Comma printing mechanism

A printing apparatus comprising:

• a row of rotatable type wheels, each type wheel having a plurality of printing characters around its periphery;
• a selector for each type wheel and means for biasing each selector to move from a reset position in which it does not engage its type wheel and interfere with rotation thereof toward an operative position in which it engages its type wheel to prevent rotation thereof and align a selected printing character thereof with a printing position, each selector moveable from the operative to the reset positions against the force of said biasing means;
• a trigger claw for each selector and means for biasing each trigger claw to move from an energized position toward a reset position in which it engages its selector, provided the selector is in its reset position, to prevent the selector from moving to its operative position, said trigger claw being movable against the force of its biasing means from the reset position to an energized position in which it does not so engage its selector and allows its selector to move from its reset position to its operative position under the force of its biasing means;
• an electromagnet for each trigger claw, each electromagnet being momentarily energizable to momentarily move its trigger claw from the reset to the energized position thereof and to thus disengage the moved trigger claw from the selector engaged thereby to allow the selector to move from its reset to its operative position under the force of the biasing means thereof;
• a comma hammer for each of a selected plurality of adjacent type wheels, each comma hammer having a comma printing end, and means for biasing each comma printing end to move from a reset position in which it is out of alignment with said printing position of the characters toward a printing position at which its printing end is aligned with the printing position for said characters, each comma hammer engaging the trigger claw of its type wheel, provided the last recited trigger claw is in its reset position, in moving from the reset toward the printing position and being held thereby at a typing position intermediate said reset and said printing position thereof;
• and
• means for resetting each selector and comma hammer prior to a printing operation, means for momentarily energizing selected electromagnets to momentarily move the trigger claws thereof from the reset to the energized positions thereof and then allow the trigger claws to return to their reset positions after the electromagnets are deenergized, said movement of the trigger claws allowing the selectors thereof to move from their reset to their operative positions and align selected characters of the type wheels thereof with the printing position, means responsive to the movement of a trigger claw from the energized to the reset position thereof to allow the comma hammer thereof to move from its reset toward its typing position, and means for momentarily energizing selected electromagnets for a second time to again momentarily move their trigger claws from the reset to the energized positions and out of engagement with the comma hammers thereof, to thereby allow the comma hammers thereof to move from the typing to the printing positions under the action of the biasing means of the comma hammers, whereby upon a first momentary energization of selected electromagnets, the trigger claws engaged thereby release the associated selectors from their reset to their operative positions to hereby align selected characters with said printing position, each comma hammer is subsequently released form its reset position upon the return of the associated trigger claw to its reset position and moves to its intermediate, typing position, and each comma hammer moves to its printing position only if the electromagnet of the trigger claw engaging it is momentarily energized a second time.