Teaching method for carrier robot and substrate processing system

Abstract

To cancel angle deviation of an arm of a carrier robot without requiring time and effort.SOLUTION: An arm 27 is extended, a shield starting position A or a shield ending position B is measured by making a laser beam L of a left-side AWC sensor 26L cross a left-side projection 33 of a left pick 30, a shield starting position C or a shield ending position D is measured by making a laser beam L of a right-side AWC sensor 26R cross a right-side projection 34 of a right pick 30, and a left-side shield distance B-A and a right-side shield distance D-C are calculated. Thereafter, a degree T of angle deviation of the arm 27 is calculated on the basis of an inter-sensor distance E, the left-side shield distance B-A and the right-side shield distance D-C. In a case where the calculated degree T of the angle deviation of the arm 27 is larger than a target angle, the arm 27 is rotated around a rotation angle Z do as to cancel the calculated degree T of the angle deviation of the arm 27.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present disclosure relates to a teaching method for a transfer robot and a substrate processing system. [Background technology]

[0002] In a substrate processing system that performs various processes on wafers as substrates, a transfer robot is used to transfer wafers to and from a substrate processing chamber or a substrate transfer chamber. The transfer robot has an arm that can rotate around a vertical axis and can extend and retract in a horizontal plane perpendicular to the axis, and a pick that is attached to the tip of the arm and holds the wafer. The transfer robot is disposed inside a substrate transfer chamber adjacent to the substrate processing chamber or the substrate transfer chamber, and transfers and retracts the arm to transfer the pick in and out of the substrate processing chamber or the substrate transfer chamber to transfer the wafer in and out.

[0003] When performing various processes on a wafer, it is necessary to accurately place the wafer at a predetermined position on a mounting table in a substrate processing chamber, and therefore it is necessary to accurately grasp the position of the transfer robot that loads and unloads the wafer in the substrate transfer chamber and the relative position of the wafer with respect to the transfer robot. This grasping of the relative position of the wafer and the position of the transfer robot is called "teaching," and various methods have been proposed as a method of teaching the transfer robot.

[0004] For example, in the processing system of Patent Document 1, the horizontal position of the pick of the transport robot is grasped using a wafer protrusion detection sensor provided at the entrance of a substrate transport chamber to which a transport container for storing and transporting multiple wafers is connected.

[0005] In addition, in the substrate processing system of Patent Document 2, a sensor installed at the loading / unloading port located at the boundary between the substrate processing chamber and the substrate transfer chamber is used to detect the passage of the wafer and thereby grasp the horizontal position of the wafer relative to the arm of the transfer robot.

[0006] Furthermore, in the wafer transfer machine of Patent Document 3, a sensor provided on the alignment wafer is used to detect the transfer arm rotating in a horizontal plane, thereby grasping the position of the transfer arm in the rotating direction. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Publication No. 2021-129023 [Patent Document 2] Patent No. 6671993 [Patent Document 3] Japanese Patent Application Publication No. 10-233426 Summary of the Invention [Problem to be solved by the invention]

[0008] The technology disclosed herein eliminates angular misalignment of the arm of a transport robot without any hassle. [Means for solving the problem]

[0009] One aspect of the technology disclosed herein is a method for teaching a transport robot, the transport robot comprising: an arm that is rotatable about a vertical axis of rotation and that extends and retracts in a horizontal plane perpendicular to the axis of rotation; and a substrate holder attached to the arm, the arm having a first protrusion disposed on the left side in a direction in which the arm extends and retracts, and a second protrusion disposed on the right side in the direction of extension and retraction, the first protrusion and the second protrusion move together with the substrate holder as the arm extends and retracts, a first sensor is disposed on the left side in the direction of extension and retraction, and a second sensor is disposed on the right side in the direction of extension and retraction. a sensor is disposed on the right side in the extension / retraction direction, the first protrusion intersects with the detection light of the first sensor when the arm extends or retracts, and the second protrusion intersects with the detection light of the second sensor when the arm extends or retracts, an angular deviation of the arm around the pivot axis is calculated based on an amount of extension of the arm when the first protrusion intersects with the detection light of the first sensor and an amount of extension of the arm when the second protrusion intersects with the detection light of the second sensor, and the arm is rotated around the pivot axis so as to eliminate the calculated angular deviation. Effect of the Invention

[0010] According to the technology disclosed herein, it is possible to eliminate angular misalignment of the arm of a transport robot without any hassle. [Brief description of the drawings]

[0011] [Figure 1] 1 is a plan view showing a configuration of a substrate processing system including a transfer robot according to an embodiment of the technology disclosed herein; [Diagram 2] 2 is a plan view for explaining the configuration of a transport robot disposed inside the transfer module in FIG. 1. [Diagram 3] FIG. 2 is a perspective view for explaining the configuration of an AWC sensor in FIG. [Figure 4] 1 is a diagram for explaining the positional relationship between a pick attached to the arm of a transport robot and an AWC sensor. FIG. [Diagram 5]13A and 13B are diagrams for explaining how the left and right protrusions intersect with the laser light of the AWC sensor when the arm of the transport robot is extended. [Figure 6] 13A and 13B are diagrams for explaining why the left and right shielding distances do not match when an angle misalignment occurs in the arm of the transport robot. [Figure 7] 11A and 11B are diagrams for explaining a method for calculating an angle deviation of an arm of a transport robot. [Figure 8] 13 is a diagram for explaining a case where the arm of the transport robot is deviated in a clockwise direction from a design value. FIG. [Figure 9] 13 is a diagram for explaining the advantage of the left and right protrusions of the pick having oblique sides. FIG. [Figure 10] 10 is a flowchart showing a process for correcting an angle deviation of an arm as a teaching method for a transport robot according to an embodiment of the technology disclosed herein. [Figure 11] FIG. 13 is a diagram showing a modified example of the pick. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] In a substrate transfer chamber adjacent to a substrate processing chamber in which a plasma process is performed on a wafer under a reduced pressure environment, a transfer robot is installed so that the position of the transfer robot in the substrate transfer chamber does not deviate from a design value. However, when the substrate transfer chamber is depressurized after the transfer robot is installed, the orientation of the arm of the transfer robot in the rotation direction may deviate from the design value due to minute deformation of the substrate transfer chamber caused by the reduced pressure, which may cause a so-called angle deviation.

[0013] A known method for eliminating this angular misalignment is for an operator to visually grasp (measure) the angular misalignment of the arm from outside through a window or the like, and then rotate the arm to eliminate the angular misalignment that has been grasped. As a method that does not rely on the operator's visual inspection, it is also possible to apply the teaching method of Patent Document 3 to measure the angular misalignment of the arm by grasping the position of the transport robot in the direction of rotation of the arm. In this case as well, the arm is rotated to eliminate the measured angular misalignment.

[0014] However, the former requires visual inspection by an operator, and the latter requires the preparation of an alignment wafer having a sensor, and both are teaching methods that require a lot of work.

[0015] In contrast, the technology disclosed herein eliminates the angle misalignment of the arm without any hassle.

[0016] Hereinafter, an embodiment of the technology according to the present disclosure will be described with reference to the drawings. Fig. 1 is a plan view showing the configuration of a substrate processing system including a transfer robot according to the present embodiment. In Fig. 1, a part of the internal configuration is shown in a see-through manner for ease of understanding.

[0017] 1, the substrate processing system 10 includes five process modules 11 (substrate processing chambers), two transfer modules 12 (substrate transport chambers), a load lock module 13, a loader module 14, and a controller 15. The controller 15 controls the operation of each component of the substrate processing system 10.

[0018] A plurality of process modules 11 are connected to each transfer module 12, and a substrate delivery chamber 16 is disposed between two transfer modules 12. In addition, a load lock module 13 is disposed between one transfer module 12 and a loader module 14.

[0019] The loader module 14 is provided with a load port 18 which is a mounting stage for a FOUP 17 which is a transport container for wafers W as multiple substrates. The loader module 14 also is provided with a wafer storage 19 which temporarily stores each wafer W, an aligner 20 which adjusts the position of the wafer W, and a mapping temporary base (MTB) 21 which is a temporary storage location for the wafers W.

[0020] The loader module 14 is made of a housing with an atmospheric pressure inside, and has a movable transfer robot 22 inside. The transfer robot 22 transfers the wafer W between the FOUP 17, the wafer storage 19, the aligner 20, the MTB 21, and the load lock module 13.

[0021] The load lock module 13 temporarily holds the wafer W when transferring the wafer W between the loader module 14, whose interior is atmospheric pressure, and the transfer module 12, whose interior is vacuum pressure. The load lock module 13 is configured so that its interior can be switched between atmospheric pressure and vacuum atmosphere. When transferring the wafer W to and from the loader module 14, the interior of the load lock module 13 is atmospheric pressure, and when transferring the wafer W to and from the transfer module 12, the interior of the load lock module 13 is vacuum atmosphere.

[0022] As described above, the interior of the transfer module 12 is maintained in a vacuum atmosphere, and the transfer robot 23 is disposed therein. The transfer robot 23 transfers the wafer W between each process module 11, the substrate delivery chamber 16, and the load lock module 13.

[0023] The process module 11 is maintained in a vacuum atmosphere, has a mounting table 24 for mounting a wafer W thereon, and performs various types of reduced pressure processing, for example, plasma processing such as etching and film formation, on the mounted wafer W. In this embodiment, since the process module 11 has two mounting tables 24, various types of reduced pressure processing are simultaneously performed on two wafers W. Correspondingly, the transport robot 23 of the transfer module 12 also transports two wafers W simultaneously.

[0024] When performing various decompression processes on the wafer W, it is necessary to separate the inside of the process module 11 from the inside of the transfer module 12, so a gate valve 25 that can be opened and closed is disposed between the transfer module 12 and the process module 11. The gate valves 25 are provided corresponding to each mounting table 24.

[0025] In the substrate processing system 10, when various decompression processes are performed on the wafer W, it is necessary to accurately place the wafer W on the placement table 24 of the process module 11 at a position determined by design. Therefore, when the wafer W is loaded into the process module 11, it is necessary to accurately grasp the position of each wafer W. Therefore, wafer detection sensors (hereinafter referred to as "AWC sensors") 26L, 26R for detecting the wafer W are disposed inside the transfer module 12. The AWC sensors 26L, 26R are disposed corresponding to the gate valves 25, with the AWC sensor 26L disposed on the left side with respect to the transfer direction of the wafer W by the transfer robot 23, and the AWC sensor 26R disposed on the right side with respect to the transfer direction of the wafer W. The AWC sensors 26L, 26R are provided in advance in the substrate processing system 10 to detect the wafer W, regardless of whether the technology according to the present disclosure is applied or not.

[0026] 2 is a plan view for explaining the configuration of the transport robot 23 arranged inside the transfer module 12. The transport robot 23 has a horizontal multi-joint (SCARA) type arm 27, a base 28 to which one end of the arm 27 is attached, a bifurcated fork 29 attached to the other end of the arm 27, and two picks 30 (substrate holders) attached to the tips of the fork 29. Note that in the transport robot 23, the arms 27 are arranged in two stages in the vertical direction, but in FIG. 2, only one stage of the arm 27 is shown for ease of understanding.

[0027] Each of the two picks 30 holds a wafer W. The arm 27 is attached to a base 28 so as to be rotatable about a vertical rotation axis Z. The arm 27 also bends and extends in a horizontal plane perpendicular to the rotation axis Z. Fig. 2(A) shows the arm 27 in a retracted state, and Fig. 2(B) shows the arm 27 in an extended state.

[0028] When the arm 27 extends and retracts, the fork 29 moves without wobbling left and right in the extension and retraction direction of the arm 27 (black arrow in the figure), and the fork 29 does not rotate. Therefore, the two picks 30 also move without wobbling left and right in the extension and retraction direction of the arm 27, and do not rotate. This allows the transport robot 23 to transport each wafer W linearly along the extension and retraction direction. In addition, by rotating the arm 27 around the rotation axis Z, the transport robot 23 can change the transport direction of each wafer W. In the following, the extension and retraction direction of the arm 27 will be simply referred to as the "extension and retraction direction". The transport robot 23 freely transports the wafer W between each process module 11, the substrate transfer chamber 16, and the load lock module 13 by combining the extension and retraction and rotation of the arm 27.

[0029] In the transfer robot 23, the fork 29 has a shape symmetrical about the center line CL of the transfer robot 23 (arm 27) along the extension / retraction direction, and the two picks 30 are disposed at positions symmetrical about the center line CL.

[0030] Fig. 3 is a perspective view for explaining the configuration of the AWC sensors 26L and 26R. Since the AWC sensor 26R has a similar configuration to the AWC sensor 26L, only the AWC sensor 26L is shown in Fig. 3, and a description of the AWC sensor 26R will be omitted.

[0031] 3, the AWC sensor 26L has a light-emitting unit 31 and a light-receiving unit 32. The light-emitting unit 31 oscillates a laser light L (detection light) toward the light-receiving unit 32, and the light-receiving unit 32 receives the laser light L. When the arm 27 is extended and the wafer W held by the pick 30 passes between the light-emitting unit 31 and the light-receiving unit 32, the light-receiving unit 32 stops receiving the laser light L at the point when the wafer W starts to intersect with the laser light L, and therefore the light-receiving unit 32 transmits an OFF signal to the control unit 15. Also, when the wafer W has finished passing between the light-emitting unit 31 and the light-receiving unit 32 and no longer intersects with the laser light L, the light-receiving unit 32 starts receiving the laser light L again, and therefore the light-receiving unit 32 transmits an ON signal to the control unit 15.

[0032] The control unit 15 calculates the extension amount of the arm 27 when receiving an off signal or an on signal, for example, the distance in the extension direction from the pivot axis Z to the center position in the extension direction of the pick 30. The distance is calculated, for example, from an encoder value of a motor (not shown) that drives the arm 27 of the transport robot 23. Hereinafter, the distance in the extension direction from the pivot axis Z to the center position in the extension direction of the pick 30 is defined as the "extension amount of the arm 27". In this case, the extension amount of the arm 27 corresponds to the distance indicated by "R" in FIG. 2(A) and FIG. 2(B). However, the extension amount of the arm 27 is not limited to the distance in the extension direction from the pivot axis Z to the center position in the extension direction of the pick 30, and may be any amount that changes with the extension of the arm 27.

[0033] Incidentally, the control unit 15 can obtain, from a design drawing or the like of the substrate processing system 10, the extension amount of the arm 27 at the time when the wafer W held at the correct position without deviation with respect to the pick 30 starts to intersect with the laser light L. Similarly, the control unit 15 can obtain the extension amount of the arm 27 at the time when the wafer W held at the correct position without deviation with respect to the pick 30 finishes intersecting with the laser light L.

[0034] The control unit 15 can grasp the positional deviation of the wafer W with respect to the pick 30 based on a comparison between the extension amount of the arm 27 when the OFF signal is received and the extension amount of the arm 27 when the ON signal is received and the former, and can grasp the positional deviation of the wafer W with respect to the pick 30 based on a comparison between the extension amount of the arm 27 when the ON signal is received and the former.

[0035] 4, each pick 30 has a left protrusion 33 (first protrusion) disposed on the left side in the extension / contraction direction, and a right protrusion 34 (second protrusion) disposed on the right side in the extension / contraction direction. The left protrusion 33 and the right protrusion 34 move together with the pick 30 as the arm 27 extends and contracts.

[0036] The left projection 33 of the pick 30 extends in a horizontal plane perpendicular to the pivot axis Z, and has a rear end side 33a extending in a direction perpendicular to the extension / contraction direction, and a hypotenuse 33b (first hypotenuse) intersecting obliquely with the direction perpendicular to the extension / contraction direction. The right projection 34 of the pick 30 extends in a horizontal plane perpendicular to the pivot axis Z, and has a rear end side 34a extending in a direction perpendicular to the extension / contraction direction, and a hypotenuse 34b (second hypotenuse) intersecting obliquely with the direction perpendicular to the extension / contraction direction.

[0037] Furthermore, in each pick 30, the left protrusion 33 and the right protrusion 34 have a shape that is symmetrical about the center line cl along the extension direction of the pick 30. Here, as described above, the two picks 30 are disposed at positions that are symmetrical about the center line CL. Therefore, the left protrusion 33 of the left pick 30 and the right protrusion 34 of the right pick 30 also have a shape that is symmetrical about the center line CL.

[0038] As described above, the AWC sensors 26L, 26R are disposed to correspond to the gate valves 25, and each gate valve 25 is disposed in the movement path of each pick 30 when the arm 27 is extended. Therefore, the AWC sensors 26L, 26R are also disposed in the movement path of the pick 30.

[0039] When the pick 30 moves, the left protrusion 33 intersects with the laser light L of the AWC sensor 26L, and the right protrusion 34 intersects with the laser light L of the AWC sensor 26R. The AWC sensor 26L (first sensor) corresponding to the left pick 30 and the AWC sensor 26R (second sensor) corresponding to the right pick 30 are designed to be disposed at positions symmetrical left and right with respect to the center line CL. Hereinafter, the AWC sensor 26L corresponding to the left pick 30 will be referred to as the "left AWC sensor 26L," and the AWC sensor 26R corresponding to the right pick 30 will be referred to as the "right AWC sensor 26R."

[0040] When the left pick 30 moves, first, the left protrusion 33 of the left pick 30 intersects with the laser light L of the left AWC sensor 26L, and when the left pick 30 moves further, the left protrusion 33 of the left pick 30 no longer intersects with the laser light L of the left AWC sensor 26L. Also, when the right pick 30 moves, first, the right protrusion 34 of the right pick 30 intersects with the laser light L of the right AWC sensor 26R, and when the right pick 30 moves further, the right protrusion 34 of the right pick 30 no longer intersects with the laser light L of the right AWC sensor 26R.

[0041] 4, for reference, each pick 30 is shown by a dashed line when the left protrusion 33 of the left pick 30 starts to intersect with the laser light L of the left AWC sensor 26L and when the right protrusion 34 of the right pick 30 starts to intersect with the laser light L of the right AWC sensor 26R. Also, each pick 30 is shown by a dashed line when the left protrusion 33 of the left pick 30 no longer intersects with the laser light L of the left AWC sensor 26L and when the right protrusion 34 of the right pick 30 no longer intersects with the laser light L of the right AWC sensor 26R.

[0042] 5 is a diagram for explaining the intersection of the left protrusion 33 and the laser light L of the left AWC sensor 26L and the intersection of the right protrusion 34 and the laser light L of the right AWC sensor 26R when the arm 27 of the transfer robot 23 is extended. Note that hereinafter, the laser light L of the left AWC sensor 26L will be simply referred to as the "left laser light L," and the laser light L of the right AWC sensor 26R will be simply referred to as the "right laser light L."

[0043] When arm 27 extends as shown in Fig. 5(A), in the left pick 30, first, left side protrusion 33 starts to intersect with left side laser light L as shown in Fig. 5(B). At this time, oblique side 33b of left side protrusion 33 intersects with left side laser light L, and then the laser light L is blocked by left side protrusion 33. Therefore, an OFF signal is transmitted from light receiving unit 32 at the timing when oblique side 33b of left side protrusion 33 intersects with left side laser light L, and control unit 15 calculates the extension amount of arm 27 at this time. The extension amount of arm 27 calculated at this time is hereinafter referred to as the "blocking start position A" of left side protrusion 33.

[0044] Furthermore, when the left pick 30 moves further, the left protrusion 33 finishes intersecting with the left laser light L, as shown in FIG. 5(C). At this time, the rear end edge 33a of the left protrusion 33 intersects with the left laser light L, and thereafter, the laser light L is no longer blocked by the left protrusion 33. Therefore, an ON signal is sent from the light receiving unit 32 at the timing when the rear end edge 33a of the left protrusion 33 intersects with the left laser light L, and the control unit 15 calculates the extension amount of the arm 27 at this point. The extension amount of the arm 27 calculated at this time is hereinafter referred to as the "blocking end position B" of the left protrusion 33.

[0045] Also, when the arm 27 extends as shown in Fig. 5(A), in the right pick 30, first, the right-side protrusion 34 starts to intersect with the right-side laser light L as shown in Fig. 5(B). At this time, the oblique side 34b of the right-side protrusion 34 intersects with the right-side laser light L, and then the laser light L is blocked by the right-side protrusion 34. Therefore, an OFF signal is transmitted from the light receiving unit 32 at the timing when the oblique side 34b of the right-side protrusion 34 intersects with the right-side laser light L, and the control unit 15 calculates the extension amount of the arm 27 at this time. The extension amount of the arm 27 calculated at this time will be referred to as the "blocking start position C" of the right-side protrusion 34 hereinafter.

[0046] Furthermore, when the right pick 30 moves further, the right protrusion 34 finishes intersecting with the right laser light L, as shown in FIG. 5(C). At this time, the rear end edge 34a of the right protrusion 34 intersects with the right laser light L, and thereafter, the laser light L is no longer blocked by the right protrusion 34. Therefore, an ON signal is transmitted from the light receiving unit 32 at the timing when the rear end edge 34a of the right protrusion 34 intersects with the right laser light L, and the control unit 15 calculates the extension amount of the arm 27 at this time. The extension amount of the arm 27 calculated at this time will be referred to as the "blocking end position D" of the right protrusion 34 hereinafter.

[0047] While the arm 27 extends from the shielding start position A to the shielding end position B, the left protrusion 33 of the left pick 30 continues to shield the left laser light L. Therefore, the difference (BA) between the shielding end position B and the shielding start position A of the left protrusion 33 coincides with the distance the arm 27 moves while shielding the left laser light L by the left protrusion 33. Also, while the arm 27 extends from the shielding start position C to the shielding end position D, the right protrusion 34 of the right pick 30 continues to shield the right laser light L. Therefore, the difference (DC) between the shielding end position D and the shielding start position C of the right protrusion 34 coincides with the distance the arm 27 moves while shielding the right laser light L by the right protrusion 34. Therefore, hereinafter, the difference between the shielding end position B and the shielding start position A of the left protrusion 33 will be referred to as the "left side shielding distance BA" (first distance), and the difference between the shielding end position D and the shielding start position C of the right side protrusion 34 will be referred to as the "right side shielding distance DC" (second distance).

[0048] Here, when the orientation of the arm 27 of the transfer robot 23 with respect to the rotation direction is not deviated from the design value, the timing at which the oblique side 33b of the left protrusion 33 and the left laser light L intersect with the oblique side 34b of the right protrusion 34 and the right laser light L intersect with each other coincides. Also, the timing at which the rear end side 33a of the left protrusion 33 and the left laser light L intersect with the rear end side 34a of the right protrusion 34 and the right laser light L intersect with each other coincides. Therefore, in this case, the shielding start position A of the left protrusion 33 and the shielding start position C of the right protrusion 34 coincide, and the shielding end position B of the left protrusion 33 and the shielding end position D of the right protrusion 34 also coincide. As a result, the left shielding distance BA and the right shielding distance DC coincide (FIG. 5(D)). In the following, the angular misalignment of the arm 27 around the rotation axis Z will be simply referred to as the "angular misalignment of the arm 27," and the "case in which the orientation of the arm 27 of the transport robot 23 in terms of the rotation direction does not deviate from the design value" will be referred to as the "case in which angular misalignment of the arm 27 does not occur."

[0049] On the other hand, when an angular deviation occurs in the arm 27, the left shielding distance BA and the right shielding distance DC do not match. Fig. 6 is a diagram for explaining the reason why the left shielding distance BA and the right shielding distance DC do not match when an angular deviation occurs in the arm 27. Note that in Fig. 6, the transport robot 23 including the arm 27 that is deviated in the counterclockwise direction is drawn with a solid line, and the transport robot 23 including the arm 27 without angular deviation is drawn with a dashed line.

[0050] For example, as shown in FIG. 6A, when the arm 27 is deviated from the design value in the counterclockwise direction, the center line CL along the actual extension / retraction direction of the arm 27 is tilted to the left with respect to the center line CL' along the design extension / retraction direction of the arm 27. Therefore, the left and right picks 30 are offset to the left from the designed positions. Meanwhile, the left AWC sensor 26L and the right AWC sensor 26R are disposed in positions symmetrical to the left with respect to the center line CL' along the design extension / retraction direction. Therefore, the left protrusion 33 of the left pick 30 is offset to the left with respect to the left AWC sensor 26L, and the right protrusion 34 of the right pick 30 is also offset to the left with respect to the right AWC sensor 26R.

[0051] At this time, when arm 27 is extended, left laser light L intersects with oblique side 33b of left protrusion 33 of left pick 30 on the right side than in the case where no angular misalignment of arm 27 occurs (FIG. 6(B)). Furthermore, left laser light L intersects with rear end side 33a of left protrusion 33 on the right side than in the case where no angular misalignment of arm 27 occurs (FIG. 6(C)). Here, left protrusion 33 becomes thicker toward the right (width in the extension / retraction direction becomes larger) due to the presence of oblique side 33b, so left shielding distance BA becomes longer than in the case where no angular misalignment of arm 27 occurs (FIG. 6(D)).

[0052] Furthermore, when the arm 27 is extended, the right-side laser light L intersects with the oblique side 34b of the right-side protrusion 34 of the right pick 30 on the right side of the arm 27, compared to when no angular misalignment occurs (FIG. 6(B)). Furthermore, the right-side laser light L intersects with the rear end side 34a of the right-side protrusion 34 on the right side of the arm 27, compared to when no angular misalignment occurs (FIG. 6(C)). Here, the right-side protrusion 34 becomes thinner toward the right (its width in the extension / retraction direction becomes smaller) due to the presence of the oblique side 34b, so the right-side shielding distance DC becomes shorter than when no angular misalignment occurs in the arm 27 (FIG. 6(D)).

[0053] That is, when an angular deviation occurs in arm 27, the left shielding distance BA and the right shielding distance DC no longer match, and further, the left shielding distance BA and the right shielding distance DC change compared to when there is no angular deviation in arm 27. In this embodiment, the angular deviation of arm 27 is calculated using the changes in the left shielding distance BA and the right shielding distance DC.

[0054] Fig. 7 is a diagram for explaining a method for calculating the angular deviation of the arm 27 of the transport robot 23. In Fig. 7 as well, the arm 27 is deviated in the counterclockwise direction from the design value, and the transport robot 23 including the arm 27 deviated in the counterclockwise direction is drawn in solid lines, and the transport robot 23 including the arm 27 without angular deviation is drawn in dashed lines.

[0055] At this time, as described above, the left shielding distance BA becomes longer than when no angular misalignment of the arm 27 occurs. This increase in the left shielding distance BA corresponds to the difference b between the shielding end position B of the left protrusion 33 when no angular misalignment of the arm 27 occurs and when angular misalignment of the arm 27 occurs, as shown in FIG. 7(A). Also, as described above, the right shielding distance DC becomes shorter than when no angular misalignment of the arm 27 occurs. This decrease in the right shielding distance DC corresponds to the difference d between the shielding end position D of the right protrusion 34 when no angular misalignment of the arm 27 occurs and when angular misalignment of the arm 27 occurs, as shown in FIG. 7(A).

[0056] Here, the magnitude of the angle shift is T (deg), and the pitch between the left AWC sensor 26L and the right AWC sensor 26R is E (hereinafter referred to as "sensor distance E"). In this case, the geometric relationship shown in Fig. 7B approximately holds between the magnitude of the angle shift T, the difference b in the shading end position B, the difference d in the shading end position D, and the sensor distance E.

[0057] If the sum of the difference b between the shielding end position B and the difference d between the shielding end position D is the distance x, then the geometric relationship shown in Fig. 7(C) approximately holds between the magnitude of the angular deviation T, the distance x, and the distance E between the sensors. Here, since the angular deviation of the arm 27 caused by slight deformation of the transfer module 12 due to reduced pressure is considered to be slight, the tangent of the magnitude of the angular deviation T (deg) can be approximated to the magnitude of the angular deviation T (rad). Therefore, the following formula (1) holds between the magnitude of the angular deviation T (deg), the distance x, and the distance E between the sensors.

[0058]

number

[0059] The left AWC sensor 26L and the right AWC sensor 26R are disposed at positions symmetrical to the left and right with respect to the center line CL' along the designed extension / retraction direction, so the difference b of the shielding end position B and the difference d of the shielding end position D are equivalent and are considered to be equal to half the distance x. Then, the following formulas (2) and (3) are established.

[0060]

number

[0061]

number

[0062] Furthermore, the following equation (4) holds between the shielding end position B when an angle misalignment occurs in arm 27 and the shielding end position B' (assumed extension amount of the first arm) when it is assumed that no angle misalignment occurs in arm 27.

[0063]

number

[0064] Furthermore, the following equation (5) holds between the shielding end position D when an angle misalignment of arm 27 occurs and the shielding end position D' (assumed extension amount of the second arm) when it is assumed that no angle misalignment of arm 27 occurs.

[0065]

number

[0066] Furthermore, since the difference between the shading start position A and the shading end position B' of the left protrusion 33 (left shading distance B'-A) ​​is considered to be equal to the difference between the shading start position C and the shading end position D' of the right protrusion 34 (right shading distance D'-C), the following equation (6) holds.

[0067]

number

[0068] By substituting the above formulas (4) and (5) into the above formula (6), the magnitude of the angular deviation T (deg) is expressed by the following formula (7). Here, the shielding start position A, the shielding end position B, the shielding start position C, and the shielding end position D are actual measured values ​​when an angular deviation of arm 27 occurs.

[0069]

number

[0070] Then, by replacing the shielding end position B-shielding start position A with the left shielding distance BA and replacing the shielding end position D-shielding start position C with the right shielding distance DC, the following formula (8) is obtained.

[0071]

number

[0072] In this way, the magnitude T of the angle deviation of the arm 27 of the transfer robot 23 can be calculated based on the left shielding distance BA, the right shielding distance DC, and the inter-sensor distance E.

[0073] Furthermore, in order to eliminate the angular misalignment of arm 27 using the magnitude T of the angular misalignment of arm 27 calculated as described above, it is necessary to determine whether arm 27 has misaligned in the clockwise direction or the counterclockwise direction.

[0074] 6, when arm 27 is deviated from the design value in the counterclockwise direction, left shielding distance BA becomes longer than when there is no angular deviation of arm 27. Also, right shielding distance DC becomes shorter than when there is no angular deviation of arm 27. That is, when arm 27 is deviated from the design value in the counterclockwise direction, left shielding distance BA becomes longer than right shielding distance DC.

[0075] On the other hand, as shown in Fig. 8(A), when the arm 27 is deviated clockwise from the design value, the center line CL along the actual extension / retraction direction of the arm 27 is tilted to the right with respect to the center line CL' along the design extension / retraction direction of the arm 27. Therefore, the left and right picks 30 are offset to the right from their designed positions. As a result, the left side protrusion 33 of the left pick 30 is offset to the right with respect to the left AWC sensor 26L, and the right side protrusion 34 of the right pick 30 is also offset to the right with respect to the right AWC sensor 26R.

[0076] At this time, when arm 27 is extended, left-side laser light L intersects with oblique side 33b of left-side protrusion 33 of left pick 30 on the left side compared to when no angular misalignment of arm 27 occurs (FIG. 8(B)). Furthermore, left-side laser light L intersects with rear end side 33a of left-side protrusion 33 on the left side compared to when no angular misalignment of arm 27 occurs (FIG. 8(C)). Here, left-side protrusion 33 becomes thinner toward the left due to the presence of oblique side 33b, so left-side shielding distance BA becomes shorter than when no angular misalignment of arm 27 occurs (FIG. 8(D)).

[0077] Furthermore, when the arm 27 is extended, the right-side laser light L intersects with the oblique side 34b of the right-side protrusion 34 of the right pick 30 on the left side than in the case where no angular misalignment of the arm 27 occurs (FIG. 8(B)). Furthermore, the right-side laser light L intersects with the rear end side 34a of the same right-side protrusion 34 on the left side than in the case where no angular misalignment of the arm 27 occurs (FIG. 8(C)). Here, the right-side protrusion 34 becomes thicker toward the left due to the presence of the oblique side 34b, so the right-side shielding distance DC becomes longer than in the case where no angular misalignment of the arm 27 occurs (FIG. 8(D)).

[0078] That is, when arm 27 is deviated from the design value in the clockwise direction, right shielding distance DC becomes longer than left shielding distance BA.

[0079] Therefore, in this embodiment, the direction of the angular deviation of arm 27 can be determined based on right shielding distance DC and left shielding distance BA. Specifically, when left shielding distance BA is longer than right shielding distance DC, it can be determined that arm 27 is deviated counterclockwise from the design value. Also, when right shielding distance DC is longer than left shielding distance BA, it can be determined that arm 27 is deviated clockwise from the design value.

[0080] FIG. 9 is a diagram for explaining the advantage of the left projection 33 and the right projection 34 of the pick 30 having the oblique sides 33b, 34b.

[0081] 9(A), a case will be considered in which the left protrusion 33 and the right protrusion 34 of the pick 30 do not have the oblique sides 33b, 34b, and the left protrusion 33 and the right protrusion 34 are rectangular in plan view. In this case, the left protrusion 33 has a front end side 33c extending in a direction perpendicular to the extension / retraction direction instead of the oblique side 33b, and the right protrusion 34 has a front end side 34c extending in a direction perpendicular to the extension / retraction direction instead of the oblique side 34b.

[0082] Even in this case, if the arm 27 is misaligned counterclockwise from the design value, the left protrusion 33 of the left pick 30 will be offset to the left relative to the left AWC sensor 26L, and the right protrusion 34 of the right pick 30 will also be offset to the left relative to the right AWC sensor 26R.

[0083] When the arm 27 is extended, the left laser light L intersects with the front end edge 33c of the left protrusion 33 of the left pick 30 on the right side of the arm 27 in the absence of any angular misalignment (FIG. 9(B)). Furthermore, the left laser light L intersects with the rear end edge 33a of the left protrusion 33 on the right side of the arm 27 in the absence of any angular misalignment (FIG. 9(C)). However, since the rear end edge 33a and the front end edge 33c extend parallel to each other, the left protrusion 33 does not become thicker toward the right side, and the width in the extension / retraction direction does not change. Therefore, the left shielding distance BA is the same as when the arm 27 does not have any angular misalignment (FIG. 9(D)).

[0084] Furthermore, when the arm 27 is extended, the right-side laser light L intersects with the front end edge 34c of the right-side protrusion 34 of the right pick 30 on the right side of the arm 27, compared to when no angular misalignment occurs (FIG. 9(B)). Furthermore, the right-side laser light L intersects with the rear end edge 34a of the right-side protrusion 34 on the right side of the arm 27, compared to when no angular misalignment occurs (FIG. 9(C)). Incidentally, since the rear end edge 34a and the front end edge 34c also extend parallel to each other, the right-side protrusion 34 does not become thinner toward the right, and the width in the extension / retraction direction does not change. Therefore, the right-side shielding distance DC is also the same as when no angular misalignment occurs in the arm 27 (FIG. 9(D)).

[0085] In this embodiment, the angular deviation of the arm 27 is calculated using changes in the left shielding distance BA and the right shielding distance DC. On the other hand, as described above, if the left protrusion 33 and the right protrusion 34 of the pick 30 do not have the oblique sides 33b, 34b, the left shielding distance BA and the right shielding distance DC do not change, and it is therefore substantially impossible to calculate the angular deviation of the arm 27. In other words, the transport robot 23 has the advantage that it is possible to calculate the angular deviation of the arm 27 due to the presence of the oblique sides 33b, 34b of the left protrusion 33 and the right protrusion 34.

[0086] In the present embodiment, the crossing angle of the oblique side 33b of the left projection 33 and the oblique side 34b of the right projection 34 with respect to the direction perpendicular to the extension / retraction direction is set to, for example, 45°. However, the crossing angle is not limited to this, and may be any angle at which the thickness of the left projection 33 and the right projection 34 changes along the direction perpendicular to the extension / retraction direction. For example, the crossing angle may be 30° or 60°. Since the larger the crossing angle, the larger the change in the left shielding distance BA and the right shielding distance DC becomes, from the viewpoint of detecting the angle deviation of the arm 27, it is preferable that the crossing angle of the oblique side 33b and the oblique side 34b with respect to the direction perpendicular to the extension / retraction direction is large.

[0087] Incidentally, when the left AWC sensor 26L and the right AWC sensor 26R are disposed inside the transfer module 12, these AWC sensors 26R, 26L may deviate from the designed positions. In addition, the left AWC sensor 26L and the right AWC sensor 26R may tilt due to slight deformation of the transfer module 12 caused by reduced pressure, and the irradiation direction of the left laser light L and the right laser light L may deviate from the designed direction. Furthermore, the irradiation direction of the left laser light L and the right laser light L may deviate, resulting in an insufficient amount of light of the left laser light L and the right laser light L reaching the left protrusion 33 and the right protrusion 34 of the pick 30. In such a case, the absolute values ​​of the measured shading start position A, shading end position B, shading start position C, and shading end position D include errors.

[0088] Here, as described above, if there is no angular misalignment of arm 27, the shielding start position A of left protrusion 33 and the shielding start position C of right protrusion 34 should coincide, and further, the shielding end position B of left protrusion 33 and the shielding end position D of right protrusion 34 should also coincide.

[0089] However, if there is a deviation or inclination from the designed position of the left AWC sensor 26L or the right AWC sensor 26R, the shielding start position A and the shielding start position C do not match because they both contain an error. In addition, the shielding end position B and the shielding end position D also do not match because they both contain an error. For example, even though the shielding start position A is 714 (mm), the shielding start position C may be 716 (mm), and even though the shielding end position B is 716 (mm), the shielding end position D may be 718 (mm). If the absolute values ​​of the shielding start position A, the shielding end position B, the shielding start position C, and the shielding end position D, which contain errors, are used as they are to calculate the magnitude T of the angle deviation of the arm 27, the magnitude T of the angle deviation cannot be obtained accurately.

[0090] In contrast to this, in the present embodiment, the absolute values ​​of the shielding start position A, the shielding end position B, the shielding start position C, and the shielding end position D are not used as they are in calculating the magnitude T of the angular deviation of arm 27. Instead, as shown in the above formula (8), the magnitude T of the angular deviation of arm 27 is calculated using relative values ​​of the extension amount of arm 27, such as the left shielding distance BA and the right shielding distance DC.

[0091] Because the shielding start position A and the shielding end position B are measured by the same left AWC sensor 26L, both include an error due to the left AWC sensor 26L. As a result, the error due to the left AWC sensor 26L is cancelled out in the left shielding distance BA. Therefore, even if there is a deviation or inclination from the designed position of the left AWC sensor 26L, the left shielding distance BA is a value that does not include an error.

[0092] In addition, because the shielding start position C and the shielding end position D are also measured by the same right AWC sensor 26R, both include an error due to the right AWC sensor 26R. As a result, the error due to the right AWC sensor 26R is also cancelled out in the right shielding distance DC. Therefore, even if there is a deviation or inclination from the designed position of the right AWC sensor 26R, the right shielding distance DC is also a value that does not include an error.

[0093] That is, in the method of calculating the magnitude T of the angular deviation of the arm 27 shown in the above formula (8), the magnitude T of the angular deviation of the arm 27 is calculated from the left occlusion distance BA and the right occlusion distance DC in which the errors due to the left AWC sensor 26L and the right AWC sensor 26R are cancelled out. This makes it possible to obtain an accurate magnitude T of the angular deviation.

[0094] 10 is a flowchart showing a correction process for the angle deviation of the arm 27 as a teaching method for a transfer robot according to an embodiment of the technology disclosed herein. This correction process is executed by the control unit 15 after the transfer robot 23 is placed in the transfer module 12 and the transfer module 12 is depressurized, for example, and before various depressurization processes are performed on the wafer W.

[0095] First, after the inside of the transfer module 12 is depressurized, the arm 27 is extended, and the laser light L of the left AWC sensor 26L and the left protrusion 33 of the left pick 30 are crossed to measure the shielding start position A and the shielding end position B. Also, the laser light L of the right AWC sensor 26R and the right protrusion 34 of the right pick 30 are crossed to measure the shielding start position C and the shielding end position D (step S101).

[0096] Next, the left side shielding distance BA is calculated from the measured shielding start position A and shielding end position B, and the right side shielding distance DC is calculated from the measured shielding start position C and shielding end position D. After that, the magnitude T of the angle deviation of the arm 27 is calculated based on the above formula (8) (step S102).

[0097] Next, it is determined whether the calculated magnitude T of the angle deviation of the arm 27 is equal to or less than the target angle (step S103). If the calculated magnitude T of the angle deviation of the arm 27 is equal to or less than the target angle, this process ends.

[0098] On the other hand, if the calculated magnitude T of the angle deviation of arm 27 is larger than the target angle, arm 27 is rotated around rotation axis Z so as to eliminate the calculated magnitude T of the angle deviation of arm 27 (step S104), and the process returns to step S101. In step S104, the right-side shielding distance DC and the left-side shielding distance BA are compared to determine the direction of the angle deviation of arm 27, and the rotation direction of arm 27 is decided.

[0099] According to this embodiment, the left AWC sensor 26L measures the shielding start position A and shielding end position B of the left protrusion 33 of the pick 30, and the right AWC sensor 26R measures the shielding start position C and shielding end position D of the right protrusion 34 of the pick 30. Then, the magnitude T of the angular deviation of the arm 27 can be calculated based on the right shielding distance DC and the left shielding distance BA. Therefore, when obtaining the magnitude T of the angular deviation of the arm 27, it is not necessary for the operator to visually grasp the angular deviation of the arm, and further, it is not necessary to prepare a wafer for alignment. This makes it possible to eliminate the angular deviation of the arm 27 without any trouble.

[0100] In particular, since the left AWC sensor 26L and the right AWC sensor 26R are provided in advance in the substrate processing system 10, the occurrence of additional costs for eliminating the angle deviation of the arm 27 can be suppressed.

[0101] Furthermore, in this embodiment, after the inside of the transfer module 12 is depressurized, the shielding start position A, the shielding end position B, the shielding start position C, and the shielding end position D are measured, and the angular deviation of the arm 27 is eliminated. As a result, when various depressurization processes are performed on the wafer W after the angular deviation of the arm 27 is eliminated, the angular deviation of the arm 27 and the deviation or inclination of the left AWC sensor 26L and the right AWC sensor 26R from the designed arrangement positions do not occur any more. This can eliminate the need to perform the correction process for the angular deviation of the arm 27 again.

[0102] Although the preferred embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist of the present disclosure.

[0103] For example, the left protrusion 33 and the right protrusion 34 of the pick 30 may have only one oblique side, but the left protrusion 33 and the right protrusion 34 may have two oblique sides. For example, as shown in Fig. 11, the left protrusion 33 of the pick 30 may have not only oblique side 33b but also oblique side 33d that intersects obliquely with the direction perpendicular to the extension / retraction direction (see the two-dot chain line in the figure) instead of the rear end side 33a. Also, the right protrusion 34 may have not only oblique side 34b but also oblique side 34d that intersects obliquely with the direction perpendicular to the extension / retraction direction instead of the rear end side 34a.

[0104] In this case as well, the thickness of left protrusion 33 and right protrusion 34 changes in the direction perpendicular to the extension / contraction direction, so that the left shielding distance BA and right shielding distance DC change when an angular deviation occurs in arm 27. Therefore, even if pick 30 shown in Fig. 11 is used, the magnitude T of the angular deviation of arm 27 can be calculated by measuring the shielding start position A, the shielding end position B, the shielding start position C, and the shielding end position D.

[0105] In addition, in this embodiment, the magnitude T of the angular deviation of the arm 27 was calculated by measuring the shielding start position A and shielding end position B of the left-side protrusion 33 of the right pick 30, as well as the shielding start position C and shielding end position D of the right-side protrusion 34 of the left pick 30.

[0106] However, the magnitude T of the angular deviation of the arm 27 may be calculated by measuring the shielding start position A and shielding end position B of the left protrusion 33 of only the right or left pick 30, and the shielding start position C and shielding end position D of the right protrusion 34 of the same pick 30. In this case, however, in the above formula (8), the inter-sensor distance E needs to use the pitch between the AWC sensors 26L and 26R corresponding to one pick 30, rather than the pitch between the left AWC sensor 26L and the right AWC sensor 26R.

[0107] The technology disclosed herein can also be applied to a case where the transfer robot 23 is equipped with only one pick 30. In this case, the magnitude T of the angular deviation of the arm 27 can be calculated by measuring the shielding start position A and shielding end position B of the left protrusion 33 of one pick 30, and the shielding start position C and shielding end position D of the right protrusion 34 of the same pick 30. However, even in this case, the inter-sensor distance E in the above formula (8) needs to use the pitch between the AWC sensors 26L and 26R corresponding to one pick 30, rather than the pitch between the left AWC sensor 26L and the right AWC sensor 26R. [Explanation of symbols]

[0108] 10. Substrate Processing System 11 Process Module 12 Transfer module 15 Control section 23 Transport Robot 26R, 26L AWC sensor 27 Arm 30 Picks 33 Left protrusion 34 Right protrusion 33a,34a Rear edge 33b,34b hypotenuse L Laser light W wafer

Claims

1. A teaching method for a transport robot, comprising: the transfer robot includes an arm that is rotatable about a vertical axis and that extends and contracts in a horizontal plane perpendicular to the axis, and a substrate holder attached to the arm; the arm has a first protrusion disposed on a left side in a direction in which the arm extends and retracts, and a second protrusion disposed on a right side in the direction in which the arm extends and retracts, As the arm expands and contracts, the first protrusion and the second protrusion move together with the substrate holding portion, A first sensor is disposed on the left side with respect to the extension / contraction direction, and a second sensor is disposed on the right side with respect to the extension / contraction direction, the first protrusion intersects with the detection light of the first sensor when the arm extends or retracts, and the second protrusion intersects with the detection light of the second sensor when the arm extends or retracts; calculating an angular deviation of the arm about the pivot axis based on an extension amount of the arm when the first protrusion intersects with the detection light of the first sensor and an extension amount of the arm when the second protrusion intersects with the detection light of the second sensor; A method for teaching a transfer robot, the method including rotating the arm about the rotation axis so as to eliminate the calculated angular deviation.

2. the first protrusion and the second protrusion have a shape symmetrical with respect to the extension / contraction direction, The method for teaching a transfer robot according to claim 1 , wherein the first sensor and the second sensor are disposed at positions symmetrical to each other with respect to the extension / contraction direction.

3. 2. The method for teaching a transport robot according to claim 1, wherein the first protrusion has a first oblique side that intersects obliquely with respect to a direction perpendicular to the extension / contraction direction in the horizontal plane, and the second protrusion has a second oblique side that intersects obliquely with respect to a direction perpendicular to the extension / contraction direction in the horizontal plane.

4. 2. The method for teaching a transport robot according to claim 1, further comprising: calculating an angular deviation of the arm around the pivot axis based on a first distance, which is a distance the arm moves from when the first protrusion starts to intersect with the detection light of the first sensor to when the arm finishes intersecting with the detection light of the first sensor, when the arm is extended or retracted, and a second distance, which is a distance the arm moves from when the second protrusion starts to intersect with the detection light of the second sensor to when the arm is extended or retracted, when the arm is extended or retracted.

5. The method for teaching a transfer robot according to claim 4 , further comprising the step of determining a direction of an angular deviation of the arm about the pivot axis based on the first distance and the second distance.

6. an extension amount of the arm when the first protrusion has finished intersecting with the detection light of the first sensor, assuming that there is no angular misalignment around the pivot axis of the arm, is defined as an assumed extension amount of the first arm; and an extension amount of the arm when the second protrusion has finished intersecting with the detection light of the second sensor, assuming that there is no angular misalignment around the pivot axis of the arm, is defined as an assumed extension amount of the second arm; 5. The method for teaching a transport robot according to claim 4, further comprising the step of calculating an angular deviation of the arm about the pivot axis by utilizing the fact that an assumed extension amount of the first arm can be calculated from an angular deviation of the arm about the pivot axis and an actual measurement value of the extension amount of the arm when the first protrusion has finished intersecting with the detection light of the first sensor, and that an assumed extension amount of the second arm can be calculated from an angular deviation of the arm about the pivot axis and an actual measurement value of the extension amount of the arm when the second protrusion has finished intersecting with the detection light of the second sensor.

7. The transfer robot is disposed inside a substrate transfer chamber, 2. The method for teaching a transport robot according to claim 1, wherein the amount of extension of the arm when the first protrusion intersects with the detection light of the first sensor and the amount of extension of the arm when the second protrusion intersects with the detection light of the second sensor are measured when the inside of the substrate transport chamber is depressurized.

8. 2. The method for teaching a transport robot according to claim 1, wherein the first sensor and the second sensor are sensors that are pre-installed in a substrate processing system to detect the substrate transported by the transport robot using the substrate holding part and the arm.

9. a substrate processing chamber for processing a substrate, a substrate transfer chamber in which a transfer robot for transferring the substrate into and out of the substrate processing chamber is disposed, and a control unit; the transfer robot has an arm that is rotatable about a vertical axis and that extends and retracts in a horizontal plane perpendicular to the axis, and a substrate holder attached to the arm; the arm has a first protrusion disposed on a left side in a direction in which the arm extends and retracts, and a second protrusion disposed on a right side in the direction in which the arm extends and retracts, As the arm expands and contracts, the first protrusion and the second protrusion move together with the substrate holding portion, A first sensor is disposed on the left side in the extension / contraction direction, and a second sensor is disposed on the right side in the extension / contraction direction, the first protrusion intersects with the detection light of the first sensor when the arm extends or retracts, and the second protrusion intersects with the detection light of the second sensor when the arm extends or retracts; The control unit calculates an angular misalignment of the arm about the pivot axis based on an amount of extension of the arm when the first protrusion intersects with the detection light of the first sensor and an amount of extension of the arm when the second protrusion intersects with the detection light of the second sensor, and rotates the arm about the pivot axis so as to eliminate the calculated angular misalignment.

Images