Variable stiffness mechanism and flexible joint based on axial force

Abstract

The application discloses a variable stiffness mechanism based on axial force and a flexible joint, and solves the problems of complex stiffness adjusting mechanism and bulky volume of the flexible joint, and the variable stiffness mechanism comprises a base, a power unit, a driving rod, a stiffness adjusting part, a spring leaf and a joint output end, the power unit is fixed on the base and connected with the stiffness adjusting part through the driving rod, the stiffness adjusting part is provided with a spring leaf constraint hole for constraining the spring leaf and arranged between the base and the joint output end, the spring leaf is provided with at least two, one end of the spring leaf is fixed on the base, the other end of the spring leaf is hingedly connected to the joint output end and passes through the spring leaf constraint hole, and the purpose of reducing the volume of the stiffness adjusting mechanism is achieved.

Description

[0001] This invention application is a divisional application of the original application filed on December 6, 2021, with the original application number 202111479739.1. Technical Field

[0002] This invention relates to the field of robotics, and more particularly to a variable stiffness mechanism and flexible joint based on axial force. Background Technology

[0003] Compared to traditional flexible joints, variable stiffness flexible joints can achieve variations in joint stiffness under different working conditions through specific control strategies. This is similar to the characteristics of human muscles: maintaining high stiffness under normal working conditions and exhibiting a degree of compliance upon collision to mitigate impact and prevent further damage to the contact object. Furthermore, the introduction of elastic elements allows the joint to store energy during collisions, improving energy utilization efficiency to some extent. Therefore, the introduction of variable stiffness flexible joints enables robots to maintain joint motion performance while ensuring environmental safety, making them widely applicable and of significant research importance in the current mechanical industry.

[0004] Patent No. 201711239915.8 provides a variable stiffness flexible joint based on leaf springs, aiming to solve the problems of complex structure, large size, complicated control process, and difficulty in linear stiffness control of variable stiffness flexible joints. It includes: an input shaft (1), an output shaft (2), a stiffness adjustment mechanism (3), a displacement detection system (4), a control system (5), and a limit protection mechanism (6). The input shaft (1) includes a first input shaft (1-1) and a second input shaft (1-2), which are concentrically connected. The second input shaft (1-2) is a square plate structure with mirrored edges at its four corners. Hyperbolic groove; the output shaft (2) includes a first output shaft (2-1), a second output shaft (2-2), and an output end cap (2-3). The first output shaft (2-1) and the second output shaft (2-2) are both cylindrical structures closed at one end. The closed end of the second output shaft (2-2) is provided with a set of sliding grooves (2-4) that are evenly distributed along the circumference and extend towards the center. The first output shaft (2-1), the second output shaft (2-2), and the output end cap (2-3) are sequentially fastened and fixed. The stiffness adjustment mechanism (3) includes a control motor (3-1), a scheduling disk (3-2), a linkage group (3-3), a leaf spring group (3-4), and a slider group (3-5). This solution requires a stiffness adjustment motor (3-1), and stiffness adjustment is achieved through mechanisms such as the scheduling disk (3-2), the linkage group (3-3), the leaf spring group (3-4), and the slider group (3-5). The mechanism is still relatively complex. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a variable stiffness mechanism and flexible joint based on axial force.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: a variable stiffness mechanism based on axial force, comprising a base, a power unit, a drive rod, a stiffness adjustment component, a spring, and a joint output end; the power unit is fixedly mounted on the base and connected to the stiffness adjustment component via the drive rod; the stiffness adjustment component has a spring constraint hole for constraining the spring and is located between the base and the joint output end; one end of the spring is connected to the base, and the other end is movably connected to the joint output end.

[0007] Furthermore, there are at least two reeds, evenly arranged around the drive rod; one end of each reed passes through the reed constraint hole and is fixed to the base, and the other end passes through the reed constraint hole and is hinged to the joint output end.

[0008] Furthermore, the other end of the reed passes through the reed constraint hole and is preferably connected to the joint output end via a ball joint.

[0009] Furthermore, the base is provided with a joint output end constraint shaft; the joint output end is provided with a corresponding joint output end constraint hole to ensure that the joint output end rotates coaxially relative to the base.

[0010] Furthermore, the base has a keyway; the drive rod is correspondingly provided with a key to prevent axial rotation of the drive rod; one end of the drive rod is movably connected to a stiffness adjustment component.

[0011] Furthermore, the power unit is an electromagnet, a cylinder, or a hydraulic cylinder; the drive rod is an iron core or a piston rod.

[0012] Furthermore, the drive rod is a screw; the stiffness adjusting component has a threaded hole corresponding to the screw; the screw passes through the threaded hole and is fixedly connected to the stiffness adjusting component.

[0013] Furthermore, the base is also provided with a guide pin; the stiffness adjustment component has a guide hole that cooperates with the guide pin, so as to ensure that the stiffness adjustment component rotates synchronously with the base through the guide pin.

[0014] This invention proposes a flexible joint based on axial force, comprising the aforementioned variable stiffness mechanism, joint motor, and stiffness adjustment motor; the stiffness adjustment motor is connected to the joint motor; the joint motor is provided with a motor output end; the base of the variable stiffness mechanism is fixedly connected to the motor output end.

[0015] Furthermore, the drive rod of the variable stiffness mechanism is a screw, which is connected to the stiffness adjustment motor. The joint motor and the stiffness adjustment motor have corresponding first slide rails and first slide rails, and the first slide rails cooperate with the first slide rails. The end of the screw is rotatably connected to the stiffness adjustment component.

[0016] Compared with existing technologies, the variable stiffness mechanism and flexible joint adopting the above technical solution have the following beneficial effects:

[0017] 1. By adopting a variable stiffness mechanism and flexible joint based on axial force according to the present invention, the power unit is arranged along the axis of the joint motor, thereby reducing the diameter of the variable stiffness flexible joint.

[0018] 2. The present invention employs a variable stiffness mechanism and flexible joint based on axial force, breaking the technical route of using an electric motor as the power source for the variable stiffness mechanism.

[0019] 3. The variable stiffness mechanism and flexible joint based on axial force of the present invention, since the drive unit (electromagnet, cylinder or hydraulic cylinder) and drive shaft (iron core, piston rod) are similar to cylindrical constraints, the electromagnet can be set on the output end of the joint motor and rotate relative to the joint motor housing, or it can be set on the joint motor and placed relative to the joint motor. This provides a more flexible layout option for the power source of the variable stiffness mechanism.

[0020] 4. The variable stiffness mechanism and flexible joint based on axial force of the present invention can be used because the electromagnet is relatively easy to customize and its shape is not restricted. This not only allows users to customize at low cost, but also allows the electromagnet to be embedded in the joint motor to achieve an integrated design of the flexible joint. Attached Figure Description

[0021] Figure 1 This is a schematic cross-sectional view of a variable stiffness mechanism based on axial force according to the present invention.

[0022] Figure 2 This is a three-dimensional structural diagram of a variable stiffness mechanism based on axial force according to the present invention.

[0023] Figure 3 This is a schematic diagram of a variable stiffness flexible joint based on axial force according to the present invention;

[0024] Figure 4 This is a cross-sectional view of a variable stiffness flexible joint based on axial force according to the present invention.

[0025] Figure 5 This is an axial schematic diagram of a motor for adjusting the stiffness of a variable stiffness flexible joint based on axial force, according to the present invention.

[0026] Figure 6This is a schematic diagram of a variable stiffness flexible joint with a second slide rail based on axial force according to the present invention.

[0027] Figure 7 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0028] Reference numerals: 1. Base; 2. Electromagnet; 3. Iron core; 4. Stiffness adjustment component; 5. Spring; 6. Joint output end; 7. Ball joint; 8. Joint motor; 9. Stiffness adjustment motor; 101. Keyway; 102. Joint output end constraint shaft; 103. Guide pin; 301. Key; 401. Spring constraint hole; 402. Guide hole; 601. Joint output mounting hole; 602. Joint output shaft hole; 603. Joint output end constraint hole; 801. Motor output end; 802. Hollow shaft; 902. Screw; 903. Screw ball joint; 904. First slide rail; 8021. First slide path. Detailed Implementation

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

[0030] A variable stiffness mechanism based on axial force includes a base 1, a power unit, a drive rod, a stiffness adjustment component 4, springs 5, and a joint output end 6. The power unit is fixedly mounted on the base 1 and connected to the stiffness adjustment component 4 via the drive rod; the connection method depends on the type of power unit. The stiffness adjustment component 4 has spring constraint holes 401 for constraining the springs 5 ​​and is located between the base and the joint output end. There are at least two springs 5, evenly arranged around an axis. One end of each spring 5 is fixed to the base 1, and the other end passes through the spring constraint hole 401 and is hinged to the joint output end 6.

[0031] The preferred hinge is a ball joint connection. Since the joint output end 6 rotates relative to the base 1, it provides the spring 5 with both tangential force and torque along the joint output end 6. Therefore, the use of a ball joint can eliminate the effect of torque, simplify the force on the spring, and facilitate the force analysis of the spring.

[0032] Depending on the type of power unit, the variable stiffness mechanism based on axial force can be divided into the following schemes.

[0033] Example 1

[0034] The power unit is an electromagnet, and the drive rod is an iron core. Specifically:

[0035] like Figure 1 and Figure 2The illustrated variable stiffness mechanism based on axial force includes a base 1, an electromagnet 2, an iron core 3, a stiffness adjustment component 4, a spring 5, a joint output end 6, and a ball joint 7. The electromagnet 2 is fixedly mounted on the base 1, and the iron core 3 passes through the electromagnet 2 and is fixedly connected to the stiffness adjustment component 4. The stiffness adjustment component 4 has a spring constraint hole 401 for constraining the spring 5, and is located between the base 1 and the joint output end 6. The iron core 3 and the base 1 are respectively provided with a key 301 and a keyway 101 for constraining the axial movement of the iron core 3. Multiple sets of keys 301 and keyways 101 can be used to prevent relative rotation between the iron core 3 and the base 1. There are at least two springs 5, evenly arranged around the drive rod. One end of each spring 5 is mounted on the base 1, and the other end passes through the spring constraint hole 401 and is movably mounted on the joint output end 7 via the ball joint 7. The base 1 and the joint output end 6 are respectively provided with a joint output end constraint shaft 102 and a joint output end constraint hole 603 to ensure that the joint output end 6 rotates coaxially with respect to the base 1. When the base rotates, the iron core and the stiffness adjustment component rotate synchronously.

[0036] A method for adjusting the stiffness of a variable stiffness mechanism based on axial force includes the following steps:

[0037] First, electromagnet 2 drives iron core 3 to move axially;

[0038] The second step is to drive the stiffness adjustment component 4 to move axially, with the iron core 3 in motion.

[0039] The third step is to move the spring constraint hole 401 on the stiffness adjustment component 4 relative to the spring 5, thereby changing the effective working length of the spring 5 and thus achieving the purpose of changing the stiffness of the variable stiffness mechanism.

[0040] Example 2

[0041] like Figure 7 As shown, the power unit is a stiffness-adjustable motor 9, and the drive rod is a screw 902. Specifically, the stiffness-adjustable motor 9 is fixedly connected to the screw 902. The base 1 and the stiffness-adjusting component 4 have threaded holes corresponding to the screw. The screw 902 cooperates with the threaded holes to drive the stiffness-adjusting component 4 to move axially, thereby changing the effective working length of the spring 5.

[0042] Example 3

[0043] like Figure 4As shown, the power unit is a stiffness-adjustable motor, and the drive rod is a screw. Specifically, the base 1 has a threaded hole corresponding to the screw. The hollow shaft 802 of the joint motor and the stiffness-adjustable motor 9 are respectively provided with a first slide rail 8021 and a first slide rail 904 for the axial movement of the stiffness-adjustable motor. The first slide rail 8021 and the first slide rail 904 cooperate. The screw passes through the threaded hole, and its other end is rotatably connected to the stiffness-adjusting component through a screw ball joint 903. That is, the stiffness-adjustable motor drives its own axial movement through the kinematic pair formed by the screw, and then drives the stiffness-adjusting component to move axially through the screw, thereby achieving the purpose of changing the effective working length of the spring.

[0044] Example 4

[0045] The power unit is a pneumatic cylinder or a hydraulic cylinder, and the drive rod is a piston rod, specifically:

[0046] One end of the piston rod is fixedly connected to the stiffness adjusting member 4. The piston rod and the base 1 are respectively provided with a key 301 and a keyway 101 to prevent the piston rod from rotating axially. There can be multiple sets of key 101 and keyway 301. The cylinder or hydraulic cylinder drives the piston rod and then drives the stiffness adjusting member 4 to move along the axis, so as to change the effective working length of the spring 5 and thus change the stiffness of the variable stiffness mechanism. When the base 1 rotates, the piston rod and the stiffness adjusting member 4 rotate synchronously.

[0047] Example 5

[0048] The power unit is an electromagnet, and the drive rod is an iron core. Specifically, one end of the iron core is rotatably connected to the stiffness adjustment component 4, and the base 1 is also provided with a guide pin 103. The stiffness adjustment component 4 has a guide hole 402 that cooperates with the guide pin 103 to ensure that the stiffness adjustment component 4 rotates synchronously with the base 1 through the guide pin 103. There can be multiple sets of guide pins 103 and guide holes 402. The electromagnet drives the iron core and then drives the stiffness adjustment component to move along the axis, thereby changing the effective working length of the spring and thus changing the stiffness of the variable stiffness mechanism. When the base rotates, the iron core does not rotate, and the stiffness adjustment component rotates synchronously.

[0049] Example 6

[0050] The power unit is a pneumatic or hydraulic cylinder, and the drive rod is a piston rod. Specifically, one end of the piston rod is rotatably connected to the stiffness adjusting component, and the base 1 is also provided with a guide pin 103. The stiffness adjusting component 4 has a guide hole 402 that cooperates with the guide pin 103 to ensure that the stiffness adjusting component 4 rotates synchronously with the base 1 through the guide pin 103. There can be multiple sets of guide pins 103 and guide holes 402. The pneumatic or hydraulic cylinder drives the piston rod, thereby driving the stiffness adjusting component to move along the axis, so as to change the effective working length of the spring and thus change the stiffness of the variable stiffness mechanism. When the base rotates, the piston rod does not rotate, and the stiffness adjusting component rotates synchronously.

[0051] Since the electromagnet and the iron core, and the cylinder or hydraulic cylinder (power unit) and the piston rod (drive rod) can all be equivalent to cylindrical constraints, the power unit only provides the axial force for the movement of the iron core. Therefore, the power unit can rotate relative to the drive rod (in which case the power unit is located on the joint motor housing or on a part fixed to the housing), or it can remain stationary relative to the drive rod (in which case the power unit is located on the output end of the joint motor).

[0052] Preferably, the base 1 is provided with an annular groove, and the joint output end is provided with an annular protrusion. The two work together as a joint output end constraint mechanism 603 to ensure that the joint output end rotates around the central axis.

[0053] like Figure 3 As shown, the present invention also provides a flexible joint based on a variable stiffness mechanism of axial force, including a joint motor 8, a stiffness adjustment motor 9, and the variable stiffness mechanism. The stiffness adjustment motor 9 is connected to the joint motor 8. The joint motor 8 is provided with a motor output end 801, and the base 1 is fixedly disposed on the motor output end 801.

[0054] Preferably, the joint motor 8 is provided with a hollow shaft for accommodating the power unit in the variable stiffness mechanism. The hollow shaft is fixedly connected to the output end of the joint motor and extends to the outer end face of the output end of the joint motor for accommodating the drive rod in the variable stiffness mechanism.

[0055] Preferably, the joint motor 8 is provided with a hollow shaft for accommodating the drive rod in the variable stiffness mechanism. One end of the hollow feature of the hollow shaft extends to the outer end face of the output end of the joint motor, and the other end is a through hole. The power unit of the variable stiffness mechanism is fixed on the tail housing of the motor. The two ends of the drive rod are respectively connected to the power unit and the stiffness adjustment component 4.

[0056] The working process of the variable stiffness mechanism based on axial force disclosed in this invention is as follows: First, the power unit drives the drive rod to provide axial force; the drive rod then drives the dynamic stiffness adjustment component to move axially; finally, the spring constraint hole on the stiffness adjustment component moves relative to the spring, changing the effective working length of the spring, thereby achieving the purpose of changing the stiffness of the variable stiffness mechanism.

[0057] The above description is a preferred embodiment of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the principle of the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A variable stiffness mechanism based on axial force, characterized in that, The device includes a base (1), a power unit, a drive rod, a stiffness adjustment component (4), a spring (5), and a joint output end (6). The power unit is a stiffness adjustment motor (9), which is connected to a joint motor (8). The joint motor (8) has a motor output end (801), and the base (1) is fixedly connected to the motor output end (801). The power unit is connected to the stiffness adjustment component (4) via the drive rod. The stiffness adjustment component (4) has a spring constraint hole (401) for constraining the spring (5) and is located between the base (1) and the joint output end (6). One end of the spring (5) is connected to the base (1), and the other end is movably connected to the joint output end (6). There are at least two springs (5), which are evenly arranged around the drive rod. One end of the spring (5) passes through the spring constraint hole (401). 01) Fixed on the base (1), the other end passes through the spring constraint hole (401) and is hinged to the joint output end (6); the drive rod is a screw, and the screw is connected to the stiffness adjustment motor (9); the base (1) has a threaded hole corresponding to the screw; the joint motor (8) is provided with a hollow shaft (802); the hollow shaft (802) and the stiffness adjustment motor (9) are respectively provided with a first slide rail (8021) and a first slide rail (904) for the axial movement of the stiffness adjustment motor, and the first slide rail (8021) and the first slide rail (904) cooperate; the screw passes through the threaded hole and the other end is rotatably connected to the stiffness adjustment component, that is, the stiffness adjustment motor drives its own axial movement through the kinematic pair formed by the screw, and then drives the stiffness adjustment component to move axially through the screw, so as to achieve the purpose of changing the effective working length of the spring; The base (1) has a keyway (101), and the drive rod is provided with a key (301) to prevent the drive rod from rotating axially. The base (1) is also provided with a guide pin (103); the stiffness adjustment component (4) is provided with a guide hole (402) that cooperates with the guide pin (103) to ensure that the stiffness adjustment component (4) rotates synchronously with the base (1) through the guide pin (103).

2. A flexible joint based on axial force, characterized in that, Includes the variable stiffness mechanism as described in claim 1.

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