JPH0419984Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a brushless motor with improved rotational accuracy.

[Technical background of the invention]

For example, a brushless motor is generally used as a motor for driving a polygon mirror in a laser printer. In this product, the rotating shaft is supported by an air bearing in order to ensure smooth rotation, and the board that constitutes the rotation control circuit is housed in a shielded case to improve resistance to electrostatic noise. , the circuit board and the motor body are connected by lead wires.

[Problems with background technology]

However, in the above configuration, although smooth rotation is achieved by the air bearing and the rotation accuracy is relatively good, due to the characteristics of the air bearing, the rotating shaft must have a large diameter and a long length to ensure a sufficient circumferential area. Furthermore, due to the structure in which the board is housed in a shield case, the overall size inevitably increases and the manufacturing cost increases.

[Purpose of invention]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a brushless motor that can be made compact as a whole and manufactured at low cost while achieving excellent rotational accuracy.

[Summary of the idea]

The present invention includes a stator that has an armature coil and is mounted on a bearing sleeve protruding from a motor bracket, and a first stator that has a frequency generating coil and a position detection element and is mounted in the motor bracket with the bearing sleeve as a reference. a base plate, a ball bearing provided in the bearing sleeve, a rotor rotatably supported by the ball bearing, and a conductive component that is attached to the outside of the motor bracket via a mounting member and is electrically conductive over almost the entire area on the component mounting surface side. a second substrate on which a layer is formed;
The rotor and the first The circuit board can be arranged in an accurate positional relationship to reduce detection errors caused by the frequency generating coil and position detection element, and the synchronization power of the PLL circuit enables high-precision rotation. Furthermore, the conductive layer of the second board The feature is that it is designed to shield from electrostatic noise.

[Example of idea]

An embodiment of the present invention will be described below with reference to the drawings. 1 is a metal motor bracket in the shape of a cylindrical container, and a cylindrical bearing tube 2 is located in the center of this bracket.
are installed in one piece. Reference numeral 3 designates ball bearings fitted into both upper and lower ends of the bearing tube 2. 4 is a stator, which is formed by winding a plurality of armature coils 6 around the upper outer periphery of a substantially cylindrical bobbin 5.
Reference numeral 7 designates a first substrate, on which a frequency generating coil (not shown) is formed by printed wiring means in an annular region near the outer periphery, and a position of a rotor 10, which will be described later, is detected inside this frequency generating coil. A position detecting element 8 is provided for this purpose. Reference numeral 9 denotes a number of conductive pins projecting downward from the first substrate 7, to which the armature coil 6, frequency generating coil, and position detecting element 8 are connected. and the first
The board 7 has a circular mounting hole 7a on the inner periphery,
By fitting this mounting hole 7a into a predetermined part of the bobbin 5, it is integrated into the stator 4. By fitting this bobbin 5 into the bearing sleeve 2 and screwing it, the bearing sleeve 2 is inserted into the motor bracket 1. It is installed based on the standard. In this state where the first board 7 is attached, the conductive pins 9 pass through the through holes 1a formed at the bottom of the motor bracket 1 and protrude downward. Reference numeral 10 denotes a rotor, in which a rotor yoke 13 is screwed to a boss 12 fitted on the rotating shaft 11, and a field permanent magnet 14 having a substantially cylindrical shape is fixed to the inner circumference of the rotor yoke 13. A ring-shaped permanent magnet 15 for frequency power generation is fixed to the lower peripheral edge of the magnet 13.
In this rotor 10, a rotating shaft 11 is rotatably supported by a ball bearing 3 and rotates around a bearing sleeve 2, and a field permanent magnet 14 is attached to an armature coil 6 of a stator 4 in a radial direction. The permanent magnet 15 for frequency power generation faces the frequency power generation coil of the first substrate 7 with a gap in the axial direction. Reference numeral 16 denotes, for example, three mounting members (only two are shown) protruding from the bottom of the motor bracket 1, which are made of, for example, plastic, and have screw holes (not shown) formed at their lower ends. 17
is located on the outside of motor bracket 1 and screws 18
This is a second board fixed to the mounting member 16 by, for example, a double-sided printed circuit board, and a conductive layer (not shown) is formed by leaving copper foil over almost the entire area on the component mounting side, that is, the top side. A predetermined conductor pattern (none of which is shown) having a ground pattern is formed on the lower surface side by etching the copper foil, and the conductive layer, the ground pattern, and the screw 18 are connected to each other so as to have the same potential. . Reference numeral 19 denotes a receiving terminal fixed to a predetermined portion on the upper surface side of the second board 17, which is connected to the conductive pin 9 protruding from the first board 7 and also connected to the conductor pattern of the second board 17. has been done. Then,
A group of electronic components constituting a rotation control circuit that controls the rotation of the rotor 10 based on the output signals from the position detection element 8 and the frequency power generation coil are arranged on the upper surface of the second substrate 17. The rotation control circuit is specifically as shown in FIG. That is, in this FIG. 3, 20 is a frequency generator composed of the frequency power generation permanent magnet 15 and a frequency power generation coil, and 21 is this frequency power generator 20.
a speed signal amplification circuit for amplifying a speed signal from 2;
2 is a PLL (phase synchronization limited loop) circuit.
The PLL circuit 22 includes a PLL circuit IC 23 (for example, TC9142P manufactured by Tokyo Shibaura Electric Co., Ltd.) and a crystal oscillator 24, and compares the phase of the output signal from the speed signal amplifier circuit 21 with the phase of a built-in reference oscillator. Then, a control signal is output that eliminates the phase difference between them. 25 is a control signal amplification circuit, 26 is a drive circuit, and the drive circuit 26 is equipped with a drive IC 27 (for example, TA7248P manufactured by Tokyo Shibaura Electric Co., Ltd.), and receives the control signal from the PLL circuit 22 via the control signal amplification circuit 21 and The armature coil 6 is controlled to be energized or disconnected based on the position signal of the rotor 10 from the position detection element 8. In addition, 28 is line L ₁
29 is a ground terminal connected to the ground pattern, 30 is a synchronization signal output terminal that outputs a synchronization signal when the rotation speed of the rotor 10 reaches a predetermined value, and 31 is a start signal. This is an input terminal.

According to this embodiment with the above configuration, since the stator 4 is attached to the bearing sleeve 2 that supports the rotor 10, the 6 groups of armature coils are reliably arranged concentrically with the field permanent magnets 14 of the rotor 10. This can reduce uneven rotation of the rotor 10. Also, the first substrate 7 is also aligned with the bearing sleeve 2 as a reference.
Since the position detecting element 8 can be arranged with accurate positional accuracy with respect to the field permanent magnet 14 of the rotor 10, the position of the rotor 8 can be detected with high precision. The frequency power generation coil of the first substrate 7 can be accurately arranged concentrically with respect to the frequency power generation permanent magnet 15, and high precision of the speed signal can be achieved. Furthermore, since the second board 17 on which the rotation control circuit is arranged is configured separately from the first board 7 and attached to the outside of the motor bracket 1, the rotation control circuit can be connected to the position detection element. Unlike the case where the output line of the position detecting element is placed on the same board as the rotor, the output line of the position detecting element does not need to be extended across the magnetic flux linkage area of the permanent magnet for frequency generation of the rotor. It can be extended in the axial direction of the rotor 10 and connected to the rotation control circuit of the second board 17.
Therefore, it is possible to prevent noise from being superimposed on the position detection signal due to the magnetic flux from the frequency power generation permanent magnet 15 interlinking with the output line of the position detection element 8, and to further improve the accuracy of the position detection element. can. Moreover,
In addition to being able to improve the accuracy of the position detection element and the speed signal in this way, since the rotation control circuit is configured with the PLL circuit 22, the synchronization force of the PLL circuit 22 causes the rotation of the rotor 10 to be Rotation stability can be significantly improved, and high-precision rotation can be achieved overall. Since high precision rotation is possible in this manner, sufficient smoothness of rotation can be ensured even if the ball bearing 3 is used as a bearing device for the rotating shaft 11, and in particular, there is no need to use an air bearing. With this, the circumferential area of the rotating shaft, as well as the diameter and length dimensions, can be set small, so that the entire motor can be made smaller and less expensive. Furthermore, since the conductive layer is formed over almost the entire upper surface of the second substrate 17,
Due to the shielding effect of this conductive layer, the electrostatic noise resistance of the rotation control circuit can be improved and a shielding case can be made unnecessary, thereby making it possible to further reduce the overall size and cost. .

In the above embodiment, all the mounting members 16 for mounting the second board 17 to the motor bracket 1 are made of plastic, but at least one of them may be made of a conductive material such as metal. By connecting the conductive layer of the second substrate 17 to the motor bracket 1, the electrostatic noise resistance can be further improved.

[Effect of idea]

As described above, in the present invention, a first board equipped with a frequency generating coil and a position detection element and a stator are mounted on the bearing sleeve of a motor bracket as a reference, and a rotor is attached to a ball bearing provided on the bearing sleeve. In addition, a second board is attached to the outside of the motor bracket on which a conductive layer is formed over almost the entire area of the component mounting surface, and the PLL is mounted on this second board.
As a result of this configuration, it is possible to improve the positional accuracy between the rotor and the armature coil, the frequency power generation coil, and the position detection element, as well as position detection. It is possible to prevent noise from being superimposed on the output signal of the element, improving the detection accuracy of the position detection signal and speed signal, and furthermore, the synchronization power of the PLL circuit can improve speed stability, so high precision rotation is possible. I can tighten it. In addition, since high-precision rotation is possible in this way, there is no need to use air bearings, and since shielding can be achieved by the conductive layer of the second board, a shielding case can be eliminated, resulting in a significant reduction in size overall. It also has excellent practical effects of being able to reduce costs.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, with FIG. 1 being a longitudinal cross-sectional view of the whole, FIG. 2 being a side view of the stator, and FIG. 3 being a circuit diagram of the rotation control circuit. In the figure, 1 is the motor bracket, 2 is the bearing sleeve, and 3 is the motor bracket.
1 is a ball bearing, 4 is a stator, 6 is an armature coil, 7 is a first substrate, 8 is a position detection element, 1
0 is a rotor, 16 is a mounting member, 17 is a second board, and 22 is a PLL circuit.

Claims (1)

[Claims for Utility Model Registration] 1. A stator having an armature coil and mounted on a bearing sleeve protruding from a motor bracket, and a stator having a frequency generating coil and a position detecting element inside the motor bracket with the bearing sleeve as a reference. A mounted first board, a ball bearing provided in the bearing sleeve, a rotor rotatably supported by the ball bearing, and a component mounting surface attached to the outside of the motor bracket via a mounting member. a second substrate on which a conductive layer is formed over substantially the entire area;
A brushless motor comprising: a rotation control circuit configured on the second substrate and having a PLL circuit to control rotation of the rotor based on output signals from the frequency power generation coil and the position detection element. 2. A utility model characterized in that a plurality of mounting members are provided, at least one of which is made of a conductive material, and the motor bracket and the conductive layer of the second board are connected via the conductive material. A brushless motor according to registered claim 1.