GB1124131A - Method of and device for detecting surface elevations in paper and other sheet material - Google Patents

Abstract

1,124,131. Measuring surface roughness electrically. L. URMENYI. March 31, 1966 [May 24, 1965; July 15, 1965(2)], Nos.21897/65, 30089/65 and 30090/65. Heading G1N. A device for detecting surface elevations, e.g. lumps, creases &c. in sheet material comprises, in general, at least one contact member permanently in contact with the surface of the sheet material and at least one feeler member which may either be in contact with the sheet material or arranged above its surface at a distance corresponding to the permissible increase in thickness of the sheet material, the feeler member being longer in a direction transverse to the direction of movement of the sheet material than the contact member. In either case, movement of the feeler member relative to the contact member produces an electrical signal indicating that a surface elevation has just passed, and in the latter case mere contact without relative movement between the feeler member and surface of the sheet material produces an electrical signal. In one embodiment, the feeler member 1, Fig. 1 of provisional Specification 30090/65 which is a stationary rod or strip or a rotating roll contacts the surface of the sheet material 8 as it passes over a supporting roller 9 and carries a capacitor plate 2. A second capacitor plate 4 is mounted on two contact members 3 which may be stationary or rotating. Members 1 and 3 are pivotable about points in a line parallel to their axes. Thus surface elevations passing under feeler member 1, cause the distance between capacitor plates 2, 4 to be altered, which change in capacitance is detected in an output circuit. If the roller 9 runs eccentric or the overall thickness of the sheet material changes, both members 1 and 3 are lifted and lowered simultaneously, producing no change in the capacitance of plates 2 and 4 and therefore no output signal. One of the members 3 may be omitted, Fig. 2 (not shown). Alternatively a number of feeler members and associated contact members may be arranged in staggered positions across the sheet material, Fig. 4 (not shown). In a further modification, two feeler members (1), (3), Fig. 5 (not shown), may be arranged side by side each carrying a capacitor plate (2), (4) which act with a common capacitor plate (10), which may be fixed or carried by contact members. The detecting circuit for this embodiment may consist of a bridge, Fig. 6 of provisional Specification Cog. 1,124,131 (not shown), in which capacitances (13), (14), between members (2) and (10) and (4) and (10) are arranged in two adjacent arms, with further variable capacitances (15), (16) in parallel if required. The other arms consist of a fixed resistance (11) and a variable resistance (12), which is arranged so that under normal conditions the bridge is balanced. In a further modification, Fig. 3 (not shown) a choke (4) may be mounted on the feeler member, the contact members carrying a U-shaped magnetic core provided with coils (6), (7). Displacement of the feeler member relative to the contact members thus causes a change in the self inductances of the coils (6), (7) or in the mutual inductance between the coils (6), (7). In a modification for detecting folds running transversely of the sheet material, the feeler member 1 is associated with an auxiliary feeler member (17), Fig. 7 of provisional Specification Cog.1,124,131 (not shown), mounted in fixed relation to the feeler member 1, in such a way that it is just out of contact with the sheet material. Thus when a fold passes under the member (17), providing it is thicker than the distance this member is situated above the surface of the sheet material, it causes the member (17) to be raised, thereby raising the member 1 without displacing the member 3. A fault signal is thereby produced as the fold passes under the member (17), but is not repeated as it passes under the member 1, when both members 1 and 3 are raised by it. In a more detailed embodiment, Fig. 9, the contact members 3 are mounted on a member 25 which also carries capacitor plate 14 insulated from 25 by members 23. The feeler member 1, which may be fixed or rotatable, see Fig. 11 (not shown), is similarly carried on a grounded capacitor plate 2, insulated from the feeler member by member 29. Members 25, 2 are pivoted at points 24, 28 by means of cross strips 21, 22 26, 27, on a bracket 20. An adjustable screw 32, co-operating with a leaf-spring 31, see also Fig. 10 (not shown), is provided by which the feeler member may be positioned either in contact, or an adjustable distance above the surface of the sheet material. In operation, with the feeler member held just above the surface of the material, if a small wrinkle passes under the feeler member 1, while it may not be sufficient to lift the member up, by merely contacting the feeler member, which may be connected, e.g. to the grid of an amplifier (66), Fig. 12 (not shown), forming part of cathode follower, a fault signal may be produced due to the reduction of the grid voltage. If such wrinkles are not required to be detected, or if the feeler member is positioned in contact with the surface of the material, the insulating member 29 may be omitted, a fault signal only being produced if the feeler member is lifted relative to the contact members. If the contact members 3 are lifted, they will, through the action of the leaf-spring 31, also lift the member 1 so that again no fault signal is produced. In a detecting circuit for use with this embodiment, Fig. 5 of provisional Specification Cog. 1,124,131 (not shown), the variable capacitance (19) of the device, which may be a number of such connected in parallel, is connected in a bridge circuit, which is arranged, under normal conditions, so that its out of balance voltage, after amplification in amplifier (25) and rectification, is approximately equal to the rectified voltage taken from a potentiometer 16. These voltages are compared by being applied to the grids of two triodes (34), (35) connected in adjacent arms of a balanced bridge. If, e.g. a lump, passes, the out of balance voltage of the first bridge changes, the voltages across the triodes (34), (35) therefore change and this bridge becomes unbalanced, transmitting a signal to two R.C. circuits of different time constants which are connected to the grids of two further triodes (42), (43) connected in a further balanced bridge circuit. If the time of the pulse is short, then, because of the relatively long time constants of both R. C. circuits, the amplitudes of the signals reaching the triodes (42), (43) is negligible and this bridge remains balanced. When a signal of longer duration, i.e. that resulting from a crease, is applied to the two R.C. circuits, because of the difference in time constant of these two circuits, the amplitude of the pulse arriving at the grid of valve (42) is larger than that at valve (47) therefore the bridge becomes unbalanced and a relay (54) connected between the cathodes of the two valves is energized opening contact (55) and closing contact (56). When this latter contact closes, pulses are transmitted from a pulse generator (57) to a computer (58), which operates a gate solenoid (59) just before the leading edge of the sheet containing the fault arrives at the gate. Pulse generating devices (61), (62) transmit pulses to the computer just before and after a future cut line appears and just before and after the leading edge of a sheet appears, in order that the gate mechanism may be correctly controlled. At the end of a pulse, the relay is reset in its original position with contact (55) closed and contact (56) open ready to receive the next fault signal. With the modification of Fig.4, the coils (6), (7) may either be connected in series as variable self inductances (14), (15), Fig.7 (not shown), in one arm of a bridge which replaces the capacitative bridge in Fig. 5 (not shown) or they may be arranged as a variable transformer (14), (15), Fig.6 (not shown), which again replaces the capacitative bridge in Fig. 5 (not shown).