Background to the Invention Glossmeters are devices used to measure the gloss or shininess of a surface. Conventionally, a parallel beam of light is projected onto the surface to be measured at a defined angle to a normal of the surface. At the same angle to the normal, reflected light from the surface is focused through a lens and onto a photo-sensitive cell. The intensity of the reflected light determines the gloss value of the surface, with values ranging between zero gloss units (representing zero reflectance) and one thousand gloss units (representing an ideal mirror).

Glossmeters are conventionally used in industries such as the automobile industry, the paints and coatings industry, the paper industry and other similar fields where the surface characteristics of the finished product are of importance. There is a substantial difference between the surface characteristics of samples in these industries. For example, the gloss value of a polished painted car panel would be approximately 100 gloss units at a 60 degree angle of incidence. This is much greater than that of a conventional mat-finish piece of paper which would typically have a gloss value of approximately 10 gloss units at the same angle of incidence. Conventional glossmeters suitable for use in both these examples require complex amplification circuitry and digital signal processing capacity to enable them to manage gloss values differing by orders of magnitude. In addition, even within the same industry there can be a substantial difference between the gloss values of different products.

There is therefore a need for a cheap and simply-constructed glossmeter that is capable of providing accurate results over a wide range of gloss values.

Summary of the Invention According to the present invention, a glossmeter for measuring the gloss of a surface of a sample comprises an integrated circuit detector device arranged to provide an output representative of a light intensity detected at a light receiving region of the detector device, the output being coupled directly to a microcontroller, an output of the glossmeter representing the measured gloss based on the output of the detector device, in which the integrated circuit detector device comprises a controllable photo-detecting array responsive to an applied control signal to adjust the sensitivity thereof, thereby controlling the output of the glossmeter.

The invention provides a glossmeter having a controllable photo-detecting array which enables the sensitivity of the device to be easily varied. In addition, since the integrated circuit detector device is arranged to provide an output directly to the microcontroller, there is no requirement for any intermediate analogue circuitry connecting the integrated circuit detector device and the microcontroller. Therefore, the cost and size of the device can be greatly reduced.

Preferably, the array comprises a plurality of photosensitive pixels and the applied control signal is operative to switch a selected proportion of said pixels on or off.

Since the device can be used in states in which different proportions of the photosensitive

pixels are on, the sensitivity of the array is easily controlled, thereby enabling, for example, high resolution in the glossmeter output at low gloss values.

Preferably, the detector device comprises a light intensity-to-frequency converter thereby providing an output frequency signal to the microcontroller having a frequency representing the intensity of the detected light.

Preferably, the glossmeter further comprises a light source to irradiate the surface of the sample and more preferably the light source is a light-emitting diode arranged to provide luminance C light.

Preferably the output frequency signal is scalable by a programmable factor.

Since the output frequency signal is scalable by a programable factor, it can be maintained in a predetermined range to allow for more efficient signal processing.

Brief Description of the Drawings An example of the present invention will now be described in detail below with reference to the accompanying drawings, in which: Figure 1 shows an example of a glossmeter according to the present invention; Figure 2 shows a block diagram of an example of a light-to-frequency convertor used in the glossmeter according to the present invention; Figure 3 shows a schematic representation of an example of a photo-detecting array suitable for use in the present invention; and,

Figure 4 shows a flow-chart of the main steps in the processing performed by a microcontroller used in the glossmeter according to the present invention.

Detailed Description Figure 1 shows an example of a glossmeter 1 according to the present invention. The glossmeter includes a light source 2 and an integrated circuit detector device 4 arranged in a fixed angular relationship to the normal 5 of a sample 6 being tested. The light source 2 and detector 4 may be arranged at any suitable selected angles to the normal 5. Typically angles of 20°, 45°, 60°, 75° or 85° to the normal may be used. As will be explained below, control of the sensitivity of the glossmeter enables the angle to be maintained at a constant value substantially independently of the gloss value of the sample surface, where previously it would have been necessary to make some adjustment.

The light source 2 has a mask 3 at its output and the detector device 4 has a mask 7 at its input. These are used to control light beam divergence angles in accordance with international standards for gloss measurement.

The glossmeter 1 also includes a system of lenses 8 and 10 used to ensure the light incident on the sample and reflected from the sample is correctly focused for detection by the integrated circuit detector device 4. A user interface 11 is provided to display information to a user about the sample being tested and to act as an input terminal to enable a user to control the operation of the glossmeter.

The detector device 4 includes a light-to-frequency convertor 12 which is shown in and will

now be described with reference to Figure 2. The convertor 12 has an array of photo- detecting elements such as photodiodes 14 arranged to receive reflected light from the surface of sample 6. A current-to-frequency convertor 16 is coupled to the photodiode array 14 and is arranged to produce a frequency output signal in dependence on the intensity of light detected by photodiode array 14. The output from the current-to-frequency convertor 16 is coupled directly to the microcontroller (not shown) where the frequency signal is processed and converted to a light intensity value for display to a user at the user interface 11.

In use, the light source 2 is switched on to cause a beam to irradiate the surface of the sample 6 via first lens 8. The incident light is reflected by the surface of sample 6 and focused on photodiode array 14 via second lens 10. The sensitivity of photodiode array 14 is controlled by two logic inputs 18 and 20 using an electronic iris technique (effectively an aperture control) to change the response of the photodiode array 14 to a given intensity of incident light. As will be explained below, in this example the sensitivity of the photodiode array can be set to one of three relative levels: 1,10 or 100 providing two orders of magnitude of possible variation in sensitivity. These levels indicate the proportion of the photodiodes of the array which are rendered active. This allows the response of the device to be optimised to a given light intensity level while preserving the full-scale output- frequency range.

Figure 3 shows a schematic representation of an example of a photo-detecting array suitable for use in the present invention. In this example the array is made up of a number (ten) of rows and columns of photosensitive pixels each of which may be in an ON or OFF state.

In Figure 3A, all the pixels are ON thereby ensuring the array has a maximum possible sensitivity. Figures 3B and 3C show, respectively, 10 pixels and 1 pixel being ON. The ratio of sensitivity of the array between the states shown respectively in Figures 3A, 3B and 3C is therefore 100: 10: 1, i. e. two orders of magnitude of variation in the array sensitivity.

Adjustment of the sensitivity of the photodiode array alters the effective sensing area of the array. Conventionally, if the sensitivity of the glossmeter was not sufficient to distinguish between two low values of light intensity reflected from a sample, it was necessary to adjust the angle of incidence between the incident light and the sample surface accordingly, to effect an increase in the intensity of the reflected light. The glossmeter of the present invention enables a user simply to adjust the sensitivity of the glossmeter so that no physical change to the angular orientation of the glossmeter relative to the sample surface is required. An additional lens 9 may be provided to convert the focussed beam of light to a parallel beam of light. Typically this would be arranged between the mask 7 and the detector 4 to provide a substantially uniform distribution of light across the detector surface.

The photodiode array 14 provides a current representative of the intensity of light incident on it. The current is coupled via connecting line 22 to current-to-frequency convertor 16 which is arranged to receive the generated current and produce an output frequency signal in dependence on it. The output frequency signal may be scaled by the converter by, for example, internally connecting the pulse train output of the convertor to a series of frequency dividers. Typically, scaling factors that may be used are 2,10 or 100.

The output frequency scaling allows the output range of the current-to-frequency convertor

16 to be optimised for a variety of measurement techniques. The output from the convertor 16 is coupled to a microcontroller (not shown) where a value for the light intensity is determined.

Figure 4 shows a flow-chart representing the structure of the code which may be programmed into the microcontroller used in the glossmeter of the present invention. In a first step, an input signal from the user interface 11 is detected. An activation signal is triggered by the user pressing a READ key (not shown) when a test is to be done. When the READ key is pressed, a voltage is generated which causes the glossmeter to power up.

When the glossmeter is powered up, a current of approximately 10mA is drawn in a standby mode and a current of approximately 25mA is drawn during a sampling routine described in more detail below.

When the read key is pressed, the microcontroller calls a capture detector routine which switches on the LED 2 and sets up the detector device ready to perform a test. With the detector device running and producing a frequency output signal a sampling routine is established. In this example, the software is arranged to count sixteen rising edges of the frequency waveform coming from the current-to-frequency convertor and initialises a timer.

The timer runs as the next sixteen edges are counted and then is stopped. A timer value is therefore determined. The timer value at the end of this period is inversely proportional to the frequency of the frequency output signal and is thus inversely proportional to the intensity of the light reflected from the surface of the sample 6. The value is then coupled to the display at the user interface 11 and may also be stored in an associated on-board memory.

Therefore a low-gloss surface returns a high reading whereas a high-gloss surface returns a

low reading. The reading output is calibrated by a software constant programmed into an associated non-volatile memory and then converted to gloss units before display. Once a test is completed, the glossmeter may be switched off or may automatically return to an unpowered state thereby conserving power. A battery may be used as a power source, in which case power conservation is important.

In one example, the display may comprise an alphanumeric LCD display. Such display devices are cheap and durable and would therefore not add substantially to the cost of the glossmeter. The microcontroller may also be programmed to send the data stored in the on- board memory to a serial printer and/or download the information to a windows based software application.

An example of a programmable light-to-frequency convertor that may be used in the glossmeter according to the present invention is the TSL230 chip set manufactured by Texas Instruments. The device comprises a programmable light-to-frequency convertor having a configurable silicon photodiode and a current-to-frequency convertor on a single monolithic CMOS integrated circuit.

An example of a suitable microprocessor that may be used as the microcontroller in the present invention, is the PIC16C74A microcontroller manufactured by Microchip. It is an 8-bit low power CMOS device having RISC architecture and a five channel on-board A-to-D convertor. It operates over a 2.5-6.0 volt voltage range and has 4K EEPROM program memory and 192 bytes of RAM for data storage.

An example of a light source which may be used, which also helps reduce the cost of the glossmeter of the present invention, is a 3mm white-discreet LED manufactured by Marl Optosource Ltd. The LED provides luminance C light as required to conform to the CIE standard on gloss measurement. Each of the components mentioned in the detailed description are provided only as examples of possible components and are in no way meant to be limiting.

The present invention provides a durable, cheap and accurate glossmeter which overcomes the problems of conventional devices discussed above. Since the integrated circuit detector device is arranged to provide an output directly to the microcontroller, there is no requirement for any intermediate analogue circuitry connecting the integrated circuit detector device and the microcontroller. In addition, the use of a controllable photo-detecting array responsive to an applied control signal to adjust its sensitivity provides a simple and convenient way of adjusting the sensitivity of a glossmeter without the requirement for complex processing circuitry.