A key performance indicator for HASEL actuators is force output as a function of stroke. These parameters are critical for ensuring that a HASEL actuator meets the requirements of a given application. Thanks to their versatility, the force and stroke of a HASEL actuator can be tuned by varying a variety of parameters that range from actuator geometry to the specific materials that are used. This document presents some general guidelines for how to tune the force and stroke of HASEL actuators.
When describing actuator force and stroke, it is typical to note the blocked force and the free stroke. Blocked force is the force applied when there is no stroke, therefore this is the maximum force that can be applied by the actuator. Free stroke is measured when there is no load applied to the actuator and is the maximum stroke that can be achieved.
As stroke increases from zero (at the blocked force), force output from the actuator will decrease exponentially until the force is zero at the free stroke. The plot below shows a representative force vs. stroke curve for HASEL actuators. Note that this curve is for a constant applied voltage. Voltage also affects force and stroke, but this won’t be discussed here.
Contracting Actuators
These actuators consist of rectangular pouches that are filled with a liquid dielectric. About half of the pouch is covered by electrodes. The pouch has a specific width and length. When activated, these actuators are designed to contract in the length direction.
There are three simple methods for tuning the force and stroke of contracting actuators:
1. Number of pouches in series. Increasing the number of pouches in series (in the length direction of the actuator) will increase the free stroke. Blocked force will not be changed by increasing the number of pouches in series. However, for a given stroke, the force will be higher. The representative curves below show how force and stroke shift as the number of pouches in series is increased.
2. Number of actuators in a stack. Increasing the number of contracting actuators in a stack will increase the blocked force but will not change the free stroke. However, for a given force, the stroke will be higher. The representative curves below show how force and stroke shift as the number of contracting actuators in a stack is increased.
3. Width of the actuator pouch. Increasing the width of a pouch will increase the blocked force but will not change the free stroke. However, for a given force, the stroke will be higher. There are limitations to how much the pouch width can be increased and still see a proportional change in performance. Consult the experts at Artimus Robotics if you are interested in actuators with custom widths. The representative curves below show how force and stroke shift as the pouch width of a contracting actuator increases.
Expanding Actuators
These actuators consist of circular pouches that are filled with a liquid dielectric. A concentric pair of electrodes are located on the outside of the pouches. When voltage is applied, the electrostatic forces cause the electrodes to zip together and the pouches expand in thickness.
Below are two common methods for tuning the force and stroke of expanding actuators:
1. Number of actuators in a stack. Increasing the number of expanding actuators in a stack will increase the free stroke but will not change the blocked force. However, for a given stroke, the force will be higher. The representative curves below show how force and stroke shift as the number of expanding actuators in a stack increases.
2. Number of actuators in an array or mechanically in parallel. Multiple stacks of expanding actuators can be placed in an array to increase the blocked force. This does not increase free stroke, but for a given stroke, the force output will be higher. The representative curves below show how force and stroke shift as the number of expanding actuators in an array increases.
These are just a few simple ways to modify the force and stroke of HASEL actuators. Many of the standard products are variations of these parameters. Please contact us with the specific force and stroke requirements for your applications so that we can specify an actuator size, shape, and configuration that will meet your needs.
About Artimus Robotics
Artimus Robotics designs and manufactures soft electric actuators. The technology was inspired by nature (muscles) and spun out of the University of Colorado. HASEL (Hydraulically Amplified Self-healing ELectrostatic) actuator technology operates when electrostatic forces are applied to a flexible polymer pouch and dielectric liquid to drive shape change in a soft structure. These principles can be applied to achieve a contracting motion, expanding motion, or other complex deformations. For more information, please visit Artimus Robotics or contact info@artimusrobotics.com.