Nonlinear Discontinuous Dynamics Averaging and PWM-Based Sliding Control of Solenoid-Valve Pneumatic Actuators

Abstract

Abstract-A pneumatic actuator with solenoid valves is a discontinuous-input system because each valve can be either in on or off state. For such an actuator, this paper proposes a slidingmode control scheme that is based on an averaged continuousinput model of the discontinuous-input open-loop system. The averaged model is obtained from the nonlinear dynamics of the open-loop system undergoing pulse-width-modulation (PWM) at the input (i.e., valve open/close action). The PWM duty cycle will be regarded as a continuous input to the proposed averaged model, and thus generated by the proposed slidingmode controller.For the sliding control design, we note that a pneumatic actuator has two chambers with a total of four on/off valves. Thus, there are sixteen possible combinations for valves' switching. Seven of these sixteen operating "modes" are considered both functional and unique. The proposed sliding control utilizes and switches between these seven modes of the open-loop system in order to select the ones with necessary and sufficient amounts of drive energy. In comparing the new 7-mode controller to previous controllers, we will demonstrate reductions in the position tracking error and the number of switches made by the actuator's on/off valves. The proposed control scheme is used in both position control of a pneumatic cylinder and bilateral control of a one degree of freedom teleoperation system. Experimental results are presented to validate our theoretical findings.

Needle-Guiding Robot for Laser Ablation of Liver Tumors Under MRI Guidance

“…In order to evaluate the robustness of the controllers to model uncertainties and disturbances, tests were also conducted with an additional 2.5 kg payload, which exceeds the mass of the moving parts in the needle-guiding robot. As observed in [20], [26], [42], [45], that employ a similar approach, the payload also results in additional friction forces. Notably, the cylinders employed in this system have a larger friction (Table II) compared to the moving parts of the robot, which were manufactured from low-friction materials (the coefficients of friction for Delrin and PTFE are respectively 0.2 to 0.35 and 0.08 to 0.14, DuPont Inc.).…”

“…Although the SMC scheme should in theory not produce overshot, in practice this is only the case if the system parameters are accurately known. Overshoot and oscillations were in fact observed experimentally with SMC schemes in [24] and [45].…”

“…Differently from SMC schemes [24], [25], [42], [45], TDC does not require the assumption of bounded disturbances. This is beneficial here since friction forces caused by the robot structure can be difficult to estimate.…”

“…Differently from previous TDC schemes [26], this controller takes into account the pressure dynamics. Differently from fuzzy-logic and neural network controllers [47], from SMC schemes [42], [45], and from other TDC schemes [48], the control law does not rely on pressure or force measurements in proximity of the cylinder. This aspect has particular advantages in the MRI environment since commercially available pressure and force sensors are typically not MRI-safe [29].…”

PSO-based PID controller design for an energy conversion system using compressed air

“…So far, different types of feedback control algorithms have been used in the control of PMs to achieve design objectives in terms of all system performance [10,18,19]. These algorithms are generally classified in two categories depending on the number of loops used in feedback block: single-loop feedback control algorithm and multi-loop feedback control algorithm.…”