Patent GB-1294629-A (GB)
Title: Printing apparatus
Inventor: JOHNSON CARL FOSTER
IPC: B41J29/26
Filed: 1971-04-19
Abstract: 1294629 Printers; magnetic card reader INTERNATIONAL BUSINESS MACHINES CORP 19 April 197 [15 April 1970] 25218/71 Headings G4H and G4M [Also in Division B6] In a printing apparatus in which the printed characters are letter-spaced in accordance with proportional escapement values, the printed characters are also recorded in recording means (e.g. a magnetic card unit) and a word underscore operation involves reading the characters of the word from the recording means, backspacing the printer to the beginning of the printed word, then moving the printer forward with printing of underscoring. Characters to be printed from a keyboard are entered in coded electric form into a register from which each actuates selected magnets to rotate/tilt a unitary print head, is recorded on a magnetic card, and is decoded to indicate escapement value and print velocity. The escapement value is loaded into a counter which is then decremented by escapement clock pulses (see below) until at zero it stops the escapement. Actuation of a word underscore key causes the magnetic card to be driven backwards and the characters of the word just recorded to be read in reverse order and supplied via the register to cause backspacing of the print head by the respective escapement values. When the beginning of the word is reached, the magnetic card is driven forwards and each character of the word is read and passed via the register to enter its escapement value via the escapement counter into a unit counter. Whenever the count in the units counter exceeds 6, an underscore code is entered into the register, an underscore character is printed, and 6 is subtracted from the units counter (6 being the escapement value of this character). When the escapement value of the last character of the word has been entered into the units counter and before the last underscore character is printed, the print head is backspaced by 6 minus the value in the units counter, and the last underscore character is printed (thus aligned with the last character of the word). The magnetic card unit may be used in place of the keyboard for entry of characters to be printed, and the system can also cause underscoring in response to a sequence of backspace codes followed by a sequence of underscore codes, recorded on the card by another system. Overscoring is also mentioned. Magnetic card unit.-The card can be driven longitudinally in either direction by energizing one of two magnets to lower a respective idler roller on to the card to press it against a respective one of two continuously-driven drive rolls rotating in opposite directions. A magnetic head having a read gap and a write gap can be positioned transversely of the card to a desired track by a screw driven via a clutch. To record a character, the card is incremented forward to check the previously recorded character for proper bit positioning and redundancy by sensing it at the read gap, the card then being reversed until this character is intermediate the two gaps, then driven forward, the first bit of the character to be recorded being gated to the write gap when the first bit of the previous character is sensed again by the read gap. The recorded characters can be read in forward or reverse order. For the latter, the card is moved back by two characters then forward by one with reading, then back by two &c. An error check is made on reading. Error handling.-If a read error occurs when the card is being read to add the escapement values into the units counter, 6 is added into this counter instead of the escapement value of the misread character. If a read error occurs during backspacing of the print head, forward movement with underscoring proceeds immediately (so that it is possible that a beginning portion of the word may not be underscored). Mechanical details of printer (Fig. 2).-When a print cycle is initiated, a print shaft 103 rotates, and the unitary print head 105 is tilted and rotated to a selected character position and is rocked by a print carrier 107 to cause imprinting. Escapement occurs by print shaft 103 rotating cam 111 which via cam follower 113, link 115, and bell-crank 117, moves pawl 119 from engagement with pinion 121. This permits continuously rotating shaft 123, via friction clutch 127, gears 125, 129, 131, shaft 133, and gears 135, 137, 139, to rotate screw 109 to move print carrier 107 axially. Once escapement is started, a magnet 141 is energized to hold pawl 119 out of contact with pinion 121. Escapement clock pulses from photo-electric detection 145 of teeth 143 decrement the escapement counter, magnet 141 being deenergized at count zero. For reverse escapement, spring clutch 150 is energized to communicate rotation of shaft 123 via gears 152, 154, 155, 156 to shaft 133 &c.