An Integrated Hybrid 3D Printing Fabrication Strategy for Rapid Prototyping Soft Haptic Displays

Current manufacturing methods for prototyping soft tactile displays rely on complex techniques with limited scalability that are incompatible with stretchable electronics. This work presents a stretchable wearable tactile display with sensing and feedback capabilities manufacture with hybrid multi-material 3D printing in a single fabrication process. The electrical wiring and sensing elements of the display are 3D printed using a strain-induced electrically conductive liquid metal (LM) emulsion which exhibits shear yielding and shear thinning behavior. The actuators and off-the-shelf electronics are combined with the LM emulsion through automated pick-and-place. Once the LM emulsion and the electronics are integrated, they are packaged with liquid elastomer and cured. Upon mechanical activation of the LM emulsion composite through a bi-axial strain of 120% and 75%, they reached a conductivity that is within an order of magnitude of the bulk LM. The sensing elements are force sensing resistors (FSR) comprised of printed filaments on a spiral architecture. Electro-mechanical characterization of the sensors indicated that their sensitivity and response time were directly related to their conductivity. Upon further activation of the FSR at compressive strains of 60%, their conductivity increased to the same order of magnitude as the bulk LM. This increase in conductivity yielded the sensors with a sensitivity that is an order of magnitude higher than that of the electrical wiring. To show the capabilities of the tactile display, we fabricated two devices, one with an embedded array of FSR, and one with an embedded array of actuators. The device with the array of FSR collected data in the form of tactile patterns, collecting both the location and magnitude of the signal, and transmitting this data in real time. The device with the array of actuators received this signal and reproduced the tactile pattern for an immersive and synchronized tactile experience between the two individuals.