Patent GB-1436960-A (GB)
Title: Method and apparatus for detecting the presence of a white ribbon in a tyre
IPC: G01B15/02
Filed: 1973-12-21
Abstract: 1436960 White wall tyre detector FUJI DENKI SEIZO KK and YOKOHAMA RUBBER CO Ltd 21 Dec 1973 [27 Dec 1972] 59608/73 Heading G1A A white ribbon in the sidewall of a vehicle tyre is detected by passing a beam of radiation from an x-ray or γ-ray source first through one sidewall alone and then through the other sidewall alone and comparing the transmitted intensities.  In the manufacture of white wall tyres a layer of white rubber compound is applied to one sidewall and covered with black rubber and the tyre is then vulcanized. The invention permits vulcanized tyres to be sorted according to whether or not they contain buried white rubber. The wall containing the white rubber is also identified to facilitate the removal of the overlying black rubber layer. The white rubber contains zinc oxide or titanium oxide which absorbs x-rays and 7-rays to a greater extent than black rubber. As shown, Fig. 3, a radiation source 2 which may be an x-ray or γ-ray generator projects a beam of radiation to a detector 3, which may be an ionization chamber. A tyre 1 is moved across the beam and produces a signal as shown in Fig. 4A, the variations being due to the different thicknesses and combinations of sections of the tyre. The peaks P1 and P2 are obtained when the beam passes through only the lower and upper sidewalls respectively so that the relative heights of these peaks can be used to determine which wall contains the white strip 14 if this is present. The output of the detector is applied to a circuit 31 which produces an output signal B representing the second differential and this is applied to a shaping circuit 32 which produces output pulses at the positive transients corresponding to the minima P1a, P2a, P3a, P4a. These pulses clock a counter 33 which provides outputs sequentially on lines I to IV which trigger two flip-flops FF 1 and FF2 to enable peak valve circuits 34, 35 for duration of the excursions between points P1a and P2a and points P3a and P4a respectively. Circuits 34 and 35 therefore store the heights of peaks P1 and P2 respectively and these signals are compared by substraction to produce a signal H which is positive for tyres with upper white walls, negative for tyres with lower white walls, and zero for black tyres, a decision circuit 37 producing a corresponding output at terminals WU, WL and BL respectively. Instead of taking the difference comparision circuit 36 may determine the ratio of the difference between the signals to the value of the first signal since this produces a smaller variation in output value for differences in size and thickness of the tyre. Circuit 31 may also identify the minima by a process involving determining when the first differential is zero. The angle of incidence of the radiation beam is preferably selected between angles Kl and K2 Fig. 3 but an angle greater than K1 (but less than 90 degrees) may be used in which case the output signal has two maxima and three minima on either side of the cental peak. The counter 33 is modified to produce five outputs which are connected to enable the peak detectors 34, 35 over the two periods closest to the central peak Fig. 5 (not shown). The internal diameter of the tyre may also be determined by gating pulses from a tyre speed transducer 4 to a counter 5 during the interval between points P1a and P3a (or P2a and P4a) these corresponding to the passage of the two edges of the same tyre wall.