JPH1169860A - Speed control device of induction motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the rotational period with high accuracy irrespective of high/low rotational speed, by increasing the frequency of the reference clock during the high rotation, and decreasing the frequency during the low rotation in a period for each rotation of a rotor in the synchronous rotation with that of an induction motor. SOLUTION: A pulse signal detected by a detecting means 6 is divided by a first motor divider 7, and transmitted to a measuring means 10. The reference clock of a CLK 8 is divided according to the division ratio signal of an inverter device 1, and the reference clock divided by the inverter 1 is transmitted to first and second counters 10a, 10b. The section of the pulse 13 of the pulse signal by the detecting means 6 is counted by the reference clock to measure the count number in the motor rotational period, and the count number of the reference clock in the motor rotational period is converted into the motor rotation frequency. The speed of an induction motor 3 can be controlled by comparing the motor rotational frequency with the set value by the inverter device 1 to control the output frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control apparatus for an induction motor for calculating a rotation speed by counting a cycle of each rotation of a rotor rotating in synchronization with the induction motor by a reference clock.

[0002]

2. Description of the Related Art A speed control device for an induction motor of this type includes:
As shown in FIG. 5, one or two marks 24a and 24b
The proximity sensor 25 detects the mark of the rotor 24 that rotates in synchronization with the induction motor 23 and has a
The section of the pulse 30 (corresponding to the cycle of one rotation of the rotor) of the pulse signal Sg22 obtained by dividing the output signal Sg21 of the proximity sensor 25 is counted (counted) by the counter 28 that counts the pulses of the reference clock. )
Then, the rotation cycle of the induction motor 23 is measured as a magnitude relationship between the number of pulses at predetermined intervals. Then, the rotation cycle represented by the magnitude of the pulse number is converted into a frequency corresponding to the rotation speed and fed back to the inverter device 21 of the induction motor 23, and compared with the set frequency, thereby eliminating the rotation fluctuation due to the load fluctuation. It is a control device.

When the speed control device generates a pulse signal Sg22 corresponding to one rotation of the rotor 24, the same position of the rotor is detected, so that the period of each rotation of the rotor can be accurately measured. Further, the rotor 24 has a simple shape.

[0004] Then, the section of the pulse 30 which is the cycle of one rotation of the rotor, which is accurately measured, is counted by the reference clock which is a short pulse.
The rotation speed can be measured with high accuracy by increasing the frequency of the reference clock that generates 9 and increasing the number of counts.

[0005]

However, when the rotation cycle at the time of low rotation is measured using the same reference clock as the high frequency at the time of high rotation, the reference clock corresponding to the pulse 30 of the pulse signal Sg22 is obtained. Is very large, the counter 28
a, 28b overflows, and there is a problem that it is impossible to count (count) the entire section of the reference clock. Conversely, when the rotation period at the time of high rotation is measured using the same reference clock as the low frequency reference clock at the time of low rotation, there is a problem that the count number decreases and the accuracy of the rotation speed is not obtained. .

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to count a cycle of each rotation of a rotor rotating in synchronization with an induction motor by using a reference clock to determine a rotation speed. Is to provide a speed control device for an induction motor that can perform high-accuracy measurement not only at a low rotation of the induction motor but also at a high rotation.

[0007]

According to the first aspect of the present invention,
A speed control device for an induction motor that counts a cycle of each rotation of a rotor that rotates in synchronization with an induction motor with a reference clock to obtain a rotation speed, wherein when the rotation speed is high, the frequency of the reference clock is increased. And a reference clock changing means for lowering the frequency of the reference clock when the rotation speed is low.

Specifically, an induction motor that is driven to rotate at a rotation speed corresponding to the output frequency of the inverter, a rotor with a mark that rotates in synchronization with the induction motor, a sensor that detects a mark on the rotor, Frequency dividing means for dividing the output of the sensor to obtain a pulse having a cycle of one rotation of the rotor, a counter for counting the cycle of one rotation with a reference clock, and the counter based on an output from the counter. A control unit that outputs an output frequency corresponding to the rotation speed of the induction motor, and a control unit that outputs the output frequency.If the output frequency in the control unit is high, the frequency of the reference clock is increased, and the rotation speed is low. And reference clock changing means for lowering the frequency of the reference clock.

According to a second aspect of the present invention, in the first aspect of the invention, the induction motor is rotationally driven by an output frequency of an inverter, and the reference clock changing means is configured to divide the output frequency from low to high. Correspondingly, the frequency of the reference clock is changed stepwise from low to high.

According to a third aspect of the present invention, in the second aspect of the present invention, the reference clock changing means is configured to control the reference clock so that the number of digits of the counter for counting is kept large in each section. Change the frequency stepwise from small to large.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1, the speed control device 12 of the induction motor according to the present embodiment includes an induction motor 3
A detecting unit 6 for measuring a cycle of one rotation of the rotor 4 rotating in synchronization with the induction motor 3, a counting unit 10 for counting the cycle by a reference clock, and a control unit 2 incorporated in the inverter device 1. , A second clock divider (reference clock changing means) 9 for the counting means 10.

The above-described induction motor 3 is, for example, a 4-pole induction motor (hereinafter, referred to as "motor"), and has a rotor 4 connected to a rotating shaft of the motor. The motor 3 is connected to the inverter device 1 and rotates at a rotation speed according to the output frequency Sg7. The rotor 4 rotates in synchronization with the rotation of the motor 3, and has marks 4a and 4b on its side. The marks 4a and 4
“b” is formed by notching both side surfaces of the rotor 4 in order to improve the balance, but is not limited thereto.

The detection means 6 comprises the rotor 4 described above,
A proximity sensor 5 for detecting the marks 4a and 4b and a first motor divider 7 are provided.
Each time 4b is detected, a pulse signal Sg1 is transmitted to the first motor divider 7. First motor divider 7
Receives the pulse signal Sg1, receives the pulse signal Sg1
Is divided by １ ／ and the pulse signal Sg2 is transmitted. Here, as shown in FIG. 3, the pulse signal Sg
1 indicates the period T of one rotation of the rotor 4 at the generation interval of two pulses, and the pulse signal Sg2 divides the pulse signal Sg1 by １ ／ to obtain the period T of one rotation of the rotor 4. Is shown. That is, the ON time A or the OFF time B of the pulse signal Sg2 corresponds to one rotation period TA · TB of the rotor 4. Since this is one rotation of the rotor 4, the rotor 4
Is detected, the cycle of one rotation can be accurately detected without being affected by the processing accuracy of the rotor 4.

As shown in FIG. 1, the measuring means 10 has a first counter 10a and a second counter 10b, and measures the rotation periods TA and TB alternately based on a reference clock. Has become. That is, the first counter 10a measures the rotation period TA (hereinafter, referred to as “motor rotation period TA”) during the ON time A of the pulse signal Sg2, and the second counter 10b measures the OFF of the pulse signal Sg2.
The rotation period TB during the time B (hereinafter referred to as “motor rotation period TB”
" ) Is measured. The first
Both the counter 10a and the second counter 10b are, for example, 1
It is a 6-bit counter and can count from 1 to 65535.

The first counter 10a is connected to the first motor divider 7 and to the CLK8 via the second clock divider 9, and receives a pulse signal Sg2ON (transmitted by the first motor divider 7). A pulse signal indicating the ON time A of the pulse signal Sg2) is received from the gate input G, and the reference clock Sg4 transmitted by the second clock divider 9 is received from the clock input CK. Further, the first counter 1
0a, upon receiving the pulse signal Sg2ON and the reference clock Sg4, as shown in FIG.
The pulse of the reference clock Sg4 corresponding to the 2ON pulse 13 is counted (counted) to measure the motor rotation period TA with high accuracy, and the motor rotation period TA is converted into a motor rotation frequency Sg6 and transmitted. I have.

As shown in FIG. 1, the second counter 10b is connected to the first motor divider 7 and to the CLK8 via the second clock divider 9 as in the first counter 10a. The pulse signal Sg2OFF (the pulse signal indicating the OFF time B of the pulse signal Sg2) transmitted from the first motor divider 7 is received from the gate input G, and the reference clock Sg4 transmitted from the second clock divider 9 is received. From the clock input CK. Further, the second counter 10b outputs the pulse signal Sg2OFF and the reference clock S
g4, the reference clock S corresponding to the pulse 14 of the pulse signal Sg2OFF, as shown in FIG.
g4 pulses are counted (counted) and the motor rotation period T
B is measured with high accuracy, and the motor rotation cycle TB is converted into a rotation frequency Sg6 and transmitted.

The above-mentioned CLK 8 is connected to a second clock frequency divider 9 as shown in FIG.
g3 is transmitted to the second clock divider 9. The source oscillation of the frequency of the reference clock Sg3 is
For example, it is 1 MHz.

The second clock frequency divider 9 is connected to the above-described inverter device 1, and upon receiving the frequency division ratio signal Sg8 from the inverter device 1, generates a reference clock Sg3 according to the frequency division ratio signal Sg8. The frequency is divided stepwise at a predetermined dividing ratio. The frequency division ratio is 1/1, 1/2, 1/10, 1/50 as shown in Table 1, and the frequency of the reference clock Sg3 is 1M according to the frequency division ratio.
Hz, 500 KHz, 100 KHz, and 20 KHz.
Then, the second clock divider 9 converts the reference clock Sg4 thus divided into the first counter 10a and the first counter 10a during the ON time A and the OFF time B of the pulse signal Sg2.
The data is transmitted to the second counter 10b.

[0019]

[Table 1]

The above-described inverter device 1 includes a measuring unit 10
And a control unit 2 connected to the
When the motor rotation frequency Sg6 is received, the motor rotation frequency Sg6 is compared with the set frequency, and the output frequency Sg7 is controlled so that the deviation becomes zero. The inverter device 1 outputs the output frequency Sg7 to the motor 3 and the frequency division ratio signal Sg8 to the second clock frequency divider 9.
Is to be sent.

The speed controller 12 of the induction motor 3 configured as described above divides the frequency of the pulse signal Sg1 detected by the detecting means 6 by the first motor frequency divider 7 and outputs the pulse signal Sg1.
g2 is transmitted to the measuring means 10. Further, the second clock divider 9 generates a reference clock Sg3 of CLK8 according to the frequency division ratio signal Sg8 of the inverter device 1.
And the reference clock Sg4 is divided by the first and second counters 1
0a and 10b. Next, the section of the pulse 13 of the pulse signal Sg2 by the detection means 6 is counted (counted) by the reference clock Sg4, and the count number in the motor rotation period TA is measured.
The count number of the reference clock Sg3 in A is converted into a motor rotation frequency. The speed of the induction motor 3 is controlled by controlling the output frequency Sg7 by comparing the motor rotation frequency with the set frequency by the inverter device 1.

In the above configuration, the operation of the speed control device 12 of the induction motor 3 according to the present embodiment will be described with an example in which the output frequency Sg7 of the inverter device 1 is 20 Hz. As shown in FIG. 2, when detecting the marks 4 a and 4 b of the rotor 4 rotating in synchronization with the motor 3, the detecting means 6 transmits a pulse signal Sg 1 to the first motor divider 7. Next, upon receiving the pulse signal Sg1, the first motor frequency divider 7 divides the frequency of the pulse signal Sg1 by １ ／ and transmits the pulse signal Sg2 to the measuring means 10.

CLK8 is a reference clock (1 MHz)
z) Send Sg3 to the second clock divider 9. When the second clock divider 9 receives the reference clock (1 MHz) Sg3, as shown in FIG.
The reference clock Sg3 is frequency-divided according to the frequency division ratio signal Sg8, and the reference clock (500 KHz) Sg4 is measured.
Send to

When receiving the pulse signal Sg2 and the reference clock (500 KHz) Sg4, the measuring means 10 counts (counts) the reference clock Sg4 corresponding to the pulses 13 and 14 of the pulse signal Sg2 and counts the motor rotation period TA · T.
Measure section B. Then, as shown in FIG. 2, the motor rotation cycle TA · TB is converted into a motor rotation frequency Sg6 and transmitted to the inverter device 1.

Next, upon receiving the motor rotation frequency Sg6, the control unit 2 of the inverter device 1 compares the motor rotation frequency Sg6 with the set frequency and controls the output frequency Sg7 so that the deviation becomes zero. Then, the inverter device 1 transmits the output frequency Sg7 to the motor 3 and the frequency division ratio signal Sg8 to the second clock frequency divider 9.

As described above, by controlling the output frequency Sg7, the speed control device 12 of the induction motor 3 can make the rotation speed of the induction motor 3 constant. Also,
The frequency division ratio signal Sg8 corresponding to the output frequency (20 Hz) Sg7 of the inverter device 1 is fed back to the second clock frequency divider 9 to divide the reference clock (1 MHz) Sg3 at a predetermined frequency division ratio (1/2). The measurement means 1
0 is the reference clock S corresponding to the pulse of the pulse signal Sg2 not only when the motor 3 rotates at high speed but also when the motor 3 rotates at low speed
Counter capable of counting (counting) g4, which has a limited counting capability (versatile counter)
Can be used to measure the motor rotation period.

As shown in FIG. 4A, in order to measure the rotation cycle with high accuracy (0.01%) when the induction motor 3 rotates at a high speed, the reference clock Sg3 of CLK8 must have a high frequency ( 1 MHz).
Also, unlike the case of the high rotation, the second clock divider 9 divides the frequency of the reference clock (1 MHz) Sg3 into the low frequency reference clock Sg4 in the low rotation as shown in FIG.
As shown in (b), high frequency (1 MHz) at low rotation
When the reference clock Sg3 is counted (counted) while the reference clock Sg3 of FIG.
This is because the pulse of g3 cannot be counted (counted). That is, the ON time A of the pulse signal Sg2 becomes longer because the motor rotation period TA becomes longer at low rotation, and when the motor rotation period TA is measured using the high frequency reference clock Sg3, it corresponds to the pulse 15 of the pulse signal Sg2. This is because the number of pulses of the reference clock Sg3 becomes very large, and a counter having a very high counting ability is required.

Specifically, the pulse 1 of the pulse signal Sg2
N pulses (65) of the reference clock Sg3 corresponding to
535 <n <1,000,000), but the measuring means 1
0 is the maximum value C of the first counter 10a (2 bytes · 65
535), the remaining pulse train D of the reference clock Sg3 is counted (counted).
Because you can't.

Accordingly, the predetermined frequency division ratio when dividing the reference clock Sg3 does not exceed the counting (counting) capability of the first counter 10a and the second counter 10b, and fully utilizes the counting capability. It is set to be able to. Specifically, as shown in Table 1, the inverter device 1
When the output frequency Sg7 is 20 Hz, the frequency division ratio is 1 /
2 and the reference clock Sg3 is 500 KHz
(Sg4). Thereby, the pulse signal Sg
The number of pulses of the reference clock Sg4 corresponding to the second pulse 15 is k (k <65535).
Can count the pulse of the reference clock Sg4 corresponding to the pulse 15 of the pulse signal Sg2.

As described above, the reference clock (1
(MHz) Sg3, the first counter 10a and the second counter 10b divide the frequency of the reference clock Sg4 such that the frequency of the reference clock Sg4 decreases during low rotation (when the rotation cycle TA is long). Since the pulse can be counted (counted), the measuring means 10
Can measure the motor rotation periods TA and TB corresponding to the pulses 15 and 16 of the pulse signal Sg2.

Since the frequency division ratio is set within a range where the sampling capability can be sufficiently utilized, accuracy of at least 0.01% can be ensured even at a low rotation speed as in a high rotation speed. That is, in each section of the output frequency Sg7 of the inverter device 1 from low to high, the counter value N for counting is used.
(Number of digits) is kept larger than a predetermined value (10000). Specifically, as shown in Table 1, the output frequency Sg7 of the inverter device 1 is (20 ≦ f <10
0), the motor rotation frequency Sg6 is (10 ≦ f <5)
0), the frequency of the reference clock Sg4 is 500K.
Hz, when the measuring means 10 counts (counts) the pulse of the 500 KHz reference clock Sg4, the value N of the first counter 10a becomes (10000 <N ≦ 50,000).
Within the range. Therefore, when the motor 3 rotates at a low speed (600
rpm to 3000 rpm) at high rotation (3000 rpm to 6 rpm).
000 rpm), the motor rotation frequency Sg6 can be measured with an accuracy of at least 0.01%.

Since the speed control device 12 of the induction motor 3 of the present invention measures the motor rotation period with high accuracy, the reference clock Sg3 oscillated by CLK8 is 1 MHz.
It is not limited to. The first counter 10a and the second counter 10a
The counter 10b has a versatile 16 from an economic point of view.
Although a bit (2 byte) counter is used, an 8-bit / 32-bit counter may be used depending on the required precision.

[0033]

According to the first aspect of the invention, by changing the reference clock, the reference clock corresponding to the detection signal is counted not only at the time of high rotation of the induction motor but also at the time of low rotation of the induction motor. As a result, the rotation cycle of the induction motor can be measured, so that there is an effect that the rotation cycle of the induction motor can be measured with high accuracy using a counter having a small counting ability (a general-purpose counter).

According to the second aspect of the invention, there is an effect that the reference clock can be easily changed without requiring an expensive encoder.

According to the third aspect of the invention, although the rotation period is measured by changing the reference clock, there is an effect that a certain accuracy can be ensured.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a speed control device for an induction motor according to an embodiment.

FIG. 2 is a feedback control block diagram of FIG. 1;

FIG. 3 is a diagram showing a waveform of Sg1 and a waveform of Sg2.

FIG. 4 is a diagram showing waveforms of Sg2, Sg3, and Sg4.

FIG. 5 is a diagram illustrating a conventional speed control device for an induction motor.

FIG. 6 is a diagram showing a waveform of Sg21 and a waveform of Sg22.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter apparatus 2 Control part 3 Induction motor 4 Rotor 5 Proximity sensor 6 Detecting means 7 First motor divider 8 CLK 9 Second clock divider (reference clock changing means) 10 Measuring means 10a First counter 10b Second counter 12 control unit 13 pulse 14 pulse 15 pulse 16 pulse

Claims (3)

[Claims] 1. A speed control device for an induction motor for calculating a rotation speed by counting a cycle of each rotation of a rotor rotating in synchronization with the induction motor with a reference clock, wherein the reference clock is used when the rotation speed is high. And a reference clock changing means for lowering the frequency of the reference clock when the rotation speed is low. 2. The induction motor is driven to rotate by an output frequency of an inverter, and the reference clock changing unit changes the frequency of the reference clock from low to high in accordance with the low to high division of the output frequency. The speed control device for an induction motor according to claim 1, wherein the speed is changed stepwise. 3. The reference clock changing means changes the frequency of the reference clock stepwise so that the number of digits of the counter for counting is kept larger than a predetermined value in each section. A speed control device for an induction motor as described in the above.