GB2553830A

GB2553830A - A dust detector and method

Info

Publication number: GB2553830A
Application number: GB1615805.7A
Authority: GB
Inventors: holland Karen; Holland Andrew
Original assignee: Scient Instruments Ltd
Current assignee: Scient Instruments Ltd
Priority date: 2016-09-16
Filing date: 2016-09-16
Publication date: 2018-03-21
Anticipated expiration: 2036-09-16
Also published as: WO2018051101A1; GB201615805D0; GB2553830B

Abstract

Dust detector 10 comprises contact surface 20 for dust particles to contact. Light source device 40 (Fig. 1) illuminates the surface at an angle (e.g. 90, 20-50 or 30 degrees to the surface). Imaging device 30 (e.g. a CMOS sensor or sensors) generates an image of dust on the contact surface such that one or more properties of the particles are detectable. Light source device 40 may comprise one or more LEDs 42, which may emit white, blue, red and/or green light, and be positioned at different angles around axis A. Surface 20 may be the sensor surface, be coated, or include a microlens array. A narrowband filter may be provided. The sensor may include a housing: top portion 14, perhaps annular, may house the light source device and aperture 18; legs 16 may support the top portion on base portion 15.

Description

(54) Title of the Invention: A dust detector and method Abstract Title: A dust detector and method (57) Dust detector 10 comprises contact surface 20 for dust particles to contact. Light source device 40 (Fig. 1) illuminates the surface at an angle (e.g. 90, 20-50 or 30 degrees to the surface). Imaging device 30 (e.g. a CMOS sensor or sensors) generates an image of dust on the contact surface such that one or more properties of the particles are detectable. Light source device 40 may comprise one or more LEDs 42, which may emit white, blue, red and/or green light, and be positioned at different angles around axis A. Surface 20 may be the sensor surface, be coated, or include a microlens array. A narrowband filter may be provided. The sensor may include a housing: top portion 14, perhaps annular, may house the light source device and aperture 18; legs 16 may support the top portion on base portion 15.

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Title: A dust detector and method

Description of Invention

This invention relates to detectors, more particularly to dust detectors and associated methods.

Atmospheric conditions in laboratories and clean manufacturing facilities, generally known as “clean rooms”, are often tested regularly to ensure safe and clean experimental and manufacturing conditions. Dust particles cannot be completely removed from a clean room since these particles may be suspended in the air, carried into a room on clothing or equipment, or may not be filtered by filtering equipment of the clean room (either due to inherent limitations of the equipment or, for example, through equipment failure). Thus, it is important that an assessment of the number of dust particles within the clean room is made with relatively frequent monitoring of dust particle levels in some instances.

There are a number of common methods in which dust particle levels are monitored. Typically, dust particles are measured through airborne monitoring or particle fallout.

Typically, an airborne monitor is located within the clean room and the monitor sucks dust particles into a chamber of the monitor. A light is used in the chamber to illuminate the dust particles suspended in the air in the chamber and the density or number of dust particles is detected optically. An airborne monitor is typically expensive.

Fallout monitors typically include a clean wafer which is positioned on a surface within the clean room. After a predetermined time period the wafer in analysed under a microscope or inserted into an analysis machine and the dust particles are reviewed. This method of dust particle analysis is typically slow and can be expensive.

Such monitors may also be unsuitable for use in all clean environments in which dust particle monitoring is required.

Embodiments of the present invention seek to alleviate one or more problems associated with the prior art.

An aspect provides a dust detector comprising: a contact surface for dust particles to contact; a light source device configured to illuminate the contact surface at a predetermined angle of incidence; and an imaging device configured to generate an image of dust particles on the contact surface from light incident on the contact surface from the light source device such that one or more properties of the dust particles on the contact surface are detectable.

An angle between the contact surface and the light incident on the contact surface from the light source device may be less than about 90 degrees.

The angle between the contact surface and the light incident on the contact surface from the light source device may be between about 20 and about 50 degrees.

The angle between the contact surface and the light incident on the contact surface from the light source device may be about 30 degrees.

The light source device may comprise more than one light source.

The light source device may include four light sources.

The light sources may be positioned at different angles about a substantially central axis through the contact surface.

A light source may be positioned at each of about 0, about 45, about 90 and about 135 degrees about the central axis of the contact surface with respect to an arbitrary radius extending from the central axis.

The light source device may include at least one light-emitting diode.

The light source device may be configured to emit light in a visible spectrum.

The light source device may be configured to emit light in at least one of a blue visible spectrum, red visible spectrum, green visible spectrum and white visible spectrum.

The light source device may be configured to emit light in more than one of a blue visible spectrum, red visible spectrum, green visible spectrum and white visible spectrum.

The light source device may be configured to emit light in more than one visible light spectrum from each of a plurality of different locations with respect to the contact surface.

A dust detector may further include a housing including a top portion which supports the light source device and a base portion which houses the imaging device.

The top portion may define an aperture generally aligned with a substantially central axis of the contact surface.

The top portion may be an annulus.

The housing further may include at least one support leg, and the or each support leg may support the top portion with respect to the base portion.

The imaging device may include a complementary metal-oxide-semiconductor image sensor.

The contact surface may be an upper or outer surface of the complementary metal-oxide-semiconductor image sensor.

Contact surface may include a coating.

The contact surface may further include a microlens array.

The contact surface may comprise two or more contact surface portions.

Each contact surface portion may comprise a separate complementary metaloxide-semiconductor image sensor.

The dust detector may further comprise a narrowband filter.

Another aspect provides a method of detecting dust particles, the method comprising: providing a contact surface for dust particles to contact; illuminating at least a portion of the contact surface at a predetermined angle of incidence with light from a light source device; providing an imaging device which is configured to generate an image of the dust particles on the contact surface using the light from the light source device, and analysing the image provided by the imaging device to determine one or more properties of the dust particles contacting the contact surface.

Some embodiments of the present invention are illustrated, by way of example only, in the figures, of which:

FIGURE 1 is a schematic illustration of a dust detector in accordance with some embodiments of the invention,

FIGURE 2 is a schematic view of a part of the dust detector in accordance with some embodiments of the invention,

FIGURE 3 is a side schematic view through the dust detector in accordance with some embodiments of the invention,

FIGURE 4 is a perspective schematic view of the dust detector in accordance with some embodiments of the invention,

FIGURE 5 is a plan schematic view of a portion of the dust detector in accordance with some embodiments of the invention,

FIGURE 6 is a side schematic view of a portion of the dust detector in accordance with some embodiments of the invention, and

FIGURE 7 is a plan schematic view of a portion of the dust detector in accordance with some embodiments of the invention.

With reference to the figures, some embodiments include a dust detector 10. The dust detector 10 is configured to detect the presence of dust and to determine one or more properties of that dust.

Dust in this instance is intended to include airborne particles that may come from a range of different sources and may have a range of different sizes and shapes.

In some instances, the dust may be from local sources such as the local environment, including: soil particles, pollution, plant pollen, human and animal hairs, textile fibres, paper fibres, human skin cells, and many other materials.

In some instances, the dust may be from remote sources and carried in with equipment or clothing for example. Indeed, dust may also include cosmic dust in some instances (and the dust detector 10 may be used on a spacecraft, for example).

This airborne dust may land on surfaces in the vicinity of the dust detector 10, which may include worktops and equipment, (i.e. dust fallout) and may contaminate those surfaces. In some instances, the direct contamination of the surfaces can corrupt experiments and/or cause operability problems for equipment. In some instances, a similar effect is seen through indirect contamination whereby the contaminated surfaces come into contact with equipment which is then, in turn, contaminated.

Typically, particles of dust have sizes that range from less than 1 micron to greater than 100 microns. Bigger particles (for example, those bigger than 100 microns) will tend to fall out of the air quickly and are generally more easily visible with the naked eye. Medium sized particles (between about 1 micron and 100 microns) will settle more slowly than bigger particles. The smallest particles (below around 1 micron) will take much longer to settle out of the air and some of the smallest particles may never settle if the atmosphere is sufficiently turbulent to keep the dust airborne. The size of a dust particle may be determined by its largest dimension.

In some embodiments, the dust detector 10 is configured to measure the properties relating to dust particles of a size of about 100 microns or less, about 50 microns or less, about 10 microns or less, about 5 microns or less, or about 5 microns to about 1 micron.

The dust detector 10 comprises a contact surface 20 for dust to contact and an imaging device 30, which is configured to generate an image of the contact surface 20 and, therefore, of any dust on the contact surface 20.

The dust detector 10 may also include a light source device 40 which is configured to illuminate at least part of the contact surface 20. The light source device 40 may be located at a predetermined orientation with respect to the contact surface 20 and may be at a predetermined distance from the contact surface 20.

The imaging device 30 may be configured to generate the image of dust that contacts the contact surface 20 using light incident on the contact surface 20 from the light source device 40. In particular, the imaging device 30 is configured, in some embodiments, to generate a measurement image of one or more shadows cast by one or more dust particles that contact the contact surface 20.

In some embodiments, the dust detector 10 may include a housing 12. The housing 12 may include a top portion 14 and a base portion 15, with the top port 14 spaced apart from the base portion 15. In some embodiments, the top portion 14 may be supported with respect to the base portion 15 by one or more support legs 16 which are coupled to both the top portion 14 and the base portion 15. In a typical, in use, orientation, the top portion 14 may be located above the base portion 15 and the or each support leg 16 may extend generally upwardly from the base portion 15 to the top portion 14. Of course, other orientations of the dust detector 10 are possible.

The top portion 14 may carry the light source device 40 and the base portion 15 may house the contact surface 20. As such, the predetermined orientation and/or distance of the light source device 40 with respect to the contact surface 20 may be defined by the relative position of the top portion 14 with respect to the base portion 15 and, in embodiments which include one or more support legs 16, by the one or more support legs 16. Therefore, in these and some other embodiments, the light source device 40 may be positioned in a predetermined location with respect to the contact surface 20.

The top portion 14 may define an aperture 18, and the aperture 18 may be generally aligned with at least part of the contact surface 20. In the typical, in use, orientation a vertical axis may pass through both the aperture 18 and the contact surface 20. The aperture 18 may, therefore, be configured to allow dust particles to fall downwardly onto the contact surface 20. In other words, the aperture 18 may reduce the risk of the top portion 14 of the housing 12 from preventing falling dust from reaching the contact surface 20 (and, therefore, making the measurements by the dust detector 10 inaccurate).

In some embodiments, a centre of the aperture may be generally aligned with a central axis A which intersects the contact surface 20 at a generally central location thereof. In some embodiments, the top portion 14 may form an annulus and the aperture 18 may be defined by that annulus. In some embodiments, however, the top portion 14 may be another shape (for example, a square or rectangular shape) and the aperture 18 could equally be another shape - which need not be the same shape as the top portion 14. In other words, an outer cross-sectional shape of the top portion 14 could be a number of different shapes and an inner cross-sectional shape of the top portion 14 could equally be a number of different shapes (and may be a different shape to the outer cross-sectional shape).

The top portion 14 may be integrally formed with the base portion 15 and/or with the or each support leg 16. However, in some embodiments, the top portion 14 may be formed separately from the base portion 15 and may be connected thereto. In such embodiments, the or each support leg 16 may be integrally formed with either of the base portion 15 or the top portion 14, or may be separately formed and then connected to both the base portion 15 and the top portion 14. In some embodiments, the top portion 14 and the base portion 15 are connected together in a removable manner such that the top portion 14 may be removed from the base portion 15 and then reattached to the base portion 15 - which may aid cleaning for example.

The or each support leg 16 may at least partially define, with the top portion 14 and the base portion 15, one or more side apertures. The one or more side apertures may allow a flow of air over the contact surface 20 in a direction generally parallel to a main plane of the contact surface 20.

In some embodiments, the contact surface 20 may be mounted within a recess in an upper surface 15a of the base portion 15. The upper surface 15a and the contact surface 20 may form a substantially planar face (which may be generally horizontal with the dust detector 10 in a typical, in use, orientation). In other words, an upper part of the contact surface 20 may be generally aligned with an upper part of the upper surface 15a. This may aid in allowing air flow over the contact surface 20 with reduced turbulence.

Accordingly, the provision of one or more side apertures and, in some embodiments the provision of a substantially planar upper surface 15a and contact surface 20, may help the flow of air over the contact surface 20 in a non-turbulent manner. This may improve measurement accuracy and may reduce the risk of a micro-climate being created (i.e. where the conditions on the contact surface 20 are different to those of the clean room).

As discussed, embodiments include a light source device 40 which is configured to illuminate at least part of the contact surface 20. In some embodiments, an angle between the contact surface 20 and the light incident on the contact surface 20 from the light source device 40 may be less than 90 degrees. In other words, the light source device 40 may be configured to illuminate the contact surface 20 from a side rather than from directly above the contact surface 20. The light source device 40 may, therefore, be referred to as a side illumination light source device 40.

The light source device 40 may be configured to illuminate a central part of the contact surface 20 (which may be the part of the contact surface which is intersected by the central axis A). In some embodiments, the light source device 40 may be configured to illuminate substantially the entire contact surface 20 (including the central part thereof).

The angle of incidence of light from the light source device 40 may, therefore, depend on which part of the contact surface 20 is considered. However, when used herein the angle of incidence of light on the contact surface 20 is an angle with respect to the plane of the contact surface 20 at the central part (i.e. at the point at which that plane is intersected by the central axis A in some embodiments).

As such, with reference to figure 2, the light source device 40 may be offset from the central axis A in some embodiments and the angle of incidence of light from the light source device 40 may be angle Y.

In some embodiments, the angle of incidence, Y, may be between about 20 and about 50 degrees. In some embodiments, the angle of incidence, Y, may be about 30 degrees to about 40 degrees and, in some embodiments, may be about 30 degrees.

The light source device 40 may include at least one light source 42. The light source 42 may be a light-emitting diode (LED) and may be configured to emit light in the visible light wavelength range (from around 390nm to around 700nm). Some embodiments have a light source device 40 including at least one light source 42 of a different type (i.e. not an LED) and some light source devices 40 of embodiments may include more than one type of light source 42.

The light source device 40 may include more than one light source 42 (for example, the light source device 40 may comprise two, three, or four light sources 42). Each light source 42 may include a cluster of sub-light sources which may each comprise an individually operable light source itself (such as an individual LED).

The or each of the light source 42 of the light source device 40 may be positioned apart from the central axis A. In other words, each of the light sources 42 may be radially offset from the central axis A (and the radial offset distance may be different for different ones of the light sources 42, if more than one light source 42 is provided).

In some embodiments, more than one light source 42 is provided and the light sources 42 may be arranged around at least part of a circle through which the central axis A passes (e.g. through a centre of the circle) and the circle may extend through a plane which is generally perpendicular to the central axis A. In such embodiments, one light source 42 may be spaced apart from another light source 42 by a portion of the circle’s circumference - i.e. the light sources 42 may be circumferentially spaced around the circle. In some embodiments, this spacing is substantially equal but in others the spacing may take one or more different forms. For example, taking an arbitrary radius of the circle as 0 degrees, the light sources 42 may be positioned at angles of one or more of about 0, about 45, about 90, and about 135 degrees around the circle. In some embodiments, light sources 42 may also or alternatively be positioned at angles of one or more of about 180, about 225, and about 270 degrees with respect to the same arbitrary radius.

Some of the above embodiments include a plurality of light sources 42 which are each located a generally equal distance from the central axis A. In some embodiments, however, the distance of one or more of the light sources 42 from the central axis A may be different to the distance of at least one other of the light sources 42 from the central axis A. As such, in some embodiments in which there are a plurality of light sources 42 provided in the light source device 40, the plurality of light sources 42 may be arranged around at least part of some other shape (i.e. a non-circular shape).

In some embodiments the light source device 40 includes at least one light source 42 which is a different height with respect to a main plane of the contact surface 20 than another light source 42 of the light source device 40.

The light source device 40 may include at least one light source 42 which is configured to emit blue visible light (e.g. in the range 606-668 THz), red visible light (e.g. in the range 400-484 THz), green visible light (e.g. in the range 526-606 THz) or white visible light. In some embodiments, the light source device 40 includes more than one light source 42 and at least one of those light sources 42 is configured to emit light of a different frequency (e.g. a different colour as defined above) to another of those light sources 42.

A single light source 42 comprising a cluster of sub-light sources may include a first sub-light source which is configured to emit light of a different frequency (e.g. a different colour as defined above) to a second of the sub-light sources. In some embodiments, a single light source 42 may be configured to emit light of a range of different frequencies (e.g. using a cluster of sub-light sources). In some such embodiments, a single light source 42 may be configured to emit visible blue, red, green, or white light (as defined above) and there may be a sub-light source provided for each colour. There may be a plurality of such light sources 42 provided, as generally described herein.

In some embodiments, the imaging device 30 may include a complementary metal-oxide-semiconductor (CMOS) image sensor. The imaging device 30 may include a plurality of pixels located across an imaging surface of the imaging device 30. The width of each pixel may be around 6 microns, for example.

The contact surface 20 may comprise part of the imaging device 30 and may be part of the CMOS image sensor. In other words, the contact surface 20 may be a surface of the imaging device 30 and, in some embodiments, of the CMOS image sensor. Indeed, in some embodiments, the contact surface 30 is the upper or outer layer of the CMOS image sensor.

The imaging device 30 may include other types of pixelated image sensor device, for example a charge-coupled device (CCD) may also be used. Thus, in such an embodiment the contact surface 20 may be part of a CCD, and may be a surface of the CCD.

In examples in which the contact surface 20 is part of the imaging device 30, the imaging device 30 will be - accordingly - configured to generate an image of the dust on its contact surface 20.

In some embodiments, the contact surface 20 may be directly exposed to the environment surrounding the dust detector 10. This may be to atmosphere or even to a vacuum in some embodiments.

The contact surface 20 may include a coating 22. The coating 22 may be around 100nm thick and the coating 22 may include Parylene^R™ The coating 22 may be provided between the CMOS image sensor and the environment around the dust detector 10.

In some embodiments, the contact surface 20 may include a microlens array (not shown). Again, the microlens array may be positioned between the upper or outer layer of the CMOS image sensor and the environment in which the dust detector 10 is located. A microlens array may improve image quality but may make cleaning of the dust detector 10 more difficult (e.g. more prone to scratches) and could also lead to inaccurate results in some instances in which dust may collect between the microlenses of the array. Nevertheless, it has been found that passing a fluid (e.g. a gas such as air) over the contact surface 20 can wash/blow away collected dust even in embodiments with microlenses (although also applicable to embodiments not including microlenses). The speed at which the fluid is passed over the contact surface 20 may be selected to achieve this effect whilst not damaging the contact surface substantively. In some embodiments, cleaning is achieved by wiping of the contact surface 20 with a cloth.

In some embodiments, the contact surface 20 may include more than one portion 20a (see figure 7, for example). The contact surface 20 may, for example, comprise four contact surface portions 20a. The contact surface portions 20a may be arranged in an array - with the contact surface portions 20a provided in one or more linear columns and/or rows.

In some embodiments, each contact surface portion 20a may be a contact surface 20 in its own right and the above description of the contact surface 20 may apply individually to each contact surface portion 20a. As such, each contact surface portion 20a may comprise an imaging device 30 as described herein. In some embodiments, the contact surface portions 20a collectively form part of the same imaging device 30 but each may be a separate CMOS image sensor of that imaging device 30. The provision of multiple contact surface portions 20a allows reading to be monitored from one or more selected contact surface portions 20a but not from others, allows the comparison of readings from different ones of the contact surface portions 20a, allows for redundancy in the event of failure or damage or excessive contamination, and/or for different configurations to be used for different ones of the contact surface portions 20a (e.g. one portion 20a may have a coating and/or microlenses and/or a filter which another portion 20a may not).

In some embodiments, the imaging device 30 may include a narrowband filter (not shown).

The narrowband filter may be configured to allow a predetermined range of light frequencies to pass therethrough to the CMOS image sensor. Accordingly, the narrowband filter may be located between the CMOS image sensor and the environment in which the dust detector is positioned (and may also be between the CMOS image sensor and the light source device 40).

The narrowband filter may allow the dust detector 10 to operate in various light conditions because the narrowband filter only allows the light of the predetermined frequency range through to the CMOS image sensor. The predetermined frequency range may be, in some embodiments, matched to the frequency or frequencies of light which the light source device 40 is configured to emit. In other words, the narrowband filter may be configured to block or attenuate light other than that emitted by the light source device 40.

In some embodiments, therefore, the narrowband filter may be an optical filter. However, in some embodiments, the narrowband filter may be configured to filter the output from the imaging device 30 - i.e. an electronic filter.

In some embodiments, the dust detector 10 further includes an analysing device 50. The analysing device 50 may be housed in the housing 12 (e.g. in the base portion 15 thereof) or may be remote from the housing 12.

The analysing device 50 may be configured to receive data from the imaging device 30 and perform one or more analysis routines in relation to the received data in order to measure properties relating to dust contacting the contact surface 20.

The analysing device 50 may be further configured to receive information regarding the operation of the light source device 40 during the capturing of the data by the imaging device 30. This information may include which light source 42 was illuminating the contact surface 20, the colour of the light (i.e. the light frequency) used to illuminate the contact surface 20, the direction of the light source 42 with respect to the contact surface 20 (which may include the angle of illumination about the central axis A and/or the angle of illumination with respect to the main plane of the contact surface 20 (e.g. at the centre of the contact surface 20 or some other predetermined part of the contact surface 20). This additional information may then be used in the analysis of the received data from the imaging device 30.

In some embodiments, the analysing device 50, therefore, includes a microprocessor which may be part of a computer - such as a desktop computer or a server.

Communication between the analysing device 50 and the imaging device 30 may be via a wired or wireless link and, in the case of a wired link; this may be an Ethernet connection. As will be appreciated, therefore, the dust detector 10 may include a communication interface which is configured to package the data from the imaging device 30 for transmission to the analysing device 50.

In some embodiments, the analysing device 50 may be separate from the dust detector 10 and may not be a part thereof (remotely or otherwise). Accordingly, some embodiments may include a combination of a dust detector 10 and an analysing device 50.

In some embodiments, the dust detector 10 may have a power supply that provides electrical power to the other parts of the dust detector 10. The power supply may, for example, be a battery. In some embodiments, the dust detector 10 may be configured to be connected to mains power supply.

Some embodiments of the dust detector 10 may be configured for clean room use and/or some may be configured for use in space. The dust detector 10 may include one or more components which are radiation hard. In other words, one or more electronic or other components may be made resistant to damage or malfunction from ionising radiation, such as particles or highenergy electromagnetic radiation, so that the dust detector 10 may operate satisfactorily in space. This may also be advantageous if the dust detector 10 is to be used in the vicinity of other scientific equipment or detectors (for example, particle accelerators or nuclear reactors). Such radiation hardening may include one or more of shielding the imaging device 30 or contact surface 20 (or other component of the dust detector 10), choosing substrates with a higher band-gap to give higher tolerances to defects, and providing an analysing device 50 with multiple processing components so that analysis routines may be calculated in parallel.

The dust detector 10 of embodiments may, therefore, be located within an environment in which there is a desire to determine one or more properties of the dust particles which are present in that environment. These one or more properties may include the number of dust particles, and/or the type of dust particles, and/or the possible sources of dust particles, and/or the shape of dust particles, and the like.

Dust particles will be deposited on the dust detector 10 like any other surface in that environment. Dust particles may, for example, fall through the aperture 18 and/or pay pass through the side aperture(s). These dust particles may then settle on the contact surface 20.

The imaging device 30 may then be used to capture one or more images of the dust particles on the contact surface 20 (or, more particularly, the shadow or shadows cast be each dust particle). This may be done using multiple different illumination techniques using the light source device 40 - e.g. different colours of light, different angles of illumination about the central axis A, and/or from different heights above the main plane of the contact surface

20. These measurement images may then be sent to the analysis device 50 to be analysed to determine one or more properties of the dust particles.

As will be understood, the size of a shadow cast by a dust particle and imaged by the imaging device 30 may well be much larger than the size of the dust particle itself. Therefore, the imaging device 30 may have a pixel width of about 6 microns, for example, and a dust particle may have a maximum dimension of just one micron. Therefore, the imaging device 30 may not normally be able to detect (i.e. image) the dust particle. However, with illumination from an angle to cast a shadow across the contact surface 20 and, hence, the imaging device 30, the shadow may cover multiple pixels of the imaging device 30. Therefore, a dust particle which may otherwise be too small to be imaged may still be imaged by using some embodiments disclosed herein. With information available about the angle of illumination it is then possible to determine the size of the dust particle (e.g. using trigonometry).

Methods of operating the dust detector 10 may include the steps of providing the contact surface 20 for dust to contact and illuminating at least a portion of the contact surface 20 with light from the light source device 40. The methods may further include providing an imaging device 30 which is configured to generate an image of the contact surface 20 using the light from the light source device 40 and analysing the image provided by the imaging device 30 to determine one or more properties relating to the dust contacting the contact surface 20.

In some embodiments, the method of operating the dust detector 10 may further include providing the analysing device 50. The analysing device 50 may use the image generated by the imaging device 30 to determine the one or more properties relating to the dust.

During operation the light source device 40 may illuminate the contact surface 20 using one or more light sources 42. In some embodiments, the angle Y (the “angle of illumination”) may be predetermined. Thus, the angles that the light is incident on the contact surface 20 at all positions on the contact surface 20 may also be predetermined.

When the contact surface 20 is illuminated by one or more light sources 42 a shadow is formed under each dust particle on the contact surface 20. In this instance “under the dust particle” means generally between the dust particle and the contact surface 20. The properties of the shadow produced by the light incident on the dust particle depend on various aspects of the configuration and operation of the dust detector 10.

For example, the number of light sources 42 being used (or the intensity of a single light source 42) affects how bright the surface is around the dust particle. Therefore, this may create a “sharper” shadow beneath the dust particle.

The angle that the light incident on the contact surface 20 and dust particle will affect the size of the shadow created by the dust particle. For example, the smaller the angle (i.e. the lower the light source 42 relative to the contact surface 20), the longer the shadow will be on an opposing side of the dust particle. Likewise, the larger the angle (i.e. the light source 42 is positioned higher above the contact surface 20) the smaller the shadow will become.

If the dust on the contact surface 20 is illuminated simultaneously by multiple light sources 42 which are positioned around the contact surface 20, then the shadow will be affected by all of the light sources 42. Likewise, if multiple light sources 42 are used individually or in a specific sequence then more information may be generated from the shadow differences produced. In some embodiments, using multiple light sources 42 located around the contact surface 20 (and thus, around the dust particles) may allow the analysing device 50 to build up a three-dimensional image of the dust being detected. In particular, a profile of the dust may be determined from different angles which may then allow the shape of one or more parts of the dust to be determined and a collection of this shape information may be combined to form a threedimensional image.

In other words, the properties of the shadow may provide additional data which may allow better focus of the dust particles, and/or may allow effective magnification of dust particles (as the shadow may be far larger than the dust particle itself). In other words, more accurate analysis of the dust (and particularly smaller dust particles) may be possible using magnification and/or better focusing.

The colour of the light emitted from a light source 42 may affect the accuracy with which the imaging device 30 images a dust particle. For example, blue light may provide more accurate measurements of smaller particles than other colours.

In some embodiments, therefore, the method of operating the dust detector 10 may include the illumination of the contact surface 20 using the light source device 40 in one or more different manners in order to generate images, using the imaging device 30, form which one or more properties of the dust on the contact surface 20 can be determined.

The method of operating the dust detector 10 may include using the imaging device 30 to generate a control image. The control image may be generated without the light source device 40 providing light on the contact surface 20.

The control image may provide information about the ambient light conditions around the dust detector 10.

In some embodiments, the control image may be generated at the start of operation or before the dust detector 10 starts to measure properties relating to the dust on the contact surface 20. Alternatively, a control image may be generated at predetermined intervals during operation or before every measurement made by the dust detector 10.

In some embodiments, the control image may be subtracted from the image generated from the dust on the contact surface 20 during normal operation (i.e. the measurement image). In other words, the control image may be used as a measurement of noise and thus the accuracy of the results during normal operation may be improved by using the control image to remove the noise.

In some embodiments, the dust detector 10 may use a single control image taken at a predetermined point during operation, which may be subtracted from all of the subsequent measurement images acquired. Alternatively, the dust detector 10 may use a control image in real time - i.e. the dust detector 10 may continuously update the control image (as a measure of the noise) and as such the dust detector 10 may subtract the most recent control image from any particular subsequently acquired measurement image.

Of course, control images may also be acquired after a measurement image has been acquired.

In some embodiments in which the imaging device 30 includes a CMOS image sensor and the contact surface 20 comprises the CMOS image sensor, the dust may contact the CMOS image sensor directly. This may improve the image generated by the imaging device 30 with respect to a dust detector 10 using a surface 20 which is not a CMOS image sensor.

It should be appreciated that similar benefits may also result from using a CCD rather than a CMOS image sensor.

When used in this specification and claims, the terms comprises and comprising and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A dust detector comprising:

a contact surface for dust particles to contact; a light source device configured to illuminate the contact surface at a predetermined angle of incidence; and an imaging device configured to generate an image of dust particles on the contact surface from light incident on the contact surface from the light source device such that one or more properties of the dust particles on the contact surface are detectable.

2. A dust detector according to claim 1, wherein an angle between the contact surface and the light incident on the contact surface from the light source device is less than about 90 degrees.

3. A dust detector according to claim 2, wherein the angle between the contact surface and the light incident on the contact surface from the light source device is between about 20 and about 50 degrees.

4. A dust detector according to claim 3, wherein the angle between the contact surface and the light incident on the contact surface from the light source device is about 30 degrees.

5. A dust detector according to any preceding claim, wherein the light source device comprises more than one light source.

6. A dust detector according to claim 5, wherein the light source device includes four light sources.

7. A dust detector according to claims 5 or 6, wherein the light sources are positioned at different angles about a substantially central axis through the contact surface.

8. A dust detector according to claim 7, wherein a light source is positioned at each of about 0, about 45, about 90 and about 135 degrees about the central axis of the contact surface with respect to an arbitrary radius extending from the central axis.

9. A dust detector according to any preceding claim, wherein the light source device includes at least one light-emitting diode.

10. A dust detector according to any preceding claim, wherein the light source device is configured to emit light in a visible spectrum.

11 .A dust detector according to claim 10, wherein the light source device is configured to emit light in at least one of a blue visible spectrum, red visible spectrum, green visible spectrum and white visible spectrum.

12. A dust detector according to claim 11, wherein the light source device is configured to emit light in more than one of a blue visible spectrum, red visible spectrum, green visible spectrum and white visible spectrum.

13. A dust detector according to claim 12, wherein the light source device is configured to emit light in more than one visible light spectrum from each of a plurality of different locations with respect to the contact surface.

14. A dust detector according to any preceding claim, further including a housing including a top portion which supports the light source device and a base portion which houses the imaging device.

15. A dust detector according to claim 14, wherein the top portion defines an aperture generally aligned with a substantially central axis of the contact surface.

16. A dust detector according to claim 14 or 15, wherein the top portion is an annulus.

17. A dust detector according to any of claims 14 to 16, wherein the housing further includes at least one support leg, and the or each support leg supports the top portion with respect to the base portion.

18. A dust detector according to any preceding claim, wherein the imaging device includes a complementary metal-oxide-semiconductor image sensor.

19. A dust detector according to claim 18, wherein the contact surface is an upper or outer surface of the complementary metal-oxidesemiconductor image sensor.

20. A dust detector according to any preceding claim, wherein contact surface includes a coating.

21. A dust detector according to any preceding claim, wherein the contact surface further includes a microlens array.

22. A dust detector according to any preceding claim, wherein the contact surface comprises two or more contact surface portions.

23. A dust detector according to claim 22, wherein each contact surface portion comprises a separate complementary metal-oxidesemiconductor image sensor.

24. A dust detector according to any preceding claim, further comprising a narrowband filter.

25. A method of detecting dust particles, the method comprising:

providing a contact surface for dust particles to contact;

illuminating at least a portion of the contact surface at a predetermined angle of incidence with light from a light source device;

providing an imaging device which is configured to generate an image of the dust particles on the contact surface using the light from

5 the light source device, and analysing the image provided by the imaging device to determine one or more properties of the dust particles contacting the contact surface.

10

26. A dust detector or method of detecting dust particles substantially as described herein with reference to the accompanying drawings.

27. Any novel feature or combination of features substantially as described herein.

Intellectual

Property

Office

Application No: Claims searched:

GB1615805.7

1-25