Wearable Intertace for Teleoperation of Robot Arms - WITRA

[Update 16] Validating WITRA motion capture with Qualisys
Update #10148  |  13 Dec 2014


As a motion capture system, or mocap, Qualisys consists of a set of motion capture cameras that can record information of spatial position of light-reflecting markers. Qualisys is a high-precision system and is widely known. We have used this system to validate the data acquisition system on WITRA. 


Figure 1: Qualisys - A High-Precision Motion Capture System

On the video below, extracted from youtube, you can see the system working. On the video you can see 12 cameras. We've only used 5, which already gives us great motion data. Each camera, after proper calibration of its measurement volume, captures the image of each reflecting marker. The image of the markers is extracted from the rest of the image. Thus, identifying each marker, Qualisys records the motion data in three coordinates. 


Double-system Motion Capture

WITRA uses three IMUs (Inertial Measurement Unit to capture the motion of the human arm. We've simultaneously captured the arm's movement with WITRA and Qualisys (using four markers: one at the shoulder, one at the elbow, one at the wrist and one at the hand). We wanted to guarantee that the motion capture system we've created on WITRA is realiable. For this purpose we compared the data from WITRA and from Qualisys in a graphical manner. 


Figure 2: Using WITRA and Qualisys simultaneously to capture the movement of the human arm

On WITRA's side, the information of each IMU is used to calculate the direct kinematics of the human arm. We can, thus, calculate the spatial position of each arm joint : shoulder, elbow, wrist plus the hand. On the side of Qualisys, each marker's motion is captured, giving us the (x,y,z) coordinates, over time, of each marker, as you can see below:


Figure 3: Qualisys data for each marker


With these two sets of data, we used MATLAB to create animations of the human arm over time. The red link shows the upper arm, the green link shows the forearm and the blue link shows the hand. On the left side you can see the animation created from WITRA's data and on the right side, from Qualisys's data. Below, you see the picture of Vinicius moving his arm.

                                                  WITRA                                                                                                             QUALISYS


Figure 4: Comparison among WITRA (upper-left corner), Qualisys (upper-right corner) and the video of the user

The comparison between the two systems, as well as with the actual video of the user will be shown on our final submission video. For now we can state that WITRA is now validated as a reliable motion capture system. 


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[1] Qualisys's website - http://www.qualisys.com/