JPS6082056A - Outer rotor type brushless motor - Google Patents

Abstract

PURPOSE:To enable to accurately control the speed of an outer rotor type brushless motor by mounting a sensor magnet in a rotor yoke to interrupt the magnetic field of a rotor magnet. CONSTITUTION:The magnetic field of a rotor magnet 49 and stator core 38 and coil 29 side is interrupted by an FG signal pattern 40b, and Hall elements 58a, 58b, 58c side are interrupted by a magnetic spacer 50 and a magnetic shielding member 41. Thus, the noise of a leakage magnetic flux produced when switching while flowing a large current to the coil 39 is not detected by an FG signal circuit pattern 40b and Hall elements 58a, 58b, 58c. Thus, accurate speed and position measurements can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the configuration of an outer rotor type brushless motor that rotates at relatively low speed and with high precision.

For example, a high degree of accuracy is required for the rotational drive of the rotating polygon mirror of a laser beam printer used for computer output, and of the rotational drive of the memory disk of computer peripheral equipment. In order to obtain such high precision rotation,
Brushless morphs are generally used because of their superior controllability.

FIG. 1 shows an example of a brushless morph. This morph is an inner rotor motor suitable for high-speed rotation, and uses hydrodynamic bearings to achieve high-precision rotation.

In the same figure, 1 is the casing, 2 is the end bracket, and 1 is the casing.
It is fastened with screw 3. 5 is a fixed shaft, the lower part of which is screwed into the end bracket 2 and fixed thereto. 7 is a stator core, which is fixed to the housing 1 with screws 8. A stator coil 9 is wound around the stator core 7. 10 is a pair of Hall IC elements for position detection, and 11 is a single Hall IC element for speed detection. Above casing l/bracket 2
A stator is formed by 11@5, core 7, coil 9, element lO, 11, etc. 12 is the coil 9 and the element lOφ1
1 is a conductive wire from the circuit board 14, and 13 is a protective cover.

1 and 1 and 01 and 1 and 2 and 3 and 3 and 3 and 4 and 5 and 5 and 5 are fitted with a small gap, respectively. 17 is a rotor magnet attached to the outer periphery of the hollow rotating shaft 15, and 18 is a balance ring also attached to the outer periphery of the shaft 15. A thrust stopper 20 made of resin or the like is fitted into the hollow upper part of the hollow rotating shaft 15. Above axis 1, 5・
The rotor (
rotor) is formed. 22 is, for example, a polygon mirror (
It is a rotating polygon mirror) and serves as a driven rotating body, and is fixed to the upper part of the hollow rotating shaft 15 with a screw 23.

The dynamic pressure bearing is made as follows. As the rotor rotates, outside air flows in from the gap INi below the hollow rotating shaft 15, and the herringbone grooves 5A, spiral grooves 5C, and herringbone grooves 5B provided on the fixed shaft 5
It flows in this order and is discharged from the small hole 20a of the thrust stopper 20. At this time, the fluid dynamic pressure in the herringbone grooves 5A and 5B increases. When the hollow rotary shaft 15 is at that position, the bearing becomes a surface, and a journal bearing is formed. Further, the fluid dynamic pressure on the lower spherical surface 20b side (fixed shaft 5 side) of the thrust stop 20 becomes higher than the fluid dynamic pressure on the outer surface, the spherical surface 20b becomes a bearing surface, the rotor floats, and a thrust bearing is performed.

Speed control is performed by detecting the R1 magnet 17 with the pole element 11 and measuring the rotational speed of R1.

Although such an inner rotor type brushless motor has a relatively simple structure, it must rotate at a considerably high speed in order to exhibit sufficient performance. This is perfect for rotating the previous example's rotating polygon mirror at a high speed of 211 (00r, p, m).Recently, memory disks and polygon mirrors have been rotated at relatively low speeds of 360 or, p, +o.

There are many devices that rotate to a certain degree. However, at this level of rotation speed, air dynamic pressure bearings cannot be used due to insufficient viscosity of the fluid. Moreover, if it is an inner mitter type, there is little inertia rotation, so it does not rotate stably.

In particular, when 'FL11t' flowing through the stator coil 39 is large, leakage magnetic flux becomes large due to sudden current changes during switching. The leakage magnetic flux causes the Hall element 1°φ11 to malfunction, making it impossible to accurately control the speed during position detection.

The present invention was made in view of these facts, and it is an object of the present invention to provide a motor that is suitable for relatively low-speed rotation, allows accurate speed control, and rotates with high mechanical precision.

To achieve this object, the present invention includes a rotor yoke attached to a rotating shaft, a rotor magnet attached to an inner diameter portion of the rotor yoke, and a rotor magnet attached to the inner diameter portion while blocking the magnetic field of the rotor magnet. The present invention is an outer rotor type brushless motor including a sensor magnet and a magnetically sensitive member attached to a stator opposite to the sensor magnet.

Embodiments of the present invention will be described in detail below to clarify the above configuration.

FIG. 2 is a sectional view of an embodiment of an outer rotor type three-phase eight-type brushless motor to which the present invention is applied.

In the figure, 31 is a housing, and 32 is an end plastic fixed shaft whose lower part is screwed into an end bracket 32 and fixed thereto. 36 is an inner housing arranged concentrically with the body 31 and fixed thereto. A core sleeve 37 is fixed to the housing 36. 38 is a stator core, and 39 is a stator coil that is wound around the stator core 38. The stator coil 39 has three phases. 40 is a printed circuit board attached to the housing 36. Reference numeral 41 designates a magnetic shielding member which is also inserted into the housing 36.

The stator is formed by the above-mentioned casing 31, brushket 32, shaft 35, housing 364, sleeve 37, core 3811, coil 39@board 40, etc. 42 is a conducting wire leading to the coil 39 and the printed circuit board 40.

Reference numeral 43 denotes a hollow rotary shaft, the inner diameter of which is finished smoothly and accurately, and is fitted onto the fixed shaft 35 with a small gap. 45 is a rotor yoke, which is concentrically attached to the flange portion 46 of the hollow rotating shaft 43 with screws 47. 49 is a rotor yoke 45. 50 is a magnetic spacer,
Similarly, it is attached to the inner circumference of the yoke 45 in parallel with the rotor magnet 49, and the magnetic spacer 50 and the magnetic shield member 41 are placed in opposing positions to form a magnetic path. 51 is a sensor magnet, and a spacer 50 is also provided on the inner circumference of the yoke 45.
The rotor magnet 49 is arranged at a position parallel to the rotor magnet 49 on both sides of the rotor magnet 49. The magnetic field on the rotor magnet 49 and stator core 3811 coil 39 side and the magnetic field on the sensor magnet 51 side are blocked by the magnetic spacer 50 and the magnetic shield member 41. A thrust stopper 53 is fitted into the hollow upper part of the hollow rotating shaft 43. The above shaft 43・
A rotor is formed by the yoke 45, the magnet 49, the spacer 50e, the magnet 51, and the retainer 53. Reference numeral 55 is a memory disk, for example, which serves as a driven rotating body, and is fixed to the upper part of the hollow rotating shaft 43 with a nut 56.

The radial dynamic pressure bearing is constructed as follows. Hering pawn grooves 35A and 35B are provided at the upper and lower parts of the outer circumference of the fixed shaft 35, respectively. The groove direction of the herringbone grooves 35A-35B is the rotation direction of the hollow rotating shaft 43 (
The arrows at the top of the drawing) are as shown in the figure. Grooves 35a1 in the rotational direction are provided on both sides of the herringbone groove 35A.
and 35a2 are provided. Grooves 35b1 and 35b2 in the rotational direction are also provided on both sides of the herringbone groove 35B, respectively. Valley groove 35Aφ35B・35a1・35a2
・35bl a35b2 and fixed shaft 35 and hollow rotating shaft 4
Grease, which is a lubricant dynamic pressure fluid, is filled into the gap with the inner space of No. 3.

The fixed shaft 35 side of the rotor thrust stop 53 is provided with a plurality of spiral grooves 53a extending from the outer periphery toward the center, as shown in FIG. 3 (viewed along line A-A in FIG. 2).

The spiral direction of the spiral groove 53a is as shown in the figure with respect to the rotational direction (arrow direction) of the rotor. Further, a small hole 53b is provided in the center of the thrust stop 53.

After the spiral groove 53a and the small hole 53b are filled with grease, the M54 is fitted into the hollow upper end of the hollow rotating shaft 43. The spiral groove 53a side of the thrust stop 53 is fixed @h35
It is placed on the upper flat surface of the shaft to form a thrust bearing.

Three Hall elements 58a, 58b, and 58C are attached to the upper surface of the printed circuit board 40 (on the sensor magnet 51 side). The rotational position of the rotor is detected by the sensor magnet 51 and Hall elements 58a, 58b-58C which are magnetically sensitive bodies. As shown in FIG. 4(a), the lower surface of the printed circuit board 40 is provided with a circuit from the input/output terminal pins of the Hall elements 58a, 58b, and 58c to the terminal 40a connected to external wiring. Apart from this, sensor magnet... ) 5
A circuit pattern (FG signal circuit pattern) 40b in the radial direction that oscillates a frequency by electromagnetic induction with 1 is provided with eight poles. The respective poles are connected to each other by a circuit turn, and are further connected to an external wiring connection terminal 40a. This FG signal circuit pattern 40b acts as a magnetically sensitive body,
This is for measuring the speed of the rotor.

A back yoke 60 having a shape shown in FIG. 2B is attached to the lower surface of the printed circuit board 40. 8i ++t+r=
rw+=+lu, Jx-1AALIw jar 4r,'--J
-2, there is a Ut non-m protrusion 60a, FG at that position
Boost signal output.

In such a motor, when current is applied to the stator coil 39, torque is generated between the stator coil 39 and the rotor magnet 49, and the rotor starts rotating. At this time, the rotor thrust stopper 5
3 is supported by a fixed shaft 35 through a coat of grease.

As the rotation speed increases, the grease gathers in the center of the bearing along the spiral groove 53a, and the fluid pressure increases.
The thrust stop 53 is pushed up and the rotor floats up.

As a result, the thrust stopper 53 or the bearing becomes a surface and serves as a thrust bearing. On the other hand, the grease filled in the gap between the fixed shaft 35 and the inner space of the hollow rotary shaft 43 flows in the direction of the apex of the herringbone grooves due to the pumping action of the herringbone grooves 53A and 53B, causing the rotation of that part. The pressure rises. As a result, the inner part of the hollow rotary shaft 43 becomes a journal and is radially supported in an aligned manner.

In the motor of the present invention, the magnetic field on the rotor magnet 49 and stator core 38 cloudy coil 39 side is applied to the FG signal circuit pattern 40b and the Hall elements 58a, 58b, 58c (
The magnetic spacer 50 and the magnetic shield member 41 block the sensor magnet 51 side). Therefore, leakage magnetic flux noise that occurs when switching is performed while flowing a large current through the coil 39 is not detected by the FG signal circuit pattern 40b and the Hall elements 58a, 58b, and 58C. Therefore, extremely accurate speed measurement and positioning can be achieved. Measurement will be possible. In particular, the FG signal circuit 40b for speed control is a pattern circuit that can be accurately placed on the board 40, so it is accurate from this point of view as well.

Furthermore, since it is an outer rotor type, the inertia rotation is large to some extent, and from this point of view, it is possible to improve accuracy with relatively low speed rotation.

Since the dynamic pressure bearing is a high viscosity dynamic pressure bearing in which the dynamic pressure fluid is grease, accurate rotation can be obtained at a relatively low rotation speed of 3800 r, P-1. Both thrust and radial bearings have excellent durability because only fluid comes into contact with their surfaces, and they do not make abnormal noises.

As described above, the outer rotor type brushless motor of the present invention can achieve highly accurate rotation with a simple configuration when rotating at a relatively low speed.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional inner rotor motor, Fig. 2 is a sectional view of an embodiment of an outer rotor type brushless motor to which the present invention is applied, Fig. 3 is a front view of an embodiment of a thrust stopper, and Fig. 4 is a sectional view of an embodiment of an outer rotor type brushless motor to which the present invention is applied. FIG. 3 is a front view of an embodiment of a printed board and a pack yoke. 35 is a fixed shaft, 38 is a stator core, 39 is a stator coil, 40 is a printed circuit board, 41 is a shield member, 43
50 is a hollow rotating shaft, 50 is a spacer, 51 is a sensor magnet, and 40b, 58a and 58b11580 are magnetically sensitive bodies. Patent applicant Canon Co., Ltd. Canon Seiki Co., Ltd.

Claims (1)

[Claims] (1) A rotor yoke attached to a rotating shaft, a rotor magnet attached to the inner diameter of the rotor yoke, a sensor magnet attached to the inner diameter so as to block the magnetic field of the rotor magnet, and the sensor magnet An outer rotor type brushless motor is equipped with a magnetically sensitive body attached to the stator and facing the stator.