JPS5914340A - Motor with encoder - Google Patents

Abstract

PURPOSE:To reduce the number of parts in a motor by directly forming many irregularities on the outer periphery of a rotor yoke having a rotor magnet and magnetically detecting the irregularities, thereby eliminating a rotary plate exclusive for an encoder. CONSTITUTION:A stator yoke 5 having a stator coil, a rotor yoke 9 having a magnet 10 opposed to the coil and a bearing which rotatably supports the yoke 9 are provided, and many irregularities 9' are formed in a gear shape on the outer periphery of the yoke 9. The irregularities 9' formed on the yoke 9 are magnetically detected by a sensor 17. Thus, a rotary plate having the irregularity exclusive for an encoder is not particularly necessarily manufactured, thereby reducing the number of parts.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor equipped with an encoder for detecting rotation angle and speed, and particularly to a motor equipped with a magnetic encoder.

In recent years, there has been a trend toward downsizing of tape recorders and VTRs, and along with this, there has been a desire for smaller and lighter motors.

Conventionally, many motors have been equipped with a frequency generator on their rotating shaft, but these have not been satisfactory in terms of size or weight. Therefore, a method of arranging the encoder in the radial direction of the motor was considered.

In the first method, as shown in FIG. 1, a yoke 5 having a coil 6 and an encoder magnetic sensor 7 is fixed to a ball bearing case provided with a metal 2 and a bearing 4 to form a stator, and an encoder is attached to the outer periphery of the yoke 5. A magnet 10 is provided on a yoke 9 on which a magnet 8, which is the object to be detected, is arranged.
This is a modele with an encoder that is fixed to a post 11 provided with a shaft 1 to form a rotor. In this method, the magnet 8 must be magnetized with multiple poles (720 poles), and in order to be miniaturized, the magnetization pitch must be 0.3
Since the van is very small, the amount of magnetic flux that can be generated is small. Therefore, there is a drawback that the sensor output is distorted due to the influence of leakage magnetic flux of the rotor magnet 10.

The second method is to coat a magnetic material instead of the detection magnet 8 described above, and perform distorted magnetic writing on it using a magnetic head °, thereby making it an encoder. As shown in FIG. 6, since the sensor has a sensitivity that responds at low magnetic flux density, the sensor is affected by leakage magnetic flux, and its output is distorted as shown in FIG. For this reason, even though the analog waveform A of the encoder output has a constant period, when it is digitally converted, the period changes as shown in Figure 7, so it falls within the period shown in Figure 12. A speed control circuit that counts the number of pulses has the disadvantage that it responds as if the speed has changed, causing the moder rotational speed to go out of order.

In Figures 6 and 8, Ef is the encoder output, e
indicates the reference voltage, and D in FIGS. 7 and 9 indicates the encoder waveform after A/D conversion.

The third method is to arrange a light emitting element 15 and a light receiving element 16 via a rotating disk 13 attached to the rotor yoke 9 and a fixed mask 14 attached to the photocoupler side, as shown in FIG. . This method uses light to extract signals, so there is no influence from the rotor magnet. However, since the rotating disk 13 is as thin as about 100 μm, it is easily deformed during operation, and the encoder performance is affected by the disk.
The gap between the masks, the scanning degree of the disc and mask slit, and the presence or absence of warpage of the disc greatly affect the cycle of the encoder output, so it is necessary to increase the accuracy of each individual machine and perform gap adjustment, which makes assembly and adjustment troublesome. There is a drawback. Also, due to the structure, the light emitting element 15 and the light receiving element 1 are arranged in the axial direction.
6, it also has the disadvantage that it is difficult to flatten it.

An object of the present invention is to reduce the number of small, lightweight, nine-part parts and to provide a highly accurate encoder output in a surface-facing flat model in which a model and a magnetic encoder are arranged close to each other.

The present invention integrates the rotor yoke and the rotor, which is the object to be detected, to reduce the size and weight.In addition, in order to obtain a stable sensor output, the magnetic flux density is higher than the leakage magnetic flux density when switching the modele magnet or coil. This method uses a magnetic sensor that responds to the encoder output waveform to prevent distortion of the encoder output waveform.

An embodiment of the present invention will be described below based on the drawings.

In FIG. 3, 10 is a molded magnet, 9 is a rotor yoke, and a large number of concave and convex portions are formed on the outer periphery of the rotor yoke in the shape of a gear. 17 is a magnetic sensor, 18 is a bias magnet for the sensor, 12 is a sensor support base for attaching the sensor to the molded stator, 5 is a molded stator yoke, l
- It is a t-mode stator. The magnetic sensor 17 is
b by vapor deposition and etching, and its resistance -
As shown in FIG. 5, the element can respond to changes in magnetic flux density over a wide range from relatively low magnetic flux density to high magnetic flux density. The modle magnet 10 is adhesively fixed to the rotor yoke 9, and forms a magnetic circuit with the stator yoke 5 along a path of magnet north pole → stator yoke → magnet south pole → rotor yoke → magnet north pole. In order to suppress the leakage magnetic flux of the magnet as much as possible, it is better for the rotor yoke 9 to be spaced apart from the stator yoke 5, and here it is a flat plate from the viewpoint of productivity. Each outer periphery has 720 irregularities. In the case of a 7-trut motor, the leakage magnetic flux density at the uneven portion of the outer periphery is several watts or less,
20-120G at 5-10 mm from the model magnetic circuit
be. In order to suppress this effect, a ferrite sensor magnet 18 is arranged after the magnetic sensor 17 as shown in Fig. 7, and the operating point magnetic flux density of the sensor 17 is raised to around 1200G as shown in Fig. 5. The magnetic flux density change in the sensor section is not easily affected by the leakage magnetic flux of the moder magnet, and as shown in FIGS. 8 and 9, a constant cycle speed signal can be obtained even after A/D conversion.

The magnetic sensor 17 is fixed in advance to the sensor support base 12 by adhesive, and is manually positioned using the model bearing as a reference, and by means such as screw tightening, while ensuring the gap size with the rotor outer circumference. Model assembly is easy.

As explained above, according to the present invention, a large number of irregularities are formed directly on the outer periphery of the rotor yoke having a rotor magnet, and these irregularities are magnetically detected by a sensor. It is not necessary to specially manufacture the motor, the number of parts is reduced, and the axial dimension is significantly shortened compared to the case where the rotary plate is installed on the rotating shaft of the motor. The dimensions of will also become smaller. As a result of these things, small size,
This allows for weight reduction.

Furthermore, by providing the sensor with a bias magnet, distortion of the output waveform is eliminated, thereby making it possible to detect the position and speed of the motor with high accuracy.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram of a magnetic system, Fig. 2 is a structural diagram of an optical system, Fig. 3 is a structural diagram showing an embodiment of the present invention, and Fig. 4 is a magnetic flux density-resistance change rate characteristic diagram of a thin film magnetic sensor. Fig. 5 is a magnetic flux density-resistance change rate characteristic diagram of the nSb magnetic sensor, Figs. 6 and 7 are output diagrams of the thin film magnetic sensor, and Figs. 8 and 9 are output diagrams of the nSb magnetic sensor. Figure 10, 1st
1 is a side and bottom view of the sensor section, and FIG. 12 is a schematic block diagram. 9... Rotor yoke, 10... Rotor magnet,
11\, M change Ihi, 1 et al.

Claims (1)

[Scope of Claims] 1. A stator yoke having a stator coil, a rotor yoke having a magnet facing the stator coil, and a bearing rotatably supporting the rotor yoke, which is integral with the outer periphery of the rotor yoke. 1. A motor with an encoder, characterized in that a large number of concavities and convexities are formed in the shape of a gear, and the concavities and convexities are magnetically detected by the sensor. 2. The motor with an encoder according to claim 1, wherein the sensor is provided on the surface of a bias magnet.