GB2160972A

GB2160972A - Improvements in the detection of variation in colour shade

Info

Publication number: GB2160972A
Application number: GB08516347A
Authority: GB
Inventors: Kundan Desai
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-06-29
Filing date: 1985-06-28
Publication date: 1986-01-02
Also published as: GB2160972B; GB8416654D0; GB8516347D0

Abstract

An apparatus for detecting colour mismatch is provided in which the electric signal from a photosensitive detector 14 representative of the amount of light reflected by a sample surface (not shown) is separately compared at 18,19 with two threshold signals and the results of the two comparisons are applied separately to respective indicators 24,27 and are also combined at 30 for application to a third indicator 31. The apparatus is contained in a housing having an internally black tube at one end through which the sample surface is both illuminated by light sources 11,12 energized by a regulated power supply and 'seen' by the photosensitive detector, the outer end of the tube being placed in contact with the sample surface to ensure constant light path distances. <IMAGE>

Description

SPECIFICATION Improvements in the detection of variation in colour shades This invention realtes to the detection of variations in colour shades, especially of manufactured goods.

Manufactured articles, and particularly those for supply to the general public or domestic market are normally finished in aesthetically pleasing colours; but there is a problem of maintaining the same colour shade in respect of articles that are supposed to be all of the same colour since a mismatch in colour shades can result in customer dissatisfaction.

Colorimeters are currently available for detecting colour mismatch. However, they are costly and furthermore the least expensive of them, so far as I am aware, suffers from the considerable disadvantage that it cannot be used on a continuous basis as the components lose sensitivity on heating up, making it necessary to switch the apparatus off frequently for restandardisation. It is therefore an object of this invention to provide an inexpensive apparatus that is not subject to the foregoing disadvantage.

According to the present invention, apparatus for detecting colour mismatch comprises a light source energised by a regulated power supply to illuminate the samples, a photosensitive detector to provide a signal representative of the amount of light reflected by each sample surface, two comparators respectively comparing said signal with threshold signals from two reference sources, and three indicating means, such as light-emitting diodes, two of which are energised, respectively, by the two outputs of the comparators individually while the third is energised by a circuit receiving the outputs of both comparators, whereby said third indicating means indicates an acceptable colour match while the other two respectively indicate a colour shade under or over the correct shade.

Arrangements according to the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of one embodiment of the invention, and Figure 2 is a diagram of the regulated power supply for lamps of the circuit of Fig.

1.

Referring firstly to Fig. 1, illumination for the coloured surface to be tested is provided by a pair of lamps 11, 1 2 in series with a resistor 13, and the light reflected off the surface falls on a photodiode 1 4. The signal from the photodiode is applied to the input of an amplifier 1 5 having a feedback circuit consisting of a capacitor 1 6 and a variable resistor 1 7 in parallel. The amplifier output is then applied to one input terminal of each of two comparators 18, 19.

At the comparator 1 8 the amplified photodiode signal, applied to the more negative input terminal, is compared with a reference signal obtained from the junction point of a reference signal circuit including a calibrating potentiometer and a fixed resistor 21 connected in series between + volts and ground. At the comparator 1 9 the amplified photodiode signal, applied to the more positive input terminal, is compared with a reference signal obtained from the junction point of a second reference signal circuit including a fixed resistor 22 and a calibrating potentiometer 23 connected between + volts and ground. The output of the comparator 1 8 is applied to a light-emitting diode 24 via an amplifier 25, the other terminal of the LED being connected to ground via a resistor 26.The output of the comparator 1 9 is applied to a second lightemitting diode 27 via an amplifier 28, the other terminal of the LED being connected to + volts via a resistor 29.

The outputs of the two comparators 18, 1 9 are also gated together at 30 and applied to a third light-emitting diode 31 via an amplifier 32, the other terminal of the LED being connected to + volts via a resistor 33. If the colour shade under examination is under or over the correct shade in regard to the amount of light it reflects, one or other of the two LEDs 24, 28, which are red, will be illuminated to give a colour shade mismatch or reject signal. However, if the colour shade is an acceptable match the third LED 31, which is green, will be illuminated to give a pass or acceptance signal. The thresholds of acceptibility can be set as desired by means of the potentiometers 20 and 23. The variable resistor 1 7 is not a potentiometer but a decade resistance box which is used as a colour shade selector.

To provide a regulated power supply for the lamps 11, 12, the circuit of Fig. 2 can be employed. This is basically an RC41 94D integrated circuit 34 which is a dual monolithic voltage regulator housed in a 1 4-pin package and featuring internal current limitation and thermal shut-down. + 1 5 volts and - 1 5 volts are connected to pins 14 and 7, respectively, the + 1 5 volts line be coupled to ground via parallel capacitors 35 and the - 1 5 volt line be likewise coupled to ground via capacitors 36. + 12 volts and - 12 volts regulated are taken from pins 1 and 8, respectively, the + 1 2 volt line being coupled to ground via parallel capacitors 37 and the - 1 2 volt line being likewise coupled to ground via capacitors 38. Pin 12 is directly connected to ground and pins 3 and 10 are respectively coupled to ground via a capacitor 39 and a resistor 40. Pins 5 and 11 are respectively coupled to the + 1 5 volt line via a capacitor 41 and a resistor 42.

The circuitry is housed in a box with an internally black tube at one end through which the sample surface being tested is illuminated and the photodiode 'sees' the surface. The outer end of the tube is placed in contact with the sample surface so that the lamps and the photodiode are the same predetermined distance away from the sample surface in every test. The tube is protected by a removable cover when the instrument is not in use.

If desired, diodes can be provided to protect the instrument against a reversal of input polarity due to misconnection by the user. A single lamp can be employed instead of the two lamps 11, 12.

Claims

1. Apparatus for detecting colour mismatch, comprising a light source energised by a regulated power supply to illuminate the samples, a photosensitive detector to provide a signal representative of the amount of light reflected by each sample surface, two comparators respectively comparing said signal with threshold signals from two reference sources, and three indicating means, such as lightemitting diodes, two of which are energised, respectively, by the two outputs of the comparators individually while the third is energised by a circuit receiving the outputs of both comparators, whereby said third indicating means indicates an acceptable colour match while the other two respectively indicate a colour shade under or over the correct shade.

2. Apparatus according to Claim 1, wherein the signal of the photosensitive detector is applied to the comparators via an amplifier network including variable resistance means for selecting the colour shade.

3. Apparatus according to Claim 1 or Claim 2, further comprising respective potentiometers for setting the reference thresholds.

4. Apparatus according to Claim 1 or Claim 2 or Claim 3, enclosed in a housing with an internally black tube at one end through which the sample surface being tested is illuminated and through which the photosensitive detector 'sees' the surface, the outer end of the tube being adapted to be placed in contact with the sample surface.

5. Apparatus for detecting colour mismatch, substantially as described with reference to the accompanying drawings.