Velocity Sensor with an Internal Feedback Control Loop

This paper presents a new velocity sensor whose output is directly proportional to velocity at 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 patch actuator to form a sensor-actuator pair for the implementation of active damping. The velocity sensor consists of a principal spring-mass seismic sensor with an internal direct velocity feedback control loop. This internal feedback loop uses a separate control spring-mass seismic sensor and a reactive actuator, which are fixed on the seismic mass of the principal sensor. The control gain is tuned to obtain two effects: first, the output signal from the principal sensor becomes directly proportional to the velocity at the base of the sensor itself and second, the fundamental resonance peak is reduced by the active damping effect of the internal feedback loop. The practical feasibility is then studied by considering a prototype model. The stability of the internal feedback control loop has been assessed first, following which the frequency response function of the sensor with and without the internal feedback loop has been measured. The experimental measurements have shown that the internal feedback loop is conditionally stable but guarantees sufficient gain margins to obtain the desired velocity output from the sensor. The sensor has been successfully tested with a closed loop, and shows the desired velocity output with no resonance at the fundamental natural frequency of the seismic sensor. © 2005 IOP Publishing Ltd.