Wave-shape pattern control of electroactive polymer gel robots

Abstract. This paper proposes wave-shape pattern control method for whole-body de-formable robots containing electroactive polymers. Mechanisms consisting of a typicalelectroactive polymer gel containing poly 2 -acrylamido -2- methylpropane sulfonic acid(PAMPS),named ’gel robots’, have been designed, developed, and controlled experimentally.We faced a common problem called, the degrees-of-freedom problem, namely controllingmany points on the gel surface with a small number of inputs. In order to solve the problem,we once reduced the number of inputs to one, and discovered that wave-shape pattern evolvesfor the beam-shaped gel even in a constant uniform electric field. This method makes use ofthe pattern formation. Wave-shaped gels with varying curvature are obtained by switchingthe polarity of a spatially uniform electric field. The method is verified through experimentswhich are carefully designed based on numerical simulations. 1 Introduction Electroactive polymers [1] change their shapes in the electric fields. The fact moti-vated us to design the whole-body deformable robots. The purpose of this study is toestablish methods for deriving a variety of shapes and motions of deformable robotswhose bodies are made of active materials. Shape control of such mechanisms isdifficult, which is commonly called the degrees-of-freedom problem [2], namely aproblem of controlling many points of continuum with a small number of inputs.In order to explore the high dimensional configuration space of elastic objects [3],probabilistic roadmaps was applied.Osada et al. developed a surfactant-driven ionic polymer gel which is made ofpoly 2-acrylamido-2-methylpropane sulfonic acid (PAMPS), and well known for itslarge deformation[4]. Although the gel reversibly bends and stretches by alternatingthe polarity of the electric fields, the spatiotemporal pattern formation has not beenstudied in depth. We have been developing deformable machines utilizing the gel,hereaftercalled”gelrobots”,andproposedmethodsforexploitingavarietyofshapesand motions of the gel[5–8]. The methods were applied and succeeded in generatingvariety of motions such as beam-shaped gels curling around an object and starfish-shaped gels turning over[9]. The pattern formation process of the gel was analyzedrefering to the living things that also have deformable bodies. They accumulate thetemporalsequenceofinputandbuildtheirbodiesinthedevelopmentalprocesscalledmorphogenesis. Uniform structures are converted to complex organs in a uniform