GB1495599A - Printing apparatus - Google Patents

Abstract

1495599 Printers DATAPRODUCTS CORP 12 May 1975 [15 May 1974] 19911/75 Heading G4H [Also in Division G3] An impact printer has a hammer bank 12 movable along the print line 50, i.e. to reduce the number of print hammers. A character drum 26 rotates and a character is printed when a hammer 23 hits the back of paper 18 whose front face presses print ribbon 29 against the desired character on the drum. The bank is moved along line 50 by a voice coil motor 64 (Fig. 8, not shown) and its velocity sensed by a magnetic velocity transducer, e.g. a tachometer (Fig. 2, not shown) giving a D.C. output whose amplitude and polarity give bank speed and direction. An optical positioner transducer controls bank motion and positioning using circuitry (Figs. 3 and 4, not shown). An error signal proportional to the difference between the applied velocity command signal and the tachometer signal is produced by a summing amplifier and is fed back to the summing amplifier which causes the hammer bank motor 64 to move at the commanded velocity. As the bank moves from one position to another, the position transducer output crosses the zero level three times and, when three crossings have been detected, deceleration is started. The bank is held at the desired position by the position servo loop and this position is known by the printer logic. The position transducer (Fig. 5, not shown) comprises a light emitting diode source, on a position encoder track with light and dark areas, co-operating with two photo-cells. After initialization the hammer bank is moved between two positions (right and left). The positions are spaced a distance equal to the character spacing so each hammer can be positioned in two print stations. In the bank, the hammer spacing is twice the character spacing so the number of hammers required is only half the number of printable characters per line. Alternatively, the hammer spacing can be made three times the character spacing.