U.S. patent number 3,596,162 [Application Number 04/822,640] was granted by the patent office on 1971-07-27 for speed control system with comparison of a sawtooth wave with a reference level.
This patent grant is currently assigned to Sony Corporation. Invention is credited to Jun Takayama.
United States Patent |
3,596,162 |
Takayama |
July 27, 1971 |
SPEED CONTROL SYSTEM WITH COMPARISON OF A SAWTOOTH WAVE WITH A
REFERENCE LEVEL
Abstract
A speed control system comprising means for producing a sawtooth
wave signal of a frequency corresponding to a frequency-modulated
signal relating to the revolution of a rotary member, means for
controlling the revolving speed of the rotary member with the
sawtooth wave signal and a circuit for changing the inclination of
the sawtooth wave.
Inventors: |
Takayama; Jun (Tokyo,
JA) |
Assignee: |
Sony Corporation (Tokyo,
JA)
|
Family
ID: |
12546178 |
Appl.
No.: |
04/822,640 |
Filed: |
May 7, 1969 |
Foreign Application Priority Data
|
|
|
|
|
May 13, 1968 [JA] |
|
|
43/39190 |
|
Current U.S.
Class: |
388/811; 388/915;
388/814 |
Current CPC
Class: |
H02P
7/2885 (20130101); Y10S 388/915 (20130101) |
Current International
Class: |
H02P
7/18 (20060101); H02P 7/288 (20060101); H02p
005/16 () |
Field of
Search: |
;318/22.290,327,328,341,326,345 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bobeck; Benjamin
Assistant Examiner: Langer; Thomas
Claims
I claim as my invention:
1. A speed system for a rotary member comprising means for
generating a sine wave signal that is frequency-modulated in
accordance with the rotational speed of said rotary member, means
for producing a sawtooth wave signal for each complete cycle of
said frequency-modulated sine wave signal with the pitch of each
said sawtooth wave signal, and hence the peak voltage thereof,
corresponding to the period of the respective cycle of said
frequency-modulated signal, means for comparing said peak voltage
of each sawtooth wave signal with a reference voltage and for
producing a comparison signal in response to said peak voltage
being in excess of said reference voltage with said comparison
signal corresponding to the extent of said excess, means responsive
to said comparison signal for providing a corresponding control
signal, means for exerting a driving force on the rotary member in
accordance with said control signal, and means for varying the
inclination of said sawtooth wave signal and thereby determining
the speed of the rotary member which is to be maintained in
correspondence to said reference voltage.
2. A speed control system according to claim 10, wherein said
rotary member is a DC motor.
3. A speed control system according to claim 1, wherein said rotary
member is a capstan.
4. A speed control system according to claim 1, wherein said means
for producing a sawtooth wave signal includes shaping circuit means
shaping said frequency-modulated signal to provide a rectangular
wave having a pitch corresponding to the period of said
frequency-modulated sine wave, differentiating circuit means
differentiating said rectangular wave to provide sets of
differentiated pulses at the rise and fall, respectively, of said
rectangular wave, and sawtooth wave generating means triggered by
one of said sets of differentiated pulses.
5. A speed control system according to claim 1, wherein said means
for providing the control signal further includes pulse width
modulating circuit means providing a wave which is pulse width
modulated in accordance with said comparison signal.
6. A speed control system according to claim 5, wherein said pulse
width modulating circuit means provides said wave only when said
comparison signal exceeds a predetermined level.
7. A speed control system according to claim 6, wherein said means
for providing the control signal further includes integration
circuit means integrating the pulse width modulated wave to provide
said control signal in the form of a varying DC voltage.
Description
BACKGROUND OF THE INVENTION
This invention relates to a speed control system for controlling
the speed of rotary members such as, for example, a motor, capstan
and so in on in magnetic recording and reproducing devices, and
more particularly to a speed control system which ensures stable
and highly sensitive speed control of the rotary members and
enables selection of the reference speed of the rotary members over
a wide range.
DESCRIPTION OF THE PRIOR ART
Hitherto, various systems have been proposed for controlling the
speed of motors and other rotary members. With these prior art
systems, however, no satisfactory followup property of control is
obtained and, in addition, the rotational speed of the rotary
members cannot be freely established at a desired value. Further,
the revolving speed control of DC motors encounters a "self-start"
problem, as set forth in copending application, U.S. Ser. No.
586,771 assigned to the same assignee as the present application.
In addition, the provision of a speed control circuit in the form
of an integrated circuit is difficult, since heat generation often
leads to breakage of the integrated circuit.
SUMMARY OF THE INVENTION
This invention is directed to a speed control system for rotary
members in which a sawtooth wave signal, frequency-modulated in
accordance with the speed of the rotary members, is produced; the
speed of the rotary members is controlled in response to the
sawtooth wave signal; and the inclination of the sawtooth wave is
varied to select the speed to be maintained. Consequently, the
speed control circuit operates with a pulse signal and hence is low
in power consumption and is easy to construct in the form of an
integrated circuit. Further, the use of this system in the speed
control of DC motors enables self-start of the motors.
The primary object of this invention is to provide a speed control
system for rotary members which permits free selection of the speed
of the rotary members over a wide range and is excellent in the
followup property of speed control.
Other objects, features and advantages of this invention will
become apparent from the following description taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit connection diagram of a rotary member speed
control system in accordance with one embodiment of this
invention;
FIG. 2 is a series of waveform diagrams for explaining the speed
control system exemplified in FIG. 1;
FIG. 3 is a circuit connection diagram showing another embodiment
of the present invention system; and
FIG. 4 is a series of waveform diagrams for explaining the speed
control system depicted in FIG. 3.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 reference numeral 1 designates a signal generator SG
which is mounted on a rotary shaft of a motor M and rotates with
the rotation of the motor M and from which a signal S.sub.1 is
derived such as depicted in FIG. 2A which is frequency-modulated in
accordance with the rotational angular velocity of the motor M. The
frequency-modulated signal S.sub.1 is fed to a waveform shaping
circuit 2 constituted by, for example, an NPN-type transistor
Ir.sub.1. Thus, there is derived from the waveform shaping circuit
2 a rectangular wave signal S.sub.2 such as depicted in FIG. 2B
which corresponds to the frequency-modulated signal S.sub.1. The
resulting rectangular wave signal S.sub.2 is applied to a
differentiation circuit 3 consisting of a capacitor C.sub.1 and a
resistor R.sub.1 to produce differentiated pulses S.sub.3 and
S.sub.4 respectively at the rise and fall of the rectangular wave
signal S.sub.2 as shown in FIG. 2C.
The differentiated pulses S.sub.3 and S.sub.4 are fed to a sawtooth
wave generator 4 consisting of transistors Tr.sub.2 and Tr.sub.3 to
drive the generator 4 with either one of the differentiated pulses
S.sub.3 and S.sub.4, that is, S.sub.3 in the illustrated example,
thus providing a sawtooth wave signal S.sub.5 such as shown in FIG.
2D which has a period equal to that of the differentiated pulse
S.sub.3 and consequently varies its peak value in accordance with
the period.
In this case the inclination of the sawtooth wave signal S.sub.5 is
rendered variable. Namely, the time constant for charge of the
signal S.sub.5 is made variable. In the illustrated example, such
variation of the time constant is made possible by connecting the
collector of the transistor Tr.sub.2 of the sawtooth wave generator
4 to a movable contact S.sub.F of a changeover switch S which is
selectively engageable with one of the switch contacts S.sub.V1,
S.sub.V2 and S.sub.V3 respectively connected to a power source
terminal 6a through series circuit R.sub.10, R.sub.20 or R.sub.30
respectively consisting of resistor R.sub.11, R.sub.21 or R.sub.31,
and variable resistor R.sub.12, R.sub.22 or R.sub.32, and a
resistor R.sub.8.
With such an arrangement, changeover of the switch S or adjustment
of the variable resistor R.sub.12, R.sub.22 or R.sub.32 causes a
change in the charge time constant thereby to change the
inclination of the sawtooth wave signal S.sub.5. It is also
possible, of course, to change the time constant by making variable
a capacitor C.sub.4 of the sawtooth wave generator 4, or by
selectively changing over a plurality of capacitors which are
provided instead of the capacitor C.sub.4 or by rendering the
resistance and capacitance values variable.
It is preferred, in this case, to improve the linearity of the
sawtooth wave signal S.sub.5 by a positive feedback circuit in
which the collector output of the transistor Tr.sub.2 is applied to
the base of the transistor Tr.sub.3 and the emitter output of the
transistor Tr.sub.3 is fed through a capacitor C.sub.3, the series
circuit R.sub.10, R.sub.20 or R.sub.30, and the switch S to a
collector load circuit of the transistor Tr.sub.2.
The sawtooth wave signal S.sub.5 is applied to the base of a
transistor Tr.sub.4 of a differential amplifier circuit consisting
of the transistors Tr.sub.4 and Tr.sub.5 of, for example, a
comparator circuit 5.
The differential amplifier circuit can be constructed by applying
to the base of the transistor Tr.sub.5 a reference DC voltage E,
produced by dividing the voltage of, for example, the power source
terminal 6a with the variable resistor R.sub.2 and the resistors
R.sub.3 and R.sub.4, and by connecting the connection point of the
emitters of the transistors Tr.sub.5 and Tr.sub.4 to the other
power source terminal 6b through an emitter resistor R.sub.7.
Thus, the sawtooth wave signal S.sub.5 fed to the base of the
transistor Tt.sub.4 is compared with the sum E.sub.1 of a voltage,
yielded in the emitters of the transistors Tr.sub.4 and Tr.sub.5 by
the aforementioned reference DC voltage E fed to the base of the
transistor Tr.sub.4, and a forward drop voltage between the base
and emitter of the transistor Tr.sub.4, thus deriving from, for
example, the collector of the transistor Tr.sub.4 a signal S.sub.5
' shown in FIG. 2D'.
In the differential amplifier circuit it is possible, if necessary,
to adjust the amplitude of the signal S.sub.5 ' by making the
aforementioned resistor R.sub.2 variable to thereby render the
reference DC voltage E variable. This leads to the variations in
the pulse width of a signal S.sub.6 described later and hence
enables adjustment of the rotational speed of the motor M. Further,
the differential amplifier connection of the transistors Tr.sub.4
and Tr.sub.5 leads to reduction of drift of the rotational speed of
the motor which is caused by the influence of the ambient
temperature variations on the signal S.sub.5 '. The signal S.sub.5
' is a triangular wave having a varying peak value and, in order to
convert the triangular wave signal S.sub.5 ' into a width-modulated
rectangular wave, the signal S.sub.5 ' is applied to, for example,
the base of an emitter-follower type transistor amplifier
consisting of a transistor Tr.sub.6 and is thereby amplified, the
amplified output being fed to a pulse width modulator circuit
7.
The pulse width modulator circuit 7 is provided with, for example,
an NPN-type transistor Tr.sub.7 having its emitter directly
connected to the power source terminal 6b , its collector connected
to the power source terminal 6a through a collector load resistor
and its base connected to the emitter of, for example, the
aforementioned transistor Tr.sub.6 (or the collector of the
transistor Tr.sub.4 ) at least through a Zener diode Z.sub.D.
Accordingly, the transistor Tr.sub.7 is adapted to be in the on
state when the level of the signal S.sub.5 ' exceeds the sum
E.sub.2 (FIG. 2D' ) of the Zener voltage of the Zener diode Z.sub.D
and the forward drop voltage between the base and emitter of the
transistor Tr.sub.7 and to be in the off state when the level of
the signal S.sub.5 ' becomes lower than the sum of the voltages. As
a result of this, the pulse width modulator circuit 7 produces a
rectangular wave comparison signal S.sub.6 such as depicted in FIG.
2E which has been modulated in pulse width in accordance with the
peak value of the triangular wave signal S.sub.5 '.
With the above arrangement, the frequency, which is capable of
feeding a sawtooth pulse S.sub.5 of a peak amplitude permitting the
start of the pulse width modulating action of the pulse width
modulator circuit, that is, the frequency of the output signal
S.sub.1 of the signal generator 1 can be determined dependent upon
the reference DC voltage E fed to the base of the transistor
Tr.sub.5 of the differential amplifier circuit. In addition, the
reference value, that is, the revolving number of the motor is
established according to the Zener voltage of the Zener diode
Z.sub.D of the pulse width modulator circuit 7 and the forward drop
voltage between the base and emitter of the transistor Tr.sub.7 and
an emitter-follower type transistor circuit is interposed as a
buffer between the differential amplifier circuit and the pulse
width modulator circuit so as to insure sufficient switching action
of the pulse width modulator circuit.
The reason why the reference value is thus established in two
stages is to improve the servo control sensitivity by sharpening
the rise of the signal fed to an integration circuit 8 described
later when the revolving number of the motor varies in excess of
the set value.
Namely, the signal S.sub.5 or S.sub.5 ' derived from the comparator
circuit 5 is a triangular wave whose height and base vary, so that
the rise of the signal S.sub.5 or S.sub.5 ' not so sharp and this
presents a problem especially when accurate servo is required. To
settle the problem, in the present example the signal S.sub.5 or
S.sub.5 ' is converted by the pulse width modulator circuit into a
pulse-width-modulated wave S.sub.6 the peak value of which is
constant and only the pulse width of which varies with changes in
that of the signal S.sub.5 or S.sub.5 ' and accordingly the base
thereof.
Consequently, since the peak value of the signal S.sub.6 at the
rise thereof becomes the same as those of the subsequent pulses,
the rise of the signal can be rendered sharp and the ripple factor
of the value integrated by the integration circuit 8 described
later can be reduced by selecting the Zener voltage of the Zener
diode so as to approximate the pulse width of the
pulse-width-modulated wave signal to the base length of the
triangular wave. If the same ripple factor is permissible, the
integration time constant can be decreased to provide for enhanced
followup property in servo control.
The rise and fall of the waveform of the signal S.sub.6 can be
improved by connecting the collector of the transistor Tr.sub.7
through the resistor R.sub.6 to the base of the transistor Tr.sub.4
as shown and by positively feeding the rectangular wave comparison
signal S.sub.6 from the transistor Tr.sub.6 back to the stage
preceding it.
The rectangular wave comparison signal S.sub.6 is applied to a
low-pass filter, that is, the integration circuit 8 consisting of a
resistor R.sub.5 and a capacitor C.sub.2 to provide a DC voltage
signal such as shown in FIG. 2F which corresponds to the pulse
width of the rectangular wave comparison signal S.sub.6, that is, a
demodulated signal S.sub.7 of the frequency-modulated signal
S.sub.1 derived from the signal generator 1, shown in FIG. 2A. The
demodulated signal S.sub.7 is fed to a DC amplifier 9 consisting of
transistors Tr.sub.8 and Tr.sub.9. The motor M is connected, for
example, between the collector of an output transistor Tr.sub.9 of
the DC amplifier 9 and the power source terminal 6a and is supplied
with a current depending upon the level of the DC voltage signal
S.sub.7 fed to the DC amplifier 9.
With the above arrangement, an increase in the revolving speed of
the motor M causes an increase in the frequency of the
frequency-modulated signal S.sub.1 derived from the signal
generator 1 thereby to shorten the period of the differentiated
pulse S.sub.3, that is, the repeating cycle of the sawtooth wave
signal S.sub.5. This leads to a decrease in the peak value of the
sawtooth wave signal S.sub.5 , by which the pulse width of the
rectangular wave comparison signal S.sub.6 is decreased to lower
the level of the DC voltage S.sub.7 applied to the DC amplifier 9.
As a result of this, the collector current of the output transistor
Tr.sub.9, that is, the current flowing to the motor M decreases to
reduce its speed. While, a decrease in the revolving speed of the
motor M causes an increase in the current fed to the motor M to
increase its speed. Accordingly, self-start of the motor M is
possible and its revolving speed is always controlled to be
constant.
With the above-described speed control system of this invention,
stable and highly sensitive control can be achieved and since the
inclination of the sawtooth wave signal S.sub.5 is rendered
variable, the reference speed of the rotary member, that is, the
motor M in the illustrated example can be selected over a wide
range.
Even if the revolving number of the motor is invariable, the
frequency-modulated signal S.sub.1 is often slightly
amplitude-modulated, as indicated by a broken line S.sub.1 ' in
FIG. 2A, by a displacement of the signal generator unit between the
magnetic center of the rotor and that of the stator which is caused
by a change in thrust in the axial direction of the motor shaft.
Accordingly, where the rectangular wave signal S.sub.2 has been
produced by shaping the waveform of the signal S.sub.1 as above
described, there is the possibility that the pulse width of the
signal varies even if the frequency of the signal S.sub.1 is
invariable. Provided that the period of the signal S.sub.2, for
example, at its rising portion agrees with that of the
frequency-modulated signal S.sub.1, the period of the signal
S.sub.2 at the falling portion does not agree with that of the
signal S.sub.1. Consequently, when a servo signal (the signal
S.sub.5 in FIG. 2) is produced by using both the rise and fall of
the signal S.sub.2, an error is introduced to make it impossible to
obtain accurate comparison output, and in the case of controlling
the revolution of a motor the established revolving number of the
motor is caused to vary.
With the rotary member speed control system of the present
invention, however, the frequency-modulated signal S.sub.1, which
is generated in relation to the revolution of the rotary member,
that is, the motor in the illustrated example, is shaped in
waveform to produce the rectangular wave signals S.sub.2, and the
sawtooth wave generator 4 is driven by either one of the
differentiated pulses S.sub.3 and S.sub.4 of the signal S.sub.2 at
its rise and fall, that is, by the differentiated pulse S.sub.3
only in the illustrated example, thereby producing one sawtooth
wave signal S.sub.5, that is, one rectangular wave comparison
signal S.sub.6 every one cycle of the frequency-modulated signal
S.sub.1. Consequently, even if the frequency modulated signal
S.sub.1 is amplitude-modulated to vary the differentiated pulse,
for example, S.sub.4, there is no possibility that the variation in
the pulse S.sub.4 appears as an error component. Thus, the speed
control system of this invention is extremely high in precision and
accordingly it ensures stable control of the motor which is not
affected by the influence of the variations in the thrust of the
motor shaft and so on.
As previously described, the reference speed of the motor M depends
upon the inclination of the sawtooth wave signal S.sub.5, the sum
E.sub.1 of the emitter voltages of the transistors Tr.sub.4 and
Tr.sub.5 and the forward drop voltage between the base and emitter
of the transistor Tr.sub.4 and the sum E.sub.2 of the Zener voltage
of the Zener diode Z.sub.D and the forward drop voltage between the
base and emitter of the transistor Tr.sub.7. In the present
invention, however, means for changing the inclination of the
sawtooth wave signal S.sub.5, that is, the means for changing the
time constant for charge of the signal S.sub.5 is provided, so that
the reference speed of the Motor M can be selected at will over a
wide range by changing over the switch S as illustrated to select
the resistors R.sub.10, R.sub.20 and R.sub.30.
Further, since the currents and voltages in the overall control
system vary in an intermittent manner, heat generation is low and
hence the device for the speed control system can be readily
produced in the form of an integrated circuit.
In FIG. 3 there is illustrated another embodiment of this invention
which is identical in fundamental circuit construction with the
example of FIG. 1, and accordingly elements similar to those in
FIG. 1 are identified by the same reference numerals and no further
detailed description will be repeated. The circuit of this example
is simpler in construction than that of FIG. 1 in constituting the
sawtooth wave generator 4 with one transistor Tr.sub.2 and in
elimination of the emitter-follower type transistor amplifier
consisting of the transistor Tr.sub.6 and the Zener diode Z.sub.D
in FIG. 1. The Zener diode Z.sub.D is incorporated to stabilize the
power source voltage.
The present example is similar in the fundamental operation to that
of FIG. 1. In FIG. 4 waveforms corresponding to those in FIG. 2 are
designated with the same reference numerals. A sawtooth wave signal
S.sub.5 such as shown in FIG. 4D, which is derived from a sawtooth
base generator 4, is applied to the base of a transistor Ir.sub.4
of a differential Zener consisting of transistors Tr.sub.4 D and T
r.sub.5 of a comparator circuit 5 and the signal S.sub.5 is
compared with the sum E.sub.1 of the emitter voltages of the
transistors Tr.sub.4 and Tr.sub.5 and a forward drop voltage
between the base and emitter of the transistor Tr.sub.4 as in the
case of FIG. 1 to generate in the collector of the transistor
Tr.sub.4 a signal S.sub.5 ' depicted in FIG. 4D', thereby producing
in the base of a transistor Tr.sub.7 a signal S.sub.5 " shown in
FIG. 4D". The resulting signal S.sub.5 " is compared with a forward
drop voltage E.sub.2 ' between the base and emitter of the
transistor Tr.sub.7 to produce in the collector of the transistor
Tr.sub.7 a rectangular wave comparison signal S.sub.6 shown in FIG.
4E. The subsequent operations are the same as those in the example
of FIG. 1.
Also in the example of FIG. 3 stable and highly sensitive control
can be achieved and the reference speed of a motor M can be freely
selected over a wide range by changing the inclination of the
sawtooth wave signal S.sub.5 by changing over a switch S as in the
case of FIG. 1.
Although, in the foregoing, the sawtooth wave signal S.sub.5
derived from the sawtooth wave generator 4 is fed to the comparator
circuit 5 and the rectangular wave comparison signal S.sub.6
resulting from comparing the signal S.sub.5 with the reference DC
voltage is applied to the integration circuit 8, it is also
possible to apply the sawtooth wave signal from the sawtooth wave
generator 4 to the integration circuit and to apply the output of
the integration circuit to the comparator circuit to be compared
with reference DC voltage.
While the present invention has been described in connection with
the case where a signal, frequency-modulated in accordance with the
rotational angular velocity of the motor M, is derived from the
signal generator 1 mounted on the rotary shaft of the motor M and
is demodulated to control the revolving speed of the motor M, the
frequency-modulated signal may be produced by other methods,
Further, the present invention is suitable for use in speed control
of rotary members such as a motor, a capstan and the like of
magnetic recording and reproducing devices and so on which is
achieved by controlling a brake mounted on a rotary shaft of the
rotary member.
It will be apparent that many modifications and variations may be
effected without departing from the scope of the novel concepts of
this invention.
* * * * *