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. 2017 Sep 1;4(3):274-284.
doi: 10.1089/soro.2016.0044.

Design of a Variable Stiffness Soft Dexterous Gripper

Loai A T Al Abeach  1 , Samia Nefti-Meziani  2 , Steve Davis  2
Affiliations

Design of a Variable Stiffness Soft Dexterous Gripper

Loai A T Al Abeach et al. Soft Robot. .

Abstract

This article presents the design of a variable stiffness, soft, three-fingered dexterous gripper. The gripper uses two designs of McKibben muscles. Extensor muscles that increase in length when pressurized are used to form the fingers of the gripper. Contractor muscles that decrease in length when pressurized are then used to apply forces to the fingers through tendons, which cause flexion and extension of the fingers. The two types of muscles are arranged to act antagonistically and this means that by raising the pressure in all of the pneumatic muscles, the stiffness of the system can be increased without a resulting change in finger position. The article presents the design of the gripper, some basic kinematics to describe its function, and then experimental results demonstrating the ability to adjust the bending stiffness of the gripper's fingers. It has been demonstrated that the fingers' bending stiffness can be increased by more than 150%. The article concludes by demonstrating that the fingers can be closed loop position controlled and are able to track step and sinusoidal inputs.

Keywords: actuators; end effector; gripper; soft robotics; variable stiffness.

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Conflict of interest statement

No competing financial interests exist.

Figures

<b>FIG. 1.</b>
FIG. 1.
Variable stiffness continuum finger.
<b>FIG. 2.</b>
FIG. 2.
First prototype three-fingered variable stiffness gripper.
<b>FIG. 3.</b>
FIG. 3.
Conceptual design of second prototype soft hand.
<b>FIG. 4.</b>
FIG. 4.
Three-fingered soft hand.
<b>FIG. 5.</b>
FIG. 5.
Kinematics of continuum finger.
<b>FIG. 6.</b>
FIG. 6.
Bending stiffness test rig.
<b>FIG. 7.</b>
FIG. 7.
Bending stiffness experimental procedure.
<b>FIG. 8.</b>
FIG. 8.
Lateral finger displacement as load increases at a finger length (Le) of 190 mm (a) and 180 mm (b) at increasing extensor pressures.
<b>FIG. 9.</b>
FIG. 9.
Percentage increase in finger bending stiffness as extensor muscle pressure is increased.
<b>FIG. 10.</b>
FIG. 10.
Response to 20 mm (a), 30 mm (b), and 40 mm (c) step displacements of contractor muscle.
<b>FIG. 11.</b>
FIG. 11.
Response to 20 mm (a), 30 mm (b), and 40 mm (c) sinusoidal displacements of contractor muscle at 0.25 and 0.5 Hz.
<b>FIG. 12.</b>
FIG. 12.
Tracking 40 mm sinusoidal displacements signal with extensor pressure of 100 kPa (a), 200 kPa (b), and 300 kPa (c).
<b>FIG. 13.</b>
FIG. 13.
The response of the three contractor muscles when producing a step change in finger length.
<b>FIG. 14.</b>
FIG. 14.
The soft gripper grasping sample products.
See this image and copyright information in PMC

References

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