JPH04165976A - Motor driver - Google Patents

Abstract

PURPOSE:To suppress heat loss of a semiconductor switching element, to realize miniaturization and to suppress electromagnetic noise at the start by a constitution wherein a voltage modifying means modifies the supply voltage to a driving circuit such that the semiconductor switching element does not enter into an activated region at the start of a motor. CONSTITUTION:At the start of a brushless motor 1, a microcomputor 18 detects collector-emitter voltages of power transistors 12, 13, 14 at the input ports I3, I4, I5 thereof. When thus detected voltages exceed an upper limit, for example, output of a base signal from an output port Q7 is interrupted and a transistor 25 in a voltage modifying circuit 24 is turned OFF thus connecting a resistor 27 between the positive terminal of a DC power supply 17 and the DC input terminal 15P of a driving circuit 8. DC supply voltage to the driving circuit 8 is lowered by an amount being born by the resistor 27 and starting current of a brushless motor 1 is suppressed thus lowering the collector-emitter voltages of the power transistors 12-14.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention provides a motor in which the conduction and disconnection of multiple phases of motor coils are controlled by a drive circuit composed of a large number of semiconductor switching elements. The present invention relates to a drive device.

(Prior Art) A laser beam printer rotates a polygon mirror using a motor, for example, a brushless morph, and reflects laser light from a semiconductor laser that flashes in accordance with a printing pattern onto a photosensitive drum. Since it is only necessary to scan the laser beam using a polygon mirror, there is no mechanical scanning part, and high-speed printing is possible. Therefore, the brushless morph that rotates the polygon mirror is 6oo.

A high speed of r, p, m to 1200 Or, I), m and a speed fluctuation rate (jitter) of about 0.04% are required.

In the brushless morph drive device, for example, six power transistors, which are semiconductor switching elements, are connected in a three-phase bridge to form a drive circuit, and the DC input terminal of this drive circuit is connected to a DC power source. The AC output terminal of the rotor is connected to a three-phase motor coil, and the six power transistors are sequentially turned on and off to control the power supply and disconnection of the three-phase motor coil to rotate the rotor.

(Problems to be Solved by the Invention) ``As mentioned above, the brushless motor for driving a polygon mirror rotates at high speed, so compared to, for example, a motor for driving a floppy disk, it cannot rotate at a constant high speed. The startup time to reach this point is extremely long, several times as long. Power transistors in drive circuits are normally used in the saturation region, but
When a large starting current flows over a long period of time as in the past, the power transistor turns on in the active region, resulting in large heat loss and the need for large heat dissipation fins, resulting in a larger overall size. There is a problem.

In addition, as mentioned above, when the power transistor turns on in the activation region, the switching operation of the power transistor becomes incomplete and the rotating magnetic field generated by the motor coil is disturbed, which causes electromagnetic noise at startup. There's a problem.

The present invention has been made in view of the above circumstances, and its purpose is to suppress the heat loss of the semiconductor switching element of the drive circuit due to the starting current, to achieve miniaturization, and to prevent the generation of electromagnetic noise at the time of starting. It is possible to supply motor drive devices that can be used.

[Structure of the Invention] (Means for Solving the Problems) A motor drive device of the present invention includes a drive circuit constituted by a large number of semiconductor switching elements, and a drive circuit connected between the drive circuit and a DC power source. A voltage changing means is provided for changing the supply voltage to the drive circuit, and by turning on and off a semiconductor switching element of the drive circuit, the motor coils of multiple phases of the motor are energized and disconnected, and when the motor is started, the voltage changing means is controlled. The present invention is characterized in that a control means is provided for changing the voltage supplied to the drive circuit so as to prevent the semiconductor switching element from entering an activated region.

(Function) According to the motor drive device of the present invention, at the time of starting the motor, the voltage supplied to the drive circuit is changed by the voltage changing means so that the semiconductor switching element does not enter the activation region, so that the starting current The heat loss caused by the semiconductor switching element is reduced, and the switching operation of the semiconductor switching element is completed at the time of startup, and the rotating magnetic field generated by the motor coil is stabilized.

(Example) Hereinafter, a first example of the present invention will be described with reference to FIGS. 1 to 4.

First, the schematic configuration of the laser beam printer will be described with reference to FIG. Reference numeral 1 denotes a motor, for example, a brushless motor, and the center portion of a hexagonal polygon mirror 3 is fixed to the shaft 2 of the motor. 4 is a semiconductor laser, which is controlled to blink at high speed according to the printed pattern by a laser drive circuit (not shown), and the laser beam 4a is irradiated onto the polygon mirror 3 through a cylindrical lens 5. It has become. The laser beam 4a reflected by the polygon mirror 3 is irradiated onto the photosensitive drum 7 via the f-θ lens 6.

Now, according to FIG. 1, the configuration of the drive device will be described. Reference numeral 8 denotes a drive circuit, which is constructed by connecting a large number, for example, six NPN type power transistors 9 to 14, which are conductive switching elements, in a three-phase bridge, and its DC input terminals r15P and 15N are connected to one side as described later. The AC output terminals 16A,
16B and 16C are the stator parts of the brushless motor 1.
ji number 1, three-phase motor coils IA, 1B and I
Each terminal is connected to one terminal of C. The other terminals of the motor coils 1A, IB, and 1C are commonly connected, and the three-phase motor coils IA, IB, and ]C are star-connected.

Reference numeral 18 denotes a macrocomputer terminal serving as a control means connected between the positive and negative terminals of the DC power supply 7, which has input ports 1 to I and output ports Q to Q7, of which Six output ports Q to Q6 are connected to the bases of the power transistors 9 to 14, respectively. Reference numeral 19 denotes a rotation detector, which outputs a pulse signal according to the rotation speed from an output terminal by detecting changes in the magnetism of a permanent magnet that rotates together with the rotor of the brushless motor 1. The output terminal is connected to the negative (-) input terminal of the subtraction circuit 20, and the other output terminal is connected to the input port I2 of the microcomputer 18. 21 is a clock pulse generation circuit;
This output terminal outputs a clock signal corresponding to the set rotational speed, and the output terminal is connected to the positive (+) input terminal of the subtraction circuit 20. The subtraction circuit 20 subtracts the pulse signal applied to the negative (-) input terminal from the clock signal applied to the positive (+) input terminal, and outputs the deviation signal from the output terminal.
Its output terminal is connected to the input port (1) of the microcomputer 18 via the amplifier circuit 22.

Therefore, in the same Figure 1, 23A, 23B and 23C
are three capacitors corresponding to three-phase motor coils IA, IB, and 1C, respectively, and these have a capacitance of, for example, 10 μF, and one terminal of each is connected to AC output terminals 16A, 16B, and 16C. , each terminal h' is a DC input terminal 1.5N, that is, a power transistor 2
to 14 emitters. Input ports I, , I4 and I5 of the microcomputer 18
are connected to the collectors of power transistors 12, 13 and 14, respectively.

Now, the voltage changing circuit 24 will be described. Reference numeral 25 denotes an NPN type transistor as a switching element, whose collector is connected to the positive terminal of the DC power supply 17, its emitter is connected to the DC input terminal 15P, and its base is connected to the output port Q7 of the microcomputer 18. A diode 26 is connected between the collector and emitter of this transistor 25, and a resistor 27 is connected in parallel to this diode 26.

Next, the operation of this embodiment will be explained with reference to FIGS. 2 and 3.

First, the normal operation of the brushless motor 1 will be described.

The microcomputer 18 is configured to sequentially output high-level base signals B1 to B6 from output ports Q1 to Q6 as shown in FIG. 2, and these are applied to the bases of power transistors 9 to 14, respectively. The power transistors 9 to 4 are controlled to be turned on or off in the saturation region. By turning on and off the power transistors 9 to 14, the motor coils IA to I
C is controlled to be energized and de-energized, and therefore motor coils lA15 to I
C generates a rotating magnetic field to rotate the rotor.

For example, consider the motor coil IA. First, the microcomputer 18 outputs the base signals B1 and B5 from the output ports Q and Q as shown in FIGS. 2(a) and (e), so that the power transistors 9 and 13 are turned on, and the DC power 17. Transistor 25. Power transistor9. motor coil IA,
The motor coil 1A is energized through the path of the motor coil IB, the power transistor] 3, and the DC power supply 17. Thereafter, the base signal B5 is no longer output from the output port Q of the microcomputer 18, the power transistor 13 is turned off, and instead, the base signal B5 is output from the output port IQ6 as shown in FIG.
As shown by , the base signal B is output and the power transistor 14 is turned on. Therefore, this time, the DC power supply
17. Transistor 25. Power transistor9. The motor coil IA is energized through a path including the motor coil IA, the motor coil IC, the power transistor 14, and the DC power supply 17. As is clear from FIG. 2, the same applies to the other motor coils 1B and ICs, and the motor coil IA
The IC generates a rotating magnetic field by energizing two phases simultaneously. Then, when the deviation signal is given to the input port 11, the microcomputer 18 calculates the width of the base signal such that the deviation signal becomes zero based on the deviation signal, and generates the base signals B1 to B6 based on the calculation result. is output from the output ports Q1 to Q6, thereby performing feedback control so that the rotation of the brushless motor 1, that is, the rotation of the rotor, reaches a set rotation speed.

Incidentally, when switching the energization of the motor coils IA to IC, an induced voltage as a switching surge is generated in these coils, and this is absorbed by the capacitors IA to IC.

For example, consider the motor coil IA. When the base signal B1 is no longer output from the output port Q of the microcomputer 18 and the power transistor 9 is turned off, the signal is instead output from the output port Q2 as shown in FIG.
As shown in b), the base signal B2 is output and the power transistor 10 is turned on. When the power transistor 9 is turned off and the forward current supply to the motor coil IA is cut off, an induced voltage is generated in the motor coil IA in the direction opposite to the power supply voltage. As a result, the motor coil I
A, capacitor 23A, DC power supply 17° transistor 2
5. Power transistor 10. A charging circuit for the capacitor 23A is formed in the path of the motor coil IB and the motor coil IA, and thereby the switching surge, that is, the induced voltage of the motor coil 1A is absorbed. Thereafter, the microcomputer 18 outputs the base signal B4 from the output port Q4 as shown in FIG. As a result, the 2.3 A charge in the capacitor is discharged. The above describes the absorption and discharge of switching surges by capacitor 23A of motor coil IA, but switching surges of other motor coils IB and ICs are similarly absorbed by capacitors 23B and 23C. And capacitors 23B and 23
The charge of C is discharged through power transistors 13 and 14.

Now, the operation of the brushless motor 1 at startup will be described.

When the microcomputer 18 is started, it outputs a high level base signal B7 from the output port Q7 as shown in FIG. As a result, the transistor 25 of the voltage change path 24 is turned on, and the entire voltage of the DC power supply 17 is applied to the DC input terminals 15P and 15 of the drive circuit 8 via this transistor 25.
Supplied between N. And microcomputer 18
As described above, the base signals B1 to B6 are output from the output ports Q to Q6 as shown in FIG. 2, so that the brushless motor 1 is started to rotate.

When the brushless motor 1 starts rotating, the motor coil]A
Since the induced voltage of 1C to 1C is small, a large starting current flows and the power transistors 12 to 14 try to enter the activation region, but in this case, the microcomputer 18
works as follows.

That is, the microcomputer 18 has an input port 13.
The voltage between the collector and emitter of the power transistors 12, 13 and 14 is detected at I4 and I5, and when the detected voltage exceeds the upper limit setting value (for example, 2V), the output capacitor is activated as shown in Fig. 3. Stop outputting base signal B7 from Q7. As a result, the transistor 25 of the voltage change circuit 24 is turned off, and the DC power supply 17
The resistor 27 is now connected between the positive terminal of the drive circuit 8 and the DC input terminal 1.5P of the drive circuit 8.
The DC voltage supplied to the drive circuit 8 is changed to a lower value for only the portion 7. Therefore, the starting current of the brushless motor is suppressed more than the above, and the power transistors 12 to 14
The voltage between the collector and emitter of is decreasing. and,
When the voltage becomes lower than the lower limit setting value (for example, IV), the microcomputer 18 again outputs the base signal B7 from the output port Q7, and the same operation is repeated thereafter.

The microcomputer 18 detects the rotation speed of the brushless motor 1 by receiving a pulse signal from one speed detector at the input port I2, and detects the rotation speed of the brushless motor 1.
The rotational speed of
, n+), the base signal B7 is continuously outputted from the output port Q7 as shown in FIG. Therefore, from this point on, the transistor 25 of the voltage changing circuit 24 is turned on continuously and the resistor 27
As a result, the full voltage of the DC power supply 17 is applied to the drive circuit 8. That is, when the brushless motor 1 reaches about 1/2 of its normal rotation, the induced voltage in the motor coils IA to IC increases, and the starting current is also suppressed to a small level. From here on, the full voltage of the DC power supply 17 is applied to accelerate the brushless motor 1.

According to this embodiment, the following effects can be obtained. That is, when starting the brushless motor 1,
Since the supply voltage to the drive circuit 8 is changed by the voltage change circuit 24 to a small value so that the power transistors 12 to 14 do not enter the activation region, the starting current can be suppressed and the heat loss of the power transistors 12 to 14 can be suppressed. Therefore, there is no need to use large heat dissipation fins, the overall size can be reduced, and it can be manufactured at low cost, which is extremely advantageous when the drive device is made into an IC chip. Furthermore, as described above, since the power transistors 12 to 14 do not perform switching operations in the activation region, the rotating magnetic field generated by the motor coils IA to IC of the brushless motor 1 becomes stable, and therefore, disturbances in the rotating magnetic field at the time of startup become stable. It is also possible to prevent the generation of electromagnetic noise.

In the above embodiment, the microcomputer 18 controls the brushless motor 1 based on the pulse signal from the rotation detector 19.
However, instead, as in the second embodiment of the present invention shown in FIG. The rotation speed of the brushless motor 1 may be indirectly detected by connecting a resistor 28 and detecting the voltage between the terminals of the resistor 28.

Further, in the above embodiment, the microcomputer 18 detects the rotational speed of the brushless motor 1, and when the rotational speed becomes approximately 1/2 of the steady rotational speed, the resistor 27 is continuously short-circuited and disabled. Alternatively, a timer control may be performed to disable the short circuit after a predetermined time from activation. Specifically, when the steady rotation speed of the brushless motor 1 is 11000 r, p, n+, the startup time is about 8 seconds, and it takes about 3 seconds to reach about 1/2 of that rotation speed. The predetermined time may be set to 3 seconds, for example.

In addition, the present invention is not limited to the embodiments described above and shown in the drawings, but is applicable not only to brushless motors for driving polygon mirrors of laser beam printers, but also to motors in general having multi-phase motor coils. Of course, modifications may be made as appropriate without departing from the scope of the invention.

[Effects of the Invention] As explained above, the motor drive device of the present invention suppresses the starting current so that the semiconductor switching element of the drive circuit does not enter the activation region, thereby reducing heat loss of the semiconductor switching element. This device has excellent effects in that it can be made small and inexpensive, stabilize the rotating magnetic field at startup, and prevent electromagnetic noise from occurring.

[Brief explanation of the drawing]

1 to 4 show a first embodiment of the present invention.
2 and 3 are time charts for explaining the operation, FIG. 4 is a schematic diagram of the laser beam printer, and FIG. FIG. 2 is a diagram corresponding to FIG. 1 showing the second embodiment. In the drawing, 1 is a brushless motor (motor), 1A to]
C is a motor coil, 3 is a polygon mirror, 8 is a drive circuit, 9 to 14 are power transistors (semiconductor switching elements), 18 is a microcomputer (control means),
19 is a rotation detector, 20 is a subtraction circuit, 21 is a clock signal generation circuit, 23A to 23C are capacitors, 24 is a voltage changing circuit (voltage changing means), and 27 is a resistor. Agent Patent Attorney Tsuyoshi Sato

Claims (1)

[Claims] 1. A DC power supply, a drive circuit constituted by a large number of semiconductor switching elements, a voltage changing means provided between the drive circuit and the DC power supply for changing the voltage supplied to the drive circuit, and the drive circuit. By turning on and off semiconductor switching elements of the circuit, the motor coils of multiple phases of the motor are controlled to be energized and disconnected, and when the motor is started, the voltage changing means is controlled to prevent the semiconductor switching elements from entering an activation region. A motor drive device comprising: control means for changing the voltage supplied to the drive circuit.