Development of Wearable Micro-Actuator Array for 3-D Virtual Tactile Displays

A novel 4 by 4 array of electromagnetic micro-actuators operating on the principle of voice-coil actuators is presented. The intended application of the array is dynamic tactile stimulation, where multiple actuators generate an illusion of touching a moving pattern. In comparison to earlier designs [1-3], the device has smaller dimensions of 2.28 mm in diameter and 7 mm in length, which allowed its use in an array capable of hosting up to a 5 by 5 set of actuators with a rectangular shape covering an area of 18 mm by 21 mm. Using finite element analysis of several conceptual designs of actuators [1,4,5], it was established that the voice-coil type device (where the coil is the moving part) has most beneficial characteristics for the envisioned application. These include sufficient force over a relatively large distance, allowing tactile stimulation of surfaces with irregular shape, fast response, and small foot-print that matches the density of the tactile sensory neurons in the human finger. Eexperimental evaluation of the operation of neighboring actuators spaced at 3.3 mm apart, indicates that there is no crosstalk between the actuators. The resulting density exceeds that of previously reported alternative designs based on moveable permanent magnets [4,6]. Static force measurement indicate that each micro-actuator can produce at least 26 mN of repulsive force over a stroke of 2100 μm with a peak force of 34 mN. The driving circuit operates at 13.5 V and generates a vibration frequency of up to 265 Hz without significant change of the force-displacement characteristics. In the higher frequency range (above 100 Hz) the actuator provides at least 15 mN of force over a slightly reduced stroke of 2300 μm, and a peak force of 21 mN. All of the above parameters meet the required threshold values of tactile human perception known from [2,3].