连杆侧无传感器下机器人柔性关节系统的零力控制

Free-force control of flexible robot joint system without sensors on link side

针对机器人直接示教应用场景,提出机器人柔性关节系统在连杆侧无传感器下的零力控制方法.引入动态LuGre摩擦模型进行关节摩擦力矩估计,采用2段四次多项式建立柔性关节系统刚度模型,基于广义动量观测关节力矩.该方法利用刚度逆模型以及关节力矩估算谐波减速器扭转位移,结合谐波减速器运动传递特性估计连杆侧角度并计算重力矩,利用连杆动力学方程估计接触力矩.构建期望的电机驱动力矩(包含估计的重力矩、摩擦力矩与接触力矩),通过对该期望电机驱动力矩的跟踪实现零力控制.在搭建的机器人柔性关节系统实验平台上进行实验.实验结果表明,完成相同的拖动示教过程时,该方法所需要的接触力矩约为1.8 N·m.基于重力矩与摩擦力矩补偿的零力控制方法需要接触力矩约为3.4 N·m.功率级脱离示教所需要的接触力矩约为14 N·m,验证了所提方法的实际效果.

A free-force control method of the flexible robot joint system without sensors on link side was proposed aiming at the application of robot direct teaching. The dynamic LuGre model was introduced to estimate the joint friction. Two-segment quartic polynomial was adopted to describe the stiffness of the flexible robot joint system. The joint torque was observed based on the generalized momenta. The torsional displacement of the harmonic drive was estimated through the inverse stiffness model and the joint torque among the algorithm. The gravity and angle on link side were figured out by combining torsional angle with motion transmission characteristics. The contact torque was obtained by utilizing the kinetic equation on link side. Then a desired motor driving torque was constructed comprising the gravity, joint friction and the contact torque. The free-force control was realized by tracking this desired motor torque. The experiments were conducted on the laboratory setup of the flexible robot joint system. The experimental results show that the contact torque is about 1.8 N·m when accomplishing the same drag teaching process. The free-force control method based on the compensation of gravity and friction requires a contact torque of about 3.4 N·m. The contact torque required for the power stage off teaching is approximately 14 N·m. The experimental results verify that the proposed method has a practical effect.