Pneumatic Adaptive Absorber: Mathematical Modelling with Experimental Verification
Pneumatic Adaptive Absorber: Mathematical Modelling with Experimental Verification
Grzegorz Mikułowski and Rafał Wiszowaty
Institute of Fundamental Technological Research, Ulica Pawinskiego 5B, 02-106 Warszawa, Poland
Received 15 April 2015; Accepted 30 November 2015
Academic Editor: Zhongdong Duan
Copyright © 2016 Grzegorz Mikułowski and Rafał Wiszowaty. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Many of mechanical energy absorbers utilized in engineering structures are hydraulic dampers, since they are simple and highly efficient and have favourable volume to load capacity ratio. However, there exist fields of applications where a threat of toxic contamination with the hydraulic fluid contents must be avoided, for example, food or pharmacy industries. A solution here can be a Pneumatic Adaptive Absorber (PAA), which is characterized by a high dissipation efficiency and an inactive medium. In order to properly analyse the characteristics of a PAA, an adequate mathematical model is required. This paper proposes a concept for mathematical modelling of a PAA with experimental verification. The PAA is considered as a piston-cylinder device with a controllable valve incorporated inside the piston. The objective of this paper is to describe a thermodynamic model of a double chamber cylinder with gas migration between the inner volumes of the device. The specific situation considered here is that the process cannot be defined as polytropic, characterized by constant in time thermodynamic coefficients. Instead, the coefficients of the proposed model are updated during the analysis. The results of the experimental research reveal that the proposed mathematical model is able to accurately reflect the physical behaviour of the fabricated demonstrator of the shock absorber.
1. Introduction
Mechanical energy dissipation is an important task desired in many industry applications [1, 2]. Currently, efforts are given to increase productivity of automated plants and the speed of transportation on production lines. In parallel to increasing the transportation speed, effective means of stopping the objects on the lines are required, which is especially evident in the production processes, where the braking distance is limited due to packaging reasons [3]. The most popular technique is based on hydraulic dampers due to their effectiveness, durability, and favourable volume to force ratio [4–9]. However, in some applications the utilization of fluid-based devices is undesirable due to the possibility of toxic contamination of the goods being produced, for example, in the pharmaceutical or food industry [10, 11]. In such cases damping solutions based on pneumatics can be applied with chemically inactive gases [10, 12–14].
There are known techniques for pneumatic cylindrical shock absorbers used in aeronautical or food industries [10, 15]. However, due to the low viscosity of gases and their compressibility, the energy dissipation efficiency of these devices does not exceed 40%, while the hydraulic dampers are characterized by the efficiency of 80% [5, 15]. There exist a number of patents that propose ways to increase the effectiveness of the cylindrical pneumatic shock absorbers [16–18]. Most of the solutions are based on a double-stage algorithm of operation. After the initial compression of the gas in the cylinder, a mechanically operated valve releases the medium out of the cylinder to the surroundings. By this way the energy accumulated in the compressed gas is dissipated and the spring-back effect is diminished. These solutions increase the effectiveness of the pneumatic absorbers, but they are limited to a single, strictly defined impact energy. When the impact energy is too low, the absorber does not release the gas at the proper moment and the absorption does not take place. Another disadvantage is related to the fact that the compressed gas is released to the surroundings, which introduces the necessity of refilling the device after each working cycle.
An improved solution considered here is based on introduction of a controlled flow between the chambers in the cylinder via the piston. In this way it is possible to dissipate energy of various magnitudes with the efficiency comparable to hydraulic devices (80%). Moreover, the gas is not released to the surroundings, which allows the device to be operated in a repeatable way. Recent developments in functional materials technology allow us to consider a novel approach to adaptive pneumatic shock absorber with utilization of a piezoelectric material for actuation of the device. A piezoelectric multilayered actuator is applied in a miniature valve positioned in the pneumatic cylinder piston [19]. In this paper we focus on mathematical modelling of the cylindrical pneumatic shock absorber (...truncated)