Vibration-free position control for a two degrees of freedom flexible-beam sensor

• A 2DOF flexible-beam sensor, based on a force/torque sensor and a simple mechanism, was designed.
• This work includes the design of the mechanism, dynamics and a new model-based control method.
• Beam vibrations are reduced thus making contour following an easier and less time consuming task.
• It includes simulations, experimental validation and continuous verification of the methods.

This work presents a position control for a two degree of freedom flexible-beam made of a composite material, whose aim is to control the tip of the flexible-beam by decreasing the vibration when the beam moves. A mechatronic unit that uses a multi-axis force/torque sensor has been specially designed and we propose to control the system by using a reduced dynamic model. The control method makes use of an inner-loop to control the position of two servo-motors, by means of PID regulators, and an outer-loop that cancels the tip vibration. Moreover, the closed-loop motor dynamics has been reduced by using a series connection of filters that invert its dynamics. The motor controllers have proved to be fast and precise, and cancel the non-modelled components of the motor friction without the need for a previous estimation. The flexible-beam vibration has been controlled by implementing an input-state feedback linearisation which includes compensation terms for the nonlinear beam dynamics, a linear feedback control law and a full state estimator. The experimental validation of the complete control method showed a significant trajectory tracking of the tip, while vibrations were prevented.