JPH04165990A - Motor drive - Google Patents

Abstract

PURPOSE:To stabilize rotating field by providing a switching circuit for forming a capacitor discharge circuit after switching of conduction before next switching of conduction. CONSTITUTION:Before a microcomputor 18 outputs a base signal from output port Q4 thereof and a power transistor 12 is turned ON, the microcomputor 18 outputs a High level base signal from an output port Q8 for a short time thus turning a transistor 27 ON. Consequently, a transistor 26 is turned ON to establish a discharge circuit of a capacitor 24 through the capacitor 24, the transistor 26 and a resistor 30 thus discharging the capacitor 24. Consequently, discharge current does not flow into power transistors 12, 13, 14 which thereby do not enter into activated regions but turned ON in saturable regions.

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 motor, 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. For this reason, brushless motors that rotate polygon mirrors are required to have high speed and stable rotation, and recently, brushless motors with 60
There is a demand for a high speed of 00 r, p, m to 1200 Or, p, m and a speed fluctuation rate (jitter) of about 0.02%.

On the other hand, in a brushless motor drive device, for example, six power transistors, which are semiconductor switching elements, are connected in a 3-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.

By the way, one of the factors that affects the rotation accuracy of brushless morphs is the stability of the rotating magnetic field, and in order to stabilize the rotating magnetic field, it is necessary to effectively absorb the switching surge that occurs when switching the energization to the motor coil. There is a need.

For this reason, in the past, a capacitor was provided corresponding to each of the three-phase motor coils, the switching surge of the corresponding motor coil was absorbed by the capacitor, and the charge absorbed by the capacitor was transferred to the power transistor of the drive circuit. It is designed to discharge electricity through the .

(Problem to be Solved by the Invention) The power transistor of the drive circuit is normally used in the saturation region, but when the charge in the capacitor is discharged through the power transistor as in the past, the discharge current is The maximum collector current of the power transistor has been reached and no more can flow, and the voltage between the collector and emitter of the power transistor becomes equal to the voltage between the terminals of the capacitor, causing the power transistor to enter the activation region. As a result, the switching operation of the power transistor becomes incomplete, and the stability of the rotating magnetic field caused by the motor coil is excessively degraded.
There was a problem that the desired speed fluctuation rate could not be obtained.

In addition, capacitors with a capacity of about 10 μF are used as surge absorption capacitors, but if a capacitor of this capacity is provided for each motor coil of each phase as in the past, the number of capacitors will increase. There are problems in that the number of parts increases, the overall size becomes large, and the cost becomes high.

The present invention has been made in view of the above circumstances, and its purpose is to provide a motor drive device that can stabilize a rotating magnetic field, improve rotation accuracy, and be made compact and inexpensive. It is in.

[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 turns on and off the semiconductor switching elements of this drive circuit to drive the motor. A control means for controlling energization and disconnection of the motor coils of a plurality of phases is provided, and one surge absorption capacitor is provided to absorb switching surges generated in the motor coil each time the motor coil is energized by the control means. The present invention is characterized in that a switching circuit is provided to form a charging circuit for the capacitor and to form a discharging circuit for the capacitor after energization switching and before the next energization switching.

(Function) According to the motor drive device of the present invention, a discharge circuit is formed in the capacitor by the switching circuit independently of the semiconductor switching element of the drive circuit, so that the semiconductor switching element enters the activation region due to the discharge current. Therefore, the switching operation of the semiconductor switching element becomes complete, the rotating magnetic field by the motor coil becomes stable, and the number of surge absorption capacitors is reduced to one due to the action of the switching circuit. You can get away with it.

(Example) An example of the present invention will be described below with reference to the drawings.

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 morph, 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 includes a large number of NPN type power transistors 9, which are semiconductor switching elements, for example, six.
The DC input terminals 15P and 15N are connected to the positive and negative terminals of the DC power supply 17, respectively, and the AC output terminals 16A, 15f3 and 16C are connected to the plurality of stators of the brushless motor 1. It is connected to one terminal of each of the three-phase motor coils IA, IB, and 1c. And motor coils IA, I
The other terminals of B and IC are connected in common, thus forming a three-phase motor coil IA.

IB and 1C are star connected. 18 is straight 2i1
5. Δ); A microcomputer serving as a control means is connected between the stop terminal and the negative terminal of i17, and this has eight output ports Q1 to Q8, of which six output ports Q1 to Q6 are connected to the Power transistors 9 to 14
are connected to the base of each. One is a rotation detector, which detects magnetic changes in the permanent magnet that rotates together with the rotor of the brushless motor 1, and outputs a pulse signal from the output terminal according to the rotation speed. The terminal is connected to the negative (-) input terminal of the subtraction circuit 20. 21 is a clock pulse generation circuit, which outputs a clock signal according to the set rotation speed from an output terminal, and the output terminal is connected to the positive (10) input terminal of the subtraction circuit 20. There is. The subtraction circuit 20 subtracts the pulse signal applied to the negative (-) input terminal from the tarokk signal applied to the positive (+) input terminal, and outputs the deviation signal from the output terminal. It is connected to input port 1 of microcomputer 18 via amplifier circuit 22 .

Therefore, in the same Figure 1, 23A, 23B and 23C
are three diodes corresponding to three-phase motor coils IA, IB, and IC, respectively, and their respective anodes are connected to AC output terminals 1.6A, 16B, and 16C, and their respective cathodes are connected in common, and their For example, the common connection point is 10μ
It is connected to one terminal of one capacitor 24 having a capacitance of F. 25 to 27 are switching circuits 28
A transistor is a switching element that constitutes a transistor.

In this case, the collector of the NPN transistor 25 is connected to the other terminal of the capacitor 24,
The emitter is connected to the DC input terminal 15N, that is, the emitters of the power transistors 12 to 14, the base is connected to the output port Q7 of the microcomputer 18, and a diode 29 is connected between the collector and the emitter. Also, PNP type! - In the transistor 26, the emitter is connected to one terminal of the capacitor 24 via the discharge resistor 30, and the collector is connected to the collector of the transistor 25. In the NPN type transistor 27, the collector is connected to the base of the transistor 26 via the resistor 31, the emitter is connected to the DC input terminal 1.5N, and the base is connected to the microcomputer 18 via the resistor 32. Connected to output port Q8.

Next, the operation of this embodiment will be explained with reference to FIG. 2.

The microcomputer 18 is configured to sequentially output high-level base signals B1 to B6 from output ports 1 to -9= to Q6 as shown in FIGS. 2(a) to (f), and these are connected to power transistors. 9 to 14, respectively, to the bases of the power transistors 9 to 1.
4 is controlled to be turned on and off in the saturation region.

Then, the motor coils IA to IC are controlled to be energized and de-energized by turning on and off the power transistors 9 to 14.
Motor coils IA to IC generate rotating magnetic fields to rotate the rotor.

For example, consider the motor coil IA. First, when the microcomputer 18 outputs base signals B1 and B5 from the output ports Q and Q as shown in FIGS. 2(a) and (e), the power transistor 9
and 13 is turned on, and the DC power supply 17. Power transistor9. The motor coil 1 is connected to the motor coil IA, motor coil IB, power transistor 13 and DC power supply 17.
A is energized. After that (electrical angle π/3), the base signal B 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 B is output from the output port Q6 as shown in FIG. 2(f). Thus, the base signal B6 is output, and the power transistor 14 is turned on.

Therefore, this time, the DC power supply 17. power transistor 9
．． Motor coil IA, motor coil IC.

The motor coil IA is energized through the path of the power transistor 14 and the DC power supply 17. As is clear from FIGS. 2(a) to 2(f), the same applies to the other motor coils IB and 1C, and motor coils IA to 1C generate rotating magnetic fields by simultaneous two-phase energization. and,
When the deviation signal is given to the input capo-1-I, the microcomputer 18 calculates the width of the base signal such that the deviation signal becomes zero based on the deviation signal, and based on the calculation result, base signal B, B6 to B6 are outputted from output ports Q 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.

Now, when switching the energization of the motor coils IA to IC, an induced voltage as a switching surge is generated in these, and this is absorbed by one capacitor 24.

For example, consider the motor coil IA. Since the base signal B is no longer output from the output port Q1 of the microcomputer 18, the power transistor 9
At a timing slightly before turning off (electrical angle 2π/3),
The microcomputer 18 outputs a high level base signal B7 from the output port Q7 as shown in FIG. 2(g), thereby turning on the transistor 25. After that, the base signal B1 is no longer output from the output port Q1 of the microcomputer 18, and the power transistor 9
When is turned off (electrical angle 2π/3), the base signal B2 is instead outputted from the output port Q2 as shown in FIG. 2(b), and the power transistor 10 is turned on. and,
By turning off the power transistor 9, the motor coil IAO
When the forward current is turned off, an induced voltage is generated in the motor coil IA in a direction opposite to the power supply voltage. With this, motor coil IA, diode 23A, capacitor 2
4. Transistor 25. DC power supply 17, power transistor 10. A charging circuit for the capacitor 24 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 IA is absorbed.

Then, the output of the gate signal B7 from the output port Q7 of the microcomputer 18 is stopped in a short time, and the absorption of the switching surge by the capacitor 24 is completed.

After that, the microcomputer]8 outputs the base signal B from the output port Q4 as shown in FIG. 2(d), and before the power transistor]2 is turned on (electrical angle π),
The microcomputer 18 outputs ports 1-Q, to 2nd.
As shown in Figure (h), a high level base signal B8 is output for a short time to turn on the transistor 27. This turns on the transistor 26 and causes the capacitor 24 to
．． A discharge circuit for the capacitor 24 is formed by the path of the transistor 26 and the resistor 30, so that the discharged charge of the capacitor 24 is discharged.

= 13- The above describes the absorption and discharge of switching surges by the capacitor 24 of the motor coil 1A, but the switching surges of the other motor coils IB and IC are also absorbed by the capacitor 24 in the same way. , and the charge on the capacitor 24 is discharged through the transistor 26 and the resistor 30.

According to this embodiment, the following effects can be obtained. That is, the capacitor 24 is connected to the motor coil IA.
, IB and IC, the capacitor 24 is discharged through the transistor 26 and the resistor 30, so that the discharge current does not flow to the power transistors 12, 13 and 14, and therefore, Unlike conventional power transistors 1.2, 1.3
and ]4 will turn on in the saturation region without entering the activation region. As a result, during the rotation of the brushless motor, the rotating magnetic field generated by the motor coils IA to ]C is stabilized, and the rotation accuracy can be improved. It is possible to eliminate the need for a speed fluctuation rate of about 0.02% at the same speed of m, thus making it possible to print at high speed and with high quality. Furthermore, 1 for 3-phase motor coils 1A to ]C.
Since it is sufficient to provide only one surge absorbing capacitor 24, the overall size can be reduced compared to the conventional one, and it can be manufactured at low cost. Moreover, as described above, by stabilizing the rotating magnetic field generated by the motor coils 1A to 1C of the brushless motor 1, it is possible to prevent the generation of electromagnetic noise due to disturbance of the rotating magnetic field at the time of startup, and the power transistor 1
Since 2 to 14 do not perform switching operations in the active region, heat loss is also reduced, and therefore, when the drive device is made into an IC chip, the chip size can be reduced.
- The layers are small and can be manufactured at low cost.

Note that the present invention is not limited to the embodiments described above and shown in the drawings, and 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, the present invention may be modified and implemented 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 discharges the capacitor that absorbed the switching surge of the motor coil through the switching circuit.
The semiconductor switching element of the drive circuit can be prevented from entering the activation region, the rotating magnetic field by the motor coil can be stabilized, and the rotation accuracy can be improved. Since only a surge absorbing capacitor is required, it is compact and inexpensive, which is an excellent effect.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and FIG. 1 is an electrical configuration diagram of a driving device, FIG. 2 is a time chart for explaining the operation, and FIG. 3 is a schematic configuration diagram of a laser beam printer. In the drawing, 1 is a brushless motor (motor), IA to I
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),
One is a rotation detector, 20 is an attenuation circuit, 21 is a clock signal generation circuit, 23A to 23C are diodes, 24 is a capacitor, 28 is a switching circuit, and 30 is a resistor. Agent Patent Attorney Tsuyoshi Sato Figure 3

Claims (1)

[Claims] 1. A drive circuit constituted by a large number of semiconductor switching elements, a control means for controlling energization and disconnection of motor coils of multiple phases of the motor by turning on and off the semiconductor switching elements of this drive circuit, and one surge absorption capacitor. , a charging circuit for the capacitor is formed in order to absorb a switching surge generated in the motor coil each time the motor coil is energized, which is controlled by the control means, and a discharging circuit for the capacitor is formed after the energization is switched and before the next energization switching. A motor drive device comprising a switching circuit forming a motor.