 is adjusted so that the distance between the camera 9 and the workpiece 11 remains constant when performing measurement;

[0091] Step S4: Using the center coordinates of the reference point fed back by the vision module, perform closed-loop position adjustment in the tool coordinate system to align the axis of the pressure foot with the center of the reference point. The center coordinates of the reference point fed back by the vision module are as follows:

[0092] In the vision module, the light source provides illumination for visual measurement, while the lens focuses the reflected light from the workpiece surface onto the photosensitive chip in the camera, ultimately producing a planar image of the workpiece surface. Machine vision algorithms identify the features of the fiducial points, and then calculate their center coordinates.

[0093] The closed-loop position adjustment steps are as follows:

[0094] (1) After the vision module measures the center coordinates of the reference point, it calculates the position deviation δy, δz between the center coordinates of the reference point and the axis of the pressure foot in the tool coordinate system {TCS}.

[0095] (2) If both δy and δz are less than the set threshold, stop adjusting; otherwise, execute step (3).

[0096] (3) The robot drives the end effector to move δy, δz in the tool coordinate system {TCS} to achieve a position compensation. After that, execute step (1).

[0097] Step S5: The pressure foot extends and presses the workpiece 11 to achieve precise positioning. The position of the reference point is obtained by the following formula:

[0098]

[0099] Among them, c α 、c β 、cγ 、s α 、s β 、s γ Represent cos(α D ), cos(β D ), cos(γ D )、sin(α D ), sin(β D ), sin(γ D );x D 、y D 、z D , α D , β D , γ D Represents the pose coordinates of the tool coordinate system {TCS} in the control system under the base coordinate system {BCS}; δ l Represents the extension of the pressure foot; δ y ,δ z represents the residual deviation of the reference point measured by the camera 9 after the reference point is aligned; i N 、j N and k N Represents the normal vector coordinates measured by the sensor built into the normal pressure foot after precise positioning is completed.

[0100] An embodiment of the present invention provides a system and method for measuring the spatial posture of a reference point. By combining a robot with a normal pressure foot on an end effector and a visual system, the problem of aligning the reference point on a workpiece is solved, and accurate measurement of the spatial coordinates of the reference point and the surface normal direction is achieved.

[0101] Those skilled in the art will appreciate that, in addition to implementing the system and its various devices, modules, and units provided by the present invention in purely computer-readable program code, it is entirely possible to implement the same functions of the system and its various devices, modules, and units provided by the present invention in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers by logically programming the method steps. Therefore, the system and its various devices, modules, and units provided by the present invention can be considered a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; the devices, modules, and units for implementing various functions can also be considered as both software modules implementing the method and structures within the hardware component.

[0102] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A spatial posture measurement system for a reference point, characterized in that: include: A robot, an end effector and a control module, wherein the end effector includes a normal pressure foot and a vision module; Under the control of the control module, the end effector measures the normal direction of the workpiece surface, the vision module identifies the center coordinates of the reference point on the workpiece, obtains the position deviation between the reference point and the axis of the normal presser foot, and the robot drives the end effector to move and compensate for the position deviation until the position deviation between the reference point and the axis of the normal presser foot is within a preset threshold range, and the normal presser foot is extended to press the workpiece; The vision module includes: a light source, a lens, and a camera. The light source provides illumination for visual measurement, and the lens focuses the reflected light from the workpiece surface onto the camera. The system includes a tool coordinate system and a base coordinate system; The tool coordinate system is located at the front end face of the normal presser foot when the distance measuring unit reading is zero; the base coordinate system is located at the center of the robot base; The position of the reference point includes the spatial position coordinates of the hole and the surface normal direction. Through the feedback of the vision module and the sensor built into the normal presser foot, the system aligns the center of the normal presser foot with the center of the reference point and ensures that the axis of the normal presser foot is perpendicular to the workpiece surface. Aligning the normal presser foot center with the reference point center specifically includes: Obtain theoretical coordinates through offline programming, and position the end effector to the reference point according to the theoretical coordinates; After the workpiece is pressed by the normal presser foot, normal measurement and adjustment are performed to make the normal presser foot axis and the camera axis perpendicular to the workpiece surface; Adjust the distance between the end effector and the workpiece so that the distance between the camera and the workpiece remains consistent with the calibration state; Using the center coordinates of the reference point fed back by the vision module, closed-loop position adjustment is performed in the tool coordinate system to achieve alignment between the normal presser foot axis and the center of the reference point; The normal measurement and adjustment are as follows: Step a: The normal direction of the workpiece surface is measured by the displacement sensor built into the normal presser foot, and the deflection angle between the normal direction and the presser foot axis is calculated; Step b: If the deflection angle is less than the set threshold, stop adjusting; otherwise, proceed to the next step; Step c: After the robot drives the end effector to deflect around the hole point and measure the deflection angle, execute step a; The closed-loop position adjustment is specifically as follows: Step A: After the vision module measures the center coordinates of the reference point, it calculates the position deviation δy, δz between it and the normal presser foot axis in the tool coordinate system {TCS}; Step B: If both δy and δz are less than the set threshold, stop adjusting; otherwise, proceed to the next step; Step C: The robot drives the end effector to move δy, δz in the tool coordinate system {TCS}, and after achieving one-time position compensation, execute step A; Determining the spatial coordinates of the final reference point includes: The spatial coordinates of the reference point are obtained using the following formula: Among them, c α 、c β 、c γ 、s α 、s β 、s γ Represents cos(α D ), cos(β D ), cos(γ D )、sin(α D ), sin(β D ), sin(γ D );x D 、y D 、z D , α D , β D , γ D Represents the pose coordinates of the tool coordinate system {TCS} in the control system under the base coordinate system {BCS}; δ l Represents the extension of the pressure foot; δ y ,δ z Represents the residual deviation of the reference point measured by the camera after the reference point is aligned; i N 、j N and k N Represents the normal vector coordinates measured by the sensor built into the normal pressure foot after precise positioning is completed.

2. The spatial posture measurement system of the reference point according to claim 1, characterized in that: The end effector also includes: a distance measuring unit, an end base plate, a guide rail and a cylinder; the end base plate is installed on the robot, and the guide rail and the cylinder are both installed on the end base plate; the normal pressure foot is installed on the guide rail and driven by the cylinder, and the distance measuring unit measures the linear displacement of the normal pressure foot.

3. The spatial posture measurement system of the reference point according to claim 2, characterized in that: The distance measuring unit includes: a grating ruler, a reading head and a bracket thereof; The grating ruler is installed on the end base plate in parallel with the guide rail, and the reading head and its bracket are fixedly connected to the normal pressure foot. When the normal pressure foot moves, the reading head and its bracket combine with the grating ruler to measure the extended position of the normal pressure foot.

4. A method for measuring the spatial posture of a reference point, based on the spatial posture measurement system of a reference point according to any one of claims 1 to 3, characterized in that: include: Step S1: Position the end effector to the reference point; Step S2: Make the normal presser foot axis and the camera axis perpendicular to the workpiece surface; Step S3: Keep the distance between the camera and the workpiece consistent with the calibration state; Step S4: using the center coordinates of the reference point fed back by the vision module, performing closed-loop position adjustment in the tool coordinate system to achieve alignment between the normal presser foot axis and the center of the reference point; Step S5: The normal presser foot extends and presses the workpiece, and finally obtains the position of the reference point.

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