Pneumatic soft grippers have nonlinear continuum deformation enabling them to adapt to irregular object shapes. Most existing pneumatic soft grippers use only open loop control. Attempts for close loop control of soft grippers are all based on air pressure regulation, which is inaccurate and cumbersome due to nonlinear performance of the soft actuator and the compressible nature of air. In this paper, we presents a controllable soft gripper based on pre-charged pneumatic (PCP) soft actuators. The soft actuators, with the same design as a normal bending pneumatic soft actuator (PSA), are pre-charged with air to a preset pressure through a one way check valve. The bending angle and bending speed of soft actuators are controlled by servomotors through tendons based on feedback data from force and proximity sensors. Kinematic models of the soft actuators are developed. Dynamic properties are experimentally studied. A prototype gripper with close loop control is developed for controllable grasping demonstration.

The Actuation of soft robotics has relied predominantly on pneumatic or hydraulic transmissions. However, these transmissions require good sealing and complicated valve control systems. Robots based on such transmissions are also tethered to bulky pneumatic or hydraulic pumps. In many practical grasping applications, soft actuators are expected to show several-fold stiffness change which is difficult to achieve in pneumatic or hydraulic soft actuators. In this paper, a novel particle transmission method is proposed for soft gripper design. In the proposed method, particles enclosed in an elastic membrane are driven by a piston, thus problems associated with sealing are resolved as long as particle diameter is greater than the clearance between the piston and the cylinder. By controlling the volume of particles injected into the elastic membrane, bending of the actuator is achieved and its stiffness is increased accordingly. In the experiments, when injected particle volume is changed from 1.0 to 1.8 times that of the actuator's initial volume, the actuator bends up to 60° and its stiffness is increased by nearly seven folds from its initial state. A sample soft robotic gripper made of three such soft actuators is developed to test the feasibility and capability of the proposed method. It is believed that the proposed method could provide an important alternative to soft robotic gripper design and development.

In this paper, a novel robotic gripper design with variable stiffness is proposed and fabricated using a modified additive manufacturing (hereafter called 3D printing) process. The gripper is composed of two identical robotic fingers and each finger has three rotational degrees-of-freedom as inspired by human fingers. The finger design is composed of two materials: acrylonitrile butadiene styrene (ABS) for the bone segments and shape-memory polymer (SMP) for the finger joints. When the SMP joints are exposed to thermal energy and heated to above their glass transition temperature (T_g), the finger joints exhibit very small stiffness, thus allow easy bending by an external force. When there is no bending force, the finger will restore to its original shape thanks to SMP's shape recovering stress. The finger design is actuated by a pneumatics soft actuator. Fabrication of the proposed robotic finger is made possible by a modified 3D printing process. An analytical model is developed to represent the relationship between the soft actuator's air pressure and the finger's deflection angle. Furthermore, analytical modeling of the finger stiffness modulation is presented. Several experiments are conducted to validate the analytical models.

The emerging demand for bio-inspired soft robotics requires novel soft actuators whose performance exceeds conventional rigid ones. Dielectric elastomer actuators (DEAs) are a promising soft actuation technology with large actuation strain and fast response. Cone DEAs are one of the most widely adopted DEA configurations for their compact structure and large force/stroke output with several configuration variations developed in recent years. By driving at a resonant frequency, the cone DEAs show a significant amplification in their power outputs, which demonstrates their suitability for highly dynamic robotic applications. However, it is still unclear how the payload conditions could affect the power outputs of cone DEAs and no work has compared the output performance of different variations of cone configurations. In this work, by considering conical configuration DEAs with generalized dissipative payloads, we conduct an extensive study on the effects of payload conditions on the power outputs of the cone DEA family. Additionally, we benchmark the performance of different cone DEA configurations and illustrate the fundamental principles behind these output patterns. The findings reported in this work establish guidelines for designing high-performance cone DEA actuators.

Leveraging the instability in bistable structures to rapidly release the stored energy is often observed in nature to improve survival and reproduction. Bistable actuators have endowed soft grippers with superior performances such as fast response and self-lock ability. However, current bistable grippers are merely determined by their structural parameters in the design processes, and their grasping modes are usually restricted. In this article, we propose a novel type of reprogrammable bistable actuators. We introduce the design, modeling, and verification of the actuators. The results show that when reprogrammed to its ultrasensitive state with a minimal energy barrier, the trigger force required to induce the fast snap-through can be reduced to less than 0.005 times of its maximum value. In this process, only a minimal energy of 0.001 mJ was needed to trigger the fast energy release of 13.1 mJ. To demonstrate the advances and uniqueness of the proposed actuator, we also prototyped multiple grippers for multimodal, fast, and ultrasensitive grasping. In the ultrasensitive state, the gripper was able to respond to the contact of the swimming fish and capture it in 0.18 s. This work broadens the frontiers of bistable actuators in the design of functional robotic grippers.

Soft robots can provide advantages for medical interventions given their low cost and their ability to change shape and safely apply forces to tissue. This article explores the potential for their use for endoscopically-guided balloon dilation procedures in the airways. A scalable robot design based on balloon catheter technology is proposed, which is composed of five balloons together with a tip-mounted camera and LED. Its design parameters are optimized with respect to the clinical requirements associated with balloon dilation procedures in the trachea and bronchi. Possessing a lumen to allow for respiration and powered by the pressure and vacuum sources found in a clinical procedure room, the robot is teleoperated through the airways using a game controller and real-time video from the tip-mounted camera. The robot design includes proximal and distal bracing balloons that expand radially to produce traction forces. The distal bracing balloon is also used to perform balloon dilation. Three actuation balloons, located between the bracing balloons, produce elongation and bending of the robot body to enable locomotion and turning. An analysis of the actuation balloons, which incorporate helical coils to prevent radial collapse, provides design formulas by relating geometric parameters to such performance criteria as maximum change in actuator length and maximum robot bending angle. Experimental evaluation of a prototype robot inside rigid plastic tubes and ex vivo porcine airways is used to demonstrate the potential of the approach.