Hardware Methods for Onboard Control of Fluidically Actuated Soft Robots

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.

A fluidic relaxation oscillator for reprogrammable sequential actuation in soft robots

“…Recently, attention for electronics-free actuation and control of soft robots has grown. [35][36][37][38][39] Equivalents of basic building blocks of digital control, such as logic gates, are being re-invented in the fluidic domain. As a result, we also see basic…”

Will microfluidics enable functionally integrated biohybrid robots?

“…As the material deformation in soft robots is typically caused by fluid pressure, microfluidic technology could help achieve a fine distribution of active actuation sites. Nevertheless, there have only been a few publications on the interface between robotics and microfluidics (56)(57)(58)(59).…”

High‐Gain Microfluidic Amplifiers: The Bridge between Microfluidic Controllers and Fluidic Soft Actuators

“…Soft fluidic actuators are typically actuated at frequencies below 1 Hz. [ 12 ] Therefore, we are targeting a minimum amplifier bandwidth of 0.25 Hz.…”

“…The latency of the fluidic circuits that we envision is the sum of the response times of each component in the circuit which includes logic, power, and analog operations. According to McDonald et al's [ 12 ] review of typical operating speeds, pressure‐driven soft fluidic actuators have response times on the order of seconds or longer; some exceptions such as Mosadegh et al's [ 8 ] high‐speed robot operating at 20 Hz were noted. With this in mind, our aim was to not impede the overall system response time by designing for an amplifier with a larger bandwidth than a microfluidic circuit and soft actuator at the input and output of the amplifier, respectively.…”

“…[11] There have been efforts to move some of this fluidic power and control on-board, thereby decreasing the reliance on bulky and rigid external hardware. [12] Of the current approaches adopted, following in the footsteps of Wehner et al [11] and Bartlett et al, [13] we propose the following steps for using microfluidic circuits for low-level motion control. Microfluidics is a mature field which contains decades' worth of literature related to the design and operation of logic circuits to control small-volume flow within soft substrates.…”