Electromagnetic Haptic Feedback System for Use with a Graphical Display using Flat Coils and Sensor Array

We have developed a haptic interaction system which wirelessly generates 3D forces onto a small magnet which can be fixed to a user's fingertip or a handheld stylus. Magnet position sensing and haptic force generation can both be performed through a thin screen, and the actuation and sensing components of the system are sufficiently thin and compact to be easily mounted behind the screen in the same enclosure. In this manner, the system is particularly well suited for use for co-located haptic and graphic display, with 3D force feedback added to an interactive display. The purpose of the work is to describe, analyze, and validate a method and device to generate haptic force feedback on a magnet held near a display screen using thin flat arrays of coils and sensors. The location of the magnet during haptic interaction is obtained by an array of Hall effect sensors. Flat rectangular coils are used to generate Lorentz forces on the interaction magnet and can act in combination to produce 3D forces in any direction, both parallel and normal to the screen surface. The active area of the haptic interaction system prototype is approximately 120 x 120 mm, with effective force generation and position sensing from the screen surface to an elevation of approximately 15 mm. The localization methods do not depend on the size, shape, or magnetization strength of the magnet, so that larger or smaller magnets may be used for greater forces or more ease of manipulation, without modifying the software other than the force actuation model. The design of the system is presented, including modeling and analysis of the sensing and actuation methods. Experimental results are given for field sensing, magnet localization, and haptic interaction with simulated objects. Forces up to 0.3 N are demonstrated to be generated in different specific desired directions while sensing planar magnet position to an accuracy within approximately 2.0 mm.