DESIGN, FABRICATION, AND CONTROL OF THE SPI-MOD CSR: A SINGLE PNEMATIC INPUT MODULAR CONTINUUM SOFT ROBOT

Benjamin Olen Saunders

doi:10.7273/000007854

Soft robotics field is a new field of robotics research that focuses on developing and advancing the use of compliant materials in the development of robots. The inherent properties of these soft materials form the foundation for robots that can safely interact with humans in work environments and adapt to irregular conditions. This foundation has led to the rapid development of soft robot prototypes that range in all sizes and are used for medical devices, search and rescue, and more. The soft nature of the robot’s alternative actuation methods, as compared to heavy rigid motors, is a large focus of soft robotics research. One of the most commonly used actuation methods in the field of soft robotics is pneumatics. Pneumatic robots typically actuate by means of manipulating the shape and properties of soft components to control the direction and force exerted by the expansion of pressurized chambers. While this power system is accessible and capable, the means by which the fluidic pressure is delivered is often cumbersome and restrictive and limits the minimum size of soft robots. For example, common pressure delivery systems for soft robots require a tube for each individually controlled chamber in a robot’s design. Thus, as a soft robot’s design and movement become more complex, more individually controlled chambers are required and the volume for the pressure delivery system increases. This direct relationship of motion complexity to volume for power delivery determines the minimum size of a high degree of freedom robot. In response to this limitation, a nascent concentric-tubed spool valve (CTSV) was developed and integrated into the design of the single pneumatic input modular continuum soft robot (SPI-Mod CSR). The CTSV exploits the three-dimensional space between two concentric tubes to create a flexible adaptable valve system that requires minimal space to supply pneumatic power to multiple chambers in a soft robot with only a single pressure delivery tube. This design allows for a significant decrease in the size of modular continuum soft robots. The SPI-MOD CSR is a continuum soft robot that is fabricated with modular, two-chamber segments that can rotate about a single axis. These segments are attached to each other at a 90-degree offset such that every segment rotates about a different axis than their adjacent segments, providing a discreet approximation of snake-like motion. The central axis of the robot was designed with a channel running through it to serve as the outer tube of the CTSV and allowing for a flexible tube to be inserted. Holes in the pressure supply tube align with the inlets of the robot's chambers allowing for chambers to be selectively pressurized. With segments only one centimeter in length and two centimeters in diameter, the SPI-Mod CSR is one of the smallest modular soft robots to date and required the development of a specialized casting method. The Intermediary Sacrificial Mold Casting method for polydimethylsiloxane (PDMS) components presented here allows for the fabrication of the complex and relatively small segments of the SPI-Mod CSR. This fabrication method uses an intermediary sacrificial mold made from Field's metal in combination with the cost-effective high-resolution capabilities of a monochrome LCD 3D printer to bypass the cure inhibition of PDMS parts resulting from chemical compounds found in resin printed parts. The sacrificial nature of the intermediary molds allows for the fabrication of geometrically complex features and fragile components. Due to the single pressure tube nature of the CTSV in the SPI-Mod CSR, the discreet step Jacobian control method was developed to approximate the control found in Jacobian inverse kinematics-based control methods. With the discreet step Jacobian control method and a custom visual feedback system, multiple tests were performed driving the end effector to designated goal positions.

DESIGN, FABRICATION, AND CONTROL OF THE SPI-MOD CSR: A SINGLE PNEMATIC INPUT MODULAR CONTINUUM SOFT ROBOT

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