Link actuation device

Abstract

A control device (70) of a link actuation device (7) comprises a posture calculation means (74), an actuator position calculation means (75), and a teaching data storage means (76). When teaching of a tip end-side link hub (13) is performed via direct teaching, the posture calculation means (74) calculates the posture of the tip end-side link hub (13) by forward transformation from the position of the actuator (10) in a state in which no preloading is applied to the parallel link mechanism (9). On the basis of the posture of the tip end-side link hub (13), the actuator position calculation means (75) calculates the position of the actuator (10) by inverse transformation in a state in which preloading is applied to the parallel link mechanism (9). The teaching data storage means (76) stores, as teaching data, a set of the posture of the tip end-side link hub (13) and the position of the actuator (10) calculated by inverse transformation.

Description

Link Actuator Related Applications

[0001] This application claims priority from Japanese Patent Application No. 2024-047916, filed March 25, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a link actuator that requires a precise and wide operating range, such as for medical equipment or industrial equipment, and to a technique for improving positioning accuracy by direct teaching.

[0003] As shown in FIG. 1, a link actuator 7, which is one aspect of a parallel mechanism, has been proposed.

[0004] In Patent Document 1, in order to improve the positioning accuracy of a mechanical body having a link mechanism, a technology is proposed in which a position where a force (preload) is applied to move the play that occurs in each rotational pair or mechanism part of the mechanical body to one side is set as the origin position.

[0005] A specific operation method of Patent Document 1 will be described below. As shown in Figure 2, consider a case where the attitude of the tip side link hub 13 is at the origin position (θ0, φ0) and the rotation angle of the base side end link member 15 corresponding to the attitude of this tip side link hub 13 is (β10, β20, β30).

[0006] At this time, as shown in Table 1, the actuator rotation position (M10, M20, M30) corresponding to the rotation angle of the base end side end link member 15 when there is no preload is added with the offset amount for the preload (Preload1, Preload2, Preload3), and the result (M10+Preload1, M20+Preload2, M30+Preload3) is set as the origin position of the actuator rotation position.

[0007] Thereafter, by performing positioning operations based on this origin position, the offset amount for the preload is always taken into account, which results in the backlash of the mechanical body being shifted to one side, thereby improving the positioning accuracy of the mechanical body.

[0008] Patent No. 5951224

[0009] However, when manually moving a mechanical body during direct teaching, it is necessary to release electrical and mechanical constraints by turning off the actuator positioning control (and releasing the brake), or by setting the torque output value to a lower value than during positioning control. In this case, the preload disappears, and if the actuator rotation positions (M1n, M2n, M3n) obtained when the preload is gone are set as teaching data as is, the positioning accuracy of the mechanical body will be worse than when the preload is present.

[0010] An object of the present invention is to provide a link actuator that can improve positioning accuracy even during direct teaching.

[0011] In the following, the present invention will be described with reference to the reference numerals of the embodiments for convenience in order to facilitate understanding.

[0012] The link actuation device of the present invention includes a parallel mechanism 9 in which a tip side link hub 13 is connected to a base side link hub 12 via a link mechanism 14 so that its posture can be changed, an actuator 10 that changes the posture of the tip side link hub 13, and a control device 70 that controls the actuator 10, wherein the control device 70 includes: posture calculation means 74 that calculates the posture of the tip side link hub 13 by forward transformation from the position of the actuator 10 when teaching the tip side link hub 13 by direct teaching, with no preload applied to the parallel mechanism 9; actuator position calculation means 75 that calculates, by inverse transformation, the position of the actuator 10 with a preload applied to the parallel mechanism 9, based on the calculated posture of the tip side link hub 13; and teaching data storage means 76 that stores, as teaching data, a set of the posture of the tip side link hub 13 and the position of the actuator 10 calculated by inverse transformation. The "direct teaching" means manually moving the tip side link hub 13 to a teaching position.

[0013] With this configuration, when teaching the tip side link hub 13 is performed by direct teaching, the actuator positions (M1n+Preload1, M2n+Preload2, M3n+Preload3) corresponding to the rotation angle of the base side end link member 15 in a preloaded state are calculated by inverse transformation (inverse kinematics) based on the attitude (θn, φn) of the tip side link hub 13 calculated by forward transformation (forward kinematics) from the position (M1n, M2n, M3n) of the actuator 10 relative to the rotation angle (β1n, β2n, β3n) of the base side end link member 15 in an unpreloaded state at a taught position n selected by the operator. Furthermore, the attitude (θn, φn) of the tip side link hub 13 and the actuator positions (M1n+Preload1, M2n+Preload2, M3n+Preload3) are stored as teaching data. Therefore, the position of the actuator 10, which eliminates the influence of backlash occurring in each revolute pair and mechanical part, etc., can be stored as teaching data, making it possible to perform highly accurate positioning control even during direct teaching.

[0014] The control device 70 may control the positioning of the actuator 10 based on the teaching data stored in the teaching data storage means 76. After the teaching by direct teaching is completed, the control device 70 shifts to the positioning control of the actuator 10 based on the stored teaching data, thereby improving the positioning control.

[0015] The parallel mechanism 9 connects the tip side link hub 13 to the base side link hub 12 via three or more sets of link mechanisms 14 in a posture-changeable manner, and each of the link mechanisms 14 has base side and tip side end link members 15, 16, one end of which is rotatably connected to the base side link hub 12 and the tip side link hub 13, respectively, and a central link member 17, both ends of which are rotatably connected to the other ends of the base side and tip side end link members 15, 16, and all of the three or more sets of link mechanisms 14 may be provided with the actuator 10.

[0016] With this configuration, the base end link hub 12, the tip end link hub 13, and three or more sets of link mechanisms 14 form a two-degree-of-freedom mechanism in which the tip end link hub 13 can rotate freely relative to the base end link hub 12 about two orthogonal axes. In other words, the tip end link hub 13 has two degrees of freedom of rotation relative to the base end link hub 12, allowing for free attitude change. This two-degree-of-freedom mechanism is compact, yet provides a wide range of movement for the tip end link hub 13 relative to the base end link hub 12. Because the actuator 10 is provided in all three or more sets of link mechanisms 14, the positioning of the tip end link hub 13 can be controlled with higher precision than if actuators were provided in only two of the three sets of link mechanisms 14.

[0017] The actuator 10 may be a motor installed in the base end link hub 12, and the control device 70 may drive the motor to control the bending angle and pivot angle of the tip end link hub 13. In this case, the control device 70 may control each motor to change the attitude of the tip end link hub 13 relative to the base end link hub 12 from the current attitude to a target link attitude (θ, φ).

[0018] The motor may be capable of positioning control and torque control. For example, when direct teaching is used to teach the distal link hub 13 to a desired position, the control device 70 controls the torque of the servo motor or stepping motor. After the teaching is completed, the control device 70 can control the positioning of the servo motor or stepping motor.

[0019] The control device 70 may limit the output of the motor when teaching the tip side link hub 13 by direct teaching. Limiting the output of the motor includes setting the motor output to zero. In this case, it is possible to prevent resistance when manually moving the tip side link hub 13 by direct teaching.

[0020] The attitude of the tip side link hub 13 calculated by the attitude calculation means 74 through forward transformation may be the bending angle and the turning angle of the tip side link hub 13. In this case, a link actuator can be provided that is compact in configuration but can operate over a wide operating range.

[0021] A preload may be applied to the parallel mechanism 9 by applying a force to move the backlash of the parallel mechanism 9 to one side using the torque of the motor. In this case, the preload can be easily applied using an existing motor without providing a separate member for applying the preload.

[0022] The force that shifts the backlash of the parallel mechanism 9 to one side may be a force that compresses the parallel mechanism 9 in a predetermined direction. The predetermined direction is determined appropriately depending on the installation state of the link actuator 7. For example, if the link actuator 7 is installed so that the central axis of the base-end link hub 12 faces the vertical direction, the predetermined direction is the vertical direction. If the link actuator 7 is installed so that the central axis of the base-end link hub 12 faces the horizontal direction, the predetermined direction is the horizontal direction. Compressing the parallel mechanism 9 in the predetermined direction reduces the moment of inertia of the parallel mechanism 9, increasing its rigidity and improving the positioning accuracy of the parallel mechanism 9.

[0023] The inverse transformation value, which is the position of the actuator 10 calculated by inverse transformation, is the output value of an absolute encoder 55 that detects the rotational position of the motor, and may represent the amount of movement from the origin position of the tip side link hub 13, which has been previously given a force that moves the parallel mechanism 9 to one side. By employing the absolute encoder 55 that detects the rotational position of the motor as an absolute angle, even if the power to the link actuator 7 is turned off and then turned on again, it is not necessary to perform initial settings again, and it becomes possible to easily return to the origin.

[0024] The teaching data may be stored in at least one of an internal storage area 81 of the controller 71 for the link actuator, an external storage device 78 that is removably installed in the controller 71 or connected to the controller 71 by communication, and an external device 73. In this case, the storage area for storing the teaching data can be selected according to the user's system configuration.

[0025] The torque of the motor that applies a force in a direction that pulls the parallel mechanism 9 to one side may be set from an input device 72 or other external device 73 that is electrically connected to the link actuator controller 71. In this case, the torque of the motor that applies a force in a direction that pulls the parallel mechanism 9 to one side can be easily set in accordance with the user's system configuration.

[0026] Any combination of at least two features disclosed in the claims and / or the specification and / or the drawings is included in the present invention. In particular, any combination of two or more of the claims is included in the present invention.

[0027] The present invention will be more clearly understood from the following description of preferred embodiments with reference to the accompanying drawings. However, the embodiments and drawings are merely for illustration and explanation, and should not be used to define the scope of the present invention, which is defined by the appended claims. In the accompanying drawings, the same reference numerals in multiple drawings indicate the same or corresponding parts.

[0028] 11 is a perspective view of a link actuation device according to a first embodiment of the present invention. FIG. 12 is a front view showing one axis of a link mechanism constituting the link actuation device. FIG. 13 is a partial cross-sectional view taken along line III-III in FIG. 2. FIG. 14 is a diagram showing one link mechanism of the link actuation device in linear form. FIG. 15 is a perspective view of an actuator of the link actuation device. FIG. 16 is a conceptual diagram showing when the link actuation device is taught by direct teaching. FIG. 17 is a diagram showing the configuration of a positioning control system using the link actuation device. FIG. 18 is a diagram showing the internal configuration of a controller of the link actuation device. FIG. 19 is a diagram showing a conversion flow when teaching the link actuation device by direct teaching. FIG. 20 is a flowchart showing the process in stages when teaching the link actuation device by direct teaching. FIG. 21 is a front view of a parallel mechanism of a link actuation device according to a second embodiment of the present invention. FIG. 22 is a view taken along arrows A-A in FIG. 22. FIG. 23 is a view taken along arrows B-B in FIG. 22.

[0029] [First Embodiment] A link actuation device according to an embodiment of the present invention will be described with reference to Figures 1 to 10. This link actuation device is used, for example, in medical equipment or industrial equipment. As shown in Figure 1, the link actuation device 7 includes a parallel link mechanism 9, which is a parallel mechanism, an actuator 10, and a control device 70.

[0030] <Parallel Link Mechanism> The parallel link mechanism 9 connects a tip side link hub 13 to a base side link hub 12 via three sets of link mechanisms 14 in a manner that allows the position to be changed. The number of sets of link mechanisms 14 may be four or more. In FIG. 2 , only one set of link mechanisms 14 is shown, and the remaining two link mechanisms are omitted. A work body that performs work on a workpiece, or the workpiece itself, is attached to the tip side link hub 13 (a tip member 40 described later). When a work body is attached to the tip side link hub 13, the workpiece is provided on the side of another device. When a workpiece is attached to the tip side link hub 13, the workpiece is provided on the side of another device.

[0031] Each link mechanism 14 has a base-side end link member 15, a tip-side end link member 16, and a central link member 17, forming a three-bar link mechanism consisting of four revolute pairs. As shown in Figure 1, the base-side and tip-side end link members 15, 16 are generally L-shaped, and one end is rotatably connected to the base-side link hub 12 and the tip-side link hub 13, respectively. As shown in Figure 2, the other ends of the base-side and tip-side end link members 15, 16 are rotatably connected to both ends of the central link member 17, respectively.

[0032] The parallel link mechanism 9 is a combination of two spherical link mechanisms. The central axes of the revolute pairs between the base-side link hub 12 and the base-side end link member 15, and the revolute pairs between the base-side end link member 15 and the central link member 17, intersect at the base-side spherical link center PA. Similarly, the central axes of the revolute pairs between the tip-side link hub 13 and the tip-side end link member 16, and the revolute pairs between the tip-side end link member 16 and the central link member 17, intersect at the tip-side spherical link center PB.

[0033] The distance from the center of each revolute pair between the base end link hub 12 and each base end end link member 15 to the base end spherical link center PA is the same. The distance from the center of each revolute pair between each base end end link member 15 and each central link member 17 to the base end spherical link center PA is the same. Similarly, the distance from the center of each revolute pair between the tip end link hub 13 and each tip end link member 16 to the tip end spherical link center PB is the same. The distance from the center of each revolute pair between each tip end link member 16 and each central link member 17 to the tip end spherical link center PB is the same.

[0034] The central axes of the revolute pairs between the base-end and tip-end end link members 15, 16 and the central link member 17 may have a certain cross angle γ or may be parallel. The arm angle, which is the angle formed by the central axis of the revolute pairs between the base-end link hub 12 and the base-end end link member 15 and the central axis of the revolute pairs between the base-end end link member 15 and the central link member 17, is set to a predetermined angle.

[0035] The three sets of link mechanisms 14 have geometrically identical shapes. "Geometrically identical shapes" refers to a geometric model, as shown in FIG. 4 , in which each link member 15, 16, 17 is represented by a straight line, i.e., a model represented by each rotation pair and the straight lines connecting these rotation pairs. The base end and tip end portions of the link members 15, 16, and 17 are symmetrical with respect to the center of the central link member 17, regardless of their orientation. FIG. 4 shows one set of link mechanisms 14 represented by straight lines. The parallel link mechanism 9 of this embodiment is a rotationally symmetric type, and the base end link hub 12 and the base end end link member 15, and the tip end link hub 13 and the tip end end link member 16 are positioned in a rotationally symmetrical manner with respect to the center line C of the central link member 17. The centers of the central link members 17 are located on a common orbital circle.

[0036] The base end link hub 12, the tip end link hub 13, and the three link mechanisms 14 constitute a two-degree-of-freedom mechanism in which the tip end link hub 13 can rotate freely around two perpendicular axes relative to the base end link hub 12. In other words, the tip end link hub 13 has two degrees of freedom of rotation relative to the base end link hub 12, allowing for free attitude change. This two-degree-of-freedom mechanism is compact, yet allows for a wide range of movement of the tip end link hub 13 relative to the base end link hub 12.

[0037] For example, if the central axes QA and QB of the base and tip link hubs 12 and 13 are defined as lines passing through the base and tip spherical link centers PA and PB and intersecting at right angles with the central axis O1 ( FIG. 1 ) of each rotation pair of the base and tip link hubs 12 and 13 and the base and tip end link members 15 and 16, respectively, the maximum bend angle θmax between the central axis QA (base central axis) of the base link hub 12 and the central axis QB of the tip link hub 13 can be approximately 90°. Furthermore, the pivot angle φ of the tip link hub 13 relative to the base link hub 12 can be set within a range of 0° to 360°. The bend angle θ is the perpendicular angle of the central axis QB of the tip link hub 13 relative to the central axis QA of the base link hub 12. On the other hand, the turning angle φ is the horizontal angle at which the central axis QB of the distal link hub 13 is inclined relative to the central axis QA of the proximal link hub 12. The maximum bending angle θmax may be 90° or more.

[0038] The position of the tip side link hub 13 relative to the base side link hub 12 is changed around the intersection O of the center axis QA of the base side link hub 12 and the center axis QB of the tip side link hub 13 as the center of rotation. Figure 4 shows a state in which the center axis QB of the tip side link hub 13 forms a certain operating angle (bend angle) with respect to the center axis QA of the base side link hub 12. Even if the position of the tip side link hub 13 relative to the base side link hub 12 changes, the distance L between the base side and tip side spherical link centers PA and PB does not change.

[0039] In this parallel link mechanism 9, when all of the following conditions 1 to 5 are satisfied, due to geometric symmetry, the base end link hub 12 and base end end link member 15, and the tip end link hub 13 and tip end end link member 16 move in the same way. Therefore, when transmitting rotation from the base end to the tip end, the parallel link mechanism 9 functions as a constant velocity universal joint in which the base end and tip end sides rotate at a constant speed with the same rotation angle.

[0040] Condition 1: As shown in Figures 3 and 4, the angles α of the central axes O1 and O2 of the rotation pairs of the base-end and tip-end link hubs 12 and 13 and the base-end and tip-end end link members 15 and 16 in each link mechanism 14, and the lengths from the base-end and tip-end spherical link centers PA and PB are equal to each other.

[0041] Condition 2: The central axes of the rotation pairs between the base end and tip end link hubs 12, 13 of each link mechanism 14 and the base end and tip end link members 15, 16, and the central axes of the rotation pairs between the base end and tip end link members 15, 16 and the central link member 17 intersect with the base end and tip end spherical link centers PA, PB at the base end and tip end.

[0042] Condition 3: The geometric shapes of the base-side end link member 15 and the tip-side end link member 16 are the same. Condition 4: The geometric shapes of the base-side portion and the tip-side portion of the central link member 17 are the same. Condition 5: The angular positional relationship between the central link member 17 and the base-side and tip-side end link members 15, 16 with respect to the plane of symmetry of the central link member 17 is the same on the base-side and tip-side.

[0043] As shown in Figure 1, the base-side link hub 12 has a flat base member 6 and three rotary shaft connecting members 21 that are integral with the base member 6. The three rotary shaft connecting members 21 are circumferentially spaced evenly on one surface of the base member 6. Each rotary shaft connecting member 21 is rotatably connected to a rotary shaft 22 (shown in Figure 3) whose axis intersects with the central axis QA (Figure 4) of the base-side link hub 12. One end of the base-side end link member 15 is connected to this rotary shaft 22.

[0044] As shown in FIG. 1 , the tip side link hub 13 includes a flat tip member 40 and three rotating shaft connecting members 41 circumferentially equidistantly spaced on the bottom surface of the tip side member 40. The center of the circumference on which each rotating shaft connecting member 41 is located is aligned with the central axis QB ( FIG. 4 ) of the tip side link hub 13. Each rotating shaft connecting member 41 is rotatably connected to a rotating shaft 43 whose axis intersects with the central axis QB ( FIG. 4 ) of the tip side link hub 13. One end of the tip side end link member 16 is connected to this rotating shaft 43. The other end of the tip side end link member 16 is connected to a rotating shaft 45, which is rotatably connected to the other end of the central link member 17. Here, the central axis or tip of a working body or workpiece (workpiece) provided on the tip side link hub 13 (tip side member 40) may be configured to coincide with or intersect with the central axis QB of the tip side link hub 13.

[0045] <Actuator> As shown in FIG. 5 , the actuator 10 that changes the posture of the distal link hub 13 is a brake-equipped rotary motor (motor) equipped with a reducer 52 that changes the posture of the distal link hub 13 ( FIG. 1 ). An output shaft 54 ​​protrudes from the motor body via the reducer 52. The motor is a servo motor or stepping motor capable of positioning control and torque control. The motor is equipped with an absolute encoder 55 that detects the rotational position (absolute angle) of the motor. As shown in FIG. 1 , the motor is installed coaxially with the rotation shaft 22 ( FIG. 3 ) on one plane of the base end member 6 of the proximal link hub 12. The motor body and reducer 52 are integrally provided, and the reducer 52 is fixed to the base end member 6 by a motor fixing member 53.

[0046] In this example, all three link mechanisms 14 are provided with actuators 10. If at least two of the three link mechanisms 14 are provided with attitude control actuators 10, the attitude of the distal link hub 13 relative to the proximal link hub 12 can be determined. The three actuators 10 are arranged so that their rotation axes 22 (FIG. 3) are perpendicular to the central axis QA (FIG. 4) of the proximal link hub 12, and the central position, which is the intersection of the rotation axes 22 (FIG. 3) of these actuators 10, is on the central axis QA (FIG. 4) of the proximal link hub 12.

[0047] The link actuation device 7 rotates each actuator 10, thereby actuating the parallel link mechanism 9. Specifically, when the actuator 10 is rotated, the rotation is reduced in speed via the reducer 52 and transmitted to the rotation shaft 22 ( FIG. 3 ). This changes the angle of the base-side end link member 15 relative to the base-side link hub 12, allowing the attitude of the tip-side link hub 13 relative to the base-side link hub 12 to be changed as desired. A working body (end effector) (not shown) is attached to the tip member 40 of the tip-side link hub 13. Examples of end effectors include a hand including a grip, a cleaning nozzle, a dispenser, a welding torch, and image processing equipment including a camera.

[0048] <Control Device> The control device 70 controls the actuator 10. The control device 70 drives the motor that is the actuator 10, enabling positioning control of the bending angle and the rotation angle of the tip-side link hub 13. The control device 70 is configured to be able to switch between the positioning control and torque control. The control device 70 applies a preload to the parallel link mechanism 9, which is a parallel mechanism, by applying a force that shifts the play of the parallel link mechanism 9 to one side using the torque of the motor. The force that shifts the play of the parallel link mechanism 9 to one side is a force that compresses the parallel link mechanism 9 in a specified direction. The torque of the motor that applies a force in the direction that shifts the parallel link mechanism 9 to one side can be set from an input device 72 electrically connected to a link actuator controller 71 or a personal computer (abbreviated as PC) 73, which is another external device, as shown in FIG. 7 . By rotating each motor provided in each actuator 10 in the same direction (clockwise or counterclockwise) with the same torque, a force is applied in a direction that moves the parallel link mechanism 9 to one side, and the backlash can be moved to one side, that is, the backlash of each rotational pair and mechanism part can be moved.

[0049] As shown in FIG. 1 , the control device 70 of the link actuation device particularly includes an attitude calculation means 74, an actuator position calculation means 75, and a teaching data storage means 76. As shown in FIG. 6 , when teaching the tip side link hub 13 by direct teaching using a finger or the like, the control device 70 limits the output of the motor and transitions to torque control. When teaching the tip side link hub 13 by manual direct teaching or the like, highly accurate positioning control can be achieved by performing direct teaching with a working body or a workpiece (work) attached to the tip member 40. Furthermore, when attaching a working body to the tip member 40, direct teaching is performed with the workpiece (workpiece) provided on another device, and when attaching a workpiece (workpiece) to the tip member 40, direct teaching is performed with the working body provided on another device.

[0050] 1 and 9 , when teaching the tip side link hub 13 by direct teaching, the attitude calculation means 74 calculates the attitude of the tip side link hub 13 by forward transformation from the position of the actuator 10 with no preload applied to the parallel mechanism. The attitude of the tip side link hub 13 calculated by the attitude calculation means 74 through forward transformation is the bend angle and rotation angle of the tip side link hub 13.

[0051] The actuator position calculation means 75 calculates, by inverse transformation, the rotational position (position) of the actuator 10 in a state where a preload is applied to the parallel mechanism, based on the calculated attitude of the tip side link hub 13. The inverse transformation value, which is the position of the actuator 10 calculated by inverse transformation, is the output value of the absolute type encoder 55 (FIG. 5) that detects the rotational position of the motor, and represents the amount of movement from the origin attitude position of the tip side link hub 13, which has been given a force in advance to move the parallel mechanism to one side.

[0052] 1 stores the attitude of the tip side link hub 13 and the position of the actuator 10 calculated by inverse transformation as a set of taught data. The control device 70 controls the positioning of the actuator 10 based on the taught data stored in the taught data storage means 76.

[0053] The posture calculation means 74 calculates the posture (θn, φn) of the tip side link hub 13 by forward transformation (forward kinematics) from the actuator rotational position (M1n, M2n, M3n) relative to the rotational angle (β1n, β2n, β3n) of the base side end link member 15 in an unpreloaded state at the teaching position n (position n in Table 1) selected by the operator during direct teaching.

[0054] Specifically, the attitude (θn, φn) of the tip side link hub 13 is calculated by performing a forward transformation on the following relational expression (1). Here, ε0 in equation (1) is calculated using equation (2). The rotation angle and the actuator rotation position are associated in advance by a relationship setting means such as a map or a relational expression. Note that the teaching position n selected during direct teaching may be only one final attitude of the tip side link hub 13, or may include multiple attitudes of the tip side link hub 13 ranging from any attitude to the final attitude.

[0055]

[0056] where γ is the angle (crossing angle) formed between the connecting end axis of the central link member 17 rotatably connected to the base end link member 15 and the connecting end axis of the central link member 17 rotatably connected to the tip end link member 16; α is the angle formed between the connecting end axis of the central link member 17 rotatably connected to the base end and tip end link members 15, 16 and the connecting end axes of the base end and tip end link hubs 12, 13 rotatably connected to the base end and tip end link members 15, 16; δn (n = 1, 2, 3, ...): the circumferential separation angle of each base end end link member 15 from the reference base end end link member 15; εn (n = 1, 2, 3, ...): the circumferential separation angle of each rotation pair from the reference phase on the circumference through which the rotation pairs of the base end link member 15 and the central link member 17 pass.

[0057] The actuator position calculation means 75 calculates the actuator rotational position (M1n+Preload1, M2n+Preload2, M3n+Preload3) corresponding to the rotational angle of the base-end side end link member 15 in a preloaded state by inverse transformation (inverse kinematics) based on the calculated attitude (θn, φn) of the tip-end side link hub 13. Specifically, by inversely transforming the following relational expression (1), the rotational angle βn of the base-end side end link member 15 is calculated, and the actuator rotational position (M1n+Preload1, M2n+Preload2, M3n+Preload3) corresponding to this rotational angle βn is calculated. The rotational angle βn and the actuator rotational position are associated in advance by a relationship setting means such as a map or a relational expression.

[0058] where γ is the angle (crossing angle) formed between the connecting end axis of the central link member 17 rotatably connected to the base end link member 15 and the connecting end axis of the central link member 17 rotatably connected to the tip end link member 16; α is the angle formed between the connecting end axis of the central link member 17 rotatably connected to the base end and tip end link members 15, 16 and the connecting end axes of the base end and tip end link hubs 12, 13 rotatably connected to the base end and tip end link members 15, 16; δn (n = 1, 2, 3, ...): the circumferential separation angle of each base end end link member 15 from the reference base end end link member 15; εn (n = 1, 2, 3, ...): the circumferential separation angle of each rotation pair from the reference phase on the circumference through which the rotation pairs of the base end link member 15 and the central link member 17 pass.

[0059] The teaching data storage means 76 stores the attitude (θn, φn) of the tip side link hub 13 and the actuator rotational position (M1n+Preload1, M2n+Preload2, M3n+Preload3) as teaching data, enabling highly accurate positioning control.

[0060] 7 is a diagram showing the configuration of a positioning control system using a link actuator 7. The control device 70 includes, for example, a controller 71 for the link actuator, drivers 77a, 77b, and 77c for each actuator, a storage device (external storage device) 78, and an input device 72. The control device 70 is electrically connected to, for example, a personal computer 73, which is an external device, and a host PLC (Programmable Logic Controller) 79, which is a host control device. The host PLC 79 controls, for example, a linear actuator (not shown) in synchronization with the link actuator 7.

[0061] As shown in FIG. 8, the controller 71 has a CPU 80, an internal storage area 81, an external storage device slot 82, a general-purpose communication interface 83, a display 84, a LAN interface 85, a field network interface 86, an input / output interface I / O, and a power supply unit.

[0062] As shown in Figures 1 and 8, the CPU 80 of the controller 71 stores the above-mentioned attitude calculation means 74 and actuator position calculation means 75. A teaching data storage means 76 (Figure 1) is stored in an internal storage area 81 of the controller 71 or in a storage device 78 shown in Figure 7, which is an external storage device. As shown in Figures 7 and 8, the storage device 78 is removably installed in an external storage device slot 82 of the controller 71, or is connected by communication via a general-purpose communication interface 83 of the controller 71. The teaching data is stored in at least one of the internal storage area 81 of the controller 71, the storage device 78, and the personal computer 73, which is an external device.

[0063] <Flowchart for Direct Teaching> Figure 10 is a flowchart showing the steps of the process for teaching the link actuator by direct teaching. The description will also refer to Figures 1 and 7 as appropriate. After starting this process, the controller 71 determines whether or not teaching by direct teaching has been selected (step S1). When the operator operates the operation key 72a of the input device 72, which indicates the start of direct teaching (step S1: YES), the control shifts from positioning control to torque control of the actuator 10 (step S2).

[0064] In step S2, the controller 71 switches off the positioning control of the actuator 10, releases the brake, or limits the output torque value of the actuator 10 and transitions to torque control. Thereafter, when the distal link hub 13 is moved to a desired posture (bend angle, swivel angle) by manual operation (step S3), the process transitions to step S4. In step S4, the posture calculation means 74 calculates the current posture (bend angle θn, swivel angle φn) of the distal link hub 13 by forward transformation (forward kinematics) from the current rotational position (M1n, M2n, M3n) of the actuator 10 relative to the rotation angle of the proximal end link member 15.

[0065] The actuator position calculation means 75 calculates, by inverse transformation (inverse kinematics), the actuator rotational positions (M1n+Preload1, M2n+Preload2, M3n+Preload3) corresponding to the rotational angle of the base-end end link member 15, taking into account the force that shifts the play of the parallel link mechanism 9 to one side, based on the calculated current attitude (bend angle θn, pivot angle φn) of the tip-side link hub 13 (step S5). Next, the teaching data storage means 76 stores the attitude (bend angle θn, pivot angle φn) of the tip-side link hub 13 and the actuator rotational positions (M1n+Preload1, M2n+Preload2, M3n+Preload3) as teaching data (step S6).

[0066] Next, the controller 71 determines whether teaching by direct teaching has ended (step S7). When the operator operates the operation key 72a of the input device 72, which indicates the end of direct teaching (step S7: YES), the actuator 10 is shifted to positioning control (step S8), and this processing ends. If it is determined that teaching has not ended (step S7: NO), the process returns to step S3. After shifting to positioning control, the controller 71 performs feedback control using the output value of the encoder 55 (FIG. 5) so that the rotation angle βn becomes the control target value. This improves positioning control.

[0067] 1 described above, when direct teaching is performed, the actuator position when a preload is applied to the parallel link mechanism 9 and the attitude of the tip-side link hub 13 are stored as a set of teaching data. Therefore, the position of the actuator 10 that eliminates the effects of backlash that occurs in each revolute pair and mechanism, etc., can be stored as teaching data, enabling precise positioning control even during direct teaching.

[0068] According to the link actuator 7, the distal link hub 13 has two degrees of freedom of rotation relative to the proximal link hub 12, allowing for free posture change. This two-degree-of-freedom mechanism is compact, yet allows for a wide range of movement of the distal link hub 13 relative to the proximal link hub 12. Because the actuator 10 is provided in all three or more link mechanisms 14, the distal link hub 13 can be positioned and controlled with higher precision than if actuators were provided in only two of the three link mechanisms 14.

[0069] <Regarding Other Embodiments> In the following description, parts corresponding to matters previously described in each embodiment are assigned the same reference numerals, and duplicated description will be omitted. When only part of the configuration is described, the other parts of the configuration are the same as those in the previously described embodiment unless otherwise specified. The same configuration produces the same effects. It is possible to combine not only the parts specifically described in each embodiment, but also parts of the embodiments together, provided that there is no particular problem with the combination.

[0070] [Second embodiment: Figures 11 to 13] The parallel link mechanism 9 may have an asymmetric structure between the base end and the tip end, as shown in Figure 11. As shown in Figures 12 and 13, the distances L1A, L1B (hereinafter referred to as "link lengths") from the respective spherical link centers PA, PB to the respective rotational pair centers C1A, C1B of the end link members 15, 16 and the central link member 17 are the same on the base end and tip end.

[0071] In contrast, the distances (hereinafter referred to as "arm lengths") L2A, L2B from the respective spherical link centers PA, PB to the respective rotational pair centers C2A, C2B of the link hubs 2, 3 and the end link members 5, 6 are different on the base end side and the tip end side. In the second embodiment, the arm length L2A on the base end side is longer than the arm length L2B on the tip end side.

[0072] Here, the rotation pair center points C1A, C1B, C2A, and C2B refer to the center points in the width direction of the end link members 15 and 16 along the rotation pair axes O1A, O1B, O2A, and O2B of each rotation pair. Even if the arm lengths L2A and L2B are different on the base end and tip end sides, as long as the link lengths L1A and L1B are the same on the base end and tip end sides, the three link mechanisms 14 (FIG. 11) will have the same geometric shape on the base end and tip end sides regardless of the posture of the parallel link mechanism 9.

[0073] As described above, the preferred embodiment has been described with reference to the drawings, but various additions, modifications, and deletions can be made without departing from the spirit of the present invention. Therefore, such additions, modifications, and deletions are also included in the scope of the present invention.

[0074] DESCRIPTION OF SYMBOLS 7...Link actuation device 9...Parallel link mechanism (parallel mechanism) 10...Actuator 12...Base end side link hub 13...Tip end side link hub 14...Link mechanism 15...Base end side end link member 16...Tip end side end link member 17...Central link member 55...Absolute type encoder 70...Control device 71...Controller 72...Input device 73...External device 74...Attitude calculation means 75...Actuator position calculation means 76...Teaching data storage means 78...External storage device 81...Internal storage area

Claims

1. A link actuation device comprising a parallel mechanism in which a tip-side link hub is connected to a base-side link hub via a link mechanism so that its posture can be changed, an actuator that changes the posture of the tip-side link hub, and a control device that controls the actuator, wherein the control device has: posture calculation means that calculates the posture of the tip-side link hub by forward transformation from the position of the actuator when teaching the tip-side link hub by direct teaching and when no preload is applied to the parallel mechanism; actuator position calculation means that calculates the position of the actuator by inverse transformation based on the calculated posture of the tip-side link hub and the position of the actuator when a preload is applied to the parallel mechanism; and teaching data storage means that stores the posture of the tip-side link hub and the position of the actuator calculated by inverse transformation as a set of teaching data.

2. A link actuation device as set forth in claim 1, wherein said control device controls the positioning of said actuator based on teaching data stored in said teaching data storage means.

3. A link actuation device as set forth in claim 1 or claim 2, wherein the parallel mechanism connects the tip-side link hub to the base-side link hub via three or more sets of link mechanisms in a manner that allows its posture to be changed, and each of the link mechanisms has base-side and tip-side end link members, one end of which is rotatably connected to the base-side link hub and the tip-side link hub, respectively, and a central link member, both ends of which are rotatably connected to the other ends of the base-side and tip-side end link members, and wherein all of the three or more sets of link mechanisms are equipped with the actuator.

4. A link actuation device as described in claim 3, wherein the actuator is a motor installed in the base end link hub, and the control device drives the motor to control the bending angle and swivel angle of the tip end link hub.

5. A link actuation device according to claim 4, wherein said motor is capable of positioning control and torque control.

6. A link actuator according to claim 4, wherein said control device limits the output of said motor when teaching of said tip-end link hub is performed by direct teaching.

7. A link actuation device according to claim 1 or claim 2, wherein the attitude of the tip-side link hub calculated by the attitude calculation means through forward transformation is the bending angle and swivel angle of the tip-side link hub.

8. A link actuator according to claim 4, wherein the torque of the motor applies a force that shifts the backlash of the parallel mechanism to one side, thereby applying a preload to the parallel mechanism.

9. A link actuator according to claim 4, wherein the force that shifts the backlash of the parallel mechanism to one side is a force that compresses the parallel mechanism in a predetermined direction.

10. A link actuation device according to claim 4, wherein the inverse transformation value, which is the position of the actuator calculated by inverse transformation, is the output value of an absolute encoder that detects the rotational position of the motor, and represents the amount of movement from the origin position of the tip-side link hub, which has been given a force in advance to move the parallel mechanism to one side.

11. A link actuation device according to claim 1 or claim 2, wherein the teaching data is stored in at least one of an internal storage area of ​​a controller for the link actuation device, an external storage device that is removably installed in the controller or connected to the controller by communication, and an external device.

12. A link actuator according to claim 4, wherein the torque of the motor that applies a force in the direction of pulling the parallel mechanism to one side can be set from an input device or other external device electrically connected to the controller for the link actuator.

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