Soft robot is known for great safety in human-centered environments due to its inherent compliance. However, the compliance resulting from the soft continuum structure and viscoelastic material also induces challenges for sensing and control of soft robots. In this paper, we propose a proprioceptive soft actuator design approach based on 3D printed conductive material and 3D printed deformable structure, such as bellows. The conductive bellow exhibits effective resistance change and structural deformation, thus provides a promising solution for the challenge of deformable soft robots that need integrated actuation and sensing. The proposed proprioceptive bellow actuator (PB actuator) achieves effective position feedback and real-time output force estimation. Using a dedicated control logic of the pressure controller, the PB actuator can not only provide anticipated motion but also estimate the interactive force based on real-time position sensing and input pressure. The design, fabrication, modeling, control, and experimental validation of our proposed PB actuator are discussed in detail in this paper. The parameters of PB actuator are highly customizable depending on the intended applications. Based on the proposed PB actuator, two specialized grippers, T and Y gripper, are designed and prototyped to demonstrate the grasping force estimation capability. The proposed proprioceptive soft robotic approach provides a promising solution to design behavior steerable soft robots.

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.

Research on quadrupedal robots inspired by canids or felids have been widely reported and demonstrated. However, none of these legged robots can deal with difficult environments that include water, such as small lakes, streams, rain, mud, flooded terrain, etc. In this paper, we present for the first time a kinematic analysis and a hydrodynamic model of dog paddling motion in a robotic system. The quadrupedal paddling gait of dogs was first analyzed based on underwater video recording. Hydrodynamic drag force analysis in a paddling gait cycle was conducted for a prototype robotic dog. The prototype robotic dog was developed using four pre-charged pneumatics soft actuators with consideration of relative positions of CG (center of gravity) and CB (center of buoyancy) and their dynamic variation in paddling. It was found that such soft actuators have great potential in developing amphibious legged robots, because they are inherently water-tight, anti-rusty, simple in structural design, and have large hydrodynamic advantage due to their mostly hemi-cylindrical shape design. Trotting and paddling of the prototype robotic dog was also demonstrated. It is believed that our findings reported in this research will provide useful guidance in future development of amphibious robotic dogs.

Fluidic and tendon driven actuators are widely applied in soft robotic hand design. Fluidic actuated soft robotic hands are highly compliant and can adapt to various objects. Tendon driven soft robotic hands are easier to control and have high dexterity and large force output, however, they are less compliant than fluidic actuated ones. Most robotic hands are designed with only one actuation method. Combining both actuation methods can tap the advantages and make up each other's limitations but at the expense of more complicated design and control. In this research, we propose a simple dual-mode actuator that provides both fluidic and tendon actuation. The two actuation modes are achieved simultaneously by twisting an elastic tube filled with gas, liquid, or even a combination. The soft robotic finger, designed as a fluidic elastomer actuator (FEA), is actuated by the fluid displaced from tube twisting, as well as by the tendon due to tube contraction in twisting. The tendon drives a compliant metacarpophalangeal (MCP) joint of the finger in order to provide a large bending angle and bending force to finger. Compared to an FEA soft finger, the proposed design can effectively increase the bending angle up to 150% (from 170 degrees to 260 degrees), and the blocking force up to 134% (from 3.2N to 4.3N). A soft robotic hand prototype with dual-mode actuators design is made for various grasping demonstrations.

Soft material robots are developing rapidly benefited from their inherent flexibility, adaptability and safety compared to rigid-bodied robots. However, most soft robots are unable to offer high force/strength due to the low rigidity of soft materials that they are composed of. Absence of position feedback is another problem for soft robots. In this research, we aim to address these two challenges in a novel designed soft smart robotic hand. The design of this soft hand is also delicately considered to make it 3D printable, which shortens the design cycle and reduces the fabrication time. This hand consists of five fingers and a palm, all of which can be actuated independently. The finger is designed with two chambers: one air-tight active chamber which can be actuated by compressed air, one passive chamber filled with loosely arranged particles. During bending actuation, particles inside the passive chamber are squeezed by pressurized air, which causes passive jamming. As a result, the stiffness of the finger is strengthened during bending, which endows the hand with larger force output and load-holding capability. Furthermore, position feedback modules made of conductive elastomers are integrated and co-printed with the finger during fabrication. In this research, a hand prototype is manufactured and several experiments regarding to its characteristics and performance are conducted for evaluation. From experimental results, the soft hand achieves maximum holding weight of 1.452kg with particles and 0.8425kg without particles at same actuation pressure of 450kPa.