JPH0690554A - Stepping motor - Google Patents

Abstract

PURPOSE:To provide a stepping motor, capable of generating a high torque without employing any magnet. CONSTITUTION:A cylindrical stator 10 is provided with a stator core 11, having eight pieces of stator teeth 12 arranged in the circumferential direction with spaces and projected inward in the radial direction thereof, and stator coils 13, wound around respective stator teeth 12. A rotor 20, received in the stator 10 so as to be rotatable around a rotary shaft, is provided with a rotor core 21 having six pieces of rotor teeth 22 arranged in the circumferential direction with spaces and projected outward in the radial direction thereof, and rotor coils 23, wound respectively around the rotor teeth 22. A rotor coil current is controlled in accordance with the rotating angle of the rotor 20 whereby a high torque can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step motor, and more particularly to the structure of a hybrid (HB) type step motor.

[0002]

As is well known, a step motor is a motor that receives an electric pulse as an input and outputs a mechanical angle corresponding to the number of pulses. There are various types of step motors, and one of them is a hybrid type step motor.

2A, 2B, and 2C show the structure of a conventional hybrid type stepping motor. The hybrid step motor includes a cylindrical stator 10 and a rotor 20 'housed in the stator 10 so as to be rotatable around a rotation axis RA. The stator 10 includes a stator core 11. The stator core 11 has eight stator teeth 12 which are arranged at intervals in the circumferential direction and protrude inward in the radial direction. A stator coil 13 is wound around each stator tooth 12.

As shown in FIGS. 2 (b) and 2 (c), the stator coil 13 includes two A-phase coils and two B-phase coils.
There are different types of coils. The A-phase coil and the B-phase coil are alternately wound around the eight stator teeth 12 along the circumferential direction. The A-phase coils wound around two stator teeth 12 facing each other are wound in the same phase (A or A bar in FIGS. 2B and 2C (a bar is attached on A). )), The A-phase coil wound around the two stator teeth 12 whose teeth are out of phase with each other by 90 ° is wound in the opposite phase (A and A in FIGS. 2B and 2C). Bar relationship). Similarly, the B-phase coils wound around the two stator teeth 12 facing each other are wound in the same phase (B or B bar in FIGS. 2B and 2C), but the phases of the teeth are different from each other. Is 90
The B-phase coil wound around the two stator teeth 12 that are shifted by ° is wound in the opposite phase (see B in FIGS. 2B and 2C).
And B bar).

On the other hand, the rotor 20 'has an annular magnet 2 between them.
3'includes a pair of rotor cores 21'a and 21'b. Rotor cores 21'a and 21'b
Faces the stator core 11. Rotor core 21 '
The a has six rotor teeth 22'a which are arranged at intervals in the circumferential direction and protrude outward in the radial direction. Similarly, the rotor core 21'b has six rotor teeth 22'b that are arranged at intervals in the circumferential direction and project outward in the radial direction. As is apparent from FIGS. 2B and 2C, the rotor teeth 22'a and the rotor teeth 22'b are out of phase with each other by π radians.

[0006]

The above-mentioned conventional hybrid type step motor has a drawback that a strong magnet is required to obtain a high torque, as will be described in detail below.

The situation will be described below using the generated torque formula. The stator 10 and rotor 2 as shown in FIG.
0'has teeth 12 and 22'a and 22'b together,
In the hybrid type step motor in which the magnet 23 'is arranged on the rotor 20', if the number of teeth of the rotor 20 'is Zr, the step motor is considered to be a two-phase multi-pole motor having the number of pole pairs Zr. If only one pole pair is taken out and considered, the two-phase motor model shown in FIG. 3 is obtained.

In FIG. 3, the two stator coils are α
And β and the two rotor coils are indicated by a and b. A current i _α is applied to each of the stator coils α and β.
And i _β flow, and voltages v _α and v _β are respectively induced. Similarly, the rotor coils a and b, a current _{i a} and _{i b} flows, respectively, and the voltage _{v a} and _{v b} are induced respectively. Further, as shown in FIG. 4, adjacent rotor teeth 22 of the rotor 20 'are
When the distance between the ′ a (22′b) and the rotor tooth 22′a (22′b) is set as a reference period of 2π radian, the stator tooth 12 and the stator tooth 12 adjacent to each other of the stator 10 are arranged.
The period between and is shorter by θ radians.

Next, the voltage equation of the generalized two-phase motor model will be described. The following conditions are assumed in the general two-phase motor model shown in FIG.

(A ₁ ) Two stator coils α and β
Are the same, and the two rotor coils a and b are also the same.

(B ₁ ) The magnetic flux density in the gap has a sinusoidal distribution.

From the condition (a ₁ ) above, the self-inductances L _α and L _{β of the} two stator coils α and β are
Are equal to each other and the self-inductances L _a and L _{b of the} two rotor coils a and b are also equal to each other. That is, when the stator self-inductance and the rotor self-inductance are Ls and Lr, respectively, the following formula 1 is established.

[0013]

[Equation 1]

When the mutual inductance between the stator and rotor is M in consideration of the above condition (b ₁ ), the voltage equation expressed by the following equation 2 is obtained.

[0015]

[Equation 2]

Where p is the Heaviside operator (differential operator d / dt), V is the voltage vector, I is the current vector, R is the resistance matrix, and L (θ) is the inductance. Represents a matrix, and Z (θ) represents an impedance matrix. The voltage vector V, the current vector I, the resistance matrix R, and the inductance matrix L (θ) are represented by the following mathematical formulas 3 to 6, respectively.

[0017]

[Equation 3]

[0018]

[Equation 4]

[0019]

[Equation 5]

[0020]

[Equation 6]

Next, the inductance matrix of the step motor will be described. Generally in two-phase motor models,
It has the following properties.

(A ₂ ) The self-inductances Ls and Lr of the stator and rotor are constant values regardless of θ.

There is a place where the mutual inductance between the coils becomes zero depending on the value of (b ₂ ) θ.

Inductance matrix L (θ) of the above equation 6
Satisfies the above conditions (a ₂ ) and (b ₂ ), but the hybrid type step motor has the following properties in terms of the operating principle.

(A ₃ ) The self-inductance of the stator and rotor is a function of θ, and is zero for any value of θ.
It doesn't.

(B ₃ ) Mutual inductance between the coils does not become zero for any value of θ.

Therefore, the inductance matrix L (θ) of the two-phase motor model shown in the above equation 6 cannot completely correspond to the inductance matrix of the step motor. Therefore, the inductance matrix L (θ) of the step motor is expressed as in the following Expression 7.

[0028]

[Equation 7]

Next, the conversion to the dq axes will be described. The voltage equation represented by the above equation 2 cannot be solved even in a steady state. Therefore, consider conversion of various quantities on the rotor side into dq axes fixed in the space shown in FIG. The above formula 2 is expressed as the following formula 8.

[0030]

[Equation 8]

Next, the matrix C is defined by the following expression 9.

[0032]

[Equation 9]

Here, the matrix Cs and the matrix E are expressed by the following equations 10 and 11, respectively.

[0034]

[Equation 10]

[0035]

[Equation 11]

The following equations 12 and 13 are converted using the matrix C defined by the above equation 9.

[0037]

[Equation 12]

[0038]

[Equation 13]

From the above equations 8, 12, and 13, the following equation 14 is obtained.

[0040]

[Equation 14]

Therefore, the following expression 15 is obtained.

[0042]

[Equation 15]

When the impedance matrix is calculated, the following Expression 16 is obtained.

[0044]

[Equation 16]

Here, G is called a torque tensor, and is expressed by the following equation 17.

[0046]

[Equation 17]

Further, it is known that the generated torque on the dq axis model can be obtained by the following formula 18.

[0048]

[Equation 18]

Since it is difficult to analyze in the stationary system shown in FIG. 5, various amounts of α-β coordinates are changed to a-b coordinates (d-axis) which rotate in synchronization with d-q axes as shown in FIG. And a axis, q axis and b
Axis is always the same)
Holds.

[0050]

[Formula 19]

The voltage vector V, the current vector I, and the resistance matrix R expressed by the equations 3 to 5 are respectively
Shown by the following formulas 20 to 22,

[Equation 20]

[0052]

[Equation 21]

[0053]

[Equation 22]

In the inductance matrix L (θ)
And the matrix Cs of the above equation 10 is represented by the following equation 23.

[0055]

[Equation 23]

The q axis of the motor is an electrical angle (π
/ 2) When the generated torque T represented by the above formula 18 is calculated in consideration of the fact that it exists at a shifted position and the d-axis component does not exist on the rotor side, the following formula 24 is obtained.

[0057]

[Equation 24]

In the hybrid type step motor, the N pole and the S pole are considered as independent poles in terms of structure. Therefore, if the torque T _N generated at the N pole is represented by the above formula 24, the torque T _S generated at the S pole is expressed by the following formula 2
It is represented by 5.

[0059]

[Equation 25]

Therefore, the torque T generated in the entire motor is expressed by the following equation 26.

[0061]

[Equation 26]

As is apparent from the above, the torque equation of the hybrid type step motor is represented by the above equation 26, and d
The axial current i _d is determined by the strength of the magnet. As a result, in the structure of the conventional hybrid type step motor, a strong magnet is required to obtain high torque.

Therefore, an object of the present invention is to provide a step motor which can generate a high torque without using a magnet.

[0064]

A step motor according to the present invention is a step motor comprising a cylindrical stator and a rotor rotatably housed in the stator about a rotation axis. A stator core having a first number of stator teeth that are spaced apart and project inward in the radial direction, and a stator coil that is wound around each of the stator teeth, and the rotor is circumferentially spaced. A rotor core having a second number of rotor teeth smaller than the first number and protruding outward in the radial direction; and a rotor coil wound around each of the rotor teeth. Current supply means for flowing
It is characterized by having a position detecting means for detecting the rotational position of the rotor and a control means for controlling the current supplying means so as to obtain high torque based on the detected position detected by the position detecting means.

[0065]

The torque can be effectively generated by controlling the rotor coil current according to the rotational position of the rotor.

[0066]

Embodiments of the present invention will now be described with reference to the drawings.

1A and 1B show the structure of a hybrid type step motor according to an embodiment of the present invention.
As shown in the figure, the hybrid step motor of the present embodiment comprises a cylindrical stator 10 and a rotor 20 housed in the stator 10 so as to be rotatable around a rotation axis RA. Since the structure of the stator 10 is the same as the conventional one shown in FIG. 2, the description thereof will be omitted.

The rotor 20 includes a rotor core 21. The rotor core 21 faces the stator core 11. The rotor core 21 has six rotor teeth 22 that are arranged at intervals in the circumferential direction and project outward in the radial direction. Each of the six rotor teeth 22 has a rotor coil 23 (see FIG. 2).
In the figure, D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , and D ₆ are wound clockwise.

Thus, the rotor coil 2 is provided on the rotor 20 side.
Since it has 3, the step motor is not shown,
It has a brush and a commutator for passing an electric current through the rotor coil 23. Further, the step motor includes a position detector (not shown) for detecting the rotational position of the rotor 20,
And a control circuit (not shown) that controls the rotor coil current based on the detected position detected by the position detector.

As described above, in the hybrid type step motor of the present invention, since the stator coil 13 and the rotor coil 23 are arranged on the stator 10 and the rotor 20, respectively, the generated torque T is expressed by the following formula 27. To be done.

[0071]

[Equation 27]

Therefore, in the present invention, the value of the d-axis current (rotor coil current) i _d in the above equation 27 can be freely changed. Further, as will be described later, the torque can be effectively generated by controlling the rotor coil current i _{d according} to the rotation position of the rotor 20 from the second term on the right side of the equation 27. Therefore, as compared to the case where the coil 13 is arranged only in the stator 10 as in the conventional hybrid type step motor, the hybrid type step motor of the present invention can generate a maximum torque of about twice.

A method of exciting the rotor coil 23 of the present invention will be described with reference to FIG. Now, let us consider the excitation of the rotor coil 23 when the stator coil A is energized and the stator coil B is to be switched in excitation. At this time, the rotor coil 23 has the relationship shown in Table 1 below between θ and the b-axis current i _b .

[0074]

[Table 1]

In the above equation 27, the b-axis currents i _b and s
Since in θ is determined by the values in Table 1 above, torque can be effectively generated by controlling the rotor coil current i _d as shown in Table 2 below.

[0076]

[Table 2]

As described above, if the rotor coil current i _d is controlled according to the rotor position, the second right side of the equation 27
The torque based on the term can be effectively used.

[0078]

As described above, according to the present invention, in the hybrid type step motor, the coil is arranged not only in the stator but also in the rotor, and the rotor coil current is controlled according to the rotation angle of the rotor, so that a high torque is achieved. Is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a hybrid type step motor according to an embodiment of the present invention, in which (a) is a cross-sectional view seen from a radial direction, and (b) is an axial direction from a line II ′ of (a). It is sectional drawing seen from.

FIG. 2 is a view showing the structure of a conventional hybrid type step motor, in which (a) is a cross-sectional view as seen from the radial direction, and (b) and (c) are lines II-II ′ and III-III ′, respectively. It is sectional drawing seen from the axial direction.

FIG. 3 is a circuit diagram showing a two-phase motor model.

FIG. 4 is a cross-sectional view showing a relationship between a stator tooth of a stator and a rotor tooth of a rotor in a linear pulse model.

FIG. 5 is a circuit diagram showing a stationary system in which various quantities on the rotor side are converted to dq axes.

FIG. 6 is a circuit diagram showing a rotating system in which various quantities of α-β coordinates are converted into ab coordinates which rotate in synchronization with dq axes.

[Explanation of symbols]

 10 stator 11 stator core 12 stator tooth 13 stator coil 20 rotor 21 rotor core 22 rotor tooth 23 rotor coil

Claims (1)

[Claims] 1. A step motor comprising a cylindrical stator and a rotor rotatably housed within the stator so as to be rotatable about a rotation axis, wherein the stator is arranged at intervals in a circumferential direction and is radially arranged. A stator core having a first number of stator teeth projecting inward, and a stator coil wound around each of the stator teeth, wherein the rotor is circumferentially spaced and radially outward. A rotor core having a second number of rotor teeth smaller than the first number, and a rotor coil wound around each of the rotor teeth, and a current for passing a current through the rotor coil. Supply means, position detecting means for detecting the rotational position of the rotor, and the current supplying means for controlling high current based on the detected position detected by the position detecting means. Step motor; and a control unit.