Work transport system

Abstract

A workpiece conveyance system (1) comprises: a robot (2) having, on a distal end thereof, a hand (5) that grips a workpiece (W), the robot comprising a sensor which can detect an external force that acts on the hand (5); a balancer (3) that is connected to the hand (5), and that can generate a pull-up force which pulls the hand (5) vertically upward; a shape measurement device (6) that measures the shape of the workpiece (W); and a control device (4) that controls the robot (2) and the balancer (3) on the basis of the shape of the workpiece (W) measured by the shape measurement device (6). The control device (4) adjusts, on the basis of the shape of the workpiece (W) measured by the shape measurement device (6), a gripping position of the hand (5) on the workpiece (W), and controls the pull-up force generated by the balancer (3) so that when the workpiece (W) is gripped at the adjusted gripping position and lifted up, an absolute value of the vertical direction external force detected by the sensor is no greater than a predetermined first threshold.

Description

[Technical Field]

[0001] The present disclosure relates to a workpiece transport system. [Background technology]

[0002] When a robot transports a workpiece supported by a hand attached to the tip, a system is known that assists the robot by using a balancer to lift the workpiece with a force corresponding to the weight of the workpiece (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2010 / 104157 Summary of the Invention [Problem to be solved by the invention]

[0004] If the gripping position of the workpiece by the hand is not appropriate, the balancer cannot achieve the appropriate balance state. However, when there are many different types of workpieces, measuring and registering information such as the mass and gripping position for each workpiece requires a great deal of man-hours. Therefore, it is desirable to be able to grip and transport workpieces at the appropriate gripping position without having to pre-register information such as the gripping position of the workpiece. [Means for solving the problem]

[0005] One aspect of the present disclosure is a work transport system comprising: a robot having a hand at its tip for gripping a workpiece and a sensor capable of detecting external forces acting on the hand; a balancer connected to the hand and capable of generating a lifting force to pull the hand vertically upward; a shape measuring device for measuring the shape of the workpiece; and a control device for controlling the robot and the balancer based on the shape of the workpiece measured by the shape measuring device, wherein the control device adjusts the gripping position of the workpiece by the hand based on the shape of the workpiece measured by the shape measuring device, and controls the lifting force generated by the balancer so that when the workpiece is gripped and lifted at the adjusted gripping position, the absolute value of the vertical external force detected by the sensor is less than or equal to a predetermined first threshold value. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is an overall configuration diagram illustrating a workpiece conveying system according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a block diagram showing the workpiece conveying system of FIG. 1. [Figure 3] 3 is a diagram showing an air pressure control circuit provided in the balancer control unit of FIG. 2. FIG. [Figure 4] 4 is a diagram showing an air pressure control circuit in a state where the first valve in FIG. 3 is turned off. FIG. [Figure 5] 4 is a diagram illustrating a balanced state in the air pressure control circuit of FIG. 3. FIG. [Figure 6] 2 is a flowchart illustrating the operation of transporting a workpiece by the workpiece transport system of FIG. 1. [Figure 7] FIG. 3 is a diagram showing a modification of the air pressure control circuit of FIG. 2. [Figure 8] 8 is a flowchart illustrating the operation of transporting a workpiece by the workpiece transport system equipped with the air pressure control circuit of FIG. 7. [Figure 9] FIG. 3 is a block diagram showing a modified example of the workpiece conveying system of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0007] A workpiece conveying system 1 according to an embodiment of the present disclosure will be described below with reference to the drawings. As shown in FIG. 1, the workpiece transport system 1 according to this embodiment includes a robot 2, a balancer 3, and a control device 4.

[0008] The robot 2 is, for example, a vertical six-axis articulated robot, and is equipped with a hand 5 at the tip of which the workpiece W can be grasped. The robot 2 is equipped with a force sensor (sensor) that can detect an external force acting on the hand 5. The hand 5 is also equipped with a camera (shape measurement device) 6 that can acquire an image of the workpiece W.

[0009] The workpiece W is, for example, a long member having a uniform cross section. The hand 5 is equipped with a pair of openable and closable jaws 8 that can horizontally pinch and grasp the workpiece W at any position in the longitudinal direction, which is placed on the mounting surface of a workpiece stand 7 such as a table. The force sensor can detect, as an external force acting on the workpiece W, for example, external forces in the directions of three axes and moments around three axes in a Cartesian coordinate system whose origin is a tool tip point (TCP) set at the center of the pair of jaws 8.

[0010] The balancer 3 is, for example, an air cylinder suspended from a cantilever 10 supported by a support 9 arranged near the robot 2, with a rod 11 arranged vertically downward so that it can be extended and retracted. The tip of the rod 11 is attached to the hand 5. When the rod 11 of the balancer 3 is driven in a direction to raise it, a pulling force directed vertically upward can be applied to the hand 5. The cantilever 10 is arranged to be rotatable around a vertical axis extending in the longitudinal direction of the support 9.

[0011] The balancer 3 is fixed to a slider 12 that is supported so as to be movable along the longitudinal direction of the cantilever 10. As a result, when the robot 2 operates, the rotation of the cantilever 10 and the movement of the slider 12 keep the balancer 3 positioned vertically above the hand 5, and a lifting force can be applied to the hand 5 regardless of the posture of the robot 2.

[0012] The camera 6 can acquire an image including the shape of the workpiece W in a plan view by, for example, photographing the workpiece W from vertically above the workpiece W.

[0013] As shown in FIG. 2, the control device 4 includes a robot control unit 13 that controls the robot 2 and a balancer control unit 14 that controls the balancer 3. When the robot control unit 13 is instructed by the transport program to grip the workpiece W, it controls the robot 2 to position the camera 6 above the workpiece W and causes the camera 6 to capture an image of the workpiece W. The robot control unit 13 also extracts the shape of the workpiece W from the image captured by the camera 6 and calculates the position of its center of gravity, thereby calculating the gripping position of the workpiece W by the hand 5.

[0014] The robot control unit 13 also controls the robot 2 to place the hand 5 at the calculated gripping position, and causes the hand 5 to grip the workpiece W. The robot control unit 13 then controls the robot 2 to raise the hand 5, and corrects the gripping position if the moment about the horizontal axis detected by the force sensor exceeds a second threshold value Th2, which is a predetermined threshold value.

[0015] The gripping position is corrected by shifting the gripping position along the longitudinal direction of the workpiece W in a direction that reduces the moment about the horizontal axis detected by the force sensor. That is, the workpiece W is placed on the work table 7, the gripping position of the hand 5 is corrected for the placed workpiece W, the workpiece W is gripped at the corrected gripping position, the workpiece W is lifted, and the above process is repeated until the magnitude of the moment detected by the force sensor falls below the second threshold value Th2.

[0016] The balancer control unit 14 includes, for example, an air pressure control circuit 15 shown in FIG. The air pressure control circuit 15 includes an air pressure source 16, three valves 17, 18, and 19, and a regulator 20. Reference numeral 21 denotes a speed controller, reference numeral 22 denotes a throttle valve with a silencer, and reference numeral 23 denotes a silencer.

[0017] The balancer control unit 14 adjusts the lifting force of the balancer 3. The lifting force of the balancer 3 is adjusted so that when the workpiece W held by the hand 5 is lifted and held still at the appropriate gripping position, the absolute value of the vertical external force detected by the force sensor is below a predetermined threshold value, a fourth threshold value Th4.

[0018] 3, the balancer control unit 14 activates the first valve 17 and the second valve 18 to supply air from the air pressure source 16 to the rod 11 side of the balancer 3 through the speed controller 21, the first valve 17, and the second valve 18 in this order. This allows the rod 11 to be pulled up, and an upward pulling force to act on the hand 5.

[0019] For example, the first valve 17 is turned on and off while the workpiece W placed on the workpiece table 7 is being gripped by the hand 5 at the adjusted gripping position. This causes the lifting force of the balancer 3 to be intermittently increased until the vertical external force detected by the force sensor reaches a third threshold value Th3, which is a predetermined threshold value. At this time, the set pressure value supplied to the regulator 20 also increases in equal amounts to the pressure value supplied to the balancer 3.

[0020] 4, when the vertical external force detected by the force sensor exceeds a predetermined third threshold Th3, the first valve 17 is turned off and the robot control unit 13 controls the robot 2 to raise the hand 5. Then, the balancer control unit 14 determines whether the vertical external force detected by the force sensor is equal to or less than a predetermined fourth threshold Th4.

[0021] If the external force does not become equal to or less than the fourth threshold value Th4, the balancer control unit 14 switches the first valve 17 on and off to adjust the pressure value applied to the balancer 3. Then, when the external force in the vertical direction detected by the force sensor becomes equal to or less than the fourth threshold value Th4, the balancer control unit 14 switches the second valve 18 as shown in FIG.

[0022] As a result, the air pressure of the set pressure value set in the regulator 20 is supplied to the balancer 3. By setting the fourth threshold value Th4 to a sufficiently small value, a balanced state can be achieved in which the force detected by the force sensor is close to zero.

[0023] The operation of the workpiece transport system 1 according to this embodiment configured as described above will be described below. To transport a workpiece W of unknown weight and shape using the workpiece transport system 1 according to this embodiment, first, the robot 2 is operated and the camera 6 mounted on the hand 5 is positioned vertically above the workpiece W.

[0024] 6, the workpiece W is placed within the field of view of the camera 6, and an image is acquired (step S1). The robot control unit 13 processes the image to extract the workpiece W and calculates the horizontal center of gravity position from the shape of the workpiece W in a plan view (step S2). The robot control unit 13 sets the gripping position of the workpiece W by the hand 5 to an attitude in which the claws 8 of the hand 5 are positioned on both sides of the calculated center of gravity position.

[0025] Next, the robot control unit 13 grips the workpiece W with the hand 5 (step S3) and raises the hand 5 (step S4). At this time, the force sensors detect the forces in the three axial directions and the moments about the three axes acting on the hand 5. The robot control unit 13 determines whether the moment about the horizontal axis exceeds a second threshold value Th2 (step S5), and if it does, corrects the gripping position (step S6) and repeats the process from step S3.

[0026] Then, with the gripping position corrected, the lifting force is adjusted by the balancer 3. First, the workpiece W is returned onto the work table 7 (step S7) and gripped by the hand 5 at the adjusted gripping position (step S8). In this state, the balancer control unit 14 causes the balancer 3 to apply a lifting force to the workpiece W, and increases the lifting force of the balancer 3 until the external force detected by the force sensor exceeds the third threshold value Th3 (steps S9 and S10).

[0027] When the pulling force exceeds the third threshold value Th3, the increase of the pulling force is stopped, and the robot control unit 13 raises the hand 5 (step S11). After that, it is determined whether the absolute value of the external force detected by the force sensor is equal to or less than the fourth threshold value Th4 (step S12), and if it exceeds the fourth threshold value Th4, the pulling force by the balancer 3 is increased again (step S13).

[0028] Here, to keep the absolute value of the external force detected by the force sensor below the fourth threshold Th4, it is necessary to adjust the pressure while the workpiece W is raised. Specifically, when the robot control unit 13 determines that a lifting force from the balancer 3 is required, it issues an air supply command to the first valve 17, switching the first valve 17 on. At this time, the first valve 17 remains on for only a moment, after which the robot 2 issues an air shutoff command to switch the first valve 17 off. The regulator 20 records (saves) a pressure equal to the pressure from the second valve 18 to the balancer 3, and continues to send this pressure. This keeps the absolute value of the external force detected by the force sensor below the fourth threshold Th4.

[0029] When the absolute value of the external force detected by the force sensor becomes equal to or smaller than the fourth threshold value Th4, the balancer control unit 14 sets the pressure at that time as the pressure of the regulator 20 and supplies air at the set pressure to the balancer 3. This causes the balancer 3 to be in a balanced state (step S14). As a result, the load acting on the robot 2 can be minimized, and the robot 2 can easily transport a workpiece W that is larger than its payload capacity (step S15).

[0030] As such, the workpiece transport system 1 according to this embodiment has the advantage that even if information such as mass and gripping position for each workpiece W is not registered, the workpiece W can be properly gripped and transported while sufficiently reducing the load acting on the robot 2.

[0031] In this embodiment, instead of setting a sufficiently small value as the fourth threshold value Th4, the first threshold value Th1, which is a threshold value of a predetermined magnitude, may be used. This makes it possible to keep the vertical load on the robot 2 within a certain range, and to easily transport a load greater than the payload capacity.

[0032] Also, although the example has been given in which the lifting force generated by the balancer 3 is gradually increased to balance with the weight of the workpiece W, an air pressure control circuit 15 shown in FIG. 7 may be used instead. That is, an electropneumatic regulator 24 may be provided that can set the pressure of the air supplied to the balancer 3 by the regulator 20 in response to an external command signal.

[0033] 8, with the workpiece W gripped at an appropriate position by the hand 5 (step S8), the balancer control unit 14 commands the electro-pneumatic regulator 24 to supply a predetermined pressure value, causing the balancer 3 to generate a constant lifting force (step S21). Thereafter, the robot control unit 13 controls the robot 2 to raise the hand 5 (step S11).

[0034] In this state, the balancer control unit 14 calculates the pressure required for the balancer 3 to achieve a balanced state based on the value of the external force detected by the force sensor, and issues the corrected pressure to the electro-pneumatic regulator 24 (step S22). As a result, the pressure of the balancer 3 is feedback-controlled until the external force detected by the force sensor becomes equal to or less than the fourth threshold value Th4 (steps S12, S22).

[0035] In addition, in this embodiment, a planar image of the workpiece W is acquired using the camera 6 mounted on the hand 5 to calculate the center of gravity position, but instead, the shape of the workpiece W may be detected using a distance sensor, an optical sensor, an ultrasonic sensor or a temperature sensor. The force sensor may be provided in a mechanical part of the robot 2, or may be provided in the control device 4 and used to estimate an external force from a current value.

[0036] Furthermore, in this embodiment, an air cylinder is used as an example of the balancer 3, but instead of this, any type of actuator such as a pneumatic, hydraulic or electric actuator may be used. Furthermore, in this embodiment, a long rectangular prism member having a uniform cross section has been exemplified as the workpiece W, but instead, a workpiece of any other shape may be employed.

[0037] 9, the control device 4 may include a storage unit 25 configured with a memory and a difference calculation unit 26 configured with a processor. The storage unit 25 stores the external forces detected by the force sensor when a predetermined reference workpiece is transported according to a program for transporting a workpiece W using the robot 2 in chronological order, in association with the coordinates of the TCP of the robot 2.

[0038] The difference calculation unit 26 sequentially calculates the absolute value of the difference between the external force detected by the force sensor and the external force stored in the memory unit 25 when a workpiece W identical to the reference workpiece is transported using the same transport program. The control device 4 may then stop the robot 2 if the absolute value of the difference calculated by the difference calculation unit 26 at each point during the transport of the workpiece W according to the transport program is greater than or equal to a fifth threshold Th5, which is a predetermined threshold.

[0039] In addition, although the present embodiment has been described as using a force sensor to detect external forces, other sensors may be used instead. For example, a torque sensor may be attached to each axis of the robot 2, and data equivalent to that of a force sensor may be calculated using the output of the torque sensor and known technology. Furthermore, in this embodiment, an example has been given in which image processing is performed in the robot control unit 13 within the control device 4, but instead, the work transport system 1 may be provided with an image processing device outside the control device 4, and image processing may be performed by the image processing device.

[0040] Furthermore, in this embodiment, the coordinates of the TCP of the robot 2 are exemplified as position data that is stored in time series in association with external forces, but instead, encoder values ​​of each axis motor may be used.

[0041] Furthermore, in the present embodiment, an example has been given in which the robot control unit 13 controls the camera 6 to acquire images, but instead, the workpiece conveyance system 1 may be provided with a camera control unit outside the control device 4, and the camera control unit may control the camera 6. In this case, it is preferable that the robot control unit 13 and the camera control unit are capable of communicating with each other. [Explanation of symbols]

[0042] 1 Work transport system 2. Robot 3. Balancer 4. Control device 5 hands 6 Camera (shape measurement device) 25 Memory section 26 Difference calculation part double work Th1 First threshold Th2 Second threshold Th3 Third threshold Th4 Fourth threshold Th5 Fifth threshold

Claims

1. a robot equipped with a hand at its tip for gripping a workpiece and a sensor capable of detecting an external force acting on the hand; a balancer connected to the hand and capable of generating a lifting force that lifts the hand vertically upward; a shape measuring device that measures the shape of the workpiece; a control device for controlling the robot and the balancer, The control device controls the robot based on the shape of the workpiece measured by the shape measurement device to adjust the gripping position of the workpiece by the hand, and controls the lifting force generated by the balancer so that when the workpiece is gripped and lifted at the adjusted gripping position, the absolute value of the vertical external force detected by the sensor is less than or equal to a predetermined first threshold value.

2. The workpiece transport system of claim 1, wherein the control device adjusts the gripping position by controlling the robot so that the hand grips and lifts the workpiece at the gripping position set based on the shape of the workpiece, and corrects the gripping position so that the moment around the horizontal axis detected by the sensor is equal to or less than a predetermined second threshold value.

3. The control of the lifting force of the balancer by the control device includes controlling the robot so that the hand grasps the workpiece placed on the mounting surface at an adjusted grasping position, controlling the balancer so that the lifting force increases until the vertical external force detected by the sensor becomes a predetermined third threshold, and then controlling the robot so that the hand is raised until the vertical external force detected by the sensor becomes equal to or less than a predetermined fourth threshold. This is the work transport system described in claim 1 or 2.

4. The control of the lifting force of the balancer by the control device includes controlling the robot so that the hand grasps the workpiece placed on the mounting surface at an adjusted grasping position, controlling the balancer so that the vertical external force detected by the sensor generates a lifting force that is a predetermined value, controlling the robot to raise the hand, and then controlling the balancer so that the lifting force is changed by a difference that makes the vertical external force detected by the sensor less than a predetermined fourth threshold value.A work transport system as described in claim 1 or claim 2.

5. The control device is provided with a memory unit that stores, in chronological order, the external forces detected by the sensor when the workpiece is transported using the robot according to the workpiece transport program, in correspondence with the robot's position data, and a difference calculation unit that calculates the absolute value of the difference between the external force detected by the sensor when a workpiece identical to the workpiece is transported according to the transport program and the external force stored in the memory unit, and the workpiece transport system described in any one of claims 1 to 4, wherein the control device stops the robot when the absolute value of the difference calculated by the difference calculation unit is greater than or equal to a predetermined fifth threshold.

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