Abstract— This paper presents a new predictive hybrid control law for a pneumatic teleoperation system using solenoid valves. Based on a predictive model of the mass flow rate of the valves, this method is used within a four-channel (4CH) bilateral control architecture for haptic teleoperation. An analysis of the controller parameters is carried out in order to achieve acceptable performances. To evaluate the new strategy, a comparison study has been performed with a classical PWM control of a teleoperation system. The results show that the accuracy in position and force tracking in steady state but also the dynamic behavior of the pressures are better in the case of hybrid control than PWM control. Index terms—Pneumatic actuators, on/off solenoid valves, hybrid control, PWM control, teleoperation, transparency. I. INTRODUCTION From its early use in the remote manipulation of radioactive materials, the application of teleoperation has expanded to include manipulation at different scales and in virtual worlds [1-4]. Teleoperation systems have the potential to play an important role in future remote or hazardous operations such as space and undersea explorations, forestry and mining, and also delicate operations such as micro-surgery and micro-assembly. In a teleoperation system, a slave manipulator tracks the motion of a master manipulator, which is driven by a human operator. To improve the task performance, information about the environment is needed. Feedback about the environment can be provided to the human operator in many forms including audio, visual, or tactile information. Force feedback from the slave side to the master side, representing slave/environment contact information, provides a highly intuitive and natural sensation for the human operator [5]. Indeed, force feedback helps the operator in probing an uncertain environment and reduces task completion times as well as damage to the manipulated object. When the contact force is reflected via the master actuator to the operator’s hand, the teleoperation system is said to be bilateral. In a bilateral teleoperation system, apart from the basic requirement of stability, there are primarily two design goals that ensure a close coupling between the human operator and the environment. The first goal is that the slave manipulator tracks the position of the master manipulator, and the second goal is that the environmental force acting on the slave, when a contact with the environment occurs, is accurately transmitted to the master [6]. Such a bilateral control allows to ensure the transparency of the teleoperation system, meaning that, through the master manipulator, the operator feels as if he/she is directly operating on the remote environment. In this study, we investigate the possibility to use electro- pneumatic systems as actuators in a teleoperation system. Pneumatic systems have recently become more popular due to their advantages of high mass-to-force ratio, producing clean power, and recent breakthroughs in valve technology. Therefore, they are used in new applications such as tele- robotics over the last few years [7-8]. Two types of valves are generally used to control pneumatic systems: proportional servovalves and solenoid valves (“on/off valves”). Proportional servovalves have been successfully used to achieve high performances in various position or/and force control systems with pneumatic actuators, but they are usually expensive as they require high-precision manufacturing. In this paper, fast-switching on/off valves were chosen due to their low cost and small size. One of our objectives is to show that a good transparency in bilateral control can be obtained with these cheap components. The traditional method for controlling systems with solenoid valves is to use Pulse Width Modulation (PWM) to control the output mass flow rate of the valve [9-10]. A main disadvantages of the PWM control is the chattering phenomenon due to the high frequency switching of the valve in steady state [11]. To overcome the PWM disadvantages, this paper presents a new control method, which is based on the hybrid control theory recently developed by Retif et al. [12]. For this strategy, a predictive approach has been developed to determine the best control vector at each sample time to track the reference state [13], [14]. In this paper, the hybrid control algorithm is applied for the force and position tracking in a 4CH bilateral teleoperation architecture. A comparison with a classical PWM control is then performed to evaluate the hybrid strategy, in term of tracking performance and saving energy. Without loss of generality and for the sake of simplicity, the master and slave actuators are supposed to be identical in this study. The master and slave are one degree of freedom (DOF) pneumatic manipulators. It should be noted that this paper does not deal with the presence of time delay in the teleoperation system’s communication channel. The structure of this paper is as follows. First, the modeling of the pneumatic manipulator composed of a cylinder and four solenoid valves is presented in Section II. Section III describes a 4CH bilateral design for hybrid and PWM control in teleoperation system. Section IV presents experimental results that validate the proposed theories. Finally, concluding remarks appear in Section V. II. MODEL OF THE PNEUMATIC SYSTEM As mentioned above, the master and the slave manipulators are identical, thus only one pneumatic robot Transparency of a pneumatic teleoperation system using on/off solenoid valves M.Q. Le, M.T. Pham, R. Moreau, T. Redarce 19th IEEE International Symposium on Robot and Human Interactive Communication Principe di Piemonte - Viareggio, Italy, Sept. 12-15, 2010 978-1-4244-7989-4/10/$26.00 ©2010 IEEE 15 978-1-4244-7990-0/10/$26.00 ©2010 IEEE