Travel

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Travel refers to the vertical motion of a key.

Total travel

The total travel of a switch is the distance between the key's resting position, and its position when fully depressed, i.e. how far down you can press the key. In typical desktop keyboards, the total travel is between 3 and 4 mm; keyboards with total travel in this range or above are referred to as "full-travel". "Full-travel" is not formally defined, however; RAFI define "full-travel" as being 2.5 mm or more, which is the total travel of the smaller switches in the RAFI full-travel key switch family.

Short travel keyboards, like laptop ones, have a travel of about 2–2.5 mm.

Travel and hysteresis.svg

Pretravel

In most switch types except standard rubber dome over membrane keyboards, a switch will actuate before it is bottomed out. The terms "pretravel" and "operating travel" refer to how far down the key must be pressed for it to actuate. Pretravel is typically around of half travel. Once the pretravel has been reached, the operator is free to let go of the key without needing to press it all the way down.

Overtravel

Overtravel refers to the travel of the switch from the point of actuation to full travel. Depending on the switch technology, and the manufacturer's perspective, there may also be a switching region in between the pretravel range and overtravel range. The term "overtravel" indicates that there is no need to press the switch further: you are exceeding the switch's operating travel. Whether or not the switch will bottom out will depend on the switch characteristics and on the operator.

Switching region

In some switches (e.g. Marquardt Butterfly the snap action motion of the contacts causes the current to switch from zero to full current instantaneously. In other types (as measured with ITT ETL18) once the contacts meet, the resistance of the switch is proportional to travel. Testing with an analogue meter, pressing the slider slowly causes the needle to move across the dial from full resistance to near-zero resistance as the slider descends; if the slider is held at a position within this region, the resistance will also remain fixed at an intermediate level. This analogue response curve leads some manufacturers to separate the travel into pretravel, overtravel and switching region. Examples of switches with manufacturer-specified switching regions include Alps SKCL/SKCM series and Clare/Pendar low profile and high profile reed. In the case of Clare/Pendar, the switching region is defined implicitly by the gap between the pretravel and overtravel regions, while the 1994 Alps catalogue visually depicted the switching region for SKCL/SKCM.

Implementation

Various techniques are available to provide an overtravel region. For example, foam and foil switches actuate when the foil disc reaches the PCB; above the disc is a foam "overtravel pad" (hence "foam and foil"), that allows the switch to keep moving even though the disc has reached the PCB. The foam compresses, allowing the key to be pressed further after the foil disc reaches the PCB.

The bridge contact system in RAFI RS 76 M (illuminated) also permits the slider to continue moving beyond the point that the contacts close. The movable contact strip is supported from above by spring, so that the slider can continue moving after movable contact strip reaches the stationary contacts.

Stacked spring switches include an overtravel region by way of triggering a second spring, or a dome, to snap into place under spring pressure before the slider has come to a stop.

Actuation and reset points

The actuation point in a keyboard switch is the point at which the switch registers a key press. Similarly, the reset point is when the key ceases to register the key press. In some descriptions, the actuation point may be referred to as the "make" or "operating" point. The reset point may also be referred to as the "break" point.

In metal contact switches (including reed switches), physical metal contacts close and pass current.

Hysteresis

In many switch designs, the actuation and reset point do not occur at the same place in the key travel. Instead, the reset point occurs higher up in travel than the actuation point. The gap between these points is referred to as the hysteresis, or lost motion. Hysteresis prevents some repeated keystrokes from occurring, but not all.

The hysteresis of the Cherry MX Blue switch is quite pronounced due to its design, and this means it becomes harder to rapidly press a key multiple times in a row ('double tap'). This makes it less suitable for playing certain types of games.