Technical Innovations
The core innovation is the technique to derive a distribution of force vectors from the movement of two layers of colored markers.
We wish to obtain 3-dimensional force vectors, but the movement of markers captured by a CCD camera is 2-dimensional. If only one layer of markers is prepared, only the magnitude of force can be measured with any degree of accuracy, or else two cameras (for stereoscopic vision) would be necessary to measure the 3-dimensional movement of markers. To use two cameras would bring about complex camera calibration and would occupy a large space. These complications would make downsizing the sensor infeasible in practice.
To solve this problem, we use two layers of markers at different depths. Equipping the two layers is equivalent to measuring 2 times 2 dimensional movement of markers(fig.3). This provides sufficient measurement information to readily obtain a force vector distribution(fig.4).
figure3: captured CCD camera image
figure4: calculated 3D force vector field