Editorial Feature

Electrostrictive Polymers for Robotic Technology

Several actuator technologies have been currently utilized for small-scale devices like piezoelectric, electromagnetic and electrostatic devices. Electrostrictive polymers (EPs) are one such technology that provides good results while being used in macroscales. These polymers are also called as artificial muscles since they have similar characteristics as that of a natural working  muscles. The actuation mechanism for certain EPs can be studied with respect to their bulk mechanical and electrical properties and others can be described using the changes occurring at molecular level.

Examples of Application

Otake et al. (2003) proposed an electro-active polymers system and derived a procedure for realizing an inversion motion of starfish-shaped gel robots upon the application of varying and time alternating electric fields.

The steps for modelling dynamic gel model are:

  • Modelling of active deformation - Poly (2-acrylamido-2-methylpropane sulphonic acid) gel and its co-polymer gel are used for this purpose as these gels are capable of undergoing large deformations when applied under changeable environmental conditions. This gel is ideal for its application in gel robotics as it moulds and reshapes itself as the robot bends towards anode side of a surfactant solution upon the application of an electric field.
  • Modeling of both active and passive deformation- In order to describe dynamic gel motions in three-dimensional space, passive deformation caused due to contact with outer world or gravity force has to be described. Hence the gel model is designed as deformable objects.
  • Deformation in spatially varying electric field.

The deformation model of robot is designed once the turn over motion control of gel robots is solved using the following steps:

  • Determining the direction of locomotion with the gel robot
  • Creating a trajectory of the robot at its center along locomotion direction
  • Enabling the robot to follow the desired trajectory when under motion control.

In the experiment by Otake et al. (2003), a repeat number of tests were performed to help evaluate the procedures. The starfish-shaped gel robots turned over each time. During the preparation process, the center of the robots successfully reached the desired position and then switched  within a timeframe of 40 seconds. The transition process occurred for six to ten seconds. However, it must be noted that the difference in rotating speed during the transition period is due to the difference in the center position of the robot.

Example of Electrostrictive Polymer for Artificial Muscle Application

With the development of various technologies, large number of EP actuated robots are expected to evolve in near future. These robots could perform non-destructive evaluation and other complex procedures. The Android head and a robotic hand were developed for increasing the effectiveness of EP actuators that are suitable for animatronics, robotics and for their application in the toys industry, a development that will continue to advance the way we interact with emerging technology.

The android head upon initial observation does question how suitable and inviting this technology will be if implemented into human society for helping understand human behaviour and interaction, though with its ability to generate facial expressions allows the human to feel comfortable in engaging in a level of communication and to not simply perceive this head as an inanimate object. The chosen EP material is modelled by tweaking control instructions and surface shape modifications in order to create the desired facial expressions. The following video is quite an extraordinary example of how electrostrictive polymers are being used in the design and development of an android head.

The robotic hand, which is also a keen research area in robotics is designed with sensors and tandems for operating various joints that mimick the human hand. This branch of robotic technology offers application in  the rehabilitation of patients suffering from limb dysfunction and damage to the central nervous system. With onventional motors currently being used for operating the index finger of a robotic hand, this can be replaced by EAP materials following the development of EAP actuators.

References

  • Pelrine. R.E, Kornbluh. R.D, Joseph. J.P, Menlo Park, CA 94025, USA, Elsevier Science S.A., 1998, A 64 (77-85)
  • Otake.M, Kagami.Y, Kuniyoshi.Y, Inaba.M, Inoue.H, Dept. of Mechano-Informatics, University of Tokyo, Complex System Engineering, Hokkaido University, Japan,International Conference on Robotics & Automation, 2003,14-19
  • Dahiya. R.S, Metta.G, Valle.M, Lorenzelli.L, Adami.A, Piezo-Polymer-FET Devices Based Tactile Sensors for Humanoid Robots, Robotics, Brain and Cognitive Sciences Department, Italian Institute of Technology,Italy, Springer 2010, Volume 54:pp 369-372

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