Passive Gravity Balancing For Two Joints Serial Manipulators Based On Stiffness Matrix

Gravity balance can reduce motor load and improve the performance of robot effectively. Based on passive gravity balance theory, in this paper, gravity balance method of serial robot using pure springs are brought out. The design, performance and control are all investigated theoretically and experimentally.Firstly, gravity balance of a single DOF link is analyzed based on energy method, which proved that completely gravity balance can be achieved by using zero-free-length spring. Differences between gravity balanced robot and normal one were investigated using Lagrange equation, which reveals that spring can improve the performance of robot dynamics. The effect of gravity balancing can be influenced by spring stiffness, position and angles. Matrix of both elastic and gravitational potential energy are studied using the principal of energy conservation. Element sign and value distribution of elastic stiffness matrix are also investigated, based on which, 4 sufficient conditions related to spring installation in robot gravity balancing are summarized.Secondly, analysis the factors which effect gravity balance,and results show that spring have significant effect robot gravity balance. Analysis gravity balance control system, choose using PID control, establishe a DC motor control system mathematical model and analysis in Matlab / Simulink, results show that gravity balance significantly enhance the dynamic performance of control system. Design a double joints gravity balancd robot virtual prototype, robot under the different load of multiple dynamic simulation in ADAMS, simulation results and the study of the gravity balance theory coincide.Finally, using LABVIEW to design the upper computer of the gravity balance experiment platform, a servo motor is debugged and the robot motion experiment is carried out. Experimental results show that gravity balancing robot dynamic performance better, the gravity balance motor energy consumption is far less than the normal. combined with the PID control and improved disturbance observer completed the improved gravity balance control scheme.