JPH0219712B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device for a rotating body that improves the transmission characteristics, particularly the phase delay, of a speed detector that generates a control output according to the rotational speed of the rotating body.

Speed control of rotating objects that require precise constant speed rotation, such as drums in video tape recorders,
In speed control of capstans, etc., a frequency generator (hereinafter referred to as FG) generates an AC signal with a frequency proportional to the rotational speed of the rotating body, and a control output corresponding to the frequency of the FG signal is generated. Speed detectors are widely used.

Figure 1 is a block diagram showing its basic configuration, where 1 is a motor, 2 is an FG, 3 is an FG signal, and 4 is a block diagram showing the basic configuration.
is a speed detector, 5 is a waveform shaper that creates a speed proportional signal 6 having a leading edge and a trailing edge from the FG signal 3, and 7 detects the period of the speed proportional signal 6 and generates a control output 8 in accordance with it. 9 is a filter for smoothing or phase compensation of the control output 8, and 10 is a motor drive circuit. In addition,
This example shows a so-called direct drive system in which the rotating body and the rotor of the motor are directly connected.

Now, in such a speed control system, in order to increase the stability of the system and improve the rotational performance,
It is generally well known that the FG frequency can be set high. As shown in the explanation below, the higher the FG frequency, the higher the speed detector 4.
This is because the phase delay of is reduced and the ripple frequency of the output is increased, so that the time constant of the filter 9 in the subsequent stage can be reduced, and the phase margin of the control system increases.

However, in actual systems, the FG frequency cannot be set unnecessarily high due to various constraints. Therefore, various efforts have been made to obtain sufficient performance even at low FG frequencies, and the most typical method is phase compensation using a filter. However, this method stabilizes a system that is originally unstable or close to it by changing part of the gain or phase frequency characteristics of the system, and it does not stabilize the system that is originally unstable or nearly so. It is not possible to expect a fundamental performance improvement like that of .

The overall operation of such a speed control device is as follows.
Since this is already widely known, the following explanation will focus on the speed detector according to the present invention.

First, the conventional speed detector 4 shown in FIG.
The operation will be explained.

If the rotational speed of the motor is Nmo and the FG frequency is fc, since the two are in a proportional relationship, it can be expressed as fc=1/Tc=K _G・Nmo (1). Here, K _G is a speed-frequency conversion constant.

Now, consider the case where the rotational speed changes over time. That is, Nm(t)=Nmo+△Nm(t)...(2). FIG. 2 shows the operation of the speed detector 4 at this time.

As the rotational speed of the motor 1 changes over time, the FG signal 3 is frequency modulated (FM), resulting in a change in the length of time between adjacent leading edges of the speed proportional signal 6. The period detector 7 outputs a control voltage according to the amount of change in this time length. That is, the second
From the figure, the control output V _F (t) is Tn<t≦Tn+ ₁
(n=0, ±1, ±2…), V _F (t) = V _FO +△V _F (t) = V _FO +Kv・△Tn = V _FO +Kv・{(Tn−Tn− ₁ )− Tc} ...(3). Here, V _FO is the rotation speed of the motor
This is the control output voltage when Nmo is constant. Also,
Kv is a period-voltage conversion constant, and here the polarity is negative. This means that the polarity of △T is △Nm
Since it is the opposite of that of , Kv is merely intended to simplify the explanation by assuming negative polarity, and this point is also the same in the embodiments of the present invention described later.
Here, the leading edge of the speed proportional signal 6 is used to detect the time length, but the same effect can be achieved even if the trailing edge is used.

Now, as is clear from Figure 2, this process is the FM signal demodulation process itself, that is,
By detecting the so-called "zero-crossing time" of the FM modulated carrier wave, the change in the carrier wave period is determined, and by converting it to voltage, the original modulation signal is restored, so the higher the modulation frequency, the higher the frequency. , it is easy to imagine that the phase delay will increase.

In fact, in equation (2), △Nm (t) is a single sine wave, that is, △Nm (t) = △Nmo cos (2πfmt + θm)
...(4) Here, fm: Rotation speed fluctuation frequency θm: Initial phase △Nmo: Rotation speed fluctuation amplitude (peak/zero value), and the FG signal, that is, the carrier wave, Vc (t) = Sin (2πfct ) ...(5), and by varying fm, θm, and △Nmo,
The demodulated output at that time is expanded into a Fourier series, the fundamental wave component is extracted, and the phase delay θv is examined. θv≒360×fm/fc [゜] ...(6) θv is proportional to fm, and fc It has become clear that it is inversely proportional to

Here, the expression "approximately equal" in equation (6) means that this speed detection method detects not the frequency itself, but the reciprocal of the frequency, that is, the change in period, and detects the change proportional to the amount of change. This is because a voltage is output, so if the fluctuation rate (ΔNmo/Nmo) is large, a slight error will occur. However, according to a trial calculation, the fluctuation rate is 10% at the peak zero value.
%, which is so large that it is hardly a target in an actual system, the error in θv is less than 1%. Note that this phase delay has also been confirmed through experiments using an actual motor control system.

Figure 3 shows that in equation (4) △Nm (t) and △V _F (t) are shown. Here, the numbers in parentheses represent the detection time. In this case, the phase delay θ _V is (6)
From the formula, θv≒360/8=45〔゜〕...(8), which can be easily confirmed from the waveforms in Figure 3.

By the way, what becomes immediately clear from such a calculation is that if the time length of a half cycle of the FG signal 3 is detected and converted to a voltage, the phase delay θv becomes (6)
This means that it becomes half of the equation. because,
This is because this is equivalent to doubling the FG frequency in the demodulation process described above.

However, in this case, unlike the case of detecting one cycle, the FG signal 3 is distorted or the FG signal 3 is distorted.
As shown in the figure, if an offset occurs in the waveform shaper 5, even if the rotational speed does not fluctuate, the output of the speed detector (B and C in Figure 4) will generate ripples, and the DC component will also change. As a result, rotational irregularities due to ripples increase and deviations in set speed occur. Furthermore, since the frequency of the ripple fundamental wave component is the FG frequency, if a filter is added to avoid an increase in rotational unevenness, its time constant must be sufficiently large with respect to the ripple frequency. As a result, there are many drawbacks, such as the effect of improving the phase delay associated with speed detection as described above is canceled out, and other countermeasures are also required.

Therefore, in an actual speed control system, the method of detecting speed from a half period of the FG signal 3 has no merit in terms of performance or cost and is hardly used.

On the other hand, in the case of a method that detects one cycle,
As is clear from FIG. 4, even if an offset occurs in the waveform shaper 5, no ripples or fluctuations in the DC component occur. However, even with this one-period detection method, as shown in Figure 3, if there is a speed fluctuation, ripples in the FG frequency will occur, and as a matter of course, the magnitude of this ripple will be smaller than that of the half-period detection method. Since the ripple frequency is large compared to , and the ripple frequency is also low, the time constant of the filter 9 in the subsequent stage must be set large. Therefore, the synergistic effect of the above-mentioned θv and the phase delay caused by the time constant element of the filter 9 greatly limits the performance of the control system.

As mentioned above, conventional speed detection requires FG
A method that detects one cycle of the signal is generally used, but if the FG frequency cannot be set to the desired height due to system constraints, the system must be prepared for imperfect performance and downgrade the specs. The reality was that it was not possible.

As described above, the present invention is capable of reducing performance deterioration even when the FG frequency cannot be set high enough in light of performance standards based on conventional systems. In other words, the objective is to provide a rotating body speed control device that can obtain higher performance than conventional systems even at the same FG frequency.

An embodiment of the present invention will be described below with reference to the drawings.

In Figure 5, 1 is the motor, 2 is the FG, and 3 is the motor.
FG signal, 4 is a speed detector, 5 is a waveform shaper that creates a speed proportional signal 6 having a leading edge and a trailing edge from the FG signal 3, 7a is a time length between adjacent leading edges of the speed proportional signal 6, i.e. a first period detector that detects the period and generates a control output 8a according to the period;
7b is a second period detector that detects the time length or period between adjacent trailing edges of the speed proportional signal 6 and generates a control output 8b in accordance with the detected time length, and 11 is a first period detector.
8c is the output of the output selector 11, that is, the output of the speed detector 4; 9 is a filter for smoothing the output 8c or for phase compensation of the control system;
10 is a motor drive circuit.

In the above configuration, let us consider a case where the rotational speed changes over time as in equation (2), similar to the conventional example. The operation of the speed detector 4 at this time is explained in the sixth section.
As shown in the figure.

When the rotational speed of the motor 1 changes over time, the FG signal 3 is frequency modulated. Therefore,
The time length between adjacent leading edges and the time length between adjacent trailing edges of the waveform-shaped velocity proportional signal 6 change. The first period detector 7a outputs control outputs 8a and 8b in response to changes in time length between adjacent leading edges, and the second period detector 7b responds to changes in time length between adjacent trailing edges. Output. This first and second
The period detectors 7a and 7b constitute the same detection method as the conventional one-period detection method described above.

Therefore, the control output 8a is V _F1 and the control output 8b is
If we set V _F2 , from Figure 6, T ₂ k<t≦T ₂ k+ ₂ (k=0, ±1, ±2,...)
, V _F1 (t) = V _FO +△V _F1 (t) = V _FO +Kv・△T ₂ k = V _FO +Kv {(T ₂ k−T ₂ k− ₂ )−Tc} ……(9) T ₂ k+ ₁ <t≦T ₂ k+ ₃ (k=0, ±1, ±2,...
), V _F2 (t) = V _FO +△V _F2 (t) = V _FO +Kv・△T ₂ k+ ₁ = V _FO +Kv {(T ₂ k+ ₁ −T ₂ k− ₁ ) − Tc}
...(10)

Now, the output selector 11 is connected to the first period detector 7
From the time T ₂ k when the output 8a of a changes, the time T ₂ k+ ₁ when the output 8b of the second period detector 7b changes
is the time at which the output 8a of the first period detector 7a and the output 8b of the second period detector 7b change.
From T ₂ k+ ₁ to time T ₂ k+ ₂ when the output 8a of the first period detector 7a changes, the second period detector 7
The output 8b of speed detector 4 is the output 8b of speed detector 4.
Select as c. Therefore, if the output 8c of the speed detector 4 is set as V _F , V _F (t)=V _F1 (t) (T ₂ k<t≦T ₂ k+ ₁ ) V _F2 (t) (T ₂ k+ ₁ <t≦T ₂ k+ ₂ ) (k=0, ±1, ±2, ...)...(11).

Here, as in the conventional example, in equation (4),
By varying fm, θm, and △Nmo, extracting the fundamental wave component by expanding the demodulated output V _F into a Fourier series and examining the phase delay θv, we find that θv≒270×fm/fc=360×fm /fc×0.75〔゜〕……(
12) It became clear that. Note that the approximate symbols in the above equation are used for the same reason as in the conventional example. From this, speed detector 4 in Fig. 5
It can be seen that the phase delay is reduced by about 25% compared to the conventional one-cycle detection method.

Similar to the conventional example, FIG. 7 shows ΔNm(t) and ΔV _F (t) at the set value shown in equation (7). The numbers in parentheses represent the detection time. In this case, the phase delay θv becomes θv≒270/8=33.75° from equation (12) (13).

As is clear from FIG. 7, ripples are also reduced and the ripple frequency is doubled, and in this respect it has both the advantages of the half-cycle detection described above. Furthermore, as the ripple frequency becomes higher, the time constant of the filter 9 at the subsequent stage can also be reduced, so it goes without saying that the phase delay of the control loop is synergistically reduced. Furthermore, according to this method, since the time length detection is the same as the conventional one-cycle detection, shortcomings in half-cycle detection, such as distortion of the FG signal 3 and offset of the waveform shaper 5, can affect the control output. Problems such as ripples or deviations in DC potential do not occur.

This feature is due to the detection of two types of time lengths, one between adjacent leading edges and the other between adjacent trailing edges of the rotational speed proportional signal, but if these detection results are simply added, that is, the In Figure 6, from equations (9) and (10), the configuration was designed to generate a control output such that V _F (t) = 1/2 {V _F1 (t) + V _F2 (t)} ... (14) If θ _V
is θ _V ≒360·fm/fc [°] (15) In other words, it becomes the same as equation (6), and calculations have revealed that the phase delay is not improved at all. This can be easily inferred from the waveforms of the first and second detector outputs in FIG.

As described above, according to the present invention, it is possible to obtain the above-mentioned two types of time lengths by detecting the two types of time lengths and alternately selecting and outputting the detection results. In order to achieve this, all that is required is to operate conventional period detectors in parallel and provide a switch circuit that alternately switches their outputs, making it possible to improve performance with an extremely simple configuration.

In the above embodiment, the waveform shaper 5 is provided at the first stage of the speed detector 4, but if the FG signal 3 has a waveform like the speed proportional signal 6, that is, a waveform having a leading edge and a trailing edge. , the waveform shaper 5 can be omitted.

Also, although the output 8c of the speed detector 4 is shown in a sample-and-hold format, the same effect can be obtained using a so-called pulse width modulation (PWM) method that changes the output duty according to changes in the cycle. It is clear that

Furthermore, as a method for detecting the period, there are methods that achieve the conversion operation, such as a method that utilizes charging and discharging of a conventionally commonly used CR circuit, or a method that counts the length of the period using a separately obtained clock signal. Any method will do.

Further, in the above embodiments, the rotating body is directly driven, but it goes without saying that similar effects can be obtained by using other drive systems such as belt drive.

As described above, according to the present invention, the time length between adjacent leading edges and trailing edges of the rotational speed proportional signal is detected, and the control output is generated in accordance with the detection result. Even at the same FG frequency, the phase delay can be reduced by about 25% compared to the conventional one-period detection method. Moreover, since the ripple frequency of the output is doubled, the time constant of the filter in the subsequent stage is also reduced, and it is also possible to reduce the phase delay, so that the speed control performance of the rotating body can be greatly improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional speed control device for a rotating body, Fig. 2 is a timing diagram for explaining the operation of a conventional speed detector, and Fig. 3 is a concrete diagram based on the conventional speed detector. Figure 4 is a control output waveform diagram calculated using numerical values, and Figure 5 is a waveform diagram showing the influence of offset in the half-cycle detection method.
The figure is a block diagram showing one embodiment of this invention.
The figure is a timing diagram for explaining the operation of the speed detector in FIG. 5, and FIG. 7 is a control output waveform diagram calculated using specific numerical values based on the speed detector in the present invention. 1... Motor, 2... Frequency generator, 4... Speed detector, 7a, 7b... Period detector, 7d, 7
e... Half cycle detection result holder, 10... Motor drive circuit, 11... Output selector, 12... Half cycle detector, 13... Control output generator. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A frequency generator that generates an alternating current signal with a frequency proportional to the rotation speed of a rotating body, and a frequency generator that generates an alternating current signal with a frequency proportional to the rotation speed of the rotating body, and a rotation speed proportional signal that has a leading edge and a trailing edge obtained based on the output of this frequency generator. In a speed control device for a rotating body that includes a speed detector that generates a control output and a drive circuit that drives the rotating body according to the output of the speed detector, the speed detector includes:
a first period detection means for detecting a time length between adjacent leading edges of the rotational speed proportional signal and generating a first control output according to the length; and a first period detection means for detecting a time length between adjacent trailing edges. and a second period detecting means for generating a second control output according to the length of the rotation speed proportional signal; The first control output is selected during the period up to the trailing edge, and the second control output is sequentially and alternately selected during the period from the trailing edge of the rotational speed proportional signal to the first leading edge following this trailing edge. 1. A speed control device for a rotating body, characterized in that it has an output means for selecting.