A Continuum Robot Variable Stiffness Joint Module and Control Method

Abstract

A continuum robot variable stiffness joint module and control method, comprising a joint disc, a flange bearing, a pushing member, a rubber pad, a connecting member, a motor base, a motor, a transmission screw, a directional nut, an elastic rod, a compression spring chute, a compression spring, a spring baffle, and a cross universal joint. The flange bearing is placed in the middle of the joint disc, the pushing member is fixed to the flange bearing, the rubber pad is fixed to the end of the pushing member, the connecting member is placed above the pushing member, the motor is placed on the motor base and drives the transmission screw to rotate, the directional nut is sleeved on the transmission screw and pushes the pushing member to contact the elastic rod, the compression spring chute is placed in the joint disc, one end of the compression spring is fixed in the compression spring chute, the spring baffle is fixed to the pushing member, the cross universal joint is placed between the connecting member and the next joint disc, and the variable stiffness joint module can realize the stiffness adjustment when the joint bends, thereby improving the payload capacity.

Description

Technical Field

[0001] The present invention relates to the field of continuum robot joint modules, and particularly to a variable stiffness joint module and a control method for a continuum robot. Background Art

[0002] Traditional industrial robotic arms are limited by few degrees of freedom and insufficient compliance, and thus have low adaptability to complex environments. Flexible robots imitate flexible biological organs such as elephant trunks and octopus tentacles. Their main motion forms are the stretching and bending deformation of elastic structures. Compared with traditional industrial robotic arms, they have better adaptability and flexibility. They can bend and deform according to the environment in complex and narrow environments to avoid collisions with complex operating environments, and have strong obstacle avoidance and environmental adaptation capabilities. They have great application value in application scenarios where traditional industrial robotic arms are difficult to work, such as rescue, medical treatment, and deep cavity detection. However, due to the small joint stiffness of flexible robots, their load capacity is limited.

[0003] Therefore, researchers have proposed solutions for joint stiffness adjustment, such as:

[0004] Patent Publication No.: CN107718040A discloses a "robot stiffness controllable joint and its stiffness control method", which uses the thermal effect of current to change the shape of a shape memory alloy metal sheet, changes the distance between the outer elastic skeleton and the inner elastic skeleton of the variable stiffness structure part, realizes the wall thickness change of the variable stiffness structure part, and thus enables the stiffness controllable joint to switch between a rigid working state and a flexible working state. However, there is a temperature change time in the control process, resulting in a slow response speed of stiffness change.

[0005] Patent Publication No.: CN202622798U discloses a "magnetorheological continuum robot manipulator", which can adjust the magnetic field intensity acting on the magnetorheological fluid in the hose by changing the current of the coil, thereby controlling the rheological properties of the magnetorheological fluid and realizing the conversion between liquid and solid phases, playing a role in adjusting the stiffness and damping of the entire manipulator. However, in practical applications, there are problems such as complex structure, poor stability, slow response, and magnetic circuit heat generation interference. Summary of the Invention

[0006] Aiming at the problems that the joint stiffness of continuum robots cannot be adjusted, the load capacity is limited, the safety is low, and the existing stiffness adjustment modules have complex structures, large volumes, and slow variable stiffness speeds, the present invention proposes a variable stiffness joint module and a control method for a continuum robot. The variable stiffness joint module can realize the stiffness adjustment when the joint bends, thereby improving the effective load capacity.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A variable stiffness joint module for a continuum robot, which consists of a joint disc, a pusher, a connecting piece, a motor, a motor base, a transmission screw, a direction nut, a compression spring chute, a compression spring, a spring baffle, three rubber pads, three elastic rods, a flange bearing and a cross universal joint;

[0009] A hollow boss is provided at the lower end of the joint disc; the three elastic rods respectively pass through three elastic rod holes on the joint disc, and the sides thereof are tangent to the stoppers on the joint disc; the lower end of the cross universal joint is placed in the cylindrical groove at the upper end of the connecting piece, and the upper end is connected to the hollow boss at the lower end of the joint disc of the previous joint;

[0010] The three pushers are arranged in a circumferential array around the center of the joint disc, and the pushers rotate around the flange bearing; the three rubber pads are fixed at the front ends of the corresponding pushers; the connecting piece is placed above the pushers and is connected to the joint disc through three fixing screws; the flange bearing is sleeved on the cylindrical shaft in the middle of the joint disc;

[0011] The motor base is fixed on the motor base fixing boss of the joint disc by screws; the motor is placed on the motor base and drives the transmission screw, and the direction nut is sleeved on the transmission screw; the compression spring chute is fixed on the joint disc by screws; the compression spring is spiral, and one end thereof is fixed on the inner wall of the compression spring chute; the spring baffle is fixed on the threaded hole on the pusher by screws.

[0012] As a further improvement of the structure of the present invention, the joint disc is a circular sheet, a cylindrical shaft is provided in the middle of the upper circular surface, and a motor base fixing boss and three groups of uniformly distributed stoppers, elastic rod holes, threaded holes and wire passing holes are provided near the edge of the circular surface.

[0013] As a further improvement of the structure of the present invention, semi-circular grooves are provided at the ends of the pushers, two threaded holes are provided on one of the pushers, a circular hole is provided in the center of the pusher, and the flange bearing is nested therein, and the rubber pad is fixed in the semi-circular groove at the front end of the corresponding pusher.

[0014] As a further improvement of the structure of the present invention, the outer shape of the connecting piece includes a hollow boss, a triangular face plate and three legs, and screw holes are provided on the legs.

[0015] The control method of the variable stiffness joint module of the continuum robot of the present invention is as follows;

[0016] When it is necessary to increase the joint stiffness, the motor is controlled to drive the gear set arranged in the motor base to rotate, so as to drive the transmission screw rod to rotate. The direction nut then moves forward from the initial position, pushing the push member to rotate clockwise around the flange bearing, that is, the end of the push member moves towards the elastic rod. As the direction nut gradually pushes forward, the pressure of the rubber pad on the elastic rod increases, increasing the friction between the elastic rod and the rubber pad, and further increasing the external applied force and torque required for joint bending. During the process of the direction nut pushing the push member to rotate, before the rubber pad contacts the elastic rod, the spring baffle and the push member will jointly contact the compression spring and gradually increase the pressure on the compression spring. When it is necessary to reduce the joint stiffness, the motor is controlled to make the transmission screw rod rotate in the reverse direction, and the direction nut retreats to the initial position. At this time, the compression spring applies an elastic force to the push member, pushing the push member to rotate counterclockwise, that is, gradually moving away from the elastic rod. The contact pressure and friction between the elastic rod and the rubber pad decrease, and thus the joint stiffness decreases.

[0017] Beneficial effects:

[0018] For the variable stiffness joint module and control method of the continuum robot of the present invention, a variable stiffness control module is added to the joint disc of the continuum robot joint, and the structure is compact; a screw-nut combination using the screw drive principle is adopted, and the displacement of the push member is changed by controlling the motor to adjust the friction between the rubber pad and the elastic rod, realizing controllable stiffness; the control method combining motor control and mechanical transmission improves the continuity of stiffness adjustment and speeds up the response speed. Description of the drawings

[0019] Figure 1 is the three-dimensional view of the variable stiffness joint module of the present invention Figure 1 ;

[0020] Figure 2 is the three-dimensional view of the variable stiffness joint module of the present invention Figure 2 ;

[0021] Figure 3 is the three-dimensional schematic diagram of the joint disc structure of the present invention;

[0022] Figure 4 is the three-dimensional schematic diagram of the push member structure of the present invention;

[0023] Figure 5 is the three-dimensional schematic diagram of the push member rotation driving device structure of the present invention;

[0024] Figure 6 is the three-dimensional schematic diagram of the push member reverse assist device structure of the present invention;

[0025] Figure 7 is the flowchart of the joint stiffness adjustment method of the present invention;

[0026] Reference numerals: 1, joint disc; 2, pusher; 3, connecting piece; 4, motor; 5, motor base; 6, transmission screw; 7, direction nut; 8, compression spring chute; 9, compression spring; 10, spring baffle; 11, rubber pad; 12, elastic rod; 13, flange bearing; 14, cross universal joint. Detailed implementation mode

[0027] The present invention will be further described in detail below in conjunction with the drawings and the specific implementation mode:

[0028] Example: Refer to Figure 1 , Figure 2 , Figure 4 , a variable stiffness joint module of a continuum robot is composed of a joint disc 1, a pusher 2, a connecting piece 3, a motor 4, a motor base 5, a transmission screw 6, a direction nut 7, a compression spring chute 8, a compression spring 9, a spring baffle 10, three rubber pads 11, three elastic rods 12, a flange bearing 13, and a cross universal joint 14;

[0029] Refer to Figure 1 , Figure 2 and Figure 3 , the joint disc 1 is a circular sheet, with a cylindrical shaft arranged in the middle of the upper circular surface, a motor base fixing convex block and three groups of evenly distributed stoppers and elastic rod holes near the edge of the circular surface, as well as threaded holes and wire passing holes, and a hollow convex platform is arranged at the lower end; the three elastic rods 12 respectively pass through the three elastic rod holes on the joint disc 1, and the sides thereof are tangent to the stoppers on the joint disc 1; the lower end of the cross universal joint 14 is placed in the cylindrical groove at the upper end of the connecting piece 3, and the upper end is connected to the hollow convex platform at the lower end of the joint disc 1 of the previous joint, which can satisfy the bending of the joint in any direction;

[0030] Refer to Figure 1 , Figure 2 , Figure 4 and Figure 6 , the three push rods of the pusher 2 are arranged in a circumferential array around the center of the joint disc 1, and semi-circular grooves are provided at the ends of the push rods. Two threaded holes are provided on one of the push rods, and a circular hole is provided in the center of the pusher 2. The flange bearing 13 is nested therein, so that the pusher 2 can rotate around the flange bearing 13; the three rubber pads 11 are respectively fixed in the semi-circular grooves at the front ends of the three push rods of the pusher 2; the outer shape of the connecting piece 3 includes a hollow convex platform, a triangular face plate and three legs, and screw holes are provided on the legs. The connecting piece 3 is placed on the pusher 2 and is connected to the joint disc 1 through three fixing screws; the flange bearing 13 is sleeved on the cylindrical shaft in the middle of the joint disc 1;

[0031] Refer to Figure 1 ,Figure 2 , Figure 5 and Figure 6 , the motor base 5 is fixed on the motor base fixing bump of the joint disk 1 by screws; the motor 4 is placed on the motor base 5, and drives the transmission screw 6 through a plurality of gears with different sizes, and the direction nut 7 is sleeved on the transmission screw 6; the compression spring chute 8 is fixed on the joint disk 1 by screws; the compression spring 9 is spiral, and one end of it is fixed on the inner wall of the compression spring chute 8; the spring baffle 10 is fixed on the threaded hole on the pusher 2 by screws.

[0032] The control method of the continuum robot variable stiffness joint module is as follows:

[0033] Referring to Figure 1 , Figure 2 , when it is necessary to increase the joint stiffness, by controlling the motor 4, the gear set arranged in the motor base 5 is driven to rotate, so as to drive the transmission screw 6 to rotate, and the direction nut 7 moves forward from the initial position, pushing the pusher 2 to rotate clockwise around the flange bearing 13, that is, the end of the pusher 2 moves towards the elastic rod 12; as the direction nut 7 gradually pushes forward, the pressure of the rubber pad 11 on the elastic rod 12 increases, thereby increasing the friction force between the elastic rod 12 and the rubber pad 11, and further increasing the external applied force and torque required for joint bending. During the process of the direction nut 7 pushing the pusher 2 to rotate, before the rubber pad 11 contacts the elastic rod 12, the spring baffle 10 and the pusher 2 will jointly contact the compression spring 9 and gradually increase the pressure on the compression spring 9; when it is necessary to reduce the joint stiffness, by controlling the motor 4 to make the transmission screw 6 rotate in the reverse direction, the direction nut 7 retreats to the initial position. At this time, the compression spring 9 exerts an elastic force on the pusher 2, pushing the pusher 2 to rotate counterclockwise, that is, gradually moving away from the elastic rod 12, the contact pressure and friction force between the elastic rod 12 and the rubber pad 11 decrease, and thus the joint stiffness decreases.

[0034] The control model of the continuum robot variable stiffness joint module is:

[0035] To = F×R×n = μN×R×n

[0036] N = f(y)

[0037] y = f(T) = vT = Ph×n×T

[0038] n = f(n’)

[0039] Where: To is the joint bending moment, F is the friction force of a single elastic rod, R is the distance from the hole of the elastic rod to the center of the circular surface of the joint disc, n is the number of elastic rods, μ is the friction coefficient between the elastic rod and the rubber pad, N is the pressure of the rubber pad on the elastic rod, y is the displacement of the direction nut advancing, i.e., the displacement of the pusher advancing, T is the motor control signal time, v is the transmission speed of the direction nut, Ph is the lead, n is the rotational speed of the transmission screw, and n' is the rotational speed of the motor.

[0040] In actual control, the motor speed is set to a constant value. Since the conditions of S = f(T) are known, the relationship of N = f(y) can be obtained through experiments, and then by changing the motor control signal, the control of the joint bending moment To can be achieved, thereby realizing the control of the joint stiffness.

[0041] Refer to Figure 1 、 Figure 5 、 Figure 6 and Figure 7 , the control method flow of the variable stiffness joint module of the continuum robot is as follows:

[0042] S1: Specify the system stiffness;

[0043] S2: Measure the current displacement y of the direction nut;

[0044] S3: Calculate the target displacement y* of the direction nut;

[0045] S4: Calculate the displacement difference e = y* - y;

[0046] S5: Judge the forward and reverse rotation of the motor according to the positive and negative of the displacement difference e;

[0047] S6: Calculate the motor control signal time T according to |e|;

[0048] S7: Input the control signal to the motor;

[0049] S8: Measure the displacement of the direction nut and judge whether it is y*. If not, enter S4. If so, the control ends.

[0050] As mentioned above, it is only the preferred embodiment of the present invention, and it is not any other form of limitation to the present invention. Any modification or equivalent change made according to the technical essence of the present invention still belongs to the scope protected by the present invention.

Claims

1. A continuum robot variable stiffness joint module is composed of a joint disc (1), a pusher (2), a connecting piece (3), a motor (4), a motor base (5), a transmission screw (6), a direction nut (7), a compression spring chute (8), a compression spring (9), a spring baffle (10), three rubber pads (11), three elastic rods (12), a flange bearing (13) and a cross universal joint (14), and is characterized in that a hollow boss is arranged at the lower end of the joint disc (1); the three elastic rods (12) respectively pass through three elastic rod holes on the joint disc (1), and the sides thereof are tangent to the stoppers on the joint disc (1); the lower end of the cross universal joint (14) is placed in the cylindrical groove at the upper end of the connecting piece (3), and the upper end is connected to the hollow boss at the lower end of the joint disc (1) of the previous joint; the three pushers (2) are arranged in a circular array around the center of the joint disc (1), and the pushers (2) rotate around the flange bearing (13); the three rubber pads (11) are fixed at the front ends of the corresponding pushers (2); the connecting piece (3) is placed above the pushers (2) and is connected to the joint disc (1) through three fixing screws; the flange bearing (13) is sleeved on the cylindrical shaft in the middle of the joint disc (1); the motor base (5) is fixed on the motor base fixing boss of the joint disc (1) by screws; the motor (4) is placed on the motor base (5) and drives the transmission screw (6), and the direction nut (7) is sleeved on the transmission screw (6); the compression spring chute (8) is fixed on the joint disc (1) by screws; the compression spring (9) is spiral, and one end thereof is fixed on the inner wall of the compression spring chute (8); the spring baffle (10) is fixed on the threaded hole on the pusher (2) by screws.

2. The variable stiffness joint module of a continuum robot according to claim 1, characterized in that the joint disc (1) is a circular sheet, a cylindrical shaft is arranged in the middle of the circular upper surface, and a motor base fixing boss and three groups of uniformly distributed stoppers, elastic rod holes, threaded holes and wire passing holes are arranged near the edge of the circular surface.

3. The variable stiffness joint module of a continuum robot according to claim 1, characterized in that, semicircular grooves are arranged at the ends of the pushers (2), two threaded holes are arranged on one of the pushers (2), a circular hole is arranged in the center of the pusher (2), the flange bearing (13) is nested therein, and the rubber pad (11) is fixed in the semicircular groove at the front end of the corresponding pusher (2).

4. The variable stiffness joint module of a continuum robot according to claim 1, characterized in that, the outer shape of the connecting piece (3) includes a hollow boss, a triangular face plate and three legs, and screw holes are arranged on the legs.

5. The control method for the continuum robot variable stiffness joint module according to any one of claims 1-4, characterized in that; The specific control steps are as follows; When it is necessary to increase the joint stiffness, by controlling the motor (4), the gear set arranged in the motor base (5) is driven to rotate, so as to drive the transmission screw rod (6) to rotate. The direction nut (7) then moves forward from the initial position, pushing the push member (2) to rotate clockwise around the flange bearing (13), that is, the end of the push member (2) moves towards the elastic rod (12). As the direction nut (7) gradually pushes forward, the pressure of the rubber pad (11) on the elastic rod (12) increases, increasing the friction force between the elastic rod (12) and the rubber pad (11), and further increasing the external applied force and torque required for joint bending. During the process of the direction nut (7) pushing the push member (2) to rotate, before the rubber pad (11) contacts the elastic rod (12), the spring baffle (10) and the push member (2) will jointly contact the compression spring (9) and gradually increase the pressure on the compression spring (9). When it is necessary to reduce the joint stiffness, by controlling the motor (4) to make the transmission screw rod (6) rotate in the reverse direction, the direction nut (7) retreats to the initial position. At this time, the compression spring (9) applies an elastic force to the push member (2), pushing the push member (2) to rotate counterclockwise, that is, gradually moving away from the elastic rod (12). The contact pressure and friction force between the elastic rod (12) and the rubber pad (11) decrease, and thus the joint stiffness decreases.

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