Wavelet thresholding technique for sEMG denoising by baseline estimation

The surface electromyography (sEMG) signal is affected by different sources of noises: current technology is considerably robust to the interferences of the power line or cable motion artefacts, but still there are many limitations in denoising the baseline. In this paper, we introduce a new technique, named baseline adaptive denoising algorithm (BADA), for denoising the sEMG signal by wavelet thresholding procedure. In particular, the thresholds are estimated using the same baseline signal with fixed and adaptive techniques. Eventually, we verify that the proposed adaptive method performs better than the standard Donoho technique and different variations, in term of noise cancellation and distortion of the signal, quantified by a new suggested indicator of the denoising quality. Copyright © 2012 Inderscience Enterprises Ltd

Anatomical calibration through post-processing of standard motion tests data

The inertial measurement unit is popularly used as a wearable and flexible tool for human motion tracking. Sensor-to-body alignment, or anatomical calibration (AC), is fundamental to improve accuracy and reliability. Current AC methods either require extra movements or are limited to specific joints. In this research, the authors propose a novel method to achieve AC from standard motion tests (such as walking, or sit-to-stand), and compare the results with the AC obtained from specially designed movements. The proposed method uses the limited acceleration range on medial-lateral direction, and applies principal component analysis to estimate the sagittal plane, while the vertical direction is estimated from acceleration during quiet stance. The results show a good correlation between the two sets of IMUs placed on frontal/back and lateral sides of head, trunk and lower limbs. Moreover, repeatability and convergence were verified. The AC obtained from sit-to-stand and walking achieved similar results as the movements specifically designed for upper and lower body AC, respectively, except for the feet. Therefore, the experiments without AC performed can be recovered through post-processing on the walking and sit-to-stand data. Moreover, extra movements for AC can be avoided during the experiment and instead achieved through the proposed method

Development of an ultra-miniaturized inertial measurement unit for jaw movement analysis during free chewing

Problem statement: Jaw movement analysis, as a clinical aid, can provide an objective basis for understanding and diagnosing jaw musculoskeletal disorders. Therefore, the use and development of devices for quantitatively measuring and analyzing jaw movement have become more common and popular in the clinic. Many types of jaw tracking devices have been developed, but most of them are still not handy and easy to be used. Approach: To improve the handiness and utility of the jaw movement analysis devices, we developed a simple to be used jaw tracking prototype by using a new ultra-miniaturized Inertial Measurement Unit (IMU) named WB-3. The WB-3 IMU was composed by 3-axis gyroscope, 3-axis accelerometer and 3-aixs magnetometer, which can not only measure the acceleration and angular speed of jaw movement, but also can measure mouth opening angle. The IMU's extremely reduced weight and size allowed it to be easily adhered to mandible during normal tests without physical restriction to the subjects. A preliminary experiment for jaw movement analysis during free chewing of three types of food with different shapes and hardness was evaluated. A group of 15 healthy subjects aged from 21-36 years old kindly participated in the experiment. Results: The parameters of chewing time, chewing frequency, power spectrum density of jaw's angular speed and acceleration, cumulative distribution function of jaw's acceleration and mouth opening angle were presented. The experimental results clearly showed that the subjects used less chewing time, less chewing frequency, less acceleration cumulative distribution and energy to eat soft food; higher values were found in the case of hard food and there was no significant difference in mouth opening angle while eating these three foods. Conclusion: Our jaw movement analysis prototype using IMU WB-3 was proved to be a valid and handy method for jaw movement and pattern analysis which may be used clinically as an assistant system for dental therapy. © 2010 Science Publications

A methodology for the performance evaluation of inertial measurement units

This paper presents a methodology for a reliable comparison among Inertial Measurement Units or attitude estimation devices in a Vicon environment. The misalignment among the reference systems and the lack of synchronization among the devices are the main problems for the correct performance evaluation using Vicon as reference measurement system. We propose a genetic algorithm coupled with Dynamic Time Warping (DTW) to solve these issues. To validate the efficacy of the methodology, a performance comparison is implemented between the WB-3 ultra-miniaturized Inertial Measurement Unit (IMU), developed by our group, with the commercial IMU InertiaCube3™ by InterSense

Reliability of the step phase detection using inertial measurement units: pilot study

The use of inertial sensors for the gait event detection during a long-distance walking, for example, on different surfaces and with different walking patterns, is important to evaluate the human locomotion. Previous studies demonstrated that gyroscopes on the shank or foot are more reliable than accelerometers and magnetometers for the event detection in case of normal walking. However, these studies did not link the events with the temporal parameters used in the clinical practice; furthermore, they did not clearly verify the optimal position for the sensors depending on walking patterns and surface conditions. The event detection quality of the sensors is compared with video, used as ground truth, according to the parameters proposed by the Gait and Clinical Movement Analysis Society. Additionally, the performance of the sensor on the foot is compared with the one on the shank. The comparison is performed considering both normal walking and deviations to the walking pattern, on different ground surfaces and with or without constraints on movements. The preliminary results show that the proposed methodology allows reliable detection of gait events, even in case of abnormal footfall and in slipping surface conditions, and that the optimal location to place the sensors is the shank

Baseline adaptive wavelet thresholding technique for sEMG denoising

The surface Electromyography (sEMG) signal is affected by different sources of noises: current technology is considerably robust to the interferences of the power line or the cable motion artifacts, but still there are many limitations with the baseline and the movement artifact noise. In particular, these sources have frequency spectra that include also the low‐frequency components of the sEMG frequency spectrum; therefore, a standard all‐bandwidth filtering could alter important information. The Wavelet denoising method has been demonstrated to be a powerful solution in processing white Gaussian noise in biological signals. In this paper we introduce a new technique for the denoising of the sEMG signal: by using the baseline of the signal before the task, we estimate the thresholds to apply to the Wavelet thresholding procedure. The experiments have been performed on ten healthy subjects, by placing the electrodes on the Extensor Carpi Ulnaris and Triceps Brachii on right upper and lower arms, and performing a flexion and extension of the right wrist. An Inertial Measurement Unit, developed in our group, has been used to recognize the movements of the hands to segment the exercise and the pre‐task baseline. Finally, we show better performances of the proposed method in term of noise cancellation and distortion of the signal, quantified by a new suggested indicator of denoising quality, compared to the standard Donoho technique

Comparison of gait event detection from shanks and feet in single-task and multi-task walking of healthy older adults

Automatic and objective detection algorithms for gait events from MEMS Inertial Measurement Units data have been developed to overcome subjective inaccuracy in traditional visual observation. Their accuracy and sensitivity have been verified with healthy older adults, Parkinson's disease and spinal injured patients, using single-task gait exercises, where events are precise as the subject is focusing only on walking. Multi-task walking instead simulates a more realistic and challenging scenario where subjects perform secondary cognitive task while walking, so it is a better benchmark. In this paper, we test two algorithms based on shank and foot angular velocity data in single-task, dual-task and multi-task walking. Results show that both algorithms fail when the subject slows extremely down or pauses due to high cognitive and attentional load, and, in particular, the first stride detection error rate of the foot-based algorithm increases. Stride time is accurate with both algorithms regardless of walking types, but the shank-based algorithm leads to an overestimation on the proportion of swing phase in one gait cycle. Increasing the number of cognitive tasks also causes this error with both algorithms

Angular sway propagation in One Leg Stance and quiet stance with Inertial Measurement Units for older adults

Postural stability degrades with age, threating the health and life quality of the older adults. One Leg Stance (OLS) is one of the standard and commonly adopted assessments for postural stability, and the postural sway in OLS has been demonstrated to be related with age. The propagation of postural sway between body segments could be a hint to the underlying mechanism of balance control. However, it is not yet fully understood. Therefore, the aim of this paper was to study the angular sways and their propagation of the head, trunk, and lower limb in healthy older adults. A cross-correlation of the normalized angular speeds was performed and the experiment with 68 older adults was conducted. The results showed that the head, hip and ankle joints affected the transfer of angular sway with a relatively lower correlation and longer latency

Movement analysis based on IMU (orientation sensor) [Japanese text]

Movement analysis based on IMU (orientation sensor) [Japanese text

Online magnetic calibration of a cutting edge 9-axis wireless Inertial Measurement Unit

In the last years there has been increasing interest on Inertial Measurement Units (IMUs) in several fields, because they can provide a measurement of the orientation, velocity, and acceleration at low cost with high performance. The main reason of the low cost is the possibility to find inertial sensors, as accelerometers, gyroscopes and magnetometers, based on Micro-Electro-Mechanical Systems (MEMS) made by silicon, with further advantages of small dimensions and mass production from the main semiconductor suppliers. In this paper, we present the development of the ultra miniaturized wireless IMU, WB-4 (Waseda Bioinstrumentation number 4), with a 3-axis accelerometer, 3-axis gyroscope and 3-axis magnetometer. Additionally, we illustrate, together with results, the algorithms used for the data filtering and calibration, with particular emphasis on a new methodology for the online calibration of the digital magnetometer