Motivation
The complexity of gripping tasks can be reduced by leveraging soft materials which passively conform to the target object. This has led to the development of a variety of soft grippers, including ones implemented industrially (see Soft Robotics Inc.).
Yet key problems remain unsolved. Most soft grippers are pneumatically actuated and are therefore tethered to bulky, noisy and inefficient air compressors — limiting their application space. They typically lack sensory feedback and require complex vision systems or added sensors to detect successful picks or other information about the target.
Actuation approach
HASEL actuators are soft, fast and electrically-driven. By combining a stack of these actuators with a soft, strain-limiting layer, we aimed to transform the linear expansion provided by each actuator pouch into controllable bending of the entire structure.
Repeatable custom fabrication pipeline enabled rapid prototyping and iteration.
The soft body of the gripper passively conforms to the target object, enabling versatile picking with simple on-off control.
Embedded sensory feedback
HASELs can simultaneously be used as actuators and sensors, based on capacitive self-sensing. As the pouch deforms, the electrodes get closer together, and the capacitance of the pouch increases. We hypothesized that this self-sensing approach could provide key benefits for gripping tasks, such as pick verification and object size detection.
Transduction principle for simultaneous actuation and sensing.
Impedance spectroscopy for simultaneous actuation and sensing, enabling pick verification and object size detection.
Algorithm design for capacitive self-sensing
We leveraged impedance spectroscopy to simultaneously drive the actuators at high-voltage and to collect sensory feedback. We apply a low-voltage sine wave and measure the response of the current using a shunt resistor to calculate the capacitance of each gripper finger.
Real-time pick verification
Real-time object size detection
Integrated high-voltage driving electronics
To make the gripper more accessible and easy-to-use, we developed compact, high-voltage driving electronics that can be controlled via USB.
Published article
Cover photo
