Patent GB-914890-A (GB)
Title: Improvements in or relating to devices for measuring without any mechanical contact the width or diameter of fixed or movable tapes or wires
IPC: G01B11/08
Filed: 1960-05-27
Abstract: 914,890. Automatic dimension control. INGBER, O. H. May 27, 1960 [May 29, 1959], No. 18762/60. Addition to 868,219. Class 38 (4). [Also in Group XL (b)] General.-The transverse dimension of an object 203, Fig. 1, such as a wire, cable, tube or tape, either stationary or moving, is measured by an apparatus in which an image of the object (illuminated by a lamp 201) is formed by a lens 206 through a diaphragm 207 on to the periphery of a rotating disc 208 beyond which is located a photoelectric cell 217. The periphery of the disc (a portion of which is shown developed in a straight line in Fig. 2) is formed with equal width slots 208 which (in one arrangement) are arranged with odd numbered slots 208i equally spaced by distance A and even-numbered slots 208p equally spaced by a different distance B, whereby the odd-numbered slot pitches e i , e iii , e v  &c. decrease progressively and the even-numbered slot pitches e ii  e iv  &c. increase progressively, with the sum of two adjacent pitches, e.g. e i +e ii  (termed a group), remaining constant. The resulting photo-electric cell signal includes a train of impulses, as shown in Fig. 4a, brought about by the occlusion of successive slots by the object, in which (for an object dimension l as illustrated) even-numbered pulses S 2 , S 4  &c. progressively increase in amplitude, whilst odd-numbered pulses S 1 , S 3 , S 5  progressively decrease in amplitude to zero and then increase negatively of the mean value of the signal, the zero or minimum value occurring when the object dimension corresponds with the slot pitch. By selecting the appropriate series of pulses, the odd ones in the example considered, and by detecting the minimum or zero point in each cycle of pulses (i.e. the phase point in each revolution of the disc), it is possible by counting the pulses from the beginning of the cycle to obtain a measurement of the object dimension. To facilitate the selection of the minimum point, the pulses of one polarity are first reversed (in practice by differentiation and selection of the appropriate components) so as to derive a waveform as shown in Fig. 4b. The odd pulses correspond to one range of dimensions and the even pulses to another. Selection of the appropriate pulse series permits measurement in either range. More than two ranges may be provided, for example three, see Fig. 7 (not shown), by arranging the slots in constant width groups of three. Variation in the range of dimension may also beeffected optically by the provision of a mechanism 206a, Fig. 1, for moving the lens so as to alter the size of image of object 203 formed on the disc. The diaphragm, Fig. 6 (not shown), comprises a pair of plates whose spacing and inclination with respect to the disc radius are adjustable. The spacing L, Fig. 2, is arranged to correspond to one or more whole groups of pitches. Measurement of wire diameter.-The application of the invention to wire measurement and the control of its manufacture is illustrated in Figs. 11, 11a. The impulses from photoelectric cell 217 (assumed to be working with a disc having two pitches per group where the wire dimension falls within the range of the odd pitches), after initial amplification, differentiation, limiting and selection of negative components, are applied to trigger a monostable multivibrator 225 having a trigger time slightly less than the time interval for a group. The multivibrator thus ignores even pulses and responds only to odd pulses to generate trains of pulses interrupted by the absence of photo-cell pulses marking the start of each disc rotation and the minimum point where the wire dimension corresponds to the pitch. By means of a group of circuits 226-231, trigger circuits 232 and 237 are caused to generate pulses 232a and 237a coinciding respectively with the start of each cycle and the minimum point. The original multivibrator pulses after passage through a gate 234 (see below) and limitation in amplitude and duration by circuits 235, 236 to form pulses 235a are applied to a ten-step stairwave generator 238, 239 which is reset by pulses 232a at the start of each cycle and whose output is transmitted through a gate 240 in response to the minimum pulses 237a so as to provide a " units " measure of the dimension. The gate voltage is integrated in circuit 241 so as to furnish a mean level measurement of units dimension and displayed on meter 244. Pulses from generator 238, 239 occurring at each tenstep are applied to a similar stair-wave generator 245 which is likewise reset by pulses 232a and has its output gated at 246 by pulses 237a to furnish a " tens " measurement. The gate pulses are integrated in circuit 247 and displayed on meter 248. Automatic control of wire diameter.-The " units " measurement is compared with a voltage from a potentiometer 243 which is set to a value corresponding to a desired " standard " dimension for the wire and any discrepancy employed to effect a correcting control in the wire making machine. A factor termed the " statistical overstepping " of the measured dimension, i.e. the frequency and extent to which the dimension differs from a predetermined critical dimension, is determined by a group of circuits 249, 252-255 in which a square wave from a multivibrator 253 initiated at predetermined unit step selected by adjustment of potentiometer 250 is opposed in circuit 255 by a square wave from a multivibrator 254 initiated by the minimum signal 237a. The resulting square wave whose duration is proportional to the extent of overstepping controls gate 256 to transmit a number of pulses from the original train 235a to integrators 257, 258 to produce a voltage representing " statistical overstepping " which is displayed on a meter 259. The capacitance associated with integrator 257 may be adjusted to two different values which are chosen in relation to a limiting level in integrator 257 whereby there may be obtained measurements of " unweighted statistical overstepping," i.e. a factor determined both by the frequency and magnitude of the overstepping, or " weighted statistical overstepping," i.e. a factor determined solely by the frequency of overstepping. The " statistical overstepping " voltage is compared in circuit 260 with a preset voltage determined by potentiometer 261 and any discrepancy employed to control a relay 262 which causes energization of a motor 263 which controls the setting of potentiometer 243 which determines the desired " standard " dimension. Thus a variation of the " statistical overstepping " from a desired amount causes the " standard " dimension of the wire to be changed. Interpolation to determine intermediate dimensions.-The apparatus operates basically to determine the dimension to the nearest pitch. Interpolation between pitches is effected by a group of circuits 223, 266-268 which produce a stair-case wave 223a, each step of which is synchronized with the start of and lasts for the duration of a cycle. The total amplitude of the wave is controlled to be of the order of the difference of amplitude of the two successive photo-electric cell pulses nearest the minimum. The wave is added to the original impulse train in circuit 222 and has the effect of causing during each cycle of the wave the interruption of synchronization of multivibrator 225 to be produced for a first number of times on one and a second number of times on the other of the two pulses nearest the minimum, the respective numbers depending on the position of the minimum relative the two pulses. The resulting pulse counts when integrated in circuits 241, 247 are thus interpolated to produce an intermediate indication. Reference is made to an alternative arrangement employing a parabolic wave in place of staircase wave 223a. Other features.-Gate 234 through which the photo-electric cell pulses pass to the counting circuits is controlled by circuit 232 so as to eliminate an initial number of pulses when the units count is liable to fall in the range 0-2 and 8-10. This has the effect of causing the " units " indication given by meter 244 always to occupy the centre part of the scale. Compensation for the eliminated pulses is effected in circuits 242 and 249. Alternative methods of eliminating alternate photo-electric cell pulses are described with reference to Figs. 8 and 9 (not shown). One method involves a gating signal developed by a photo-electric cell trigger by slots in the disc disposed concentrically with the measuring slots. The other method uses a separate synchronized multivibrator to develop a gating signal. With this method and that shown in Fig. 11, where the disc has an odd number of slots, the other possible range of measurement is brought into use merely by reversing the disc rotation. The dimension of wire insulation may be determined by measuring the wire before and after it is covered and subtracting either the final measurement voltage or the pulse counts. Three alternative ways of doing this are described with reference to Figs. 13-15 (not shown). Undesirable signals introduced by the diaphragm may be eliminated by the use of disc formed in two portions, one being the photographic " negative " of the other, each portion having a diaphragm, but only one having the image of the object to be measured formed on it.