C. Y. Shee

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.

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.

Design and Calibration of an Optical Micro Motion Sensing System for Micromanipulation Tasks

An optical sensing system has been developed using a pair of orthogonally placed position sensitive detectors (PSD) to track 3D displacement of a microsurgical instrument tip in real-time. An infrared (IR) diode is used to illuminate the workspace. A ball is attached to the tip of an intraocular shaft to reflect IR rays onto the PSDs. Instrument tip position is then calculated from the centroid positions of reflected IR light on the respective PSDs. The system can be used to assess the accuracy of hand-held microsurgical instruments and operator performance in micromanipulation tasks, such as microsurgeries. In order to eliminate inherent nonlinearity of the PSDs and lenses, calibration is performed using a feedforward neural network. After calibration, percentage RMS error is reduced from about 5.46 % to about 0.16%. The system RMS noise is about 0.7 mum. The sampling rate of the system is 250 Hz.

Post-acute stroke patients use brain-computer interface to activate electrical stimulation

Through certain mental actions, our electroencephalogram (EEG) can be regulated to operate a brain-computer interface (BCI), which translates the EEG patterns into commands that can be used to operate devices such as prostheses. This allows paralyzed persons to gain direct brain control of the paretic limb, which could open up many possibilities for rehabilitative and assistive applications. When using a BCI neuroprosthesis in stroke, one question that has surfaced is whether stroke patients are able to produce a sufficient change in EEG that can be used as a control signal to operate a prosthesis.

Automatic control of mechanical forces acting on cell biomembranes using a vision-guided microrobotic system in computer microscopy.

A prototype for automatic control of mechanical forces acting on cell biomembranes is proposed in this paper. This prototype consists of vision‐guided position control of the holder and micro‐force sensor, automatic mechanical property characterization of cell biomembranes and automatic control of mechanical forces acting on cell biomembranes. A template‐free calibration method and autofocusing of multiple objects are introduced in the vision‐guided position control to minimize external biological contamination and position the cell, holder and micro‐force sensor into the same focal plane, respectively. A third‐order polynomial modified from biomembrane point‐load model describing the relationship between the measured mechanical force and the deformations of biomembranes is proposed. This simplified model is easily identified and inversed to facilitate the automatic control of mechanical forces. Experimental results based on zebrafish embryos demonstrate the feasibility of the proposed prototype.

A study of a hand-held instrument's angular motion due to physiological tremor in micromanipulation tasks

Angular motion of a hand-held instrument due to physiological tremor during micromanipulation tasks was recorded with a six degree-of-freedom accelerometer-based sensing unit placed in the instrument. Methods to get angular velocities and angular accelerations from the acceleration readings of accelerators in the sensing unit are described. Statistics of angular velocity and angular acceleration of the instrument due to the tremor obtained from ten normal subjects are reported. Assumption of very small tremor angular velocities in micromanipulation tasks to calculate tremor angular accelerations analytically is validated.

Rate-Dependent Hysteresis Model of Piezoelectric using Singularity Free Prandtl-Ishlinskii Model

Actuators using advance materials like piezoelectric and shape memory alloy are gaining popularity in applications involving high frequency, high precision and also when theres a need in compactness. As time is required for the switching of polarization, the phenomena hysteretic behavior of these materials changes with rate. Most present hysteresis models are based on rate-independent assumption and cannot be applied for non-periodic applications. To make matters worse, the hysteresis actually becomes ill-conditioned when the velocity is high at the turning point. This paper proposes a phenomena rate-dependent model using a modified Prandtl-Ishlinskii (PI) operator without singularity to model the behavior of piezoelectric actuators, even when subjected to varying frequency signals. Past work had shown that the weights of the Prandtl-Ishlinskii operators vary linearly with velocity when the velocity is less than 900mum/s. As the first weight becomes negative when operating at higher frequencies, the threshold value has to be kept large to avoid the singularity problem when computing the inverse Prandtl-Ishlinskii model. Similar ill-conditioned problems also arise when the actuators are subjected to heavy loads. Thus, this paper proposes extensions to the PI operator by mapping the hysteresis data through a linear transformation onto a domain where the singularity problem is removed. The inverse weights are obtained and subsequently used to compute the inverse hysteresis model and implemented as an open-loop feedforward control of a piezoelectric actuator.

Design and implementation of a mechatronic device for wrist and elbow rehabilitation

This paper presents a compact, portable and modular mechatronic device, which can be used for wrist and elbow rehabilitation in a user-friendly manner. Portability, modularity, compactness & degree of freedom are the main concerns of the device. Applied postoperatively, this device may be used on an inpatient or an outpatient basis. The designed device can be used for different exercises of wrist and elbow just by simply plugging in or out some of the links or by adjusting the position of some of the links. In addition, instead of going with the usual approach of using different actuators for different degrees of freedom, a single actuator is used in this project. By adjusting the links position, the patient can perform different exercises. The therapist or the patient will then select appropriate settings to run different exercises.

Automatic Vision Guided Small Cell Injection: Feature Detection, Positioning, Penetration and Injection

Vision guided automatic cell injection system has become increasingly important in the past ten years. The existing cell injection systems mainly deal with large cells with size bigger than 40 micrometers. However, when dealing with small cells, the internal and external disturbances presented in the system may affect the success rate of injections significantly. In this paper, the system setup of vision guided cell injection system is presented. Feature tracking, micropipette positioning, cell membrane penetration and biological material injection processes for small cell with size around 20 micrometers are discussed. Sum of square difference (SSD) tracking algorithm based on 2 dimensional (2D)-to-2D feature correspondences is used to handle disturbances. A modified proportional position controller is adopted to control the micropipette. The importance of cell membrane penetration modeling is emphasized.

Real-time estimation and prediction of periodic signals from attenuated and phase-shifted sensed signals

The use of linear filters to extract desired signals from sensed signals which contain a mixture of the desired and undesired signals inherently alters amplitude and phase characteristics of the desired signals. Attenuation and phase-shift incurred in the extracted desired signals is undesirable in applications such as real-time physiological tremor compensation. Algorithms based on Fourier linear combiners (FLC) such as a Weighted-frequency Fourier Linear Combiner (WFLC), and a Bandlimited Multiple Fourier Linear Combiner (BMFLC) can estimate and extract periodic signals without altering the amplitude and phase characteristics. The proper performance of the algorithms usually requires prefiltering of the sensed signals using linear filters. Moreover, in some situations, the sensed signals have been prefiltered by inevitable linear filters present in the sensors or sensor modules. Modification made to WFLC and BMFLC to compensate for the change in amplitude and phase characteristics of the extracted desired periodic signals due to the prefiltering for real-time applications is presented. A way to perform prediction of a periodic signal using the WFLC or BMFLC algorithm is also shown.