Jagadeesan Jayender

Modeling and Control of Shape Memory Alloy Actuators

This brief describes a new model for shape memory alloy (SMA) actuators based on the physics of the process and develops control strategies using the model. The model consists of three equations - the temperature dynamics described by Joules heating-convectional cooling, the mole fraction distribution with temperature given by statistics to describe a two state system, and a constitutive equation relating the changes in temperature and mole fraction to the stress and strain induced in the SMA. This model is used to develop two control schemes for controlling the strain in an SMA actuator. The first control scheme describes a gain-scheduled proportional-integral (PI) controller, the gains of which are obtained by means of linear quadratic regulator (LQR) optimization. The second control scheme is an Hinfin loop-shaping controller using normalized coprime stabilization which ensures robust stability by minimizing the effect of unmodeled dynamics at high frequencies. Simulation and experimental results show fast and accurate control of the strain in the SMA actuator for both control schemes.

Robot-assisted Tactile Sensing for Minimally Invasive Tumor Localization

The 10 mm incisions used in minimally invasive cancer surgery prevent the direct palpation of internal organs, making intraoperative tumor localization difficult. A tactile sensing instrument (TSI), which uses a commercially available sensor to measure distributed pressure profiles along the contacting surface, has been developed to facilitate remote tissue palpation. The objective of this research is to assess the feasibility of using the TSI under robotic control to reliably locate underlying tumors while reducing collateral tissue trauma. The performance of humans and a robot using the TSI to locate tumor phantoms embedded into ex vivo bovine livers is compared. An augmented hybrid impedance control scheme has been implemented on a Mitsubishi PA10-7C to perform the force/position control used in the trials. The results show that using the TSI under robotic control realizes an average 35% decrease in the maximum forces applied and a 50% increase in tumor detection accuracy when compared to manual manipulation of the same instrument. This demonstrates that the detection of tumors using tactile sensing is highly dependent on how consistently the forces on the tactile sensing area are applied, and that robotic assistance can be of great benefit when trying to localize tumors in minimally invasive surgery.

Autonomous Image-Guided Robot-Assisted Active Catheter Insertion

Interventional cardiologists are at great risk from radiation exposure due to lengthy procedures performed under X-ray radiations. Angioplasty is one such procedure wherein the clinician guides a catheter into the femoral artery under X-rays and the procedure often extends to over 50 min. A clinician performs several hundred such procedures over his/her lifetime, leading to an accumulation of the total radiation he/she is exposed to. In this paper, we investigate autonomous robot-assisted insertion of an active catheter instrumented with shape memory alloy (SMA) actuators using image guidance. The tip of the active catheter is tracked in real time to provide information on the location of the catheter that determines the optimal stroke length of insertion for the robot and the necessary bending angle for the active catheter. The catheter is autonomously guided from the point of entry to the site of plaque buildup, thereby shielding the clinician from harmful radiation due to the X-rays used for imaging and providing a more ergonomic approach for catheter insertion. Experimental results are given to illustrate the robot-assisted catheter insertion procedure using image guidance.

Robot-assisted Active Catheter Insertion: Algorithms and Experiments

Angioplasty is a frequently performed clinical procedure in which a catheter is inserted into a blood vessel under image guidance to open narrowed or blocked arteries and to allow normal blood flow to resume. This paper is concerned with the development of algorithms for a robot-assisted method for a more accurate, safer and more reliable approach for catheter insertion that can reduce the potential for injury to patients and radiation exposure or discomfort to clinicians. A force control algorithm is presented for a robot to control the force of insertion of a catheter and prevent the catheter from buckling or “bunching up” during insertion. In addition, the paper also describes a master—slave control strategy to precisely control the bending angle of the tip of an active catheter instrumented with Shape Memory Alloy (SMA) actuators. A novel model for SMAs and a robust H∞ loop-shaping controller have been implemented to guarantee robust performance of the active catheter. The algorithms for catheter insertion developed in this paper may help to prevent damage to the epithelial cells of an artery and enable easier guidance of the catheter into appropriate branches. In addition, a robotics-based approach could make it possible for a clinician to remotely perform the insertion of the active catheter from a safe and comfortable environment, thereby reducing exposure to harmful X-ray radiation. Experimental results are presented to illustrate the performance of the algorithms.

A Robust Position and Force Control Strategy for 7-DOF Redundant Manipulators

This paper is concerned with robust position and contact force control for 7-DOF redundant robot arms. An outer-inner loop controller, called the augmented hybrid impedance control scheme is developed. A 6-DOF force/torque sensor is used to measure the interaction forces. These are fed back to the outer-loop controller that implements either a force or an impedance controller in each of the 6 DOF of the tool frame. The force controller is provided with a force set point, and desired inertia and damping are introduced in the force control loop to improve transient performance. The inner loop consists of a Cartesian-level potential difference controller, a redundancy resolution scheme at the acceleration level, and a joint-space inverse dynamics controller. Experimental results for two 7-DOF robot arms (redundant, dextrous, isotropically enhanced, seven-turning pair robot (REDIESTRO) and Mitsubishi PA10-7C) are given to illustrate the performance of the force control strategy. A successful application of the proposed scheme to a surface cleaning task is described using the REDIESTRO, while position and force tracking experiments are described for the Mitsubishi PA10-7C robot.

Modelling and gain scheduled control of shape memory alloy actuators

This paper describes a gain-scheduled controller for a shape memory alloy (SMA) actuator. For accurate control of an SMA actuator, it is important to develop a precise model for the SMA. A model has been proposed based on concepts from physics. The equations include Joules heating - convectional cooling to explain the dynamics of temperature, Fermi-Dirac statistics to explain the variation of mole fraction with temperature, and a stress-strain constitutive equation to relate changes in mole fraction and temperature to changes in stress and strain of the SMA. This model is then used to develop a gain-scheduled controller to control the strain in the SMA. Simulation and experimental results show fast and accurate control of the strain in the SMA actuator

H ∞ Loop Shaping Controller for Shape Memory Alloy Actuators

This paper describes a Robust H∞Controller for a Shape Memory Alloy actuator. A formulation based on concepts from physics, has been used to model the Shape Memory Alloy (SMA). The modelling equations include Joules heating - convectional cooling to explain the dynamics of temperature, Fermi-Dirac statistics to explain the variation of mole fraction with temperature, and a stress-strain constitutive equation to relate changes in mole fraction and temperature to changes in stress and strain of the SMA. An H∞loop shaping controller using normalized coprime stabilization is designed such that the gains are high when the model describes the SMA accurately and low at higher frequencies when the model is inaccurate. Simulation and experimental results show fast and accurate control of the strain in the SMA actuator.

Autonomous robot-assisted active catheter insertion using image guidance

In this paper, we investigate autonomous robot- assisted insertion of an active catheter instrumented with shape memory alloy (SMA) actuators using image guidance. An Augmented Hybrid Impedance Control (AHIC) algorithm is implemented on a Mitsubishi robot (PA 10-7C) to insert the active catheter. The robot is constrained to move in Cartesian space along a pre-defined trajectory while controlling the force of insertion. A closed-loop control scheme has been developed to accurately control the bending in the active catheter. The tip of the active catheter is tracked in real-time to provide information on the path of the catheter and for determining the future course of insertion. The catheter is autonomously guided from the point of entry to the site of plaque buildup, thereby shielding the surgeon from the harmful radiation due to the X-rays used for imaging, providing a more ergonomic approach for catheter insertion. Experimental results are given to illustrate the robot-assisted catheter insertion procedure.

Bilateral telemanipulation of a flexible catheter in a constrained environment

This paper describes some novel research results on bilateral teleoperation of a flexible catheter in a constrained environment. The dynamics of the catheter in a constrained environment is highly nonlinear and is affected by a large number of factors such as friction, flexibility of the catheter, force of insertion, shape and size of the catheter, etc. As a result, the distal end of the catheter almost never follows the actuated end of the catheter which could cause fatigue to the clinician/user attempting to insert the catheter in a blood vessel. In addition, there is a time delay of up to 0.8 second before the distal end of the catheter advances after the near end is actuated. This delay is sufficient to cause instability in the control loop. We have developed a teleoperation framework using wave variables to perform robot- assisted catheter insertion in a constrained environment while reflecting the forces at the tip of the catheter to the clinician. Experimental results showing the effect of different factors such as the velocity and stroke length of insertion on the delays introduced in control loop and errors between the master and slave position are included. To the best of our knowledge, this work is among the first to attempt to provide an understanding of the effects of various factors on the flexing of the catheter. In addition, master-slave insertion of a catheter instrumented with shape memory alloys (SMA) has also been performed and the results are included in this paper.

A Robust Controller for Shape Memory Alloy Actuators

This paper describes a robust mixed-synthesis controller for shape memory alloy (SMA) actuators. The weights for the controller are chosen such that the disturbance rejection criterion is met for low frequencies and robust stability is maintained for high frequencies. Simulation and experimental results show fast and accurate response for strain in the SMA under no perturbation. The performance of the controller is also verified in the presence of load and cooling rate perturbations. The response shows that the controller maintains good disturbance rejection and robust stability. Sinusoidal references are tracked with negligible error in the presence of perturbations. In addition, the controller is also tested for SMA actuators operating in water. The excellent results validate further both the model and the controller used for the SMA actuators