A disc-shaped balance weight tension spring gravity compensation mechanism
By setting a disc-shaped balance block tension spring gravity compensation mechanism at the pitch axis end of the robotic arm, the non-linearly changing lever arm counteracts the gravitational torque, solving the problem that traditional mechanisms cannot achieve complete gravity balance, improving the stability and control accuracy of the robotic arm, while reducing motor heating and energy consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DALIAN UNIV OF TECH
- Filing Date
- 2024-08-29
- Publication Date
- 2026-05-29
AI Technical Summary
Traditional spring-designed robotic arm gravity compensation mechanisms cannot achieve complete gravity balance, resulting in reduced dynamic characteristics of the robotic arm, motor overheating, and poor control performance.
A disc-shaped balance block and tension spring gravity compensation mechanism is adopted. By setting it at the pitch axis end of the robotic arm, the nonlinear changes of the balance block and tension spring are used to counteract the gravitational torque of the robotic arm, thus achieving complete gravity compensation.
It improves the stability and control precision of the robotic arm, reduces motor heat generation and energy consumption, lowers the weight and space occupied by the mechanism, and enhances adaptability and ease of installation.
Smart Images
Figure CN118849051B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a disc-shaped balance block tension spring gravity compensation mechanism, which belongs to the technical field of robot compensation; its main purpose is to achieve perfect balance of the gravitational torque acting on the pitch axis at any rotation angle of the pitch link. Background Technology
[0002] The RoboMaster robot's arm axis is parallel to the ground. Due to the weight of the arm, additional torque is generated at the joints, reducing the robot's dynamic characteristics. Furthermore, when stationary, if the motor stops, the arm will fall due to its own weight and cannot maintain its original launch position. Traditional compensation structures use springs, where the force change is linear, resulting in a linear change in the lever arm. However, the change in gravitational torque is non-linear. Therefore, current mainstream spring-based compensation robot arm balancing devices cannot achieve complete gravitational balance. Thus, a new gravity compensation mechanism needs to be designed. This mechanism must overcome the shortcomings of traditional linkage mechanisms, such as numerous springs, heavy weight, low flexibility, and large space occupation. Applying this mechanism to the RoboMaster robot can effectively solve the problems of overheating, excessive inertia, and poor control performance of the gimbal's pitch axis motor, thereby improving the accuracy of gravity compensation.
[0003] This mechanism can also be widely used at the pitch axis joints of various robotic arms to reduce motor power consumption and simplify control. Summary of the Invention
[0004] To address the aforementioned problems, the purpose of this invention is to provide a disc-shaped balance block tension spring gravity compensation mechanism. This mechanism is energy-saving, highly accurate, stable, and occupies little space, thereby improving the accuracy of pitch link launches and the overall performance of the RoboMaster robot.
[0005] The technical solution adopted in this invention is as follows: a disc-shaped balance block tension spring gravity compensation mechanism, which is installed at the pitch shaft end of the robotic arm and fastened by bolts. In the compensation mechanism, the balance block screw passes through the shaft end connecting plate, the balance block, and the structural reinforcing plate in sequence and cooperates with the balance block nut to clamp and fix the shaft end connecting plate and the structural reinforcing plate on both sides of the balance block respectively; the wire hanging post screw passes through the shaft end connecting plate, the wire hanging post, and the structural reinforcing plate in sequence and acts with the wire hanging post nut; the compensation mechanism is connected to the pitch shaft through the shaft end connecting plate.
[0006] The balance block has a balance line groove on the side near the structural reinforcement plate, and one end of the tension spring is set on the machine body, while the other end passes around the balance line groove and is connected to the robotic arm.
[0007] The extreme radius of the balanced linear groove is as follows:
[0008] r st = [ mgL k sin α 2 - r α ] 2 + mgL 4k cos 2 α 2
[0009] r st The radius of the balancing linear groove is m; the mass of the robotic arm is k; the spring constant is L; the length of the robotic arm is g; and the acceleration due to gravity is R. α α is the radius of the tension spring; α is the angle variable.
[0010] Since the change in force within a spring is linear, the change in lever arm is also linear. However, the change in gravitational torque is non-linear. Therefore, to improve accuracy, a disc-shaped balance block tension spring mechanism is designed to make the lever arm change non-linearly, achieving complete gravity compensation for the joints of the robotic arm over a large rotation range. The balance block uses a spring design for compensation in a passive gravity compensation method. When the robotic arm rotates, the balance block causes the spring to deform, resulting in a corresponding change in the spring force as the mechanism moves. This converts the changing gravitational potential energy of the robotic arm into elastic potential energy, achieving complete gravity balance for the robotic arm joints within the effective working space.
[0011] The main components related to the gravity compensation mechanism include the robotic arm (i.e., the upper arm, pitch link), the body, joint hinges, tension springs, steel wire ropes, pulleys, and counterweights. The counterweights are fixed to the robotic arm. When the robotic arm rotates, it drives the counterweights to rotate together around the center of the joint hinges. One end of the steel wire rope is fixed to the rim of the counterweight wheel, and the other end is guided by the pulley and connected to the tension spring. The other end of the tension spring is fixed to the body. The robotic arm and the body are connected by joint hinges.
[0012] During operation, the robot arm's own weight generates an additional torque on the hinge center. Since the counterweight is fixed to the robot arm, it also rotates, causing the steel cable to begin winding around the counterweight. The tension spring is stretched by the steel cable, resulting in elastic deformation. The tension generated by this deformation produces an opposing torque on the hinge center point, the magnitude of which depends on the spring stiffness and stretch, as well as the dimensions of the counterweight. By studying the relationship between the robot arm's structural dimensions and the torque, it is possible to completely cancel out the two torques at every position during the upper arm's rotation, thus achieving gravitational balance for the robot arm.
[0013] By adopting the above technical solution, the disc-shaped balance block tension spring gravity compensation mechanism has the following characteristics:
[0014] 1. This disc-shaped balance block tension spring gravity compensation mechanism has a good balancing effect, which can maintain the horizontal state of the pitch link in a static state, reduce the pitch link's sway, improve stability, and help with aiming and firing.
[0015] 2. Based on the structural characteristics of the disc-shaped balance block, a belt drive is used to cleverly transform the linearly changing force and lever arm in the spring to balance the nonlinearly changing gravitational torque. When the robotic arm rotates, the disc-shaped balance block causes the spring to deform, resulting in a corresponding change in the spring force as the mechanism moves. This converts the changing gravitational potential energy of the robotic arm into elastic potential energy, achieving complete gravitational balance of the robotic arm joints within the effective working space and improving control accuracy.
[0016] 3. The disc-shaped balance block tension spring gravity compensation mechanism is a purely mechanical structure with zero power consumption. It can also save the power required for the motor to maintain the pitch link horizontal state, greatly reducing motor heat generation, reducing motor energy consumption, and improving the overall performance of the RoboMaster robot.
[0017] 4. This mechanism consists only of a balance block with a gravity compensation line, a shaft end connecting plate that transmits torque to the shaft, a structural reinforcement plate that increases structural stability, and anti-loosening nuts and screws for clamping. Compared with traditional linkage mechanisms, it is lighter, more flexible, occupies less space, is easier to install, has a high degree of adaptability, and is more adaptable.
[0018] The beneficial effects of this invention are as follows: This disc-shaped balance block tension spring gravity compensation mechanism overcomes the shortcomings of traditional linkage-based gravity balancing mechanisms, which can only balance nonlinear gravitational torque changes with linear lever arm variations. By studying the relationship between the structural dimensions of the disc-shaped balance block and the torque, the lever arm is made to change nonlinearly to achieve complete gravity compensation for the joints of the robotic arm over a large rotation range. This not only reduces pitch link sway and improves stability, aiding in aiming and launching, but also significantly reduces motor heat generation, lowers motor energy consumption, and improves the overall performance of the RoboMaster robot. Furthermore, compared to traditional linkage mechanisms, this mechanism is lighter, more flexible, occupies less space, is easier to install, has higher adaptability, and better versatility. Attached Figure Description
[0019] Figure 1 This is a three-dimensional diagram of a disc-shaped balance block tension spring compensation mechanism.
[0020] Figure 2 This is a side view of a disc-shaped balance block tension spring compensation mechanism.
[0021] Figure 3 This is a formal drawing of a disc-shaped balance block tension spring compensation mechanism.
[0022] Figure 4 This is a working diagram of a disc-shaped balance block tension spring compensation mechanism.
[0023] Figure 5 This is a force diagram of a robotic arm with a gravity balancing device.
[0024] In the diagram: 1. Balance block nut, 2. Balance block screw, 3. Shaft end connecting plate, 4. Balance block, 4a. Balance line groove, 5. Hanging post, 5a. Hanging post nut, 5b. Hanging post screw, 6. Structural reinforcement plate, 7. Tension spring, 8. Robotic arm. Detailed Implementation
[0025] This invention provides an example of a technical solution: a disc-shaped balance block tension spring gravity compensation mechanism, installed at the pitch joint motor of a RoboMaster robot. The disc-shaped balance block tension spring gravity compensation mechanism includes a balance block with a gravity compensation line, a shaft end connecting plate for transmitting torque to the shaft, a structural reinforcing plate to increase structural stability, and anti-loosening nuts and screws for tightening. The gravity compensation mechanism is located at the pitch shaft end and is fastened with bolts. One end of the balance block with the balance line groove is connected to the shaft via a shaft end connecting plate, and the other end is formed into a housing by a structural reinforcing plate and fastened with nuts.
[0026] Figures 1 to 4 An example is given where a balance block 4 with a balance groove is clamped on both sides by shaft end connecting plates 3 and structural reinforcing plates 6 using three sets of anti-loosening nuts and cylindrical head hexagonal screws to form a stable housing. Another set of anti-loosening screws and cylindrical head hexagonal screws pass through the hanging post 5 and press against the shaft end connecting plate 3 and structural reinforcing plate 6. In the compensation mechanism, the balance block screw 2 passes sequentially through the shaft end connecting plate 3, the balance block 4, and the structural reinforcing plate 6, engaging with the balance block nut 1 to clamp and fix the shaft end connecting plate 3 and the structural reinforcing plate 6 to both sides of the balance block 4; the hanging post screw 5b passes sequentially through the shaft end connecting plate 3, the hanging post 5, and the structural reinforcing plate 6, engaging with the hanging post nut 5a; the compensation mechanism is connected to the pitch shaft via the shaft end connecting plate 3. The balance block 4 has a balance groove 4a on the side near the structural reinforcing plate 6. One end of the tension spring 7 is mounted on the machine body, and the other end passes around the balance groove 4a and connects to the robotic arm 8. The extreme radius of the balance groove is as follows:
[0027] r st = [ mgL k sin α 2 - r α ] 2 + mgL 4k cos 2 α 2
[0028] r st The radius of the balancing linear groove is m; the mass of the robotic arm is k; the spring constant is L; the length of the robotic arm is g; and the acceleration due to gravity is R. α α is the radius of the tension spring; α is the angle variable.
[0029] Since the change in force within a spring is linear, the change in lever arm is also linear. However, the change in gravitational torque is non-linear. Therefore, to improve accuracy, a disc-shaped balance block tension spring mechanism is designed to make the lever arm change non-linearly, achieving complete gravity compensation for the joints of the robotic arm over a large rotation range. The balance block uses a spring design for compensation in a passive gravity compensation method. When the robotic arm rotates, the balance block causes the spring to deform, resulting in a corresponding change in the spring force as the mechanism moves. This converts the changing gravitational potential energy of the robotic arm into elastic potential energy, achieving complete gravity balance for the robotic arm joints within the effective working space.
[0030] The main components related to the gravity compensation mechanism include the robotic arm (i.e., the upper arm, pitch link), the body, joint hinges, tension springs, steel wire ropes, pulleys, and counterweights. The counterweights are fixed to the robotic arm. When the robotic arm rotates, it drives the counterweights to rotate together around the center of the joint hinges. One end of the steel wire rope is fixed to the rim of the counterweight wheel, and the other end is guided by the pulley and connected to the tension spring. The other end of the tension spring is fixed to the body. The robotic arm and the body are connected by joint hinges.
[0031] During operation, the robot arm's own weight generates an additional torque on the hinge center. Since the counterweight is fixed to the robot arm, it also rotates, causing the steel cable to begin winding around the counterweight. The tension spring is stretched by the steel cable, resulting in elastic deformation. The tension generated by this deformation produces an opposing torque on the hinge center point, the magnitude of which depends on the spring stiffness and stretch, as well as the dimensions of the counterweight. By studying the relationship between the robot arm's structural dimensions and the torque, it is possible to completely cancel out the two torques at every position during the upper arm's rotation, thus achieving gravitational balance for the robot arm.
[0032] Derivation of the equation for the profile curve of the balance block
[0033] By establishing a mechanical model of the static balance system of the robotic arm, considering the influence of the wire rope diameter and the change in the angle between the wire rope and the lower arm axis during operation, the equation of the outer contour curve of the balance block is derived.
[0034] Figure 5 This is a force diagram of a robotic arm with a gravity balancing device. M is the position of the robotic arm's center of mass, point O is the center of the joint hinge, L is the distance from the robotic arm's center of mass to point O, h is the length of the arm, and r0 is the vertical distance from the initial position of the balance block's rotation center to the wire rope.
[0035] Initially, MO is in a vertical position, with a = 180°. When the upper arm rotates clockwise by the torque generated by its own weight, the balance block fixed to the robotic arm rotates through an angle of π - α. The wire rope begins to wind around the counterweight, and the spring generates an opposing torque on the counterweight. To maintain static equilibrium of the entire mechanism, the torque generated by the weight of the upper arm should be equal to the torque generated by the wire rope passing through the counterweight.
[0036] mgLsina=Fr (1)
[0037] In the formula: m - mass of the upper arm; r - vertical distance from the center of rotation of the counterweight to the wire rope.
[0038] Differentiating both sides of equation (1) with respect to a, we can obtain the equation
[0039] mgLcosa= r+ F (2)
[0040] From arc differential
[0041] dx = rd (3)
[0042] dF = -kdx (4)
[0043] In the formula: k - the combined stiffness of the spring and the steel wire; x - the total deformation of the spring and the steel wire. From formulas (3) and (4), we can obtain:
[0044] = -k (5)
[0045] Substituting equation (5) into equation (1), we obtain the differential equation.
[0046] (6)
[0047] Equation (6) is a differential equation in terms of r and α, which can be solved using the double-angle formula for triangles:
[0048] (7)
[0049] A tension spring and a wire rope are connected in series; their combined stiffness is:
[0050] (8)
[0051] Where: k1—tension spring stiffness; Substituting equation (8) into equation (7) for the stiffness of the wire rope, we get:
[0052] (9)
[0053] The diameter of the wire rope was neglected when deriving the equation for the balance block's profile. In fact, there is a distance equal to the radius of the wire rope between the actual line of action of the wire rope and the surface of the balance block. This difference will cause errors in the gravitational torque compensation in two ways. First, a larger effective radius will cause the effective lever arm of the spring tension force to increase at each point of tangency. Second, because of the larger effective radius, more wire will be wound around the balance block, resulting in a larger spring deformation. Therefore, the radius r of the wire rope itself must be removed.
[0054] The corrected equation for the vertical distance from the center of rotation of the counterweight to the wire rope is:
[0055] (15)
[0056] The final contour curve equation of the balance block is:
[0057] r st = [ mgL k sin α 2 - r α ] 2 + mgL 4k cos 2 α 2 (16)
[0058] This disc-shaped balance block tension spring gravity compensation mechanism provides excellent balancing, maintaining the pitch link's horizontal position when stationary, reducing pitch link sway, improving stability, and aiding in aiming and launching. Based on the structural characteristics of the disc-shaped balance block, a belt drive is used to cleverly transform the linearly changing force and lever arm of the spring to balance the nonlinearly changing gravitational torque. When the robotic arm rotates, the disc-shaped balance block causes the spring to deform, resulting in a corresponding change in the spring force as the mechanism moves. This converts the robotic arm's changing gravitational potential energy into elastic potential energy, achieving complete gravitational balance of the robotic arm joints within the effective working space and improving control accuracy.
[0059] This disc-shaped balance block tension spring gravity compensation mechanism is a purely mechanical structure with zero power consumption. It eliminates the need for the motor to maintain the pitch link's horizontal state, significantly reducing motor heat generation and energy consumption, and improving the overall performance of the RoboMaster robot. The mechanism consists only of a balance block with a gravity compensation line, a shaft-end connecting plate that transmits torque to the axis, a structural reinforcement plate to increase structural stability, and anti-loosening nuts and screws for tightening. Compared to traditional linkage mechanisms, it is lighter, more flexible, occupies less space, is easier to install, has higher adaptability, and better versatility.
Claims
1. A disc-shaped balance block tension spring gravity compensation mechanism, wherein the compensation mechanism is mounted on the pitch shaft end of a robotic arm and fastened by bolts, characterized in that: In the compensation mechanism, the balance block screw (2) passes through the shaft end connecting plate (3), the balance block (4), and the structural reinforcing plate (6) in sequence and cooperates with the balance block nut (1) to clamp and fix the shaft end connecting plate (3) and the structural reinforcing plate (6) on both sides of the balance block (4); the hanging post screw (5b) passes through the shaft end connecting plate (3), the hanging post (5), and the structural reinforcing plate (6) in sequence and acts with the hanging post nut (5a); the compensation mechanism is connected to the pitch shaft through the shaft end connecting plate (3); The balance block (4) has a balance line groove (4a) on one side near the structural reinforcing plate (6), and one end of the tension spring (7) is set on the machine body, and the other end passes around the balance line groove (4a) and is connected to the robotic arm (8). The extreme radius of the balanced linear groove is as follows: r st The radius of the balancing linear groove is m; the mass of the robotic arm is k; the spring constant is L; the length of the robotic arm is g; the acceleration due to gravity is r. α α is the radius of the tension spring; α is the angle variable.