Abstract
Soft robots provide significant advantages over their rigid counterparts. These compliant, dexterous devices can navigate delicate environments with ease without damage to themselves or their surroundings. With many degrees of freedom, a single soft robotic actuator can achieve configurations that would be very challenging to obtain when using a rigid linkage. Because of these qualities, soft robots are well suited for human interaction. While there are many types of soft robot actuation, the most common type is fluidic actuation, where a pressurized fluid is used to inflate the device, causing bending or some other deformation. This affords advantages with regards to size, ease of manufacturing, and power delivery, but can pose issues when it comes to controlling the robot. Any device capable of complex tasks such as navigation requires multiple actuators working together. Traditionally, these have each required their own mechanism outside of the robot to control the pressure within. Beyond the limitations on autonomy that such a benchtop controller induces, the tether of tubing connecting the robot to its controller can increase stiffness, reduce reaction speed, and hinder miniaturization. Recently, a variety of techniques have been used to integrate control hardware into soft fluidic robots. These methods are varied and draw from disciplines including microfluidics, digital logic, and material science. In this review paper, we discuss the state of the art of onboard control hardware for soft fluidic robots with an emphasis on novel valve designs, including an overview of the prevailing techniques, how they differ, and how they compare to each other. We also define metrics to guide our comparison and discussion. Since the uses for soft robots can be so varied, the control system for one robot may very likely be inappropriate for use in another. We therefore wish to give an appreciation for the breadth of options available to soft roboticists today.
Highlights
Many of the challenges facing the robotics community, such as adapting to complex and unstructured environments or performing delicate object manipulation tasks, can be addressed using soft robots (Whitesides, 2018)
External control systems often have multiple valves connected to a shared pressure source and many tubes leading to the robot
There are a variety of commercially available valves, and we will discuss those which have been demonstrated for use in soft robots
Summary
Many of the challenges facing the robotics community, such as adapting to complex and unstructured environments or performing delicate object manipulation tasks, can be addressed using soft robots (Whitesides, 2018). While there have been efforts towards generating pressure onboard soft robots (Wehner et al, 2014; Rich et al, 2018), controlling many actuators typically requires some pressure control apparatus located externally from the robot to be connected directly to each DoF This makes a robot controlled in such a manner inherently less autonomous due to the stiff, bulky tubes connecting the robot and the pressure supply (Figures 1B,C). Techniques from fields as varied as microfluidics and materials science have been investigated within the framework of soft robotics as a means for embedding control These methods include traditional pneumatic and hydraulic components, microfluidic valves, macrofluidic pressure activated valves, exploiting viscous effects, and integrating smart fluids.
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