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Soft Robotics

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Self-Sensing Electroadhesive Polymer Gripper with Magnetically Controllable Surface Geometry

Author(s): Dirk Sindersberger* and Gareth J. Monkman

Pp: 60-89 (30)

DOI: 10.2174/9789815051728122010005

* (Excluding Mailing and Handling)

Abstract

Compared to most conventional industrial end effectors, electroadhesive
grippers enable the handling of sensitive, soft, or air-permeable materials [1]. This
makes them highly suitable for integration into soft robotic designs. The prehension
force is based on a strong electric field generated by electrodes resulting in a
polarisation of the dielectric and the generation of mirror charges in the workpiece.
When the electrode supply voltage is deactivated, the electric field rapidly drops, but an
electrostatic field remains due to the remanent polarisation of the dielectric. The
residual charge on the gripper surface reduces only slowly and, in combination with
other influencing factors, can prevent the workpiece from being ejected temporarily or
completely. A solution to this problem is presented by means of a magnetically
deformable soft gripper surface based on a combination of gripper dielectric and a
magneto-active polymer (MAP) actuator. The increased distance between the
workpiece and the dielectric enables precise and controlled workpiece ejection.

In addition to compliance and deformability, the employment of soft smart materials
enables the integration of self-sensing mechanisms for the measurement of surface
deformation. Direct mechanical coupling between the magnetic polymer and the
electrodes allows the actual deformation of the surface to be determined. The ability to
measure this deformation allows the magnetic field to be increased until the required
displacement is reached, regardless of the prevailing adhesion forces. Since
electroadhesive forces are also dependent on the workpiece materials, simply applying
a fixed magnetic flux would not be sufficient to achieve the same deformation for
every material. The self-sensing capability is independent of the gripping process and
can therefore also be used to recognise a particular surface topology. By applying a
mechanical force, the end effector can be pressed onto a three-dimensional workpiece,
causing the surface to deform inwards and physically comply with the workpiece
shape. The deformation achieved can then be targeted by the magnetic drive before
each gripping process, thereby creating optimum contact with the workpiece. Ejection
of the workpiece then follows by means of an inverse process, whereby the
deformation of the surface is reversed and the workpiece ejected by reducing the
contact area.

Embedded electrically conductive thermoplastic electrodes within the soft silicone
dielectric have the necessary flexibility to support such movements whilst serving as
the necessary electrodes for electroadhesion. Since the implementation of the end
effector is based entirely on soft materials, the self-sensing magnetically controllable
electroadhesive gripper (SMEG) can be produced in a simple shape deposition
manufacturing (SDM) process [2, 3] and is highly applicable to the field of soft
robotics [4]. 

Keywords: 3D Print, Compliant Gripper, Deformable Surface, Elastomer, Electroadhesive, Electroconductive Thermoplastics, Gripper, Magnetic drive, Magnetoactive Polymer, Self-sensing, Soft gripper, Soft Robotics.

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