JPH0545094Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a small electric motor, and particularly to a small electric motor having an encoder disk for detecting the position of a rotor.

(Prior art) Small electric motors, such as stepping motors, are normally used in open-loop drive, but when they are used in closed-loop drive (self-excited drive), their characteristics, especially high-speed response, dramatically improve. known to improve. Open loop drive can be achieved by using optical or magnetic encoders. Therefore, in the past, an encoder disk was placed outside the electric motor, and the rotor of the electric motor and the encoder disk were connected using a coupling or the like.

On the other hand, in addition to the purpose of improving the characteristics of electric motors through closed-loop driving, there are applications such as the home position of typewriters and printers, the track 00 of floppy disk devices, etc., and the absolute position of movable parts of devices driven by electric motors. In order to detect this, a sensor such as a transmission type photointerrupter is attached to the outside of the motor, and a flag, etc. is attached to the movable part linked to the motor, thereby detecting the absolute position of the movable part of the device. There is.

There is also a sensor that uses a reflective photointerrupter. An encoder disk used in combination with such a reflective photointerrupter is formed by alternately forming light reflecting surfaces and light non-reflecting surfaces at predetermined intervals. Such an encoder disk having a reflective surface and a non-reflective surface is manufactured by roughening a predetermined area of the surface by printing or etching.

(Problems to be Solved by the Invention) According to the conventional closed-loop drive stepping motor described above, since the encoder disk disposed outside and the rotor are connected by a coupling, hysteresis occurs in the coupling part during driving. It is easy to cause problems.

Furthermore, even in the case of the above-mentioned stepping motor, which is designed to detect the absolute position of the movable part of the device, the structure is such that an encoder disk, sensor, and flag are attached to the outside of the motor.
The design of the device lacks space flexibility, and
Easily affected by dirt, dust, etc.

Furthermore, in conventional small electric motors that use a reflective photointerrupter as a sensor, the encoder disk is made by printing or etching, which makes it difficult to align the printed pattern or etched surface with respect to the outer diameter of the disk, making it difficult to The dispersion becomes larger. Furthermore, when using the etching method, it is difficult to obtain an etched surface of stable quality.

The present invention was devised to solve these conventional problems; it does not have problems such as hysteresis in the case of closed-loop drive, can prevent deterioration of detection accuracy and malfunction due to dirt and dust, and has characteristics The purpose is to provide a small electric motor with stable quality and no variation in quality.

(Means for solving the problem) The present invention incorporates an encoder disk into an electric motor, rotatably supports the rotor shaft by an oil-impregnated bearing, and positions the encoder disk on the side of the rotor facing the oil-impregnated bearing. In addition to forming a positioning projection, a recess for storing oil from the oil-impregnated bearing is provided closer to the rotor shaft than the positioning projection.

(Function) The encoder disk is positioned and attached to the side surface of the rotor facing the oil-impregnated bearing within the electric motor using the positioning protrusion. The impregnated oil from the oil-impregnated bearing that flows out due to the rotation of the rotor shaft is collected in a recess provided on the side of the rotor.
It will not be scattered due to the centrifugal force caused by the rotation of the rotor.

(Example) Hereinafter, an example of a small electric motor according to the present invention will be described with reference to the drawings.

In FIG. 1, stator coils 12, 12 wound around bobbins are fitted into two cup-shaped stator cases 11, 11, respectively, and magnetic pole plates 13, 13 are installed at the open ends of the stator cases 11, 11. It's embedded. The inner periphery of the bottom of the cup-shaped stator cases 11, 11 is formed into a comb-teeth shape and is bent at right angles to form magnetic pole parts 11a, 11a.
The inner peripheral edge portions are also formed into a comb-teeth shape and are bent at right angles to form magnetic pole portions 13a, 13a. A pair of stator cases 11, 11 and magnetic pole parts 11a, 13a of the magnetic pole plate 13 are fitted so as to mesh with each other at a predetermined interval alternately.
A cylindrical space is formed at the inner peripheral portion of the stator case 11 and the magnetic pole plate 13 by 1a and 13a. In this way, the stator has stator case 1
1, a stator unit consisting of a stator coil 12 and a magnetic pole plate 13 are stacked one above the other, and base plates 14 and 15 are fixed to the upper and lower surfaces of the stator, respectively.

Oil-impregnated bearings 1 are mounted on the base plates 14 and 15, respectively.
6 and 17 are fitted and fixed, and a rotor shaft 18 is rotatably supported by oil-impregnated bearings 16 and 17. The rotor shaft 18 has the magnetic pole portions 11a, 13
A rotor 20 is fitted and fixed in the cylindrical space formed by a, and a cylindrical rotor magnet 19 is fitted and fixed on the outer circumference of the rotor 20. The rotor magnet 19 is magnetized to have an appropriate number of poles in the circumferential direction, and the rotor magnet 19 faces the magnetic pole portions 11a and 13a at an appropriate interval.

A cylindrical protrusion 20a is formed on one side (the upper side in FIG. 1) of the rotor 20 in the direction of the axis 18 so as to surround the outer circumference of the oil-impregnated bearing 16.
A recess 20b for storing oil is formed along the outer peripheral edge of the oil-impregnated bearing 16 on the inner peripheral side of the cylindrical protrusion 20a. The protrusion 20a serves as a positioning protrusion for attaching the encoder disk 21 concentrically to the rotor 20,
An encoder disk 21 is attached to the protrusion 20a in a fixed relationship with the magnetic poles of the rotor magnet 19. As shown in FIG. 4, the encoder disk 21 has cutouts 21a formed at predetermined intervals on the periphery, so that the cutouts 21a are light non-reflective parts and the remaining parts are light non-reflective parts. The light non-reflecting portions 21a and the reflecting surfaces 21b are arranged alternately in the circumferential direction, and the rotor magnet 1
They are formed at intervals corresponding to twice the number of magnetic poles of 9. The encoder disk 21 can be formed by pressing a material such as aluminum or stainless steel.
When attaching the encoder disk 21 formed in this way to the rotor 20, the notch 2
1a can be used to mechanically align the encoder disk 21 with respect to the magnetic poles of the rotor, thereby increasing the accuracy of the mounting position of the encoder disk 21.

In FIG. 2, a part of the base plate 14 has a window hole 14a above the encoder disk 21.
is formed. The base plate 14 has a screw hole 1 located on a line passing through the center of the rotor shaft 18 and the center of the window hole 14a and on the outer diameter side from the position of the window hole 14a.
4b is formed, and a rectangular small hole 14c is formed at a predetermined distance from the window hole 14a. In FIGS. 1 to 3, a sensor unit 23 is attached to the window hole 14a. The sensor unit 23 includes a sensor holder 24 and a reflective photointerrupter 25 embedded in the sensor holder 24 as a sensor. An exit window for light from the photo interrupter 25 and an entrance window for reflected light are formed on the front end surface of the sensor holder 24. The tip of the sensor holder 24 is connected to the base plate 1.
The fork portion 26a of the adjustment lever 26 is fitted into the window hole 14a of No. 4 and is attached by screwing the screw 27 into the screw hole 14b of the base plate 14.
attaches the flange 24b of the sensor holder 24 to the base plate 14.
The sensor unit 23 is attached to the window hole 14a of the base plate 14 by pressing the sensor unit 23 against the window hole 14a of the base plate 14. The window hole 14a of the base plate 14 is formed to be long in the tangential direction to the arc centered on the rotor shaft 18, so that the sensor unit 23 can be moved within a certain range in the longitudinal direction of the window hole 14a. Since the distance between the inner circumferential sides of the fork portions 26a of the adjustment lever 26 and the outer diameter of the cylindrical portion of the sensor holder 24 into which the fork portions 26a fit are made the same, the position of the photo interrupter 25 can be adjusted. It is regulated by a lever 26.

In FIGS. 1 and 3, the adjustment lever 26 is made of a metal plate, and on the opposite side of the fork portion 26a with the screw 27 in between, a downward protrusion 26c is formed. When mounted on the plate 14, the protrusion 26c hits the base plate 14, and the fork part 26a hits the collar part 24b of the sensor holder 24, so that the sensor unit 23 is elastically pressed against the base plate by the elasticity of the adjustment lever 26 itself. It's being pushed to 14. The adjustment lever 26 also has a relatively long arm 26d in the diagonal direction, and a bent portion 26e formed at the tip of the arm 26d fits into the small hole 14 of the base plate 14.
The adjustment lever 26 is prevented from rotating by being fitted into the hole c. Arm 26d of adjustment lever 26
Wing-shaped parts 26f, 26g are formed on both sides from the tip of the arm 26f, and a gap 27 is formed between these wing-shaped parts 26f, 26g and the arm 26d.
h, 26i are formed. The arm 26d of the adjustment lever 26 has a narrow portion 26j at the base of the pair of wing-shaped portions 26f and 26g.

As mentioned above, when the adjustment lever 26 is attached to the base plate 14 with the screw 27, if the tip of a flathead screwdriver is faced to one of the above-mentioned gaps 26h and 26i and rotated, the screwdriver While the tip was exposed, the area was forcibly spread out,
The arm 26d is forcibly bent at the narrow portion 26j. As a result, the adjustment lever 26 rotates slightly around the screw 27 except for the tip from the narrow portion 26j,
The photo interrupter 25 is moved slightly in the longitudinal direction of the window hole 14a. That is, it is possible to adjust the position of the photo interrupter 25 in this way, and after the adjustment, the photo interrupter 25 is positioned on the spot without any special fixing operation.

Photo interrupter 2 positioned in this way
5 is located above the encoder disk 21, and the light emitted from the light emitting part of the photo interrupter 25 is reflected on the reflective surface 21 of the encoder disk 21.
b, and enters the light receiving section of the photo interrupter 25. As shown in FIG. 1, a damping prevention leaf spring 29 interposed between the rotor 20 and the base plate 15 biases the rotor 20 in the thrust direction. Encoder disk 21 and photo interrupter 2
Between 5 and 5 is helpful for retention.

Note that if the axial center of the rotor magnet 19 and the axial center of the stator are offset so that the rotor is always pressed upward in FIG. 1 by magnetic force, it is not necessary to provide the leaf spring 29.

The rotational operation of the rotor portion in the above embodiment is basically the same as that of a general small electric motor. That is, when the drive coil 12 is energized based on the detection output of the photo interrupter 25, the rotor magnet 19
is urged to rotate.

Here, when the reflective photo interrupter 25 faces the reflective surface 21b of the encoder disk 21, the reflected light from the reflective surface 21b enters the photo interrupter 25, whereas the photo interrupter 25 is opposed to the reflective surface 21b of the encoder disk 21. When facing the non-reflecting portion 21a, reflected light from the upper end surface of the rotor 20 enters the photo interrupter 25. Therefore, the reflective photo interrupter 25
If the distance between and the reflective surface 21b of the encoder disk 21 is defined as the detection distance at which the maximum photocurrent is obtained,
Photo interrupter 25 is encoder disk 2
When facing the non-reflective portion 21a of No. 1, the detection distance becomes longer by the thickness of the encoder disk 21, thereby reducing the photocurrent. If the upper end surface of the rotor 20 is made of a material with low reflectance, such as black plastic, the synergistic effect of the difference in light reflectance and the difference in detection distance will produce a signal with a good signal-to-noise ratio. can be obtained.

When a stepping motor is driven in a closed loop (self-excited), it is necessary to adjust the magnetic pole position of the rotor magnet and the encoder disk so that they have a predetermined positional relationship. According to the above embodiment, the cutout portion 21a of the encoder disk 21
The mounting position of the encoder disk 21 can be determined using this, and a motor with uniform characteristics can be stably manufactured.

Incidentally, in this type of electric motor, a sintered oil-impregnated bearing is normally used as in the illustrated embodiment.
Generally, in sintered oil-impregnated bearings, when the rotor shaft rotates and is at a high temperature, impregnated oil flows out and acts as a lubricant, and when the rotor shaft stops rotating and returns to normal temperature, the spilled oil returns to the bearing. Give back within. However, in conventional electric motors, if the oil spreads and scatters over a wide area when the shaft is rotating, the spilled oil is not always sufficiently reduced when the motor is stopped, and the impregnated oil gradually decreases, causing oil shortage. After that, there is not enough lubrication, which may shorten the life of the motor.
or generate noise. In particular, oil adhering to the rotor is further spread out due to centrifugal force during rotation.
It may adhere to the encoder disk and cause trouble in detecting the rotational position of the rotor.

In this regard, according to the embodiment of the present invention, the recess 20b that can store the oil from the oil-impregnated bearing 16 is provided on the side surface of the rotor 20 facing the oil-impregnated bearing 16, so that when the rotor 20 rotates at high temperatures, the oil-impregnation occurs. The impregnated oil flowing out of the bearing 16 is collected in the recess 20b and is not diffused outward due to centrifugal force. Therefore, when the temperature decreases due to the stoppage of rotation, the oil accumulated in the recess 20b is returned to the oil-impregnated bearing 16.
Since the oil flows back inside, the motor will not run out of oil even after long-term use, and the life of the motor will be extended.Also, since oil will not be splashed on the encoder disk 21, the sensor facing the encoder disk 21 will not run out of oil. There is no distortion or amplitude fluctuation of the output signal, and there is no problem in detecting the rotational position of the rotor.

Further, the encoder disk 21 is connected to the rotor shaft 1
According to the embodiment of the present invention, the inner diameter portion of the encoder disk 21 is connected to the positioning protrusion 20a formed on the side surface of the rotor 20. Since the encoder disk 21 is fitted into the rotor shaft 18, the concentricity of the encoder disk 21 with respect to the rotor shaft 18 can be determined with high precision, and from this point of view as well, the rotational position of the rotor can be detected with high precision.

Note that recesses for storing oil from the oil-impregnated bearing may be formed on both side surfaces of the rotor.

Next, another embodiment of the small electric motor according to the present invention will be described with reference to FIGS. 5 and 6. 5 and 6, numerals 34 and 35 are upper and lower base plates, 36 and 37 are oil-impregnated bearings, 38 is a rotor shaft, 39 is a rotor magnet, 40 is a rotor,
41 is an encoder disk. Rotor 40
is a boss 42 that is press-fitted and fixed to the rotor shaft 38.
and a collar 4 which has a smaller diameter than this boss 42 and is press-fitted and fixed to the rotor shaft 38 in close proximity to the boss 42.
3 and a rotor magnet 39 fixed to the outer periphery of the boss 42. The fixation of the rotor magnet 39 to the bosses 42 is due to the fact that these bosses 42
This is done by filling an adhesive 44 between the boss 42 and the rotor magnet 39, and by filling a circumferential groove formed on the outer periphery of the boss 42 with the adhesive 44, the boss 42 and rotor magnet 3
9 are now more firmly fixed.

A protrusion 42a for positioning the encoder disk 41 is formed in a cylindrical shape on the side surface of the boss 42 constituting the rotor 40, which faces the oil-impregnated bearing 36 so as to surround the end of the oil-impregnated bearing 36. , a recess 42b for collecting oil from the oil-impregnated bearing 36 on the side closer to the rotor shaft 38 than the protrusion 42a.
is formed. A washer 45 is interposed between the boss 42 and the oil-impregnated bearing 36.

As shown in FIG. 6, the encoder disk 41 includes light non-reflecting portions 41a which are punched out radially at regular intervals in the circumferential direction, and the non-reflecting portions 4.
1a and a reflective surface 41b. The encoder disk 41 is basically the same as the encoder disk 21 in the first embodiment, but a non-reflective portion 41a and a reflective surface 41b are formed at fine intervals to provide fine resolution.

In addition, the structure on the stator side may be the same as that of the embodiment described above, or may be any other suitable structure.

The embodiments shown in FIGS. 5 and 6 have the same effects as the embodiments described above.

(Effects of the invention) According to the invention, a recess is provided on the side surface of the rotor that faces the oil-impregnated bearing so that the oil from the oil-impregnated bearing can be stored. It accumulates in the water and is not dispersed or scattered outward due to centrifugal force. Therefore, when the temperature drops due to the stoppage of rotation, the oil that has accumulated in the recesses flows back into the oil-impregnated bearing, so the motor will not run out of oil even after long-term use, extending the life of the motor. However, since oil does not splash on the encoder disk, there is no problem in detecting the rotational position of the rotor.

In addition, since the encoder disk is fitted into a positioning protrusion formed on the side surface of the rotor, the concentricity of the encoder disk with respect to the rotor shaft can be achieved with high precision, which makes it possible to detect the rotational position of the rotor. It can be done with high precision.

In this way, according to the present invention, the electric motor can be stably driven in a closed loop.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing an embodiment of a small electric motor according to the present invention, FIG. 2 is a reduced plan view of the same embodiment with the sensor removed, and FIG. 3 is a plan view of the above embodiment. FIG. 4 is a plan view of the encoder disk used in the above embodiment, FIG. 5 is a longitudinal sectional view showing the main part of another embodiment of the small electric motor according to the present invention, and FIG. 6 is a plan view of the encoder disk used in the above embodiment. FIG. 3 is a plan view showing a part of the encoder disk used. 16, 17...oil-impregnated bearing, 18...rotor shaft,
20...Rotor, 20a...Positioning protrusion, 2
0b... recess, 36, 37... oil-impregnated bearing, 38...
...Rotor shaft, 40...Rotor, 42a...Protrusion for positioning, 42b...Recess.

Claims (1)

[Scope of utility model registration request] The rotor shaft is rotatably supported by an oil-impregnated bearing,
A protrusion for positioning the encoder disk is formed on the side surface of the rotor facing the oil-impregnated bearing, and a recess for collecting oil from the oil-impregnated bearing is provided on the rotor shaft side of the positioning protrusion. small electric motor.