Transfer Function Compensation in Gyroscope-free Inertial Measurement Units for Accurate Angular Motion Sensing.

Gyroscope-free inertial measurement units have been gaining popularity in applications such as motion sensing of hand-held microsurgical instruments. Various accelerometer placement configurations have been proposed in the past. However, the effect of non-identical transfer functions of accelerometers on the accuracy of angular motion sensing has been underestimated and never been taken into consideration. In this paper, significant effect of different phases at different accelerometer outputs due to non-identical transfer functions on the accuracy is highlighted, and a method is proposed to make the transfer functions of all the accelerometers identical. Effectiveness of the method is confirmed with an experiment using ADXL-203 accelerometers.

Placement of Accelerometers for High Sensing Resolution in Micromanipulation.

High sensing resolution is required in sensing of surgical instrument motion in micromanipulation tasks. Accelerometers can be employed to sense physiological motion of the instrument during micromanipulation. Various configurations of accelerometer placement had been introduced in the past to sense motion of a rigid-body such as a surgical instrument. Placement (location and orientation) of accelerometers fixed in the instrument plays a significant role in achieving high sensing resolution. However, there is no literature or work on the effect of placement of accelerometers on sensing resolution. In this paper, an approach of placement of accelerometers within an available space to obtain highest possible sensing resolution in sensing of rigid-body motion in micromanipulation tasks is proposed. Superiority of the proposed placement approach is shown in sensing of a microsurgical instrument angular motion by comparing sensing resolutions achieved as a result of employing the configuration following the proposed approach and the existing configurations. Apart from achieving high sensing resolution, and design simplicity, the proposed placement approach also provides flexibility in placing accelerometers; hence it is especially useful in applications with limited available space to mount accelerometers.

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.

Design and development of a novel balancer with variable difficulty for training and evaluation.

This paper presents a novel, portable and cost-effective balance trainer with the necessary important features to improve the reach of rehabilitation to the masses. There are three factors that contribute to a person's ability to maintain standing balance: Proprioceptive feedback (from the joints), vision, and the vestibular system. These systems can be affected by injury, infection, or brain damage caused by stroke. One example of such injuries is ankle injury. A large focus of the physiotherapy and sports medicine community is using postural-control tasks to prevent, assess and rehabilitate patients. Unfortunately, there are presently two extreme ends of balance training devices. On one end, there is high-end equipment which only large hospitals are capable of buying. On the other end are the simple balance boards which offer limited features. To develop the new balance trainer - the Pro.Balance - therapists at the Singapore General Hospital drafted a new 'wish list' of requirements. The prototype was built at the Nanyang Technological University, Singapore, and was commercialized by Lab Rehab Pte Ltd as the Pro.Balance. The device has a small footprint, incorporating only the most important and frequently used functions. These functions include being able to provide different levels of difficulty, setting different difficulties in different directions, the storing of a patient's performance, real-time visual feedback to aid the patient and different types of modes for different purposes. Springs are used to vary the amount of supporting moments, thus varying the difficulty levels. This paper describes the design and features of the Pro.Balance.

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.

System to assess accuracy of micromanipulation.

The authors had previously developed an optical micro motion sensing system (M2S2) using a pair of orthogonally placed position sensitive detectors (PSD) to track 3D displacement of the tip of a microsurgical instrument in real-time. In the M2S2 system, 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 position of reflected IR light on the PSDs. The M2S2 system together with a test platform is used as an evaluation system to assess the accuracy and physiological tremor of subjects performing micromanipulation tasks. Since the need to use the ball at the instrument tip prevents the subjects from performing the manipulation tasks precisely, a laser light is provided as a guide for the subjects to aim at the target precisely. A laser diode module is placed inside the instrument to provide the required laser light. The instrument intraocular shaft is replaced with a same-sized hollow tube to let the laser light from the instrument pass through down to the target. The laser light spot position on the platform is used to access the performance of the subjects. The laser light spot position is calculated from the tilt angle information provided by an accelerometer placed inside the instrument, and the instrument tip position information given by M2S2.