Workpiece positioning device that uses an imaging unit

Abstract

Positioning device, which includes: an image transmission unit (12) which is set up to take an image from above a workpiece (W) which in turn is fixed on a table (13) of a machine tool (5); a motion unit (21) configured to cause the image display unit to position itself in a plane parallel to the table at a desired relative position with respect to the table; an image processing unit (22) which is configured to process the image of the workpiece which is captured by the image acquisition unit and to detect a position of at least two feature points (A0, B0) of the workpiece in the image; a storage unit (23) configured to store as a relative reference position a relative position of the imaging unit with respect to the table when a reference workpiece (W0) is captured by the imaging unit, and as a reference point image position positions of the at least two feature points of the reference workpiece in the image of the reference workpiece captured by the imaging unit; a computation unit (24) configured to calculate an amount of rotational deviation in a plane parallel to the table by comparing the relative position of the imaging unit with respect to the table when the workpiece is captured by the imaging unit with the relative reference position, and by comparing a direction of a line segment combining the two feature points (A0, B0) in the image of the reference workpiece with a direction of a line segment combining the corresponding two feature points A1 (x2, y2) and B1 (x3, y3) with respect to a reference origin (O) of the table in the image of the workpiece, wherein the amount of rotational deviation consists of: - a rotation angle Θ, which is calculated by: Θ = tan − 1 { ( y 3 − y 2 ) / ( x 3 − x 2 )} , and - the coordinates xc, yc of a center of rotation C (xc, yc) of the workpiece (W), which are calculated by: xc = (x 2 + x 3 ) / 2, yc = ( y 2 + y 3 ) / 2 ; and a program change unit (25) which is set up to generate an amount of correction for the corrected rotation angle Θ and the corrected center of rotation C such that the amount of rotational deviation calculated by the computation unit becomes zero, and thereby change a program of the machine tool.

Description

Background of the invention

[0001] The present invention relates to a workpiece positioning device for a machine tool using an imaging unit such as a visual sensor.

[0002] In some cases, a workpiece is formed with two feature points, such as holes, protrusions, notches, or the like, for positioning or phasing. Such feature points engage with a pin, a pipe fitting, or a stopper provided on the table of the machine tool to achieve positioning and phasing of the workpiece. In JP H07-4 737 B2, a reference hole is formed in a workpiece as a feature point. An imaging unit, e.g., a camera, captures an image of the reference hole of the workpiece through a hole formed through the table.

[0003] To achieve more precise positioning or the like, a touch probe mounted on a spindle of a machine tool is used. The workpiece is preferably positioned and phased using an electrical contact sensing technique by the touch probe and the above-described technique using the feature point. Furthermore, the description of JP 4 840 144 B2 discloses a device configured to non-contact measure a distance between a workpiece and a sensor.

[0004] The document DE 10 2005 022 344 A1 discloses a method for determining the position of a workpiece. The workpiece is clamped on a workpiece table for machining by a tool. After a worker has activated a command for visual measurement of the workpiece via a controller, the workpiece table moves into the detection range of a camera. First processing means generate geometric parameters based on the image data. A simplified geometric model of the workpiece, which describes the outer contours of the workpiece, is stored in a memory. Second processing means are capable of determining position information describing the position of the workpiece in relation to a reference position by comparing the geometric model and the previously determined geometric parameters.Such position information, which is used to determine the position of the workpiece in relation to a tool intended for its processing, is stored in the form of a matrix and is thus available for subsequent processing of the workpiece by a tool. Summary of the invention

[0005] However, in JP H07-4 737 B2, it is required that the center of the hole in the stage be positioned in front of the imaging unit when the stage is moved back to the origin during imaging. In other words, in JP H07-4 737 B2, the relative position between the stage and the imaging unit is a fixed positional relationship at all times during image acquisition.

[0006] Furthermore, in JP 4 840 144 B2, the sensor and the workpiece are moved relative to each other. When the workpiece enters a length measurement range within a predetermined range, a detection signal from the sensor is output. Thus, if a burr or the like is present in the outer profile of the workpiece, for example, there is a possibility that misdetection may occur. Furthermore, if a feature is printed as a dot on the workpiece, it is not possible to detect such a feature point. Furthermore, overshoot may occur during workpiece detection, and a long time is required due to the additional moving distance.

[0007] The present invention has been made in view of such circumstances, and its object is to provide a positioning device capable of positioning a workpiece with ease and in a short time.

[0008] According to the invention, a device according to the independent claim is provided.

[0009] These objects, features and advantages, as well as other objects, features and advantages of the present invention, will become more apparent from the detailed description of exemplary embodiments of the present invention as shown in the accompanying drawings. Short description of the drawings

[0010] They show: Fig. 1 is a schematic view of the positioning device based on the present invention; Fig. 2 is a flow chart showing the operation of the positioning device, which in turn is Fig. 1 is shown; Fig. 3 an enlarged view of a table and a workpiece; and Fig. 4 an enlarged view of a workpiece and a reference workpiece. Detailed description

[0011] Embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, like elements are designated by like reference numerals. To facilitate understanding, the scale of the figures has been changed as desired.

[0012] Fig. Figure 1 is a schematic view of a positioning device based on the present invention. As shown in Fig. As shown in FIG. 1, a tool (not shown) mounted on a spindle 11 on a machine tool 5 is configured to machine a workpiece W fixed on a table 13. The spindle 11 of the machine tool 5 is capable of reciprocating motion in a vertical direction (e.g., the Z direction) as well as rotation. The positioning device 10 of the present invention mainly includes the machine tool 5 and a control device 2 that controls the machine tool 5.

[0013] As in Fig. As shown in Figure 1, an imaging unit 12, e.g., a camera, is fixed to the spindle 11. The positional relationship between the imaging unit 12 and the spindle 11 is thus fixed. The optical axis of the imaging unit 12 preferably runs parallel to the spindle 11, and the field of view of the imaging unit 12 covers the entire workpiece W.

[0014] The workpiece W is, for example, a flat workpiece, a curved workpiece, or an uneven workpiece, and includes at least two feature points. The feature point is, for example, a hole, a protrusion, a groove, or the like. Alternatively, the feature point of the workpiece W may be a pattern, a character, or the like printed on the workpiece. In other words, the feature point of the workpiece W in the present invention may be a part of the top surface of the workpiece W, which is flat and cannot be detected by a contact-type sensor.

[0015] The table 13 is connected to a movement unit 21 of the control device 20. The movement unit 21 causes the table 13 to move in two directions, e.g., the X direction and the Y direction, which are orthogonal to each other in a plane parallel to the table surface of the table 13. Since the spindle 11 of the machine tool 5 is immobile in the X direction and Y direction, the movement unit 21 is capable of positioning the spindle 11 and the imaging unit 12 in a desired relative position with respect to the table 13 in a plane parallel to the table 13.

[0016] The control device 20 includes: an image processing unit 22 that processes an image of the workpiece captured by the imaging unit 12 and detects a position of the feature point of the workpiece in the image; and a storage unit 23 that stores, as a relative reference position, a relative position of the imaging unit 12 with respect to the table 13 when a reference workpiece W0 is captured by the imaging unit 12, and also stores, as a reference point image position, a position of a feature point of the reference workpiece in the image of the reference workpiece W0 captured by the imaging unit 12.

[0017] Furthermore, the control unit 20 includes a calculation unit 24 that calculates an amount of deviation between the position of the feature point of the reference workpiece W0 and the feature point of the workpiece W by comparing the relative position of the imaging unit 12 with respect to the table 13 when the workpiece W is captured by the imaging unit 12 with the relative reference position, and by comparing the position of the feature point of the workpiece W in the image of the workpiece W captured by the imaging unit 12 with respect to the point image position with the reference point image position. Furthermore, the control device 20 includes a program modification unit 25 that modifies the program of the machine tool 5 by generating a correction amount such that the amount of deviation calculated by the calculation unit 24 becomes zero.

[0018] Fig. Figure 2 shows a flow chart showing the operation of the positioning device, which in turn is shown in Fig. 1. With reference to Fig. 1 and Fig. 2, a description will be given below of the operation of the positioning device according to the present invention. First, in step S11, the reference workpiece W0 is fixed on the table 13. The reference workpiece W0 has a size similar to that of the workpiece W and also includes at least two feature points. Furthermore, assume that the reference workpiece W0 and the workpiece W are fixed on the table 13 by a suitable fixing frame or the like.

[0019] Then, in step S12, the imaging unit 12 is relatively moved by the moving unit 21 to a desired position with respect to the table 13. The desired position refers to a relative position between the table 13 and the imaging unit 12 at which a feature point can be sufficiently imaged when the reference workpiece W0 and the workpiece W described below are picked up. Then, the storage unit 23 stores, as the relative reference position, the position of the reference workpiece W0 after the imaging unit 12 is moved (step S13).

[0020] Next, in step S14, the imaging unit 12 captures the reference workpiece W0. The image processing unit 22 processes the captured image and acquires the position of a feature point of the reference workpiece W0 in the image. The storage unit 23 stores the position of the feature point of the reference workpiece W0 in the image as the reference point image position (step S15). The processing up to steps S11 to S15 is preprocessing for determining the relative reference position and the reference point image position. If such preprocessing is performed in advance and the relative reference position and the reference point image position are stored in the storage unit 23, the processing in steps S11 to S15 may be omitted.

[0021] Then, in step S16, the reference workpiece W0 is removed, and the workpiece W is fixed on the table 13. Then, in step S17, the imaging unit 12 is moved relative to the above-described desired position with respect to the table 13 by the moving unit 21. The relative position of the workpiece W with respect to the table 13 after the imaging unit has been moved can be stored in the storage unit 23.

[0022] In step S18, the imaging unit 12 captures the workpiece, and the image processing unit 22 processes the captured image and detects the positions of the feature points of the workpiece W in the image. The positions of the feature points can be stored in the storage unit 23.

[0023] Then, in step S19, the calculation unit 24 compares the relative position of the workpiece W and the relative reference position of the reference workpiece W0. In step S20, the calculation unit 24 compares the position of the feature point in the image of the workpiece W and the reference point image position in the image of the reference workpiece W0. Further, using the result of the comparison, the calculation unit 24 calculates the amount of deviation between the position of the feature point of the reference workpiece W0 and the feature point of the workpiece W (step S21).

[0024] Fig. 3 shows an enlarged view of the table and the workpiece. In Fig. 3, the reference origin O of the table 13, the reference point image position a0 (x0, y0) of the reference W0, and the position a1 (x1, y1) of the corresponding feature point of the workpiece W are shown. In such a case, the amount of deviation a1-a0 is calculated as (x1-x0, y1-y0). Of course, a similar amount of deviation with respect to the other feature point can also be calculated. Then, in step S22, the program modification unit 25 generates an amount of correction for correcting the amount of deviation and modifies the program of the machine tool 5 to add the amount of correction to the program.

[0025] In this way, in the present invention, the program is changed to correct the amount of deviation, rather than precisely positioning the workpiece. Thus, there is no need for precise positioning of the workpiece, so that as a result, it is possible to position the workpiece within a short time. Furthermore, as is apparent from the above description, in the present invention, it is not required that the relative position between the table 13 and the imaging unit 12 be a fixed relationship at all times during image acquisition; it is thus possible to position the workpiece with ease.

[0026] When the feature point is a hole, a projection, a groove, or the like, the imaging unit 12 is required to be positioned substantially directly above the feature point in order to obtain a sufficiently good image. In this regard, in the present invention, the imaging unit 12 is moved relative to a desired position at which the feature point can be captured with sufficient quality. Thus, in the invention, the feature point is not required to be a hole, a projection, a groove, or the like, and it is possible to accurately determine the position of the feature point even when the feature point is a pattern, a character, or the like printed on the workpiece W, for example. Therefore, there may be a case where there is no need for additional formation of a feature point on the workpiece W.

[0027] Furthermore, even if there is a need to form the feature point, such as a hole, a protrusion, a groove, or the like, on the workpiece W, the feature point can be formed at any location on the workpiece W because the imaging unit 12 can be moved. As such, in the present invention, the relative position between the table and the imaging unit is not required to be a fixed relationship at all times, so the degree of freedom in the position for forming the feature point is increased according to the present invention.

[0028] Furthermore, Fig. 4 an enlarged view of the workpiece and the reference workpiece. As in Fig. 4, a case may occur in which the workpiece W is rotated in the table 13 with respect to the reference workpiece W0 (rotational deviation). In Fig. 4, the angle of rotation relative to a rotation center C of the workpiece W with respect to the reference workpiece W0 is represented by . In such a case, at least two feature points are used.

[0029] In the Fig. 4 shown example, in step S18 according to Fig. 2, the feature points A1 (X2, Y2) and B1 (X3, Y3) of the workpiece W are detected in the image with respect to the reference origin O of the table 13. The feature points A1 and B1 of the workpiece W correspond to the feature points A0 and B0 of the reference workpiece W0, respectively. As can be seen from Fig. As can be seen in Figure 4, the feature points A0 and B0 correspond to the X coordinates in the image.

[0030] The angle of rotation θ, which Fig.4 is an angle between the direction of the line segment that combines the two feature points A0 and B0 in the image of the reference workpiece W0 and the direction of a line segment that combines the corresponding two feature points A1 and B1 in the image of the workpiece W. The rotation angle θ is calculated from the following equation (1): θ=tan−1{(y3−y2) / (x3−x2)}

[0031] The coordinate (xc, yc) of the center of rotation C is calculated from the following equation (2): xc=(x2+x3) / 2, yc=(y2+y3) / 2

[0032] The calculation unit 24 calculates an amount of rotational deviation as the rotation angle θ and the coordinate of the rotation center C. Further, the program change unit 25 calculates a correction amount for the thus corrected rotation angle θ and the thus corrected rotation center C, and causes the correction amount to be reflected in the program of the machine tool 5 as described above. It is obvious that an advantage similar to that described above can also be obtained in this case. Advantage of the invention

[0033] In the first aspect of the invention, since the program is changed to correct the amount of deviation, there is no need for precise positioning of the workpiece, and therefore, as a result, it is possible to position the workpiece in a short period of time.

[0034] Furthermore, since the imaging unit is relatively moved, the position of the feature point can be accurately determined even if the feature point is a pattern, a character, or the like printed on the workpiece, and in addition, the degree of freedom in the position for forming the feature point can be increased.

[0035] In the second aspect of the invention, even if the amount of deviation includes an amount of rotational deviation, then an advantage similar to that described above can be obtained.

Claims

[1] Positioning device comprising: an imaging unit (12) configured to capture an image from above a workpiece (W) which in turn is fixed on a table (13) of a machine tool (5); a movement unit (21) arranged to cause the imaging unit to position itself at a desired relative position with respect to the table in a plane parallel to the table; an image processing unit (22) configured to process the image of the workpiece captured by the imaging unit and to detect a position of at least two feature points (A0, B0) of the workpiece in the image; a storage unit (23) configured to store, as a relative reference position, a relative position of the imaging unit with respect to the table when a reference workpiece (W0) is captured by the imaging unit, and to store, as a reference point image position, positions of the at least two feature points of the reference workpiece in the image of the reference workpiece captured by the imaging unit; a calculation unit (24) configured to calculate an amount of rotational deviation in a plane parallel to the table by comparing the relative position of the imaging unit with respect to the table when the workpiece is captured by the imaging unit with the relative reference position with the relative reference position, and by comparing a direction of a line segment combining the two feature points (A0, B0) in the image of the reference workpiece with a direction of a line segment combining the corresponding two feature points A1 (x2, y2) and B1 (x3, y3) with respect to a reference origin (O) of the table in the image of the workpiece, wherein the amount of rotational deviation consists of: - a rotation angle Θ, which is calculated by: Θ=tan−1{(y3−y2) / (x3−x2)}, and - the coordinates xc, yc of a center of rotation C (xc, yc) of the workpiece (W), which are calculated by: xc=(x2+x3) / 2, yc=(y2+y3) / 2; and a program changing unit (25) configured to generate an amount of correction for the corrected rotation angle Θ and the corrected rotation center C such that the amount of rotational deviation calculated by the calculating unit becomes zero, and thereby change a program of the machine tool.

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