EP0352357A1

EP0352357A1 - Control electromagnet

Info

Publication number: EP0352357A1
Application number: EP88112286A
Authority: EP
Inventors: Beatriz Elvira Katz
Original assignee: ALTERNATIVE ENERGY RESEARCH CENTER Inc
Current assignee: ALTERNATIVE ENERGY RESEARCH CENTER Inc
Priority date: 1988-07-29
Filing date: 1988-07-29
Publication date: 1990-01-31
Also published as: BR8903875A

Abstract

In a stationary electromagnet creating a multipole-nuclei dipole field for controlling the rotation around its axis of a movable element housing a permanent magnet, each of the electromagnet poles is shaped in the form of a circle arc having a corresponding opening angle of about 85 ± 15 degrees. Also the permanent magnet poles have faces shaped in the form of a circle arc, and in a preferred embodiment the permanent magnet is provided with grooves on both the pole faces, said grooves being parallel to the permanent magnet rotation axis.

Description

This invention relates to an apparatus for electromagnetically controlling the rotation of a movable element around its axis.
Moving a rotatable element housing a permanent magnet around its axis is a known technique, which was disclosed in pending applications EP-A-87104786.6 and EP-A-88.100015.2, both in the name of Alternative Energy Research Company (the present applicant). In EP-A-87104786.6 such technique was used to revolve a cylinder housing a permanent magnet in order to stop it in preselected positions. This cylinder is part of an apparatus for displaying informations and its rotation is used to modify the information appearing on the display.
In EP-A-88100015.2 some preferred embodiments of the electromagnet controlling the permanent magnet rotation were disclosed. These electromagnets were mainly designed for moving a cylinder, housing a permanent magnet, in six different positions by selectively activating at least one of the electromagnet poles. The final result is that a dipole field is formed, where at least one of the nuclei is a multipole nucleus, i.e. the north or the south pole (or both) is consisted of at least two poles of the electromagnet.
The main disadvantage of the disclosed apparatuses is that misalignements of the permanent magnet can occur; that is, the permanent magnet can stop in a position which is offset by several degrees from the required position. These misalignements can dramatically and negatively affect the operation of the whole device, particularly if said device is used for displaying informations.
The present invention solves the aforementioned problems by means of an apparatus in which permanent magnet misalignements do not exceed one degree.
According to the present invention there is provided an apparatus for controlling the rotation of an axially symmetrical movable element around its axis, the apparatus comprising a stationary electromagnet controlling the rotation of a permanent magnet housed in said movable element, the stationary electromagnet having three evenly spaced poles which carry each at least one coil consisted of one or more windings, characterized in that at least the inner surfaces of said electromagnet poles are shaped in the form of a circle arc and in that the opening angle of said arc is from about 70 degrees to about 100 degrees. The invention also relates to a method for electromagnetically controlling the rotation of a movable element housing at least one permanent magnet around its axis by means of the above disclosed apparatus, said apparatus having one coil for each pole, characterized in that said electromagnet is activated by contemporaneously feeding to said three coils a current that for each coil has an intensity lower than the critical intensity of the relating hysteresis loop, while the sum of said currents has an intensity which is above said critical intensity, and in that said current is codirectionally fed along a first direction to two of said coils, the third and last coil being fed in a second direction which is opposite to said first direction.
Moreover, the invention relates to a matrix panel formed by a plurality of the above disclosed apparatuses.
The invention will now be further described, by way of illustrative and non-limiting examples, with reference to the accompanying drawing, in which:

- Fig. 1 is a cross sectional view of the electromagnet and the permanent magnet;
-Fig. 2 is a cross section of a pole of the electromagnet having a different configuration;
-Fig. 3 is a cross section of a third type of pole;
-Fig. 4 is a side view of the electromagnet; and
-Fig. 5 is a diagram of a matrix area formed by a plurality of apparatuses according to the invention.

Referring now to the drawing, wherein like reference numerals designate like or corresponding parts throughout the several views, Figure 1 shows a cross section of an apparatus formed by an electromagnet 1 and a permanent magnet 2. The electromagnet has three poles 4, 4′, 4˝ and a base 3; said poles 4, 4′, 4˝ are shaped in the form of a circle arc having a common center 8 and the lenght of this circle arc is such that the relating opening angle, which in Figure 1 is shown by α, has a value in the range from about 70 degrees to about 100 degrees. Actually it was experimentally established that such a range value is dramatically effective to avoid any mispositioning of the permanent magnet, and that the optimum value for the angle is about 82 degrees.
While the disclosed electromagnet can be used with any kind of permanent magnet, the most accurate positioning thereof is achieved when a permanent magnet 2 of the type shown in fig. 1 is also used.
Said magnet 2 has two lateral faces 6 which are substantially parallel and plain, and two arc-shaped faces 7,9 corresponding to the north and south pole of the magnet 2. In a preferred configuration the opening angle of faces 7, 9 is similar to that of poles 4 - 4˝.
The main and most important feature of magnet 2 is that a groove 5 is provided on each face 7, 9; said grooves are longitudinally extending along faces 7, 9, are positioned at the middle line of said faces and are parallel to the rotation axis 8 of the permanent magnet 2. The magnetic flux can thus be correctly directed from pole 4′ to magnet 2 through the two portions of face 7 as defined by the groove 5 on said face, and from magnet 2 to poles 4˝ and 4 through the similar two portions as defined by groove 5 on face 9, or viceversa.
Thus, if the apparatus is correctly dimensioned and assembled, in each selected position of the permanent magnet, a first groove 5 is located at the middle of one pole, and the other groove 5 is located at the middle of the space between the other two poles.
For an improved direction control of the magnetic flux, poles 4 - 4˝ can be modified as disclosed in Figures 2 and 3.
In the embodiment shown in Fig. 2, a groove 11 is provided on the inner side of a pole 10, i.e. on the side which faces the permanent magnet. In the alternative embodiment of Fig. 3, a pole 12 is end-slotted, thus presenting a gap 13 at its upper end. In both cases, the groove 11 and slot 13 are provided at the position where groove 5 of permanent magnet stops (in front of pole 4′ - fig. 1).
A plain, a grooved and an end-slotted pole are each shown in the perspective view of Figure 4. Obviously, in a preferred embodiment the electromagnet poles are identical, and generally the most preferred poles are grooved poles.
As shown in Figure 4, on each pole 4, 4′, 4˝ is provided a coil 14, 15 and 16; each of said coils comprises one winding consisting of a preselected number of turns. To activate the electromagnet 1, a first coil, e.g. coil 15 on pole 4′, is fed along a first direction with a current having an intensity which is sufficient to energize pole 4′ but is lower than the critical intensity of the relating hysteresis loop. Identical currents are codirectionally fed to pole 4 and pole 4˝ along a direction opposite to that by which the first current is fed to pole 4′. The global effect of these three currents when simultaneously fed to poles 4, 4′ and 4˝ is the activation of electromagnet 1, which is thus forming a multipole nuclei dipole field. For example, pole 4′ will be the north pole while south pole will be formed by poles 4 and 4˝ together.
The total number of electrodes which are thus needed for each apparatus is three. A matrix panel formed by a plurality of such apparatuses will have the circuitry schematically shown in Fig. 5, where, in order to have a more simple drawing, poles 4 - 4˝ are represented munch smaller than in fig. 1.
As previously disclosed, each pole of the electromagnet has one coil connected to a single electrode, and each electrode will connect all the poles on the same line, or on the same column or on the same diagonal. In fig. 5, for instance, all poles 4′ on the left column are connected by means of electrode 18; electrode 20 is connecting all poles 4˝ of the bottom line; and electrode 21 is connecting all poles 4 positioned on the same diagonal.
The total number of electrodes for a matrix according to the invention will thus be greatly reduced with respect to known matrixes, and such a matrix is therefore much more simple and easy to make than any previous matrix, and also, thanks to the apparatuses according to the invention, much more accurate in positioning the elements housing the permanent magnets. To control said elements it is necessary, as previously shown, to feed all the three electrodes intersecting at the desired element. For instance, with reference to fig. 5, if elements A and B have to be activated, electrodes 18, 20′ and 21 for element A and electrodes 18′, 20 and 21 for element B are fed. Other elements, for instance element C or element D are not activated because only one or two electrodes connecticting the same (20 for element C - 18 and 20 for element B) are fed, so that the critical intensity for controlling the related electromagnet is not reached. This allows to control all points of the matrix with a reduced number of electrodes and control component parts.

Claims

1. An apparatus for controlling the rotation of an axially symmetrical movable element around its axis, the apparatus comprising a stationary electromagnet (1) controlling a permanent magnet (2) housed in said movable element, said stationary electromagnet having three evenly spaced poles (4, 4′, 4˝) which have each at least one coil (14, 15, 16) consisted of one or more windings, characterized in that at least the inner surfaces of said electromagnet poles are shaped in the form of a circle arc and in that the opening angle (α) of each circle arc, with reference to the rotation axis, is from about 70 degrees to about 110 degrees.

2. An apparatus according to claim 1, characterized in that said circle arc angle (α) is about 82 degrees.

3. An apparatus according to claim 1, characterized in that said permanent magnet (2) has a groove (5) along each of its two poles, said groove (5) being positioned at the middle of the pole faces (7, 9), parallel to the rotation axis (8) of said magnet (2).

4. An apparatus according to claim 3, characterized in that the poles faces (7, 9) of said permanent magnet are shaped in the form of a circle arc having a radius and an opening angle similar to those of the cited electromagnet poles (4 - 4˝).

5. An apparatus according to any preceding claim, characterized in that each pole (10, 12) of said electromagnet (1) has a groove (11), a slot (13) or the like positioned at the middle of said pole, facing the permanent magnet (2), and parallel to the rotation axis (8) of said permenent magnet (2),

6. An apparatus according to any preceding claim, characterized in that each pole (4-4˝; 10; 12) of said electromagnet (1) has a single coil consisting of one winding.

7. A method for electromagnetically controlling the rotation of a movable element housing at least one permanent magnet around its axis, by means of an apparatus according to claim 6, characterized in that said electromagnet (1) is activated by contemporaneously feeding to said three coils (14-16) a current that, for each coil, has an intensity lower than the critical intensity of the relating hysteresis loop, while the sum of said currents has an intensity above said critical intensity, and in that said current is codirectionally fed along a first direction to two of said coils, the third and last coil being fed in a second direction which is opposite to said first direction.

8. A matrix panel, formed by a plurality of apparatuses, each adapted to control by means of an electromagnet the rotation of a movable element around its axis, characterized in that said apparatuses are made according to any one of the preceding claims.

9. A matrix panel according to claim 8, characterized in that three series of electrodes, in vertical, horizontal and diagonal directions, series connect the electromagnets of its movable element, each electromagnet being fed by three electrodes which must be all energized to control its angular position.