Development of voice-coil micro-actuator for 3-D virtual tactile displays

An electromagnetic micro-actuator operating on the principle of voice-coil actuators is presented. Using finite element analysis of several conceptual designs of actuators [1-3], 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 footprint that matches the density of the tactile sensory neurons in the finger. Finite element analysis based on ANSYS was used to determine the dimensions of the components of the actuator. In comparison to earlier designs [3-5], this novel device has smaller sizes (2.28 mm in diameter and 7 mm in length), which makes it suitable for use in an array to be worn on the fingertip. Based on the static measurements of a test prototype, it is estimated, that the micro-actuator can produce at least 26 mN of repulsive force on the fingertip over a stroke of 2100 μm with a peak force of 34 mN. The driving circuit operates with 13.5V 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 stroke of 2300 μm, and a peak force of 21mN. The perceivability of the device on human fingertip approves the expectations drawn from the fact that all of the above parameters meet the required values of the thresholds of the human perception known from [4] and [5]. Due to its increased stroke, the voice-coil micro-actuator proved to be very suitable for the envisioned application allowing contact with the curved surface of the fingertip.