Velocity sensor with an internal feedback control loop

Abstract

This paper presents a new velocity sensor whose output is directly proportional to velocityat low frequencies, but has a well damped resonance after which it has a controlled roll-off.It is designed to be used in a feedback loop with a closely located piezoelectric patchactuator to form a sensor–actuator pair for the implementation of active damping.The velocity sensor consists of a principal spring–mass seismic sensor with aninternal direct velocity feedback control loop. This internal feedback loop uses aseparate control spring–mass seismic sensor and a reactive actuator, which are fixedon the seismic mass of the principal sensor. The control gain is tuned to obtaintwo effects: first, the output signal from the principal sensor becomes directlyproportional to the velocity at the base of the sensor itself and second, the fundamentalresonance peak is reduced by the active damping effect of the internal feedback loop.The practical feasibility is then studied by considering a prototype model. Thestability of the internal feedback control loop has been assessed first, followingwhich the frequency response function of the sensor with and without the internalfeedback loop has been measured. The experimental measurements have shown thatthe internal feedback loop is conditionally stable but guarantees sufficient gainmargins to obtain the desired velocity output from the sensor. The sensor hasbeen successfully tested with a closed loop, and shows the desired velocity outputwith no resonance at the fundamental natural frequency of the seismic sensor.