JPS58119761A - Rotating phase detector for rotor - Google Patents

Abstract

PURPOSE:To detect an accurate rotating phase by magnetizing a rotor magnet of a brushless motor which rotatably drives a video head or the like by fixing a tucked magnet substantially at the center of the magnetized pole. CONSTITUTION:Video heads 1, 2 are fixed at the prescribed positions under an upper rotary cylinder 3 at an interval of 180 deg.. A brushless motor which rotatably drives the heads 1, 2 is coupled directly to a rotational shaft 5, and consists of a rotor magnet 29, a rotor plate 15, a stator coil 30, a stable yoke 31 and Hall elements 32, 32', 32'' as magnetic detectors. Tucked magnets 36, 37 are fixed to the side face of the magnet 29, thereby detecting the rotating phase positions of the heads 1, 2 together with the elements 32. The magnet 29 before magnetization is mounted on a plate 15 which is attached to the shaft 5, and magnets 36, 37 are fixed at the prescribed positions at an interval of the prescribed angle. The magnets 36, 37 are set substantially to the center of the magnetized poles of the magnet 29, and which is magnetized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotational phase detection device for a rotating body, and more particularly to a rotational phase detection device for a rotating body driven by a brushless motor.

As is well known, a brushless motor detects the magnetic pole position of a rotor magnet divided into multiple poles without contact, and uses the position detection signal to sequentially switch the exciting current to each stator coil to generate rotational force. This motor has the features of a long life and no sliding noise. On the other hand, by comparing the rotational phase of a rotating body driven by a motor with the phase of a reference signal and controlling the rotation of the motor using this phase error signal, servo control can rotate the rotating body at an accurate speed and phase. Used to control rotating objects.

For example, in a video tape recorder (hereinafter abbreviated as VTR), which is a magnetic recording and reproducing device, the rotational phase of the video head is detected in order to rotate the video head at a predetermined speed and match the rotational phase with a reference phase. Furthermore, a brushless motor equipped with a rotor magnet position detection device is used as the cylinder motor that drives the cylinder to which this video head is attached.

When using a brushless motor to drive a rotating body that requires rotational phase detection, as in this VTR cylinder example,
Generally, a rotational phase detection device for the rotating body and a magnetic pole position detection device for the rotor magnet are separately required. This resulted in the following drawbacks.

(1) The device has a large number of parts, its mechanism is complicated, and the number of wiring between the detection device and the circuit board is large, so the cost is high in terms of both parts and assembly man-hours.

(2) The installation of the detection device and the wiring require a considerable amount of space, which increases the size of the device.

Therefore, in order to eliminate these drawbacks, the present inventors first published Japanese Patent Application No. 55-124561 (filed on September 10, 1982) "Rotational Phase Detection Device for Rotating Body" and Japanese Patent Application No. 55-1
24552 (filed on September 10, 1982) In a "cylinder motor," a rotor magnet or a rotor plate to which this rotor magnet is fixed is attached with a small tack magnet for detecting the rotational phase, and the rotor magnet and a nuclear tack magnet are attached. By detecting the superimposed magnetic flux from both with the same magnetic detection element and simultaneously obtaining the rotor magnet position detection signal and rotational phase detection signal, the dedicated tack head for detecting the rotational phase is removed. presented a method to do so. According to this method, the drawbacks of the prior art described above can be overcome. However, a new positioning means is required to determine the mutual positional relationship between the rotor magnet, tack magnet, and rotating body.

The present invention has been made in order to eliminate the inconveniences in the prior art as described above, and therefore, an object of the present invention is to eliminate the need for new positioning means, and to eliminate the need for a rotor magnet, a tack magnet, a rotating body, etc. It is an object of the present invention to provide a rotational phase detection device having a structure that can easily and accurately determine the mutual positional relationship between components, and to achieve miniaturization and low cost.

In order to achieve the above object, the present invention includes a magnetic detection element that detects the magnetic flux of a rotor magnet of a brushless motor that drives a rotating body, and a magnetic detection element that rotates in synchronization with the rotor magnet and that rotates a predetermined number of times during one rotation. , a magnetic flux change applying means for changing the density of the magnetic flux generated by the rotor magnet and detected by the magnetic detection element; and a magnetic flux change applying means for detecting the density of the magnetic flux applied by the magnetic flux change applying means to the magnetic detection element. The signal obtained is used as the rotational phase detection signal of the one rolling element, and the magnetic flux change applying means is fixed to at least one of the rotor magnet and the rotor plate to which the rotor magnet is attached, or In a state in which the fixed positioning means is provided, or in a state in which the rotor plate is further fixed at a predetermined angular position of the rotating shaft of the brushless motor, the fixed position of the magnetic flux change applying means is located approximately in the center of the magnetized pole of the rotor magnet. The rotor magnet is magnetized in such a manner. Further, the rotating body is attached to the rotating shaft by providing positioning means to determine the mutual positional relationship between the rotor magnet, the magnetic flux change applying means, and the rotating body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a rotational phase detection device for a rotating body according to the present invention will be described below with reference to FIG. 1, taking a VTR cylinder as an example. FIG. 1 shows a cylinder assembly driven by a flat brushless motor directly connected to the shaft, and (a) is a block diagram of its oscillation ms and control device;
(b) is a plan view of the stator, and (C) is a plan view of the rotor.

In FIG. 1(a), two video heads 1 and 2 are fixed at predetermined positions below an upper rotary cylinder 3, 180 degrees apart from each other. This upper rotating cylinder 3 has a screw 5
1.52 to the disk 4. This disk 4 is fixed to the rotating shaft 5 by a screw 53. The rotating shaft 5 is rotatably supported by bearings 7 and 8 provided at the upper and lower ends of the central portion of the lower fixed cylinder 6. The magnetic tape 9 travels in a diagonal direction with respect to the rotation axis 5 of the cylinder while contacting both the upper rotation cylinder 3 and the lower fixed cylinder 60 over approximately half a circumference. The upper rotating cylinder 3 is directly driven by a brushless motor directly connected to its rotating shaft 5. As the upper rotating cylinder 3 rotates, the video head 1
and 2 alternately scan diagonally from the lower end of the magnetic tape 9 toward the upper end to record or reproduce video signals. This recording and reproduction is performed via a rotary transformer.

10 and 11 are a rotating coil and a fixed coil of a rotary transformer, respectively. A rotating coil 10 of a rotary transformer fixed to the disk 4 is connected to the video heads 1 and 2. On the other hand, a fixed coil 11 of a rotary transformer fixed to the lower fixed cylinder 6 is connected to a video signal recording circuit 27. This rotary transformer 10.
A video signal is recorded on the magnetic tape 9 by supplying a recording current to the video heads 1 and 2 via the magnetic tape 1. Further, video signals reproduced from the magnetic tape 9 by the video heads 1 and 2 are sent to a video signal reproduction circuit (not shown) via rotary transformers 10 and 11.

When recording and reproducing this video signal, it is necessary to control the rotational phase of the video heads 1 and 2, as is well known. For example, during recording, the rotation speed of the video head 1.2 is made to match the reference speed so that the vertical synchronization signal of the video signal is recorded at a predetermined position of the magnetic deso 9, and
It is necessary to match the rotational phase with the phase of the vertical synchronization signal. For this purpose, a rotational phase detection device is required.

In FIG. 1, a part of the component of a brushless motor that rotationally drives the video heads 1 and 2 is also used as this rotational phase detection device. First, this brushless motor will be explained.

This brushless motor is a flat motor with an axial gap directly connected to a rotating shaft 5, and as shown in FIGS. 1(a) to (C), a rotor magnet 29, a rotor plate 15.
It is composed of a stator coil 30, a stator yoke 31, and Hall elements 32, 32' and 32' as magnetic detection elements. The rotor magnet 29 is a flat permanent magnet that is magnetized into eight equal parts in a fan shape, as shown in FIG. 1(C). This rotor magnet 29 is attached to the rotor plate 15 made of a high magnetic permeability material such as iron. This rotor plate 15 has a structure that also serves as a boss, and is fixed to the rotating shaft 5 with screws 54.

A flat stator coil 30 is arranged opposite the magnetic pole surface of the rotor magnet 29.

This stator coil 30 is a flat stator yoke 31
It is fixed to the lower fixed cylinder 6 via. This stator coil 30 is a three-phase stator coil consisting of six coil blocks as shown in FIG. 1(b),
Each of the two coil blocks located symmetrically with respect to the central axis includes a U-phase coil (30-1) and a ■-phase coil (30-1).
-2), a W-phase coil (30-3).

A substrate 33 is attached to the periphery of the stator coil 300. On this board 33 are stator coils (3
Three Hall elements 32, 32', 32 are placed at predetermined positions corresponding to 0-1) to (30-3), 120 degrees apart from each other.
' has been fixed. These Hall elements 32, 32'
, 32 constitute a position detection device for detecting the magnetic pole position of the rotor magnet 29. The position detection signal is taken out via the wiring pattern of the board 33, amplified by the amplifier 34, and then sent to the energization control signal forming circuit 35.

This energization control signal forming circuit 35 generates 3-phase or 6-phase energization control signals having a predetermined O flow angle. This energization control signal is sent to the drive circuit 26 and
The stator coil 300 is energized via the wiring pattern of the board 33.

In this way, depending on the position of the rotor magnet 29,
The excitation current of the stator coil 30 is sequentially switched, a rotating magnetic field is generated by this excitation, and rotational torque is applied to the rotor magnet 29. As a result, the rotor magnet 29 and the video heads 1 and 2 that are directly connected to the rotor magnet are rotationally driven.

Next, the rotational phase detection device will be explained. In FIG. 1, as shown in FIG. 1(C), the rotor magnet 29
The first tack magnet 36 and the second tack magnet 37 fixed to the side surfaces of the video heads 1 and 2, and the Hall element 32 as a magnetic detection element shown in FIGS. It is used as a detection device.

The first tack magnet 36 is the rotor magnet 29
At the center position of the arc where the polarity between the magnetic poles is N pole,
It is also installed with the N pole facing up. The second tack magnet 37 is attached at the center of the arc of the portion of the rotor magnet 29 where the polarity between the magnetic poles is 8, with the 8 poles facing upward. In other words, these tack magnets are configured to locally produce a strong magnetic field with each polarity at points 36 and 37. Therefore, these tack magnets 36 and 37 function as a magnetic flux changing means that changes the magnetic flux density of the rotor magnet 29 detected by the Hall element 32.

As shown in FIG. 1(C), the first tack magnet 36 and the second cod 9 magnet 37 are attached to the rotor magnet 29 so as to have opposite polarities, and the jgl tack magnet 36 and The positional relationship is determined so that the first video head 1 corresponds to the first video head 1, and the second tack 1 magnet 37 and the second video head 2 correspond to each other. In this way, two tack magnets with different polarities are
By arranging them in correspondence with the respective video heads, it becomes possible to identify the video head scanning the magnetic tape 9.

On the other hand, the Hall element 32 arranged on the stator is connected to the rotor magnet 29, which is necessary for the brushless motor, as described above.
However, by also detecting the magnetic flux of the tack magnets 36 and 37, it can also be used as a tack head for detecting the rotational phase of the video heads 1 and 20.

FIG. 1 (!1) shows the configuration of the cylinder control device during brazing. The Hall element 32 is connected to the rotor magnet 2
9 and tack magnets 36 and 37 are detected. This detection signal is amplified by an amplifier 38, and only the magnetic flux detection signals from the tack magnets 36 and 37 are separated by a comparator 39, resulting in one pair of positive and negative tack pulses per cylinder rotation. This tack pulse is adjusted by the phase adjustment circuit 19 so that the phase relationship between the video heads 1 and 2 is correct for each positive and negative pulse, and then by the pulse forming circuit 20 with a duty ratio of 50%.
After being made into the phase detection signal SW, it is sent to the phase comparison circuit 21.

On the other hand, the vertical synchronizing signal separated from the video signal applied to the input terminal 22 by the vertical synchronizing signal separation circuit 23 is frequency-divided by the frequency dividing circuit 24 into 172 frequencies. Then, the phase adjustment circuit 25 at the next stage outputs a reference signal SP whose phase is adjusted so that the vertical synchronization signal is recorded at a predetermined position on the magnetic tape 9, and this reference signal SP is sent to the phase comparison circuit 21. In the phase comparison circuit 21, the reference signal SP
The phases of the phase detection signal SW and the above-mentioned phase detection signal SW are compared, and the phase error signal thereof is sent to the drive circuit 26, whereby the input power of the motor is changed so that the phase difference between the two is eliminated. With such a phase control system, the rotational phase of the video heads 1 and 2 matches the phase of the reference signal 8P formed from the vertical synchronization signal, and the rotational speed becomes a constant speed determined by the frequency of the reference signal 8P. . As a result, the video signal applied to the input terminal 22 is transferred to the board 28 and the rotary transformer 1 by the video signal recording circuit 27.
0.11 to the video heads 1 and 2, and the video signal is stably recorded on the magnetic tape 9.

Next, the quadruple magnet 29 and the tack magnet) 36.
From the signal detected by the superimposed magnetic flux of 37,
A specific example of a circuit for separating the magnetic flux signals of the tack magnets 36 and 37, that is, tack pulses, and its operation will be described in the second section.
This will be explained using the drawings and FIG.

Figure 2 is iF! FIG. 3 is a block diagram showing in more detail the configuration of the main parts of the rotational phase detection device in A, and FIG. 3 is a timing chart of signals of each part in FIG.

In FIG. 2, 32, 32' and 32' are Hall elements, which constitute a position detection/rotational phase detection device 4o. 41
is a DC power supply for supplying bias current to each Hall element. As described above, each Hall element detects the magnetic flux in which the magnetic flux of the rotor magnet 29 and the magnetic flux of the tack magnets 36 and 37 are superimposed. As shown in Figure 1 (C), attach the tack magnet) 36, 37 to the rotor magnet
By locating the magnetic field in the center of the rotor magnet 29 so that a strong magnetic field is generated with each polarity, the waveform of the output signal of each Hall element is determined by the sine of the rotor magnet 29, for example, as shown in the signal U shown in FIG. 3 (1). The waveform has a waveform in which a positive tack pulse due to the magnetic flux of the tack magnet 36 and a negative tack pulse due to the magnetic flux of the tack magnet 37 are superimposed on the maximum and minimum parts of the wave-like magnetic flux change, respectively.

The output signals of each of these Hall elements are taken out as differential output signals in order to reduce the influence of the offset, and are sent to the next stage amplifier 34, where they are differentially amplified with a sufficiently high gain. Therefore, the amplified signal becomes a signal obtained by amplifying the vicinity of the average value of the output signals of each Hall element, and becomes a correct position detection signal of the rotor magnet 29 that is not affected by the above-mentioned tack signal.

Next, a method of detecting the rotational phase of the video heads 1 and 2 will be explained.

In FIG. 2, the differential output signals of Hall element 32 are sent to amplifier 38 and differentially amplified. If linear amplification is performed at this time, the amplified signal U will have a waveform similar to the original signal as shown in No. 31W(1). This amplified signal U is sent to the comparator (3
9-1) and (39-2). Comparator (39-1
), the reference voltage VRI shown in FIG. 3(1) and the amplified signal U are compared, and the first tack pulse TPI shown in FIG. 3(2) is output during the period when the amplified signal U is greater than VRI. . In addition, the comparator (39-2) compares the reference voltage VR2 and the amplified signal U, and during the period when the amplified signal U is smaller than VB2,
A second tack pulse TP2 shown in FIG. 3(3) is output. With this precision, the signal detected by the magnetic flux of the first tack magnet 36 is separated and becomes the first tack pulse TP1.
Thus, the signal obtained by detecting the magnetic flux of the second tack magnet 37 is separated and becomes the second tack pulse TP2.

This first. The second tack pulses TPI and TP2 are each sent to a phase adjustment circuit (“9”L (192),
The predetermined delay amount Tl5T shown in Fig. 3 (4) * (5)
After being delayed by 2 days, it is sent to the pulse forming circuit 20.

In this pulse forming circuit 20, the signal TPI'.

From TP2', a phase detection signal SW with a duty ratio of 50% shown in FIG. 3 Φ) is formed. In addition, at this time, the first. The delay amount 'r1. Adjust T2. In other words, during the 180 degree period when the phase detection signal SW is at a low level, the first
The second video head 1 scans the magnetic tape 9, and during the next 180 degree period when the phase detection signal SW is at a high level, the phase is adjusted to 5 so that the second video head 2 scans the magnetic tape 9. Thus two tack pulses TPI.

TP2 is a separate phase adjustment circuit (19-1).

(19-2), so the first tack magnet 36 and the @2 tack magnet 37 do not necessarily have to be attached to the rotor magnet 29 at 180 degree intervals, as shown in FIG. 1(C). You may lose at 135 degree intervals like this.

Now, in the above embodiment, in order to perform a predetermined function with the rotational phase detection device consisting of the Hall element 32 and the tack magnets 36 and 37, that is, the function of detecting the phase in which the video heads 1 and 2 scan the magnetic tape 9. To do this, it is necessary to determine the mutual positional relationship of the parts as shown in Figure 4.

FIG. 4 is a relationship explanatory diagram showing, by arrows, components that should have a predetermined positional relationship among the components of the cylinder assembly shown in FIG. 1; The following items are required when positioning these parts.

(1) Immediately after a certain period of time has elapsed after the Hall element 32 as a rotational phase detection element detects the magnetic flux of the tack magnet 36, 37, the video heads 1 and 2 are each positioned a predetermined distance above the lower end of the magnetic tape 9. In order to scan
(ie, the lower fixed cylinder 6 provided with a lead for guiding the running of the magnetic tape 9), determine the mutual positional relationship.

(2) The Hall element 32 also serves as a rotor position detection element of the brushless motor. Therefore, the stator coil 30 should be arranged in a predetermined positional relationship with the Hall element 32. This has already been described using the embodiment shown in FIG.

(3) As described in the embodiment of FIG. 1, in order to reliably separate the tack pulse and the rotor position detection signal from the output signal of the Hall element 32,
6.37, respectively, the N pole of rotor magnet 29 and 8
Place it in the center of the pole opening angle.

(4) Attach the video heads 1, 2 and tack magnets (36, 37) to the rotating shaft 5 in a predetermined angular positional relationship.

Among the above (1) to (4), the present invention particularly focuses on (3) and (
4) provides an effective positioning means. That is, it provides an effective positioning means between the parts enclosed by broken lines in FIG.

The means for doing so will be explained below using the embodiment shown in FIG.

(a) To attach the rotor magnet (29) before magnetization to the rotating shaft 5, attach it to the rotor plate 15 provided with a positioning means, and also attach the rotor magnet (29) to the rotor plate 15 provided with a positioning means.
9) and the rotor plate 15 at a predetermined position separated by a predetermined angle.
), the rotor plate 15, rotor magnet (29), and tack magnet 3 are located near the center of the magnetized pole 5.
6. The rotor assembly consisting of 37 is set in a magnetizing machine (not shown), and the rotor magnet (29) is magnetized.

The rotating shaft 5 is provided with a positioning means such as a notch for fixing the position of the rotor plate 15, and a positioning means such as a notch for fixing the position of the video head 1.2 is provided on the rotary shaft 5. will be established.

In this case, as shown in FIG. Fixed. Therefore, if positioning means is provided to attach the disk 4 to the rotating shaft 5, it is equivalent to providing positioning means for the video heads 1 and 2.

cb> The rotor magnet (29) before magnetization is applied to the rotor plate 15, and a tack magnet screw (36, 37) is attached to at least one of the rotor magnet (29) and the rotor plate 15 at a predetermined position separated by a predetermined angle. When the rotor plate 15 is fixed at a predetermined angular position on the rotating shaft 5, the fixing position of the tack magnets 36 and 37 is approximately at the center of the magnetized pole of the rotor magnet (29). , the rotor assembly consisting of the rotor plate 15, rotor tag net (29), tack magnet screw) 36, 37 is set in a magnetizer (not shown), and the rotor magnet is magnetized. With the rotor plate 15 fixed to the rotating shaft 5, the rotor magnet 29
The difference is that magnetization is performed.

The rotary shaft 5 is provided with positioning means such as a notch for determining the mounting position of the video head 1.2, as in (a) above.

(C) In the same manner as in the above <El) or C), with positioning means for fixing the tack magnet screws) 36 and 37 provided on at least one of the rotor magnet (29) before magnetization and the rotor plate) 15. magnetize the low tag net (29), and then use the fixed positioning means to attach the tack magnet screw (29) to a predetermined location.
．． Fix 37. Other positioning is performed in the same manner as in (a) or Φ).

By using any of the above means (a) to (C), it becomes extremely easy to arrange the tack magnet 36, 37 at the center of the opening angle of the magnetized poles of the rotor magnet 29, and this tack magnet 36. 37 and the video heads 1 and 2 can be set accurately and easily.

In one or more embodiments, a tack magnet 36 is attached to the rotor magnet as a magnetic flux changing means for changing the magnetic flux density generated by the rotor magnet and detected by the magnetic detection element.
．． 37 has been described, the magnetic flux changing means is not limited to this tack magnet. Further, the magnetic detection element is not limited to the Hall element described in the above embodiment.

As described above, according to the present invention, a magnetic flux changing means is provided for changing the magnetic flux density generated by the rotor magnet of the brushless motor and detected by the magnetic detection element for detecting the position of the rotor magnet, and the change in the magnetic flux is detected. By using the detected signal as a rotational phase detection signal of the rotating body driven by the brushless motor, the magnetic detection element can also be used for detecting the rotational phase, and the rotor magnet, the magnetic flux changing means, and the rotating body can be detected. Since it is possible to easily and accurately set the mutual positional relationship, the rotational phase detection device can be simplified and downsized.

Cost reduction is achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, in which (a) is a cross-sectional view and a block diagram of a control device, (a) is a plan view of a stator, and (C) is a plan view of a rotor. , FIG. 2 is a block diagram showing in more detail the configuration of the main parts of the rotational phase detection device in FIG. 1, FIG. 3 is a timing chart of signals of each part in FIG. 2, and FIG. An explanatory diagram showing the positional relationship of the component parts of the cylinder assembly,
It is. Description of symbols 1.2...Video head, 3...Upper rotating cylinder, 4...Disk, 5...Song rotation axis, 15...Song rotor play), 29 ... curved rotor machinette), 32... Hall element, 36, 37...
Four Tack Magnet Agent Patent Attorney Akio Namiki Figure 1 Figure 2 n Figure 3 (6)

Claims (1)

[Scope of Claims] l) A rotor magnet that is divided into multiple poles and magnetized, a stator coil, and a magnetic detection element that detects the magnetic flux generated by the rotor magnet as a signal indicating the relative position of the magnet with respect to the stator coil. , a rotational phase detection device for a rotating body driven by a brushless motor, comprising means for switching energization to a stator coil based on the detected relative position detection signal, the rotating body rotating in synchronization with the rotor magnet; A magnetic flux change applying means for changing the density of the magnetic flux generated by the rotor magnet and detected by the magnetic detection element a predetermined number of times during one rotation; In the rigid plate phase detection device of a positive rotation body, the signal obtained by detection by the magnetic detection element is used as a rotational phase detection signal of the rotor, the rotor magnet before being magnetized is made of a high magnetic permeability material. The magnetic flux is imprinted on the formed rotor plate, and the magnetic flux change applying means is fixed to at least one of the rotor magnet and the rotor plate, or a fixed positioning means for the magnetic flux change applying means is provided. A rotational phase detecting device for a rotating body, characterized in that the rotor magnet O is magnetized so that the fixed position of the change imparting means is located approximately at the center of the magnetized pole of the rotor magnet. 2. In the rotational phase detection device according to claim 1, the rotary shaft of the brushless motor is provided with a positioning means for brazing each of the rotating body and the rotor plate, and a positioning means is provided for mounting the wrinkles. The rotational phase detection device is characterized in that the rotational body and the rotor plate are fixed at a predetermined angular position of the rotational shaft. 3) A rotor magnet divided into multiple poles and magnetized, a stator coil, a magnetic detection element that detects the magnetic flux generated by the rotor magnet as a relative position indication signal with respect to the magnet O stator coil, and the detected relative A rotational phase detection device for a rotating body driven by a brushless motor, which has means for switching energization to a stator coil in response to a target position detection signal, the rotational phase detecting device rotating in synchronization with the rotor magnet, a magnetic flux change applying means that changes the density of magnetic flux generated by the rotor magnet and detected by the magnetic sensing element by the number of times; and a change in the magnetic flux density applied by the magnetic flux change applying means is detected by the magnetic sensing element. In the rotational phase detection device for a rotating body, the signal obtained by the above-mentioned rotor is used as a rotational phase detection signal of the rotating body, in which the rotor magnet before magnetization is attached to a rotor plate made of a high magnetic permeability material, and the The magnetic flux change applying means is fixed to either one of the rotor magnet and the rotor plate, or a fixed positioning means for the magnetic flux change applying means is provided, and the rotor plate is fixed at a predetermined angle of the rotating shaft of the brushless motor. A rotating body characterized in that the rotor magnet is magnetized such that the fixed position of the magnetic flux change imparting means is located approximately at the center of the magnetized pole of the rotor magnet. 4) In the rotational phase detection device according to claim 3, the rotary body is mounted on the rotating shaft of the brushless motor with positioning means; The rotational phase detection device is characterized in that the rotating body is fixed at a predetermined angular position of the rotating shaft after the rotor plate is fixed.