WO1995020176A1

WO1995020176A1 - Instrument for automatically applying coverslips and method

Info

Publication number: WO1995020176A1
Application number: PCT/AU1995/000035
Authority: WO
Inventors: Raymond Anthony Keefe; Peter John Meikle
Original assignee: Australian Biomedical Corporation Ltd.
Priority date: 1994-01-25
Filing date: 1995-01-25
Publication date: 1995-07-27
Also published as: AUPM352194A0

Abstract

An instrument for automatically applying coverslips to microscopic specimen slides includes a gripper mechanism (15) for withdrawing slides (14) from a slide rack (13) and placing the slides in turn on a walking beam conveyor (16) which transports the slides sequentially to various stations in the instrument. At a first said station a nozzle dispenses an exact amount of mountant onto the upper surface of the slide in a thin streak (19). At a second station a laydown head (22) places a coverslip over the slide in a manner whereby the coverslip progressively contacts the slide at a rate which decreases as the angle at which the coverslip meets the slide is reduced. A transfer head (26) sequentially removes single coverslips from a stack (36) of coverslips by a combination of bending and shearing and transfers each coverslip in turn to the laydown head.

Description

INSTRUMENT FOR AUTOMATICALLY APPLYING COVERSLIPS AND METHOD

The present invention relates to an instrument for automatically applying coverslips to microscopic specimen slides in the field of histology and pathology. In one particular form the invention relates to apparatus within such an instrument for reliably lifting and separating a single glass coverslip from a stack of coverslips within the instrument. More generally the invention relates to an instrument for efficiently and reliably applying conventional glass coverslips to slides containing specimens of varying topography using conventional mounting media. The invention in a further more specific form may relate to a method and apparatus within the instrument for placing a selected coverslip onto a slide in a manner which produces a higher percentage of acceptable samples than has been achievable in the past.

The need to automate the coverslipping process has been recognized and several instruments of the general kind contemplated herein are known. However known instruments suffer disadvantages which render them only moderately acceptable to the end user. For example, US patent 4,428,793 describes an instrument in which slides are picked-up one at a time from a solvent filled input tray to have mounting media dispensed thereon in an arc using a pressure pump and dispensing needle. A glass coverslip is picked up from the top of a stack, within the instrument, using a suction cup and means to bend the coverslip concave relative to the remaining coverslips of the stack in order to separate the top coverslip from the one immediately below. The selected coverslip is then lowered onto the slide at an angle and at a uniform rate so as to progressively spread the mounting media on the slide until the coverslip is parallel to, and affixed on, the slide. This prior art

-strument suffers disadvantages in that it is slow because the slides are processed one at a time and the reliability is not to the level generally considered acceptable in the industry because coverslip are not always separated when lifted from the stack and often bubbles are formed in the mounting media due to the procedure of lowering the coverslip onto the slide. Also, because of this lowering procedure and the form of the mounting media on the slide excess mounting media can flow from under the coverslip and a large quantity of toxic solvent is present which produces a high level of toxic fumes. There is no self contained fume control system.

According to another known instrument the slides are stored horizontally in a reservoir of solvent. A glass coverslip is moved forward from the bottom of a stack and mounting media dispensed on top of the coverslip by two pressure pump dispensers. The slide is moved over the coverslip with the sample facing downward and rollers push the coverslip and mounting media upward to contact the slide. The rollers then move outward to spread the mountant. A fume extraction and filter system is used to absorb toxic fumes.

The disadvantages of this instrument are that it is slow, bubbles are trapped in the mounting media and a large volume of solvent is required for the slide storage area. However, toxic fumes are controlled.

In a still further known instrument the coverslip is plastic tape with the mounting media attached to it in a dry uniformly distributed film. A slide is passed horizontally under a solvent dispenser and then under a roller which rolls the tape onto the slide. A knife then cuts the tape to length. The solvent on the slide activates the mounting media which adheres the coverslip to the slide.

The disadvantages of this instrument are that it cannot handle lumpy samples, toxic solvent fumes are not filtered and the plastic tape is optically inferior and not as durable as a glass coverslipper. However, it is fast and does not require an open solvent reservoir in the input station.

It is an object of the present invention to provide an improved instrument which overcomes one or more of the above disadvantages of known instruments. Accordingly, one broad form of the invention provides an instrument for automatically applying coverslips to slides containing specimens, characterized in that, said instrument includes a gripper mechanism for withdrawing slides sequentially from a slide rack, a walking beam conveyor for transporting each slide sequentially to various stations in the instrument, said gripper mechanism is adapted to place said slides in turn on said walking beam, a first said station adjacent a mounting media dispenser whereat mounting media is dispensed onto a said slide in a linear streak, a second said station adjacent a coverslip laydown head whereat a coverslip is laid upon a said slide in a manner causing said mounting media to be spread over said slide specimen without trapping air bubbles between said slide and coverslip, and a third said station, being an output station whereat completed said slides are placed sequentially into a further slide rack, said instrument further includes a transfer head for sequentially picking up coverslips from the top of a stack located within the instrument in a manner ensuring that only one coverslip is picked-up at a time, and transferring each coverslip in turn to said laydown head in synchronism with other instrument operations.

According to another form of the invention there is provided a coverslip transfer head for sequentially picking up coverslips from the top of a stack of coverslips, characterized in that, said transfer head includes a spring loaded plunger arranged between two spaced suction cups such that when the plunger is in an extended position over a stack of coverslips the plunger extends vertically downwardly beyond the lowermost position of the suction cups, and the suction cups are inclined outwardly and downwardly relative to the vertical axis of the plunger such that when a coverslipper is held by the two suction cups and the plunger is extended the coverslip assumes a concave-up configuration, and control means for controlling movement of the transfer head and suction pressure to one or both of the suction cups.

According to another form of the invention there is provided a method of lifting the top coverslip from a stack of coverslips, characterized in that, said method comprises using a combination of bending and shearing to ensure that the top coverslip is separated from the coverslip immediately therebelow.

In a still further form the invention provides a method of controlling operation of a coverslip transfer head as defined hereinabove, characterized in that, said method comprises the steps of lowering the transfer head from above a said stack of coverslips until the suction cups contact the top coverslip and the spring loaded plunger is compressed; applying vacuum to one said suction cup and raising the head so that one end of the coverslip is raised and the coverslip is bent upwards away from the stack and is translated sideways slightly due to the bending thereof in combination with the plunger extending; lowering the head to translate the coverslip and thus bring both suction cups again into contact with the top coverslip; applying vacuum to both suction cups; and raising the head thereby causing the plunger to extend and bend the coverslip concave-up about the plunger, thus peeling it away from the stack.

A still further form of the invention provides a method of controlling the operation of a laydown head in a coverslipping instrument, characterized in that, said method comprises the steps of moving the head towards a specimen slide in a manner whereby a coverslip held by the head approaches the slide with the plane of the coverslip being at an acute angle to the plane of the slide, said slide having a strip of mounting media extending substantially centrally along the surface thereof in the direction the coverslip is to be progressively brought into contact with the slide, said strip stopping short of opposed ends of the slide, causing the edge of the coverslip which first approaches the slide to contact the mounting media strip before contacting the slide and progressively causing the coverslip and slide to come together at a rate which is dependant upon, inter alia, the characteristics of the mounting media, and which varies as the angle between the plane of the two parts reduces, so as to maintain an even distribution of mounting media over the respective surfaces of the coverslip and slide as the respective surfaces are brought together, thereby minimizing the possibility that air bubbles are trapped between the surfaces.

In order that the invention may be more readily understood, one particular embodiment will now be described with reference to the accompanying drawings wherein:

Figure 1 is a front perspective view of an instrument according to the invention; Figure 2 is a perspective view of a slide rack for insertion into the instrument of Figure 1; Figure 3 is a plan view of a glass microscope slide showing a mounting media streak or strip arranged thereon by the instrument of

Figure 1; and Figures 4(a) - 4(e) show the various stages in the operation of a pick-up head of the instrument of Figure 1 in picking up a coverslip from a stack of coverslips within the instrument.

Referring to Figure 1 the instrument is shown to comprise essentially an outer cover or casing 10 having a lid 11 which, during operation of the instrument, is closed to contain any toxic fumes. An input door and receptacle 12 is adapted to receive a rack 13 such as the rack shown in Figure 2. The rack 13 contains a series of microscope slides containing tissue samples which have been already processed. The input door and receptacle 12 is pivotal from a horizontal position (not shown) for loading of the rack 13, to the vertical position shown in Figure 1.

Once a rack of slides is loaded into the receptacle 12 and a program initiated, a first slide 14 of the kind shown in Figure 3 is removed from the rack 13 by means of gripper mechanism 15. The gripper mechanism 15 comprises a pair of spaced fingers which move towards the rack 13 and grip opposed longitudinal sides of a slide 14 and withdraw the slide from rack 13 in a horizontal orientation. The gripper mechanism 15 then places the selected slide on a walking beam 16 for transportation through various stations within the instrument. The walking beam 16 is essentially a conveyor which is translated sideways in discrete steps and moved downwardly and back to its original position between each step. This enables the slide to be moved horizontally and placed on a table between each sideways step whereby a series of slides may be stepped through the instrument in a continuing process. The table (not shown) comprises horizontal surfaces on either side of the walking beam at a level slightly below the upper or transport position of the walking beam but above the lower position thereof.

A first processing station for a slide moving through the instrument is at a mountant dispensing nozzle where mounting media or mountant is dispensed onto the upper surface of the slide in a thin strip or streak 18 as shown in Figure 3. The mounting media streak 18 extends in the longitudinal direction of the slide 14 centrally thereon and over a length which is less than the length of a coverslip to be placed thereon. A mountant bottle 19 contains mountant and is connected to the dispensing nozzle via tubing 20 which extends via a positive displacement pump

(not shown) within the instrument. The positive displacement pump provides an exact amount of mountant which is consistent through each dispensing operation independent of ambient temperature and the type of mounting media in use. A waste container 21 is arranged below the dispensing nozzle 17 for the purpose of containing any waste mountant which may be dispensed during priming of the instrument or at other times during a processing cycle.

After mountant is dispensed onto a slide it is transported via the walking beam 16 to a second station which is a coverslip laydown station immediately below coverslip laydown head 22. The laydown head 22 is preloaded with a coverslip as will be described shortly and places the coverslip over the slide in a manner considerably reducing the likelihood of air bubbles occurring in the mountant between the slide and coverslip. More specifically, the laydown head includes suction cup 23 which receives a coverslip and holds the coverslip firmly at an acute angle to the slide which is in a horizontal position therebelow. The laydown head is moved downwardly whereby the coverslip approaches the slide with one of the short sides of the coverslip 24 (see broken lines 24 in Figure 3), approaching the short side of the slide adjacent the end of the slide where the strip or streak 18 is nearest. The procedure is such that the inclination and positioning of the coverslip 24 ensures that the lowermost short edge of the coverslip contacts the mountant before contacting the slide. Continued downward movement of the laydown head 22 with the coverslip 24 inclined relative to the slide ensures that the coverslip is progressively laid onto the slide. In other words as the laydown head 22 is moved vertically downward, the coverslip is caused to bend or flex because of its very thin construction and progressively makes contact with the slide (with mountant being spread therebetween) until it is fully in contact with the slide as shown by the dotted lines of Figure 3. The rate at which the head 22 is moved downwardly varies as the coverslip progressively contacts the slide, and in fact the descent rate of the head is reduced towards the end of the procedure to take into account the rapidly reducing angle at which the coverslip meets the slide. The actual rate of descent depends upon the characteristics of the mountant and these characteristics include features such as surface tension, viscosity and wetting characteristics.

To ensure that only a single coverslip 24 is delivered to the laydown head 22 each time a transfer occurs from a stack 36 of coverslips within a coverslip magazine receptacle 25 to the laydown head 22, a coverslip transfer head 26 is utilized. The coverslip transfer head 26 is shown in more detail in Figures 4(a) - 4(e). The coverslip transfer head 26 comprises a plunger 27 which is biased downwardly by spring 37 and which extends downwardly from a movable base member 28 and is arranged between a pair of suction cups 29. The lower surface of the base member 28 is curved, whereby the suction cups 29 are angle outwardly and downwardly relative to the longitudinal axis of the plunger 27. In other words, the longitudinal axis of the suction cups diverge downwardly relative to the longitudinal axis of the plunger 27. Separate vacuum hoses 30 are connected to the respective suction cups of the transfer head for selectively applying vacuum for suction purposes to one or both of the suction cups. The procedure for lifting the top coverslip from the stack 36 of coverslips in the magazine receptacle 25 is as follows. Firstly the transfer head is moved downwardly towards the stack so that the plunger is brought into contact with the top coverslip of the stack and continued downward movement forces the plunger to retract upwardly until the suction cups are flattened against the top coverslip (see Figure 4(b)). At this time, vacuum is connected to one of the suction cups and the head is moved upwards vertically away from the stack. During this movement the plunger extends and provides a downward force to the centre of the coverslip. Because an end of the coverslip is lifted, this causes a small sideways translation of the top coverslip relative to the coverslip immediately therebelow. This shearing motion breaks any adhesion between the coverslips (due to residue between them) whilst the bending action allows air in between the top and immediately adjacent coverslip to prevent moisture which may be present around the edges of the coverslips from holding the coverslips together. This procedure is shown in Figure 4(c).

The next step causes the transfer head to be again moved vertically down so that it assumes a position similar to that shown in Figure 4(b) - see Figure 4(d). This second downward movement produces a second sideways translation of the top coverslip and once fully down the second or other suction cup is connected to vacuum. The transfer head is then raised and both edges of the coverslip are raised relative to the centre portion of the coverslip due to the spring loaded plunger extending downwardly - see Figure 4(e). This produces a concave-up shape in the top coverslip which is securely attached to the transfer head and can be removed from the stack because it is now free from the coverslip immediately below. This method of coverslip separation involving shearing of the coverslips relative to each other and bending of the coverslip is far superior to a method involving bending only.

Once the top coverslip has been removed from the stack and firmly held by the transfer head 26, the transfer head is moved to a position adjacent the laydown head 22 and the coverslip is transferred to the laydown head. This is achieved by rotational movement of the laydown head whereby a suction cup thereon is caused to engage the coverslip and vacuum is applied prior to releasing the vacuum which is applied to the suction cups of the transfer head. When the coverslip is firmly held by the laydown head 22 the procedures hereinabove are initiated to place the coverslip onto a slide at the laydown station.

It will be evident that the use of a walking beam 16 facilitates high throughput of the instrument since a production line is established whereby slides are withdrawn one by one and moved progressively through the instrument. During the time when the walking beam 16 is down and moving back to its starting point, a new slide is drawn from the input rack while mounting media is dispensed simultaneously onto another slide and a coverslip is laid onto a still further slide.

As is evident in Figure 1, the instrument further includes a mountant type dial 31, a keypad 32 and a fume filter cover 33. The keypad enables various machine operations to be initiated or programmed and the mountant type dial 31 enables selection of a program dependent upon the characteristics of a particular mountant being used. The fume filter cover 33 ensures that any toxic fumes are retained within the machine and not dispersed into the environment in which the instrument is used.

It should be apparent to persons skilled in the art that the instrument of the present invention provides considerable improvements over prior art instruments. The unique construction and operation of the transfer head 26 ensures that only a single coverslip is lifted from a stack and transferred to a laydown head. Furthermore, the unique laydown procedure considerable reduces the possibility of air bubble formation between the coverslip and a slide. This is achieved by matching the laydown procedure to the characteristics of the mounting media in use including varying the vertical descent of the coverslip in a manner which ensures an even distribution of the mounting media in front of the two surfaces as they come together. An output rack is arranged within a receptacle 34 to receive completed slides and an output cover 35 ensures that the internal functions of the instrument are isolated in an airtight manner from the working environment.

Claims

CLAIMS:

1. An instrument for automatically applying coverslips to slides containing specimens, characterized in that, said instrument includes a gripper mechanism for withdrawing slides sequentially from a slide rack, a walking beam conveyor for transporting each slide sequentially to various stations in the instrument, said gripper mechanism is adapted to place said slides in turn on said walking beam, a first said station adjacent a mounting media dispenser whereat mounting media is dispensed onto a said slide in a linear streak, a second said station adjacent a coverslip laydown head whereat a coverslip is laid upon a said slide in a manner causing said mounting media to be spread over said slide specimen without trapping air bubbles between said slide and coverslip, and a third said station, being an output station whereat completed said slides are placed sequentially into a further slide rack, said instrument further includes a transfer head for sequentially picking up coverslips from the top of a stack located within the instrument in a manner ensuring that only one coverslip is picked-up at a time, and transferring each coverslip in turn to said laydown head in synchronism with other instrument operations.

2. An instrument as defined in claim 1, characterized in that, said coverslip transfer head comprises a vertically extending spring loaded plunger arranged between two spaced suction cups, the axis of the suction cups is inclined outwardly and downwardly relative to the vertical axis of the plunger and the plunger, in its downward extended position is below the level of the suction cups, and control means for controlling movement of the transfer head and suction pressure to one or both of the suction cups.

3. An instrument as defined in claim 2, characterized in that, said coverslip laydown head includes a suction cup for holding a coverslip received from said transfer head, and said laydown head is movable to place said received coverslip onto a slide on which mounting media has been spread, the placement of the coverslip onto a slide comprises lowering the coverslip at an angle to the slide so that the edge of the coverslip which first approaches the slide contacts the mounting media before contacting the slide and once the said edge contacts the slide, continuing the downward movement of the coverslip, at a rate dependent upon the characteristics of the mounting media, whereby the angle between the coverslip and slide is gradually reduced and the rate of downward movement is varied, again according to the characteristics of the mounting media, to ensure that an even distribution of mounting media occurs in advance of the respective surfaces of the coverslip and slide as they are brought together.

4. An instrument as defined in claim 3, characterized in that, said rate of downward movement is decreased towards the end of the procedure to account for the increasing rate at which the coverslip and slide come together.

5. A coverslip transfer head for sequentially picking up coverslips from the top of a stack of coverslips, characterized in that, said transfer head includes a spring loaded plunger arranged between two spaced suction cups such that when the plunger is in an extended position over a stack of coverslips the plunger extends vertically downwardly beyond the lowermost position of the suction cups, and the suction cups are inclined outwardly and downwardly relative to the vertical axis of the plunger such that when a coverslipper is held by the two suction cups and the plunger is extended the coverslip assumes a concave-up configuration, and control means for controlling movement of the transfer head and suction pressure to one or both of the suction cups.

6. A method of lifting the top coverslip from a stack of coverslips, characterized in that, said method comprises using a combination of bending and shearing to ensure that the top coverslip is separated from the coverslip immediately therebelow.

7. A method of controlling operation of a coverslip transfer head as defined in claim 5, characterized in that, said method comprises the steps of lowering the transfer head from above a said stack of coverslips until the suction cups contact the top coverslip and the spring loaded plunger is compressed; applying vacuum to one said suction cup and raising the head so that one end of the coverslip is raised and the coverslip is bent upwards away from the stack and is translated sideways slightly due to the bending thereof in combination with the plunger extending; lowering the head to translate the coverslip and thus bring both suction cups again into contact with the top coverslip; applying vacuum to both suction cups; and raising the head thereby causing the plunger to extend and bend the coverslip concave-up about the plunger, thus peeling it away from the stack.

8. A method of controlling the operation of a laydown head in a coverslipping instrument, characterized in that, said method comprises the steps of moving the head towards a specimen slide in a manner whereby a coverslip held by the head approaches the slide with the plane of the coverslip being at an acute angle to the plane of the slide, said slide having a strip of mounting media extending substantially centrally along the surface thereof in the direction the coverslip is to be progressively brought into contact with the slide, said strip stopping short of opposed ends of the slide, causing the edge of the coverslip which first approaches the slide to contact the mounting media strip before contacting the slide and progressively causing the coverslip and slide to come together at a rate which is dependant upon, inter alia, the characteristics of the mounting media, and which varies as the angle between the plane of the two parts reduces, so as to maintain an even distribution of mounting media over the respective surfaces of the coverslip and slide as the respective surfaces are brought together, thereby minimizing the possibility that air bubbles are trapped between the surfaces.

9. A method according to claim 8, characterized in that, said rate is reduced as the two surfaces come together.

10. A method according to claim 9, in that, both the coverslip and slide are rectangular and the direction of the strip of mounting media is parallel to the longer sides thereof.