Alt-text for Figure 1:
Schematic of the simulator and its operation. The wheelchair user propels the wheelchair located on the simulator. This wheelchair includes two instrumented wheels that measure the forces and moments applied on the handrims along the three axes X, Y and Z, as well as the angular position of the wheels. The force, moment and angle data are sent to a computer that runs a real time system (xPC Target). The real-time system implements a model that represents a virtual wheelchair.
In figure 1, the real time system is subdivided into four blocks. The first two blocks receive the force, moment and angle data from the left and right instrumented wheel respectively. Each block also receives the values of the two haptic biofeedback parameters, namely MEFT(θ), the target MEF pattern, and ε(θ), the biofeedback intensity modulator. These two parameters will, in general, stay constant throughout a propulsion trial. The two first blocks’ role is to calculate the biofeedback moments MBFR and MBFL that will be applied on the left and right wheels respectively to guide the user towards MEFT.
Biofeedback moments MBF on each side are then subtracted from applied propulsive moments MzL and MzR to obtain Meff effective propulsive moments. These effective moments are inputted to the dynamic model of the virtual wheelchair (third block), that calculates at which velocity should each wheel turn. The third block, labelled “Wheelchair dynamic model”, outputs the angular velocities for the left and right wheels (ωL and ωR).
The velocities outputted by the third block “Wheelchair dynamic model” are checked by a fourth block “Velocity controllers” that insures that the velocities commanded are appropriate. Finally, the angular velocity commands are sent to the motors, which are attached to rollers. The motors react by turning at the commanded velocities, driving at the same time the rollers and wheelchair wheels at the correct velocities. The wheelchair wheels, located just above the rollers, are kept in contact with the rollers at all times.