Drive mechanism, robot arm, and drive method

Abstract

To provide a drive mechanism which can absorb an impact caused by a collision while achieving high rigidity, and to provide a robot arm and a drive method.SOLUTION: A drive mechanism according to the disclosure includes: a drive part configured to be drivable; an engaging part provided at the drive part; a driven part; an engaged part which is provided at the driven part and configured to engage with the engaging part to drive the driven part; and an elastic body which is configured to exert an elastic force set based on a distance between the engaging part and the engaged part on the driven part in a direction such that the distance between the engaging part and the engaged part is reduced.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a drive mechanism, a robot arm, and a drive method. [Background technology]

[0002] Series elastic actuators are known as robot drive mechanisms that achieve mechanical compliance. By incorporating a series elastic actuator into a robot arm, even if the robot arm collides with an obstacle such as a person, workpiece, or equipment, the elastic body of the series elastic actuator absorbs the impact, thereby minimizing damage caused by the collision. Furthermore, because the elastic body of the series elastic actuator absorbs the torque fluctuations that occur upon contact, it is now possible to perform previously difficult tasks, such as a robot arm grasping a workpiece and inserting it into a fitting object with limited clearance for assembly, or a robot arm grasping a cleaning blade and scanning the surface of a window while making contact with it to clean it.

[0003] However, because a series elastic actuator is equipped with an elastic body such as a spring, it is generally difficult to control. In particular, if the lowest resonance frequency of the elastic body is low and the workpiece held by the robot arm is heavy, feedback control based on conventional classical control theory can cause problems such as vibration of the elastic body and deterioration of the positioning accuracy of the robot arm.

[0004] Therefore, for tasks where it is difficult to control a series elastic actuator, a robot arm equipped with a conventionally widely known, highly rigid drive mechanism is used. By increasing the rigidity of the robot arm, it is possible to suppress vibration and deterioration of positional accuracy.

[0005] However, robot arms may collide with and damage obstacles. Patent Document 1 describes a fail-safe mechanism for solving the problem that a robot arm equipped with a highly rigid drive mechanism may collide with a surrounding obstacle and damage the obstacle, including a person. Specifically, the document describes a robot arm equipped with a first position sensor for detecting the angle of the input side of the gear and a second position sensor for detecting the angle of the output side, at a joint connecting two links of the robot arm. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2017-507041 Summary of the Invention [Problem to be solved by the invention]

[0007] However, even with the robot arm described in Patent Document 1, if a collision causes a sudden, large impact that cannot be controlled in time, damage to obstacles such as workpieces and people is unavoidable. In particular, even in the case of industrial robots that are operated so that people cannot physically enter the robot's operating area, such as with safety fences, people will enter the robot's range of motion during non-routine tasks such as robot repair or teaching correction, so the possibility of injury to people due to unexpected robot movements is extremely high, and in fact, there have been many cases of this happening in Japan.

[0008] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a drive mechanism, a robot arm, and a drive method that are capable of achieving high rigidity and absorbing impacts due to collisions. [Means for solving the problem]

[0009] The present application discloses a drive mechanism comprising: a drive unit configured to be drivable; an engagement unit provided on the drive unit; a driven unit; an engaged unit provided on the driven unit and configured to be able to drive the driven unit by engaging with the engaging unit; and an elastic body configured to apply an elastic force based on the distance between the engaging unit and the engaged unit to the driven unit in a direction to reduce the distance between the engaging unit and the engaged unit.

[0010] The elastic body may be connected to the engaging portion and the engaged portion, and may be configured to be able to execute a first operating mode in which the driving portion drives the driven portion when the engaging portion and the engaged portion are engaged, and a second operating mode in which the driving portion drives the driven portion via the elastic body when the engaging portion and the engaged portion are not engaged.

[0011] The engagement between the engaging portion and the engaged portion may be disengaged when a force equal to or greater than a predetermined value acts in the rotational direction.

[0012] The device may also include a second elastic body configured to be able to act on the engaging portion or the engaged portion with an elastic force for engaging the engaging portion with the engaged portion, and an adjustment mechanism configured to be able to release the engagement between the engaging portion and the engaged portion by adjusting the elastic force acting from the second elastic body on the engaging portion or the engaged portion.

[0013] The driving part may have an annular part with the rotation axis of the driving part as its central axis, the driven part may have a columnar part surrounded by the annular part and with the rotation axis as its central axis, the engaging part may be provided on the annular part and have a recess recessed in the outer diameter direction, and the engaged part may be provided on the columnar part and have a convex part protruding in the outer diameter direction and contacting the recess.

[0014] The present application discloses a robot arm including a drive mechanism, a first link on which the drive part of the drive mechanism is provided, and a second link on which the driven part of the drive mechanism is provided.

[0015] Furthermore, the present application discloses a driving method including the steps of: driving an engaging portion provided on a driving portion configured to be drivable and an engaged portion provided on a driven portion while the driving portion is engaged with the engaged portion; disengaging the engaging portion from the engaged portion; applying an elastic force based on the distance between the engaging portion and the engaged portion to the driven portion in a direction that reduces the distance between the engaging portion and the engaged portion; and moving the driven portion relative to the driving portion to engage the engaging portion with the engaged portion. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of a robot arm according to an embodiment. [Figure 2] 1 is a schematic cross-sectional view of a drive mechanism according to an embodiment, taken along a plane perpendicular to a rotation axis. [Figure 3] 5A to 5C are schematic diagrams illustrating a driving method of a driving mechanism according to an embodiment. [Figure 4] 5A to 5C are schematic diagrams illustrating a driving method of a driving mechanism according to an embodiment. [Figure 5] 10 is a flowchart of a driving method for a drive mechanism according to an embodiment. [Figure 6] 10A and 10B are schematic diagrams illustrating a scene in which engagement is released in a driving method for a drive mechanism according to an embodiment. [Figure 7] FIG. 10 is a schematic diagram of a drive mechanism according to another embodiment. [Figure 8] 10 is a flowchart of a driving method for a drive mechanism according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to these embodiments.

[0018] [First embodiment]

[0019] 1 is a schematic diagram of a robot arm 20 equipped with a drive mechanism 30 according to this embodiment. For ease of explanation, the drive mechanism 30 in the figure is shown in cross section.

[0020] The robot arm 20 is a vertical articulated robot arm with multiple joints (e.g., seven axes) and includes a base (not shown) and multiple links connected to the base. Each link includes an actuator A (FIG. 3) rotatably mounted relative to the link to rotate the next link around the rotation axis.

[0021] FIG. 1 shows link L2, which includes an output section O1 (an example of a “driver”) of an actuator A provided on one link L1 of the multiple links provided in the robot arm 20 and configured to rotate relative to the link L1; an input section I2 (an example of a “driven section”) configured to engage with the output section O1 and thereby rotate with the rotation of the output section O1; and link L3, which includes an output section O2 (an example of a “driver”) of an actuator provided on link L2 and configured to rotate with the rotation of the output section O2 and thus rotate with the rotation of the output section O2 (an example of a “driven section”). Similarly, the other links may include an input section that engages with an actuator provided on a base end link and an output section of an actuator that engages with an input section provided on a tip end link to rotate the tip end link. Furthermore, a holding means such as a gripper for holding an object may be mounted on the tip end link (e.g., link L3).

[0022] FIG. 2 shows a cross-sectional view of the output portion O1 and the input portion I2 of the drive mechanism 30 according to this embodiment, cut along a plane perpendicular to the rotation axis AX1.

[0023] The output section O1 of the actuator is a section that transmits a driving force to the input section I2, thereby driving the input section I2 and the link L2 that is provided integrally therewith. As shown in the figure, the output section O1 of the actuator according to this embodiment has a portion (hereinafter sometimes referred to as the "annular portion") that is formed in an annular shape with the rotation axis AX1 as the central axis. The output section O1 is configured by the actuator to be rotatable relative to the link L1 around the rotation axis AX1. Here, the actuator may be a means known as an actuator mounted on a robot arm, and for example, the actuator for driving each link may be composed of a servo motor, which is an electric motor.

[0024] An engagement portion E1 for engaging with the input portion I2 of the link L2 is provided on the output portion O1 of the actuator of the link L1. The engagement portion E1 according to this embodiment is provided on the inner peripheral surface of the annular output portion O1 and has a recess R11 recessed in the outer diameter direction.

[0025] On the other hand, the input part I2 and the link L2 provided integrally therewith are parts (driven parts) that are driven by the transmission of the driving force of the output part O1 of the actuator. As shown in the figure, the input part I2 according to this embodiment is surrounded by the annular part of the output part O1 and has a part (hereinafter sometimes referred to as the "pillar part") that is formed in a columnar shape (for example, a cylindrical shape) with the rotation axis AX1 as its central axis.

[0026] The input portion I2 of the link L2 is provided with an engaged portion E2 for engaging with the output portion O1 of the link L1. The engaged portion E2 according to this embodiment is provided on the outer peripheral surface of the columnar portion and has a protrusion P21 that protrudes in the radial direction.

[0027] In this embodiment, the configuration including such a protrusion P21 is realized by a plunger. The plunger is rotatable integrally with the link L2 and includes a tubular portion P21C extending from the outer circumferential surface of the columnar portion in an outer radial direction substantially perpendicular to the rotation axis AX1, a ball P21B supported by the inner circumferential surface of the tubular portion P21C with a portion of the ball P21B protruding from the tubular portion P21C, and a spring P21S (an example of a "second elastic body"; FIG. 6) inserted between the ball P21B and the inner bottom surface of the tubular portion P21C and biasing the ball P21B toward the tip of the tubular portion P21C.

[0028] According to the above configuration, the ball P21B is biased in the radially outward direction by the spring P21S, and therefore, by bringing the ball P21B, which is the convex portion of the input portion I2, into contact with the concave portion R11 of the output portion O1, the engaging portion E1 provided on the output portion O1 and the engaged portion E2 of the input portion O2 are engaged (hereinafter, sometimes referred to as the "locked state"), and it becomes possible to transmit driving force from the output portion O1 to the input portion I2.

[0029] Furthermore, as will be described later, when a large circumferential force acts on the input portion I2 or the output portion O1, the engaging portion E1 of the output portion O1 and the engaged portion E2 of the input portion I2 can be disengaged. Because the spring P21S can be compressed inward, when the engaging portion E1 and the engaged portion E2 are disengaged, the ball P21B of the input portion I2 comes off the engaging portion E1 and rides up onto the cylindrical inner circumferential surface of the annular portion. Because the spring P21S maintains its compressed state, the ball P21B of the input portion I2 presses the inner circumferential surface of the output portion O1 in the outward radial direction.

[0030] The configurations of the engaging portion E1 and the engaged portion E2 are not limited to those shown in this embodiment. For example, the engaging portion may have a convex portion protruding inward, and the engaged portion may have a concave portion recessed inward. Also, instead of a ball plunger, known configurations such as a torque transmission mechanism using electromagnetic force (e.g., an electromagnetic friction clutch), a torque transmission mechanism using fluid (e.g., a fluid clutch), a torque transmission mechanism using magnetic material (e.g., a magnetic powder clutch), a force limiter mechanism, a link lock mechanism, or a powered lock mechanism may be used. The input portion may be formed as a column and the output portion as an annular portion, or the engaging portion and engaged portion may have other shapes. However, as described below, when a mechanical locking mechanism such as a ball plunger is used, the locked state between the engaging portion E1 and the engaged portion E2 can be maintained as long as a force less than a predetermined value acts in the rotational direction. This does not require an external driving force such as electricity or compressed air, and is therefore not dependent on problems caused by the external driving force.

[0031] The drive mechanism 30 further includes an elastic body that applies an elastic force based on the distance between the engaging portion E1 and the engaged portion E2 to the input portion I2 in a direction that reduces the distance between the engaging portion E1 and the engaged portion E2. In this embodiment, such elastic bodies include a first spring S11 and a second spring S12, one end of which is connected to the output portion O1 and the other end of which is connected to the input portion I2. More specifically, the annular portion of the output portion O1 is formed with a recess (hereinafter sometimes referred to as a "second recess R12") recessed radially outward from the inner circumferential surface over an area having a predetermined central angle (e.g., 30 degrees or more and 90 degrees or less), while the input portion I2 is formed with a protrusion (hereinafter sometimes referred to as a "second protrusion P22") protruding radially outward near the bottom surface of the second recess R12 so that a portion of the protrusion is present in an area surrounded by the second recess R12.

[0032] The first spring S11, which is one of the elastic bodies, has one end connected to a side surface (surface facing the circumferential direction) of the second recess R12 and the other end connected to a side surface (surface circumferentially facing the wall surface of the second recess) of the second protrusion P22, extending in the circumferential direction, while the second spring S12, which is the other elastic body, has one end connected to the other side surface (surface facing the circumferential direction) of the second recess R12 and the other end connected to the other side surface (surface circumferentially facing the wall surface of the second recess R12) of the second protrusion P22, extending in the circumferential direction. Furthermore, the first spring S11 and the second spring S12 are configured to have their natural lengths when the engaging portion E1 and the engaged portion E2 are engaged with each other.

[0033] With the above configuration, when the engaging portion E1 and the engaged portion E2 are engaged, the first spring S11 and the second spring S12 are at their natural lengths and exert almost no elastic force on the input portion I2. However, when the engaging portion E1 and the engaged portion E2 are disengaged, one of the first spring S11 and the second spring S12 compresses and the other expands, thereby exerting an elastic force on the input portion I2 that reduces the distance between the engaging portion E1 and the engaged portion E2.

[0034] The configuration of the elastic body is not limited to that shown in this embodiment. For example, the number of springs may be one, three or more depending on the application. However, compared to the case where there is only one spring, symmetrically arranging multiple springs makes it possible to improve stability.

[0035] Furthermore, the first spring S11 and the second spring S12 do not necessarily have to be at their natural lengths at the position where the engaging portion E1 and the engaged portion E2 engage, and may be, for example, compressed or extended. If the resultant force acting on the input portion I2 from multiple springs is zero, for example, even if the first spring and the second spring are provided as compression springs, it is possible to support the input portion I2 so that it is stable at the position where the engaging portion E1 and the engaged portion E2 engage.

[0036] The drive mechanism 30 according to this embodiment further includes a damping element for damping vibrations caused by an elastic body. In this embodiment, the damping elements include a first damper D11 and a second damper D12, one end of which is connected to the output port O1 and the other end of which is connected to the input port I2. More specifically, the first damper D11, which is one of the damping elements, extends in the circumferential direction, with one end connected to a side surface (a surface facing the circumferential direction) of the second recessed portion R12 and the other end connected to a side surface (a surface facing the circumferential direction) of the second protruding portion P22. The second damper D12, which is the other elastic damping element, extends in the circumferential direction, with one end connected to the other side surface (a surface facing the circumferential direction) of the second recessed portion R12 and the other end connected to the other side surface (a surface facing the circumferential direction) of the second protruding portion P22.

[0037] The drive mechanism 30 further includes a displacement sensor SE1 for acquiring the amount of displacement between the engaging portion E1 and the engaged portion E2 and the load based on the amount of displacement. The displacement sensor may include, for example, a readable portion such as a scale or a magnet, and a reading portion such as a read head for the scale or a Hall element for the magnet, and one of the readable portion or the reading portion may be provided in the second recess R12 (for example, a position in the second recess R12 that is close to the second protrusion P22 in the locked state), and the other may be provided in the second protrusion P22. The displacement sensor SE1 can acquire the amount of displacement between the engaging portion E1 and the engaged portion E2, and therefore can detect whether the engaging portion E1 and the engaged portion E2 are in a locked state in which they are engaged, or in an unlocked state (unlocked state) in which they are not engaged. Furthermore, in the unlocked state, the displacement sensor SE1 can acquire the amount of displacement between the engaging portion E1 and the engaged portion E2, and therefore can acquire the elastic force acting from the elastic body (first spring S11 and second spring S12) based on the amount of displacement.

[0038] Additionally, the drive mechanism 30 includes a sensor SE2 for detecting the load torque (or load) occurring between the output part O1 and the input part I2. Particularly in the locked state of this embodiment, the first spring S11 and the second spring S12 are at their natural lengths, and the displacement sensor SE1 measures zero displacement between the engaging part E1 and the engaged part E2, making it difficult to obtain information about the load torque occurring between the output part O1 and the input part I2. Therefore, particularly in the locked state, the control device 10 is configured to obtain information about the load torque detected by the sensor SE2 and control the robot arm 20 based on the information about the load torque detected by the sensor SE2. The sensor SE2 may be, for example, a strain gauge attached to the plunger support member (e.g., the cylindrical part P21C). The drive mechanism 30 may further include a sensor for detecting the load acting between the engaging portion E1 and the engaged portion E2. The sensor SE2 may be, for example, a strain gauge that detects the strain of the spring P21S. The strain gauge detects the strain of the spring P21S, thereby detecting the load with which the input portion I2 (ball P21B) presses the output portion O1. The greater this load, the stronger the engagement between the engaging portion E1 and the engaged portion E2. Therefore, the sensor can detect whether the output portion O1 and the input portion I2 are firmly engaged and whether force is being transmitted efficiently. The control device 10 is configured to obtain information regarding the strain of the spring P21S detected by the sensor (including information that varies depending on the strain) and control the robot arm 20 based on this information.

[0039] The drive mechanism 30 having the above-described configuration is housed in the housing of each link of the robot arm 20, for example.

[0040] The robot arm 20 further includes sensors for acquiring the load and displacement (angular position of the output shaft) of the servo motor, which is an actuator. The magnitude of the load can be acquired, for example, from a current sensor that acquires the amount of current flowing through the servo motor. The displacement of the servo motor can be acquired from an optical sensor such as an encoder, an electromagnetic sensor (including electromagnetic induction type and capacitance type), a magnetic sensor such as a Hall element, or a strain sensor.

[0041] [Control device configuration]

[0042] 3 is a functional block diagram of a robot system 100 according to this embodiment. A control device 10 (FIG. 3) controls a robot arm 20. The control device 10 according to this embodiment includes a start position acquisition unit 10A that acquires a starting position of a reference position of the robot arm 20 (for example, a center point of a link corresponding to the hand position; hereinafter referred to as a "reference position" or "reference portion") and a posture at that time, a target position acquisition unit 10B that acquires a target position and a posture at that time, a path acquisition unit 10C that acquires a path connecting the start position and the target position, a control command acquisition unit 10D that acquires control commands for controlling servo motors corresponding to the driving units of each actuator A according to the path acquired by the path acquisition unit 10C, and a storage unit 10E.

[0043] The start position acquisition unit 10A acquires, for example, a start position and the posture of the robot arm 20 at that time input from a teaching device (not shown) connectable 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 reference position and posture at that time as the start 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 posture of the reference position are taught as the start position by a computer program.

[0044] The target position acquisition unit 10B acquires, for example, a target position input from a teaching device and the orientation at that time, similar to the start position. The target position acquisition unit 10B can acquire multiple target positions and the orientations at that time.

[0045] The route acquisition unit 10C acquires a route (planned trajectory) connecting the start position and the target position by calculation processing or the like.

[0046] The control command acquisition unit 10D acquires, by calculation or the like, control commands for controlling each motor mounted on the drive unit of each actuator A in order to move the reference position along the path, and supplies the control commands to the robot arm 20. For example, the control command acquisition unit 10D can calculate, by inverse kinematics calculation, the rotation angle of each motor for positioning the reference position on the path, generate control commands based on this, and store the control commands in the storage unit 10E.

[0047] The storage unit 10E stores computer programs (including path generation algorithms) for executing the processes shown in the respective embodiments, as well as necessary data and other information.

[0048] 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 memory such as a static random access memory (SRAM) or a dynamic random access memory (DRAM), a nonvolatile memory 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. The nonvolatile memory is a storage medium that non-transitoryly stores information. The volatile memory temporarily stores at least a portion of these computer programs and the results of arithmetic processing. The memory unit 10E is configured from these memory elements. Furthermore, the memory unit 10E functions as a start position acquisition unit 10A, a target position acquisition unit 10B, a path acquisition unit 10C, and a control command acquisition unit 10D by the computational elements executing the computer programs stored in the memory unit 10E. However, at least some of these arithmetic elements, nonvolatile storage elements, etc. may be installed in remote locations connected to a communication network such as the Internet. For example, the arithmetic elements may be configured to acquire computer programs or necessary data via a communication network. The control device 10 may also include two or more processors as arithmetic elements. Furthermore, the control device 10 may be configured to be able to execute multiple computer programs, and control by the control device 10 may be realized based on a first computer program. The first computer program may be non-transitory stored in the nonvolatile storage element of the storage unit 10E.

[0049] The control device 10 and the robot arm 20 are configured to be able to send and receive information via wireless or wired communication means.

[0050] A teaching device for teaching the robot system 100 to perform an operation may be connected to or integrated with the control device 10. The teaching device may also be provided on the robot arm 20, and, for example, an input / output means including a display may be used as part of the teaching device. The teaching device may, for example, comprise a portable teaching pendant. Like the control device 10, the teaching device comprises a computing element, a volatile memory element, and a non-volatile memory element, and further comprises 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 input means in which input is made by pressing the display.

[0051] [Drive method]

[0052] A method for driving the robot arm 20 and the drive mechanism 30 mounted on the robot arm 20 will be described below. Fig. 4 is a schematic diagram showing a method for driving the robot arm 20 and the drive mechanism 30 mounted on the robot arm 20. In the example of Fig. 4, an example is shown in which the link at the tip of the robot arm 20 corresponds to link L2 provided integrally with input part I2. Link L2 at the tip is provided with a holding part for holding an object to be held. Fig. 5 shows a flowchart of such a driving method.

[0053] The control device 10 controls the robot arm 20 to drive each link in a locked state in which the engaging portion E1 and the engaged portion E2 are engaged (step S51). Specifically, the path acquisition unit 10C of the control device 10 acquires, by calculation or the like, a path (planned trajectory) connecting the start position acquired by the start position acquisition unit 10A and one or more target positions acquired by the target position acquisition unit 10B. The control command acquisition unit 10D acquires, by calculation or the like, control commands for controlling each actuator A according to the path acquired by the path acquisition unit 10C, and supplies the control commands to the robot arm 20. In the locked state, the driving force of the output portion O1 of the actuator is transmitted to the input portion I2 via engagement between the engaging portion E1 and the engaged portion E2. Therefore, as the output portion O1 of the actuator of the link L1 rotates, the input portion I2, the link L2 integrally provided therewith, and the holding portion provided at the tip of the link L2 also rotate (FIG. 4(A)).

[0054] During such normal operation, a part of the robot arm 20 may interfere with and collide with an obstacle (which may be a person, a workpiece, equipment, or another robot arm) (step S52, FIG. 4(B)). The figure shows a state in which link L2 interferes with and collides with an obstacle. At this time, link L2 is prevented from rotating because it is interfering with the obstacle. As a result, a large force acts in the rotational direction between link L1, which is attempting to rotate, and link L2, which is prevented from rotating.

[0055] The drive mechanism 30 is configured so that when a predetermined force acts in the rotational direction between the link L1 and the link L2, the engagement between the engaging portion E1 and the engaged portion E2 is released. Fig. 6(A) is a schematic diagram illustrating the force acting on the ball P21B, which is an example of a convex portion, in the normal state (locked state) when the engaging portion E1 and the engaged portion E2 are engaged, and Fig. 6(B) is a schematic diagram illustrating the magnitude of the force Fp when the engagement is released. For ease of explanation, the cylindrical portion P21C is omitted from the figure.

[0056] As described above, a force Fg acts on the ball P21B in the radially outward direction from the spring P21S. Meanwhile, because the ball P21B is in contact with the recessed portion R11 of the output portion O1, a force also acts on the ball P21B from the recessed portion R11 of the output portion O1. As shown in the figure, when the recessed portion R11 has two symmetrically inclined surfaces that are inclined at an angle θ with respect to the radially outward direction, a force Fc acts on the ball P21B from each inclined surface in a direction perpendicular to the inclined surface. When the ball P21B is stationary, the force acting in the radially outward direction and the force acting in the radially inward direction balance each other, so the relationship between the forces Fg and Fc is Fg = 2Fc(sin θ).

[0057] 6(B), when the engagement is released, a force Fp acts on the ball P21B in the rotational direction, and the normal force acting on the ball P21B from one of the inclined surfaces becomes 0. If the force acting on the ball P21B from the other inclined surface is defined as force Fc1, then immediately before the ball P21B moves, the forces Fg, Fc1, and Fp have the relationships Fg = Fc1(sin θ) and Fp = Fc1(cos θ), and therefore have the relationship Fp = Fg / (tan θ).

[0058] Therefore, the engaging portion E1 and the engaged portion E2 are configured so that the locked state between the engaging portion E1 and the engaged portion E2 is maintained as long as a force less than Fg / (tan θ) acts between the link L1 and the link L2 in the rotational direction, and the engagement between the engaging portion E1 and the engaged portion E2 can be released when a force of Fg / (tan θ) or more acts. Note that a more accurate value for when the locked state is released may be obtained by further considering the effect of centrifugal force accompanying the rotation of the link L2 and the effect of elastic force due to compression of the spring P23.

[0059] 4(C) shows a schematic diagram of a state in which the engagement portion E1 and the engaged portion E2 are disengaged due to a force equal to or greater than Fg / (tan θ) acting in the rotational direction when link L2 collides with an obstacle. At this time, the engagement portion E1 and the engaged portion E2 separate (step S54). When the control device 10 determines that the state has transitioned to the unlocked state based on a signal from the displacement sensor SE1, which acquires the amount of displacement between the engagement portion E1 and the engaged portion E2, the control device 10 stops driving the robot arm 20.

[0060] In the unlocked state, the first spring S11 compresses and the second spring S12 expands. Therefore, an elastic force acts from the first spring S11 to the second protrusion P22 of the input portion I2 in a direction (clockwise on the page) that reduces the distance between the engaging portion E1 and the engaged portion E2. Similarly, an elastic force acts from the second spring S12 to the second protrusion P22 of the input portion I2 in a direction (clockwise on the page) that reduces the distance between the engaging portion E1 and the engaged portion E2.

[0061] Therefore, as shown in Figure 4(D), when the obstacle that was preventing the drive of link L2 is removed, input part I2 moves in a direction (clockwise on the paper) in which the distance between engaging part E1 and engaged part E2 becomes smaller, i.e., in a direction in which engaging part E1 and engaged part E2 approach each other (step S55).

[0062] Then, the engaging portion E1 and the engaged portion E2 return to the locked state (step S56). That is, the input portion I2 rotates in the circumferential direction due to the elastic forces of the first spring S11 and the second spring S12, so that the ball P21B rotates and slides on the inner circumferential surface of the annular portion of the output portion O1, and eventually fits into the recess R12.

[0063] When the control device 10 determines that the locked state has been restored based on a signal from the displacement sensor SE1, which acquires the amount of displacement between the engaging portion E1 and the engaged portion E2, it controls the robot arm 20 in the locked state to re-drive each link. Note that the control device 10 may also drive the output portion O1 in the unlocked state to promote engagement between the engaging portion E1 and the engaged portion E2.

[0064] As described above, the drive mechanism 30 and drive method according to this embodiment enable the drive of the robot arm 20 with high rigidity in the locked state. Furthermore, since the locked state is released and the rigidity is reduced when an impact from a collision occurs, safety in the event of a collision can be improved compared to when the locked state is maintained. Furthermore, when a load such as an obstacle is removed, the elastic force automatically aligns the robot arm, allowing it to automatically return to the locked state.

[0065] [Second embodiment]

[0066] The second embodiment of the present invention will be described below. In each embodiment, components having the same functions or configurations as those in other embodiments will be given the same names, and detailed descriptions will be omitted, with the focus being on differences.

[0067] While the first embodiment applies the present invention to a rotationally driven drive mechanism, the second embodiment corresponds to an embodiment in which the present invention is applied to a linearly driven drive mechanism. FIG. 7 is a schematic diagram of a drive mechanism 300 according to this embodiment. This drive mechanism 300 includes a motor as an actuator A0, a ball screw rotated by the motor, a nut unit 310 that is reciprocally movable by being threadedly engaged with the ball screw, an output unit O10 (an example of a "drive unit") that is configured to be driven integrally with the nut unit 310, and an input unit I20 (an example of a "driven unit") that is engaged with the output unit O10 and is therefore reciprocally movable in accordance with the reciprocating movement of the output unit O10. The output unit O10 may be provided, for example, as a stage for transporting articles.

[0068] The output part O10 is formed with a recess recessed downward in the plane of the drawing as an engagement part E10 for engaging with the input part I20.

[0069] The input part I20 is a part (driven part) that is driven by the driving force transmitted from the output part O10 of the actuator. As shown in the figure, the input part I20 according to this embodiment is provided with a protrusion that protrudes downward from the paper surface as an engaged part E20 for engaging with the output part O10. The protrusion may be formed of a plunger, as in the first embodiment.

[0070] The drive mechanism 300 further includes a first spring S110 and a second spring S120, one end of which is connected to the output portion O10 and the other end of which is connected to the input portion I20, as elastic bodies that apply an elastic force based on the distance between the engaging portion E10 and the engaged portion E20 to the input portion I20 in a direction that reduces the distance between the engaging portion E10 and the engaged portion E20.

[0071] According to the above configuration, the control device (not shown) controls the motor serving as the actuator A0 while the engaging portion E10 and the engaged portion E20 are in a locked state engaged with each other, thereby moving the input portion I20 and the item being conveyed thereby back and forth.

[0072] During such normal operation, if the input portion I20 or the like interferes with and collides with an obstacle, a large force acts in the drive direction, causing the engagement between the engaging portion E10 and the engaged portion E20 to be released. However, when the engagement is released and the distance between the engaging portion E10 and the engaged portion E20 increases, one of the first spring S110 and the second spring S120 expands or compresses, causing an elastic force to act in a direction that reduces the distance between the engaging portion E10 and the engaged portion E20, and the engaging portion E10 and the engaged portion E20 return to the locked state.

[0073] As described above, the drive mechanism 300 and drive method according to this embodiment also enable high-rigidity drive in the locked state. Furthermore, since the locked state is released and rigidity is reduced when an impact due to a collision occurs, safety in the event of a collision can be improved compared to when the locked state is maintained. Furthermore, the elastic force can automatically return the mechanism to the locked state.

[0074] [Third embodiment]

[0075] In the first and second embodiments, when a large force is applied to the robot arm or the like by, for example, colliding with an obstacle, the drive mechanism is configured to transition from a locked state in which the engaging portion and the engaged portion are engaged to an unlocked state in which the engagement between the engaging portion and the engaged portion is released. Furthermore, when the control device detects the unlocked state, it stops driving the robot arm or the like.

[0076] However, as described below, the drive mechanism may be configured to be able to actively switch from a locked state to an unlocked state. Furthermore, in the unlocked state, the control device may be configured to drive a robot arm or the like.

[0077] [Switching mechanism]

[0078] The drive mechanism according to the third embodiment includes a switching mechanism for actively switching between a locked state in which the engaging portion and the engaged portion are engaged with each other and an unlocked state in which the engaging portion and the engaged portion are not engaged with each other. The switching mechanism may be composed of, for example, a plunger configured to be movable forward and backward, an electromagnetic coil that generates an electromagnetic force for moving the plunger forward and backward, and an electromagnetic plunger having a spring that applies a biasing force to the plunger. For example, the drive mechanism in the first embodiment may be equipped with an electromagnetic plunger that functions as the switching mechanism instead of the plunger. This drive mechanism may be configured to maintain the locked state between the engaging portion and the engaged portion by the biasing force of the spring, as in the first embodiment, during normal operation, and to transition from the locked state to the unlocked state by generating an electromagnetic force from the electromagnetic coil to move the plunger in a direction that releases the engagement (for example, the inner diameter direction in the first embodiment) based on a control command from a control device.

[0079] [Control in unlocked state]

[0080] The output part O1 and the input part I2 are connected via the first spring S11 and the second spring S12, which are elastic bodies. Therefore, when the output part O1 is driven in the unlocked state (e.g., FIG. 4(D)), the driving force of the output part O1 is transmitted to the input part O2 via the elastic bodies. This allows the drive mechanism 30 to function as a series elastic actuator (SEA). The torque output from the motor is transmitted to a rigid link via the elastic bodies, making it easy to realize a tracking operation in which a robot arm moves a member while contacting an object. For example, Japanese Patent No. 6329149 and European Patent No. 2890528 disclose examples of SEAs.

[0081] In the following, the operating mode in which the driving unit drives the driven unit when the engaging unit and the engaged unit are engaged may be referred to as the first operating mode, and the operating mode in which the driving unit drives the driven unit via an elastic body when the engaging unit and the engaged unit are not engaged may be referred to as the second operating mode.

[0082] In the second operating mode, an equation of motion is established with parameters including the inertia, mass, and length of the part driven by the SEA, external force, and the elastic modulus of the mechanical spring, which is the elastic body of the series elastic actuator. Therefore, the control device 10 is configured to perform mechanical compliance control, which controls impedance based on the elastic modulus and displacement of the mechanical spring. The series elastic actuator may be connected to the drive shaft of a servomotor, which is the driving unit, and may include a gear for transmitting power to the elastic body, such as the mechanical spring. Furthermore, the series elastic actuator 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 viscous damper mechanism, is added, or when damping due to friction between gears is taken into account, the equation of motion is established with the viscosity constant added as a parameter.

[0083] 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 gear's output shaft via an elastic body, the torque generated on the gear's output shaft is proportional to the current flowing through the servomotor and the gear ratio. The equation of motion establishes this torque as equal to the sum of the angular acceleration of the gear's output shaft multiplied by its inertia, the angular acceleration of the gear's output shaft multiplied by its viscosity, and the elastic body's displacement multiplied by its modulus of elasticity. By deriving the transfer function of the series elastic actuator based on this equation of motion, mechanical compliance control, which controls impedance, becomes possible. Furthermore, predictive control (feedforward control) is also possible by measuring the transfer function in advance or presetting the behavior for each payload.

[0084] [Drive method]

[0085] The driving method according to this embodiment will be described below with reference to the flowchart of FIG.

[0086] The control device 10 controls the robot arm 20 in a first operation mode to drive each link while the engaging portion E1 and the engaged portion E2 are engaged and locked (step S81). The first operation mode is an operation mode in which the input portion I2 and the output portion O1 are driven integrally. The first operation mode is similar to step S51 in the first embodiment, and therefore a detailed description thereof will be omitted.

[0087] Next, when the robot arm is to perform a tracing operation of moving the held object while contacting it with the target object, the control device 10 transitions to the second operation mode. Specifically, the output part O1 is rotated while generating an electromagnetic force in the electromagnetic coil to move the plunger (for example, ball P21B) in the inner diameter direction, thereby releasing the engagement between the engaging part and the engaged part (step S82).

[0088] Then, in the second operating mode, the control device 10 performs mechanical compliance control by transmitting a driving force from the output portion O1 to the input portion I2 via the elastic body (step S83). Note that in the second operating mode, the plunger may be configured to be able to slide on the inner circumferential surface of the annular portion of the output portion O1. When the plunger slides on the inner circumferential surface of the annular portion, a frictional force that weakens the elastic force is generated, thereby making it possible to reduce vibration caused by the elastic force.

[0089] As described above, the drive mechanism and drive method according to this embodiment enable driving of a robot arm with high rigidity in the locked state, and enable driving of a robot arm with low rigidity in the unlocked state. Therefore, by switching the operation mode depending on the situation, it becomes possible to drive the robot arm appropriately.

[0090] Furthermore, the present invention can be modified in various ways without departing from the spirit of the present invention. For example, some components of one embodiment can be added to other embodiments within the scope of ordinary creativity of a person skilled in the art. Also, some components of one embodiment can be replaced with corresponding components of other embodiments. [Explanation of symbols]

[0091] 10 Control device 20 Robot Arm 30 Drive mechanism 300 Drive Mechanism E1 Engagement part E2 Engaged part E10 Engagement part E20 Engaged part P21 Convex part P22 convex part R11 recess R12 recess

Claims

1. A drive mechanism for a robot arm, comprising: a driving unit configured to be drivable; an engagement portion provided on the drive portion; A driven part; an engaged portion provided on the driven portion and configured to be able to drive the driven portion by engaging with the engaging portion; an elastic body configured to apply an elastic force based on the distance between the engaging portion and the engaged portion to the driven portion in a direction that reduces the distance between the engaging portion and the engaged portion; a detection means for detecting a displacement amount between the engaging portion and the engaged portion in an unlocked state in which the engaging portion and the engaged portion are not engaged with each other; A drive mechanism comprising:

2. the elastic body is connected to the engaging portion and the engaged portion, a first operation mode in which the driving portion drives the driven portion while the engaging portion and the engaged portion are engaged with each other; 2. The drive mechanism according to claim 1, wherein a second operation mode is executable in which the drive portion drives the driven portion via the elastic body when the engaging portion and the engaged portion are not engaged with each other.

3. 3. The drive mechanism according to claim 1, wherein the engagement between the engaging portion and the engaged portion is disengaged when a force equal to or greater than a predetermined value acts in the rotational direction.

4. a detection unit that detects a locked state in which the engaging portion and the engaged portion are engaged with each other or an unlocked state in which the engaging portion and the engaged portion are not engaged with each other; a control means for controlling the drive unit to promote engagement between the engaging portion and the engaged portion when the detection unit detects the unlocked state; The drive mechanism according to claim 1 or 2, comprising:

5. the drive unit includes an annular portion having a rotation axis of the drive unit as a central axis, the driven part includes a columnar part surrounded by the annular part and having the rotation shaft as a central axis, the engaging portion is provided on the annular portion and includes a recess recessed in an outer diameter direction, The drive mechanism according to claim 1 , wherein the engaged portion comprises a protrusion provided on the columnar portion, protruding in an outer diameter direction and coming into contact with the recess.

6. The drive mechanism according to claim 1; a first link provided with the drive unit of the drive mechanism according to claim 1; a second link provided with the driven part of the drive mechanism according to claim 1; A robotic arm comprising:

7. A method for driving a drive mechanism in a robot arm, comprising: a step of driving the driven part by driving the driving part in a state in which an engaging part provided in the driving part configured to be drivable and an engaged part provided in the driven part are engaged with each other; a step of releasing the engagement between the engaging portion and the engaged portion; a step of applying an elastic force based on the distance between the engaging portion and the engaged portion to the driven portion in a direction that reduces the distance between the engaging portion and the engaged portion; acquiring a displacement amount between the engaging portion and the engaged portion in an unlocked state in which the engaging portion and the engaged portion are not engaged with each other; controlling the driving unit to move the driven unit relative to the driving unit and bring the engaging unit into engagement with the engaged unit; A driving method including:

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