Robot control devices, robot systems, robot control programs

Abstract

To easily achieve proper gripping of a work-piece by a plurality of fingers.SOLUTION: A robot control device 5 includes. a movement control unit 55 which causes a robot arm 2, provided with a hand 3, to move; and an opening / closing control unit 56 which causes a plurality of fingers 31, provided in the hand 3, to open or close in a prescribed opening / closing direction. The movement control unit 55 causes the robot arm 2 to execute a contact motion to bring the fingers 31 into contact with a work-piece W in a pressing direction. The opening / closing control unit 56 causes the fingers 31 to execute an opening motion after the contact motion. After the fingers 31 have become out of contact with the work-piece W due to the opening motion, the movement control unit 55 causes the robot arm 2 to execute an approaching motion to cause the hand 3 to move, in a pressing direction, up to a grasping position. In a state where the hand 3 is situated at the grasping position, the opening / closing control unit 56 causes the fingers 31 to execute a closing motion so as to cause the fingers 31 to grasp the work-piece.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The technology disclosed herein relates to a robot control device, a robot system, and a robot control program.

Background Art

[0002] Conventionally, a control device for a robot that grips a workpiece with a plurality of fingers has been known. For example, Patent Document 1 discloses a technique for adjusting the interval between a plurality of fingers according to the shape of a workpiece or the like when gripping the workpiece with the plurality of fingers.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] ]> By the way, in the workpiece gripping operation, first, the hand is moved to a position where the workpiece can be gripped, that is, a position where the workpiece is disposed between a plurality of fingers, and from that state, the fingers are closed to grip the workpiece with the fingers. That is, appropriately moving the hand to the gripping position is necessary for gripping the workpiece.

[0005] However, if the position accuracy of the hand and the position accuracy of the workpiece are low, the hand may not be appropriately moved to the position where the workpiece can be gripped due to interference of the fingers with the workpiece or the like.

[0006] The technology disclosed herein has been made in view of such points, and the object thereof is to simply realize appropriate gripping of a workpiece by a plurality of fingers.

Means for Solving the Problems

[0007] The robot control device disclosed herein comprises a movement control unit for moving an arm equipped with a hand, and an opening / closing control unit for opening and closing a plurality of fingers provided on the hand in a predetermined opening / closing direction, wherein the movement control unit causes the arm to perform a contact operation in which the fingers contact a workpiece in a pressing direction intersecting the opening / closing direction, the opening / closing control unit causes the fingers to perform an opening operation after the contact operation, the movement control unit causes the arm to perform an approach operation in which the hand moves in the pressing direction to a predetermined gripping position in which the workpiece is positioned between the plurality of fingers after the fingers have become non-contact with the workpiece due to the opening operation, and the opening / closing control unit causes the fingers to grip the workpiece by performing a closing operation when the hand is in the gripping position.

[0008] The robot system disclosed herein comprises a hand provided with a plurality of fingers that can be opened and closed, an arm on which the hand is provided, and the robot control device.

[0009] The robot control program disclosed herein causes a computer to perform the following functions: a contact operation in which at least one of a plurality of fingers provided on the hand, which are capable of opening and closing in a predetermined opening and closing direction, contacts the workpiece in a pressing direction intersecting the opening and closing direction; a function to cause the finger to perform an opening operation after the contact operation; a function to cause the arm to perform an approach operation in which, after the finger is no longer in contact with the workpiece due to the opening operation, the hand moves in the pressing direction to a predetermined gripping position in which the workpiece is positioned between the plurality of fingers; and a function to cause the finger to grip the workpiece by causing the finger to perform a closing operation when the hand is in the gripping position. [Effects of the Invention]

[0010] According to the robot control device, proper gripping of a workpiece with multiple fingers can be easily achieved.

[0011] According to the robot system described above, it is possible to easily achieve proper gripping of a workpiece with multiple fingers.

[0012] According to the robot control program, proper gripping of a workpiece by multiple fingers can be easily achieved. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic diagram showing the configuration of the robot system. [Figure 2] Figure 2 is a magnified view of the hand. [Figure 3] Figure 3 shows a schematic hardware configuration of the robot control device. [Figure 4] Figure 4 is a block diagram showing the configuration of the control system of the control unit. [Figure 5] Figure 5 is a flowchart showing the processing steps for a robot's picking operation. [Figure 6] Figure 6 shows an example of a hand positioned in the preparation position. [Figure 7] Figure 7 shows a hand positioned at a location offset from the preparation position. [Figure 8] Figure 8 shows a hand with fingers in contact with a workpiece. [Figure 9] Figure 9 shows a hand with fingers in an opening motion. [Figure 10] Figure 10 shows a hand in a state where the fingers are not in contact with the workpiece as a result of the opening operation. [Figure 11] Figure 11 shows a hand positioned in the gripping position. [Figure 12] Figure 12 shows the hand in the state after the gripping operation has been completed. [Figure 13] Figure 13 shows a hand performing the first opening motion when gripping a workpiece with different widths at the top and the main body. [Figure 14] Figure 14 shows a hand that performs a second opening motion when gripping a workpiece with different widths at the top and the main body. [Figure 15]FIG. 15 is a diagram showing a hand that opens its fingers with respect to a workpiece having a recess formed therein. [Figure 16] FIG. 16 is a diagram showing a hand that picks up a deformable workpiece, showing a state in which the fingers are in contact with the workpiece. [Figure 17] FIG. 17 is a diagram showing a hand that picks up a deformable workpiece, showing a state in which the fingers are in contact with the side surface of the workpiece. [Figure 18] FIG. 18 is a diagram showing a hand that picks up a deformable workpiece, showing a state in which the hand has reached the gripping position. [Figure 19] FIG. 19 is a diagram showing a hand that picks up a deformable workpiece, showing a state in which the fingers have completed the gripping operation. [Figure 20] FIG. 20 is an enlarged view of the hand according to the modified example.

MODE FOR CARRYING OUT THE INVENTION

[0014] Hereinafter, exemplary embodiments will be described in detail based on the drawings. FIG. 1 is a schematic diagram showing the configuration of a robot system 100.

[0015] The robot system 100 includes a robot 1 and a robot control device 5 that controls the robot 1. The robot 1 has a robot arm 2 and a hand 3 provided with a plurality of fingers 31 that can be opened and closed. The hand 3 is provided on the robot arm 2.

[0016] In this example, the robot 1 grips the workpiece W with the fingers 31 and performs a picking operation of transporting the workpiece W. Specifically, the robot 1 takes out a specific workpiece W in the container 91 and transports it to a predetermined location. A plurality of workpieces W are accommodated in the container 91. The container 91 is placed on, for example, a shelf 92.

[0017] In this example, robot 1 is an industrial robot. The space in which robot 1 is placed is defined by a three-axis orthogonal robot coordinate system. For example, the Z axis is set in the vertical direction, and the X and Y axes are set horizontally, orthogonal to each other.

[0018] Robot 1 is further equipped with a force sensor 41 (see Figure 2) that detects the pressing force of the finger 31 onto the workpiece W. Robot 1 is also further equipped with an imaging device 42.

[0019] The robot arm 2 is configured to operate in three dimensions. In this example, the robot arm 2 is a vertical articulated robot arm. The robot arm 2 is supported by a base 10. The robot arm 2 has a plurality of links 21 and a plurality of joints 22 that connect the plurality of links 21. A hand 3 is connected to the link 21 at the tip of the robot arm 2.

[0020] The robot arm 2 has servo motors 23 (see Figure 3) that rotate each joint. Each servo motor 23 has an encoder 24 (see Figure 3).

[0021] Hand 3 is an end effector attached to robot arm 2. Figure 2 is an enlarged view of hand 3. Hand 3 has multiple fingers that open and close in a predetermined opening and closing direction. Specifically, hand 3 has a first finger 31A and a second finger 31B. The first finger 31A and the second finger 31B are supported on the body 30 of hand 3 so as to be slidable in the opening and closing direction. The first finger 31A and the second finger 31B extend from the body 30 in a direction substantially perpendicular to the opening and closing direction.

[0022] Hand 3 further includes multiple servo motors that independently open and close multiple fingers. Specifically, Hand 3 has a first servo motor 32A that drives the first finger 31A and a second servo motor 32B that drives the second finger 31B. The gripping force of the first finger 31A and the second finger 31B is adjusted by the torque of the first servo motor 32A and the second servo motor 32B. The first servo motor 32A and the second servo motor 32B each have an encoder 33 (see Figure 3). The first servo motor 32A and the second servo motor 32B are examples of drive sources.

[0023] Furthermore, when the first finger 31A and the second finger 31B are not distinguished, they may simply be referred to as "finger 31." Also, when the first servo motor 32A and the second servo motor 32B are not distinguished, they may simply be referred to as "servo motor 32."

[0024] A force sensor 41 is provided for each of the multiple fingers 31. Specifically, a force sensor 41 is provided for both the first finger 31A and the second finger 31B. The force sensor 41 provided for the first finger 31A is referred to as the "first force sensor 41A," and the force sensor 41 provided for the second finger 31B is referred to as the "second force sensor 41B." When the first force sensor 41A and the second force sensor 41B are not distinguished, they are simply referred to as the "force sensor 41." The force sensor 41 detects forces in a direction that intersects, or more specifically, is approximately perpendicular to, the opening and closing direction. The direction of the force detected by the force sensor 41 may be approximately the same as the extension direction of the finger 31. In this example, the force sensor 41 detects forces in three orthogonal axial directions and moments around these three axes. One of the three orthogonal axial directions intersects with the opening and closing direction. The force sensor 41 is an example of a sensor.

[0025] The imaging device 42 captures a two-dimensional image. The imaging device 42 is mounted on the robot arm 2. More specifically, as shown in Figure 1, the imaging device 42 is attached to the link 21 at the tip of the robot arm 2. For example, the imaging device 42 captures the workpiece W inside the container 91 from above the container 91. The imaging device 42 outputs the captured image to the robot control device 5.

[0026] Figure 3 shows a schematic hardware configuration of the robot control device 5. The robot control device 5 receives the detection results from the force sensor 41 and the images captured by the imaging device 42 as input. The robot control device 5 controls the servo motor 23 of the robot arm 2 and the servo motor 32 of the hand 3. For example, the robot control device 5 supplies current to the servo motor 23. At this time, the robot control device 5 provides feedback control of the supplied current based on the output of the encoder 24. The robot control device 5 also controls the servo motor 32 of the hand 3 to open and close the two fingers 31. At this time, the robot control device 5 provides feedback control of the supplied current based on the output of the encoder 33. For example, the robot control device 5 causes the robot 1 to perform a picking operation in which the hand 3 takes a workpiece W from inside the container 91 and transports the workpiece W to a predetermined location.

[0027] The robot control device 5 includes a control unit 51, a storage unit 52, and a memory 53.

[0028] The control unit 51 controls the entire robot control device 5. The control unit 51 performs various calculation processes. For example, the control unit 51 is formed by a processor such as a CPU (Central Processing Unit). The control unit 51 may also be formed by an MCU (Micro Controller Unit), MPU (Micro Processor Unit), FPGA (Field Programmable Gate Array), PLC (Programmable Logic Controller), system LSI, etc.

[0029] The memory unit 52 stores programs and various data executed by the control unit 51. For example, the memory unit 52 stores the robot control program 54. The memory unit 52 is made up of non-volatile memory, an HDD (Hard Disk Drive), or an SSD (Solid State Drive), etc.

[0030] Memory 53 temporarily stores data, etc. For example, memory 53 is made of volatile memory.

[0031] Figure 4 is a block diagram showing the configuration of the control system of the control unit 51. The control unit 51 implements various functions by reading the robot control program 54 from the storage unit 52 into the memory 53 and processing it. Specifically, the control unit 51 functions as a movement control unit 55 that moves the robot arm 2, an opening / closing control unit 56 that opens and closes multiple fingers 31 in the opening / closing direction, and a position identification unit 57 that identifies the position of the workpiece W.

[0032] The movement control unit 55 controls the current applied to the servo motor 23 to adjust the rotation angle of the joint 22, thereby deforming and moving the robot arm 2. Hereinafter, unless otherwise specified, the movement of the robot arm 2 includes the deformation of the robot arm 2.

[0033] The opening / closing control unit 56 controls the current applied to the servo motor 32 to open and close multiple fingers 31. Specifically, the opening / closing control unit 56 calculates the torque command value (or rotational angle position command) for the servo motor 32 and outputs the calculated torque command value to the servo amplifier of the servo motor 32. The servo motor applies a current to the servo motor 32 according to the torque command value. The opening / closing control unit 56 controls multiple servo motors 32 independently. In other words, the opening / closing control unit 56 opens and closes multiple fingers 31 independently. For example, the opening / closing control unit 56 can open or close only one finger 31 while keeping the other fingers 31 stopped. The opening / closing control unit 56 can also open one finger 31 and close the other fingers 31. Furthermore, the opening / closing control unit 56 independently controls the torque of multiple servo motors 32. For example, the opening / closing control unit 56 can make the driving force of each finger 31 different when closing multiple fingers 31. Furthermore, the opening / closing control unit 56 may adjust the current applied to the servo motor 32, for example, the torque command value, according to the force in the opening / closing direction detected by the force sensor 41.

[0034] The positioning unit 57 identifies the position of the workpiece W from the image captured by the imaging device 42. Specifically, the positioning unit 57 identifies the workpiece W in the captured image by image processing and determines the position of the workpiece W. Since the imaging device 42 is moved by the robot arm 2, the position of the imaging device 42 is known. Therefore, the positioning unit 57 can identify the position of the subject in the captured image, i.e., the workpiece W. In this example, since the captured image is a two-dimensional image, the positioning unit 57 identifies the two-dimensional position of the workpiece W. More specifically, the positioning unit 57 identifies the position of the workpiece W in the XY plane of the robot coordinate system.

[0035] Furthermore, the positioning unit 57 also controls the imaging device 42. In other words, the positioning unit 57 causes the imaging device 42 to photograph the workpiece W.

[0036] The movement control unit 55 and the opening / closing control unit 56 work together to cause the robot arm 2 and hand 3 to perform a picking operation of the workpiece W. Specifically, the movement control unit 55 and the opening / closing control unit 56 move the hand 3 to a gripping position where the workpiece W can be grasped by the robot arm 2, have the fingers 31 grasp the workpiece W at the gripping position, and have the robot arm 2 transport the workpiece W to a predetermined location. The gripping position is the position where the workpiece W is positioned between multiple fingers 31.

[0037] In this case, the fingers 31 may interfere with the workpiece W when the hand 3 moves to the gripping position. In that case, the movement control unit 55 and the opening / closing control unit 56 resolve the interference between the fingers 31 and the workpiece W by opening the fingers 31, and then move the hand 3 to the gripping position.

[0038] In simple terms, the movement control unit 55 causes the robot arm 2 to perform a contact operation in which the finger 31 comes into contact with the workpiece W in a pressing direction intersecting the opening and closing direction. Once the finger 31 comes into contact with the workpiece W, the opening and closing control unit 56 causes the finger 31 to perform an opening operation after the contact operation. This opening operation of the finger 31 is an operation that eliminates contact between the finger 31 and the workpiece W, and can therefore also be called a "disconnection operation". After the finger 31 is no longer in contact with the workpiece W due to the opening operation, the movement control unit 55 causes the robot arm 2 to perform an approach operation in which the hand 3 moves in the pressing direction to the gripping position. With the hand 3 in the gripping position, the opening and closing control unit 56 causes the finger 31 to grip the workpiece W by performing a closing operation.

[0039] Here, the movement control unit 55 performs force control of the robot arm 2 so that contact between the finger 31 and the workpiece W is maintained during the opening operation of the finger 31. More specifically, in the force control of the robot arm 2, the movement control unit 55 controls the robot arm 2 so that the pressing force of the finger 31 in the pressing direction against the workpiece W becomes a predetermined target value. Since contact between the finger 31 and the workpiece W is maintained during the opening operation of the finger 31, the finger 31 opens while following the surface of the workpiece W. As the finger 31 opens, it may eventually come to a state where it is no longer in contact with the workpiece W. Hereinafter, unless otherwise specified, "pressing force" refers to the pressing force in the pressing direction.

[0040] The movement control unit 55 performs so-called admittance control as force control for the robot arm 2. Specifically, the movement control unit 55 adjusts the position of the hand 3 so that the pressing force reaches a target value. The movement control unit 55 performs admittance control using a mechanical model having mass, springs, and dampers, which corresponds to the robot arm 2. A function representing the mechanical model of the robot arm 2 is stored in the memory unit 52. The movement control unit 55 determines the current pressing force based on the pressing force detected by the force sensor 41. The movement control unit 55 reads the function of the mechanical model from the memory unit 52 and determines the target position of the hand 3 by substituting the pressing force detected by the force sensor 41 into the function. The movement control unit 55 calculates the joint angles of the robot arm 2 to achieve the target position of the hand 3. The movement control unit 55 adjusts the applied current to the servo motor 23 to achieve the calculated joint angles.

[0041] The picking operation will be further explained below using a flowchart. Figure 5 is a flowchart showing the processing of the picking operation of robot 1.

[0042] First, in step S101, the movement control unit 55 and the position identification unit 57 perform imaging of the workpiece W. Specifically, the movement control unit 55 moves the robot arm 2 so that the imaging device 42 is positioned at a predetermined imaging position. The predetermined imaging position is a position determined in advance according to the picking operation. For example, the imaging position is above the container 91 and is a position where the entire inside of the container 91 is within the field of view. However, if there are other objects around the container 91, such as when the container 91 is placed on a shelf 92, the imaging position is set to a position where the robot arm 2 and hand 3 do not interfere with the other objects.

[0043] When the imaging device 42 is positioned at the imaging location, the position identification unit 57 instructs the imaging device 42 to take an image. As a result, the workpiece W inside the container 91 is photographed.

[0044] The position determination unit 57 determines the position of the workpiece W, specifically the position of the workpiece W in the XY plane of the robot coordinate system, from the image captured by the imaging device 42.

[0045] Next, in step S102, the movement control unit 55 moves the robot arm 2 to a predetermined preparation position for the hand 3. Figure 6 shows an example of the hand 3 positioned in the preparation position. Figure 7 shows the hand 3 positioned at a location offset from the preparation position.

[0046] The preparation position is a position where the hand 3 and the workpiece W are aligned in approximately a straight line in the direction of movement of the hand 3 in subsequent force control, i.e., the pressing direction, and where the fingers 31 do not interfere with the workpiece W. In this example, the pressing direction is approximately perpendicular to the opening and closing direction, and specifically, it is the Z direction of the robot coordinate system. The XY coordinates of the preparation position are set based on the position of the workpiece W identified by the position identification unit 57. The Z coordinate of the preparation position is predetermined according to the target workpiece W. Specifically, the Z coordinate of the preparation position is a position higher than the height (dimension in the Z direction) of the workpiece W.

[0047] Furthermore, the movement control unit 55 sets the hand 3 to a predetermined ready posture in the ready position. The ready posture is the posture of the hand 3 when force control is performed later. Specifically, the ready posture is a posture in which the opening and closing direction of the fingers 31 is approximately perpendicular to the pressing direction. In this example, the posture of the hand 3 is adjusted so that the opening and closing direction coincides with the X direction of the robot coordinate system.

[0048] Furthermore, while the movement control unit 55 moves the hand 3 to the preparation position, the opening / closing control unit 56 moves the multiple fingers 31 to predetermined initial positions. For example, the initial position is a position where the spacing between the multiple fingers 31 is wider than the width of the workpiece W (dimension in the opening / closing direction). The initial position is predetermined according to the target workpiece W. Alternatively, the initial position may be determined for each picking operation based on the width of the workpiece W obtained from the image captured by the imaging device 42.

[0049] However, the XY coordinates of the preparation position identified by the position identification unit 57 may deviate from the appropriate preparation position depending on the resolution of the captured image and the accuracy of the image processing. Also, depending on the position accuracy of the robot arm 2, the position of the hand 3 may deviate from the preparation position identified by the position identification unit 57. In other words, the hand 3 may deviate from the appropriate preparation position due to various factors, as shown in Figure 7.

[0050] Next, in step S103, force control is initiated to control the pressing force of the finger 31 against the workpiece W. Specifically, the movement control unit 55 moves the robot arm 2 so that the pressing force of the finger 31 against the workpiece W becomes a predetermined target value. The pressing force is generated when the finger 31 comes into contact with the workpiece W. The movement control unit 55 moves the finger 31, i.e., the hand 3, in the pressing direction to bring it closer to the workpiece W so that the pressing force is generated.

[0051] For example, the target value of the pressing force is a value that does not excessively press the workpiece W, but is sufficient to confirm contact between the finger 31 and the workpiece W. Based on the mechanical model stored in the memory unit 52, the movement control unit 55 calculates the target position of the robot arm 2 such that the pressing force becomes the target value. The movement control unit 55 moves the robot arm 2 to the target position. In this way, the movement control unit 55 adjusts the position of the robot arm 2, i.e., the hand 3, so that the pressing force detected by the force sensor 41 becomes the target value.

[0052] As a result, if the pressing force is less than the target value, the movement control unit 55 moves the hand 3 toward the workpiece W in the pressing direction. On the other hand, if the pressing force is greater than the target value, the movement control unit 55 moves the hand 3 toward the workpiece W in the pressing direction. When the hand 3 is in the preparation position, none of the fingers 31 are in contact with the workpiece W, so the pressing force is 0. Therefore, the movement control unit 55 moves the hand 3 toward the workpiece W in the pressing direction. In other words, when force control is started from the preparation position, the movement control unit 55 first moves the hand 3 toward the workpiece W in the pressing direction.

[0053] When force control is initiated, in step S104, the movement control unit 55 determines whether the hand 3 has reached the gripping position. In this example, the XY coordinates of the preparation position are the same as the XY coordinates of the gripping position, and the hand 3 moves only in the Z direction. Therefore, in step S104, the movement control unit 55 determines whether the position of the hand 3 in the pressing direction, i.e., the Z-direction position, has reached the Z-coordinate of the gripping position. The Z-coordinate of the gripping position is predetermined according to the target workpiece W. Specifically, the Z-coordinate of the gripping position is the position where the fingers 31 can grip an appropriate portion of the workpiece W in the height direction.

[0054] If hand 3 has not reached the gripping position, the movement control unit 55 determines in step S107 whether or not the fingers 31 have come into contact with the workpiece W. If hand 3 is properly positioned in the preparation position as shown in Figure 6, the possibility of fingers 31 coming into contact with workpiece W is low even if hand 3 moves in the pressing direction. On the other hand, if hand 3 is not properly positioned in the preparation position as shown in Figure 7, fingers 31 may come into contact with workpiece W if hand 3 moves in the pressing direction. However, even if hand 3 is properly positioned in the preparation position, depending on the positional accuracy of the robot arm 2, hand 3 may not move straight in the pressing direction, and fingers 31 may come into contact with workpiece W. Figure 8 shows hand 3 with fingers 31 in contact with workpiece W. In Figure 8, the second finger 31B is in contact with workpiece W.

[0055] Specifically, the movement control unit 55 determines whether the pressing force detected by any of the force sensors 41 is equal to or greater than the target value. If none of the fingers 31 are in contact with the workpiece W, the movement control unit 55 returns to the process of step S104. At this time, since the movement control unit 55 is continuing force control, it continues to move the hand 3 in the pressing direction. Then, the movement control unit 55 executes the process of step S104 again. In other words, the movement control unit 55 continues to move the hand 3 in the pressing direction until the hand 3 reaches the gripping position or until any of the fingers 31 make contact with the workpiece W. Note that the movement of the robot arm 2 until the fingers 31 make contact with the workpiece W corresponds to a contact operation in which the fingers 31 make contact with the workpiece W in the pressing direction.

[0056] If any of the fingers 31 come into contact with the workpiece W, in step S108, the opening / closing control unit 56 causes the hand 3 to perform an opening operation of the fingers 31. Specifically, the opening / closing control unit 56 stops the fingers 31 that are not in contact with the workpiece W, while opening the fingers 31 that are in contact with the workpiece W. For example, as shown in Figure 8, if the first finger 31A does not come into contact with the workpiece W, but the second finger 31B comes into contact with the workpiece W, the opening / closing control unit 56 stops the first finger 31A, while causing the second finger 31B to perform an opening operation.

[0057] Even while the finger 31 is opening, the movement control unit 55 continues to control the force of the robot arm 2 so that contact between the finger 31 and the workpiece W is maintained. Figure 9 shows the hand 3 that causes the finger 31 to open. In parallel with the opening of the second finger 31B, the movement control unit 55 adjusts the position of the hand 3 in the pressing direction by the robot arm 2, as shown in Figure 9, to maintain the state in which the second finger 31B is pressed against the workpiece W with a pressing force that is approximately equal to the target value. As a result, the second finger 31B opens while conforming to the surface shape of the part of the workpiece W that the second finger 31B is in contact with. In the example in Figure 9, as the second finger 31B opens, the hand 3 moves closer to the workpiece W in the pressing direction.

[0058] Subsequently, in step S109, the opening / closing control unit 56 determines whether the finger 31 has opened to a state where it is not in contact with the workpiece W. Specifically, the opening / closing control unit 56 determines whether the pressing force of the finger 31 against the workpiece W has become 0. As a result of the opening operation of the finger 31 and the force control of the robot arm 2 being performed in parallel, when the finger 31 extends beyond the workpiece W in the opening / closing direction, the finger 31 will be in a state where it is not in contact with the workpiece W. At this time, the pressing force becomes 0. Figure 10 shows the hand 3 in a state where the finger 31 is not in contact with the workpiece W as a result of the opening operation. As shown in Figure 10, as a result of the opening operation, both the first finger 31A and the second finger 31B are in a state where they are not in contact with the workpiece W.

[0059] When finger 31 opens to a state where it does not contact the workpiece W, in step S110, the opening / closing control unit 56 stops the opening movement of finger 31. The opening / closing control unit 56 may stop the opening movement of finger 31 immediately when the pressing force becomes 0, or it may continue the opening movement of finger 31 for a while after the pressing force becomes 0 before stopping the opening movement. In the example in Figure 10, the opening movement of the second finger 31B continues for a predetermined amount after the pressing force becomes 0, and then the opening movement of the second finger 31B is stopped.

[0060] Furthermore, if finger 31 is still in contact with workpiece W even when finger 31 is fully extended, the process will be restarted from step S101.

[0061] When the opening movement of the fingers 31 is stopped, the process in step S104 is executed again. Even when the opening movement of the fingers 31 is stopped, the movement control unit 55 continues to control the force. Therefore, the movement of the hand 3 in the pressing direction continues. In step S104, the movement control unit 55 determines whether the hand 3 has reached the gripping position. If the hand 3 has not reached the gripping position, the movement control unit 55 determines in step S105 whether the fingers 31 have come into contact with the workpiece W. In other words, the movement control unit 55 continues to move the hand 3 in the pressing direction until the hand 3 reaches the gripping position or one of the fingers 31 comes into contact with the workpiece W. The movement of the hand 3 to the gripping position in the pressing direction after the fingers 31 have come into contact with the workpiece W due to the opening movement of the fingers 31 corresponds to the approaching movement.

[0062] Furthermore, if finger 31 comes into contact with workpiece W again, the processes from step S108 onwards described above will be executed. If the width of workpiece W is gradually increasing in the pressing direction, even if finger 31 comes into contact with workpiece W due to the opening movement of finger 31, finger 31 may come into contact with workpiece W again due to the movement of hand 3 in the pressing direction.

[0063] On the other hand, in step S104, if it is determined that the hand 3 has reached the gripping position, the movement control unit 55 stops force control. Then, in step S105, the opening / closing control unit 56 causes the hand 3 to perform a gripping operation. Figure 11 shows the hand 3 in the gripping position. In the gripping position, as shown in Figure 11, the workpiece W is positioned between the multiple fingers 31. In this state, the multiple fingers 31 perform a closing operation.

[0064] Furthermore, if hand 3 moves from the preparation position to the gripping position without fingers 31 contacting the workpiece W, steps S104 and S107 are repeated until step S105 is executed.

[0065] Figure 12 shows the hand 3 in the state after the gripping operation is completed. During the gripping operation, the timing at which each finger 31 contacts the workpiece W differs depending on the positional relationship between the multiple fingers 31 and the workpiece W. At this time, the opening / closing control unit 56 controls the torque of each servo motor 32. During the closing operation of the fingers 31, the opening / closing control unit 56 operates all servo motors 32 with the same torque. When any of the fingers 31 contact the workpiece W, the finger 31 that is in contact with the workpiece W will find it difficult to move in the closing direction due to the resistance of the workpiece W. The fingers 31 that are not in contact with the workpiece W will continue to move in the closing direction. Eventually, as shown in Figure 12, all fingers 31 will contact the workpiece W and grip the workpiece W. In other words, the amount of movement of each finger 31 in the closing direction may differ depending on the positional relationship between the multiple fingers 31 and the workpiece W. The workpiece W is gripped by the fingers 31 at approximately the same position as before the start of the gripping operation.

[0066] However, if the workpiece W is simply resting on the placement surface, the workpiece W may move from its position before the start of the gripping operation if the pressing force of the closing finger 31 is greater than the frictional force between the workpiece W and the placement surface.

[0067] Once the gripping operation is complete, in step S106, the movement control unit 55 causes the robot arm 2 to perform a transport operation. Specifically, the movement control unit 55 moves the robot arm 2 so that the workpiece W is transported to a predetermined location. The opening / closing control unit 56 may move the multiple fingers 31 to the center position of the hand 3 in the opening / closing direction while still gripping the workpiece W until the workpiece W reaches the predetermined location. This allows the movement control unit 55 to maintain a constant positional relationship between the hand 3 and the workpiece W, enabling the workpiece W to be transported to the predetermined location with high positional accuracy. Once the workpiece W has been transported to the predetermined location, the opening / closing control unit 56 causes the hand 3 to perform an opening operation, releasing the grip of the workpiece W from the fingers 31.

[0068] Thus, the picking operation is completed. If a picking operation for another workpiece W is to be performed, the process in step S101 is executed again.

[0069] Thus, with the picking operation of the robot system 100, even if the fingers 31 interfere with the workpiece W when moving the hand 3 to the gripping position of the workpiece W, the interference can be resolved and the hand 3 can be properly moved to the gripping position. As a result, the workpiece W can be properly gripped by the fingers 31.

[0070] For example, even if there is a discrepancy between the actual position of the workpiece W and the position of the workpiece W recognized by the robot control device 5, the hand 3 can still be moved appropriately to the gripping position. As mentioned above, when identifying the position of the workpiece W using images captured by the imaging device 42, depending on the resolution, brightness, and field of view, the workpiece W may not be properly photographed, and the accuracy of the identified position of the workpiece W may decrease. For example, as shown in Figure 1, when photographing a workpiece W inside a container 91 placed on a shelf 92, the imaging device 42 may not be able to be placed in an appropriate position due to constraints caused by interference between the robot arm 2 and the shelf 92, or the inside of the container 91 may be dark. In such cases, it may not be possible to obtain an appropriate image of the workpiece W, making it difficult to identify the position of the workpiece W with high accuracy. Naturally, these problems can be resolved by adopting a high-performance imaging device, but this leads to increased costs.

[0071] Even if the accuracy of the position of the workpiece W recognized by the robot control device 5 is low, the fingers 31 can be brought into contact with the workpiece W by roughly aligning the preparation position of the hand 3 with the workpiece W and moving the hand 3 from the preparation position in the pressing direction. Once the fingers 31 are in contact with the workpiece W, the contact between the fingers 31 and the workpiece W can be released by opening the fingers 31, creating a state where the workpiece W can fit between multiple fingers 31. Subsequently, the hand 3 can be moved further closer to the workpiece W to be properly positioned for gripping.

[0072] In other words, the preparation position of the hand 3 only needs to be adjusted to the position of the workpiece W by moving the hand 3 from the preparation position in the pressing direction so that the fingers 31 can contact the workpiece W. The positional accuracy of the preparation position does not need to be very high.

[0073] This is not limited to cases where the robot control device 5 determines the position of the workpiece W from the image captured by the imaging device 42, but also applies when the robot control device 5 is given the position of the workpiece W from an external source. For example, if the position of the workpiece W is roughly determined, the robot control device 5 may have the position of the workpiece W pre-programmed. Even if there is a discrepancy between the externally given position of the workpiece W and the actual position of the workpiece W, the robot system 100 can achieve proper gripping of the workpiece W through the aforementioned operations.

[0074] Furthermore, even if the positional accuracy of the hand 3 adjusted by the robot arm 2 is not high, the hand 3 can still be moved appropriately to the gripping position. In other words, even if the position of the hand 3 deviates from the target when moving the hand 3 from the preparation position to the pressing direction, as long as the fingers 31 can make contact with the workpiece W, the hand 3 can be moved appropriately to the gripping position by the aforementioned opening motion of the fingers 31, etc.

[0075] Furthermore, even if there is variation in the size of the workpiece W, the hand 3 can be appropriately moved to the gripping position. In other words, even if there is variation in the size of the workpiece W, the hand 3 can be appropriately moved to the gripping position by releasing the contact after the fingers 31 have made contact with the workpiece W through the opening motion of the fingers 31. Variation in the size of the workpiece W includes not only cases where there is variation in the size of workpiece W of the same type, but also cases where multiple types of workpiece W with differences in size or shape are to be gripped. In other words, the hand 3 can be appropriately moved to the gripping position regardless of the type of workpiece W.

[0076] Furthermore, this picking operation allows the fingers 31 to briefly contact the workpiece W when moving the hand 3 to the gripping position, so the spacing between the multiple fingers 31 when moving the hand 3 to the gripping position does not need to be excessively large. This makes it possible to narrow the spacing between the multiple workpieces W before gripping, thereby improving the workpiece filling rate. In other words, if the spacing between the multiple fingers 31 is set large to prevent the fingers 31 from contacting the workpiece W, then the spacing between two workpieces W must be large to prevent the fingers 31 from interfering with the workpiece W adjacent to the workpiece W to be gripped. In that case, the workpiece filling rate in the container 91, etc., decreases. By reducing the spacing between the multiple fingers 31 of the hand 3 when moving to the gripping position, the possibility of the fingers 31 interfering with the workpiece W adjacent to the workpiece W to be gripped can be reduced. As a result, the spacing between multiple workpieces W can be reduced, and consequently, the workpiece filling rate can be improved.

[0077] In addition to the above, when the robot control device 5 causes the finger 31 to open after it has made contact with the workpiece W, it performs force control of the robot arm 2 so that contact with the workpiece W in the pressing direction of the finger 31 is maintained. This allows the finger 31 to open along the surface shape of the part of the workpiece W that is in contact with it. As a result, the robot control device 5 can easily determine that the finger 31 has opened until contact with the workpiece W is released, based on the pressing force of the finger 31 on the workpiece W.

[0078] The following provides further details on some specific examples of picking operations. Figure 13 shows the hand 3 performing the first opening operation when gripping a workpiece W with different widths at the top w1 and the main body w0. Figure 14 shows the hand 3 performing the second opening operation when gripping a workpiece W with different widths at the top w1 and the main body w0. For example, even with a workpiece W like the one shown in Figure 13, the hand 3 can be appropriately moved to the gripping position. The workpiece W shown in Figure 13 has an upper part w1 that is narrower than the main body w0. Assume that the picking operation is performed according to the flowchart described above, and the second finger 31B makes contact with the upper part w1 of the workpiece W due to the force control in step S103. After this, the opening operation of the second finger 31B in step S108 causes the second finger 31B to spread wider than the upper part w1 of the workpiece W in the opening and closing direction. Subsequently, since the force control continues, the hand 3 moves in the pressing direction, and as shown in Figure 14, the second finger 31B makes contact with the main body w0 of the workpiece W. When the second finger 31B makes contact with the body w0 of the workpiece W, the opening operation of the second finger 31B in step S108 is performed again. When the second finger 31B extends beyond the body w0 of the workpiece W in the opening and closing direction, the hand 3 moves in the pressing direction due to the continued force control and reaches the gripping position. In this way, even with a workpiece W as shown in Figure 13, the hand 3 can be appropriately moved to the gripping position.

[0079] Alternatively, even with a workpiece W as shown in Figure 15, the hand 3 can be appropriately moved to the gripping position. Figure 15 shows the hand 3 causing the fingers 31 to perform an opening operation on a workpiece W in which a recess w2 is formed. In the workpiece W shown in Figure 15, the recess w2 is formed on the upper part of the workpiece W, that is, the part facing the hand 3 in the preparation position. The inner surface of the recess w2 does not have a surface parallel to the pressing direction, but has a curved surface or an inclined surface inclined with respect to the pressing direction. Assume that the picking operation is performed according to the flowchart described above, and the first finger 31A and the second finger 31B come into contact with the recess w2 of the workpiece W by force control in step S103. After this, the opening operation of the fingers 31 in step S108 causes the first finger 31A and the second finger 31B to perform an opening operation. At this time, the hand 3 moves away from the workpiece W in the pressing direction by force control of the robot arm 2 so that the first finger 31A and the second finger 31B can perform an opening operation along the inner surface of the recess w2. When the first finger 31A and the second finger 31B withdraw from the recess w2, the first finger 31A and the second finger 31B spread out beyond the workpiece W in the opening and closing direction. Subsequently, due to the continued force control, the hand 3 moves in the pressing direction and reaches the gripping position. Thus, depending on the shape of the workpiece W, the hand 3 moves not only toward the workpiece W in the pressing direction when the fingers 31 are opened, but also toward the side away from the workpiece W.

[0080] Furthermore, in the case of a workpiece W whose inner surface has a bottom surface parallel to the opening and closing direction and an edge surface rising from the periphery of the bottom surface parallel to the pressing direction, the first finger 31A and the second finger 31B that perform the opening operation may be constrained by the edge surface when they come into contact with it. The movement control unit 55 may control the robot arm 2 so that the hand 3 moves by a predetermined amount toward the side away from the workpiece W in the pressing direction if the torque (or applied current) of the servo motor 32 remains above a predetermined value for a predetermined period of time or longer. By repeating this operation, the first finger 31A and the second finger 31B can eventually escape from the recess w2. The movement control unit 55 may determine whether the first finger 31A or the second finger 31B is constrained in the opening and closing direction based on the force in the opening and closing direction detected by the force sensor 41, rather than the torque or current of the servo motor 32.

[0081] Furthermore, even with a deformable workpiece W as shown in Figure 16, the hand 3 can be appropriately moved to the gripping position. Figure 16 shows the hand 3 picking a deformable workpiece W, with the fingers 31 in contact with the workpiece W. Assume that the picking operation is performed according to the flowchart described above, and the second finger 31B comes into contact with the workpiece W due to the force control in step S103. For example, the workpiece W basically has a roughly rectangular parallelepiped shape when viewed from the front. However, the workpiece W can be deformed by its own weight or contact with the fingers 31. As shown in Figure 16, the workpiece W deforms into a roughly parallelogram shape when viewed from the front. After this, the opening operation of the second finger 31B in step S108 causes the second finger 31B to spread wider than the workpiece W in the opening and closing direction. Subsequently, since the force control continues, the hand 3 moves in the pressing direction toward the gripping position. Along the way, the first finger 31A may come into contact with the side of the workpiece W. Figure 17 shows a hand 3 picking a deformable workpiece W, with the fingers 31 in contact with the side of the workpiece W. When the first finger 31A makes contact with the workpiece W, in addition to force control, an opening movement of the first finger 31A is performed. As a result, the first finger 31A opens along the side of the workpiece W, and the hand 3 moves in the pressing direction to the gripping position. Figure 18 shows a hand 3 picking a deformable workpiece W, with the hand 3 having reached the gripping position. Subsequently, the first finger 31A and the second finger 31B perform a gripping movement, causing the first finger 31A and the second finger 31B to grip the workpiece W. Figure 19 shows a hand 3 picking a deformable workpiece W, with the fingers 31 having completed the gripping movement. The workpiece W deforms in response to the closing movement of the first finger 31A and the second finger 31B, returning to its original state as a roughly rectangular parallelepiped when viewed from the front.

[0082] Furthermore, the workpiece W may move during the picking operation. A force parallel to the placement surface of the workpiece W may act on the workpiece W due to the opening and closing movements of the fingers 31. If this parallel force is greater than the frictional force between the workpiece W and the placement surface, the workpiece W may move. Even if the workpiece W moves, the picking operation can be performed properly as long as it does not move out of the space between the fingers 31.

[0083] Furthermore, during the opening motion of finger 31, it is possible that finger 31 performing the opening motion may come into contact with another workpiece W positioned next to the workpiece W to be gripped. In this case, if the pressing force of finger 31 is greater than the frictional force between the other workpiece W and the surface it is placed on, the other workpiece W can be shifted parallel to the surface it is placed on. As a result, the picking operation can be performed appropriately even when the distance between the workpiece W to be gripped and the other workpiece W is narrow.

[0084] As described above, the robot control device 5 includes a movement control unit 55 that moves the robot arm 2 (arm) on which the hand 3 is attached, and an opening / closing control unit 56 that opens and closes a plurality of fingers 31 on the hand 3 in a predetermined opening / closing direction. The movement control unit 55 causes the robot arm 2 to perform a contact operation in which the fingers 31 come into contact with the workpiece W in a pressing direction intersecting the opening / closing direction. The opening / closing control unit 56 causes the fingers 31 to perform an opening operation after the contact operation. After the fingers 31 are no longer in contact with the workpiece W due to the opening operation, the movement control unit 55 causes the robot arm 2 to perform an approach operation in which the hand 3 moves in the pressing direction to a predetermined gripping position in which the workpiece W is positioned between the plurality of fingers 31. The opening / closing control unit 56 causes the fingers 31 to perform a closing operation when the hand 3 is in the gripping position, thereby causing the fingers 31 to grip the workpiece.

[0085] The robot system 100 also includes a hand 3 with multiple openable and closable fingers 31, a robot arm 2 (arm) to which the hand 3 is attached, and a robot control device 5.

[0086] Furthermore, the robot control program 54 causes the robot control device 5 (computer) to perform the following functions: a function to cause the robot arm 2 (arm) to which the hand 3 is provided to perform a contact operation in which at least one of the multiple fingers 31 provided on the hand 3, which can be opened and closed in a predetermined opening and closing direction, to contact the workpiece W in a pressing direction intersecting the opening and closing direction; a function to cause the fingers 31 to perform an opening operation after the contact operation; a function to cause the robot arm 2 to perform an approach operation in which the hand 3 moves in the pressing direction to a predetermined gripping position in which the workpiece W is positioned between the multiple fingers 31 after the fingers 31 have become non-contact with the workpiece W due to the opening operation; and a function to cause the fingers 31 to grip the workpiece W by causing the fingers 31 to perform a closing operation when the hand 3 is in the gripping position.

[0087] With this configuration, by causing the fingers 31 to open from a state where they are in contact with the workpiece W until the contact is released, it is possible to create a state where the workpiece W can fit between multiple fingers 31. This allows the hand 3 to move in the pressing direction. As a result, the hand 3 can be appropriately moved to the gripping position.

[0088] Furthermore, the movement control unit 55 performs force control of the robot arm 2 so that contact between the finger 31 and the workpiece W is maintained during the opening movement of the finger 31.

[0089] In this configuration, the force of the robot arm 2 is controlled during the opening movement of the fingers 31 to maintain contact between the fingers 31 and the workpiece W. This allows the fingers 31 to move smoothly until the workpiece W can fit between the multiple fingers 31. In other words, without force control, if the surface of the part of the workpiece W that the fingers 31 are in contact with is not parallel to the opening and closing direction of the fingers 31, the contact between the fingers 31 and the workpiece W may be immediately released when the fingers 31 open in the opening and closing direction. Once the contact between the fingers 31 and the workpiece W is released, the hand 3 moves in the pressing direction. At this time, if the fingers 31 have not opened to a point where the workpiece W can fit between the multiple fingers 31, the fingers 31 will immediately contact the workpiece W as soon as the hand 3 moves in the pressing direction. Then, the opening movement of the fingers 31 is performed again. In this way, without force control, the opening movement of the fingers 31 and the movement of the hand 3 in the pressing direction may be repeated, causing the tips of the fingers 31 to trace a step-like trajectory. In contrast, when force control is performed, the pressing position of the hand 3 is also adjusted so that contact between the fingers 31 and the workpiece W is maintained during the opening movement of the fingers 31. This allows the fingers 31 to move smoothly until the workpiece W can fit between the multiple fingers 31.

[0090] Specifically, the movement control unit 55 controls the robot arm 2 so that the pressing force of the fingers 31 on the workpiece W in the pressing direction reaches a predetermined target value.

[0091] In this configuration, the force control of the robot arm 2 is adjusted so that the pressing force of the finger 31 on the workpiece W in the pressing direction reaches a target value. The target value may be a constant value or a variable value. By adjusting the pressing force, it is possible to prevent the finger 31 from separating from the workpiece W during the opening movement of the finger 31, or the finger 31 from pressing the workpiece W excessively.

[0092] Furthermore, the opening / closing control unit 56 determines, based on the pressing force of the finger 31 against the workpiece W, that the finger 31 no longer makes contact with the workpiece W during the opening operation of the finger 31.

[0093] With this configuration, when contact between the finger 31 and the workpiece W is eliminated, the pressing force becomes 0. In other words, the opening / closing control unit 56 can easily determine that contact between the finger 31 and the workpiece W has been eliminated by monitoring the pressing force.

[0094] The opening / closing control unit 56, in the opening operation of the fingers 31, stops the fingers 31 that are not in contact with the workpiece W, while opening the fingers 31 that are in contact with the workpiece W.

[0095] This configuration prevents the spacing between multiple fingers 31 from becoming excessively large during the opening operation of the fingers 31. Using the state shown in Figure 7 as an example, the opening / closing control unit 56 opens only the second finger 31B, which is in contact with the workpiece W, and keeps the first finger 31A, which is not in contact with the workpiece W, stationary. If the first finger 31A were to open in the same way as the second finger 31B, the spacing between the first finger 31A and the second finger 31B would become excessively large. For example, if a structure such as the wall of the container 91 or another workpiece W exists in the opening direction of the first finger 31A, there is a risk that the first finger 31A may interfere with the structure or the other workpiece W. If the first finger 31A interferes with something, it may also hinder the opening operation of the second finger 31B. On the other hand, by not moving the first finger 31A, which is not in contact with the workpiece W, it is possible to prevent the first finger 31A from interfering with surrounding workpieces W, etc.

[0096] Furthermore, in the robot system 100, the hand has multiple servo motors 32 (drive sources) that independently open and close multiple fingers, and the opening / closing control unit 56 independently controls the multiple servo motors 32.

[0097] With this configuration, each of the multiple fingers 31 can be opened and closed independently. Such a hand 3 and opening / closing control unit 56 can achieve the opening operation of only the finger 31 that is in contact with the workpiece W as described above.

[0098] Furthermore, the robot system 100 is equipped with a force sensor 41 that detects the pressing force of the finger 31 onto the workpiece W.

[0099] With this configuration, contact between the finger 31 and the workpiece W can be easily determined based on the detection result of the force sensor 41.

[0100] Furthermore, force sensors 41 are provided for each of the multiple fingers 31.

[0101] With this configuration, it is possible to easily distinguish between fingers 31 that are in contact with the workpiece W and fingers 31 that are not in contact with the workpiece W based on the detection results of the force sensor 41.

[0102] Other embodiments As described above, the embodiments described herein have been presented as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited thereto and can be applied to embodiments that have been modified, replaced, added, or omitted as appropriate. Furthermore, it is possible to combine the components described in the embodiments above to create new embodiments. In addition, the components described in the attached drawings and detailed description may include not only components essential for solving the problem, but also components that are not essential for solving the problem, in order to illustrate the technology. Therefore, the mere presence of such non-essential components in the attached drawings and detailed description should not be immediately assumed to mean that those non-essential components are essential.

[0103] For example, robot 1 is not limited to industrial robots. Robot arm 2 is not limited to vertical articulated robot arms. Robot arm 2 may be a horizontal articulated, parallel link, rectangular coordinate, or polar coordinate robot arm, etc. Any robot arm can be used as long as it can move hand 3 in the pressing direction.

[0104] The configuration of hand 3 is just one example. Any configuration can be adopted as long as it has multiple fingers, including at least one finger that can open and close.

[0105] For example, the number of fingers 31 is not limited to two. The number of fingers 31 may be three or more.

[0106] Not all of the multiple fingers 31 are capable of opening and closing. In other words, it is sufficient if at least one of the multiple fingers 31 is capable of opening and closing. In that case, the contact operation is performed so that the finger 31 capable of opening and closing contacts the workpiece W. Specifically, in the preparation position, it is preferable to position the hand 3 with a certain margin so that when the hand 3 is moved in the pressing direction, the finger 31 that is not capable of opening and closing will not reliably contact the workpiece W.

[0107] In a configuration where all of the multiple fingers 31 are capable of opening and closing, the multiple fingers 31 do not necessarily have to open and close independently. In other words, the multiple fingers 31 may open and close simultaneously or in conjunction with each other. Specifically, there may be only one common drive source (e.g., servo motor 32) for all of the multiple fingers 31.

[0108] The drive source for finger 31 is not limited to the servo motor 32. For example, the drive source may be an air actuator.

[0109] The force sensor 41 does not have to be provided on each finger 31. For example, one force sensor 41 may be provided on the hand 3. Even with such a configuration, when any finger 31 comes into contact with the workpiece W, the force sensor 41 can detect the pressing force via that finger 31.

[0110] The sensor is not limited to the force sensor 41. The sensor only needs to be able to detect force in at least the pressing direction. The sensor may also be a motor current sensor or torque sensor. For example, it may be detected that a finger pressing force is being generated on the workpiece when the applied current or torque of the servo motor 23 when moving the hand 3 in the pressing direction is above a predetermined threshold. Alternatively, in a configuration where the finger 31 and the servo motor 32 are connected by a link as shown in Figure 20, and the reaction force from the workpiece W on the finger 31 affects the torque of the servo motor 32, the pressing force of the finger 31 on the workpiece W may be determined based on the applied current or torque of the servo motor 32. For example, it is determined that a finger pressing force is being generated on the workpiece W when the applied current or torque of the servo motor 32 is above a predetermined threshold. Note that in Figure 20, only the configuration of the first finger 31A is shown, and the configuration of the second finger 31B is not shown.

[0111] The robot 1 does not necessarily have to be equipped with an imaging device 42. For example, if the position of the workpiece W is known, such as when the arrangement of workpieces W within the workpiece W is generally determined, the robot control device 5 may control the robot arm 2, etc., based on the known position of the workpiece W. According to the picking operation described above, if the general position of the workpiece W is known, appropriate gripping of the workpiece W by multiple fingers 31 can be easily achieved.

[0112] Alternatively, the imaging device 42 does not have to be mounted on the robot arm 2. For example, the imaging device 42 may be mounted on a robot arm other than the robot arm 2. Or, if there is no object that shields the workpiece W, such as a shelf, the imaging device 42 may be fixedly positioned around the workpiece W.

[0113] The device for acquiring the position information of the workpiece W is not limited to the imaging device 42, but may also be a three-dimensional vision sensor or a stereo camera, etc. In other words, the device for acquiring the position information of the workpiece W may acquire point cloud data, RGB-D images, RGB images, depth images, voxels, etc. of the workpiece W.

[0114] Furthermore, the Z-coordinate of the gripping position (i.e., the position in the pressing direction of the gripping position) does not necessarily have to be predetermined according to the workpiece W. For example, if the device that acquires the position information of the workpiece W also acquires three-dimensional information of the workpiece W, the Z-coordinate of the gripping position may be determined based on the three-dimensional information acquired by the device.

[0115] The flowchart for the picking operation is merely an example. The steps in the flowchart may be modified, replaced, added, or omitted as appropriate, as long as proper gripping of the workpiece W by multiple fingers 31 is achieved. Furthermore, the order of the steps in the flowchart may be changed, or serial processing may be processed in parallel.

[0116] For example, in the picking operation described above, the contact operation in which the finger 31 makes contact with the workpiece W in the pressing direction is realized by force control of the robot arm 2. However, the force control in step S103 may be replaced with position control of the robot arm 2, i.e., the hand 3. In other words, in step S103, the movement control unit 55 may perform position control of the robot arm 2 so as to move the hand 3 to the gripping position in the pressing direction. The movement control unit 55 may then monitor whether the finger 31 makes contact with the workpiece W during position control, and may start force control of the robot arm 2 if the finger 31 makes contact with the workpiece W.

[0117] Furthermore, in the aforementioned picking operation, the positions of the multiple fingers 31 in the opening and closing direction when performing the contact operation (i.e., the initial positions) are such that the spacing between the multiple fingers 31 is wider than the width of the workpiece W (dimension in the opening and closing direction). However, the spacing between the multiple fingers 31 may be narrower than the width of the workpiece W (dimension in the opening and closing direction). With this configuration, the likelihood of the fingers 31 contacting the workpiece W increases as the hand 3 moves to the gripping position, while preventing the fingers 31 from contacting workpieces W that are not intended for use.

[0118] Furthermore, the force control of the robot arm 2 is not limited to admittance control. For example, the force control may be PI control, which takes the deviation between the target value and the pressing force detected by the force sensor 41 as input and outputs an operation command value for the robot arm 2.

[0119] The functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, dedicated processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuits. In this disclosure, a circuit, unit, or means is hardware that performs the enumerated functions, or hardware programmed to perform the enumerated functions. The hardware may be hardware disclosed herein, or other known hardware that is programmed or configured to perform the enumerated functions. If the hardware is a processor, which is considered a type of circuit, then the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or the processor. [Explanation of Symbols]

[0120] 100 Robot Systems 1 Robot 2. Robot arm (arm) 3 Hands 31 fingers 41. Force sensor (sensor) 5. Robot control device (computer) 54 Robot Control Program 55 Movement control unit 56 Opening / Closing Control Unit Double job

Claims

1. A movement control unit that moves an arm equipped with a hand, The hand comprises an opening / closing control unit that opens and closes a plurality of fingers provided on the hand in a predetermined opening / closing direction, The movement control unit causes the arm to perform a contact operation in which the finger contacts the workpiece in a pressing direction intersecting the opening and closing direction. The opening / closing control unit causes the finger to perform an opening operation after the contact operation. The movement control unit causes the arm to perform an approaching motion to move the hand in the pressing direction to a predetermined gripping position where the workpiece is positioned between the multiple fingers, after the fingers have become non-contact with the workpiece due to the opening motion. The opening / closing control unit is a robot control device that causes the fingers to perform a closing operation when the hand is in the gripping position, thereby causing the fingers to grip a workpiece.

2. In the robot control device according to claim 1, The movement control unit is a robot control device that performs force control of the arm so as to maintain contact of the finger with the workpiece during the opening movement of the finger.

3. In the robot control device according to claim 2, The movement control unit is a robot control device that controls the arm in the force control so that the pressing force of the finger on the workpiece in the pressing direction becomes a predetermined target value.

4. In the robot control device according to claim 3, The opening / closing control unit is a robot control device that determines, based on the pressing force of the finger against the workpiece, when the finger opens, the finger no longer makes contact with the workpiece.

5. In the robot control device according to any one of claims 1 to 4, The opening / closing control unit is a robot control device that, in the opening operation of the fingers, stops the fingers that are not in contact with the workpiece among the plurality of fingers, while opening the fingers that are in contact with the workpiece among the plurality of fingers.

6. A hand equipped with multiple fingers that can be opened and closed, The arm on which the aforementioned hand is provided, A robot system comprising a robot control device according to any one of claims 1 to 5.

7. In the robot system according to claim 6, The hand has multiple drive sources that independently open and close multiple fingers, The opening / closing control unit is a robot system that independently controls a plurality of the drive sources.

8. In the robot system according to claim 6 or 7, A robot system further comprising a sensor for detecting the pressure applied by the finger to the workpiece.

9. In the robot system according to claim 8, The aforementioned sensors are provided in each of the multiple aforementioned fingers of the robot system.

10. A function that causes the arm on which the hand is mounted to perform a contact operation in which at least one of a plurality of fingers provided on the hand, which are capable of opening and closing in a predetermined opening and closing direction, contacts the workpiece in a pressing direction intersecting the opening and closing direction, A function that causes the finger to perform an opening motion after the aforementioned contact motion, The function includes causing the arm to perform an approaching motion to move the hand in the pressing direction to a predetermined gripping position where the workpiece is positioned between the multiple fingers, after the fingers have become non-contact with the workpiece due to the opening motion, A robot control program that enables a computer to perform a function of causing the fingers to grip a workpiece by having the fingers perform a closing motion when the hand is in the gripping position.

Images