Parallel type force control end effector

Abstract

The application discloses a parallel force control end effector in the technical field of robot intelligent manufacturing, which comprises a moving platform, three supporting points arranged on the moving platform, and a single-degree-of-freedom driving unit connected with each supporting point through a supporting chain structure, wherein the distance from each supporting point to the center of the moving platform is equal, and the bottom of the single-degree-of-freedom driving unit is connected with a fixed base. The parallel force control end effector is composed of the moving platform, three single-degree-of-freedom driving units moving independently, the supporting chain structure and the fixed base. The fixed base is connected with a robot end flange, and the three-degree-of-freedom force control function of the end effector is utilized to complete the contact type operation of the robot, and the parallel force control end effector has the advantages of large force-to-mass ratio, high output force value, low system inertia and the like, and solves the high-frequency dynamic contact force control problem during grinding of large and complex components of the robot.

Description

Technical Field

[0001] This invention relates to a parallel force-controlled end effector in the field of intelligent manufacturing technology for robots. Background Technology

[0002] With the development of robotics technology, the application of robots is no longer limited to non-contact operations such as handling and painting. Robots are increasingly being used in more complex contact-based work scenarios, such as grinding, polishing, and shaft-hole assembly. In contact operations, in addition to position control and positioning accuracy, the robot system also needs force control capabilities and precision. Therefore, force-controlled end effectors, independent of the robot's control loop, have become an important component of robotics technology.

[0003] In existing technologies, force-controlled end effectors mostly employ pneumatic, hydraulic, or electric drive methods. Voice coil motors, double-acting cylinders, or low-friction cylinders are the primary drive mechanisms. However, these actuators cannot achieve high-precision force control, especially in the case of insufficient accuracy in controlling high-frequency dynamic contact forces during grinding. Summary of the Invention

[0004] The purpose of this invention is to provide a parallel force-controlled end effector to solve the problem of high-frequency dynamic contact force control during the grinding of large and complex components by robots.

[0005] To achieve the above objectives, the present invention provides a parallel force-controlled end effector, including a moving platform with three fulcrums. Each fulcrum is equidistant from the center of the moving platform. Each fulcrum is connected to a single-degree-of-freedom drive unit via a branch structure. The bottom of the single-degree-of-freedom drive unit is connected to a fixed base.

[0006] Compared with the prior art, the beneficial effects of this invention are that it consists of a moving platform, three independently moving single-degree-of-freedom drive units, a branch structure, and a fixed base. The fixed base is connected to the robot's end effector flange, and utilizes the three-degree-of-freedom force control function of the end effector to complete the robot's contact operation. It has advantages such as a large force-to-weight ratio, high output force value, and low system inertia, solving the problem of high-frequency dynamic contact force control during the grinding of large and complex components by robots.

[0007] As a further improvement of the present invention, the three-degree-of-freedom drive unit includes a hollow shaft, in which a pneumatic muscle is disposed. The hollow shaft is coupled with a linear bearing, the lower end of which is connected to a side cover. The lower end of the hollow shaft extends into the side cover and is connected to a nonlinear drive mechanism. The nonlinear drive mechanism is coupled with a reverse multiple stroke mechanism.

[0008] This design embeds the pneumatic muscle within a hollow shaft, which engages with a linear bearing, allowing only axial movement. The lower end of the hollow shaft is connected to a nonlinear drive mechanism. As the hollow shaft moves, the nonlinear drive mechanism passively generates a parallel force matching the nonlinear characteristics of the pneumatic muscle, thereby outputting an upward thrust. This, in conjunction with a reverse multiple stroke mechanism, constructs a force-position curve parallel to the pneumatic muscle.

[0009] As a further improvement of the present invention, the nonlinear drive mechanism includes a nonlinear spring, the initial state of which is a compressed state, the upper end of which is connected to the lower end of the hollow shaft, the lower end of which is connected to the movable tray, and the movable tray is connected to the reverse multiple stroke mechanism.

[0010] Thus, the nonlinear spring force-position curve also exhibits nonlinear characteristics. However, unlike the gas spring, as the spring is gradually compressed, i.e., the deformation increases, the spring output force shows a nonlinear upward trend. This is achieved by driving the reverse multiple stroke mechanism through the movable tray, thereby changing the force-position curve of the nonlinear spring.

[0011] As a further improvement of the present invention, the reverse multiple stroke mechanism includes a pair of fixed racks respectively disposed on both sides of the side cover. The fixed racks are equipped with gears, which are mounted on a rotating shaft. The rotating shaft is disposed on a bracket, which is mounted on the outer periphery of the hollow shaft. The gears also mesh with the movable rack, and the lower end of the movable rack is connected to the movable tray.

[0012] This mechanism firstly changes the direction of the spring's output force. Since the spring is initially compressed, under external force, the rack and pinion transmission gradually releases the spring's travel, causing its absolute deformation to continuously increase, while the output force decreases non-linearly. Secondly, this mechanism also functions to double the speed and travel. Through the cooperation of the fixed rack, gears, and moving rack, the travel of the moving rack end is doubled, effectively doubling the variable speed. The doubled travel function maintains the spring's deformation consistent with the gas spring, while the doubled speed effect improves the spring mechanism's response speed and reduces the impact of spring lag on the force control device's response rate.

[0013] As a further improvement of the present invention, the nonlinear spring is a conical spring, which can better match the nonlinear characteristics of the pneumatic muscle to obtain a parallel force output curve.

[0014] As a further improvement of the present invention, the supporting guide structure has a main guide post, which is located in the middle of the chassis. A nonlinear spring is sleeved on the outer periphery of the main guide post. The axis of the main guide post coincides with the axis of the pneumatic muscle. Four auxiliary guide posts are also distributed on the chassis with the main guide post as the center. The upper end of the auxiliary guide posts passes through the movable tray.

[0015] In this way, the direction of the up-and-down movement of the movable tray is always parallel to the axis of the pneumatic muscle by using the dominant and auxiliary columns.

[0016] As a further improvement of the present invention, the branch structure includes a ball joint, the ball joint connects the fulcrum and the joint bearing, the joint bearing is connected to the swing arm, the middle part of the swing arm is machined with a bushing, the lower end of the swing arm is connected to the upper end of the pneumatic muscle extending from the hollow shaft, the bushing is sleeved on the pin, the two ends of the pin are connected to the shaft bracket, and the shaft bracket is set on the top of the hollow shaft.

[0017] By using ball joints and joint bearings, multi-angle swing control can be achieved, thereby enabling better contact with the workpiece being processed and completing robot contact operations. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the present invention.

[0019] Figure 2 This is a schematic diagram of the single-degree-of-freedom driving unit structure of the present invention.

[0020] Figure 3 The internal structure of the single-degree-of-freedom drive unit of this invention Figure 1 .

[0021] Figure 4 The internal structure of the single-degree-of-freedom drive unit of this invention Figure 2 .

[0022] Figure 5 The internal structure of the single-degree-of-freedom drive unit of this invention Figure 3 .

[0023] Figure 6 This is a schematic diagram of the force control principle of the present invention.

[0024] The components include: 1. Moving platform, 2. Ball joint, 3. Joint bearing, 4. Swing rod, 5. Bushing, 6. Pin, 7. Shaft bracket, 8. Linear bearing, 9. Side cover, 10. Fixed base, 11. Hollow shaft, 12. Bracket, 13. Wheel axle, 14. Gear, 15. Fixed rack, 16. Moving rack, 17. Movable tray, 18. Nonlinear spring, 19. Main guide column, 20. Auxiliary guide column, 21. Pneumatic muscle. Implementation

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

[0026] like Figure 1-6 The parallel force-controlled end effector shown includes a moving platform 1 with three fulcrums. Each fulcrum is equidistant from the center of the moving platform 1. Each fulcrum is connected to a single-degree-of-freedom drive unit via a branch structure. The bottom of the single-degree-of-freedom drive unit is connected to a fixed base 10.

[0027] The three-degree-of-freedom drive unit includes a hollow shaft 11, a pneumatic muscle 21 is installed inside the hollow shaft 11, the hollow shaft 11 is engaged with a linear bearing 8, the lower end of the linear bearing 8 is connected to a side cover 9, the lower end of the hollow shaft 11 extends into the side cover 9 and is connected to a nonlinear drive mechanism, the nonlinear drive mechanism is engaged with a reverse multiple stroke mechanism, a chassis is installed at the bottom of the side cover 9, and a support and guide structure is installed on the bottom.

[0028] The nonlinear drive mechanism includes a nonlinear spring 18, which is initially in a compressed state. The upper end of the nonlinear spring 18 is connected to the lower end of the hollow shaft 11, and the lower end of the nonlinear spring 18 is connected to the movable tray 17. The movable tray 17 is connected to the reverse multiple stroke mechanism.

[0029] The reverse multiple stroke mechanism includes a pair of fixed racks 15 respectively disposed on both sides inside the side cover 9. Each fixed rack 15 is equipped with a gear 14, which is mounted on a rotating shaft 13. The rotating shaft 13 is mounted on a bracket 12, which is installed on the outer periphery of the hollow shaft 11. The gear 14 also meshes with a movable rack 16, the lower end of which is connected to a movable tray 17. The nonlinear spring 18 is a conical spring.

[0030] The main guide column 19 is supported and guided. The main guide column 19 is located in the middle of the chassis. The nonlinear spring 18 is sleeved on the outer periphery of the main guide column 19. The axis of the main guide column 19 coincides with the axis of the pneumatic muscle 21. Four auxiliary guide columns 20 are also distributed on the chassis with the main guide column 19 as the center. The upper end of the auxiliary guide column 20 passes through the movable tray 17.

[0031] The branch structure includes a ball joint 2, which connects the fulcrum and the joint bearing 3. The joint bearing 3 is connected to the rocker arm 4. The rocker arm 4 has a bushing 5 machined at its end. The bushing 5 is fitted onto the pin 6. Both ends of the pin 6 are connected to the shaft bracket 7. The shaft bracket 7 is located on the top of the hollow shaft 11.

[0032] This invention proposes a parallel drive configuration of an opposing pneumatic muscle 21 and a nonlinear spring 18, using this as a single-axis drive and employing a 3PRS configuration to design a three-degree-of-freedom parallel force-controlled end effector. The detailed principle and features are as follows.

[0033] From a biomimetic perspective, human movements are characterized by high adaptability, instantaneous dynamic response, and explosive force output. Complex and advanced applications of robots require a high degree of anthropomorphism in their force output capabilities to the external environment. That is, while accurately outputting force values, they must also possess the corresponding characteristics of human movements. Force control devices designed based on traditional drive units (such as motor reducers, hydraulic mechanisms, and cylinders) typically have low dynamic response. Pneumatic actuators are a novel type of drive device based on biomimetic design. They possess advantages such as a high force-to-weight ratio, high output force, and low system inertia, making them an ideal drive unit for human-like human control devices.

[0034] To match the nonlinear characteristics of the pneumatic muscle 21 and obtain a parallel force output curve, a conical spring force is employed. To construct a force-position curve parallel to the pneumatic muscle 21, a reverse multiple stroke mechanism, namely the double rack and pinion 14 mechanism, is designed. This mechanism has two functions: First, it can change the direction of the spring's output force. The spring is initially compressed; under external force, the rack and pinion transmission mechanism of gear 14 gradually releases the compressed spring's stroke, thus continuously increasing the absolute amount of its deformation, while the output force decreases nonlinearly. Second, this mechanism also functions as speed and stroke doubling. Through the cooperation of the fixed rack 15, gear 14, and moving rack 16, the stroke of the moving rack 16 is doubled, and the variable speed is doubled. The stroke doubling function keeps the deformation of the compressed spring consistent with the pneumatic muscle, while the speed doubling effect improves the response speed of the spring mechanism and reduces the impact of spring lag on the response rate of the force control device.

[0035] To achieve lightweight and miniaturized design, the support and guide mechanism is combined with the drive mechanism. The pneumatic muscle 21 is built into the hollow shaft 11, which cooperates with the linear bearing 8 and can only move axially. The lower end of the hollow shaft 11 contacts the nonlinear spring 18. As the hollow shaft 11 moves, the spring passively deforms, thus outputting an upward thrust. To achieve precise force control, a reverse multiple stroke mechanism, namely the double rack and pinion gear 14 mechanism, is designed to change the force-position curve of the nonlinear spring 18. When compressed air is supplied to the pneumatic muscle, the muscle contracts. Because the pneumatic muscle is fixed at its lower end, it drives the hollow shaft 11 to move downward.

[0036] When the hollow shaft 11 is expanded by the pneumatic muscle 21 and driven to move downward, the gear 14, connected to the lower end of the hollow shaft 11 via the bracket 12, will rotate downward along the fixed rack 15 and around the rotating shaft 13. Since it meshes with both the fixed rack 15 and the movable rack 16, one end of the movable rack 16 is movable, and the other end is connected to the movable support plate. The movable support plate is connected to the lower end of the nonlinear spring 18. When the hollow shaft 11 moves downward, the nonlinear spring 18 also moves downward, the movable support plate 17 moves downward, and the movable rack 16 also moves downward. Through the cooperation of the fixed rack 15, the movable rack 16, and the gear 14, the nonlinear spring 18 moves downward with double the stroke, achieving parallelism between the force-position curve of the nonlinear spring 18 and the force-position curve of the pneumatic muscle 21, satisfying the force control principle. Figure 6 As shown, PAM is the pneumatic muscle 21, and the linkage mechanism is the other mechanism in the single-degree-of-freedom drive unit except for the pneumatic muscle 21. The output force is the difference between the force of the pneumatic muscle 21 and the linkage mechanism.

[0037] This invention employs a 3PRS configuration, using a biomimetic single-DOF drive unit as the drive mechanism for each branch, and designs a 3-DOF parallel force-controlled end effector. It consists of a moving platform 1, three independently moving single-DOF drive units, joint bearings 3, and a fixed base 10. The fixed base 10 is connected to the robot's end flange. Utilizing the three-DOF force control function of the end effector, it completes the robot's contact-type operations, solving the problem of high-frequency dynamic contact force control during the grinding of large and complex components by the robot.

[0038] This invention is not limited to the above embodiments. Based on the technical solutions disclosed herein, those skilled in the art can make some substitutions and modifications to some of the technical features without creative effort, and all such substitutions and modifications are within the protection scope of this invention.

Claims

1. A parallel force-controlled end effector, characterized in that, It includes a moving platform with three fulcrums. Each fulcrum is equidistant from the center of the moving platform. Each fulcrum is connected to a single-degree-of-freedom drive unit through a branch structure. The bottom of the single-degree-of-freedom drive unit is connected to a fixed base. All three single-degree-of-freedom drive units include hollow shafts, with pneumatic muscles installed inside the hollow shafts. The hollow shafts are fitted with linear bearings, and the lower end of the linear bearings is connected to the side cover. The lower end of the hollow shafts extends into the side cover and is connected to the nonlinear drive mechanism. The nonlinear drive mechanism is fitted with a reverse multiple stroke mechanism. A chassis is installed at the bottom of the side cover, and a support and guide structure is installed on the bottom. The nonlinear drive mechanism includes a nonlinear spring, which is initially in a compressed state. The upper end of the nonlinear spring is connected to the lower end of the hollow shaft, and the lower end of the nonlinear spring is connected to the movable tray. The movable tray is connected to the reverse multiple stroke mechanism. The reverse multiple stroke mechanism includes a pair of fixed racks respectively disposed on both sides inside the side cover. The fixed racks are equipped with gears, which are mounted on a rotating shaft. The rotating shaft is disposed on a bracket, which is mounted on the outer periphery of the hollow shaft. The gears also mesh with the movable rack, and the lower end of the movable rack is connected to the movable tray. The branch structure includes a ball joint, which connects the fulcrum and the joint bearing. The joint bearing is connected to the rocker arm. The end of the rocker arm is machined with a bushing, which is fitted onto the pin. Both ends of the pin are connected to the shaft bracket, which is located on the top of the hollow shaft.

2. The parallel force-controlled end effector according to claim 1, characterized in that: The nonlinear spring is a conical spring.

3. A parallel force-controlled end effector according to claim 2, characterized in that: The supporting guide structure is a main guide column, which is located in the middle of the chassis. A nonlinear spring is sleeved on the outer periphery of the main guide column. The axis of the main guide column coincides with the axis of the pneumatic muscle. Four auxiliary guide columns are also distributed on the chassis with the main guide column as the center. The upper end of the auxiliary guide columns passes through the movable tray.

Images