Design, kinematics, and control of a soft spatial fluidic elastomer manipulator

Abstract

This paper presents a robotic manipulation system capable of autonomously positioning a multi-segment soft fluidic elastomer robot in three dimensions. Specifically, we present an extremely soft robotic manipulator morphology that is composed entirely from low durometer elastomer, powered by pressurized air, and designed to be both modular and durable. To understand the deformation of a single arm segment, we develop and experimentally validate a static deformation model. Then, to kinematically model the multi-segment manipulator, we use a piece-wise constant curvature assumption consistent with more traditional continuum manipulators. In addition, we define a complete fabrication process for this new manipulator and use this process to make multiple functional prototypes. In order to power the robot's spatial actuation, a high capacity fluidic drive cylinder array is implemented, providing continuously variable, closed-circuit gas delivery. Next, using real-time data from a vision system, we develop a processing and control algorithm that generates realizable kinematic curvature trajectories and controls the manipulator's configuration along these trajectories. Lastly, we experimentally demonstrate new capabilities offered by this soft fluidic elastomer manipulation system such as entering and advancing through confined three-dimensional environments as well as conforming to goal shape-configurations within a sagittal plane under closed-loop control.

Dynamics and trajectory optimization for a soft spatial fluidic elastomer manipulator

“…This model is consistent with continuum manipulator literature [29] and is developed and validated in the context of the soft fluidic elastomer manipulator in [28].…”

“…2. Left: A soft continuum manipulator composed entirely from low durometer rubber developed by the authors in [28]. Right: An array of high capacity fluidic drive cylinders [20] used to drive the manipulator's distributed fluidic elastomer actuators.…”

“…In a segment subject to circumferential and longitudinal strain that deforms under constant curvature, material strain and bend angle θ can be related by decomposing the actuated region into J cross-sectional x-y slices of z-axis length w as outlined in [28] and the law of cosines…”

Visual servoing control of soft robots based on finite element model

“…In [10], a cascaded curvature controller is designed to control a highly compliant 2D manipulator actuated by bi-directional fluidic elastomer actuators. Then the method is extended to control a soft spatial fluidic elastomer manipulator [11]. In many practical cases, such as the significant contacts with the environment and the nonconstant deformation, the CCM does not capture all features of soft robots.…”

“…For overactuated system, the contribution of actuators with minimal energy can be computed by (11). Considering that the matrix J (x) has full row rank, the Pseudo-inverse matrixĴ + (x) can be computed byĴ…”