Abstract
In this paper, the needle insertion motion control of a magnetic resonance imaging (MRI) compatible robot, which is actuated by a pneumatic cylinder with long transmission lines, is considered and a pressure observer based adaptive dynamic surface controller is proposed. The long transmission line is assumed to be an intermediate chamber connected between the control valve and the actuator in series, and a nonlinear first order system model is constructed to characterize the pressure losses and time delay brought by it. Due to the fact that MRI-compatible pressure sensors are not commercially available, a globally stable pressure observer is employed to estimate the chamber pressure. Based on the model of the long transmission line and the pressure observer, an adaptive dynamic surface controller is further designed by using the dynamic surface control technique. Compared to the traditional backstepping design method, the proposed controller can avoid the problem of “explosion of complexity” since the repeated differentiation of virtual controls is no longer required. The stability of the closed-loop system is analytically proven by employing the Lyapunov theory. Extensive experimental results are presented to demonstrate the effectiveness and the performance robustness of the proposed controller.
Highlights
The magnetic resonance imaging (MRI) technique is widely used in clinical diagnosis due to its ability to image without the use of ionizing x-rays and superior soft tissue contrast as compared to computed tomography (CT) scanning
The rest of this paper is Models and Problem organized as follows: Section 2 Formulation presents the dynamic models and problem statement; Section 3 gives the design and stability proof of the pressure observer based adaptive dynamic surface controller; As shown in Figure 1, a 5-DOF MRI compatible robot for abdominal and Section 4 presents the experimental results to demonstrate the performance of the proposed controller; thoracic and punctures was built in our laboratory
The transmission line was as an intermediate chamber connected
Summary
The magnetic resonance imaging (MRI) technique is widely used in clinical diagnosis due to its ability to image without the use of ionizing x-rays and superior soft tissue contrast as compared to computed tomography (CT) scanning. Since long transmission lines have a significant influence on the pressure dynamics of the pneumatic system and MRI-compatible pressure sensors are not commercially available, precise position control is one of the main technical challenges in robot development. The backstepping design method has been proven to be a very effective way to develop nonlinear robust controllers for pneumatic servo systems This method has the problem of “explosion of complexity” since the requirement of repeated differentiation of virtual controls. The focus of this paper is dealing with the issue of long transmission lines and realizing a high accuracy control of a pneumatic actuator with a pressure observer. The long transmission line is assumed to be an intermediate chamber connected between the control valve and the actuator in series, and a pressure observer based adaptive dynamic surface control is proposed.
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