Design of Soft Continuum Manipulators Using Parallel Asymmetric Combination of Fiber Reinforced Elastomers

Abstract

Soft continuum manipulators have large workspace, dexterity and adaptability, but at the cost of complex design construction highlighted by concatenating several individually controlled serial segments. In this paper, we propose a new designarchitecture for a soft continuum manipulator composed of a parallel combination of pneumatic actuators. The BR2 manipulator, featured in this paper is asymmetric as it combines one soft bending (B) actuator and two soft rotating (R2) actuators, as opposed to state of the art symmetric architectures that adopt bending segments. Spatial deformation modes are achieved by combining curvature and torsion of the individual actuators. This paper formulates a forward analysis method based on Cosserat rod mechanics to predict the spatial deformation of the manipulator under the effect of external loads with an accuracy less than 9 % of the manipulator length. The model takes into account ‘the coupling effect’ inherent to the asymmetric combination, where pressurizing the rotating actuator attenuates the bendingcurvature and vice versa. Consequently, the paper studies the optimal design of the manipulator constituents that minimize the coupling, and thus maximize the workspace and dexterity. A detailed performance study of the BR2 manipulator on aswiveling base demonstrates a spatial workspace quantified by an axisymmetric area, and sufficient dexterity such that at least 87% of the workspace can be approached with two or more orientations. These are validated through obstacle avoidance, and a pick and place task. The manipulator is also capable ofwhole arm manipulation by spiraling along cylindrical objects of varying diameters. These performance attributes surpass any other single segment module and is a potential building block for constructing customized continuum manipulators.

Open Loop Position Control of Soft Continuum Arm Using Deep Reinforcement Learning

“…A single trajectory having four waypoints is analyzed for three loading cases. The trajectory as reported in the simulation is replicated on the prototype with no feedback and therefore we expect the observed errors to be of the same order of magnitude as those reported in [6]. Two important observations highlighted in the purview of this test are:…”

“…The advantages associated with the design is promising for agriculal applications such as autonomous berry harvesting, weeding, and pruning. Our preliminary investigations [5], [6] of the manipulator reveal large nonlinear elastic deformation, with stiffness varying as a function of applied pressure. Furthermore, there exists elastic coupling between the different actuators, and sizable attenuation in the end effector workspace due to external loads or disturbances.…”

“…The BR 2 manipulator presented in [6], is a continuum robotic arm made from combining soft actuators namely Fiber Reinforced Elastomeric Enclosures (FREEs). FREEs are made of a hollow cylindrical tube reinforced with inextensible fibers wrapped in a helical shape on its outer surface.…”

“…An ε−greedy action selection strategy (ε = 0.1) is used while training. To expedite training we use the model developed in [6] to train the system on a simulation. The simulation is based on a Cosserat rod formulation [17], with the elasticity and precurvature parameters fit with experimental results [5].…”

“…In this paper, we investigate the control of a unique soft continuum arm known as the BR 2 manipulator [5], [6]. Unlike several other existing soft manipulators, the BR 2 has a completely parallel architecture from an asymmetric combination of soft pneumatic building blocks known as FREEs (Fiber Reinforced Elastomeric Enclosures) that bend and rotate simultaneously, the combination of which yields a spatial deformation pattern as shown in Fig.…”