Friction Modelling of Pneumatic Cylinders for servo-positioning systems.

Pneumatic actuators are widely used in the industrial field thanks to their cost-effectiveness, versatility, and mechanical simplicity compared to other types of actuators. Furthermore, the use of air enables greater flexibility in their application, even in flammable or explosive environments and, air as a driving fluid, is considered a sustainable resource compared to other fluids as oils. This thesis presents a comprehensive study focused on examining the three distinct regimes of friction, namely pre-sliding, transition, and gross-sliding, in the context of pneumatic actuation systems. The primary objective of this research is to gain a deep understanding of the frictional behaviours that occur when pneumatic actuators are employed, which is crucial for enhancing the efficiency, control, and reliability of such systems. The investigation begins with a complete review of the fundamental principles of friction and its role in pneumatic actuation and then experimental work is conducted to characterize and differentiate the three distinct frictional regimes. Different test setups are utilized to control parameters like pressure and velocity allowing for the study of each regime's behaviour. A system made by a cart constrained by a linear guide with recirculating ball bearings, which is actuated by a double-acting pneumatic cylinder and a 5/3-way proportional flow valve is used. This system is used for the study of transition and gross-sliding regimes. For the pre-sliding regime, experimental trials coming from the literature are taken in account due to the impossibility of conducting this type of tests. Experimental data are then collected to examine the frictional behaviour. Numerical models from existing literature are considered in this study as Polito, Dahl, LuGre and Leuven models. Those models are widely used in the literature thanks to their efficiency offering different approaches (static and dynamic) and different accuracy. The results obtained from these numerical simulations are then compared with the experimental results to validate the different models. The findings of this research contribute to a comprehensive understanding of the pre-sliding, transition, and gross-sliding regimes of friction in pneumatic actuation systems. By clarifying the factors influencing these regimes and their impact on system performance, this study provides valuable insights for the design and control of pneumatic actuators in various applications, including robotics, automation, and manufacturing. Additionally, the knowledge gained from this research can aid in the development of optimized control strategies, materials selection, and lubrication techniques, ultimately leading to more efficient and reliable pneumatic actuation systems. These insights have the potential to make a significant impact on industries where pneumatic actuators play a critical role in achieving precise and controlled motion.