A Safe and Rapidly Switchable Stiffness Hydrostatic Actuator through Valve-controlled Air Spring

We developed a safe and high-performance hydrostatic actuator based on the switchable stiffness mechanism implemented with an air spring and solenoid valve. Rolling diaphragm-based hydrostatic transmission provides high transparency to the manipulator. Air spring and solenoid valve can adjust the stiffness rapidly. The block stiffness experiment shows that the ratio of adjustable stiffness is 9.63 at 100 kPa. We demonstrated that compliant mode could mitigate the impact force to the level that a tangerine would not be crushed. Since the time for adjusting stiffness is less than 12 ms, it would be beneficial to introduce vision or tactile sensors for feedback applications.

Related paper [IROS 2021]

Power Transmission Design of Fast and Energy-Efficient Stiffness Modulation

We developed a power transmission design of fast and energy-efficient stiffness modulation for human assistive device. We first designed a variable stiffness spring with a double slider crank mechanism to change the effective length of the leaf spring to modulate the output stiffness. Also, positioning the leaf spring’s bending location to the center enabled a fast and energy-efficient stiffness modulation. We integrated a variable stiffness spring with a negative stiffness generation module using developed elliptical shaped cam with compression spring. We provide a theoretical modeling of each drivetrains and characterization of stiffness modulation(speed and range) with negative stiffness with corresponding power consumption.

Related paper [ICRA 2021]