JPH0530642A - Motor drive - Google Patents

Abstract

PURPOSE:To interrupt DC power supply for a motor driving circuit quickly upon occurrence of abnormality. CONSTITUTION:A rotation detector 20 detects rotation of a brushless motor 1. When the rotation detector 20 does not detect a rotation signal even if a start signal for the brushless motor 1 is outputted, an abnormality detecting circuit 31 outputs the starting signal repeatedly several times and when the rotation signal is not detected yet, an overcurrent is fed through a current fuse 25 disposed between a driving circuit 8 and a DC power supply 17 thus blowing out the fuse forcibly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor drive device in which a plurality of motor coils of a plurality of phases are controlled by a drive circuit composed of a large number of semiconductor switching elements.

[0002]

2. Description of the Related Art In a laser beam printer, a polygon mirror is rotated by a motor, for example, a brushless motor, and laser light from a semiconductor laser that blinks in accordance with a print pattern is reflected by the polygon mirror to irradiate the photosensitive drum. Since only the laser beam needs to be scanned by the polygon mirror, there is no mechanical scanning portion and high speed printing is possible. Therefore, as a brushless motor that rotationally drives the polygon mirror,
High speed from 6000 rpm to 12000 rpm and 0.
A velocity fluctuation rate (jitter) of about 02% is required.

Thus, the drive device for the brushless motor is
For example, a drive circuit is configured by connecting three power switching transistors, which are three semiconductor switching elements, in a three-phase bridge, the DC input terminal of the drive circuit is connected to a DC power source, and the AC output terminal of the drive circuit is connected to a three-phase motor coil. 3 by connecting and turning on and off 6 power transistors sequentially
It is configured to rotate the rotor by controlling the on / off of the phase motor coil.

[0004]

Since the brushless motor for driving the polygon mirror is rotated at a high speed as described above, the brushless motor is driven at a higher speed than the motor for driving a floppy disk. The startup time to reach it is several times, which is extremely long. The power transistor of the drive circuit is usually used in the saturation region, but when a large starting current flows for a long time as in the past,
Since the power transistor is turned on in the activation region, the heat loss becomes large and the temperature rise becomes remarkable.

Therefore, if one of the power transistors is broken open due to such a repetitive temperature rise, normal control of the on / off of the motor coil of the brushless motor cannot be performed, and at the time of start-up. Becomes a starting failure, and an abnormal state occurs in which the rotation is stopped during operation. As a result, a relatively large current corresponding to the starting current continues to flow in the motor coil, and finally the motor The coil may smoke or ignite.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a motor drive device capable of rapidly cutting off the DC power supply to the drive circuit when an abnormality occurs.

[0007]

A motor drive device according to the present invention is provided with a current fuse between a drive circuit composed of a large number of semiconductor switching elements and a DC power supply, and the drive circuit of the drive circuit is activated based on a start signal. The semiconductor switching element is turned on / off to provide a control means for controlling the on / off state of the motor coils of a plurality of phases of the motor, and a rotation detection means for detecting the rotation of the motor is provided, which receives a rotation detection signal from the rotation detection means. If the rotation detection signal is not present despite the output of the start signal to the motor, the output of the start signal is repeated a predetermined number of times, and when there is still no rotation detection signal, an overcurrent is forcedly flown to the current fuse. It is characterized by the configuration of providing an abnormality detection means for forming the.

[0008]

According to the motor drive device of the present invention, the abnormality detecting means outputs the start signal a predetermined number of times when the rotation detecting signal is not output from the rotation detecting means despite the output of the start signal to the motor. Repeatingly, when there is still no rotation detection signal, a cutoff circuit for forcibly flowing an overcurrent to the current fuse is formed, so that the current fuse is immediately blown to cut off the DC power supply to the drive circuit.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

First, a schematic structure of a laser beam printer will be described with reference to FIG.

Reference numeral 1 is a motor, for example, a brushless motor, and a hexagonal polygon mirror 3 is fixed to the shaft 2 at the center thereof. Reference numeral 4 denotes a semiconductor laser, which is controlled by a laser driving circuit (not shown) to blink at high speed in accordance with a print pattern.
Is irradiated onto the polygon mirror 3 via the cylindrical lens 5. Then, the laser beam 4a 'reflected by the polygon mirror 3 is reflected by the f-θ lens 6
The photosensitive drum 7 is irradiated with the light through.

Now, the structure of the drive unit will be described with reference to FIG.

Reference numeral 8 is a drive circuit, which has a large number, for example, 6
NPN type power transistors 9 to 14, which are semiconductor switching elements, are three-phase bridge-connected,
The DC input terminals 15P and 15N are respectively connected to the positive terminal and the negative terminal of the DC power supply 17 via a later-described cutoff circuit 24, and the AC output terminals 16A, 16B and 16C.
Is connected to one terminal of each of the three-phase motor coils 1A, 1B, and 1C, which are a plurality of phases, of the stator of the brushless motor 1. Then, the motor coils 1A, 1B and 1
The other terminals of C are commonly connected, so that the three-phase motor coils 1A, 1B and 1C are star-connected.

Reference numeral 18 is a microcomputer as a control means connected between the positive terminal and the negative terminal of the DC power source 17, which has input ports I1 to I5 and an output port Q1.
Through Q6, and the six output ports Q1 through Q6 are connected to the bases of the power transistors 9 through 14, respectively.

Reference numerals 19A, 19B, and 19C are three capacitors corresponding to the three-phase motor coils 1A, 1B, and 1C, respectively. These capacitors have a capacitance of, for example, 10 μF, and one terminal of each of them has an AC output. Terminals 16A, 16
The other terminals are connected to the DC input terminals 15N, that is, the emitters of the power transistors 12 to 14, respectively. The input ports I3, I4 and I5 of the microcomputer 18 are connected to the collectors of the power transistors 12, 13 and 14, respectively.

Reference numeral 20 is a rotation detector as a rotation detecting means, which detects a magnetic change of a permanent magnet rotating together with the rotor of the brushless motor 1 so as to output a pulse signal corresponding to the rotation speed from an output terminal. One output terminal is connected to the negative (-) input terminal of the subtraction circuit 21, and the other output terminal is connected to the input port I2 of the microcomputer 18. Reference numeral 22 denotes a clock pulse generation circuit, which outputs a clock signal corresponding to the set rotation number from an output terminal S based on a start signal as will be described later.
Is connected to the positive (+) input terminal of the subtraction circuit 21. The subtraction circuit 21 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. The terminal is connected to the input port I1 of the microcomputer 18 via the amplifier circuit 23.

Now, the cutoff circuit 24 will be described. That is, 25 is the positive terminal of the DC power supply 17 and the DC input terminal 15P.
Is a current fuse connected between and. Reference numeral 26 is a thyristor as a switching element, the anode of which is connected to the DC input terminal P via the resistor 27, and the cathode of which is connected to the negative terminal of the DC power supply 17.

28 is an emergency DC power supply circuit, which is constructed by connecting a series circuit of a reverse current blocking diode 29 and an electrolytic capacitor 30 between the positive terminal and the negative terminal of the DC power supply 17.

In FIG. 1, reference numeral 31 is an abnormality detecting circuit as an abnormality detecting means, which is an electrolytic capacitor 30.
Is connected in parallel to the DC power supply voltage. In the abnormality detection circuit 31, the input terminal D is connected to one output terminal of the rotation detector 20, the input terminal S is connected to the output terminal S of the clock pulse generation circuit 22, and the output terminal R is clock pulse generation. The output terminal G is connected to the input terminal R of the circuit 22 and the output terminal G is connected to the gate of the thyristor 26. The gate pulse signal is supplied to the thyristor 26 at the same time as the start signal is supplied to the clock pulse generation circuit 22 as described later. Is becoming

Reference numeral 32 is an abnormality notifying circuit, which is constituted by connecting a series circuit of a resistor 33 and a light emitting diode 34 as an indicator between the anode of the diode 29 and the anode of the thyristor 26.

Next, the operation of this embodiment will be described with reference to FIG.

First, the normal operation of the brushless motor 1 will be described. The microcomputer 18 outputs the high level base signal B from the output ports Q1 to Q6 as shown in FIG.
1 to B6 are sequentially output, and these are supplied to the bases of the power transistors 9 to 14, respectively, and the power transistors 9 to 14 are on / off controlled in the saturation region. The motor coil 1A is turned on and off by turning on and off the power transistors 9 to 14.
To 1C are controlled to be turned on and off, whereby the motor coils 1A to 1C generate a rotating magnetic field to rotate the rotor.

Consider, for example, the motor coil 1A. First, the microcomputer 18 outputs base signals B1 and B5 from the output ports Q1 and Q5 as shown in FIGS. 2 (a) and (e).
Power transistors 9 and 13 are turned on, and DC power supply 1
7, current fuse 25, power transistor 9, motor coil 1A, motor coil 1B, power transistor 1
The motor coil 1A is energized through the path of the DC power supply 3 and the DC power supply 17. After that, the base signal B5 is not output from the output port Q5 of the microcomputer 18, the power transistor 13 is turned off, and instead, the base signal B6 is output from the output port Q6 as shown in FIG. The power transistor 14 turns on. Therefore, this time, the DC power supply 17, the current fuse 25, the power transistor 9, the motor coil 1A, the motor coil 1C, the power transistor 14, and the DC power supply 17 are energized to the motor coil 1A. As is clear from FIG. 2, the same applies to the other motor coils 1B and 1C, and the motor coils 1A to 1C generate a rotating magnetic field by the two-phase simultaneous energization.

When the deviation signal is applied to the input port I1, the microcomputer 18 calculates the width of the base signal based on the deviation signal so that the deviation signal becomes zero, and the base signal based on the calculation result is calculated. B1 to B
6 is output from the output ports Q1 to Q6, and feedback control is performed so that the rotation of the brushless motor 1, that is, the rotation of the rotor becomes a set rotation speed (steady rotation speed).

By the way, when the energization of the motor coils 1A to 1C is switched, an induced voltage, which is a switching surge, is generated in these, and this is absorbed by the capacitors 19A to 19C.

Consider, for example, the motor coil 1A. When the base signal B1 is not output from the output port Q1 of the microcomputer 18 and the power transistor 9 is turned off, instead, the output port Q2 is output.
As shown in FIG. 2B, the base signal B2 is output, and the power transistor 10 is turned on. When the power transistor 9 is turned off to cut off the energization in the forward direction to the motor coil 1A, the motor coil 1A is cut off.
Generates an induced voltage in the opposite direction of the power supply voltage. As a result, a charging circuit for the capacitor 19A is formed in the path of the motor coil 1A, the capacitor 19A, the DC power supply 17, the current fuse 25, the power transistor 10, the motor coil 1B, and the motor coil 1A.
The switching surge of A, that is, the induced voltage is absorbed.

Thereafter, the microcomputer 18 outputs the base signal B4 from the output port Q4 as shown in FIG. 2 (d).
When the power transistor 12 is turned on and the power transistor 12 is turned on, a discharge circuit for the capacitor 19A is formed via the power transistor 12, and the charge charged in the capacitor 19A is discharged.

The above is the capacitor 1 of the motor coil 1A.
9A describes the absorption and discharge of switching surge, but the other motor coils 1B and 1C
Similarly, the switching surge of is absorbed by the capacitors 19B and 19C, and the charges charged in the capacitors 19B and 19C are discharged through the power transistors 13 and 14.

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

First, when the brushless motor 1 is started,
The abnormality detection circuit 31 outputs a start signal from the output terminal R on the basis of the start command and supplies it to the clock pulse generation circuit 22. When the clock pulse generation circuit 22 is supplied with the activation signal, the clock pulse generation circuit 22 outputs the clock signal having a cycle corresponding to a predetermined low rotation speed from the output terminal S. Therefore, the microcomputer 18 outputs the output ports Q1 to Q6 from FIG.
Since the base signals B1 to B6 are output as shown in (3), the brushless motor 1 is started to rotate. Then, according to the rotation of the brushless motor 1, the rotation detector 20
Outputs a pulse signal as a rotation detection signal.

After that, the clock pulse generating circuit 22 performs a starting operation for sequentially changing the cycle of the clock signal from a large one corresponding to a predetermined low rotation speed to a small one corresponding to a set rotation speed. Therefore, the brushless motor 1 is sequentially rotated up to the set rotation speed.

Now, let us consider a case where the brushless motor 1 does not start for some reason, although the starting signal is given to the clock pulse generating circuit 22. In this case, the rotation detector 20 does not output the pulse signal which is the rotation detection signal, although the clock pulse generation circuit 22 outputs the clock signal. Therefore, the abnormality detection circuit 31 uses the clock pulse generation circuit 2 at the input terminal S.
It is detected that the pulse signal is not applied to the input terminal D from the rotation detector 20 even though the clock signal from 2 is applied, and a fixed time (for example, 0.1 seconds) is elapsed after the output of the start signal. The start signal is again output from the output terminal R and applied to the input terminal R of the clock pulse generation circuit 22.

When the start signal is applied again, the clock pulse generation circuit 22 outputs a clock signal having a cycle corresponding to a predetermined low rotation speed, and then sets the cycle of the clock signal to a cycle corresponding to the set rotation speed. A start-up operation is performed that is sequentially changed toward. The abnormality detection circuit 31 detects again whether or not the brushless motor 1 is activated by the clock signal from the clock pulse generation circuit 22 and the presence or absence of the pulse signal from the rotation detector 20, and if it is not activated, Further, a start signal is output to cause the clock pulse generation circuit 22 to perform a start operation.

In this way, the abnormality detection circuit 31 outputs a predetermined number of times (for example, 1 to 3 times) after the first activation signal is output.
If the brushless motor 1 does not start despite the output of the starting signal of, the gate signal is output from the output terminal G to be given to the thyristor 26 of the cutoff circuit 24, and therefore the thyristor 26 is turned on. .. As a result, an overcurrent is forced to flow through the current fuse 25 via the resistor 27 and the thyristor 26, and the current fuse 25 quickly melts and disconnects the drive circuit 8 from the DC power supply 17.

When the thyristor 26 is turned on, the resistance 3
Since a current flows through the light emitting diode 34 via 3, the light emitting diode 34 emits light to inform that the current fuse 25 is forcibly blown due to the occurrence of an abnormality.

Further, consider a case where the rotation of the brushless motor 1 is stopped for some reason while the brushless motor 1 is operating (during steady rotation). Even in this case, the abnormality detection circuit 31 detects that the pulse signal from the rotation detector 20 disappears even though the clock signal is output from the output terminal S of the clock pulse generation circuit 22, and the output terminal R Then, the clock pulse generating circuit 22 carries out the above-mentioned starting operation.

Subsequent operations are the same as when the brushless motor 1 is started as described above, and if the brushless motor 1 does not start despite the output of the start signal a predetermined number of times, the thyristor 26 turns on. As a result, the current fuse 25 is blown.

By the way, the causes of the brushless motor 1 failing to start or stopped rotating during operation (during steady rotation) are the lock accident of the brushless motor 1 and the power transistors 9 to 14 of the drive circuit 8. There are various possibilities, such as short circuit break or open break, and inoperability of other components.
If the abnormality detection circuit 31 as described above is provided, the current fuse 25 may be damaged by a provisional decree or any accident.
Even if there is a case where the current fuse 25 is not directly blown, the current fuse 25 is quickly blown by the operation of the abnormality detection circuit 31 without continuously supplying an excessive current to the drive circuit 8 and the brushless motor 1. ..

According to this embodiment, the following effects can be obtained.

That is, when the brushless motor 1 does not start even though the start signal is given from the abnormality detecting circuit 31 to the clock pulse generating circuit 22, after that, the abnormality detecting circuit 31 outputs a predetermined number of times (for example, 1). Through 3
Output a start signal, but still brushless motor 1
When the rotation of the brushless motor 1 does not start, an overcurrent is caused to flow through the current fuse 25 by the cutoff circuit 24 and the current fuse 25 is forcibly blown to cut off the DC power supply 17 to the drive circuit 8 of the brushless motor 1. ..

Therefore, when the brushless motor 1 fails to start for some reason at the time of starting, or when the brushless motor 1 stops rotating for some reason during operation, or when an abnormal state occurs, Since the current fuse 25 is forcibly blown, it is possible to prevent the motor coils 1A to 1C of the brushless motor 1 and other parts from smoking or igniting.

Furthermore, even if the voltage of the DC power supply 17 drops when the thyristor 26 is turned on by the abnormality detection circuit 31 and a passing current is made to flow through the current fuse 25, the emergency DC power supply circuit 28 causes the DC of the abnormality detection circuit 31 to flow. Since the power supply voltage is secured, the thyristor 26 can be reliably turned on, that is, the current fuse 25 can be reliably blown.

Since the light emitting diode 34 is made to emit light when the thyristor 26 of the cutoff circuit 24 is turned on, it can be notified that the current fuse 25 is blown due to an abnormality, which is extremely convenient for the user. Is.

Although the abnormality detecting circuit 31 is provided separately from the microcomputer 18 in the above embodiment, the abnormality detecting circuit 31 is provided in the microcomputer 18 itself.
The function may be provided, and in this case, the microcomputer 18 also serves as the abnormality detecting means.

Further, although the emergency DC power supply circuit 28 and the abnormality notifying circuit 32 are provided in the above embodiment, they may be provided if necessary.

In addition, the present invention is not limited to the above-described embodiments, and is not limited to, for example, a brushless motor for driving a polygon mirror of a laser beam printer, but can be applied to motors having a plurality of phases of motor coils. Needless to say, the present invention can be appropriately modified and implemented without departing from the scope of the invention.

[0047]

As described above, the motor drive device of the present invention is designed to cut off the DC power supply to the drive circuit when the motor does not start despite the output of the start signal. When an abnormality occurs, the power supply will be cut off promptly, and the smoke of the motor and other parts,
It has an excellent effect of being able to prevent ignition.

[Brief description of drawings]

FIG. 1 is an electrical configuration diagram of a drive device showing an embodiment of the present invention.

FIG. 2 is a time chart for explaining the operation

FIG. 3 is a schematic configuration diagram of a laser beam printer.

[Explanation of symbols]

In the drawings, 1 is a brushless motor (motor), 1A to 1
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), 20 is a rotation detector (rotation detection means), and 21 is subtraction. Circuit, 22 is a clock signal generation circuit, 24 is a cutoff circuit,
Reference numeral 25 is a current fuse, and 31 is an abnormality detection circuit (abnormality detection means).

Claims (1)

Claim: What is claimed is: 1. A direct current power supply, a drive circuit including a large number of semiconductor switching elements, a current fuse provided between the drive circuit and the direct current power supply, and a start signal based on a start signal. Control means for turning on and off the semiconductor switching elements of the drive circuit to control the on / off of the motor coils of a plurality of phases of the motor, rotation detecting means for detecting the rotation of the motor, and a rotation detection signal of the rotation detecting means. If the rotation detection signal is not present despite the output of the start signal to the motor, the output of the start signal is repeated a predetermined number of times, and when there is still no rotation detection signal, an overcurrent is forced to the current fuse. An apparatus for driving a motor, comprising: an abnormality detecting unit that forms an interruption circuit that flows to the motor.