Printing ribbon feeding mechanism in a printer

Claim 1

In a ribbon feeding mechanism having a pair of ribbon reel supporting shaftS each adapted to mount thereon a printing ribbon reel and having a ratchet wheel coaxially secured thereto, and means for alternately driving said shafts in respective opposite directions so as to wind a printing ribbon onto the reel mounted on the driven shaft while unwinding the ribbon from the reel mounted on the other shaft, wherein the improvement comprises an actuating lever; means for swinging said lever; a ratchet feeding member having two arms interposed between said pair of ratchet wheels, a portion of said member intermediate said two arms being pivotally mounted on said actuating lever in such a manner that said member is reciprocated between said ratchet wheels in a direction substantially perpendicular to a line passing through the axes of said shafts, said member having a pair of ratchet feeding claws one of said claws engaging one of said ratchet wheels when said member is pivoted in one direction on said actuating lever while the other claw engages the other ratchet wheel when said member is swung in the opposite direction, said claws rotating the respective engaged wheels when said member is reciprocated; a detent member pivotally mounted between said ratchet wheels and having a pair of detent claws, one of said detent claws being engaged with one of said ratchet wheels when said detent member is pivoted in one direction so as to prevent said one ratchet wheel from rotating in the direction opposite to the direction of rotation imparted by the associated ratchet feeding claw, while the other detent claw engages the other ratchet wheel when said detent member is pivoted in the opposite direction; a compression spring having respective ends secured to said ratchet feeding member and to said detent member in such a manner that, when said ratchet feeding member is pivoted in a direction to engage said one ratchet feeding claw with said one ratchet wheel, said detent member is pivoted by said spring in a direction to engage said one ratchet wheel with said one detent claw, whereas, when said ratchet feeding member is pivoted in the opposite direction, said detent member is pivoted in the opposite direction by said spring; a pair of detecting levers pivotally mounted adjacent respective ratchet wheels, each detecting lever having a detecting arm engageable with a coil of printing ribbon wound on a reel mounted on the associated shaft for detecting the diameter of the ribbon coil wound on the reel, and an operating arm, whereby each operating arm is moved according to changes in the diameter of the coil of ribbon on the associated reel, said operating arms respectively abutting against the arms of said ratchet feeding member during the reciprocating movement of the latter when the diameter of the associated coil of ribbon is reduced to a predetermined value as the coil of ribbon is unwound from the reel, and thereby pivoting said ratchet feeding member from the engaged ratchet wheel to the other ratchet wheel whereby the ribbon feed is reversed.