Point-Wise Vibration Pattern Production via a Sparse Actuator Array for Surface Tactile Feedback

Surface vibration tactile feedback is capable of conveying various semantic information to humans via handheld electronic devices, such as smartphones, touch panels, and game controllers. However, covering the entire contacting surface of the device with a dense arrangement of actuators can affect its normal use. Determining how to produce desired vibration patterns at any contact point with only a few sparse actuators deployed on the surface of the handheld device remains a significant challenge. In this work, we develop a tactile feedback board in the size of a smartphone with only five actuators, and achieve the precise production of vibration patterns that can focus at any desired position on the board. Specifically, we investigate the vibration characteristics of a single passive coil actuator and construct its vibration pattern model for any position on the feedback board surface. Optimal phase and amplitude modulation, determined using the simulated annealing algorithm, is employed with five actuators in a sparse array. The vibration patterns from all actuators are superimposed linearly to synthetically generate different onboard vibration energy distributions for tactile sensing. Experiments demonstrated that point-wise vibration pattern production on our tactile board achieved an average level of about 0.9 in the Structural Similarity Index Measure (SSIM) evaluation, when compared to the ideal single-point-focused target vibration pattern. Four point-wise patterns focused on the top, bottom, left, and right parts of the tactile board were applied, to guide continuous directional movements without visual assistance, which shows significant implications for machine-assisted cognition based on vibration tactile feedback.