Method and device in a motor

The invention relates to a method and a device for causing a first body (3, 7, 14), which is held in engagement with a second body (1, 8, 12), to move along said body, said second body comprising material which may be caused to undergo a dimensional change across the intended direction of movement due to magnetostrictive, electrostrictive or piezoelectrical action. Said first body (3, 7, 14) is continuously held in cooperation through form engagement with a zone (2, 10A, 10B, 15) on said second body, which is caused to undergo a dimensional change across the intended direction of movement under the influence of a magnetic field or an electrical field said zone (2, 10A, 10B, 15) by displacement of said magnetic or electric field in the intended direction of movement being displaced in said direction during simultaneous driving action on said first body (3, 7, 14) through form engagement for coupled movement together with said zone (2, 10A, 10B, 15).

The present invention relates to a method and a device for causing a first 
body, which is held in engagement with a second body, to move therealong, 
said second body being composed of or consisting of materials which due to 
magnetostrictive, electrostrictive or piezoelectrical action may be caused 
to undergo a dimensional change across the intended movement direction. 
It is previously known to use the material deformations obtained in 
materials of the kind mentioned initially under the influence of a 
magnetic or an electric field, in order to bring about a movement of a 
mechanical element, e.g. in electrical contact means, in printers or in 
step motors, adjusting motors etc. For use in motors it has proved to be 
advantageous to use magnetostrictive materials, and particularly so called 
giant magnetostrictive materials, i.g. materials consisting of an alloy 
between rare earth metals and magnetic transition metals. The largest 
magnetostriction known so far has been established within this group of 
alloys, i.g. the property of undergoing, under the influence of a magnetic 
field, a dimensional change corresponding to the magnitude of the magnetic 
field. All those motor constructions are characteristic in that the 
material deformation generated by magnetic or electric influence in a 
repeated manner is transformed into an outer mechanical movement. This 
generally results in motor constructions with a relatively low movement 
velocity, linear or rotating. 
A motor construction of this kind which per se is excellent is described in 
the international publications WO 88/05618 and WO 90/07821. In one 
embodiment described in one of said applications, a giant magnetostrictive 
rod (Terfenol rod) is by shrinking fixed within a tube. By actuating a 
partial zone of the rod from one end thereof to the other under the 
influence of a magnetic field which is movable along said rod, the giant 
magnetostrictive rod is caused to move stepwise along the tube. The step 
dimension corresponds to the axial elongation caused within the actuated 
zone. A typical dimension of this elongation is about 10 .mu.m. Each of 
said steps requires a zone displacement along the entire length of the 
giant magnetostrictive rod. The zone displacement can take place with a 
very high velocity and is in principle limited by the elastic wave 
velocity of the material, which for the giant magnetostrictive material 
which is called Terfenol amounts to about 1700 m/s. Since each step 
requires a zone displacement along the entire length of the rod, the 
resulting movement velocity of the motor is substantially lower than the 
movement velocity of said zone. 
The object of the present invention is to provide a method and a device in 
which materials of the kind mentioned initially are used to cause a first 
body, which is held in engagement with a second body of said material, to 
move along said body, and thereby bring about a motor allowing very fast 
and at the same time exact movements, linear or rotating, and which has 
high velocity and acceleration performances and renders possible a good 
positional control and rigid and exact position adjustment 
characteristics. 
The object mentioned above is obtained by giving the method and the device 
according to the invention the characteristic features specified in the 
appended claims. 
The invention is described below with reference to schematical examples of 
embodiments illustrated in the appended drawings, in which

FIGS. 1-3 are very schematic figures intended to illustrate the pricipal 
construction of a variant of the motor according to the invention, in 
which a sliding movement is imposed to a body which is movable along an 
elongated rigid body. The rigid body 1 consists of an elongated rod having 
upper and lower plane parallel sides. The elongated body is made of a 
magnetostrictive, electrostrictive or a piezoelectrical material. Under 
the influence of a magnetic or an electric field, not shown, a zone 2 of 
the rod 1 is caused to undergo a contraction in the transversal direction 
of said rod. By moving the magnetic or the electrical field along the rod 
the deformed zone 2 may be caused to move along the rod 1 in the form of a 
contraction wave propagating in the longitudinal direction of said rod. In 
FIGS. 1-3 the deformation zone has been illustrated as a V-shaped 
deformation zone. In reality the deformation zone 2 probably is not 
v-shaped but will form a bow shaped recess on the upper and lower sides 
respectively of the rod 1. The V-shape in FIGS. 1-3 have been chosen in 
order to facilitate the understanding of the power transmission between 
the movable part and the fixed part of the motor. 
In accordance with the invention a body 3 which is movable along the rod 1 
is arranged for cooperation due to form engagement with the deformed zone 
2 of the rod 1. The body 3 consists of an upper part 3A and a lower part 
3B, which are interconnected and are held pressed against the rod 1 in the 
deformed zone 2 via an intermediate lubricant film 4 between the contact 
surfaces. There is thus no direct mechanical contact between the surfaces. 
The lubricant 4 is supplied through lubrication channels 5 in the body 3, 
said body also comprising return channels 6 for said lubricant. The 
surface of the upper part 3A and the lower part 3B, respectively, of the 
body 3 which faces the deformed zone 2, is shaped with a configuration 
which as close as possible corresponds to the shape of the deformation 
zone of the rod 1. However, in FIGS. 1-3 said form is illustrated as a 
V-shaped surface. The lubricant 4 is supplied with such a pressure and 
such a flow, that a thin lubricating film continuously is maintained 
between the contact surfaces. 
FIG. 2 illustrates an initiated displacement of the deformation zone 2 
along the rod 1 in a direction to the right in the figure. In the initial 
phase of the movement of zone 2 in the longitudinal direction of rod 1, a 
certain compression of the lubricant film 4 is obtained, so that stable 
pressure conditions are established in the lubricant film. The sloping 
surface of the upper respective the lower part 3A, 3B of the body 3, as 
seen to the left in the figures, is then actuated via the lubricant film 4 
by a distributed load. This condition is most clearly illustrated in FIG. 
3. The distributed load f has in FIG. 3 been marked as an evenly 
distributed load. In reality the distributed load f probably is variable 
along the surface. This distributed load f is composed into a resulting 
force F acting on the upper and the lower part 3A, 3B respectively of the 
body 3. The force F acts perpendicularly towards the engagement surface 
between the body 3 and the deformation zone 2 of the rod 1. The force P 
has a vertical component F.sub.V and a horizontal component F.sub.H. The 
force component F.sub.H thus acts in parallel with the axial direction of 
the body 1 and causes the body 3 to move along the body 1. A prerequisite 
of this is, however, that the lubricant film 4 is continuously maintained, 
for instance by hydrostatically journalling the body 2 on the body 1. The 
lubricant to be used should have a low viscosity. Conceivable lubricants 
are e.g. a thin lubricant oil, water or pressure air. 
If, in the principal exemple according to FIGS. 1-3, the body 1 instead 
consists of a rod having a circular cross section, the body 3 forms a 
ring, and the deformation zone, instead of having V-shape has a double 
conical shape, composed of two frustums of a cone. 
The body 3 is thus caused to move along the elongated body 1 together with 
the deformation zone 2 propagating along the rod. This results in that the 
body 3 can obtain very rapid and at the same time exact movement. 
FIG. 4 schematically illustrates a principal variant of an embodiment 
according to the invention, in which no lubrication of the contact 
surfaces between the movable and the fixed part of the motor i required. 
This motor variant also comprises an elongated rod 1 of a 
magnetostrictive, electrostrictive or a piezoelectrical material. The rod 
1 has upper and lower plane parallel sides. In this figure as well as in 
FIGS. 1-3, the deformation zone 2 has been indicated as two straight 
planes sloping towards each other. The body 7 which is movable along the 
body 1 consists, in this principal embodiment, of an upper roller 7A and a 
lower roller 7B which are connected to each other and are held pressed 
against the sloping surfaces of the deformation zone 2 by means, not 
shown. When the deformation zone 2 is caused to move to the right in the 
figure, the sloping surfaces thereof will act on the periferal surfaces of 
the rolls 7A and 7B with a force F, which is directed perpendicularly 
towards said sloping surfaces and extending through the rotational center 
of the respective roller. The roller 7A, 7B are thus each influenced by a 
force F having a vertical component F.sub.V and a horizontal component 
F.sub.H. Under the influence of the horizontal force components F.sub.H, 
the rollers are caused to preform a rolling movement in parallel with the 
movement direction of the movable deformation zone 2. No lubrication of 
the contact surfaces between the rollers and the deformation zone is 
required. The body 7 is thus caused to move by rolling movement along the 
rod 1 as the deformation zone 2 moves along the rod. 
FIGS. 5-7 schematically illustrate some embodiments, in which the rod or 
the body along which the movable body shall be displaced, consists of a 
gland magnetostrictire material, e.g. Terfenol. 
The motor illustrated in FIG. 5 thus comprises an elongated rod 8 of a 
giant magnetostrictive material. Rod 8 has plane parallel upper and lower 
sides. Above respectively underneath the rod 8 a series of magnetic coals 
9A and 9B respectively are disposed for generating a magnetic field 
resulting in curved deformation zones 10A, 10B of said rod 8. By 
controlling the magnetic coils 9A one after the other as well as the 
magnetic coils 9B one after the other, the deformation zones 10A, 10B are 
caused to move like a deformation wave along the rod 8. The arrangement of 
the magnetic coils 9A, 9B and the control of the switching in of the 
magnetic coils are suitably carried out in a manner corresponding to the 
manner described in the publication WO 90/07821 mentioned previously. 
The body which shall be displaced along the rod, in this case consists of 
an upper roller 7A and a lower roller 7B, which are interconnected by 
means of rigid frame elements 11, fixing the rollers 7A and 7B at a 
constant distance from each other. The distance is adjusted so that the 
periferal surface of the rollers are in contact with the upper surfaces of 
the deformed zones 10A and 10B. This means that the rollers must be 
positioned on the body 8 with a certain preload. Alternatively the rollers 
7A, 7B may be interconnected by means of a resilient element which 
constantly keeps the rollers 7A, 7B pressed against the upper and lower 
surface respectively of the rod 8. The frame element 11 is suitably 
provided with guide elements, not shown, e.g. guide rollers, for guiding 
the frame 11 so that the axes of the rollers 7A and 7B constantly are 
maintained in a plane perpendicular to the rod 8. 
By suitable control of the engagement of the magnetic coils 9A, 9B, the 
deformation zones 10A, 10B and thus the rollers 7A, 7B are caused to move 
along the rod 8 in the desired direction with a great velocity and high 
precision. 
FIG. 6 illustrates an embodiment comprising a rigid rod 12 of a giant 
magnetostrictive material, e.g. Terfenol. The rod 12 has a circular cross 
section and is surrounded by magnetic coils 13 disposed adjacent each 
other and arranged in a connecting and control arrangement designed in 
accordance with the technique known from the publication WO 90/07821. A 
ring 14 is disposed by shrinking on the rod 12, said ring having a width 
corresponding to the length of the deformed zone 15 and having an internal 
shape and internal dimensions corresponding to shape and dimensions of the 
deformated zone 15. A lubricating film is arranged in the manner mentioned 
previously, in the contact surfaces between the ring 14 and the 
deformation zone 15, so that said surfaces are not in direct metallic 
contact with each other. 
By controlling the engagement of the magnetic coils 13 in a manner known 
per se, the deformation zone 15 is thus caused to move axially in the 
desired direction along the rod 12. By the form dependent engagement 
between the ring 14 and the deformation zone 15, the ring 14 is then 
caused to move along with the deformation zone in the desired movement 
direction. 
FIG. 7 illustrates a variant of the embodiment shown in FIG. 6. The rod 12 
of giant magnetostrictive material, e.g. Terfenol, supports an annular 
body 14A, adapted to a deformation zone 15 of the body 1. As mentioned 
previously it is made sure that a lubrication film is continuously 
maintained in the contact surfaces between the annular body 14 and the 
deformation zone 15. In order to reduce the mass of the annular body 14A 
at the same time as its radial stiffness is secured, the rod 12 and the 
annular body 14A are surrounded by a outer tube element 16 being arranged 
coaxially and having a high radial stiffness. In this embodiment a 
suitable lubricant is also supplied between the outer periferal surface of 
the annular body and the inner surface of the tube 16, so that a lubricant 
film is continuously maintained and so that the axial movement of the 
annular body 14A is not prevented. By this arrangement a slidable radial 
support of the annular body 14A is obtained, by means of which the 
diameter of the annular body 14A is kept constant irrespective of the 
actual pressure load in the contact surface with the deformation zone of 
the rod 12. 
According to the embodiment shown in FIG. 8, the rigid rod may be composed 
of a number of bars 17 of a giant magneostrictive material, said bars 
being disposed edgeways adjacent each other, the ends of said bars being 
connected, e.g. articulately connected with an elongated, elastically 
bendable plane section 18, so that the dimensional change of the bars 17 
in the longitudinal direction causes a bending of said section. Suitably, 
both flat sections 18 are in form engagement with a pair of rollers 7A, 
7B, arranged in accordance with the embodiment illustrated in FIG. 5. In 
this embodiment it is possible to use the fact that the magnetostrictive 
rods have a larger dimensional change longitudinally than transversally. 
The bars 17 together with the sections 18 forms a composite body, which 
undergoes a dimensional change in the transverse direction under the 
influence of a magnetic field, i.e. crosswise with respect to the intended 
movement direction. 
Possibly the bars 17 may be arranged in contact with each other and 
together forming said composite body. In this case, the sections 18 are 
deleted. 
Even if the invention is described with reference to embodiments in which a 
first body is movable along a second body of magnetostrictive material, 
which is shaped as a straight, linear rod, the invention of course is 
equally applicable for rods extending in a circular shape, so that the 
body which is movable along said rod will describe a circular movement. 
Nor is the invention limited to the use of mgnetostrictive material of the 
kind undergoing a decrease of the transversal dimensions and an increase 
of the longitudinal dimensions under the influence of a magnetic field, 
but is equally applicable for use of magnetostrictive materials undergoing 
an increase of the transversal dimensions and a decrease of the 
longitudinal dimensions under the influence of a magnetic field. When 
using the invention it is thus possible to use magnetostrictive materials 
with positive magnetostriction or magnetostrictive materials having a 
negative magnetostriction. Instead of generating a wave through 
propagating along the rod, a bulge propagating along the rod wall be 
obtained, said bulge cooperating by form engagement with a movable body 
having a complementary shape. 
According to a variant of an embodiment not shown, the body which is 
displacable along a rod is formed with a plurality of zones, disposed 
adjacent each other for simultaneous cooperation through form engagement 
with corresponding deformation zones of the rod, said deformation zones 
being generated due to magnetostrictive, electrostrictive or 
piezoelectrical action.