Dynamic and Accurate Force Feedback for Electromagnetic Haptic Display

As the implementation way of bilateral interactions in virtual reality, haptic display can not only bring users touch feedback for the better sense of immersion, but also enable them to operate objects in virtual environments on their own initiative. In this article, we present an electromagnetic haptic display system, which performs contactless forces on the magnetic stylus in the magnetic field excited by three iron-core coils with adjustable position and orientation, for the production of haptic feedback. High-frequency pulses and H-bridge circuits are employed for the rapid current drive in coils, and it is proved that the refresh rate of our haptic device is able to fulfill the simulation of dynamic haptic feedback like push, pull and squeeze. In addition, the processes of current generation in single coil and magnetic field generation for coil array are clearly analyzed, and a Varying-Model Predictive Control algorithm is proposed, where the predictive model is updated adaptively according to the real-time motions of stylus and coils, to generate the required magnetic field smoothly and precisely. Experiments show that the magnetic flux density measured at the position of stylus follows the reference value well in three dimensions with the aid of the proposed algorithm, and dynamic and accurate electromagnetic haptic display can be achieved.