WO1991014935A1

WO1991014935A1 - A method and an apparatus for cleaning control

Info

Publication number: WO1991014935A1
Application number: PCT/DK1991/000086
Authority: WO
Inventors: Ole Holm Petersen
Original assignee: Abk Bygge- Og Miljøteknik A/S
Priority date: 1990-03-22
Filing date: 1991-03-20
Publication date: 1991-10-03
Also published as: DK74390A; DK163538B; DK163538C; FI924223A0; DK74390D0; FI924223A

Abstract

A method and an apparatus for cleaning control by measuring the degree of dirt on a surface by means of a dust collecting adhesive foil by optically measuring an area of the adhesive foil exposed to dust and by comparing the obtained measuring value to a reference value. The optical measuring is effected by means of a laser beam source with associated optical members for generating a beam of substantially parallel laser rays that are made to pass substantially perpendicular through the adhesive foil and to be successively focused on a detector for display on a measuring instrument. The simple method and design of the apparatus provide inter alia for making the apparatus portable.

Description

A method and an apparatus for cleaning control.

The invention relates to a method of cleaning control by measuring the degree of dirt on a surface by means of a dust collecting adhesive foil, in which an optical measuring is effected of an area of adhesive foil exposed to dust and a comparison of the obtained measuring value with a reference value, and a mesuring apparatus for carrying out the method.

Methods and measuring apparatuses of this type are known in which the optical measuring is generally based on measuring light transmitted by diffusion and in which an analysis of the size and quantity of particles on the adhesive tape is performed, frequently by means of advanced image data analyzing equipments. Such types of a measuring apparatus are, however, expensive and typically stationary so that a measuring of the cleanliness degree cannot be effected on the spot where the adhesive foil is being exposed.

The method according to the invention is characterized in that the area of the adhesive foil exposed to dust is placed substantially perpendicular to the radiation axis of a laser beam emitted from a laser beam source which laser beam after passage through the adhesive foil is focused on an intensity measuring photodetector, the output signal of which is fed to a measuring instrument the display of which is compared to the reference value.

A substantial simplification of the measuring is thus obtained without noticeable decline in accuracy and reproduceability of the measurings.

The measuring apparatus according to the invention is characterized by comprising a laser beam source with associated optical members for the generation of a beam of substantially parallel laser rays, a holder designed to arrange an adhesive foil dust probe and means for positioning said holder in said parallel beams with the adhesive foil substantially perpendicular to the axis of radiation and means for focusing the beam passing through the adhesive foil holder on an intensity measuring photodetector and a measuring instrument for measuring the output signal of the detector and comparing it to a reference value.

It has thus been made possible to manufacture the measuring apparatus in an inexpensive, simply operating, portable design, thereby allowing the cleaning control to be effected quickly and on site.

Instead of performing a thorough analysis of the quantity and size of the dust particles on the adhesive tape the simplification is obtained by merely measuring the quantity of directly transmitted (laser) light, i.e. light that is neither absorbed nor scattered by the dust particles on the adhesive tape.

The invention and the preferred embodiments thereof will now be explained in detail with reference to the drawings, in which

Fig. 1 illustrates a dust-absorbing adhesive tape,

Fig. 2 is a side elevation of the adhesive tape, Fig. 3 is a sketch of a measuring apparatus according to the invention, and

Fig. 4 illustrates a holder, disposed on a vacuum cleaner pipe, for the exposure of the adhesive foil by measuring the dirt degree of a shaggy surface.

Prior to use the adhesive foil illustrated in Figs 1 and 2 is provided on its adhesive surface with a cover sheet, not shown. Immediately before the exposure of the adhesive foil the cover sheet is removed and a reference measurement of the unexposed adhesive tape is either effected at once, or part of the adhesive tape is maintained unexposed (see Figs 1 and 2) for effecting the reference measurement later on. The exposure on a smooth surface is obtained by pressing the adhesive foil against the surface, the adhesive side facing downwards; on a shaggy surface by arranging the adhesive foil in a holder, illustrated in Fig. 4, inserted in a vacuum cleaner pipe, and subsequent vacuum cleaning of the shaggy surface for a predetermined period. In order to obtain a uniform distribution of the dust particles across the adhesive foil, said holder may have a turbulence forming, conical contraction as illustrated in Fig. 4.

After exposure, the adhesive tape is placed in measuring position within the measuring apparatus in Fig. 3, in which laser beams from a laser diode LD by means of lenses L₁ and L₂ are made to impinge on the adhesive foil in a parallel beam at the measuring position S. Part of the incident laser light will then be scattered and part of the light will be absorbed by the dust particles on the adhesive foil, while the remainder by means of a lens L₃ with relatively large focal length (f) will be focused, preferably through a pinhole diaphragm P_s, on a detector D_s, for measuring the transmitted intensity whose output signal is fed to the measuring instrument M for displaying a measuring figure.

When an area A(o) of the adhesive foil surface is exposed to dust is hit by light with an intensity I(o), part of the light will be removed by absorption in the dust particles and another part will be removed by scattering. The quantity of light I (removed) which the dust removes is determined by the effective area of the dust A(eff), i.e.

I (removed) ₌ A(eff) ₌ E · A

I(o) A(o) A(o)

wherein E is the extinction coefficient and A is the area of the projection of dust perpendicular to the light beam. E depends on the ratio between the par ticle size and the wavelength of the light and is close to 2 when this ratio is large (Broomhead et al, 1960). In practice E is an average value determined by the optical properties and the actual size of the particles.

By measuring transmitted light intensities with and without dust on the adhesive tape (I(dust), I(ref)) the result is:

I (removed) _{= 1-} I (dust) _{= 1-} measuring figure (dust) I(o) I(ref) measuring figure(ref), wherein I (dust) is the current signal from the detector measured by the measuring instrument M in connection with an adhesive foil exposed to dust and I(ref) is the measured current signal from the detector in connection with an unexposed adhesive foil (reference).

The purpose of the pinhole diaphragm is to prevent scattered light from becomning a part of the measured transmitted light intensity. It applies to the illustration in Fig. 3 that the angle θ from the main beam, within which scattered light is detected, is determined by θ ≈ tg θ = ∅ (pinhole) /2 · f [rad], wherein f is the focal length for the lens L₃ and thus also the distance between lens L₃ and the pinhole diaphragm P_s (f = 150 mm).

Scattered light within 3° from the main beam is by and large merely due to diffraction. As regards particle sizes less than about 20 μm (in diameter), less than 2% of the totally scattered, reflected and absorbed light will fall within 0.14° from the main beam corresponding to a pinhole diameter of 1 mm for f = 150 mm (J.R. Hodkinson and Greenleaves 1963). Due to the detection of scattered light no more than 2% too high intensity of transmitted light will consequently be measured, by this masuring set-up.

In view of the fact that the light scattering angle depends on the particle size there may, by using a stepwise variable pinhole diaphragm, e.g. ∅(pinhole) = 0.2 mm, 0.3 mm, 0.6 mm, 1.0 mm, 2.0 mm and 3.0 mm, corresponding to detection angles of 0,024°, 0,036°, 0,072°, 0,12°, 0,24° and 0,36°, respectively, be obtained numeric values giving a rough description of the particle size distribution.

In the illustrated example of the measuring apparatus according to the invention the radiation source is preferably a laser diode and the photodetector a photodiode and the apparatus has been made portable by accommodating a battery for power supply to the measuring circuitry.

Claims

P A T E N T C L A I M S

1. A method of cleaning control by measuring the degree of dirt on a surface by means of a dust collecting adhesive foil, in which an optical measuring is effected of an area of the adhesive foil exposed to dust and a comparison of the obtained measuring value with a reference value, characterized in that the area of the adhesive tape foil exposed to dust is placed substantially perpendicular to the radiation axis of a laser beam emitted from a laser beam source which laser beam after passage through the adhesive foil is focused on an intensity measuring photodetector, the output signal of which is fed to a measuring instrument the display of which is compared to the reference value.

2. A method as claimed in claim 1, characterized in that the reference value is obtained by measuring an area of said adhesive foil that is not exposed to dust.

3. A method as claimed in claim 2, characterized by using for the sampling an adhesive foil item of which only part is exposed to dust, following which in the same measuring operation a measuring is effected on the part exposed to dust as well as on the part not exposed to dust of the adhesive foil item serving to produce the reference value.

4. A method as claimed in claim 2, characterized in that prior to sampling the dust the reference value is calibrated by effecting the measuring on the part of the adhesive foil which is successively used for sampling the dust.

5. A method as claimed in any of the preceding claims for measuring the dirt degree of a smooth surface, characterized by taking a dust sample from the surface by means of an adhesive foil item.

6. A method as claimed in any of claims 1 to 5, for measuring the dirt degree of a shaggy surface, characterized in that a dust sample is taken from the surface by disposing an adhesive foil item in a holder that is inserted in a vacuum cleaner pipe, and vacuum cleaning for a predetermined time, thereby causing part of the absorbed dust to settle on the adhesive foil.

7. A method as claimed in claim 4, characterized by imparting turbulence to the air in the area of said holder for the adhesive foil, by means of a conical contraction, thereby causing the dust to be uniformly distributed across the adhesive foil.

8. A method as claimed in any of the preceding claims, characterized in that the laser beam is focused on the photodetector by means of a lens with comparatively large focal length and through a pinhole diaphragm having an aperture such that the detection angle of radiation is less than 0.12°.

9. A measuring apparatus for carrying out the method as claimed in any of the preceding claims, characterized by comprising a laser beam source with associated optical members for generating a beam of substantially parallel laser rays, a holder designed to arrange an adhesive foil dust probe and means for positioning said holder in said parallel beam with the adhesive foil substantially perpendicular to the axis of radiation and means for focusing the beam passing through the adhesive foil tape holder on an intensity measuring photodetector and a measuring instrument for measuring the output signal from the detector and comparing it to a reference value.

10. A measuring apparatus as claimed in claim 9, characterized in that the light source is a laser diode and the photodetector is a photodiode.

11. A measuring apparatus as claimed in claim 10, characterized in that a pinhole diaphragm is arranged in front of the photodiode and a lens with comparatively large focal length is arranged behind the adhesive foil holder.

12. A measuring apparatus as claimed in claim 11, characterized in that the aperture of the pinhole diaphragm is stepwise variable to obtain radiation detection angles of e.g. 0,024°, 0,036°, 0,072°, 0,12°, 0,24° and 0,36°.

13. A measuring apparatus as claimed in claim 11, characterized in that the aperture of the pinhole diaphragm is chosen so that the radiation detection angle is less than 0.12°.

14. A measuring apparatus as claimed in claims 9, 10, 11, 12 or 13, characterized by being portable.