JPH09222433A - Revolution speed detection device for dc motor with brush - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a revolution speed of a motor from a low speed to a high speed by automatically exchanging a circuit constant of a comparison voltage wave form generating means in accordance with a frequency of a pulse wave form. SOLUTION: A voltage wave form from a current detection means 1 is inputted to a comparison voltage wave form generating means 4 and a comparing means 5, respectively through a noise removing means 2 and an amplifier means 3. The voltage wave form of the amplifier means 3 and the comparison voltage wave form of the generating means 4 are inputted to the comparing means 5 and both the wave forms are compared, then a pulse wave form is outputted to a revolution speed calculation means 6 and a circuit constant exchanging means 7. The calculation means 6 calculates a revolution speed of a motor by counting the number of pulses of the pulse wave form in a unit of time. The exchanging means 7 exchanges a circuit constant of the generating means 4 to an optimum value in accordance with a frequency of the pulse wave form, i.e., the revolution speed of the motor. Thereby, it is possible to accurately detect the revolution speed of the motor in a wide range from a low revolution speed to a high revolution speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotation speed detection device for a DC brush motor, and more particularly, to a rotation speed detection device for a DC brush motor that generates a pulse from the current waveform of the DC brush motor to detect the rotation speed. Regarding

[0002]

2. Description of the Related Art Conventionally, as a device for detecting the rotation speed of a DC brush motor without using an encoder, a tachogenerator, etc., the rotation speed of the DC brush motor is detected from the waveform of the current flowing through the DC brush motor. There is known a device that does. The current includes an AC component due to a change in the contact area between the brush and the commutator piece as the rotor rotates, and its waveform is a vibration waveform having a frequency proportional to the rotation speed of the rotor. When the current is detected by using a resistor or a Hall element, the output has a voltage waveform corresponding to the current waveform.

In principle, the detection of the motor rotation speed by the voltage waveform will be described below. The rotation speed of the motor is detected by a voltage waveform in which a noise component is removed by a filter, which is shown by a solid line A in the upper part of FIG. This is performed by generating a pulse from the solid line B in the upper part of FIG. 4) and counting the pulse. That is, the voltage waveform and the comparison voltage are input to a comparator, and when the voltage value of the voltage waveform is larger than the voltage value of the comparison voltage, the comparator outputs a voltage of, for example, 5 V, and the voltage waveform Is smaller than the voltage value of the comparison voltage, the comparator is configured to output a voltage of 0V, for example. With such a configuration, as indicated by a solid line C in the lower part of FIG. 4, the comparator outputs one pulse per one cycle of the voltage waveform, that is, the current waveform (hereinafter referred to as one cycle / one pulse conversion). ) Will be done. In FIG. 4, the vertical axis and the horizontal axis represent voltage value and time, respectively. Then, assuming that the number of pulses per second is P and the number of commutator pieces is S, the rotational speed R (rpm) of the motor can be calculated by the following equation.

[0004]

[Equation 1]

Incidentally, the comparison voltage is obtained by
It is generated by removing the AC component through a comparison voltage waveform generating means such as a low pass filter or an integrating circuit. However, since it is actually difficult to completely remove the AC component, the waveform of the comparison voltage (hereinafter, referred to as a comparison voltage waveform) contains some AC component. In order to perform accurate 1-cycle 1-pulse conversion, it is desired that the comparison voltage waveform has a sufficiently small AC component as compared with the voltage waveform, that is, a smooth waveform.

FIG. 7 is a block diagram showing an example of a rotation speed detecting device for a DC brush motor based on the above-mentioned conventional technique. In the figure, 11 is a DC brush motor,
Reference numeral 12 is a DC power supply, R is a resistor for detecting voltage, reference numeral 2'is a filter for removing noise components of the voltage waveform, and reference numeral 3'is an AC of the voltage waveform. An amplification circuit for amplifying the component, a reference numeral 4'is a low-pass filter for generating a comparison voltage waveform, a reference numeral 5'is a comparator, and a reference numeral 6'is a comparator 5 '. It is a counter that counts the number of pulses per unit time of the pulse waveform generated by.

[0007]

When the comparison voltage waveform is generated by the low pass filter, the comparison voltage waveform becomes smoother as the cutoff frequency of the low pass filter is set lower than the frequency of the voltage waveform. However, if the cutoff frequency is set extremely low,
Since the phase delay of the comparison voltage waveform with respect to the voltage waveform becomes large, for example, as shown in FIG. 5, the comparison voltage B changes due to a sudden change in the DC component of the voltage waveform A due to a load change or the like.
Cannot be followed, and accurate one-cycle / one-pulse conversion cannot be performed. The solid line C in FIG. 5 represents the pulse waveform generated by the comparator.

On the other hand, when the cutoff frequency and the frequency of the voltage waveform are close to each other, the low-pass filter is almost ineffective, so that a smooth comparison voltage waveform cannot be generated and accurate one-cycle / one-pulse conversion becomes difficult. . Further, if the cutoff frequency is set higher than the frequency of the voltage waveform, the low pass filter is completely ineffective, and one cycle / one pulse conversion cannot be performed. That is, in the rotation speed detection circuit of the DC brush motor shown in FIG. 7, the frequency band in which accurate one-cycle / one-pulse conversion is performed is limited by the set value of the cutoff frequency of the low-pass filter 103. That is, there is a problem that the range of the motor rotation speed that can be accurately detected is limited.
Similarly, when an integrator circuit is used as the comparison voltage waveform generating means, the set value of the time constant of the integrator circuit causes
There is a problem in that the frequency band in which accurate one-cycle / one-pulse conversion is performed is limited, and the range of motor rotation speed that can be accurately detected is limited.

Therefore, it is an object of the present invention to provide a DC brush motor rotation speed detecting device capable of accurately detecting the motor rotation speed over a wide range from low rotation speed to high rotation speed. .

[0010]

In view of the above-mentioned circumstances, a rotation speed detection device for a DC brush motor according to the present invention includes a current detection unit that detects a voltage of a current flowing through the DC brush motor, and an output from the current detection unit. Noise removing means for removing a noise component of the voltage waveform, an amplification means for amplifying the noise-free voltage waveform, and a comparison voltage waveform for removing an AC component of the amplified voltage waveform A voltage waveform generating means, a comparing means for generating a pulse waveform by comparing the voltage waveform with the comparison voltage waveform, a pulse number per unit time of the pulse waveform, and a rotation speed of the DC brush motor. And a circuit constant switching unit that switches the circuit constant of the comparison voltage waveform generation unit according to the frequency of the pulse waveform. It is characterized by the following.

In this specification, the circuit constant means
It is a general term for the cutoff frequency of the low-pass filter and the time constant of the integration circuit. A low cutoff frequency or a large time constant is called a large circuit constant, and a high cutoff frequency or a small time constant is called. It is assumed that the circuit constant is small.

[0012]

In the present invention, when the comparison voltage waveform is generated from the voltage waveform that fluctuates corresponding to the fluctuation of the rotation speed of the DC brush motor, the circuit constant of the comparison voltage waveform generation means corresponds to the voltage waveform. It is automatically switched according to the frequency of the pulse waveform. That is, even if the frequency of the voltage waveform changes due to a change in the number of rotations of the motor, the circuit constant of the comparison voltage waveform generation means is switched to a value suitable for the frequency, so that the comparison voltage waveform generation means can reliably operate. In addition to generating the comparison voltage waveform, the phase delay is suppressed as small as possible to improve the followability of the comparison voltage waveform with respect to the fluctuation of the voltage waveform, and one period / one pulse conversion is surely performed.

[0013]

EXAMPLES Examples of the present invention will be described below.
FIG. 1 is a block diagram showing a rotation speed detecting device for a DC brush motor (hereinafter, simply referred to as a motor) according to the present invention. The current detecting means 1 detects a current flowing through the motor and outputs a voltage waveform corresponding to the waveform of the current. The voltage waveform output from the current detection means 1 is subjected to noise component removal by the noise removal means 2 and then amplified by the amplification means 3 and input to the comparison voltage waveform generation means 4 and the comparison means 5, respectively. It The voltage waveform from the amplification unit 3 and the comparison voltage waveform generated by the comparison voltage generation unit 4 are input to the comparison unit 5, and a pulse is generated based on a comparison between the voltage waveform and the comparison voltage waveform. Output a waveform. Then, the pulse waveform output from the comparison means 5 is input to the rotation speed detection means 6 and the circuit constant switching means 7. The rotation speed calculation means 6 calculates the rotation speed of the motor by counting the number of pulses of a pulse waveform per unit time. On the other hand, the circuit constant switching means 7 switches the circuit constant of the comparison voltage waveform generating means 4 to an appropriate value according to the frequency of the pulse waveform, that is, the rotation speed of the motor.

FIG. 2 is a circuit diagram showing a first embodiment of a motor rotation speed detecting device according to the present invention. In the present embodiment, a low pass filter is used as the comparison voltage waveform generating means. In FIG. 2, reference numerals 11 and 12 are a motor and a DC power source, respectively. Reference numeral 101 denotes a current sensor, which detects a current flowing through the conductor from a magnetic field generated around the conductor connecting the motor 11 and the DC power supply 12, and outputs the magnitude of the current as the voltage level. . That is, the voltage waveform output from the current sensor 101 corresponds to the current waveform of the motor 11. Since the noise component due to the sliding of the brush and the commutator of the motor 11 is superimposed on the voltage waveform, the noise component is removed by the bandpass filter 102 and then amplified by the amplifier circuit 103.

The voltage waveforms amplified by the amplifier circuit 103 are respectively low-pass filter 104 and comparator 1.
It is input to 05. The low-pass filter 104 is composed of a plurality of resistors R1 to R5, a capacitor C and an operational amplifier 401 which are connected in parallel with each other. The resistor R1 of the plurality of resistors is always the capacitor C,
A low-pass filter is configured together with the operational amplifier 401, and the resistors R2 to R5 are sequentially connected to and disconnected from the resistor R1 by a circuit constant switching circuit 107 described in detail later. That is, in the low-pass filter 104, the circuit resistance switching circuit 107 increases or decreases the number of resistors connected in parallel to the resistor R1 to change the combined resistance value of the resistors and switch the cutoff frequency.

The voltage waveform input to the low-pass filter 104 has its AC component removed or attenuated to become a comparison voltage waveform. The comparison voltage waveform is input to the comparator 105 and serves as a comparison reference when a pulse waveform is generated from the voltage waveform. The comparator 105 compares the input voltage waveform with the comparison voltage waveform, and outputs a voltage of 5 V when the voltage value of the voltage waveform is larger than the voltage value of the comparison voltage waveform, for example. When the voltage value of the voltage waveform is smaller than the voltage value of the comparison voltage waveform, a voltage of 0V is output to output a pulse waveform corresponding to the voltage waveform.

If a noise component that cannot be completely removed by the bandpass filter 102 is superimposed on the voltage waveform, an erroneous pulse waveform may be output as shown by the solid line C'in FIG. is there. In such a case, the correct pulse waveform shown by the solid line C can be obtained by providing the comparator 105 with hysteresis.

The pulse waveform output from the comparator 105 is input to the counter 106 and the circuit constant switching circuit 107, respectively. The counter 106 counts the number of pulses of the input pulse waveform, and calculates the number of rotations of the motor 11 from the number of pulses per unit time and the number of commutator pieces of the motor 11 that is input in advance. The motor rotation speed R (rpm) is calculated by the following equation, where P is the number of pulses per second and S is the number of commutator pieces.

[0019]

[Equation 2]

On the other hand, in the circuit constant switching circuit 107, the input pulse waveform is converted by the frequency-voltage converter 701 into a voltage corresponding to the frequency of the pulse waveform, and the voltage is respectively divided into four comparators 702 and 703. , 704, 7
Enter 05. Further, the comparators 702, 703, 70
4, 705 have different reference voltages, and output 0V voltage when the input voltage is lower than the reference voltage, and 5V voltage when the input voltage is higher than the reference voltage. Is output. In this embodiment, the comparator 7
The reference voltages of 02, 703, 704 and 705 are respectively set as reference voltage 1, reference voltage 2, reference voltage 3 and reference voltage 4,
The voltage values increase in the order of reference voltage 1, reference voltage 2, reference voltage 3, and reference voltage 4.

The circuit constant switching circuit 107 also includes a semiconductor switch 706. The semiconductor switch 706
Are four switch circuits SW1, SW2, SW3, SW4
And the switch circuit of the comparator 7 is provided.
ON / OFF by signals from 02, 703, 704, 705
OFF control is performed. The switch circuits SW1, SW2
One of the terminals of SW3 and SW4 is the low-pass filter 1
No. 04 resistor R1 and the other terminals are connected to resistors R2, R3, R4 and R5, respectively.

Next, the operation of the circuit constant switching circuit 107 will be described. The frequency-voltage converter 701 outputs a voltage according to the frequency of the input pulse waveform. That is, the output voltage value is low when the frequency of the pulse waveform is low, and the output voltage value is high as the frequency of the pulse waveform is high. The voltage output from the frequency-voltage converter 701 is the comparator 70.
2, 703, 704, and 705 and are compared with the reference voltage 1, the reference voltage 2, the reference voltage 3, and the reference voltage 4, respectively. For example, when the frequency of the pulse waveform is low and the output voltage value is lower than the reference voltage 1, the comparators 702, 703, 704, and 705 output a voltage of 0V, and the switch circuit SW1 of the semiconductor switch 706. , SW
2, SW3 and SW4 are all open. Therefore, since only the resistor R1 is connected to the resistor of the low-pass filter, the combined resistance value of the resistors is maximized, and the cut-off frequency of the low-pass filter 104 is set to the lowest value.

Next, the frequency of the pulse waveform increases,
When the voltage value output from the frequency-voltage converter 701 is higher than the reference voltage 1 and lower than the reference voltage 2, only the comparator 702 outputs a voltage of 5V, and the other comparators Output a voltage of 0V. Therefore, only the switch circuit SW1 is closed, and the resistor R2 is connected in parallel to the resistor R1. By connecting the resistor R1 and the resistor R2 in parallel to each other, the combined resistance value of the resistors is reduced, and the cutoff frequency of the low-pass filter 104 is set to a value one step higher.

Further, when the frequency of the pulse waveform further rises and the voltage value output from the frequency-voltage converter 701 is higher than the reference voltage 2 and lower than the reference voltage 3, the comparison is made. Since the devices 702 and 703 output the voltage of 5V and the other comparators output the voltage of 0V, the switch circuits SW1 and SW2 are closed, and the resistors R1 and R2.
2, R3 are connected in parallel with each other, the combined resistance value of the resistors is further reduced, and the cutoff frequency of the low-pass filter 104 is set to a value one step higher.

Similarly, when the frequency of the pulse waveform further rises and the voltage value output from the frequency-voltage converter 701 sequentially becomes higher than the reference voltage 3 and the reference voltage 4, the comparators 704 and 705. Sequentially outputs a voltage of 5 V, and the switch circuits SW3 and SW4 are sequentially closed. Therefore, the resistors R4, R5 are sequentially connected in parallel to the resistors R1, R2, R3, so that the combined resistance value of the resistors gradually decreases, and the cutoff frequency of the low-pass filter 104 is set to a sequentially higher value. . On the contrary, when the frequency of the pulse waveform decreases and the voltage value output from the frequency-voltage converter 701 gradually decreases, the resistor R1 is connected to the resistor R1 contrary to the above case. R5, R4, R3
The connection of R2 is sequentially cut off, and the low-pass filter 10
The cutoff frequency of 4 is set to a sequentially lower value.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention using an integrating circuit as the comparison voltage waveform generating means. In FIG. 3, the same symbols as those in FIG. 2 indicate the same components as those in FIG. The integrating circuit 114 is composed of a plurality of resistors R1 to R5 and a capacitor C which are connected in parallel with each other. Resistor R of the plurality of resistors
Reference numeral 1 always forms an integrating circuit together with the capacitor C, and the resistors R2 to R5 are sequentially connected and disconnected to the resistor R1 by the circuit constant switching circuit 107. That is, as in the first embodiment described above, the integrating circuit 114
Means that the circuit constant switching circuit 107 increases or decreases the number of resistors connected in parallel to the resistor R1 to change the combined resistance value of the resistors and switch the time constant.

That is, when the frequency of the pulse waveform input to the circuit constant switching circuit 107 is low, the integrating circuit 114 sets the combined resistance value of the resistors to a large value and the time constant to a large value, and As the frequency becomes higher, the combined resistance value of the resistors becomes smaller and the time constant is set to a smaller value. Since the configuration and operation of the circuit constant switching circuit 107 in the second embodiment are exactly the same as those in the first embodiment, detailed description is omitted to avoid redundancy.

In the circuit constant switching circuit 107 of the first and second embodiments described above, four comparators are used to switch the circuit constants in five stages. By increasing the number and the number of reference voltages, switch circuits, and resistors corresponding thereto, it is possible to correspond to a wider range of pulse waveform frequencies and to perform more detailed switching of circuit constants. Further, in the first and second embodiments described above, the current sensor is used as the current detecting means, but instead of this, the current detection using the resistor R as shown in FIG. 7 is performed. You can go. Further, the present invention is not limited to the above-described embodiments, and various modifications can be made, which are not excluded from the scope of the present invention.

[0029]

As described above, in the rotation speed detecting device for a DC brush motor according to the present invention, when the rotation speed of the motor is low and the frequency of the pulse waveform output from the comparing means is low, the circuit When the circuit constant of the comparison voltage waveform generating means is set to a large value by the constant switching means and the number of rotations of the motor is high and the frequency of the pulse waveform output from the comparing means is high, the circuit constant switching means controls the comparison voltage waveform generating means. Since the circuit constant is set small, the optimum comparison voltage waveform can always be generated, and accurate 1-cycle 1-pulse conversion can be performed over a wide range from the low rotation range to the high rotation range, that is, the rotation of the motor. The number can be detected accurately. Furthermore, by using a comparator with hysteresis as the comparison means, it is possible to prevent generation of an erroneous pulse waveform due to noise components that cannot be completely removed by the noise removal means, and to detect the motor rotation speed more accurately. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram of a rotation speed detection device for a DC brush motor according to the present invention.

FIG. 2 is a circuit diagram showing a first embodiment of a rotation speed detecting device for a DC brush motor according to the present invention.

FIG. 3 is a circuit diagram showing a second embodiment of the rotation speed detection device for a DC brush motor according to the present invention.

FIG. 4 is a time chart of a voltage waveform, a comparison voltage waveform, and a pulse waveform.

FIG. 5 is a time chart of a voltage waveform, a comparison voltage waveform, and a pulse waveform.

FIG. 6 is a time chart of a voltage waveform, a comparison voltage waveform, and a pulse waveform.

FIG. 7 is a block diagram of a rotation speed detection device for a DC brush motor according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 current detection means 2 noise removal means 3 amplification means 4 comparison voltage generation means 5 comparison means 6 rotation speed calculation means 7 circuit constant switching means 11 DC brush motor 12 DC power supply 101 current sensor 102 bandpass filter 103 amplification circuit 104 low-pass filter 105 comparator 106 counter 107 circuit constant switching circuit 114 integrating circuit 401 operational amplifier 701 frequency-voltage converter 702, 703, 704, 705 comparator

Claims (5)

[Claims] 1. A current detecting means for detecting a voltage of a current flowing through a DC brush motor, a noise removing means for removing a noise component of a voltage waveform output from the current detecting means, and a voltage waveform from which the noise is removed. Amplifying means for amplifying the voltage waveform, a comparison voltage waveform generating means for removing the AC component of the amplified voltage waveform to generate a comparison voltage waveform, and a pulse waveform for comparing the voltage waveform and the comparison voltage waveform. And a rotation speed calculation means for counting the number of pulses per unit time of the pulse waveform and calculating the rotation speed of the DC brush motor, and the comparison voltage waveform generation means according to the frequency of the pulse waveform. A circuit constant switching means for switching the circuit constant of, and a rotation speed detection device for a DC brush motor. 2. The rotation speed detecting device for a DC brush motor according to claim 1, wherein the comparing means is a comparator with hysteresis. 3. The comparison voltage waveform generating means includes a resistor,
The rotation speed detection device for a DC brush motor according to claim 1, wherein the rotation speed detection device is a low-pass filter including a capacitor and an operational amplifier. 4. The comparison voltage waveform generating means includes a resistor,
The rotation speed detection device for a DC brush motor according to claim 1, wherein the rotation speed detection device is an integration circuit including a capacitor. 5. The circuit constant switching means receives a frequency-voltage converter for converting the frequency of the pulse waveform output from the comparing means into a voltage, and a different reference voltage, and the reference voltage and the frequency. At least two comparators that compare the output voltage of the voltage converter, a plurality of semiconductor switches that correspond to the respective comparators and are ON / OFF controlled by the output from the comparators, and A plurality of resistors which are connected corresponding to the semiconductor switches and which are connected / disconnected in parallel by turning on / off the semiconductor switches and which form a part of the comparison voltage waveform generating means. Item 3. A rotation speed detection device for a DC brush motor according to Item 1.