Active vibration cancellation is a particular type of vibration control that uses actuators, sensors and electronic control to reduce vibrations without necessarily adding damping or introducing vibration isolation. Vibration is attacked with a counter-force that drives the system of interest to respond in a way that is exactly opposite to the system's response to other inputs. The total response of the system at the location of interest can then be driven to zero, or at least be significantly redeuced. In vibration damping, energy is removed from a resonant system. In vibration isolation, the transmissibility from one subsystem to another is reduced. In vibration cancellation, a force is introduced to counteract the influence of forces disturbing the system and causing unwanted vibration.

Active vibration cancellation can be particularly effective when the disturbance source driving a system to an undesirable response has most of its energy at a single frequency, or perhaps at a fundamental frequency and integer multiples or harmonics of that frequency. This situation often arises in rotating machinery where the main disturbance is likely to occur once per rotation. Another common case is that of a translating or reciprocating device that forces a system response. In that case, unwanted responses at the harmonic frequencies may result from nonlinearities in the disturbing element or in its interaction with the system.

A typical active vibration cancellation system consists of one or more sensors to measure both the disturbance input and the unwanted vibration response, one or more actuators to supply the physical counter-force, electronic conditioning and amplification, and some means of digital processing. For simpler cases, the processing can be accomplished with a microcontroller. For more complex ones, a digital signal processor (DSP) may be used. Control algorithms can be specialized for computational efficiency and adaptability to disturbance inputs that change their character over time.

CSA has developed several active vibration cancellation controllers to attack different physical systems. Pictured below are examples of measured vibration responses at different harmonic frequencies for two systems and the level of reduction in vibration achieved with CSA's active cancellation systems. CSA is currently developing an integrated sensor/actuator/controller package for low-cost autonomous vibration cancellation.

Contact eric.anderson@csaengineering.com with questions about active vibration cancellation.

Active Systems
Products and Solutions: Industrial