DETECTION OF POSTURE AND MOTION BY ACCELEROMETER SENSORS

Chrison Joiakim James

Mtech Biomedical Engineering School of Bioscience and Technology

VIT University Vellore, India

chrison2009@vit.ac.in

Sasi Kumar Professor

School of Bioscience and Technology VIT University Vellore, India

sasikumar.k@vit.ac.in

Abstract— The suitable placement of a small number of calibrated piezo-resistive accelerometer devices may success to assess postures and motions reliably. This finding, which was obtained in a previous investigation, led to the further development of this methodology and to an extension from the laboratory to conditions of daily life. The intention was to validate the accelerometric assessment against behavior observation and to examine the retest reliability. Multiple number of students and patients are included for the obtaining the signal acquisition.

I. INTRODUCTION The introduction of this technology for the measuring the

various body activities is to determine the body movement relevant to defined body patterns. A set of activities used for this project include like walking, sitting and also miscellaneous categories of climbing up and down the stairs. The assessment of posture and motion is an essential issue in ambulatory monitoring because physiological responses, such as changes in heart rate or blood pressure, may result from changes in body position and physical activity. Continuous 24-hrs recordings of posture and motion can be generally useful in behavior assessment and can be accomplished by constant study and validation of the measurement.

In order to have the effectiveness of the validation study, the perfect programmed and cross checked algorithm is formulated, which is bailable for the healthy patients and rehabilitated patients. The constant use of the various use of sensors and accessing device can induce stress and pain onto the body surface to the patient which can indirectly affect the actual movement reading and enhancing the noise. The introduction of the small and precise sensor used will increase the perfect reading and the measurement.

A period of interview is introduced to limit the error during the measurement part. To increase the effectiveness, continuous assessing is entertained and practiced.

II. METHODOLOGY The assessment of posture, motion and physical activity

will depend on the special aims of a given study. Among these are:

1. detection of change in body position in response to movements

2. kinematic analysis, i.e. determined to the patterns of movement or tremors

3. determination of distinct states of activities 4. accessing for 24-h period for behavioral

measurements

III. EASE OF USE Accordingly, the methods for assessing physical activity

vary considerably with respect to type and positioning of sensor, number of recording sites (channels), signal processing (e.g. filtering), and statistical procedures. Most investigators use either electromyographic recordings or accelerometer recordings. The registration of the surface electromyogram (EMG) requires the selection of a suitable recording site, preparation of the skin, and application of electrolyte and electrodes allowing for local hydration, as well as amplification, filtering, and rectification of the raw signal and, finally, processing of the EMG by integration or contour following method (cf. Fridlund & Cacioppo, 1986). Although the EMG is measured in mVolts, an absolute calibration for between-subject designs is not possible because the measurement depends on electrode positioning and individual differences in morphology and muscular function. The accelerometer is a widely used method because of its ease of application(MMA7361L).However, the available accelerometers in relevant technical aspects even among capacitive sensors: general and axial sensitivity (uni-, bi- or tri-axial), frequency range, resonant frequency, damping, and temperature drift. In many instances, such specifications are not given by manufacturers. The directional sensitivity is not an all-or-none characteristic but has to be measured by relating signal amplitude and angle of inclination. The available accelerometers, furthermore, differ in size and mass, durability, and price.

Hence the use of such skin place sensor for the measurement of the muscle activity can be defined to corresponding action exhibited. They require additional features like flat design surface to place the sensors so that they can be attached to the body for the axial orientation of accelerometer sensors. Special care should be taken for uniaxial for the response charactertics for the factors of the inclination degree and the direction of the movements.

The reading from the accelerometers sensors are then sampled, amplified and filtered for the stark outputs in

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corresponding to the activities exhibited by the body. Both input from the EMG signals can also be included with quantitative accelerometer methods of expansion of this particular work. The calibration of the sensor will be based between the subjects for the result comparison. To dispatch the instrumental part, the multichannel accelerometery is implemented from the sensors to the digital acquisition part.

IV. PROCEDURE A variant of different age groups can be considered for

data acquisition. Healthy males of age 20 to 30, 30 to 40 and 40 to 50 are considered and are told to perform the physical activity. The sensor are placed on to various measuring points of the body, they are sternum, wrist, thigh and lower leg. The sensor can be attached to skin for perfect stability. The sensor leads are then connected to the signal condition unit for the amplification and filtering purpose, then connected to the DAQ and finally obtained on the LABVIEW for analysis of the data.

After placement of the sensors, the participants are made to do the listed activities like walking, standing, sitting and along with climbing up and down the stairs for fixed duration of seconds. Each activity is repeated thrice for considering the average measured as the final output.

Products Accelerometers used are MMA7361L (Freescale), Digital Accelerometer of ±1.6g response, 3 axis, fully integrated applicable for motion detection and platform stabilization of bandwidth 2250(Hz), voltage supply 3to5.25 (V)

Data Analysis

The digital signals obtained from the DAQ is array of numerical data for each typical movements produced. As stated earlier, the averaged measurement of each activities of each patients can be compared based on mathematical approach. The largest deviation from the median taken on data of a particular activity can determine the change in pattern of movement exhibited. The repeated process on the particular activity hence can provide data comparitive results for the movements. The analysis on the data is comparitive method when compared to acquisition of EMG signals.

Results A complete hand swing were reduced to limitation due to the normal movement of a walk. The deviation from the default was obtained with one axis(consider X) moving the forward and backward direction due change in the shift from the center position.

Fig 1. Sample graph of reading of 3 axis og hand swing

The above graph shows the sample input obtained in the when the input samples is 100 and at the rate of 1k. The values on the x direction show the voltage and on the y direction show the sample rate during the whole cycle of movement of the hand.

Advancements to be made

Interfacing the signal condition and DAQ can be mediated by the Bluetooth or RF which can introduce advancementfor connectivity and data transfer. The mobility freed for the different movements and activity measurement. Introduction of adavanced will make useful for the rehabilitation purpose and also for the disabled patient for monitoring purpose.

V. CONCLUSION The results obtained in this study demonstrated that the

survey for monitoring the human activities could detect detailed motion details during movements like walking, standing and changes in body shifts due to various activities. We strongly suggest this can be used in rehabilitation and eligibility for monitoring and measuring the body movements.

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