FR2562987A1 - Device for the fine positioning of a material surface - Google Patents

Abstract

The invention relates to a device for fine positioning. Such a device, enabling a plate 30 to be positioned along two orthogonal axes X, Y, comprises two crossed bars 1, inset, on the one hand, in the wall of a casing 26 and, on the other hand, in tabs 27 integral with the plate 30. Each bar is equipped with a heating element which allows it to be thermally expanded in a measured way in its own X or Y direction. A positioning precision of a fraction of a micron can be obtained over a range of several millimetres. According to the applications, the device may comprise only one or three bars 1.

Description

DEVICE FOR POSITIONING THE END OF A MATERIAL SURFACE
The present invention relates to a device for fine positioning of a material surface. Such a device is intended to achieve very precise positioning, for example to a fraction of a micron, within a narrow range of movement, which may not exceed a few millimeters. It finds application in the field of manipulation tables, which it can ensure microscopic displacements, in that of optical fibers (centering and connection), in that of manufacturing integrated or hybrid circuits where rigorous positioning3 are necessary, in that of lasers (mirror adjustment), etc.

 A positioning device according to the invention comprises at least one positioning member of which a first part is secured to a reference base and a second part is secured to the surface to be positioned, the relative position of these two parts being able to be modified by mutual displacement induced in a direction defined by the thermal expansion of a body brought to a variable temperature.

 The use of the phenomenon of thermal expansion of a body makes it possible to obtain displacements defined with extreme precision. Their slowness and low amplitude do not present any drawbacks for carrying out micrometric position adjustments in the applications envisaged.

 The aforementioned expansion body may consist of the solid material from which said positioning member is made at least partially.

 The latter may also have the structure of a deformable container filled with a liquid, this liquid constituting the aforementioned expansion body.

 The advantage offered by a liquid expansion body lies in an expansion coefficient higher on average than that of a solid. On the other hand, the positioning accuracy may be less good than with a solid. It is possible to combine the respective advantages of solids and liquids by using a double positioning member, comprising a first partial member made of solid material at least in part and a second partial member having the structure of a deformable container filled with liquid. , these partial members being associated in such a way that the effects of their own thermal expansion cumulate, while the corresponding solid and liquid expansion bodies are heated or cooled separately. The body with liquid expansion body provides a relatively large amplitude displacement large, while the body with solid expansion body provides the desired positioning precision.

 When a positioning member with a deformable container filled with liquid is used, the interior volume of the deformable container can be connected by a tube to a second substantially non-deformable container, placed at a distance, the assembly being filled with liquid, and heating or cooling the liquid in the second container. Here is exploited another advantage offered by a liquid expansion body, which thus removes the heat source from the surface to be positioned.

In general, the expansion body can be heated by means of an electrical resistance placed in its vicinity. When its constituent material is electrically conductive, it can also be heated by creating an effect
Joule within this matter (solid or liquid).

 If it is a question of being able to move the surface to be positioned in any direction of a plane, the device should comprise two positioning members arranged so as to induce respective displacements in crossed directions, preferably at an angle. straight, these directions being parallel to said plane. To allow the positioning of the surface in any direction of space, the device may include three positioning members arranged so that the directions of the displacements which they induce form a trihedron, preferably trirectangle. In all cases, the positioning members can attack a common movable plate to which the surface to be positioned belongs, said members being capable of bending laterally so that each of them does not oppose the expansion of the other positioning member (s) .Such a provision introduces only negligible errors, due to the smallness of the displacements used. When the device comprises two positioning members, the common plate which they attack can be supported by small columns oriented perpendicular to the directions of movement induced by said members, these small columns being capable of bending laterally so as not to hinder the expansion of said members.

 As a variant, in a device comprising two positioning members, the surface to be positioned of the first can serve as a reference base for the second. Similarly, if it comprises three positioning members, the surface to be positioned of the first can serve as a reference base for the second, the surface to be positioned of the second serving as a reference base for the third. In both cases, the surface to be positioned of the last member is that which receives the movements induced by all the members of the device.

 It should also be that the positioning member or each positioning member that a device according to the invention comprises is provided with a circuit for regulating the heating or cooling power of the expansion body as a function of one or more several parameters recorded by one or more measurement sensors, such as the temperature of the expansion body, the position of the surface to be positioned of the device and / or the speed of movement of this surface.

 In order to accelerate the displacements induced by the contraction of the expansion body of the positioning member or of each positioning member that a device according to the invention comprises, it is advantageous to provide at least one means of cooling this body. expansion, which can implement for example ventilation, a Peltier effect device or a vortex effect device. It is also possible to use such a cooling means to effect temperature regulation below ambient temperature.

 Other characteristics and advantages of the invention will emerge more clearly from the description which follows, with reference to the appended drawings, of nonlimiting exemplary embodiments.

 FIG. 1 illustrates the fundamental structure of a positioning member according to the invention.

 Figures 2 to 6 schematically show five alternative embodiments of such a member.

 FIG. 6a represents a variant of the heating circuit of FIG. 6.

 Figures 7 and 8 show a positioning member endowed with a temperature and position regulation circuit, respectively.

 Figures 9 and 10 show two embodiments of a device comprising two positioning members.

 Figures 11 and 12 show two embodiments of a device comprising three positioning members.

 FIG. 12a represents a section along C - C of the object of FIG. 12.

 For the sake of clarity, the heating elements of the devices in FIGS. 10 to 12 have been omitted.

 Schematically shown in Figure 1 a positioning member according to the invention, consisting of a metal bar 1 fixed at one end to a reference base 2 and having at its free end a surface 3, which can be positioned with a large precision along the longitudinal direction of the bar 1 by sending. an electric current dosed in a heating resistor 4 surrounding the bar. The latter is thus more or less heated and expands proportionally by bringing its end surface 3 to a neighboring position such as 3 '. The amplitude of displacement of the surface 3 is low, in practice of the order of a millimeter. However, the positioning thereof can be carried out very precisely, typically to within + lux.

 The surface 3 may not belong directly to the bar 1, but, as will be seen below, to a plate attached to the corresponding end thereof.

 FIG. 2 shows a variant where the bar 1 is replaced by an oblong container 5 closed at its end for fixing to the base 2 and closed at its other end by a sliding piston 6. The interior volume of the container 5, limited by the piston 6, is filled with a liquid 7. When a current is applied to the heating resistor h, the liquid 7 expands and causes the piston 6 and the surface 3 which belongs to it to move.

 In the embodiment shown in FIG. 3, the free end of the container 5 is no longer closed by a piston 6, but by a membrane 8 which deforms under the effect of the thermal expansion of the liquid 7 induced by the heating resistance 4. The outer surface of the membrane 8 constitutes the surface to be positioned, which comes in 3 ′ as a result of the expansion of the liquid 7.

 FIG. 4 shows a variant of the embodiment of FIG. 3. The container 5 is connected by a tube 9 to a second container 10. All of the elements 5, 9, 10 are filled with a liquid 7, which is heated for expansion no longer in the container 5, but in the container 10 placed at a distance and provided with the resistance 4.

 The advantage of using a liquid expansion body (Figures 2 to 4) instead of a solid body (Figure 1) lies in the higher value of the coefficient of expansion of liquids, leading to large displacements for low power thermal. However, the positioning accuracy of surface 3 is lower, because the same temperature variation corresponds to a greater displacement. The advantages of solids and liquids can however be combined, for example as shown in FIG. 5. Here we find a container 10 heated by a resistor 4 and connected by a tube 9 to a container 5 wedged on a base 2, the whole being filled with a liquid 7. The container 5 contains a piston 16 formed by a fairly long rod which is provided with a second heating resistor 14. This mixed device makes it possible to achieve a "large" positioning of the surface 3 located at the free end of the bar 16 by expansion of the liquid 7 by means of the heating resistor 4, and a "fine" positioning by expansion of the bar 16 by means of the heating resistor 14. The coarse positioning can for example, with mercury , cover a range of 30 mm + 0.01 mm, and fine positioning a range of 0.05 mm + 0.1 µm.

 In accordance with Figure 6, it is possible to heat a bar not using an additional resistance, but by creating a Joule effect directly within the material of the bar, provided that -this conductive of electricity. In the example of this figure, a metal bar 1 is provided with two contact collars 11 by means of which is sent into the bar an electric heating current, coming from the secondary of a transformer 12 manually adjustable.

 According to FIG. 6a, the heating current is adjusted not by moving a plug on the secondary of the transformer 12 (FIG. 6), but by chopping according to a variable duty cycle, using a switch 13, the current from the secondary of a fixed transformer 12a. This supply mode is of course also applicable to cases where a separate heating resistor is used. Heating by the direct Joule effect can also be used for positioning devices using a liquid. The Joule effect can then be created either within the conductive wall of the container 5 or 10 containing the liquid 7, or within the latter when it is a conductive liquid (mercury).

 The position of the surface 3 of a positioning member according to the invention can be adjusted by simple metering of the heating current, with control of the position 3 'reached.

One can also provide a regulation loop (Figures 7 and 8).

 FIG. 7 shows a rod 1 provided with a heating resistor 5- and with a temperature probe 15 placed in an internal channel 17. The desired temperature is introduced on a control device 18, and a supply device 19 adjusts the heating power by comparison between the desired temperature and the temperature measured by the probe 15.

 Increased accuracy and stability can be achieved by providing position control (Figure 8). Here, the position of the surface to be positioned 3 is recorded by a micrometric detector 20 (optical comparator) which transmits its measurement on the one hand to a display device 21, on the other hand to the supply device 19, which also receives from the device command 18 a set value defining the desired position 3 '. It is at this position that the surface 3 is stabilized. The regulation can additionally relate to the speed of movement of the surface 3 during positioning (which is advantageous for example for coincidence and connection by welding of two optical fibers).

FIG. 9 shows an example of application of a positioning device according to the invention, in two dimensions, comprising two positioning members A, B situated in a plane. The expansion bar of each of them is split into two parts la, lb, each part la being provided with a heating resistance 4. These two positioning members A, B and a leaf spring 22 are arranged at 1200 in a sleeve 23 surrounding an optical fiber 24 with the interposition of a layer of adhesive 25. The three elements A, B and 22 are oriented towards the core 24a of the optical fiber, which must be precisely centered in the sleeve 23. The spring 22 presses the optical fiber against the end surfaces 3 of the bars of the members
A, B, the parts lb of which are immobilized in the sleeve 23 not far from their contact faces with the parts la. Sending currents dosed in the resistors 4 makes it possible to center the core 24a of the optical fiber exactly. The adhesive 25 is then hardened, which freezes the assembly, including the parts of bars 1b, the parts 1a being able to be removed.

 The positioning device of FIG. 10 also comprises two bars 1. These are crossed at right angles and embedded on the one hand in two of the side walls of a parallelepipedic shoemaker 26, and on the other hand in lugs 27 integral of a plate 30 whose surface here is the surface to be positioned. This plate is carried on the bottom 26a of the bootmaker 26 by four columns 28 oriented perpendicular to the bars 1. When one of these expands under the effect of a controlled heating, it causes the plate 30 to move in translation in its plane in its own direction X or Y, while the other bar- and the columns 28 flex slightly to allow the movement of the plate 30 in translation in its plane.

FIG. 11 represents a device similar to that of FIG. 10, but comprising three bars 1 oriented in the directions of a trirectangle trihedron XY Z. These three bars are embedded on the one hand in the walls of a base 32 in the form of triangular trihedron and on the other hand in a similar part 33, which is positioned in the three directions
X, Y, Z of the bars 1 by selective thermal expansion and proportioned of these. As in the previous device, the bars 1 must be able to flex laterally to allow the positioning piece 33 to move relative to the base 32.

 In the device of FIG. 12, on the other hand, the three bars 1 do not need to be flexible laterally. They are in fact associated with respective plates 43, 53, 63 to form three positioning members cascaded. On a fixed base 42 is embedded a first bar lz carrying a plate 43 which serves as a base, thanks to a tab 43a which it comprises, to a second bar lx whose plate 53 in turn constitutes the base, by a leg 53a, a third bar ly 53 are square. The plate 43 slides against the king2 base, guided laterally by a slide 42a thereof against which it remains applied by means of an oblique return spring 34 (figure '2a). Likewise, the plate 53 is guided by the plate 43 and the slide 43b which the latter comprises, while the plate 63 is guided by the plates 53 and 43, an application spring similar to the spring 34 being provided in each case. .

 The regulation of the state of a positioning member according to the invention requires that the latter can quickly lose the calories it has received during heating periods. Its cooling can be natural. However, it is advantageous to provide a cooling device annexed to the positioning member, operating by forced or non-forced ventilation or comprising Peltier effect elements. When compressed gas is available, it is possible to use a vortex cooling.

 When the heating of the expansion body of a positioning member according to the invention is carried out by the Joule effect within the very material of this body, it is advantageous to choose the latter from among the conductive bodies offering a fairly high resistivity. A semiconductor body may be suitable in this regard.

 Another possible means for heating the expansion body is induction heating, for example using a microwave, which allows, by an appropriate choice of the materials used, in particular in the case of a liquid expansion body , to strictly circumscribe the heating to the expansion body.

Claims (15)

 1. Fine positioning device for a material surface, characterized in that it comprises at least one positioning member (1), a first part of which is secured to a reference base (2) and a second part of which is secured of the surface to be positioned (3), the relative position of these two parts being able to be modified by mutual displacement induced in a direction defined by the thermal expansion of a body brought to a variable temperature.  2. Device according to claim 1, characterized in that the aforementioned expansion body consists of the solid material which is at least partially made of the positioning member (1).  3. Device according to claim 1, characterized in that the positioning member has the structure of a deformable container (5) filled with a liquid (7), the latter constituting the aforementioned expansion body.  4. Device according to claim 1, characterized in that the positioning member is double and comprises a first partial member (16) made of solid material at least in part and a second partial member having the structure of a deformable container (5) filled with liquid (7), these partial organs being associated in such a way that the effects of their own thermal expansion accumulate, while the corresponding solid and liquid expansion bodies are heated or cooled separately.  5. Device according to claim 3 or 4, characterized in that the interior volume of the deformable container (5) is connected by a tube (9) to a second container (10) substantially non-deformable, placed at a distance, the assembly being filled with liquid (7), and the heating or cooling of the liquid is carried out in the second container (10).  6. Device according to any one of claims 1 to 5, characterized in that the expansion body is heated by means of an electrical resistance (4) placed in its vicinity.  7. Device according to any one of claims 1 to 5, characterized in that the expansion body is electrically conductive and that it is heated by creation of a Joule effect within the material which constitutes it.  8. Device according to any one of claims 1 to 7, characterized in that it comprises two positioning members (1) arranged so as to induce respective displacements in crossed directions (X, Y), preferably at right angle.  9. Device according to any one of claims 1 to 71 characterized in that it comprises three positioning members (1) arranged so that the directions of movement which they induce form a trihedron (X, Y, Z) , preferably trirectangle.  10. Device according to claim 8 or 9, characterized in that the positioning members (1) attack a common movable plate (30, 33) to which the surface to be positioned belongs, said members being capable of bending laterally.  11. Device according to claim 10, characterized in that it comprises two positioning members (i) and that the common plate (30) which they attack is supported by balusters (28) oriented perpendicular to the directions of the induced displacements by said members, these columns being capable of bending laterally.  12. Device according to claim 8, characterized in that it comprises two positioning members (1), the surface to be positioned of the first serving as a reference base for the second.  13. Device according to claim 9, characterized in that it comprises three positioning members (1), the surface to be positioned of the first serving as a reference base for the second, and the surface to be positioned of the second serving as reference base for the third.  111. Device according to any one of claims 1 to 13, characterized in that the positioning member or each positioning member (1) which it comprises is provided with a circuit for regulating the heating power or cooling the expansion body as a function of one or more parameters recorded by one or more measurement sensors (15, 20).  15. Device according to claim 14, characterized in that a regulation parameter is the temperature of the expansion body.  16. Device according to claim 14, characterized in that a regulation parameter is the position of the surface to be positioned.  17. Device according to any one of claims 1 to 16, characterized in that the positioning member or each positioning member that it comprises is provided with at least one cooling means.