WO1990007821A1

WO1990007821A1 - Method and device in a motor

Info

Publication number: WO1990007821A1
Application number: PCT/SE1989/000748
Authority: WO
Inventors: Carl Tyrén; Fredy Olsson; Lothar Erik Kiesewetter
Original assignee: Jacobsson Industrier I Stockholm Ab
Priority date: 1988-12-27
Filing date: 1989-12-27
Publication date: 1990-07-12
Also published as: SE8804650L; AU4831990A; SE8804650D0

Abstract

The invention relates to a method for causing a first body (10; 20) having magnetostrictive properties, and a second body (11), against which said first body is in bearing contact with a certain grip between the contact surfaces, to move with respect to each other while substantially maintaining said grip, wherein a magnetic field profile having a field strength variating in the longitudinal direction of the body is generated in a longitudinal section in said first body and is caused to be moved along the same line as said first body is moved along with respect to said second body. According to the invention electric current is supplied separately to individual coils in a set of coils (12). Furthermore, the supply of current is controlled to cause said coils (12) to generate partial magnetic fields, forming together said magnetic field profile. The invention is related also to a device for carrying out the method. Said device comprises a plurality of sets of coils (12, 12A-12D, 12F-12I), which are arranged along said second body (11), and power supply means are provided for a controllable supply of electric current to said coils (12, 12A-12D, 12F-12I). Furthermore, control means (23-27) are provided for controlling current separately to each of said coils (12, 12A-12D, 12F-12I).

Description

Method and Device in a Motor

The invention relates to a method for causing a first body having magnetos rictive properties and a second body, against which said first body is in bearing contact with a certain grip between the contact surfaces, to move with respect to each other while substantially maintaining said grip, wherein a magnetic field profile having a strength variating in the longitudinal direction of the body is generated in a longitudinal section in said first body and is caused to move along the same line as said first body is moved along, with respect to said second body, and a device for carrying out the method.

An object of the invention is to provide a method and a device of the above-mentioned type which is suitably utilized in linear motors, in which a high grade of accuracy of the generated movement is required, e.g. shifting motors with high accuracy adjustment, wherein the requirement with respect to length of stroke and power output is small, but also in such linear motors in which larger stroke and power output is required, e.g. motors used as power and motion generating units in operating lifting devices. Another suitable area of use is i.e. torque motors or turning motors in servo systems and the like. Another object of the invention is to provide a method and a device of the above-mentioned type which make possible a finely adjustable and accurate control of the intended movement in a simple way.

The international application PCT/SE88/00010 dis¬ closes a method and a device, which are based on the fact that magnetostrictive materials change their geometrical dimensions under influence of a magnetic field. A rod of magnetos rictive material of a certain composition will thus be increased in length under influence of a magnetic field while at the same time the transversed dimensions of the rod are decreased. In an embodiment shown in said application a cylindrical rod of a magnetostrictive material of the kind which undergoes a simultaneous change in length and transversal contraction under influence of a magnetic field, is by means of shrinking disposed within a cylindrical tube, preferably made of a non-magnetic material, so as to clamp the magnetostrictive rod within the tube with a certain clamping grip. Along the entire length the rod is surrounded by a great number of magnetic coils disposed adjacent to each other, each of said coils being connected sequencally, one after the other, to a power supply for generating a magnetic field. Each magnetic coil is dimensioned so as to generate a magnetic field influencing only a partial section of the magnetostrictive rod. Each of the coils is dimensioned in such a way that the mgnetic field generated by the coil influences one longitudinal section of the magnetostrictive rod only. The dimensioning is made also in such a way that the magnetic field generated when current is supplied to the coil causes an increase in length of the section being influenced, said section simultaneously undergoing a transversed contraction of such a magnitude that the clamping grip against the tube decreases considerably and preferably is eliminated.

In the method and device described in the above- referenced international application there exist certain problems in connection with switching on and switching off, respectively, adjacent coils that provide the magnetic field. A result of these problems is e.g. losses due to friction and irregular movement of the rod. One possibility to limit the problems is to control the current to each of the coils so that rapid switchings are avoided. E.g. this can be accomplished by increasing the current in one coil while at the same time decreasing the current in an adja¬ cent coil. However, the problems still remain to some extent. Another possibility mentioned in the above-mentioned patent application is that one coil only is arranged around the rod and that the coil is moved along the coil in reverse direction in relation to the movement of the rod. However, several problems are connected to a coil being moved along the rod, e.g. electric wiring and bearing.

An object of the present invention is to provide a method according to which the above-mentioned problem is substantially overcome, and a device for carrying out the method.

Another object of the invention is to provide a method and a device according to which an accurate control of the magnetic field generated in the rod is made possible in dependence of actual operating conditions. Said objects and other objetcts of the invention are accomplished by means of a method and a device, the charac¬ teristics thereof apprearing in the accompanying claims.

The invention will be described by means of embodi¬ ments with reference to the accompanying drawings, in which FIG. 1 diagramatically shows a device for carrying out the method according to the invention, comprising a magnetostrictive rod clamped within a tubelike body,

FIG.1A is a shaft showing the states of control signals generated to carry out the method according to the invention,

FIG. 2 is a longitudinal sectional view of an alternative embodiment of the device according to the invention,

FIG. 3 is a wiring diagram of an electric control circuit included in the device according to the invention, FIG. 4 is a diagramatic longitudinal sectional view of an alternative embodiment of the device according to the invention.

With reference to FIG. 1 the device comprises a rod 10 of magnetostrictive material surrounded by a cylindrical hollow body 11. Around the hollow body 11 a number of coils 12, 12A-12I are winded, each of said coils separately being connected to a power supply unit (see FIG. 3). The coils are separated by a number of annular soft iron disks 13, which function as flow conductors for the magnetic field generated by the coils. A tube 14 made of soft iron bear against the peripheral surfaces of the soft iron disks. Also other materials with good magnetic field conducting properties can be used. The dashed line 15 defines the starting position of the rod 10, before any current is supplied to the coils. When current is supplied to the coils 12-12D a mechanical contraction in the transversed direction and a increase in the longitudinal direction take place in the rod 10 and the rod reaches the position marked with the solid line 16. Supply of current to the coils 12A-12D is indicated with "1" in the first four columns in the first row of FIG. 1A. Remaining coils are not influenced in this state, and no current is supplied to them. The magnetic profile, which the rod hereby is exposed for, causes in a longitudinal section of the rod a contraction in the transverse direc¬ tion of the rod, and the outline of the rod follows the line 17, whereby the longitudinal section being influenced no longer is in contact with the hollow body. The next step for accomplishing a desired movement of the rod 10 is to decrease the current to the coil 12A while approximately at the same time the current to the coil 12, which is a coil most adjacent to the previously innermost coil 12D, is increased. The new state is indicated also in the second line of FIG. LA. Dash and dot line 17 indicate the contour of the rod when the rod is exposed for a magnetic field generated by the coils 12B-12E. The section of the rod 10 undergoing contraction in the transverse direction has thus been moved along the hollow body a distance substantially corresponding to the height of a coil. However, in spite of this "movement" the rod remains in the projected position indicated by line 16 in FIG. 1. The method is then repeated firstly until all coils have been supplied with current and secondly from the beginning, whereby the magnetostrictive rod is caused to move the desired distance within the hollow body. If the strength of the respective magnetic field is adjusted in such a way that the longitudinal section being influenced is released from contact with the inside of the tube the movement of the magnetostrictive rod takes place without any slip resistance.

The embodiment shown in FIG. 2 comprises a hollow body 20 of magnetostrictive material, which is surrounded by an outer cylindrical hollow body 20, and in this case the coils 18 are winded on a bobbin 21 enclosed in the hollow body 11. From the figure it is clear that in this embodiment an annular portion of the hollow body 20 under¬ goes contraction when the coils 19 are supplied with electric current and generate a local magnetic field in the hollow body 20. In other aspects this embodiment corre- sponds to the embodiment previously described in connection with FIG. 1. The major advantage with this embodiment is that the outer hollow body protects other components, e.g. the coil, very well.

The circuit diagram shown in FIG. 3 relates to an embodiment of a control circuit for the control of supply of current to the coils generating the magnetic fields required to accomplish the desired movement. The control circuit comprises an oscillator 23, the output thereof constituting in form of pulses a time base for the control circuit. The output is supplied to a counter 24 which is increased one step for each pulse. The counter has a number of output terminals, that are connected to a memory circuit 25. The present value of the counter can be read at said output terminals. Said value is an address to a position in the memory circuit 25, at which a control signal corre- sponding to the control pulses according to FIG. 1A is stored. The control signal is supplied to gate terminals of a number of MOSFET driving transistors 28 through a buffer circuit 26 and a protection circuit 27. Each of said driving transistors 28 is in a conventional manner loaded by a coil 12 and a diode 29 connected in backward direction in parallel with said coil. It is possible to connect a computer in section A-A, said computer in that case supply¬ ing componements on the right side of the section A-A with control signals. The computer makes possible a control of the supply of current to the coils which is considerably more complex. The number of coils being supplied with current at any moment is readily modified also during operation. A measuring transistor 30 can also be included in the load circuit of the driving transistor. By means of such a measuring transistor different operational conditions, such as the value and phase shift in relation to the voltage over the load of the load current, can be recorded and by means of a feedback influence the control of the supply of current.

In a development of the device according to the invention not shown here there is included also circuits providing a more accurate control of the current supply to the coils. The current can e.g. be supplied in a pulse width modulated form by means of a modulator circuit.

FIG. 4 shows a somewhat modified embodiment of the method according to the invention. The device shown thereon correspond to the device of FIG. 1 and comprises a rod 10 of magnetostrictive material, a hollow body 11 and a number of coils 12, 12A-12D. The latter coils 12A-12D are supplied with the current, whereby the rod undergoes contraction, so that cavity 22 is formed between the rod and the hollow body in the manner previously described in connection with FIG. 1. To balance movements appearing in the rod when the rod is influenced by said previously described forwardly moving magnetic field profile a second magnetic field is generated in one end of the rod. Said second magnetic field pulsates with a frequency which accomplish a balancing movement in that end of the rod. The magnetic field is generated by a supply of current to a number of coils 31 situated around the portion of the hollow body where the end of the rod resides.

According to what has been stated above an important feature according to the invention is that the rod 12 is made of a magnetostrictive material. Preferably the rod 10 is manufactured by so called giant magnetostrictive material, i.e. an alloy between rare earth metals such as samarium (Sm), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er) , thulium (Tm) . In the present most common applications also magnetic transition metals such as iron (Fe), kobolt (Co) and nickel (Ni) are included but in other applications, e.g. together with super conductive materials the transition metals are not included. The invention is not limited to the described and in the figures illustrated embodiment, but may be subject to variations within the scope of the appended claims. Thus, the magnetostrictive body may be clamped between two plane- parallel plates and by using the magnetic field in the principal way described above, the magnetostrictive body may be caused to move between the plates in the planes thereof, the clamping grip with respect to the plates being kept substantially unchanged. Possibly the grip between the magnetostrictive body and the plate may be obtained solely through the dead weight of the body, the body resting only upon and being supported by a plane plate and thus does not need to be clamped between two plane-parallel plates.

Especially in applications with long hollow bodies certain practical problems may arise if coils are provided along the entire length of the hollow body. Instead a plurality of coils are arranged in a pack, the length thereof corresponding substantially to the length of the rod. The pack of coils is then moved along the hollow body together with the rod.

Claims

1. Method of causing a first body (10;20) having magneto- strictive properties and a second body (11), against which said first body is in bearing contact with a certain grip between the contact surfaces, to move with respect to each other while substantially maintaining said grip, comprising the steps of generating a magnetic field profile having a field strength variating in the longitudinal direction of the body; and causing said profile to move along the same line, along which said first body is moved with respect to said second body, c h a r a c t e r i s e d in that the electric current is supplied separately to individual coils in a set of coils (12) ; and that the supply of current is controlled, so that said coils (12) are caused to generate partial magnetic fields forming together said magnetic field profile.

2. Method according to claim 1, c h a r a c t e r i s e d in that said set of coils is selected among a plurality of coils arranged along said second body.

3. Method according to claim 1 or 2, c h a r a c t e ¬ r i s e d in that said magnetic field profile is caused to move along said bodies by increasing the current to at least one coil adjacent to one of the outermost coils of said set, while at the same time decreasing the current to at least the outermost coil in the other end of the set of coils, such steps then being repeated in the direction initiated.

4. Method according to claim 3, c h a r a c t e r i s e d in that the current to the rest of the coils of said set remains substantially unchanged.

5. Method according to any of claim 1-4, c h a r a c t e ¬ r i s e d in that a separate magnetic field is caused to influence an end portion of said first body to balance movements of the body caused by other coils.

6. Method according to any of claim 1-5, c h a r a c t e ¬ r i s e d in that the current to the coils is controlled in dependance of actual operational conditions.

7. Method according to any of claim 1-6, c h a r a c t e ¬ r i s e d in that the current to the coils is controlled in dependance of changes of magnetic fields in said bodies.

8. Method according to any of claim 1-7, c h a r a c t e - r i s e d in that the current to the coil is controlled in dependance of the characteristics of the current floating through said coils.

9. Device for carrying out the method according to any of claim 1-9, comprising a first body (10;20) having magneto- strictive properties and a second body (11), against which said first body is in bearing contact with a certain grip between the contact surfaces, c h a r a c t e r i s e d in that several sets of coils (12,12A-12D,12F-12I) are arranged along said second body (11), that power supply means are provided to supply in a controlled manner elec¬ tric current to the coils (12,12A-12D,12F-12I) and that control means (23-27) are provided for controlling sepa¬ rately the current to each of said coils (12,12A-12D,12F- 121).

10. Device according to claim 9, c h a r a c t e r i s e d in that there is provided means for measuring the current through said coils.

11. Device according to 9 or 10, c h a r a c t e r i s e d in that said second body consists of a hollow body (11), surrounding said first body formed as a rod (10), and that said coils are winded on the surface of said second body.

12. Device according to any of claim 9-11, c h a r a c ¬ t e r i s e d in that said second body consists of a hollow body (11) surrounding said first body formed as a hollow body (20), and that said coils are provided within said first body.