Workpiece handling system

Abstract

A workpiece handling system (1) includes a robot (2) having a hand (5) that grips a workpiece (W) at a front end, and a sensor that detects an external force acting on the hand (5); a balancer (3) that is connected to the hand (5) and generates a lifting force that lifts the hand (5) vertically upward; a shape measuring device (6) that measures the shape of the workpiece (W); and a control device (4) that controls the robot (2) and the balancer (3) based on the shape of the workpiece (W) measured by the shape measuring device (6). The control device (4) adjusts a gripping position at which the workpiece (W) is gripped by the hand (5) based on the shape of the workpiece (W) measured by the shape measuring device (6). When the workpiece (W) is gripped and lifted at the adjusted gripping position, the control device (4) controls the lifting force generated by the balancer (3) so that the absolute value of the external force in the vertical direction detected by the sensor becomes equal to or less than a predetermined first threshold value.

Description

Technical Field

[0001] This disclosure relates to a workpiece handling system. Background Technology

[0002] A system is known in which, when a robot is used to move a workpiece supported by a hand mounted at its front end, a balancer is used to lift the workpiece with a force corresponding to the weight of the workpiece to assist the robot (e.g., see Patent Document 1).

[0003] Existing technical documents

[0004] Patent Document 1: International Publication No. 2010 / 104157 Summary of the Invention

[0005] The problem the invention aims to solve

[0006] When the hand grips the workpiece in an inappropriate position, it is impossible to achieve a proper balance using a balancer. However, with a wide variety of workpieces, pre-measuring and recording information such as the mass and gripping position of each workpiece requires a significant amount of time. Therefore, it is desirable to be able to grip and move workpieces from appropriate positions without pre-registering their gripping positions.

[0007] Solution for solving the problem

[0008] One aspect of the present invention is a workpiece handling system comprising: a robot having a hand at its front end for holding a workpiece and having 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 for measuring the shape of the workpiece; and a control device that controls the robot and the balancer based on the shape of the workpiece measured by the shape measuring device, wherein the control device adjusts the holding position of the hand holding the workpiece based on the shape of the workpiece measured by the shape measuring device, and when holding and lifting the workpiece in the adjusted holding position, controls the lifting force generated by the balancer such that the absolute value of the vertical external force detected by the sensor is below a predetermined first threshold. Attached Figure Description

[0009] Figure 1 This is an overall structural diagram illustrating a workpiece handling system according to one embodiment of the present invention.

[0010] Figure 2 It is shown Figure 1 A block diagram of a workpiece handling system.

[0011] Figure 3 It is shown Figure 2 The diagram shows the air pressure control circuit of the balancer control unit.

[0012] Figure 4 This indicates that it is closed. Figure 3 The diagram shows the state of the first valve in the pneumatic control circuit.

[0013] Figure 5 This is an explanation Figure 3 A diagram showing the balance state of the air pressure control loop.

[0014] Figure 6 This is an explanation of the use of Figure 1 A flowchart of the workpiece handling system's actions for handling workpieces.

[0015] Figure 7 It is shown Figure 2 A diagram showing a modified example of the pneumatic control circuit.

[0016] Figure 8 This explains the use of... Figure 7 A flowchart illustrating the workpiece handling action of a workpiece handling system with a pneumatic control circuit.

[0017] Figure 9 It is shown Figure 2 A block diagram of a modified workpiece handling system. Detailed Implementation

[0018] The workpiece handling system 1 according to one embodiment of the present invention will be described below with reference to the accompanying drawings.

[0019] like Figure 1 As shown, the workpiece handling system 1 of this embodiment includes a robot 2, a balancer 3, and a control device 4.

[0020] Robot 2 is, for example, a vertical six-axis articulated robot, with a hand 5 at its front end capable of holding a workpiece W. Robot 2 has a built-in force sensor (sensor) capable of detecting external forces acting on the hand 5. Additionally, the hand 5 is equipped with a camera (shape measuring device) 6 capable of acquiring images of the workpiece W.

[0021] The workpiece W is, for example, an elongated component with a uniform cross-sectional shape. The hand 5 has a pair of openable and closable claws 8, which can grip and hold the workpiece W at any position along its length on the mounting surface of a workpiece table or similar surface in the horizontal direction. A force sensor can detect external forces acting on the workpiece W, such as forces along the three axes of an orthogonal coordinate system with the tool tip point (TCP) at the center of the pair of claws 8 as the origin, and torques around the three axes.

[0022] The balancer 3, for example, is a cylinder, suspended from a cantilever beam 10 supported by a support column 9 located near the robot 2, and configured to extend a rod 11 vertically downwards. The front end of the rod 11 is attached to a hand 5. If the rod 11 of the balancer 3 is driven in the direction that raises it, a lifting force in the vertical direction can be applied to the hand 5. The cantilever beam 10 is configured to rotate about a vertical axis extending along the length axis of the support column 9.

[0023] Furthermore, the balancer 3 is fixed to the slider 12, which is supported to move along the length of the cantilever beam 10. Thus, when the robot 2 moves, the balancer 3 is maintained in a vertical position above the hand 5 by the rotation of the cantilever beam 10 and the movement of the slider 12, so that the lifting force can be applied to the hand 5 regardless of the posture of the robot 2.

[0024] Camera 6, for example, can acquire an image of the shape of a top view of workpiece W by photographing workpiece W from a vertically above it.

[0025] like Figure 2 As shown, the control device 4 includes a robot control unit 13 for controlling the robot 2 and a balancer control unit 14 for controlling the balancer 3.

[0026] When the handling program instructs the robot to hold the workpiece W, the robot control unit 13 controls the robot 2 to position the camera 6 above the workpiece W, so that the camera 6 can acquire an image of the workpiece W. In addition, the robot control unit 13 extracts the shape of the workpiece W from the image acquired by the camera 6 and calculates its center of gravity position, thereby calculating the holding position of the hand 5 holding the workpiece W.

[0027] Furthermore, the robot control unit 13 controls the robot 2 to position the hand 5 at the calculated gripping position, so that the workpiece W is gripped by the hand 5. Then, the robot control unit 13 controls the robot 2 to raise the hand 5, and when the torque around the horizontal axis detected by the force sensor exceeds a predetermined threshold, namely the second threshold Th2, the gripping position is corrected.

[0028] The gripping position is corrected as follows: the gripping position is moved along the length of the workpiece W in the direction that reduces the torque detected by the force sensor around the horizontal axis. That is, the workpiece W is placed on the workpiece table 7, the gripping position held by the hand 5 is corrected relative to the placed workpiece W, the workpiece W is gripped in the corrected gripping position, the workpiece W is lifted, and the above process is repeated until the magnitude of the torque detected by the force sensor converges to below the second threshold Th2.

[0029] The balancer control unit 14, for example, has Figure 3 The air pressure control circuit 15 is shown.

[0030] The pneumatic control circuit 15 includes a pneumatic power source 16, three valves 17, 18, and 19, and a regulator 20. Reference numeral 21 is a speed controller, reference numeral 22 is a throttle valve with a silencer, and reference numeral 23 is a silencer.

[0031] The balancer control unit 14 adjusts the lifting force generated by the balancer 3.

[0032] The lifting force generated by the balancer 3 is adjusted such that, when the workpiece W is lifted and held in an appropriate gripping position by the hand 5 and kept stationary, the absolute value of the vertical external force detected by the force sensor converges to a predetermined threshold, namely the fourth threshold Th4, or below.

[0033] Specifically, such as Figure 3 As shown, the balancer control unit 14 activates the first valve 17 and the second valve 18, allowing air from the pneumatic source 16 to pass through the speed regulator 21, the first valve 17, and the second valve 18 in sequence, and supplying it to the lever 11 side of the balancer 3. This allows the lever 11 to be raised, applying an upward lifting force to the hand 5.

[0034] For example, with the workpiece W placed on the workpiece table 7 held in the adjusted gripping position by hand 5, the first valve 17 is opened and closed. This intermittently increases the lifting force generated by the balancer 3 until the vertical external force detected by the force sensor reaches a predetermined threshold, i.e., the third threshold Th3. At this time, the set pressure value supplied to the regulator 20 also increases equal to the pressure value supplied to the balancer 3.

[0035] When the vertical external force detected by the force sensor exceeds the predetermined third threshold Th3, such as Figure 4 As shown, the first valve 17 is closed, 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 below a predetermined threshold, namely the fourth threshold Th4.

[0036] If the external force does not fall below the fourth threshold Th4, the balancer control unit 14 switches the opening and closing of the first valve 17 and adjusts the pressure applied to the balancer 3. Then, when the vertical external force detected by the force sensor falls below the fourth threshold Th4, the balancer control unit 14, as follows... Figure 5 As shown, switch the second valve 18.

[0037] Therefore, the air pressure set at the set pressure value of the regulator 20 is supplied to the balancer 3. By pre-setting the fourth threshold Th4 to be sufficiently small, a balance state can be achieved in which the force detected by the force sensor is approximately close to zero.

[0038] The operation of the workpiece handling system 1 configured as described in this embodiment will be explained below. When using the workpiece handling system 1 of this embodiment to handle a workpiece W whose weight and shape are unknown, firstly, the robot 2 is operated, and the camera 6 mounted on the hand 5 is positioned vertically above the workpiece W.

[0039] Then, as Figure 6 As shown, the workpiece W is positioned within the field of view of the camera 6, and an image is acquired (step S1). The robot control unit 13 processes the image, extracts the workpiece W, and calculates the horizontal center of gravity position based on the shape of the top view of the workpiece W (step S2). The robot control unit 13 sets the gripping position of the workpiece W held by the hand 5 to the posture of arranging the claws of the hand 5 on both sides of the calculated center of gravity position.

[0040] Next, the robot control unit 13 uses the hand 5 to grasp the workpiece W (step S3) and raises the hand 5 (step S4). At this time, the force acting on the hand 5 in the three-axis directions and the torque around the three axes are detected by the force sensor. The robot control unit 13 determines whether the torque around the horizontal axis exceeds the second threshold Th2 (step S5). If it does, the grasping position is corrected (step S6), and the process starting from step S3 is repeated.

[0041] Then, with the gripping position corrected, the lifting force generated by the balancer 3 is adjusted.

[0042] First, place the workpiece W back onto the workpiece stage 7 (step S7), and hold the workpiece W with hand 5 in the adjusted holding position (step S8). In this state, the balancer control unit 14 uses 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 Th3 (steps S9, S10).

[0043] When the lifting force exceeds the third threshold Th3, the increase in lifting force is stopped, and the robot control unit 13 raises the hand 5 (step S11). Then, it is determined whether the absolute value of the external force detected by the force sensor is below the fourth threshold Th4 (step S12). If it exceeds the fourth threshold Th4, the lifting force generated by the balancer 3 is increased again (step S13).

[0044] Specifically, when the absolute value of the external force detected by the force sensor falls below the fourth threshold Th4, the pressure needs to be adjusted while the workpiece W is being raised. Specifically, if the robot control unit 13 determines that a lifting force generated by the balancer 3 is needed, it issues an air supply command to the first valve 17 to open it. The opening state of the first valve 17 is momentary, after which the robot 2 issues an air cut-off command to close it. The regulator 20 records (saves) the same pressure as the pressure from the second valve 18 to the balancer 3, maintains, and continuously supplies this pressure. Thus, the absolute value of the external force detected by the force sensor is suppressed below the fourth threshold Th4.

[0045] When the absolute value of the external force detected by the force sensor falls below the fourth threshold Th4, the balancer control unit 14 sets the pressure at that moment to the pressure of the regulator 20 and supplies air at the set pressure to the balancer 3. As a result, the balancer 3 becomes balanced (step S14). Consequently, the load acting on the robot 2 can be minimized, and the robot 2 can easily handle workpieces W with a lifting weight of more than 200 tons (step S15).

[0046] Thus, the workpiece handling system 1 according to this embodiment has the following advantages: even without registering information such as mass and gripping position for each workpiece W, it is possible to properly grip the workpiece W and handle the workpiece W while sufficiently reducing the load acting on the robot 2.

[0047] Furthermore, in this embodiment, instead of a pre-set sufficiently small value, a predetermined threshold, namely the first threshold Th1, can be used as the fourth threshold Th4. This allows the load applied to the robot 2 in the vertical direction to be suppressed within a certain range, and enables the easy handling of loads larger than the load-bearing capacity.

[0048] Furthermore, an example was given illustrating the scenario where the lifting force generated by the balancer 3 is gradually increased to achieve weight balance with the workpiece W. However, alternatively, another method can be used... Figure 7 The air pressure control circuit 15 is shown.

[0049] That is, an electric pneumatic regulator 24 can also be configured, which can set the pressure of the air supplied to the balancer 3 by the regulator 20 according to the command signal from the outside.

[0050] Therefore, as Figure 8As shown, with the workpiece W held in an appropriate position by the hand 5 (step S8), the balancer control unit 14 instructs the electro-pneumatic regulator 24 to supply a predetermined pressure value, so that the balancer 3 generates a certain lifting force (step S21). Afterwards, the robot control unit 13 controls the robot 2 to raise the hand 5 (step S11).

[0051] In this state, the balancer control unit 14 calculates the pressure required for the balancer 3 to achieve equilibrium based on the value of the external force detected by the force sensor, and instructs the electro-pneumatic regulator 24 to adjust the pressure accordingly (step S22). Thus, the pressure of the balancer 3 is controlled by feedback until the external force detected by the force sensor falls below the fourth threshold Th4 (steps S12, S22).

[0052] In addition, in this embodiment, the camera 6 mounted on the hand 5 is used to acquire an image of the workpiece W from a top view and calculate the position of the center of gravity. However, instead, a distance sensor, a light sensor, an ultrasonic sensor, or a temperature sensor can also be used to detect the shape of the workpiece W.

[0053] Alternatively, a force sensor can be installed in the mechanism of the robot 2, or a force sensor installed in the control device 4 that estimates the external force based on the current value can be used.

[0054] In addition, in this embodiment, a cylinder is described as the balancer 3, but instead, any type of actuator, such as pneumatic, hydraulic or electric, can be used.

[0055] In addition, in this embodiment, a slender quadrangular prism component with a uniform cross-section is used as an example of workpiece W, but other workpieces of any shape can also be used instead.

[0056] In addition, such as Figure 9 As shown, the control device 4 may also include a storage unit 25 composed of a memory and a differential calculation unit 26 composed of a processor. The storage unit 25 stores the external force detected by the force sensor when the robot 2 moves the predetermined reference workpiece according to the workpiece W's handling program in a time sequence, corresponding to the coordinates of the robot 2's TCP.

[0057] When the differential calculation unit 26 moves the same workpiece W as the reference workpiece according to the same handling procedure, it sequentially calculates the absolute value of the difference between the external force detected by the force sensor and the external force stored in the storage unit 25.

[0058] Furthermore, the control device 4 can also stop the robot 2 when the absolute value of the difference calculated by the difference calculation unit 26 at each moment during the process of moving the workpiece W according to the handling program is above a predetermined threshold, namely the fifth threshold Th5.

[0059] Furthermore, while this embodiment illustrates a scheme using a force sensor to detect external forces, alternative schemes using other sensors can also be employed. For example, torque sensors can be installed on each axis of robot 2, and the output of the torque sensors and known techniques can be used to calculate data equivalent to that of the force sensors.

[0060] In addition, in this embodiment, an example is given of a scheme in which image processing is performed in the robot control unit 13 within the control device 4. However, alternatively, an image processing device can be provided outside the control device 4 in the workpiece handling system 1, and the image processing device can be used to perform image processing.

[0061] In addition, in this embodiment, the coordinates of the TCP of robot 2 are used as an example of position data stored in time sequence in correspondence with external forces. However, the encoder values ​​of each axis motor can also be used instead.

[0062] Furthermore, while this embodiment illustrates an example of using a robot control unit 13 to control a camera 6 to acquire images, alternatively, a workpiece handling system 1 can be equipped with a camera control unit external to the control device 4, using the camera control unit to control the camera 6. In this case, it is preferable that the robot control unit 13 and the camera control unit can communicate.

[0063] Explanation of reference numerals in the attached figures:

[0064] 1: Workpiece handling system

[0065] 2: Robot

[0066] 3: Balancer

[0067] 4: Control device

[0068] 5: Hand

[0069] 6: Camera (shape measuring device)

[0070] 25: Storage Department

[0071] 26: Difference Calculation Department

[0072] W: Workpiece

[0073] Th1: First threshold

[0074] Th2: Second threshold

[0075] Th3: Third threshold

[0076] Th4: Fourth Threshold

[0077] Th5: The fifth threshold

Claims

1. A workpiece handling system, characterized in that, have: A robot with a hand at its front end to hold a workpiece and sensors that can detect the external force acting on that hand; A beam, which is positioned above the robot; A cylinder, which is suspended from the beam and connected to the hand, and is capable of generating a lifting force that lifts the hand vertically upward; A shape measuring device for measuring the shape of the workpiece; Pneumatic power source; A regulator is provided in a pneumatic control circuit that supplies a set pressure value of air from the pneumatic source to the cylinder. A valve that switches between a first supply state of air pressure from the pneumatic source to the cylinder without passing through the regulator and a second supply state via the regulator; as well as Control device, which controls the valve The control device is configured to control the robot based on the shape of the workpiece measured by the shape measuring device. The cylinder has a rod connected to the hand and capable of moving in the vertical direction. The upward force is generated by applying an upward force to the rod using air pressure. When the air pressure supplied to the cylinder increases in the first supply state, the lifting force increases, and the set pressure value of the regulator also increases equal to the increase in air pressure. The control device adjusts the gripping position of the hand on the workpiece based on the shape of the workpiece measured by the shape measuring device. When the hand holds and lifts the workpiece, if the absolute value of the vertical external force detected by the sensor is below a first threshold, the control device switches from the first supply state to the second supply state, thereby continuously supplying the cylinder with the increased set pressure value of the regulator from the pneumatic source. If the absolute value of the vertical external force detected by the sensor is not below the first threshold, the lifting force and the set pressure value are adjusted in the first supply state.

2. The workpiece handling system according to claim 1, characterized in that, The adjustment of the gripping position by the control device is performed as follows: the robot is controlled to grip and lift the workpiece using the hand at the gripping position set according to the shape of the workpiece, and the gripping position is corrected so that the torque around the horizontal axis detected by the sensor becomes below a predetermined second threshold.

3. The workpiece handling system according to claim 1 or 2, characterized in that, The lifting force of the cylinder controlled by the control device is as follows: the robot is controlled to hold the workpiece placed on the mounting surface with its hand in the adjusted gripping position, and the set pressure value is controlled to increase the lifting force until the vertical external force detected by the sensor reaches a predetermined third threshold. Then, the robot is controlled to raise its hand until the vertical external force detected by the sensor falls below the first threshold.

4. The workpiece handling system according to claim 1 or 2, characterized in that, The control of the set pressure value of the cylinder by the control device is performed as follows: the robot is controlled to hold the workpiece placed on the mounting surface by its hand in the adjusted gripping position; the set pressure value is controlled to generate a lifting force that is a predetermined value for the vertical external force detected by the sensor; the robot is controlled to raise its hand; and then the set pressure value is controlled to change the lifting force by an amount equivalent to a difference, the difference causing the vertical external force detected by the sensor to be below the first threshold.

5. The workpiece handling system according to claim 1 or 2, characterized in that, The control device includes a storage unit that stores, in a time sequence, the external forces detected by the sensors when the robot moves the workpiece according to the workpiece handling procedure, in correspondence with the robot's position data; And a differential calculation unit, which calculates the absolute value of the difference between the external force detected by the sensor and the external force stored in the storage unit when a workpiece identical to the workpiece is transported according to the transport procedure. The robot is stopped when the absolute value of the difference calculated by the difference calculation unit is above a predetermined fifth threshold.

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