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Patent 1303666 Summary

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Claims and Abstract availability

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(12) Patent: (11) CA 1303666
(21) Application Number: 596011
(54) English Title: SERVO SYSTEM FOR A MOTOR
(54) French Title: SERVOMECANISME POUR MOTEUR
Status: Deemed expired
Bibliographic Data
(52) Canadian Patent Classification (CPC):
  • 318/89
  • 318/92
(51) International Patent Classification (IPC):
  • G11B 15/473 (2006.01)
  • G11B 19/28 (2006.01)
  • H02P 5/00 (2006.01)
(72) Inventors :
  • ABE, FUMIYOSHI (Japan)
  • HASEGAWA, AKIRA (Japan)
(73) Owners :
  • SONY CORPORATION (Japan)
(71) Applicants :
(74) Agent: GOWLING WLG (CANADA) LLP
(74) Associate agent:
(45) Issued: 1992-06-16
(22) Filed Date: 1989-04-07
Availability of licence: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): No

(30) Application Priority Data:
Application No. Country/Territory Date
086460/88 Japan 1988-04-08

Abstracts

English 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.


Claims

Note: Claims are shown in the official language in which they were submitted.


WE CLAIM AS OUR INVENTION
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

- 35 -

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.
- 36 -

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;
- 37 -

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

- 38 -

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.

- 39 -

Description

Note: Descriptions are shown in the official language in which they were submitted.


" 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
..... ,~ .. ..... . .. .

~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
- - 5

, ... . .

:~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

-- 6

-` 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 =

-- 10

~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.

-- 11 --

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
- 12

, . . .

~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
- 13

~ 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

- 14

~, ,.

. :'

-
13U3666
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

- 16

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
- 17

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.
; .
- 18
:
'

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 =

-- 19

~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

- 20

,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

- 22


. . ,

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]

- 23

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

- 25

~,~ . ,

~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

- 27

, . ...

~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

- 28

",,~,.. ..... . .

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

-- 29

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

- 30

, . . .

.


,

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

- 31

~ ,. .... .. .




: ' .

~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

- 32

,
:

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

- 33

~" 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.




- 34

Representative Drawing
A single figure which represents the drawing illustrating the invention.
Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date 1992-06-16
(22) Filed 1989-04-07
(45) Issued 1992-06-16
Deemed Expired 1997-06-16

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Application Fee $0.00 1989-04-07
Registration of a document - section 124 $0.00 1989-10-23
Maintenance Fee - Patent - Old Act 2 1994-06-16 $100.00 1994-06-02
Maintenance Fee - Patent - Old Act 3 1995-06-16 $100.00 1995-06-02
Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
SONY CORPORATION
Past Owners on Record
ABE, FUMIYOSHI
HASEGAWA, AKIRA
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
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Description 
Date
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Representative Drawing 2001-10-23 1 16
Drawings 1993-11-01 7 175
Claims 1993-11-01 5 161
Abstract 1993-11-01 1 25
Cover Page 1993-11-01 1 14
Description 1993-11-01 33 1,227
Maintenance Fee Payment 1995-06-02 1 43
Maintenance Fee Payment 1994-06-02 1 46