This section describes some examples of empirical tests that have been carried out to characterize PneuNets actuators. The aim of presenting these examples is to help you think about what types of tests you may need to perform to help guide your design. You may find the methods described useful for characterizing the behavior of your own actuator designs.

In many of these examples, the researchers conducted the tests in order to validate the results of their Modeling and Analysis. The tests were carried out using an evaluation platform based on the Soft Robotics Toolkit control board.

A summary of the results from these experiments can be found in the Variation: Material and Variations: Morphology sections.

Bending Curvature Estimation

This test was carried out by Polygerinos et al. (2013).

One end of the actuator was mounted in a rigid fixture (similar to the "encastre" boundary condition used in the FEM model). The actuator was inflated and the trajectory of its tip was observed.

Polygerinos et al. (2013)

A high definition camera was positioned to view the actuator from the side. The checkerboard pattern in the background was used in registering and aligning the camera (in order to address lens distortion and improve accuracy). As you can see in the photographs (left), a ruler was mounted beside the actuator to provide a scale for pixel-to-length conversion during image analysis.

To estimate the trajectory of the tip, the soft actuator was pressurized and depressurized three times while the camera recorded the motion. The resulting image frames were post-processed and analyzed with video analysis software (Kinovea 0.8.15). The x and y coordinates of the actuator tip throughout its motion were tracked, creating a trajectory for the tip’s motion. These coordinates were then used to produce the following graph.

Polygerinos et al. (2013)

Force Delivery Capability

This test was carried out by Polygerinos et al. (2013).

A 6-axis force/torque sensor was used to measure the force capacity of the actuator. Again, one end of the actuator was mounted in a rigid fixture, and a short rod to the force sensor was brought in contact with the tip of the actuator. The pressure inside the actuator was gradually increased in increments of 1 psi, and the force exerted by its tip was recorded. The experiment was repeated three times to assess accuracy and repeatability.

Polygerinos et al. (2013)

Effect of Actuator Morphology on Pressure Requirements

Mosadegh et al. (2013) investigated the effect of varying actuator morphology on the pressure required to achieve bending. A variety of actuators, all of the same overall length, were fabricated. The number of chambers, the wall thickness, and the chamber height was varied in each actuator. The actuators were clamped at one end. Each actuator was inflated and the pressure required for it to fully bend was recorded.

Mosadegh et al. (2013)