JPS6412190B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an improvement of a motor rotation speed detection device that detects the rotation speed of an electric motor from the output of a rotation detector such as an encoder installed in the electric motor. .

<Prior Art> Usually, the speed control system of an electric motor is as shown in FIG.

In FIG. 2, 1 is an electric motor whose drive is controlled by a drive control device 2, 3 is an encoder that outputs rotational position pulses of the electric motor 1, and 4 is an encoder 3.
This is a speed detection device that detects the rotational speed of the electric motor 1 from the output from the drive control device 2 based on the output V of the speed detection device 4 corresponding to the rotational speed of the electric motor 1 and the value of a separately set speed setting value S. A control signal is given to the motor 1 from the motor 1, and the rotational speed of the motor 1 is controlled.

The present invention presents improvements in the speed detection device 4 in this speed control system.

Next, details of this speed detection device 4 will be specifically explained with reference to FIG.

As shown in this figure, 11 is a timing generation circuit to which output pulses EP and high frequency pulses CP from the encoder are given, 12 is a counting circuit that counts these high frequency pulses CP and receives a clear signal CL from the timing generation circuit, and 13 1 is a latch circuit that receives the latch signal EN from the timing generation circuit 11 and latches the counting output of the counting circuit 12; 14 is a read-only memory (14) in which a conversion table for converting the latched counting output into speed data is written; ROM).

In such a conventional speed detection device, the pulse signal EP from the encoder is sent to the timing generation circuit 1.
1, the counting output of the counting circuit 12 is latched in the latch circuit 13 by the latch signal EN, the counting circuit 12 is cleared by the clear signal CL, and the counting circuit 12 starts counting high frequency pulses CP. The latch circuit 13 latches the count output of the previous timing, and the count output latched every time the pulse output EP from the encoder is inputted is proportional to the pulse period of the encoder. Further, speed information V of the motor can be obtained via the ROM 14 in which speed data corresponding to the latch output is written in order to convert the latch output into speed data.

For example, if the pulse EP of the encoder is 1KHz, to detect the speed with 1% accuracy, it is 1M
A high frequency pulse of Hz or higher is required.

In this way, the rotational speed of the motor can be detected with the resolution of the high-frequency pulse CP for counting.

<Problems to be solved by the invention> By the way, the speed control of electric motors is often performed over a wide range (for example, from several tens of rpm to several
1000 rpm), this conventional speed detection device cannot maintain uniform resolution over such a wide range of speed settings.

In other words, as the rotational speed of the motor increases and the pulse output of the encoder becomes shorter, the counting output of the counting circuit decreases, and the resolution of speed detection decreases accordingly, making it difficult to control the speed with high precision. cannot be done.

In other words, if you try to measure the speed with an accuracy of 1% for a set speed of several 1000 rpm, you will need a counting circuit, latch circuit, and ROM with extremely large digits for a set speed of several 10 rpm. is not realistic.

Conversely, if the rotation speed of the motor is slow and the period of the encoder pulse output is long, high-frequency pulses
The counting circuit 12 that counts CP overflows,
In some cases, the speed may be output as fast even though it is actually slow.

As described above, the conventional speed detection device has the above-mentioned problems.

<Object of the present invention> The object of the present invention is to solve the above problems and provide a motor rotation speed detection device that has the same resolution and accurate output no matter what speed range the motor rotates. be.

<Means for Solving the Problem> The configuration of the present invention for solving this problem is as follows.

A motor speed detection device that receives a rotational position pulse from an encoder installed on the motor and detects the rotational speed of the motor includes a timing generation circuit that generates a timing signal based on the rotational position pulse, and a timing generation circuit that inputs a high-frequency pulse to set the rotational speed. a frequency divider that determines the frequency division ratio of the high frequency pulse according to a change in the value; and a counting circuit that clears the content and starts counting the divided high frequency pulses when the timing signal is applied; a comparison means that stops supplying the frequency-divided high-frequency pulse to the counting circuit when the counted value of the counting circuit matches a value corresponding to the speed lower limit; and a latch that latches the counted value of the counting circuit based on the timing signal. This motor speed detection device is characterized in that it is comprised of a circuit and a memory means for outputting a rotation speed value stored in advance in accordance with the latched value.

<Example> Next, an example of a motor speed detection device embodying the present invention is shown in FIG. 1 and will be described in detail.

In FIG. 1, the same reference numerals as those in the conventional example shown in FIG. 3 have the same functions, so a description thereof will be omitted.

The features of the present invention include a frequency division ratio of 15 that can set the high frequency pulse CP to an arbitrary frequency division ratio N, and a counting circuit 12.
A comparison circuit 16 is provided to compare the output C of the motor with the lower limit value S _L of the rotational speed.

Next, the operation of this embodiment will be explained.

In this device, when detecting the rotational speed of the electric motor, the high frequency pulse CP is counted by the output pulse of the encoder. At this time, if the period of the high frequency pulse CP is _T1 , the pulse CP is
5, and if the division ratio is N, the period T ₂ of the output pulse from the frequency divider 15 is T ₂ = NT ₁
The counting circuit 12 counts pulses of this period. The period of the encoder pulse EP is
If T _E , the counting output C of the counting circuit 12 is C
= T _E /NT ₁ is given.

Next, when the rotational speed setting value is multiplied by n, the period T _E ′ of the pulse EP of the encoder becomes T _E ′=T _E /n, and the counting output C of the counting circuit 12 becomes T _E /n.
(nNT ₁ ). Here, if the frequency division ratio N of the high frequency pulse CP is changed to N/n by the division period 15, we get
The counting output C of the counting circuit 12 is the same as the counting output before speed setting. That is, for any speed setting value, the dividing ratio of the high frequency pulse CP is changed by the frequency divider 15 according to the setting value, and the divided high frequency pulse CP is counted, so that the Velocity information V can be obtained with a constant resolution.

Next, when the rotational speed of the motor decreases and the period of the pulse EP of the encoder increases, the counting circuit 12 is about to overflow.
The output C of this counting circuit 12 is compared with the speed lower limit set value S _L set in the comparator 16, and when the counting output C becomes larger than this lower limit set value S _L ,
The comparator 16 outputs logic "1" to logic "0" to the AND gate 17, stops the supply of the high frequency pulse CP to the counting circuit 12, and stops the counting operation.
Therefore, the count output remains at the speed lower limit set value. Then, when the next encoder pulse EP arrives, the counting circuit 12 is cleared and becomes ready to start counting again. At this time, the lower speed limit value is latched in the latch circuit 13.

In this way, overflow of the counting circuit can be prevented and erroneous measurements of the rotational speed of the motor can be prevented.

FIG. 4 shows a specific embodiment of the timing generation circuit 4, and its operation will be explained with reference to the timing chart shown in FIG.

In FIGS. 4 and 5, reference numeral 41 denotes a flip-flop circuit whose set terminal S is supplied with an encoder pulse EP shown in A, and "1" is outputted from an output terminal Q by this encoder pulse EP. B is a high frequency pulse CP. The “1” output of this C is
A high frequency pulse CP is applied to an input terminal D of a flip-flop circuit 42, which is applied to a clock input terminal CP. This output is the encoder pulse
The signal is taken into the flip-flop circuit 42 by the high-frequency clock CP following the EP, and "1" is output from its output terminal Q as shown in D. At the same time, a "0" output is output from the output terminal of the flip-flop circuit 42 to the reset terminal R of the flip-flop circuit 41, thereby resetting the flip-flop circuit 41. Further, this output D is appropriately delayed by a delay circuit 43 and becomes an output.
This rising edge to the output causes the counting circuit 1 to
When the count output of 2 is latched and the output is at the "1" level, if the count circuit 12 is cleared by the high frequency clock CP, the count output can be latched without any effect on the counting operation. Counting circuit 12
can be reset.

In this way, the timing generation circuit 11 outputs a latch output to the latch circuit 13, and the counting circuit 1
2 can be cleared.

<Effects of the Invention> As described above, according to the motor rotation speed detection device of the present invention, the speed can always be detected with a constant resolution, no matter what the rotation speed of the electric motor is. Further, if the cycle of the output pulses of the encoder becomes longer for some reason, the lower limit value of the rotational speed is output, so that erroneous measurement of the rotational speed of the motor can be prevented.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a motor rotation speed detection device according to an embodiment of the present invention, FIG. 2 is a block diagram showing a motor speed control system, and FIG. 3 is a diagram of a conventional motor rotation speed detection device. FIG. 4 is a circuit diagram showing the timing generation circuit, and FIG. 5 is a timing chart showing the operation of the timing generation circuit. 11... Timing generation circuit, 12... Counting circuit, 13... Latch circuit, 14... ROM, 15
... Frequency divider, 16 ... Comparator, 17 ... AND gate, 41, 42 ... Flip-flop circuit, 4
3...Delay circuit.

Claims (1)

[Claims] 1. A motor speed detection device that receives a rotational position pulse from an encoder installed on the motor and detects the rotational speed of the motor, which includes a timing generation circuit that generates a timing signal based on the rotational position pulse, and a timing generation circuit that receives a high-frequency pulse and detects the rotational speed. a frequency divider that determines a frequency division ratio of the high frequency pulse according to a change in a set value; and a counting circuit that clears the content and starts counting the frequency-divided high frequency pulse when the timing signal is applied. , a comparison means for stopping supply of the frequency-divided high-frequency pulse to the counting circuit when the counted value of the counting circuit matches a value corresponding to a speed lower limit value, and latching the counted value of the counting circuit by the timing signal. A motor speed detection device comprising a latch circuit and memory means for outputting a rotation speed value stored in advance in accordance with the latched value.