In the past decades, numerous research works have been conducted to develop human machine interface (HMI) systems, which has exhibited their great potentials in various applications, including biomedical engineering, entertainment, and many other areas. The most advanced HMIs are known as closed-loop HMIs, that consist of multiple motion sensors for capturing human movements, a control panel for collecting, analyzing, and transmitting data to target robotics, and human five-sense feedback systems, including vision, touch, smell, temperature, and gustation. Up to now, the research of closed-loop HMI systems in wearable formats is still in its infancy. In this thesis, the new HMI system is studied from four aspects, including strain sensors for capturing human motions, actuators for haptic feedback, flexible batteries for powering the HMI system, and a closed-loop HMI system for teleoperating robots.

In the strain sensors part, we have developed two types of epidermal sensors based on self-powered technologies, including piezoelectric, and triboelectric effects. Benefitted from the advanced functional materials and excellent mechanical characteristics, the strain sensors are capable of operating stably under various mechanical deformations, including stretching over 15%, bending over 150º, and twisting over 90º. By mounting the sensors around human joints for motion capturing, the two sensors could convert human mechanical motions into electrical signals for later recognition.

In addition to the self-developed strain sensors, we also studied novel wearable actuators based on mechanical vibration for realizing haptic feedback. The self-developed actuator could provide a wide vibration intensity range from 0 to 0.71 kPa at the resonant frequency of 60 Hz. Due to the advanced structure design, the actuator could operate in various severe surroundings, including hot air, water, and sand. To well fit the different parts of skin surface areas, we developed three actuators with different sizes, whose diameters range from 3.5 mm to 11 mm with a constant thickness of 3.2 mm. To realize a haptic feedback to users, we are capable of mounting these actuators arrays onto the whole human body.

The power management as an indispensable part in the HMI system, provides and regulates the electricity for data collection, analysis, and communication. Unfortunately, commercial batteries consist of hazardous materials in a bulky format, which limits their wide applications in current skin-integrated electronics. To solve the problem, we developed a stretchable, biocompatible, sweat-activated battery (SAB) that can be directly mounted onto human skin with a high capacity of 42.5 mAh and power density of 7.46 mW/cm². The high performance sweat-activated battery enables powering Bluetooth wireless operation for continuously monitoring human physiological information for over 6 hrs, demonstrating its great potential in powering HMI systems.

Based on the abovementioned investigations on HMI systems, we have developed a closed-loop HMI systems, providing both haptic and visual feedbacks. Based on skin-integrated electronics, the HMI system could interface with users’ whole body for human motion caption and feedback via Bluetooth, Wireless Fidelity (Wi-Fi), and Internet. The integration of visual and haptic feedback systems enables users to teleoperate a 7 degree-of-freedom (DOF) prosthetic hand, and a 13-DOF humanoid robot in various areas, including medical treatment, industrial manufacturing, entertainment experiences, surgical training, and many others. As a result, we have developed a skin-integrated, close-loop human machine interface systems as the next generation of HMI with the following properties: (a) Fully flexible configurations with skin-integrated elements so that they can accurately capture extensive body motional information as precious instructions; (b) Long-range wireless transmission, that enables transporting users’ instructions to manipulate the targeted equipment or machine at any corner of the world as long as covered by Internet; (c) Well-designed feedback systems which allow users synchronously receiving enough information from the robots and making adjustments timely.