JPH0715336Y2 - Brushless motor - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a brushless motor having a stator and a rotor arranged in a metal bracket, and more particularly to a brushless motor having improved resistance to electrostatic noise.

[Technical background of the invention]

As this type of brushless motor, for example, a polygon mirror driving motor of a laser printer configured as described below has been conventionally provided. That is, a stator, a rotor, a position detection element for detecting the rotational position and rotational speed of the rotor, and a frequency power generation coil are arranged in a metal bracket that is in the shape of a substantially cylindrical container. A drive circuit equipped with an IC and the like is arranged, and this double-sided printed circuit board is fixed to the outer bottom of the bracket with a mounting screw made of metal leaving a gap. Then, the signal ground of the drive circuit is connected to the bracket via a mounting screw in order to improve the nozzle resistance thereof.

[Problems of background technology]

By the way, in this type of motor, for example, it may be desired that the signal ground of the drive circuit and the bracket are in an insulated state in order to perform withstand voltage evaluation. However,
In the above-mentioned conventional configuration, there is a problem that the withstand voltage cannot be evaluated because the signal ground and the bracket are in the conductive state via the mounting screw. However, if the double-sided printed circuit board is simply attached to the bracket via the insulating mounting member, stray capacitance is generated between the conductive pattern of the double-sided printed circuit board and the bracket, and electrostatic noise is received. When the bracket is electrified, a surface current is induced in the conductor pattern, and the magnetic flux resulting from the surface current drives the drive IC.
Cause a malfunction.

[Purpose of device]

Therefore, an object of the present invention is to provide a brushless motor that can make the signal ground of the drive circuit and the bracket in an insulating state without deteriorating the electrostatic noise resistance.

[Outline of device]

According to the present invention, the circuit board on which the drive circuit is arranged is attached to the bracket through an insulating mounting member so that the signal ground of the drive circuit and the bracket are insulated from each other, and the circuit board is driven on the bracket side. Is mounted on the component IC mounting surface and a conductor pattern is provided on at least the part where the package part other than the connection terminals of the driving IC is arranged on the component mounting surface, so that the magnetic flux resulting from the current generated when the bracket is charged is for driving.
Do not interlink with the IC as much as possible, and further, by providing a solder plating layer on the signal ground provided on the surface opposite to the component mounting surface of the board to reduce the impedance, the signal ground caused by noise It is characterized in that it tries to suppress potential fluctuations in the field as much as possible.

[Example of device]

An embodiment in which the present invention is applied to a polygon mirror driving motor of a laser printer will be described with reference to the drawings. Reference numeral 1 denotes a metal bracket having a substantially cylindrical container shape, and a bearing cylinder 3 for internally mounting a bearing 2 is provided upright at the center of the inner bottom portion of the metal bracket. Reference numeral 4 denotes a stator, which is formed by winding a plurality of armature coils 6 around a bobbin 5, and the bobbin 5 is fitted into the bearing cylinder 3 and fixed to the bracket 1. Reference numeral 7 denotes a rotor. The rotor yoke 10 is screwed to a boss 9 fitted to the rotary shaft 8, and a substantially cylindrical permanent magnet 11 for magnetic field is fixed to the inner peripheral portion of the rotor yoke 10. An annular permanent magnet 12 for frequency power generation is fixed to the peripheral edge of the lower end of 10. The rotary shaft 8 of the rotor 7 is rotatably supported by the bearing 2, and the field permanent magnet 11 faces the armature coil 6 of the stator 4. Reference numeral 13 is a pressurizing boss attached to the lower end of the rotary shaft 8. Reference numeral 14 denotes a first substrate, which is attached to the lower end portion of the bobbin 5 below the rotor 7 with a predetermined gap in a fitted state. A frequency power generation coil (not shown) is formed by a printed wiring means in an annular region facing to. With the rotation of the rotor 7, magnetic flux from the frequency generating permanent magnet 12 is linked to the frequency generating coil to induce a speed detection signal having a frequency corresponding to the rotation speed of the rotor 7. Reference numeral 15 is a position detection element disposed on the first substrate 14, which is located on the inner peripheral side of the frequency power generation coil and is fixed via a mounting seat 16 to generate a position detection signal corresponding to the rotational position of the rotor 7. Output. Reference numeral 17 denotes a large number of conductive pins, which are provided on the first substrate 14 so as to extend in the axial direction of the rotor 7 and project downward, penetrate through the elongated holes 1a formed in the bottom portion of the bracket 1 and project below the bracket 1. ing. The position detecting element 15 disposed on the first substrate 14, the frequency generating coil, and each armature coil 6 of the stator 4 are connected to the conductive pin 17. Reference numeral 18 denotes, for example, three mounting members which are provided on the outer bottom portion of the bracket 1 so as to project downward by adhesion or the like, and are made of insulating plastic. Now, 19 is the second corresponding to the substrate
Board, which is made of double-sided printed circuit board,
It is screwed to the lower end of the mounting member 18 and attached in an insulated state to the bracket 1 with a gap left. On the surface (upper surface) of the second substrate 19 on the bracket 1 side, a large number of electronic components constituting a drive circuit are arranged, and the specific arrangement state thereof is as shown in FIG. In FIG. 2, 20 is a receiving terminal connected to the conductive pin 17 of the first substrate 14, 21 is a crystal oscillator, and 22 is an IC for phase synchronization control loop.
(For example, TC9142P made by Toshiba Corporation), and 23 is for driving I
C (for example, TA7248P manufactured by Toshiba Corporation). Second substrate
Reference numeral 19 denotes a double-sided printed circuit board, on which the printed wiring means 19a and 19b (only shown in FIG. 3) are formed. As a countermeasure against electrostatic noise, the conductor pattern is not formed except the conductor pattern of the wiring for the connection terminal. Reference numeral 24 is a solder resist covering predetermined portions on both surfaces of the second substrate 19. This is a signal ground 23a of the driving IC 23 among the conductor patterns provided on the surface (lower surface) opposite to the component mounting surface. It is provided so that it is not covered. Then, a solder plating layer 25 is provided on the signal ground 23a left from the coating of the solder resist 24.

Next, the electrical configuration of the drive circuit will be described with reference to FIG.
The position detection signal of the rotor 7 obtained by the position detection element 15 is input to the driving IC 23, whereby the armature coils 6 of the stator 4 are sequentially energized. On the other hand, the speed detection signal from the frequency generator 26 including the frequency generating coil and the frequency generating permanent magnet 12 is amplified by the amplifier circuit 27 and input to the phase synchronization control loop circuit 28. The phase synchronization control loop circuit 28 is an IC for the phase synchronization control loop.
22 and a crystal oscillator 21 for oscillating a reference frequency, and outputs a control signal for comparing the speed detection signal and the reference frequency to reduce the frequency difference and the phase difference. This control signal is amplified by the amplifier 29 and input to the driving IC 23, so that the rotation speed and the rotation phase of the rotor 7 are controlled.

The motor configured as described above is used by being attached to the metal frame of a laser printer. Generally, however, prior to installation in a laser printer, the following withstand voltage evaluation and electrostatic resistance are performed. Noise evaluation is performed. That is, as shown in FIG. 5, a metal frame
The bracket 1 of the motor is fixed to 30, and the signal ground of the second substrate 19 and the frame 30 are grounded. Then, as a withstand voltage evaluation, for example, a voltage of 600 V or more is applied between the frame 30 and the signal ground, and as an electrostatic noise resistance evaluation, between the discharge probe 31 and the frame 30 opposed to the frame 30. For example, a voltage of 15 KV or more is applied to discharge.

In this embodiment, the second board 19 is insulated from the bracket 1, so that the withstand voltage evaluation can be performed without any problem. On the other hand, in the electrostatic noise resistance evaluation, when the discharge probe 31 is discharged, the frame 30 and the bracket 1 are charged. The signal ground of the second board 19 is insulated from the bracket 1, and stray capacitance is generated between the bracket 1 and the conductor pattern 19a of the second board 19. A noise current is generated in the conductor pattern 19a due to the charging. However, in the present embodiment, since the conductor pattern is not formed in the portion where the package portion other than the connection terminals of the drive IC 23 on the component mounting surface side of the substrate 19 is formed, even if a noise current flows in the conductor pattern, the drive IC 23 Since the surface current is not generated in the part, it is possible to suppress the magnetic flux from interlinking with the driving IC23 as much as possible, and thus the driving IC23
It is possible to surely prevent the erroneous operation of and to improve the electrostatic noise resistance. Further, since the solder plating layer 25 is provided on the signal ground 23a of the driving IC 23 in the conductor pattern 19b on the lower surface of the second substrate 19 to reduce the impedance, noise on the signal ground 23a is generated. Even if a current flows, the potential fluctuation in the signal ground 23a can be minimized, and the noise resistance can be further improved.

In the above embodiment, the present invention is applied to the polygon mirror driving motor of the laser printer, but the present invention is not limited to this, and can be widely applied to brushless motors in general.

[Effect of device]

As described above, the present invention has a structure in which the board on which the drive circuit is arranged is attached to the bracket through the insulating mounting member, and the signal ground of the board and the bracket are securely insulated to prevent electrostatic discharge. As a measure against noise, a conductor pattern is provided on at least the part of the board on the bracket side other than the part where the package part other than the connection terminals of the driving IC is arranged, and the signal ground provided on the opposite side is solder-plated. Since the layers are provided, even if the stray capacitance is generated between the bracket and the conductor pattern due to the insulating state as described above, the magnetic flux may be linked to the driving IC due to electrostatic noise. It is possible to prevent the potential fluctuation of the signal ground from occurring as much as possible, and thus it is possible to improve the electrostatic noise resistance, which is an excellent effect.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is an overall vertical sectional view, FIG. 2 is a plan view of a second substrate, FIG. 3 is an enlarged sectional view of the same, and FIG. The block diagram and FIG. 5 are side views showing connection states in withstand voltage evaluation and electrostatic noise resistance evaluation. In the drawings, 1 is a bracket, 4 is a stator, 7 is a rotor,
18 is a mounting member, 19 is a second substrate (substrate), and 23 is a drive I
C and 23a are signal grounds, and 25 is a solder plating layer.

Claims (1)

[Scope of utility model registration request] 1. A structure in which a rotor and a stator are arranged in a metal bracket, and a substrate on which a drive circuit including a driving IC and the like is arranged is attached to the bracket with a gap left therebetween. As a measure against electrostatic noise, a conductor pattern is provided on a part mounting surface on the bracket side of the substrate on which the driving IC and the like are mounted, except for a portion on which a package portion other than connection terminals of the driving IC is arranged. In addition, a solder plating layer is provided on the signal ground of the conductor pattern of the driving IC provided on the surface of the board opposite to the component mounting surface, and the board is insulated from the bracket through an insulating mounting member. A brushless motor characterized by being attached in a state.