Jang Ho Cho

Gain-Scheduling Control of Teleoperation Systems Interacting With Soft Tissues

Surgical teleoperation systems are being increasingly deployed recently. There are, however, some unsolved issues such as nonlinear characteristics of the interaction between the slave robot and soft tissues and difficulty in employing force sensors in the surgical end-effectors of the slave. These issues make it difficult to generalize any approach to develop a control for the system. This paper addresses these issues by proposing a H∞ suboptimal controller preserving robust stability and performance. The environment, i.e., soft tissues, is characterized with the nonlinear Hunt-Crossley model. This nonlinear characteristics of soft tissues are expressed with an affine combination of linear models within a predefined parameter polytope. For this linear parameter-varying system, a gain-scheduling control scheme is employed to design a suboptimal controller while guaranteeing its stability. To avoid using any force measurement in slave, we used position-position (PP) control architecture. The developed gain-scheduling control is validated with quantitative experimental results. The developed gain-scheduling PP control scheme shows good tracking capacity and high transparency for varied experimental conditions. Error of the transmitted impedance is significantly lower compared with other conventional control schemes for frequencies less than 2 Hz, which is frequently recommended for surgical teleoperation.

Analytical and Psychophysical Comparison of Bilateral Teleoperators for Enhanced Perceptual Performance

This paper focuses on the human perception capabilities for haptic interaction with remote environments. The perception capabilities are compared for two well-known control methods with two kinds of haptic cues. Analytical and psychophysical methods are used to analyze the performance. The first control method aims at maximizing the transparency of the remote interactions (i.e., transparency-based method), whereas the second one aims at maximizing the detection and discrimination abilities of the human operator (i.e., perception-based method). For each of these two control methods, two kinds of haptic cues are studied, which use position and force cues from remote environments. Hybrid matrix formulation is employed, and it is analyzed in the frequency domain for these studies. Psychophysical experiments are then conducted for human-centered evaluation and comparison of the control methods. Analytical and experimental results clearly show that the perception-based method, when compared with the transparency-based method, enhances the human operators perceptual capabilities of remote environments irrespective of force cues. For each of the two control methods, the force cues always contribute more to the increase in perceptual sensitivity when compared with the case of position cues.

A psychophysical evaluation of haptic controllers: viscosity perception of soft environments

In this paper, human viscosity perception in haptic teleoperation systems is thoroughly analyzed. An accurate perception of viscoelastic environmental properties such as viscosity is a critical ability in several contexts, such as telesurgery, telerehabilitation, telemedicine, and soft-tissue interaction. We study and compare the ability to perceive viscosity from the standpoint of detection and discrimination using several relevant control methods for the teleoperator. The perception-based method, which was proposed by the authors to enhance the operators kinesthetic perception, is compared with the conventional transparency-based control method for the teleoperation system. The fidelity-based method, which is a primary method among perception-centered control schemes in teleoperation, is also studied. We also examine the necessity and impact of the remote-site force information for each of the methods. The comparison is based on a series of psychophysical experiments measuring absolute threshold and just noticeable difference for all conditions. The results clearly show that the perception-based method enhances both detection and discrimination abilities compare with other control methods. The results further show that the fidelity-based method confers a better discrimination ability than the transparency-based method, although this is not true with respect to detection ability. In addition, we show that force information improves viscosity detection for all control methods, as predicted from previous theoretical analysis, but improves the discrimination threshold only for the perception-based method.

Identification of dynamic parameters of an industrial robot using a recursively-optimized trajectory

Dynamic parameters of a robot affect the performance of advanced control schemes significantly. In this study experiments to identify the dynamic parameters of AT2 robot are carried out. The excitation trajectory for identification is parameterized with Fourier series. The trajectory is optimized to minimize effects of uncertainty using condition number as the index. Recursive optimization is proposed so that the trajectory is robust from selection of the initial values and better optimization result can be obtained. The dynamic parameters of AT2 robot is estimated using the optimized excitation trajectory and weighted least-square method.

Gain-scheduling control of a teleoperation system

This paper presents a control design framework for robust teleoperation. The teleoperation system with uncertainties is modeled as a linear parameter varying plant to employ the gain-scheduling control framework. The time-varying transmission delay, disturbances, and uncertainty of the environment are considered in the design of the control. The usual assumption that the human operator and the environment are passive is not made in this method. The control scheme employs an online estimation of the environment including disturbance and transmission time delay between master and slave. Simulation results show that position and force tracking errors are small, and the system shows stable behavior in spite of the uncertainties. A transparency analysis in the frequency domain shows that the developed control scheme guarantees perfect transparency in the low frequencies.

Trajectory Generation for Assembly Tasks Via Bilateral Teleoperation

Abstract in Undetermined For assembly tasks, the knowledge of both trajectory and forces are usually required. Consequently, we may use kinesthetics or teleoperation for recording human demonstrations. In order to have a more natural interaction, the operator has to be provided with a sense of touch. We propose a bilateral teleoperation system which is customized for this purpose. We introduce different coordinate frames to make the design of a 6-DOF teleoperation straightforward. Moreover, we suggest using tele-admittance, which simplifies instructing the robot. The compliance due to the slave controller allows the robot to react quickly and reduces the risk of damaging the workpiece.

Haptic Rendering of Drilling into Femur Bone with Graded Stiffness

This paper presents haptic rendering method of drilling into femur bone with graded stiffness. Volume rendering is preferred than surface rendering in drilling or burr simulation because the volume rendering can contain information such as density and rigidity of each voxel. However, it is difficult to implement real-time graphics and haptic rendering because of the large computational workload. Therefore, we propose surface-data-based haptic rendering of drilling process of stiffness graded material. Contact surface update and bone erosion algorithms are suggested to implement the drilling process. The proposed algorithms are adapted to the closed reduction and internal fixation surgery simulator. The proposed method allows the user of the simulation to feel the different forces according to the drilled depth.

Development of a 4 DOF exoskeleton robot for elbow and wrist rehab

It is important to control impedance between a patient and a robot to maximize the effect of the robot rehabilitation therapy. This paper presents a 4 DOF exoskeleton robot for elbow and wrist rehabilitation, which includes a unified actuator module per each joint. The unified actuator module consists of a frameless motor, an incremental encoder, an absolute encoder, a harmonic drive, a torque sensor, and a motor controller. The interaction force between a patient and the robot can be computed based on the torque signal of each joint. This enables us to design impedance controller to implement proper impedance to the patient. All the components of the unified actuator module were carefully selected to minimize overall weight and size. A second-order state-space model for the unified actuator module is developed via experiments. A H2 optimal controller was designed based on the state-space model.

Design of an intermediate layer to enhance operator awareness and safety in telesurgical systems

This paper presents a novel control architecture for enhanced operator awareness and improved safety in telesurgical systems. We introduce an intermediate layer between the master and slave sides which allows us to modify the slave motion for safety and the force feedback for operator awareness. The intermediate layer is then designed with a performance objective for the specific task at hand. The control scheme is validated via experiments using a suture and an industrial manipulator. More specifically we show that operator awareness should be implemented as an integrated part of the safety level to maintain safety during surgery.

Surface-Data-Based Haptic Rendering for Simulation of Surgery of Closed Reduction and Internal Fixation

This paper presents a surface-data-based haptic rendering method for simulation of surgery of closed reduction and internal fixation (CRIF). Volumetric data is often employed in the simulation of bone surgery because the volume rendering can easily handle information such as density and rigidity of each voxel. However, it is difficult to implement real-time graphics and haptic rendering because of the large computational workload. Therefore, we propose a surface-data- based haptic rendering method for real-time rendering. Mechanical properties and graphics of the inner part of the bone should be modeled in addition to the surface data to simulate drilling into the bone. An algorithm is developed to construct the surface of the drilled hole. This method allows the user of the simulation to feel the varying forces according to the drilled depth.