Load sensing variable ratio actuator

Abstract

This invention discloses a load-sensitive variable transmission ratio actuator, comprising a load-sensitive variable transmission mechanism and a drive unit. The load-sensitive variable transmission mechanism adopts a structure combining a five-bar linkage and a torsion spring. The drive unit drives the fourth link to rotate, and transmits the driving torque to the first link via the five-bar linkage. When the actuator output is subjected to load torque, the torsion spring undergoes elastic deformation, causing changes in the linkage configuration of the five-bar linkage and the lever arm ratio corresponding to the load torque and drive torque. This allows the actuator transmission ratio to continuously adjust with the absolute value of the load torque, achieving adaptive transmission of output torque and motion speed. This invention can automatically adjust the transmission ratio according to the load torque, improving torque adaptability and energy utilization efficiency under different operating conditions.

Description

Technical Field

[0001] This invention relates to the field of robot actuators, and more specifically to a load-sensitive variable transmission ratio actuator. Background Technology

[0002] Actuators in powered exoskeletons, prostheses, and robotic systems need to provide corresponding torque and speed under different motion conditions to meet the needs of movements such as walking, jumping, and climbing stairs. Existing actuators typically use motors with fixed-ratio reduction gears to drive the system, reducing output speed and increasing output torque to meet load requirements. However, the load conditions of robots and exoskeletons continuously change during actual operation, and the torque and speed requirements vary depending on the working condition. For example, some working conditions require low speed and high torque, while others require high speed and low torque.

[0003] Because the transmission ratio of a fixed-ratio actuator remains constant during operation, it is difficult to adjust the torque-speed relationship according to load changes. This results in the actuator failing to maintain transmission characteristics that match actual needs under different load conditions, leading to low efficiency. To adapt to changing load requirements, existing variable-ratio actuators include active and passive types. Active variable-ratio mechanisms typically require additional motors, clutches, or speed-changing mechanisms for adjusting the transmission ratio, complicating the actuator structure and control process. Passive variable-ratio mechanisms utilize mechanical deformation caused by the load to adjust the transmission ratio. Some existing passive variable-ratio mechanisms can use elastic elements to change transmission characteristics according to load torque, but different mechanisms vary in transmission ratio adjustment range, structural form, and load adaptability. Therefore, how to automatically change the transmission ratio according to changes in actuator load torque using a mechanical structure, and achieve adaptive transmission between driving torque and output torque without adding an additional active speed-changing drive mechanism, remains a technical problem that needs to be solved in the field of robotics and exoskeleton actuators.

[0004] Therefore, to solve the above problems, a new actuator is needed that can automatically adjust the transmission ratio according to the load torque, thereby improving torque adaptability and energy utilization efficiency under different working conditions. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to overcome the defects in the prior art and provide a load-sensitive variable transmission ratio actuator that can automatically adjust the transmission ratio according to the load torque, thereby improving torque adaptability and energy utilization efficiency under different working conditions.

[0006] The load-sensitive variable transmission ratio actuator of the present invention includes a load-sensitive variable transmission mechanism and a drive unit;

[0007] The load-sensitive variable transmission mechanism includes a five-bar linkage and a torsion spring. The five-bar linkage includes a first link, a second link, a third link, a fourth link, and a fixed frame. The fixed frame is rotatably connected to the first link and the fourth link, respectively. The first link serves as an output link, with its end forming the actuator output end. The fourth link serves as an input link. The second link is connected to the first link, and the third link is connected to the fourth link, forming a relative rotational connection between the second and third links. The torsion spring is connected between the third and fourth links. When the actuator output end bears the load torque, the torsion spring undergoes elastic deformation to change the linkage configuration of the five-bar linkage.

[0008] The load-sensitive variable transmission mechanism is configured such that as the absolute value of the load torque at the actuator output increases, the deformation of the torsion spring increases, and the lever arm ratio corresponding to the load torque and the driving torque in the five-bar linkage changes, thereby causing the transmission ratio of the actuator to change continuously with the load torque.

[0009] The drive unit is used to provide drive torque to the load-sensitive variable transmission mechanism to drive the fourth link to rotate, and transmit the drive torque to the first link through the five-bar linkage, so that the actuator output end generates corresponding output motion and output torque.

[0010] Furthermore, in the five-bar linkage, the fixed frame is arranged along a preset reference axis, and the first link, second link, third link and fourth link have corresponding link lengths and link angles relative to the reference axis; the end of the fourth link is connected to the drive unit; a torsion spring is installed between the third link and the fourth link so that the third link and the fourth link can generate a relative angular displacement related to the load torque.

[0011] Furthermore, the load-sensitive variable transmission mechanism determines the transmission ratio based on the position of the load torque acting on the first link and the position of the driving torque acting on the fourth link, and the transmission ratio satisfies: ;in, For load-sensitive variable transmission mechanisms, The force arm on the third link corresponding to the load torque. This is the force arm on the third link that corresponds to the driving torque;

[0012] When the load torque is zero, the torsion spring is in its initial state, and the transmission ratio corresponds to the transmission ratio of the five-bar linkage in its initial configuration. When the load torque increases, the torsion spring undergoes elastic deformation, causing a relative angular displacement between the third and fourth links, and changing... and The ratio between them increases the transmission ratio.

[0013] Furthermore, the linkage configuration of the five-bar linkage is solved based on the load angle and load torque at the actuator output, specifically including:

[0014] Establish the closed-loop kinematic equations of the five-bar linkage based on the length and angle of each link; differentiate the closed-loop kinematic equations in time to obtain the angular velocity relationship between the input link and the output link;

[0015] The relationship between load torque and driving torque is established based on the principle of virtual work; and the Newton-Raphson iterative method is used to solve the closed-loop kinematic equations and the relationship between load torque and driving torque to obtain the driving angle of the fourth link, the link angles of the second and third links, and the driving torque.

[0016] Furthermore, the drive unit includes a motor and a reducer connected to the motor, and the output end of the reducer is connected to the fourth link;

[0017] The relationship between the motor torque and the actuator output torque is determined based on the transmission ratio of the load-sensitive variable transmission mechanism and the efficiency of the reducer.

[0018] The power transfer relationship between the actuator's input torque and output torque is determined based on the transmission ratio of the load-sensitive variable transmission mechanism and the reduction ratio of the reducer.

[0019] Furthermore, the actuator input power is determined based on the motor mechanical power, motor output angular velocity, and motor electrical power. The actuator input torque requirement is adjusted according to the transmission ratio corresponding to the load torque, so that the drive unit uses a smaller transmission ratio under low load conditions and a larger transmission ratio under high load conditions.

[0020] Furthermore, an actuator dynamics model considering the parameter variations of the load-sensitive variable transmission mechanism is established;

[0021] The dynamic model includes the equivalent stiffness that varies with load angle and load torque. and angular transmission ratio And based on equivalent stiffness and angular transmission ratio Establish a state-space model of the actuator; during real-time control, adjust the equivalent stiffness according to the preset working area. and angular transmission ratio Local stabilization is performed to reduce the computational load required for real-time calculations by the microcontroller.

[0022] Furthermore, a linear quadratic regulator (LQR) is used to control the position and state of the actuator, and the state vector of the actuator is constructed to include the load position, load speed, and state variables related to the dynamic state of the actuator.

[0023] The state feedback gain matrix is ​​obtained by solving the Riccati equation, and the desired motor torque is generated based on the state feedback gain matrix, state error, and desired load position, so that the actuator can maintain the tracking control of the output position when the load torque changes and the angular transmission ratio and equivalent stiffness change.

[0024] The beneficial effects of this invention are as follows: This invention discloses a load-sensitive variable transmission ratio actuator, comprising a load-sensitive variable transmission mechanism and a drive unit. The load-sensitive variable transmission mechanism adopts a structure combining a five-bar linkage and a torsion spring. Utilizing the elastic deformation of the torsion spring caused by changes in the load torque at the actuator output end, the linkage configuration of the five-bar linkage and the lever arm ratio corresponding to the load torque and drive torque change, thereby causing the actuator's transmission ratio to continuously change with the load torque. The drive unit drives the input linkage to rotate and transmits torque to the output end via the five-bar linkage. This invention can automatically adjust the force and speed transmission relationship according to the load state, improving the actuator's torque output capability and energy utilization efficiency under different load conditions. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0026] Figure 1 This is a schematic diagram of the main structure of the load-sensitive variable transmission ratio actuator of the present invention;

[0027] Figure 2 This is a schematic diagram illustrating the working principle of the load-sensitive variable transmission ratio actuator of the present invention;

[0028] Figure 3 This is a schematic diagram of the embedded control hardware control principle of the present invention;

[0029] Figure 4 This is a schematic diagram of the load-sensitive variable transmission mechanism of the present invention;

[0030] Figure 5 This is a schematic diagram of the underlying control principle of the load-sensitive variable transmission ratio actuator of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings, as shown in the figures:

[0032] This embodiment discloses a load-sensitive variable transmission ratio actuator, including a load-sensitive variable transmission mechanism (LS-VRT) and a drive unit;

[0033] The load-sensitive variable transmission mechanism includes a five-bar linkage and a torsion spring. The five-bar linkage includes a first link, a second link, a third link, a fourth link, and a fixed frame. The fixed frame is rotatably connected to the first link and the fourth link, respectively. The first link serves as an output link, with its end forming the actuator output end. The fourth link serves as an input link. The second link is connected to the first link, and the third link is connected to the fourth link, forming a relative rotational connection between the second and third links. The torsion spring is connected between the third and fourth links. When the actuator output end bears the load torque, the torsion spring undergoes elastic deformation to change the linkage configuration of the five-bar linkage.

[0034] The load-sensitive variable transmission mechanism is configured such that as the absolute value of the load torque at the actuator output increases, the deformation of the torsion spring increases, and the lever arm ratio corresponding to the load torque and the driving torque in the five-bar linkage changes, thereby causing the transmission ratio of the actuator to change continuously with the load torque.

[0035] The drive unit provides driving torque to the load-sensitive variable transmission mechanism to drive the fourth link to rotate, and transmits the driving torque to the first link through a five-bar linkage, causing the actuator output to generate corresponding output motion and output torque. The drive unit includes a motor and a reducer connected to the motor, and the output end of the reducer is connected to the fourth link.

[0036] In this embodiment, in order to systematically apply the actuator of the present invention, an output angle detection unit and a control unit are also involved; the output angle detection unit is used to detect the load angle at the output end of the actuator; the control unit is connected to the drive unit and the output angle detection unit respectively, and is used to control the drive unit according to the actuator state corresponding to the load angle and the load torque.

[0037] The output angle detection unit includes a magnetic element disposed at the output end of the actuator and a magnetic sensor disposed corresponding to the magnetic element; the magnetic sensor is used to acquire the load angle at the output end of the actuator; the control unit includes a microcontroller, which is connected to the drive unit through a communication bus and generates control commands for the drive unit according to the load angle.

[0038] Each link of the five-bar linkage is made of lightweight metal material, and the torsion spring is made of spring steel. The stiffness of the torsion spring is used to determine the elastic torque between the third and fourth links. The output angle detection unit is located at the end of the first link. A crossed roller bearing is provided between the third and second links to allow relative rotation between the second and third links. The actuator also includes a bearing assembly for supporting the output end of the actuator and the rotational connection position of each link, as well as a mounting bracket for fixing the actuator.

[0039] Specifically, such as Figure 1 As shown, the actuator of this invention includes: connecting rods 1–4, a drive motor, a torsion spring, and a fixed frame. The five connecting rods are made of 7075 aluminum alloy, with lengths of 120mm, 100mm, 40mm, 50mm, and 100mm respectively. The torsion spring is made of spring steel with a wire diameter of 4mm, a mean diameter of 28mm, an effective number of coils of 7, and a stiffness of 4.28 Nm / rad. A crossed roller bearing between connecting rods 3 and 2 allows for relative rotation. A magnet mounted at the end of connecting rod 1, in conjunction with a magnetic sensor, is used to measure the angular position of the output shaft. Other components include a hinge pin, a spacer ring, an output shaft, and additional bearings. The actuator mounting bracket is used to mount the actuator on a test bench for experimental testing.

[0040] Figure 2 The working principle of the actuator of this invention is demonstrated. The red link is the output link, and the blue link is the input link. The force on link 3... The lever arms relative to the load and the drive pivot point are respectively and When the load torque of the output link When it is zero ( Figure 2 (a) (d)), spring torque The transmission ratio is zero, and the transmission ratio is equal to the four-bar linkage where the output rod length is equal to the sum of the lengths of connecting rod 3 and connecting rod 4. When the load torque increases in the positive direction ( Figure 2 In (b) (c)), the spring is under force Deformation under action, lever arm ratio (i.e., transmission ratio) The torque gradually increases. The same behavior occurs under negative load torque. Figure 2 (e) (f)). That is, Figure 2 In (a) and (d), under zero load torque, the torque transmission is consistent with the four-bar linkage. The transmission ratio is smaller than the positive load torque ( Figure 2 (b) to large positive load torque ( Figure 2 The transmission ratio increases from the small load torque (c) to the large load torque. Figure 2 From medium (e) to large negative load torque ( Figure 2 (f) increases.

[0041] Real-time control is achieved using embedded control hardware (see...) Figure 3A dual-core high-performance microcontroller unit (MCU) (such as ESP32) executes the real-time control algorithm. The brushless geared motor is driven by an integrated driver, simplifying the system design by eliminating the need for external drive circuitry. Key motor parameters are shown in Table 1. The MCU controls the motor driver via a CAN bus. A 21-bit magnetic encoder measures the load angle with an accuracy of 0.07° by detecting a radially magnetized magnet mounted on the output shaft. A digital power monitor is installed at the input of the motor driver to monitor its current and power consumption.

[0042] Table 1

[0043]

[0044] In this embodiment, in the five-bar linkage, the fixed frame is set along a preset reference axis, and the first link, second link, third link and fourth link have corresponding link lengths and link angles relative to the reference axis; the end of the fourth link is connected to the drive unit; a torsion spring is installed between the third link and the fourth link so that the third link and the fourth link can generate a relative angular displacement related to the load torque.

[0045] Specifically, such as Figure 4 As shown, the five-bar linkage consists of links 1 to 5, where link 5 is the fixed frame, link 1 is the output link, and link 4 is the input link. The lengths of the five links are as follows: The fixed frame is placed along the x-axis, with point A located at (0,0) and point E located at... The angles between connecting rods 1, 2, 3, and 4 and the x-axis are respectively... Stiffness is The torsion spring is connected between link 3 and link 4. Load torque. Acting on link 1, driving torque It acts on link 4.

[0046] Point B is located at Point D (connected to link 4) is located at Point C is the intersection of link 2 and link 3. The closed-loop kinematic equations of the five-bar linkage are:

[0047] (1)

[0048] (2)

[0049] To obtain the angular velocity relationship, the closed-loop equation is differentiated with respect to time:

[0050] (3)

[0051] (4)

[0052] According to the principle of virtual work:

[0053] (5)

[0054] because Substituting into the virtual work equation and simplifying, we get:

[0055] (6)

[0056] (7)

[0057] Given load angle and load torque The driving torque can be calculated by combining the Newton-Raphson iteration method with equations (1), (2) and (7). ,angle and connecting rod angle .

[0058] The transmission ratio can be:

[0059] (8)

[0060] In this embodiment, the motor torque The output torque is transmitted to the actuator through the reducer. Assuming the reducer efficiency Assuming the power flow direction is constant, the torque relationship is as follows:

[0061] (9)

[0062] Actuator input power Represented as:

[0063] ; ; (10)

[0064] in, For the mechanical power of the motor, This refers to the motor's output speed. This refers to the electrical power of the motor.

[0065] The actuator dynamics equation of this invention, neglecting friction, is as follows:

[0066] ;

[0067] Among them, equivalent stiffness and angular transmission ratio It varies with load angle and load torque. Since real-time LQR calculation on the MCU is computationally intensive, it will... and The values ​​are fixed to constants to reduce complexity. The LQR algorithm is used to control the actuator of this invention because it can still maintain efficient operation even when load changes cause actuator parameters to change.

[0068] The state-space representation of the system is as follows:

[0069] ;

[0070] The state vector is:

[0071] ;

[0072] ;

[0073] ;

[0074] Motor desired torque :

[0075] ; ;

[0076] Where K is the state feedback gain matrix, which is obtained by solving the Riccati equation. For feedforward gain, The desired load location.

[0077] State error weight matrix Control weight matrix .

[0078] The transmission ratio of the load-sensitive variable ratio actuator proposed in this invention increases with the increase of load torque, reaching a maximum value of 3.03 under positive torque at a load angle of 30° and a minimum value of 1.35 under zero load at 90°. Compared with a four-bar actuator, the load-sensitive variable ratio actuator can reduce input energy by up to 58.16% and increase output torque by 55%.

[0079] In reciprocating oscillation tests, the load-sensitive variable ratio actuator achieved a maximum energy saving of 23.13%, stemming from the increased load-sensitive gear ratio, which reduces the required motor current and thus lowers resistive losses. This advantage is particularly significant under high torque conditions, where the efficiency of the fixed ratio actuator drops drastically. Temperature rise tests confirmed that, under the same load, the operating temperature of the load-sensitive variable ratio actuator is significantly lower than that of the four-bar actuator, avoiding thermal overload and demonstrating improved thermal performance over long-term operation.

[0080] A closed-loop step tracking method using a fixed-gain LQR controller achieved a rise time of 0.12 s and a settling time of 0.29 s. This demonstrates that despite the variable ratio characteristics of the load-sensitive variable-ratio actuator, a simplified constant-gain controller is sufficient for positioning tasks. The approximation of fixed parameters effectively reduces the computational burden on the MCU, enabling real-time control without performance loss.

[0081] Compared to previous passive continuously variable transmission (CVT) designs, the load-sensitive variable ratio actuator of this invention uses a rigid five-bar linkage with a single torsion spring, which has higher load capacity and more predictable kinematics than compliant systems (such as elastic passive transmissions). The load-sensitive variable ratio actuator provides technical support for efficient, high-torque drives in robots, exoskeletons, and prostheses.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A load-sensitive variable transmission ratio actuator, characterized in that: This includes a load-sensitive variable transmission mechanism and a drive unit; The load-sensitive variable transmission mechanism includes a five-bar linkage and a torsion spring. The five-bar linkage includes a first link, a second link, a third link, a fourth link, and a fixed frame. The fixed frame is rotatably connected to the first link and the fourth link, respectively. The first link serves as an output link, with its end forming the actuator output end. The fourth link serves as an input link. The second link is connected to the first link, and the third link is connected to the fourth link, forming a relative rotational connection between the second and third links. The torsion spring is connected between the third and fourth links. When the actuator output end bears the load torque, the torsion spring undergoes elastic deformation to change the linkage configuration of the five-bar linkage. The load-sensitive variable transmission mechanism is configured such that as the absolute value of the load torque at the actuator output increases, the deformation of the torsion spring increases, and the lever arm ratio corresponding to the load torque and the driving torque in the five-bar linkage changes, thereby causing the transmission ratio of the actuator to change continuously with the load torque. The drive unit is used to provide drive torque to the load-sensitive variable transmission mechanism to drive the fourth link to rotate, and transmit the drive torque to the first link through the five-bar linkage, so that the actuator output end generates corresponding output motion and output torque.

2. The load-sensitive variable transmission ratio actuator according to claim 1, characterized in that: In the five-bar linkage, the fixed frame is set along a preset reference axis, and the first link, second link, third link and fourth link have corresponding link lengths and link angles relative to the reference axis; the end of the fourth link is connected to the drive unit; a torsion spring is installed between the third link and the fourth link so that the third link and the fourth link can generate a relative angular displacement related to the load torque.

3. The load-sensitive variable transmission ratio actuator according to claim 1, characterized in that: The load-sensitive variable transmission mechanism determines the transmission ratio based on the position of the load torque acting on the first link and the position of the driving torque acting on the fourth link, and the transmission ratio satisfies: ;in, For the transmission ratio of the load-sensitive variable transmission mechanism, The force arm on the third link corresponding to the load torque. This is the force arm on the third link that corresponds to the driving torque; When the load torque is zero, the torsion spring is in its initial state, and the transmission ratio corresponds to the transmission ratio of the five-bar linkage in its initial configuration. When the load torque increases, the torsion spring undergoes elastic deformation, causing a relative angular displacement between the third and fourth links, and changing... and The ratio between them increases the transmission ratio.

4. The load-sensitive variable transmission ratio actuator according to claim 2, characterized in that: The linkage configuration of the five-bar linkage is determined based on the load angle and load torque at the actuator output, specifically including: Establish the closed-loop kinematic equations of the five-bar linkage based on the length and angle of each link; differentiate the closed-loop kinematic equations in time to obtain the angular velocity relationship between the input link and the output link; The relationship between load torque and driving torque is established based on the principle of virtual work; and the Newton-Raphson iterative method is used to solve the closed-loop kinematic equations and the relationship between load torque and driving torque to obtain the driving angle of the fourth link, the link angles of the second and third links, and the driving torque.

5. The load-sensitive variable transmission ratio actuator according to claim 1, characterized in that: The drive unit includes a motor and a reducer connected to the motor, and the output end of the reducer is connected to the fourth link. The relationship between the motor torque and the actuator output torque is determined based on the transmission ratio of the load-sensitive variable transmission mechanism and the efficiency of the reducer. The power transfer relationship between the actuator's input torque and output torque is determined based on the transmission ratio of the load-sensitive variable transmission mechanism and the reduction ratio of the reducer.

6. The load-sensitive variable transmission ratio actuator according to claim 5, characterized in that: The actuator input power is determined based on the motor's mechanical power, output angular velocity, and electrical power. The actuator's input torque requirement is adjusted according to the transmission ratio corresponding to the load torque, so that the drive unit uses a smaller transmission ratio under low load conditions and a larger transmission ratio under high load conditions.

7. The load-sensitive variable transmission ratio actuator according to claim 4, characterized in that: Establish an actuator dynamics model that considers the parameter variations of the load-sensitive variable transmission mechanism; The dynamic model includes the equivalent stiffness that varies with load angle and load torque. and angular transmission ratio And based on equivalent stiffness and angular transmission ratio Establish a state-space model of the actuator; during real-time control, adjust the equivalent stiffness according to the preset working area. and angular transmission ratio Local stabilization is performed to reduce the computational load required for real-time calculations by the microcontroller.

8. The load-sensitive variable transmission ratio actuator according to claim 7, characterized in that: A linear quadratic regulator (LQR) is used to control the position and state of the actuator. The state vector of the actuator is constructed to include load position, load speed and state variables related to the dynamic state of the actuator. The state feedback gain matrix is ​​obtained by solving the Riccati equation, and the desired motor torque is generated based on the state feedback gain matrix, state error, and desired load position, so that the actuator can maintain the tracking control of the output position when the load torque changes and the angular transmission ratio and equivalent stiffness change.

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