The circular actuator fabricated in this documentation uses an equibiaxial prestretch of 3 (i.e. the membrane is stretched three times equally in all directions). In order to achieve this prestretch, the acrylic frame and the initial piece of VHB must have the correct dimension ratio (3:1). The important dimensions to consider are the outside diameter of the acrylic frame and the outer diameter of the stencil used to cutout the initial piece of VHB.
We make the rigid frame out of acrylic so that it can be reused multiple times. The VHB can be simply peeled off and the frame washed in order to use it again. The two stencils are made using the red cover foil that is attached to VHB 4910 when it is sold from 3M, because it does not stick to VHB and therefore does not damage it upon removal.
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- The acrylic frame used in this documentation has an outer diameter of 6 inches and an inner diameter of 5 inches.
- The frame can be made using a laser cutter.
- The .DXF file should have two concentric circles of the given dimensions.
- You can also use 15 cm and 13 cm for outer and inner diameter dimensions respectively.
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- The first stencil is a circle with outer diameter equal to 1/3 of the outer diameter of the acrylic frame you make.
- In our case, the stencil will be 2 inches in diameter or 5 cm.
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- The stencil used when painting the active area has outer diameter equal to the inner diameter of the acrylic frame.
- In this example, that would be 5 inches or 13 cm.
- The inner diameter can be whatever you want it to be, but in this example it is 1.5 inches or 3.75 cm.
- This stencil can be also be laser cut or simply drawn and cut out with scissors.
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