A joint stiffness control mechanism and control method for a continuum robot

Abstract

The present application proposes a joint stiffness control mechanism and control method for a continuum robot, comprising a joint circular frame, a spring frame, a shape memory spring, a spring cover, a support screw, a connecting rod, a push rod, axis one, axis two, a rubber pad, a baffle, a fixing screw, a steel wire rope, a semiconductor refrigeration plate, a thermally conductive copper foil, a heat sink and a temperature sensor. The spring frame is placed in the middle of the joint circular frame, the shape memory spring is installed on the spring frame, the spring cover is fixed to the top of the shape memory spring through the support screw, the connecting rod and the push rod are connected to the spring frame in sequence through axis one and axis two, the rubber pad is fixed on the push rod, the semiconductor refrigeration plate contacts the shape memory spring through the thermally conductive copper foil, and is cooled through the temperature feedback of the temperature sensor. The joint stiffness control mechanism can realize the adjustment of the joint bending stiffness, thereby controlling the load of the joint.

Description

Technical Field

[0001] The present invention belongs to the interdisciplinary field of robotics, control science, computer science and sensor technology, and particularly relates to a joint stiffness control mechanism and a control method for a continuum robot. Background Art

[0002] Traditional industrial robotic arms are composed of rigid links, offering advantages such as large load capacity and precise movement. However, they have few degrees of freedom and lack flexibility, resulting in inevitable rigid collisions in complex working environments, posing a safety hazard. Bionic continuum robots mimic flexible biological organs such as elephant trunks and octopus tentacles, and their primary forms of movement are the expansion and contraction and bending of elastic structures. Compared to traditional industrial robotic arms, they offer greater adaptability and flexibility. In complex and confined environments, they can bend and deform to suit the environment, avoiding collisions with complex operating environments. They possess strong obstacle avoidance and environmental adaptability, making them highly valuable in applications where traditional industrial robotic arms struggle, such as rescue, medical treatment, and deep cavity exploration. However, continuum robots have limited load capacity, and their end caps struggle to withstand the heavy loads of rigid robotic arms, primarily due to the relatively low stiffness of their joints. Therefore, researchers have proposed solutions for adjusting joint stiffness. For example, Patent Publication No. CN107718040A discloses a "robot stiffness controllable joint and stiffness control method thereof", which uses the thermal effect of electric current to change the shape of a shape memory alloy metal sheet, change the distance between the outer elastic skeleton and the inner elastic skeleton of the variable stiffness structure, and achieve a change in the wall thickness of the variable stiffness structure, thereby enabling the stiffness controllable joint to switch between a rigid working state and a flexible working state. However, the control process involves a temperature change time, resulting in a slow response speed to the stiffness change. Patent Publication No. CN202622798U discloses a "magnetorheological continuum robot manipulator", which can adjust the magnetic field strength of the magnetorheological fluid in the hose by changing the current of the coil, thereby controlling the rheological properties of the magnetorheological fluid and achieving conversion between liquid and solid, thereby adjusting the stiffness and damping of the entire manipulator. However, in actual applications, there are problems such as complex structure, poor stability, slow response, and heat interference in the magnetic circuit. Summary of the Invention

[0003] In response to the problems that the joint stiffness of a continuum robot cannot be controlled, or the stiffness control mechanism is complex and bulky, and the stiffness control has low precision and slow speed, this application proposes a joint stiffness control mechanism and control method for a continuum robot.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] The present invention provides a joint stiffness control mechanism for a continuum robot, which consists of a joint circular surface frame, a spring frame, a shape memory spring, a spring cover, a support screw, a connecting rod, a push rod, an axis one, an axis two, a baffle, a fixed screw, a steel wire rope, a semiconductor refrigeration plate, a heat-conducting copper foil, a heat sink and a temperature sensor. The joint circular surface frame is in the shape of a circular sheet, and at least three guide grooves are provided in the middle of the circular upper surface of the joint circular surface frame, and evenly distributed guide groove protrusions, a stopper and a steel wire rope hole are provided near the edge of the circular surface; the stopper is provided below the corresponding baffle and fixed by a fixed screw, and the shape of the spring frame includes a middle circular ring and supporting legs evenly distributed on the circumference, which are placed in the corresponding guide groove and slide up and down in the guide groove; the lower end of the shape memory spring is installed on the middle circular part of the spring frame; the shape of the spring cover It includes an intermediate ring and at least two supporting legs evenly distributed on the circumference, with screw holes provided at the ends of the supporting legs. The spring cover is placed in the guide groove of the joint circular surface frame and the top of the shape memory spring, and is fixedly connected to the circular surface of the joint circular surface frame in parallel through the support screw; one end of the connecting rod is hinged to the corresponding supporting leg on the spring frame through the corresponding axis one; the push rod is hinged to the corresponding connecting rod through axis two; the heat-conducting copper foil is fixed to the guide groove surface corresponding to the joint circular surface frame; the temperature sensor is fixed to the surface of the heat-conducting copper foil; the steel wire rope passes through the corresponding steel wire rope holes on the joint circular surface frame, and the side surface of the steel wire rope is tangent to the baffle on the joint circular surface frame; the semiconductor refrigeration plate is in contact with the shape memory spring through the corresponding heat-conducting copper foil, and the heat sink is fixed to the surface of the semiconductor refrigeration plate.

[0006] As a further improvement to the control mechanism of the present invention, a rubber pad is fixed in the front end groove of the push rod.

[0007] As a further improvement to the control mechanism of the present invention, the shape memory spring is in a spiral shape.

[0008] As a further improvement to the control mechanism of the present invention, the connecting rod is Y-shaped.

[0009] The present invention provides a control method for a joint stiffness control mechanism of a continuum robot, the specific steps of which are as follows:

[0010] When the joint stiffness needs to be increased, the shape memory spring is energized, the temperature of the shape memory spring rises, and the elongation increases. Since the upper end of the shape memory spring is constrained by the spring cover and cannot move, the lower end of the shape memory spring moves downward, thereby pushing the spring frame downward along the guide groove of the joint circular surface frame, thereby driving the lower end of the corresponding connecting rod to move toward the outer direction of the circumference, thereby pushing the push rod to move toward the corresponding steel wire rope; increasing the pressure between the rubber pad and the steel wire rope, and increasing the friction between the steel wire rope and the rubber pad, thereby increasing the external force and torque required for joint bending; the thermal conductive copper foil conducts heat from the shape memory spring to the temperature sensor and the semiconductor cooling chip, and the temperature of the shape memory spring is monitored by the temperature sensor;

[0011] When it is necessary to reduce the joint stiffness, the semiconductor refrigeration chip is energized, and the semiconductor refrigeration chip quickly transfers heat to the heat sink. The heat sink dissipates heat, causing the shape memory spring to cool down quickly and shrink. The spring frame rises, the push rod retreats, the contact pressure between the wire rope and the rubber pad decreases, the friction decreases, and the joint stiffness decreases.

[0012] As a further improvement of the control method of the control mechanism of the present invention, the control model of the control method of the joint stiffness control mechanism of the continuum robot is:

[0013] To=F×R×n=μN×R×n

[0014] N=f(y)

[0015] y=f(z)

[0016] z=f(T)

[0017] Where: To is the joint bending moment, F is the friction force of a single wire rope, R is the distance between the wire rope hole and the center of the joint circular surface, n is the number of wire ropes, μ is the friction coefficient between the wire rope and the rubber pad, N is the pressure of the rubber pad on the wire rope, y is the displacement of the push rod, z is the displacement of the spring frame, and T is the temperature of the shape memory spring.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention provides a joint stiffness control mechanism for a continuum robot, which adds a stiffness control mechanism to the joint circular surface frame of the continuum mechanism and has a compact structure. It adopts a shape memory spring, adjusts the length and stiffness of the shape memory spring by temperature, and adjusts the friction between the rubber pad and the steel wire rope to achieve controllable stiffness. It adopts a semiconductor refrigeration plate to cool the shape memory spring, improving the problem of slow cooling recovery of the shape memory spring, and has the advantage of fast response. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The present invention is a three-dimensional view of the joint stiffness control mechanism Figure 1 ;

[0021] Figure 2 The present invention is a three-dimensional view of the joint stiffness control mechanism Figure 2 ;

[0022] Figure 3 It is a three-dimensional schematic diagram of the joint circular frame structure of the present invention;

[0023] Figure 4 It is a three-dimensional schematic diagram of the compression connecting rod slider mechanism of the present invention;

[0024] Figure 5 This is a three-dimensional schematic diagram of the structure of the shape memory spring temperature adjustment system of the present invention;

[0025] Figure 6 It is a schematic diagram of the heat conduction structure of the heat sink of the present invention;

[0026] Figure 7 This is a flow chart of the joint stiffness control method of the present invention;

[0027] Figure numerals: 1. joint circular surface frame; 2. spring frame; 3. shape memory spring; 4. spring cover; 5. support screw; 6. connecting rod; 7. push rod; 8. axis one; 9. axis two; 10. rubber pad; 11. baffle; 12. fixing screw; 13. wire rope; 14. semiconductor refrigeration plate; 15. thermal conductive copper foil; 16. heat sink; 17. temperature sensor. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0029] Example: Refer to Figure 1 、 Figure 2 A joint stiffness control mechanism of a continuum robot is composed of a joint circular surface frame 1, a spring frame 2, a shape memory spring 3, a spring cover 4, three support screws 5, three connecting rods 6, three push rods 7, three axis 1s 8, three axis 2s 9, three rubber pads 10, three baffles 11, three fixing screws 12, three steel wire ropes 13, three semiconductor cooling sheets 14, three thermal conductive copper foils 15, three heat sinks 16 and three temperature sensors 17;

[0030] Reference Figure 1 、 Figure 2 and Figure 3 The joint circular surface frame 1 is a circular sheet, with a three-petal guide groove in the middle of the circular surface, and three evenly distributed guide grooves, blocks and wire rope holes are provided near the edge of the circular surface;

[0031] Reference Figure 1 、 Figure 2 and Figure 4, the spring frame 2 is placed in the three-petal guide groove of the joint circular surface frame 1 and can slide up and down; the lower end of the shape memory spring 3 is fixed on the spring frame 2; the spring cover 4 is placed in the three-petal guide groove of the joint circular surface frame 1 and the top of the shape memory spring 3, and is fixedly connected to the joint circular surface frame 1 through the support screw 5; the connecting rod 6 is hinged to the spring frame 2 through the axis 1 8, the push rod 7 is hinged to the connecting rod 6 through the axis 2 9, and the rubber pad 10 is fixed in the front end groove of the push rod 7;

[0032] Reference Figure 1 、 Figure 2 、 Figure 5 and Figure 6 The thermally conductive copper foil 15 is fixed to the three-lobed guide groove surface of the joint circular frame 1, the temperature sensor 17 is fixed to the surface of the thermally conductive copper foil 15, the semiconductor cooling sheet 14 is fixed to the surface of the thermally conductive copper foil 15, and the heat sink 16 is fixed to the surface of the semiconductor cooling sheet 14. The support screw 5, connecting rod 6, push rod 7, shaft 1 8, shaft 2 9, rubber pad 10, baffle 11, two fixing screws 12, wire rope 13, semiconductor cooling sheet 14, thermally conductive copper foil 15, heat sink 16 and temperature sensor 17 are each evenly distributed on the joint circular frame 1 in three portions.

[0033] The control method of the joint stiffness control mechanism of the continuum robot is as follows: when the joint stiffness needs to be increased, by energizing the shape memory spring, the temperature of the shape memory spring increases and the elongation increases, thereby pushing the spring frame downward along the multi-petal guide groove of the joint circular surface frame, driving the lower ends of the multiple connecting rods to move toward the outer direction of the circumference, pushing the multiple push rods to move toward the multiple steel ropes respectively, increasing the pressure between the rubber pad and the steel rope, and increasing the friction between the steel rope and the rubber pad, thereby increasing the external applied force and torque required for joint bending; the thermal conductive copper foil transfers heat from the shape memory spring to the temperature sensor and the semiconductor refrigeration chip, and the temperature sensor monitors the temperature of the shape memory spring; when the joint stiffness needs to be reduced, by energizing the semiconductor refrigeration chip, the semiconductor refrigeration chip quickly transfers heat to the heat sink, and the heat sink dissipates heat to quickly cool the shape memory spring and shrink, the spring frame rises, the push rods retreat, the contact pressure between the steel rope and the rubber pad decreases, the friction decreases, and the joint stiffness decreases.

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

[0035] To=F×R×n=μN×R×n

[0036] N=f(y)

[0037] y=f(z)

[0038] z=f(T)

[0039] Where: To is the joint bending moment, F is the friction force of a single wire rope, R is the distance between the wire rope hole and the center of the joint circular surface, n is the number of wire ropes, μ is the friction coefficient between the wire rope and the rubber pad, N is the pressure of the rubber pad on the wire rope, y is the displacement of the push rod, z is the displacement of the spring frame, and T is the temperature of the shape memory spring.

[0040] In actual control, the functional relationship of y=f(z) is first obtained through geometric relationships, and the relationship between N=f(y) and z=f(T) is obtained through experiments. Then, the temperature T is controlled by the PID control method, thereby controlling the joint bending torque To and realizing the control of the joint stiffness.

[0041] Reference Figure 1 、 Figure 2 and Figure 7 The control method of the joint stiffness control mechanism of the continuum robot is as follows:

[0042] S1: given system stiffness;

[0043] S2: measure ambient temperature;

[0044] S3: Calculate the temperature of the shape memory spring;

[0045] S4: current-controlled shape memory spring;

[0046] S5: measuring the temperature of the shape memory spring;

[0047] S6: Determine whether the shape memory spring has returned to its original state. If so, proceed to S7; otherwise, proceed to S3.

[0048] S7: Control the cooling of semiconductor refrigeration chip;

[0049] S8: Measure the temperature of semiconductor refrigeration chip;

[0050] S9: Determine whether the semiconductor refrigeration chip has reached the ambient temperature. If so, end the control; otherwise, enter S7.

[0051] The above description is merely a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent variation based on the technical essence of the present invention shall still fall within the scope of protection claimed by the present invention.

Claims

1. A joint stiffness control mechanism for a continuum robot, comprising a joint circular surface frame (1), a spring frame (2), a shape memory spring (3), a spring cover (4), a support screw (5), a connecting rod (6), a push rod (7), a shaft (8), a shaft (9), a baffle (11), a fixed screw (12), a steel wire rope (13), a semiconductor cooling sheet (14), a heat-conducting copper foil (15), a heat sink (16) and a temperature sensor (17), characterized in that: The joint circular surface frame (1) is in the shape of a circular sheet. At least three guide grooves are provided in the middle of the circular upper surface of the joint circular surface frame (1), and evenly distributed guide groove protrusions, stoppers and wire rope holes are provided near the edge of the circular surface; the stoppers are provided below the corresponding baffles (11) and fixed by fixing screws (12); the shape of the spring frame (2) includes a middle circular ring and legs evenly distributed on the circumference, which are placed in the corresponding guide groove and slide up and down in the guide groove; the lower end of the shape memory spring (3) is installed on the spring frame (2) On the middle circular part; the shape of the spring cover (4) includes a middle ring and at least two legs evenly distributed on the circumference, and the ends of the legs are provided with screw holes. The spring cover (4) is placed on the guide groove of the joint circular surface frame (1) and the top of the shape memory spring, and is fixedly connected to the circular surface of the joint circular surface frame (1) in parallel through the support screw (5); one end of the connecting rod (6) is hinged to the corresponding leg on the spring frame (2) through the corresponding shaft one (8); the push rod (7) is hinged to the corresponding connecting rod (6) through the shaft two (9); The heat-conducting copper foil (15) is fixed on the guide groove surface corresponding to the joint circular frame (1); the temperature sensor (17) is fixed on the surface of the heat-conducting copper foil (15); the steel wire rope (13) passes through the corresponding steel wire rope holes on the joint circular frame (1), and the side surface of the steel wire rope (13) is tangent to the baffle (11) on the joint circular frame (1); the semiconductor refrigeration plate (14) is in contact with the shape memory spring (3) through the corresponding heat-conducting copper foil (15), and the heat sink (16) is fixed on the surface of the semiconductor refrigeration plate (14).

2. The joint stiffness control mechanism of a continuum robot according to claim 1, characterized in that: A rubber pad (10) is fixed in the front end groove of the push rod (7).

3. The joint stiffness control mechanism of a continuum robot according to claim 1, characterized in that: The shape memory spring (3) is in a spiral shape.

4. The joint stiffness control mechanism of a continuum robot according to claim 1, characterized in that: The connecting rod (6) is Y-shaped.

5. The control method of the joint stiffness control mechanism of the continuum robot according to any one of claims 1 to 4, characterized in that: The specific steps are as follows: When the joint stiffness needs to be increased, the shape memory spring (3) is energized, the temperature of the shape memory spring (3) increases, and the elongation increases. Since the upper end of the shape memory spring (3) is constrained by the spring cover (4) and cannot move, the lower end of the shape memory spring (3) moves downward, thereby pushing the spring frame (2) to press down along the guide groove of the joint circular frame (1), thereby driving the lower end of the corresponding connecting rod (6) to move toward the outer circumference, thereby pushing the push rod (7) to move toward the corresponding steel wire rope (13); increasing the pressure between the rubber pad (10) and the steel wire rope (13), and increasing the friction between the steel wire rope (13) and the rubber pad (10), thereby increasing the external applied force and torque required for joint bending; the heat-conducting copper foil (15) conducts heat from the shape memory spring (3) to the temperature sensor (17) and the semiconductor refrigeration plate (14), and the temperature of the shape memory spring (3) is monitored by the temperature sensor (17); When the joint stiffness needs to be reduced, the semiconductor refrigeration plate (14) is energized, and the semiconductor refrigeration plate (14) quickly conducts heat to the heat sink (16). The heat sink (16) dissipates heat to quickly cool the shape memory spring (3) and shrink it. The spring frame (2) rises, the push rod (7) retreats, the contact pressure between the wire rope (13) and the rubber pad (10) decreases, the friction force decreases, and the joint stiffness decreases.

6. The control method of the joint stiffness control mechanism of the continuum robot according to any one of claims 1 to 4, characterized in that: The control model of the control method of the joint stiffness control mechanism of the continuum robot is: To=F×R×n=μN×R×n N=f(y) y=f(z) z=f(T) Where: To is the joint bending moment, F is the friction force of a single wire rope, R is the distance between the wire rope hole and the center of the joint circular surface, n is the number of wire ropes, μ is the friction coefficient between the wire rope and the rubber pad, N is the pressure of the rubber pad on the wire rope, y is the displacement of the push rod, z is the displacement of the spring frame, and T is the temperature of the shape memory spring.

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