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Compensator for Printhead Backlash

IP.com Disclosure Number: IPCOM000041695D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Alexander, RW: AUTHOR [+4]

Abstract

Backlash or play between a printhead and its drive motor in a matrix printer can be compensated for during direction change by adding one or more dot column or slice counts to the original direction count before permitting recording during travel in the opposite direction. With a matrix printer, particularly one capable of bidirectional printing, there occurs both inadvertent and planned reversals of printhead direction. There exists some amount of mechanical play in the drive train from the motor to the printhead or print elements. This play directly results in misalignment between either the starting points of successive print lines for intentional direction changes or an offset over-printing in the case of unintentional temporary direction change of the head due to inadvertence, such as impact.

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Compensator for Printhead Backlash

Backlash or play between a printhead and its drive motor in a matrix printer can be compensated for during direction change by adding one or more dot column or slice counts to the original direction count before permitting recording during travel in the opposite direction. With a matrix printer, particularly one capable of bidirectional printing, there occurs both inadvertent and planned reversals of printhead direction. There exists some amount of mechanical play in the drive train from the motor to the printhead or print elements. This play directly results in misalignment between either the starting points of successive print lines for intentional direction changes or an offset over-printing in the case of unintentional temporary direction change of the head due to inadvertence, such as impact. In matrix printers, the recording of dot columns is usually controlled by a slice count obtained from a transducer attached to the motor shaft. Transducers measure displacement and issue printsignals at specified intervals of motor rotation for controlling the dot recording for each character slice. Transducer signals in phase quadrature can provide an indication of motor and, hence, printhead direction. From these transducer signals both the head direction and character and slice counts are known. In those instances where the mechanical play approximates one slice or dot width, the slice count existing immediately prior to the sensed change in direction is increased by one, but the corresponding slice data from the character generator are suppressed for that added count. The count suppression allows the motor or slice count source to change its direction and move for one slice count to take up the play while the printhead remains stationary. An example of a printhead turn-around within a character column B-B is shown in Fig. 1. The character column is twelve slices wide, 0-11, and the printhead changes direction twice. During the first direction changes, the printhead reaches slice 9 but the slice count is advanced to 9 and printing is suppressed for that one count. Although the drive motor reverses, the printhead does not move until the motor decrements its count to 8, due to the backlash or play. Printing is then no longer suppressed and overprinting occurs in registration from slices 8 to 5. Thereafter, a second reversal decre...