Study On Robot Joint Based On Reversing Ball Screw Mechanism

Robot actuator is a basic part whose structure, weight, size and accuracy will directly affect the robot servo system. This research is one part of the Project "Research on A New Type of Multi-Screw-Style General Actuator", which is supported by Subject of Fundamental Parts and Systems, Theme of Robot Technology, National High-tech Research and Development Program (863 Program) (Authorized Number: 2002AA423140). The robot actuator based on reversing-ball-screw reducing mechanism proposed innovatively in this paper is featured by smaller size, high accuracy, big output moment and compact structure and so on, which is published as an invent patent named as "hydraulically-driven longitudinal robot joint (application number: published number: CN1436639A)". Aiming at the characteristic of the reversing-ball-screw actuator, systematic research is done in detail including innovation of structure, mechanism design and manufacture, finite element analysis, kinematics and ball bearing contact analysis, design and analysis of control system, simulation of PID control, simulation of self-adaptive fuzzy control and experimental study and so on. The position control of the robot joint is explored which is based on the variable-frequency hydraulic technology. The major research is listed as follow: 1.The robot rotary joint is classified into longitudinal joint and crosswise joint and the joint modules are divided into module of longitudinal joint, module of crosswise joint and link module. The transmission theory of reversing-ball-screw is put forward in this paper and the structure innovation is included. The robot joint based on single-screw, double-screw, electrical-drive and hydraulic-drive is put forward according to the idea of standardization and modularization. 2.Study about the reversing-ball-screw actuator is done in detail including mechanism and kinematics design, finite element analysis, ball bearing contact analysis of screw pair and thrust pair, the analysis indicates that the main parts can bear the design load and the rolling contact pair including the screw pair and splined pair will not fail to work because of excessive plastic deformation. The dynamic characteristic is analyzed through finite element method and the restrain modal is solved. 3.Aiming at the difficulty of machining internal spiral groove with big lift angle and small size, the approximating method of using circular-arc cutter is put forward, which is proved to be a feasible method within range of the permissible error through the digital simulation using typical software such as the Program files function of I-DEAS and the Manufacturing Module of UG. After rough machining on the reformed numeric control machine of multi-DOFs, the high-speed air grinder, grinding wheel of CBN (cubic boron nitride) and carborundum wheel are used for finishing machining and the machining precision is acceptable. 4.The mathematical model is built for the hydraulic-driven servo control system. The control system and the control method are analyzed based on the Matlab software package Simulink. Because of I type control system, there is not steady-state error and the PID control is aimed at the stability, and response time and minimized transient error. The digital simulation of PID control is carried out according to the PID parameters, which indicates that the control system has a favorable position tracking accuracy against sinusoidal input and square-wave input. 5.The fuzzy control theory is applied to study the control characteristic of the hydraulic-driven joint. The control performance of simple fuzzy control and self-adaptive fuzzy control is simulated. Because the hydraulic system parameter is often variable, the simple fuzzy control cannot adapt to the change and the self-adaptive PID fuzzy control is adaptive to the change, which is proved to have a good control performance through the digital simulation. 6.The position control technology of the robot joint is explored which is based on the variable-frequency hydraulic technology that has been applied to superpower control system. The mathematic model of position control based on variable-frequency hydraulic technology is built and the position feedback control simulation proves a lagging system response because the load pressure of the variable-frequency hydraulic volume control system follows the load and the position and pressure (or dynamic pressure) feedback is necessary. In this paper, some innovative progresses are achived in the following aspects: 1. The robot rotary actuator based on reversing-ball-screw mechanism is proposed, which is a published patent for invention named as "hydraulical-drive longitudinal robot joint"(published number: CN1436639A). The modularized hydraulical-drive screw actuator and electric-drive screw actuator are designed, whose static and dynamic analysis and contact analysis are carried out. 2. The robot rotary actuator with a composite reversing-ball-screw mechanism is proposed, which includes serial reversing-ball-screw mechanism, parallel reversing-ball-screw mechanism, serial double-reversing-ball-screw mechanism andparalled double-reversing-ball-screw mechanism. And the composite mechanism is featured by smaller size, high accuracy, big output moment and compact structure. What's more, the actuators are modularized which are hydraulically-driven or electrically-driven. 3. Aiming at the difficulty of machining internal spiral groove with big lift angle and small size, the approximating method of using circular-arc cutter is put forward within range of the permissible error. The grinding method through the high-speed pneumatic grinder is also proposed. In this paper, the spiral groove is machined within the permissible error by the pneumatic CBN grinding wheel with a speed of 200 thousand r/m. 4.Based on the above modularized joint, the 4 DOFs lettering robot is putforward, which is composed of longitude joint modular, crosswise joint modular and link modular and is granted a patent for a utility model (patent number: ZL200320114568.3). The reversing-ball-screw mechanism is applied to the motion switching mechanism of enigine, which is published as an invention patent named as "computer-controlled engine and the controlling method (published number: CN1523215A)"...