Acquisition and Processing of Kinematic Variables for Biomechanical Analysis of Movement

Abstract

We designed and developed a datalogger system to store and to transmit static and dynamic linear acceleration and angular velocity variables, from a 3-axis accelerometer and a 2-axis gyroscope MEMS technology. Datalogger has a wireless real-time transmission data, or storage data in a flash memory for later downloading. Data transmission is performed by ZigBee protocol. Using up the three datalogger simultaneously is possible. Each datalogger achieves a sampling rate of 100Hz, such as a high resolution video camera of 100 frames per second. The signal provided by MEMS accelerometers, combines dynamic acceleration and static acceleration due to gravity. For the analysis of movement, dynamic acceleration is needed only. Therefore, was developed a data processing system in MATLAB to remove unwanted components, using the angular position data, calculated from angular velocity data from gyroscope. For the operation of algorithm, estimation of initial Euler angles at rest is required to place the device in an initial quadrant of the Cartesian plane. Initial angle is calculated from the first accelerometry data, which has static acceleration components only, behaving as an inclinometer. This initial angle is the reference point, and the angular velocity data, measured by gyroscope, are used to obtain the rotation angles variation across entire trajectory with theoretical component of gravity force elimination by data subtracting in each axis, in order to calculate data of linear velocity and of linear position. Linear and angular position graphs give information about the angles of movement in each lever, in order to find patterns into motion gesture assessments. The system operates with up three simultaneous datalogger that can be placed at three different points of a limb, in order to analyze the movement, by simulating three points as in the cinematographical technics with three markers.