Using Pot-Magnets to Enable Stable and Scalable Electromagnetic Tactile Displays

Abstract

Abstract-We present the design, fabrication, characterization and psychophysical testing of a scalable haptic display based on electromagnetic (EM) actuators. The display consists of a 4x4 array of taxels, each of which can be in a raised or a lowered position, thus generating different static configurations. One of the most challenging aspects when designing densely-packed arrays of EM actuators is obtaining large actuation forces while simultaneously generating only weak interactions between neighboring taxels. In this work we introduce a lightweight and effective magnetic shielding architecture. The moving part of each taxel is a cylindrical permanent magnet embedded in a ferromagnetic pot, forming a pot-magnet. An array of planar microcoils attracts or repels each pot-magnet. This configuration reduces the interaction between neighboring magnets by more than one order of magnitude, while the coil/magnet interaction is only reduced by 10%. For 4 mm diameter pins on an 8 mm pitch, we obtained displacements of 0.55 mm and forces of 40 mN using 1.7 W. We measured the accuracy of human perception under two actuation configurations which differed in the force vs. displacement curve. We obtained 91% of correct answers in pulling configuration and 100% in pushing configuration.

Emerging Material Technologies for Haptics

“…In another configuration, this device may be used for micromanipulation. Several other examples of haptic devices based on electromagnetic actuation, including both flexible and soft devices.…”

“…Electromagnetic actuation serves the majority of motion control needs in existing devices and systems, and can achieve high bandwidths and dynamic ranges such as are needed in many tactile display applications. Zarate et al developed a tactile display based on electromagnetic actuators using two soft elastomeric membranes . Figure A shows an image of their device (top).…”

“…Images of the tactile display showing six different actuation states presenting six different symbols. Reproduced with permission . Copyright 2016, IEEE.…”

Miniature Soft Electromagnetic Actuators for Robotic Applications

“…To avoid otherwise high interaction forces between neighboring magnets, we fabricated magnetic shield, consisting of a high magnetic permeability elastomer composite, covering all but the coil side of the magnet (Figure A; Figure S2, Supporting Information). This ensures that each vibrotactile actuator can respond independently, and that the static magnetic forces do not disturb the soft structures involved . The dynamics of the resulting actuators can be modeled by building on the results of Section S6 of the Supporting Information, and accounting for the motion of the magnet and membrane.…”

Bioinspiriertes Design und additive Fertigung von weichen Materialien, Maschinen, Robotern und haptischen Schnittstellen

“…Diese künstlichen Muskeln zeigen, wie in den Abschnitten 2.1 und 3.1 erörtert, viel schnellere Reaktionen als pneumatische künstliche Muskeln und werden deshalb genutzt, um vibrotaktile Empfindungen bei haptischen Schnittstellen zu erzeugen (Abbildung c) . Haptische Schnittstellen unter Verwendung von DEAs als Bewegungsgenerator sind gewöhnlich robuster, leichter, nachgiebiger und besser am Körper tragbar als piezoelektrische und elektromagnetische Aktuatoren; ein noch zu lösendes Problem sind jedoch die hohen Antriebsspannungen (in der Regel einige kV), die zu einem Sicherheitsproblem für die Benutzer und zur Erfordernis einer umfangreichen Steuerungs‐ und Antriebselektronik führen können . Einige aktuelle Arbeiten versuchen, die Antriebsspannungen von DEAs auf einige Hundert Volt zu senken; damit wäre die Vorstellung einer breiten Anwendung “smarter” Materialien als haptische Schnittstellen realistischer.…”