Dec. 20, 1966 J. L. BAYNEY E.T A.
3,293,656
WELOCITY MODULATED RECORDING LIGHT INTENSIFIER
Filed Oct. 7, 1964
28 3O 32
w ANW
DFFERENTATOR RECT FER CONTROL
CRC
J/4MMA's A. AAAy/VAy
AAAA/ G/A/MAW
° 4-see 4 4.e.
A 77 OAMAy
United States Patent Office 3,293,656
Patented Dec. 20, 1966
f 2
slower the vibration of the mirror, the recording bright
3,293,656 neSS is made less.
VELOCITY MODULATED RECORDENG The novel features that are considered characteristic
LGHST INTENSFER of this invention are set forth with particularly in the ap
James L. Blayney, Pacoima, and Ralph Gilman, Alta pended claims. The invention itself both as to its orga
dena, Calif., assignors to California Institute Research nization and method of operation, as well as additional
Foundation, Pasadena, Calif., a corporation of Cali objects and advantages thereof, will best be understood
fornia from the following description when read in connection
Filed Oct. 7, 1964, Ser. No. 402,079 With the accompanying drawings, in which:
8 Claims. (Cl. 346-109)
O FIGURE 1 is a block diagram of an arrangement in
This invention relates to apparatus of the type which accordance with this invention;
employs a moving beam of light for making recordings, FIGURE 2 is a circuit diagram exemplifying certain
such as a galvanometer, and more particularly to im circuitry of the type represented by block diagrams in
provements therein. FIGURE 1; and
In apparatus which employs a light beam for making 15 FIGURE 3 is a circuit diagram of another embodiment
a recording, such as the indicated galvanometer, usually of the circuitry shown by block diagrams in FIGURE 1.
a mirror is supported so that it can be vibrated by what While the embodiment of the invention will be shown
ever forces or signals are applied thereto. A lamp is and described as an improvement on a moving mirror
positioned so that light therefrom falls upon the mirror type of galvanometer, it is to be understood that this
and is reflected from the mirror onto a moving recording 20 is by way of example only, and should not be considered
surface, such as a film which is wrapped around a rotat as a limitation upon the invention. Those skilled in the
ing drum. If the mirror moves rapidly, less light falls art will appreciate that the techniques taught herein are
upon a given area of the recording surface than occurs usable for other types of instruments in which the prob
when the mirror moves slowly. Thus, a recording of a lem of achieving a usable recording from a light beam
high frequency signal which is applied to move the mirror 25 which is moved at varying velocities is presented.
is lighter than a recording of a low frequency signal. As Referring now to FIGURE 1, a galvanometer will
a matter of fact, as the frequency of the signal applied to normally have a stand 10 which supports a mirror 12
move the mirror increases, although the mirror will vi in a manner (not shown), so that the mirror can be
brate adequately with the frequency applied thereto, be vibrated or moved in response to signals applied to the
cause of the reduction in the amount of light falling on 30 deflecting coil (not shown) of the galvanometer. The
the recording surface except at those locations where mirror Support normally is such that the mirror pivots
the mirror reverses direction of motion, the recording about an axis in response to the electrical signals applied
trace between the extremes is so light to be indistinguish to the galvanometer.
able so that for the higher frequency all that is seen is A recording light source 14 is also provided in a
substantially a grey rectangle while for the relatively 35 galvanometer, and its light output is permitted to shine
lower frequencies, the individual wave shape trace can be on the galvanometer mirror i2. The light reflected from
SC. the moving mirror A2 is directed onto a stationary mir
Attempts to cure this by either increasing the sensitivity ror 16 which in turn reflects the light onto the surface
of the recording medium or increasing the intensity of the of a recording drum 18, upon which a recording medium
40 may be placed.
light being reflected thereon does serve to extend the us
able frequency range of a galvanometer in the high fre As thus far described, the galvanometer structure is
quency direction. However, because of the overex conventional and well known. There is provided in ac
posure which occurs on the low frequency range, the cordance with this invention an additional light source
recorded wave shapes are blurred on the low frequency 20 and a photosensitive cell 22, both of which may be
range and thus one has to sacrifice low frequency band 45 Supported upon a suitable stand 24 in the manner shown
width to obtain some high frequency bandwidth. adjacent the reflecting surface of the moving mirror 12,
An object of the present invention is to provide an ar and So as not to interfere with the path of the light
rangement for maintaining substantially constant the from the recording light source 14 and from the moving
amount of light which falls on a recording medium, and mirror 2 to the stationary mirror 16. The photosensitive
apparatus of the type described, regardless of the speed 50 cell 22 may be, for example, a solar cell. A mask 26
at which the mirror is moved. has a slot therethrough which permits light from the
Another object of the present invention is the provi Source 20 to shine on the mirror 12 when in a quiescent
sion of a novel arrangement for compensating for changes State and to be reflected onto the photosensitive cell 22.
in velocity of a recording light beam in apparatus of the The opening in the mask 26 is such that the substantially
type described. 55 rectangular area of the cell 22 is half filled by the
Still another object of the present invention is the pro rectangularly focussed beam from the mirror 12 such
vision of a novel, useful arrangement for modulating the that the signal output from the photosensitive cell varies
intensity of a recording light source in accordance with directly with the deflection amplitude.
the velocity of the mirror reflecting light from said source 60 The output of the photosensitive cell is applied to a
onto a recording medium. differentiator arrangement 28. The operation of a differ
These and other objects of the invention may be entiator, as is well known, will have an amplitude which
achieved in an arrangement wherein light is derived from is a function of the rate of change of the input signal,
the moving mirror which directs light from a light source varying directly therewith.
onto a recording surface. The derived light has an am The output of the differentiator 28 is then applied to
plitude which is a function of the deflected position of
65 a rectifier arrangement 30 wherein it is converted to a
the moving mirror. This is converted into an electrical unidirectional signal. The output of the rectifier 30 is
then applied to a lamp control circuit 32 which effectively
signal which is differentiated, then rectified, and then ap determines the amount of current supplied to the Iannp
plied to control the intensity of the light source used for 14 in response to the rectified signal. Therefore, the
making a recording. Accordingly, the higher the fre 70 light output of the lamp 14 varies directly with the
quency of vibration of the mirror, the brighter the illu Velocity of the vibrating mirror and the higher the fre
mination received from the recording light source. The quency applied to cause the mirror to vibrate the higher
3,293,656
A.
the intensity of the light emitted by the light source 4 A first and a second diode, respectively 86, 88, rec
during the high velocity portions of the cycles. Accord tify the differentiating circuit outputs. Diode 86 is con
ingly, the system described herein operates to modulate nected between the junction of capacitor 78 and resistor
the recording light with the velocity of the moving mir 88 and the base of a transistor 96. Diode 88 is con
ror 2 so that the amount of light which is reflected 5 nected between the junction of capacitor 82 and resistor
onto the recording medium is increased with increase in 84 and the base of transistor 96.
velocity of the mirror to compensate for the effects of A potentiometer 92, connected across the potential
such increase in velocity. source, serves the same function as is served by poten
FIGURE 2 is a circuit diagram which exemplifies a tiometer 53 in FiGURE 2; namely, setting the quiescent
preferred arrangement of the circuitry represented by I.0 lamp brightness. The movable arm of the potentionneter
the rectangles 28, 3G, 32 in FIGURE 1. The photo is connected to the base of transistor 93 through a re
Sensitive cell 22 is connected across the primary wind sistor 94.
ing 56P of a transformer 50. The transformer 50 has a The collector of transistor 90 is connected to the base
center tap secondary winding 58S. The transformer of a transistor 96. The emitter of transistor 90 is con
operates to differentiate the input signal from the photo nected to the emitter of a transistor 98, and also to one
Sensitive cell, since the lower the frequency of the in side of the filament of lamp 4. The collector of tran
put signal, the lower the voltage output which is in sistor 96 is connected to the base of transistor 93. The
duced across the secondary winding, and conversely the collector of transistor 98 and the emitter of transistor
higher the signal input, the higher the voltage which is 96 are both connected to the operating potential source.
induced across the secondary winding. Diodes 52, 54. 20 The other end of the filament of lamp 4 is connected
have their cathodes connected to opposite ends of the to ground. It should be apparent that the current pass
Secondary winding 50S and their anodes connected to ing through the lamp 4 is under the control of the
gether in the usual rectifier configuration. The con three transistors with transistor 90 controlling transistors
nected together anodes of the diodes are connected to $5 and 98.
the base electrode 56B of a transistor 56. The center 25 The operation of the circuit shown in FIGURE 3 is
tap of the Secondary winding is connected to the mov Substantially identical to that described for FIGURE. 2.
able arm of a potentiometer 58. One end of the poten The transformer is eliminated and in its place a phase
tiometer resistor is connected to ground and the other Splitter transistor and differentiating circuits are used
end is connected through a second resistor 60 to an for accomplishing the functions provided by the trans
operating potential source. A zener diode 62 is con 30 former.
nected across the resistor of the potentiometer 58 for the There has accordingly been described and shown here
purpose of insuring a substantial consistency of the volt in a novel, useful arrangement for compensating for
age which is applied to the transistor 56 and to another changes in light level of a recording light beam with
transistor 64. Variations in velocity of said light beam.
The collector 56C of transistor 56 is connected to the What is claimed is:
operating potential source, the emitter 56E of transistor . In apparatus of the type wherein light from a source
55 is connected to the base 64B of transistor 64. The of light is directed onto a movable mirror to be redirected
collector 64C of transistor 64 is connected to the oper Onto a recording medium, said movable mirror being
ating potential source and the emitter 64E of the tran moved responsive to signals whose wave form is de
sistor 64 is connected to one end of the filament of 40 sired to be recorded on said recording medium, the im
the recording lamp 4, the other end of which is con provement comprising a light-to-electrical transducer,
nected to ground. A capacitor 53 is connected between means for illuminating said light-to-electrical transducer
the junction of the diodes 52, 54 and the movable arm With light reflected from said mirror for generating an
of the potentiometer 58. electrical signal having an amplitude increasing with the
The capacitor 53 and the transformer 50 are selected 45 angular velocity of said mirror, and means for varying
in accordance with the recording frequency range and the intensity of said light source with said electrical sig
recording drum speed desired to be covered. The po nal for compensating for the effects of changes in velocity
tentiometer 58 is adjusted for the quiescent lamp bright of said moving mirror on said recording medium.
ness since its setting is fed to the base of the transistors 2. In apparatus as recited in claim 1 wherein said
56 in a path through the secondary winding 50S and the 50 light-to-electrical signal transducer comprises a solar cell
diodes 52, 54. The variations in potential which are which has only a portion of its light receiving surface
introduced through the transformer 50 are added to the illuminated from said movable mirror when said movable
quiescent voltage level and thus serve to increase the mirror is in its quiescent state.
lamp brightness with increase in velocity of the mirror. 3. In apparatus of the type wherein light from a source
FIGURE 3 is a circuit diagram of another embodiment 55 of light is directed onto a movably supported mirror to be
of the invention which does not use a transformer. A redirected therefrom onto a recording medium, and said
photosensitive cell 70 performs the same function as movable mirror is deflected in response to signals which
the cell 22 in FIGURE 2. Its output is applied to the are desired to be recorded on said recording medium,
base of transistor 72. The collector of transistor 72 is means for compensating for the effects of increases in
connected through a resistor 74 to a source of oper 60 velocity of said movable mirror on said recording medium
ating potential and the emitter of transistor 72 is also comprising light-to-electrical signal converting means, an
connected to the operating potential source through a auxiliary light Source, means for directing light from said
resistor 74. Transistor 72 serves to amplify the out auxiliary light source onto said moving mirror to be re
put of the photosensitive cell 70 and applies its output 65
directed thereby onto said light-to-electrical signal trans
to two differentiating circuits. ducing means to cause it to generate an electrical signal
The capacitor 78 and resistor 80 constitute one differ output having an amplitude which is a function of the
entiating circuit and capacitor 82 and resistor 84 con displacement of said moving mirror, differentiating circuit
stitute the other differentiating circuit. Capacitor 78 is means, means for applying the output of Said light-to
connected between the collector of transistor 72 and 70 electrical signal transducing means to said differentiating
one end of resistor 80. The other end of resistor 80 circuit means, rectifier means connected to said differen
is connected to the operating potential source. Capac tiating circuit means for rectifying the signal received
itor 82 is connected between the emitter of transistor 72 therefrom and amplifier means for controlling the inten
and one end of resistor 84. The other end of resistor sity of said light source responsive to the output of said
34 is connected to the operating potential source. 75 rectifier means for compensating for the effects of in
3,293,656
5 6
creases in velocity of motion of said moving mirror on movable along said resistance, means connecting said re
said recording medium. sistance across said source of operating potential, and
4. Apparatus as recited in claim 3 wherein said dif means connecting said potentiometer slider to the center
ferentiating circuit means comprises a transformer having tap of said transformer second winding.
a primary and a secondary winding, said primary winding 8. In apparatus of the type wherein light from a source
being coupled to said light-to-electrical signal transducing of light is directed onto a movably supported mirror to
means and said secondary winding being connected to said be redirected therefrom onto a recording medium, and
rectifier means. Said movable mirror is deflected in response to signals
5. Apparatus as recited in claim 4 wherein said dif which are desired to be recorded on said recording me
ferentiating circuit means comprises a network including O dium, means for compensating for the effects of increases
a capacitor, and a resistor connected to one end of Said in velocity of said movable mirror on said recording
capacitor, said capacitor other end being connected to medium comprising a photosensitive cell, an auxiliary
receive said light-to-electrical signal transducing means light source, and means for positioning said auxiliary light
output, and said rectifier means being connected to said Source and photosensitive cell relative to said moving
one end of said capacitor. mirror to illuminate said photosensitive cell with light re
6. In apparatus as recited in claim 3 wherein said light flected from said moving mirror which is received from
to-electrical signal transducer comprises a photosensitive Said auxiliary light source, a first transistor having a base,
cell, an auxiliary light source, and means for positioning emitter and collector electrodes, a source of operating
said auxiliary light source and photosensitive cell relative potential, means coupling said photosensitive cell to said
to said moving mirror to illuminate said photosensitive 20 first transistor base, a first resistor connected between said
cell with light reflected from said moving mirror which first transistor collector and said source of operating
is received from said auxiliary light source. potential, a second resistor connected between said first
7. In apparatus of the type wherein light from a source transistor emitter and said source of operating potential,
of light is directed onto a movably supported mirror to be a first capacitor having one end connected to said first
redirected therefrom onto a recording medium, and said transistor collector, a third resistor connected between
movable mirror is deflected in response to signals which said source of operating potential and the other end of
are desired to be recorded on said recording medium, said first capacitor, a second capacitor having one end
means for compensating for the effects of increases in connected to said first transistor emitter, a fourth resistor
velocity of said movable mirror on said recording medium connected between said source of operating potential and
comprising a photosensitive cell, an auxiliary light source, 30 the other end of said second capacitor, a second transis
and means for positioning said auxiliary light source and tor having base, emitter and collector electrodes, a first
photosensitive cell relative to said moving mirror to rectifier connected between the other end of said first ca
illuminate said photosensitive cell with light reflected from pacitor and said second transistor base, a second rectifier
said moving mirror which is received from said auxiliary connected between the other end of said second capacitor
light source, a transformer having a primary winding and 35 and said second transistor base, potentiometer means for
a center tap Secondary Winding, means connecting said applying a potential from said source of operating poten
photosensitive cell to said transformer primary winding, tial to said second transistor base for establishing a quies
first and second rectifier means, means respectively con cent illumination level for said source of light, means con
necting said first and Second rectifier means to opposite necting the emitter of said second transistor to said
ends of Said secondary winding, a transistor having a 40 source of light, and means coupling the collector of said
base collector and emitter electrode, means connecting said second transistor to said source of operating potential.
first and second rectifier means to the base of said transis
tor, a source of operating potential, means connecting the References Cited by the Examiner
collector of said transistor to said source of operating po 45
UNITED STATES PATENTS
tential, means coupling said source of light between said 2,415,880 2/1947 Hassler ------------ 346-109
emitter and said source of operating potential to be con 2,958,010 10/1960 Carter et al. ------ 346-109 X
trolled responsive to current flowing through said transis
tor collector and emitter, and means for establishing a RICHARD B. WILKINSON, Primary Examiner,
quiescent illumination level for said source of light com 50
prising a potentiometer having a resistance and a slider J. W. HARTARY, Assistant Examiner.
