Multi-joint robot arm, multi-joint robot arm drive method, control device, and computer program

Abstract

To provide a multi-joint robot arm which can convey even a workpiece having the weight by reducing a load on a robot arm with a simple structure, and provide a driving method of the multi-joint robot arm, a control device and a computer program.SOLUTION: A multi-joint robot arm 20 comprises: a first link L2; a first actuator A2 which is configured to be able to move the end of the first link L2 upward by rotating the first link L2 according to a first rotational axis facing the horizontal direction; a second link L3 which is connected to the first link L2; and a second actuator A3 which is configured to be able to move the end of the second link L3 by rotating the second link L3 according to a second rotational axis. The multi-joint robot arm can be attached with a supporting actuator SA2 which supports the upward movement of the end of the first link L2 by the first actuator A2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multi-joint robot arm, a drive method for a multi-joint robot arm, a control device, and a computer program. [Background technology]

[0002] 2. Description of the Related Art Conventionally, there have been proposed transport systems for transporting workpieces, such as objects that exceed the transportable weight capacity of a robot arm.

[0003] Patent Document 1 describes a transport system for holding a member together with a multi-joint robot arm by a crane provided separately from the multi-joint robot arm.

[0004] Patent Document 2 describes a transport system for holding an object together with a multi-joint robot arm by a balancer arm provided separately from the multi-joint robot arm.

[0005] Patent Document 3 describes a transport system including a transport robot for moving a heavy workpiece in a horizontal direction and a lifting unit for lifting the workpiece. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 05-340107 [Patent Document 2] JP 2009-262304 A [Patent Document 3] JP 2014-050910 A Summary of the Invention [Problem to be solved by the invention]

[0007] The transport systems described in Patent Documents 1 to 3 reduce the load on the robot arm by using a lifting device other than a robot arm, such as a crane or a balancer arm, to lift and lower the workpiece. However, in these transport systems, the workpiece swings up and down when it is lifted and lowered, which places a large load on the robot arm and may even cause the robot arm to break down.

[0008] In addition, it is not easy to synchronize a lifting device such as a crane with a robot arm due to differences in path lengths, etc.

[0009] Therefore, an object of the present invention is to provide a multi-joint robot arm, a driving method for a multi-joint robot arm, a control device, and a computer program that have a simple configuration and can reduce the load on the robot arm, even when transporting a heavy workpiece. [Means for solving the problem]

[0010] The present application discloses a multi-joint robot arm, which includes a first link, a first actuator configured to move an end of the first link upward by rotating the first link about a first rotation axis oriented in a horizontal direction, a second link connected to the first link, and a second actuator configured to move the end of the second link by rotating the second link about a second rotation axis, and is configured to be able to attach an auxiliary actuator that assists the first actuator in moving the end of the first link upward.

[0011] Here, the term "horizontal direction" includes the vertical direction, i.e., a direction that is at an angle of 90 degrees to the direction in which gravity acts and a direction that is substantially at an angle of 90 degrees, and further includes a direction that is at an angle of 60 degrees or more and 120 degrees or less to the vertical direction.

[0012] Furthermore, "a second link connected to a first link" includes a configuration in which the second link is connected to the first link via a movable member such as a joint.

[0013] The articulated robot arm may be installed on a surface having a normal line perpendicular to the surface, such as a floor, or on a surface having a normal line parallel to the horizontal surface, such as a wall.

[0014] When the articulated robot arm is placed on a floor, the articulated robot arm may include a base that does not move relative to the floor, a link connected to the base, an actuator that rotates the link about a rotation axis oriented in a vertical direction, a first link connected to the link, a first actuator configured to move an end of the first link upward by rotating the first link about a first rotation axis oriented in a horizontal direction, a second link connected to the first link, and a second actuator configured to move the end of the second link by rotating the second link about a second rotation axis.

[0015] With this configuration, by arranging the tip of the link that rotates about the rotation axis oriented in the vertical direction so that it faces horizontally, it is possible to make the rotation axis of the first link connected to this link always face horizontally. Therefore, by configuring it so that an auxiliary actuator that assists the first actuator in moving the end of the first link upwards can be attached, it can be preferably used to compensate for the gravity of the auxiliary actuator.

[0016] In addition, since many links are connected to the tip end side, the load on the first link, which is subjected to a large rotational moment, can be suitably reduced.

[0017] On the other hand, when the articulated robot arm is installed on a wall, the articulated robot arm may include a base that does not move relative to the wall, a first link connected to the base, a first actuator configured to move an end of the first link upward by rotating the first link about a first rotation axis oriented horizontally, a second link connected to the first link, and a second actuator configured to move the end of the second link by rotating the second link about a second rotation axis.

[0018] With this configuration, by providing the tip of the base so that it faces horizontally, it is possible to keep the rotation axis of the first link connected to this base facing horizontally at all times. Therefore, by configuring it so that an auxiliary actuator that assists the upward movement of the end of the first link by the first actuator can be attached, it is possible to suitably use the auxiliary actuator for gravity compensation.

[0019] In addition, since many links are connected to the tip end side, the load on the first link, which is subjected to a large rotational moment, can be suitably reduced.

[0020] In addition, among the actuator, the first actuator, and the second actuator, only the first actuator may be configured to be able to have an auxiliary actuator attached thereto, and the actuator and the second actuator may be configured so that no actuators that assist them are attached thereto.

[0021] According to this configuration, the auxiliary actuator can be suitably used for gravity compensation.

[0022] In addition, the device may further include a third link and a third actuator configured to move an end of the third link upward by rotating the third link about a third rotation axis oriented horizontally, and the third link may be provided closer to the tip than the first link.

[0023] The auxiliary actuator may be an elastic body. The elastic body includes a spring. The elastic body includes a compression spring that exerts an elastic force that urges the end of the first link upward. The spring may be an air spring, a coil spring, or a leaf spring.

[0024] Furthermore, the elastic body may be arranged so that when the angle between the extension direction of the end of the first link and the vertical direction is small (including when the angle is the same), the elastic force due to the elastic body is small (including when the elastic force is zero), and when the angle between the extension direction of the end of the first link and the vertical direction is large, the elastic force due to the elastic body is large.

[0025] The auxiliary actuator may be a viscous body, and the viscous body may be compressed air in an air cylinder for applying a viscous force that urges the end of the first link upward.

[0026] The auxiliary actuator may be an electric motor. The electric motor includes a motor. The motor includes a motor that applies a rotational force that moves the end of the first link upward.

[0027] When the first actuator and the auxiliary actuator both include a motor, the motor of the first actuator and the motor of the auxiliary actuator may be provided to have a coaxial rotation shaft.

[0028] The first actuator may comprise a flexible drive mechanism.

[0029] The second actuator may comprise a flexible drive mechanism.

[0030] The third actuator may comprise a flexible drive mechanism.

[0031] The robot may further include a control unit for controlling the first actuator and the second actuator, and the control unit may be configured to control the first actuator and the second actuator based on a distance between a path of a reference part of the articulated robot arm and an actual position of the reference part.

[0032] The control unit may be configured to be able to execute a first control mode in which the first actuator, the second actuator, and the auxiliary actuator are controlled, and a second control mode in which the first actuator and the second actuator are controlled, among the first actuator, the second actuator, and the auxiliary actuator.

[0033] This application discloses a method for driving a multi-joint robot arm, which includes the steps of: rotating a first link about a first rotation axis oriented horizontally using a first actuator to move an end of the first link upward; rotating a second link connected to the first link about a second rotation axis using a second actuator to move an end of the second link; and assisting the upward movement of the end of the first link by the first actuator using an auxiliary actuator.

[0034] Note that each step may be performed simultaneously. For example, a first actuator may be used to rotate a first link about a first rotation axis oriented in a horizontal direction to move an end of the first link upward, while a second link may be rotated about a second rotation axis to move an end of the second link, and an auxiliary actuator may be used to assist the upward movement of the end of the first link by the first actuator.

[0035] The present application discloses a control device. The control device controls a multi-joint robot arm including a first link, a first actuator configured to move an end of the first link upward by rotating the first link about a first rotation axis oriented in a horizontal direction, a second link connected to the first link, a second actuator configured to move the end of the second link by rotating the second link connected to the first link about the second rotation axis, and an auxiliary actuator that assists the first actuator in moving the end of the first link upward by rotating the first link about the first rotation axis. The control device is configured to execute the steps of: moving the end of the first link upward by rotating the first link about the first rotation axis using the first actuator; moving the end of the second link by rotating the second link connected to the first link about the second rotation axis using the second actuator; and assisting the first actuator in moving the end of the first link upward by rotating the first link about the first rotation axis using the auxiliary actuator. This application discloses a computer program. The computer program includes a computer, and generates a control command for a control device that controls a multi-joint robot arm including a first link, a first actuator configured to move an end of the first link upward by rotating the first link about a first rotation axis oriented in a horizontal direction, a second link connected to the first link, a second actuator configured to move the end of the second link by rotating the second link connected to the first link about the second rotation axis, and an auxiliary actuator that assists the first actuator in moving the end of the first link upward. The control command includes control commands for executing the steps of: moving the end of the first link upward by rotating the first link about the first rotation axis using the first actuator; moving the end of the second link by rotating the second link connected to the first link about the second rotation axis using the second actuator; and assisting the first actuator in moving the end of the first link upward by rotating the first link about the first rotation axis using the auxiliary actuator. [Brief description of the drawings]

[0036] [Figure 1] FIG. 1 is a functional block diagram of a robot system according to an embodiment. [Diagram 2] FIG. 2 is an external view of a robot arm according to an embodiment. [Diagram 3] FIG. 3 is a schematic diagram conceptually showing a configuration for mounting an auxiliary actuator according to one embodiment. [Figure 4] FIG. 4 is a flowchart showing a method for driving a robot arm according to an embodiment. [Diagram 5] FIG. 5 is a graph showing a speed control method in a driving method for a robot arm according to an embodiment. [Figure 6]FIG. 6 is an external view of a robot arm according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to the embodiments.

[0038] [First embodiment] Fig. 1 shows a functional block diagram of a robot system 100. Fig. 2 shows the appearance of a robot arm 20 according to this embodiment.

[0039] As shown in FIG. 1, a robot system 100 includes a robot arm 20 and a control device 10 that controls the robot arm 20 .

[0040] As shown in FIG. 2, the robot arm 20 is, for example, a vertical articulated robot arm having seven axes, and includes a base B fixed to a substantially horizontal surface FL such as a floor surface, a link L1 connected to the base B, a joint J1 on which an actuator A1 for rotating the link L1 about a rotation axis is mounted, a link L2 (an example of a "first link") connected to the link L1, a joint J2 on which an actuator A2 (an example of a "first actuator") for rotating the link L2 about a rotation axis (an example of a "first rotation axis") oriented in the horizontal direction is mounted, a link L3 (an example of a "second link") connected to the link L2, and an actuator A2 for rotating the link L3 about the rotation axis (an example of a "second rotation axis"). The actuator includes a joint J3 on which is mounted a second actuator 3 (an example of a "second actuator"), a link L4 (an example of a "third link") connected to link L3, a joint J4 on which is mounted an actuator A4 (an example of a "third actuator") for rotating link L4 about the rotation axis, a link L5 connected to link L4, a joint J5 on which is mounted an actuator A5 for rotating link L5 about the rotation axis, a link L6 connected to link L5, a joint J6 on which is mounted an actuator A6 for rotating link L6 about the rotation axis, a link L7 connected to link L6, and a joint J7 on which is mounted an actuator A7 for rotating link L7 about the rotation axis.

[0041] As shown in the figure, the link L7 is provided with a holding mechanism for holding a workpiece (sometimes called a "held object"). The holding mechanism may be a gripper having at least a pair of movable plates for clamping the workpiece as shown in the figure, and an actuator configured to be able to drive each of the movable plates to change the distance between the movable plates. However, the holding mechanism for holding the workpiece may adopt various configurations, and may, for example, be one having a plurality of suction pads for holding the workpiece and an actuator for generating negative pressure in the suction pads based on a control signal transmitted from a control device, or one having a coil for electromagnetically generating a magnetic field for magnetically holding a workpiece made of a magnetic material such as metal. Furthermore, when the workpiece is a long substance, a canning member having a hole or the like for hooking a cylindrical portion or the like at the end and a clamp such as a collet for securely holding the workpiece after insertion into the hole may be provided.

[0042] The base B is a portion that is fixed to a substantially horizontal surface FL. In this embodiment, the base B has a portion that extends in a direction perpendicular to the surface FL, that is, in a vertical direction.

[0043] Link L1 is a member rotatably connected to base B via joint J1. Link L1 is made of a rigid member and includes a base end portion connected to base B and extending in a substantially vertical direction, and a tip end portion that is integral with the base end portion and extends substantially perpendicular to the base end portion. Link L1 rotates relative to base B about a rotation axis oriented in a substantially vertical direction, so the tip end portion always extends in a substantially horizontal direction regardless of the rotation angle.

[0044] The joint J1 is a member for rotating the link L1 relative to the base B along a rotation axis oriented in a substantially vertical direction. The joint J1 includes an actuator A1 (FIG. 1) and a rotating part that is rotated by the actuator A1. The rotating part is connected to the link L1 so as to rotate integrally with the link L1. Therefore, when the actuator A1 rotates the rotating part of the joint J1, the link L1 also rotates integrally. The joint J1 may include, for example, a bearing that rotates relative to the base B as the rotating part.

[0045] The actuator A1 mounted on the joint J1 is a member for applying a rotational force for rotating the link L1 relative to the base B along a rotation axis oriented in a substantially vertical direction. The actuator A1 according to this embodiment is configured with a known drive mechanism equipped with a serial elastic actuator, also called an SEA (Serial Elastic Actuator), and an example of an SEA is described, for example, in Japanese Patent No. 6329149 and European Patent No. 2890528. The actuator A1 is configured with a drive unit A1A and an elastic body A1B connected to the drive unit A1A. The drive unit A1A is configured with, for example, a servo motor, which is an electric motor. The elastic body A1B is configured with, for example, a mechanical spring. In the actuator A1, the power output from the drive unit A1A is transmitted to the link L1 on the output side via the elastic body A1B, causing the link L1 to rotate.

[0046] Furthermore, the actuator A1 is provided with a plurality of sensors including a sensor for acquiring the magnitude of the load, a sensor for acquiring the amount of displacement of the elastic body A1B, and a sensor for acquiring the amount of displacement of the servo motor.

[0047] The magnitude of the load can be obtained, for example, from a current sensor that obtains the amount of current flowing through a servo motor that constitutes the drive unit A1A.

[0048] The amount of displacement of the elastic body A1B can be obtained from optical sensors provided at both ends of the elastic body A1B to obtain the amount of displacement (rotation angle) at both ends of the elastic body A1, a magnetic sensor that detects the magnetic field generated from a magnet or the like attached to the elastic body A1B, or a strain sensor or the like provided on the elastic body A1B. It is also possible to obtain the torque generated based on the amount of displacement of the elastic body A1B and the elastic constant of the elastic body A1B.

[0049] As in the above, the amount of displacement of the servo motor can be obtained from an optical sensor such as an encoder, a magnetic sensor such as a Hall element, or a strain sensor.

[0050] Link L2 is a member rotatably connected to link L1 via joint J2. Link L2 is made of a rigid member and includes a base end portion connected to link L1 and extending in a substantially horizontal direction, and a tip end portion that is integral with the base end portion and extends substantially perpendicular to the base end portion. Link L1 rotates relative to base B about a rotation axis oriented in a substantially vertical direction, so that the base end portion of link L2 always extends in a substantially horizontal direction regardless of the rotation angle.

[0051] The joint J2 is a member for rotating the link L2 relative to the link L1 along a rotation axis oriented in a substantially horizontal direction, which is the extension direction of the tip end portion of the link L1 and the extension direction of the base end portion of the link L2. The joint J2 includes an actuator A2 and a rotating part rotated by the actuator A2. The rotating part is connected to the link L2 so as to rotate integrally with the link L2. Therefore, when the actuator A2 rotates the rotating part of the joint J2, the link L2 also rotates integrally. The joint J2 may include, for example, a bearing that rotates relative to the base B as the rotating part.

[0052] The actuator A2 mounted on the joint J2 is a member for applying a rotational force for rotating the link L2 relative to the link L1 along a rotation axis oriented in a substantially horizontal direction. The actuator A2 according to the embodiment is configured with a known drive mechanism equipped with serial elastic actuators, also called SEA (Serial Elastic Actuators), and includes a drive unit A2A and an elastic body A2B. The actuator A2 has substantially the same configuration as the actuator A1 except for the output and the like, and therefore a detailed description thereof will be omitted.

[0053] Link L3 is a member rotatably connected to link L2 via joint J3. Link L3 is made of a member having rigidity, and includes a base end portion connected to link L2 and extending in the extension direction of the tip end portion of link L2, and a tip end portion that is integral with the base end portion and extends approximately perpendicular to the base end portion. Link L3 rotates relative to link L2 according to a rotation axis whose axis is the extension direction of the tip end portion of link L2, so the extension direction of link L3 varies depending on the extension direction of the tip end portion of link L2.

[0054] The joint J3 is a member for rotating the link L3 relative to the link L2 according to a rotation axis directed in the extension direction of the tip end portion of the link L2 and in the extension direction of the base end portion of the link L3. The joint J3 includes an actuator A3 and a rotating portion rotated by the actuator A3. The rotating portion is connected to the link L3 so as to rotate integrally with the link L3. Therefore, when the actuator A3 rotates the rotating portion of the joint J3, the link L3 also rotates integrally. The joint J3 may include, for example, a bearing that rotates relative to the link L2 as a rotating portion. The actuator A3 according to the embodiment is configured by a known drive mechanism that includes a serial elastic actuator, also called SEA (Serial Elastic Actuators), and includes a drive unit A3A and an elastic body A3B. The actuator A3 has substantially the same configuration as the actuator A1 except for the output and the like, and therefore a detailed description thereof will be omitted.

[0055] Hereinafter, links L4 to L7 and joints J4 to J7 (including the actuators mounted on each joint) have similar configurations, so detailed description will be omitted. For example, actuator A7 (FIG. 1) mounted on joint J7 is composed of a series elastic actuator including a drive unit A7A and an elastic body A7B connected to drive unit A7A.

[0056] Comparing the forces acting on the joints J1 to J7, the joint J2 rotates the link L2 along a rotation axis oriented in a substantially horizontal direction. Since the link L2 has a base end portion connected to the link L1 and extending in a substantially horizontal direction, and a tip end portion integral with the base end portion and extending substantially perpendicular to the base end portion, a rotation moment is generated in the joint J2 that rotates the tip end portion of the link L2 in a downward direction due to gravity acting on the tip end portion of the link L2. Since the links L3 to L7 are connected to the tip side of the link L2, and a holding mechanism for holding a workpiece is further provided, a rotation moment is generated that rotates the tip end portion of the link L2 in a downward direction due to gravity acting on the links L3 to L7, the holding mechanism, and the workpiece. For this reason, a large rotation moment is generated in the joint J2. When rotating link L2, actuator A2 mounted on joint J2 needs to move the tip portion of link L2 upward against the rotational moment generated by gravity acting on links L3 to L7, the holding mechanism, and the workpiece.

[0057] On the other hand, the joint J1 rotates the link L1 about a rotation axis oriented in a substantially vertical direction relative to the base B. For this reason, when the actuator A1 mounted on the joint J1 rotates the link L1, there is almost no need to move the tip side portion of the link L1 upward against the rotation moment generated due to gravity acting on the links L2 to L7, the holding mechanism, and the workpiece.

[0058] The joint J3 rotates the link L3 relative to the link L2 according to a rotation axis oriented in the extension direction of the tip side portion of the link L2 and the base side portion of the link L3. Therefore, the magnitude of the rotation moment that the actuator A3 mounted on the joint J3 must resist when rotating the link L3 varies greatly depending on the rotation angle of the joint J2. When the extension direction of the base side portion of the link L3 is oriented in a substantially horizontal direction, the posture of the link L2 approaches, so the rotation moment that the actuator A3 must resist becomes large. However, since the tip side portion is shorter than the link L2, in normal cases, the rotation moment that the actuator A3 must resist is smaller than the rotation moment that the actuator A2 must resist. As the extension direction of the base side portion of the link L3 approaches a substantially vertical direction, the posture of the link L1 approaches, so the rotation moment that the actuator A3 must resist becomes smaller.

[0059] As described above, among the actuators A1 to A7 mounted on the joints J1 to J7, a large rotational moment in a direction that hinders rotation is always generated in the actuator A2 unless the joint J2 faces vertically or backward, and the rotational moment in a direction that hinders rotation becomes significantly larger when the weight of the work held by the holding mechanism becomes large. When the weight of the work becomes large, it is possible to use a lifting device such as a crane, but this puts a large load on the robot arm due to the up and down movement when the work is lifted, which may cause the robot arm to break down. Therefore, the inventors of the present application have devised a robot arm 20 to which an auxiliary actuator can be attached that assists the actuator A2 in moving the tip side portion of the link L2 upward.

[0060] In this embodiment, among the actuators A1 to A3, a power assist tool (one example of an "auxiliary actuator") for assisting only the actuator A2 can be attached, and the actuators A1 and A3 are configured such that power assist tools for assisting these actuators cannot be easily attached. With this configuration, it becomes possible to suitably use the power assist tool to compensate for gravity. For example, when the robot arm 20 holds a workpiece having a normal weight, a power assist tool is not attached, and when the robot arm 20 holds a workpiece having a weight exceeding the normal weight, a power assist tool for assisting the actuator A2 is attached to the robot arm 20, making it possible to hold a workpiece having a weight of, for example, 150% of the conventional carrying capacity.

[0061] Fig. 3 is a schematic diagram conceptually showing a configuration for attaching a power assist tool to assist the actuator A2. Fig. 3(A) shows the state before the power assist tool is attached to the joint J2, and Fig. 3(B) shows the state after the power assist tool is attached to the joint J2.

[0062] The fixed part J21 of the joint J2 in Fig. 3 is a part fixed to the tip side part of the link L1, and in this embodiment, has a central axis extending in the horizontal direction. The rotating part J22 of the joint J2 in Fig. 3 is a part that rotates about a rotation axis that is oriented in the horizontal direction relative to the link L1 and the fixed part J21. The rotating part J22 is connected to the link L2 so as to rotate integrally with the link L2.

[0063] The power assist tool is provided to engage with the fixed part J21 and the rotating part J22. For example, a hole H1 is provided in the fixed part J21, a hole H2 is provided in the rotating part J22, and the power assist tool SA2 according to this embodiment is provided with a protrusion P1 that engages with the hole H1 and a protrusion P2 that engages with the hole H2, so that the power assist tool SA2 is configured to be able to engage with the joint J2. Here, the protrusion P2 is provided to be able to rotate around the central axis of the cylindrical power assist tool SA2. Therefore, the protrusion P2 is configured to be able to rotate in conjunction with the rotation of the hole H2 by the actuator A2.

[0064] An elastic body is provided inside the power assist tool SA2, one end of which is connected to the projection P1 and the other end of which is connected to the projection P2. The elastic body may be a spring such as an air spring, a coil spring, or a leaf spring.

[0065] The elastic body in this embodiment may be, for example, a leaf spring. The leaf spring may be provided so that when the tip portion of the link L2 extends vertically upward (when the angle between the extension direction of the end of the first link and the vertical direction is small), the elastic force is zero, i.e., the elastic body is at its natural length, and as the tip portion of the link L2 rotates downward (as the angle between the extension direction of the end of the first link and the vertical direction becomes larger), the elastic body stretches to generate a large elastic force for directing the tip portion of the link L2 upward (in other words, a large elastic force that prevents the tip portion of the link L2 from rotating downward).

[0066] The elastic body may be a compression spring. In this case, the compression spring may be provided so that when the tip portion of the link L2 rotates downward, the compression spring is compressed, and the more compressed the spring is, the greater the elastic force that is generated to move the tip portion of the link L2 upward.

[0067] As the tip portion of link L2 approaches the horizontal direction, the load on actuator A2 increases. Therefore, by using an elastic body as power assist tool SA2 as described above and arranging the elastic body so that a greater elastic force is generated as the tip portion of link L2 approaches the horizontal direction, it is possible to suitably reduce the load on joint J2.

[0068] The power assist tool SA2 may be a motor that generates a rotational force for moving the tip end (end) of the link L2 upward. In this case, the protrusion P2 is provided rotatably around the central axis of the cylindrical power assist tool SA2, and the power assist tool SA2 is attached to the actuator A2 so that the rotation axis of the actuator A2 and the rotation axis of the power assist tool SA2 are coaxial. The power assist tool SA2 can be configured to rotate the protrusion P2 in synchronization with the rotation of the actuator A2 based on a control command received from the control device 10. Here, a servo motor having the same configuration as the motor of the actuator A2 may be used as the motor of the power assist tool SA2, and the servo motor of the power assist tool SA2 may also receive the control command received by the servo motor of the actuator A2. With such a configuration, it is possible to rotate the two in synchronization with each other with a simple configuration.

[0069] Furthermore, a power assist tool may be configured to be attachable to the actuator A4. If it is known that the joint J4 will often rotate around a rotation axis oriented substantially horizontally, a power assist tool may also be attached to the joint J4. The configuration of the power assist tool is similar to that of the power assist tool SA2, and therefore a description thereof will be omitted.

[0070] In addition, when the power assist tool is made of an elastic body, multiple types of power assist tools equipped with elastic bodies having different elastic moduli may be prepared so that an appropriate power assist tool can be attached depending on the weight of the workpiece.

[0071] With the above configuration, an equation of motion is established with parameters including the inertia, mass, and length of the part driven by the series elastic actuator corresponding to the flexible driving mechanism provided in each of the actuators A1 to A7, external force, and the elastic modulus of the mechanical spring which is the elastic body provided in the series elastic actuator. Therefore, the control device 10 is configured to perform mechanical compliance control that controls impedance based on the elastic modulus and displacement amount of the mechanical spring.

[0072] The series elastic actuators constituting the actuators A1 to A7 may be connected to the drive shaft of a servomotor, which is the drive unit, and may include a gear for transmitting power to an elastic body such as a mechanical spring. Furthermore, the series elastic actuator may include a damper mechanism for mitigating impact based on viscosity and a clutch mechanism for switching the transmission of power. When a viscous body such as a viscous damper mechanism is applied, or when damping caused by friction between gears is added, an equation of motion is established in which a viscosity constant is added as a parameter.

[0073] For example, in the case of a series elastic actuator in which a gear is connected to the drive shaft of a servomotor and a load (such as a downstream link) is connected to the output shaft of the gear via an elastic body, the torque generated in the output shaft of the gear is proportional to the current flowing through the servomotor and the gear ratio, and an equation of motion is established in which this torque is equal to the sum of the angular acceleration of the output shaft of the gear multiplied by the inertia, the angular acceleration of the output shaft of the gear multiplied by the viscosity of the gear, and the displacement of the elastic body multiplied by the elastic modulus. By deriving the transfer function of the series elastic actuator based on this equation of motion, mechanical compliance control that controls impedance becomes possible.

[0074] With the above-mentioned configuration, it is possible to rotate multiple links of the robot arm 20, so that the position and posture of the work held by the holding mechanism can be freely changed. Note that the information indicating the position in this disclosure may include information indicating the posture if it is considered reasonably necessary. Furthermore, the robot arm 20 may include an input / output means including an imaging device for image recognition of the work, etc., and a display for transmitting and receiving information to and from the user. Furthermore, the robot arm 20 may include a link that is driven by a non-elastic actuator in part. For example, since the link L1 always extends in the vertical direction, the actuator A1 may be configured from a drive mechanism including a non-elastic actuator.

[0075] A controller 10 (FIG. 1) controls a robot arm 20. As described above, the controller 10 controls the robot arm 20 based on mechanical compliance control using a series elastic actuator, rather than conventional position control.

[0076] As shown in the figure, the control device 10 includes a start position acquisition unit 10A that acquires the start position and the posture at that time of the reference position of the robot arm 20 (for example, the center point of link L7 corresponding to the hand position, or the center point of the holding mechanism. Hereinafter, referred to as the "reference position" or "reference portion"), a target position acquisition unit 10B that acquires the target position and the posture at that time, an allowable range acquisition unit 10C, a path acquisition unit 10D that acquires a path connecting the start position and the target position, a control command acquisition unit 10E that acquires control commands to control servo motors corresponding to the driving units of each actuator A1 to A7 according to the path acquired by the path acquisition unit 10D, and a memory unit 10F.

[0077] The start position acquisition unit 10A acquires, for example, a start position input from a teaching device 50 connectable to the control device 10 and the posture of the robot arm 20 at that time. The teaching device 50 may be a teaching device 50 that follows online teaching in which the robot arm 20 is actually moved on-site to teach a reference position and posture at that time as a start position, or a teaching device 50 that follows offline teaching such as a text type, simulator type, emulator type, or automatic teaching type in which the position and posture of a reference position are taught as a start position by a computer program.

[0078] The target position acquisition unit 10B acquires, for example, a target position and a posture at that time input from the teaching device 50, similar to the start position. The target position acquisition unit 10B can acquire a plurality of target positions and postures at that time.

[0079] The allowable range acquisition unit 10C acquires information indicating an allowable range within which the actual reference position of the robot arm 20 can deviate from the path based on the path of the reference position. For example, when the angle of a given link driven by the series elastic actuator when the reference position of the robot arm 20 reaches a certain target position is α, information indicating the allowable range of the link is acquired as, for example, angle information of α±β. β is information in angle units that can be preset as a range of elastic deformation based on the elastic modulus of the elastic body of the series elastic actuator. In order to have flexibility in multiple directions, the robot arm 20 is equipped with multiple series elastic actuators. In this case, the allowable range acquisition unit 10C can acquire information indicating the allowable range for each of multiple links driven by the series elastic actuator.

[0080] The information indicating the allowable range may be position information indicating a predetermined range that a reference position, which is another part of the robot arm 20, can take as a result of a change in the angle of the link. That is, when the angle of a predetermined link is α+β, the tip of the link is displaced by a distance obtained by multiplying β by the length of the link, and accordingly, a downstream part of the robot arm 20 is also displaced. Therefore, the allowable range acquisition unit 10C may acquire position information indicating a predetermined range that the reference position can take by using another part of the robot arm 20 as the reference position. The following description will be centered on the case where the center point of the workpiece held by the tip link L7 is used as the reference position of the robot arm 20. It is preferable that the allowable range is configured to allow the reference position to deviate from the path by at least ±5 mm or more.

[0081] The information indicating the allowable range can be determined in advance as a constant based on the elasticity or viscosity of the drive mechanism in a computer program stored in the storage unit 10F. Therefore, the control device 10 may be configured so that the arithmetic element reads out the computer program to obtain the information indicating the allowable range. Alternatively, the control device 10 may obtain the information indicating the allowable range from the teaching device 50.

[0082] The path acquisition unit 10D acquires a path (planned trajectory) connecting the start position and the target position by calculation processing or the like.

[0083] The control command acquisition unit 10E acquires, by calculation processing or the like, control commands for controlling each motor for moving the reference position along a path, and supplies the control commands to the robot arm 20. For example, the control command acquisition unit 10E can calculate, by inverse kinematics calculation, the rotation angle of each motor for positioning the reference position on the path, generate a control command based on the calculated rotation angle, and store the control command in the storage unit 10F.

[0084] The storage unit 10F stores computer programs (including route generation algorithms) for executing the processes shown in each embodiment, as well as necessary data and other information.

[0085] Regarding the hardware configuration of the control device 10 described above, the control device 10 can be configured from a computer including, for example, a processor such as a central processing unit (CPU) or a graphical processing unit (GPU), a volatile storage element such as a static random access memory (SRAM) or a dynamic random access memory (DRAM), a non-volatile storage element such as a NOR flash memory, a NAND flash memory, or a hard disk drive (HDD), and a communication means such as a bus connecting these elements. The non-volatile storage element is a storage medium that stores information non-transitory. The volatile storage element temporarily stores at least a part of these computer programs and the results of the arithmetic processing. The storage unit 10F is configured from these storage elements. In addition, the storage unit 10F functions as a start position acquisition unit 10A, a target position acquisition unit 10B, an allowable range acquisition unit 10C, a path acquisition unit 10D, and a control command acquisition unit 10E by the computation element executing the computer program stored in the storage unit 10F. However, at least some of these computing elements, non-volatile storage elements, etc. may be installed in a remote location connected to a communication network such as the Internet. For example, the computing element may be configured to obtain a computer program or necessary data via the communication network.

[0086] The control device 10 and the robot arm 20 are configured to be able to transmit and receive information via wireless or wired communication means.

[0087] A teaching device 50 for teaching an operation to the robot system 100 may be connected to or integrally provided to the control device 10. The teaching device 50 may also be provided to the robot arm 20, and for example, an input / output means including a display may be used as a part of the teaching device 50.

[0088] The teaching device 50 includes, for example, a portable teaching pendant. Like the control device 10, the teaching device 50 includes a calculation element, a volatile memory element, and a non-volatile memory element, and further includes a display means having a display and an input means having a plurality of operation keys and a lever. The input means may be configured as a touch panel type input means that performs input by pressing the display.

[0089] Next, a description will be given of a method for driving the robot arm 20 of the robot system 100. FIG 4 is a flowchart showing the method for driving the robot arm 20.

[0090] First, the operator determines whether or not to attach a power assist tool depending on the weight of the workpiece to be transported, and if the weight of the workpiece to be transported is equal to or greater than a predetermined value, the operator attaches the power assist tool to the robot arm 20. For example, the operator attaches power assist tools to hold the joints J2 and J4 (step S41). Note that if the weight of the workpiece to be transported is less than the predetermined value, the power assist tool is not attached to the robot arm 20.

[0091] Next, the start position acquisition unit 10A, the target position acquisition unit 10B, and the allowable range acquisition unit 10C of the control device 10 acquire information indicating the start position, information indicating a plurality of target positions, and information indicating the allowable range, respectively (step S42). The control device 10 may acquire these pieces of information by reading them out from the storage unit 10F that stores them in advance. Alternatively, the control device 10 may acquire these pieces of information by using the teaching device 50. Furthermore, when the control device 10 obtains a path by calculation based on the information indicating the start position and the information indicating the target position, the control device 10 may read out a path generation algorithm that causes the distance between the object surface and the reference position to fall within a permissible range, and obtain information indicating the permissible range by obtaining a path based on the algorithm.

[0092] Here, the start position may be determined based on a position where a workpiece to be held by the robot arm 20 is initially placed. The target position may be determined based on a position where a workpiece to be transported by the robot arm 20 is finally placed.

[0093] The allowable range may also be determined based on the weight of the workpiece. For example, a allowable range may be determined for each of the joints J1 to J7 based on the weight of the workpiece so that the joints J1 to J7 are prevented from being overloaded while the robot arm 20 is transporting the workpiece.

[0094] Next, the path acquisition unit 10D of the control device 10 acquires a path connecting the start position and a plurality of target positions by calculation based on the path generation algorithm read out from the storage unit 10F (step S43).

[0095] Next, the control command acquisition unit 10E acquires control commands for the actuators A1 to A7 based on the path information (step S44). Note that, if the control commands for implementing a series of operations are stored in advance in the storage unit 10F, the control device 10 may acquire this information by reading out the control commands from the storage unit 10F.

[0096] Next, the robot arm 20 drives each of the links L1 to L7 based on the control command received from the control device 10. First, the robot arm 20 moves to a start position and holds the workpiece. After that, the robot arm 20 repeats the operation of moving the workpiece to the target position (steps S45 to S49). At this time, for example, when lifting the workpiece upward, a step is executed in which the actuator A2 is used to rotate the link L2 about a horizontally oriented rotation axis to move the end of the link L2 upward, while the actuator A2 is used to assist the upward movement of the end of the link L2. On the other hand, when moving the workpiece horizontally, since it is not necessary to use the actuator A2 to rotate the link L2 about a horizontally oriented rotation axis, it is possible to drive another actuator to move the workpiece horizontally without using the power assist tool SA2 to assist the actuator A2 in the upward movement of the end of the link L2. For this reason, the power assist tool SA2 can be suitably used as an auxiliary actuator for compensating for gravity.

[0097] While the workpiece is being moved (step S46), the control device 10 controls the amount of displacement so that it falls within an allowable range. In order to keep the amount of displacement within the allowable range, the control device 10 periodically determines whether or not a displacement exceeding the allowable range has occurred (step S47).

[0098] If the control device 10 determines that a displacement exceeding the allowable range has occurred (NO), the control device 10 generates a control command to decelerate the movement speed of the robot arm 20 and sends it to the drive unit of the robot arm 20 to decelerate it (step S48). FIG. 5 is a graph for explaining the deceleration operation when the allowable range is exceeded during the movement of the workpiece. In this graph, the horizontal axis represents time, and the vertical axis represents the angle of the link driven by the series elastic actuator. In this graph, a specific target link has an angle α1 at time t11 as the start position (or first target position), an angle α2 at time t2 as the first target position (or second target position), and a path P (planned trajectory) is set in which the angle changes with time and the angle increases. The allowable range based on the path of this link is ±β1 centered on the angle of the link. Furthermore, in this graph, the actual angle change is indicated by a solid line A.

[0099] As shown in this graph, when at time t11 the link angle falls outside the allowable range based on path P, as described above, the control device 10 reduces the link rotation speed and the workpiece movement speed to control the link angle to fall within the allowable range. On the other hand, between time t11 and time t2, since the link angle falls within the allowable range, the control device 10 controls the link rotation and workpiece movement to continue without decelerating to move solid line A closer to path P.

[0100] In this way, an actuator consisting of a flexible drive mechanism is controlled based on the distance between the path of the reference position of the robot arm 20 and the actual reference position.If the distance between the path of the reference position and the actual reference position is within an acceptable range, the workpiece continues to move without slowing down.This makes it possible to continue moving the workpiece as long as it is within the acceptable range, even if the workpiece vibrates up and down due to its weight or other reasons.

[0101] Furthermore, since a power assist tool SR2 is attached to assist the joint J2, when the tip portion of the link L2 approaches the horizontal direction and a large load is placed on the joint J2, the load on the joint J2 can be reduced by the power assist tool SR2.

[0102] At this time, since the elastic modulus and other parameters of the joint J2 are changed by attaching the power assist tool SR2, there is a possibility that the actual reference position may deviate from the path, but as described above, if the distance between the path of the reference position and the actual reference position is within the allowable range, the movement of the workpiece is continued. Therefore, it is possible to control the robot arm 20 based on the same computer program whether the power assist tool SR2 is attached or not.

[0103] In particular, by configuring a flexible drive mechanism with one or more actuators, it becomes possible to set a large tolerance range, for example, allowing the distance between the reference position path and the actual reference position to be ±5 mm or more.

[0104] Thereafter, the robot arm 20 repeats steps S46 to S49 to move the workpiece to the next target position.

[0105] When the workpiece reaches the final target position, the driving of the robot arm 20 ends.

[0106] As described above, according to this embodiment, the power assist tool that generates torque in the upward direction is detachably provided, so that it can be removed and not used when a large torque is not required, thereby reducing the cost of the robot arm, while it can be attached and transported when a large torque is required. Compared to the case where an external lifting device such as a crane is used, the power assist tool is attached to a position close to a joint (e.g., joint J2) that is a driving joint for the upward and downward movement that is particularly affected by the weight, thereby improving the tracking ability and suitably reducing the load on the joint due to the weight. In addition, the need to synchronize the robot arm and the lifting device as in the case where an external lifting device is used is reduced. As described above, it is possible to provide a multi-joint robot arm, a driving method for the multi-joint robot arm, a control device, and a computer program that can reduce the load on the robot arm and transport it with a simple configuration.

[0107] [Second embodiment] Hereinafter, a robot system including a robot arm according to the second embodiment will be described. Configurations that a person skilled in the art can understand based on the description of the first embodiment will be appropriately assigned the same or similar reference numerals, and descriptions will be omitted or simplified, with differences being mainly described. 6 is a schematic diagram showing the appearance of a robot arm 200 according to the second embodiment. A control device that controls the robot arm 200 will not be described.

[0108] The robot arm 200 is, for example, a multi-joint robot arm having two or more joints, and includes a base B0 (an example of a "base that does not move relative to the wall") fixed to a substantially horizontal surface WL such as a wall surface, a link L10 (an example of a "first link") connected to the base B via a joint J10, a joint J10 on which an actuator (an example of a "first actuator") for rotating the link L10 about a horizontal rotation axis (an example of a "first rotation axis") is mounted, a link L20 (an example of a "second link") connected to the link L10, and a joint J20 on which an actuator (an example of a "second actuator") for rotating the link L20 about a rotation axis (an example of a "second rotation axis") is mounted. A holding mechanism for holding a workpiece W (sometimes called a "held object") is provided in the link L20.

[0109] Unlike the first embodiment, in the robot arm 200 according to this embodiment, the base B0 is attached to a plane WL perpendicular to the floor surface. However, the present invention can be applied even in such an embodiment. For example, the present invention can be applied by attaching a power assist tool for assisting the joint closest to the base and having a rotation axis facing horizontally.

[0110] In this embodiment, the joint J10, which corresponds to the joint for rotating the link L10, has a rotation axis that always faces horizontally, and the actuator mounted on the joint J10 can move the end of the link L10 upward by rotating the link L10 according to the rotation axis that faces horizontally. Therefore, by attaching a power assist tool (an example of an "auxiliary actuator") that assists the actuator mounted on the joint J10 in moving the end of the link L10 upward, it is possible to assist the movement of the joint J10.

[0111] For example, an air cylinder having one end connected to the base B0 and the other end connected to the link L10 can be connected as a power assist tool, and the air cylinder can be provided so as to generate a force that prevents the end of link L10 from descending (i.e., a force that moves the end of link L10 upward) as the end of link L10 descends (as the extension direction of link L10 becomes greater from the horizontal direction). In order to detachably attach the air cylinder, the base B0 and the link L10 may be provided with an engagement portion for attaching the air cylinder.

[0112] As described above, the robot arm 200 of this embodiment can also provide a multi-joint robot arm, a driving method for a multi-joint robot arm, a control device, and a computer program that have a simple configuration and reduce the load on the robot arm, making it possible to carry the robot arm.

[0113] [Variations] Hereinafter, a robot system according to a modified example of the robot arm 20 according to the first embodiment will be described. Configurations that a person skilled in the art can understand based on the explanation of the first or second embodiment will be appropriately denoted with the same or similar reference numerals, and explanations will be omitted or simplified, and differences will be mainly described. The robot system according to the modification has features different from the control devices according to the other embodiments. The control device 10 according to the modification has at least two control modes. Specifically, the control device 10 has a first control mode in which all actuators (i.e., actuator A1, actuator A2, power assist tool SA2, and actuator A3) among actuator A1, actuator A2, power assist tool SA2, and actuator A3 in the first embodiment are controlled, and a second control mode in which actuators other than the power assist tool 2 (i.e., actuator A1, actuator A2, and actuator A3) are controlled.

[0114] When the power assist tool SA2 is not attached to the robot arm 20, the control device controls each actuator based on the second control mode, and when the power assist tool SA2 is attached to the robot arm 20, the control device controls each actuator based on the first control mode. The control device may include a sensor that detects whether the power assist tool SA2 is attached or not.

[0115] The control command acquisition unit 10E of the control device 10 acquires different control commands according to the control mode when acquiring control commands for controlling each actuator through arithmetic processing or the like.

[0116] That is, in the actuator A2, when establishing an equation of motion with parameters including the inertia, mass, and length of the part driven by the series elastic actuator corresponding to the flexible driving mechanism, external force, and the elastic modulus of the mechanical spring, which is an elastic body of the series elastic actuator, as described in, for example, Japanese Patent No. 6329149, the deflection amount of a spring such as a mechanical spring is proportional to the torque (τSEA) in the series elastic actuator and inversely proportional to the overall stiffness (keq) of the system, and the overall stiffness (keq) of the system depends on the stiffness (or spring constant) (kSEA) of the spring. Furthermore, when a gear is added to the series elastic actuator, the overall stiffness (keq) of the system depends on the stiffness (or spring constant) (kSEA) of the spring and the stiffness (kgear) of the gear train, and these system parameters are known either by inference from the design or by determination through a characteristic evaluation experiment. Therefore, it is possible to obtain the system parameters when the power assist tool SA2 is attached. For example, when a spring is attached as the power assist tool SA2, the overall stiffness (keq) of the system becomes larger compared to when the power assist tool SA2 is not attached.

[0117] Therefore, the control command acquisition unit 10E is configured to acquire, in the first control mode, a control command based on a system parameter in which the overall rigidity of the system when the power assist tool SA2 is attached has a first value, and to acquire, in the second control mode, a control command based on a system parameter in which the overall rigidity of the system when the power assist tool SA2 is not attached has a second value that is smaller than the first value.

[0118] By adopting the above-mentioned configuration, in addition to the configuration described in the above embodiment, it is possible to improve the tracking performance.

[0119] In addition, the present invention can be modified in various ways without departing from the spirit of the present invention. For example, some components in one embodiment can be added to other embodiments within the scope of ordinary creativity of a person skilled in the art. Also, some components in one embodiment can be replaced with corresponding components in other embodiments. [Explanation of symbols]

[0120] 10. Control device 10A.Start position acquisition section 10B.Target position acquisition section 10C. Tolerance range acquisition section 10D. Route acquisition section 10E. Control command acquisition unit 10F. Storage section 20. Robot Arm 50. Teaching device 100. Robot Systems SA. Auxiliary Actuator A1~A7. (Series Elastic) Actuators J1~J7.Joints

Claims

1. A multi-joint robot arm for holding a workpiece, A first link; a first actuator configured to be able to move an end portion of the first link upward by rotating the first link about a first rotation axis oriented in a horizontal direction; A second link connected to the first link; a second actuator configured to rotate the second link about a second rotation axis to move an end of the second link; An auxiliary actuator, which is an electric motor, is configured to be detachable and which assists the upward movement of the end portion of the first link by the first actuator. Articulated robot arm.

2. A third link; a third actuator configured to rotate the third link about a third rotation axis oriented in a horizontal direction, thereby moving an end of the third link upward; The third link is provided closer to the tip side than the first link. The articulated robot arm of claim 1.

3. The first actuator comprises a flexible drive mechanism.

3. The articulated robot arm according to claim 1 or 2.

4. a control unit for controlling the first actuator and the second actuator, the control unit is configured to control the first actuator and the second actuator based on a distance between a planned trajectory of a reference portion of the articulated robot arm and an actual position of the reference portion.

4. A multi-joint robot arm according to any one of claims 1 to 3.

5. The control unit is a first control mode in which the first actuator, the second actuator, and the auxiliary actuator are controlled, and and a second control mode for controlling the first actuator and the second actuator among the first actuator, the second actuator, and the auxiliary actuator.

5. The articulated robot arm of claim 4.

6. A method for driving a multi-joint robot arm for holding a workpiece, comprising the steps of: using a first actuator to rotate a first link about a first rotation axis oriented in a horizontal direction, thereby moving an end of the first link upward; a step of rotating a second link connected to the first link about a second rotation axis using a second actuator, thereby moving an end of the second link; and assisting the upward movement of the end portion of the first link by using an auxiliary actuator that is an electric motor and that is configured to be detachable from the articulated robot arm. A method for driving a multi-joint robot arm.

7. a first link; a first actuator configured to be able to move an end of the first link upward by rotating the first link about a first rotation axis oriented in a horizontal direction; a second link connected to the first link; a second actuator configured to be able to move an end of the second link by rotating the second link connected to the first link about a second rotation axis; A control device for controlling an articulated robot arm for holding a workpiece, the articulated robot arm being configured to be able to attach and detach an auxiliary actuator that is an electric motor and that assists the first actuator in moving an end portion of the first link upward, the control device comprising: using the first actuator to rotate the first link about the first rotation axis, thereby moving an end of the first link upward; using the second actuator to rotate the second link connected to the first link about the second rotation axis, thereby moving an end of the second link; using the auxiliary actuator to assist the upward movement of the end of the first link.

8. A control device having a computer, the control device controlling a multi-joint robot arm for holding a workpiece, the control device comprising: a first link; a first actuator configured to be able to move an end of the first link upward by rotating the first link about a first rotation axis oriented in a horizontal direction; a second link connected to the first link; and a second actuator configured to be able to move the end of the second link by rotating the second link connected to the first link about a second rotation axis, the control device being configured to be able to attach and detach an auxiliary actuator which is an electric motor that assists the first actuator in moving the end of the first link upward. using the first actuator to rotate the first link about the first rotation axis, thereby moving an end of the first link upward; using the second actuator to rotate the second link connected to the first link about the second rotation axis, thereby moving an end of the second link; using the auxiliary actuator to assist the first actuator in moving the end of the first link upward; generating control instructions for executing the Computer program.

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