JPS62464B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a speed detection device that digitally detects the speed of a variable speed rotating body. For example, when variable speed control is applied to a motor, speed detection is essential for motors that require speed accuracy. Furthermore, when performing high-precision control, analog systems have their limits, so digital systems with no drift are used. In order to improve speed accuracy, a pulse train with a frequency proportional to the speed is obtained using a pulse pickup, etc., and compared with the speed setting pulse train. Moreover, there are many cases in which detection is required with a response within a predetermined time. In this case, even if it is a digital type, there are the following problems. That is, in a digital system, accuracy and response time are generally contradictory elements, and when the variable speed range is wide, it is difficult to maintain constant accuracy over the entire range and to keep the response time within a constant time. For example, if the variable speed range is 1:n, the pulse interval of the pulse train changes from 1 to n, and if the frequency of the reference clock pulse train is increased to improve accuracy at high speeds, the counter will overflow at low speeds. This caused the inconvenience of storage, and to avoid this, accuracy at high speeds had to be sacrificed. There is also a method of switching the detection method depending on the frequency of the pulse train, such as counting the pulse train itself for a certain period of time at high speeds and measuring the period at low speeds, but the detection response time is not constant, and the accuracy must be set to a predetermined value. This poses practical problems, such as the need to increase the number of bits. The present invention has been made in view of the above circumstances, and it is possible to measure the pulse interval between adjacent pulses in a pulse train in advance so that the pulse interval to be measured is always constant, and to determine how many pulses in the pulse train should be measured. It is an object of the present invention to provide a speed detection device that can keep both accuracy and response time constant over the entire variable speed range. Hereinafter, the present invention will be explained in detail based on illustrated embodiments. FIG. 1 shows an embodiment of the present invention, in which 1 is a counter that counts the number of clock pulses f _ck in one pulse interval of pulse train f ₁ , and 2 is a counter that counts the count result n of this counter 1 and a constant k to k/ A calculator that calculates n, rounding up the decimal places. 3
is a preset counter that uses the output of this arithmetic unit 2 as a preset value.The gate is opened at the falling edge of the pulse train _f1 , and after that, it counts down at the falling edge of the pulse train _f1 , and counts down k/n counters. count. 4 is a counter that counts the down-count operation time of the preset counter 3, that is, the number of clock pulses _fck between k/n pulses of the pulse train _f1 ; 5 is the output m of this counter 4;
From the output k/n of the arithmetic unit 2 and the clock pulse frequency f _ck

A calculator 6 calculates the formula and outputs the frequency of the input pulse train f ₁ as a digital code, and 6 is a pulse pickup that obtains the pulse train f ₁ with a frequency proportional to the speed of the rotating body 7. Next, the operation will be explained with reference to the time chart shown in FIG. In counter 1, the pulse train
The pulse interval of _f1 is counted by the clock pulse _fck . Using this count result, for example, n ₁ and a constant k, the arithmetic unit 2 calculates k/n ₁ , and the value rounded up after the decimal point is loaded into the preset counter 3 at time t ₁ . In preset counter 3, pulse train
The gate is opened at the falling edge of the f ₁ pulse, and thereafter, a down count is performed at the falling edge of the pulse train f ₁ to count ₁ k/n. The counter 4 uses a clock pulse _fck to count from the falling edge of the pulse at time _t1 to the falling edge of the k/n- _th pulse (time _t2 ) which is output after a certain time. From this result m ₁ , in computing unit 5

Calculate [Formula] and output the frequency of the input pulse train _f1 as a digital code. In addition, the counter 1 counts the interval between the (k/n ₁ - 1)th pulse and the k/n _1st pulse, and the calculation unit 2 uses the result n ₂ to calculate k/n ₂ . The result is inputted into the preset counter 3 again at time _t2 . Thereafter, the counter 4 counts the pulses of the pulse train _f1 ( _t2 to _t3 ) in the same manner as described above, and the arithmetic unit 5 performs calculations using the result _m2 . By repeating these operations, the speed of the rotating body 7 is output as a digital value. In this case, the pulse train
Maximum value of f ₁ , clock pulse frequency f _ck , constant k
The value of is determined as appropriate depending on the required accuracy, response time, and variable speed range. For example, if the maximum value of f ₁ is
10KHz, variable speed range 1:100, response time 10m
s, if the accuracy is ±0.02%, f _ck = 500kHz,
Setting k=5000 satisfies the request. Note that calculations and timing management in the calculation units 2 and 5 are performed using a microcomputer.
If there is a problem with calculation time, it can be solved by having 1/n data in the table. As described above, according to the present invention, the interval between adjacent pulses in a pulse train is measured in advance so that the pulse interval to be measured is always constant, and it is determined how many pulses in the pulse train should be measured. The response time and accuracy are kept constant over the entire variable speed range, and there are no problems such as overflow.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the speed detection device according to the present invention, and FIG. 2 is a time chart for explaining the operation. 1 and 4...Counter, 2 and 5...Arithmetic unit,
3...Preset counter, 6...Pulse pick-up, 7...Rotating body.

Claims (1)

[Claims] 1. A counter that counts the reference clock pulse _fck to measure the pulse interval of an input pulse having a frequency corresponding to the rotational speed of the rotating body, and an arithmetic unit that divides the constant k by the clock pulse count number n. , a preset counter that counts down every time an input pulse arrives with k/n as a preset value, a counter that counts the number of clock pulses m during the measurement time of k/n input pulses, and a digital A speed detection device comprising: a calculation unit that outputs a speed detection value of a quantity;