Abstract. Tribological performance of the materials greatly depends on the temperature of the contacting zones and surfaces and hence on the heat conducting behaviour of the materials. Heat conduction of polymers is, however, greatly affected even by a very narrow (few tens of nm) modified layer formed on the surface after subjecting the polymer to plasma treatment. In this article the heat flow inhibiting properties of plasma modified surface layers were investigated on polyethylene terephthalate (PET) and polyamide-6 (PA6) engineering polymers. Nitrogen Plasma Immersion Ion Implantation gave rise to compositional and structural changes of the polymers in a depth of 110 nm. It was found that even this thin layer exhibited significant heat flow inhibiting effect. The modified layer considerably decreased the thermal conductivity coefficient of the treated polymer and resulted in a reduced heat transmission for PET and PA6 by 33 and 28%, respectively. This new information supports and is in accordance with the former tribological results about extra friction heat generation experienced under NPIII surface layer of PA6 and PET during dry sliding.
This paper presents a novel control design, developed to realise fast and accurate positioncontrol of a pneumatic actuator using inexpensive on/off solenoid valves. In contrast to conventional controlmethods, the proposed control method operates chatter free, based on air compression. The controlprinciple was developed by investigating the dynamics of a pneumatic actuator with an identifiedmathematical model. This new approach is applied to a pneumatic double acting cylinder, controlled by apair of 5/3 way directional single solenoid valves. The described closed-loop circuit copes with thediscontinuities associated with the valve’s switching dynamics, and relatively long response time. Theexperimental apparatus uses an analogue displacement encoder for metering the piston’s position andvelocity, and doesn’t incorporate pressure sensors thus ensuring a low cost system design. The results ofexperiments with various step responses show that the proposed control method performs well. Themeasured steady-state position errors are equal to the used potentiometer’s travel resolution, which is 0,01mm. Therefore this novel control and the related pneumatic system design could be a cost effectivealternative to the servo-pneumatic positioning systems.
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