Force/Position Control Strategy Of Ball Screw Feed System Based On Sliding Mode Control Architecture

In recent years,with the development of high-precision machining,man-machine collarboration and other fields,where position or force control alone cannot satisfy the pursuit of high precision and stability.However,for systems with a single control input,position or force control is achieved by switching between two independent controllers(position controller and force controller),which often leads to oscillation of the controlled position and force.Researchers propose comprehensive force/position control methods without switching,which typically requires some weighting factors or frequency-based decoupling,resulting in a complex controller design process.Based on this,this paper uses the idea of sliding mode control architecture for reference to construct a smooth switching strategy of force/position control,which provides a new idea for realizing the smooth transition between the two control modes.According to the structure characteristics and working principle of the ball screw feed drive system,the equivalent mass model of the ball screw feed system was established by lumped parameter method,so as to satisfy the accurate characterization of the dynamic characteristics of the system.On the basis of clarifying the interaction mechanism between ball screw feed system and environmental obstacles,a spring-damping system was introduced to describe the changing trend of the interaction force.At the same time,combined with the core idea of sliding mode control,the force/position control architecture of ball screw feed system was constructed,which considered the influence of nonlinear friction force and interaction force during the table motion.The chattering phenomenon in the sliding stage is weakened by using disturbance observer to suppress external disturbance.On the basis of clear working principle of the disturbance observer,considering the influence of velocity measurement noise,the constraint relation between the inner loop sensitivity and the complementary sensitivity transfer function is established,and the practical design criterion of the disturbance observer is derived.Based on the idea of sliding mode control architecture,a smooth switching strategy of force/position control was constructed.The equivalent control input of the system was estimated by the observer and an appropriate reaching law was selected to ensure the convergence and stability of the motion.In addition,the reaction force observer is used to estimate the interaction force,which improves the system bandwidth and reduces the cost.Based on the above theoretical modeling and analysis,the performance analysis experimental platform of the ball screw feed system was built,and the smooth switching strategy of force/position control was verified experimentally.Experimental results show that compared with the classical discontinuous control method,the maximum forward trajectory tracking error of the proposed method in the position control mode is 13μm(reduced by 60.6%),and the maximum negative trajectory tracking error is 8μm(reduced by 73.3%),which significantly improves the motion accuracy of the feed system.Moreover,no chattering occurs in the force control mode,and smooth transition between the two control modes is realized.