Method of controlling robot and robot system

Abstract

The invention relates to a method for controlling a robot and a robot system. Techniques for maintaining a holding force of a piezoelectric actuator when the piezoelectric actuator is not energized are provided. The method according to the present disclosure includes: (a) a step for determining whether or not a holding force is sufficient when power is not supplied to a piezoelectric actuator included in a tool section attached to the tip of a robot arm; (b) a step for executing a holding force restoring operation of the piezoelectric actuator when it is determined that the holding force is insufficient; and (c) when it is determined that the holding force is sufficient, performing a robotic work on the workpiece.

Description

Technical Field

[0001] The present disclosure relates to a method for controlling a robot and a robot system. Background Art

[0002] A robot having a piezoelectric actuator at the front end of a robotic arm is disclosed in Patent Document 1. The piezoelectric actuator is used to compensate for the position error of the fingertip of the robot.

[0003] Patent Document 1: Japanese Patent Laid-Open No. 3-228588

[0004] The piezoelectric actuator has the advantage of being able to maintain a holding force even when not energized. However, in a state where the piezoelectric actuator is not actuated, the holding force of the piezoelectric actuator decreases over time. If the holding force of the piezoelectric actuator decreases, when the inertial force and external force during the operation of the robot are large, the position of the piezoelectric actuator shifts, and there is a problem that the position accuracy deteriorates. Summary of the Invention

[0005] According to a first aspect of the present disclosure, there is provided a method for controlling a robot. The method includes: (a) a step of determining whether the holding force when non-energized of a piezoelectric actuator included in a tool unit mounted at the front end of a robotic arm is sufficient; (b) a step of performing a holding force recovery operation of the piezoelectric actuator when it is determined that the holding force is insufficient; and (c) a step of performing a robot operation on a workpiece when it is determined that the holding force is sufficient.

[0006] According to a second aspect of the present disclosure, there is provided a robot system. The robot system includes: a robot including a robotic arm; a tool unit including a piezoelectric actuator and mounted at the front end of the robotic arm; and a control device. The control device is configured to perform the following processes: (a) a process of determining whether the holding force when non-energized of the piezoelectric actuator is sufficient; (b) a process of performing a holding force recovery operation of the piezoelectric actuator when it is determined that the holding force is insufficient; and (c) a process of performing a robot operation on a workpiece when it is determined that the holding force is sufficient. Brief Description of the Drawings

[0007] Figure 1 It is an explanatory diagram showing the structure of the robot system in the embodiment.

[0008] Figure 2 It is a functional block diagram of the information processing device in the embodiment.

[0009] Figure 3 It is an explanatory diagram showing the state at the time of holding force confirmation in the first embodiment.

[0010] Figure 4It is a flowchart showing the processing steps of the robot operation.

[0011] Figure 5 It is an explanatory diagram showing the state at the time of holding force confirmation in the second embodiment.

[0012] Figure 6 It is an explanatory diagram showing the state at the time of holding force confirmation in the third embodiment.

[0013] Explanation of Reference Numerals

[0014] 10: Robot system; 100: Robot; 110: Base; 120: Manipulator; 122: Tip; 200: Robot controller; 300: Information processing device; 310: Processor; 312: Robot operation execution unit; 320: Memory; 330: Interface circuit; 340: Input device; 350: Display device; 510: First stage; 520: Second stage; 600: Tool unit; 610: Moving device; 611: Piezoelectric actuator; 612: Movable table; 613: Fitting; 614: Position sensor; 620: Inkjet device; 622: Inkjet head; 710: Force sensor; 712: Elastic member; 714: Block; 720: Force sensor; 730: Acceleration sensor. Detailed Description of the Invention

[0015] A. First Embodiment

[0016] Figure 1 It is an explanatory diagram showing an example of a robot system in one embodiment. The robot system 10 includes: a robot 100, a robot controller 200 that controls the robot 100, an information processing device 300, a first stage 510 on which a workpiece WK is placed, and a second stage 520 on which a force sensor 710 is placed. The information processing device 300 is, for example, a personal computer.

[0017] In Figure 1 are depicted three axes X, Y, and Z of an orthogonal coordinate system that defines a three-dimensional space. The X-axis and the Y-axis are horizontal axes, and the Z-axis is a vertical axis. In this example, the XYZ coordinate system is a robot coordinate system with a reference point preset in the robot 100 as the origin.

[0018] The robot 100 includes a base 110 and a manipulator 120. A tool unit 600 is attached to the tip 122 of the manipulator 120. The tool unit 600 has a moving device 610 and an inkjet device 620 as an end effector.

[0019] The mobile device 610 includes a piezoelectric actuator 611, a movable stage 612 that is driven by the piezoelectric actuator 611 to move, and a fitting 613 fixed to the movable stage 612. The mobile device 610 is used, for example, to finely adjust the printing position of the inkjet device 620.

[0020] As the mobile device 610, for example, a single-axis stage capable of moving the movable stage 612 in one axial direction can be used. Additionally, a multi-axis stage capable of moving the movable stage 612 in two or more directions can also be used. In the present embodiment, a single-axis stage is used as the mobile device 610, and the movable stage 612 can move along the moving direction Dm driven by the piezoelectric actuator 611. The piezoelectric actuator 611 can maintain a holding force even when not energized. That is, the movable stage 612 maintains its position by its holding force even when the piezoelectric actuator 611 is not energized. In the present embodiment, the holding force direction Dh of the piezoelectric actuator 611 is a direction parallel to the moving direction Dm of the movable stage 612.

[0021] On the movable stage 612, the inkjet device 620 is installed via the fitting 613. The fitting 613 is an installation auxiliary component for installing other devices and components on the movable stage 612. However, the fitting 613 can also be omitted, and the inkjet device 620 can be directly installed on the movable stage 612. The movable stage 612 and the fitting 613 are holding force acting components on which the holding force of the piezoelectric actuator 611 acts.

[0022] The inkjet device 620 includes an inkjet head 622. The inkjet head 622 performs printing by ejecting ink onto the printing area on the surface of the workpiece WK. Preferably, the inkjet head 622 can eject multiple types of inks to perform color printing. The printing area on the surface of the workpiece WK may not include a flat surface but may include a curved surface portion. As can be understood from this description, the robot system 10 of the present embodiment functions as a DTS (Direct To Shape) printing device for printing on the surface of a three-dimensional object.

[0023] As the end effector, any device or mechanism other than the inkjet device 620 can be used. For example, as the end effector, a coating device for applying a liquid agent, a welding device for welding, a manipulator for precision assembly, etc. can be used.

[0024] The force sensor 710 is used to confirm the holding force of the piezoelectric actuator 611. As the force sensor 710, for example, a load cell can be used. Alternatively, a three-axis force sensor or a six-axis force sensor can also be used. The force sensor 710 is supported by an elastic member 712 such as a spring, thereby attempting to increase the position displacement of the force sensor 710. However, the elastic member 712 can also be omitted.

[0025] Near the front end of the robotic arm 120, a TCP (Tool CenterPoint), which is the control point of the robot 100, is set. In Figure 1 the example of, the TCP is set near the surface of the inkjet head 622. It should be noted that the control point TCP can be set at any position.

[0026] The robotic arm 120 is successively connected by six joints J1 to J6. Among these joints J1 to J6, three joints J2, J3, and J5 are bending joints, and the other three joints J1, J4, and J6 are twisting joints. In the present embodiment, a six-axis robot is illustrated, but a robot having an arbitrary robotic arm structure with multiple joints can also be used. In addition, the robot 100 of the present embodiment is a vertical multi-joint robot, but a horizontal multi-joint robot can also be used.

[0027] Figure 2 is a block diagram showing the functions of the information processing device 300. The information processing device 300 includes a processor 310, a memory 320, and an interface circuit 330. An input device 340 and a display device 350 are connected to the interface circuit 330. In addition, a robot controller 200 is also connected. The robot 100, the mobile device 610, the inkjet device 620, and the force sensor 710 are connected to the information processing device 300 via the robot controller 200. However, a part of them can also be directly connected to the information processing device 300.

[0028] The processor 310 has a function as a robot operation execution unit 312. The robot operation execution unit 312 executes a robot operation using a robot control program RP. In the present embodiment, the robot operation is an operation of printing on a workpiece WK using the inkjet device 620.

[0029] The functions of the robot operation execution unit 312 are respectively realized by the processor 310 executing a computer program stored in the memory 320. However, a part or all of the functions of the robot operation execution unit 312 can also be realized by a hardware circuit.

[0030] A robot control program RP generated by a teaching process is stored in the memory 320. The robot control program RP is composed of a plurality of commands for operating the robot 100 and includes coordinate values of a plurality of teaching points.

[0031] As described in the prior art, in a state where the piezoelectric actuator 611 is not operated, the holding force of the piezoelectric actuator 611 decreases over time. Therefore, it is desirable to confirm whether the holding force of the piezoelectric actuator 611 is sufficient at an appropriate timing when the robot operation is not being performed.

[0032] Figure 3 This is an explanatory diagram showing the state during the holding force confirmation in the first embodiment. In this example, by moving the robotic arm 120, the fitting 613 is pressed against the force sensor 710, thereby applying an external force to the fitting 613. The application direction Df of the external force is opposite to the holding force direction Dh of the piezoelectric actuator 611. At this time, the piezoelectric actuator 611 is maintained in a non-energized state. The confirmation of whether the holding force of the piezoelectric actuator 611 is sufficient can be performed, for example, using any one of the following confirmation methods M1 and M2.

[0033] Confirmation method M1 of holding force

[0034] (1a) While applying an external force to the fitting 613 as the holding force acting component along the direction Df opposite to the holding force direction Dh, measure the external force through the force sensor 710 to obtain a force measurement value. At this time, it is preferable to gradually increase the external force and unload when the force measurement value reaches a preset reference value.

[0035] (1b) Using the force measurement value, determine whether the holding force of the piezoelectric actuator 611 when non-energized is sufficient. This determination can be performed, for example, as follows.

[0036] (1b-1) When the force measurement value reaches the reference value without decreasing, it is determined that the holding force of the piezoelectric actuator 611 is sufficient.

[0037] (1b-2) When the force measurement value decreases before reaching the reference value, calculate the amount of decrease.

[0038] (1b-3) When the amount of decrease in the force measurement value is less than a preset decrease threshold and the force measurement value then increases and reaches the reference value, it is determined that the holding force of the piezoelectric actuator 611 is sufficient.

[0039] (1b-4) When the amount of decrease in the force measurement value is equal to or greater than the decrease threshold, it is determined that the holding force of the piezoelectric actuator 611 is insufficient.

[0040] Confirmation method M2 of holding force

[0041] (2a) Apply an external force to the fitting 613 as the holding force acting component along the direction Df opposite to the holding force direction Dh. At this time, it is preferable to gradually increase the external force and unload when the force measurement value measured by the force sensor 710 reaches a predetermined reference value.

[0042] (2b) While applying an external force, use the position sensor 614 included in the moving device 610 to measure the position of the movable table 612, which is the holding force acting component. Since the fitting 613 is fixed to the movable table 612, the position of the movable table 612 can be regarded as the position of the fitting 613. As the position sensor 614, an encoder can be used, for example.

[0043] (2c) Using the position measurement value of the position sensor 614, determine whether the holding force of the piezoelectric actuator 611 when non-energized is sufficient. This determination can be performed as follows, for example.

[0044] (2c-1) Measure the amount of change in the position of the movable table 612 before and after the application of the external force.

[0045] (2c-2) When the amount of change in the position of the movable table 612 is less than a preset change amount threshold, it is determined that the holding force of the piezoelectric actuator 611 is sufficient.

[0046] (2c-3) When the amount of change in the position of the movable table 612 is equal to or greater than the change amount threshold, it is determined that the holding force of the piezoelectric actuator 611 is insufficient.

[0047] Note that most force sensors such as load cells sense force with a slight displacement, and there is a possibility of generating a large force just by slightly moving the robotic arm 120. Therefore, a structure is adopted in which the force sensor 710 is pressed against the fitting 613 side by using an elastic member 712 to increase the displacement of the force sensor 710, so as to prevent the generation of an excessive force. Furthermore, a configuration in which the force sensor 710 can slide by using a sliding member such as a linear guide can also be adopted. In addition, instead of applying an external force to the fitting 613 by moving the robotic arm 120, an actuator that moves the force sensor 710 can be used to move the force sensor 710, thereby applying an external force to the fitting 613. In this case, the elastic member 712 can be omitted.

[0048] In Figure 3 's example, the holding force is confirmed for one holding force direction Dh, but multiple force sensors 710 with different directions can also be arranged to confirm the holding force in each of the multiple holding force directions. In addition, only one force sensor 720 can be used to change the joint angle of the robotic arm 120 to confirm the holding force in each of the multiple holding force directions. For example, in Figure 3 's structure, by rotating the wrist joint J6 of the robotic arm 120 by 180 degrees, the holding force in one holding force direction Dh and the holding force in the opposite direction can be confirmed respectively.

[0049] Figure 4This is a flowchart showing the processing steps of a robot operation. In step S10, a new workpiece WK is prepared as the operation object. The preparation of the new workpiece WK can be performed by, for example, another robot or an operator.

[0050] In step S11, the robot operation execution unit 312 confirms the holding force of the piezoelectric actuator 611 when non-energized. In step S12, the robot operation execution unit 312 determines whether the holding force of the piezoelectric actuator 611 is sufficient. The processing of steps S11 and S12 can be performed according to the above-described confirmation methods M1 or M2.

[0051] When the holding force of the piezoelectric actuator 611 is sufficient, the process proceeds to step S13 described later. On the other hand, when the holding force of the piezoelectric actuator 611 is insufficient, the process proceeds to step S17, and the robot operation execution unit 312 performs a holding force recovery operation for the piezoelectric actuator 611. The holding force recovery operation is an operation of driving the piezoelectric actuator 611 and repeating the reciprocating motion of the movable table 612. The moving stroke of the piezoelectric actuator 611 in the holding force recovery operation is preferably larger than the moving stroke of the piezoelectric actuator 611 in the robot operation.

[0052] Steps S13 to S15 are robot operations. In step S13, the robot operation execution unit 312 moves the tool unit 600 to the printing start position of the next printing area. Here, it is assumed that one or more printing areas are set on the surface of the workpiece WK. In addition, when multiple printing areas are set, it is assumed that they are set at mutually separated positions. During the movement of the tool unit 600 in step S13, it is preferable to maintain the piezoelectric actuator 611 in a non-energized state.

[0053] In step S14, the robot operation execution unit 312 performs printing in the printing area using the inkjet device 620. At this time, the piezoelectric actuator 611 can also be used for fine adjustment of the printing position. Specifically, for example, when printing a single printing range, consider a case where a "modification operation" of moving the inkjet device 620 in the sub-scanning direction is performed during printing. This modification operation can be performed by the movement of the robotic arm 120 or by using the moving device 610. In either case, as long as the piezoelectric actuator 611 is used for fine adjustment of the printing position, the modification operation can be implemented with high precision.

[0054] However, it is preferable to maintain the piezoelectric actuator 611 in a non-energized state during the period when ink is ejected from the inkjet head 622. That is, generally, during the execution of the operation of the end effector, it is preferable to operate the end effector while maintaining the piezoelectric actuator 611 in a non-energized state. Thereby, during the execution of the operation of the end effector, the position of the end effector can be held by the holding force of the piezoelectric actuator 611.

[0055] In step S15, the robot operation execution unit 312 determines whether there is a next printing area where printing is not completed. If there is a next printing area, the process returns to step S13, and the robot operations of steps S13 to S15 are performed again. On the other hand, if there is no next printing area, the process proceeds to step S16, and the robot operation execution unit 312 moves the tool unit 600 to the initial position by operating the robotic arm 120. The initial position is the initial position and the initial posture in the state before the start of the operation, and is preset according to the type of operation. In the movement in step S16, it is preferable to keep the piezoelectric actuator 611 in a non-energized state. After step S16, the process returns to step S10, a new workpiece WK is prepared, and the processes after step S11 are performed again.

[0056] The confirmation of the holding force of the piezoelectric actuator 611 in steps S11 and S12 and the holding force recovery operation in step S17 are performed at a timing when no robot operation is being performed. Thus, if the holding force confirmation and recovery operations are performed at a timing when no robot operation is being performed, even if a holding force confirmation process and a holding force recovery process are added, the production capacity can be maintained without being reduced.

[0057] It should be noted that in step S14 shown by the double-layer frame, the piezoelectric actuator 611 is energized and operates. In addition, as described above, in step S17, the piezoelectric actuator 611 may also be energized and operate. In other steps, the piezoelectric actuator 611 is preferably kept in a non-energized state. When the holding force of the piezoelectric actuator 611 during non-energization decreases, there is a possibility that the position and posture of the inkjet device 620 change along with the operation of the robotic arm 120 in steps S13 and S16. Therefore, if the holding force confirmation and recovery operations of the piezoelectric actuator 611 are performed as described above, it is possible to prevent an abnormal situation in which the position and posture of the inkjet device 620 change during the operation of the robotic arm 120.

[0058] As described above, in the first embodiment, it is determined whether the holding force of the piezoelectric actuator 611 during non-energization is sufficient. If it is determined that the holding force is insufficient, the holding force recovery operation of the piezoelectric actuator 611 is performed. In addition, if it is determined that the holding force is sufficient, the robot operation for the workpiece WK is performed. As a result, it is possible to perform the robot operation while maintaining the holding force of the piezoelectric actuator 611 during non-energization.

[0059] B. Second Embodiment

[0060] Figure 5It is an explanatory diagram showing the state at the time of holding force confirmation in the second embodiment. In the second embodiment, a force sensor 720 is provided at the tip of the robotic arm 120. As this force sensor 720, for example, a six-axis force sensor can also be used.

[0061] A block 714 supported by an elastic member 712 is placed on the second stage 520. The block 714 is used to apply an external force to the fitting 613 of the tool unit 600. When applying an external force to the fitting 613, the block 714 can be moved, or the tool unit 600 can be moved using the robotic arm 120.

[0062] The device configuration of the second embodiment is the same as that of the first embodiment except for the force sensor and its installation position. In the second embodiment, the confirmation methods M1 and M2 described in the first embodiment can also be applied. In addition, Figure 4 the processing steps described in can also be applied to the second embodiment. The second embodiment also has substantially the same effects as the first embodiment.

[0063] C. Third Embodiment

[0064] Figure 6 It is an explanatory diagram showing the state at the time of holding force confirmation in the third embodiment. In the third embodiment, the force sensor is omitted, and instead, an acceleration sensor 730 is provided on the fitting 613. However, the acceleration sensor 730 can also be provided at other positions of the tool unit 600. It should be noted that generally, acceleration can be specified as a robot action, but the acceleration applied to the fitting 613 may not necessarily be the same as the acceleration specified as a robot action. Therefore, it is preferable to accurately measure the acceleration of the fitting 613 using the acceleration sensor 730.

[0065] As a method for confirming the holding force of the piezoelectric actuator 611 in the third embodiment, for example, the following method can be used.

[0066] Holding Force Confirmation Method M3

[0067] (3a) While operating the robotic arm 120 to apply an acceleration to the movable worktable 612 and the fitting 613 as the holding force acting members in a direction Da opposite to the holding force direction Dh of the piezoelectric actuator 611, the acceleration measurement value is obtained using the acceleration sensor 730. In this case, the robotic arm 120 is accelerated so that the acceleration reaches a preset acceleration reference value.

[0068] (3b) Using the acceleration measurement value, it is determined whether the holding force of the piezoelectric actuator 611 when non-energized is sufficient. This determination can be performed as follows, for example.

[0069] (3b-1) Measure the amount of change in the position of the movable table 612 before and after the addition of acceleration using the position sensor 614 included in the mobile device 610. Since the fitting 613 is fixed to the movable table 612, the position of the movable table 612 can be considered as the position of the fitting 613. As the position sensor 614, for example, an encoder can be used.

[0070] (3b-2) When the amount of change in the position of the movable table 612 is less than a preset change threshold, it is determined that the holding force of the piezoelectric actuator 611 is sufficient.

[0071] (3b-3) When the amount of change in the position of the movable table 612 is equal to or greater than the change threshold, it is determined that the holding force of the piezoelectric actuator 611 is insufficient.

[0072] Note that, instead of acceleration, the robotic arm 120 can be accelerated so that the inertial force calculated by multiplying the acceleration by the load weight becomes a preset force reference value. In the above confirmation method M3, since the holding force of the piezoelectric actuator 611 can be confirmed even without the force sensor 710 and its pressing structure described above, it has the advantages that the overall structure of the device becomes simple and it is easy to save space. Figure 3 It should be noted that both the acceleration and deceleration in one movement of the robotic arm 120 can be used to confirm the holding force in both the left and right directions. In addition, instead of using one movement of the robotic arm 120, multiple movements of the robotic arm 120 can be used to perform the confirmation of the holding force along multiple directions. For example, in a state where the wrist joint J6 of the robotic arm 120 is rotated 180 degrees to reverse the orientation of the movable table 612, by moving the robotic arm 120 in the same direction, the holding force along multiple directions can be confirmed.

[0073] The device configuration of the third embodiment is the same as that of the first embodiment except that the force sensor and its pressing structure are not required. In addition,

[0074] the processing steps described above can also be applied to the third embodiment. The third embodiment also has substantially the same effects as the first embodiment and the second embodiment. Figure 4 The processing steps described above can also be applied to the third embodiment. The third embodiment also has substantially the same effects as the first embodiment and the second embodiment.

[0075] · Other methods

[0076] The present disclosure is not limited to the above-described embodiments, and can be implemented in various ways without departing from its gist. For example, the present disclosure can also be implemented by the following aspects. The technical features in the above-described embodiments corresponding to the technical features in each of the following-described aspects can be appropriately replaced and combined in order to solve part or all of the problems of the present disclosure or to achieve part or all of the effects of the present disclosure. In addition, if the technical feature is not described as an essential feature in this specification, it can be appropriately deleted.

[0077] (1) According to a first aspect of the present disclosure, there is provided a method for controlling a robot. The method includes: (a) a step of determining whether a holding force when the piezoelectric actuator included in the tool unit mounted at the front end of the robotic arm is non-energized is sufficient; (b) a step of performing a holding force recovery operation of the piezoelectric actuator when it is determined that the holding force is insufficient; and (c) a step of performing a robot operation on a workpiece when it is determined that the holding force is sufficient.

[0078] According to this method, it is possible to perform a robot operation while maintaining the holding force when the piezoelectric actuator is non-energized.

[0079] (2) In the above method, it may be that the tool unit includes a holding force acting member, and the holding force of the piezoelectric actuator acts on the holding force acting member. It may also be that the step (a) includes: (a1) a step of obtaining a force measurement value, which is a measurement value of the external force by the force sensor, while applying an external force to the holding force acting member in a direction opposite to the holding force direction in which the holding force acts; and (a2) a step of determining whether the holding force is sufficient using the force measurement value.

[0080] According to this method, it is possible to determine whether the holding force is sufficient using a force sensor.

[0081] (3) In the above method, it may be that the tool unit includes: a holding force acting member, on which the holding force of the piezoelectric actuator acts; and a position sensor that measures the position of the holding force acting member. It may also be that the step (a) includes: (a1) a step of obtaining a position measurement value, which is a measurement value of the position sensor, while applying an external force to the holding force acting member in a direction opposite to the holding force direction in which the holding force acts; and (a2) a step of determining whether the holding force is sufficient using the position measurement value.

[0082] According to this method, it is possible to determine whether the holding force is sufficient using a position sensor that measures the position of the holding force acting member.

[0083] (4) In the above method, it may also be that the tool part includes a holding force acting member, and the holding force of the piezoelectric actuator acts on the holding force acting member. It may also be that the process (a) includes: (a1) a process of obtaining an acceleration measurement value, which is the measurement value of the acceleration by an acceleration sensor, while moving the robotic arm so as to apply an acceleration to the holding force acting member in a direction opposite to the holding force direction in which the holding force acts; and (a2) a process of determining whether the holding force is sufficient using the acceleration measurement value.

[0084] According to this method, it is possible to determine whether the holding force is sufficient using an acceleration sensor.

[0085] (5) In the above method, it may also be that the holding force recovery operation is performed in such a way that the moving stroke of the holding force acting member on which the holding force of the piezoelectric actuator acts is greater than the moving stroke of the holding force acting member during the robot operation.

[0086] According to this method, it is possible to recover the holding force of the piezoelectric actuator.

[0087] (6) In the above method, it may also be that the process (c) includes: a process of performing the operation of the end effector of the robot while maintaining the piezoelectric actuator in a non-powered state.

[0088] According to this method, it is possible to maintain the position of the end effector using the holding force of the piezoelectric actuator during the execution of the operation of the end effector.

[0089] (7) In the above method, it may also be that the tool part includes an inkjet head, and the robot operation is a process of performing printing on a printing area including a curved surface part on the surface of the workpiece using the inkjet head.

[0090] According to this method, it is possible to accurately perform direct forming printing.

[0091] (8) According to the second aspect of the present disclosure, a robot system is provided. The robot system includes: a robot including a robotic arm; a tool part including a piezoelectric actuator and mounted at the front end of the robotic arm; and a control device. The control device is configured to perform the following processes: (a) a process of determining whether the holding force when the piezoelectric actuator is non-powered is sufficient; (b) a process of performing a holding force recovery operation of the piezoelectric actuator when it is determined that the holding force is insufficient; and (c) a process of performing a robot operation on a workpiece when it is determined that the holding force is sufficient.

[0092] The present disclosure can also be implemented in various ways other than those described above. For example, it can be implemented by a robot system including a robot and a robot control device, a computer program for implementing the functions of the robot control device, a non-transitory storage medium recording the computer program, and the like.

Claims

1. A method for controlling a robot, characterized in that, It includes the following processes: (a) A process of determining whether the holding force when the piezoelectric actuator included in the tool part installed at the front end of the robotic arm is non-energized is sufficient; (b) A process of performing a holding force recovery action of the piezoelectric actuator when it is determined that the holding force is insufficient; and (c) A process of performing a robotic operation on the workpiece when it is determined that the holding force is sufficient.

2. The method for controlling a robot according to claim 1, wherein the tool part includes a holding force acting member, and the holding force of the piezoelectric actuator acts on the holding force acting member, the process (a) includes: (a1) A process of applying an external force to the holding force acting member in a direction opposite to the holding force direction in which the holding force acts, and obtaining a force measurement value that is the measurement value of the external force by a force sensor; and (a2) A process of determining whether the holding force is sufficient using the force measurement value.

3. The method for controlling a robot according to claim 1, wherein the tool part includes: a holding force acting member, on which the holding force of the piezoelectric actuator acts; and a position sensor that measures the position of the holding force acting member, the process (a) includes: (a1) A process of applying an external force to the holding force acting member in a direction opposite to the holding force direction in which the holding force acts, and obtaining a position measurement value that is the measurement value of the position sensor; and (a2) A process of determining whether the holding force is sufficient using the position measurement value.

4. The method for controlling a robot according to claim 1, wherein the tool part includes a holding force acting member, and the holding force of the piezoelectric actuator acts on the holding force acting member, the process (a) includes: (a1) A process of moving the robotic arm so as to apply an acceleration to the holding force acting member in a direction opposite to the holding force direction in which the holding force acts, and obtaining an acceleration measurement value that is the measurement value of the acceleration by an acceleration sensor; and (a2) A process of determining whether the holding force is sufficient using the acceleration measurement value.

5. The method for controlling a robot according to claim 1, wherein the holding force recovery action is performed in such a way that the moving stroke of the holding force acting member on which the holding force of the piezoelectric actuator acts is greater than the moving stroke of the holding force acting member in the robotic operation.

6. The method for controlling a robot according to claim 1, wherein the process (c) includes: a process of performing the operation of the end effector of the robot while maintaining the piezoelectric actuator in a non-energized state.

7. The method for controlling a robot according to claim 1, wherein the tool part includes an inkjet head, and the robotic operation is a process of performing printing on a printing area including a curved surface part on the surface of the workpiece using the inkjet head.

8. A robot system, characterized in that, It comprises: a robot including a robotic arm; a tool part including a piezoelectric actuator and installed at the front end of the robotic arm; and Control device The control device is configured to perform the following processes: (a) A process of determining whether the holding force when the piezoelectric actuator is non-energized is sufficient; (b) A process of performing a holding force recovery operation of the piezoelectric actuator when it is determined that the holding force is insufficient; And (c) A process of performing a robot operation on the workpiece when it is determined that the holding force is sufficient.

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