Sensitivity of Resonant Moving Magnet Actuators to Haptic Environments

Haptic feedback devices are used in many electronic interfaces, such as game controllers, to enhance the user experience. The experimental characterization of a common haptic feedback device, the so-called moving magnet actuator (MMA), comprising an electromagnetically actuated permanent magnet, reveals significant variations when interacting with human users. Impedance spectra of three MMAs were recorded in free-hanging and rigidly clamped configurations, as well as in various user-interaction scenarios. Initial measurements in nonuser cases showed distinct, narrow peaks associated with high quality factors and different resonance frequencies for each configuration, while user interaction led to notable changes in resonance frequency and quality factor. When placed in a user's hand, the device's resonance frequency is nearly identical to the free-hanging configuration, albeit with a significantly lower quality factor. Closing the hand and increasing the grip strength initially shifts the resonance frequency downward toward the clamped configuration. At higher grip strength, however, the compression of the tissue reduces its damping effect, increasing the quality factor associated with the resonance. Similar behavior can be observed when holding the MMA between two fingers. This indicates that by varying the grip strength, the resonance behavior shifts between the edge cases of free-hanging and clamped configurations, suggesting that the resonance properties of such actuators may be a feasible method for determining a user's grip strength and handling style of electronic devices. Further work is planned to develop a robust model for parameter estimation from measured impedance spectra and to create a system for real-time measurement of grip strength.