The knit textile bending actuators documented here consist of two layers of fabric sewn around a balloon. This section describes the primitive motions of a textile actuator, and discusses some of the design considerations involved in making your own actuator. Textile actuators can also be designed to produce multiple motions by adding additional layers and balloons. The adding a motion section describes this in more detail.
As described in the title page, textile actuators produce motion when a balloon constrained by fabric is inflated. The air pressure from the balloon transmits its strain directly into all surfaces in contact with the balloon. In order to control and utilize this strain, the right materials need to be selected.
| In many cases, radial expansion is not desired beyond a certain diameter. In order to constrain the radial expansion without inhibiting the actuator's capabilities, a fabric with anisotropic stretch properties, such as one-way stretch, must be used. One-way stretch fabrics stretch significantly more in one direction than the other. Much like the fibers wound around the fiber-reinforced actuators, one-way stretch fabrics constrains the actuator's radial expansion while allowing it to stretch axially. Shown to the right is a one-way stretch fabric with arrows drawn to demonstrate the anisotropic stretch properties. Shown below to the left is the fabric stretched in its most stretchy direction, and to the right is the fabric stretched in its least stretchy direction. Approximately the same tension is applied in both cases. |
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An extending actuator can be made by putting a one-way stretch fabric on top of another piece of one-way stretch fabric. See the motion primitives videos below to see an extending actuator in action.
In order to create a bending motion, a significant difference in axial stretch properties between the top and bottom layers is necessary. These materials are described in more detail in the fabric section. An woven fabric is shown below to the left and the same fabric has tension applied to the right. Notice that this fabric does not stretch.
| Another way to utilize one-way stretch fabrics is to cut it at an angle. For example, cutting a fabric layer on the bias at an angle of 45° allows the stretchiest direction to twist the actuator when pressurized. See a twisting actuator below in the motion primitives videos. |
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Motion primitives:
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Bending Top material: one-way stretch Bottom material: woven |
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Extending Top material: one-way stretch Bottom material: one-way stretch |
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Twist-extend Top material: one-way stretch cut at 45° Bottom material: one-way stretch cut at 45° |
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