JP7303686B2 - Work position detection method for robots - Google Patents

Description

The present invention relates to a robot used for transporting a plate-shaped work such as a glass substrate for a liquid crystal display panel, and more particularly to a method for detecting the position of the work on the hand of the robot.

2. Description of the Related Art In a manufacturing line of a liquid crystal display device or the like, robots are used to transport works such as substrates between different processing devices. In that case, the work is transported by inserting the robot hand into the load lock chamber or cassette of the processing equipment from which the work is carried in, holding the work on the hand, and then removing the hand with the work on it from the load lock chamber, etc. The robot arm or the entire robot is moved with the work placed on the hand, then the hand is inserted into the load lock chamber of the processing equipment to which the work is to be carried in, the work is stored in the load lock chamber, and then only the hand is moved. from the load lock chamber. The hand is, for example, shaped like a fork. The robot consists of, for example, a horizontal articulated mechanism that is configured by connecting two arms and has a hand at the tip, an elevating mechanism that vertically moves the hand together with the horizontal articulated mechanism, and a vertical axis as a rotation axis. and a rotation mechanism for rotating the entire horizontal multi-joint mechanism in a horizontal plane. The horizontal articulated mechanism moves the hand forward or backward along the same straight line by decreasing or increasing the angle formed by the two arms. In order to change the direction in which the hand moves in the horizontal plane, it is necessary to rotate the horizontal multi-joint mechanism by a rotation mechanism. Further, a transport mechanism is provided for linearly moving the entire robot in a horizontal plane. An example of such a robot is described in Patent Document 1. In the following description, the forward and backward direction of the hand is called the front-back direction, and the direction perpendicular to the front-back direction is called the left-right direction.

If the work is not placed on the specified position on the hand, there is a risk of an error occurring when the work is stored in the load lock chamber to which it is transferred. In the case of a rectangular workpiece, the specified position is generally defined as a state in which the four sides of the workpiece are aligned with respect to the front-rear direction and left-right direction of the hand at a predetermined position on the hand. In the following description, a side of the work that should be parallel to the front-rear direction of the hand is called a vertical side of the work, and a side that should be parallel to the left-right direction of the hand is called a horizontal side of the work. The deviation of the workpiece from the designated position on the hand includes the deviation from the designated position in the front-rear direction of the hand, the deviation from the designated position in the left-right direction of the hand, and the difference between the horizontal side of the workpiece and the left-right direction of the hand. Three types of deviations in the formed angle are conceivable. The angle formed by the horizontal side of the work and the horizontal direction of the hand is called the tilt angle, and the tilt angle is 0 when the work is at the specified position. Of these, the deviation in the front-rear direction and the tilt angle can be compensated for by providing the hand with a sensor for detecting the lateral side of the work. When the work is in the reference position, sensors for detecting the work are arranged at two positions corresponding to the lateral edges of the work on the hand. By controlling the forward or backward amount of the hand and the turning amount of turning the hand with the horizontal multi-joint mechanism so as to detect be able to. Alternatively, it is possible to obtain the amount of deviation and perform compensation based on the amount of deviation when transporting the workpiece to the load lock chamber of the transport destination.

However, in the case where the horizontal side of the workpiece is larger than the horizontal length of the hand, it is possible to detect the vertical side of the workpiece depending on the sensor provided on the hand. Therefore, the amount of deviation cannot be determined, and the deviation cannot be compensated for. Therefore, in Patent Document 2, an edge detection sensor is attached at a position that is not affected by the operation of the horizontal multi-joint mechanism. is detected by this edge detection sensor. As the edge detection sensor, a light shielding one-dimensional position sensor such as a line sensor can be used. The shift in the lateral direction of the mounting position of the work in the hand can be compensated for by adjusting the amount of movement of the robot by the transport mechanism based on the detection result of the edge detection sensor. In order to further improve the work transfer efficiency, Patent Document 2 discloses a robot in which two sets of independently controlled horizontal multi-joint mechanisms are provided and a hand is attached to each horizontal multi-joint mechanism. This robot is constructed so that the forward and backward directions of the two hands are the same, and the two hands can be positioned so as to precisely overlap each other in the vertical direction. The distance between the hands in the vertical direction is narrow, and the horizontal edge of the work held on the hand is detected by one line sensor provided in common for the two hands.

Japanese Patent Application Laid-Open No. 2003-117862 JP 2008-302451 A

In a robot that has two or more horizontal multi-joint mechanisms each having a hand and is used for transporting a work, when an edge detection sensor for detecting the position of the edge of the work, that is, the position of the vertical side of the work is shared between the hands, the edge If the works overlap in the detection space of the detection sensor, the edges of the work cannot be detected. In order to detect the lateral position of the workpiece on the hand, there must be no workpiece other than the workpiece to be detected within the detection space of the edge detection sensor. Therefore, when two or more hands each hold a work, the work other than the work to be detected is moved so that the work other than the work to be detected does not exist in the detection space of the edge detection sensor. need arises. However, it takes time to move the hand to move the work, and depending on the position of the robot, it may not be possible to advance the hand to move the work due to interference from walls around the robot. It can happen. If the hand cannot be moved forward due to the position of the robot, it is possible to move the robot to a wider space or change the direction of the hand with the horizontal multi-joint mechanism. also takes time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a work position detection method that enables a robot having a plurality of hands to detect the edge position of the work by eliminating overlapping of the works without large movements of the hands.

A workpiece position detecting method according to the present invention is a workpiece position detecting method for a robot having a plurality of hands and capable of placing a workpiece on each hand. a multi-joint mechanism capable of advancing and retreating the hand along the first direction while fixing the orientation of the hand in the first direction; an edge detection sensor commonly attached to the main body of the plurality of hands; , and is configured such that the plurality of hands can be positioned to overlap each other in the vertical direction by driving the multi-joint mechanism, and the edge detection sensor detects each of the hands when the plurality of hands moves in the first direction. It has a detection space so as to include an area through which the work mounted on the hand passes, and is configured to detect the position of the side of the work in a second direction orthogonal to the first direction in the detection space. The robot further comprises, for each hand, a mechanism for rotating the hand in a direction deviating from the first direction around a wrist axis connecting the multi-joint mechanism and the hand, and for determining the position of the side in the second direction. By rotating the hand holding the workpiece not to be detected by the mechanism around the wrist axis of the hand, the workpiece not to be detected is moved out of the detection space, and the position of the side is detected. detecting the position of the side of the workpiece to be processed by an edge detection sensor.

According to the work position detection method of the present invention, by simply rotating the hand around the wrist axis, overlapping of the works can be eliminated and the edges of the work to be detected can be detected by the edge detection sensor. It is possible to reduce the time required for

In the work position detection method of the present invention, it is preferable that the edge detection sensor is attached to the main body so as to detect the position of the side of the work placed on the hand in the retracted position. Since the hand in the retracted position is least likely to be interfered with by walls surrounding the robot, this configuration reduces the space that must be provided around the robot in order to eliminate overlapping of workpieces. Therefore, the robot can be installed in a small space.

In the workpiece position detection method of the present invention, each of the plurality of hands is provided with a pair of sensors spaced apart along the second direction, and the hand is moved toward the workpiece to place the workpiece on the hand. When moving forward, the tilt angle of the work with respect to the hand is determined using a pair of sensors, and the hand is rotated around the wrist axis according to the tilt angle, so that the tilt angle is zero. can be placed on By placing the work on the hand in this way, it is possible to simplify the calculation of the amount of movement of the robot when carrying the placed work to the destination.

In the workpiece position detection method of the present invention, the multi-joint mechanism for each hand is attached to the main body along the common axis, and the position of the common axis viewed from the wrist axis of the hand when retreating along the first direction. It is preferable to attach the edge detection sensor to the main body at a position in the forward direction. According to this configuration, the edges of the workpiece can be detected by the edge detection sensor when the hand is in the retracted position, and a sufficient distance can be secured between the wrist axis and the edge detection sensor to hold a workpiece that is not a detection target. It is possible to reduce the rotation angle when rotating the hand to rotate around the wrist axis.

In the workpiece position detection method of the present invention, the multi-joint mechanism for each hand is attached to the main body along the common axis, and the position of the common axis viewed from the wrist axis of the hand when retreating along the first direction. It is preferable to attach the edge detection sensor to the main body at a position in the forward direction. According to this configuration, the edges of the workpiece can be detected by the edge detection sensor when the hand is in the retracted position, and the distance between the wrist axis and the edge detection sensor can be sufficiently secured, so that the hand of the workpiece which is not a detection target can be detected. can be rotated around the wrist axis.

According to the present invention, in a robot having a plurality of hands, it is possible to eliminate overlapping of workpieces and detect the edge positions of workpieces without large movements of the hands.

(a) and (b) are a side view and a plan view, respectively, of a robot according to an embodiment of the present invention. FIG. 10 is a side view showing the robot with the horizontal multi-joint mechanism raised; It is a figure explaining a motion of the hand of a robot.

Preferred embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a robot according to one embodiment of the present invention, and (a) and (b) are a side view and a plan view, respectively. The robot shown in FIG. 1 is of a horizontal multi-joint type that transports a substantially rectangular plate-like work 50 such as a glass substrate used for manufacturing a liquid crystal display panel, and has two hands 13A and 13B that hold the work 50 respectively. is a so-called double-handed robot. 2 shows a state in which the horizontal articulated mechanism is raised in the robot shown in FIG.

The robot comprises a base 22 which is movable on a pair of mutually parallel rails 21 linearly provided on the floor, and a motor (not shown) provided on the base 22 and built in the base 22. ), a rotary table 23 that rotates in a horizontal plane around a rotary shaft 31 and an elevating mechanism 24 that is provided upright with respect to the rotary table 23 are provided. A cover 25 is attached to the rail 21 to cover it. The lifting mechanism 24 includes a fixed portion 24A attached to the turntable 23 and a moving portion 24B that moves up and down with respect to the fixed portion 24A by a motor (not shown). 1(a) shows the robot of the present embodiment with the moving part 24B of the lifting mechanism 24 positioned at the lowest position in its lifting range, while FIG. 2 shows the moving part 24B raised. It shows the robot in a state. A support portion 26 for holding a horizontal articulated mechanism is provided in the moving portion 24B so as to extend in the horizontal direction. ing. The upper horizontal articulated mechanism includes a first arm 11A that is attached to the support portion 26 and is rotatable in the horizontal plane around the common shaft 32, and a first arm 11A that is attached to the tip of the first arm 11A and is rotatable in the horizontal plane around the shaft 33A. A hand 13A is attached to the tip of the second arm 12A. Similarly, the lower horizontal articulated mechanism includes a first arm 11B that is attached to the support portion 26 and can rotate in the horizontal plane around the common shaft 32, and a first arm 11B that is attached to the tip of the first arm 11B and rotates around the shaft 33B. and a second arm 12B that can rotate in a horizontal plane, and a hand 13B is attached to the tip of the second arm 12B. The main body of the robot is the portion of the robot excluding the horizontal articulated mechanism and the hands 13A and 13B attached thereto.

The hands 13A and 13B have a fork-like shape in which a plurality of rod-like members are arranged in parallel so that the plate-like work 50 can be conveyed while being held in a horizontal state by being held from below. While holding the work 50, the hands 13A and 13B are entirely covered with the work 50 except for the root side where the hands 13A and 13B are connected to the second arms 12A and 12B. The hands 13A and 13B take out a workpiece 50 stored in a load lock chamber or the like and hold it on the hands 13A and 13B, or move the workpiece 50 when storing the held workpiece 50 in the load lock chamber or the like. The direction in which the hands 13A and 13B advance or retreat is parallel to the direction in which the rod member extends. The width of the hands 13A and 13B in the left-right direction, ie, the direction perpendicular to the front-rear direction, is shorter than the width of the workpiece 50 to be conveyed in the left-right direction.

In this robot, the horizontal multi-joint mechanism moves the hands 13A and 13B linearly in a direction perpendicular to the direction in which the support portion 26 extends by means of a link mechanism incorporated in the first arms 11A and 11B and the second arms 12A and 12B. is configured for forward and backward motion. That is, both hands 13A, 13B move forward and backward in the same direction. Forward movement is movement in which the tips of the hands 13A and 13B move away from the common shaft 32, and backward movement is movement in the opposite direction to the forward movement. The first arms 11A, 11B and the second arms 12A, 12B as a whole perform a bending motion, and in spite of that, the hands 13A, 13B are kept in a constant orientation in the horizontal plane. They are attached at the positions of the tips of the second arms 12A and 12B so as to be rotatable in the horizontal plane around the wrist shafts 34A and 34B. In the upper horizontal multi-joint mechanism, the first arm 11A and the second arm 12A are moved by driving a motor (not shown) provided in the support part 26, and the hand 13A is supported while maintaining its orientation. It moves in a direction perpendicular to the direction in which the portion 26 extends. Similarly, in the lower horizontal articulated mechanism, the first arm 11B and the second arm 12B are moved by driving the motor (not shown) provided in the support part 26, and the hand 13B maintains its orientation. It moves in a direction perpendicular to the direction in which the support portion 26 extends. In this robot, the hand 13A and the hand 13B can be moved independently, and the wrist axis 34A and the wrist axis 34B are precisely aligned in the vertical direction during these movements. can be accurately superimposed on each other in the vertical direction.

Each of the hands 13A and 13B includes a sensor 27 for detecting the lateral side of the rectangular workpiece 50 located in the backward direction of the hands 13A and 13B. The sensors 27 are provided at two locations on the left and right ends of each of the hands 13A and 13B. and compensation for the tilt angle formed by the lateral side of the workpiece 50 and the lateral direction of the hands 13A and 13B.

Furthermore, if the robot is in a position where it is stationary with respect to the support section 26 to which the horizontal multi-joint mechanism is attached and the workpiece 50 is held by the hands 13A and 13B, the hands 13A and 13B can move. An edge detection sensor 28, for example, a light shielding sensor, is provided at a position through which the longitudinal side of the work 50 passes due to the forward and backward movement of the . In the example shown here, the edge detection sensor 28 is attached to the moving portion 24B of the lifting mechanism 24 . The edge detection sensor 28 detects lateral deviation of the placement position of the work 50 on the hands 13A and 13B. It is configured. The edge detection sensor 28 has a U-shaped outer shape , and detects the vertical side of the workpiece 50 when the workpiece 50 enters the detection space, using the U-shaped opening as a detection space. The edge detection sensor 28 is commonly provided for the work 50 held by both hands 13A and 13B. In the robot of this embodiment, the distance between the hands 13A and 13B in the vertical direction is constant, and the width of the opening of the edge detection sensor 28 is greater than the distance between the hands 13A and 13B. The work 50 can pass through when all of the 13B are loaded with the work 50.例文帳に追加The robot of the present embodiment is a transfer robot, and moves forward the hands 13A and 13B to take out the work 50 from a load lock chamber or the like and store the work 50 in the load lock chamber. The workpiece 50 leaves the detection space when the hands 13B are advanced, and enters the detection space when the hands 13A and 13B are retracted.

Even if the edge detection sensor 28 is commonly provided for the workpiece 50 mounted on each of the hands 13A and 13B, in order to detect the position of the side of the workpiece 50, the detection space of the edge detection sensor 28 is required. Only the workpiece 50 to be detected must exist in the space, and the workpiece 50 not to be detected must not exist in the detection space. When both hands 13A and 13B hold workpieces 50, the hand that does not hold the workpiece 50 to be detected is moved so that only the workpiece 50 to be detected exists within the detection space. There is a need to. Conventionally, a hand carrying a workpiece 50 not to be detected is advanced so that only the workpiece 50 to be detected exists in the detection space. In addition, it may be difficult to move the hand in such a manner to avoid collisions with walls around the robot. Therefore, in this embodiment, as a robot, a motor (not shown) provided for each of the hands 13A and 13B rotates the hands 13A and 13B around the wrist shafts 34A and 34B within a range of, for example, ±several degrees from their original forward and backward directions. Use something that can rotate. Then, the hand holding the workpiece 50 other than the detection target is rotated around the wrist axis so as to deviate from the original front-rear direction. As a result, the workpiece 50 held by the hand rotated around the wrist axis comes out of the detection space of the edge detection sensor 28, so that only the workpiece 50 to be detected exists in the detection space. .

FIG. 3 is a diagram schematically showing detection of the vertical side of the workpiece 50 by the edge detection sensor 28 in the robot of this embodiment. It is assumed that the work 50 is a glass substrate, and that the other side of the work 50 can be seen through when represented in a plan view. For the sake of explanation, the works 50 held by the hands 13A and 13B are denoted as works 50A and 50B, respectively. (a) is a plan view showing a state in which the hands 13A and 13B are in the retracted position and vertically overlapped, and (b) is a side view corresponding to (a). Since there are two works 50A and 50B in the detection space of the edge detection sensor 28, it is impossible to detect the position of the sides of either of the works 50A and 50B. Assuming that the position of the side of the workpiece 50B held by the lower hand 13B is to be detected, in this embodiment, the upper hand 13A is moved away from the edge detection sensor 28 around the wrist axis 34A. rotate. As a result, the work 50A held by the upper hand 13A is out of the detection space of the edge detection sensor 28, and the edge detection sensor 28 detects the sides of the work 50B held by the lower hand 13B. become able to. In FIG. 3, (c) is a plan view showing a state in which the hand 13A is rotated around the wrist axis 34A, and (d) is a side view corresponding to (c).

On the other hand, in a conventional robot that does not rotate the hand about the wrist axis in a direction inclined from the original front-rear direction, it is necessary to advance the hand holding the workpiece 50 that is not the object of detection. In the example shown in FIG. 3, it is necessary to advance the upper hand 13A in order to detect the side of the workpiece 50B held by the lower hand 13B. In FIG. 3, (e) is a plan view showing a state in which the upper hand 13A is advanced, and (f) is a side view corresponding to (e).

Next, the position of the edge detection sensor 28 in the robot will be explained. When the horizontal articulated mechanism to which the hands 13A and 13B are attached moves up and down in the vertical direction, it is preferable that the edges of the workpiece 50 can be detected regardless of the height of the hands 13A and 13B. It is preferable that an edge detection sensor 28 is provided at a position that moves up and down together with the mechanism. In the transfer robot, the hands 13A and 13B are moved in parallel to prevent the work 50 and the hands 13A and 13B from colliding with surrounding objects while the entire robot is moving in parallel on the horizontal plane. 13A and 13B are in a retracted state. It is preferable to detect the vertical side of the workpiece 50 when the hands 13A and 13B are in the retracted state. Further, when the hand holding a work other than the detection target is rotated around its wrist axis, it is preferable that the amount of rotation is small. From the viewpoint of reducing the amount of rotation, it is preferable to attach the edge detection sensor 28 as far away as possible from the position of the wrist axis when the hand is in the retracted state. For example, when viewed from the wrist shafts 34A and 34B of the hands 13A and 13B in the retracted state, the edge detection sensor is detected at a position on the forward direction side of the position of the common shaft 32, which is the mounting position of the horizontal articulated mechanism in the support section 26. It is preferably attached to the robot.

Next, the operation of the robot of this embodiment to take out the work 50 stored in the load lock chamber or cassette and hold it on the hand 13B will be described. At this time, it is assumed that the hand 13A is already in the retracted state and is holding another work. It is assumed that the hand 13B does not hold the workpiece 50 and is in a retracted state. The robot moves along the rail 21 to the front of the target load-lock chamber, and the lifting mechanism 24 adjusts the height of the hand 13B to the height of the load-lock chamber. Then, the arms 11B and 12B are driven to move the hand 13B forward and enter the load-lock chamber to a position below the work 50 stored in the load-lock chamber. When the hand 13B is lifted by the elevating mechanism 24 in this state, the workpiece 50 is placed on the hand 13B. At this time, the lateral sides of the workpiece 50 are detected by a pair of sensors 27 provided on the hand 13B, and the advance amount of the hand 13B is controlled so that the lateral sides coincide with the reference positions of the hand 13B. do. The tilt angle can be obtained from the detection results of the pair of sensors 27 . Ideally, the tilt angle should be zero, so by rotating the hand 13B around the wrist axis 34B so that the tilt angle detected by the pair of sensors 27 is zero, the workpiece 50 is It is placed on the hand 13B so that its lateral side and the left-right direction of the hand 13B are aligned. If the tilt angle is corrected when the work 50 is placed on the hand 13B, the direction of the vertical side of the work 50 and the front-rear direction of the hand 13B match. It simplifies the calculations when performing 50 position compensation.

If it is necessary to rotate the turntable 23 around the rotation shaft 31 and also rotate the hand 13B in the front-rear direction when transferring the workpiece 50 to another load-lock chamber, for example, by the robot, the value of the tilt angle is is memorized, and the tilt angle is also taken into consideration when rotating the turntable 23 around the rotation shaft 31 without performing an operation to make the tilt angle of the work 50 on the hand 13A zero. It is sufficient to determine the amount of rotation. In this case, since the tilt angle is not corrected when the workpiece 50 is placed on the hand 13B, the time can be shortened accordingly.

When the workpiece 50 is placed on the hand 13B in the load lock chamber, the arms 11B and 12B are driven to retract the hand 13B, and the hand 13B is in a retracted state. At this time, the detection space of the edge detection sensor 28 is filled with the works 50 placed on the hands 13A and 13B. Since it is necessary to determine the lateral position of the workpiece 50 on the hand 13B, which is a newly placed workpiece, the hand 13A is rotated around its wrist axis 34A as described above to move the workpiece on the hand 13A. 50 is withdrawn from the detection space, and the edge detection sensor 28 detects the position of the vertical side of the workpiece on the hand 13B. From the detected position of the vertical side, the shift amount of the workpiece 50 in the left-right direction in the hand 13B is determined. Based on this amount of deviation, the movement amount of the robot to transport the work 50 by parallel movement along the rail 21 to another load lock chamber is determined, so that the work 50 can be accurately transported to the destination load lock chamber. be able to store. When the robot moves parallel to the destination of the workpiece 50 without correcting the tilt angle, it is necessary to consider the influence of the tilt angle when calculating the amount of movement of the robot.

In the robot of this embodiment described above, the hand attached to the tip of the horizontal multi-joint mechanism is moved in the forward direction by rotating the hand around the wrist axis of the hand while the hand is in the retracted state. A work that is not to be detected can be moved out of the detection space of the edge detection sensor 28, and the time required to detect the position of the vertical side of the work can be shortened. Moreover, since the hand is not moved forward, the position of the vertical side of the workpiece can be detected even if the space around the robot is narrow.

In the robot described above, a mechanism for turning the entire horizontal multi-joint mechanism around the rotation shaft 31 is provided in addition to the horizontal multi-joint mechanism for moving the hand forward and backward. If a load lock chamber or the like is provided only on one side along the extending direction of the rail 21, the above-described inclination angle can be compensated for by rotating the hands 13A and 13B around the wrist axes 34A and 34B. Therefore, it is possible to mount the lifting mechanism 24 directly on the base 22 without providing the rotating shaft 31 and the rotating table 23. As shown in FIG. Also, the above description relates to a robot having two hands 13A and 13B. By rotating the workpiece, it is possible to shorten the time required to detect the position of the vertical side of the workpiece. Moreover, since the hand is not moved forward, the position of the vertical side of the workpiece can be detected even if the space around the robot is narrow.

11A, 11B... first arm; 12A, 12B... second arm; 13A, 13B... hand; 21... rail; 22... base; 25... Cover; 26... Support portion; 27... Sensor; 28... Edge detection sensor; 31... Rotary shaft; 32... Common shaft;

Claims (5)

A workpiece position detection method for a robot having a plurality of hands and capable of placing a workpiece on each hand, comprising:
The robot includes a main body of the robot, a multi-joint mechanism provided for each hand and capable of moving the hand forward and backward along the first direction while fixing the orientation of the hand in the first direction, and and an edge detection sensor attached to the main body in common to the plurality of hands, and by driving the multi-joint mechanism, the plurality of hands can be positioned to overlap each other in the vertical direction. cage,
The edge detection sensor has a detection space so as to include an area through which the work mounted on each hand passes when the plurality of hands move in the first direction, and the edge detection sensor has the first edge detection space within the detection space. configured to detect the position of the side of the workpiece in a second direction perpendicular to the direction,
The robot further comprises, for each hand, a mechanism for rotating the hand in a direction deviating from the first direction around a wrist axis connecting the multi-joint mechanism and the hand,
The work that is not subject to detection of the position of the side in the second direction is rotated around the wrist axis of the hand by rotating the hand holding the work that is not subject to detection of the position of the side in the second direction. A work position detection method, comprising the step of withdrawing from the detection space and detecting the position of the side of the work whose position of the side is to be detected by the edge detection sensor. 2. The work position detection method according to claim 1, wherein said edge detection sensor is attached to said main body so as to detect the position of said side of said work placed on said hand in a retracted position. each of the plurality of hands includes a pair of sensors spaced apart along the second direction;
When the hand is advanced toward the work in order to place the work on the hand, the tilt angle of the work with respect to the hand is obtained using the pair of sensors, and the tilt angle is determined according to the tilt angle. 3. The workpiece position detection method according to claim 1, wherein the workpiece is placed on the hand so that the tilt angle is zero by rotating the hand around the wrist axis. each of the plurality of hands includes a pair of sensors spaced apart along the second direction;
When the hand is advanced toward the work in order to place the work on the hand, the pair of sensors is used to determine the tilt angle of the work with respect to the hand, and the tilt angle is stored. 3. The workpiece position detection method according to claim 1, wherein the workpiece is placed on the hand. the articulated mechanism for each hand is attached to the body at a common axis;
2. The edge detection sensor is attached to the main body at a position in the forward direction relative to the position of the common axis when viewed from the wrist axis of the hand when the hand is retracted along the first direction. 5. A workpiece position detection method according to any one of items 1 to 4.

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