JPH0628501B2 - Step Motor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepper motor, and more particularly to a flexible circular spline and a flexible spline that meshes with the rigid circular spline to bend the flexible spline into an elliptical shape and to form an ellipse thereof. The present invention relates to a step motor combined with a harmonic gear device that can obtain a high reduction ratio by rotating.

2. Description of the Related Art A step motor incorporating a harmonic gear device is disclosed, for example, in Japanese Patent Publication No. 48-15049 (published on May 11, 1973). The stepper motor described in this publication has an outer rigid circular spline, an inner flexible spline including teeth that engage with the teeth of the circular spline, and a radial outer side with respect to the flexible spline. A magnetic field generating means having a plurality of magnetic poles for applying a magnetic field to bend the flexible spline into an elliptical shape and engage the flexible spline at two points diametrically opposed to the circular spline, and a magnetic pole of the magnetic field generating means, Exciting means for sequentially rotating the elliptical shape of the flexible spline to generate relative rotation between the circular spline and the flexible spline in proportion to the difference in the number of teeth of the splines.

This step motor rotates the ellipse of the flexible spline by sequentially exciting the magnetic poles of the magnetic field generating means,
As a result, a large reduction ratio is obtained with respect to a circular spline, so that it has the advantage that the resolution of the step motor becomes extremely high, and that it does not require a complicated and bulky reduction gear to obtain that high resolution. A compact high resolution stepping motor can be obtained with an extremely simple structure.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the above step motor, since the magnetic field generating means deforms the flexible spline into an ellipse only by its magnetic attraction force, the magnetic attraction force must be increased. In addition, it was necessary to line a leaf spring made of a good magnetic material so as to reduce the magnetic resistance or reluctance with respect to the flexible spline. This leaf spring is wound inside a flexible spline in a roll shape, and is fixed to the spline by spot welding or the like. Therefore, when the flexible spline is deformed into an ellipse, a sound is generated due to the deformation, and when the ellipse is rotated at a high speed, the sound becomes loud and the noise from the motor becomes loud. Also, in order to cope with the circumferential displacement when the leaf spring is deformed, lubricating oil must be supplied, and when it is cut off, friction heat is generated,
Furthermore, there is a risk of abrasion.

Therefore, an object of the present invention is to form an elliptical deformation of a flexible spline into an elliptical shape by using magnetic repulsion force instead of relying solely on a magnetic attraction force, and to provide a backing material for a flexible spline. It is to provide a step motor which is not necessary.

Means for Solving the Problems In order to achieve such an object, in a step motor with a harmonic gear device according to the present invention, a flexible permanent magnet piece generates a magnetic field in a portion corresponding to a tooth of a flexible spline. The flexible spline is mounted corresponding to the magnetic poles of the means and is not provided with any backing material. This permanent magnet piece
A plastic magnet in which a rare earth cobalt magnet material is bonded with an organic binder is preferable. As described above, since the permanent magnets are attached to the flexible splines in correspondence with the magnetic poles of the magnetic field generating means, not only the magnetic attraction force but also the magnetic repulsion force can be applied to the flexible splines. The ellipse is formed and its rotation is precisely and easily performed. Further, the magnetic attraction force is much increased as compared with the case where there is no permanent magnet, and the magnetic field strength of the magnetic field generating means can be reduced, whereby the size of the entire motor can be reduced.

In a preferred embodiment of the invention, the plurality of magnetic poles of the magnetic field generating means are fixed inside the motor housing so as to form a generally circular cavity, and inside the magnetic field generating means a flexible spline is attached to the motor housing. The splines are fixed to each other, and as many permanent magnet pieces as the magnetic poles are fixed to the side of the spline facing the magnetic poles. Inside the flexible spline, a rigid circular spline having teeth meshing with the spline is rotatably mounted, and an output shaft is mounted on the circular spline. When the magnetic poles of the magnetic field generating means are excited, the flexible spline is deformed into an ellipse, and when the other magnetic poles are sequentially excited, the ellipse rotates and the difference in the number of teeth between the flexible spline teeth and the rigid circular spline teeth. A rotation with a large reduction ratio corresponding to is obtained.

Embodiment One embodiment of the present invention will be described below with reference to the drawings. First, prior to the description of the embodiments of the present invention, a general description will be given of the principle of the harmonic gear device. As shown in FIG. 1, the harmonic gearing has a rigid circular spline 1
And a flexible spline 2 that meshes with the circular spline 1, and the flexible spline 2 is bent into an elliptical shape by a wave generator 3. The wave generator 3 not only bends the flexible spline 2 into an elliptical shape but also rotates the elliptical shape, and is provided with a ball bearing 4 so as not to rotate the flexible spline when the ellipse rotates. There is.

Since the flexible spline 2 is bent into an ellipse, its teeth engage with the circular spline only at two points indicated by arrows A and B. The number of teeth of the circular spline 1 is different from the number of teeth of the flexible spline. For example, the circular spline 1 is formed with two more teeth than the teeth of the flexible spline 2.

2 (a) to 2 (d), the relationship between the circular spline 1 and the flexible spline 2 when the wave generator 3 is rotated clockwise is shown. When the wave generator 3 is in the position shown in FIG. 2 (a), one tooth 5 of the circular spline 1 meshes with one tooth 6 of the flexible spline 2. When the wave generator 3 is rotated 90 ° as shown in FIG. 2 (b), the elliptical shape of the flexible spline 2 rotates, and the position where the circular spline 1 and the flexible spline 2 mesh with each other is the wave generator. It moves according to the rotation of the long axis of 3. As shown in FIG. 2 (c), when the wave generator 3 is rotated 180 °, the teeth 5 and 6 are re-engaged with each other, but the position is displaced by one tooth in the direction opposite to the rotation direction. Then, as shown in FIG. 2 (d), when the wave generator 3 rotates 360 °, the teeth 5 and the teeth 6 are displaced by the number of two teeth in the direction opposite to the rotation direction. In this way, if a movement in which the meshing positions are sequentially shifted is taken out as an output, a large reduction ratio can be obtained.

Incidentally, when the flexible spline 2 is fixed and the output shaft is provided on the circular spline 1, the speed ratio R is as follows: the number of teeth of the flexible spline 2 is Zf, the number of teeth of the circular spline is Zc (= Z
f + 2) Therefore, in the reduction ratio, Obtained as. That is, a large reduction ratio can be easily obtained by increasing the number of teeth.

Although the flexible spline 2 is provided inside the rigid circular spline 1 in the above example, the flexible spline 2 is of course provided.
Can also be provided outside the circular spline 1.

Next, the principle of a step motor using such a harmonic gear device will be described. In the example of FIG. 1, the wave generator bends the shape of the flexible spline into an ellipse, but in the step motor, this wave generator replaces the magnetic field generating means. For convenience of explanation, FIG. 3 will be described with reference to FIG. 1 of Japanese Patent Publication No. 48-15049.

In FIG. 3, an electromagnet 12 having a large number of magnetic poles serving as a magnetic field generating means is attached inside a motor housing 10, and a rigid circular spline 16 is fixed to a core 14 of the electromagnet at substantially the center thereof. Inside the circular spline 16 is a cylindrical flexible spline 18 that meshes with the circular spline 16.
Is rotatably arranged with a gap between each magnetic pole, and the flexible spline 18 is connected to the output shaft 22 via bearings 20 and 20.
Is installed. Further, inside the flexible spline 18, the leaf spring material 2 made of a magnetic material for reducing reluctance is used.
4 is wound in a roll shape and fixed.

In operation, when two adjacent magnetic poles form a set and are excited by two diametrically opposed sets, the flexible spline 18 is magnetically attracted at the two points and deformed into an elliptical shape. Next, when the pair of magnetic poles is demagnetized and the adjacent magnetic pole pair is excited, the elliptical shape starts to rotate, and by changing this excitation next, the ellipse rotates and the wave of FIG. It has the same effect as rotating the generator. That is, the magnetic field generating means functions as a wave generator of a normal harmonic gear device, and compared with an ordinary step motor, even if the magnetic pole is excited for one cycle, the output is performed at the reduction ratio i shown above. Since the shaft rotates, the step motor has high resolution and high torque.

The present invention improves the above step motor with a harmonic gear device, and one embodiment thereof will be described below. Fig. 4 ~
In FIG. 6, a motor housing 30 has a large number of magnetic poles 32 (in this example, 24 magnetic poles) serving as magnetic field generating means.
Poles) are fixed side by side so as to form a substantially circular cavity as a whole. Each magnetic pole is composed of a core 34 and a coil 36, and a current is supplied to the coil 36 from a lead wire 38.

A flexible spline 40 is arranged inside the magnetic pole group, and one end edge 42 of the spline extends radially outward and is formed in a so-called silk hat shape. It is fixed by etc. The flexible spline 40 is preferably made of a good magnetic material, such as low carbon steel. The part made of this magnetic material may be only the part corresponding to the magnetic pole,
It is only necessary to reduce the magnetic resistance (reluctance) of the magnetic field from the magnetic pole 32.

In the present invention, a permanent magnet piece 46 is fixed to the outer surface of the flexible spline corresponding to the magnetic pole 32 so as to face the magnetic pole. As many permanent magnet pieces 46 as the magnetic poles 32 are preferably attached by alternately arranging N poles and S poles as shown in FIG. In addition, the permanent magnet piece 46
Is made of a flexible permanent magnet material, preferably a so-called plastic magnet in which a rare earth cobalt magnet material is bonded with an organic binder so as to cope with the elliptical deformation of the flexible spline. What the inventors used is
Tohoku Metal Industry Co., Ltd. LS-40, LS-60, L
It was a plastic magnet with a product number of S-80.

Inside the flexible spline 40, a rigid circular spline 48 having teeth meshing with the spline 40 is provided. The circular spline 48 is formed in a hollow cylindrical shape and is rotatably supported by the motor housing 30 via bearings 50 and 52. One end edge 54 of the circular spline 48 is projected from the housing 30 so that an output member (not shown) such as a shaft can be attached to this portion. The number of teeth of the circular spline 48 is different from the number of teeth of the flexible spline 40 as described above.

The motor housing 30 is made up of three parts for assembling the respective parts, which are fixed to each other by screws or the like. However, it may be divided into two parts or an integrated structure as long as it can be incorporated.

Referring to FIGS. 7 and 8, the connection of each magnetic pole and its excitation method are shown. In FIG. 7, the magnetic pole 32 is 24
24 pieces of permanent magnet pieces 46 are fixedly attached to the flexible spline 40 corresponding to this, and the permanent magnet pieces 46 have opposite polarities (to be exact, to the adjacent magnet pieces). Are arranged so as to have a polarity on the surface facing the magnetic pole). For convenience of explanation, a and b are provided on each magnetic pole lead 38.
....., and the leads facing in the diametrical direction are marked with a ', b' ... l '.

In FIG. 8, when a current in the direction of the arrow is supplied to the lead a and the lead b ′, the magnetic path m ₁ as shown in the drawing is formed,
As a result, the flexible spline 40 is magnetically attracted in the direction of arrow 60. Similarly, magnetic poles m ₂ and
The suction force can be further increased by forming m ₃ . This attractive force is much larger than that of the known variable-type reluctance type because it uses not only the reluctance of the flexible spline 40 but also the attractive force of the magnet piece 46 (so-called Coulomba).

On the other hand, the leads k ', l are simultaneously supplied with the current shown in FIG. As a result, a magnetic field that repels the magnet piece 46 is generated from the magnetic pole 32, and as a result, a force that presses the flexible spline 40 inward, that is, a repulsive force is applied. In this way, the lead a,
b ', c, d', f'and leads a ', b, c', d,
Currents that generate a magnetic field in the direction of attracting the flexible spline 40 are supplied to e ′ and f, and the leads g, h ′, i,
j ', k, l'and leads g', h, i ', j, k',
When a current for generating a magnetic field in a direction repulsive to the flexible spline 40 is supplied to l, the flexible spline 40 is bent into an elliptical shape as shown in FIG. Therefore, the meshing is performed only at two points on the short shaft 64.

Next, when the currents of the leads b to f and b'to f'are kept as they are and the currents of the leads a and a'are made to flow in the opposite directions, and the currents of the leads g and g'are also made to the opposite direction, the attraction magnetic field The repulsive magnetic field rotates by one magnetic pole, and the ellipse rotates by one magnetic pole. In this way, when the directions of the exciting currents of the magnetic poles are sequentially reversed, the elliptical shape is rotated while the flexible spline 40 is fixed. As described with reference to FIGS. (A) to (d), the rigid circular spline 48 is rotated by the difference in the number of teeth. The table below shows the excitation methods described above.

If the order of the excitation steps is reversed, the direction of rotation will be reversed.

In the above example, the full step drive using all the magnetic poles is used, but the half step drive in which every other magnetic pole is excited may be used.

FIG. 9 shows two diametrically opposed magnetic poles (eg a,
a ') shows a drive circuit that excites a').
For example, it is composed of _four transistors Q _{1 to} Q ₄ for exciting the coil a and the coil a ′. For excitation in the suction direction,
The transistors Q ₁ and Q ₄ are turned on, and the transistor Q
_{When 2} and Q ₃ are turned off, a current is supplied in the direction of the solid line, and an attractive magnetic field is generated from the coils a and a ′. On the contrary, when the transistors Q ₂ and Q ₄ are turned off, a current is supplied in the direction of the broken line, and the coils a and a ′ form a repulsive magnetic field. As described above, the excitation of each magnetic pole can be performed in both polarities, that is, in bipolar drive by a very simple drive circuit.

This bipolar drive eliminates the disadvantage of requiring a pair of windings when driven unipolarly (that is, the method in which current flows in the windings in only one direction), and it also eliminates the Since no electromotive force due to induction is generated, high-speed and high-torque driving is possible.

When the output torque of the step motor shown in the above-mentioned embodiment was actually measured, a nominal value of 10 N · m could be obtained. In the above embodiment, the number of magnetic poles is 24 (the number of phases is 12).
However, it was also confirmed that a maximum of 32 poles (16 phases) is possible.

EFFECTS OF THE INVENTION As described above, in the present invention, the permanent magnet piece exerts not only the attractive force of the flexible spline but also the repulsive force and exerts a great force in forming an ellipse, and also has a variable luctance even during the attraction. In addition to the above, a so-called Coulomb car using magnetic poles can be used, so that an ellipse can be formed extremely efficiently with a small magnetic field. Therefore, the magnetic field generating means is also downsized, and the entire motor can be downsized.

Since the force of forming an ellipse is strong, there is no need for a reluctance reduction auxiliary member for a flexible spline, which is required in a known step motor, and the accompanying noise is completely eliminated. Since the problem of lubrication mentioned above is eliminated, it is only necessary to apply dry lubrication to the meshing portion of the spline.

Further, since the stepper motor according to the present invention uses the permanent magnet, the stepper motor can have more poles than the variable reluctance stepper motor. Therefore, the resolution and the torque can be increased.

Further, when the flexible spline is arranged on the outer side, it is extremely easy to correct the deviation of the rotation center of the ellipse (so-called dedoidal) from the outside of the spline by using a circular ring or the like.

[Brief description of drawings]

FIG. 1 is a schematic front view of a known harmonic gear device, FIGS. 2 (a) to (d) are operation explanatory views of the harmonic gear device, FIG. 3 is a partially cutaway perspective view of a known step motor, 4 is a partially cutaway side view of the step motor according to the present invention, FIG. 5 is a partially cutaway perspective view of the step motor according to the present invention shown in FIG. 4, and FIG. 6 is a step view of the step motor shown in FIG. A partially broken perspective view of the flexible spline, FIG. 7 is a front view showing the relationship between the magnetic field generating means and both splines, and FIG. 8 is an enlarged view of a part of FIG. 7, showing a magnetic field and its force. FIG. 9 is a circuit diagram showing a drive circuit for exciting the coil. 1,16,48 ... Circular spline, 2,18,40 ... Flexible spline, 3 ... Wave generator, 10,30 ... Housing, 12 ... Electromagnet, 24 ... Leaf spring material, 32 ... … Magnetic poles, 46… Permanent magnet pieces.

Claims (7)

[Claims] 1. A rigid circular spline, a flexible spline having teeth that engage with the teeth of the circular spline, and a magnetic field applied to the flexible spline from the outside in the radial direction. A magnetic field generating means having a plurality of magnetic poles, which is bent into an elliptical shape and engages with the circular spline at two points facing each other in the diametric direction, and the magnetic poles of the magnetic field generating means are sequentially excited to form a flexible spline. Rotate the elliptical shape,
As a result, in the step motor having an exciting means for causing relative rotation in proportion to the tooth number difference between the circular spline and the flexible spline, the portion corresponding to the tooth of the flexible spline is A flexible permanent magnet piece is attached to correspond to the magnetic pole of the magnetic field generating means, and the elliptical deformation of the flexible spline is strengthened not only by magnetic attraction but also by repulsion. Step motor. 2. The step motor according to claim 1, wherein the permanent magnet is a plastic magnet material in which a rare earth cobalt magnet material is bonded with an organic binder. 3. A step motor according to claim 1, wherein the same number of permanent magnet materials as the number of magnetic poles of the magnetic field generating means are provided. 4. A third claim in which the number of magnetic poles is 24.
The step motor according to the item. 5. A magnetic pole of the magnetic field generating means is fixed inside a motor housing so that a plurality of magnetic poles are circular as a whole to form a stator, and a flexible spline is fixed inside the motor housing inside the stator. 2. The step motor according to claim 1, wherein a rigid circular spline is rotatably disposed with respect to the motor housing inside the flexible spline, and an output shaft is attached to the circular spline. . 6. A step motor according to claim 5, wherein the flexible spline extends radially outward at one of its edges, and the extended edge is attached to the housing. 7. A flexible spline formed into an ellipse has a major axis portion which is attracted by a magnetic pole of the magnetic field generating means and a permanent magnet piece and a minor axis portion which is repulsive force between the magnetic pole and the magnet. Therefore, the step motor according to claim 5, which is formed respectively.