JPH0817583B2 - Speed servo circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed servo circuit of a motor suitable for application to a motor for driving a floppy disk, and more particularly to a speed servo circuit having excellent transient characteristics.

2. Background Art and its Problems The speed servo circuit used to control the rotation speed of a motor to a reference rotation speed is generally constructed as shown in FIG.

Rotation signal generating means such as a control object serving as the motor (1) obtaining a rotation signal S _M which is proportional to the rotational speed of the motor (1) is a frequency generator (FG) (2) is provided, and the rotation signal S _M The reference signal S _REF supplied to the terminal (3) is supplied to the speed deviation forming means (4) to determine a deviation amount (PWM signal) of the motor rotation speed with respect to the reference signal S _REF . Is the DC control voltage by the low-pass filter (5)
The DC control voltage V _CTL is converted to V _CTL and the converted DC control voltage V _CTL is supplied to the motor driver (6), whereby the motor (1) is controlled to a rotation speed corresponding to the reference signal S _REF .

As is well known, such a speed servo circuit (10) has a drawback that it takes a long time to settle because the rise of the rotation of the motor (1), that is, the transient characteristic is bad and an overshoot occurs.

That is, a feedback control system such as the speed servo circuit (10) shown in FIG. 2 can be represented as a control block shown in FIG. In the figure, ω is the rotation frequency of the motor (1) after feedback control, ω _ref is the reference frequency, and the motor (1) including the low-pass filter (5) and the motor driver (6) is a first-order lag element, respectively. Therefore, the transfer function of this feedback control system is as follows.

If the denominator of equation (1) is expressed as f (s) = T ₁ T ₂ s ² + (T ₁ + T ₂ ) s + AK ₁ +1 (2), then equation (2) is expressed using the damping factor ξ. And it becomes like the formula (3).

f (s) = T ₁ T ₂ (s ² + 2ξω _n s + ω _n ² ) (3) The smaller the damping factor ξ is, the larger the overshoot at the rising of the motor speed, and conversely ξ If it is> 1, the overshoot becomes small or can be made zero.

 Here, it can be transformed as in the equation (2).

From the relationship with equation (3), Becomes In the case of the motor rotation speed control, since T ₁ << T ₂ is usually satisfied, the equation (5) can be transformed into the equation (7).

The amount of overshoot is determined by the ratio of the numerator and denominator in equation (7), and since K ₁ is usually sufficiently large, ξ <1.0 (8) Therefore, in the conventional feedback control system, it is clear from equation (8). As always, overshoot occurs.

Incidentally, by decreasing the proportional gain K _1, can be suppressed overshoot, the proportional gain K ₁ is in inversely proportional to the constant deviation of the motor speed, the more steady-state deviation Decreasing the proportional gain K ₁ Therefore, in general, the steady-state deviation was made small and the occurrence of overshoot was inevitable. Therefore, the settling time is naturally long.

FIG. 4 shows the rising characteristic of the monitor rotation speed in the conventional circuit. In this example, it is the transient characteristic when K ₁ = 5, and the overshoot occurs until the target rotation speed is reached. It can be seen that the settling time is considerably long.

SUMMARY OF THE INVENTION Therefore, in the present invention, overshoot is suppressed and transient characteristics are improved without deteriorating the steady deviation.

SUMMARY OF THE INVENTION Therefore, in the present invention, a differential control system using a digital circuit is introduced into the feedback control system. Then, specifically, for example, as shown in FIGS. 9 and 10, a rotation signal proportional to the rotation speed of the motor M to be controlled.
Rotation signal generating means (2) for obtaining S _M, and a measurement counter (21) for measuring the rotation speed of the motor from the rotation signal
And a first constant device (41) for the measurement data obtained from this measurement counter, and a memory circuit (42) for storing the measurement data obtained one time before obtained from the measurement counter.
And a second constant calculator (43) for the measurement data one time before output from the memory circuit, and a subtracter (44) for subtracting the outputs of the first and second constant calculators. Circuit (40) and data counter (23) to which differential characteristic data obtained from this digital differentiating circuit is loaded
And a servo circuit that is connected to the data counter and outputs a control voltage V _CTL for keeping the rotation speed of the motor constant. The control voltage output from the servo circuit is used as a DC control voltage for the motor. The rotation speed is controlled.

Embodiment Next, a speed servo circuit for a motor according to the present invention will be described in detail with reference to FIGS.

FIG. 1 shows a motor speed servo circuit (1) according to the present invention.
0), which is the case of application to the conventional circuit of FIG. The speed deviation signal forming means (4) has a digital processing structure, and means for imparting a differential characteristic of the speed deviation signal to this forming means (4), a digital differentiating circuit (not particularly shown) in this example. Is provided.

FIG. 5 shows a feedback control system for obtaining the transfer function in the speed servo circuit (10) shown in FIG. 1, and in this case, it is expressed as a differential element added by sk by inserting a differential circuit. You can

 The transfer function at this time is expressed by equation (8).

f (s) T ₁ T ₂ s ² + (T ₁ + T ₂ + AK) s + AK ₁ +1
(9) f (s) can also be expressed as follows.

f (s) = T ₁ T ₂ (s ² +2 ξω _n s + ω _n ² ) ... (10) here, Is.

In the equation (12), k represents a differential gain, so that the damping factor ξ can be made larger than 1 by increasing k. If ξ> 1, the damping effect will be large, so it is possible to completely eliminate the overshoot by setting this k to an appropriate value.

The curve l _{1 in} FIG. 6 shows the transient characteristic when k = 8. Thus, by adding the differential control system, the overshoot can be improved and the settling time of the motor (1) can be shortened accordingly. In the example shown, the settling time is about 2.0 seconds.

In this case, if the proportional gain K ₁ is made larger than that of the conventional _one , for example, K ₁ = 20th place can also improve the steady-state deviation, and in the case of the curve l ₁ , the actual motor rotation speed is
It will be 394 rpm.

FIG. 7 shows another example of the speed servo circuit (10) according to the present invention. This example is an example in which the steady-state deviation is improved in addition to the improvement of the transient characteristic.

Rotation signal obtained from the rotation signal generating means (2) S _M and the reference signal S _REF supplied to the terminal (3) is supplied to the first signal forming means (11), the motor with respect to the reference frequency omega _ref ( A first speed deviation signal S ₁ having a pulse width corresponding to the rotation speed deviation of 1) is formed. The first signal forming means (11) includes a differentiating element. The first speed deviation signals S ₁ is a pulse-width modulated signal in response to the reference signal S _REF is speed deviation, corresponding to the speed deviation signal ΔV shown in Figure 2.

The first speed deviation signal S ₁ is supplied to the second signal forming means (13) together with the reference clock CKa applied to the terminal (12), and the speed deviation polarity is provided for each rotation cycle of the rotation signal S _M. A second speed deviation signal S ₂ having a polarity corresponding to the pulse width and a pulse width corresponding to the speed deviation amount is formed.

Reference clocks CKa, as described below, is selected to be a frequency higher than the frequency of the rotation signal S _M obtained when the motor (1) reaches the reference rotational speed, also a polarity of the speed deviation, the reference in this example When the rotation speed is higher than the rotation speed, the polarity is positive, and when the rotation speed is lower, the polarity is negative. Therefore, when the speed is higher than the reference rotation speed, the second speed deviation signal S ₂ is a positive pulse signal having a pulse width corresponding to the speed deviation amount. When the speed is slow, a negative second speed deviation signal S ₂ having a pulse width corresponding to the speed deviation amount is obtained. The positive or negative pulse is obtained for each rotation cycle of the rotation signal S _M.

Second speed deviation signal S ₂ is further third signal forming means (14) and supplied to a second speed deviation signal corresponding to the pulse width and polarity of S ₂ motor control voltage V _CTL (DC voltage)
DC level is controlled. That is, when the second speed deviation signal S ₂ is a positive polarity pulse signal is controlled so that the DC level of the motor control voltage V _CTL is lower than the reference value, than the reference value in the opposite case Controlled to be high.

Therefore, the motor driver (6) is driven by the motor control voltage _VCTL , and the motor (1) is controlled to the reference rotation speed.

Now, since the DC level of the control voltage V _CTL by a second speed deviation signal S ₂ is intended to increase or decrease, the second and third signal forming means (11), (13) should be regarded as a kind of integration circuit Can be.

For convenience of explanation, the differential element and the low-pass filter (5)
Excluding the first-order lag element and considering only the steady deviation, the feedback control system showing the transfer function in this case includes the integral element K ₂ / s (K ₂ is the integral gain) as shown in FIG. Can be represented as a block, ω and ω
The relationship with _ref is At this time, the value of ω at t → ∞ is Therefore, the deviation Δω becomes Δω = ω _ref −ω _ref = 0 (16), and the steady-state deviation Δω becomes zero.

Therefore, the speed servo circuit (10) shown in FIG. 7 can control the motor (1) to a reference rotation speed that is completely proportional to the reference signal S _REF . Therefore, the transient characteristic at this time is as shown by the curve l ₂ in FIG.

FIG. 9 is a double of the conventional speed servo circuit (10) shown in FIG. 2 to which the technique shown in FIG. 7 is applied. In this case, the first speed deviation signal S ₁ is the speed shown in FIG. Since it becomes the deviation signal ΔV, the control voltage (denoted as V ₃ ) which is the output of the third signal forming means (4) and the low-pass filter (5)
The control voltage (denoted as V ₁ ) smoothed by is superimposed in the mixing circuit (15), and this superimposed control voltage V
_CTL is supplied to the motor driver (6).

Also with this configuration, transient characteristics and steady-state deviation can be improved.

Next, examples of the present invention will be described. Fig. 10 is No. 9
This is an embodiment corresponding to the figure, and only the main part is shown.

In this embodiment, the first and second speed deviation signals S ₁ and S ₂ are digitally formed. The first signal forming means (11) is a measurement counter (21) and bias data. Has a memory (or register) (22) and a data counter (23) for use, bias data (initial data) is loaded to the measurement counter (21) in synchronization with the rotation signal S _M , and the data counter (23) is loaded. Is also loaded with the measurement data of the measurement counter (21) in synchronization with this rotation signal S _M.

Therefore, the rotation signal S _M (FIG. 11A) is supplied to the first mono-multi (25) to form the first multi-output M ₁ (FIG. 11B) which is synchronized with its falling edge, and This first multi-output M ₁ is further supplied to the second mono-multi (26) to form a second multi-output M ₂ (FIG. 7C) synchronized with its rising edge. The second multi-output M ₂ is used as a load pulse for the N-bit measurement counter (21), and the bias data is loaded during the low level period of the _second multi-force M ₂ . Bias data is measured by the measurement counter (2
The value is set to a predetermined value 2 ^M (M <N) such that the time point at which the value of 2 ^N-1 after 1) gives a carry once becomes the target rotation speed.

First multi-output M ₁ is used as a gate pulse to gate the clock CKb for measuring counter (21),
Therefore, this clock CKb and the first multi-output M ₁ are supplied to the AND gate (27). It becomes the operation of the measurement counter (21) as shown in FIG. 11 D if analog manner shown, biased data loaded in the second multi-output M ₂ is turned multiple output M ₂ of the second to the high level The count-up operation starts from the time when the measurement signal (21) reaches the full count within one rotation cycle of the rotation signal S _M , and then the count-up operation continues again, and the first multi-output obtained next.
At the time of M ₁ , the measurement counter (21) supplies the measurement data to the digital differentiating circuit (40).

In this example, a first constant unit (41), a memory circuit (42) for storing measurement data of one time before obtained by the measurement counter (21), and a memory circuit of one time before output from the memory circuit (42). Constant device (second constant device) for the measured data of
A differentiation circuit (40) is composed of (43) and a subtracter (44) for subtracting the first and second constant device outputs. When the differential gain (constant) of the first constant device (41) is k (k is an appropriate integer value of 1 or more), the differential gain of the second constant device (43) is selected as (k-1). To be done.

Store the measurement data to the memory circuit (42) is performed by the first multi-output M _1.

Now, when the differential element sk is interposed, the input (ω _ref
−ω) is changed as follows and the latch circuit (2
8) Supplied to.

Now, if the motor rotation frequency at a certain control time point is ω _n and the motor rotation frequency before one time point is ω _n-1 , the differentiation circuit (4
The output ω '(latch circuit (2
8)) is ω ′ = k (ω _ref −ω _n ) − (k−1) (ω _ref −
ω _n-1 ) = ω _ref −ω _n − (k−1) ω _n + (k−1) ω _n−1 = ω _ref −ω _n − (k−1) (ω _n −ω _n-1 ). ‥‥‥
(17) On the other hand, when the differentiating circuit (40) is not provided, ω ′ = ω _ref −ω _n (18)

(K-1) (ω _n −ω _n-1 ) in the third term on the right side of equation (17)
Is equal to dω / dt, the output ω'is output in a state where differential characteristics are provided by providing the differentiating circuit (40).

In the case where a differential characteristic is given to the output ω ′ in this way,
The damping effect as described above can be obtained.

The output of the measurement counter (21) provided with the differential characteristic, that is, the measurement data is latched by the latch circuit (28).
When the latched measurement data is illustrated in analog form,
11 It looks like Figure E.

Period of measurement data rotation signal S _M at the time the first multi-output M ₁ is obtained, i.e. changes in accordance with the rotational speed of the speed of the motor (1). When the motor rotation speed is high, the one rotation cycle becomes shorter, so the measurement data to be latched is small. Conversely, when the motor rotation speed is low, the one rotation cycle becomes longer, so the measurement data at this time is increased. Becomes larger.

The latched measurement data is loaded into an N-bit data counter (23). Therefore, the data counter (2
The clock CKa '(which may be the same as or different from CKa) obtained at the terminal (32) is supplied to 3) and is also supplied to the frequency divider (33), which divides it by 1/2 ^N. Fig. 12B
The reference clock CKa shown in FIG.
The latched measurement data is loaded in synchronization with the fall timing of Ka.

After data loading is measured data counted up loaded by a clock CKa ', MSB pulse P _M that indicates the MSB bit of the count-up count data
(FIG. 12A) and the clock CKa are supplied to the pulse forming means (30) to form the first speed deviation signal S ₁ .

MSB pulse P _M is the count data of the data counter (23), at 0-2 during the ^N-1 is "0", while the 2 ^N-1 to 2 ^N -1 "1"
And the data counter (23) and the frequency divider (33) have the same clock CK
Since it is driven by a ', the pulse cycle of the reference clock CKa divided by 1/2 ^N and the MSB pulse P _M match.

However, MSB pulse P _M of the phase with respect to the reference clock CKa is different depending on the magnitude of the measured data to be loaded into the data counter (23). That is, when the number of revolutions of the motor (1) is high, the measurement data latched by the _first multi-output M1 is a value of 2 ^N-1 or less.
The pulse P _M is “0” and remains “0” until the measurement data loaded in the data counter (23) becomes 2 ^N−1 (see FIGS. 12A and 12B).

A data counter with a limiter is used as the data counter (23). If a borrow occurs as a result of the operation, the count data is forcibly set to 0, and if a carry occurs, 2 ^{N -1} is set.

The pulse forming means (30) can be constituted by a flip-flop or the like, and if it is set at the falling edge of the MSB pulse P _M and reset at the falling edge of the reference clock CKa, the pulse forming means (30) of FIG. When there is a phase relationship, the first speed deviation signal S ₁ as shown in FIG.

On the other hand, when the rotation speed of the motor (1) is slow, the measured data loaded into the data counter (23) is 2 ^N-1 or more, so the MSB at that time can be seen from the timing of the reference clock CKa. The pulse P _M is "1" (Fig. 12D). Accordingly, the first speed deviation signals S ₁ obtained at this time is as shown in FIG E, a signal having a pulse width corresponding to the speed deviation is obtained.

MSB pulse P _M and the reference clock CKa is further supplied to the second signal forming means (13).

The second signal forming means (13) obtains a negative pulse having a pulse width corresponding to the speed when the motor rotational speed is fast, and a positive pulse having a pulse width corresponding to the slow speed when the motor rotational speed is slow. When the measurement data (analog conversion value) shown in FIG. 13C is used, the phase relationship between the MSB pulse P _M and the reference clock CKa is shown in FIGS. 13D and E. Therefore, the reference clock CKa
On the other hand, when the phase of the MSB pulse P _M is advanced, that is, when the rotation speed is slow, the negative pulse S _2M shown in FIG.
A second speed deviation signal S ₂ having obtained.

Therefore, in the second signal forming means (13), the reference clock
When the rising edge of CKa is later than the falling edge timing of the MSB pulse P _M , a negative pulse is obtained. The pulse width differs depending on the number of rotations. The faster the rotation, the wider the pulse width. Therefore, MSB pulse P _M from the rising timing of the negative pulse is the reference clock
Is obtained until the fall timing.

When the rotation speed is slow, MSB pulse P _M and reference clock CKa
Since the phase relationship with and is opposite to the above, and the rising edge of the reference clock CKa is later than the falling edge timing of the MSB pulse P _M , the second speed deviation signal S having the positive pulse S _2P
2 is obtained, and the pulse width becomes wider as the rotation speed becomes slower.

As described above, the second speed deviation signal S ₂ has a polarity corresponding to whether the rotation speed is faster or slower than the reference rotation speed, and
The deviation amount are those having a pulse width corresponding, the reference when the rotational speed of and the MSB pulse P _M and the reference clock CKa in phase, either positive or negative pulse is not output.

The second speed deviation signal S ₂ is cleared every cycle at the falling _edge of the rotation signal S _M , and the positive or negative polarity pulses S _2P and S _2M obtained within this one rotation cycle are the first It is self-holding after the pulse is obtained. Therefore, the rotation signal
One pulse S _2P or S _2M is generated in one period of S _M. Then, both the sections without the pulses S _2P and S _2M are held at high impedance.

Second speed deviation signal S ₂ is supplied to the third signal forming means for converting to a DC control voltage V ₃ (14). A charge pump can be used for the third signal forming means (14), and if the positive pulse S _2P is charged for the pulse width period and the negative pulse S _2M is discharged for the pulse width period, the rotation is performed. A DC control voltage V ₃ (FIG. 13H) corresponding to several speed deviations can be obtained.

As described above, the DC control voltage V ₃ based on the second speed deviation signal S ₂ is a sure that the DC level is changed when the speed deviation occurs, therefore, the DC control voltage
By controlling the rotational speed of the motor (1) with V _3, the steady-state deviation Δω
It is possible to correctly control to a regular rotation speed in the absence of.

The out-of-range detection circuit (35) is a measurement counter (21)
And (N + 1) th bit, while the (N + 2) A counter can count bit, the period of the first low-level multi-output M _1, (N + 1) th bit is "0",
If it is not "1", it is determined that the rotation of the motor (1) is too fast. At this time, the output of the out-of-range detection circuit (35) produces pulse forming means (30) and second signal forming means (1
3) Forcibly generate "L" and a negative pulse _S2M .

On the contrary, when the (N + 2) th bit becomes "1",
It is determined that the motor speed is too slow, and in this case, the operation opposite to the above is forcibly performed.

In FIG. 10, the MSB pulse P _M and the reference clock C
Instead of forming the _second speed deviation signal S ₂ based on Ka, the first speed deviation signal S ₁ itself is used to form the second speed deviation signal S ₂ based on this and the reference clock CKa. You can also do it.

EFFECTS OF THE INVENTION As described above, according to the present invention, the feedback control system is provided with the differential characteristic imparting means by the digital circuit. Transient characteristics, i.e. overshoot, can be suppressed or eliminated altogether. Therefore, the settling time until the motor rotation speed reaches the reference rotation speed can be significantly shortened as compared with the conventional case.

Moreover, since it is not necessary to reduce the proportional gain K ₁ when improving the transient characteristic, the steady-state deviation is small. Of course,
By configuring as shown in FIG. 7 or 9, it is possible to eliminate the steady-state deviation. Therefore, according to the present invention, a floppy disk or the like which needs to be driven at a regular rotation speed while the rotation speed rises quickly. It is extremely suitable when applied to a motor control system.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a speed servo circuit according to the present invention, FIG. 2 is a system diagram of a conventional speed servo circuit, and FIG. 3 is a control block diagram for explaining the control operation, FIG. FIG. 6 is a transient characteristic diagram of motor rotation, FIG. 5 is a control block diagram of FIG. 1, FIGS. 7 and 9 are system diagrams showing other examples of the speed servo circuit according to the present invention, and FIG. FIG. 10 is a control block diagram of FIG. 7, FIG. 10 is a systematic diagram of an essential part showing a concrete example of FIG. 9, and FIGS. 11 to 13 are waveform charts for explaining the operation thereof. (1) is a motor, (2) is a rotation signal generating means, (11),
(13) and (14) are first to third signal forming means, S ₁ and S ₂ are first and second velocity deviation signals, V _CTL is a control voltage, and (40) is a digital differentiation which is differentiation characteristic giving means. Circuit.

Claims (1)

[Claims] 1. A rotation signal generating means for obtaining a rotation signal proportional to the rotation speed of a motor to be controlled, a measurement counter for measuring the rotation speed of the motor from the rotation signal, and measurement data obtained by the measurement counter. First
Constant circuit, a memory circuit for storing the measurement data obtained one time before obtained from the measurement counter, a second constant device for the measurement data outputted one time before outputted from the memory circuit, and the first and the second A digital differentiating circuit having a subtracter for subtracting the output of the constant device 2, a data counter into which the differential characteristic data obtained from this digital differentiating circuit is loaded, and a rotational speed of the motor connected to the data counter. A speed servo circuit which is provided with a servo circuit which outputs a control voltage for keeping it constant, and which controls the rotation speed of the motor by using the control voltage output from the servo circuit as a DC control voltage.