Data Acquisition & Synchronization from an Optical Tracker, Accelerometers & EMG

 

Author: Hamid LAMRAOUI
Last Update: 20 July 2006

English Version | French Version

 

PROJECT DESCRIPTION:

Data acquisition and synchronization from an optical tracker, the NDI Polaris Vicra, 3 axis Analog Devices ADXL330 accelerometer and electromyograph signals (EMG) are the first stage in the project " Active Pathological Tremor Compensation using Functional Electrical Stimulations ". Data stored (position, acceleration and EMG) will be the ones collected throughout experiments on patients affected by pathological tremor.

Data acquisition software was developed on Labview whilst signal processing and analysis will be carried out on Matlab.

Below are the different stages for this part:

Machine-machine interface development between the Polaris and PC:

Communication protocol used for this device is RS232 (serial communication). The software has been created from an older version of the device (NDI Polaris). Some features have been tested such as accuracy, spatial frequency, etc.

The Polaris Vicra is able to distinguish and provide simultaneously six tool positions thanks to their shape. Indeed, on each tool, reflectors are fixed so that shape constituted by the reflector position on the tool is unique. The position sensor will be used only in the first stages of the project, patient's upper limbs positions will be calculated, with Matlab, from motion sensed by the accelerometers. Data measured by the optical tracker will allow confirming position computed on Matlab.

 

Data acquisition from accelerometers:

The analogical signals coming from the three axes are collected thanks to a DAQ card (NI 6036E), in PCMCIA connection (using a laptop to collect data of the experiments on the patients), 16 analog input, which will make it possible to connect 5 accelerometers maximum. Signal processing (filtering, reduction of noise, etc) will be carried out off line on Matlab.

 

Signal synchronization:

Since a hardware synchronization of the Polaris Vicra is not possible, this one was carried out using the synchronization functions in Labview library. Despite this software synchronization, we obtain good results (delay of a few ms maximum) for the experiments.

 

The first tests with only accelerometers and Polaris Vicra were carried out (EMG system not ready yet). With regard to the calibration of the accelerometers, a simple program taking only into account the sensitivity (volt/g) and the 0g was made.

Another more complete program will be developed thereafter which will take account of the hysteris, deviations, bias effects and other accelerometer defects.