Compliant mechanism for industrial robot polishing end effector

Abstract

The invention relates to a compliant mechanism for an industrial robot polishing end effector, which comprises an inner shell, positive stiffness characteristic mechanisms, negative stiffness characteristic mechanisms and an outer shell, the inner shell is of a hollow cylindrical structure and is connected with one ends of the three negative stiffness characteristic mechanisms and one ends of the three positive stiffness characteristic mechanisms, and the other ends of the three negative stiffness characteristic mechanisms are connected with the outer shell; the two mechanisms are uniformly distributed in the cylindrical surface of the inner shell, the other ends of the two mechanisms are connected with the outer shell, the inner shell can be sleeved on the bearing to move along with the movement of the bearing, the two mechanisms are driven to move, the outer shell is further driven to move, and the movement of the whole mechanism is realized. The flexible control device acts on the end effector of the grinding industrial robot to achieve flexible control, vibration generated in the grinding process can be restrained, force fluctuation is reduced, grinding force is controlled within the expected range, meanwhile, force overshoot is avoided, the body health of workers is guaranteed, a workpiece, the end effector and the grinding environment are prevented from being damaged, and the working efficiency is improved. And the surface quality of the workpiece is improved, and the production efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial robots and relates to a compliant mechanism used for polishing an end effector of an industrial robot. Background Art

[0002] With the rapid development of numerical control and artificial intelligence, industrial robots have been widely used in various industrial fields such as automobiles, express logistics, aerospace, and shipbuilding. Robot-assisted manufacturing has been widely used, bringing about improvements in process efficiency and product quality. Nowadays, robot polishing is widely used in intelligent manufacturing and is the focus of research in countries around the world.

[0003] Grinding efficiency directly affects the quality of the product, so the grinding operation is a key part of the entire production process. In recent years, the manual labor in grinding processing has been gradually replaced by industrial robots, which effectively improves the grinding efficiency and surface quality. Industrial robot processing is more flexible, efficient and economical. It can be equipped with actuators, sensors and different end effectors to achieve precise force control. At the same time, robot processing can process large workpieces. For complex curved workpieces, no special fixtures are required, which reduces the processing cost.

[0004] When the robot performs the grinding task, it will have direct contact with the workpiece and generate contact force. Excessive contact force will cause damage to the robot body and even harm the operator and the grinding environment. Therefore, the contact force must be controlled within a certain range. At present, there are two main methods for force control of robot grinding, namely direct force control and indirect force control. Direct force control is achieved by controlling the torque of the joint. However, it greatly relies on the precise dynamic model of the robot and the real-time and robust control methods, resulting in low force control accuracy, large inertia, and relatively slow response speed. Indirect force control is achieved by the robot end effector, which has stronger flexibility and lower inertia. At the same time, the mixed control of force and displacement can significantly improve the accuracy and response speed through indirect force control. In order to achieve force control, the end effector should show compliance to avoid excessive contact with the workpiece. The actuator can achieve passive compliance control or active compliance control. Passive compliance means that when the robot contacts the environment, it absorbs or stores energy through some auxiliary compliance mechanisms, so that it can naturally comply with external forces. It is the simplest way to control contact force. Active compliance control means that on the basis of position control, the robot uses force feedback information to take certain control strategies to actively control the force. However, in order to achieve high stability and select feedback strategies, active compliance control first requires a good force control algorithm, then needs to have a fast learning ability to cope with changes in the robot and the external environment, and also requires stronger robustness to adapt to the interference of the external environment. Therefore, the feed speed (i.e., moving speed) should be low enough to ensure accurate force control, but this will reduce processing efficiency. At the same time, the active compliance control algorithm and mechanical structure are far more complex than passive compliance control, and the accuracy of force control is not good enough. Especially when the end effector contacts the workpiece or the surface is irregular, force overshoot is inevitable and relatively large, which may cause damage to precision instruments and safety risks.

[0005] In order to overcome the shortcomings of active compliance control, this paper focuses on passive compliance control and designs a compliant mechanism. The compliant mechanism can effectively suppress the vibration generated during grinding and provide a stable contact force within a certain range of motion, thereby achieving high-speed grinding. Therefore, there is no force overshoot when the end effector contacts the workpiece, that is, the compliant mechanism acts as a buffer or isolator. Summary of the invention

[0006] In order to achieve the above-mentioned purpose, the present invention provides a compliant mechanism for the end effector of an industrial robot for grinding, which solves the problems existing in the prior art. The compliant mechanism is used for grinding mechanical parts, and acts on the end effector of the grinding industrial robot to realize flexible control, which can suppress the vibration generated during the grinding process, reduce force fluctuations, and control the contact force generated when the workpiece contacts the end of the actuator within the desired range, while avoiding force overshoot, which not only ensures the health of the workers, prevents the workpiece, the end effector and the grinding environment from being damaged, but also improves the surface quality of the workpiece and improves production efficiency.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a compliant mechanism for grinding the end effector of an industrial robot, comprising an inner shell, a positive stiffness characteristic mechanism, a negative stiffness characteristic mechanism and an outer shell, the upper half of the inner shell is connected to one end of the negative stiffness characteristic mechanism, and the lower half is connected to the positive stiffness characteristic mechanism, and the other ends of the positive stiffness characteristic mechanism and the negative stiffness characteristic mechanism are both connected to the outer shell, characterized in that: the inner shell is a hollow structure, which can be sleeved on a bearing and move with the movement of the bearing, thereby driving the positive stiffness characteristic mechanism and the negative stiffness characteristic mechanism to move; the other ends of the positive stiffness characteristic mechanism and the negative stiffness characteristic mechanism are directly connected to a fixed outer shell, and the outer shell moves with the movement of the positive stiffness characteristic mechanism and the negative stiffness characteristic mechanism, thereby realizing the movement of the overall compliant mechanism.

[0008] Furthermore, the inner shell is cylindrical as a whole, and a groove is provided at the upper end, and the grinding tool can be fixed through the groove.

[0009] Furthermore, there are three positive stiffness characteristic mechanisms, all of which are in the same horizontal plane and evenly distributed in the lower half of the cylindrical surface of the inner shell.

[0010] Furthermore, there are three negative stiffness characteristic mechanisms, all of which are in the same horizontal plane and evenly distributed in the upper half of the cylindrical surface of the inner shell. Each negative stiffness characteristic mechanism and a positive stiffness characteristic mechanism are located on the same busbar, and the negative stiffness characteristic mechanism is located above the positive stiffness characteristic mechanism.

[0011] Furthermore, the outer shell is also cylindrical with a hollow structure inside, and its diameter is about twice that of the inner shell and its height is about half that of the inner shell. Six M6 threaded holes are provided on the top of the outer shell, and the six M6 threaded holes are evenly distributed in the same annular surface, which can be connected with a flange to fix the overall compliant mechanism.

[0012] The beneficial effects of the present invention are:

[0013] 1. Instead of using a single mechanism design, a stiffness combination method is used to combine negative stiffness and positive stiffness. The Young's modulus is compensated by the stiffness combination mechanism, and there is no need to use materials with low Young's modulus and high strength-to-modulus ratio (these materials are not easy to obtain in practice, and it may be difficult to form a specific shape using special materials), which reduces the overall structure's requirements for material performance.

[0014] 2. The vibration generated during grinding can be better suppressed without affecting the grinding performance of the end effector. Generally speaking, there is no conflict between sensitivity and performance.

[0015] 3. The stability and overload bearing capacity of the compliant mechanism itself are better than other independent compliant mechanisms, that is, the designed compliant mechanism is more solid and durable.

[0016] 4. The cylindrical structure is suitable for rotational motion, which can keep the force uniform during the movement of the compliant mechanism, and can make the center of mass of all structures of the end effector on the same axis, so that each mechanism can maintain the same state of motion.

[0017] 5. Considering the stability and load-bearing capacity of the compliant mechanism, a total of three groups of positive stiffness characteristic mechanisms and negative stiffness characteristic mechanisms are selected for design, and a uniform distribution structure is adopted, that is, three positive stiffness characteristic mechanisms and three negative stiffness characteristic mechanisms are evenly distributed on the inner shell of the compliant mechanism, and the adjacent mechanisms are 120° apart, and the negative stiffness characteristic mechanism is set at the top and the positive stiffness characteristic mechanism is set at the bottom. By arranging them reasonably, the combined structure can remain stable during movement in the set direction, and can also connect the outer shell of the compliant mechanism.

[0018] 6. The overall structure is simple and light, which saves materials and reduces load while being easy to manufacture and install. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Attached Figure 1 It is a schematic diagram of the overall structure of the compliant mechanism for the industrial robot grinding end effector of the present invention;

[0020] Attached Figure 2 This is a schematic diagram of the internal structure of the compliant mechanism of the industrial robot grinding end effector of the present invention;

[0021] Attached Figure 3 It is a schematic diagram of the present invention being used for the industrial robot grinding end effector to grind a workpiece.

[0022] In the above figures: 1. Inner shell; 2. Positive stiffness characteristic mechanism; 3. Outer shell; 4. Negative stiffness characteristic mechanism; 5. M6 threaded hole; 6. Groove; 7. Industrial robot; 8. Force sensor; 9. Flange; 10. Compliant mechanism; 11. Grinding bearing; 12. Grinding head; 13. Grinding workpiece. DETAILED DESCRIPTION

[0023] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0024] like Figure 1 to Figure 2 As shown, a compliant mechanism for grinding an industrial robot end effector comprises an inner shell, a positive stiffness characteristic mechanism, a negative stiffness characteristic mechanism and an outer shell. The inner shell is in a hollow cylindrical shape, the upper part is connected to one end of the negative stiffness characteristic mechanism, the lower part is connected to one end of the positive stiffness characteristic mechanism, the other ends of the positive stiffness characteristic mechanism and the negative stiffness characteristic mechanism are both connected to the outer shell, the inner shell can be sleeved on the bearing and move with the movement of the bearing, thereby driving the positive stiffness characteristic mechanism and the negative stiffness characteristic mechanism to move, the other ends of the positive stiffness characteristic mechanism and the negative stiffness characteristic mechanism are both directly connected to the fixed outer shell, the outer shell moves with the movement of the positive stiffness characteristic mechanism and the negative stiffness characteristic mechanism, thereby realizing the movement of the overall compliant mechanism. The negative stiffness characteristic mechanism adopts a steady-state beam, and three steady-state beams are evenly distributed on the cylindrical surface of the inner shell at an inclined angle, and the three steady-state beams are all in the same plane. When the steady-state beam is deformed to a certain extent, the overall stiffness of the beam will decrease as the deformation increases, that is, negative stiffness is generated; the positive stiffness characteristic mechanism adopts a multi-layer buckling structure, in which each layer is an independent module, each layer has the same length, each multi-layer buckling structure is designed as 3 layers, and they are evenly distributed directly below the negative stiffness characteristic mechanism. When the multi-layer buckling structure is deformed to a certain extent, the overall stiffness will increase as the deformation increases, that is, positive stiffness is generated. The combined stiffness method combines positive stiffness and negative stiffness, and controls the overall stiffness within the desired range by offsetting the positive and negative stiffness, thereby controlling the contact force within the desired range.

[0025] like Figure 3As shown, a force sensor is connected to the end of the industrial robot to detect force changes in various directions during the grinding process. The flange is connected to the sensor, the compliance mechanism is fixed to the flange through an M6 threaded hole, the grinding bearing is sleeved in the compliance mechanism through an inner shell of a hollow structure, and the grinding head is fixed to the end of the grinding bearing. The industrial robot end, force sensor, flange, compliance mechanism, grinding bearing and grinding head together constitute a grinding industrial robot end effector based on the compliance mechanism, which is used to grind workpieces. When performing the grinding task, the grinding head rotates rapidly, and the grinding head will vibrate when in contact with the workpiece surface, thereby generating contact force. The grinding head transmits the contact force to the grinding bearing, and the grinding bearing then transmits the contact force to the compliant mechanism. The negative stiffness characteristic mechanism and the positive stiffness characteristic mechanism inside the compliant mechanism will be squeezed and deformed under force. When the squeeze deformation reaches a certain extent, the stiffness of the negative stiffness characteristic mechanism will decrease with the increase of deformation, and the stiffness of the positive stiffness characteristic mechanism will increase with the increase of deformation. The positive and negative stiffnesses offset each other, and the negative stiffness characteristic mechanism and the positive stiffness characteristic mechanism of the compliant mechanism work together to stabilize the overall stiffness of the end effector within the desired range during the entire grinding process, thereby controlling the contact force generated during the grinding process within the desired range, suppressing the vibration of the end effector, and avoiding force overshoot.

[0026] The above examples are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A compliant mechanism for an industrial robot grinding end effector, comprising an inner shell (1), a positive stiffness characteristic mechanism (2), a negative stiffness characteristic mechanism (4) and an outer shell (3), wherein the upper half of the inner shell (1) is connected to one end of the negative stiffness characteristic mechanism (4), and the lower half is connected to one end of the positive stiffness characteristic mechanism (2), and the other ends of the positive stiffness characteristic mechanism (2) and the negative stiffness characteristic mechanism (4) are both connected to the outer shell (3), characterized in that: The inner shell (1) is a hollow structure and can be sleeved on a bearing and move with the movement of the bearing, thereby driving the positive stiffness characteristic mechanism (2) and the negative stiffness characteristic mechanism (4) to move; the other ends of the positive stiffness characteristic mechanism (2) and the negative stiffness characteristic mechanism (4) are directly connected to a fixed outer shell (3), and the outer shell (3) moves with the movement of the positive stiffness characteristic mechanism (2) and the negative stiffness characteristic mechanism (4), thereby realizing the movement of the overall compliance mechanism (10).

2. The compliant mechanism for polishing the end effector of an industrial robot according to claim 1, characterized in that: The inner shell (1) is cylindrical as a whole, and a groove (6) is provided at the upper end, and a grinding tool can be fixed through the groove (6).

3. The compliant mechanism for polishing the end effector of an industrial robot according to claim 1, characterized in that: There are three positive stiffness characteristic mechanisms (2), all of which are in the same horizontal plane and evenly distributed in the lower half of the cylindrical surface of the inner shell (1).

4. The compliant mechanism for polishing the end effector of an industrial robot according to claim 1, characterized in that: There are three negative stiffness characteristic mechanisms (4), all of which are in the same horizontal plane and evenly distributed on the upper half of the cylindrical surface of the inner shell (1). Each negative stiffness characteristic mechanism (4) and a positive stiffness characteristic mechanism (2) are located on the same generatrix, and the negative stiffness characteristic mechanism (4) is located above the positive stiffness characteristic mechanism (2).

5. The compliant mechanism for polishing the end effector of an industrial robot according to claim 1, characterized in that: The outer shell (3) is also cylindrical, with a hollow structure inside, and a diameter approximately twice that of the inner shell (1), and a height approximately half that of the inner shell (1); six M6 threaded holes (5) are arranged on the top of the outer shell (3), and the six M6 threaded holes (5) are evenly distributed in the same annular surface, and can be connected to the flange (9) to fix the overall compliance mechanism (10).

Images