Drive for thermal printing lift-off correction

DETAILED DESCRIPTION What is claimed is: 1.
A thermal printer having a power source to power heat-producing elements in a column simultaneously moved across the area of a printed character which can be selectably activated as said elements pass across a character printed while in contact with a thermal transfer medium which forms a bond for lift-off correction of thermal printing from said transfer medium at temperatures above ordinary room temperatures and below a temperature at which printing from said transfer medium is effected, keyboard selection means to select a lift-off correction mode of operation, and means operative during each said lift-off correction mode of operation to apply power from said power source to substantially all of said heat-producing elements as said elements move across said character area, said power being in a series of pulses having the net effect of producing said temperature for lift-off correction and being applied to adjoining of said heat producing elements in substantially equal form and opposite phase.
2.
The thermal printer as in claim 1 in which said pulses are square waves having a lower level of substantially zero and an upper level in the order of magnitude of the level of power from said power source to said transfer medium supplied by said printer source prior to operation of said keyboard selection means.
3.
The thermal printer as in claim 2 in which said square waves are symmetrical, at least for said heat-producing elements above the bottom part of said column corresponding to an underline of a character.
4.
The thermal printer as in claim 1 in which said heat-producing elements in the bottom part of said column corresponding to an underline of a character receive greater power than the other of said elements.
5.
The thermal printer as in claim 1 also comprising operator-selectable control means which sets the level of printing power and the level of power from said pulses in one setting.
6.
The thermal printer as in claim 2 also comprising operator-selectable control means which sets the level of printing power and the level of power from said pulses in one setting