Torsion Series Elastic Actuator

Abstract

To provide a disc-shaped torsional spring of a spring assembly for a rotary series elastic actuator (SEA) for use in robotic applications.SOLUTION: The SEA includes a motor, a gear transmission assembly, a spring assembly, and sensors. In one example, a robotic joint includes the SEA as well as two links coupled with each other at a joint assembly, the two links being designated as input and output links. Each link has a joint housing body which is concentrically connected so that they freely rotate relative to each other. The housing frame of the SEA is fixed at the joint housing body of the input link while an output mount of the spring assembly may be concentrically coupled with the joint housing body of the output link. When an external force or torque is applied to between the two links, a control action of a control loop may cause a rotation and motive force of the motor that lead to the deflection of the spring assembly to balance with the external force / torque and inertial force from body masses moving together with the links.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 62 / 649,034, filed March 28, 2018, and entitled “TORTION SERIES ELASTIC ACTUATOR,” which is hereby incorporated by reference in its entirety.

[0002] background Unless otherwise indicated herein, the material described in this section is not prior art to the claims of this application and is not admitted to be prior art by inclusion in this section. [Background technology]

[0003] A robot is an automated machine that consists of movable body segments powered by actuators, often DC and AC motors, hydraulic actuators, and pneumatic actuators. In many applications, a robot is designed and controlled to perform a task based on the position, trajectory, or velocity of its body segments. The actuators are typically equipped with gear transmissions to reduce the output speed and increase the output force appropriate for a particular task. Sensors that detect the position or velocity of the actuator's output are typically on board to provide feedback signals to a computing device that controls the actuator's movement. Summary of the Invention [Problem to be solved by the invention]

[0004] In other applications, robots are required to apply precise force or rotational forces to the environment, or are desired to perform tasks based on force for better stability, safety, or efficiency. For example, when physically contacting a rigid environment, a position-controlled robot has a high probability of becoming unstable, whereas a force-controlled robot does not. When interacting or colliding with humans, force-controlled robots are safer because they comply with physical interactions. When assisting human movements, force-controlled robots can provide a more natural interaction because the human body is moved by muscles, which are force-controlled actuators. [Means for solving the problem]

[0005] Position control oriented actuators with gear reduction are usually limited to precisely control the output force without force feedback in the control loop due to force nonlinearities in the gear reduction stage, such as friction and stiction. A Series Elastic Actuator (SEA) is an actuator configuration with a counter element for force measurement that can achieve high performance in force control with several advantages including inherent stability, shock resistance, and safety. The SEA consists of an actuator, a gear transmission assembly, an elastic element (e.g., a spring or a set of springs), and a sensor. One or more sensors in the SEA are used to detect the deflection of the elastic element. The elastic element is usually a spring or a set of springs whose deflection is proportional to the force applied to it. The elastic element or spring with the sensor is placed in series with the actuator to the output of the SEA and acts as a force sensor. A feedback control loop in the control computer using the force feedback signal controls the output force of the SEA. The present invention includes a rotary series elastic actuator that can control precise rotational force (torque). [Brief description of the drawings]

[0006] The detailed description will be set forth with reference to the accompanying drawings, in which the leftmost digit(s) of a reference number identifies the figure in which the reference number first appears. Use of the same reference number in different figures indicates similar or identical components or structures. [Figure 1] FIG. 1 illustrates an exemplary rotational series elastic actuator (SEA), according to some embodiments. [Diagram 2] FIG. 1 illustrates an exemplary robotic joint assembly with an SEA, according to some embodiments. [Diagram 3] FIG. 2 illustrates an exemplary robotic joint assembly, excluding the SEA, in accordance with some embodiments. [Figure 4] FIG. 2 illustrates a cross-sectional view of an exemplary SEA with a robotic joint assembly, in accordance with some embodiments. [Diagram 5] FIG. 2 illustrates a cross-sectional view of an exemplary SEA excluding a robotic joint assembly, in accordance with some embodiments. [Figure 6] FIG. 2 illustrates another exemplary cross-sectional view of an SEA, excluding an attached joint assembly, in accordance with some embodiments. [Figure 7] 1 illustrates yet another exemplary cross-sectional view of an SEA, excluding an attached joint assembly, according to some embodiments. [Figure 8] 1A-1C illustrate an exemplary spring assembly that may be incorporated into an SEA, according to some embodiments. [Figure 9] FIG. 1 illustrates the internal mechanisms within a spring assembly of an SEA, according to some embodiments. [Figure 10] 1 illustrates an exemplary tool tip designed to tighten a string in the internal mechanism of a spring assembly, according to some embodiments. [Figure 11] 2 illustrates an exemplary disc spring of a spring assembly of an SEA, according to some embodiments. [Figure 12] FIG. 2 illustrates a top view of an exemplary disk-shaped spring of a spring assembly of an SEA, according to some embodiments. [Figure 13]FIG. 2 illustrates another exemplary disc spring of a spring assembly of an SEA, according to some embodiments. [Figure 14] FIG. 2 illustrates another exemplary disc spring of a spring assembly of an SEA, according to some embodiments. [Figure 15] 1 illustrates an exemplary internal mechanism of a spring assembly of an SEA and a bottom torsion spring of a disc spring, according to some embodiments. [Figure 16] 1 illustrates an exemplary arrangement of a spring assembly of an SEA, according to some embodiments. [Figure 17] 4 illustrates another exemplary arrangement of a spring assembly of an SEA, according to some embodiments. [Figure 18] FIG. 3 illustrates a side view of a spring assembly of an SEA with spacer 314 removed, according to some embodiments. [Figure 19] 1 illustrates an exemplary exploded view of a spring assembly of an SEA, according to some embodiments. [Figure 20] 1 illustrates an exemplary portion of a disc spring under stress, according to some embodiments. [Figure 21] 1 illustrates an exemplary portion of a disc spring under stress, according to some embodiments. [Figure 22] FIG. 2 illustrates another exemplary exploded view of a robotic joint assembly with an SEA 10, according to some embodiments. [Figure 23] FIG. 2 illustrates an exemplary diagram of an SEA with a protective cover over the spring assembly, according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Described herein are implementations and embodiments of an exemplary actuator assembly for robotic applications, including a rotary-type Series Elastic Actuator (SEA). The SEA includes a motor, a gear transmission assembly, a spring assembly, and a sensor. The stationary components of the motor and gear transmission are typically fixed to the SEA housing frame. The rotational output of the motor is connected to the input of the gear transmission, and the output of the gear transmission is coupled to the input mount of the spring assembly.

[0008] The spring assembly may include two disk-shaped springs, an internal mechanism, and a rotational position sensor. The disk-shaped spring may include concentric, circular inner and outer mount segments and a set of elastically deformable spirals connecting the inner and outer mount segments. The two outer mount segments of the two springs may be coupled to each other via a spacer. The two inner mount segments of one spring and the other spring are designated as the input and output mounts of the spring assembly, respectively. The internal mechanism may be disposed between the two spring layers and configured to amplify the deflection of the spring assembly between the input and output mounts. The rotational position sensor may be coupled to the internal mechanism to read the amplified deflection. The sensor reading of the spring deflection is converted to a torque value and transmitted back to the control loop.

[0009] In a robotic joint, there may be two links coupled to each other through a joint assembly. The two links are designated as input and output links. Each link may have a joint housing body that may be concentrically connected through a joint bearing, and they are free to rotate with respect to each other. The housing frame of the SEA may be fixed to the joint housing body of the input link, while the output mount of the spring assembly of the SEA may be coaxially coupled to the joint housing body of the output link. Rotation of the motor rotor relative to the motor stator results in rotation of the output link relative to the input link, plus deflection of the spring, if any. When an external force or torque is applied between the two links, the control action of the control loop may result in rotation of the motor and motive force leading to deflection of the spring assembly to balance the external force / torque and the inertial force from the body mass moving with the links.

[0010] 1 illustrates an exemplary embodiment of a rotary series elastic actuator (SEA) 10. The rotary SEA includes a motor 100, a gear transmission assembly 200, a spring assembly 300 with a sensor (e.g., absolute encoder) 334, and another sensor (e.g., absolute encoder). Additional components and detailed aspects of the SEA 10 are further described in the following paragraphs in association with additional figures.

[0011] The motor 100 may be a rotary direct current (DC) motor, an alternating current (AC) motor, a hydraulic motor, or a pneumatic motor, among other possibilities. For example, the motor type may be a brushless DC motor, which may require additional sensors (e.g., Hall effect sensors or quadrature encoders) for commutation. The motor may include a stationary part (stator), a rotating part (rotor), and a motor output shaft attached to the rotor. The motor generates rotational motion and motive force on the motor shaft.

[0012] The gear transmission assembly 200 may include a set of gear transmission components and an SEA housing frame to which a stationary part of the gear transmission set is fixed. A stator of the motor 100 may also be commonly fixed at the SEA housing frame. In one exemplary robot joint assembly, the SEA housing frame may be fixed at one robot link. The gear transmission set may have an input, an output, and a stationary part. For example, in some cases, the gear transmission may be a harmonic drive composed of a wave generator, a flexspline, and a circular spline. In a preferred configuration of the present invention, the wave generator, the flexspline, and the circular spline may be assigned as the input, output, and stationary parts of the gear transmission set, respectively. The motor output shaft may be coupled to the input part of the gear transmission assembly 200 to transmit the rotational motion and motive force to the gear transmission. The output part of the gear transmission assembly 200 may be coupled to the transmission output part. The rotational speed of the output part of the gear transmission 200 may be reduced from the rotational speed of the input part of the gear transmission 200 by a factor of the gear reduction ratio, but the motive power applied to the input part of the gear transmission 200 from the motor 100 may be amplified at the output part of the gear transmission 200 by a factor of the gear reduction ratio.

[0013] The sensor 250 may be an absolute encoder or a potentiometer, among other possibilities, and may include a rotating shaft connected to a transmission output of the gear transmission 200 via a timing belt. The sensor 250 may measure the angle of rotation of the output of the gear transmission assembly.

[0014] The spring assembly 300 may include two torsion springs 360, a spacer, and an internal mechanism with a sensor 334. Each of the two torsion springs 360 includes a circular inner mount segment 364, a circular outer mount segment 366, and a set of elastically deformable spirals 362 connecting the inner and outer segments. The two springs are coupled to each other via a spacer, and the internal mechanism is between the two springs. One spring of the spring assembly 300 has an input mount, and the other spring has an output mount. The input mount of the spring assembly 300 may be coupled with a transmission output of the gear transmission set 200, and the output mount of the spring assembly 300 may be connected to another robot link. The internal mechanism with a sensor 334 (e.g., an absolute encoder) detects the rotational deflection of the spring assembly 300 between the input mount and the output mount. The spring deflection may be proportional to the applied torque applied between the input and output mounts of the spring assembly, so that the measurement signal of the sensor 334 may be converted to a measured torque applied to the spring assembly. The measured torque may be fed back to a feedback control loop that may control the motor 100 to generate a desired torque at the output mount of the spring assembly. When an external torque equivalent to the desired torque in the control loop is applied to the output mount of the spring assembly, the control action of the motor causing a rotational motion and force of the output of the gear transmission may deflect the spring assembly to generate a desired torque that balances the external torque. Meanwhile, the rotational position or speed of the output mount of the spring assembly may be controlled by a feedback control loop that controls the rotational motion of the motor 100 using a commutation sensor of the motor 100 or a position feedback signal from the sensor 250. The angular position of the output mount of the spring assembly may be the sum of the angular position of the output portion of the gear transmission and the deflection angle of the spring assembly 300. The angular position of the gear transmission output can be measured directly by sensor 250 and converted from the multi-turn motor angle.

[0015] FIG. 2 shows an example of a robot joint assembly that may include an SEA 10, an input link 40, and an output link 50. The SEA housing frame of the SEA 10 may be attached to the joint housing body 42 of the link 40, while the output mount of the spring assembly 300 of the SEA 10 is coupled to the joint housing body 52 of the output link 50 through a joint. In the joint, an outer ring of a joint bearing (e.g., a cross roller bearing) may be fixed to the joint housing body 42 of the input link. One side of a bore shaft located at an inner ring of the joint bearing may be coupled to the joint housing body 52 of the output link 50, and the other side of the bore shaft may be coupled to the output mount of the spring assembly 300 of the SEA 10. The SEA 10 generates a motive torque that is transmitted to the output link 50. The output link may be rotated relative to the link 40 about the axis 30 and may exert a force on the environment.

[0016] FIG. 3 shows an example of a robot joint assembly excluding the SEA 10. The bore shaft 60 has its outer ring attached to the inner ring of a joint bearing, which is attached to the joint housing body 42. The upper mounting section 64 of the bore shaft 60 may be coupled to the output mount of the spring assembly 300 of the SEA 10. The opposite end of the bore shaft 60 is coupled to the joint housing body 52 of the link 50. The bore shaft may have through holes 68 for power cables or sensor lines to pass through the joint. The protruding portion 66 of the bore shaft 60, together with the protruding portion 48 of the joint housing body of the link 40, may act as a hard stop, limiting the rotation angle of the link 50 relative to the link 40.

[0017] FIG. 4 shows a cross-sectional view of an exemplary embodiment of the SEA 10 with articulation assembly. As described above, the SEA 10 includes the motor 100, the gear transmission assembly 200, and the spring assembly 300. The SEA housing frame 211 of the SEA 10 is attached to the joint housing body 42, and the spring assembly 300 is disposed inside the joint housing body 42. The output mount of the spring assembly 300 of the SEA 10 is coupled to the upper mount section 64, FIG. 3, of the bore shaft 60, whose other side mount is coupled to the other joint housing body 52. ​​The rounded center portion of the bore shaft 60 has its outer ring fitted into the inner ring of the joint bearing 62, which is fixed to the joint housing body 42. The joint bearing 62 is preferably a cross roller bearing that supports all-directional loads from the link 50, FIG. 3, and allows free rotation only with respect to the axis 30, FIG. 2. Thus, the output mount of the spring assembly 300, the bore shaft 60, and the joint housing body 52 are rigidly connected and rotate together relative to the joint housing 42. The rotational angle of the joint housing body 52 relative to the joint housing body 42 or the SEA housing frame 211 is the sum of the transmission output 240 and the rotational deflection of the spring assembly 300 between the input and output mounts. With a properly controlled motive force from the motor 100, the rotational deflection of the spring assembly 300 can be proportional to the torque applied to the joint housing body 52 relative to the housing body 42.

[0018] More specifically, Figure 5 shows a cross-sectional view of the SEA 10 in another plane, excluding the articulation assembly. The stationary portion of the motor 100 may be attached to the motor base 106, while the motor shaft 104 is rigidly coupled to the input of the gear transmission, the Harmonic Drive® wave generator 222, via a shaft coupler 234 and a coupler clamp 232. The shaft coupler 234 is fixed to the wave generator 222. The shaft coupler 234, which slides on the motor shaft 104, has a tapered circumference with several slots in the axial direction, into which a ring-type coupler clamp 232, with a female portion of the tapered circumference, is seated. Tightening a set of screws axially connecting the shaft coupler 234 and the coupler clamp 232, contracts the tapered circumference of the shaft coupler 234, forming a rigid connection between the shaft coupler 234 and the motor shaft 104.

[0019] The stationary part of the gear transmission, the circular spline 226 of the Harmonic Drive®, is fixed to the SEA housing frame 211. The output of the gear transmission, the flexspline 224, is attached to the input mount of the spring assembly 300 via the transmission output 240 which is fixed to the SEA housing frame 211 via a bearing 212. The bearing 212 is preferably a four-point contact thin wall bearing or a cross roller bearing and may be fixed to the transmission output 240 by an inner bearing cap 214 and to the SEA housing frame 211 by an outer bearing cap 216. The Harmonic Drive® components are assembled in a typical manner where the outer ring of the wave generator 222 slides on the inner circumference of the flexspline 224 while the toothed circumferential portion of the flexspline 224 meshes with the toothed portion of the inner circumference of the circular spline 226.

[0020] 5, transmission output 240 may include a concentrically assembled timing belt pulley 244 that may be coupled to sensor 250 via sensor input pulley 258 and timing belt 248. Sensor 250 may be secured to SEA housing frame 211 via sensor holder 254. Sensor 250 is preferably an absolute encoder or potentiometer and may be used to read the absolute angular position of link 50, FIG. 3, relative to link 40, FIG. 3. Further details regarding spring assembly 300 are described below with respect to FIGS. 8-19.

[0021] FIG. 6 shows a cross-sectional view of another exemplary SEA 10A embodiment without the articulation assembly attached. Similar to the SEA 10 of the examples of FIGS. 4 and 5 described above, the SEA 10A includes a stationary component (stator) 102A attached to a motor housing 106A, with a motor rotor 104A concentrically disposed inside the stator and attached to a motor rotor holder 232A. The motor rotor holder 232A is coupled to the motor housing via a bearing 107A, such that the motor rotor 104A and rotor holder 232A are free to rotate relative to the stator 102A. One side of the rotor holder 232A is fixed to a motor shaft 234A, which is coupled to a wave generator 222A of a harmonic drive®, which is the input part of a gear transmission. A non-contact sensor 105A consisting of a circular rotor and a stationary component (e.g., a quadrature or absolute encoder) may be assembled on the opposite side of the rotor holder 232A. The stationary portion of the sensor 105A is attached to an extension of the motor housing 106A, while the circular rotor of the sensor 105A is concentrically coupled to the rotor holder 232A. The sensor 105A may be used for motor commutation and / or sensing the position of the motor rotor 104A and the transmission output 240A.

[0022] The stationary part of the gear transmission, the circular spline 226A of the harmonic drive®, is fixed to the SEA housing frame 211A to which the motor housing 106A is attached. The output part of the gear transmission, the flexspline 224A, is attached to the input mount of the spring assembly 300 of FIG. 5 via the transmission output section 240A, which is fixed to the SEA housing frame 211A via the bearing 212A. The bearing 212A is preferably a four-point contact thin-walled bearing or a cross-roller bearing, and may be fixed to the transmission output section 240A by the inner bearing cap 214A and to the SEA housing frame 211A by the outer bearing cap 216A. The motor shaft 234A may be extended and connected to the central hole of the transmission output section 240A via the bearing 109A to more firmly support the rotor holder 232A against the motor stator 102A. The Harmonic Drive® components are fitted together in a typical manner, with the toothed circumferential portion of the flexspline 224A meshing with the toothed portion on the inner circumference of the circular spline 226A, and the outer ring of the wave generator 222A sliding against the inner circumference of the flexspline 224A.

[0023] Transmission output 240A may include a concentrically assembled timing belt pulley 244A that may be coupled to sensor 250, FIG. 5, via a sensor input pulley and a timing belt. Sensor 250 may be fixed to SEA housing frame 211A. Sensor 250 may be an absolute encoder or potentiometer and may be used to read the absolute angular position of link 50, FIG. 3, relative to link 40, FIG. 3.

[0024] 7 shows yet another cross-sectional view of another exemplary SEA 10B embodiment without the articulation assembly attached. The stationary part (stator) 102B of the motor 100B is attached to the motor housing 106B, while the motor rotor 104B is concentrically disposed inside the stator and attached to the motor rotor holder 232B. The motor rotor holder 232B is coupled to the motor housing via two bearings 107B and 109B, so that the motor rotor 104B and rotor holder 232B rotate freely relative to the stator 102B. One end of the rotor holder 232B is fixed to the Harmonic Drive® wave generator 222B, which is the input of the gear transmission. One end of the rotor holder 232B, which slides into the central bore of the wave generator 222B, has a tapered cylindrical bore with several slots in the axial direction, into which the male counterpart of the tapered cylindrical bore, the tapered cylinder 234B, is seated. Tightening a set of screws that axially connect the rotor holder 232B and the tapered cylinder 234B, causes the bore of the tapered cylinder to bulge against the wall of the central bore of the wave generator 222B, creating a rigid connection between the rotor holder 232B and the wave generator 222B. A non-contact sensor 105B (e.g., a quadrature encoder or absolute encoder), consisting of a circular rotor and a stationary part, can be assembled on the opposite side of the rotor holder 232B. The circular rotor of the sensor 105B is concentrically coupled to the rotor holder 232B, while the stationary part of the sensor 105B is attached to an extension of the motor housing 106B. The sensor 105B may be used for motor commutation and / or sensing the position of the motor rotor 104B and the transmission output 240B.

[0025] The stationary part of the gear transmission, the harmonic drive® circular spline 226B, is fixed to the SEA housing frame 211B to which the motor housing 106B is attached. The output part of the gear transmission, the flexspline 224B, is attached to the input mount of the spring assembly 300 of FIG. 5 via the transmission output section 240B, which is fixed to the SEA housing frame 211B via a bearing 212B. The bearing 212B is preferably a four-point contact thin wall bearing or a cross roller bearing and may be fixed to the transmission output section 240B by an inner bearing cap 214B and to the SEA housing frame 211B by an outer bearing cap 216B. Harmonic Drive® components are assembled in the typical manner such that the outer ring of wave generator 222B slides circumferentially around flexspline 224B while the toothed circumferential portion of flexspline 224B meshes with the toothed inner circumferential portion of circular spline 226B.

[0026] Transmission output 240B may include a concentrically assembled timing belt pulley 244B that may be coupled to sensor 250, FIG. 5, via a sensor input pulley and a timing belt. Sensor 250 may be fixed to SEA housing frame 211B. Sensor 250 is preferably an absolute encoder or potentiometer and may be used to read the absolute angular position of link 50, FIG. 3, relative to link 40, FIG. 3.

[0027] FIG. 8 shows an exemplary embodiment of a spring assembly 300 including two flat circular torsion springs 360 with a sensor 334 for detecting spring deflection, a spacer 314, and an internal mechanism 320, shown in FIG. 9 below. The flat circular torsion spring 360 consists of a circular inner mount segment 364, a circular outer mount segment 366, and a set of elastically deformable spirals 362 connecting the inner and outer segments. The inner mount segment 364 and the outer mount segment 366 are concentric. The outer segments 366 of the two springs are concentrically stacked and firmly connected to each other via the spacer 314. The internal mechanism 320, shown in FIG. 9 below, for detecting spring deflection is disposed between the two springs 360 and is connected to the sensor 334. The inner mount segments 364 of the two springs 360 are designated as the input and output mounts of the spring assembly 300, respectively. For convenience in cabling the sensor 334 , the inner mounting segment 364 on the side of the sensor 334 may preferably be the output mount of the spring assembly 300 .

[0028] FIG. 9 shows the internal mechanism 320 of the spring assembly 300, which may include a base arm 356, a swing arm 322, a string 342, and a pulley 344. For example, the internal mechanism 320 may be disposed in an internal cavity of a spacer 314 in the spring assembly 300. The central portion 357 of the base arm 356 may be fixed to the inner surface of the inner mount segment 364 of one spring 360. The two arms of the base arm 356 may extend over the spring surface without exceeding the inner diameter of the outer mount segment 366 of the spring 360 of FIG. 6. At both ends of the arms, two pulleys 344 may be connected to the base arm 356 via bearings for free rotation. The stationary portion of the sensor 334, which appears in FIG. 8, may be attached to the central portion 357 of the base arm concentrically with the inner mount segment 364 of the spring 360 of FIG. 8, with the exposed portion of the rotating shaft 336 of the sensor 334 outside the base arm as the sensor input. The center portion 327 of the swing arm 322 may be fixed to the inner surface of the inner mount segment 364 on the other spring in FIG. 8. The two arms of the swing arm 322 may be splayed on the surface of the other spring, but not exceeding the inner diameter of the outer mount segment 366 of the other spring 360. The end portions of the two arms of the swing arm 322 may be formed as a circular arc whose center may coincide with the center of the inner mount segment 364 of the spring 360. The base arm 356 and the swing arm 322 may be configured such that the end portions of the two arms of the swing arm 322 are located on the same side of the splayed arms of the base arm, are at the same height as the two pulleys on the base arm, and do not have physical contact during their relative rotation with respect to the axis 310 connecting the two center points of the two springs 360.

[0029] 9, a string 342 (e.g., a Vectran or Kevlar string), one end of which may be attached to the end of one arm of the swing arm 322, passes through an arc 329 of one arm of the swing arm 322 and one pulley 344 of the base arm 356, wraps around the sensor shaft 336, passes through the other pulley 344 of the base arm 356 and the arc 329 of the other arm of the swing arm, and is secured at the end of the other arm of the swing arm 322. At both ends of the swing arm, each end of the string 342 may be attached to the swing arm body using two screws. During securing, the string may be tensioned appropriately. When the swing arm 322 (or the inner mount segment 364 of the spring 360) rotates relative to the base arm (or the inner mount segment 364 of the other spring 360) during elastic deflection of the spring 360, the relative rotation of the swing arm 322 may be amplified and transmitted to the rotating shaft 336 of the sensor 334. The amplification factor may be proportional to the ratio between the radius of the arc at the swing arm and the radius of the sensor shaft 336. The amplification ratio may be between 1:5 and 1:30. In this embodiment, the mechanism 320 has a ratio of about 1:16, which when combined with the 14-bit absolute encoder of the sensor 334, creates a total of about 18 bits of resolution in detecting spring deflection. If the spring assembly 360 has a stiffness of 400 Nm / rad, the mechanism 320 with 18 bits of resolution may detect a change in torque applied to the spring assembly of about 0.01 Nm. In other examples, mechanism 320 may have a ratio in the range of about 1:8 to 1:24 and spring assembly 360 may have a stiffness in the range of about 200 Nm / rad to about 600 Nm / rad. In some particular examples, mechanism 320 may have a stiffness in the range of about 200 Nm / rad to about 900 Nm / rad.

[0030] As a detailed explanation of tensioning the string, FIG. 10 shows a tool tip 400 designed to tighten the string 342 of FIG. 9 during the assembly process. One end of the string 342 is fixed with two screws 394 at the end of one arm of the swing arm 322 of FIG. 9, and the other end of the string can be tightened and fixed to the end of the other arm of the swing arm 322 using the tool tip 400 and the two screws 394 shown in FIG. 9 above. The tool tip 400 can have an integral small cylindrical portion 410 and a large cylindrical portion arranged axially concentrically. In the large cylindrical portion there can be an open hole 422 for a hex key or equivalent and one or more slots 426 at the end of the cylinder into which the string 342 can be hooked. The small cylindrical portion has a concentric through hole for the screw 394. In the process of routing the string 342 around the mechanism 320, as shown in FIG. 9 above, at the end of the other arm of the swing arm 322, the outer screw 394 closer to the arc 329 is loosely tightened so that there is a gap between the screw head and the swing arm body. Another screw 394 inserted into the hole 412 from the hexagonal hole 422 side is slightly tightened into the swing arm body, and the tool tip 400 is coupled to the swing arm body at the location of the inner screw 394. The string 342 then winds around the outer screw under the screw head and around the small cylindrical part 410 and is fixed in the slot 426. Winding the string 342 around the small cylinder 410 by rotating the tool tip 400 with a hexagonal key or equivalent inserted into the hole 422 puts tension on the string. During the tensioning process, friction at the mating surfaces between the tool tip and the swing arm body prevents the tool tip 400 from rotating in the unwinding direction. Once the string 342 is tensioned, the outer screw 394 is tightened to secure the string 342 to the swing arm body 322. For a secure lock, the tool tip 400 can be removed and another screw 394 can re-lock the hanging string end after the first lock.

[0031] As an explanation of the spring 360 of FIG. 6, FIGS. 11-14 show details of an exemplary embodiment of the disk-shaped spring 360. As mentioned above, the spring 360 may include a circular inner mount segment 364, a circular outer mount segment 366, and a set of deformable spirals 362 connecting the inner and outer mount segments. The inner mount segment 364 and the outer mount segment 366 are shaped as concentric circular hoops. There are several through holes and threaded holes in the inner 364 and outer 366 mount segments for connecting other components. The diameter 373 and thickness 371 of the spring 360 may depend on the intended rotational stiffness, the maximum allowable torque, the shape of the deformable spiral, and the strength of the material. For example, the deformable spiral 362 may be formed from a steel alloy material. 11 and 12, the spring 360 has a diameter of about 76 millimeters (mm), a thickness of about 5 mm, a stiffness of about 800 Nm / rad, and a maximum allowable torque of about 35 Nm, with a safety factor of greater than 2 based on the yield strength of the recommended material (e.g., maraging steel C300, or 17-4 stainless steel in the H-900 treatment condition). Thus, the spring assembly 300 of FIG. 8, which includes two springs 360 connected in series, has a stiffness of about 400 Nm / rad and a maximum allowable torque of about 35 Nm.

[0032] As another exemplary embodiment of spring 360 with a change in the shape of the spiral, spring 360A of FIG. 13 has the same outer diameter and thickness, but has a stiffness of about 1000 Nm / rad and a maximum allowable torque of about 50 Nm, with a safety factor of more than 2 for the same material mentioned above. Thus, spring assembly 300 of FIG. 8, including a series connection of two springs 360A, has a stiffness of about 500 Nm / rad and a maximum allowable torque of about 50 Nm. Another change in spring design is the thickness, which is proportional to the stiffness of the spring in the same configuration. For example, if a spring with the same profile as spring 360A has a thickness of about 6 millimeters, the spring will have a stiffness of about 1200 Nm / rad and a maximum allowable torque of about 60 Nm, giving spring assembly 300 of FIG. 8 a stiffness of about 600 Nm / rad. Thus, in some examples, the spring may have a diameter between 60mm and 90mm, and a thickness between 2mm and 8mm. In these examples, the spring stiffness may vary between 200Nm / rad and 1200Nm / rad, and a maximum allowable torque between 25Nm and 60Nm. In other examples, the spring stiffness may vary between 400Nm / rad and 1800Nm / rad, and a maximum allowable torque between 20Nm and 100Nm.

[0033] Spiral 362 has an inner thick section 363 near inner mount segment 364, a middle thin section 365, and an outer thick section 367 near outer mount segment 366. When the thickness is measured perpendicular to the centerline between the two boundary splines of the spiral, the ratio of the thickness of the thickest part of inner thick section 363 to the thinnest part of center thin section 365 to the thickest part of outer thick section 367 is about 10:1:9 for spring 360 of FIG. 12 and about 9:1:8 for spring 360A of FIG. 13. Also, the thinnest thickness of middle thin section 365 is about 1.36 mm for spring 360 of FIG. 12 and about 1.47 mm for spring 360A of FIG. 13. In some examples, the center thin section can be between 1.00 mm and 1.70 mm for either spring 360 or 306A. The spiral 362 starting from the inner mount segment 364 may wind around the inner mount segment 364 while successively approaching the outer mount segment 366. The spiral is configured to wind around as much as possible (more than a semicircle in springs 360 and 360A) without touching each other, occupying most of the inner area between the inner 364 and outer 366 mount segments, minimizing the diameter 373 and thickness 371 of spring 360 in FIG. 13 for a given stiffness and maximum allowable torque. The splines of the spiral are configured so that deformation of the spiral occurs evenly throughout the spiral body without stress concentrations when torque acts between the inner 364 and outer 366 mount segments. The curvature of the inner sharp corner 375 and the outer sharp corner 376 may be designed to avoid stress concentrations.

[0034] 14 illustrates another exemplary disk-shaped spring of spring assembly 300 of SEA 10, according to some embodiments. As another exemplary embodiment of spring 360B with a changed spiral shape and number of spirals, spring 360B of FIG. 14 has a smaller outer diameter than springs 360 and / or 360A, but the same thickness. For example, spring 360B has a diameter of 66 mm and a thickness of 5 mm, but has a stiffness of about 820 Nm / rad, a maximum allowable torque of about 30 Nm, and a safety factor of greater than 2 for the same materials as springs 360 and / or 360A described above.

[0035] While springs 360, 360A, and 360B described above are three example springs that may be used with SEA 10, it should be understood that other arrangements of springs 360 may also be used. For example, springs having five or more deformable spirals may be used.

[0036] FIG. 15 shows an exemplary internal mechanism 320 of an SEA and a bottom torsion spring 360 of a disc spring of a spring assembly, according to some embodiments. The spring 360 may include a circular inner mount segment 364, a circular outer mount segment 366, and a set of deformable spirals 362 connecting the inner and outer mount segments. The internal mechanism 320 may include a base arm 356, a swing arm 322, a string 342, and a pulley 344. As shown, the internal mechanism 320 is placed on the bottom spring 360 within an internal cavity created by a spacer 314. In the current example, two pulleys 344 may be connected to the base arm 356 via bearings for free rotation at either end of the arm. Again, FIG. 10 shows a tool tip 400 designed to tighten the string 342 secured by a screw 394 at the end of each arm of the swing arm 322.

[0037] 16 and 17 show example arrangements of spring assemblies 300A and 300B of an SEA 10, according to some embodiments. In spring assembly 300A, the spirals 362 of both the top and bottom springs 360 are oriented in the same direction. However, the springs 360 are offset from one another by 90 degrees, so that the spirals 362 are also offset by 90 degrees. In spring assembly 300B, the top and bottom springs are aligned along the X and Y axes (e.g., not offset from one another), but the spirals 362 are oriented in opposite directions.

[0038] While the spring assemblies 300A and 300B described above are two example assemblies that may be used with the SEA 10, it should be understood that other arrangements of the spring assembly 300 may also be used. For example, the spring assembly 300 may have a pair of matching springs 360 that may be arranged in the same direction, with the spirals aligned along the X and Y axes. In another example, the spring assembly 300 may utilize two different springs, such as springs 300A and 300B.

[0039] FIG. 18 shows a side view of the spring assembly 300 of the SEA 10 with the spacer 314 removed, according to some embodiments. In the current example, the spring assembly 300 includes an internal mechanism 320 with two flat and circular torsion springs 360 and a sensor 334 that detects the deflection of the springs 360. As shown, the two springs are stacked concentrically and offset from each other in the Z direction. The two springs 360 are also securely coupled to each other via a fastener 393 that extends through both the springs 360 and the spacer 314, as shown below with respect to FIG. 19. In general, the internal mechanism 320 located between the two springs 360 is configured to detect the deflection of the springs 360 with the sensor 334. In some cases, the swing arm 322 of the internal mechanism 320 may be disposed within an internal cavity of the spacer 314.

[0040] FIG. 19 shows an exemplary exploded view of a spring assembly 300 of the SEA 10, according to some embodiments. The spring assembly 300 includes two flat circular torsion springs 360, a spacer 314, and an internal mechanism 320 with a sensor 334 for detecting spring deflection. Each of the flat circular torsion springs 360 consists of a circular inner mount segment 364, a circular outer mount segment 366, and a set of elastically deformable spirals 362 connecting the inner and outer segments. The outer segments 366 of the two springs are stacked concentrically and rigidly coupled to each other via the spacer 314. The internal mechanism 320 for detecting spring deflection is disposed between the two springs 360 and coupled to the sensor 334. The inner mount segments 364 of the two springs 360 are designated as the input and output mounts of the spring assembly 300, respectively. For convenience in cabling the sensor 334, the inner mount segment 364 on the side of the sensor 334 may preferably be the output mount of the spring assembly 300. In the present example, the springs 360 are aligned so that each set of elastically deformable spirals 362 run in opposite directions. However, in other embodiments, the springs 360 are aligned so that each set of elastically deformable spirals 362 run in the same direction or are stacked.

[0041] In some cases, the internal mechanism 320 of the spring assembly 300 may include a base arm 356, a swing arm 322, and a pulley 344. For example, the internal mechanism 320 may be disposed within the internal cavity of the spacer 314 as shown within the spring assembly 300. The base arm 356 may be fixed to the inner surface of the inner mount segment of the spring 360. The two arms of the base arm 356 may extend over the spring surface to an extent not exceeding the inner diameter of the outer mount segment of the spring 360. At both ends of the arms, two pulleys 344 may be connected to the base arm 356 via bearings for free rotation. The stationary portion of the sensor 334 may be attached to the base arm concentrically with the inner mount segment of the spring 360.

[0042] As the swing arm 322 rotates relative to the base arm 356 during elastic deflection of the spring 360, the relative rotation of the swing arm 322 may be amplified and transmitted to the rotating shaft 336 of the sensor 334. The amplification factor may be proportional to the ratio between the radius of the arc at the swing arm and the radius of the sensor shaft 336. The amplification ratio may be between 1:5 and 1:30. In some cases, the mechanism 320 has a ratio of about 1:16, which when combined with the 14-bit absolute encoder of the sensor 334, creates a total of about 18 bits of resolution in detecting the deflection of the spring. For example, if the spring assembly 360 has a stiffness of 400 Nm / rad, the mechanism 320 with 18-bit resolution can detect a change of about 0.01 Nm in the torque applied to the spring assembly. In other examples, the mechanism 320 can have a ratio in the range of approximately 1:8 to 1:24 and the spring assembly 360 can have a stiffness in the range of approximately 200 Nm / rad to approximately 900 Nm / rad.

[0043] As described above, the spring 360 may include a circular inner mount segment 364, a circular outer mount segment 366, and a set of deformable spirals 362 connecting the inner and outer mount segments. The inner mount segment 364 and the outer mount segment 366 are shaped as concentric circular hoops. There are several through holes and threaded holes in the inner 364 and outer 366 mount segments for connecting other components. The diameter 373 and thickness 371 of the spring 360 may depend on the intended rotational stiffness, maximum allowable torque, the shape of the deformable spiral, and the strength of the material.

[0044] 20 and 21 show an exemplary portion of a disk-shaped spring 360 under pressure, according to some embodiments. For example, the minimum radius 372 of the sharp corner 375 in FIG. 12 may be 0.6 mm or more, and the minimum radius 374 in FIG. 21 of the sharp corner 376 in FIG. 13 may be 0.57 mm or more. As a result, the spiral 362 can only elastically deform within the intended maximum allowable torque. For example, when a torque of 30 Nm is applied, the stress (von Mises) along the spiral of the spring 360 in FIG. 12 and the spring 360A in FIG. 20 does not exceed about 460 MPa and about 410 MPa, respectively. In this particular example, there are four deformable spirals. A different number of spirals can be employed, but the shape of the spiral can be changed depending on the specific stiffness and maximum allowable torque.

[0045] 12, when the maximum allowable torque is applied between the inner 364 and outer 366 mount segments, multiple points of the spiral body interfere with each other and act as hard stops. When excessive torque rotates the inner mount segment 364 counterclockwise relative to the outer mount segment 366, the four outer narrow channels 381 may cause the central thin section 365 of one spiral 362 to bulge and interfere with the outer thick section 367 of the other spiral 362. The width of the outer narrow channels is about 0.7 mm for spring 360 of FIG. 12 and about 0.8 mm for spring 360A of FIG. 13. Similarly, when excessive torque is applied in the opposite direction, the four inner narrow channels 383 may cause the central thin section 365 of one spiral 362 to contract inward and interfere with the inner thick section 363 of the other spiral 362, preventing excessive deformation of the spirals. The width of the inner narrow channel is approximately 0.8 mm for spring 360 and approximately 0.9 mm for spring 360A. These interferences cause a non-linear increase in the stiffness of spring 360 and act as a hard stop to prevent excessive deformation of the spring if more than the intended maximum allowable torque is applied. In some examples, the outer narrow channel can be between 0.5 mm and 0.9 mm and the inner narrow channel can be between 0.6 mm and 1.1 mm for either spring 360 or 306A.

[0046] FIG. 22 shows another exemplary exploded view of a robot joint assembly with a SEA 10, according to some embodiments. The SEA housing frame of the SEA 10 may be attached to the joint housing body 42 of the link 40, while the output mount of the spring assembly 300 of the SEA 10 is coupled to the upper mount section 64 of the joint housing body 52 of the output link 50 via the joint bearing 62. In the joint, the outer ring of the joint bearing (e.g., a cross roller bearing) may be fixed to the joint housing body 42 of the input link. One side of the bore shaft, which seats on the inner ring of the joint bearing, may be coupled to the joint housing body 52 of the output link 50, and the other side of the bore shaft may be coupled to the output mount of the spring assembly 300 of the SEA 10. The SEA 10 generates a motive torque that is transmitted to the output link 50. The output link may rotate relative to the link 40 about the axis 30 and may exert a force on the environment.

[0047] 23 shows an example diagram of an SEA 10 with a protective cover over the spring assembly, according to some embodiments. In the current example, the rotating SEA 10 includes a motor 100, a gear transmission assembly 200, and a spring assembly 300 with a sensor (e.g., absolute encoder) 334. Additional components and detailed aspects of the SEA 10 are further described in the following paragraphs in conjunction with additional figures.

[0048] 1-23 show various views, examples, and embodiments, it should be understood that the features of FIGS. 1-23 can be applied to any of the embodiments shown. Furthermore, terms such as "about," "approximately," and "substantially" are relative terms, and indicate that although two values ​​may differ, the difference is such that the device or method still provides the indicated or desired result, or that the operation of the instrument or method is not adversely affected to the point that it cannot perform its intended purpose. By way of example and not of limitation, if a height of "about X mm" is described, the lower or upper limit of the height is still "about X mm" if the desired function can be performed or the desired result can be achieved.

[0049] Although the subject matter has been described in language specific to structural features, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the particular features described. Rather, the particular features are disclosed as exemplary forms of implementing the claims.

Claims

1. A disk-shaped torsion spring of a spring assembly for a rotary series elastic actuator, comprising: Circular inner mount, A circular outer mount; and a set of elastically deformable spirals, each of the elastically deformable spirals including an inner thick segment coupled to the circular inner mount, an outer thick segment coupled to the circular outer mount, and an intermediate thin section coupled between the inner thick segment and the outer thick segment; the set of elastically deformable spirals includes at least three individual spirals; 11. A disc-shaped torsion spring, wherein each said elastically deformable spiral prevents at least one other elastically deformable spiral from undergoing undue deformation during use.

2. 2. The disc-shaped torsion spring of claim 1, wherein the relative thickness of the inner thick segment to the intermediate thin section is in a ratio of between 11:1 and 8:1, and the relative thickness of the intermediate thin section to the outer thick segment is in a ratio of between 1:10 and 1:

7.

3. 2. A disc-shaped torsion spring according to claim 1, wherein the torsion spring has a stiffness between 400 Nm / rad and 1800 Nm / rad.

4. 2. A disc-shaped torsion spring according to claim 1, characterized in that the torsion spring has a maximum allowable torque between 20 Nm and 100 Nm.

5. 2. The disc-shaped torsion spring of claim 1, wherein a corner radius of the first elastically deformable spiral at the junction between the outer thick segment and the circular outer mount is 0.57 mm or greater.

6. 2. The disc-shaped torsion spring of claim 1, wherein a corner radius of the first elastically deformable spiral at the junction between the inner thick segment and the circular inner mount is 0.6 mm or greater.

7. 1. A spring assembly for a rotary series elastic actuator, comprising: a first torsion spring including a first set of elastically deformable spirals, a first circular inner mount, and a first circular outer mount; a second torsion spring including a second set of elastically deformable spirals, a second circular inner mount, and a second circular outer mount, the first circular outer mount being coupled to the second circular outer mount via a spacer; and an internal mechanism between the first torsion spring and the second torsion spring, the internal mechanism including a sensor that detects a rotational deflection of the spring assembly and provides the rotational deflection as a measured torque input to a motor controller; 11. A spring assembly, comprising: said first set of elastically deformable spirals and said second set of elastically deformable spirals each including at least three individual spirals.

8. 8. The spring assembly of claim 7, wherein said first torsion spring is concentrically aligned with said second torsion spring.

9. 8. The spring assembly of claim 7, wherein the internal mechanism comprises: a base arm including a first end and a second end; A swing arm including a first arm and a second arm, the first arm and the second arm being formed in an arc shape; a first pulley coupled to the first end of the base arm and configured to rotate freely relative to the base arm; a second pulley coupled to the second end of the base arm and configured to rotate freely relative to the base arm, the second end being opposite the first end; and a string coupled to the first arm of the swing arm and the second arm of the swing arm, the string tensioning the first pulley, a sensor shaft of the sensor, and the second pulley.

10. 10. The spring assembly of claim 9, the swing arm is secured to the first circular inner mount; the base arm is secured to the second circular inner mount; a rotation sensor having a stationary portion fixed to the second circular inner mount, a sensor shaft disposed between the first torsion spring and the second torsion spring and concentrically aligned with the first circular inner mount and the second circular inner mount; the swing arm and the base arm face each other and are configured to rotate relative to each other and with the first and second circular inner mounts in response to torque applied between the first and second circular inner mounts.

11. 10. The spring assembly of claim 9, wherein the string is tensioned first around the first pulley, then around the sensor shaft of the sensor, and then around the second pulley.

12. A torsion spring, Inner mount, Outer mount, a first elastically deformable spiral including an inner thick segment coupled to the inner mount, an outer thick segment coupled to the outer mount, and an intermediate thin section coupled between the inner thick segment and the outer thick segment; a second elastically deformable spiral including an inner thick segment coupled to the inner mount, an outer thick segment coupled to the outer mount, and an intermediate thin section coupled between the inner thick segment and the outer thick segment; a third elastically deformable spiral including an inner thick segment coupled to the inner mount, an outer thick segment coupled to the outer mount, and an intermediate thin section coupled between the inner thick segment and the outer thick segment; Including, 1. A torsion spring, characterized in that each elastically deformable spiral of a set of elastically deformable spirals prevents at least one other elastically deformable spiral from undergoing undue deformation during use.

13. 13. The torsion spring of claim 12, further comprising a fourth elastically deformable spiral, the fourth elastically deformable spiral including an inner thick segment coupled to the inner mount, an outer thick segment coupled to the outer mount, and an intermediate thin section coupled between the inner thick segment and the outer thick segment.

14. 13. The torsion spring of claim 12, wherein the inner mount is circular and the outer mount is circular.

15. 13. The torsion spring of claim 12, wherein the torsion spring is disk-shaped.

16. 13. The torsion spring of claim 12, wherein the torsion spring is associated with a spring assembly for a rotary series elastic actuator.

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