Robust stability of teleoperation systems with time delay: a new approach.

In this paper, we propose an approach to the control of linear teleoperation systems under time delays. Unlike traditional delay-robust control systems that guarantee passive communication channel through the transmission of wave variables, the new approach uses the concept of absolute stability for the physically expressive Lawrence's four-channel structure for transmitting the standard power variables, i.e., force and position. By incorporating kinesthetic performance requirements, we derive an absolutely stable four-channel controller that is transparent when time delay is negligible. Experimentally, the study evaluates and compares the performance of the proposed controller with that of a benchmark wave variable-based controller. The results indicate contact stability for large delays, a lack of position drift, and improved position and force tracking in both the free motion and rigid contact regimes for small delays.

Needle deflection estimation using fusion of electromagnetic trackers.

We present a needle deflection estimation method to compensate for needle bending during insertion into deformable tissue. We combine a kinematic needle deflection estimation model, electromagnetic (EM) trackers, and a Kalman filter (KF). We reduce the impact of error from the needle deflection estimation model by using the fusion of two EM trackers to report the approximate needle tip position in real-time. One reliable EM tracker is installed on the needle base, and estimates the needle tip position using the kinematic needle deflection model. A smaller but much less reliable EM tracker is installed on the needle tip, and estimates the needle tip position through direct noisy measurements. Using a KF, the sensory information from both EM trackers is fused to provide a reliable estimate of the needle tip position with much reduced variance in the estimation error. We then implement this method to compensate for needle deflection during simulated prostate cancer brachytherapy needle insertion. At a typical maximum insertion depth of 15 cm, needle tip mean estimation error was reduced from 2.39 mm to 0.31 mm, which demonstrates the effectiveness of our method, offering a clinically practical solution.

Bounded-Impedance Absolute Stability of Bilateral Teleoperation Control Systems.

Available passivity-based robust stability methods for bilateral teleoperation control systems are generally conservative, as they consider an unbounded range of dynamics for the class of passive operators and environments in the complex plane. In this paper, we introduce a powerful 3D geometrical robust stability analysis method based on the notions of wave variables and scattering parameters. The methodology, which was originally a 2D graphical method used in microwave systems for single-frequency analysis [1], is further developed in this paper for teleoperation and haptic systems. The proposed method provides both mathematical and visual aids to determine bounds or regions on the complex frequency response of the passive environment impedance parameters for which a potentially unstable system connected to any passive operator is stable, and vice-versa. Furthermore, the method allows for the design of bilateral controllers when such bounds are known, or can even be utilized when the environment dynamics are active. The geometrical test can also be replaced by an equivalent mathematical condition, which can easily be checked via a new stability parameter. The proposed method results in less conservative guaranteed stability conditions compared to the Llewellyn's criterion; thus, promising a better compromise between stability and performance. The new method is numerically evaluated for two bilateral control architectures.

Hand force estimation using Fast Orthogonal Search.

The use of the Fast Orthogonal Search (FOS) method is presented for the estimation of human hand force based on electromyogram (EMG) signal readings and sensed elbow angular position. The use of inexpensive and easily portable EMG electrodes and position sensors would be advantageous in many applications compared to the use of force sensors which are often very expensive and require bulky frames to be used. A single degree-of-freedom robotic experimental testbed has been constructed which allows for data collection, model identification and validation of EMG-force models. FOS identifies the models extremely rapidly with similar or better accuracy compared to existing methods.

A haptic-based system for medical image examination.

This paper presents a haptic-based simulator for training of radiology residents and sonographers. The system consists of a force feedback haptic device providing means to interact in real-time with volumetric images of a virtual patient, captured pre-operatively from several subjects. The training system allows trainees to develop radiology techniques and knowledge of the patient's anatomy with minimum practice on live patients, or in places or at times when radiology devices or patients with rare cases may not be available. The haptic interface guarantees position correspondence between the operator's hand and a virtual probe position that slices medical volume sets in the plane of the probe. Thus the simulated procedure becomes nearly identical to the real examinations at the hospital. Different configurations of the system are implemented and presented. Future potential applications for the system are discussed as well.