Win Tun Latt

Feedforward Controller of Ill-Conditioned Hysteresis Using Singularity-Free Prandtl–Ishlinskii Model

Piezoelectric, magnetostrictive, and shape memory alloy actuators are gaining importance in high-frequency precision applications constrained by space. Their intrinsic hysteretic behavior makes control difficult. The Prandtl-Ishlinskii (PI) operator can model hysteresis well, albeit a major inadequacy: the inverse operator does not exist when the hysteretic curve gradient is not positive definite, i.e., ill condition occurs when slope is negative. An inevitable tradeoff between modeling accuracy and inversion stability exists. The hysteretic modeling improves with increasing number of play operators. But as the piecewise continuous interval of each operator reduces, the model tends to be ill-conditioned, especially at the turning points. Similar ill-conditioned situation arises when these actuators move heavy loads or operate at high frequency. This paper proposes an extended PI operator to map hysteresis to a domain where inversion is well behaved. The inverse weights are then evaluated to determine the inverse hysteresis model for the feedforward controller. For illustration purpose, a piezoelectric actuator is used.

Estimating Displacement of Periodic Motion With Inertial Sensors

Inertial sensors, like accelerometers and gyroscopes, are rarely used by themselves to measure displacement. Accuracy of inertial sensors is greatly handicapped by the notorious integration drift, which arises due to numerical integration of the sensors zero bias error. A solution is proposed in this paper to provide drift free estimation of displacement from inertial sensors.

A Hand-held Instrument to Maintain Steady Tissue Contact during Probe-Based Confocal Laser Endomicroscopy

Probe-based confocal laser endomicroscopy (pCLE) provides high-resolution in vivo imaging for intraoperative tissue characterization. Maintaining a desired contact force between target tissue and the pCLE probe is important for image consistency, allowing large area surveillance to be performed. A hand-held instrument that can provide a predetermined contact force to obtain consistent images has been developed. The main components of the instrument include a linear voice coil actuator, a donut load-cell, and a pCLE probe. In this paper, detailed mechanical design of the instrument is presented and system level modeling of closed-loop force control of the actuator is provided. The performance of the instrument has been evaluated in bench tests as well as in hand-held experiments. Results demonstrate that the instrument ensures a consistent predetermined contact force between pCLE probe tip and tissue. Furthermore, it compensates for both simulated physiological movement of the tissue and involuntary movements of the operators hand. Using pCLE video feature tracking of large colonic crypts within the mucosal surface, the steadiness of the tissue images obtained using the instrument force control is demonstrated by confirming minimal crypt translation.

Bandlimited Multiple Fourier Linear Combiner for Real-time Tremor Compensation

Surgical accuracy of the hand-held instruments depends on the active compensation of disturbance and tremor. Physiological tremor is one of the main causes for imprecision in micro-surgery procedures. One of the popular tremor compensation methods is based on weighted-frequency Fourier linear combiner (WFLC) algorithm, that can adapt to the changes in frequency as well as amplitude of the tremor signal. WLFC estimates the dominant frequency and the amplitude. For the case of tremor with frequency variation or comprising of two or three frequencies close in spectral domain, the WFLC performance is degraded. In this paper, we present a bandlimited multiple Fourier linear combiner that can track the modulated signals with multiple frequency components. We also discuss the tremor sensing with accelerometers. Using the proposed algorithm the drift caused by the accelerometers is also eliminated. The proposed filter is tested in real-time for 1-DOF cancellation of tremor.

Double adaptive bandlimited multiple Fourier linear combiner for real-time estimation/filtering of physiological tremor

Tremor is the root cause for human imprecision during microsurgery. Accurate filtering of physiological tremor is extremely important for compensation in robotics assisted microsurgical instruments/ procedures. A study on several surgeons tremor is conducted and the characteristics of the tremor are analyzed. A double adaptive bandlimited multiple Fourier linear combiner is designed to estimate the modulated signals with multiple frequency components for filtering and compensation of tremor in realtime. A separation procedure to separate the intended motion/drift from the tremor portion is developed. The proposed methods are compared with the existing weighted-frequency Fourier linear combiner (WFLC) algorithm on the tremor data of surgeons/subjects. Critical validation of the algorithm is performed, experiments are conducted for 1-degree of freedom (DOF) cancellation of tremor. Our experiments showed that our newly developed algorithm has a tremor compensation of at least 65% compared to 46% for the WFLC algorithm.

Drift-Free Position Estimation of Periodic or Quasi-Periodic Motion Using Inertial Sensors

Position sensing with inertial sensors such as accelerometers and gyroscopes usually requires other aided sensors or prior knowledge of motion characteristics to remove position drift resulting from integration of acceleration or velocity so as to obtain accurate position estimation. A method based on analytical integration has previously been developed to obtain accurate position estimate of periodic or quasi-periodic motion from inertial sensors using prior knowledge of the motion but without using aided sensors. In this paper, a new method is proposed which employs linear filtering stage coupled with adaptive filtering stage to remove drift and attenuation. The prior knowledge of the motion the proposed method requires is only approximate band of frequencies of the motion. Existing adaptive filtering methods based on Fourier series such as weighted-frequency Fourier linear combiner (WFLC), and band-limited multiple Fourier linear combiner (BMFLC) are modified to combine with the proposed method. To validate and compare the performance of the proposed method with the method based on analytical integration, simulation study is performed using periodic signals as well as real physiological tremor data, and real-time experiments are conducted using an ADXL-203 accelerometer. Results demonstrate that the performance of the proposed method outperforms the existing analytical integration method.

A Low-Cost Flexure-Based Handheld Mechanism for Micromanipulation

With the advancement in the knowledge of surgical procedures and cell micromanipulation, there is a demand for a handheld instrument to perform micromanipulation. Hence, this paper presents a 3-DOF handheld mechanism for micromanipulation driven by three piezoelectric actuators. Flexure-based joints are utilized because of its advantages like the nonexistence of backlash and assembly errors. However, it is difficult and expensive to make such compact mechanism using traditional machining methods. In addition, the traditional machining methods are limited to simple design. To reduce the cost of fabrication and also to allow more complex designs, Objet (a rapid prototyping machine) is proposed to be used to build the mechanism. With regards to the handheld applications, the size of the mechanism is a constraint. Hence, a parallel manipulator design is the preferred choice because of its rigidity and compactness. For the illustration of an application, the mechanism is designed with an intraocular needle attached to it. Possible applications of this design include enhancement of performance in microsurgery and cell micromanipulation. Experiments are also conducted to evaluate the manipulators tracking performance of the needle tip at a frequency of 10 Hz.

A compact hand-held active physiological tremor compensation instrument

This paper presents research, design, and development of a compact version of a hand-held active physiological tremor compensation instrument called “ITrem”. The instrument comprises three main portions: sensing, filtering, and manipulation. Accelerometers are employed to sense three degrees-of-freedom motion of the instrument tool tip. Minimal-phase filtering is performed to extract tremulous motion of the tip from its total motion. As for manipulation, piezoelectric actuators and flexure based mechanism are employed to move the tool tip to an opposite direction but an equal in magnitude of the tremulous motion. The performance of the instrument was evaluated using a micro motion sensing system (M2S2). The preliminary results of bench tests as well as hand-held tests are shown.

Compact Sensing Design of a Handheld Active Tremor Compensation Instrument

Active physiological tremor compensation instruments have been under research and development recently. The sensing unit of the instruments provides information on three degrees-of-freedom (DOF) motion of the instrument tip using accelerations provided by accelerometers placed inside the instruments. A complete vector of angular acceleration of the instrument needs to be known to obtain information on three DOF motions of the tip. Sensing resolution of angular acceleration about the instrument axis is directly proportional to the width of the proximal-end sensing unit. To keep the sensing resolution high enough, the width of the unit has to be made large. As a result, the proximal-end sensing unit of the instruments is bulky. In this paper, placement of accelerometers is proposed such that the angular acceleration about the instrument axis need not be known to obtain information on the three DOF motions of the tip. With the proposed placement, the instrument is no longer bulky and fewer number of accelerometers is required, thereby making the instrument compact and better in terms of ergonomics and reliability. Experiments were conducted to show that the proposed design of placement works properly.

Physiological tremor sensing using only accelerometers for real-time compensation

A hand-held tremor compensation instrument, Micron, has been under research recently. The sensing part of the instrument comprises a magnetometer and accelerometers. The use of the magnetometer is to provide accurate instrument orientation information. The drawbacks of relying on the magnetometer include the requirement for on-site calibration of the magnetometer and sub-optimal estimation of the tremor due to sub-optimal estimation of the instrument orientation. To eliminate the problems associated with the magnetometer, an algorithm of sensing the tremor using only accelerometers is proposed. The algorithm is tested with real accelerometer output data and the results are shown and discussed.