Mechatronic robot arm with active vibration absorbers

Serial robots are typically able to cover large workspace, but their mass/stiffness ratio does not allow combining high accuracy and high dynamic of the end effector operations. Widely spread usage of serial robots, even for tasks such as drilling, leads to high accuracy demands through its workspace. Absolute measurement of the end point for position feedback can be challenging due to objects or even a workpiece in the workspace. Moreover, inbuilt motors of the serial robot cannot response in the frequency range high enough as vibration of the end point. Instead, an additional spring-mass system is attached to the robot to suppress vibrations. The narrow frequency range of a passive dynamic absorber can be extended with active elements between the robot and absorber. An active approach is also necessary because of robots eigenfrequencies and eigenmodes variability. The study deals with a planar flexible robot equipped with a three-degree-of-freedom planar active absorber. The absorber is tuned passively to one value of multiple eigenfrequency. The linear-quadratic regulator control with a state observer has been designed as an active absorber control algorithm. Feedback inputs are absorber body acceleration, end effector acceleration, and relative motions in three absorber actuators realized by voice coils. The end effector vibration suppression along the robot trajectory is achieved using gain scheduling of local controller's outputs.