AU7745498A - Carrier method and apparatus - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE

SPECIFICATION

STANDARD PATENT Applicant(s): COMMINWEALTH SCIENTIFIC AND INDUSTRIAL

RESEARCH

ORGANI SATION invention Title: CARRIER METHOD AND) APPARATUS The following statement is a full description of this invention, including the best method of performing it known to me/us: -2-

TITLE

Carrier Method and Apparatus FIELD OF THE INVENTION This invention relates to a method and apparatus for mounting elongate specimens onto a substrate for investigation of the specimens.

BACKGROUND OF THE INVENTION The invention can be applied to the preparation of fibre snippets for inspection by instruments using image analysis techniques, and in particular to the preparation of wool snippets for measurement of the distribution of fibre diameter, which is the context in which the invention will 20 be described. However the invention is more widely applicable and can be applied generally to fibres with relatively high electrical conductivity, that is, fibres with a charge relaxation time of approximately 1 ms or less, and includes metallic fibres, natural fibres such as 25 cotton or wool (which have, for example, been stored in an ambient atmosphere with a relative humidity greater than about 30%) and insulating fibres (for example whose surfaces have been coated with an antistatic film).

The diameter, colour and medullation of wool fibres are properties which have a significant influence on the commercial value of wool for both growers and processors.

The distribution of these properties between fibres in a mass of wool can be measured by cutting a sample of wool into short lengths (snippets) and inspecting a large number of them. In the past each snippet was inspected visually, but in recent years this laborious task has been greatly H: \n\Keeppers\po2231 CAP CSrRO.ds 22107f98

I

simplified by the development of snippet inspection instruments which employ image processing techniques. For example, the distribution of fibre diameter in a sample of wool is one of the most important parameters for determining the commercial value of the wool and its processing performance, and in past years was measured visually by inspecting a large number of snippets with a projection microscope. This laborious task has been greatly simplified by the development of snippet inspection instruments such as OFDA (Optical Fibre Diameter Analyser) FIDAM (Fibre Image Display And Measurement) and DIAS (Digital Image Analysis System).

The operating principle is the same for each of these known instruments; first, thf, snippets in the sample are deposited onto a transparent substrate, usually a glass microscope slide, and then they are compressed by a glass cover slide to ensure that they remain within the depth of field of the inspection system. Next, the slide unit containing the snippet sample is transferred to a motor driven stage and scanned by a video camera attached to a microscope. An image of the snippets is formed on a photodiode array in the video camera and then transferred to an I image processing unit where it is digitised and analysed by 25 custom designed software to obtain the fibre diameter distribution.

Samples are prepared in a similar manner for each of the abovementioned instruments. Snippets are separated for 30 inspection by brushing them through the apertures of a wire mesh with a rotating brush or paddle, so that they fall onto the surface of the glass slide situated below the mesh. When the snippet deposition is completed the sample is covered by a second slide and then transferred to the inspection rtage.

The presentation of the snippet sample is a critical H\ann%\eep\Pe\Poa92J CAP CSIRQ.doc 22/07196 7 component of all the inspection instruments since biases may be introduced into the diameter measurement by nonuniformities in the distribution of snippets across the surface of the sample. Use of the above prior method for rearing snippet samples is unsatisfactory for two preparing snippet reasons:i) the distribution of snippets on the slide is not uniform; 0 ii) growth of snippet networks beneath the mesh, 1 0 followed by intermittent detachment, leads to deposition of snippet clumps on the slide.

Other known snippet inspection instruments for determining Othr known snippet inspec atliqi distributions involve dispersing the snippets in a liuid carrier Thus in the FDA (Fibre Diameter Analyser) snippets are dispersed into an isopropanol/water mixture snipet are dispersed into a film of light petroleum liquid which is transported through an inspection zone on a lSnpie ihice ir recorded on s: strip of photographic film. Snippet images are the film by exposure to a ligt flash. In these instruments, however, the possibilitY exists that the snippets will be swelled by the liquid carrier thereby corrupting the measurements.

S

An object of the present invention is to provide an An for mounting elongate improved method and apparatus for mounting ate specimens, such as for example fibre snippets, onto a substrate preparator to cnducting investigations on the *specmens. The improved method and apparatus of the invention employs electrostatic forces to deposit specimens uniformly over the surface of a substrate and align them in a specified direction.

CAP cSIRO.d.. 2 2/C*198 SUMMARY OF THE INVENTION According to a first aspect of the invention there is Sprovided a method of mounting elongate specimens onto a substrate for investigation comprising i) establishing an electric field through which the substrate, onto which the specimens are to be 7 mounted, is moveable, the field being shaped such that a portion extends substantially perpendicularly to the substrate and another portion extends substantially parallel to the substrate in the direction of movement thereof, ii) introducing the specimens in an electrically charged state into the substantially perpendicularly orientated portion of the electric field, whereby the specimens are transported under the influence of the perpendicular field to be deposited and retained upon the substrate in a substantially upright position, Iiii) moving the substrate into the parallel orientated portion of the field, whereby the changed field direction moves the specimens into lengthwise contact with the substrate, 0 iv) removing the substrate from the electric field.

According to a second aspect of the invention there is provided apparatus for mounting elongate specimens onto a substrate for investigation comprising means for moving the substrate between first and second electrodes, the first and second electrodes being arranged to establish an electric field orientated substantially perpendicularly to the plane of the substrate as it is moved between the pFq=',?-723! C~ic~d~ 2/013 6 electrodes, the first electrode being associated with a feed supply for the specimens and having a construction allowing entry of the specimens into the electric field while simultaneously imparting an electric charge to each specimen, the second electrode being located closely adjacent to the plane of the substrate; and a third electrode arranged to establish, in co-operation with an edge region of the second electrode, an electric field orientated substantially parallel to the plane of the substrate, the third electrode being located adjacent to the second electrode such that the direction of the substantially parallel field corresponds to the direction of movement of the substrate between the first and second electrodes.

Preferably the substrate onto which the specimens are mounted is transparent. Also the means for moving a substrate between the first and second electrodes may be a continuous carrier tape which may itself form the substrate onto which the specimens are mounted or it may carry individual substrates such as glass slides between the ii 'electrodes. Where a continuous carrier tape is employed as the substrate, it may form part of an automated inspection apparatus wherein the tape transports specimens continuously from a station for mounting them onto the tape F| to an optical inspection station.

DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described with reference to the accompanying drawrings in which: Figure 1 schematically illustrates one embodiment of apparatus according to the invention, Fig. 2 illustrates use of the apparatus of Fig. 1 for -:A-?S~Bls 2210-/3? -7discrete substrates, Fig. 3 schematically illustrates an optical inspection instrument embodying the invention, and Fig. 4 schematically illustrates the action of fibre snippets within the electric field during their mounting onto a substrate according to the invention.

DESCRIPTION OF THE PREFERRED

EMBODIMENTS

In the drawings the same reference numerals have been used between the figures to denote the same components.

Operation of the invention can be understood by reference to the first embodiment, shown schematically in Fig. 1. A snippet sample 1 is loaded into a hopper 2 and the snippets are separated by a rotating brush 3 which feeds them through the apertures of a grounded wire mesh 4, which forms the first electrode, at the base of the hopper.

A transparent carrier tape 5 formed from a material with high optical transmittance and high tensile strength, for 25 example Mylar polyester film with a thickness of moves beneath the hopper with constant speed in the direction shown by arrow A in Fig. 1. A second (extraction) electrode 6 and a grounded third (induction) electrode 7 are mounted just below the tape adjacent but spaced from each other in the direction of movement of the Stape, that is, in the locations shown in Fig. 1.

When a high DC voltage from a power supply 8 is connected between the second (extraction) electrode 6 and ground an electric field with a strong vertical component is created in the air gap between the carrier tape 5 and the first electrode, that is, the mesh 4 at the base of the hopper 2.

ZAP /7/ -8 At the same time an electric field with a strong horizontal gap between the second (extraction) and third (induction) 7 electrodes 6 and 7. The surfaces 6a and 7a of the second and third electrodes on both sides of the air gap are bevelled and polished to increase the strength of the electric field.

The electric fields in both air gaps are indicated by dashed lines in Fig. 1. The vertical field below the mesh 4 transports snippets to the moving tape 5 where they are pinned at one end and stand erect on the tape surface (as shown in Fig. The conducting snippets each receive an induced charge of the same polarity on leaving the mesh 4 and when they enter the electric field they are immediately attracted to the tape 5 below by strong Coulomb forces.

This prevents the build-up of a snippet network beneath the mesh 4 and therefore eliminates deposition of snippet clumps onto the carrier tape 5. During the deposition process, repulsive forces between neighbouring snippets .with the same charge polarity also distribute the snippets more uniformly over the surface of the tape A strong horizontal field is experienced by snippets on the I" 25 surface of the moving tape 5 as they approach the air gap I' *between the second (extraction) and third (induction) electrodes 6 and 7. The erect snippets are then rotated with the changing field direction until they lie down in contact with the surface of the tape (as shown in Fig. 4).

At the same time they are aligned in the direction of movement of the tape as shown in the figures. When the snippets are laid down on the tape they remain pinned to its surface by adhesive contact forces and therefore do not require compression by a cover plate to confine them within the depth of field of the inspection system.

Without wishing to be bound by theory it is thought that 1 Cip C 9 the adhesive contact forces which pin the snippets to the substrate are due to, mainly, van der Waals' forces at the contact points between the snippets and the carrier tape.

Thus movement of snippets across the air gap between electrodes 4 and 6 is thought to be controlled mainly by gravitational and viscous drag forces and translation and rotation of snippets by Coulomb forces only becomes effective near the surface of the tape. When a snippet collides with the tape one end is pinned to the surface at the contact points by strong van der Waals' adhesive forces whose magnitude may be several hundred times larger than the weight of the snippet. The other end rotates about the contact point under the action of opposing Coulomb and gravitational forces, wherein the turning moment of the Coulomb force exceeds that of the gravitational force and the snippet is aligned in the direction of the local surface electric field.

A second embodiment of the invention is shown schematically 20 in Fig. 2. The apparatus is identical to that shown in Fig. 1 except for the transparent plate, e.g. a microscope slide 9, which is placed on the carrier tape 5 and transported between the electrodes 4 and 6.

S 25 If the thickness of the slide is much less than the width of both air gaps the gaps between electrodes 4 and 6, and 6 and 7) then the vertical and horizontal electric fields remain practically the same at the surface of the ii tape 5 and the surface of the slide 9. Consequently the snippets are deposited onto the slide 9 in the same way as they are deposited onto the carrier tape 5, that is, the snippets are distributed uniformly over the surface of the slide and are aligned in the direction of its movement.

For a slide with a thickness of 0.15mm the apparatus is operated with approximately 3kV DC applied to the second (extraction) electrode 6, which is separated from the first H.aie\P~\J 21C~ SR~o 2/107198 10 B 10 i electrode (mesh 4) by an air gap of 4mm and from the third (induction) electrode 7 by an air gap of imm. If a microscope slide with a thickness of 1mm is used as the substrate the magnitudes of the parameters must be scaled up by a factor of approximately 7.

It was found that the deposition rate of snippets and their distribution on the surface of the substrate are both improved significantly when the snippet gauge length is reduced below 1mm. The size of the apertures in the mesh 4 is chosen to reduce multiple passage of snippets yet still maintain an adequate deposition rate. For 0.5mm snippets the deposition rate is approximately 1200 per minute through a 270pm mesh; for 0.2mm snippets and a 180[m mesh 15 this deposition rate is more that doubled.

In the apparatus shown if Fig. 3 the speed of the carrier tape 5 is controlled by a DC servo motor which drives a 4.H take up spool 17 through a gear box and the tape tension is adjusted by a brake on the feed spool 18. Snippets (which, if they are wool, are conditioned before inspection in air with a relative humidity greater than about 30% to ensure that their charge relaxation time is less than approximately 1 ms, that is, so that they behave as good electrical conductors) after being mounted onto the tape in accordance with the invention, are transported by the B. tape through the optical inspection zone The optical system consists of a diffuse light source 12 30 which illuminates the snippets through the carrier tape and a focusing lens 13 which forms an image of the snippets on a sensor in a video camera 14. Output from the camera is fed to a video monitor 15 and an image processing unit 16.

Snippets are cleaned from the surface of the tape by a sponge contact pad 11 located just before the take-up spool.

H:ann\\KeepNPem\PO92JL CAP CS!ROdac 2207199 11 In apparatus according to Fig. 3, it is possible to produce I sharply focused snippet images in a form suitable for image processing at rates exceeding 1000 per minute for long snippets and 2000 per minute for 0.2mm snippets.

The invention confers a number of advantages, viz; i) alignment of snippets on the surface of the substrates (or slide) increases the packing density of the snippets, and at the same time reduces the number of contacts and intersections between neighbouring snippets, thereby simplifying the image processing algorithms and decreasing the processing time; ii) pinning of snippets to the surface of a moving substrate, in the form of a transparent carrier tape, allows continuous inspection of snippets without the need for compression by a cover 20 plate; iii) the use of a tape to convey snippets in air from a dispenser to an inspection zone eliminates the possibility of swelling when snippets are transported by a liquid carrier. It also avoids the manual operations which are part of the FIDAM, OFDA, and DIAS instruments, that is, the mounting of snippets between glass plates and their transfer to and from a scanning stage.

ersons skilled in the art will appreciate that additions and modification may be made to the invention without departing from its spirit and scope. All such additions and modifications are to be understood as encompassed by the invention as above described.

:uixw.e -3P c323L CAP csIao.doe 22/07l98

Claims (3)

1. 2. The method of claim 1 comprising introducing the specimens by passing them through a wire mesh that constitutes a first electrode.
2. 3. The method of claim 2 comprising establishing the electric field by passing a DC voltage between two electrodes positioned in an adjacent spaced apart HAnn\%Kee\Pr O2 3 1 CAP CSIRO.dOc 22107/90
3. 13- configuration beneath the substrate. 4. Apparatus for mounting elongate specimens onto a substrate for investigation comprising means for moving the substrate between first and second electrodes, the first and second electrodes being arranged to establish an electric field orientated substantially perpendicularly to the plane of the substrate as it is moved between the electrodes, the first electrode being associated with a feed supply for the specimens and having a construction allowing entry of the specimens into the electric field while simultaneously imparting an electric charge to each specimen, the second electrode being located closely adjacent to the plane of the substrate; and a third electrode arranged to establish, in co-operation with an edge region of the second electrode, an electric field orientated substantially parallel to the plane of the substrate, the third electrode being located adjacent to :3 the second electrode such that the direction of the substantially parallel field corresponds to the direction of movement of the substrate between the first and second electrodes. The apparatus according to claim 4 wherein the substrate onto which the specimens are mounted is transparent. 6. The apparatus according to either claim 4 or claim 5 wherein the means for moving the substrate between the first and second electrodes is a continuous carrier tape. 7. The apparatus according to claim 6 wherein the tape forms part of an automated inspection apparatus wherein the tape transports specimens continuously from a station for mounting them onto the tape to an optical inspection station. H:\Mneep\?e \P8231 Chp CSiao-oc 22/07198 14 8. The apparatus according to either claim 6 or 7 wherein the tape supports at least one glass slide positioned between the electrodes, the specimens being mounted on the glass slide. 9. The apparatus according to any one of claims 4 to 8 wherein the first electrode comprises a wire mesh positioned at the base of a feed hopper. The apparatus according to claim 9 wherein the mesh has an aperture size of about 270pm. 11. The apparatus according to claim 9 wherein the mesh has an aperture size of about 180pm. 12. A method of mounting elongate specimens onto a k asubstrate for investigation substantially as described herein with reference to and as illustrated in the .I 20 accompanying drawings. 13. Apparatus for mounting elongate specimens onto a substrate for investigation substantially as described herein with reference to as illustrated in the 25 accompanying drawings. Dated this 22nd day of July 1998. 30 COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANISATION By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent Attorneys of Australia CAp CSIRO.&Sc 22I07I92