JPH08280189A - Motor controller - Google Patents

Abstract

PURPOSE: To prevent the extremely high rotating speed of a motor by driving the motor with an output equal to the sum of the period error value corresponding to the actual period and the target period of measured FG signals, the frequency of the FG signals found from the measured FG signals, and error value of the target frequency of the FG signals. CONSTITUTION: An FG section 2 generate FG signals of a frequency proportional to the rotating speed of a motor 1. The FG signals are inputted to the input capture 3 of a microcomputer 10 which counts and latches the FG signals. A period error value calculating section 4 finds the period of the FG signals from the count value of the capture 3 and outputs the period error value corresponding to the difference between the found period and a target period. A frequency error value calculating section 11 finds the frequency of the FG signals from the count value of the capture 3 and outputs the frequency error value corresponding to the difference between the found frequency and target frequency. The motor 1 is driven through an LPF 6 and motor drive circuit 7 by adding the period and frequency error values to each other by means of an adder 12. Therefore, the run out of control of the motor 1 can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to speed control of drum motors and capstan motors of VTRs.

[0002]

2. Description of the Related Art A speed control method for a drum servo system or a capstan servo system of a VTR is such that an error signal corresponding to the cycle of an FG (Frequency Generator) signal is generated regardless of the analog servo, digital servo or software servo system. It detects and controls the rotation speed of a motor. Here, a case of software servo using a microcomputer will be described as an example.

FIG. 5 is a block diagram showing an outline of a conventional motor control device. In the figure, 1 is a motor, 2 is an FG unit that generates an FG signal having a frequency proportional to the rotation speed of the motor 1, and 3 is an input capture that counts clock pulses and latches the count value when the FG signal is input.
Reference numeral 4 denotes a cycle error value calculator that calculates the cycle of the FG signal from the count value of the input capture 3 and calculates a cycle error value according to the difference from the target value. Reference numeral 5 denotes a duty cycle corresponding to the output of the cycle error value calculator 4. PWM (Pulse Width Modulatio
n) A PWM converter that outputs a signal, 6 is an LPF (Low Pass Filter) that smoothes the PWM signal, 7 is a motor drive circuit that drives a motor according to the output of the LPF 6, and 10 is a microcomputer. The cyclic error value calculation unit 4 uses CP
It is configured by software in a U (Central Processing Unit) (not shown).

In addition, in the drum servo system or the capstan servo system of the VTR, a phase control loop is added in addition to the speed control loop having the above-mentioned configuration, but it is omitted here for simplification of description.

Next, the operation will be described. When the motor 1 rotates, an FG signal having a frequency proportional to the rotation speed is generated in the FG unit 2 by n (n is a positive integer) pulses per rotation, and is input to the microcomputer 10 and is counted by the input capture 3 at the time of input. The value is latched.

When the count value at the time of inputting the FG signal is latched in the input capture 3, the following calculation is first performed in the period error value calculation section 4. The number of bits of the PWM signal is M, and the count value latched at that time is T
_n , the count value latched at the previous time point is T _n-1 ,
_Let K ₁ be a coefficient for adjusting the gain, and calculate T _FG = T _n −T _n−1 N ₁ = (T _FG −T ₀ ) × K ₁ . However, T ₀ is the value of T _FG when the cycle of the FG signal is the target value.

Next, the ranges of N ₁ are compared, and if N ₁ ≧ 2 ^M-1 , N ₁ = 2 ^M-1 -1 N ₁ <-2 ^M-1 If N ₁ = -2 ^M-1 If -2 ^M-1 ≤ N ₁ <2 ^M-1 , leave N ₁ unchanged.

When the rotation speed of the motor 1 is the target value, that is, when the cycle of the FG signal is the target value, N ₁ = 0, and when the rotation speed of the motor 1 is slower than the target value, that is, FG
When the cycle of the signal is larger than the target value, N ₁ becomes a positive value, and when the rotation speed of the motor 1 is faster than the target value, that is, when the cycle of the FG signal is smaller than the target value, N ₁ becomes a negative value. .

Further, for PWM conversion, N ₀ = N ₁ +2 ^M-1 . In addition, the count value T _n is set to T in preparation for the next calculation.
Substitute in _n-1 .

[0010] In PWM converter 5, the duty N _0/2 ^M × according to the value of the output N ₀ of the periodic error value computing section 4
A 100% PWM signal is output.

When the rotation speed of the motor 1 is the target value, that is, when the period of the FG signal is the target value, N ₁ = 0, so N ₀ = 2 ^{M -1} , and the duty of the PWM signal is 50%.
Becomes When the rotation speed of the motor 1 is slower than the target value, that is, when the cycle of the FG signal is larger than the target value, N ₁ becomes a positive value, so N ₀ > 2 ^M−1 , and the duty of the PWM signal is 50% or more. growing. When the rotation speed of the motor 1 is faster than the target value, that is, when the cycle of the FG signal is smaller than the target value, N ₁ becomes a negative value, so N ₀ <2
^It becomes ^M-1 , and the duty of the PWM signal becomes smaller than 50%.

In this way, the PWM signal having a duty corresponding to the rotation speed of the motor 1 is smoothed by the LPF 6,
It is input to the motor drive circuit 7. The motor drive circuit 7 is
The reference voltage is adjusted so that a predetermined rotation speed is obtained by a PWM signal having a duty of 50% with respect to a predetermined load torque. The motor 1 is decelerated when the rotation speed is high, and is accelerated when the rotation speed is low. 1 is driven,
Speed control is performed so that the rotation speed of the motor 1 approaches the target value.

The relationship between the period of the FG signal and N ₀ at this time is shown in FIGS. 6a and 6b. When the coefficient K ₁ is sufficiently large, N ₀ takes a value in the range of 0 to (2 ^M −1) according to the period of the FG signal as shown in FIG. 6a. However, the coefficient K
_{If 1} cannot be made sufficiently large, even if the rotation speed approaches infinity and the period of the FG signal becomes 0, N ₁ = (0−T ₀ ) × K ₁ > −2 ^M−1 , and N ₀ is (2 ^M-1 −T ₀ × K ₁ ) to (2 ^M −
Only the value in the range of 1) is taken, and the output range becomes narrow when the cycle of the FG signal deviates to the shorter side.

[0014]

Since the conventional motor control device is constructed as described above, when the coefficient K ₁ cannot be made sufficiently large, the load torque becomes smaller than a predetermined value, or the motor drive circuit If the reference voltage adjustment accuracy is insufficient or the motor rotation speed deviates to a higher speed, the rotation speed becomes extremely high, resulting in a runaway condition.

The present invention has been made in order to solve the above problems, and even when the coefficient K ₁ cannot be made sufficiently large, the output range can be widened and the load torque becomes smaller than a predetermined value. It is an object of the present invention to provide a motor control device that can prevent the rotation speed from becoming extremely high even if the adjustment accuracy of the reference voltage of the motor drive circuit is insufficient.

[0016]

According to a first aspect of the present invention, there is provided a motor control device for measuring a cycle of an FG signal, and a difference between a cycle of the measured FG signal and a cycle of a target FG signal. And a calculation means for calculating a cycle error value according to the above, and a calculation for calculating the frequency of the FG signal from the measured cycle of the FG signal and calculating a frequency error value according to the difference between this and the frequency of the target FG signal. Means, an addition means for adding the cycle error value and the frequency error value, and a motor drive means for driving the motor according to the output of the addition means.

Further, a motor control device according to a second aspect of the present invention has a measuring means for measuring the cycle of the FG signal, and a cycle corresponding to the difference between the cycle of the measured FG signal and the cycle of the target FG signal. A calculation means for calculating an error value and the measured F
Calculating means for calculating the frequency of the FG signal from the cycle of the G signal and calculating a frequency error value corresponding to the difference between the frequency of the FG signal and the frequency of the target FG signal; and switching means for switching the cycle error value and the frequency error value. The motor drive means is provided for driving the motor according to the output of the switching means.

According to a third aspect of the present invention, the motor control device measures the period of the FG signal, and a period corresponding to the difference between the period of the measured FG signal and the period of the target FG signal. A calculation means for calculating an error value and the measured F
The calculation means calculates the frequency of the FG signal from the cycle of the G signal and calculates the frequency error value according to the difference between the frequency of the FG signal and the frequency of the target FG signal.

[0019]

In the motor control device according to the first aspect of the present invention, the frequency error value in which the output range in the region where the cycle of the FG signal is smaller than the target value is wider than the cycle error value is added to the cycle error value and output. Therefore, even when the cycle of the FG signal deviates to the shorter side, that is, the motor rotation speed deviates to the faster side, a wide range of output can be obtained.

In the motor control device according to the second aspect of the present invention, when the cycle of the FG signal is smaller than the target value, the output range in the region where the cycle of the FG signal is smaller than the target value is wider than the cycle error value. Since the error value is output by switching to the cyclic error value, a wide range of output can be obtained even when the cycle of the FG signal deviates to the shorter side, that is, when the motor rotation speed deviates to the faster side.

In the motor control device according to the third aspect of the present invention, the period corresponding to the frequency of the FG signal is obtained by measuring the period of the FG signal and performing division by the value corresponding to the period of the FG signal. To be

[0022]

【Example】

Example 1. FIG. 1 is a block diagram showing an outline of a motor control device according to the first embodiment. In the figure, 1 is a motor,
2 is an FG unit that generates an FG signal having a frequency proportional to the rotation speed of the motor 1, and 3 is a clock pulse,
An input capture 4 for latching a count value at the time of inputting a G signal, a cycle error value calculator 4 for calculating the cycle of the FG signal from the count value of the input capture 3 and calculating a cycle error value according to a difference from a target value, 11 Is a frequency error value calculation unit that calculates the frequency of the FG signal from the count value of the input capture 3 and calculates a frequency error value according to the difference from the target value; 12 is an addition unit that adds the cycle error value and the frequency error value; 5 is P of duty according to the output of the addition unit 12
A PWM converter that outputs a WM signal, 6 is an LPF that smoothes the PWM signal, 7 is a motor drive circuit that drives a motor according to the output of the LPF 6, and 10 is a microcomputer. Period error value calculator 4 and frequency error value calculator 1
1, the addition unit 12 is configured by software in a CPU (not shown).

In practice, a phase control loop may be added in addition to the speed control loop having the above configuration, but it is omitted here for simplification of description.

Next, the operation of this embodiment will be described. When the motor 1 rotates, an FG signal having a frequency proportional to the rotation speed is generated in the FG unit 2 by n (n is a positive integer) pulses per rotation, and is input to the microcomputer 10 and is counted by the input capture 3 at the time of input. The value is latched.

When the count value at the time of inputting the FG signal is latched in the input capture 3, the following calculation is first performed in the period error value calculation section 4. The number of bits of the PWM signal is M, and the count value latched at that time is T
_n , the count value latched at the previous time point is T _n-1 ,
_Let K ₁ be a coefficient for adjusting the gain, and calculate T _FG = T _n −T _n−1 N ₁ = (T _FG −T ₀ ) × K ₁ . However, T ₀ is the value of T _FG when the cycle of the FG signal is the target value.

When the rotation speed of the motor 1 is the target value, that is, when the cycle of the FG signal is the target value, N ₁ = 0, and when the rotation speed of the motor 1 is slower than the target value, that is, FG
When the cycle of the signal is larger than the target value, N ₁ becomes a positive value, and when the rotation speed of the motor 1 is faster than the target value, that is, when the cycle of the FG signal is smaller than the target value, N ₁ becomes a negative value. . The relationship between the cycle of the FG signal and N ₁ at this time is shown in FIGS. 2a and 2b. FIG. 2b is an enlarged display of the vicinity of T ₀ in FIG. 2a.

When the frequency of the clock pulse of the input capture 3 is f _CK and the frequency of the FG signal is f _FG , N ₁ can be expressed as N ₁ = (f _CK / f _FG -T ₀ ) × K _1. Therefore, the gain G ₁ of N ₁ with respect to the frequency of the FG signal is G ₁ = −f _CK / f _FG ² × K ₁ . When the target value of the frequency of the FG signal is f _FG0 , the gain G ₁ near the target value is G ₁ = −f _CK / f _FG0 ² × K ₁ .

N ₁ is one input to the adder 12, and T _FG is an input to the frequency error value calculator 11. The frequency error value calculation unit 11 performs the following calculations.
Let K ₂ be the coefficient for adjusting the gain, and calculate N ₂ = − (K ₂ / T _FG −K ₃ ). However, K ₃ = K ₂ / T ₀ , and K ₂ / T _FG has a value proportional to the frequency of the FG signal.

When the rotation speed of the motor 1 is the target value, that is, when the frequency of the FG signal is the target value, N2 = 0,
When the rotation speed of the motor 1 is slower than the target value, that is, F
When the frequency of the G signal is lower than the target value, N2 becomes a positive value, and when the rotation speed of the motor 1 is faster than the target value, that is, when the frequency of the FG signal is higher than the target value, N2
Is a negative value. The relationship between the period of the FG signal and N2 at this time is shown in FIGS. 2a and 2b.

Here, N ₂ is N ₂ =-(K ₂ × f _FG /
Since it can be expressed as f _CK −K ₃ ), the gain G _{2 of} N ₂ with respect to the frequency of the FG signal is G ₂ = −K ₂ / f _CK . If K ₁ and K ₂ are set so that G ₁ = G ₂ near the target value of the frequency of the FG signal, the cyclic error value calculation unit 4
And the gain of the frequency error value calculation unit 11 become equal.

Next, the addition unit 12 performs the following calculation. N ₃ = (N ₁ + N ₂ ) / 2 Further, the ranges of N ₃ are compared, and if N ₃ ≧ 2 ^M−1, then N ₃ = 2 ^M−1 −1 N ₃ <−2 ^M−1, then N ^{_{3 = -2 M-1 -2 M}} -1 ≦ N 3 <2 M-1 if N ₃ is left as it is. The relationship between the cycle of the FG signal and N3 at this time is shown in FIG.
a and FIG. 2b.

Next, N ₀ = N ₃ +2 ^M-1 is set for PWM conversion. Further, the count value T _n is substituted for T _n−1 to prepare for the next calculation.

[0033] In PWM converter 5, according to the value of the output N ₀ of the adder 12, the duty N _0/2 ^M × 100
% PWM signal is output.

When the rotation speed of the motor 1 is the target value, that is, when the frequency of the FG signal is the target value, N ₁ = N ₂ = 0, so N ₀ = 2 ^{M -1} , and the duty of the PWM signal is 50%. Becomes When the rotation speed of the motor 1 is slower than the target value, that is, when the frequency of the FG signal is smaller than the target value, N ₁ and N ₂ are positive values, so N ₀ > 2 ^M−1 , and the duty of the PWM signal is Greater than 50%.
When the rotation speed of the motor 1 is faster than the target value, that is, F
When the frequency of the G signal is higher than the target value, N ₁ and N ₂ have negative values, so N ₀ <2 ^M−1 , and the duty of the PWM signal becomes smaller than 50%.

In this way, the PWM signal having a duty corresponding to the rotation speed of the motor 1 is smoothed by the LPF 6,
It is input to the motor drive circuit 7. The motor drive circuit 7 is
The reference voltage is adjusted so that a predetermined rotation speed is obtained by a PWM signal having a duty of 50% with respect to a predetermined load torque. The motor 1 is decelerated when the rotation speed is high, and is accelerated when the rotation speed is low. 1 is driven,
Speed control is performed so that the rotation speed of the motor 1 approaches the target value.

If the coefficient K ₁ cannot be increased sufficiently, the load torque becomes smaller than a predetermined value, or the reference voltage adjustment accuracy of the motor drive circuit is insufficient, so that the motor rotation speed is high. even shifted to boric, the output N ₀ of the adder as shown in FIGS. 2a and 2b, compared with the period error output N _1, the period of the FG signal is large the gain is the goal value is less than the side, the output range Since it is also wide, the degree to which the rotation speed of the motor becomes faster than in the past is reduced.

Example 2. In the above embodiment, the method of adding and using the output of the period error value calculating unit 4 and the output of the frequency error value calculating unit 11 has been described, but the output of the period error value calculating unit 4 and the frequency error value calculating unit 11 are used. The output may be switched and used. FIG. 3 is a block diagram showing an outline of a motor control device according to the second embodiment of the present invention. In the figure, instead of the output of the period error value calculation unit 4 and the output of the frequency error value calculation unit 11 being input to the addition unit 12, they are input to a newly provided switching unit 13, and the output of the switching unit 13 is PWM. It is the same as the case of the first embodiment shown in FIG. 1 except that it is inputted to the converter 5.

Next, the operation of this embodiment will be described. When the motor 1 rotates, an FG signal having a frequency proportional to the rotation speed is generated in the FG unit 2 by n (n is a positive integer) pulses per rotation, and is input to the microcomputer 10 and is counted by the input capture 3 at the time of input. The value is latched.

When the count value at the time of inputting the FG signal is latched in the input capture 3, the period error value calculation unit 4 _first calculates the period error value N ₁ , and then the frequency error value calculation unit 11 calculates the frequency error value N 1. ₂ is calculated. The calculation method is the same as in the case of the first embodiment, so the explanation is omitted.

Next, the following processing is performed in the switching section 13 based on the calculation result of the cyclic error value calculation section 4. If N ₁ ≧ 0, then N ₃ = N _{1 If} N ₁ <0, then N ₃ = N _2, that is, if the frequency of the FG signal is below the target value, then N ₃
The cycle error value N ₁ is selected as, and if the frequency of the FG signal is larger than the target value, the frequency error value N ₂ is selected as N ₃ . Furthermore, the ranges of N ₃ are compared, and if N ₃ ≧ 2 ^M−1, then N ₃ = 2 ^M−1 −1 N ₃ <−2 ^M−1 then N ₃ = −2 ^M−1 −2 ^{M− If 1} ≤ N ₃ <2 ^M-1 , leave N ₃ unchanged. The period of the FG signal at this time and N ₃ , N ₁ , and N ₂
Are shown in FIGS. 4a and 4b. FIG. 4b is an enlarged view of the vicinity of T ₀ in FIG. 4a.

Next, N ₀ = N ₃ +2 ^M-1 is set for PWM conversion. In addition, the count value T _n is set to T in preparation for the next calculation.
Substitute in _n-1 .

In the PWM converter 5, the switching unit 1
3 according to the value of the output N _0, Duty N _0/2 ^M × 1
A PWM signal of 00% is output.

When the rotation speed of the motor 1 is the target value, that is, when the frequency of the FG signal is the target value, N ₁ = 0, so N ₀ = 2 ^M−1 , and the duty of the PWM signal is 50.
%. When the rotation speed of the motor 1 is slower than the target value,
That is, when the cycle of the FG signal is larger than the target value, N ₁
N ₁ as N ₀ from a positive value is selected N _0> 2
^It becomes ^M-1 , and the duty of the PWM signal becomes larger than 50%. When the rotation speed of the motor 1 is faster than the target value, that is, when the cycle of the FG signal is smaller than the target value, N ₁ ,
N ₂ is N ₂ is selected as N ₀ from a negative value N ₀
<2 ^M-1 , and the duty of the PWM signal becomes smaller than 50%.

In this way, the PWM signal of the duty corresponding to the rotation speed of the motor 1 is smoothed by the LPF 6,
It is input to the motor drive circuit 7. The motor drive circuit 7 is
The reference voltage is adjusted so that the PWM signal having a duty of 50% with respect to a predetermined load torque provides a predetermined rotation speed. 1 is driven,
Speed control is performed so that the rotation speed of the motor 1 approaches the target value.

If the coefficient K ₁ cannot be increased sufficiently, the load torque becomes smaller than a predetermined value or the reference voltage adjustment accuracy of the motor drive circuit is insufficient, so that the motor rotation speed is high. 4a and 4b, the output N _{0 of the} switching unit has a larger gain on the side where the cycle of the FG signal is smaller than the target value and the output range is smaller than the cycle error output N ₁ , as shown in FIGS. 4a and 4b. Since it is also wide, the degree to which the rotation speed of the motor becomes faster than in the past is reduced.

In the first embodiment, the cyclic error value N
1 and the gain of the frequency error value N ₂ are equalized, and N ₁
Although the case where the output N ₀ is calculated by adding and N ₂ and dividing by 2 is shown, the gains of N ₁ and N ₂ may not be equal, and addition of N ₁ and N ₂ is optional. You may add by weighting.

In the second embodiment, the cyclic error value N
₁ and the gain of the frequency error value N ₂ are equalized, and N ₁
Output N by switching N ₁ and N ₂ depending on whether is 0 or more
_Although the case where it is set to ₀ is shown, N ₁ and N ₂
Gains may be unequal, and may be switched depending on whether N ₁ is a predetermined value other than 0 or not, or may be switched depending on whether N ₂ is a predetermined value or more instead of N _1. You may

Further, in the first and second embodiments, the frequency error value N ₂ is shown as N ₂ =-(K ₂ / T _FG -K ₃ ) and an error value proportional to the frequency shift is used. , N ₂ = − (K ₂ / T _FG −K ₃ ) ⁿ , (n is an integer of 2 or more) However, when n is an even number, if K ₂ / T _FG −K ₃ <0, then N ₂ = −N ₂ For example, an error value proportional to the n-th power of the frequency shift may be used.

Further, in Examples 1 and 2, FG
When the cycle of the signal is the target value, the cycle error value N ₁ and the frequency error value N ₂ are set to 0, and the duty of the PWM signal is set to 50%.
The cycle error value N ₁ and the frequency error value N 2 may be values other than 0, and the duty of the PWM signal may be a value other than 50%.

Further, in the first and second embodiments, the case where the microcomputer is used and the period error calculating unit and the frequency error calculating unit are processed by software has been described, but the hardware such as a digital circuit may be used. Good.

Further, in the first and second embodiments, the case where the PWM converter is used as the means for converting the digital value into the analog amount is shown, but other conversion means such as a D / A converter may be used.

Although not added in Examples 1 and 2, (1 + sτ) is set at an appropriate position in the control loop.
The rotation speed of the motor can be made closer to the target value by adding a filter having a characteristic such that the gain becomes large in a low frequency region such as / sτ or a digital filter having an equivalent characteristic.

[0053]

According to the motor control device of the first aspect of the present invention, since the period error value and the frequency error value are added and output as shown in the first embodiment, the period of the FG signal is short. Even when the motor rotation speed deviates to the higher direction, that is, when the motor rotation speed deviates to the higher direction, the gain is higher than that in the case of the cyclic error value alone, and a wide range output can be obtained. Therefore, when the coefficient K ₁ cannot be increased sufficiently, the load torque becomes smaller than a predetermined value, or the reference voltage adjustment accuracy of the motor drive circuit is insufficient. Even if it does, it is effective in preventing the rotation speed of the motor from becoming extremely high.

According to the second aspect of the motor control device of the present invention, as shown in the second embodiment, the cycle error value is switched when the rotation speed of the motor is faster than the target value, and the frequency error value is switched when the rotation speed is slower than the target value. Therefore, even when the cycle of the FG signal deviates to the shorter side, that is, when the motor rotation speed deviates to the faster side, the gain is higher than that in the case of the cycle error value alone, and a wide range of output can be obtained. Therefore, when the coefficient K ₁ cannot be increased sufficiently, the load torque becomes smaller than a predetermined value, or the reference voltage adjustment accuracy of the motor drive circuit is insufficient. Even if it does, it is effective in preventing the rotation speed of the motor from becoming extremely high.

According to the motor control device of the third aspect of the present invention, the period of the FG signal is measured as shown in the first and second embodiments, and the division is performed by the value corresponding to the period of the FG signal. , A value corresponding to the frequency of the FG signal is obtained, so that there is an effect that the frequency error value can be obtained without the need for the means for measuring the frequency of the FG signal, only by the means for measuring the period of the FG signal. .

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of a motor control device according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an error value detection characteristic of the motor control device according to the first embodiment of the present invention.

FIG. 3 is a block diagram showing an outline of a motor control device according to a second embodiment of the present invention.

FIG. 4 is a characteristic diagram showing an error value detection characteristic of the motor control device according to the second embodiment of the present invention.

FIG. 5 is a block diagram showing an outline of a conventional motor control device.

FIG. 6 is a characteristic diagram showing an error value detection characteristic of a conventional motor control device.

[Explanation of symbols]

1 motor, 2 FG section, 3 input capture,
4 cycle error value calculator, 5 PWM converter, 6 LP
F, 7 Motor drive circuit, 10 Microcomputer, 11 Frequency error value calculator, 12 Adder, 13
Switching unit.

Claims (3)

[Claims] 1. A motor, a motor driving means for driving the motor, a frequency signal generating means for generating a frequency signal having a frequency proportional to a rotation speed of the motor, and a cycle measuring means for measuring a cycle of the frequency signal. A cycle error value calculating means for calculating a cycle error value according to a difference between the output of the cycle measuring means and a target value, a frequency measuring means for measuring the frequency of the frequency signal, and an output of the frequency measuring means and a target value. And a frequency error value calculating means for calculating a frequency error value according to the difference between the output of the cycle error value calculating means and an output of the frequency error value calculating means. A motor control device for controlling the rotation speed of the motor according to the above. 2. A motor, a motor driving means for driving the motor, a frequency signal generating means for generating a frequency signal having a frequency proportional to a rotation speed of the motor, and a cycle measuring means for measuring a cycle of the frequency signal. A cycle error value calculating means for calculating a cycle error value according to a difference between the output of the cycle measuring means and a target value, a frequency measuring means for measuring the frequency of the frequency signal, and an output of the frequency measuring means and a target value. A frequency error value calculating means for calculating a frequency error value according to the difference between the output of the periodic error value calculating means and a switching means for switching the output of the frequency error value calculating means. A motor control device that controls the rotation speed of the motor according to the above. 3. The motor control device according to claim 1, wherein the frequency measuring means calculates the frequency of the frequency signal from the output of the cycle measuring means.