NL1043657B1 - Cryogenic Double Axis Scanner - Google Patents

Abstract

The invention concerns a double axis fine positioning mechanism, also referred to as a scanner, especially 5 designed for use in a cryogenic environment. This involves the use of a piezo stroke increasing feature, the use of parallel kinematics, thermal expansion compensation and the integration of an optical aperture. 1043657

Description

Cryogenic double axis scanner \

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The invention concerns a double axis fine positioning ; mechanism, also referred to as a scanner, especially ;

§ designed for use in a cryogenic environment. . Many experiments in a cryogenic environment need E objects to be positioned over millimetre distances with ; sub-nanometer resolution.

Available cryogenic

| positioners use piezo actuators to generate sequences of sub-micron steps to cover distances up to tens of millimetres, Fine positioning, or scanning, with sub- nanometer resolution is often possible using the same positioner but the scanning range is limited to approximately 1 micron.

This limitation is an intrinsic consequence of the severely reduced range of piezo actuators at cryogenic temperatures in combination with practical dimensional restriction that limit the size of positioners in many cryogenic experiments, which in turn limits the size and therefore range of the used piezo actuators.

Large range alternatives for piezo actuators are impractical or even impossible for reasons of size, force, stiffness, costs and magnetic properties.

The | latter is relevant because many cryogenic experiments \

involve strong magnetic fields and the actuator and \ complete scanner must be non-magnetic, precluding the | use of electromagnetic actuators in these applications. | Increasing the micron level double axis scanning range is needed to allow sensitivity analyses during | experiments and to compensate long term thermal drift | and mechanical settling.

The solution is using a | separate double axis scanner containing piezo actuator | range increasing features. | 1043657 $

| Planar motion along two perpendicular axes is typically achieved by stacking two single axis positioners, which effectively can be scen as 2 positioners in series. A | fundamental drawback of this is the loss of drive S stiffness of the planar motion output with respect to the | base on which the stack of positioners is placed. This | drive stiffness is a direct limitation for the achievable | positioning range, resolution and stability of a scanner, 9 This drive stiffoess can be improved significantly by 19 using 2 positioners in a parallel configuration instead | of in series. In this sv-called parallel kinematics configuration cach positioner directly supports a : common motion platform with respect to z common base, ; Another effect of a cool down to cryogenic temperatures | 15 is that the mismatch of thermal expansion between the ‚ piezo actuator and rest of the scanner, especially in ; combination with range increasing features, causes the motion output platform to show a large offset with | respect to its position ai normal ambient temperatures. | 20 Preventing this offset is desired in order to maintain | correct alignment of the experiment when going to cryogenic temperatures. This offset can be passively : eliminated by using a piezo actuator with an integrated piece of compensation material at one or both ends, seclected with respect to its coefficient of thermal | expansion and dimensions such that this piezo aciustor | shows the same thermal expansion as the rest of the scanner.

| Another desirable feature, especially for optical based experiments, is an open aperture throughout the scanner, enabling the passing of for instance light or | optical fibers. A well-considered configuration of all elements in a scanner allows the integration of such an } optical aperture. | This invention concerns a double axis scanner with ; range increasing features, parallel kinematics, passive offset elimination and an integrated open aperture. | The exact nature of this invention, as well as its ; objectives become clear in the accompanying drawings . wherein: . Fig.l Is a side view of a double axis scanning ; mechanism according the invention. ; Fig.2 Is a top view of the driving mechanism of a \ double axis scanning mechanism according the invention, Fig.3 Is a top view of the table mechanism of a double axis scanning mechanism according the 28 invention. Fig.4 Is a view of a piezo actuator with integrated compensation material according the invention.

The scanner is a combination of a driving mechanism DM with a table mechanism TM on top. First the driving mechanism DM is described. The stationary base DB contains an interface IFY which is \ moved along the y-axis INY using a piezo actuator PAY. | The attached flexure F1Y, being rigid in y-translation | and flexible in x-translation and z-rotation, transfers | this motion to intermediate body IBY, causing a 1043657 | à rotation of IBY about pivot point P2Y which is formed | by flexure F2Y 1, being rigid in y-translalion and | flexible in x-translation and z-rotation, and flexure | F2Y2, being rigid in x-translation and flexible in y- | 5 translation and z-rotation, This results in y-motion | OUTY of flexure F3Y, being rigid in v~transiation and flexible in x-translation and z-rotalion, and the | connected table T.

| DB also contains an interface IFX which is moved along # 10 the x-axis INK using a piezo actuator PAX. The attached } flexure FIX, being rigid in x-translation and flexible in | y-translation and z-rolation, transfers this motion to ® intermediate body IBX, causing a rotation of IBX about pivoi point P2X which is formed by flexure P2X1, being : 1S rigid in x-translation and flexible in y-iranslation and z-rotation, and floxare F2X2, being rigid in y- ; translation and flexible in x- translation and z-rotation. This resulis in x-motion OUTX of flexure FIX. being | rigid in x-translation and flexible in y-transiation and z-rotation, and the connected table T.

} This configuration allows T to be positioned in x- direction and y-direction with the piezo actuators PAX } and PAY, while the z-rotation of T is not constrained.

: Contact of IFX with PAX and IFY with PAY, even for | 25 negative motion INX and INY, is guaranteed by the |l springs SX and SY generating the preload forces PX and | PY.

| The OUTY and OUTX motion is given by: OUTY = | INY*BY/AY and OUTX = INX*BX/AX. Making the ratios BY/AY and BX/AX larger than | makes it possible to | amplify the actuator stroke to the required ontput : stroke.

| 1043657

The whole DM, excluding the piezo actuators PAX and | PAY, is made out of a single piece of material in order E to prevent occurrence of hysteresis and play, which is a | necessity when aiming for sub-nanometer resolution.

The piezo actuators PAX and PAY contain a picce of compensation material CM at one or both ends, sclected | with respect to its coefficient of thermal expansion and dimensions, such that PAX and PAY show the same thermal expansion as the rest of the DM. Hereby avoiding temperature related motion of T in a passive | Way. | On top of the driving mechanism DM a table mechanism TM is placed. The stationary base TB is connected to a set of 2 parallel flexures FTI! and FT12, each being rigid in y-translation and flexible in x-translation and z-rotation, which connect to an intermediate body IT at the other end. A second set of parallel flexures FT13 and FT14, each being rigid in x-translation and flexible in y-translation and z-rotation, is connected to IT and 29 connect to sample table ST at the other end. Additionally, 2 L-shaped flexures FT2 and FT3, each | being flexible in x-translation, y-translation and z- rotation, connect TB and ST, This configuration allows ST to move along the axes X and Y, while constraining | all other degrees of freedom. | The drive mechanism DM and table mechanism TM are | rigidly connected via their stationary bases DB and TR | and additionally T and ST are rigidly connected at | connection point CP, As a result, the motion of table T | and table ST is limited to x- and y-motion and the other | degrees of freedom are constrained. | An open aperture OA in both DM and TM allows light to | pass through the mechanisms, for instance for | 1043657 |

: applications in which optical components like lenses

# need to be moved, but it can also be used to feed through for instance an optical fiber,

The whole TM is made out of a single piece of material in order to prevent occurrence of hysteresis and play, which is a necessity when aiming for sub-nanomelier

| resolution.

Claims (6)

CONCLUSIONS | ; 1. The invention relates to a device, characterized in: A so-called scanner comprises an actuation module 3 in which movement is forced on a plateau by a piezo actuator which is attached to a . side is connected to the fixed base of the actuation . module and on the other side to a coupling piece ; which is connected to a mechanical | transmission, consisting of an intermediate frame and four elastic elements, which is connected to | this plateau; the first elastic element, which is stiff in horizontal direction, hereinafter referred to as x-direction, and slack in: vertical direction, hereinafter referred to as y-direction, and also slack about an axis of rotation which is perpendicular to both the x-direction and the y-direction, hereinafter referred to as z-direction, is connected on one side to the coupling piece and on the other side to the | intermediate frame and is in line with the x-movement of the | piezo actuator and transmits this x-movement to the intermediate frame; this intermediate frame contains a z-rotation axis, wherein the rotation axis is not in line with the first elastic element and wherein the z-rotation axis is formed by a second and third elastic element, oriented at right angles to each other and both connected on one side with the fixed base and on the | 30 other side with the intermediate frame, where the second | elastic element is stiff in x-direction and slack in y- | direction and also rotation slack about the z-direction and \ where the third elastic element is stiff in y- |l | direction cn slack in x-direction and also slack rotation around z-direction; the y-distance “A*“ between the first elastic element and the z-rotation axis of the intermediate frame causes the intermediate frame to rotate about this z-rotation axis and thus an x movement of the fourth elastic element, which is rigid in x-direction ] and slack in y-direction and also rotations slack about z- | direction and which at y-distance “B” from the z-role | 16 axle is attached to the intermediate frame, resulting in, | the other side of the fourth slastic element is coupled to the plateau, which will be translated in x direction relative to the fixed base; iS the actuation module contains a second piezo actuator, coupler and mechanical transmission, all at right angles to the versions mentioned, but otherwise | identical in configuration, Resulting | | that the plateau can be moved in x-on y-direction 26 translated with respect to the fixed base with | using the piezo aciuators according to the principles of the parallel kinematics, with the plateau still suspended slack for rotatics about the z- : direction; at least one preload spring is used | to apply a nearly constant force to | the platform or both intermediate frames in such a way | that both piezo actuators have a compressive force | suffer over their entire stroke; the ratio A/B is greater than 1 so that the amplitude | of the resulting plaieau movement is greater than the amplitude of the piezo movement, so that cok | 1043657 in cryogenic conditions sufficient movement of | the table remains; the scanner contains a table module which contains a . contains a fixed reference to which a table is . hung up; the suspension of this table consists of ten . first two parallel elastic elements, each stiff in y-direction and slack in x-direction and | i also rotation slack about the z-direction, which on one side are connected to the fixed reference and on the other side \ to an intermediate body, secondly two parallel elastic elements, each stiff in x-direction and slack in y- direction and also rotation slack about the z direction. which on one side at the | 1s intermediate body and on the other side are connected to the table, thirdly two elastic : clements, each slack in X-direction, V-direction and A also rotation slack about the z direction, which are connected to the fixed reference on one side and to the table on the other side; the fixed base and plateau of the actuation | module are rigidly connected to the fixed reference and table of the table module, respectively. As a result, the piezo actuators can only impose an x and y movement on the table and that | the other degrees of freedom of the table are rigid | hung up; the actuation module, except the piezo | actuators, and the table module each from a single | piece of material exist causing friction and play | are prevented: | this material is not magnetic like | e.g. titanium, copper, phosphor bronze, | 1043657 | | 10 : boryliium copper, aluminum, technical ceramics or ; synthetic; the actuation module and inafel module both contain a through-hole in the z-direction which are arranged concentrically to allow the passage of light or the passage of, for example, optical fibers through the entire scanner; } both piezo actuators san cen or both | invent a, non-magnetic, passive E ij compensating material, so specified as regards thermal : coefficient of expansion and dimensions such that both piezo | actuators are related to thermal expansion : behave as if they are made of the same material as the | 15 rest of the actuation module, | 2. A device according to the foregoing | conclusions where the ratio B/A is less than or equal to | is on Ì, in order to increase the amplitude of the | 20 to reduce or keep the table movement at | relative to the motion amplitude of the piczo actuators. | A device according to any one of the preceding claims wherein the biasing springs in the current | module are separate parts, 4 A device according to any of the foregoing | claims with the preload springs removed | 30 and their function has been replaced by gluing or otherwise connecting one or both ends of the piezo actuators to the fixed base or | connectors in the actuation module, | 1043657 A device according to any one of the preceding claims wherein the materials used are not non-magnetic. | 6. A device according to any of the foregoing; claims where the piczo actuators are not passive; contain compensation material, | 7, A device according to any of the foregoing . conclusions where the piezo actuators replace | be used by an alternative such as cen : glecirostrictive, magnetostrictive or | electromagnetic actuator. | | 1043657 |