A rotation center calibration method, a pose adjustment mechanism and a wafer testing device

Abstract

The present application relates to a kind of rotation center calibration method, pose adjustment mechanism and wafer testing device, method includes controlling any rotation axis to move at least twice along corresponding target axis, any rotation axis and corresponding target axis are perpendicular to each other;Corresponding to the rotation axis after any one movement, the rotation trajectory corresponding to target point is obtained by the end tool rotating around the rotation axis;According to the radius of rotation trajectory, determine the target offset of target rotation center compared with initial rotation center in target axis direction;Based on all target offsets of all rotation axes, calibrate the target rotation center of multi-axis motion mechanism, so that target point and target rotation center coincide.The present application can simplify the calibration model by individually calibrating each offset, and reduce the three-dimensional space to two-dimensional plane, and then calibrate, and by adjusting the position of rotation axis on target axis to obtain multiple sets of rotation trajectory data during calibration process, accurate calibration result is obtained by approximation fitting.

Description

Technical Field

[0001] This invention relates to the field of robot calibration technology, and in particular to a rotation center calibration method, a pose adjustment mechanism, and a wafer testing device. Background Technology

[0002] Silicon photonics wafer testing equipment is primarily used for performance testing of silicon photonics chips formed from silicon photonics wafers. During actual testing, a six-axis motion mechanism adjusts the orientation of its end-effector (optical fiber or fiber array) to align and couple with the optical waveguide on the chip. To reduce optical power loss during silicon photonics wafer testing, edge coupling can be used to improve testing accuracy.

[0003] When using edge coupling, to prevent wafer damage due to large end-tool swing, the rotation center needs to be placed at the target point of the end-tool in the six-axis motion mechanism. This ensures that the target point of the end-tool does not shift in the X, Y, or Z directions during rotation. Although the theoretical rotation center can be calculated based on the structural dimensions of the six-axis motion mechanism and the end-tool, the actual rotation center differs from the theoretical rotation center due to installation errors and structural offsets during actual installation. Therefore, rotation center calibration is necessary. Summary of the Invention

[0004] To address at least one of the aforementioned technical problems, this invention proposes a rotation center calibration method, a pose adjustment mechanism, and a wafer testing device.

[0005] According to some embodiments of the present invention, a method for calibrating a rotation center is provided, applied to a multi-axis motion mechanism having an initial rotation center, the multi-axis motion mechanism being connected to an end-effector, and the end-effector having a target point; the method includes: controlling any rotation axis of the multi-axis motion mechanism to move at least twice along a corresponding target axis, wherein any rotation axis is perpendicular to the corresponding target axis; obtaining a rotation trajectory corresponding to the target point obtained by the end-effector rotating around the rotation axis after any one movement of the rotation axis; determining a target offset of the target rotation center corresponding to the target point relative to the initial rotation center of the multi-axis motion mechanism in the direction of the target axis based on the radius of the rotation trajectory corresponding to the rotation trajectory; and calibrating the target rotation center of the multi-axis motion mechanism based on all target offsets corresponding to all rotation axes of the multi-axis motion mechanism, so that the target point coincides with the target rotation center.

[0006] In some possible implementations, obtaining the rotation trajectory of the target point includes: acquiring an image of the target point captured by a camera along the axial direction of the rotation axis; determining the pixel coordinates corresponding to the target point based on the position of the target point in the image; and obtaining the rotation trajectory corresponding to the target point based on a plurality of the pixel coordinates.

[0007] In some possible implementations, controlling any rotation axis of the multi-axis motion mechanism to move at least twice along a corresponding target axis includes controlling the rotation axis to move stepwise along the target axis direction; controlling the multi-axis motion mechanism to rotate about the rotation axis includes controlling the multi-axis motion mechanism to rotate stepwise about the rotation axis.

[0008] In some possible implementations, determining the target offset of the target rotation center corresponding to the target point relative to the initial rotation center of the multi-axis motion mechanism in the target axis direction, based on the rotation trajectory radius corresponding to the rotation trajectory, includes: determining the correspondence between the rotation trajectory radius and the position of the rotation axis on the target axis based on the dispersion value of the rotation trajectory; and determining the position of the rotation axis on the target axis when the rotation trajectory radius is minimized as the target offset of the target rotation center corresponding to the target point relative to the initial rotation center of the multi-axis motion mechanism in the target axis direction.

[0009] In some possible implementations, determining the correspondence between the radius of the rotation trajectory and the position of the rotation axis on the target axis based on the discreteness value of the rotation trajectory includes: determining the initial pixel coordinates of the target point on the image as reference coordinates after each movement of the rotation axis; obtaining the sum of the distances between each pixel coordinate of the target point in the rotation trajectory and the reference coordinates; establishing a fitting polynomial based on the sum and the position of the rotation axis on the target axis, and determining the fitting polynomial as the correspondence between the radius of the rotation trajectory and the position of the rotation axis on the target axis.

[0010] In some possible implementations, determining the position of the rotation axis on the target axis at which the rotation trajectory radius is minimized as the target rotation center of the target point relative to the initial rotation center of the multi-axis motion mechanism in the target axis direction includes: determining the point with the smallest sum based on the fitted polynomial, and determining the position of the rotation axis on the target axis corresponding to the point with the smallest sum as the target rotation center of the target point relative to the initial rotation center of the multi-axis motion mechanism in the target axis direction.

[0011] In some possible implementations, after determining the target rotation center corresponding to the target point relative to the initial rotation center of the multi-axis motion mechanism in the target axis direction based on the rotation trajectory radius corresponding to the rotation trajectory, the method further includes: controlling different rotation axes to move along the target axis, and determining a new target rotation center relative to the initial rotation center in the target axis direction; correcting the previously determined target offset based on the newly determined target offset.

[0012] In some possible implementations, the multi-axis motion mechanism is a six-axis motion mechanism, which includes an X-axis, Y-axis, Z-axis, U-axis, V-axis, and W-axis. The X-axis, Y-axis, and Z-axis are linear motion axes, and the U-axis, V-axis, and W-axis are rotational axes. The method includes: controlling the W-axis to move along the X-axis; after each movement of the W-axis, controlling the six-axis motion mechanism to rotate around the W-axis; and determining the X-axis offset of the target rotation center relative to the initial rotation center based on the change in the rotation trajectory of the target point; controlling the W-axis to move along the Y-axis; after each movement of the W-axis, controlling the six-axis motion mechanism to rotate around the W-axis; and determining the Y-axis offset of the target rotation center relative to the initial rotation center based on the change in the rotation trajectory of the target point; and controlling the U-axis... The six-axis motion mechanism moves along the Z-axis, and after each movement along the U-axis, it is controlled to rotate around the U-axis. Based on the change in the rotation trajectory of the target point, a first offset of the target rotation center relative to the initial rotation center in the Z-axis direction is determined. The V-axis moves along the Z-axis, and after each movement along the V-axis, the six-axis motion mechanism is controlled to rotate around the V-axis. Based on the change in the rotation trajectory of the target point, a second offset of the target rotation center relative to the initial rotation center in the Z-axis direction is determined. Based on the first offset and the second offset, the Z-axis offset of the target rotation center relative to the initial rotation center in the Z-axis direction is determined. Based on the X-axis offset, the Y-axis offset, and the Z-axis offset, the target rotation center of the six-axis motion mechanism is calibrated so that the target point coincides with the target rotation center.

[0013] In some possible implementations, before controlling any of the rotating axes of the multi-axis motion mechanism to move at least twice along the corresponding target axis, the method further includes: determining the theoretical coordinates of the target point based on the dimensional parameters of the multi-axis motion mechanism and the end tool; and determining the range of step movement of any of the rotating axes on the target axis based on the theoretical coordinates.

[0014] According to some embodiments of the present invention, a fiber optic array pose adjustment mechanism is provided, including a six-axis motion mechanism, a camera, and a controller. The end of the six-axis motion mechanism is equipped with a fiber optic array. The camera is used to acquire image data of the fiber optic array. The controller is used to execute a rotation center calibration method as described in the above embodiments so that the rotation center of the six-axis motion mechanism passes through the end face center of the fiber optic array.

[0015] According to some embodiments of the present invention, a wafer testing device is provided, including a fiber array pose adjustment mechanism as described in the above embodiments.

[0016] The implementation of this invention has the following beneficial effects:

[0017] The rotation center calibration method of the present invention calibrates each rotation center offset separately, reducing the three-dimensional spatial quantity to a two-dimensional plane before calibration, which simplifies the calibration model. Furthermore, during the calibration process, multiple sets of rotation trajectory data are obtained by adjusting the position of the rotation axis on the target axis, and accurate calibration results are obtained by approximation fitting.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit the invention.

[0019] Other features and aspects of the invention will become clear from the following detailed description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0020] To more clearly illustrate the technical solutions and advantages in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart illustrating the steps of a rotation center calibration method according to an embodiment of the present invention is shown.

[0022] Figure 2 A coordinate system diagram of a six-axis motion mechanism according to an embodiment of the present invention is shown;

[0023] Figure 3 A schematic diagram showing the X-axis offset and Z-axis offset of the rotation center according to an embodiment of the present invention;

[0024] Figure 4 A schematic diagram showing the Y-axis offset of the rotation center according to an embodiment of the present invention is shown;

[0025] Figure 5 A diagram illustrating the definition of the sum value D according to an embodiment of the present invention is shown;

[0026] Figure 6 This diagram illustrates the RD relationship curves according to an embodiment of the present invention.

[0027] Figure 7 A structural diagram of a fiber optic array pose adjustment mechanism according to an embodiment of the present invention is shown.

[0028] Figure 8 A structural diagram of a wafer testing apparatus according to an embodiment of the present invention is shown. Detailed Implementation

[0029] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or server that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0031] Various exemplary embodiments, features, and aspects of the present invention will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0032] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0033] In this document, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Furthermore, the term "at least one" in this document means any combination of at least two of any one or more elements. For example, including at least one of A, B, and C can mean including any one or more elements selected from the set consisting of A, B, and C.

[0034] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art will understand that the present invention can be practiced without certain specific details. In some instances, methods, means, elements, and circuits well known to those skilled in the art have not been described in detail in order to highlight the spirit of the invention.

[0035] Please refer to Figures 1 to 7 , Figure 1 The flowchart illustrates a rotation center calibration method according to an embodiment of the present invention. Figure 2 A coordinate system diagram of a six-axis motion mechanism according to an embodiment of the present invention is shown. Figure 3 This diagram illustrates the X-axis offset and Z-axis offset of the rotation center according to an embodiment of the present invention. Figure 4 A schematic diagram showing the Y-axis offset of the rotation center according to an embodiment of the present invention is shown. Figure 5 A diagram illustrating the definition of the sum value D according to an embodiment of the present invention is shown. Figure 6 The diagram illustrates the RD relationship curve according to an embodiment of the present invention. Figure 7 This diagram illustrates a structural diagram of a fiber optic array pose adjustment mechanism according to an embodiment of the present invention. Figure 8 A structural diagram of a wafer testing apparatus according to an embodiment of the present invention is shown.

[0036] To facilitate understanding of the rotation center calibration method of this invention, the reasons and principles for the rotation center calibration of a six-axis motion mechanism are first introduced. In some application scenarios, to ensure that the target point of the end-effector does not shift in the X, Y, and Z directions during the rotational motion of the six-axis motion mechanism, it is necessary to adjust the rotation center of the six-axis motion mechanism to the target point of the end-effector. For example, in silicon photonics wafer testing scenarios, the optical fiber or fiber array mounted at the end of the six-axis motion mechanism serves as the end-effector. To prevent interference between the optical fiber or fiber array and another adjacent bare chip during edge coupling testing of any bare chip under test on the wafer under test when adjusting its pose angle, the rotation center of the six-axis motion mechanism needs to be adjusted to the center point of the tip of the optical fiber or the tip surface of the fiber array. This ensures that the center point of the tip of the optical fiber or the tip surface of the fiber array remains unchanged during the pose adjustment of the six-axis motion mechanism. That is, the target point applied in silicon photonics wafer testing scenarios refers to the center point of the tip of the optical fiber or the tip surface of the fiber array.

[0037] The six axes of the six-axis motion mechanism are the U-axis, V-axis, W-axis, X-axis, Y-axis, and Z-axis. The three linear motion axes are the X-axis, Y-axis, and Z-axis, and the three rotary axes are the U-axis, V-axis, and W-axis. The U-axis rotates around the X-axis, the V-axis around the Y-axis, and the W-axis around the Z-axis. To adjust the center of rotation to the target point of the end-effector of the six-axis motion mechanism, the U-axis, V-axis, and W-axis need to be moved until all three rotary axes pass through the target point of the end-effector. Initially, the three rotary axes of the six-axis motion mechanism pass through the initial origin O0, and the initial positions of the three rotary axes are... Figure 2 After the rotation center is calibrated, the U0, V0, and W0 axes pass through the new origin O1. The positions of the calibrated rotation axes are then determined. Figure 2 The rotation axes are U1, V1, and W1. The movement of the rotation axes is determined by the vector (R, S, T), where (R, S, T) = (X1, Y1, Z1) - (X0, Y0, Z0), where (X0, Y0, Z0) are the coordinates of the origin O0 of the rotation axes at the initial position, (X1, Y1, Z1) are the coordinates O1 of the target point of the end tool, and R represents the X-axis offset of the rotation center. Figure 3 The distance in the X direction between midpoint O1 and point O0, where S represents the offset in the Y direction of the rotation center, i.e. Figure 4 The distance in the Y direction between midpoint O1 and point O0, where T represents the Z-direction offset of the rotation center, i.e. Figure 3 The distance in the Z direction between the midpoint O1 and the point O0 is such that the process of calibrating the center of rotation is the process of determining the vector (R, S, T).

[0038] This invention provides a method for calibrating the center of rotation. This method is applied to multi-axis motion mechanisms, which have an initial center of rotation, such as... Figure 2 Point O0 in the diagram. The multi-axis motion mechanism can be a six-axis motion mechanism or other types of motion mechanisms. For ease of understanding, this embodiment of the invention uses a six-axis motion mechanism as an example, where the six-axis motion mechanism can be a series six-axis motion mechanism or a parallel six-axis motion mechanism; this embodiment does not impose any limitations on this. The six-axis motion mechanism is connected to an end-effector, which has a target point. The rotation center calibration method is used to determine the offset of each rotation center when each rotation axis passes through the target point. Specifically, the method includes:

[0039] Step S101: Control any rotating axis of the multi-axis motion mechanism to move at least twice along the corresponding target axis, wherein any rotating axis is perpendicular to the corresponding target axis.

[0040] In a six-axis motion mechanism, the target axis is one of the X-axis, Y-axis, and Z-axis, and the rotation axis is one of the U-axis, V-axis, and W-axis.

[0041] Step S102: Obtain the rotation trajectory corresponding to the target point obtained by rotating the end tool around the rotation axis after any movement corresponding to the rotation axis.

[0042] Step S103: Based on the radius of the rotation trajectory corresponding to the rotation trajectory, determine the target offset of the target rotation center corresponding to the target point relative to the initial rotation center of the multi-axis motion mechanism in the target axis direction.

[0043] Step S104: Based on all target offsets corresponding to all rotation axes of the multi-axis motion mechanism, calibrate the target rotation center of the multi-axis motion mechanism so that the target point coincides with the target rotation center.

[0044] In a specific implementation, the process of determining the X-axis offset is used as an example to explain steps S101 to S103 above. First, the X-axis offset is the distance between the target rotation center and the initial rotation center in the X-axis direction, so the corresponding target axis is the X-axis. At this time, the rotation axis can be either the V-axis or the W-axis. When the W-axis is used as the rotation axis, the six-axis motion mechanism is controlled to rotate around the W-axis, that is, the end tool rotates around the W-axis. The target point has a rotation trajectory, and the plane on which the rotation trajectory is located is parallel to the XOY plane. The radius of the rotation trajectory is related to the X-axis offset and the Y-axis offset. Keeping the position of the W-axis on the Y-axis unchanged, by controlling the W-axis to move along the X-axis, if the distance between the target point and the W-axis is greater, the radius of the rotation trajectory of the target point is larger, and vice versa. If the distance between the target point and the W-axis is smaller, the radius of the rotation trajectory of the target point is smaller. When the radius of the rotation trajectory of the target point reaches the minimum value, the X-axis offset can be determined based on the difference between the current position and the initial position of the W-axis on the X-axis.

[0045] Based on the above, the rotation center calibration method of the present invention adopts a dimensionality reduction approach, reducing the three-dimensional spatial coordinate parameters to two-dimensional planar coordinate parameters, thereby determining the offset of the rotation center in a single target axis direction. The determination process employs an approximation fitting method, which continuously adjusts the position of the rotation axis on the target axis and obtains the corresponding rotation trajectory radius to gradually approximate the actual target offset. Compared with the traditional circle fitting method, the approximation fitting method uses more data, which can reduce data errors and improve the accuracy of the target offset, thereby improving the accuracy of the target rotation center calibration.

[0046] In this embodiment, after determining the target offset in one target axis direction, a new target axis needs to be selected, and steps S101 to S103 are executed again to determine the target offset in the new target axis direction. The number of iterations depends on the number of moving axes of the multi-axis motion mechanism. For example, a four-axis motion mechanism needs to execute steps S101 to S103 at least twice to complete the rotation center calibration, while a six-axis motion mechanism needs to execute steps S101 to S103 at least three times to complete the rotation center calibration.

[0047] In the above embodiments, for any target axis, there are two possible choices for the rotation axis, and the target offset corresponding to the target axis can be determined based on either rotation axis. For example, in the X-axis offset determination process described above, the target axis is the X-axis, and the rotation axis can be either the V-axis or the W-axis. The X-axis offset can be determined based on either the V-axis or the W-axis. That is, when the rotation axis is configured as the V-axis, one X-axis offset can be obtained, and when the rotation axis is configured as the W-axis, another X-axis offset can be obtained. In practical applications, due to factors such as equipment errors and measurement errors, the target offset determined based on different rotation axes may be different.

[0048] In a further embodiment, target offsets determined by different rotation axes can be used for mutual verification and correction, thereby reducing errors and improving the accuracy of the rotation center offset. Specifically, after step S103 above, the method further includes: controlling different rotation axes to move along the target axis, and determining the target offset of the new target rotation center relative to the initial rotation center in the target axis direction; correcting the previously determined target offset based on the newly determined target offset. Based on the above steps, by changing the rotation axis and performing cyclic operations, the cumulative error and measurement error can be reduced, and the accuracy of calibration can be improved. In some possible cases, the offset in each movement axis direction of the six-axis motion mechanism is verified, then the entire calibration process needs to be executed six times in a loop from step S101 to step S103.

[0049] In this embodiment, the specific method of the above correction is not limited. For example, the average value of the two target offsets determined based on different rotation axes can be used as the final target offset; or, the difference between the new target offset obtained by changing the rotation axis and the previously obtained target offset can be calculated. If the difference is less than or equal to the preset error range, no processing is performed, and if the difference is greater than the error range, error compensation is performed.

[0050] In some embodiments, the offsets in the direction of the moving axis can be determined sequentially to achieve a balance between calibration speed and calibration accuracy. Specifically, taking a six-axis motion mechanism as an example, the rotation center calibration method further includes:

[0051] Control the W-axis to move along the X-axis at least twice. After each movement of the W-axis, control the multi-axis motion mechanism to rotate around the W-axis and obtain the rotation trajectory of the target point. Based on the change of the rotation trajectory of the target point, determine the X-direction offset of the target rotation center relative to the initial rotation center in the X-axis direction.

[0052] Control the W-axis to move along the Y-axis at least twice. After each movement of the W-axis, control the multi-axis motion mechanism to rotate around the W-axis and obtain the rotation trajectory of the target point. Based on the change of the rotation trajectory of the target point, determine the Y-direction offset of the target rotation center relative to the initial rotation center in the Y-axis direction.

[0053] Control the U-axis to move along the Z-axis at least twice. After each movement of the U-axis, control the multi-axis motion mechanism to rotate around the U-axis and obtain the rotation trajectory of the target point. Based on the change of the rotation trajectory of the target point, determine the first offset of the target rotation center relative to the initial rotation center in the Z-axis direction.

[0054] Control the V-axis to move along the Z-axis at least twice. After each movement of the V-axis, control the multi-axis motion mechanism to rotate around the V-axis and obtain the rotation trajectory of the target point. Based on the change of the rotation trajectory of the target point, determine the second offset of the target rotation center in the Z-axis direction relative to the initial rotation center.

[0055] Based on the first offset and the second offset, determine the Z-axis offset of the target rotation center relative to the initial rotation center.

[0056] Based on the X-axis offset, Y-axis offset, and Z-axis offset, the target rotation center of the six-axis motion mechanism is calibrated so that the target point coincides with the target rotation center.

[0057] When the correction method uses mean correction, the above steps can be expressed as follows: First, select the X-axis as the target axis and the W-axis as the rotation axis to determine the X-axis offset; then select the Y-axis as the target axis and the W-axis as the rotation axis to determine the Y-axis offset; subsequently, select the Z-axis as the target axis and the U-axis as the rotation axis to determine the first offset; again, select the Z-axis as the target axis and the V-axis as the rotation axis to determine the second offset; finally, the average of the first offset and the second offset is determined as the Z-axis offset.

[0058] Based on the above steps, when determining the X-axis and Y-axis offsets, the W-axis is selected as the rotation axis, i.e., the rotation axis remains unchanged, and no additional verification steps are performed on the obtained X-axis and Y-axis offsets. However, when determining the Z-axis offset, the U-axis and V-axis are selected successively as rotation axes, and the average of the Z-axis offsets determined under different rotation axes is used as the final Z-axis offset. This eliminates the accumulation error that may occur during the determination of the X-axis and Y-axis offsets, thereby improving the accuracy of the rotation center calibration. Furthermore, the entire calibration process is executed four times, which reduces the number of iterations compared to the six iterations of full verification calibration, thus improving calibration efficiency.

[0059] In this embodiment of the invention, the rotation trajectory of the target point is obtained based on a camera. The camera can capture images of the target point from the X, Y and Z directions respectively, and obtain the corresponding X-direction image, Y-direction image and Z-direction image.

[0060] As can be seen from the above, the rotation center calibration method of the present invention adopts a dimensionality reduction approach. When the six-axis motion mechanism rotates around the rotation axis, the position of the rotation axis in its axial direction does not affect the radius of the rotation trajectory. Furthermore, the plane containing the rotation trajectory is perpendicular to the rotation axis. Since the rotation axis is perpendicular to the two-dimensional coordinate plane, the projection data of the rotation trajectory on the two-dimensional coordinate plane (that is, the image data taken along the axial direction of the rotation axis) can be obtained, and the coordinate data of the rotation trajectory on the projection plane can be determined, so that the radius of the rotation trajectory can be accurately determined subsequently.

[0061] Specifically, obtaining the rotation trajectory of the target point in step S102 includes: acquiring an image of the target point captured by the camera along the axis of rotation; determining the pixel coordinates corresponding to the target point based on the position of the target point in the image; and obtaining the rotation trajectory corresponding to the target point based on the multiple pixel coordinates.

[0062] In one specific implementation, the target offset is the X-axis offset, the target axis is the X-axis, and the rotation axis is the W-axis. When the six-axis motion mechanism rotates around the W-axis, the plane containing the rotation trajectory of the target point is parallel to the XOY plane. The XOY plane contains the X-axis and is perpendicular to the W-axis. At this time, the camera captures the target point along the W-axis axis, and the image is the Z-axis image of the target point. Based on the Z-axis image, the pixel coordinates of the target point can be obtained, and then the radius of the rotation trajectory can be determined.

[0063] In this embodiment, the rotation trajectory of the target point should include the coordinates of multiple pixels. For example, when the rotation axis is the W-axis and the image plane is parallel to the XOY plane, the pixel coordinates can be expressed as (Xd-α, Yd-α), where d is the position of the rotation axis on the target axis and α is the angle of rotation of the rotation axis. The projection coordinates of the rotation trajectory on the target plane are then expressed as a set of point coordinates (Xd-α, Yd-α), i.e., {(Xd-α, Yd-α)}.

[0064] The rotation center calibration method in this embodiment involves moving the rotation axis to the target axis, controlling the six-axis motion mechanism to rotate around the rotation axis after each movement, and acquiring multiple pixel coordinates to form a set of rotation trajectory data. This process of moving the rotation axis and rotating around the rotation axis is repeated to acquire multiple sets of rotation trajectory data, continuously approximating the minimum value of the rotation trajectory radius, ultimately yielding the target offset. It should be understood that when controlling the rotation axis to move along the target axis, reducing the distance of each movement and increasing the number of movements improves the accuracy of the calibration results; similarly, when controlling the six-axis motion mechanism to rotate around the rotation axis, increasing the number of projection points improves the accuracy of the rotation trajectory radius, thus contributing to the overall accuracy of the calibration results.

[0065] In some embodiments, both the movement of the rotation axis and the rotation around the rotation axis are controlled by stepping. That is, controlling any rotation axis of the multi-axis motion mechanism to move at least twice along the corresponding target axis includes controlling the rotation axis to move step by step along the target axis direction; controlling the multi-axis motion mechanism to rotate around the rotation axis includes controlling the multi-axis motion mechanism to rotate step by step around the rotation axis. Based on stepping control of movement and rotation, the data volume alignment can be guaranteed when determining the offset of each rotation center. For example, if there are N positions of the rotation axis on the target axis, that is, N rotations around the rotation axis, and there is data for N rotation trajectories, and the angle range of rotation around the rotation axis is A° to B°, with an angle step of stepAngle°, then each rotation trajectory contains m projection point coordinates, m = (BA) / stepAngle + 1.

[0066] In a further embodiment, before controlling any rotary axis of the multi-axis motion mechanism to move at least twice along the corresponding target axis, the method further includes: determining the theoretical coordinates of the target point based on the dimensional parameters of the multi-axis motion mechanism and the end effector; and determining the range of step movement of any rotary axis on the target axis based on the theoretical coordinates. Based on the above steps, after determining the theoretical coordinates, the range of step movement of the rotary axis can be set near the theoretical coordinates. Since the theoretical coordinates of the target point calculated based on the dimensional parameters are close to the actual coordinates of the target point, rapid calibration can be achieved by approximating and fitting near the theoretical coordinates.

[0067] In one specific implementation, approximation fitting can be performed within a symmetrical range on both sides of the theoretical coordinates. Specifically, if the theoretical coordinates of the target point are (Xs, Ys, Zs), and the step size of the rotation axis moving along the target axis is stepL, when the W-axis is the rotation axis and the X-axis is the target axis, then the range of variation of the W-axis on the X-axis is: Xs-stepL*N / 2 to Xs+stepL*N / 2.

[0068] Similarly, a symmetrical angle range can also be used when controlling a six-axis motion mechanism to rotate around a rotation axis. In some embodiments, the rotation angle range of the six-axis motion mechanism is symmetrical about 0°, that is, the rotation angle range around the rotation axis is -C° to C°. Based on the above configuration, the rotation angle range of the six-axis motion mechanism is fixed, the initial rotation angle of the six-axis motion mechanism is -C°, and the six-axis motion mechanism rotates step by step to C°. In some possible cases, the initial rotation angle of the six-axis motion mechanism can also be set to 0°. The six-axis motion mechanism first rotates clockwise from 0° to C°, then automatically resets to zero, and then rotates counterclockwise from 0° to -C°. After obtaining the coordinates of all pixels, the six-axis motion mechanism automatically resets to zero. By setting a symmetrical angle range, the coordinates of the projected points contained in the rotation trajectory are symmetrical about the 0° line. The symmetrical pixel coordinates can be used for mutual verification, which helps to detect and remove bad data in a timely manner. In addition, after the rotation axis moves to different positions on the target axis, the rotation axis always starts to rotate from 0° and the rotation angle range and angle step are consistent. By comparing the pixel coordinates of the same angle in different rotation trajectories, the size of the rotation trajectory radius can also be intuitively determined.

[0069] In some embodiments, step S103 may further include: based on the correspondence between the rotation trajectory radius and the position of the rotation axis on the target axis, determining the position of the rotation axis on the target axis where the rotation trajectory radius is smallest as the target rotation center of the target point relative to the initial rotation center of the multi-axis motion mechanism in the target axis direction.

[0070] The embodiments of the present invention do not limit the method of obtaining the correspondence between the radius of the rotation trajectory and the position of the rotation axis on the target axis in the above steps. That is, the radius of the rotation trajectory can be directly obtained based on the distance between the pixel point in the rotation trajectory and the origin of the image coordinates and a correspondence with the position of the rotation axis can be established. Alternatively, the radius of the rotation trajectory can be obtained by circle fitting and a correspondence with the position of the rotation axis can be established. Or other methods can be used to establish the correspondence between the radius of the rotation trajectory and the position of the rotation axis.

[0071] In some embodiments, the correspondence between the radius of the rotation trajectory and the position of the rotation axis on the target axis can be determined based on the discreteness value of the rotation trajectory; that is, the correspondence between the radius of the rotation trajectory and the position of the rotation axis can be established by calculating the discreteness of the projection points. Specifically, the method includes:

[0072] S201. After each movement of the rotation axis, the initial pixel coordinates of the target point on the image are determined as the reference coordinates.

[0073] S202. Obtain the sum of the distances between the coordinates of each pixel point corresponding to the target point and the reference coordinates in the rotation trajectory.

[0074] S203. Based on the sum and the position of the rotation axis on the target axis, establish a fitting polynomial and determine the fitting polynomial as the correspondence between the radius of the rotation trajectory and the position of the rotation axis on the target axis.

[0075] In one specific implementation, the rotation axis is the W-axis, the target axis is the X-axis, and the rotation angle range of the six-axis motion mechanism is symmetrical about 0°. After each movement of the rotation axis, the initial pixel coordinates of the target point on the image are the coordinates on the 0° line. The reference coordinates are designated as (x0, y0), and the pixel coordinates of the target point's rotation trajectory are (xi, yi), i = 1, 2, ..., m. The distance between the pixel coordinates and the reference coordinates is di. The sum of the distances between the pixel coordinates and the reference coordinates of the target point's rotation trajectory is D = d1 + d2 + ... + dm. This sum D represents the dispersion of the rotation trajectory. The position of the rotation axis on the target axis is R (i.e., the distance between the rotation axis and the initial rotation center on the target axis is R). After each movement of the rotation axis, the value of R changes, corresponding to a value D, thus forming a point set P(Ri, Di). Polynomial fitting is performed on the point set, and the resulting fitting polynomial D(R) represents the correspondence between the radius of the rotation trajectory and the position of the rotation axis on the target axis. In some preferred embodiments, the above polynomial fitting can be parabolic fitting.

[0076] The reason for establishing a correspondence between the pixel coordinates in the rotation trajectory and the reference coordinates in steps S201-S203 is that, in practical applications, there may be situations where the rotation angle range of the rotation axis is small, such as approximately 2°. In such cases, if a circle fitting method is used, the calculated radius of the rotation trajectory will have a large error, ultimately affecting the accuracy of the calibration results. Therefore, by calculating the distance and sum of each pixel coordinate and the reference coordinates, i.e., calculating the discreteness of each pixel coordinate in the rotation trajectory, the degree of deviation from the rotation center can be equivalently represented, thereby reducing the error and improving the accuracy of the calibration results.

[0077] Specifically, assuming the rotation radius is r, the rotation angle is θ, and the reference coordinates are the initial projection point coordinates on the 0° line (x0=r, y0=0), the coordinates of the projection point in the rotation trajectory are... Then there is

[0078]

[0079] Based on the above formula, when the rotation angle is consistent each time, the distance d between the pixel coordinates and the reference coordinates is only related to the radius r, and d is proportional to r. Furthermore, since the six-axis motion mechanism rotates stepwise around the rotation axis with consistent angular steps, the larger the radius of the rotation trajectory, the greater the dispersion of the projected point coordinates. Consequently, the sum of the distances D between the pixel coordinates and the reference coordinates in the corresponding rotation trajectory also increases. Therefore, D can be used to equivalently represent the trend of the radius change of the rotation trajectory.

[0080] The reason for using polynomial fitting in this embodiment is that when the rotation axis moves along the target axis, it first approaches the rotation center and then moves away from the rotation center. Correspondingly, the radius r of the rotation trajectory first decreases to a minimum value and then increases. The D value is positively correlated with the radius r of the rotation trajectory. Similarly, the D value also first decreases to a minimum value and then increases. By establishing polynomial fitting for the D value, the position of the rotation axis on the target axis when the D value is minimum can be accurately determined, thereby determining the target offset.

[0081] Based on the above, in a further embodiment, based on the above determination of the correspondence between the fitting polynomial and the position of the rotation axis on the target axis, the method for determining the target offset includes: determining the point with the minimum sum based on the fitting polynomial, and determining the position of the rotation axis corresponding to the point with the minimum sum on the target axis as the target offset of the target rotation center of the target point relative to the initial rotation center of the multi-axis motion mechanism in the target axis direction. Specifically, the R value obtained when D(R) is minimized is the target offset.

[0082] This invention also provides a fiber optic array pose adjustment mechanism, which is applied in wafer testing. The mechanism includes a six-axis motion mechanism 14, a camera 15, and a controller. A fiber optic array 20 is mounted at the end of the six-axis motion mechanism. The fiber optic array 20 is used to couple with the optical waveguide on the wafer, thereby enabling wafer performance testing. The camera 15 is used to acquire image data of the fiber optic array 20 for feedback control to adjust the pose of the fiber optic array 20. The controller is used to execute a rotation center calibration method as described in some of the above embodiments, so that the rotation center of the six-axis motion mechanism passes through the center of the light output end face of the fiber optic array 20, ensuring that the fiber optic array 20 will not interfere with the wafer due to excessive movement during the coupling test with the optical waveguide, thus preventing damage to the wafer.

[0083] This invention also provides a wafer testing device 10, which includes a probe station 11 and a fiber array pose adjustment mechanism as described in the above embodiments. A wafer is placed on the probe station 11, which can move and rotate to adjust the wafer's pose so that the optical waveguide end face on the wafer is aligned with the output port end face of the fiber array, thereby achieving coupling performance testing. Specifically, the probe station 11 is connected to a driving component 13, which is used to realize the X-axis movement, Y-axis movement, Z-axis movement, and rotation around the Z-axis of the probe station 11. In a further embodiment, the wafer testing device 10 uses edge coupling to test the wafer. Applying edge coupling in the silicon photonics wafer testing process can reduce optical power loss during silicon photonics wafer testing and improve testing accuracy.

[0084] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method of centering calibration of a rotating body, characterized by, The method is applied to a multi-axis motion mechanism having an initial rotation center, the multi-axis motion mechanism being connected with an end tool, the end tool being provided with a target point; the method comprises: controlling any rotation axis of the multi-axis motion mechanism to move along a corresponding target axis at least twice, any rotation axis being perpendicular to the corresponding target axis; acquiring a rotation track corresponding to the target point obtained by rotating the end tool around the rotation axis after any movement of the rotation axis; determining a corresponding relationship between a rotation track radius and a position of the rotation axis on the target axis based on a discrete degree value of the rotation track; determining the position of the rotation axis on the target axis at which the rotation track radius is the smallest as a target offset of a target rotation center corresponding to the target point relative to the initial rotation center of the multi-axis motion mechanism in the direction of the target axis; calibrating the target rotation center of the multi-axis motion mechanism based on all target offsets corresponding to all rotation axes of the multi-axis motion mechanism, so that the target point coincides with the target rotation center.

2. The method of center of rotation calibration according to claim 1, wherein, The acquiring of the rotation track of the target point comprises: acquiring an image of the target point captured by a camera along an axial direction of the rotation axis; determining a pixel point coordinate corresponding to the target point based on a position of the target point in the image; obtaining the rotation track corresponding to the target point according to a plurality of pixel point coordinates.

3. The method of center of rotation calibration according to claim 2, wherein, The controlling of any rotation axis of the multi-axis motion mechanism to move along a corresponding target axis at least twice comprises controlling the rotation axis to step move along the direction of the target axis. The controlling of the multi-axis motion mechanism to rotate around the rotation axis comprises controlling the multi-axis motion mechanism to step rotate around the rotation axis.

4. The method of center of rotation calibration according to claim 3, wherein The determining of the corresponding relationship between the rotation track radius and the position of the rotation axis on the target axis based on the discrete degree value of the rotation track comprises: determining an initial pixel point coordinate of the target point on the image after each movement of the rotation axis as a reference coordinate; acquiring a sum value of distances between each pixel point coordinate corresponding to the target point in the rotation track and the reference coordinate; establishing a fitting polynomial based on the sum value and the position of the rotation axis on the target axis, and determining the fitting polynomial as the corresponding relationship between the rotation track radius and the position of the rotation axis on the target axis.

5. The method of center of rotation calibration according to claim 4, wherein, The determining of the position of the rotation axis on the target axis at which the rotation track radius is the smallest as the target offset of the target rotation center corresponding to the target point relative to the initial rotation center of the multi-axis motion mechanism in the direction of the target axis comprises: determining the position of the rotation axis on the target axis corresponding to the point with the minimum sum value based on the fitting polynomial as the target offset of the target rotation center corresponding to the target point relative to the initial rotation center of the multi-axis motion mechanism in the direction of the target axis.

6. The method of center of rotation calibration according to any one of claims 1-5, wherein, The method further comprises, after determining the target offset of the target rotation center corresponding to the target point relative to the initial rotation center of the multi-axis motion mechanism in the target axis direction according to the rotation trajectory radius corresponding to the rotation trajectory of the target point: controlling different rotation axes to move along the target axis, and determining a new target offset of the target rotation center relative to the initial rotation center in the target axis direction; correcting the previously determined target offset based on the newly determined target offset.

7. The method of center of rotation calibration according to claim 6, wherein, The multi-axis motion mechanism is a six-axis motion mechanism, which includes an X-axis, a Y-axis, a Z-axis, a U-axis, a V-axis, and a W-axis, wherein the X-axis, the Y-axis, and the Z-axis are linear motion axes, and the U-axis, the V-axis, and the W-axis are rotation axes, and the method comprises: controlling the W-axis to move along the X-axis, and after each movement of the W-axis, controlling the six-axis motion mechanism to rotate around the W-axis, and determining an X-direction offset of the target rotation center relative to the initial rotation center in the X-axis direction according to changes in the rotation trajectory of the target point; controlling the W-axis to move along the Y-axis, and after each movement of the W-axis, controlling the six-axis motion mechanism to rotate around the W-axis, and determining a Y-direction offset of the target rotation center relative to the initial rotation center in the Y-axis direction according to changes in the rotation trajectory of the target point; controlling the U-axis to move along the Z-axis, and after each movement of the U-axis, controlling the six-axis motion mechanism to rotate around the U-axis, and determining a first offset of the target rotation center relative to the initial rotation center in the Z-axis direction according to changes in the rotation trajectory of the target point; controlling the V-axis to move along the Z-axis, and after each movement of the V-axis, controlling the six-axis motion mechanism to rotate around the V-axis, and determining a second offset of the target rotation center relative to the initial rotation center in the Z-axis direction according to changes in the rotation trajectory of the target point; determining a Z-direction offset of the target rotation center relative to the initial rotation center in the Z-axis direction based on the first offset and the second offset; calibrating the target rotation center of the six-axis motion mechanism based on the X-direction offset, the Y-direction offset, and the Z-direction offset, so that the target point coincides with the target rotation center.

8. The method of center of rotation calibration according to claim 3, wherein, Before the controlling of any rotation axis of the multi-axis motion mechanism moving along the corresponding target axis at least twice, the method further comprises: determining a theoretical coordinate of the target point based on size parameters of the multi-axis motion mechanism and the end tool; determining a range of stepwise movement of any rotation axis on the target axis based on the theoretical coordinate.

9. An optical fiber array pose adjustment mechanism, comprising: A six-axis motion mechanism, a camera, and a controller are included, the end of the six-axis motion mechanism is provided with a fiber array, the camera is used to acquire image data of the fiber array, and the controller is used to perform a rotation center calibration method as claimed in any one of claims 1-8 so that the rotation center of the six-axis motion mechanism passes through the center of the end face of the fiber array.

10. A wafer testing apparatus, characterized by comprising: A fiber array pose adjustment mechanism as claimed in claim 9 is included.

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