WO2008048150A1

WO2008048150A1 - Microscope system comprising arrangement for two- dimensional positioning of a platform

Info

Publication number: WO2008048150A1
Application number: PCT/SE2006/001178
Authority: WO
Inventors: Anders Rosenqvist
Original assignee: Anders Rosenqvist
Priority date: 2006-10-18
Filing date: 2006-10-18
Publication date: 2008-04-24

Abstract

In an arrangement for two-dimensional positioning of a platform (32) in a microscope system, the platform (32) may travel along a first direction, which is perpendicular to the optical axis (33) of the system, supported by two guiding elements (12, 22). An actuator (18) introduces a deflection at a point (20) near one end (14) of a guiding element (12). The deflection propagates along different directions through a plurality of parts (11, 14, 12, 38, 32) and results in that parts of the platform (32) are moved along the optical axis (33). Some of the parts (11, 12, 32) that propagate the deflection, each give, by using other parts (10, 16, 22) as fulcrums of levers, multiplicative contributions to a total gear ratio, meaning that the move of the platform (32) near the optical axis (33) is just a fraction of the deflection introduced by the actuator (18).

Description

MICROSCOPE SYSTEM COMPRISING ARRANGEMENT FOR TWO- DIMENSIONAL POSITIONING OF A PLATFORM

Field of the Invention The present invention relates to an arrangement for positioning of a platform in a microscope system.

Background Art

Microscopes need to be focused on the physical object under study in order to give useful images thereof. Therefore the physical object has to be positioned with great precision with respect to the optical parts of the microscope. Each time a new part of the physical object is brought into the field of view of the microscope, the focus may have to be adjusted using a positioning arrangement that is able to handle the focusing with a precision as well as a resolution of sometimes as small as a tenth of a micrometer. For an automated microscope, the individual focus adjustments should be performed quickly since the analysis of a physical object may need several thousands of them. Thus there is a need for a reasonably stable positioning arrangement that, at least, can achieve finely resolved and fast focusing. With a positioning arrangement that, in addition, is small, light weight and cost efficient, it would be possible to achieve cost reduction and performance improvements of existing automated microscope designs and possible to produce portable cost efficient automated microscopes for new market segments. In order to contribute to the cost efficiency, it would be beneficial if the focusing of the positioning arrangement could provide a gear ratio larger than one. Such a gear ratio would allow for the use of a low cost, coarse resolution, focusing actuator while at the same time achieve focusing with a fine resolution. Thus it would be useful with stable, fast, small, light weight and cost efficient positioning arrangements that in addition can produce a fine focusing resolution from a coarse resolution actuator.

To achieve focusing by automating the moves of the intrinsic focusing mechanism of a standard microscope may be expensive. Such an approach also involves moving of quite large masses which probably results in a quite slow speed and in problems with vibrations after the intended move. For automated microscopy of an object that is an ordinary microscope slide, which is about 1 by 3 inches wide and about 1 millimeter thick, it may be wiser to have a fixed revolver/objective and to focus by just moving the object. The latter approach may even eliminate the need for a standard microscope frame in the automated microscope.

The positioning arrangement of an automated microscope with fixed revolver/objective needs to position the object in three dimensions. Such a positioning system may use three separate cascaded systems for x, y and z (focus) respectively. However, the three cascaded systems will most probably contain redundant parts, which do not contribute to stability, speed, small size, light weight or cost efficiency.

One three-dimensional flexure approach, which is disclosed in US 4635887, is probably stable and fast, quite small and also light weight, but its possible range in x and y is too small for automated microscopy and it does not provide any gear ratio as defined above.

Another approach, which is disclosed in WO 2005/119329 and in the patent family of US 6407858, is to separate the three-dimensional positioning arrangement into one two-dimensional arrangement (either x or y, z) and one cascaded arrangement for the remaining dimension. When such a positioning arrangement is used for searching an object for interesting areas, the search can be made in a pattern that seldom uses the positioning arrangement of the remaining dimension. Then that arrangement does not have to be so fast, which allows for the use of slower, stable and cost efficient designs of the prior art. The two-dimensional positioning arrangement (either x or y, z) will be the only one discussed in the following.

By way of the patent family of US 6407858, it is known to use a hinged tiltable plate that supports a linear positioning arrangement for x positioning and to change the tilt of the plate using a linear actuator for focusing. Provided that the relative positions of the hinge, the actuator and the optical axis are properly chosen, there will be a gear ratio greater than one. In order to achieve a gear ratio of about twenty, the plate may have to be quite long, probably in the order of half a meter, which makes it less useful for portable microscopes. The motor driving the x positioning will most probably have to be included in the parts that move during focusing. The motor will therefore be included in the moving masses and focusing speed will suffer.

By way of WO 2005/119329, it is known to use a double flexure for two- dimensional positioning. The double flexure achieves a gear ratio greater than one and does not seem to contain any expensive parts. The drawbacks of the double flexure is that it is quite big and therefore needs space inside the automated microscope. In order to give it a low mass, its parts may have to be slim, possibly making it sensitive to vibrations. In order to achieve focusing with a resolution that is fine enough, both actuators have to have a quite fine resolution, which probably limits the speed of x movements.

Summing up, there are a number of problems caused by the prior art-techniques mentioned above: Automated microscopes designed according to these techniques are large, heavy, slower than necessary in z (focus), sensitive to vibration and/or slower than necessary in x.

Summary of the Invention

An object of the present invention is to eliminate or at least alleviate the above- mentioned problems. This object is achieved wholly or partially with an arrangement according to claim 1 or its dependent claims. More specifically the invention relates to a microscope system comprising an arrangement for two- dimensional positioning of a platform along a first dimension and along a second dimension which is perpendicular to the first dimension, where the arrangement comprises first and second guiding elements, where the two guiding elements permit the platform to be positioned along the first dimension, where at least one of the first and second guiding elements define a position of the platform along a third dimension, which is perpendicular to both the first dimension and the second dimension, where at least one of the first and second guiding elements define a tilt of the platform around the third dimension, where both guiding elements jointly define the position of the platform along the second dimension as well as a tilt of the platform around the first dimension, where the definitions possibly depend on the position of the platform along the first dimension, where a first actuator which has an adjustable first length and which is connected to the rest of the arrangement can deflect the position of at least one end of the second guiding element by a first change along a fourth dimension when the first length is changed by a second change, where the first change results in that the second guiding element propagates a third change of position along a fifth dimension to a connection at the platform, where the third change results in a fourth change of position along the second direction to at least a point which is situated at an intersection of the platform and an optical axis of the microscope, and where a total gear ratio, defined as the second change divided by the fourth change, has an absolute value greater than one. Other embodiments are defined in the dependent claims.

There are a number of advantages with the present invention. A positioning arrangement according to the present invention does not significantly add to the dimensions of the microscope system. The components for implementing the positioning along the second dimension are almost all already there for implementing of the positioning along the first dimension. A positioning arrangement according to the present invention therefore leads to a compact, vibration resistant design. At the same time the present invention has few movable parts and the parts that move have low masses. The resolution of an actuator that may position the platform along the first dimension does not influence the performance along the second dimension, so it can be chosen to be larger, making it possible with faster x movements while still have good focus adjustment performance.

With the present invention it is not only possible to achieve a gear ratio greater than one, it is also possible to let gear ratios from individual parts in the arrangement multiply. Thereby long, vibration sensitive or heavy, levers can be avoided. The advantages of the present invention will be described in more detail below.

Brief Description of Drawings

The present invention will now be described in more detail by way of embodiments which refer to the accompanying drawings, in which

Fig. 1 schematically illustrates an example of an arrangement for two-dimensional positioning according to a preferred embodiment of the present invention;

Fig. 2 schematically illustrates another example of such an arrangement according to another preferred embodiment;

Fig. 3 schematically illustrates a first alternative way of introducing deflections from an actuator to an arrangement according to the present invention; Fig. 4 schematically illustrates a second alternative way of introducing deflections from an actuator to an arrangement according to the present invention; and Fig. 5 schematically illustrates a third alternative way of introducing deflections from an actuator to an arrangement according to the present invention.

Description of preferred embodiments In Fig. 1 an arrangement according to a preferred embodiment of the present invention is schematically illustrated. The arrangement may be a part of a microscope system and its main use may be for two-dimensional positioning of some object which is under study and which is supported by a platform (32). The positioning is made along a first dimension, which is denoted x in Fig. 1, and along a second dimension, which is denoted z in Fig. 1, and which is approximately perpendicular to the first dimension. The second dimension (z) may be approximately parallel to an optical axis (33) when the arrangement is part of microscope system or some other system comprising optical representations. The platform (32) is supported by two guiding elements (12, 22). The end points (14, 16, 24, 26) of the guiding elements are somehow mounted to the positioning arrangement or directly to parts of a master system comprising the arrangement. It will now be described in detail the result of a single actuator (18) affecting a single end (14) like in the arrangement of Fig. 1. An actuator (18) may introduce a first deflection at a point (20) near one end (14) of one of the guiding elements (12). By deflection it is meant a relative change of position of a part of the positioning arrangement. The deflection (change of position) at (20) is preferred to be of the temporary kind, i.e. it is supposed be to small enough with respect to the materials of the involved parts to only cause so called elastic deformations of the involved parts. Thus, when the actuator returns to its state prior to the deflection, the deflection will cease. It may however be possible to design the positioning arrangement for use of so called plastic (non-elastic) deformations, but the behaviour of the positioning arrangement will then probably be too hard to predict. Throughout this detailed description, for clarity and simplicity, it will be assumed that the end points (14, 16, 24, 26; 114, 116; 214, 224; 314, 324; 414, 424) are mounted to a plate (10; 110; 210; 310; 410). In Fig. 1, the plate is depicted with an integrated bending element (11), which is limited by the dashed line (13). For all of the embodiments this means that the bending elements (11; 111; 211; 311, 361; 411) are supposed to be deflectable while the rest of the plate (10; 110; 210; 310; 410), if it exists in reality, is stiff and rigidly fixed to the positioning arrangement or its master system and not noticably affected by deflections of the corresponding bending elements.

As a consequence, in the arrangement of Fig. 1, the guiding element (22) is not affected by deflections caused by the actuator (18). The guiding element (22), which may be a polished cylindrical steel rod, defines, via bearings (34, 36), which may be glide bearings with a tight fit, possibly using expandable slits, a number of parameters of the platform (32). The guiding element (22) defines the position along the y dimension, the tilt around the y dimension, the state of rotation around the z dimension and the z position(s) for the bearings (34, 36). The platform (32) may be spring loaded in order to prevent plays between parts, if any, from moving around. The x position of the platform (32) may be defined by the actuator (28) which may be connected to the point (30) of the platform (32). At the other end of the platform (32) there is the connection (38), which may be a sligthly modified split glide bearing, in contact with guiding element (12), which may, too, be a polished cylindrical steel rod. The connection (38) may rest on the guiding element (12), possibly being spring loaded for controlling the play in the z dimension between connection (38) and guiding element (12). There should be some play in the y dimension, so that the y position may be defined only by the guiding element (22) like described above for this embodiment. The connection (38) should also allow for the guiding element (12) to be tilted around the y dimension. The guiding element (38) gets its position in the z dimension from the guiding element (12). Thus, guiding elements (12, 22) together define the tilt of the platform (32) around the x dimension. As the platform moves along the x dimension, the z position of the guiding element (38) as well as the tilt of the platform (32) around the x dimension will probably change even if the actuator (18) is at rest. An exception is when guiding elements (12, 22) are perfectly parallel.

Since it is often useful to position along x and z in an independent way, the control of the arrangement according to Fig. 1 may be made easier and faster by use of, for example, a correction table. The correction table may, as a function of the x position of the platform (32) and of the state of the actuator (18), provide how much z should be corrected per micrometer of x position change in order to keep the same z position after the x position change. The correction table may, for example, be calculated during production and testing of the positioning arrangement or achieved through calibration during its use.

When the bending element (11) is deflected, it is rotated at the end (14) of the guiding element (12). Therefore the guiding element (12) may have to fastened to the bending element (11) and the plate (10) at the other end (16) in a way that does not require the guiding element (22) to be twisted. A slightly loose fastening or a roller bearing at one end (14; 16) may work.

Assuming that the point (20) is deflected in the positive z dimension by a change of one length unit and that the bending element (11) is fixed at (13), the end (14) will be deflected in the positive z direction by a change of one length unit divided by a gear ratio contribution (>=1) for the bending element (11). The deflection of the end (14) does not necessarily have to be along the second dimension. It may be along any fourth dimension as long as it it possible to propagate the deflection further to the platform (32). Further assuming that the end (16) has a fixed position and works as a fulcrum for the guiding element (12) being a lever, the connection (38) will be deflected in the positive z direction by a change of one length unit divided by the product of the gear ratio contribution for the bending element (11) and the gear ratio contribution for the guiding element (12). Thus the gear ratios of the bending element (11) and the guiding element (12) have been multiplied. The gear ratio of the guiding element (12) may depend on the present position of the platform (32) along the x dimension. Further assuming that the bearings (34, 36) fix their end of the platform (32) to the guiding element (22) at least along the z dimension, the guiding element (22) will act as a fulcrum for the platform (32) being a lever with respect to the deflection of the connection (38). The deflection of the guiding element (12) at the connection (38) does not necessarily have to be along the second dimension. It may be along any fifth dimension as long as it is possible to convert it to a deflection along the second dimension at the connection (38). For example, the connection (38) may have a slope that rests at the guiding element (12). Thus, the resulting deflection of the platform (32) at the optical axis (33) will be an even smaller fraction of the deflection introduced by the actuator (18) than the deflection at the connection (38). The total gear ratio will, for the preferred embodiment schematically shown in Fig. 1, be the product of the individual gear ratios of the bending element (11), the guiding element (12) and the platform (32) respectively. That product may be as large as around 5*2*2=20 for the embodiment of Fig. 1. A total gear ratio of 20 would mean that a 0,125 micrometer resolution at the optical axis (33) can be achieved with an actuator (18) having a resolution of 2,5 micrometers. Such a quite coarse resolution may be achieved by a full step of a 200 step per revolution stepper motor that is coupled to a screw having a 0,5 millimeter pitch. Such an actuator is really fast and cost efficient and the bending element, if made in one piece with the plate, is almost for free.

If a gear ratio of 20 were to be achieved with a single tilted plate as in the prior art, that plate may have to be about half a meter long. In order to make it stable enough to resist shocks and vibrations, such a tilted plate would probably have a considerable mass and therefore contribute to slow focusing performance.

With the present invention it is not only possible to multiply gear ratios from individual levers. In addition, the components for the levers are there anyway and do neither add to the mass, to the cost nor to the overall dimensions of the positioning arrangement.

Since the parts of the platform (32) that are closest to the guiding element (22), will hardly be deflected in the z direction at all, an actuator (28) for the x movement, which is fix with respect to the arrangement or its master system, may be fixed to the platform (32) at a point (30). There is probably no need for the actuator (28) to move along with for example the platform (32) in its z deflections. There is probably no need either for a joint allowing for a change of angle at the point (30). The moving parts of the arrangement according to Fig. 1 thus have a low mass which is beneficial for the speed of the system. Since the x actuator (28) is only used for x positioning, it may have a quite coarse resolution, like 10 micrometers or so, which contributes to the speed of x movements.

PLATFORM TILT

The arrangement illustrated in Fig. 1, uses tilting of the platform (32) around the x dimension to achieve deflections in the z dimension at the optical axis (33). For a microscope with an oil immersion objective with a numerical aperture of about 1.25 the focus depth is quite small, about some tenths of a micrometer. A possible field of view for a microscope system with an area sensor camera is about 100 micrometers in radius. It is probably acceptable if the platform (32), and its physical object, is tilted by 0,1 micrometer on a distance of a 100 micrometers along the y dimension. That tilt corresponds to 10 micrometers per centimeter. For an arrangement according to Fig. 1 where the distance from the guiding element (22) to the optical axis (33) may be for example 5 cm, a working focus interval with an acceptable tilt would then be ± 0,05 mm. If ± 0,05 mm is not a wide enough focus interval for the system then either a separate coarse focus system may have to be added or some of the other preferred embodiments below may be successful instead.

OTHER EMBODIMENTS

Another preferred embodiment is schematically illustrated in Fig. 2. The only difference with respect to the embodiment illustrated in Fig. 1 is that the guiding element (122) is integrated in the plate (110). Such an integration reduces the number of components needed to build the arrangement and might improve the stability of the system. On the other hand it may be harder to make the guiding element (122) cylindrical and to polish it than to manufacture the corresponding guiding element (22). Another preferred embodiment (not illustrated by any figure) uses a lead screw of the x actuator (28) as guiding element (22). That lead screw preferrably cooperates with nuts instead of bearings (34, 36). The lead screw, which will be required to be quite straight, then both guides the platform (32) and controls its x position. In Fig. 3 an alternative way of connecting the actuator (218) is illustrated. There the actuator (218) is directly connected to the end (214) of the guiding element (212). The deflections that are introduced by the actuator (218) propagate through the guiding element (212) and the platform (not shown) like in the embodiments of Figs. 1 and 2, but the total gear ratio is now a product of two factors only, namely the individual gear ratios of the guiding element (212) and the platform (not shown) respectively. Here, the bending element (211) does not contribute to the total gear ratio, but it defines the position of the end (214) along the x and y dimensions. In Fig. 4, it is shown how a single actuator (318) may introduce simultaneous deflections to two ends (314, 324). If these deflections are identical, there may be no tilt of the platform (not shown) around the x dimension. However, if the guiding element (322) defines the tilt of the platform around the y dimension, there will instead be tilt of the platform around the y dimension. Assuming that the two bending elements (311, 361) perform equally and that the two guiding elements (312, 322) also do so, the total gear ratio will still be a product of two factors, namely the individual gear ratios of the bending element (311), and the guiding element (312) respectively. Here, the platform will not contribute to the total gear ratio. If the assumptions are not true, it is however still quite easy to calculate the deflections of the parts involved. In Fig. 5, as single bending element (411) that propagates deflections to two ends (414, 424) is illustrated. Except for really small deflections, the forces needed to stretch the bending element (411) may be too large for a reliable design. This far, different embodiments with one actuator at one end of the plate have been described. It is possible, using for example duplicate versions of the actuator arrangement in Fig. 4, to introduce identical deflections to all four ends of the guiding elements. If so, the guiding elements and the platform will all have individual gear ratios being one. The total gear ratio would then be the individual gear ratios of the bending elements. There would however be no tilt of the platform.

There are other similar possible embodiments using different numbers of actuators, different numbers of deflectable ends, different ways of connecting the deflectable ends to actuators and different ways of letting the guiding elements define the positions and tilts of the platform. Having studied the disclosed details of the present invention, it will be possible for a person skilled in the art to explore these embodiments and to calculate the corresponding tilts and gear ratios.

Still another preferred embodiment involves an elevator concept. In that embodiment the plate is not fixed all the time, but instead it is movable in the z dimension while guided by additional guiding elements. There are also stops at the additional guiding elements that, once a certain height has been reached for the plate, stop the plate from going further up in the positive z direction. At that height, when one or more actuators try to pull the plate further up, the bending elements start to bend and the principles of the embodiments described above are again applicable. Such an elevator concept may be useful for levelling the platform with different levels of a microscope slide magazine while changing slides.

It is also possible to include an electromagnetic focusing system in the embodiments described above. Such an electromagnetic focusing system may consist of one or more plates of a magnetically susceptible material that are attached to, for example, the lower surface of the platform (32; 132) and one or more electromagnets that are fixed to the arrangement or its master system and being close to these plates. By adjusting the current through the electromagnets, an adjustable force that pulls the platform (32; 132) in, for example, the negative z direction, may be achieved. The deflections of such a force will be approximately added to the deflections that are propagated through the guiding elements. Although such a force may only be able to adjust the z position of the platform (32; 132) by a very small distance, it may be useful for fast compensation of vibrations in the z dimension. The vibrations may be measured by some accelerometer and used by a control system using a feed forward principle.

Due to tilts of guiding elements and platforms, parallel parts may sometimes only be essentially parallel. Due to the same reason, movements that are supposed to be along a certain dimension may only be essentially along this certain dimension.

The invention is not restricted to the described embodiments, but may be varied within the scope of the appended claims.

Claims

1. A microscope system comprising an arrangement for two-dimensional positioning of a platform (32; 132) along a first dimension and along a second dimension which is perpendicular to the first dimension, c h a r a c t e r i s e d by first and second guiding elements (12, 22; 112, 122; 212, 222; 312, 322; 412,

422), the two guiding elements permitting the platform to be positioned along the first dimension, at least one of the first and second guiding elements defining a position of the platform along a third dimension, which is perpendicular to both the first dimension and the second dimension, at least one of the first and second guiding elements defining a tilt of the platform around the third dimension, both guiding elements jointly defining the position of the platform along the second dimension as well as defining a tilt of the platform around the first dimension, the definitions possibly depending on the position of the platform along the first dimension, a first actuator (18; 118; 218; 318; 418) which has an adjustable first length and which is connected to the rest of the arrangement to deflect the position of at least one end (14; 114; 214; 314; 414) of the second guiding element

(12; 112; 212; 312; 412) by a first change along a fourth dimension when the first length is changed by a second change, the first change resulting in that the second guiding element propagates a third change of position along a fifth dimension to a connection (38; 138) at the platform, the third change resulting in a fourth change of position along the second direction to at least a point which is situated at an intersection of the platform and an optical axis (33; 133) of the microscope, and that a total gear ratio, defined as the second change divided by the fourth change, has an absolute value greater than one.

2. A microscope system as claimed in claim 1, characterised in that the fourth dimension is essentially parallel to the second dimension.

3. A microscope system as claimed in claim 1 or 2, characterised in that the fifth dimension is essentially parallel to the second dimension.

4. A microscope system as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the first actuator is connected (20; 120; 320; 420) to the at least one end (14; 114; 314; 414) through a bending element (11; 111; 311;411).

5. A microscope system as claimed in any one of the preceding claims, c h a r a cterised in that the total gear ratio is essentially a product of individual gear ratios for the bending element (11; 111; 311; 411). the guiding element (12; 112; 312; 412) and the platform.

6. A microscope system as claimed in claims 1-4, characterised in that the total gear ratio is essentially a product of individual gear ratios for the bending element (11 ; 111 ; 311 ; 411) and the guiding element (12; 112; 312;

412).

7. A microscope system as claimed in claims 1-4, characterised in that the total gear ratio is essentially the same as an individual gear ratio for the bending element (11 ; 111 ; 311 ; 411).

8. A microscope system as claimed in claim 1-3, characterised in that the first actuator is directly connected to the at least one end (214).

9. A microscope system as claimed in claim 8, characterised in that the total gear ratio is essentially a product of individual gear ratios for the guiding element (212) and the platform.