# Studies regarding the Use of Pneumatic Muscles in Precise Positioning Systems
## 1 Introduction
The proposed model describes the force/length hysteresis at different excitation intervals and with different internal pressures. The Jiles-Artherton model [27] was used to establish the pneumatic muscle hysteresis model and its compensation control. The needed parameters of the model were identified using adaptive weighted particle swarm optimization. [PERSON] and [PERSON] used the Preisach model to describe hysteresis nonlinearity in the relationship between the contraction and internal pressure of pneumatic muscle [28]. The model was also used for the control of a parallel manipulator driven by three pneumatic muscles. In [29], the proposed technique used the dynamic Preisach model and adaptively tuned the parameters of the model by recursive parameter estimation if the distortion occurred due to speed variations. In [30], the generalized Prandtl-Iskhlinskii model was used for characterizing the hysteresis of a pneumatic muscle. The model could accurately describe asymmetric hysteresis and had high accuracy in the trajectory tracking of the pneumatic artificial muscle. The research conducted to date in the field of modeling the hysteresis of a pneumatic muscle highlights the conclusion that the models are not suitable for generalization. They were developed by a certain type of muscle which was the object of the research. The difficulty of identifying a generalized model for pneumatic muscle hysteresis is due to the \"soft\" character of the artificial muscle, combining elastomer physics with textile physics [31]. Electro-pneumatic systems are among the most widely used systems when it comes to areas of activity with special environmental conditions due to the clean working agent (air) and their advantages, high working forces and speeds. Even if their positioning accuracy can still be improved, pneumatic positioning systems are an alternative to electro-mechanical ones as they are reliable and long-lasting. Most pneumatic positioning systems, which combine control valves, cylinders, and position transducers, rely on directional airflow control to control positioning. This type of system achieves precise positioning with the help of a rigorous control of the air flow. In this situation,the air loss resulting from the impossibility of a perfect seal between the movable element (rod or piston) and the fixed one (cylinder liner) must be taken into account. A positioning system must be able to reach and maintain the required position anywhere along the length of the stroke. Based on the well-known presence of hysteresis in pneumatic muscle function, this paper presents the methods and results of an experimental study that highlights the behavior of a pneumatic actuator under different pressures and with different loads applied. Positioning accuracy is an imposed condition in many applications but is limited in the case of using pneumatic muscles due to their inherent non-linearity and hysteresis. The aim of this paper is to model the axial contraction/pressure hysteresis of a small pneumatic muscle and to establish an accurate positioning control. The proposed method of increasing positioning accuracy is based on pressure control using a proportional pressure regulator and a Programmable Logic Controller (PLC). The structure of the paper includes a section that describes the materials and methods of the research. The experimental setup and the used components, and the method used for the experiment, are presented. The third section of the paper presents several experiments and results for determining the hysteretic behavior of a pneumatic muscle of 10 mm diameter and 100 mm length. In this section, some polynomial regression functions are developed, which can be used to configure the pneumatic actuation system. In the last section of the paper, the conclusions of the research and future directions are presented.