A study of compliant-based actuators for passive-active vibration control in vehicle suspension system

Abstract

This work proposes a method for controlling vibration transmissibility using compliant-based actuators. The compliant actuator combines a conventional actuator with elastic elements in a series configuration, such as passive springs, with the aim of controlling the vibration at important low frequencies. In contrast to the rigid actuator, a compliant actuator provides better accuracy and robustness for force control. At high frequencies, the actuator behaves like a passive spring with low impedance, providing lower output impedance and better shock resistance to the actuator than the stiff actuator. The benefits of compliant actuators for vibration control applications, demonstrated in this work, are twofold: (i) vibration reduction over a wide frequency bandwidth by passive control means; (ii) improvement of vibration control performance when active control is applied using the compliant actuator. The vibration control performance is compared with the control performance achieved using the well-known vibration absorber and conventional rigid actuator systems. The performance comparison showed that the compliant actuator provided a better flexibility in achieving vibration control over a certain frequency bandwidth. The investigation on passive and active control characteristics of the compliant actuator are conducted in relation to the compliant stiffness and damping parameters, which reveal a strong influence of the parameters to the overall passive-active vibration suppression performance. The active control characteristics are analyzed by using the Proportional and Derivative (PD) control strategy which demonstrated the capability of effectively changing the respective effective stiffness and damping of the system. These attractive dual passive-active control characteristics are therefore advantageous for achieving an effective vibration control system, particularly for controlling the vibration over a specific wide frequency bandwidth. The optimization strategy for determining the parameters of a compliant actuator to achieve effective control of vibration transmissibility is also investigated. An optimization strategy for the compliant actuator system is proposed by minimizing the H2 norm of the transfer function associated with the force transmissibility of the system, while the active control performance is investigated by using the derivative-type controller. The effectiveness of the proposed optimization strategy is demonstrated by comparison of various compliant actuator systems and the conventional rigid actuator system. It is shown that the overall passive-active control vibration performance can be improved satisfactorily. The investigation on control stability performance of the compliant actuator is also performed. The results show that the compliant actuator with varying compliant stiffness offers promising robustness and control stability for controlling vibration for the given control gain used in the system. The development of a vehicle vibration control system by integrating a compliant actuator in the existing vehicle suspension system. The compliant actuator is attached to the vehicle body and consists of a servo motor, a compliant element and a set of pinion-rack. A vehicle ride model is developed for the vibration control performance analysis, combining the vehicle suspension system with the compliant actuator model. The investigation results show that the compliant actuator can provide beneficial passive and active vibration control characteristics, particularly at low frequency region around the vehicle body resonance. The operational bandwidth of compliant actuator can be adjusted according to the selected compliant stiffness and it has the benefits of protecting the actuator against potential shocks received during vehicle ride. These benefits offer an attractive alternative for the actuator used in vehicle suspension system, compared to the conventional rigid actuator. The active vibration control results using an output feedback control demonstrate the effectiveness of the proposed system in reducing the vehicle body acceleration at important low frequencies. The last part of the thesis presents a case study of the proposed compliant actuator. Here, a new design of the compliant mechanism is proposed. Hence, the characteristics of a compliant mechanism are initially investigated using a flexible beam structure, which is deployed in various angle configurations. The co-rotational finite element method is used to model and simulate the dynamics behavior of the compliant mechanism. The results demonstrate that different configurations of the compliant mechanism will significantly influence the compliant stiffness, which in turn affects the vibration control performance. These properties assist in the selection of suitable control parameters for optimizing the vibration control performance, demonstrated through the force transmissibility analysis. The results show that the proposed compliant actuator with a flexible beam structure offers potentials for vibration control applications, such as for suppressing undesirable vibration normally encountered in various aerospace applications; as an alternative to a compliant actuator with a mechanical passive spring as the compliance.

Date of Award	14 May 2017
Original language	English
Awarding Institution	Univerisity of Nottingham
Supervisor	Dunant Halim (Supervisor) & Atanas A. Popov (Supervisor)