Dual-axis Accelerometer Research Articles

Diagnosis of parametric defects in dual axis IC accelerometers

Microelectromechanical systems fabrication and packaging may induce parametric defects which have to be efficiently diagnosed to improve fabrication yield and device reliability. In this work, the possibilities of diagnosing single parametric defects in dual axis IC accelerometers are explored. The proposed method is a reuse of a mixed-signal diagnosis strategy based on Lissajous compositions. It consists of a dynamic correlation of the two orthogonal output signals of the device. This leads to a Lissajous trace which is able to manifest parametric deviations. Several device parameters have been studied and characterized under different deviation levels. The definition of a metric and the evaluation of its diagnosis efficiency is used to optimize the diagnosis procedure against noisy measurements. The method has been experimentally applied to diagnose the misalignment degree in a commercial dual axis accelerometer. The Lissajous characterization of the defect is illustrated and experimental results are reported. Misalignment diagnosis results show the viability of the proposal.

Convection behavior analysis of CMOS MEMS thermal accelerometers using FEM and Hardee’s model

This paper presents convection behavior investigation of CMOS MEMS convective accelerometers using both analytical and FEM techniques. In a first part, a newly developed accelerometer 3D model is used in FEM simulations to model convection behavior as a function of design geometry and temperature. Using various sizes of two different cover shapes, sensitivity reading and its maximum position in cavity are found to be largely affected by both cover size and shape. In addition, a sensor with cavity width of 600 μm produces sensitivity saturation starting at a cavity depth of 200 μm, for both cover shapes. Using FEM data and curve fitting, differential temperature is claimed to be linearly linked to the effective heater temperature to the power of 1.7. Using the same cavity design and from computed heating efficiency values, we found that a 60 μm width heater offers the best efficiency. This cavity and heater designs give an optimal detector position of 120 μm from heater center along the sensitive axis. Moreover, dual axis accelerometers are found to be more power efficient than single axis ones. In the second part, we present Hardee's spherical model and investigate its possible application on convective accelerometers. It is shown that inner and outer isotherms deformation, caused by accelerometer design and convection process, should be modeled by including sensor geometry parameters in the derived governing equations. Moreover, Hardee's biasing temperature relation has to be revised if it is to be used for convective accelerometers.

A low cross-sensitivity dual-axis silicon-on-insulator accelerometer integrated as a system in package with digital output

This paper introduces a novel dual-axis accelerometer structure with low cross-sensitivity. The device is fabricated in an SOI process, namely SOIMUMPs, and its fabrication is finalized by an in-house release step. The device measures 1 × 1 mm2 with four proof masses that are able to sense accelerations in the X and Y axes independently. Two commercial capacitance-to-digital converters are used to read both axes outputs of the device in a system in package implementation. Simulations show a sensitivity of 25 fF/g and the fabricated device exhibits a sensitivity of 101 digital counts/g or 16.83 fF/g. The measured cross-sensitivity is <1 % throughout the 4 g linear range. The rotational motion and Z accelerations have no impact on the device X and Y readings, thanks to the particular geometry and differential nature of the device.

Measuring Activity Levels at an Acute Stroke Ward: Comparing Observations to a Device

Background. If a simple system of instrumented monitoring was possible early after stroke, therapists may be able to more readily gather information about activity and monitor progress over time. Our aim was to establish whether a device containing a dual-axis accelerometer provides similar information to behavioural mapping on physical activity patterns early after stroke. Methods. Twenty participants with recent stroke ≤2 weeks and aged >18 were recruited and monitored at an acute stroke ward. The monitoring device (attached to the unaffected leg) and behavioural mapping (observation) were simultaneously applied from 8 a.m. to 5 p.m. Both methods recorded the time participants spent lying, sitting, and upright. Results. The median percentage and interquartile range (IQR) of time spent lying, sitting, and upright recorded by the device were 36% (15–68), 51% (28–72), and 2% (1–5), respectively. Agreement between the methods was substantial: Intraclass Correlation Coefficient (95% CI): lying 0.74 (0.46–0.89), sitting 0.68 (0.36–0.86), and upright 0.72 (0.43–0.88). Conclusion. Patients are inactive in an acute stroke setting. In acute stroke, estimates of time spent lying, sitting, and upright measured by a device are valid.

The Effect of a Designed Health Education Intervention on Physical Activity Knowledge and Participation of Adults with Intellectual Disabilities

The purpose of this study was to assess novel methods of health education and promotion to increase physical activity among adults with intellectual disabilities. A pre-post delayed treatment design was employed to assess the effect of the intervention. The intervention was administered at two agencies that serve adults with intellectual disabilities. Forty-two adults ranging in age from 19 to 62 with mild to moderate intellectual disability participated in the study. Participants were equally divided by gender. An eight-session intervention employed a combination of video instruction, pictorial memory tools, and interactive class activities as educational methods. Physical activity knowledge was evaluated using Illingworth, Moore, and McGillivray's Nutrition Activity Knowledge Scale (NAKS) and the Physical Activity Recommendations Assessment (PARA). Average daily minutes of physical activity were measured using dual-axis accelerometers. Paired and independent samples t-tests were used to assess the knowledge scales. Wilcoxon signed-rank tests and Mann-Whitney U-tests were used to assess physical activity participation. Overall, there were mean improvements in scores for both the NAKS (p < .05) and the PARA (p < .001) following the intervention. Physical activity also improved, but not significantly. The education and training methods used in this curriculum are promising for future health education programs in this population. Additional interventions may be necessary to improve physical activity participation.

Reflection and transmission properties of a wall-floor building element: comparison between finite element model and experimental data

Changes in the Swedish construction code introduced in 1994 enabled the construction of wooden multi-storey buildings. The main issue in those is disturbing vibrations and noise propagating throughout the construction. Therefore, gaining knowledge about their behavior is of crucial importance for the industry. In this study, a mockup of a wall/floor junction was investigated by comparing both experimental and simulation (FEM) results. The mockup resembles a section of a real wooden building. It is 9.3 m long and 3.6 m wide. The structure was built using wooden beams as load-bearing components and chipboards as the floor surface. Likewise, a gypsum wall was placed in the middle surrounded by a wooden frame. The reflection and transmission properties of the structure were studied when subjected to harmonic excitations. The junction has been studied experimentally using dual-axis accelerometers attached to the T junction, post-processing the data using the scattering matrix formulation, which allows separating the transmitted and reflected wave as the wave propagates towards the junction, as well as the rate of wave conversion. Subsequently, a FE model of the structure was created allowing the comparation between both cases. This project was funded by Interreg IV, Silent Spaces.

Automated method to distinguish toe walking strides from normal strides in the gait of idiopathic toe walking children from heel accelerometry data

Toe walking mainly occurs in children due to medical condition or physical injury. When there are no obvious signs of any medical condition or physical injury, a diagnosis of Idiopathic Toe Walking (ITW) is made. ITW children habitually walk on their toes, however can modify their gait and walk with a heel–toe gait if they want to. Correct gait assessment in ITW children therefore becomes difficult. To solve this problem, we have developed an automated way to assess the gait in ITW children using a dual axis accelerometer. Heel acceleration data was recorded from the gait of ITW children using boots embedded with the sensor in the heel and interfaced to a handheld oscilloscope. An innovative signal processing algorithm was developed in IgorPro to distinguish toe walking stride from normal stride using the acceleration data. The algorithm had an accuracy of 98.5%. Based on the statistical analysis of the heel accelerometer data, it can be concluded that the foot angle during mid stance in ITW children tested, varied from 36° to 11.5° while as in normal children the foot stance angle is approximately zero. This algorithm was later implemented in a system (embedded in the heel) which was used remotely to differentiate toe walking stride from normal stride. Although the algorithm classifies toe walking stride from normal stride in ITW children, it can be generalized for other applications such as toe walking in Cerebral Palsy or Acquired Brain Injury subjects. The system can also be used to assess the gait for other applications such as Parkinson's disease by modifying the algorithm.

Experimental Vibration Analysis of a Composite UAV Wing

This article describes the details of an experimental investigation focusing on vibration characteristics of a carbon composite ultralight unmanned aerial vehicle (UAV). Modal characteristics of the UAV wings are obtained and compared for two separate configurations: (1) wings mounted on the suspended aircraft to simulate a free-free arrangement and (2) a single wing mounted vertically in a fixture to test in a shaker-table approach. All structural components are fabricated from oven-cured laminated carbon composite materials using uniaxial and biaxial prepreg fabric. Multiple dual-axis accelerometers on the wing structure are used to determine the dynamic properties.

A dual axis CMOS micromachined convective thermal accelerometer

We present a dual axis accelerometer made with a frontside bulk micromachining on a 0.35 μm CMOS. The accelerometer is based on thermal convection where a central suspended hot plate creates a hot gas bubble. In-plane acceleration applied to the body will change the temperature distribution on the device, the latter being measured by four detectors containing six serially connected thermocouples. The paper will present the modelling of the device with a specific spherical model as well as measurements of sensitivity and linearity.

Instrumentation of an Inertial Kinetic Exercise Device with a Dual Axis Accelerometer

INSTRUMENTATION OF AN INERTIAL KINETIC EXERCISE DEVICE WITH A DUAL AXIS ACCELEROMETER. PURPOSE/INTRODUCTION: An inertial kinetic exercise (IKE) device has potential utility for injury rehabilitation, speed development in athletes, and to counteract space flight-induced muscle atrophy. Yet such high-speed devices often elicit greater levels of data variability. Prior research assessed IKE data reproducibility when instrumentation entailed a single-axis accelerometer. RESULTS showed a high degree of reproducibility, though values may improve if instrumentation entailed a dual-axis accelerometer, which permits gravity compensation without compromising the capacity to measure acceleration. Thus the current project assessed data reproducibility from two IKE workouts instrumented with a dual-axis (Model DE-ACCM5G) accelerometer. We hypothesized a high level of performance variable reproducibility would occur from IKE instrumentation with a dual-axis accelerometer. METHODS: Each workout entailed two one-minute sets of high-speed elbow flexion actions interspersed by a 90-second rest. Variables, compared for both intra- and inter-workout analyses, were examined with intraclass correlation coefficients (ICC). RESULTS: Intra-workout ICC values collected from subjects (n = 16) were as follows: average acceleration = 0.85, mean torque = 0.75, maximum torque = 0.75, total torque = 0.73, mean force = 0.89, maximum force = 0.89 and total force = 0.76. Inter-workout ICC values collected from those same subjects were as follows: average acceleration = 0.71, mean torque = 0.73, maximum torque = 0.70, total torque = 0.72, mean force = 0.82, maximum force = 0.90 and total force = 0.74. The overall average intra- and inter-workout ICC values for the aforementioned variables were 0.80 and 0.76, respectively. CONCLUSIONS: Research suggests ICC values > 0.75–0.80 shows a high level of reproducibility. Though inter-workout average acceleration ICC results were less than suggested values, they demonstrate less dispersion for this same variable than when instrumentation entailed a single-axis accelerometer. PRACTICAL APPLICATIONS: Preliminary results suggest instrumentation with a dual-axis accelerometer yields a high level of reproducibility, though continued research is warranted. Instrumentation of the IKE may be optimized with the use of a dual-axis accelerometer.

Operational modal analysis of a multi-span skew bridge using real-time wireless sensor networks

A large-scale field deployment of high-density, real-time wireless sensors networks for the acquisition of local acceleration measurements across a medium length, multi-span highway bridge is presented. The advantages, performance characteristics, and limitations of employing this emerging technology in favor of the traditional cable-based acquisition systems are discussed in the context of the in-service instrumentation and ambient vibration testing of a multi-span bridge. Of particular highlight in this study is the deployment of a large number of stationary rather than reference-based accelerometers to uniquely permit simultaneous acquisition of vibration measurements across the structure and thereby ensure consistent temperature, ambient vibration, and traffic loading. The deployment consisted of 30 dual-axis accelerometers installed across the girders of the bridge and interfaced with 30 wireless acquisition and transceiver nodes operating in two star topology networks. Real-time wireless acquisition at a per channel sampling rate of 128 samples per second was maintained across both networks for the specified test durations of 3 min with insignificant data loss. Output-only system identification of the structure from the experimental data is presented to provide estimates of natural frequencies, damping ratios, and operational mode shapes for 19 modes. The analysis of the structure under test provides a unique case study documenting the measured response of a multiple-span skewed bridge supported by elastomeric bearings. The feasibility of embedded wireless instrumentation for structural health monitoring of large civil constructions is concluded while highlighting relevant technological shortcomings and areas of further development required. In particular, previously undocumented obstacles relating to radio transmission of the sensor data using low-power 2.4 GHz wireless instrumentation, such as the effect of solid piers within the line-of-sight and the reflection of the radio waves on the surface of the water, are discussed.

Vertically aligned accelerometer for wheeled vehicle odometry

A new application for accelerometers is presented and evaluated instead of using it to measure the linear acceleration of the vehicle, which is usually performed with traditional odometry. In the present case, a dual orthogonal axis accelerometer is vertically aligned in the center of a wheel. Then the rotational position of the wheel can be detected and RPM can be counted based on the accelerometer angular position. A microcontroller is used to measure the value of each accelerometer axis, and with a proper algorithm 12 wheel positions are detected combining the x-axis and y-axis values. The wheel position is transmitted by means of a wireless link to another microcontroller or computer located on board of the vehicle to estimate the traveled distance. This embedded wireless device is now named accelodometer. Field results on a pick-up tested at up to 40 km/h and with an autonomous robotic vehicle showed that this accelodometer presented advantages with respect to both usual accelerometer and incremental encoder, avoiding the accumulative error due to the sensor drift. The repeatability of the device was established within the 0.01% in 4 km path. A resolution of 1/12 of the wheel perimeter was determined.

Hyolaryngeal excursion as the physiological source of swallowing accelerometry signals

Swallowing dysfunction, or dysphagia, is a serious condition that can result from any structural or neurological impairment (such as stroke, neurodegenerative disease or brain injury) that affects the swallowing mechanism. The gold-standard method of instrumental swallowing assessment is an x-ray examination known as the videofluoroscopic swallowing study, which involves radiation exposure. Consequently, there is interest in exploring the potential of less invasive methods, with lesser risks of biohazard, to accurately detect swallowing abnormalities. Accelerometry is one such technique, which measures the epidermal vibration signals on a patient's neck during swallowing. Determining the utility of accelerometry signals for detecting dysphagia requires an understanding of the physiological source of the vibrations that are measured on the neck during swallowing. The purpose of the current study was to determine the extent to which movement of the hyoid bone and larynx contributes to the vibration signal that is registered during swallowing accelerometry. This question was explored by mapping the movement trajectories of the hyoid bone and the arytenoid cartilages from lateral videofluoroscopy recordings collected during thin liquid swallowing, and comparing these trajectories to time-linked signals obtained from a dual-axis accelerometer placed on the neck, just anterior to the cricoid cartilage. Participants for this study included 43 adult patients referred for videofluoroscopic swallowing studies to characterize the nature and severity of suspected neurogenic dysphagia. A software program was created to allow frame-by-frame tracking of structural movement on the videofluoroscopy recordings. These movement data were then compared to the integrated acceleration data using multiple linear regressions. The results concur with previous studies, implicating hyolaryngeal excursion as the primary physiological source of swallowing accelerometry signals, with both the hyoid and the larynx contributing approximately equal amounts to the explained variance of the dependent variable, the integrated accelerometry signal.

Impairment of Stance Control in Children With Sensory Modulation Disorder

To compare stance control between children with sensory modulation disorder (SMD) and typically developing children in various visual and somatosensory conditions. Thirty-one children participated in this study, including 17 children with SMD and 14 matched typically developing children. The Sensory Profile was used to screen for sensory modulation problems, which were further confirmed by measures of electrodermal response and the Evaluation of Sensory Processing. Stance parameters for an assessment of postural stability were obtained with a dual-axis accelerometer on the lumbar area. The children with SMD presented atypical sensory responses in terms of both electrophysiological and behavioral measures. The results for stance showed a greater body sway in the SMD group than in the control group (p < .05). However, the group difference was not always significant under the conditions of reliable somatosensory input and sway-referenced vision. Our findings first confirmed impaired stance control in children with SMD.

Fuzzy clustering of human motor motion

Acquisition of the behavioural skills of a human operator and recreating them in an intelligent autonomous system has been a critical but rather challenging step in the development of complex intelligent autonomous systems. Development of a systematic and generic method for realising this process by acquiring human postural and motor movements is explored. This is achieved by breaking down the human motion into a number of segments called motion or skill primitives. The proposed methodology is developed based on studying the movement of the human hand. The motion is measured by a dual-axis accelerometer and a gyroscope mounted on the hand. The gyroscope locates the position and configuration of the hand, whereas the accelerometer measures the kinematics parameters of the movement. The covariance and the mean of the data produced by the sensors are used as features in the clustering process. A fuzzy clustering method is developed and applied to identify different movements of the human hand. The proposed clustering approach identifies the sequence of the motion primitives embedded in the data produced from the human wrist movement. A review of the previous work in the area is carried out and the developed methodology is described. An overview of the experimental setup and procedures to validate the approach is given. The results of the validation are analysed critically and some conclusions are drawn.

Augmentative Communication Based on Realtime Vocal Cord Vibration Detection

A binary switch based on the detection of periodic vocal cord vibrations is proposed for individuals with multiple and severe disabilities. The system offers three major advantages over existing speech-based access technologies, namely, insensitivity to environment noise, increased robustness against user-generated artifacts such as coughs, and reduced exertion during prolonged usage periods. The proposed system makes use of a dual-axis accelerometer placed noninvasively in proximity of the vocal cords by means of a neckband. Periodic vocal cord vibrations are detected using the normalized cross-correlation function computed from anterior-posterior and superior-inferior accelerometry signals. Experiments with a participant with hypotonic cerebral palsy show the proposed system outperforming a popular commercial sound-based system in terms of sensitivity, task time, and user-perceived exertion.

Vibration testing of a carbon composite fuselage

This paper describes the details of an experimental investigation focusing on the vibration characteristics of a composite fuselage structure of an ultralight unmanned aerial vehicle (UAV). The UAV has a total empty weight of 70.3 kg and 6.3 m in length. The fuselage structure consists of the fuselage body with an integrated vertical stabiliser. All structural components are fabricated from oven-cured laminated carbon composite materials using uniaxial and biaxial prepreg fabric. The modal characteristics of the fuselage structure are determined for a free-free configuration which is simulated by suspending the structure from its wing attachment points through the use of springs. A centrally located shaker system is used to induce vertical oscillations in the structure, which is instrumented with nineteen dual axis accelerometers. Dynamic properties such as the frequency, damping and associated mode shapes are obtained for aeroelastic analysis. The design and implementation of the vibration tests along with the experimental results are presented.

In-Service Diagnostics of a Highway Bridge from a Progressive Damage Case Study

Development of diagnostic and prognostic routines for application to in-service measurements from highway bridges necessitates analysis of experimental measurements from in-service highway bridges under natural or prescribed induced damage. This is generally limited to the unique opportunity of investigating end-of-service life bridges prior to reconstruction and consequently only a limited library of such case studies exist. This paper documents a field test of an end-of-service bridge span with prescribed progressive damage to a bearing as well as several diaphragm connections. Thirty dual-axis accelerometers were distributed across the bridge span with data acquisition and transmission facilitated by a real-time lossless wireless sensor network. A highway department service truck applied traffic excitation to the structure through routine passes on a consistent lane of traffic. Output-only system identification was applied to the baseline time history response to develop a state-space model of the brid...

Accelerometers and Force Sensing Resistors for Optimal Control of Walking of a Hemiplegic

We developed a method for use of accelerometers and force sensing resistors (FSRs) within an optimal controller of walking for hemiplegic individuals. The data from four dual-axis accelerometers and four FSRs were inputs, while six muscle activation profiles were outputs. The controller includes two stages: 1) estimating the target gait pattern using artificial neural networks; and 2) optimal control minimizing tracking errors (from the estimated gait pattern) and muscle efforts. The controller was tested using data collected from six healthy subjects walking at five speeds (0.6-1.4 m/s). The average root mean square errors (RMSEs) normalized by the peak-to-peak value of the target signals [normalized RMSE (NRMSE)] were below 6%, 7%, 8%, and 3% for estimation of joint angles, hip acceleration, ground reaction force, and movement of the center of pressure, respectively. Using the estimated data as inputs, the simulation generated the target healthy-like gait patterns and reproducible muscle activation profiles in 90% of 300 tested gait trials. Overall tracking NRMSE was between 2% and 9%. The optimal controller was developed for testing the feasibility of healthy-like gait patterns in hemiplegic individuals, and generating a knowledge base that is required for the synthesis of a sensory-driven control of walking assisted by functional electrical stimulation.

Synergistic control of forearm based on accelerometer data and artificial neural networks

In the present study, we modeled a reaching task as a two-link mechanism. The upper arm and forearm motion trajectories during vertical arm movements were estimated from the measured angular accelerations with dual-axis accelerometers. A data set of reaching synergies from able-bodied individuals was used to train a radial basis function artificial neural network with upper arm/forearm tangential angular accelerations. The trained radial basis function artificial neural network for the specific movements predicted forearm motion from new upper arm trajectories with high correlation (mean, 0.9149-0.941). For all other movements, prediction was low (range, 0.0316-0.8302). Results suggest that the proposed algorithm is successful in generalization over similar motions and subjects. Such networks may be used as a high-level controller that could predict forearm kinematics from voluntary movements of the upper arm. This methodology is suitable for restoring the upper limb functions of individuals with motor disabilities of the forearm, but not of the upper arm. The developed control paradigm is applicable to upper-limb orthotic systems employing functional electrical stimulation. The proposed approach is of great significance particularly for humans with spinal cord injuries in a free-living environment. The implication of a measurement system with dual-axis accelerometers, developed for this study, is further seen in the evaluation of movement during the course of rehabilitation. For this purpose, training-related changes in synergies apparent from movement kinematics during rehabilitation would characterize the extent and the course of recovery. As such, a simple system using this methodology is of particular importance for stroke patients. The results underlie the important issue of upper-limb coordination.