Enhancing the Lifetime of the Pneumatic Cylinder in Automatic Assembly Line Subjected to Repeated Pressure Loading

This study demonstrates the application of parametric accelerated life testing (ALT) as a procedure to identify design deficiencies and correct them in generating a reliable quantitative (RQ) specification. It includes: (1) a system BX lifetime that X% of a product population fails with a parametric ALT scheme, (2) fatigue design, (3) ALTs with alternations, and (4) judgement as to whether the design(s) secures the desired BX lifetime. A (generalized) life–stress model through the linear transport process and a sample size formulation are suggested. A pneumatic cylinder in a machine tool was used as a case study. The cylinder was failing in a flexible manufacturing system. To reproduce the failure and modify the design, a parametric ALT was performed. At the first ALT, the metal seal made of nickel-iron alloy (36% Ni) partially cracked and chipped and had a crisp metal sound. It was modified by changing the seal from a metal to a polymer (silicone rubber). At the second ALT, the piston seal leaked due to seal hardening and wear. The failure modes of the silicone seal in the laboratory tests were similar to those returned from the field. For the third ALT, the seal material was changed from silicone rubber to (thermoset) polyurethane. There were no concerns during the third ALT and the lifetime of the pneumatic cylinder was shown to have a B1 life of 10 years.

Heat Transfer Model of Pneumatic End-Position Cylinder Cushioning

In this paper a thermal model of a pneumatic cylinder with an integrated pneumatic end cushioning is presented. Being a part of a multidomain model presented in former research, this model is needed to simulate and analyse the thermodynamic processes in the pneumatic end cushioning and to elaborate a novel design strategy for damping systems with a higher capability on kinetic energy absorption and robust performance under fluctuating operating conditions. For this purpose, a proper heat exchange model is inevitable to calculate the pressure in the cushioning volume and consequently the deceleration of the load. An approach of splitting the complex geometry of cylinder into simple geometries, such as plain or cylindrical surfaces, is used in this study for a fast computation of convective heat flow rates. To validate this approach, the simulation results were compared with the measurements, carried out at different supply pressures, piston speeds and end cushioning throttle openings. The model will be used further for sensitivity analysis and robust optimisation of the cushioning system design.

Medical Grabbing Servo System with Friction Compensation Based on the Differential Evolution Algorithm

This paper introduces a pneumatic finger cylinder servo control system for medical grabbing. First, according to the physical structure of the proportional directional valve and the pneumatic cylinder, the state equation of the gas in the servo system was obtained. The Stribeck friction compensation model of a pneumatic finger cylinder controlled by a proportional valve was established and the experimental platform built. To allow the system output to better track the change in the input signal, the flow-gain compensation method was adopted. On this basis, a friction compensation control strategy based on a differential evolution algorithm was proposed and applied to the position control system of a pneumatic finger cylinder. Finally, the strategy was compared with the traditional proportional derivative (PD) strategy and that with friction compensation. The experimental results showed that the position accuracy of the finger cylinder position control system can be improved by using the friction compensation strategy based on the differential evolution algorithm to optimize the PD parameters.

Testing and Analysis of Fasteners

By considering the tightening process, the experimental testing will be conducted to explore the mechanism of bolt selfloosening under biaxial loading. The most common mode of failure is overloading: Operating forces of the application produce loads that exceed the clamp load, causing the joint to loosen over time or fail catastrophically. Over torque might cause failure by damaging the threads and deforming the fastener, though this can happen over a very long time. Also, the bolts may fail under fatigue. The components used in the system are bolts, pneumatic cylinder and flow control valve. The pneumatic cylinder is actuated with the help of compressor. The flow of air in the cylinder will be controlled with the help of pneumatic cylinder which will be acted on the bolts in two directions that is from downward & upward direction. This means the load will be tensile and shearing load. The bolts are attached to the plates. Because of actuation of the pneumatic cylinder the bolts will become loose. These bolts will be tested by using biaxial loading. The result & conclusion was drawn after the experimental testing. Keywords: Bi-axial Loading, Fasteners, Bolt Loosening, Residual Torque, Fastener Overloading

Three-dimensional loading control of a pneumatic three-universal–prismatic–universal robot

Multidimensional force loading has been widely used in the fields of component and material testing. The pneumatic-driven multidimensional force loading parallel mechanism can meet the requirements of complex force loading. A three-dimensional loading robot based on a pneumatic three-universal–prismatic–universal parallel mechanism is designed to apply time-varying three-dimensional loads on a target. Based on the principle of vector superposition, inverse and forward kinematics are deduced. A second-order mathematical model of a metal seal pneumatic cylinder driven by a flow proportional valve is established. Based on the immersion and invariance technique, the leakage flow in the cylinder is taken as the interference term and estimated. Meanwhile, because of the strong nonlinearity of the actuator, based on suitable disturbance estimation, the control rate of the system is designed through the sliding mode surface, and the stability of the control algorithm is analyzed on the basis of the Lyapunov stability theory. The experimental results show that the immersion and invariance controller exhibits a better control performance than the proportional–integral–differential controller: the steady-state control mean square error is reduced by approximately 21% on average and the dynamic (0.2 Hz) tracking mean square error is approximately 10.35 N.

Pneumatic actuator positioning with pilot controlled check valves

Tests of accuracy and repeatability of the pneumatic cylinder positioning in intermediate positions using a check valve are presented. The tests were performed under different loads and for different piston speeds and operating pressure in a pneumatic system with throttle check valves and an optical linear displacement sensor measuring the position of the actuator rod. Assessment of the effect of the cylinder performance parameters on the accuracy and repeatability of piston rod positioning was done and limitations and possible applications of the pneumatic cylinder positioning in intermediate positions with a check valve were identified.