GB1249321A - Improvements in and relating to information retrieval apparatus - Google Patents

Abstract

1,249,321. Positioning systems. SELECTRO-MICRO CO. Ltd. 8 Sept., 1969 [3 July, 1968, 12 July, 1968], Nos. 31671/68 and 33307/68. Heading G4H. In a film positioning unit the count in a counter 10 (Fig. 1) holding the datum position of the film is initially incremented by an amount representing the maximum count of an auxiliary counter 56, the count in the counter 10 which is incremented as the film moves then being compared with the required position represented by the data in store 18: At equality i.e. when a signal exists on lead 34, the film continues to move at a slow speed with the incremental pulses being fed to count down the auxiliary counter 56 until its count reaches zero when the film is at the required position. The direction of movement of the film is determined by the relative values of the datum and required positions. Register stages 70A, 70B, 70C, 70D (Fig. 2) control the pulsing of the counter 56, the movement of the film at high speed, the slowing down of the film at the equality output from the comparator and the stopping of the film when the counter 56 has been counted down to zero. The film may be returned to its original datum position by operating a switch D to alter the direction of movement of the film and to set a destination/datum store 94 to its " O " state. The system then operates as before except that the comparator equality signal is given on lead 36 and at equality of the datum and actual position register stage 70E is actuated to release the film cassette. The pulses as the film moves are derived from a photo-cell 5 sensing markers on the film, the counter being set to count either light to dark or dark to light transitions in accordance with the direction of movement. When a required position is keyed in contact A2 (Fig. 4 not shown) is closed to enable a shift register (208) so that as the keys are selectively operated to read in a four digit word four stages of the shift register are sequentially enabled to control a routing gate (204) connected to the destination store. When a datum position is keyed in, a shift register (210) is enabled so that the four digits are fed via a further routing gate (206) to the datum store and also under the control of sequential pulses on four leads (234, 236, 238, 240) to the counter 10.