Validity Testing of a Simplistic Design Version of a Kinematic Arm for Postural Measurement of Human Body Segments (May 2017)

Abstract

In all engineering industries complaints about back pain and low back injuries are very high. Major factor for such back injuries are associated with Load handling tasks. In industries type of such lifting activities in percentage is to extend 77% and bending activity up to 56%.According to US department of labour report back injuries account to be 20% of all injuries and 25% of annual worker compensation goes for such injuries. So one of the important areas of Kinematic And kinetic measurements are useful is load lifting. Different methods have been evolved for carrying out Kinematic measurements, selection depend upon type of study, type of kinematic parameter to obtained merits and demerits of the methods and cost of study. Need of alternative methods which satisfy the study requirements and also compensate the cost leads to a development of "Kinematic Arm” In one of study made by Belli et al(1992) Developed Kinematic arm for three dimensional recording of human movements. They Validate and tested successfully the device. Error values for static quasi-static human motions are less than tracking system and film or video analysis ,Also device is five times cheaper than above two well known methods. Based on the guidelines of study by Belli et al a Kinematic arm has been designed and fabricated for validation testing of positional measurements of human body segments subject to different postures during load lifting. The Kinematic arm consists of four light rigid pipe linked together by three joints. One end of arm is connected to fixed reference point while other end can move freely in the three spatial directions. the free movement is allowed in all spatial directions by orientation of the axes of the three revolute joints. At each joint a potentiometer (multi turn 50 Kilo-ohm) is mounted and connected to an electronic interface to measure the angle between two link elements involved. Three potentiometers are connected in series and fed a constant current from the circuit. Output from potentiometer is amplified and measured and calibrated in terms of angles. Angles a1(t),a2(t),a3(t).measured and by appropriate trigonometric equations can calculate instantaneous position. Equation for velocity and acceleration have been established in order to evaluate the exact performance of kinematic arm for positional measurements Kinematic arm is tested for the static and quasi-static conditions for different body postures successfully. Results obtained are within the range of theoretical estimation of errors.