The bipedal saddle space: modelling and validation.

Better understanding of human balance control is pivotal for applications such as bipedal robots and medical technologies/therapies targeting human locomotion. Despite the inverted pendulum model being popular for describing bipedal locomotion, it does not properly capture the step-to-step transition dynamics. The major drawback has been the requirement for both feet to be on the ground which generates a discontinuity along the intersection of the potential energy surfaces produced by the two legs. To overcome this problem, we propose a generalized inverted pendulum-based model that can describe both single and double support phases. The full characterization of the system's potential energy allows the proposed model to drop the main limitation. This framework also enables optimal strategies to be designed for the transition between the two feet without the optimization algorithms. The proposed theory has been validated by comparing the human locomotor strategies output of our planner with real data from multiple experimental studies. The results show that our model generates trajectories consistent with human variability and performs better than existing well-known methods.

Multi-step prediction of physiological tremor for robotics applications.

The performance of surgical robotic devices in real-time mainly depends on phase-delay in sensors and filtering process. A phase delay of 16-20 ms is unavoidable in these robotics procedures due to the presence of hardware low pass filter in sensors and pre-filtering required in later stages of cancellation. To overcome this phase delay, we employ multi-step prediction with band limited multiple Fourier linear combiner (BMFLC) and Autoregressive (AR) methods. Results show that the overall accuracy is improved by 60% for tremor estimation compared to single-step prediction methods in the presence of phase delay. Experimental results with the proposed methods for 1-DOF tremor estimation highlight the improvement.

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.

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.

Estimation and filtering of physiological tremor for real-time compensation in surgical robotics applications.

BACKGROUND: Physiological tremor is the main cause of imprecision in microsurgical procedures/robotics applications. Existing methods, such as weighted-frequency Fourier linear combiner (WFLC), rely on estimating the tremor under the assumption that it has a single dominant frequency. This paper focuses on developing a new algorithm for accurate tremor filtering in real time. METHODS: A study conducted on several novice subjects and microsurgeons showed the tremor to contain several dominant frequencies in a band, rather than a single dominant frequency. Based on the tremor characteristics, a new algorithm band-limited multiple Fourier linear combiner (BMFLC) has been developed to estimate a band of signals with multiple dominant frequencies. A separation procedure to separate the intended motion/drift from the tremor portion is also discussed. RESULTS: A simulation study was first conducted to validate the theoretical development on recorded tremor data. The experimental set-up was designed to study the real-time performance of the proposed algorithm. Tremor sensing using accelerometers is also discussed, with the proposed algorithm. Our experiments showed that the developed BMFLC algorithm had an average tremor compensation of 64% compared to 43% for the WFLC algorithm in real-time for one degree of freedom (1-DOF) cancellation of tremor. CONCLUSIONS: The BMFLC algorithm can be applied for the three axes separately and 3-DOF cancellation of tremor can be achieved. Further research is required to deal with complex gestures involved during microsurgery.

Influence of visual feedback and speed on micromanipulation accuracy.

Accuracy in micromanipulation tasks is limited and it is important to identify various factors affecting it. This paper studies the effect of visual magnification, speed and handedness to micromanipulation accuracy using microscope and LCD screen for feedback. Magnification of visual feedback increases the accuracy, but large magnification does not provide further improvement beyond 16x. Further, we observed a trade off between speed and accuracy in tracing a circular path, i.e. faster speed reduces the speed control ability of the hand. Finally, dominant/non-dominant hand is found to affect accuracy in motion.

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 boundary element model for investigating the effects of eye tumor on the temperature distribution inside the human eye.

A three-dimensional boundary element model of the human eye is developed to investigate the thermal effects of eye tumor on the ocular temperature distribution. The human eye is modeled as comprising several regions which have different thermal properties. The tumor is one of these regions. The thermal effects of the tumor are simulated by taking it to have a very high metabolic heat generation and blood perfusion rate. Inside the tumor, the steady state temperature is governed by the Pennes bioheat equation. Elsewhere, in normal tissues of the eye, the temperature satisfies the Laplace's equation. To compute the temperature on the corneal surface, the surface boundary of each region is divided into triangular elements.

Self-calibration method for vision-guided cell micromanipulation systems.

A new self-calibration method for a piezoelectric actuator-based vision-guided cell micromanipulation system is proposed. This method consolidates all the system parameters' uncertainties into a matrix instead of classifying into intrinsic and extrinsic. The position difference of the micromanipulator tip in the image plane between the measured and estimated output which is based on estimations of relevant parameters is assumed to be caused by the matrix. This matrix is estimated by means of collecting several pairs of known input and the corresponding output differences. Matrix standard deviation and gray-value based matching are applied to identify the output differences. Biological contamination is reduced since a calibration template is not required. This self-calibration is particularly suitable for cell micromanipulation systems where the micromanipulator is frequently dismounted and mounted.

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 implementation of a two degree-of-freedom micromanipulation assessment system.

A two degree-of-freedom (DOF) micro motion sensing system to assess micromanipulation accuracy and physiological tremor has been developed. The system employs a position sensitive detector (PSD) module and a laser diode placed inside an instrument used in micromanipulation. A laser light is shined from the laser diode onto the PSD surface which is faced upward. The PSD detects the centroid position of the laser light spot falling onto its surface. A few markers are overlaid in a circular pattern on the PSD surface as reference for path dependent tests. Ambient light disturbance is eliminated by modulating the laser light on and off. Advantages and limitation of the system comparing to other similar systems are described.

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.

Active tremor compensation in microsurgery.

This work presents the development of an intelligent microsurgical instrument to perform real-time tremor compensation within a handheld tool. The intelligent instrument senses its own motion, distinguishes between voluntary and erroneous motion, and manipulates its tip to cancel the undesired component in real-time. The on-board sensing unit is made up of a magnetometer-aided all-accelerometer inertial measurement unit and sensor fusion is performed via a quaternion-based Kalman filtering. Tremor is modeled and filtered by an adaptive zero-phase notch filter. The intraocular shaft manipulator is a three DOF piezoelectric actuated mechanism driven by a feedforward controller with inverse rate-dependent hysteresis model. Laboratory experimental results of the system are presented.

The inferior boundary condition of a continuous cantilever beam model of the human spine.

The continuous cantilever beam model of the human spine usually assumes that the beam tangent at the inferior end of the structure is exactly perpendicular to the surface in which it is built into. The model used in this paper allows for realistic imperfections in the beam so that a small non-zero rotation is allowed at its inferior end. Such a model is used to investigate the lateral deformation of the muscle-relaxed spine as it supports asymmetrical loads in the frontal plane. By comparing the model deformations with previously published results, it was easily seen how such imperfections can effect the solution quantitatively. This was found to be especially true when the model was used to estimate the gross flexural rigidity of the spine in the frontal plane. It could also explain why some spines are more prone to lateral curvature and instability than others. Considering the importance of such a parameter when used in the continuous model, an investigation into the true nature of the inferior model boundary condition could be warranted.