Smart materials are being applied more and more widely in semi-active vibration reduction systems. Actuators built with their use are characterized by nonlinearities and hysteretic effects. Their omission in mathematical descriptions may lead to deterioration of the vibration reduction systems. For that reason, it is important to take into account these negative phenomena associated with the actuators at the controller synthesis stage. One method for determining the control laws in semi-active vibration reduction systems that is frequently discussed in academic literature is “Clipped-LQR”. The present paper proposes modification of that method to allow inclusion in the controller synthesis of the hysteretic properties and other nonlinearities of an actuator. The method developed was verified by determining the controller for the semi-active suspension of a machine operator’s seat. A magnetorheological damper was used as an actuator. The dynamic properties of the foam covering of the operator’s seat were included in model. Simulation tests were performed on the vibration reduction system and function of vibration transmissibility was determined. The semi-active vibration reduction system tested was compared to a passive system. The considerations presented herein relate to the semi-active suspension of a machine operator’s seat, and the method presented may be applied to other controlled systems with many degrees of freedom.

Laboratory investigations of an active vehicle suspension of an in-series structure of the slow-active type are presented in this paper. The multidimensional model is reduced to a case representing quarter car suspension. Control laws for active vibration reduction systems are usually determined based upon linear models of objects. Active suspensions are characterised by nonlinearity, connected most often with actuating systems and their energetic restrictions. This causes divergences between theoretical quality factors and those determined experimentally. The second essential problem is finding a compromise between opposed quality factors (for example, minimum power requirement and high efficiency of vibration reduction).Thanks to the use of the proper control law in the active vibration reduction system of vehicle suspension, the goal of ensuring a high level of ride comfort, good vehicle handling and incessant contact of the wheels with the road surface with a minimum power requirement may be attained. The authors, in seeking a compromise, determined classical LQR controllers for the proposed quality indicators realising the aims mentioned above. These controllers are determined for a linearised suspension model obtained from identification. Experimental characteristics are determined for all of the suspension control systems.

Studies of systems with energy regeneration have been carried out for years, because they primarily cover the assemblies with electrodynamic actuators. This paper addresses the issue of active reduction of mechanical vibration using an electrohydraulic actuator. The testing procedure aims to assess the potential use of those assemblies in a different frequency band and force range than in electrodynamic actuators. The paper explains the operating principle of the system, and the findings of laboratory tests are presented. The tested vibration reducing system is the physical model of a 2 degree-of-freedom (DOF) suspension. An initial analysis has been conducted to explore the potential use of the energy produced by the vibration of unsprung mass in the first degree of the suspension system, for power supply to the active component incorporated in the second suspension degree. The energy recuperated from the first suspension DOF is transferred by a dedicated hydraulic system and stored in an accumulator. Results of the experiments revealed that the mechanical parameters of the system can be selected in such a way that for specific interfering signals the accumulated energy should be at least equal to the energy used up by the system.

The article discusses a prototype of a Shape Memory Alloy (SMA) spring intended for controlled vibration reduction systems. The spring has been subject to experiments and the article presents selected static and dynamic characteristics. The experiments were conducted at the Dynamics and Control of Structures Laboratory of the AGH University of Science and Technology. They permitted the formulation of a mathematical model for the SMA spring. The model takes into account the phenomena of energy accumulation and dissipation. The parameters of the spring model have been determined, based on the experimental data. The model takes into account the relationship of stiffness and damping to alloy temperature and the frequency of excitation. It has been demonstrated that the properties of the spring may be altered under controlled conditions. The spring model was then used in simulations. They served as the basis for the determination of the frequency response characteristics, which were then compared to the characteristics of a real spring. The mathematical model developed may be applied in the design of passive, semi-active, and active vibration reduction systems, as well as in the synthesis of adaptive smart vibration reduction systems.

Use of springs made of an alloy with shape memory (SMA) to shape the dynamic characteristics of a resonance vibration screen is proposed in this paper. These springs change spring constant as a result of temperature changes. Thus it is possible to change their resonance frequency in real time. In the paper a mathematical model of a controlled SMA spring was formulated and its parameters were identified. In the model both the effect of spring coefficient changes and damping changes depending upon alloy temperature and spring vibration frequency were taken into consideration. Experimental investigations of the examined spring and screen physical model were carried out and selected characteristics were also included. The investigations were carried out at the Dynamics and Control of Structures Laboratory of AGH University of Science and Technology. The control law was formulated. Simulation investigations of the mathematical vibration screen model in both open and closed loop systems were made. It was shown that the elaborated control system is robust of vibration mass changes by as much as ±30%.