GB1382759A - Erasing typewriter - Google Patents

Abstract

1382759 Correction with typewriters INTERNATIONAL BUSINESS MACHINES CORP 12 July 1973 [3 Aug 1972] 33255/73 Heading G4H An erasing typewriter has a keyboard, a printing mechanism to print keyboard-entered characters, a memory to store the characters, an erasing mechanism operable from the keyboard to erase characters previously printed by the printing mechanism, and control means operable to drive the printing mechanism to reprint previously-erased characters drawn from the memory in accordance with a selection from the keyboard of which are wanted for reprinting. The memory can store a line of characters. Keying of a character causes access of the memory location corresponding to its position in the line to check whether the location contains a character with a "symbol not appear' bit set to identify the character for later reprinting. If it does, this character and all subsequent ones in the memory are read and re-stored one location to the right, in turn, to make room for the keyed character, which is then stored in the memory. If the "symbol not appear" bit was not set, the keyed character is stored in the memory unless it is not a space and there is already a character stored in that location which is not a space: since this indicates that the operator is attempting to type over a character which has not been erased, printing and storing are inhibited. An erase key is depressed to erase one character, or depressed further against a spring to erase a whole word (the end of which is detected by a "space" in the memory), and if the key is still in the latter state when erasure of the word has been completed, erasure will continue back to the beginning of the line. (In a modification, a second depression can be used to interrupt the latter type of erasure). The system performs the erasures by "printing" the characters from the memory but with an erasure ribbon in place so that the ribbon lays down a white cover-up transfer layer or lifts the ink from the paper on an adhesive layer. (In a modification, rotary rubber erasers are used. A toggle switch on the keyboard controls whether or not the erasure is to be accompanied by deletion from the memory. If it is not, the "symbol not appear" bits of the erased characters in the memory are set. If it is, a further bit in each erased character in the memory is set to indicate that its location can be used for another character and the characters to the right in the memory are read and re-stored one location to the left. After corrections have been made, a retype key can be depressed to cause the system to reprint the characters erased but having the "symbol not appear" bit set, and to space over without reprinting any characters encountered which remain on the paper from previous printing, under control of the memory, with resetting of the "symbol not appear" bits.