GB682303A - A machine for regulating a moving stream of objects - Google Patents

Abstract

682,303. Letters sorting. POSTMASTER GENERAL. Feb. 18, 1949. No. 4492/49. Class 78 (i). [Also in Group XL (b)] Before being fed to a facing machine as described in Specification 675,556, [Group XL (b)], letters longer than a pre-determined maximum and following the previous letter with less than a predetermined minimum spacing are rejected photoelectrically. As shown letters follow each other along a route 10 successively interrupting light beams to the photo cells AP, BP and CP. Distance AB represents the minimum letter spacing and distance AC the maximum letter length. Each interruption and restoration of the light beam produces a negative pulse from the photo cell which is used to reverse the condition of an electronic device such as that shown in Fig. 2 which has two stable conditions. If VI conducts a negative pulse its suppressor grid blocks it and V2 conducts until a negative pulse is applied in turn to its suppressor. In a modification, Fig. 3 (not shown), the circuit has only one stable condition which is reversed by a pulse but the system restores automatically when the charge on a condenser connected between the anode of V2 and the grid of VI has leaked away. Each reversal produces a positive pulse at P. The two operations which the apparatus performs are described with reference to Figs. 5 and 6 which must be read by means of the key forming part of Fig. 6. Rejecting a letter following too closely the previous one (Fig. 5). As a first letter interrupts the light to photo-cell B the negative pulse produced reverses the condition of a device 15 as described above and the positive potential 17 resulting is applied to a known gating valve 14 (Fig. 4, not shown). The next letter interrupts light to a cell A reversing a device of the modified self-restoring type which also supplies a pulse to the gating valve. Unless the first letter has left beam B, the negative pulse produced as it leaves restoring the device 15 and cutting off positive potential 17, positive potentials 17 and 18 together cause gating valve 14 to conduct and operate a further electronic device 20 and the positive potential 21 produced is used to operate a diverter (not shown) which pushes the letter out of the stream. As the second letter leaves photo-cell A, device 20 restores to normal. Device 16 restores automatically. Rejecting a long letter (Fig. 6). As the start of the letter passes photo-cell B device 24 operates and applies a positive pulse to gating valve 23. Subsequent darkening of photo-cell C and operation of device 25 applies a further positive pulse to gating valve 23 which will operate unless the trailing edge of the letter has passed A restoring device 24 to normal. The gating valve operates device 29 and the positive pulse produced actuates a diverter to reject the letter. As its trailing edge leaves devices A, B and C, devices 24, 25 and 29 restore.