JP3045936B2 - PM type stepping motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PM (permanent magnet) type stepping motor using a multi-pole magnetized permanent magnet as a rotor. The present invention relates to a stepping motor suitable for:

[0002]

2. Description of the Related Art As a typical configuration of a PM type stepping motor, FIG. 9 shows a stepping motor using a claw pole of a two-phase or four-phase drive winding which is widely used. FIG. 10 shows a stepping motor using a pole-type magnetic pole.

In FIG. 9, reference numeral 91 denotes a rotor having a cylindrical shape and using a permanent magnet having an N-pole and an S-pole alternately and multipolarly magnetized on the outer peripheral surface thereof. The stator 92 has a yoke 9 having claw-pole-type pole teeth 93 of a number corresponding to the number of magnetic poles of the rotor 91.
4 and two sets of electromagnets having solenoid windings 95 and 96. The two sets of electromagnets are arranged such that the magnetic field distribution generated when each of the windings is driven is shifted from each other in the rotation direction of the rotor by a half of the magnetic pole pitch of the rotor. The magnetic flux flowing from the permanent magnet magnetic pole of the rotor 91 to the yoke 94 changes by one cycle at a mechanical rotation angle (this is called a mechanical angle) corresponding to the angle of the magnetic pole pitch of the rotor.
The rotation angle of the rotor measured by setting the change of one cycle to 360 ° is called an electrical angle. Using this expression, the two sets of electromagnets are arranged at an electrical angle of 90 °. Assuming that the origin measured by the electrical angle of the magnetic flux distribution generated when a current flows through the winding 95 is 0 °, a magnetic flux distribution having an electrical angle of 90 ° is generated when a current flows through the winding 96 in the same direction. At this time, the winding 95 is called a 0 ° winding and the winding 96 is called a 90 ° winding. 180 ° if the current direction of winding 95 is reversed
When the direction of the current of the winding 96 is reversed, a 270 ° magnetic flux distribution is generated. Each time these drive windings and energization directions are switched, the rotor 91
In the case of the mechanical angle, the rotor 91 advances by ず つ of the magnetic pole pitch of the rotor 91.

In a claw-pole magnetic pole stepping motor, 0 ° windings and 90 ° windings are stacked in the axial direction of the rotor. In the salient pole stepping motor, the windings are arranged in the circumferential direction. FIG. 10 shows a configuration example of the salient pole stepping motor in a state where the axial direction of the rotating shaft 101 is arranged perpendicular to the paper surface. In this example, since the cylindrical permanent magnet rotor 102 is magnetized in two poles, one rotation of the rotor is 360 ° in both the electrical angle and the mechanical angle. Each of the salient poles of the yoke 103 having four salient poles is provided with four windings 104, 105, 106, and 107. If the winding 104 is a 0 ° winding, the winding 105
Is 90 °, winding 106 is 180 °, winding 107 is 270
° winding. By switching the windings to be driven in this order, the rotor 102 advances by 90 ° in mechanical angle. 0 ° winding and 180 ° winding are connected in series so as to have opposite phases, and 90 ° winding and 270 ° winding are connected in series so as to have opposite phases. As a line, FIG.
Can be operated as two-phase drive windings, like the two sets of windings.

The above is the basic operation of the stepping motor. In this operation, the rotor moves in a staggered manner.
In order to realize smoother movement, micro-step driving is used. In micro step drive,
The magnitude of the current flowing through each of the two drive windings is also controlled to realize a smooth movement. FIG. 11 is an example of a current flowing through two sets of drive windings by micro-step drive. In this example, the section of 360 ° in electrical angle is divided into 40 minute sections, that is, the section of 90 ° is divided into 10 minute sections, and the magnitude of current flowing through two sets of drive windings is controlled.
The magnitude of the current is changed with a waveform close to a cosine wave with respect to the rotation angle for the drive winding of 0 °, and with a waveform approximating a sine wave for the drive winding of 90 °. As a result, while the normal drive advances in steps of 90 degrees in electrical angle, the micro-step drive method steps in steps of 9 degrees in electrical angle, enabling smooth movement with less vibration. .

[0006] Another purpose of the micro-step drive is to generate a rotational torque with little torque pulsation. The waveform of the current flowing through the drive winding is approximated to a sine wave and a cosine wave as shown in FIG. Assuming that the rotation angle is θ,
When the current I flows through the 0 ° drive winding, the generated torque is I
K · cos θ, and if the motor is designed so that the torque generated when current I flows through the 90 ° drive winding becomes I · K · sin θ, the drive winding of 0 ° The flowing current is I
m · cos θ, and the current flowing through the 90 ° drive winding is Im ·
By setting sin θ, the torque T generated by the motor
Is T = Im · K · (cos ² θ + sin ² θ).
Since (cos ² θ + sin ² θ) = 1, under this condition, a constant torque and Im · K can be obtained irrespective of the angle θ, and smooth rotation with small speed fluctuation can be realized.

[References] (1) Stepping motor with salient magnetic poles Takashi Mishiro: "Precision small motor for electronic equipment" General Electronic Publishing
pp.108-109 (1977) (2) Regarding micro-step drive Hideji Watanabe: Focus on differences in rotor structure Changes in torque characteristics at frequency, full motor utilization, Nikkei BP pp.98-111 (1990)

[0008]

In an actual stepping motor, a torque and a force other than the torque and the force due to the drive current act on the rotor, thereby preventing the generation of vibration and the realization of a smooth movement. In the stepping motor having pole teeth and salient poles shown in FIGS. 9 and 10, magnetic attraction acts between the permanent magnet and the yoke magnetic pole even when no current flows through the drive winding. The rotational torque component of the sum of the suction forces is the detent torque. The presence of detent torque is one of the main factors that limit the reduction of vibration and the achievement of smooth movement in microstep driving.

As a method of reducing vibration and speed fluctuation due to detent torque, one method is to superimpose a current change that just cancels out detent torque on a current waveform of microstep driving. The disadvantage of this method is that it requires precise design or measurement of the detent torque, and the circuit becomes complicated. The drastic response is to reduce the detent torque.

FIG. 12 shows the relationship between the magnetic poles of the multi-pole magnetized permanent magnet, one salient pole of the yoke, and the torque generated between them in the direction of the rotation angle. In FIG. 12, the armature magnetic pole 121-1 schematically represents one of the pole teeth or salient poles of the stepping motor. The armature magnetic pole 121-1 is a multi-pole magnetized permanent magnet magnetic pole 13 of the rotor.
2. In the permanent magnet magnetic pole 132, N poles and S poles are alternately magnetized at equal intervals. The magnetization pitch of the pair of N and S poles is an electrical angle of 360 °.

121-1, 121-2, 121-3, 1
Reference numeral 21-4 denotes a state where the rotor rotates and the armature magnetic poles are at electrical angles of 0 °, 90 °, 180 °, and 270 °, respectively. Reference numeral 123 denotes a state of a change in detent torque with respect to a rotation angle measured by an electrical angle. In this example, the value of the detent torque changes sharply near 0 ° and 180 °, and is slightly gentle near 90 ° and 270 °. The steepness of the change may be reversed depending on the magnetization pitch of the permanent magnet or the size and shape of the armature magnetic pole. In either case, in principle, the electrical angle is 0 °, 90 °.
At 180 °, 270 ° and 270 °, the mutual attraction in the rotational direction is in a balanced state, and the magnitude of the resulting torque is zero.

For this reason, the detent torque is based on the symmetry of the generated attraction force, and if the component having one cycle at an electrical angle of 360 ° is the basic component, the secondary component 124 and the fourth component 12
It contains many even-order high-frequency components such as 5. The two-phase or four-phase stepping motor shown in FIGS. 9 and 10 has armature magnetic poles at 90 ° electrical angle intervals.
For this reason, the second-order component 12 having one cycle at an electrical angle of 180 °
Numeral 4 cancels out the secondary component of the detent torque generated by the armature magnetic pole shifted by an electrical angle of 90 °. Therefore, as the detent torque of the motor, the fourth-order component 1
Only torques higher than 25 will appear to the outside.

A detent having an electric angle of 90 ° as one cycle
The torque is useful as a stop position holding function of the stepping motor, and a motor that strongly outputs this component can hold the stop position with detent torque even when the drive current is cut off. However, it is an obstacle to smoothly move the motor with low vibration.

The torque generated when a constant current flows through the drive winding 130 wound around the armature magnetic pole 121-1 is indicated by reference numeral 126. When the armature magnetic pole is located at the center of the permanent magnet magnetic pole (positions of 0 ° and 180 ° in FIG. 12), the generated torque is 0, and the armature magnetic pole changes between the N pole and the S pole, that is, in FIG. 90 °, 2
The torque generated at the position of 70 ° becomes maximum. One cycle of the fundamental wave component of the generated torque 126 is 12
7, the electrical angle is 360 °. When the width of the armature magnetic pole is smaller than that of the permanent magnet as shown in the figure, the torque generated by the drive current near 0 ° and 180 ° is small. And a third high-frequency component indicated by reference numeral 129. Although higher-order components also exist, the largest factor preventing the waveform of the torque generated by the drive current from becoming a sine wave or a cosine wave is the presence of a third-order high-frequency component.

The present invention has a magnetic pole configuration in which the detent torque does not include the fourth-order high-frequency component in principle and the torque generated by the drive current does not include the third-order high-frequency component in principle, so that the motor can move smoothly even at a low speed. It is an object of the present invention to provide a stepping motor capable of performing the following.

[0016]

SUMMARY OF THE INVENTION A PM stepping motor according to the present invention comprises a permanent magnet rotor which is multipole-magnetized alternately by NS at equal intervals in a circumferential direction around a rotating shaft, and a peripheral magnet surrounding the rotor. In a PM type stepping motor having four armatures each having four salient poles, each of which is provided with a drive winding and arranged at equal intervals in the direction, the armature having one unit, the armature is opposed to the magnetic poles of the permanent magnet rotor. The tip of the salient pole of the armature is divided into four portions, and the NS of the permanent magnet rotor has an electrical angle expressed as 360 ° of the magnetic pole magnetization pitch of the pair of NS, and is relative to the first portion. The second part is arranged at an electrical angle of 45 °, the third part is arranged at an electrical angle of 60 ° with respect to the first part, and the fourth part is the first part. Are placed at an electrical angle of 105 ° with respect to . In this configuration, the yoke of the armature can be formed by powder metallurgy or metal injection molding.

[0017]

FIG. 1 is a diagram illustrating the principle of the present invention. In the drawing, reference numeral 2 denotes a permanent magnet rotor which is multiply-polarized and magnetized at equal intervals alternately with NS developed in the rotation direction. A pitch at which a pair of N and S poles is magnetized is defined as one cycle. Since the actual size of the pitch of one cycle differs depending on the size of the motor and the number of magnetized poles, the pitch is expressed as an electrical angle of 360 ° to express the relative size with the dimensions of other parts.

According to the principle of the present invention, one armature salient pole facing the permanent magnet magnetic pole is defined as 1-1, 1-2, 1--1 in FIG.
It is divided into at least four parts as shown by 3, 1-4. As described above, the second portion is arranged at an electrical angle of 45 ° with respect to the first portion, and the third portion is arranged at an electrical angle of 60 ° with respect to the first portion. And the fourth part is 105 electrical degrees with respect to the first part.
° are offset.

FIG. 2 shows the relationship between the fourth-order components of the detent torque generated by the four parts.
The fourth-order component of the portion 1-1 is 21 and the fourth-order component of the detent torque by the portion 1-2 shifted by 45 ° in electrical angle from the portion 1-1 is 22. Both are just out of phase and canceled. Detent torque 2 by parts 1-3
3 and the detent torque 24 by the parts 1-4 have the same relationship, and cancel each other out.

FIG. 3 shows the interrelationship between the third harmonic components of the torque generated by the drive currents generated by the four portions. The torque by the part 1-1 is 31 and the part 1
The torque of the portion 1-3 arranged at an electrical angle of 60 ° from -1 is 33. Both are just out of phase and canceled. The torque 32 due to the portion 1-2 and the torque 34 due to the portion 1-4 have a similar relationship, and cancel each other out.

As a result, it is possible to realize a stepping motor having a magnetic pole configuration in which the detent torque has no fourth-order high-frequency component and the drive current has no third-order high-frequency component.

[0022]

FIG. 4 shows an armature yoke according to an embodiment of the present invention. The magnetic poles corresponding to the four portions in FIG.
It corresponds to three salient poles. This arrangement shows a case where the permanent magnet rotor 45 is magnetized with six poles. Since it is magnetized with six poles, an electrical angle of 360 ° corresponds to a mechanical angle of 120 °. The four salient poles 41, 42, 43, 44 are in a clockwise direction as shown in the figure, with respect to a 90 ° mechanical angle, 41 is −17.5 °, 42 is −2.5 °, 43 Is formed at a position shifted by + 17.5 ° and 44 is formed at a position shifted by + 2.5 °. As shown in FIG. 5, the armature yoke as a motor is formed by stacking four armature yokes of FIG. 4 and rotating each of the four by 90 °. In the configuration of FIG. 5, one salient pole is divided into four portions, and each portion has a mechanical angle of 20 ° and a portion corresponding to 43 with the origin of 41 in FIG. 3
The portions corresponding to 5 ° and 44 are at positions shifted by 15 °.
When these are expressed in electrical angles, 60 °, 105 °, 45 °
°, the arrangement satisfies the relationship shown in FIG.

In the embodiment shown in FIG. 5, the armature yoke is constituted by a four-layer structure, but the same effect can be obtained by a three-layer structure.

FIGS. 6 and 7 show the principle of changing from a four-layer structure to a three-layer structure. In FIG. 6, reference numerals 61, 62, 63, and 64 denote four parts viewed from the permanent magnet side. In order to form a three-sheet configuration, it is necessary that the width of one part in the rotation direction be 105 ° or less in electrical angle. FIG. 6 shows the case of just 105 °. Part 6 of part 63 corresponding to an electrical angle of 15 °
5 is moved to a part of the part 67 in the three-piece configuration as shown by the arrow, and the part 64 is moved to a part of the part 67 in the three-piece configuration. Even if such a change is made, the four salient poles and the three
A salient pole having a single sheet configuration is completely magnetically equivalent. Therefore, the condition shown in FIG. 1 can be satisfied even with the three-sheet configuration.

FIG. 7 shows that the width of one part in the rotation direction is 10
The case where the angle is smaller than 5 ° is shown, and the portions 71, 72,
The case where the width of 73 and 74 is 90 electrical degrees is shown.
In this case, the part 77 is divided into two parts. However, in practice, by providing a notch corresponding to the cut at the tip of the magnetic pole, it is possible to realize a three-piece configuration as in FIG.

FIG. 8 shows a shape in which an armature yoke equivalent to a three-layer armature yoke is integrally formed.
Powder metallurgy and metal injection molding are suitable for forming a magnetic body having such a shape. The powder metallurgy method and the metal injection molding method can use a magnetic output material having a high hardness such as an iron-cobalt alloy or sendust which is difficult to process, in addition to a feature that a shape as shown in FIG. 8 can be directly formed using a mold. There is a feature. Iron-cobalt alloy has a high saturation magnetic flux density and is suitable for realizing a small-sized and high-torque motor. Sendust has particularly high resistivity and small iron loss. In the present invention, the detent and the detent
The fourth order high frequency component of the torque is canceled. However, a magnetic flux change corresponding to the fourth high-frequency component occurs at each magnetic pole. The frequency of this magnetic flux change is four times the frequency of the oblique magnetic flux change that generates torque. Therefore, it is necessary to select a material having a small loss in a high-frequency magnetic flux change, and a powder metallurgy method and a metal injection molding method, which have a high degree of freedom in material selection, are extremely suitable methods for the present invention.

The effect of the present invention is derived from the relative arrangement of the salient pole tip shape of the armature with respect to the magnetization pitch of the permanent magnet magnetic pole. Therefore, it is possible to obtain a relative positional relationship even for a so-called outer-rotor type motor or a linear motor developed linearly, in which the positional relationship between the rotor and the stator in FIG. 4 is reversed, and the present invention is applied. Clearly what you can do. Also, the number of salient poles has been described as four, but the unit of four salient poles is an integral multiple thereof, for example, eight.
It is clear that it consists of one salient pole.

[0028]

As described above, according to the present invention,
Among the detent torques generated by the attractive force between the salient poles of the armature of the stepping motor and the permanent magnets, the rotation angle and the rotation angle corresponding to the fourth order cycle, which were difficult to cancel in the motor in the conventional configuration, The component generated by the displacement can be canceled, and at the same time, the third harmonic component of the torque generated by the drive current can be canceled.
Even in the conventional configuration, the secondary high-frequency component of the detent torque is canceled in principle inside the motor. By applying the present invention, not only the secondary but also the fourth-order high-frequency component of the detent torque is not provided, and The torque due to the drive current is 3
Does not contain secondary high frequency components. Therefore, the generated torque per a fixed amount of drive current has a sine waveform with respect to the rotation angle, and a smooth movement can be realized by direct drive even at low speed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

FIG. 2 is an explanatory diagram of a detent torque fourth-order component accompanying FIG. 1;

FIG. 3 is an explanatory diagram of a third-order component of the driving current torque accompanying FIG. 1;

FIG. 4 is an explanatory diagram of a shape of an armature yoke according to an embodiment of the present invention.

FIG. 5 is a perspective view showing a more specific configuration of the armature yoke according to the first embodiment.

FIG. 6 is a view for explaining the principle of a configuration change of the armature yoke according to the first embodiment;

FIG. 7 is an explanatory view of the principle of another example of the configuration change of the armature yoke according to the embodiment.

FIG. 8 is a perspective view of an armature yoke according to another embodiment of the present invention.

FIG. 9 is a schematic configuration diagram of a conventional claw-pole type stepping motor.

FIG. 10 is a schematic configuration diagram of a conventional salient magnetic pole type stepping motor.

FIG. 11 is a current waveform diagram illustrating an example of micro-step driving.

FIG. 12 is an explanatory diagram showing a relationship among a magnetic pole of a permanent magnet, a yoke salient pole, and torque.

[Explanation of symbols]

1-1, 1-2, 1-3, 1-4 Sections divided into four armature magnetic poles 2 permanent magnet rotors 41, 42, 43, 44 salient poles 45 permanent magnet rotor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02K 37/00-37/24

Claims (2)

(57) [Claims] 1. NS at equal intervals in the circumferential direction about a rotation axis
An armature having, as a unit, a permanent magnet rotor alternately magnetized with multiple poles, and four salient poles, each of which is provided with a drive winding and arranged at equal intervals in a circumferential direction surrounding the rotor. Wherein the tip of the salient pole of the armature facing the magnetic pole of the permanent magnet rotor is divided into four parts, and a pair of NS poles of the NS of the permanent magnet rotor. An electrical angle represented by a magnetization pitch of 360 °, and the second portion is 45 ° in electrical angle with respect to the first portion.
The third part is arranged at an electrical angle of 60 ° with respect to the first part, and the fourth part is arranged at an electrical angle of 105 ° with respect to the first part. A PM type stepping motor, which is disposed. 2. The PM type stepping motor according to claim 1, wherein the yoke of the armature according to claim 1 is formed by powder metallurgy or metal injection molding.