ON THE DESIGN OF A PORTABLE FORCE ILLUSION DEVICE FOR NAVIGATION AIDS

Navigation aids rely mostly on (audio)visual cues when it comes to communication with the user An alternative and more intuitive communication modality may be provided by means of haptic guidance generated by a portable mechatronic device. Especially visually impaired and blind people may benefit from a device that generates the illusion of an external force; it may possibly eliminate the need for a guide dog. This paper investigates constant-velocity crank-driven mechanisms which are able to generate such a force illusion by means of a reciprocating mass. The focus of this paper is on the generation of the illusion itself rather than manipulating the direction of this force. The force illusion is a result of successive positive and negative reaction forces with unequal amplitude, generated by a reciprocating mass. The acceleration ratio of the mass is selected as the main evaluation criterion for comparing different types of candidate mechanisms. Because the input is a simple motor rotating at a constant velocity, the synthesis of the mechanism is key to generating proper acceleration profiles. A brute-force approach is used for the synthesis procedure, i.e., characteristic distances and link lengths are varied with steps of 1mm for each of the candidate mechanisms, thereby generating very large numbers of variants. Kinematic performance reveal typical acceleration ratios in the range of] to 19; where a ratio of one does not result in a force illusion while a ratio of 19 might be demanding on the physical design. An objective evaluation leads to selecting the Square Recti-Linear mechanism as the overall most promising candidate mechanism. A prototype of this mechanism is then presented to demonstrate the working principle. The shape of the prototype's force profile over time is measured experimentally and is shown to be very similar to the profile obtained by simulation. The reciprocating mass accounts for almost one fifth of the total mass of the prototype, resulting in a strong force illusion in comparison with gravitational forces.