WO2011138603A1

WO2011138603A1 - Stage for an optical instrument

Info

Publication number: WO2011138603A1
Application number: PCT/GB2011/050868
Authority: WO
Inventors: Maurice Leo Bowe; Richard Albert Norman
Original assignee: Objective Imaging Limited
Priority date: 2010-05-04
Filing date: 2011-05-04
Publication date: 2011-11-10
Also published as: GB201007322D0

Abstract

Disclosed is a stage component for use in manufacturing a motorised stage for an optical instrument, the component comprising: a base member, a top member and an intermediate member; wherein the top member is supported on, and is movable in a first axis relative to, the intermediate member; and wherein the intermediate member is supported on, and is movable in a second axis relative to, the base member; characterised in that at least a selected one of the stage members is arranged such that, in use, it is supported at a proximal end region, the opposed distal end region being unsupported such that a specimen holder formed on, or to be attached to, the distal end region projects outwards from the selected stage member.

Description

STAGE FOR AN OPTICAL INSTRUMENT

Field of the Invention

The present invention relates to a component for use in an improved stage for an optical instrument, a stage comprising the component, and an optical instrument comprising the stage. The invention also relates to a method of making the component, stage and optical instrument.

Background of the Invention

It is known to provide optical instrument (e.g. microscope) stages with motors, to enable automated adjustment of the stage (and hence specimens located on a specimen holder mounted on the stage) in the x and y axes.

Conventional motorised stages comprise at least 3 plates:- a static intermediate plate, on which are guides (in the form of grooves or the like) for a motorised upper plate and a motorised lower plate. One of the motorised plates moves in the x axis and the other moves in the y axis. Typically the motor used is a stepper motor although DC servo motors may also be used for this purpose.

Stepper motors are useful in this context, as they allow for fairly precise adjustment of the position of the stage. However, they do suffer from a number of disadvantages, including "backlash" in which, when the motor reverses direction there is a lag, during which there is no movement of the stage. This can lead to a loss of accuracy in the position of the stage.

Such backlash typically arises because of the manner in which motive force is transmitted from the motor to the stage. Conventionally motorised stages are driven by one or more stepper motors, the motors acting to rotate a ballscrew (also referred to as a "leadscrew") which is engaged with a screw thread on the stage. It is necessary to provide some tolerance in the physical engagement between the ballscrew and the thread. As a result, there is inevitably a small gap between the trailing edge of the ballscrew and the nearest thread. When the motor reverses direction, what was previously the trailing edge of the ballscrew becomes the leading edge, and the initial movement of the motor is needed to close the gap between the leading edge and the screw thread, leading to loss of accuracy. Although the loss is initially small, it accumulates with each reversal of direction of the stage and so can become significant and is a major disadvantage. The prevalence of mechanical backlash in conventional stages necessitates compensatory movements through software and/or electronics to ensure accurate positioning.

Conventional motorised stages are also rather heavy. The stage is usually attached to the optical instrument via a geared coupling, to allow the stage to be raised or lowered. The large mass of the motorised stage can, over time, cause a slight gradual downward drift of the gear wheel. This is a particular problem when using the microscope to perform time-lapse photography - the gradual slight downward movement of the stage can cause loss of focus.

Another problem associated with conventional motorised microscope stages is that the stage assembly is rather thick: the ideal stage, from the microscopist's viewpoint, would be essentially planar, to facilitate manipulation of the specimen on the stage.

One reason why a conventional microscope stage assembly is typically thick and very solidly built is to ensure that the stage is extremely stable. This is because any instability can cause a specimen mounted on the stage to move or vibrate. This is extremely undesirable since even very small movements can render observation of the specimen impossible when viewing at high magnification, causing the specimen to shift out of focus and/or out of the field of view. This problem is very well know to those skilled in the art and, as a result, conventional stages are formed by 'stacking' the stage components one on top of another to create a relatively massive stage with optimised stability. Summary of the Invention

In a first aspect the invention provides a stage component for use in manufacturing a motorised stage for an optical instrument, the component comprising a base member, a top member and an intermediate member; wherein the top member is supported on, and is movable in a first axis relative to, the intermediate member; and wherein the intermediate member is supported on, and is movable in a second axis relative to, the base member; characterised in that at least a selected one of the stage members is arranged such that, in use, it is supported at a proximal end region, the opposed distal end region being unsupported such that a specimen holder formed on or to be attached to the distal end region projects outwards from the selected stage member.

Desirably the first and second axes are orthogonal to one another and desirably are both substantially horizontal. Typically the first and second axes are Ύ' and 'X' axes such that, for a user, one axis of movement (Y) is directly towards or away from the user of the optical instrument, and the other axis of movement (X) is to the left and right of the user.

In general terms, the intermediate member takes the form of a generally horizontal platform, mounted on the base member, so as to be movable in one horizontal axis relative to the base member, whilst the top member takes the form of a further generally horizontal platform mounted on the intermediate member so as to be movable in a horizontal axis relative to the intermediate member, the two aforementioned horizontal axes being essentially orthogonal.

In a second aspect, the invention provides a motorised stage for use with an optical instrument, the stage comprising: the component of the first aspect of the invention; a drive or motor to cause movement of the top member relative to the intermediate member, and a drive or motor to cause movement of the intermediate member relative to the base member; and one or more inputs for electrical power for the said drive(s) or motor(s). In a third aspect the invention provides an optical instrument comprising the motorised stage of the second aspect or the component of the first aspect. Typically the optical instrument is a microscope, especially an instrument adapted and configured for performing transmission light microscopy, but the instrument could in principle be any optical instrument where precise controlled movement of a sample relative to the instrument is desired, e.g. a micro-lithographic instrument or the like.

Preferred features of the various aspects of the invention will now be described in greater detail.

The stage component of the first aspect of the invention may be provided in generic form to manufacturers of optical instruments in a simplified configuration e.g. without a specimen holder, so that the instrument manufacturer may attach a suitable specimen holder dedicated for use with the particular instrument concerned. In such embodiments, the stage component will preferably include the associated motor drive(s) for the stage members, and the component will preferably comprise a plurality of attachment points to allow, for example, attachment of the stage component to different sizes or types of apparatus and/or in different orientations.

In other embodiments, the stage component of the first aspect of the invention will be in a form specifically configured and adapted for use with a transmission light microscope. In this form, the stage component will conveniently comprise a specimen holder already formed on, or attached to, the distal end of the selected stage member. The component will also be configured for attachment to a light microscope and will conveniently be compatible with universal or common stage mounting brackets or attachments.

Preferably, but not necessarily, the selected stage member which is arranged to have a supported proximal end region and an opposed unsupported distal end region is the top member. In a preferred embodiment, the supported end region is supported on a lower stage member, such as the intermediate stage member (where the selected stage member is the top member).

It will be appreciated that the supported proximal "end region" of the selected stage member is not restricted to the support being provided solely at the very end of the stage member, but may extend from the proximal end by some amount. For example, where the stage member in question is supported on another, lower, stage member, then the depth of the supported proximal end region may extend by an amount approximately equal to the width of the lower stage member. This may be a width of at least 5 cm, typically at least 6 cm and conveniently about 7 cm. Further, because the selected supported stage member will be movable relative to the lower stage member, it is conceivable and envisaged that, in use, the supported stage member may be in a relatively retracted position, such that the proximal end of the stage member may be withdrawn so far as to overhang the lower stage member, although this will not normally be the case.

When the instrument is in use to analyse or process a specimen, the distal end region of the selected stage member will always extend beyond the edge of the lower stage member, even when the selected stage member is maximally retracted relative to the lower stage member. As a guide, it is envisaged that, even when the selected stage member is maximally retracted, the centre of the specimen holder will be positioned about at least 5 cm beyond the lower stage member, preferably at least about 6 cm, and more preferably at least 6.5-7.5 cm. When the selected stage member is in a typical operating position, the centre of the specimen holder will be positioned at least about 8 cm beyond the lower stage member, preferably at least about 9 cm.

In particular, in preferred embodiments, the distal end region of the stage member will project in such a way that the specimen holder (and any specimen mounted thereon) will be positioned in the light path of light passing through the functional optics of the instrument. The overall effect of the arrangement of the invention is such that specimen holder is effectively 'suspended' in free space above the stage, but in the light path. This is highly advantageous in terms of allowing unhindered access to the specimen holder and/or to any specimen mounted thereon. However, such an arrangement is highly counter-intuitive to the person skilled in the art, because it would be expected to be unstable and thus highly susceptible to movement, vibration etc. which would interfere with analysis of the specimen.

The specimen holder will typically be dimensioned so as to accommodate a conventionally-sized microscope slide. The specimen holder will desirably comprise some form of biasing or urging means, typically a spring means such as a sprung clip, for retaining a microscope slide in a fixed position on or within the specimen holder.

In some embodiments the specimen holder is cantilevered on one of the members of the microscope stage component, preferably on the top member. Desirably the specimen holder is provided at one edge of the top member and is desirably not otherwise supported. In one embodiment, the top member is provided with a groove or recess at an edge thereof, and an edge of the specimen holder is accommodated within the groove or recess. Optionally other fixture means to fix the specimen holder to the top member may alternatively or additionally be used. The preferred embodiments of the invention have the specimen holder projecting into space, with little or no stage components immediately adjacent above or below the specimen holder to impede access to, or manipulation of, a specimen on the specimen holder.

The stage of the invention, and optionally also the component of the first aspect of the invention, comprises a drive or motor, typically an electric motor. It is conceivable that a single motor may be employed to cause the movement of both the top member and the intermediate member (relative to the intermediate and bottom members respectively). It is however greatly preferred that a separate motor is used to cause the movement of the respective members. It is a highly preferred feature of the invention that the motor is such that it directly drives movement of the stage, without requiring any intervening transmission member. This may conveniently be accomplished by use of a linear shaft motor (LSM). Desirably two LSMs are provided, one causing movement of the top plate (relative to the intermediate member), and one causing movement of the intermediate member (relative to the base member). In a linear shaft motor, a magnetic shaft runs through an aperture in a coil of the motor. Application of an electric current to the coil induces movement of the coil relative to the magnetic shaft. The coil may be fixed, in which case the shaft is forced to move through the coil or, more conventionally, the shaft is fixed and the coil moves along the shaft. Direct attachment of the coil, or shaft, as appropriate, to the stage member thus brings about direct driving of the movement of the stage member.

By providing a repeating array of very small permanent magnets along the length of the shaft, it is possible to cause precisely-defined relative movements of the shaft and motor, which is especially convenient for application in the present invention. In addition, because the motor does not actually bear on the shaft, there is no wear, the LSM is very quiet and has low power consumption. Another significant advantage of the use of an LSM is that it avoids the use of the ballscrew/thread arrangement of conventional motorised stages, or other form of indirect drive transmission, and thereby eliminates the mechanical "backlash" which is normally associated with conventional motorised stages. Suitable LSMs are available from several sources, including Nippon Pulse America Inc. (4 Corporate Drive, Radford, Va 24141) and Faulhaber Group (MicroMo Electronics, Inc. 14881 Evergreen Avenue, Clearwater, Fla 33762).

The top member and the intermediate member are preferably independently movable, in at least one axis, relative to the base member. In a preferred embodiment of the component and stage of the invention, the bottom member is static (at least in respect of the X and Y axes). Accordingly, the intermediate member is driven by a motor to cause the said movement of intermediate member relative to the base member.

In addition to movement in the horizontal X/Y axes, the stage component of the first aspect of the invention, or at least a part thereof, is arranged to be movable in the vertical Z, axis. This Z axis movement may be accomplished manually, by a user. In other embodiments, Z axis movement is accomplished by a motor or drive means. The motor or drive may move the entire stage, or may move part of the stage, such as a stage member or a specimen holder mounted on or attached to a stage member. Generally, the amount of travel required in the Z axis is less then that required in the X or Y axes, for example, to adjust focus. Accordingly the type of motor or drive suitable for movement in the Z axis is rather different to those used for moving the stage members in the X/Y axes. A preferred drive comprises a piezoelectric device, and a suitable piezoelectric device is available from the Cedrat Groupe (15 Chemin de Malacher, 38246 Meylan Cedex, France).

In one embodiment, the top member is supported at a proximal end region but is unsupported at a distal end region. This arrangement helps to minimise the mass of the stage component and of a stage comprising the component. The reduction in mass of the stage components in turn allows for a reduced size motor to drive the stage with lower power consumption, relative to conventional stages. Additionally the lighter stage is far less prone to slight downward drift under its own weight, and is therefore especially useful when employing time-lapse photography.

Desirably a guide mechanism is provided to guide the relative movement of the top and intermediate members. Conveniently the guide mechanism comprises one or more guide rails or a guide channel on one of the members between which relative movement occurs, and a guide follower provided on the other member. In one embodiment the guide follower comprises a carriage which runs along a guide rail provided on the other member of the pair of members. The guide rail may be formed from a durable substance, typically metal, and the carriage may employ devices such as re-circulating ball bearings to substantially eliminate friction between the carriage and the rail.

The stage component of the first aspect of the invention, and the stage of the second aspect of the invention, will advantageously comprise a position detecting mechanism to detect the relative position of the top and intermediate members relative to one another and/or relative to the bottom member.

In a preferred embodiment the position detecting means will comprise an optical element which detects one or more markings provided on at least one of the members. Conveniently, the position detecting means comprises an optical encoder. Advantageously the optical encoder is located on the guide follower. Desirably the guide rail or channel followed by the guide follower is provided with at least one reference mark and a plurality of other marks detectable by the optical encoder, such that the relative position of the guide follower, and hence of the member on which the guide follower is mounted, can be determined. The plurality of detectable marks are, in one embodiment, laser etched on the guide rail or guide channel, typically at regular intervals.

Other position detecting means are of course suitable for use in the invention. Examples include magnetic encoders, strain gauges, Hall-effect sensors and similar devices for accurately determining position.

Another advantage of the invention is that it reduces the depth of the stage and allows the space around the objective lens, the specimen holder, and the sub-stage condenser, to remain uncluttered relative to conventional motorised stage microscopes, thus facilitating manipulation of the sample, objective lens and condenser.

For the avoidance of doubt it is hereby expressly stated that any features described herein as "preferable", "desirable", "advantageous", "convenient" or the like may be present in the invention in isolation, or in any combination with any one or more other such features so described, unless the context dictates otherwise. Also, features so described in relation to one aspect of the invention are equally applicable to the other aspects of the invention, unless the context dictates otherwise.

The invention is further described below by way of illustrative embodiment, and with reference to the accompanying drawings.

Brief Description of the Drawings

Figure 1 is a perspective view of an embodiment of a motorised stage in accordance with the invention;

Figure 2 is a plan view of the embodiment shown in Figure 1 ;

Figure 3 is a side elevation of the embodiment shown in Figure 1 ; Figure 4 is a perspective view of the embodiment shown in Figure 1 , but with a cover removed to show more clearly the internal features of the apparatus;

Figures 5 and 6 are a plan view and side elevation, respectively, of the embodiment shown in Figure 4;

Figure 7 is a perspective view, from the underside, of a second embodiment of apparatus in accordance with the invention;

Figure 8 is a cut-away drawing, to a different scale, of part of the embodiment shown in Figure 7; and

Figure 9 is an exploded perspective view of a different embodiment of a stage component in accordance with the first aspect of the invention.

Detailed Description of an Embodiment

Referring to Figures 1-3, an embodiment of a motorised stage, indicated generally by reference numeral 2, in accordance with the invention comprises a X/Y axis-static base member 4, an intermediate member 6, and a top member 8.

The entire stage is for mounting on a microscope and is arranged so as to be movable in the z axis (i.e. vertically up or down) relative to an objective lens assembly of the microscope, so as to allow adjustment of focus.

The base member takes the form of a platform with a substantially horizontal planar upper surface, about 220 mm long and 140 mm wide, and is formed from anodised aluminium. A substantially circular aperture 10 is formed in the base member 4. The motorised stage is intended for use with a transmission light microscope, and the aperture 10 allows light to pass through the base member 4 to illuminate specimens placed in a specimen holder 12, which is borne by the top member 8. In addition the aperture 10 allows for possible close approach to the stage of a sub-stage assembly component of the microscope (the sub-stage assembly comprising e.g. one or more of a light source, one or more filters, a condenser and the like). The base member is large, so as to facilitate attachment to a transmission light microscope via a conventional stage mounting bracket, but otherwise the base member could be made considerably smaller if some other attachment means were utilised. The intermediate member 6 is considerably smaller than the base member 4. Intermediate member 6 is also formed primarily from anodised aluminium and is a generally rectangular, thin platform with essentially horizontal upper and lower surfaces. The intermediate member is mounted so as to be horizontally movable in the X axis relative to the static base member 4. The intermediate member 6 is about 100 mm long and 70 mm wide.

The top member 8 is generally similar to the intermediate member, in that it too is a generally rectangular, thin platform with essentially horizontal upper and lower surfaces. However, the top member 8 is mounted on the intermediate member orthogonally, and is arranged so as to be horizontally movable in the Y axis relative to the intermediate member 6. The top member is cantilevered on the intermediate member, such that the top member is entirely supported thereon at a proximal end region of the top member, whilst a distal end region of the top member is unsupported and projects into free space above the base member 4, and more specifically, above the aperture 10 in the base member. Accordingly, movement of the supporting intermediate member (relative to the X/Y-axis static base member) causes corresponding movement of the top member (relative to the base member). The top member is about 130 mm long and 100 mm wide, and is formed from aircraft-quality pre-stressed aluminium. Use of this material makes the top member very light but strong and stable, resistant to vibration.

At one end of the top member there is a narrow, rectangular-section groove provided in the edge thereof. An edge of the specimen holder 12 is inserted into this groove, such that the specimen holder is attached to, and supported by, the top member. The specimen holder takes the form of a substantially square or rectangular frame 14 defining a rectangular aperture 16. Within the aperture 16 are small flanged portions 18, at opposite ends thereof. A microscope slide of conventional dimensions can be inserted into the aperture 16 and is supported by the flanged portions. A sprung clip 20 is also provided to hold an inserted slide firmly within the specimen holder. In other embodiments, the specimen holder 12 is formed as an integral part of the top member. The cantilevered arrangement of the top member, and the way in which the specimen holder projects from an edge of the top member, allows the specimen holder to be positioned such that it is readily accessible from above or below, enabling the specimen to be manipulated with ease. The invention thus provides a motorised stage which confers ease of manipulation of a specimen mounted on a specimen holder attached to the stage.

Movement of the intermediate and top members in the X and Y axes respectively, and relative movement of the entire stage in the Z axis, can position a specimen on the specimen holder in any position in three dimensional space (within the limits of travel of the components) relative to an objective lens used to inspect the specimen.

The significant operable portions of the base, intermediate and top members are at least partially protected against shock, dust, liquid spills etc. by a shield 22, which is fitted to the base member 4 and forms a cover over an end portion of the motorised stage. The shield 22 is formed from a moulded polymer material. The shield surrounds a central aperture, within which is placed a transparent window 24, made of synthetic plastics material. The transparent window allows for superficial inspection of the components of the stage 2 without requiring removal of the shield. In other embodiments the shield may be entirely opaque.

The operation of the motorised stage will now be further described, with reference to Figures 4-6.

A guide mechanism is provided to guide the movement of the intermediate member 6 relative to the base member 4. As best seen in Figures 4 & 5, the base member 4 comprises a recessed channel portion 30. Within the channel 30 is a metal guide rail 32. A carriage (not shown in the drawings) on the underside of the intermediate member 6 is engaged with the guide rail 32 and acts as a guide follower.

The bottom member 4 comprises a further channel portion 34, which is narrower than channel portion 30. Within channel 34 is fixed a thin metal rod 36 of circular section. The rod 36 forms the shaft of a linear shaft motor (LSM). The motor coil which runs on fixed shaft 36 is mounted on the underside of the intermediate member 6. Thus, movement of the motor coil (not visible in the Figures) along fixed shaft 36 causes movement of the intermediate member 6 in the X axis relative to the static base member 4. The motor coil is provided with a small printed circuit board (PCB) which controls movement of the motor along the fixed shaft 36. The LSM provides about 80mm of travel in the X axis. There is a small gap (about l-2mm) between the shaft and the motor coil which runs along it. Accordingly, the motor has no wear and is very quiet in operation.

The apparatus is provided with position detecting means. The guide rail 32 has a very precise laser-engraved scale marked thereon. The scale is read by an optical reader mounted on the underside of the intermediate member 6, such that the position of the intermediate member on the X axis (relative to the base member) can be accurately determined. The system is accurate to about 1 μιη. Optical encoders are commercially available from, inter alia, Renishaw, Sony and Numerik Jena.

A somewhat similar arrangement of guide rail, guide follower, shaft and electric motor is provided to cause guided movement of the top member 8 relative to the intermediate member 6. The details, however, are slightly different.

Firstly, the orientation of the guide rail, and the motor shaft, is at 90° to those provided to cause movement of the intermediate member since of course the top member moves orthogonally relative to the intermediate member.

Secondly, in the linear shaft motor used to cause movement of the top member (relative to the intermediate member), the motor coil is fixed, and the shaft is free to move. Thus, the intermediate member 6 comprises a recessed rectangular-section channel. Within the channel is fixed a motor coil. A linear metal shaft, mounted on the underside of the top member 8, is free to move within the motor coil.

A guide rail and guide follower arrangement guides the movement of the top member relative to the intermediate member and, as with the bottom/intermediate member arrangement, a laser-engraved scale on the guide rail is ready by an optical reader to allow precise determination of the position of the top member, along the Y axis, relative to the intermediate member. The maximum travel along the Y axis is about 50mm.

The stage also comprises a microprocessor (and associated circuitry) to process positional data provided by the position detecting means associated with the members, and to control the movement of the linear shaft motors. The processor and associated circuitry are, for the most part accommodated within a covered compartment 42 located on top of the top member 8.

Also provided is an electrical power input to accept electrical power from a power source. Any suitable power source may be utilised. Typically the power source will be mains source which is rectified and/or transformed to provide e.g. a 12v D.C. supply. The electrical power is required to operate the motors and associated electronics.

Figures 7 and 8 illustrate a second embodiment of a motorised stage in accordance with the invention. The embodiment shown in Figures 7 and 8 is very similar to the embodiment shown in Figures 1-6 and, in general, comprises substantially identical features. However, the second embodiment differs in particular from the first embodiment in the manner in which the specimen holder is secured to the member of the stage component.

A screw at each side of the apparatus secures the specimen holder to the top stage member 8. Each screw passes through a respective annular component 50 located on the underside of the stage member 8. One such component 50 is visible in Figure 7.

Figure 8, drawn to a different scale compared to Figure 7, shows the arrangement more clearly. Screw 52 passes through annular component 50 and top stage member 8 and is secured by a screw-threaded engagement with the specimen holder 12. Annular component 50 comprises a groove, within which is seated compression spring 54, such that tightening of the screw 52 forces spring 54 into compression, the spring 54 therefore acting as urging means. Accordingly, adjustment of the screw 52 and/or its counterpart screw on the other side of the apparatus, can be made to alter level of the specimen holder. Normally the specimen holder will be adjusted so as to approach as closely as possible to horizontality, but the arrangement also allows for the plane of the specimen holder to be deliberately made non-horizontal, if desired.

Figure 9 is a perspective exploded view of one embodiment of a stage component in accordance with the first aspect of the invention, supplied in generic form for use with a variety of optical instruments (not necessarily a transmission light microscope).

The component has a different appearance from the embodiment shown in Figures 1- 8, but the functional arrangement is generally similar, and analogous components are numbered with corresponding reference numerals. Thus, the stage component comprises an X/Y -static base member, an intermediate member 6, and a top member. The base member comprises a base plate 4a and a base cover 4b. The top member 8 comprises a top plate 8a and a top cover 8b. The base member is provided with an LSM drive (not shown) to drive the intermediate member 6 relative to the base member, and the intermediate member 6 is provided with an LSM drive 60 to drive the top member relative to the intermediate member.

The stage members are formed with guide rails 32 and guide followers and optically- read position detecting means, in a manner analogous to the embodiment shown in Figures 1-8.

The top plate 8a is shaped and configured to receive one of a variety of different specimen holders at an unsupported distal end 62 thereof, and includes a plurality of differently-sized circular apertures drilled therein to receive a variety of different types of attachment pins, screws, lugs etc. Similarly, the base plate 4a also comprises a plurality of differently-sized circular apertures, to facilitate mounting of the stage component in a number of different optical instruments. Other embodiments of the invention can, of course, be envisaged, within the scope of the appended claims.

Claims

1. A stage component for use in manufacturing a motorised stage for an optical instrument, the component comprising: a base member, a top member and an intermediate member; wherein the top member is supported on, and is movable in a first axis relative to, the intermediate member; and wherein the intermediate member is supported on, and is movable in a second axis relative to, the base member; characterised in that at least a selected one of the stage members is arranged such that, in use, it is supported at a proximal end region, the opposed distal end region being unsupported such that a specimen holder formed on, or to be attached to, the distal end region projects outwards from the selected stage member.

2. A component according to claim 1, comprising a specimen holder.

3. A component according to claim 1 or 2, comprising one or more linear shaft motors to cause the relative movement of the members.

4. A component according to any of the preceding claims, wherein the movement of the stage members is guided by a guide mechanism, which guide mechanism comprises one or more guide rails or channels provided on a first stage member, and a co-operating guide follower provided on a second stage member, which second member moves relative to the first stage member.

5. A component according to any of the preceding claims, further comprising a position detection mechanism to detect the relative position of the top and/or intermediate members.

6. A component according to claim 5, wherein the position detection mechanism comprises a laser-etched or laser-engraved scale on a first member which is read by an optical reader mounted on a second member which moves relative to the first member.

7. A component according to any of the preceding claims, additionally comprising a microprocessor and associated circuitry, the microprocessor processing data input from a position detection mechanism, and controlling movement of one or more motors which move the stage members.

8. A component according to any of the preceding claims, in which a motor directly drives movement of a stage member without any intervening transmission, thereby avoiding backlash when the direction of travel of the stage member is reversed.

9. A component according to any one of the preceding claims, wherein the base member is static in respect to the X and Y axes.

10. A component according to any one of the preceding claims, wherein the specimen holder is formed on or attached to the top member.

11. A component according to claim 10, wherein the specimen holder is supported by the top member only.

12. A motorised stage comprising a component according to any of the preceding claims, and further comprising an electrical power input to accept electrical power to operate one or more electrical motors.

13. An optical instrument comprising a component according to any of claims 1-11, or a stage according to claim 12.

14. A light microscope according to claim 13.

15. A component for use in manufacturing a motorised stage of an optical instrument, or a motorised stage comprising such a component, substantially as hereinbefore defined and with reference to the accompanying drawings.