When the magnetostrictive rod is magnetized along its longitudi- nal axis, a change in its length is achieved. This change of length creates forces and movements which affect different me- chanical systems depending on the field of application. Exam- ples of fields in which an actuating device according to the in- vention is useful is for sound and vibration sources, for vibration control, direct and indirect movement control, material treat- ment, and in electromechanical power converters.

PRIOR ART The Swedish patent publication No. 468964 shows a known ac- tuating device composed of a number of stator cells stacked on each other, each comprising a magnetic coil. Within the stator cells drive cells are arranged comprising a cylindrical rod of a magnetostrictive material and magnetic return conductors in the

form of discs connected to the end surfaces thereof. The mag- netostrictive material works almost linearly and with the highest efficiency within a certain area around a certain constant mag- netization level. To achieve this level, a drive cell is provided with permanent magnets in the form of massive discs arranged on opposite sides of the coil.

To achieve a high output density, i. e. a high mechanical output per volume or mass of the actuating device, it is necessary to provide cooling of the actuating device. In the actuating device mentioned above the cooling is accomplished with cooling chan- nels being arranged in cooling jackets surrounding the stator cells. The stator cells are fixed to the cooling jackets which are fixed to an outer fixture frame.

A problem with using surrounding cooling jackets for cooling the actuating device is the fact that the cooling jackets provide extra material which takes up space in the limited volume which is de- fined by the surrounding fixture frame. Thus, the size of the cooling jacket also settles the size of the coil which in turn ef- fects the output density and efficiency of the actuating device. A smaller coil has a higher resistance due to a smaller copper area, which either leads to larger losses and thus a lower effi- ciency at the same magnetizing or a smaller output density at an unchanged degree of efficiency. Another problem with the cool- ing jackets is that the cooling of the magnetostrictive rod is not efficient, partly due to the large distance between the cooling channels and the rod and partly due to the fact that intermediate material deteriorates the heat transfer.

DESCRIPTION OF THE INVENTION The object of the invention is to obtain an actuating device hav- ing a high efficiency and a high output density. The object is achieved by an actuating device having an efficient cooling without the need of adding any extra material to the actuating

device. What is characterizing an actuating device according to the invention appears from the appended claims.

Thanks to the fact that at least a part of the inlet section or out- let section of the cooling channel extends at least partly in ex- isting permanent magnet members, there is not need for adding any extra material or components, for example in the form of cooling jackets to the actuating device for cooling thereof. An actuating device according to the invention is thus a compact construction using the available volume in a maximal way so that a high output density and a high degree of efficiency is achieved. The available volume may instead be used for opti- mizing the size of the coil for achieving low specific losses.

In a preferred embodiment of the invention, the cooling channel comprises a gap arranged between the rod and the coil. By cooling directly against the rod, the cooling thereof will be very efficient. Another advantage with arranging the cooling in a gap between the coil and the rod is that the space in the gap may be used for different purposes, for example for arranging means for improving the heat transfer between the rod and the cooling me- dium or for arranging means for keeping together and supporting the rod.

According to a preferred embodiment of the invention, the actu- ating device comprises a stator cell and a drive cell which are arranged movable relative to each other along the whole longi- tudinal axis of the drive cell. The drive cell comprises the mag- netostrictive rod and a first part of a magnetic return conductor member. The stator cell comprises the coil, the permanent mag- netic member, and a second part of the magnetic return con- ductor member. The advantage with this embodiment of the in- vention is the fact that the drive cell could be inserted or taken out of the stator cell when needed. This is an advantage, for ex- ample during assembling of the actuating device since it is pos- sible to finish the of the stator cell and the drive cell independ-

ently of each other before they are put together. Thus, the re- quirement of tolerance at the manufacturing is reduced and the assembly will be simpler, less expensive, and faster. The main- tenance is also simplified when the drive cell can easily be taken out of the stator cell and it is enough to change a part thereof, should something be broken.

Further advantages with this embodiment is achieved by ar- ranging the permanent magnet members in the stator cell and not in the drive cell. One advantage is that, for a given length of the drive cell, the rod is admitted a larger active length, i. e. there is room for more magnetostrictive material in the drive cell. As an alternative, the drive cell could be made shorter having the same amount of magnetostrictive material. Another advantage is that the drive cell comprises fewer boundary sur- faces between the rod and the other components of the mag- netic circuit, which is an advantage from a manufacturing point of view.

According to a further preferred embodiment, the actuating de- vice comprises a stator and a stack. A stator is a plurality of stator cells stacked on each other, and a stack is a plurality of drive cells stacked on each other. The higher the stack, the larger the change of length is achieved thanks to the magne- tostrictive effect. The stator and the stack are arranged movable relative to each other. The advantages mentioned above re- garding the assembly and maintenance will increase with an in- creasing number of stator and drive cells included in the stack and the stator.

In an alternative embodiment of the invention, the cooling chan- nel comprises one or a plurality of gaps in the coil. If the actu- ating device comprises a stator and a stack, i. e. a plurality of drive cells and stator cells, it could be an advantage from an as- sembly point of view to arrange the gaps in the coil instead of between the coil and the rod. Then no extra arrangement in the

form of guiding means for facilitating the insertion of the stack into the stator are needed.

To sum up, it could be said that the invention yield mechanical, thermal, magnetic, and electrical advantages. A mechanical ad- vantage is that the actuating device is easy to assembly and maintain. A thermal advantage is the efficient cooling. A mag- netic advantage is the fact that a larger part of the length of the drive cell can be utilized for magnetostrictive material, which implies a larger length/radius ratio, i. e. fewer drive cells will be needed for the same length of the stack. An electrical advantage is that the coil can be made larger and thus the losses can be reduced.

DESCRIPTION OF THE DRAWINGS An embodiment of the device according to the invention shall hereafter be described with support of the appended drawings.

Figure 1 shows a partly cut, schematic perspective view of an embodiment of an actuating device according to the invention.

Figure 2 shows a cross-sectional view of the actuating device in figure 1.

Figure 3 shows a section A-A through the actuating device in figure 2.

Figure 4a shows a cooling channel in a section C-C through the actuating device in figure 2.

Figure 4b shows an alternative embodiment of a cooling chan- nel.

Figure 5 shows a section B-B through the actuating device in figure 2.

Figure 6 shows an actuating device comprising a plurality of drive cells and stator cells stacked on each other.

Figure 7 shows an alternative embodiment comprising cooling channels arranged in the coil.

Figures 8a and 8b shows two different embodiments which com- prising means for improving the heat transfer be- tween the magnetostrictive rod and the cooling me- dium.

DESCRIPTION OF EMBODIMENTS The figures 1-5 show a first embodiment of an actuating device according to the invention. The actuating device consists of a stator cell 1 and a drive cell 2. The drive cell comprises an es- sentially cylinder-shaped rod 3 of a magnetostrictive material and two center plates 4a, 4b, which have the shape of circular discs and which bears on both end surfaces of the rod 3. When a variable magnetic field is applied on the rod, it will be elon- gated or shortened in its longitudinal direction. The star cell 1 comprises a magnetizing coil 5 which surrounds the rod 3 and has an axis of symmetry which essentially coincides with the longitudinal axis of the rod. Furthermore, the stator cell com- prises two permanent magnet members 6,7 arranged on oppo- site sides of the coil 5 so that they are directly aligned with the magnetic flux generated when the coil 5 is transversed by a magneti- zation current. The stator cell 1 also comprises end discs 8a, 8b in the form of holed discs, which are arranged concentrically around the center discs 4a, 4b, and a wall element 9 having the shape of a tube with essentially the same axial length as the coil 5 and surrounds the coil. The wall element 9 is in both its ends provided with flanges 9a, 9b arranged across the longitudinal axis of the rod and among other

things has the purpose to form a support surface for the permanent magnetic members 6,7, and to conduct the magnetic flux to/from the permanent magnets. The wall element 9, the center discs 4a, 4b, and the end discs 8a, 8b are magnetic return conductor and form to- gether with the coil 5 and the rod 3, and the permanent magnet members 6,7 a closed magnet circuit. The magnetic flux in the mag- netic circuit is shown with arrows in the left part of figure 2. The center discs 4a, 4b and the end discs 8a, 8b are, for example, made of soft magnetic powder material and/or laminated magnetically posi- tioned soft magnetic material. The wall element 9 is, for example, made of wound magnetic or powder based material.

Figure 3 shows a section through one of the permanent magnet members 6 which has the form of a ring-shaped disc, whose plan of propagation is essentially perpendicular to the longitudinal axis of the rod 3. The permanent magnet member 6 comprises three perma- nent magnets 6a, 6b, 6c arranged side by side. One side of the per- manent magnets bears on the flange 9a of the wall element and their other side bears on the end disc 8a. The outside diameter of the permanent magnet members 6,7 is equal to or larger than the outer diameter of the wall element 9. The permanent magnets 6a, 6b, 6c have the form of truncated sections of a circle and are arranged so that radial channels 10a, 10b, 10c with an essentially rectangular cross-section is formed between two adjacent permanent magnets, see figure 4a. Two the sides of the channel are formed by the per- manent magnets 6a, 6b, and the other two sides are formed by the end plate 8a and the flange 9a of the wall element. The permanent magnet member 6 comprises, besides the permanent magnets 6a, 6b, 6c, also the channels 10a, 10b, 10c between the permanent magnets. In a corresponding way radial channels 10d-10f are ar- ranged in the second permanent magnet member 7. The channel 10e is not shown in figure 1. The radial channels 10a, 10b, 10c in the first permanent magnet member 6 form inlet channels for the cooling medium and the radial channels 10d-10f in the second permanent magnet member 7 form outlet channels for the cooling medium. Con-

nection devices 11a, 11b for the cooling medium are arranged at the orifice of the channels.

Figure 4b shows an embodiment of the invention in which the perma- nent magnet member 6 has the shape of a solid disc in which radial channels 10g having a cross-section formed as a semi-circle is cut out. The sides of the channel is defined by the permanent magnet member 6 and the end disc 8a.

The coil 5, which is arranged around the rod 3, has a inside diameter which is larger than the outside diameter of the rod and thus a cir- cular gap 12 is formed between the rod and the coils. The gap 12, which in the following is denoted the first gap, extends along the whole length of the coil 5. Figure 5 shows the gap 12 in a cross- section. The permanent magnet members 6,7 have an inside di- ameter which is essentially larger than the inside diameter of the coil. Within the permanent magnets 6,7 and between the end disc 8a and the end surfaces of the coil 5 there are a second gap and a third gap 14. Those gaps 13,14 are connecting to the inlet channels 10a- 10c as well as to the outlet channels 10d, 10e and also to the first gap 12. The cooling medium is supplied to the actuating device through the inlet channels 10a-10c in the first permanent magnet member 6 and passes through the second gap 13 to the first gap 12 and then through the third gap 14 to the outlet channels 10d, 10e in the second permanent magnet member 7, whereby both the coil 5 and the rod 3 are cooled. In the right part of figure 2 the flow of cooling medium in the actuating device is shown with arrows. The cooling medium may, for example, be a gas or a liquid.

The coil is wound so that both of its connection wires can be led out essentially in the center of the wall element 9 where an electric con- nection device 15 is arranged and to which two conductors for pro- viding driving current to the coil 5 are connected. The coil 5 may in another embodiment be wound so that both of its connection wires can be led out in the radial channels 10a-10f in the permanent mag- nets 6,7, whereby the connection device to the coil is arranged at

the permanent magnets. The center discs 4a, 4b and the rod 3 have a diameter which is smaller than the inner diameter of the coil, the permanent magnet members 6,7 and the end discs 8a, 8b so that drive cell 2 may be moved to and fro through the stator cell 1 without getting stuck therein. To further facilitate the insertion of the drive cell 2 into the stator cell 1, a guiding means 16 is arranged so that they run at least partly within the first gap 12.

An arbitrary number of stator cells and drive cells can be coupled in series for the purpose of achieving a correspondingly higher magne- tostrictive effect. Figure 6 shows an embodiment of an actuating de- vice in which three stator cells 1, 1b, 1c are stacked on each other.

Adjacent stator cells are arranged so that the end discs 8a, 8b bear on each other. The stator cells stacked on each other are kept to- gether by clamps 24 arranged around the flanges 9a, 9b of the cen- ter discs. The stator cells 1a-1c surround the three drive cells 2a, 2b, 2c. The drive cells 2a-2c are arranged so that their longitudinal axes co-incides and center discs 4a, 4b of adjacent drive cells bear on each other. The drive cells are pre-stressed with springs not shown in the figure so that they are pressed against each other with a cer- tain force and cannot be separated from each other during operation.

In the following, the drive cells stacked on each other are denoted a stack 17 and the stator cells stacked on each other are denoted a stator 18.

In the center of the stator 18, there is a space with an essentially cir- cular cross-section. The size of the space is defined by the inside diameter of the coil 5, the end plates 8a, 8b, and the permanent magnet members 6,7. The drive cells 2a-2c are formed so that the stack 17 may run freely through the space in the stator 18, which means that the rod 3 and the center discs 4a, 4b must have an outer diameter which is smaller than the diameter of the space. A number of guiding means 16 in the form of elongated bars, whose longitudi- nal axes are parallel to the longitudinal axis of the stack 17, are ar- ranged so that the stack 17 easily could be moved in and out of the stator at assembly or maintenance. In this example, the number of

guiding means 16 is three. The guiding means are arranged between the stack 17 and the stator 18. The guiding means 16 are fixed in the stator 18 and run along the walls of the space. in the center discs 4a, 4b, there are notches 25 for the guiding means 16, see figure 1.

When the stack 17 is to be inserted into the stator 18, the guiding means 16 slides in the notches 25 in the center discs 4a, 4b. The guiding means 16 have a coating which results in low friction and do not need to be taken away during operation.

In another embodiment of the invention, the guiding means may be used during the assembly to build the stack. The guiding means will then also have the further function of keeping the drive cells together during the assembling. When the stack is inserted into the stator, the drive cells might be exposed to magnetic forces from the permanent magnets, which forces will act separatingly on the drive cells from each other. Then guiding means keeping the stack together are ad- vantageous. After assembly, the guiding means are released so that they will not prevent movement of the stack during operation. In this embodiment the end discs are provided with notches for guiding the guiding means at the assembling.

In one end of the actuating device both the stack 17 and the stator 18 are fastened to an outer fixture. In the other end of the actuating device, the stack 17 is arranged so that it is free to move when the magnetic field is varied. The take-out of power and motion from the actuating device is effectuated at its free end. In another embodi- ment, the take-out of power and movement may be effectuated at both ends of the stack.

In an alternative embodiment, the coil may be provided with channels for transport of the cooling medium for cooling of both the coil and the magnetostrictive rod. Figure 7 shows an embodiment in which two circular longitudinal gaps 21a, 21b are arranged between the windings in the coil 20. Those gaps are connected to the inlet and the outlet channels of the permanent magnet member in the same way as was described in the previous embodiment. The stack is

formed so that the center disc and the rod have the same diameter.

In this embodiment, there is no gap between the rod and the coil and thus no guiding means for guiding the stack into the stator is needed, since the stack may slide directly against the inside of the coil. The inside of the coil and the envelope surface of the stack may be pro- vided with a cover with low friction to simplify the insertion of the stack.

In an embodiment of the invention, means for improving the heat transfer between the rod and the cooling medium is arranged in the gap between the coil and the magnetostrictive rod. Those means sometimes also function so that they support the rod mechanically which is an advantage, since there is a risk, at least in certain cases, that the rod will crack. There are many ways to improve the heat transfer, for example by making the surface of the rod rough and provide it with flanges, longitudinal or helical grooves and thus in- creasing the heat transferring surface. Another example is shown in figure 8a in which a number of rings 22 of a material with a high heat transfer property are arranged around the rod. The rings may, for in- stance be made of any heat conducting metal, for example insulated copper. To prevent winding short circuit, the rings may be provided with openings. The rings work both as enhancers of the heat transfer and as a mechanical support for the rod. Different kinds of surface enlarging elements may be arranged around the rod, for example a braid of the heat conducting material, for example glass fiber, see figure 8b. The advantage with a surface enlarging element is that it fills the gap so that the speed of the cooling medium increases and thus improves the cooling. A further method for improving the heat transfer is to apply some kind of coating on the rod, for example a coating of glass fiber.