The design of the piano action, or mechanism of the piano, has not drastically changed since the late 19th century. The most recent innovations have been in the materials used. For example, Kawai use ABS (a type of plastic) parts in the action to reduce friction. They also help withstand the problems caused by extremes of atmospheric conditions. These parts are also more light-weight, allowing potential improvement in note repetition.
Sauter pianos of Spaickingen, Germany have patented an extra ’r2’ jack-spring in their upright actions which improves repetition. Their top range of grand pianos use soundboard spruce from the Val de Fiemme, Italy. This is the same source from which the famous Stradivarius violins were made.
As sound is transmitted across the grain, the best spruce is the fast-growing kind, that has good space between its growth rings. Fazioli pianos, Sacile, Italy (est.1981), also use this source, and make only grand pianos!
Another more recent addition has been to install magnets in grand piano actions to assist repetition. This is known as the magnetic balance action and was designed by Steingraeber & Söhne . It allows the pianist to even out the weight of touch across the whole keyboard with simple adjustments.
Some furniture designers are called on to help with the casework of pianos.