Meccanica 36: 691–700, 2001. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. A Model of Contact Forces in Pneumatic Motor Vanes A. MANUELLO BERTETTO 1 , L. MAZZA 2 , S. PASTORELLI 2 and T. RAPARELLI 2 1 Università di Cagliari, Department of Mechanical Engineering, P.za D’Armi, 1; 09123, Cagliari, Italy 2 Politecnico di Torino, Department of Mechanics, C.so Duca degli Abruzzi, 24; 10129 Torino, Italy (Accepted: 14 January 2002) Abstract. The paper presents an investigation on the dynamic equilibrium of a pneumatic motor vane. The investigation was based on an analysis of the vane’s free body diagram. In particular, a model was formulated for determining the contact forces between vane, rotor and stator and the contact configuration from the known motor geometry, friction coefficients and chamber pressures. In addition, the paper presents experimental measure- ments of friction coefficients in vane-rotor and vane-stator contact together with a validation of the model through comparison with a FEM model. Sommario. In questo lavoro viene presentato uno studio dell’equilibrio dinamico della paletta di un motore pneumatico, basato sull’analisi dello schema di corpo libero della paletta stessa. In particolare è stato formulato un modello per determinare le forze di contatto tra paletta, rotore e statore e la configurazione di contatto dati la geometria del motore, i coefficienti d’attrito e le pressioni nelle camere. Inoltre sono riportati i risultati sperimentali delle misure di attrito nel contatto tra paletta e rotore e tra paletta e statore con una validazione del modello tramite un confronto con un modello FEM. Key words: Pneumatic vane motor, Contact forces, Friction forces, Tribology. 1. Introduction Pneumatic motors are widely used in a variety of industrial applications thanks to their high specific power output, wide torque and speed range, and suitability for use in hazardous en- vironments. One of the problems currently being investigated regards minimizing dissipation in pneumatic vane motors, and the feasibility of using them with lubricated or unlubricated compressed air, or in the presence of water. Research is addressing the use of new materials for vane sliding surfaces [1, 2], as well as the development of appropriate vane geometries [3]. Effective design can be furthered by dynamic models of vane equilibrium. For example, the paper [4] is devoted to the formulation of the conditions under which the vane loses contact with the stator. This paper presents a model of vane equilibrium which makes it possible to evaluate the contact forces between vane, rotor and stator once the motor geometry, rotational speed and chamber pressures are known. Specifically, the study addresses a pneumatic motor used in robotics applications [5], for which the authors have carried out an extensive experimental investigation focusing chiefly on techniques for measuring chamber pressures [6]. The aim of the presented study is to define a simple model which is able to provide information on the motor performance, meanwhile it is less costly to solve in terms of computing time and power if compared with FEM model for example.