Mechanical Boom Vibration Mitigation using Active Force Control

In off-highway vehicles, an undesirable vibration in a mechanical structure is a well-known problem. Such vibrations are discomforting in humans and can even lead to serious health issues related to orthopedics. Passive vibration attenuation approaches are popular in engineering practice but rely heavily on vehicle structural changes. Moreover, such approaches are known to be less effective on low frequency vibrations. In the last decade or so, there has been significant technological advancement in actuators as well as sensing mechanisms. This has enabled us to realize active vibration control as an important tool in managing excessive vibration levels. It is noteworthy that a typical active vibration control assumption is that the controlled structure maintains its dynamic properties throughout the control procedure. This simplifies linear-time invariant (LTI) model-based control design approaches. We note that in certain applications, such as gantry cranes, spraying mechanical booms, etc. a system has time-varying behavior. This poses a challenge in defining a precise nominal model for LTI-based control approaches. So, it is interesting to investigate a control system structure which adjusts its control performance in response to changing system properties over a given period. In this work, we present one specific variant of active vibration control known as active force control (AFC). The beauty of AFC design is that the control action is generated simply through the following two steps: i) obtain the difference between a vibrating structure body acceleration and actuating force on the input side of the structure; ii) multiply the difference with an inverse transfer function of an actuator and then appropriately add to existing control action. We present experimentation on an actual representative mechanical boom model realized in MATLAB. The efficacy of results (60% to 70% reduction) is reported with respect to classical PID like an active control scheme.