The action of the keybed is what provides the mechanical interface between the musician's fingers and the keyboard. At one extreme the action could be as simple as a momentary pushbutton switch. At the other extreme would be a full grand piano action with about 5-10 moving parts. There is a tradeoff that must be struck between complexity, cost, comfort, and playing precision.
Most mass-produced electronic keyboards are one of two varieties:
1. A "synth" action, where there is a single moving part. This is by far the most common type, being standard for synthesizers at all price points, and common even in inexpensive digital pianos. Metal weights may be added to the tip of this kind of key for a more expressive, substantial feel.
2. A digital piano action with a second lever (the hammer) to add momentum and sometimes escapement. There can be many variations of this type of mechanism. Yamaha and Fatar are the largest manufacturers of this style of keybed. Yamaha and Fatar keybeds are used by most of the higher end keyboard manufacturers.