Two-Stage Switching Hybrid Control Method Based on Improved PSO for Planar Three-Link Under-Actuated Manipulator

The planar three-link passive-active-active (PAA) under-actuated manipulator does not satisfy the small-time local controllability (STLC), which makes it more difficult to control than other planar under-actuated manipulators. This paper presents a two-stage switching hybrid control method based on improved particle swarm optimization (PSO) for the PAA under-actuated manipulator. According to the model reduction strategy, the control process is divided into two stages. The workspace of the manipulator is analyzed to guarantee the target position within the reachable region. In order to reduce the probability of falling into local optimum, we introduce the Metropolis criterion of simulated annealing algorithm and crowding factor of artificial fish swarm algorithm into PSO algorithm to calculate the target angles of two active joints. At each control stage, we design the Lyapunov function to maintain the angle of an active joint unchanged while we build the sliding surface and select the power function as reaching law to make the other active joint converge to the target angle. The control law switches to next stage when the rotated joint converges to the target angle. The proposed method not only retains the rapidity of sliding mode control, but also reduces the total chattering of the system by the Lyapunov function method. Simulation results demonstrate that the proposed method has shorter steady-state adjustment time than that of existing typical control methods, and its overshoot is almost zero.