JP7624850B2 - Robot arm control device, control method, system, and program - Google Patents

Description

The present invention relates to a robot arm control device, control method, system, and program.

Conventionally, it is known to set parameters related to the object held by a robot arm, and perform inertia compensation and gravity compensation based on the set parameters. Patent Document 1 discloses technology related to a power-assisted assisting arm that has a mechanism that acts on the arm to balance the weight of the work with gravity, and drives the arm according to the magnitude of the force acting on the work. Patent Document 2 discloses technology that switches between impedance control and force control of a power assisting device according to conditions, such as the operating state. Patent Document 3 discloses technology that supports the weight of an object held by a robot arm with a weight compensation device.

Japanese Unexamined Patent Publication No. 11-198077 JP 2005-306546 A JP 2000-198091 A

In conventional technology, when a robot arm holds an object, if the weight of the object is supported by another device rather than the robot arm, there is no need for the robot arm to perform gravity compensation for the object. However, in conventional technology, the gravity compensation function of the robot arm cannot be stopped independently of inertia compensation. Furthermore, if the weight of the object is set to zero, for example, to set parameters related to the object on the premise that gravity compensation will not be performed, gravity compensation will not be performed, but since the weight of the object is not actually zero, inertia compensation may not function properly. In particular, there are concerns about a decrease in positioning stability due to inertia compensation not functioning properly, and a decrease in positioning accuracy due to gravity compensation after inertia compensation adjustment.

One of the objectives of the present invention is to provide a technology that enables inertia compensation of a robot arm to function more appropriately, regardless of whether gravity compensation is required.

The control device for a robot arm according to one embodiment of the present invention is configured to be able to set gravity compensation for an object held by the robot arm independently of setting inertia compensation for the object.

A method for controlling and setting a robot arm according to one embodiment of the present invention includes accepting a setting for gravity compensation for an object held by the robot arm independently of a setting for inertia compensation for the object.

A system according to one embodiment of the present invention includes a multi-joint robot arm that holds an object, a control device for the robot arm, and a support device that supports the weight of the object, and the control device performs inertia compensation for the object held by the robot arm without performing gravity compensation for the object.

A program according to one embodiment of the present invention causes a computer to execute a control setting method that includes accepting gravity compensation settings for an object held by a robot arm independently of inertia compensation settings for the object.

The present invention provides a technology that allows inertia compensation of a robot arm to function more appropriately, regardless of whether gravity compensation is required.

FIG. 1 is a diagram illustrating a configuration of a robot system according to an embodiment. FIG. 1 is a schematic side view of a robot arm according to an embodiment. FIG. 1 is a schematic side view of a robot system according to an embodiment. FIG. 1 is a schematic side view of a robot system according to an embodiment. 1 is a flowchart showing a process in a robot system according to an embodiment.

The present invention will be described below through embodiments of the invention with reference to the drawings. However, the following embodiments do not limit the invention according to the claims, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. The same or equivalent components, parts, and processes shown in each drawing are given the same reference numerals, and duplicate descriptions will be omitted as appropriate.

The configuration of the robot system according to this embodiment will be described with reference to Figures 1 to 3. Figure 1 is a diagram showing functional blocks of the robot system according to this embodiment. Figure 2 is a diagram showing a schematic diagram of an example of a robot arm. Figure 3 is a diagram showing a schematic diagram of an example of a robot system that holds an object.

The robot system 100 includes a robot arm 20, a control device 10 that controls the robot arm 20, a display device 60, an input device 62, and a support device 70.

In the robot system 100 according to this embodiment, the support device 70 is a device that supports the weight of the held object W. The support device 70 includes a self-weight support device 71 and an operation jig 72. The self-weight support device 71 is configured to include a support (assist structure) fixed to a base (not shown). The operation jig 72 is configured to be able to hold the held object W. The operation jig 72 includes, for example, a balance tool (balancer) configured to include an elastic body, a motor, or an air cylinder. The operation jig 72 is connected to the self-weight support device 71. The self-weight support device 71 is configured to support the weight of the held object held by the operation jig 72 via the operation jig 72. The support device 70 is operated by the robot arm 20 via the operation jig 72 to transport the held object. That is, the robot arm 20 operates to transport the held object W by holding (grasping) the held object or the operation jig 72 of the support device 70. In the following description, even when the robot arm 20 does not directly hold the object, but indirectly holds the object by holding the support device 70, it may be said that the robot arm 20 holds the object.

For example, as shown in FIG. 3, the operation jig 72 is supported near one end (first end) of the operation jig 72 in the longitudinal direction so as to be rotatable around the longitudinal direction (vertical direction) of the self-weight support device 71 as an axis. An operation unit 73 is provided on the upper surface near the other end (second end) of the operation jig 72. The held object W is held on the lower surface near the second end of the operation jig 72. The held object W is held by any method. For example, the held object W may be held by a suction pad provided on the lower surface near the second end of the operation jig 72, or may be held by electromagnetic force. The robot arm 20 grasps the operation unit 73 and operates to rotate the operation jig 72 in the d1 direction, for example, around the longitudinal direction of the self-weight support device 71 as an axis, thereby being able to transport the held object W held by the operation jig 72. That is, the operation jig 72 (including the balance tool) operates in synchronization with the operation of the robot arm 20, thereby being able to transport the held object W.

The robot arm 20 can also transport the object W held by the operating jig 72 by directly gripping the object W instead of using the operating unit 73 and rotating the operating jig 72 in the direction d1 around the self-weight support device 71 as an axis.

With reference to FIG. 4, support device 70a, which is a modified example of support device 70, will be described. Support device 70a is a crane-type support device. Support device 70a includes a support pillar 711a, an arm 712a, and an operating tool 72a. The support pillar 711a and the arm 712a form a self-weight support device. The operating tool 72a includes a balance tool (balancer) that includes one or more of, for example, an elastic body, a motor, a hanging mechanism, or an air cylinder.

The lower end of the support 711a in the longitudinal direction is fixed to a base (not shown). One end of the arm 712a is supported near the upper end of the support 711a with its longitudinal direction extending horizontally. One end of the operation jig 72a is provided with an attachment mechanism for attaching the operation jig 72a to a rail (not shown) provided on the underside of the arm 712a. The attachment mechanism is composed of any member, and may include, for example, a hook. The operation jig 72a is connected to the arm 712a via the attachment mechanism. The operation jig 72a is removable from the arm 712a (i.e., from the support device 70). The other end of the operation jig 72a is provided with a holding mechanism configured to hold the object W. The holding mechanism is composed of any member, and may include, for example, a hook.

The robot arm 20 operates to grasp the operating jig 72a and move it in the direction d2. In synchronization with the operation of the robot arm 20, the attachment mechanism of the operating jig 72a moves along the rail of the arm 712a in the direction d2, whereby the entire operating jig 72a moves and the held object W is transported in the direction d2.

Returning to the explanation of Figs. 1 to 3, the robot arm 20 is, for example, a vertical articulated robot, and includes a base (not shown), multiple links 20L, multiple joints 20J, an end effector 20E, one or more drive units 30, one or more series elastic actuators 40, and a pressure detection unit 50. The robot arm 20 holds and operates a support device 70 (operation jig 72) via the end effector 20E. The robot arm 20 is not limited to a vertical articulated robot, and may be, for example, a horizontal articulated robot device or a parallel link robot device.

The link 20L is made of a rigid member and includes, for example, a link 20L corresponding to a torso rotatably attached to the base, a link 20L corresponding to a lower arm rotatably attached to the torso, a link 20L corresponding to an upper arm rotatably attached to the lower arm, and a link 20L (not shown) corresponding to a wrist rotatably attached to the upper arm.

The end effector 20E (an example of a "holding mechanism") has a function of holding an object (e.g., a held object or a support device 70). The end effector 20E is attached to the tip of a link 20L that corresponds to a wrist, and is configured to be able to hold an object by clamping it between movable plates 20E1 and 20E2 that open and close by an actuator. However, the end effector 20E is not limited to this, and may be, for example, one that includes multiple suction pads for holding the surface of the object and an actuator that generates negative pressure on the suction pads based on a control signal sent from the control device 10, or one that holds the object by electromagnetic force. The robot arm 20 shown as an example in this embodiment can perform a tracing operation by a drive mechanism that is distinct from the holding mechanism.

The robot arm 20 according to this embodiment includes a series elastic actuator 40 provided in at least one joint 20J that connects the links 20L together, and in the joint 20J that connects the link 20L and the held object W. For example, the series elastic actuator 40 is mounted on all of the joints 20J of the robot arm 20.

The series elastic actuator 40 (an example of a "flexible drive mechanism") is composed of, for example, a drive unit 42 and an elastic body 44 connected to the drive unit 42. The drive unit 42 is composed of, for example, a servo motor. The elastic body 44 is composed of, for example, a mechanical spring (e.g., a leaf spring). Leaf springs have high torsional rigidity and are therefore suitable for the tracing operation in this embodiment. The power output from the drive unit 42 in the series elastic actuator 40 is transmitted to the output side link 20L via the elastic body 44, causing it to rotate. Furthermore, the series elastic actuator 40 according to this embodiment is equipped with a sensor (not shown) for acquiring the amount of displacement of the mechanical spring.

The pressure detection unit 50 detects the contact pressure when the robot arm 20 brings the target object into contact with the surface of some other object. By controlling the contact pressure detected by the pressure detection unit 50 to be substantially constant, a tracing operation can be performed to make the target object trace the surface of some other object.

With the above-described configuration of the robot arm 20, an equation of motion is established with parameters including the inertia, mass, and length of the part driven by the series elastic actuator 40, which corresponds to a flexible drive mechanism, external force, and the spring constant of the mechanical spring, which is the elastic body 44. Therefore, the control device 10 is configured to perform mechanical compliance control that controls impedance based on the spring constant and displacement of the mechanical spring.

The series elastic actuator 40 may be connected to the drive shaft of a servo motor, which is the drive unit 42, and may include a gear that transmits power to a mechanical spring. Furthermore, the series elastic actuator 40 may include a damper mechanism that absorbs impact based on viscosity, and a clutch mechanism for switching the transmission of power. When a viscous body such as a damper mechanism having viscosity is added, a viscosity constant is added as a parameter to the equation of motion. For example, an equation of motion is established in which the viscosity constant multiplied by the change in the link angle over time is considered as the torque.

When there are links 20L other than the link 20L driven by the series elastic actuator 40, such links 20L are driven by a drive unit 30 consisting of, for example, a servo motor. The drive unit 30 rotates the output link 20L around a drive shaft. The drive unit 30 may be mounted on the link 20L. With the above configuration, it is possible to rotate multiple links 20L, and therefore it is possible to change the position and posture of the joint 20J corresponding to the tip of the link 20L.

In this embodiment, the control device 10 is configured to be able to set gravity compensation for the held object W independently of the setting of inertia compensation for the held object W of the robot arm 20. As a result, according to this embodiment, the inertia compensation of the robot arm 20 can function more appropriately regardless of whether gravity compensation is required.

In general, in a robot arm having a flexible drive mechanism, problems may arise such as: (1) if inertia compensation does not function properly, positioning stability (vibration suppression function) decreases (flexible joints are prone to shaking); and (2) if gravity compensation does not function optimally in response to inertia compensation, the positioning position may not be optimal (compensation for sinking of the robot arm due to flexibility is not optimal). According to this embodiment, even if the robot arm 20 has a flexible drive mechanism, the inertia compensation of the robot arm 20 can be made to function more appropriately, regardless of the need for gravity compensation as described above.

As shown in FIG. 1, the control device 10 includes a compensation setting input unit 11, a control command acquisition unit 12, a compensation execution unit 13, a tracing operation execution unit 14, an error detection unit 16, and a judgment unit 18.

The compensation setting input unit 11 accepts input of setting information for inertia compensation for the held object W by the robot arm 20 and setting information for gravity compensation for the held object W. The compensation setting input unit 11 accepts input of setting information for inertia compensation and gravity compensation for the held object W, for example, in response to a user operation. The compensation setting input unit 11 can also accept input of setting information for inertia compensation and input of setting information for gravity compensation independently in response to a user operation. The setting information for inertia compensation and gravity compensation accepted by the compensation setting input unit 11 is converted into a control command and output to the control command acquisition unit 12.

The inertia compensation setting information and gravity compensation setting information include any information for executing inertia compensation and gravity compensation. For example, the inertia compensation setting information may include setting information on whether to execute inertia compensation. The gravity compensation setting information may include setting information on whether to execute gravity compensation. Furthermore, the gravity compensation or inertia compensation setting information may include parameter settings related to the held object W for gravity compensation or inertia compensation. The parameter settings related to the held object W for gravity compensation or inertia compensation may include, for example, parameter settings of the weight and center of gravity position information (or tool center point) of the held object W.

In this embodiment, gravity compensation is control that applies a force to the robot arm 20 to offset (cancel) the gravity acting due to the weight of an object held by the robot arm 20. Inertia compensation is control that applies a force to the robot arm 20 to offset the inertial force acting due to the weight of an object held by the robot arm 20. In this embodiment, gravity compensation and inertia compensation performed based on the setting information input via the compensation setting input unit 11 do not include control that offsets the gravity and inertial force due to the robot arm 20's own weight, unless otherwise specified.

The control command acquisition unit 12 acquires control commands for controlling the servo motors corresponding to the driving units 30 of the robot arm 20 and the servo motors of the serial elastic actuator 40. The control commands are generated based on various information including, for example, the start position and posture at that time of the reference position of the robot arm 20 (for example, the center point of the joint 20J corresponding to the hand position. Hereinafter, also referred to as the "reference position"), the target position and posture at that time, the allowable range in which the reference position of the robot arm 20 can deviate from the target position based on the target position, and the movement path connecting the start position and one or more target positions. As will be described later, in the operation method of the robot arm according to this embodiment, it is possible to acquire a path that moves the held object W held by the robot arm 20 along the surface of the object while the held object W is in contact with the object. The control command acquisition unit 12 acquires control commands for controlling each servo motor to move the reference position along the path by arithmetic processing or the like. For example, the control command acquisition unit 12 uses inverse kinematics to calculate the rotation angle of each servo motor for positioning the reference position on the path, and generates a control command based on this.

The compensation execution unit 13 controls to execute inertia compensation and gravity compensation based on the control command related to inertia compensation and gravity compensation acquired by the control command acquisition unit 12. That is, the compensation execution unit 13 controls to execute inertia compensation and gravity compensation based on the setting information of inertia compensation for the held object and the setting information of gravity compensation for the held object received via the compensation setting input unit 11. For example, it is assumed that the setting information of inertia compensation indicates that inertia compensation is enabled, and the setting information of gravity compensation indicates that gravity compensation is disabled. In this case, the compensation execution unit 13 controls to execute inertia compensation and disable gravity compensation (do not execute gravity compensation) based on the setting information of inertia compensation for the held object and the setting information of gravity compensation for the held object received by the compensation setting input unit 11. Gravity compensation and inertia compensation are executed based on the driving of the drive unit 30 and the series elastic actuator 40.

In this embodiment, the weight of the held object W is supported by a support device 70, which is a device different from the robot arm 20. In this case, the robot arm 20 does not need to perform gravity compensation for the held object W. Therefore, in this embodiment, it is effective that the compensation execution unit 13 can be controlled to execute inertia compensation and not execute gravity compensation based on the setting information of inertia compensation for the held object received by the compensation setting input unit 11 and the setting information of gravity compensation for the held object.

The tracing operation execution unit 14 elastically deforms the series elastic actuator 40 of the robot arm 20, thereby causing the robot arm 20 to perform a tracing operation in which the held object contacts the target object and traces it. The tracing operation refers to moving the held object relative to the target object while keeping the held object in contact with the target object. Here, the relative movement is not limited to translational movement, but also includes rotational movement of the held object relative to the target object. The tracing operation execution unit 14 is configured to elastically deform the elastic body 44 of the series elastic actuator 40 so that the contact pressure detected by the pressure detection unit 50 is substantially constant or within a predetermined range. This makes it possible to perform assembly work while suppressing damage such as galling to the target object or the assembly part.

The error detection unit 16 detects error information based on the measured value of the contact pressure detected by the pressure detection unit 50 during the operation of the robot arm 20. For example, if the measured value of the contact pressure during the tracing operation by the pressure detection unit 50 exceeds a threshold value, the error detection unit 16 determines that there is some kind of defect in the held object or the target object and detects error information.

The judgment unit 18 judges the operation of the robot arm 20 after the error based on the error content of the error information detected by the error detection unit 16. Specifically, if the first error information occurs for the first time during the tracing operation, the judgment unit 18 replaces the object held by the robot arm 20 and then executes the tracing operation again. On the other hand, if the second error information occurs during the tracing operation again after the object has already been replaced, the operation of the robot arm 20 is stopped. If the first error information is the first error information, it is highly likely that the object being traced is an abnormality in itself, such as a foreign object adhering to the object being traced, so that the error problem may be solved by having the robot arm 20 perform the tracing operation again. On the other hand, if the second error information is the second error information, it is highly likely that the error problem is an abnormality in the manufacturing lot unit or the assembly part itself of the object being traced, so that the error problem may not be solved even if the object is replaced. Therefore, in such a case, the operation of the robot arm 20 is stopped. Note that the second error information is not limited to the second error, and may be the third error or later. Information corresponding to the type of error determined by the determination unit 18 of the control device 10 (particularly the second error information) may be displayed on the display device 60 to notify the user.

Regarding the hardware configuration, the control device 10 can be configured from a computer having a processor such as a central processing unit (CPU) or a graphical processing unit (GPU), a volatile memory element (storage unit) such as a static random access memory (SRAM) or a dynamic random access memory (DRAM), a non-volatile memory element (storage unit) such as a NOR flash memory, a NAND flash memory, or a hard disk drive (HDD), and a communication means such as a bus that connects these. The non-volatile memory element stores, for example, a computer program for executing each process shown in this embodiment. The volatile memory element temporarily stores at least a part of these computer programs and the results of the calculation process. However, at least a part of these calculation elements, non-volatile memory elements, etc. may be installed in a remote location connected to a communication network such as the Internet. For example, the calculation element may be configured to acquire the computer program or necessary data via the communication network.

The control device 10, the robot arm 20, the display device 60, and the input device 62 are each configured to be able to send and receive information via wireless or wired communication means. A teaching device (not shown) for teaching the robot system 100 how to operate may be connected to the control device 10. The teaching device may be a teaching device that follows online teaching, in which the robot arm 20 is actually moved on-site to teach the position and orientation of the reference part at that time as a starting position, or a teaching device that follows offline teaching, such as a text type, simulator type, emulator type, or automatic teaching type, in which the position and orientation of the reference part is taught as a starting position by a computer program.

The display device 60 and the input device 62 may be a computer equipped with a display section and an input section, or may be configured as an integrated device such as a touch panel.

The display device 60 displays a screen for making various settings for the control device 10 in response to data received from the control device 10. The input device 62 accepts input of various user operations and outputs data corresponding to the input to the control device 10. For example, the display device 60 can display a screen for separately (independently) setting inertia compensation for the held object W by the robot arm 20 and setting gravity compensation. The input device 62 can accept input of setting information for inertia compensation for the held object W by the robot arm 20 and setting information for gravity compensation for the held object W in response to user operations, and output the information to the control device 10.

With reference to FIG. 5, a processing flow including a control setting method will be described as an example of a processing flow in the control device 10 in this embodiment. Each processing step described below is realized, for example, by the processor of the control device 10 reading and executing a computer program stored in the storage unit.

In step S501, the control device 10 accepts settings for inertia compensation and gravity compensation for the held object W of the robot arm 20. At this time, the control device 10 can accept settings for gravity compensation for the held object W independently of settings for inertia compensation for the held object W.

In step S502, the control device 10 controls the operation of the robot arm 20 to start transporting the held object W. The operation of the robot arm 20 may be controlled according to teaching data previously stored or set in the control device 10, or may be controlled by the control device 10 according to a user operation.

In step S503, the control device 10 performs inertia compensation and gravity compensation based on the inertia compensation and gravity compensation settings received in step S501.

In step S504, the control device 10 determines whether the operation of the robot arm 20 is complete. If the operation is not complete (No in S504), the process proceeds to step S503. If the operation is complete (Yes in S504), the process shown in FIG. 5 ends.

As described above, according to this embodiment, the control device 10 is configured to be able to set gravity compensation for the held object W independently of the setting of inertia compensation for the held object W of the robot arm 20. As a result, the inertia compensation of the robot arm 20 can function more appropriately regardless of whether gravity compensation is required.

The present invention is not limited to the above-described embodiment, but can be modified and applied in various ways. Any of the aspects described in the above-described embodiment and modified examples can be applied in combination with other aspects to the extent that it is not inconsistent with the understanding of a person skilled in the art.

In addition to the series elastic actuator, various other driving mechanisms can be used as driving mechanisms with flexibility. Here, "having flexibility" means having elasticity, viscosity, or both elasticity and viscosity. Elasticity refers to the property of being deformed when stress is applied and returning to the original shape when the stress is removed, and is sometimes expressed as the term flexibility, which indicates the ease of elastic deformation. Viscosity refers to the property of generating stress that makes the flow speed of a fluid uniform. In order to impart viscosity and elasticity, magnetic fluids, mechanical springs (leaf springs, torsion coil springs), air springs, magnetic springs, vane motors, variable dampers using electro-viscous fluids whose viscosity can be adjusted according to the applied voltage, etc. may be used.

The implementation modes described through the above embodiments of the invention can be combined or modified or improved as appropriate depending on the application, and the present invention is not limited to the above-mentioned embodiments. It is clear from the claims that such combinations or modified or improved forms are also included in the technical scope of the present invention.

10...Control device, 20...Robot arm, 30...Drive unit, 40...Series elastic actuator, 70...Support device, W...Holding object

Claims (14)

A control device for a robot arm, the control device being configured to be able to set gravity compensation for a held object independently of setting of inertia compensation for the held object of the robot arm,
A control device configured to enable the weight of the held object in the inertia compensation setting to be set to a value different from the weight of the held object in the gravity compensation setting . The control device according to claim 1, further comprising an input unit that accepts the setting of the gravity compensation in response to a user operation, independently of the setting of the inertia compensation. The control device according to claim 2, further comprising a control unit that performs the inertia compensation and controls to disable the gravity compensation based on the inertia compensation setting and the gravity compensation setting received via the input unit. The control device according to claim 3, wherein the inertia compensation setting includes parameter settings related to the retained object for the inertia compensation. The control device according to any one of claims 1 to 4, wherein the weight of the held object is supported by a support device other than the robot arm. The control device according to claim 5, wherein the support device includes a balancing tool. The control device according to claim 6, wherein the balancing tool includes an elastic body, a motor, or an air cylinder. The control device according to any one of claims 1 to 7, wherein the robot arm is provided with a flexible drive mechanism. The control device according to claim 8, wherein the robot arm is provided with a series elastic actuator as the drive mechanism. A multi-joint robot arm that holds an object;
A control device for the robot arm;
A support device for supporting the weight of the held object;
Equipped with
The control device is configured to be able to set gravity compensation for the held object independently of setting of inertia compensation for the held object,
The system is configured such that the weight of the retained object in the inertia compensation setting can be set to a value different from the weight of the retained object in the gravity compensation setting . the support apparatus includes a balancing tool;
The system of claim 10 , wherein the balancing tool moves in synchronization with the movement of the robotic arm. The system of claim 11, wherein the balance tool is removable from the support device. A control setting method for a robot arm, comprising: receiving a setting of gravity compensation for a held object independently of a setting of inertia compensation for the held object of the robot arm;
A control setting method configured so that a weight of the held object in the inertia compensation setting can be set to a value different from a weight of the held object in the gravity compensation setting . On the computer,
receiving a setting of gravity compensation for the held object independently of a setting of inertia compensation for the held object of the robot arm ;
A program for executing a control setting method configured so that the weight of the held object in the inertia compensation setting can be set to a value different from the weight of the held object in the gravity compensation setting .

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