JPH11150933A - Stepping motor and image reader using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a stepping motor, which can be rotated smoothly in one direction, and which can be rotated at high torque in the other direction. SOLUTION: Corner parts on one side of pole teeth 12a to 12d of a rotor 12 for a step motor are formed of curves 12e, or corner parts on one side of pole teeth 10a to 10d of a stator 10 are formed of curves. Alternatively, the corner parts on one side of the pole teeth of the rotor are formed of the curves, and the corner parts of the stator which are faced with corner parts of the rotor are formed of curves. Alternatively, small teeth 12f are formed at the pole teeth of the rotor, or small teeth 10f are formed at the pole teeth of the stator. Corner parts on one side or both sides out of the small teeth formed at the rotor (the pole teeth of the rotor) and the small teeth formed at the pole teeth of the stator are formed of curves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepping motor (stepping motor) and an image reading apparatus using the stepping motor, and more particularly to pole teeth (or a plurality of pole teeth provided on pole teeth) of a rotor / stator of the stepping motor. Small teeth).

[0002]

2. Description of the Related Art FIGS. 9 to 12 show a structure of a conventional step motor, an example of a driving circuit, an exciting current waveform,
3 shows the operating position of the rotor.

[0003] As shown in FIG.
A stator 10 having pole teeth 10a to 10d directed to two centers, and a rotor arranged at the center of the four pole teeth 10a to 10d of the stator 10 and having a magnet having N poles and S poles. And a motor winding 14 for sequentially magnetizing the pole teeth of the stator 10 to the N pole or the S pole.

FIG. 10 shows an example of a unipolar drive circuit for driving such a step motor.
Transistors Tr1 to Tr1 functioning as switching elements
By switching ON / OFF of Tr4, a drive current is selectively passed from power supply E to any two of windings A'-A, / A '-/ A, B'-B, / B'-/ B. , Rotate the step motor. FIG. 11 shows a waveform of a current flowing through the winding of the drive circuit.

FIG. 12 shows the relationship between the direction of the current shown in FIG. 10 and the position of the rotor. When current flows in the order of steps 1 to 4, the rotor rotates clockwise. On the other hand,
When current flows from step 4 to step 1, the rotor rotates counterclockwise.

[0006]

The rotation of the rotor depends on the attraction force generated between the pole teeth of the rotor and the pole teeth of the stator. In a conventional stepping motor, each pole tooth has a U-shape. Due to this shape, when the rotor is rotated at each step, the rotor is rotated with a strong suction force, and tends to generate vibration, smooth rotation is not obtained, and rotation speed unevenness (wahula) occurs. . Further, depending on the type of the motor, there is a motor in which a plurality of small teeth are provided for each one pole tooth, but there is a problem similar to the above.

On the other hand, in an image reading apparatus that uses a stepping motor as a driving source and moves an illumination source or a mirror to read an image of a document, a stepping motor is used to move the illumination source or the mirror to one side for image reading. The motor is rotated in one direction, and after reading the image, the stepping motor is rotated in the other direction in order to return the illumination source and the mirror to the initial positions. When reading an image, it is necessary to rotate the step motor smoothly so as to prevent uneven rotation speed in order to obtain a high-accuracy read image, but uneven rotation speed is a problem when returning. Instead, it is desirable to apply a high torque to the motor in order to return quickly.
However, the conventional motor still has the problem of uneven rotation speed.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a step motor capable of rotating smoothly in one rotation direction and rotating with high torque in the other rotation direction.

Another object of the present invention is to provide an image reading apparatus using a motor having motor characteristics suitable for image reading.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a step motor comprising a stator and a rotor rotatably disposed with respect to the stator. The corner portion is formed by a curve, or one corner portion of the pole teeth of the stator is formed by a curve, or one corner portion of the pole teeth of the rotor is formed by a curve, and during rotation, A corner portion of the stator facing the corner portion of the rotor is formed by a curve, or a small tooth is formed on each of the pole teeth of the rotor, or a pole tooth is formed around the rotor, Small teeth are formed on each of the pole teeth of the stator,
One or both corners of the small teeth formed on the rotor (or the rotor teeth) or the small teeth formed on the pole teeth of the stator are formed by curves. .

According to another aspect of the present invention, there is provided an image reading apparatus for scanning an image on a document using a step motor, wherein the step motor has a characteristic of smoothly rotating in one rotation direction when reading an image. It is characterized by having a higher torque characteristic with respect to the other rotation direction of the return to the initial position after reading than the one rotation direction.

[0012]

Next, a step motor (hereinafter, simply referred to as a motor) and an image reading apparatus using the motor according to an embodiment of the present invention will be described. First, in Examples 1 to 4, the structure of the motor will be described.
In the following, an image reading apparatus using such a motor will be described.

(Embodiment 1) FIG. 1 is a sectional view showing a motor according to Embodiment 1 of the present invention. This sectional view is a section in a direction perpendicular to the rotation axis of the motor. Although only one rotor is shown in the cross-sectional view, the motor may be provided with a plurality of rotors stacked on the rotating shaft in several stages. The stator 10 has four pole teeth 10a to 10d, and a rotor 12 is rotatably arranged at the center of the stator 10. The rotor 12 has, for example, four pole teeth 12a to 12d, and one corner portion 12e of each pole tooth 12a to 12d.
(Corner) (looking at the counterclockwise rotation indicated by the arrow CCW,
(A tip side) is formed with a smooth curve. Although the shape of this curve is not particularly limited, it may be an arc having a predetermined curvature or a part of a curve having a quadratic function or more (for example, a quadratic function curve, a cubic function curve, etc.). preferable. The length of the radius of curvature in the case of a circular arc is not particularly limited, but is preferably larger than the width of the pole teeth before the curve is formed.

In a motor having a rotor having such a pole tooth shape, when the rotor is rotated counterclockwise,
Each of the corner portions 12e formed by the curves of the rotor pole teeth 12a to 12d approaches the right-angled corner portion of each of the pole teeth 10a to 10d of the stator 10, so that the rotation becomes smooth, Vibration is reduced. However, the torque will decrease. On the other hand, when the rotor is rotated in the clockwise direction, the corners formed at right angles that are not formed by the curve of the pole teeth of the rotor toward the right corners of the pole teeth 10a to 10d of the stator 10 are formed. Each will approach, and the same level of vibration will occur as before,
There is no reduction in torque, and the torque remains almost unchanged.

As described above, the reason why the formation of the curve on the pole teeth of the rotor causes the rotor to rotate smoothly and reduce the vibration is inferred as described below. FIG. 2 is a graph showing the angle-static torque characteristics of the motor, and among them,
FIG. 2A shows the characteristics of the conventional motor, and FIG. 2B shows the characteristics of the motor of the present invention. 2a and 2b
The vertical axis represents the torque, and the horizontal axis represents the angle (displacement angle). As is clear from FIG. 2a, in the conventional motor,
The angle-static torque characteristic becomes trigonometric (sine curve). As is apparent from this characteristic, the torque changes considerably sharply before reaching the stable point where the pole teeth stop.
For this reason, vibration occurs.

On the other hand, as is apparent from FIG. 2B, in the angle-static torque characteristic of the motor of the present invention, the torque decreases almost exponentially toward the stable point, and gradually changes to the stable point. For this reason, almost no vibration occurs and smooth rotation is achieved.

This is as follows when viewed from the step pulse response characteristic (transient characteristic). FIG. 3 is a graph showing the step response characteristics of the motor.
FIG. 3A is a graph showing the step response characteristics of the motor of the present invention, and FIG. 3B is a graph showing the step response characteristics of the conventional example. As is clear from FIG. 3B, in the conventional motor, a large overshoot is generated for each step and it takes time until the motor is stabilized. From this, it can be said that vibration occurs and smooth rotation cannot be obtained. On the other hand, as is clear from FIG. 3a, the motor of the present invention has a slight overshoot and is stable in a short time. From this,
In the motor of the present invention, it can be said that smooth rotation can be obtained.

(Embodiment 2) In Embodiment 1, the rotor pole teeth are provided with a smooth curved shape. In Embodiment 2, however, the stator pole teeth are provided with a smooth curve shape. FIG.
FIG. 4 is a sectional view showing a motor according to a second embodiment of the present invention. The stator 10 has four pole teeth 10a to 10d, and one corner 10e (corner) of each pole tooth 10a to 10d (the tip side when viewed in the counterclockwise direction indicated by the arrow CCW) is smooth. It is formed by curves. A rotor 12 is rotatably arranged at the center of the stator 10. The rotor 12 has, for example, four pole teeth 12a to 12d. The shape of the curve formed on the pole teeth of the stator is not particularly limited, but may be an arc having a predetermined curvature or a curve having a quadratic function or more (for example, a quadratic function curve, a cubic function curve, or the like). ) Is preferred. The length of the curved part is
Although not particularly limited, the width is preferably larger than the width of the pole teeth before the curve is formed.

In a motor having a stator having such a pole tooth shape, when the rotor is rotated in a counterclockwise direction, the rotor is moved toward the corner portion 10e where the curves of the pole teeth 10a to 10d of the stator 10 are formed. Each of the perpendicular corners of the pole teeth will approach, resulting in smooth rotation and reduced vibration. However, the torque will decrease. On the other hand, when the rotor is rotated in the clockwise direction, the corners formed at right angles to the pole teeth of the rotor toward the right corners not formed by the curves of the pole teeth 10a to 10d of the stator 10 are formed. Each comes closer, and the same level of vibration occurs as before, but there is no decrease in torque,
The torque hardly changes.

The angle-static torque characteristics and the step pulse response characteristics (transient characteristics) of the motor in the second embodiment are the same as those in the first embodiment, and it is considered that smooth rotation can be obtained for the same reason.

(Embodiment 3) The embodiment 3 has a smooth curve corner formed on the rotor-side pole teeth of the embodiment 1 and a smooth curve formed on the stator-side pole teeth of the embodiment 2. It is a combination of a corner portion and a smooth curve provided on both pole teeth of the rotor and the stator. FIG.
FIG. 9 is a sectional view illustrating a motor according to a third embodiment of the present invention. When the rotor rotates in the counterclockwise direction, the pole teeth 12a of the rotor
The corners 12e and 10e having smooth curves are provided on the side where the stator teeth 12d and the stator pole teeth 10a to 10d approach, respectively.
And form. Also in the third embodiment, smooth rotation can be obtained for the same reason as in the first and second embodiments.

(Embodiment 4) Embodiments 1 to 3 relate to a motor consisting of a rotor and a stator without small small teeth on the pole teeth. In Embodiment 4, a plurality of pole teeth are provided on the pole teeth. It is directed to a motor provided with small teeth. FIG. 6 is a sectional view showing a motor according to a fourth embodiment of the present invention. The stator 10 has four pole teeth 10a to 10d, and each pole tooth is provided with a plurality of small teeth 10f. Further, the rotor 12 is provided with a plurality of small teeth on a circumference (when there are pole teeth, the small teeth are provided on the pole teeth). A corner portion having a smooth curve is formed on one or both of the small teeth 10f and 12f similarly to the motors of the first to third embodiments (note that in the drawings, Not shown for simplicity). Even in such a configuration, smooth rotation can be obtained as in the first to third embodiments based on the above-described reason.

Fifth Embodiment In a fifth embodiment, the motor of the present invention having the characteristics described in the first to fourth embodiments is used in an image reading apparatus. FIG. 7 is a side view showing main components of the optical system of the image reading apparatus, and FIG. 8 is a perspective view showing a moving mechanism for moving a specific component among the main components.

Since this configuration is already known, the outline of the optical system is, for example, a transparent platen 20 made of glass for mounting a document, and a document placed on the platen 20 (not shown). Illumination source 22 for illuminating the document, a first mirror 24 for sequentially reflecting light reflected from the document,
A mirror 26, a third mirror 28, a lens 30 for transmitting light from the third mirror, a CCD 32 for receiving light from the lens 30 and converting the light into a voltage, and a CCD for driving the CCD 32
A driver 34 is provided.

In order to scan the original, the illumination source 22 and the first mirror 24 are moved at a certain speed, for example, as indicated by arrows, and the second and third mirrors are moved at half the speed. Must be moved at speed. Therefore, the rotation is transmitted from the motor 40 to the rotation shaft 44 via the belt 42, and further, the rotation of the rotation shaft 44 is transmitted to the belt 48 applied to the pulley 46, and the first mirror table 50 attached to the belt 48 And the second mirror base 52 are moved. The illumination source 22 and the first mirror 24 are mounted on the first mirror base 50 and are moved at a certain speed. The second mirror table 52 includes the second mirror 26 and the third
A mirror 28 is mounted and moved at half the speed.

Now, when the first mirror table 50 and the second mirror table 52 move in the directions indicated by the arrows, and if the image of the original is to be read, in order to obtain a high-precision image without deviation,
It is desirable that the rotation speed unevenness of the motor be as small as possible. For this reason, in the rotation direction in which the motor is rotated in this movement direction, torque is not so much required, but smooth rotation is desired. On the other hand, after the image reading is completed, it is desirable to quickly return the first mirror base 50 and the second mirror base 52 to the initial position (home position) in order to read the image of the next document. Since the rotational speed unevenness does not matter, it is desirable that the torque be high.

When the motor of the present invention described in the first to fourth embodiments is used as the motor 40, the motor can be smoothly rotated at the time of reading a document.
At the time of return, since the torque does not decrease, the motor can be rotated at a high speed.

[0028]

As described above, according to the present invention,
A step motor that can rotate smoothly in one rotation direction and can rotate with high torque in the other rotation direction is obtained.

Further, an image reading apparatus using a motor having motor characteristics suitable for image reading can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a motor according to a first embodiment of the present invention.

FIG. 2 is a graph showing the angle-static torque characteristics of the motor, of which FIG. 2a shows the characteristics of a conventional motor, and FIG. 2b shows the characteristics of the motor of the present invention.

3 is a graph showing a step response characteristic of a motor, of which FIG. 3a is a graph showing a step response characteristic of a motor of the present invention, and FIG. 3b is a graph showing a step response characteristic of a conventional example. is there.

FIG. 4 is a cross-sectional view illustrating a motor according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating a motor according to a third embodiment of the present invention.

FIG. 6 is a sectional view showing a motor according to a fourth embodiment of the present invention.

FIG. 7 is a side view illustrating main components of an optical system of the image reading apparatus.

FIG. 8 is a perspective view showing a moving mechanism for moving a specific part of the main parts.

FIG. 9 is a diagram showing a structure of a conventional step motor.

FIG. 10 is a diagram illustrating an example of a drive circuit of a conventional step motor.

FIG. 11 is a diagram showing an exciting current waveform of a conventional step motor.

FIG. 12 is a diagram showing an operating position of a conventional rotor.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Stator 10a-10d The pole tooth of a stator 10e The corner part formed by the smooth curve of the pole tooth of the stator 12 Rotor 12a-12d The pole tooth of the rotor 12e The corner part formed by the smooth curve of the pole tooth of the rotor 10f Stator 12f Small teeth provided on the pole teeth of the rotor 24 First mirror 26 Second mirror 28 Third mirror 30 Lens 32 CCD 34 CCD driver 50 First mirror base 52 Second mirror base 40 motor

Claims (9)

[Claims] 1. A step motor comprising a stator and a rotor rotatably disposed with respect to the stator, wherein one corner of the pole teeth of the rotor is formed by a curve. 2. A step motor comprising a stator and a rotor rotatably disposed with respect to the stator, wherein one corner portion of the pole teeth of the stator is formed by a curve. 3. A stepping motor comprising a stator and a rotor rotatably disposed with respect to the stator, wherein one corner of the pole teeth of the rotor is formed by a curved line, and the rotor is rotated during rotation. A step motor wherein a corner portion of a stator facing the corner portion is formed by a curve. 4. A stepper motor comprising a stator and a rotor rotatably disposed with respect to the stator, wherein each of the rotor's pole teeth is formed with small teeth, or pole teeth are formed around the rotor. Are formed on each of the pole teeth of the stator, and each of the small teeth formed on the rotor (or the pole teeth of the rotor) or the small teeth formed on the pole teeth of the stator is formed. A step motor, wherein one or both corners are formed by a curve. 5. The stepping motor according to claim 1, wherein the corner formed by the curve is an arc having a predetermined curvature or a part of a function having a quadratic function or higher. Characterized step motor. 6. The step motor according to claim 5, wherein the radius of curvature of the arc of the corner formed by the curve is greater than the width of the pole teeth or the small teeth. 7. A step motor comprising a stator and a rotor rotatably disposed with respect to the stator, wherein the step motor has a characteristic of smoothly rotating in one rotation direction of the motor, and has a characteristic of rotating in the other rotation direction of the motor. A rotor or a stator and both pole teeth or small teeth provided on the pole teeth are formed so as to have higher torque characteristics than the one rotation direction. 8. A step motor comprising a stator and a rotor rotatably disposed with respect to the starter, wherein the torque curve in the angle-static torque characteristic of the motor intersects the stable point of the angle with a triangle. A step motor having a rotor or a stator and both pole teeth or small teeth provided on the pole teeth formed to have a lower slope than the function. 9. An image reading apparatus that scans an image on a document using a step motor, wherein the step motor has a characteristic of smoothly rotating in one rotation direction during image reading, and an initial step after image reading. An image reading apparatus having a higher torque characteristic with respect to the other rotation direction of the return to the position than the one rotation direction.