JPH06284795A - Stepping motor operation/stop detecting circuit - Google Patents

Abstract

PURPOSE:To provide a stepping motor operation/stop detecting circuit capable of detecting a stepping motor operated/stopped by measuring a time for changing a current flowing through a drive circuit. CONSTITUTION:An overcurrent signal 30, output by a comparator 28 provided in a drive circuit 10, is fed out to a timer circuit 40 connected to a CPU37, and a time of high level of this signal 30 is measured by the timer circuit 40. This measured time is compared with a preset time by the CPU37, to judge whether a motor is stopped or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection circuit for detecting the operation / stop of a stepping motor, and more particularly to a stepping motor stop detection circuit for detecting the operation / stop of a stepping motor during driving of the stepping motor.

[0002]

2. Description of the Related Art Conventionally, a stepping motor is used as a spacing motor in a serial printer, for example, to convey a carriage having a print head. FIG. 6 is a perspective view of a main part showing a configuration of a printing mechanism section of a conventional serial printer. The print head 2 is mounted on a carriage 3, and the carriage 3 is provided with a stepping motor 1 (hereinafter referred to as a motor) via a synchronous belt 4. ). The side frame 5 is provided on the side portion of the serial printer. When the power is turned on, the motor 1 is driven to convey the carriage 3 to the left and the carriage 3 is abutted against the side frame 5, and it is detected that the carriage 3 is at a specific position. Can be determined.

Next, the print reference position determining operation of the serial printer having the above structure using the stepping motor will be described with reference to FIG. Regarding the above-mentioned abutment,
In order to detect that the carriage 3 has hit the side frame 5, as shown in the figure, a slit disk 6 mounted on the rotating shaft of the motor 1 and a transmission type photo interrupter for detecting the slit 7 of the slit disk 6. (Hereinafter referred to as a photo sensor) 8 is installed. That is, when the motor 1 is rotating, the output of the photo sensor 8 is repeatedly turned on and off, but when the carriage 3 hits the side frame 5, the motor 1 is stopped, so that the slit disk 6 is stopped and the photo sensor 8 is stopped. The output of does not change in the on or off state. Therefore, since the output of the photo sensor 8 does not change, it can be detected that the carriage 3 has hit the side frame 5.

Another conventional mechanism for detecting that the carriage 3 is at a specific position will be described with reference to FIG. FIG. 7 is a main part perspective view showing a configuration of a printing mechanism section of a serial printer when a micro switch is provided. Instead of the slit disk 6 and the photo sensor 8, a micro switch 9 is provided on the side frame 5. Other structures are the same as those in FIG.

In FIG. 7, the micro switch 9 is turned off when the carriage 3 is separated from the side frame 5, and when the carriage 3 approaches the side frame 5, the lever of the micro switch 9 is pushed down. Turns on. Since the position of the carriage 3 when the micro switch 9 is turned on is specified, the initial position of the carriage 3 can be detected. As described above, by installing the micro switch 9 on the side frame 5, it is possible to detect that the carriage 3 is at a specific position by the output of the micro switch 9, and as a result, the print position is determined based on the detected position. be able to.

[0006]

However, when a stepping motor is used, for example, in a serial printer having the above-described structure, the stepping motor will be used unless mechanical reference position detecting means such as a slit disk, a photo sensor, and a micro switch are provided. It was not possible to determine whether it was physically stopped or operating.

In the present invention, it is possible to detect whether the motor is operating or stopped by observing the time constant for changing the current when the stepping motor is used, without providing the above-mentioned mechanical reference position detecting means such as the micro switch. The purpose is to provide a circuit.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, a plurality of motor coils are selectively phase-excited to flow a current through the motor coils to drive a stepping motor. A drive that detects whether or not the current flowing through the coil exceeds a reference value, outputs an on / off current excess signal, and controls the current flowing through the motor coil by turning on / off the current excess signal. Whether the stepping motor is operating by comparing a circuit, a measuring unit that measures the ON time or the OFF time of the current excess signal, and the ON time or the OFF time measured by the measuring unit with a set time. A determination means for determining whether the vehicle is stopped is provided.

[0009]

When the stepping motor is driven by passing a current through the motor coil of the drive circuit, the output of the current excess signal is turned on / off depending on whether the current flowing through the motor coil exceeds the reference value. As a result, when the current does not exceed the limit, the excess current signal is turned on to turn on the current to the motor coil, and when it exceeds the limit, the excess current signal is turned off and the current is not passed to the motor coil. Take control. The measuring means measures the on-time or off-time of the current excess signal, and the determining means compares the measured on-time or off-time with the set time. At this time, when the on time or the off time is longer than the set time, the determination means determines that the stepping motor is operating, and when the on time or the off time is shorter than the set time, it determines that the stepping motor is stopped. As a result, it is possible to determine whether the stepping motor is operating or stopped without providing any mechanical means as in the conventional case.

[0010]

Embodiments of the present invention will be described in detail below with reference to the drawings. Note that elements common to the drawings are given the same reference numerals.

FIG. 1 is a circuit block diagram for driving a four-phase stepping motor of the present embodiment with a constant current. Reference numeral 11 is a pnp transistor for controlling the total current supplied to the stepping motor (hereinafter referred to as a motor). It turns on through the preamplifier 13 while 12 is on. 14 to 17 are motor coils 18 to 2 of the first to fourth phases of the motor 1, respectively.
ON / OFF of the npn transistor connected to 1 is controlled by the first phase excitation command signal 22 to the fourth phase excitation command signal 25, respectively. Reference numeral 26 is a current detection resistor, and a voltage proportional to the total current flowing through the motor coils 18 to 21 appears in the current level signal 27. Reference numeral 34 denotes a flywheel diode, which forms a circulation route for discharging stored energy when the pnp transistor 11 is turned off while the energy is stored in the motor coils 18 to 21 and the npn transistors 14 to 17 are turned on. Reference numeral 36 is a driving power source.

Reference numeral 28 denotes a comparator, to which a current level signal 27 is inputted to its minus input, and to the plus input of the comparator 28, a current setting signal 29 is inputted via a resistor 35. The comparator 28 constantly compares the voltage level of the current level signal 27 with the voltage level input to the plus input of the comparator 28, and the voltage level of the current level signal 27 is higher than the plus input voltage of the comparator 28. When it is high, a low level is output as the current excess signal 30, and when the voltage level of the current level signal 27 is lower than the positive input voltage level of the comparator 28, a high level is output as the current excess signal 30. . 31 is a feedback resistor, which is an overcurrent signal 3
When 0 is at a low level, the comparator 2 is used rather than the current setting signal 29.
When the positive input voltage of 8 is decreased and the current excess signal 30 is at a high level, the positive input voltage of the comparator 28 is made higher than that of the current setting signal 29 so that the comparator 28 has a hysteresis characteristic and high-speed output change. It prevents the oscillation due to. The excess current signal 30 is a negative feedback circuit that is input to the gate 32 together with the energization permission signal 33, and the energization command signal 12 is turned on only when the energization permission signal 33 is on and the excess current signal 30 is at a high level. Further, the current excess signal 30 is input to the timer circuit 40 described later. The drive circuit 10 is configured as described above.

Next, the control circuit 50 will be described with reference to FIG. A central processing unit (CPU) 37 reads the count value of the timer circuit 40 via a bus 39 according to a program stored in a read-on memory (ROM) 38. Further, according to the program, the CPU 37 resets the count value of the timer circuit 40 and controls the motor 1 via the input / output (I / O) port 41. The current excess signal 30 shown in FIG. 1 is input to the timer circuit 40 as the timer control input signal 42, and the timer circuit 40 counts the clock signal 43 supplied from the CPU 37 only while the signal is at a high level. When 42 becomes a low level, counting is stopped, the count value is held, and the count end signal 44 connected to the I / O port 41 is turned on. CPU3
7 can reset the count value of the timer circuit 40 by a timer reset signal 45 input from the I / O port 41 to the timer circuit 40. When the count end signal 44 is turned on, the CPU 37 reads the count value of the timer circuit 40, and compares the count value with a later-described ton12 which is the set time stored in the ROM 38. The motor control signal group 46 of the I / O port 41 is controlled by the CPU 37 via the I / O port 41 as the energization permission signal 33 and the first phase excitation command signal 22 to the fourth phase excitation command signal 25 of FIG. It is supposed to do.

Next, the normal rotation drive operation of the stepping motor having the drive circuit 10 and the control circuit 50 will be described with reference to FIG.
~ It demonstrates based on FIG. FIG. 2 is a waveform diagram for explaining the operation state of the present embodiment, and FIG. 3 is a waveform diagram showing the drive state of the motor coil.

In FIG. 1, when the energization permission signal 33 is turned on and the current setting signal 29 is output, the minus input of the comparator 28 is lower than the plus input, so the comparator 28 outputs the current excess signal 30 at a high level. . Further, as shown in FIG. 3, the two phases are constantly excited and sequentially turned on / off in accordance with the direction in which the first phase to fourth phase excitation command signals 22 to 25 are to be rotated. As a result, the energization command signal 12 is turned on, the PNP transistor 11 is turned on, and current flows to the motor coils 18 to 21. Motor coils 18-21
Is a two-phase excitation, the PNP transistor 11
The current that has passed through passes through two of the four motor coils 18 to 21 and flows to the current detection resistor 26.

The voltage of the current level signal 27 is applied to the negative input of the comparator 28 by the current detecting resistor 26. The comparator 28 compares the voltage level of the current level signal 27 with the comparator 2
8 is compared with the voltage level of the positive input, and the comparison result is output as the current excess signal 30 that is on, that is, high level, or off, that is, low level. Current level signal 2
7 has the waveform shown in FIG. In addition, V ₁ and V in FIG.
₂ is the voltage level of the positive input of the comparator 28. The current passes through the motor coils 18-21 and the current level signal 2
When the voltage level of 7 rises to reach V2, the comparator 28 outputs a low level as described above, which causes the feedback resistor 31 to change the positive input level of the comparator 28 from V ₂ to V _1.
Acts to lower to.

When the low level is output as the current excess signal 30, the PNP transistor 11 cuts off the current, and as a result, the voltage level of the current level signal 27 gradually decreases and reaches V ₁ . This causes the comparator 28 to output a high level, and the feedback resistor 31 again raises the positive input level of the comparator 28 from V ₁ to V ₂ . The above is the operation performed during normal rotation of the motor.

By the way, as described above, the current excess signal 3
0 is input to the timer circuit 40. Next, the rotation and stop detection operation of the motor will be described based on the flowchart of FIG. FIG. 4 is a flow chart for explaining the rotation / stop detection operation of the motor.

When the excess current signal 30 is at a low level (step 1), the CPU 37 controls the I / O port 41.
Outputs the timer reset signal 45 to the timer circuit 40 (step 2). After that, when the current excess signal 30 is output at a high level (step 3), the timer circuit 40 counts the clock signal 43 sent from the CPU 37. At this time, the time measured by the timer circuit 40 is the time represented by ton shown by the arrow in FIG. 2, that is, the on time of the current excess signal 30, and when the current excess signal 30 outputs a low level, the timer circuit 40 , A count end signal 44 is sent to the CPU 37 via the I / O port 41 to end the count (step 4).

Thereafter, the CPU 37 reads the count value held in the timer circuit 40 (step 5), and ROM
The value of the preset time ton12 stored in 38 is compared with the count value (step 6). Here ton1
2 will be described with reference to FIG. FIG. 5 is an explanatory diagram showing current level signals when the motor is stopped and rotating.

The waveform 61a is the waveform of the current level signal 27 when the motor 1 is rotating, and the waveform 61b is the waveform of the current level signal 27 when the motor 1 is stopped. As can be seen from the figure, the waveform 61a represented by the current level signal 27 when the motor 1 is rotating has a longer cycle than the waveform 61b when the motor 1 is stopped. This is because the counter electromotive force is generated in the motor coil due to the rotation of the motor 1. Therefore, time ton1 from a voltage level V ₁ of the current level signal 27 when the motor 1 is rotating until it reaches the V ₂ reaches from V ₁ to V ₂ when the motor 1 is stopped Is longer than the time ton2 (ton1> ton2). The set time ton12 described above in the figure is smaller than ton1 and ton2
Greater than (ton1>ton12> ton2), t
It is almost half the time of on1 and ton2. But t
If the value satisfies on1>ton12> ton2, it does not necessarily have to be half the time.

As described above, the CPU 37 compares the ton12 with the count value, and when the count value is smaller than the ton12, the CPU 37 determines that the motor 1 is stopped (step 7). In addition, the count value is ton12
If it is greater than, it is determined that the motor 1 is rotating (step 8)

Here, the magnitude relation between ton1 and ton2 will be described by means of equations. The resistance value of the current detection resistor 26 is Ri, the voltage of the driving power supply 36 is Vd, and the motor coil 18
The waveform of the current level signal 27 will be described first, where Rj is the resistance component of .about.21, L is the inductance, and Er is the counter electromotive force generated in each motor coil during motor rotation.

The current voltage of the current level signal 27 while the energization command signal 12 is on is obtained from the following equation. Motor 1
Is a part of the current waveform when a voltage (Vd-Er) is applied to the series circuit of Rj and L when rotating, and as shown in FIG. Since it is driven, twice the current flows through the current detection resistor 26. If the current I corresponding to 1 is t = 0 at the start of energization,

[Equation 1] The equation in which the point A in the partially enlarged view of the current level signal 27 shown in FIG. 5 is t = 0 is as shown in the equation (3), where Vi = V ₂ at t = 0.

[Equation 2]

Next, the equation corresponding to the equation (1) in which the motor 1 is stopped is as shown in the equation (6) because there is no back electromotive force Er.

[Equation 3]

The time required for the current level signal 27 to reach from V ₁ to V ₂ is when the motor 1 is rotating.
If n1 and ton2 when the vehicle is stopped, the equations (10) and (11) are satisfied.

[Equation 4] By solving the equations (10) and (11), the equations (12) and (13) are obtained.

[Equation 5] Here, in order to know the magnitude relation between Expression (12) and Expression (13),
Subtracting the logarithmic function variable of equation (13) from the logarithmic function variable of equation (12) gives

[Equation 6]

From the above, looking at the first term of the denominator of equation (14), it is the same as the denominator of the variable of the logarithmic function of equation (9),
The variable of the logarithmic function in equation (9) is positive and the numerator (2 · Ri · V
Since d) is positive, the denominator is also positive. Therefore, the first term of the denominator of equation (14) is positive. Similarly, considering the second term of the denominator of Expression (14), it is the same as the denominator of the logarithmic function variable of Expression (5), and the variable of the logarithmic function of Expression (5) is positive and the numerator {2
Ri * (Vd-Er)} is positive because the back electromotive force Er of the motor does not exceed the applied voltage Vd, and the denominator is also positive. Therefore, the second term of the denominator of equation (14) is positive.
Since the denominator and the numerator of Expression (14) are both positive, the value of Expression (14) is positive, and as a result, ton1> ton2.

As another embodiment, the comparator 2 in the above embodiment is used.
Instead of measuring the time during which 8 outputs a high level, that is, the on-time, the time during which a low level is output, that is, the off-time may be measured. In this case,
Time taken from V ₂ to decrease to V ₁ of the current level signal 27 is longer from V ₁ longer the time it takes up to V _2, is shorter as shortened, similarly to the foregoing embodiment, the OFF time It is possible to detect the rotation and stop of the motor 1 by utilizing.

[0029]

As described in detail above, according to the present invention, the stepping motor can be operated by measuring the driving time or the non-driving time of the driving circuit using the measuring means and comparing the time with the set time. By providing the determination means for determining whether the motor is operating or stopped, it is possible to detect whether the motor is operating or stopped without providing mechanical operation or stop detection means. In the present invention, a circuit for driving the motor can be used, and as a result, the number of parts can be reduced as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a control system of an embodiment according to the present invention.

FIG. 2 is a waveform diagram illustrating an operating state of the embodiment.

FIG. 3 is a waveform diagram showing a driving state of a motor coil.

FIG. 4 is a flowchart illustrating a motor rotation / stop detection operation.

FIG. 5 is an explanatory diagram showing a current level signal.

FIG. 6 is a main part perspective view showing a printing mechanism section of a conventional serial printer.

FIG. 7 is a main part perspective view showing a printing mechanism section of a conventional serial printer.

[Explanation of symbols]

 10 Drive Circuit 18-21 Motor Coil 27 Current Level Signal 28 Comparator 30 Current Excess Signal 37 CPU 40 Timer Circuit

Claims (2)

[Claims] 1. A stepping motor is driven by selectively supplying a plurality of motor coils with phase excitation to cause a current to flow through the motor coils. Whether or not the current flowing through the motor coils exceeds a reference value. A drive circuit that detects whether or not it outputs an on / off current excess signal and controls the current flowing to the motor coil by turning on / off the current excess signal, and measures the on time or off time of the current excess signal And a determination unit that determines whether the stepping motor is rotating or stopped by comparing the ON time or the OFF time measured by the measuring unit with a set time. A stepping motor operation / stop detection circuit characterized by: 2. The stepping motor operation / stop detection circuit according to claim 1, wherein the measuring means is a timer circuit.