TACT Switch™ Pre-stroke and Its Effects

In the previous installment, we explained the structure of a middle-stroke type of TACT Switch™ and the over-travel it creates. In this article, we look at pre-stroke and the different feel and effects that each structure creates.

View the previous article here.

Over-travel and Pre-stroke

In the previous article, we explained that the compression of rubber in a long-stroke or middle-stroke type TACT Switch™ creates an over-travel after the contact closes. There are also some middle-stroke types with a pre-stroke prior to movement by the moving contact. As feeling curves, they look like this.

Over-travel and Pre-stroke

With a short-stroke type TACT Switch™, a sharp tactile click occurs as the metal dome inverts, but there is no additional travel once the contact closes. It feels like your finger is bumping into something, which can be tiring when operating the switch over long periods. Over-travel is the cushioning effect on this impact achieved using rubber. With middle-stroke and long-stroke types of TACT Switch™, the push feel experienced by the user can be fine-tuned by adjusting this over-travel. Alps Alpine's middle-stroke TACT Switch™ lineup also includes series with a pre-stroke zone, meaning users do not have to apply a lot of force at the start of the push, but are instead gradually drawn into pushing harder.

Example of a Pre-stroke Structure

Example of a Pre-stroke Structure

A pre-stroke zone can be created in a middle-stroke TACT Switch™ by inserting a gap between rubber stem (pusher) and metal dome. At the start of the push, until the stem makes contact with the metal dome, only a small amount of force is required, equivalent to the elasticity of the rubber. After making contact with the metal dome, the normal amount of force is required.

The internal structure of such a TACT Switch™ and the relationship with the feeling curve are as illustrated.

feeling curve

Using a Pre-stroke Design to Prevent Rattling


Rattling is noise caused by parts making contact with one another when vibrations are applied to the product. Rattling as a result of play between parts can be actively prevented using a pre-stroke structure. Making use of the elasticity of the rubber stem in a pre-stroke state, it is possible to prevent noise from vibrations in end products by preloading switches with keytops already wedged in place, which cancels out any play among TACT Switch™, keytop and housing.

TACT Switch™ Varieties with Pre-stroke

Alps Alpine currently supplies the following middle-stroke TACT Switch™ varieties with pre-stroke designs.

  • Compact middle stroke type
    realizing a clear operating feel.

  • Middle stroke type realizing low
    operation sound and a clear
    operating feel.

  • Compact and quiet middle
    stroke type.

  • Switch with 0.9mm stroke
    realizing a refined operating

So far we have explained the structure of TACT Switch™ products and the feel and effects they create. Next time, we will look at ways to minimize operating sound.

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