A passive variable stiffness series elastic actuator with a hollow structure

Abstract

The present invention discloses a passive variable stiffness series elastic driver with a hollow structure, which comprises a driving device, a reducer, an elastic element, an encoder, and a hollow shaft frame. Each part is assembled in a shell, and the coaxial positioning of each part is achieved by the hollow shaft frame. The driving device is used to generate a driving torque; the input end of the reducer is connected to the driving device, and the output end is connected to the input end of the elastic element; the elastic element adopts a thin-walled cylindrical torsion spring structure with a passive variable stiffness characteristic, and the output end is connected to an external load, and elastic deformation occurs when subjected to load torque. The encoder is respectively matched with the driving device and the elastic element to measure the rotation angle. The design of the present invention has a high power density, and the passive variable stiffness characteristic can take into account both the torque measurement accuracy under small loads and the control bandwidth under large loads. It is suitable for robots that require bionic joints and helps to improve the current development status of domestic series elastic drivers.

Description

Technical Field

[0001] The present invention relates to robot technology, and particularly to a passive variable stiffness series elastic actuator with a hollow structure. Background Art

[0002] In recent years, the manufacturing industry and robot technology have developed rapidly. The types of robots that require flexible joints, such as legged mobile robots, exoskeleton rehabilitation robots, and collaborative robots, have been increasing continuously, and the demand for flexible joints in the robot field has also been increasing accordingly. Different from traditional rigid actuators, elastic actuators have the advantages of high energy utilization rate, strong impact resistance, high torque measurement accuracy, passive compliance, and bionic characteristics, and have been widely favored and applied in robots that require flexible joints.

[0003] The series elastic actuator is a type of elastic actuator. The adopted solution is to add an elastic element inside the actuator to isolate the impact load between the motor end and the load end, enabling the robot to have physical compliance and better torque control ability, showing the advantages of compliance, safety, high energy utilization efficiency, large output torque, strong impact resistance, and high force control accuracy. However, after comprehensively analyzing the development status of domestic series elastic actuators, it is found that domestic series elastic actuators have various defects such as few types, large volume, low torque, difficult control, and high price, and there is still a large gap with foreign countries in terms of actual application.

[0004] There are two difficult problems that need to be solved urgently for series elastic actuators: one is that due to the introduction of multiple encoders and elastic elements, series elastic actuators often have a larger volume and lower power density, which is not conducive to being arranged on robots; the other is that due to the introduction of elastic elements, the control of series elastic actuators becomes gradually difficult as the load increases. Therefore, if a series elastic actuator with high power density, a hollow structure, and passive variable stiffness ability is designed, it will help to improve the development status of domestic series elastic actuators. Summary of the Invention

[0005] To solve the above problems, the present invention proposes a passive variable stiffness series elastic actuator with a hollow structure, and conducts targeted design on the key components and the layout of each part to achieve a smaller axial length and higher power density, which is mainly used to build the flexible joints of robots.

[0006] The passive variable stiffness series elastic actuator with a hollow structure of the present invention includes a drive circuit board, a drive device, a reducer, an elastic element, an encoder, and a hollow shaft frame, and each part is assembled in a housing.

[0007] The hollow shaft frame is fixed to the housing; the driving device is used to generate a driving torque and is sleeved on the hollow shaft frame through the central hole; the driving device includes a rotor part and a stator part; the stator part is fixed to the housing, and the rotor part is connected to the input end of the reducer.

[0008] The reducer is sleeved on the hollow shaft frame through the central hole. The input end of the reducer is fixed to the rotor of the driving device and is connected to the central frame shaft through bearings; the fixed end of the reducer is fixed to the housing; the output end of the reducer is fixed to the elastic element.

[0009] The elastic element is a thin-walled cylindrical torsion spring with connecting flanges at both ends, having multiple sections of repeatedly bent structures in the circumferential direction and bosses designed axially between adjacent repeatedly bent structures. One end of the elastic element sleeved on the outside of the reducer is used as the input end and is connected to the output end of the reducer; the other end is used as the output end and is connected to the output end cover on one side of the housing; when the elastic unit bears a small load, it exhibits a fixed torsional stiffness; when bearing a large load, the bosses in the elastic unit come into physical contact with the repeatedly bent structures, increasing the torsional stiffness of the elastic unit;

[0010] There are two encoders, which are respectively connected to the driving device and the elastic element; the two encoders are sleeved on the hollow shaft frame through the central hole, and the stator part is fixed to the hollow shaft frame; the rotor parts are respectively fixed to the driving device and the elastic element;

[0011] The driving circuit board is used to receive control instructions to control the output of the driving device; the driving circuit board is fixed on the driving circuit board end cover on the other side of the housing and is connected to the multi-stage winding stator and the two encoders through wires respectively.

[0012] The advantages of the present invention are as follows:

[0013] 1. The present invention has a passive variable stiffness series elastic actuator with a hollow structure. Aiming at the problems of the series elastic actuator being unfavorable for layout, poor controllability, low power density, etc., a hollow shaft structure and a thin-walled cylindrical torsion spring with passive variable stiffness characteristics are adopted. Further, the overall structure has a high power density, can provide space for hollow wiring, and its passive variable stiffness characteristics can take into account the torque measurement accuracy under small loads and the control bandwidth under large loads, and is applicable to occasions such as legged mobile robots, exoskeleton rehabilitation robots, and collaborative robots that require bionic joints, which helps to improve the development status of domestic series elastic actuators.

[0014] 2. The present invention has a passive variable stiffness series elastic actuator with a hollow structure. When it is necessary to disassemble one of the components such as the driving device, the reducer, the hollow shaft frame, or the driving circuit board, it is not necessary to change the installation of other components with the housing.

[0015] 3. The passive variable stiffness series elastic actuator with a hollow structure according to the present invention installs the elastic element outside the reducer, which can reuse the space in the axial direction, effectively compress the axial length of the series elastic actuator, reduce the volume of the series elastic actuator, and improve the power density of the series elastic actuator. Description of the Drawings

[0016] Figure 1 It is an exploded schematic view of the passive variable stiffness series elastic actuator with a hollow structure according to the present invention;

[0017] Figure 2 It is a structural schematic view of the passive variable stiffness series elastic actuator with a hollow structure according to the present invention;

[0018] Figure 3 It is a structural schematic view of the elastic element in the passive variable stiffness series elastic actuator with a hollow structure according to the present invention;

[0019] Figure 4 It is a schematic view of the contact state between the side surface of the boss and the repeatedly bent structure in the elastic element.

[0020] In the figure:

[0021] 1 - housing 2 - drive circuit board 3 - drive device

[0022] 4 - reducer 5 - elastic element 6 - encoder

[0023] 7 - hollow shaft frame 101 - drive circuit board end cover 102 - motor part housing

[0024] 103 - reducer part housing 104 - output end cover 104a - outer ring end cover

[0025] 104b - inner ring end cover 104c - bearing gland 301 - permanent magnet rotor

[0026] 302 - multi - stage winding stator 401 - wave generator 402 - flexspline

[0027] 403 - rigid spline 501 - inner ring connection flange 502 - outer ring connection flange

[0028] 503 - repeatedly bent structure 504 - boss Detailed Embodiment

[0029] The present invention will be further described in detail below with reference to the accompanying drawings.

[0030] The present invention provides a passive variable stiffness series elastic actuator with a hollow structure. The overall exterior is a housing 1, and the fixed element part is installed inside the housing 1. The element part includes a drive circuit board 2, a drive device 3, a reducer 4, an elastic element 5, an encoder 6, and a hollow shaft bracket 7, as Figure 1 , Figure 2 shown.

[0031] The housing 1 is used to protect each element part and is a cylindrical structure composed of multiple parts. From left to right, they are the drive circuit board end cover 101, the motor part housing 102, the reducer part housing 103, and the output end cover 104. Among them, the drive circuit board end cover 101 is used to install the drive circuit board 2; the motor part housing 102 is used to install the drive device 3; the reducer part housing 104 is used to install the reducer 4 and the elastic element 5; the output end cover is used to connect the load. The above-mentioned parts of the housing are fixed together by screws in the circumferential direction to form an integral body. When it is necessary to disassemble a certain element part, it is not necessary to change the installation conditions between other element parts and the housing.

[0032] The hollow shaft bracket 7 is used to achieve coaxial positioning between each element part and the fixation of the encoder 6, and provides a routing channel for the drive line through the hollow part of the hollow shaft bracket, as well as protection for the line. The hollow shaft bracket 7 includes a shaft part and a connecting surface at the end. Among them, the shaft part coaxially penetrates the motor part housing 102 and the reducer part housing 103; at the same time, the connecting surface at the end of the hollow shaft bracket is fixedly connected to the circumferential direction of the central hole of the motor part housing 102 by bolts.

[0033] The drive device 3 is used to generate a driving torque and is a permanent magnet synchronous motor, including a permanent magnet rotor 301 and a multi-stage winding stator 302; it is sleeved on the hollow shaft bracket 7 through the central holes opened on the permanent magnet rotor 301 and the multi-stage winding stator 302. Among them, the outer circle of the multi-stage winding stator 302 is fixedly bonded and interference-fitted with the circumferential direction of the motor part housing 102 by silicone rubber glue. A single deep groove ball bearing is arranged between the permanent magnet rotor 301 and the multi-stage winding stator 302 for isolation, and axial positioning and circumferential relative rotation are achieved through electromagnetic suction and a single high-speed bearing. The permanent magnet rotor 301 is designed with threaded holes according to the mounting hole positions on the rotor of the encoder 6 and the mounting hole positions at the input end of the reducer 4, for mating with bolts to connect the rotor of the encoder 6 and the reducer 4.

[0034] The reducer 4 is an existing harmonic reducer, including a wave generator 401, a flexible gear 402 and a rigid gear 403. The wave generator 401 is sleeved on the hollow shaft frame 7 through the central hole thereof. Among them, the wave generator 401 is coaxially and fixedly connected to the permanent magnet rotor 301 in the driving device as the input end. At the same time, a bearing is provided between the wave generator 401 and the central frame shaft 7. The rigid gear 403 is fixed to the reducer part housing 103 by bolts. The flexible gear 402 is connected to the elastic element 5 by bolts.

[0035] As Figure 3 shown, the elastic element 5 is a thin-walled cylindrical torsion spring, including an inner ring connecting flange 501, an outer ring connecting flange 502, a thin-walled cylindrical outer shell with a repeatedly bent structure 503, and a boss 504 located on the thin-walled shell. It is formed by milling through a four-axis numerical control machine tool, and is integrally sleeved outside the reducer 4, which can reuse the space in the axial direction, effectively compress the axial length of the series elastic actuator, reduce the volume of the series elastic actuator, and improve the power density of the series elastic actuator.

[0036] The bottom end of the elastic element 5 is the inner ring connecting flange 501, and the top end is the outer ring connecting flange 502. Any one end is used as the input, and is connected to the output end of the reducer 4 through the flange designed at this end; the other end is used as the output, and is connected to the output end cover 104 through the flange at this end.

[0037] Between the above-mentioned inner ring connecting flange 501 and outer ring connecting flange 502 is a thin-walled cylindrical outer shell with a repeatedly bent structure 503. The thin-walled cylindrical outer shell is a shell formed by arranging multiple groups of repeatedly bent structures 503 at equal intervals in the circumferential direction. Each section of the repeatedly bent structure 503 has its starting end connected to the inner ring connecting flange 501 and its ending end connected to the outer ring connecting flange 502. Between the starting end and the ending end is a waveform structure formed by a plurality of continuously bent U-shaped bends. At the same time, there is a boss 504 at the center position between adjacent repeatedly bent structures 503. The boss 504 is designed on the inner ring connecting flange 501 or the outer ring connecting flange 502. Specifically, adjacent bosses 504 need to be located on opposite sides. At the same time, both sides of the boss 504 have a specific inclination angle α. This angle α needs to satisfy the angle generated by the longitudinal section where the repeatedly bent structure 503 and the boss 504 are in physical contact, so that the sides of the two are completely attached when they are in contact, as Figure 4 shown.

[0038] The above-mentioned elastic unit 5 has the characteristic of passive variable stiffness, showing a small torsional stiffness when the load is small and a significantly increased torsional stiffness when the load is large. The torsional stiffness of the elastic unit 5 is affected by parameters such as the distance from the end of each bend to the connecting flange, the bend thickness, the bend fillet radius, the bend spacing, the number of bend petals, and the material.

[0039] When the elastic unit 5 is working, when it bears a small load, the elastic unit 5 exhibits an approximately fixed torsional stiffness; when it bears a large load, the boss 504 in the elastic unit 5 will physically contact the repeatedly bent structure, causing the torsional stiffness of the elastic unit 5 to increase significantly. When the elastic unit 5 is working, when it bears a small load, the torsional stiffness is an approximately fixed small value. At this time, the load value calculated through the deformation amount is relatively accurate, which can ensure the accuracy of torque measurement and torque control; when it bears a large load, the value of the torsional stiffness increases significantly, so as to avoid excessive deformation of the elastic element 5, which makes the control bandwidth of the drive control system of the passive variable stiffness series elastic actuator be controlled within a small range, ensuring good controllability of the system.

[0040] The encoder 6 is two encoders respectively connected to the drive device 3 and the elastic element 5 for measuring the rotation angle. The two encoders are sleeved on the hollow shaft frame 7 through the central hole, and the stator part is fixed to the hollow shaft frame 7; the rotor parts are respectively fixed to the end of the drive device 3 and the elastic element 5.

[0041] The output end cover 104 is composed of three parts, including an outer ring end cover 104a, an inner ring end cover 104b and a bearing gland 104c. Among them, the outer ring end cover 104a is fixedly connected to the housing 103 of the reducer part in the circumferential direction; at the same time, an outer ring bearing connection is provided between the outer ring end cover 104a and the output end of the elastic element 5. The central hole of the inner ring end cover 104b is sleeved on the stator end of the encoder 6 connected to the elastic unit, and an inner ring bearing is provided between the inner ring end cover 104b and the stator. At the same time, the inner ring end cover 104 is fixedly connected to the flange on the circumference of the output end of the elastic unit 105 by screws. The bearing gland 104c is coaxially fixed to the inner ring end cover 104b, and the axial positioning of the inner and outer rings of the inner ring bearing is realized by cooperating with the annular shoulder designed on the circumference of the stator end of the encoder 6 and the annular shoulder designed on the circumference of the central hole of the inner ring end cover 104b.

[0042] In the above output end cover 104, load connection holes are provided on the outer circumference of the inner ring end cover 104b to realize the connection between the external load and the inner ring end cover 104. Further, through the above assembly relationship, the load can be loaded on the elastic element 5.

[0043] The drive circuit board 2 is used to receive control instructions to control the output of the drive device 3. The drive circuit board 2 is fixed on the drive circuit board end cover 101 and is connected to the multi-stage winding stator 302 and the two encoders 6 respectively through wires, and has a power input interface and a signal input interface. The circuit drive board 2 is designed for DC brushless motors and permanent magnet synchronous motors, and uses a chip with a control algorithm, a peripheral communication circuit and a high-frequency electronic commutator to receive control instructions to control the output of the drive device 3.

Claims

1. A passive variable stiffness series elastic actuator with a hollow structure, characterized in that: It includes a drive circuit board, a drive device, a speed reducer, an elastic element, an encoder and a hollow shaft bracket, and each part is assembled in a housing; The hollow shaft bracket is fixed in the housing; the drive device is used to generate a driving torque and is sleeved on the hollow shaft bracket through a central hole; it includes a rotor part and a stator part; The stator part is fixed to the housing, and the rotor part is connected to the input end of the speed reducer; The speed reducer is sleeved on the hollow shaft bracket through a central hole; the input end of the speed reducer is fixed to the rotor of the drive device and is connected to the central frame shaft through a bearing; the fixed end of the speed reducer is fixed to the housing; the output end of the speed reducer is fixed to the elastic element; The elastic element is a thin-walled cylindrical torsion spring with connecting flanges at both ends, having multiple repeatedly bent structures in the circumferential direction and bosses designed axially between adjacent repeatedly bent structures; one end of the elastic element sleeved outside the speed reducer is used as the input end and is connected to the output end of the speed reducer; the other end is used as the output end and is connected to the output end cover on one side of the housing; when the elastic unit bears a small load, it exhibits a fixed torsional stiffness; when bearing a large load, the bosses in the elastic unit come into physical contact with the repeatedly bent structures, increasing the torsional stiffness of the elastic unit; There are two encoders, which are respectively connected to the drive device and the elastic element; the two encoders are sleeved on the hollow shaft bracket through a central hole, and the stator part is fixed to the hollow shaft bracket; the rotor parts are respectively fixed to the drive device and the elastic element; The drive circuit board is used to receive control instructions to control the output of the drive device; the drive circuit board is fixed on the drive circuit board end cover on the other side of the housing and is connected to the multi-stage winding stator and the two encoders through wires respectively.

2. The passive variable stiffness series elastic actuator with a hollow structure according to claim 1, characterized in that: The housing is composed of multiple parts, including a drive circuit board end cover, a motor part housing, a speed reducer part housing and an output end cover; among them, the drive circuit board end cover is used to install the drive circuit board; the motor part housing is used to install the drive device; the speed reducer part housing is used to install the speed reducer and the elastic element; the output end cover is used for the connection between the load and the elastic unit; each part of the housing is fixed by screws to form an integral body.

3. The passive variable stiffness series elastic actuator with a hollow structure according to claim 1, characterized in that: The drive device is a permanent magnet synchronous motor, including a permanent magnet rotor and a multi-stage winding stator; the permanent magnet rotor and the multi-stage winding stator are isolated by being connected through a single deep groove ball bearing, and axial positioning and circumferential relative rotation are achieved through electromagnetic attraction and a single high-speed bearing.

4. The passive variable stiffness series elastic actuator with a hollow structure according to claim 1, characterized in that: The speed reducer is a harmonic speed reducer, having a wave generator, a flexspline and a circular spline, and is sleeved on the hollow shaft bracket through the central hole of the wave generator; the wave generator is fixedly connected to the permanent magnet rotor and is also connected to the central frame shaft through a bearing; the circular spline is fixed on the speed reducer part housing; the flexspline is fixedly connected to the elastic element.

5. The passive variable stiffness series elastic actuator with a hollow structure according to claim 1, characterized in that: The starting end of the repeatedly bent structure is connected to one connecting flange of the elastic element, and the ending end is connected to the other connecting flange; between the starting end and the ending end are multiple continuously bent U-shaped bends; at the same time, bosses are designed at the central positions between adjacent repeatedly bent structures, and adjacent bosses are located on opposite sides.

6. The passive variable stiffness series elastic actuator with a hollow structure according to claim 1, characterized in that: Both sides of the boss have a specific inclination angle α, and the angle α needs to satisfy that when the repeatedly bent structure comes into physical contact with the boss, a plane contact occurs between the repeatedly bent structure and the boss.

7. The passive variable stiffness series elastic actuator with a hollow structure according to claim 1, characterized in that: The output end cover is composed of three parts, including an outer ring end cover, an inner ring end cover and a bearing gland; among them, the outer ring end cover is fixedly connected to the part of the reducer housing in the circumferential direction; the outer ring end cover is also connected to the output end of the elastic element in the circumferential direction through an outer ring bearing; the central hole of the inner ring end cover is sleeved on the end part of the stator of the encoder connected to the same elastic unit and is connected through an inner ring bearing; at the same time, the inner ring end cover is fixedly connected to the output end of the elastic unit; the bearing gland is coaxially fixed with the inner ring end cover, and the axial positioning of the inner and outer rings of the inner ring bearing is realized by matching with the annular shoulder designed on the circumferential direction of the encoder stator end part and the annular shoulder designed on the circumferential direction of the central hole of the inner ring end cover; a load connection hole is opened on the outer circumference of the above-mentioned inner ring end cover to connect to the outside, so that the load can be loaded on the elastic element.

Images