JPH1080178A - DC brushless motor drive circuit - Google Patents

Abstract

(57) Abstract: The present invention relates to a motor driving device for a DC brushless motor, and in particular, it is necessary to vary a set value of a motor overcurrent limiting circuit in accordance with the number of rotations of the motor to flow a large overcurrent. The present invention provides a small-capacity motor drive circuit. SOLUTION: A PWM signal is outputted in accordance with a motor rotation detection signal detected by an encoder 4a provided in the vicinity of a DC brushless motor, and the output is controlled based on data obtained by detecting a driving current of the DC brushless motor. In this method, the overcurrent of the motor is adjusted by this control, and in particular, the overcurrent at the time of starting the motor and a constant overcurrent during the normal operation are supplied, so that the motor is reliably driven. Further, the PLL lock is reliably performed in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor driving device for a DC brushless motor, and more particularly to a DC brushless motor driving circuit for limiting overcurrent.

[0002]

2. Description of the Related Art In recent years, DC brushless motors that have little mechanical noise and do not adversely affect nearby electronic equipment have been widely used in the field of electronic equipment. The drive control of this DC brushless motor is usually performed by P
This is performed by LL (Phase Locked Loop) control.
That is, the rotational speed of the DC brushless motor is measured by an encoder, a pulse signal based on the measured speed is compared with a reference pulse, a drive current according to the phase difference is supplied to the DC brushless motor, and the motor is rotated at a constant speed. Control.

[0003] Such a DC brushless motor has only a winding resistance (armature winding resistance) of about several ohms (ohms) due to its characteristics. Therefore, at the start of driving the motor,
Since the armature reaction does not occur in the motor, a large starting current flows. For example, when the motor is started with the power supply voltage set to 24 V, a current of about 10 A flows through the armature winding of the motor. Such a large current causes burnout of the armature winding and the like.

Therefore, a conventional motor drive circuit is provided with an overcurrent protection circuit for preventing such a large current from flowing. This overcurrent protection circuit limits the current flowing through the armature winding to about two to three times the rated motor current. Therefore, for example, when the rated current of the motor is 1.4 A, 4 A (in this case, about 2.9 times)
Use a protection circuit to limit the current (overcurrent) by the time.
For example, when the rated current of the motor is 1.2 A,
Current (overcurrent) up to 5A (again, about 2.9 times)
Use a protection circuit to limit the Since these overcurrent protection circuits are configured by connecting a current limiting resistor to the motor driver circuit, the set value of the overcurrent protection circuit once set does not vary, and the motor is controlled by one type of set value. Driving.

[0005]

As described above, in the conventional motor drive circuit, an overcurrent protection circuit is provided to set the overcurrent value. However, the number of windings in the motor, the number of windings of the stator and the rotor, and the like. The rated current does not match the design value due to installation errors and the like.
For example, as described above, even if the overcurrent value is set to, for example, 3.5 A from the rated current of the motor, the measured value is often set to a small overcurrent value such as 1.7 A. Therefore, when the motor is actually started and the supply current to the motor gradually increases, the overcurrent protection circuit operates at, for example, about 1.7 A of the actually measured value, and no more current may be supplied.
In such a case, the motor is started, and when the rotation speed reaches the reference value by the PLL control, the rotation speed of the motor is set to a constant value. At this time, the supply current to the motor is about 1.7 A at the maximum. is there. Therefore, when the operation of the overcurrent protection circuit is completed, the rotation speed of the motor is locked to a constant speed by the PLL control, and the rated current of the motor (1.4 A)
And the supply current (1.7 A) is small (about 0.3 A), so that hunting becomes easy when the motor is started. That is, the phase lock range (phase lock width) drawn into the PLL lock is narrow, and the phase lock requires time.

The above-mentioned overcurrent protection circuit also works for an overload at the time of starting the motor, but works for an overload generated at the time of normal operation, causing a difference between the measured values of the motor current at both times. . That is, the time constant of the drive circuit and the input impedance of the motor are different between the time of starting the motor and the time of overload during operation. For example, the actual measured value of the current at the time of overload during operation is 1.7 A, for example. In some cases, for example, 2.6 A is actually measured as the current at the time of starting the motor. FIG. 7 is a waveform chart for explaining the above-mentioned reason. When the motor is started, there is no (or small) coil component of the armature winding, and the current waveform is sharp as shown in (I). As shown in II), the current waveform becomes smooth, resulting in a difference between the time constant and the input impedance in both cases.

In such a case, a difference of, for example, 0.9 A occurs between the overcurrent at the time of starting the motor and the overcurrent for the overload during the normal operation, and the motor drive circuit compensates for this difference. Requires a large drive circuit.
This causes an increase in the cost of the circuit.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a small-capacity motor drive circuit in which the set value of an overcurrent limiting circuit of a DC brushless motor is varied according to the number of rotations of the motor.

[0009]

According to a first aspect of the present invention, there is provided a DC brushless motor driving circuit having an overcurrent limiting means, comprising a motor rotational speed detecting means. This can be achieved by providing a DC brushless motor driving circuit that changes the overcurrent limiting level of the overcurrent limiting means in accordance with the detection output of (1).

Here, the motor rotation speed detecting means is, for example, an encoder, and the overcurrent limiting means is, for example, a CPU, which controls the overcurrent in accordance with the rotating speed of the motor detected by the overcurrent limiting means, and detects a difference in impedance or the like. , The overcurrent control corresponding to the driving state of the DC brushless motor can be performed.

According to a second aspect of the present invention, the change of the overcurrent limit level is performed, for example, by changing the overcurrent at the time of starting the motor and the overcurrent at the time of normal driving. This is a configuration in which changes are made between.

With this configuration, the difference between the overcurrent at the time of starting the motor and the overcurrent at the time of normal driving, which is particularly problematic, is adjusted, and an accurate overcurrent limit setting is performed. The invention according to claim 3 embodies the invention according to claim 1, wherein the overcurrent limiting unit is configured, for example, based on a difference between a current at the time of starting the motor and an overcurrent at the time of normal driving. The overcurrent limit level is changed.

Here, the current at the time of starting the motor and the overcurrent at the time of normal driving are detected, for example, by detecting the current flowing through the armature winding of the motor through a resistor, and outputting the current value to the CPU. The overcurrent detection method is not limited to the above-described method, and may be configured using another circuit element, for example, a transistor.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. <First Embodiment> FIG. 1 is a block diagram of a motor drive circuit according to the first embodiment. The motor drive circuit of this example is C
It comprises a PU 1, a timing generation circuit 2, and a motor driver 3, and the output of the motor driver 3 is supplied to a DC brushless motor 4. The CPU 1 is a central processing unit that performs various controls such as rotation control, voltage control, and overcurrent control of the DC brushless motor 4, and performs control according to a program stored in a ROM (not shown). The encoder 4a is a device that detects the rotation speed of the DC brushless motor 4, detects the rotation speed of the motor using a photoelectric conversion element such as a photocoupler, and outputs a rotation detection signal to the CPU 1. The CPU 1 receives this signal and a reference clock (reference CL).
K), and outputs the difference to the timing generation circuit 2 as a PWM signal.

The Hall sensor 4b provided in the vicinity of the DC brushless motor 4 is a sensor for detecting an arrangement position of a rotor magnet (for example, a permanent magnet). The switching is detected, and this detection signal is output to the timing generation circuit 2.

The timing generation circuit 2 has a Hall sensor 4b.
The switching timing of the windings of the motor 4 is known based on the signal output from the controller 4, and a drive signal is output to the motor driver 3 based on the switching timing. Motor 4
Drives a motor 4 by passing a drive current through each winding (armature winding) according to a drive signal output from the motor driver 3.

A resistor R is connected between the motor driver 3 and the ground, and the current flowing through each winding of the motor 4 flows into the ground through the resistor R. Motor driver 3
The connection point between the resistor R and the resistor R is supplied to an A / D input (analog-digital conversion input) of the CPU 1 so that a voltage generated between the motor driver 3 and the resistor R can be detected. still,
In this example, the resistance value of the resistor R is set to, for example, 0.5Ω.

FIG. 2 shows the reference clock (reference C).
LK). This circuit includes an oscillator 6, an inverter 9, and a frequency divider 10. The oscillator 6 is composed of a crystal oscillator 7 constituting a Colpitts circuit, capacitors C1 and C2, a resistor R, and an inverter 8,
An oscillation frequency based on the natural frequency of the crystal unit 7 is output to a frequency dividing circuit 10 via an inverter 9. Dividing circuit 10
Divides the frequency of an input signal a plurality of times and outputs the frequency to the CPU 1 as a reference clock (reference CLK) having a predetermined frequency.

The processing operation of the motor drive circuit having the above configuration will be described. In addition, the motor drive circuit of this example is
For example, it is a drive circuit of a DC brushless motor that drives various rollers, a photosensitive drum, and the like in the printer device.

FIG. 3 is a flowchart for explaining the processing operation of the motor of this embodiment. First, the DC brushless motor 4 for driving various rollers, photosensitive drums, and the like is started by initial setting processing of the printer device.

When a drive start signal for the motor 4 is input, the CPU 1 counts "T _M " and "Φ _M " (step (hereinafter referred to as S) 1). This counting process is a process of counting the rotation speed of the DC brushless motor 4 detected by the encoder 4a and the cycle of the above-described reference clock (reference CLK). The counter is provided from the encoder 4a by a counter (not shown) provided in the CPU 1. and the count value "T _M" counts the rotation detection signal output, also a count value "[Phi _M" by counting the signal outputted from the frequency divider 10 of the above. Incidentally, the count value "T _M" is intended to indicate a pulse width of the rotational speed signal of the motor encoder 4a is detected, the corresponding pulse width "tm" shown in FIG. The count value “Φ _M ” indicates the pulse width of the reference clock, and corresponds to the pulse width “φm” shown in FIG. Therefore, when the pulse width "tm" is wide, the count value "T _M" is increased, the count value even when the pulse width "φm" broad "[Phi _M" increases.

On the other hand, in the above processing (S1), the CPU 1
The voltage data supplied to the A / D input is also converted into digital data and read. Next, the CPU 1 determines whether or not the count value of “T _M ” is smaller than “128” (S
2). At the beginning of the rotation of the DC brushless motor 4, the rotation speed is slow because the speed gradually increases from the motor stopped state.
For example, FIG. 4 shows that after the DC brushless motor 4 starts rotating, the rotation speed is changed to 20 rpm, 50 rpm, 100 rpm,
"T" when gradually increasing to 500 rpm and 1030 rpm
_M ”(however,“ n ”and“ C
PU1 set current "and its" actual measurement value "are also shown).

Here, as can be seen from FIG. 4, "T _M "> 128 at the beginning of rotation of the DC brushless motor 4, and
The judgment (S2) is N (No). Therefore, CPU
1 shifts to the judgment (S3). In this judgment (S3), the value of “n” is

[0024]

(Equation 1)

It is to judge whether or not. The value of “n” is determined by the CPU when the DC brushless motor 4 is started.
1 is a value that determines the set voltage, and as described in the above-described conventional example, the motor rotation speed is different between when the motor is started and when the motor is overloaded, so that there is a difference between the set current of the CPU 1 and the actually measured value. Since accurate current control cannot be performed, this is a numerical value for adjusting this. Note that the value of this “n” is “44”
At this time, as shown in FIG. 4, the rotation speed of the DC brushless motor 4 is 1030 rpm.

The above equations will be described in more detail.
Is C when the rotation speed of the DC brushless motor 4 is variable.
It is a figure which shows the set value of PU1, The straight line of the figure shows the overcurrent measured value at the time of starting, and the straight line shows the overcurrent measured value at the time of normal drive. That is, as described in the conventional example, the time constant of the drive circuit and the input impedance of the motor differ between when the motor is started and when the motor is overloaded, and the actual measured value of the current when the motor is overloaded is 1.7 A, for example. On the other hand, the current value at the time of starting the motor is increased to, for example, 2.6 A.
It is necessary to adjust the difference of 9A.

Therefore, in order to adjust this difference, the present embodiment performs control according to the curve of FIG. In other words, when the current value during overload during operation is, for example, 1.7 A, the current value at the time of starting the motor is further higher by 0.9 A.
As shown by, the current value at the time of overload during operation is reduced to 0.8 A, and as a result, the current value at the time of starting the motor is 1.7 A (2.
6A-0.9A) (arrow b in FIG. 5). Therefore, the rotation speed of the DC brushless motor 4 is 1030 rpm
Until it reaches the value of "n" shown in the curve. The value of this “n” is the above equation (1). Note that the resistance R
Is 0.5Ω, and the set current of the CPU 1 is set to 0.8 A so that the measured current at the time of starting the DC brushless motor 4 becomes 1.7 A as described above. For this purpose, N1 is a set value at the time of start-up as a set value of the A / D input,
If N2 is a steady state set value,

[0028]

(Equation 2)

If the input value of the A / D input is “n”, the arithmetic expression for overcurrent control is

[0030]

(Equation 3)

## EQU1 ## Therefore, the CPU 1 performs the PWM control until the expression set as described above is satisfied (N in S3, S4). That is, PWM = (Φ _M −1
28) + 20X (T _M over 128) + X (where, X is PWM value to the control rotation speed at rated torque)
The rotational speed of the DC brushless motor 4 is increased according to the correction value indicated by. That is, the CPU 1 compares the rotation speed “T _M ” of the motor 4 with the reference clock “Φ _M ”, outputs a PWM signal based on the phase difference to the motor 4, and gradually increases the speed of the DC brushless motor 4. .

Thereafter, when the rotation speed of the DC brushless motor 4 increases and the count value of “T _M ” becomes smaller than “128” (Y in S2), the CPU 1 sets the value of “n” to “4”.
4 "is determined (S5). Here, when the value of "n" is "44", the rotation speed of the motor is 1030 rpm as described above, and the output of the PWM signal is immediately stopped (Y in S5, S6). When the value of “n” is “4”
If “4” has not been reached, P is determined by the above processing (S4).
The output of the WM signal is continued, and the rotation speed of the motor increases (S
5 is N, S4), and when the value of "n" reaches "44", the output of the PWM signal is stopped (S5 is Y, S6).

Therefore, by stopping the PWM control at this time, the rotation of the motor is locked at the rotation speed (1030 rpm) of the DC brushless motor 4 at this time. Therefore, the DC brushless motor 4 is locked at this rotation speed and is driven at a constant rotation speed.

As described above, when the DC brushless motor 4 is started, the overcurrent protection circuit according to the present embodiment has the set value of 1.7 A.
The DC brushless motor 4 is reliably locked at 1030 rpm. On the other hand, CPU1
When the value of is normally rotated at a rotation speed of 1030 rpm, if an overload is applied for some reason, the overcurrent protection circuit operates. The current at this time is also substantially limited to 1.7 A due to the relationship of impedance and the like.

As described above, the current value of the overcurrent is set according to the rotation speed of the DC brushless motor 4.
With this configuration, the peak current at the time of starting the motor can be guided to a lower side, the specification value of the DC brushless motor 4 and the rated current of the motor driver 3 can be reduced, and the cost of the device can be reduced. <Second Embodiment> The motor driving device of this embodiment is the same as the above-described embodiment, and the system block diagram of FIG.
This is a configuration using the oscillation circuit of FIG. However, the difference is that the overcurrent control at the time of starting the motor is set to the value of the overcurrent during the normal rotation. That is, the control shown in FIG. 5 is performed.

As in the above-described embodiment, the horizontal axis in FIG. 5 indicates the number of rotations of the DC brushless motor 4 and the vertical axis indicates the CPU 1.
, The straight line in the figure shows the measured overcurrent at startup, and the straight line shows the measured overcurrent during normal driving. Then, control according to the curve in FIG. 5 is performed to eliminate this difference.

That is, in the case of this example, assuming that N1 'is a start-time set value and N2' is a steady-state set value as A / D input set values,

[0038]

(Equation 4)

If the input value of the A / D input is “n ′”, the arithmetic expression for overcurrent control is

[0040]

(Equation 5)

## EQU1 ## Based on the value of “n ′” set in this way, the control processing according to the flowchart shown in FIG. 3 is performed. Note that the processing in FIG. 3 has been described in the first embodiment, and thus details are omitted. In this example, the determination (S5) in FIG. 3 is “n> 67”. Thus, in this example, "T _M" is a time less than "128" (S2 is Y), and "n" is exceeds "67" (S5 is Y), the output of the PWM signal is set to "0", The rotation speed of the DC brushless motor 4 is locked at 1030 rpm, and thereafter the motor is driven at this rotation speed.

As described above, in this example, when the DC brushless motor 4 is started, the overcurrent protection circuit is set to 2.6 A, which is the set value.
And the DC brushless motor 4 is reliably locked when its rotation speed is 1030 rpm. On the other hand, CP
When the value of U1 normally rotates at a rotation speed of 1030 rpm,
When an overload is applied for some reason, the overcurrent protection circuit operates. The current at this time is also substantially limited to 2.6A.

As described above, the current value of the overcurrent is set according to the rotational speed of the DC brushless motor 4.
With this configuration, the peak current at the time of starting the motor is guided to a higher side, and when the rotation of the DC brushless motor 4 is locked, an extremely wide lock width can be used.
Reliable motor lock can be performed.

In the above description of the two embodiments,
Although an external circuit (the oscillation circuit shown in FIG. 2) is used as the oscillation circuit, a configuration in which an oscillation circuit is provided in the CPU 1 may be used. In the present embodiment, the motor drive circuit of the present invention is driven by PLL control. However, the present invention is not limited to PLL control.

Further, the motor drive circuit of the present embodiment can be applied not only to driving various rollers and photosensitive drums in a printer, for example, but also to driving motors used in other electronic devices. it can.

[0046]

As described above, according to the present invention, the set value of the overcurrent limiting circuit can be varied according to the number of revolutions of the motor, and a small capacity motor drive device can be provided.

Further, by setting the overcurrent at the time of starting the motor to be relatively large, it is possible to reliably lock the motor at a predetermined rotation speed.

[Brief description of the drawings]

FIG. 1 is a system block diagram of a motor drive device according to an embodiment of the present invention.

FIG. 2 shows a circuit for generating a reference clock (reference CLK).

FIG. 3 is a flowchart illustrating a processing operation of the present example.

FIG. 4 shows “T _M ”, “n”,
FIG. 4 is a diagram for explaining data such as data.

FIG. 5 is a diagram illustrating a control example of an overcurrent limiting circuit.

FIG. 6 is a diagram illustrating pulse widths of “tm” and “Φm”.

FIG. 7 is a diagram illustrating a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CPU 2 Timing generation circuit 3 Motor driver 4 DC brushless motor 4a Encoder 4b Hall sensor 6 Oscillator 7 Crystal oscillator 8, 9 Inverter 10 Divider circuit

Claims (3)

[Claims] 1. A DC brushless motor driving circuit having overcurrent limiting means, comprising: a motor rotation speed detecting means, wherein an overcurrent limiting level of the overcurrent limiting means is changed according to a detection output of the rotation speed detecting means. DC brushless motor drive circuit characterized in that: 2. The DC brushless motor drive circuit according to claim 1, wherein the change of the overcurrent limit level is performed between an overcurrent at the time of starting the motor and an overcurrent at the time of normal driving. 3. The overcurrent limiting unit according to claim 1, wherein the overcurrent limiting unit changes the overcurrent limiting level based on a difference between a current at the time of starting the motor and an overcurrent during normal driving. DC brushless motor drive circuit.