GB1396560A - Superposed sheet detection - Google Patents

Abstract

1396560 Feeding sheets XEROX CORP 12 Sept 1972 [16 Sept 1971 21 Oct 1971] 42325/72 Heading B8R [Also in Division G1] In apparatus for monitoring the thickness of successively conveyed sheets of material, e.g. in a printing press or a copy reproducing machine, signals representing the thickness of the corresponding sheets are generated and an initial one of the signals is compared with each successive signal. In a copy reproducing machine, Fig. 1 (not shown), sheets from a stack are conveyed to the machine via a thickness monitoring station. The monitoring station shown in Fig. 2, consists of a fixed roller 42 which carries a belt for conveying the sheets to the machine, and a rotatable member 101 which rotates anticlockwise to allow a sheet through the space between the roller 42 and member 101. The member 101 co-operates with a strain gauge 105 as shown, the gauge being arranged in a D.C. bridge circuit, Fig. 3, In an alternative, Fig. 4, a light source 110 co-operates with a photo-resistor 111 so that its resistance varies with the position of impingement of light thereon. In further alternatives, a variable capacitor or variable inductor may co-operate with member 101, in which case an A.C. bridge is utilized, or a rotary potentiometer may be used, or the strain gauge may co-operate with any suitable device responsive to the thickness of sheet material. As shown in Fig. 3, the bridge output is connected to a switch 308 which may contact either a terminal 309 or a terminal 310. Upon detection of the leading edge of the first sheet conveyed to the machine, e.g. using a mechanical switch or a photo-cell, a switch control 318 causes switch 308 to contact terminal 309, the bridge output, which represents the thickness of this first sheet, then being stored at 311. The detection of the leading edge of the next sheet then causes switch 308 to contact terminal 310 and switches 315, 317 to close for a preset time. During this time the bridge output, which represents the thickness of the next sheet, is compared with the stored signal in a comparator 316. If the difference does not exceed a threshold, monitoring of the next sheet proceeds as above. However, if the difference does exceed a threshold, indicating that a sheet is too thin, too thick or comprised of superposed sheets, a switch 319 is operated which causes the sheet or sheets to be rejected and a switch 313 to be closed whereby the storage device is discharged. This completes a cycle, and a new cycle may then be initiated. Means are provided in the machine for detecting whether the first sheet supplied thereto is composed of superposed sheets whereby a switch 314 is closed to discharge the storage means. The output of the bridge may be applied to digital circuitry, Fig. 5 (not shown), for comparing the thickness signals.