ITT snap-action array
|This article requires photographic illustration|
|This article requires illustration in the form of diagrams — this design is very hard to explain without the use of diagrams!|
|Inventor||Michael Muller, Reed A. Palmer, Harry R. Marker|
|Sense method||Metal contact|
|Patents||US 4316066 (1980)|
ITT snap-action array is an non-discrete contact array, which shares the same patent as ITT discrete snap-action.
The design provides hysteresis and tactility; it is also likely to generate audible feedback, but this is not mentioned in the patent. The actuator leaf is also similar to that used in Fujitsu Leaf Spring.
US patent 4371760 filed a year later and attributed solely to Michael Muller depicts a thin, flat equivalent of this keyboard.
Flat metal plates resembling metal foil are stamped with a subtle upwards curve; each plate has two cuts stamped into it, with the resulting metal tongues being bent downwards. Pressing down on these plates causes them to invert in a snap action, and the tongues then connect with exposed PCB pads. Only one tongue is required, but dual tongues and dual pads are provided for redundancy.
Each stamped metal piece contains a corresponding pair of metal fingers next to the snap-action plate. These metal stampings are cut into lengths of different numbers of key positions; at least one position must have its fingers angled downwards, as these fingers connect the whole stamping to exposed pads on the PCB. Again, only one finger is required, but two fingers and two pads are provided for redundancy. The entire stamping thus becomes a section of matrix, and cutting the stampings into smaller numbers of key positions isolates these matrix sections. Most connector fingers are left unbent, as they are not used and do not connect to the PCB.
An actuator leaf serving a dual role as the return spring, interposes the slider and snap-action leaf. This return spring acts as the motion reducer, providing overtravel and allowing the force against the snap action plate to be higher than the operator force though mechanical advantage. When a single plate is inverted through snap action, current passes between the connector fingers and contact tongues.
- Some Apple II machines
The following images are believed to be from an Apple II Plus computer.