Page "Clutch" Paragraph 54

When inactive it is disengaged and the driven member is stationary.

When " tripped ", it locks up solidly ( typically in a few to tens of milliseconds ) and rotates the driven member just one full turn.

If the trip mechanism is operated when the clutch would otherwise disengage the clutch remains engaged.

Variants include half-revolution ( and other fractional-revolution ) types.

These were an essential part of printing telegraphs such as teleprinter page printers, as well as electric typewriters, notably the IBM Selectric.

They were also found in motor-driven mechanical calculators ; the Marchant had several of them.

They are also used in farm machinery and industry.

Typically, these were a variety of dog clutch.