Jarosław Konieczny

Energy Recovering in Active Vibration Isolation System — Results of Experimental Research

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.

Optimal Control of Slow-Active Vehicle Suspension - Results of Experimental Data

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.

Modified Clipped-LQR Method for Semi-Active Vibration Reduction Systems with Hysteresis

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.

Bench Tests of Slow and Full Active Suspensions in Terms of Energy Consumption

This paper is focused on the problem of active suspensions of wheeled vehicles with electro-hydraulic actuators. Two dynamic structures first with actuator connected with spring in series and second in parallel – called slow active and full active respectively – were considered. The considerations described in the paper concern physical quarter-vehicle models of suspensions. These models were constructed and installed on a rig for dynamic tests of structures. A laboratory rig enables the simulation of real conditions by disturbing investigated suspension by kinematic excitation. Research was carried out for various algorithms controlling the actuator of the active unit. For evaluation of laboratory research results, comparisons were proposed of frequency response functions and of time curves of instantaneous power taken by the active system from supply, obtained at the same excitation signals. Quantitative aggregated indicators in the form of an averaged coefficient of vibration transmissibility and power required for the active unit to achieve vibration transmissibility function were also proposed.

Application of an SMA Spring for Vibration Screen Control

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%.

Mathematical Model of a Shape Memory Alloy Spring Intended for Vibration Reduction Systems

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.

The Control System for a Vibration Exciter

The paper presents the control system for an electro-hydraulic vibration exciter. A vibration exciter is used to carry out kinematic and forced excitations. Such excitations are needed during the static and dynamic examinations of suspension assemblies and their elements, such as damping springs. The most important elements of the exciter are: a hydraulic servo valve, a hydraulic actuator, a control system and a hydraulic supply station. An inductor works in a negative feedback loop. A set point generator and controller are parts of a real-time control system. The authors used a cRIO-9022 industrial computer from National Instruments analogue input and output modules. Apart from supporting I/O modules, the cRIO controller in a real-time system communicates with an FPGA circuit that forms a control loop. The use of an FPGA (Field Programmable Gate Array) allowed for implementing a hardware control loop through a vibration exciter, as well as other control loops used in the research (such as controlling an active executive element). The use of such a system architecture enabled the parallel operation of multiple control threads. The selected structure also allows for flexible selection of the measuring channels, which are essential for system monitoring and data acquisition.

Laboratory Tests of Shape Memory Alloy Wires

In this paper, tests on Shape Memory Alloy (SMA) wires for use in controlled actuators have been discussed. Selected static and dynamic characteristic curves being the result of experiments were presented in the article. Experiments were conducted at the Dynamics and Control of Structures Laboratory of the AGH University of Science and Technology. Laboratory tests of SMA wires used as actuators have been presented in the paper. Actuators made from the wires contract by about 4-5% of their length when heated, like small muscles, and loosen when cooled. SMA wires used as drives are significantly smaller than traditional solutions using motors or electromagnet to execute work. However, these actuators have flaws, such as strongly non-linear hysteresis. These are main problems in designing actuators, which is why SMA wires are often used in the construction of two-state actuators working as on-off actuators. The problems with SMA wires in their applications as drives are their static and dynamic properties, sensitivity to the environment, poor repeatability of production, non-linearity and hysteresis loop. The tested wires were made from a nickel and titanium alloy; this is an alloy which is often used in drive systems.

Robot Control System for Stereotactic Surgery

The article presents a prototype of a robot control system for stereotactic brain surgery. The development of neuroimaging, as well as the implementation of modern devices for neurosurgery, has undoubtedly contributed to significant progress in this field of medicine. Reaching a pathology located deep inside does not pose significant difficulty from the technical point of view; it is the selection of the access route that is the problem - to prevent the occurrence of permanent neurological deficits, such as severe paresis, vision disorders, speech or consciousness disorders. Obviously, knowledge of brain anatomy allows for adopting appropriate surgical tactics; however, some patients with a high-risk access route are not qualified for surgery. Even the hand of the most skilled operator does not guarantee precise removal of the tumour whilst bypassing important neural pathways, hence the necessity of introducing robots, which increase the level of surgical precision. A neural surgeon is able to perform very complicated surgical actions; however, human psychophysical limitations in neurosurgical procedures are becoming increasingly important, as surgeons are more and more frequently willing to perform operations with accuracy higher than 1 mm, but this is virtually impossible without any enhancement. Apart from the natural limitations of precision of the human hand, the surgeons mental and physical condition deteriorates during a several-hour-long surgical procedure, thus lowering the surgeons fitness and precision of movement. High concentration and a frequently unnatural position during the surgery cause additional tiredness. Therefore, numerous research centres and commercial companies are working on surgical robots. It seems that neurosurgery is particularly inclined for the introduction of robots enhancing the precision of a surgeons work.

Active Vehicle Suspension with a Weighted Multitone Optimal Controller: Considerations of Energy Consumption

Vibration reduction is a significant problem in the design and construction of vehicle suspensions (Lozia and Zdanowicz, IOP Conf Ser Mater Sci Eng 148:12014, 2016; Konieczny et al., J Low Freq Noise Vib Act Control 32:81–98, 2013). Passive semi-active and active methods are used in order to reduce vibrations. Considerations related to active and semi-active vibration reduction and the influence of disturbances on such objects can be found in many publications. In the case of these systems, the aim is always to find a compromise between their efficiency and energy consumption. The control law for such systems is usually determined as a solution to the optimisation problem with quadrant quality indicator. Energy limitation is taken into account by selection coefficients of the weighting matrix associated with the control signals vector. The efficiency of vibration reduction is able to be improved in the entire useful frequency range of the system operation but this generally results in an increase in the demand for external energy. An additional problem in the case of vehicle suspensions includes the need for increased vibration reduction for selected frequencies. This is related to the internal vibration frequencies of the driver’s internal organs. The paper presents the synthesis of a weighted multitone optimal controller (WMOC) for an active vibration reduction system. The control signal in this case is determined on the basis of the identified sinusoidal disturbances vector. The vibration transmissibility function and the energetic indicators for the active suspension were determined while taking note of nonlinearities occurring in the actual vehicle. The analysis of energy indicators (e.g. energy, maximum power) is presented, depending on the level of vibration reduction efficiency. The results were compared with analogous linear-quadratic regulator (LQR).