CA1303666C - Servo system for a motor - Google Patents

Servo system for a motor

Info

Publication number
CA1303666C
CA1303666C CA000596011A CA596011A CA1303666C CA 1303666 C CA1303666 C CA 1303666C CA 000596011 A CA000596011 A CA 000596011A CA 596011 A CA596011 A CA 596011A CA 1303666 C CA1303666 C CA 1303666C
Authority
CA
Canada
Prior art keywords
speed
rotor
signal
rotational speed
servo
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
CA000596011A
Other languages
French (fr)
Inventor
Fumiyoshi Abe
Akira Hasegawa
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sony Corp
Original Assignee
Sony Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to JP63086460A priority Critical patent/JPH01259780A/en
Priority to JP086460/88 priority
Application filed by Sony Corp filed Critical Sony Corp
Application granted granted Critical
Publication of CA1303666C publication Critical patent/CA1303666C/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Abstract

ABSTRACT OF THE DISCLOSURE
A servo system for a motor having a rotor that comprises a phase detector circuit for detecting a rotational phase of the rotor and for defining a plurality of angular positions of the rotor, each angle between adjacent angular positions being equal, a rotating device for rotating the rotor at a predetermined constant rotational speed, a speed detector circuit for detecting a rotational speed of the rotor at each of the angular positions, an error detector circuit for detecting errors of the speed detector circuit at each of the angular positions when the rotor is rotated at the predetermined constant rotational speed, a memory for storing the detection errors at each of the angular positions, and a servo control circuit for controlling a rotational speed and/or phase of the rotor in accordance with the rotational speed detected by the speed detector circuit and the detection errors read from the memory.

Description

" 13V;~6;66~
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates genera~ly to a servo system for a motor having a rotor and, more particularly, is directed to a servo system for servo-controlling the rotation of a motor such as a drum motor for rotating a rotary head drum of a video tape recorder, its capstan drive motor, a motor for driving a spindle of a disk apparatus with high accuracy.
Description of the Prior Art Rotating members such as a rotary head drum of a video tape recorder and a disk drive portion of a disk apparatus have to be rotated with accuracy as high as possible, and the rotational phase thereof needs to be synchronized with an external reference signal.
Therefore, a drum drive motor and a disk drive motor are servo-controlled for their rotational speed and for thelr rotational phase. The speed servo is effected by controlling a frequency of a rotation detecting signal FG
from a rotation detecting apparatus whose frequency corresponds to a rotational speed of a motor, and hence the rotation detecting apparatus must be high in accuracy for its detection.
The phase-servo is effected in such a fashion that the 2S phase relation between a reference position signal PG
generated once per revolution of the motor and a signal REFP
indicating a reference phase is controlled to have a predetermined phase relation. Generally, the phase servo is carried out by the phase data which is available only per revolution of the motor is to simplify the arrangement of ~ 3~3666 the phase servo loop. In this case, a very small error within one rotation of the motor is relatively small because of the inertia of the rotating member and can be ignored.
As a rotation speed detecting apparatus employed widely in the prior art, there is known such a rotation detecting apparatus that comprises a rotary member and a magnetic sensor element. In this case, the rotary member which has a plurality of N and S magnetic poles magnetized at a predetermined pitch on the outer peripheral surface thereof is coaxially attached to the rotary shaft of a motor and the magnetic sensor element is located facing the outer peripheral surface of the rotary member to sense the N - S
magnetic pattern.
Although the above-mentioned rotation detecting apparatus is simple in construction, it is difficult to obtain the rotation detecting apparatus which carries out the detection with high accuracy because of mechanical factors such as an error o magnetized pattern of magnetic poles of the rotary member, its eccentricity and so on. For example, even though the motor is correctly rotated at a constant speed, an error signal is generated due to the error of the magnetized pattern, causing the rotation detecting apparatus to erroneously determine that the motor is not rotated at the constant speed. Then, the servo system servo-controls the motor so as to remove the error signal such that undesired and irregular rotation is applied to the motor in order to remove the error caused by the magnetized pattern and so on. In order to solve the above-mentioned problems, there is proposed a method in which two magnetic sensor elements are located relative to ..... ,~ .. ..... . .. .

~3~3666 the magnetized pattern at the positions displaced in phase, thereby making the rotation detection higher in accuracy.
This previously-proposed method is disclosed in official gazette of Japanese laid-open patent No. 58-186812.
Further, the phase-servo is performed by the use of one phase data that is derived per revolution of the motor so that fine phase control within one revolution of the motor cannot be effected.
In the xotational speed control of the motor, the rotational speed of the motor is detected by measuring the cycle of a rotation detecting signal DT having the frequency corresponding to the rotational speed of the motor and which is derived from the rotation speed detecting element coaxially attached to the rotary shaft of the motor.
This cycle measuring method has a defect that at a low speed the speed detection and hence the responsiveness in the speed control are degraded because the cycle measuring time is increased as the rotational speed is decreased.
Therefore, in order to improve the responsiveness in the low-speed region, there is proposed a method in which when the motor is rotated at low speed, the grade of an inclined portion of a waveform of the rotation detecting signal DT is measured. This previously-proposed method is disclosed in official gazette of Japanese laid-open patent No. 59-116050.
According to the above-mentioned method, the rotational speed of the motor can be detected on the principle that the grade of the inclined portion of the triangular wave signal generated by the rotation of the motor is proportional to the rotational speed of the motor. However, if the -?36~6 peak-to-peak value of the resultant triangular wave signal is not constant, the grade of the inclined portion to be detected is also changed with the result that the rotational speed cannot be accurately detected. To solve this problem, in the prior art, the gain adjustment of a triangular wave signal generator is carried out by manually adjusting its volume. In this case, however, the gain adjustment is very cumbersome and it cannot follow the change of temperature and aging change.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an improved servo system for a motor having a rotor which can remove the afore-noted defects.
Another object of the present invention i`s to provide a servo system for a motor having a rotor which can obtain highly-accurate speed and phase data of a rotor by correcting errors caused by mechanical factors.
Still another object of the present invention is to provide a servo system for a motor having a rotor which can automatically adjust the gain of a signal having a frequency proportional to a rotational speed of a motor, thereby detecting a rotational speed with high accuracy.
A further object of the present invention is to provide a servo system for a motor having a rotor which can always effect accurate rotation control regardless of a rotational speed of a motor.
In accordance with an aspect of the present invention, there is provided a servo system for a motor having a rotor comprising:
phase detector means for detecting a rotational phase , ... . .

:~3~3~i~6 of said rotor and for defining a plurality of angular positions of said rotor, each angle between adjacent said angular positions being equal;
rotating means for rotating said rotor at a predetermined constant rotational speed;
speed detector means for detecting a rotational speed of said rotor at each of said angular positions;
error detector means for detecting detection errors of said speed detector means at each of said angular positions when said rotor is rotated at said predetermined constant rotational speed memory means for storing said detection errors at each of said angular positions; and servo controlling means for controlling a rotational speed and/or phase of said rotor in accordance with the rotational speed detected by said speed detector and said detection errors read from said memory means.
In accordance with other aspect of the present invention, there is provided a servo system for a motor having a rotor comprising:
frequency generator means for generating a recurrent signal which is cyclical and has generally linear portions, the frequency of said recurrent signal being proportional to a rotational speed of said rotor;
first speed detector means for detecting the rotational speed of said rotor by detecting time in which said rotor rotates for a predetermined angle and for outputting a first speed signal;
second speed detector means for detecting the rotational speed of said rotor by detecting a grade of said -` 13~)36Ç;6 linear portion of said recurrent signal and for outputting a second speed signal;
comparing means for comparing said first and second speed signals and for outputting a compared result;
gain control means for controlling a gain of said recurrent signal according to said compared result of said comparing means so that said first and second speed signals become equal; and servo control means for controlling the rotational speed of said rotor in accordance with one of said first and second speed signals.
In accordance with a further aspect of the present invention, there is provided a servo system for a motor having a rotor comprising:
a frequency generator for generating first and second recurrent signals each of which is cyclical and has generally linear portions separated by non-linear portions, the frequency of said recurrent signals being proportional to the rotating speed of said rotor, and said recurrent signals being angularly displaced from each other so that the non-linear portions of one occur apprcximately in the middle of the linear-portion of the other;
first speed detector means for detecting a rotational speed of said rotor by detecting time in which said rotor rotates for a predetermined angle and for outputting a first speed signal;
second speed detector means for detecting the rotational speed of said rotor by detecting a grade of said linear portions of said first and second recurrent signals and for outputting a second speed signal;

, 13~3666 comparing means for comparing said first and second speed signals and for outputting a compared result; and gain control means for controlling gains of said first and second recurrent signals according to said compared result so that said first and second speed signals become equal.
In accordance with a yet further aspect of the present invention, there is provided a servo system for a motor having a rotor comprising:
frequency generator means for generating a recurrent signal which is cyclical and has generally linear portions, the frequency of said recurrent signal being proportional to a rotational speed of said rotor;
speed detector means for detecting the rotational speed of said rotor by detecting a grade of said linear portion of said recurrent signal;
peak detector means for detecting a peak-to-peak value of said recurrent signal;
gain control means for controlling a gain of said recurrent signal according to an output of said peak detector so that said peak-to-peak value of said recurrent signal becomes equal to a predetermined value; and servo control means for controlling the rotational speed of said rotor in accordance with an output of said speed detector means and a speed reference signal.
The preceding and other objects, features and advantages of the present invention will be apparent from the following detailed description of preferred embodiments which are to be read in conjunction with the accompanying drawings, wherein like reference numerals identify the same ~3~3666;
or similar elements.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram showing an embodiment of a servo system according to the present invention;
Figs. 2A to 2H are timing charts used to explain the operation of the servo system shown in Fig. 1, respectively;
Fig. 3 is a flow chart to which reference will be made in explaining the operation of a microcomputer that carries out the operation of the block shown by a broken line in Fig. 1:
Fig. 4 is a block diagram showing another embodiment of a servo system according to the present invention;
Figs. 5A and 5B are, respectively, waveform diagrams of FG signals used to explain the speed detection shown in Fig.
4; and Figs. 6 to 10 are flow charts to which reference will be made in explaining the operation of the servo system according to the present invention, respectively.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
-The present invèntion will now be described in detail with reference to the drawings.
Fig. 1 is a block diagram showing an embodiment of a servo system for a motor having a rotor according to the present invention.
As Fig. 1 shows, a drum motor 10 having a rotor (direct current motor) is provided to drive, for example, a rotating drum of a video tape recorder tVTR). In this embodiment, the drum motor 10 is rotated one revolution per 1/3 frame of a video signal.
The drum motor 10 is attached at its rotary shaft of _ g .

13V3~6~i the rotor with a rotation detecting apparatus 11 and a pulse generator 12 that generates a reference position signal for a rotational phase. The rotation detecting apparatus 11 generates a rotation detecting signal FG whose frequency corresponds to the rotational speed of the drum motor 10.
In this case, the rotation detecting signal FG has 48 cycles per one revolution of the drum motor 10. The rotation detecting signal FG is supplied to a divide-by-N frequency dividing circuit 13 (hereinafter referred to as an N-frequency dividing circuit), in which N is 8. Thus, the N
-frequency dividing circuit 13 generates a signal dg having 6 cycles per one revolution of the drum motor 10. The N-frequency dividing circuit 13 is also supplied with the rotational position pulse PG that is generate~ by the pulse generator 12 one per one revolution of the drum motor 10.
Then, the N-frequency dividing circuit 13 is reset in response to the rotational position pulse PG which is shown in Fig. 2A. Thus, the output signal dg from the N-frequency dividing circuit 13 is synchronized with the rotational position pulse PG in phase as shown in Fig. 2B.
The output signal dg of the N-frequency dividing circuit 13 and the rotational position pulse PG are supplied to a rotational phase position detecting circuit 22. The detecting circuit 22 is formed of, for example, a counter in which the pulse PG is supplied to the reset terminal of the counter and the signal dg is supplied to the clock terminal thereof. The detecting circuit 22 therefore generates numbers ~0], ~1], [2], [3], [4] and [5] (see Fig. 2C) that indicate six rotational angular positions S0, Sl, S2, ... S5 which are calculated at every rotational angle of 360/6 =

~3~336~i 60 with the generation position of the pulse PG as the reference.
A clock generator 14 is provided which generates a clock signal whose frequency is sufficiently higher than that of the rotation detecting signal FG. The clock signal from the clock generator 14 is supplied to a clock terminal of a quantization counter 15. On the other hand, an external reference signal FR with the frame cycle of a video signal ~see Fig. 2H) is supplied through a terminal 17 to the reset terminal of the quantization counter 15 so that the output count value of the quantization counter 15 includes a phase information of the external reference signal FR of the frame cycle.
The output count value of the quantization counter 15 is supplied to a data input terminal of a latch circuit 16.
The signal dg from the frequency dividing circuit 13 is supplied to the latch circuit 16 as a latch pulse.
Accordingly, as shown in Fig. 2D, in the latch circuit 16, there are sequentially latched count values C0, Cl, C2, Cn (n is a positive integer) of the quantization counter 15 at the respective rotational phase positions S0 to S5 at every rotational angular position of 60 with the reset time point by the external reference signal FR as the reference.
The latched output Cn of the latch circuit 16 is supplied to a cycle data calculating circuit 21. The cycle data calculating circuit 21 calculates as the count values of the quantization counter 15, times to~ tl, t2, t3, t4 and t5 in which the motor or rotor rotates between adjacent two rotational phase positions S0 and Sl, Sl and S2, S2 and S3, S3 and S4, S4 and S5, and S5 and S0.

1 3~3i61~;
Thus, to = Cl - co tl C2 Cl t2 = C3 ~ C2 t3 = C4 - C3 t4 = Cs - C~
t5 = C6 - C5 to = C7 ~ C6 tl = C8 - C7 The thus obtained cycle data tm (m = 0 to 5) are supplied to a calculating and comparing circuit 26.
The reference signal FR of frame cycle from the terminal 17 is supplied to a cycle reference calculating circuit 18. The calculating circuit 18 performs the calculation expressed as TFR x 1/3 x 8/48 = tr where TFR is one cycle of the reference signal FR. The resultant reference cycle tr corresponds to the rotational time of the rotational angular extent of 60 and is supplied to the calculating and comparing circuit 26.
A memory circuit 24 is provided which is formed of a non-volatile memory that stores error data. The memory circuit 24 stores, as will be described later, error data eO
to e4 (see Pig. 2F) concerning time errors CmO~ Cml ...Cm5 (see Fig. 2G) which are brought about by mechanical factors relative to the rotational times between two adjacént rotational phase positions S0 and Sl, Sl and S2, ... S4 and S5, S5 and S0. To the memory circuit 24, there are supplied , . . .

~3~36~6 positional data ~0], ~1] ... [5] with respect to the rotational phase positions S0 to S5 from the rotational phase position detecting circuit 22 as read address signals.
Thus, the error data eO to e4 are read out of the memory circuit 24 and are fed to a time error correcting circuit 25. The time error correcting circuit 25 receives the positional data from the rotational phase detecting circuit 22 and produces the time errors CmO to Cm5 which are caused by the mechanical factors between the adjacent two rotational phase positions S0 and Sl to S~ and S0. The time errors CmO to Cm5 are supplied to the calculating and comparing circuit 26.
In the calculating and comparing circuit 26, the refere~ce cycles tr between the two adjacent rotational phase positions S0 and Sl to S5 and S0 are respectively corrected by the time errors CmO to CmS and are obtained as corrected reference cycle data rO to r5 expressed as rO = tr + Cm rl z tr + Cml r2 = tr + Cm2 r3 = tr + Cm3 r4 = tr + Cm4 rS = tr + Cm5 The calculating and comparing circuit 26 compares the corrected reference cycle data rO to r5 with the measured cycle data to to t5 to thereby produce a speed servo error signal. The speed servo.error signal is added with a phase servo error signal that will be described later, and is supplied through a servo gain adjusting circuit 27 to the drum motor 10, thus the drum motor 10 being servo-controlled ~ 3t~36~
in speed.
While the reference cycle data tr are corrected by the time errors as described herein-above, the cycle data tm may be corrected by the time errors and then are compared with the reference cycle data tr. The cycle data tm obtained immediately after the reset by the signal FR is not used.
The phase-servo will be described next.
The output data Cn from the latch circuit 16, the rotational phase position signal from the rotational phase position detecting circuit 22, the cycle data tm from the cycle data calculating circuit 21 and the time errors CmO to Cm5 from the time error forming circuit 25 are supplied to a phase data calculating circuit 23. Also, the reference cycle data tr from the cycle reference calculàting circuit 18 is fed to the phase data calculating circuit 23.
The phase data calculating circuit 23 takes in the latch output Cn produced at a time point in which the first pulse PG i8 produced immediately after the quantization counter 15 is reset by the external reference signal FR.
The latch output is designated by reference letter dd ~see Fig. 2H). The rotational phase is servo-controlled in such a manner that the latch output dd becomes equal to a phase reference REF (corresponding to a locking-phase difference between the external synchronizing signal FR and the pulse PG).
Prior to the description of the phase servo error in this embodiment, let us first consider a case in which the phase data calculating circuit 23 produces a phase servo error at the cycle of the pulse PG, or once per one revolution of the drum motor 10. In this case, the phase ~, ,.

. :' -data calculating circuit 23 latches the output of the latch circuit 16 at the cycle of the pulse PG. qO, ql, q2, ...
assume latched outputs where qO = dd. Then, the cycle of the pulse PG is calculated as the count value of the quantization counter 15. Assuming that this count value is een, then the following equation will be satisfied as een = qn ~ qn-l ~n = 1, 2, ...) Phase data HDPn of the cycle of the pulse PG is obtained as HDPo dd HDPl = HDPo + (eel - PGREF) .

Pn HDPn_l + (een - PGREF) where PGREF is the cycle of the correct pulse PG, or the lS count value of the quantization counter 15 corresponding to the 1~3 frame cycle in this embodiment.
By comparing the thus described phase data HDPn (n = 0, 1, 2, 3, ...) with the phase reference REF, it is possible to obtain one phase servo error per one revolution of the drum motor 10. In the present embodiment, however, one phase servo error is not produced per one revolution of the drum motor 10 but phase servo errors are respectively prodùced at six rotational phase positions S0 to S5 per one revolution of the drum motor 10.
This embodiment utilizes the cycle data tm and the reference cycles rm which are corrected by the time errors CmO to CmS. More specifically, the phase data PHn at the respective rotational phase positions S0 to S5 are given as PHo = dd + (to ~ (tr + CmO)) ; 30 = dd + (to ~ rO) ~ _ .
: ' :

- ~ .
~3~ 6~;
PHl = PHo + (tl rl) PH2 = PHl + (t2 r2) PHn PHn_l + (tn rn) Thus, the phase data calculating circuit 23 produces six phase data PHn per one revolution of the drum motor 10, and they are fed to a phase comparator 28. The phase comparator 28 receives the phase reference REF from a phase reference generating circuit 29 and compares it with the phase data PHn~ thereby producing six phase servo errors per one revolution of the drum motor 10. The resultant phase servo errors are supplied to the calculating and comparing circuit 26, in which they are added with the speed servo errors.
In this phase-servo operation, the cycle data generated just after the quantization counter 15 is reset by the signal FR is by-passed and is not utilized.
The writing of error data on the memory circuit 24 will be described herein-below.
In order to obtain the error data, at first, the drum motor 10 is rotated at a constant speed by the inertia of the drum.
The requirements for the error data are as follows:
(1) the drum motor 10 has to be rotated alone or load fluctuation factors such as a tape and the like to the drum motor are removed;
(2) the phase servo to drum moror is stopped;
~3) the servo gain in the speed servo loop is decreased; and ~ 4) the rotational speed of the drum motor 10 is increased when the constant rotation of the drum motor 10 by the inertia of the drum is not sufficiently smooth. In this 13~3666 case, if the measuring cycle of the error data is Tl when To represents an actual servo cycle, the error data will be obtained such that the multiplication of To/Tl is performed in the time error correcting circuit 25 thereby to correct the error data eO to e4. Of course, the thus corrected error data eO to e4 may be stored in the memory circuit 24.
The above-mentioned requirements ~2) and (3) are not always needed. But instead, if it is arranged to reduce the servo errors to zero on the assumption that the servo gain is not infinite, the drum motor 10 may be phase-servo-controlled and the speed servo gain does not have to be decreased.
In the above-mentioned state that the drum motor 10 is rotated at the constant speed, the afore-noted cycle data tm ~m = 0 to 5) are calculated per one revolution of the drum motor 10. Then, the accuracy error data eO to e4 between the cycle data tm and the cycle data to are calcùlated as eO Z tl - to el - t2 ~ to e2 = t3 - to e3 = t4 - to e4 z ts - to The difference between the cycle data tm and the reference cycle tr is not calculated but the error between the cycle data to and the cycle data tm is calculated in order to reduce the amount of data stored in the memory circuit 24 by the amount of the cycle data to.
The error data eO to e4 are calculated over a plurality of rotations of the drum motor 10 similar to the above manner and are then averaged. If satisfactory accuracy is obtained, the error 03~
data eO to e4 are written in the memory circuit 24.
Since the error data eO to e4 are not error data between the reference cycle tr and the cycle data tm as earlier noted, the time error correcting circuit 25 generates the time errors CmO to Cm5 between the cycle data tm and the reference cycle tr. The calculating equations therefor are given as follows.
CmO = 0 + K = to ~ tr Cml = eO + K = tl - tr Cm2 = el + K = t2 ~ tr Cm3 = e2 + K = t3 - tr Cm4 = e3 + K = t4 - tr Cm5 = e4 + K = tS ~ tr Where K = _ eO + e1 + ... + e4 In the foregoing, CmO ~ Cml + ... Cm5 = 0 is satisfied per one revolution of the drum motor 10.
In the writing-process of error data eO to e4, the equality is satisfied as to + tl + -- ~ t5 = 6 tr While in the above embodiment the non-volatile memory i8 used as the memory circuit 24 as described above, the following modification is also possible. In the video tape recorder, there is such a case that the rotating drum is not applied with a load (or a tape is not wound around the rotating drum). Thus, at every time that the rotating drum i8 not applied with a load, the error data are refreshed by writing the error data eO to e4 in a RAM ~random access memory) provided as the memory circuit 24, whereby the servo system of the invention can always be effected following temperature characteristics, aging change and so on.
; .

:
' L3~3~
The present invention can be applied to a servo system for a motor having a rotor which is required to rotate with high acciracy as well as the servo system of the drum motor in the video tape recorder.
The servo error generating circuit shown by a broken line 20 in Fig. 1 may be realized by a software by utilizing a microcomputer. Fig. 3 is a flow chart of an example of the algorithm of a servo loop in that case and is useful in explaining the operation thereof.
Referring to Fig. 3, the routine begins with step 51, and it is determined at the next decision step 52 whether or not the count content of the quantization counter 15 is latched in the latch circuit 16 by the FG pulse from the N-frequency dividing circuit 13. If the count content is latched by the FG pulse as represented by a YES at step 52, the routine proceeds to step 53. In step 53, it is checked that the latch is carried out at what number of the FG pulse by using the PG pulse. This is equivalent to determining which of the rotational phase positions S0 to S5 the count content of the quantization counter 15 is latched at. Then, the latched count content Cn is read at step 54. The routine proceeds to the next decision step 55, and it is determined at step 55 whether or not the quantization counter 15 is reset by the frame signal FR for the values of the previously-read latch data Cn_l and the present latch data Cn. If the quantization counter 15 is reset by the frame signal FR as represented by a YES at step 55, the latched content is ignored and the routine returns to step 51. If the quantization counter 15 is not reset by the frame signal FR as represented by a NO at step 55, cycle data tn =

~3~3f~6~;
Cn ~ Cn 1 is calculated at step 56. Then, the routine proceeds to step 57, and in step 57, the reference cycle tr from the cycle reference calculating circuit 18 and the cycle data tn obtained at step 56 are compared with each other. The compared results are corrected by the error correcting values CmO to Cm5 corresponding to the respective rotational phase positions S0 to S1 to thereby control the rotation of the drum motor 10.
The N-frequency dividing circuit 13 is used to determnine the number of rotational phase positions per one revolution of the drum motor 10. The frequency-dividing ratio of the N-frequency dividing circuit 13 may be selected freely, and the N-frequency dividing circuit 13 may be omitted. Further, the time error data CmO to Cm5 may be directly stored in the memory circuit 24.
According to the present invention, as described above, even if there is a fixed distortion caused by the mechanical factors during one revolution of the drum motor, the speed control can be precisely effected by the use of error data correponding to the plurality of rotational phase positions per one revolution of the drum motor and stored in the memory circuit. Therefore, the servo gain can be increased and hence, a powerful servo performance against external disturbance can be obtained.
If one rotational reference phase position is produced per one revolution of the drum motor, the accurate phase position information can be obtained by using error data at a plurality of rotational phase positions per one revolution. Thus, a plurality of phase data can be obtained per one revolution of the drum motor and hence the ,i, . ...

.
~ 3~
phase-servo can be improved in efficiency.
Another embodiment of the servo system according to the present invention will be described in accordance with another aspect of the present invention.
Fig. 4 shows an example of a speed control circuit according to the present invention whose responsiveness in the low-speed region is improved.
Referring to Fig. 4, there is provided a direct current motor 101. A rotation detecting element 102 is coaxially connected to the rotary shaft of the direct current motor 101. The rotation detecting element 102 generates sinusoidal two-phase rotation detecting signals DTA and DTB
whose frequencies are proportional to the rotational speed of the motor 101 and of which the phases are different from each other by 90. In this embodiment, the rotation detecting signals DTA and DTB are supplied to and are converted to pulse signals by a waveform shaping circuit 103 that is formed of a comparator. A signal having a frequency twice as high as the original one, which results from passing either or both of the pulse-converted rotation detecting signals DTA and DTB from the waveform shaping circuit 103 through an exclusive-OR gate 111 is supplied to a cycle counting circuit 104 which carries out the cycle counting by counting the number of clocks, for example, between the leading and trailing edges. The cycle counting circuit 104 is formed of the servo system which was described in, for example, Fig. 1. Although the output from the cycle counting circuit 104 represents of the detected rotational speed of the motor 101, the responsiveness in the low speed mode is not satisfactory. The reason thereof is ~ ~3(~36~6~that, as described before, time necessary for counting the cycle is increased with the decrease of the rotational speed of the motor and the rotational speed measured by the cycle counting operation becomes an average rotational speed during the counting period.
The two-phase rotation detecting signals DTA and DTB
from the rotation detecting element 102 are supplied to analog-to-digital ~A/D) converters 121 and 122, respectively. In the A/D converters 121 and 122, as shown in Figs. 5A and 5B, the levels of the signals DTA and DTB
are respectively sampled at two time points tl and t2 that are distant by period ~. This period T iS shorter than the cycle (cycle in which the motor 101 is rotated at low speed) of the signals DTA and DTB. The sampled values are supplied through gain adjusting circuits 124 and 125 to a speed measuring circuit 126. The speed measuring circuit 126 calculates level differences ~Ll and ~L2 of the sampled values at two time points as shown in Figs. 5A and 5B and determines the larger level difference. Then, the grade of the signal between the time points tl and t2 is calculated from the larger level difference. This grade becomes steep as the frequency becomes higher while it becomes gentle as the frequency becomes low, if peak-to-peak value of the signals DTA and DTB is constant so that the grade corresponds to the frequency of the signals DTA and DTB.
Accordingly, the rotational speed can be calculated from the grade, namely, the level difference between the time points tl and t2.
The reason that the rotational speed is calculated from . . , 13t}3~6 the larger level difference of the rotation detecting signals DTA and DTB having two phases which are different by 90 between the time points tl and t2 is that the rotational speed has to be calculated from the level difference of the signals DTA and DTB between the two time points wherein their grades are substantially straight. As shown in Figs.
5A and 5B, the larger level difference of the two signals DTA and DTB always corresponds to the level difference between the two time points in substantially the straight line. Fùrther, in this embodiment, a plurality of measured results, for example, three measured results are averaged as a final speed detected output so as to improve the detection accuracy. In this case, the measuring may be effected about once in one cycle of the signals DTA and DTB and is effected a plurality of times per one cycle.
The speed detected output from the speed measuring circuit 126 and the speed detected output from the cycle measuring circuit 104 are respectively supplied to one and the other fixed contacts of a switching circuit 128. On the other hand, the pulse-shaped signals DTA and DTB from the waveform-shaping circuit 103 are supplied to an exclusive-OR
gate 111 from which is derived the signal having a frequency twice as high as that of the signals DTA and DTB. This signal is supplied to the frequency measuring circuit 112 which measures its frequency and produces an output corresponding to the rotational speed. The output corresponding to the rotational speed from the frequency measuring circuit 112 is supplied to a switching signal forming circuit 127. The switching signal forming circuit 127 generates a switching signal SW which goes to level tl]

13~366~
when the rotational speed is higher than a predetermined speed and which goes to level 10] when the rotational speed is lower than the predetermined speed. The switching circuit 128 responds to the switching signal SW to connect its movable contact to the fixed contact which selects the output of the cycle measuring circuit 104 upon high speed and to the other fixed contact which seiects the output of the speed measuring circuit 126 upon low speed, respectively. The speed detected output from the switching circuit 128 is supplied to a speed servo signal forming circuit 114, in which it is compared with the speed reference signal REF applied thereto from a terminal llS.
The speed servo signal forming circuit 114 generates a speed servo error signal on the basis of the comparèd output. The resulting speed servo error signal is supplied to the direct current motor 101 and the motor 101 is servo-controlled in such a manner that the rotational speed thereof becomes equal to the speed corresponding to the speed reference signal REF.
When the speed detected output from the cycle measuring circuit 104 and the speed detected output from the speed measurinq circuit 126 are selectively switched by the switching circuit 128 and then fed to the speed servo signal forming circuit 114, the switching circuit 128 is not changed in position between the low speed and the high speed but may be changed in position even in the low speed between the constant speed mode (equal speed mode) and the transition speed mode. The switching circuit 128 is changed in position so as to always select the detected output of the cycle measuring circuit 104.

~; - 24 .~, . ~ .
' 13(~366~i To this end, the output signal from the frequency measuring circuit 112 is supplied to the switching signal forming circuit 127 which therefore determines whether the rotational speed of the motor 101 is low or high. Also, the output from the cycle measuring circuit 104 and the output from the speed detecting circuit 126 are supplied to the switching signal forming circuit 127 which therefore determines the constant speed rotation mode and the transition speed mode, or the high acceleration and deceleration speed modes (in the low speed region). In other words, the determination of the latter mode will be made as follows. The output of the cycle measuring circuit 104 becomes equal to the average value within one cycle of the output signals DTA and DTB and the output of the speed measuring circuit 126 is nearly equal to the momentary value so that acceleration mode : speed measured output > cycle measured output deceleration mode : speed measured output < cycle measured output are utilized, whereby if a difference therebetween is more than the predetermined value, the mode is determined as the transition mode by the acceleration or deceleration.
When the switching circuit 128 is changed in position as described above, the high-speed response can be effected upon the transition mode and the accurate control can be effected upon the constant speed mode.
In this embodiment, in order to improve the measuring accuracy of the speed measuring circuit 126, the gains for the signals DTA and DTB are automatically adjusted. In ~,~ . , ~3t~3666 addition, it is determined whether the signals DTA and DTB
are satsifactory or not.
To this end, the digital values from the A/D converters 121 and 122 are supplied to an automatic gain control circuit 123. The automatic gain control circuit 123 calculates the peak-to-peak value between the rotation detected signals DTA and DTB having two phases or phases A
and B. On the basis of the peak-to-peak value, gain adjusting signals are respectively supplied from the automatic gain control circuit 123 to the gain adjusting circuits 124 and 125 which are controlled so as to provide predetermined peak-to-peak value of the signals DTA and DTB, respectively.
Figs. 6 to 9 are, respectively, flow charts used to explain an example of the processing made by the automatic gain control circuit 123. Fig. 6 is a flow chart of a main routine for automatic gain adjustment and Pigs. 7, 8 and 9 are flow charts of sub-routines each explaining one step in the main routine of Fig. 6, respectively.
The automatic gain control operation is effected before the direct current motor 101 is operated. In the motors such as a capstan motor of a video tape recorder having relatively long time period in which the motor is not used, the time period in which the motor is not used is utilized to effect the automatic gain control at any time. Futher, the automatic gain control operation is effected under the condition that the motor is rotated at low speed because the speed measuring circuit 126 is used in the rotation at low speed.
Referring initially to the main routine of Fig. 6, at -~ - 26 .

.

:13Q3~

first, in order to form data that is used to adjust the level (peak-to-peak value) of the rotation detecting signal, the signal level (or peak-to-peak value) of the rotation detecting signal DTA having the phase A is measured at step 201. Also, the signal level ~or peak-to-peak value) of the rotation detecting signal DTB having the phase B is measured for serving the same purpose at step 202. The sub-routine for measuring the signal levels of the rotation detecting signals DTA and DT8 having the phases A and B at steps 201 and 202 are illustrated in a flow chart of Fig. 7. In this case, the algorithms therefor are the same for the rotation detecting signals DTA and DTB having the phases A and B.
As shown in Fig. 7, the output digital values from the A~D converters 121 and 122 which are sampled àt an interval of TS seconds and analog-to-digital-converted are latched during a period of T seconds ~T is more than one cycle of the signals DTA and DTB) and the maximum and minimum values thereof are obtained at step 301. Then, the peak-to-peak value is calculated by subtracting the minimum value from the maximum value at step 302. At the next step 303, a difference between the resulting peak-to-peak value and the previously-obtained peak-to-peak value stored in the memory is calculated and the difference is added to or subtracted from the peak-to-peak value stored in the memory, thereby integrating the peak-to-peak value. At the next decision step 304, by determining whether the difference becomes smaller than a predetermined value or not, it is determined whether or not the integrated data, namely, the peak-to-peak value stored in the memory is stable or not. If the determined result is not stable as represented by a ~O at , . ...

~3~36~6 step 304, the routine goes back to step 301 and the foregoing steps in the sub-routine are repeatedly executed until the peak-to-peak value becomes stable. The routine is returned to the main routine when it is stabilized.
The peak-to-peak value has to be measured with high accuracy. To this end, the sampling number in the A/D
converters 121 and 122 is increased, or the sampling cycle is made short. In this embodiment, in addition, the rotational speed of the motor 101 is slightly fluctuated so that the positions of the maximum and minimum values of the waveforms of the signals DTA and DTB may be sampled with ease. To this end, as shown in Fig. 4, there is provided a switching circuit 129 and a fluctuating speed reference data REFN is generated from the automatic adjusting control lS circuit 123. Then, upon automatic adjustment, instead of the correct speed reference data REF, the fluctuating speed reference data REFN is supplied through the switching circuit 129 to the speed servo signal forming circuit 114.
Alternatively, the speed reference data is not fluctuated but the sampling cycles in which the signals DTA
and DTB are sampled by the A/D converters 121 and 122 may be changed.
If the peak-to-peak values of the signals DTA and DTB
having the phases A and B are obtained as described above, according to the main routine, the control signal to be supplied to the gain adjusting circuits 124 and 125 are obtained from the peak-to-peak values of the signals DTA and DTB having the phases A and B, the output of the speed measuring circuit 126 and the output from the cycle measuring circuit 104. More specifically, at step 203, the ",,~,.. ..... . .

13(~36~i~
level gains to be supplied to the gain adjusting circuits 124 and 125 are calculated. Fig. 8 is a flow chart of the gain adjustinq routine at step 203 in the flow chart of Fig.
6.
The gain adjustment is effected on the basis of the principle that the speed data provided as the speed measured output and the speed data provided as the cycle measured output become the same finally. This will be described more fully with reference to the flow chart of Fig. 8.
Referring to Fig. 8, a ratio between the speed data from the speed measuring circuit 126 and the speed data from the cycle measuring circuit 104 is calculated at step 401.
Then, a difference between the resultant speed data ratio and the previously-calculated speed data ratio stored in the m mory is calculated, and the speed data ratio is integrated by adding to or subtracting from the speed data ratio stored in the memory the calculated difference at step 402. It is determined at the next decision step 403 whether or not the speed data ratio stored in the memory is larger than 1. The speed data from the speed measuring circuit 126 is proportional to the gain so that if the speed data ratio is larger than 1 as represented by a YES at step 403, or the speed data from the speed measuring circuit 126 is larger, the gain adjusting signal which decreases the gain for the signal having one phase, for example, the signal DTA having the phase A is supplied to the gain adjusting circuit 124 at step 404. If it is determined that the speed data ratio is smaller than 1 as represented by a NO at the decision step 403, or the speed data from the speed measuring circuit 126 is smaller, the gain control signal which increases the gain i~"` 13(~366~i for the signal DTA having the phase A is supplied to the gain adjusting circuit 124, at step 405.
The gain for the signal DTB having the phase B is obtained by calculating a ratio between the peak-to-peak value of the signal DTA having the phase A and the peak-to-peak level of the signal DTB having the phase B at step 406 and by multiplying the resultant ratio with the gain of the signal DTA having the phase A at step 407.
After the gains for the signals DTA and DTB having the phases A and B are adjusted, it is determined at the next decision step 408 by determining whether a difference between the stored speed data ratio and the speed data ratio obtained last is less than a predetermined value whether or not the integrated data of the speed data ratio is stabilized. If the difference is beyond the predetermined value, the sub-routine goes back to step 401, and the foregoing steps are repeatedly executed. If the difference becomes less than the predetermined value, the sub-routine returns to the main routine shown in Fig. 6.
In the main routine of Fig. 6, the processing enters the rcutine (step 204) in which it is determined whether the measured and adjusted values are satisfactory or not. These determinations are effected by checking whether or not five parameters fall within the tolerance range as shown in a flow chart of Fig. 9. Thus, it is determined whether the rotation detecting element 102 is satisfactory or not.
Referring to Fig. 9, it is determined at decision step 501 whether or not the peak-to-peak values of the signals DTA and DTB having the phases A and B fall within the standardized values. If the answer is YES, it is determined , . . .

.

, 13~?36~
at the next decision step 502 whether or not the ratio between the peak-to-peak values of the signals DTA and DTB
having the phases A and B falls within l ' dl (dl represents a predetermined tolerance value). If the ratio is less than l ' dl as represented by a YES at step S02, the s,ub-routine proceeds to the next decision step 503. At step 503, it is determined whether the gains for the signals having the phases A and B are abnormal or not. If they are not abnormal as represented by a YES at step 503, a ratio between the gains of the signals having the phases A and B
i5 calculated and it is determined at step 504 whether or not the gain ratio is abnormal. If it is not abnormal as represented by a YES at step 504, it is determined at the next decision step 505 whether or not a ratio between the speed data from the cycle measuring circuit 104 and the speed data from the speed measuring circuit 126 is less than 1 ' d2 (d2 represents the tolerance value). If it is less than l ~ d2, or the checked results at steps 501 to 505 are all satisfactory, the answer is [OK] and the sub-routine in Fig. 9 returns to the main routine. If on the other hand the checked result is not good at any one step in the steps 501 to 505, the checking succeeding to that step is not executed and an answer is lNGl and the sub-routine returns to the main routine shown in the flow chart of Fig. 6.
In the main routine shown in Fig. 6, it is determined at decision step 205 whether the result at the decision step 204 is [OK~ or not. If it is [OK], it is determined that the automatic gain adjustment is completed and this fact is, for example, displayed. If on the other hand the result is [NG], it is determined that the automatic gain adjustment is ~ ,. .... .. .

: ' .

~w~ 13t~36~

not satisfactory or is impossible and an alarm, for example, is made.
Fig. lO shows a flow chart of another automatic gain adjusting method.
According to this method, under the condition that the motor lOl is rotated at a constant speed, maximum differentiated values (maximum grades) of the rotation detecting signals DTA and DTB having the phases A and B are controlled to fall within predetermined values with reference to the speed data from the cycle measuring circuit 104.
Referring to Fig. lO, under the condition that the motor 101 is rotated at the constant speed, the pea~-to-pea~
values of the signals DTA and DTB having the phases A and B
are obtained at step 601. This processing is effected in accordance with the sub-routine shown in Fig. 7.
Then, the maximum value of the differentiated value of the waveform with respect to the signal DTA is calculated at step 602. This maximum value is obtained in such a manner that the values of the signal DTA at two time points distant by the time I are sampled by a plurarity of times per cycle of the signal DTA and the maximum level reference between the two time points is obtained as the above maximum value.
Similarly, the maximum value of the differentlated value of the waveform with respect to the signal DTB having the phase B is calculated at step 603.
Then, the gains for the signals DTA and DTB having the phases A and B are determined on the basis of the speed data from the cycle measuring circuit 104 and the maximum differentiated values of the signals DTA and DTB having the , :

13~3/6~
phases A and B at step 604. Since the motor 101 is rotated at the constant speed, the maximum differentiated value in that constant speed must become a predetermined constant value. Thus, the gains for the signals DTA and DTB having the phases A and B are determined in such a manner that the maximum differentiated values become the predetermined constant value.
After the gains are determined as described above, it is determined in step 605 whether or not the measured and adjusted values are satisfactory. This determination is carried out by adding a step for checking a relationship between the peak-to-peak values of the signals having the phases A and B and the maximum differentiated values to the decision routine shown in Fig. 9.
Similarly to the main routine shown in Fig. 6, it is determined at decision step 606 whether the checked result at step 605 is ~OKl or not. If an answer is [OK], it is decided that the automatic gain adjustment is finished and this is, for example, displayed to indicate the same. If on the other hand the answer is ~NG], it is decided that the automatic gain adjustment is not satisfactory or is impossible and this is displayed to indicate the same, similarly. It is needless to say that the circuit of the present invention can be simplified by utilizing a microcomputer.
Further, in the motor such as the capstan motor for the video tape recorder having a time period in which the motor is not used, if such time period is used to perform the automatic gain adjustment, the rotational speed of the motor can be detected while temperature characteristic, aging ~" 13~3fii6~

chan~e and so on of the rotation detecting element are always compensated for.
It should be understood that the above description is presented by way of example on the preferred embodiments of the invention and it will be apparent that many modifications and variations thereof could be effected by one with ordinary skill i~ the art without departing from the spirit and scope of the novel concepts of the invention so that the scope of the invention should be determined only by thè appended claims.

Claims (10)

1. A servo system for a motor having a rotor comprising:
phase detector means for detecting a rotational phase of said rotor and for defining a plurality of angular positions of said rotor, each angle between adjacent said angular positions being equal;
rotating means for rotating said rotor at a predetermined constant rotational speed;
speed detector means for detecting a rotational speed of said rotor at each of said angular positions;
error detector means for detecting detection errors of said speed detector means at each of said angular positions when said rotor is rotated at said predetermined constant rotational speed;
memory means for storing said detection errors at each of said angular positions; and servo controlling means for controlling a rotational speed and/or phase of said rotor in accordance with the rotational speed detected by said speed detector and said detection errors read from said memory means.
2, A servo system for a motor having a rotor according to claim 1, wherein said phase detector means comprises a pulse generator for generating a pulse per revolution of said rotor at a reference angular position, and a frequency generator for generating a frequency signal whose frequency is proportional to the rotational speed of said rotor.
3. A servo system for a motor having a rotor according to claim 1, wherein said speed detector means detects time in which said rotor rotates for a predetermined angle.
4. A servo system for a motor having a rotor according to claim 2, wherein said speed detector means comprises oscillating means for generating a clock signal, counter means for counting said clock signal, latch means for latching a content of said counter means in response to said frequency signal generated by said frequency generator, and calculating means for calculating time in which said rotor rotates between two adjacent said angular positions based on an output of said latch means.
5. A servo system for a motor having a rotor comprising:
frequency generator means for generating a recurrent signal which is cyclical and has generally linear portions, the frequency of said recurrent signal being proportional to a rotational speed of said rotor;
first speed detector means for detecting the rotational speed of said rotor by detecting time in which said rotor rotates for a predetermined angle and for outputting a first speed signal;
second speed detector means for detecting the rotational speed of said rotor by detecting a grade of said linear portion of said recurrent signal and for outputting a second speed signal;
comparing means for comparing said first and second speed signals and for outputting a compared result;
gain control means for controlling a gain of said recurrent signal according to said compared result of said comparing means so that said first and second speed signals become equal; and servo control means for controlling the rotational speed of said rotor in accordance with one of said first and second speed signals.
6. A servo system for a motor having a rotor according to claim 5, further comprising selecting means for selecting one of said first and second speed signals in such a manner that said first speed signal is selected when the rotational speed of said rotor is higher than a predetermined rotational speed and that said second speed signal is selected when the rotational speed of said rotor is lower than said predetermined rotational speed, said servo control means controlling the rotational speed of said rotor in accordance with selected one of said first and second speed signals.
7. A servo system for a motor having a rotor according to claim 5, further comprising selecting means for selecting one of said first and second speed signals in such a manner that said second speed signal is selected when the rotational speed of said rotor is lower than a predetermined rotational speed and when a changing rate of the rotational speed of said rotor is larger than a predetermined value, said changing rate being detected according to the difference between said first and second speed signals detected by said comparing means.
8. A servo system for a motor having a rotor comprising:
a frequency generator for generating first and second recurrent signals each of which is cyclical and has generally linear portions separated by non-linear portions, the frequency of said recurrent signals being proportional to the rotating speed of said rotor, and said recurrent signals being angularly displaced from each other so that the non-linear portions of one occur approximately in the middle of the linear-portion of the other;

first speed detector means for detecting a rotational speed of said rotor by detecting time in which said rotor rotates for a predetermined angle and for outputting a first speed signal;
second speed detector means for detecting the rotational speed of said rotor by detecting a grade of said linear portions of said first and second recurrent signals and for outputting a second speed signal;
comparing means for comparing said first and second speed signals and for outputting a compared result; and gain control means for controlling gains of said first and second recurrent signals according to said compared result so that said first and second speed signals become equal.
9. A servo system for a motor having a rotor according to claim 8, wherein said second speed detector means detects the rotational speed of said rotor by selecting a maximum grade of said first and second recurrent signals.
10. A servo system for a motor having a rotor comprising:
frequency generator means for generating a recurrent signal which is cyclical and has generally linear portions, the frequency of said recurrent signal being proportional to a rotational speed of said rotor;
speed detector means for detecting the rotational speed of said rotor by detecting a grade of said linear portions of said recurrent signal;
peak detector means for detecting a peak-to-peak value of said recurrent signal;
gain control means for controlling a gain of said recurrent signal according to an output of said peak detector so that said peak-to-peak value of said recurrent signal becomes equal to a predetermined value; and servo control means for controlling the rotational speed of said rotor in accordance with an output of said speed detector means and a speed reference signal.
CA000596011A 1988-04-08 1989-04-07 Servo system for a motor Expired - Lifetime CA1303666C (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
JP63086460A JPH01259780A (en) 1988-04-08 1988-04-08 Servo device
JP086460/88 1988-04-08

Publications (1)

Publication Number Publication Date
CA1303666C true CA1303666C (en) 1992-06-16

Family

ID=13887562

Family Applications (1)

Application Number Title Priority Date Filing Date
CA000596011A Expired - Lifetime CA1303666C (en) 1988-04-08 1989-04-07 Servo system for a motor

Country Status (2)

Country Link
JP (1) JPH01259780A (en)
CA (1) CA1303666C (en)

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS6026487A (en) * 1983-07-25 1985-02-09 Sony Corp Rotating speed controller
JPS62171480A (en) * 1986-01-22 1987-07-28 Hitachi Ltd Speed controller

Also Published As

Publication number Publication date
JPH01259780A (en) 1989-10-17

Similar Documents

Publication Publication Date Title
US5304907A (en) Servo system that controls a motor and compensates for system irregularities
US4240069A (en) Angle coder with variable input angle
US5142226A (en) Position detection device having absolute position detection apparatus and interpolation apparatus
US4363048A (en) Time counting clock generator
US4503374A (en) Speed detection apparatus and method
US4707683A (en) Increasing precision of encoder output
US4764824A (en) Dual servo system for rotating tape head control
US4642562A (en) Phase difference demodulator
US5032779A (en) Driving circuit for stepping motor
CA1303666C (en) Servo system for a motor
US4710770A (en) Phase modulation type digital position detector
JPH07229910A (en) Pulse counter circuit
US4994723A (en) Digital servo system for controlling rotational speed of rotary body
KR900005075Y1 (en) Generating circuit for head switching signal
US4599569A (en) Method and apparatus for detecting a phase or frequency error of a signal
US5880566A (en) Absolute angular position calculation apparatus for a rotating motor and velocity control apparatus adopting the same
JP2967622B2 (en) Frequency measurement circuit
KR100372946B1 (en) Control device of motor
JPH05188067A (en) Servo motor speed detecting device
JP2733949B2 (en) Rotation speed detector
JP3655798B2 (en) Rotation phase signal generator
US5493550A (en) Velocity detection circuit
JP2611099B2 (en) Displacement measuring device
JP2987833B2 (en) Switching pulse generator for rotating drum
SU1615615A1 (en) Digital tachometer

Legal Events

Date Code Title Description
MKLA Lapsed