METHOD OF POSITIONING BY MEANS OF AN ACTUATOR HAVING THREE BRIDGES

Abstract: Three thermomechanical actuators in one plane for adjusting the angular position of two parts by rotating them in said plane. Two adjoining actuators of said three actuators are heated (e.g. by irradiation of a laser beam) and subsequently cooled down in order to reduce the length of said heated actuators, thereby maintaining the length of the third actuator unchanged. Rotation in both directions can be obtained and tightly controlled.

Description: Method of positioning by means of an actuator having three bridges The invention relates to a method of positioning a component in a device means of an actuator, which actuator is provided with two parts which extend in a mam plane and are interconnected by means of three bπdges, which three bπdges can each be shortened in a shortening direction which extends parallel to the main plane in that the bridge is localh heated and subsequently cooled down, m which method the two parts of the actuator are rotated relative to one another about an axis ot rotation extending substantial]}, perpendicularly to the main plane through shortening of at least one of said three bπdges The invention also relates to an actuator suitable for use in such a method, which actuator is provided with two parts which extend in a mam plane and are interconnected by means of three bridges, which three bridges can each be shortened in a shortening direction extending parallel to the main plane through local heating of the bridge and subsequent cooling down, while the two parts are rotatable relative to one another about an axis of rotation extending substantially perpendicularly to the main plane through shortening of at least one of said three bridges. A method and an actuator of the kinds mentioned in the opening paragraphs are known from EP-B-0 638 895. The two pans of the known actuator are plate-shaped and extend in the main plane. The three bπdges have the shape of stπps and also extend in the mam plane. As seen in the main plane, the three bπdges are mutually positioned in a kind of timber frame arrangement, a first and a second bπdge of the three extending substantialh parallel to one another and the third bridge extending obliquely between the two other bridges. According to the known method, the two parts of the actuator are rotated relative to one another in that the first bπdge is shortened. This is done through local heating of the first bridge by means of a laser beam and subsequent cooling down. Since the first bridge is shortened, the two parts of the actuator are rotated relative to one another through a very limited angle about an axis of rotation which extends substantially perpendicularly to the main plane and which passes substantially through a point of intersection of the second and the third bridge. Said angle is increased in that this process is repeated a number of times. The two parts of the actuator are rotated in an opposite direction relative to one another about an axis of rotation which passes substantially through a point of intersection of the first and the third bndge in that the second bπdge is shortened. Since the actuator has a high rigidity, as seen in the mam plane, and a very limited mutual rotation of the two parts of the actuator is obtained as a result of shortening the bnαges, a highly accurate positioning is possible by means of the actuator. An incorrectly adiusted angular rotation can be corrected either direction m that the two pans of the actuator are rotatable relative to one another in two mutually opposed directions. The Known method may be used, for example, for accurately adjusting a position of a component, such as a magnetic scanning unit, in a scanning device for magnetic tape iniormation earners or or a component in an image recording device, such as a CCD image sensor. A disadvantage of the known method and the known actuator is that a maximum achievable angle of rotation between the two parts of the known actuator is very limited, so that a positioning of components is possible over very limited distances only by means of the known method. This is because a tensile stress arises in a bridge during shortening of this bridge, which stress increases in proportion as the bridge is further shortened. The yield point of the bπdge mateπal is locally strongly reduced during heating of the bridge. If the built-up tensile stress in the bridge becomes greater than this reduced yield point, a renewed heating of the bπdge will lower the built-up tensile stress owing to plastic deformation of the heated mateπal, i.e. through a lengthening of the bridge. A further buildup of the tensile stress and a further shortening of the bπdge are retarded thereby, or even become impossible. It is an object of the invention to provide a method and an actuator of the kind mentioned in the opening paragraphs again a positioning in two mutually opposed directions is possible with a comparable accuracy, but whereby a considerably greater maximum angle of rotation between the two Dans of the actuator is achievable. To achieve the aoove oDject. a method according to the invention is characteπzed in that the shortening directions of the three bπdges are mutually substantially parallel, and the two parts of the actuator are rotated relative to one another by an alternate shortening of two mutually adjoining bridges of the three bridges. To achieve the above object, an actuator according to the invention is characteπzed in that the shortening directions of the three bπdges are mutually substantially parallel, and the two parts can be rotated relative to one another by an alternate shortening of two mutually adjoining bπdges of the three bπdges. Since two mutually adjoining bπdges of the three bπdges are shortened, the third bπdge is deformed, as seen in the mam plane, so that the two parts of the actuator are rotated relative to one another about an axis of rotation directed substantially perpendicularh to the mam plane and situated adiacent a central portion of the third bπdge. The shortening directions or the three bπdges of the actuator according to the invention are mutually substantiallv parallel, with the result that a tensile stress is built up in the two mutually adjoining bπdges duπng shortening of these two bπdges. Since the two adjoining bπdges are alternately shortened, i.e are heated in turn, the yield point is lowered in only one of these two bπdges each time. A plastic deformation, i.e. a lengthening of the heated bπdge under the influence of the tensile stress built up in this bπdge, is prevented to a large extent because the non-heated bπdge, which has a comparatively high yield point and shows only elastic deformation as a result, temporanly absorbs the tensile stress present in the heated bπdge. A shortening of the bπdges, once achieved, is thus largely maintained duπng a renewed heating of one of the bπdges, so that the relevant bπdge is further shortened duπng a renewed cooling-down, and the two parts of the actuator can be rotated relative to one another through a comparatively great angle. The object of the invention is furthermore achieved by means of a simple construction and with limited dimensions of the actuator. A special embodiment of a method according to the invention is characteπzed in that the two parts of the actuator are rotated relative to one another in a first direction by an alternate shortening of a first and an adjacent second bπdge of the three bπdges. and in that the two parts of the actuator are rotated relative to one another in a second direction opposed to the first direction by an alternate shortening of the second and the adjacent third bπdge. In this special embodiment, said second bπdge lies between the first and the third bπdge. When the first and the second bπdge are alternately shortened, the third bπdge is deformed, as seen in the main plane, so that the two parts of the actuator are rotated relative to one another about a first axis of rotation directed substantially perpendicularly to the main plane and situated between the second bπdge and the third bπdge Said first direction is defined by the positions of the first and the second bπdge with respect to the third bπdge. When the second and the third bπdge are alternately shortened, the first bπdge is deformed as seen in the main plane, so that the two parts of the actuator are rotated relative to one another about a second axis of rotation directed substantially perpendicularly to the main plane and situated between the first bπdge and the second bπdge Said second direction is defined by the positions of the second and the third bridge relative to the first bπdge and is opposed to said first direction. A relative rotation of the two parts of the actuator in two mutually opposed directions is thus possible in a simple manner by means of a simple and compact construction of the actuator. A special embodiment of an actuator according to the invention is charactenzed in that the bπdges have a width, seen perpendicularly to the shortening direction. \\ hich is substantially smaller than twice a spot diameter of a laser beam used or designed to be used for shortening the bndges. In this special embodiment, a comparatively large portion of the widths of the bπdges is heated by the laser beam, so that a comparatively great shortening of the bπdges is achieved in a single heating step. This gives the actuator a high effectivity. A further embodiment of an actuator according to the invention is characteπzed in that the width of the bπdges is at most equal to the spot diameter. In this further embodiment, the bπdges are heated by the laser beam in a substantially uniform manner, seen in the width direction, whereby the effectivity of the actuator is further enhanced. A yet further embodiment of an actuator according to the invention is characterized in that a distance present between the bridges and the width of the bridges have a same order of magnitude. An angle of rotation through which the two parts of the actuator are rotated relative to one another as a result of a shortening of one of the bridges is smaller in proportion as the distance between the bπdges is greater, so a comparatively great relative rotation of the two parts of the actuator is obtained upon each shortening of one of the bridges by means of this yet further embodiment of the actuator according to the invention. A particular embodiment of an actuator according to the invention is characteπzed in that a distance present between the bπdges is substantially greater than the width of the bπdges. In this particular embodiment, a comparatively small, but comparatively very accurate relative rotation of the two pans of the actuator is obtained upon each shortening of one of the bπdges. A further embodiment of an actuator according to the invention is characteπzed in that the actuator is provided with a coupling member which is fastened to one of the two parts of the actuator at a distance from the bπdges as seen parallel to the shortening direction and in a fixed position as seen in a displacement direction directed substantially perpendicularly to the shortening direction, which coupling member is uncoupled from the corresponding part when seen in the rotation direction of the actuator. A mutual rotation of the two parts ot the actuator is converted into a translation of the coupling member in said displacement direction by means of said coupling member. Since the two parts of the actuator are mutually rotatable in two opposed directions, the coupling member is displaceable also in a direction opposed to said displacement direction. A transmission ratio obtaining between said translation and said rotation is defined by said distance which is present between the coupling member and the bπdges. as seen parallel to the shortening direction A still further embodiment of an actuator according to the invention is characteπzed in that the coupling member compπses a blade spπng which extends substantially parallel to the displacement direction and substantially perpendicularly to the main plane Said blade spπng has a comparatively low πgidity as seen in a direction parallel to the shortening direction of the bndges Owing to this low πgidity, a necessary uncoupling in the rotation direction between the coupling member and the two parts or the actuator is provided in a constructionally particularly simple and effective manner A particular embodiment of an actuator according to the invention is characteπzed in that the two parts of the actuator, the three bπdges, and the blade spπng are manufactured from a single piece of sheeting, the blade spπng being bent from the mam plane into a position substantially perpendicular to the main plane. The actuator can thus be manufactured in a simple manner as a single integral component. The invention will now be explained in more detail below with reference to a number of embodiments as shown in the drawing, in which Fig 1 diagrammatically shows a first embodiment of an actuator according to the invention which is suitable tor use m a method according to the invention, Fig 2 diagrammatically shows how two parts of the actuator according to Fig 1 are rotated relative to one another in a first direction Fig 3 diagrammatically shows how the two parts of the actuator according to Fig 1 are rotated relative to one another in a second direction opposed to the first direction. Fig 4 diagrammatically shows a second embodiment of an actuator according to the invention which is suitable for use in a method according to the invention, and Fig 5 diagrammatically shows a portion of a device and a component therein which is to be positioned by means of a method according to the invention. Fig. 1 diagrammatically shows a first embodiment of an actuator 1 according to the invention which is suitable for use in a method according to the invention. The actuator 1 comprises a plate-shaped first part 3 and a plate-shaped second part 5 which both extend in a mam plane of the actuator 1. The two pans 3 and 5 are interconnected by means of a first bndge 7. a second bπdge 9. and a third bndge 11. which also extend in said ma plane and have a stπp shape. In the embodiment shown, the two pans 3 and 5 and the three bndges 7. 9. ana 11 are formed in that two round openings 13 and 15 were provided in a metal mam plate 17. The first part 3 of the actuator 1 can be fastened to a base part 19 of a device, of which a few examples will be given further below, by means of a fastening member which is not shown in the Figure and which may be of a kind which is usual and known per se. A component (not shown) of the device, or which also a few examples will be given further below, can be fastened to the second pan 5 of the actuator 1, which component is to be positioned in an accurate position relative to the base part 19 of the device by means of the actuator 1 and by a method according to the invention. The three bridges 7, 9, 11 can each be shortened by a technique as described in detail in EP-B-0 638 895 parallel to respective shortening directions Y- , Y 2 , Y 3 which are substantially parallel to the main plane of the actuator 1 and to a longitudinal direction of the bridges 7, 9, 11. In this technique, a bridge 7, 9, 11 is shortened in that the bridge 7, 9, 11 is locally heated in the longitudinal direction of the bridge 7, 9, 11, as seen, for example, in the center of the bridge 7, 9, 11, by means of. for example, a laser beam. Since the bridge 7, 9, 11 is locally heated, the mateπal of the bπdge 7. 9, 11 expands locally, so that locally a compression stress aπses in the mateπal. The heating also strongly reduces the yield point of the mateπai, i.e. the strain limit for plastic deformation of the mateπal. locally. The result of the created compression and the reduced yield point is that the material is locally plastically deformed substantially in directions perpendicular to the longitudinal direction of the bridge 7. 9. 11. Subsequently, the bπdge 7. 9. 11 is locally cooled down again. A local shrinkage of the plastically deformed mateπal aπses as a result, so that the bridge is shortened in the longitudinal direction, i.e. parallel to the shortening direction Y-, Y 2 , Y 3 . The shortening of the bndge 7. 9, 11 resulting from a single heating step is comparatively small, but it can be considerably increased in that a number of consecutive heating steps are applied to the bridge 7, 9. 11. Further details on this technique can be found in EP-B-0 638 895. According to the invention, the shortening directions Y], Y 2 , Y 3 of the three bridges 7. 9, 11 are mutually substantially parallel. In the method according to the invention, the two parts 3 and 5 of the actuator i are rotated relative to one another in that two adjoining / bndges 7, 9 or 9, 11 of the three bπdges 7. 9, 11 are alternately shortened by the technique descπbed above. If the first bπdge 7 and the second bπdge 9 are shortened, as shown diagrammatically in Fig. 2, the third bπdge 11 is deformed, as seen mainly in the main plane, so that the second part 2 of the actuator 1 is rotated relative to the first part 3 m the main plane about a first axis of rotation 21 which is substantially perpendicular to the mam plane ana is situated between the second bndge 9 and the third bπdge 11. The rotation about the first axis or rotation 21 takes place in a first direction of rotation Ri which is defined by the position or the first bndge 7 and of the second bndge 9 relative to the third bndge 11. If the second bndge 9 and the third bπdge 11 are shortened, as is diagrammatically shown in Fig. 3, the πrst bnαge 7 is deformed as seen mainly in the main plane, so that the second part 3 of the actuator 1 is rotated relative to the first part 3 in the main plane about a second axis of rotation 23 which is again substantially perpendicular to the main plane and is situated between the first bπdge 7 and the second bπdge 9. The rotation about the second axis of rotation 23 takes place in a second direction of rotation R 2 which is defined by the position of the second bπdge 9 and of the third bridge 11 relative to the first bridge 7 and is opposed to the first direction of rotation R \ . The two parts 3 and 5 of the actuator 1 can thus be rotated relative to one another in two mutually opposed directions of rotation R] and R 2 . Since each heating step applied to a bridge 7, 9, 11 leads to only a comparatively small shortening of the relevant bπdge 7, 9, 11 and accordingly to a comparatively small mutual rotation of the two parts 3 and 5, a very accurate, stepwise mutual rotation of the two parts 3 and 5 can be achieved by the method. The accuracy of the mutual rotation of the two parts 3 and 5 is increased in that the actuator 1 is very ngid. seen in the mam plane. Shortening of the two mutually adjoining bπdges 7, 9 or 9. 11 gives nse to a tensile stress in the two bndges 7, 9 or 9, 11 which increases in proportion as the two bndges 7, 9 or 9, 11 are further shortened. Since the two mutually adjoining bndges 7, 9 or 9, 11 are alternately shortened in the method according to the invention, a tensile stress can be built up in the two Dndges 7. 9 or 9, 11 which is greater than the lowered yield point which the matenal of the bndges 7. 9, 11 has dunng the heating step. Fig. 2 shows a situation, for example, w nere a tensile stress T 2 and a tensile stress T 3 are present in the second bndge 9 and in the third bndge 11, respectively, which stresses are greater than said yield point. If the second bndge 9 is locally heated, the yield point of the material in the second bndge 9 will decrease locally, so that the second bridge 9 is locally plastically deformed under the influence of the tensile stress T 2 , i.e. is lengthened. Said plastic deformation resulting from the tensile stress T- , however, is verv small because the tensile stress T^ in the third bndge 1 1 πses strongly alreadv upon a very small lengthening of the second bπdge 9 owing to elastic deformation of the third bπdge 11 The third bπdge 11 thus absorbs the tensile stress T 2 present in the second bπdge 9 for a major portion, so that a further lengthening of the second bndge 9 is pre\ented and a local plastic detormation or the second bndge 9 perpendicular to the longitudinal direction or the second bnαge 9 anses through expansion of the heated matenal When the second bndge 9 is subseαuenth cooled down the plastically deformed matenal ill shπnk riereov the second bndge 9 is snortened m longitudinal direction This causes the tensile stress in the second bndge 9 to nse again so that the third bndge 11 is partly relieved again of its stress again Since a tensile stress can be built up in the two bndges 9 11 m this manner which is much greater than said lowered yield point the two bndges 9 11 can oe snortened to a comparatively great extent so that the two parts 3 and 5 are rotatable relatn e to one another through a compara eh great angle As Fig 1 shows, the actuator 1 is further provided with a coupling member 25 which, seen in a direction parallel to the shortening directions Y \ , Y 2 , Y 3 , is situated at a distance H from the three bπdges 7, 9, 11 The coupling member 25 compπses a blade spπng 27 which extends substantially parallel to an X-direction which is perpendicular to the shortening directions Yi, Y 2 , Y 3 Furthermore, the blade spπng 27 is substantially perpendicular to the main plane of the actuator 1. The blade spπng 27 was manufactured together with the main plate 17 mentioned above, from which the two parts 3 and 5 and the three bπdges 7, 9, 11 are made, from one single piece of sheeting, the blade spπng 27 being bent from the ma Diane into a position substantially perpendicular to the main plane about a bending line 29 which extends parallel to the X-direction The blade spπng 2 7 is thus fastened in a fixed position seen parallel to the X-direction to the second part 5 of the actuator 1 Since an end 31 or the blade spnng 27 has a comparatively low ngiditv relative to the second part 5 in a direction parallel to the shortening directions Yi, Y 2 . Y , the coupling member 25 is uncoupled from the second part 5 as seen in the directions of rotation Ri, R 2 ot the actuator 1 The ract that the blade spπng 27 is fastened m a fixed position to the second part 5 seen parallel to the X-direction and is uncoupled rrom the second part 5 in the rotation directions R Ri implies that a rotation or the second part 5 relative to the first part 3 is converted via the coupling member 25 into a translation of the end 31 of the blade spπng 27 parallel to the X-direction Since the two parts 3, 5 of the actuator 1 are rotatable relative to one another in two mutually opposed directions Ri, R , the end 31 of the blade spπng 27 can similarly be displaced in a direction X' opposed to the X-direction A transmission ratio obtains between the translator \ movement ot the end 31 and the relative rotational movement of the two parts 3 and 5, which ratio is defined by said distance H between the blade spπng 27 and the three bπdges 7, 9, 11 and which increases in proportion as the distance H increases. Fig 1 shows two further dimensions which characteπze the actuator 1, I e. a width W which the bndges " 9 11 have, as seen perpendicularly to the shortening directions Yi, \ ;, Y~. and a distance D present between the bndges 7 9 11 Said width W is preferabh substantialh smaller than twice a spot diameter of a laser beam to be used for shortening the bπdges 7 9, 11 It is achieved thereby that a comparatively large portion of the bπdges 7, 9, 11, as seen in the width direction, is heated by the laser beam, so that a comparatively great shortening ot the bπdges 7, 9. 11 is achieved duπng a single heating step The actuator 1 has a high effectivity as a result of this The effectivity of the actuator 1 is further enhanced when the width W of the bndges 7 9. 11 is equal to or smaller than said spot diameter, which means that the bndges 7, 9, 11 are uniformly heated by the laser beam, seen in the width direction. Said distance D between the bπdges 7, 9, 11 has an order of magnitude in the actuator 1 which is equal to an order of magnitude of the width W of the bπdges 7, 9, 11. A ratio between said distance D and width W defines a ratio between a mutual angle of rotation of the two parts 3 and 5 and a shortening of the two mutually adjacent bπdges 7, 9 or 9, 11. Given a predetermined value of the shortening of the mutually adjoining bπdges 7, 9 or 9, 11, the mutual angle of rotation of the two parts 3 and 5 is greater in proportion as the ratio between the distance D and the width W is smaller Fig 4 diagrammatically shows a second embodiment of an actuator 1 ' according to the invention which is suitable for use in a method according to the invention Components of the actuator 1 conespondmg to components of the actuator 1 discussed above have been given the same reference numerals in Fig 4 In the actuator 1 , a distance D' is present between the bπdges 7. 9. 11 which is substantially greater than the width W of the bndges 7 9. 11 Said distance D' is achieved through the application of two elongate slots 33 and 35 in the main plate 17 w ich extend perpendicularly to the shortening directions Yi, Y Y 3 A comparatively small ratio is obtained thereby between the mutual angle ot rotation of the two parts 3 and 5 and the snortenmg ot the mutually adjoining bndges 7 9 or 9 11, so that only a comparatively small, but comparatively highly accurate mutual rotation of the two parts 3 and 5 of the actuator 1 ' is obtained upon a shortening of the bπdges Fig 5 diagrammatically shows a portion of a device, in particular a playback device for optical discs The Figure shows an auxiliary plate 37, a manipulator 39. and a pπnted circuit board 41 on hich a photodiode 43 is rastened as part ot this device The auxiliary plate 37 is fastened in three locations 45, 45', and 45", to three fastening points 47, 47', and 47" of, for example, a displaceable slide or a main frame of the playback device, which is not shown in Fig. 5 for reasons of simplicity. The pπnted circuit board 41 is glued by a lower side 49 to a earner plate 51 of the manipulator 39, which earner plate extends parallel to an X-direction and parallel to a Y-direction. As Fig. 5 shows, the manipulator 39 compπses two actuators la and lb according to the invention which are provided with a common first part 3. The two blade spπngs 27a. 27b of the actuators la, lb are fastened to the earner plate 51 and extend substantially parallel to the X-direction and perpendicularly to the earner plate 51. Furthermore, the manipulator 39 compπses a third blade spπng 53 which extends substantially parallel to the Y-direction and which compπses a hoπzontal portion 53' and a vertical portion 53". said vertical portion 53" being fastened to the earner plate 51. The manipulator 39 is manufactured from a single piece of sheeting, the blade spnngs 2~a, 27b of the actuators la, lb and the vertical portion 53" of the third blade spπng 53 being bent from a main plane of said piece of sheeting about respective bending lines 29' and 55. The carrier plate 51 is provided with three support elements 59 at a lower side 57, by means of which elements the carrier plate 51 rests on an upper side 61 of the auxiliary plate 37. The carrier plate 51 is fastened to the auxiliary plate 37 by means of two welded joints 63 between the upper side 61 of the auxiliary plate 37 and the common first part 3 of the actuators la, lb, and by means of two further welded joints 65 between the upper side 61 of the auxiliary plate 37 and the horizontal portion 53' of the third blade spπng 53. To prevent sagging of the auxiliary plate 37, the auxiliary plate 37 rests on three support elements 67 of said slide or said main frame, which elements are provided perpendicularly below the support elements 59 of the manipulator 39. The photodiode 43 can be positioned by means of the actuators la, lb by a method according to the invention relative to said slide or said main frame in directions parallel to the X-direction and parallel to the Y-direction, duπng which the earner plate 51 slides over the upper side 61 of the auxiliary plate 37 by means of the three support elements 59 When the blade spnng 27a of the actuator la is displaced parallel to the X-direction. the earner plate 51 is rotated about an axis of rotation 69 which coincides substantially with an imaginary line of intersection of the blade spnngs 27b and 53", such that the photodiode 43 is displaced in a direction A lying in the main plane of the manipulator 39, as shown in Fig. 5. When the blade spπng 27b of the actuator lb is displaced parallel to the X-direction, the earner plate 51 is rotated about an axis of rotation 71 which coincides substantially with an imaginary line of intersection of the blade spπngs 27a and 53", so that the photodiode 43 is displaced in a direction B also lying the mam plane of the manipulator 39 as shown in Fig. 5. The photodiode 41 is thus capable of being positioned into a desired position parallel to the X-direction and the Y-direction through a suitable combination of displacements in said directions A and B. A method and an actuator according to the invention may also be used for positioning other components in a playback unit for optical discs such as. for example, lenses, and also for positioning components in devices of a different kind. Examples of this are the positioning of an image sensor in an image recording device, or positioning of a magnetic scanning unit in a scanning device for magnetic information earners. The bndges of an actuator according to the invention may also be heated in a manner other than by means of a laser beam in a method according to the invention, for example by means of a local electnc cunent The invention also covers embodiments of an actuator without means for converting the mutual rotation of the two parts into a translation, or with means for converting said rotation into a translation in a direction diffeπng from the X-direction perpendicular to the shortening directions of the bπdges as mentioned above. The means for converting said rotation into a translation, moreover, may be constructed m a different manner, for example in that a πgid rod is used instead of said blade spπng, which rod is pivotably fastened to the second part of the actuator.

Claims: CLAIMS: 1. A method oϊ positioning a component in a device by means of an actuator, which actuator is provided with two parts which extend in a main plane and are interconnected by means of three bπdges. which three bndges can each be shortened in a shortening direction which extends parallel to the main plane in that the bridge is locally heated and subsequently cooled down, in which method the two parts of the actuator are rotated relative to one another about an axis of rotation extending substantially perpendicularly to the mam plane through shortening of at least one of said three bridges, characteπzed in that the shortening directions of the three bndges are mutually substantially parallel, and the two parts of the actuator are rotated relative to one another by an alternate shortening of two mutually adjoining bridges of the three bridges. 2. A method as claimed in claim 1, characterized in that the two parts of the actuator are rotated relative to one another in a first direction by an alternate shortening of a first and an adjacent second bridge of the three bridges, and in that the two parts of the actuator are rotated relative to one another in a second direction opposed to the first direction by an alternate shortening of the second and the adjacent third bridge. 3. An actuator suitable for use in a method as claimed in claim 1 or 2. which actuator is provided with two parts which extend in a main plane and are interconnected by means of three bπdges. which three bridges can each be shortened in a shortening direction extending parallel to the ma plane through local heating of the bridge and subsequent cooling down, while the two parts are rotatable relative to one another about an axis of rotation extending substantially perpendicularly to the mam plane through shortening of at least one of said three bndges. charactenzed in that the shortening directions of the three bndges are mutually substantially parallel, and the two parts can be rotated relative to one by an alternate shortening of two mutually adjoining bridges of the three bridges. 4. An actuator as claimed in claim 3, characterized in that the bridges have a width, seen perpendicularly to the shortening direction, which is substantially smaller than twice a spot diameter of a laser beam used or designed to be used for shortening the bridges. 5. An actuator as claimed in claim 4, characteπzed in that the width of the bπdges is at most equal to the spot diameter. 6. An actuator as claimed in claim 3, characteπzed in that a distance present between the bridges and the width of the bπdges have a same order of magnitude. 7. An actuator as claimed in claim 3, characteπzed in that a distance present between the bndges is substantially greater than the width of the bndges. 8. An actuator as claimed in claim 3, characterized m that the actuator is provided with a coupling member which is fastened to one of the two parts of the actuator at a distance from the bridges as seen parallel to the shortening direction and in a fixed position as seen in a displacement direction directed substantially perpendicularly to the shortening direction, which coupling member is uncoupled from the corresponding part when seen in the rotation direction of the actuator. 9. An actuator as claimed in claim 8. characteπzed in that the coupling member compnses a blade spnng which extends substantially parallel to the displacement direction and substantially perpendicularly to the main plane. 10. An actuator as claimed in claim 9, characteπzed in that the two parts of the actuator, the three bπdges, and the blade spπng are manufactured from a single piece of sheeting, the blade spπng being bent from the main plane into a position substantially perpendicular to the main plane.

Inventors: JANSEN NORBERT E T, POST JAN H, VERHOEVEN ERIK C M, JANSEN, NORBERT, E., T., POST, JAN, H., VERHOEVEN, ERIK, C., M.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2000
Main classification: G11B7
IPC codes: G11B5, G11B7, H02N10