Light beam modulating and deflecting system

A light beam modulating and deflecting system comprising a stationary electrode secured to a stationary body, and a rotatable electrode secured to a rotating body, on which a light source is mounted, and opposed in slightly spaced relation to the stationary electrode to form a capacitor together with the stationary electrode. A high frequency signal modulated with a light modulating signal is applied to the stationary electrode, thereby to feed the light modulating signal from the stationary electrode to the rotatable electrode. The system may comprise a plurality of light sources, stationary electrodes and rotatable electrodes, and high frequency signals modulated with various light modulating signals may be applied to the respective stationary electrodes, thereby to independently modulate the light sources via the rotatable electrodes. Or, the system may comprise a plurality of light sources and a set of the stationary electrode and the rotatable electrode, and a plurality of high frequency signals having frequencies different from one another and modulated with various modulating signals may be combined and applied to the stationary electrode, followed by signal separation and demodulation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a light beam modulating and deflecting system 
used to record and read out information by scanning a scanning surface 
with a light beam such as a laser beam, and more particularly to a light 
beam modulating and deflecting system which has at least one light source 
(semiconductor laser, light emitting diode or the like) mounted on a 
rotating body and which simultaneously carries out both modulation and 
deflection of the light beam emitted from the light source rotating 
together with the rotating body, wherein the light beam is deflected 
through the rotation of the rotating body and, at the same time, modulated 
by means of the drive current for the light source. 
2. Description of the Prior Art 
Laser sources can generate light beams exhibiting high spatial interference 
and a high spectral line brightness that cannot be obtained with the other 
types of light sources. By virtue of these advantages, laser sources are 
used for many optical read out and recording systems. For example, the 
laser sources are used for read out systems such as in facsimile 
transmitters, automatic readers for label bar codes, and film flaw 
detectors. The laser sources are also used for recording systems such as 
in video disc recorders and facsimile receivers. In the past, these 
laser-based systems employed mainly the gas lasers such as He-Ne, He-Cd 
and Ar lasers. However, the gas laser sources are intrinsically large in 
size and, in addition, necessitate additional light scanners and light 
modulators for deflecting and modulating the light beam during scanning 
with the light beam. Consequently, such systems using gas lasers are, in 
general, large in size and expensive. Thus, recently, semiconductor laser 
systems which are small and exhibit high efficiency have come into 
increasingly wide use. One example of such a system is that disclosed in 
Japanese patent application No. 54(1979)-84224 in which a semiconductor 
laser source is rotated to form linear scanning lines. 
The semiconductor laser scanning system described in Japanese patent 
application No. 54(1979)-84224 is small in size and inexpensive, and yet 
can modulate and deflect the light beam without necessitating additional 
devices. In this system, electric power is supplied to the rotating light 
source by use of brushes. However, semiconductor laser sources are easily 
damaged by electric shocks and, therefore, break due to the electrical 
noise caused by the brushes. This conventional system is also 
disadvantageous in that it cannot be used for long periods of time because 
of wearing of the brushes. 
SUMMARY OF THE INVENTION 
The primary object of the present invention is to provide a light beam 
modulating and deflecting system in which a light beam is deflected 
through the rotation of a rotating body and modulated by means of a drive 
current for the light source. 
Another object of the present invention is to provide a light beam 
modulating and deflecting system using no electric contacting means such 
as brush. 
The specific object of the present invention is to provide a light beam 
modulating and deflecting system which is compact in size and inexpensive, 
and exhibits long life. 
The present invention provides a light beam modulating and deflecting 
system comprising a stationary electrode secured to a stationary 
supporting body, and a rotatable electrode secured to a rotating body, on 
which a light source is mounted, and opposed in slightly spaced relation 
to said stationary electrode to form a capacitor together with said 
stationary electrode, a high frequency signal modulated with a 
predetermined light modulating signal being applied to said stationary 
electrode, whereby the light modulating signal is fed from said stationary 
supporting body side to said rotating body side. In the present invention, 
power necessary for energizing the light source is fed from the stationary 
electrode to the rotatable electrode without using any electric contact 
means therebetween. Accordingly, the system in accordance with the present 
invention has exhibits longer life than a power feeding mechanism using 
brushes and eliminates the risk of the semiconductor laser source breaking 
due to electric shocks. Furthermore, the system can be made smaller in 
size than a power feeding mechanism using a generator. The rotating body 
of the system is light in weight since the components secured thereto are 
light, and can be driven with a low-power motor. The system in accordance 
with the present invention is also advantageous in that electrical 
adjustments of the parts of the system can be conducted even when the 
rotating body is being halted. In addition, in the present invention, a 
plurality of light sources can be mounted on the rotating body and can 
easily be light-modulated independently from one another. 
In the present invention, an air layer may exist between the stationary and 
rotatable electrodes. However, to obtain a larger capacity, it is 
advantageous to insert a dielectric exhibiting a large dielectric constant 
between the electrodes. To minimize the reactance of the capacitor, a high 
frequency signal modulated with a light modulating signal is employed. It 
is also possible to feed the light modulating signal as such, supply the 
electric power necessary for circuits of the rotating body by using 
another means such as rotary transformer, and position an amplifying 
circuit in the rotating body. 
In one aspect of the present invention, a plurality of light sources are 
mounted on the rotating body and a plurality of stationary electrodes and 
rotatable electrodes are positioned, high frequency signals modulated with 
light modulating signals different from one another being applied to the 
respective stationary electrodes, whereby the respective light modulating 
signals are transmitted to the rotatable electrodes and the light 
intensities of the light sources are modulated independently from one 
another. In this case, the frequencies of the high frequency signals may 
be the same or different from one another. When the frequencies thereof 
are different from one another, it is possible to increase the degree of 
signal separation by use of a filter circuit. Furthermore, it is possible 
to classify the light sources into several groups and modulate each group 
of light sources by one light modulating signal. 
To accomplish the above objects, the light beam modulating and deflecting 
system in accordance with the present invention is formed to supply 
electric power to the rotating body provided with at least one light 
source such as semiconductor laser without using any means that contacts 
the rotating body. Namely, in the system in accordance with the present 
invention, at least one stationary electrode is secured to the stationary 
supporting body, and at least one rotatable electrode is secured to the 
rotating body provided with at least one light source in such a manner 
that these electrodes can maintain the capacitor function therebetween 
even during rotation of the rotatable electrode, thereby supplying 
electric power to the rotating body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will hereinbelow be described in further detail with 
reference to the accompanying drawings. 
Referring to FIGS. 1 and 2 showing an embodiment of the light beam 
modulating and deflecting system in accordance with the present invention, 
semiconductor laser sources 1 are mounted on a rotating body 2. The 
rotating body 2 is secured to a rotating shaft 5 of a high-speed rotating 
motor 4, and rotates together with the motor 4. As the rotating body 2 
rotates, laser beam 1' emitted from the semiconductor laser sources 1 (1a, 
1b, 1c and d) scan a scanning surface in the a.fwdarw.b direction. The 
rotating body 2 is formed by, for example, a hollow body, and is provided 
therein with a printed circuit board 7 for driving and controlling the 
semiconductor laser sources 1. The printed circuit board 7 includes 
rectifying and smoothing circuits and the like. 
Between the rotating body 2 and the rotating shaft 5 are positioned a 
stationary electrode 3 and a rotatable electrode 6. The stationary 
electrode 3 is secured to the stationary supporting body. The rotatable 
electrode 6 is secured to the rotating shaft 5 and the rotating body 2 so 
as to rotate together with the rotating shaft 5. The stationary electrode 
3 is slightly spaced apart from the rotatable electrode 6 so that the 
former may not rotate together with the latter. 
A method of modulating the light beam in the system in accordance with the 
present invention shown in FIGS. 1 and 2 will be explained below with 
reference to FIGS. 3 and 4. 
FIG. 3 is a schematic diagram showing one form of electric circuit employed 
in the system in accordance with the present invention, and FIGS. 4A to 4D 
show wave forms in the circuit shown in FIG. 3. In FIGS. 4A to 4D, the 
horizontal axis shows time, and the vertical axis the relative current 
value. 
In FIG. 3, a high-frequency oscillator G outputs a signal as shown in FIG. 
4A. When a desired light modulating signal f as shown in FIG. 4B is 
applied to the high-frequency oscillator G, the output thereof is 
modulated to a signal as shown in FIG. 4C. The modulated signal thus 
obtained is fed to the stationary electrode 3. Accordingly, by the 
electric power thus applied to the stationary electrode 3, a signal having 
the wave form as shown in FIG. 4C is induced at the rotatable electrode 6 
via a layer of a dielectric (including air) positioned between the 
electrodes 3 and 6. Electrodes 3 and 6 form capacitive coupler 20. The 
signal induced at the rotatable electrode 6 is then passed through a 
rectifying circuit constituted by diodes D1 and D2, and a smoothing 
circuit formed by capacitors C1 and C2 and a coil L1, to yield a rectified 
signal as shown in FIG. 4D. The rectified signal is sent to the 
semiconductor laser source 1. As a result, the semiconductor laser source 
1 emits light at an intensity corresponding to the light modulating signal 
f. 
FIGS. 5 to 7 show various arrangements of the capacitors which may be 
employed to transmit signals in the system in accordance with the present 
invention. In FIGS. 5A and 5B showing capacitors for transmitting two 
signals, stationary electrodes 3 and 3' are positioned concentrically, and 
a guard 8 for preventing signals from leaking is interposed between 
electrodes 3 and 3'. Similarly, rotatable electrodes 6 and 6' are 
positioned concentrically on the inner and outer sides of another guard 8, 
and opposed to the stationary electrodes 3 and 3', respectively, as shown 
in FIG. 5B so that the rotation center 9 aligns with the center of the 
concentric stationary electrodes 3 and 3'. In this arrangement, one signal 
is fed from the stationary electrode 3 to the rotatable electrode 6, and 
the other from the stationary electrode 3' to the rotatable electrode 6'. 
FIG. 6 shows another arrangement of capacitors for transmitting two 
signals. In FIG. 6, a set of the stationary electrode 3 and the rotatable 
electrode 6 opposed to each other and a set of the stationary electrode 3' 
and the rotatable electrode 6' opposed to each other are positioned in the 
direction of the rotation axis 9. 
FIGS. 7A and 7B show three capacitors formed by electrodes positioned on an 
inner rotatable cylinder 10 and an outer stationary cylinder 11. 
Stationary electrodes 3, 3' and 3" are positioned on the inner surface of 
the outer stationary cylinder 11 and isolated from one another by guards 
8. Rotatable electrodes 6, 6' and 6" are positioned on the outer surface 
of the inner rotatable cylinder 10 and isolated from one another by 
another set of guards 8. Three signals are respectively transmitted from 
the stationary electrodes 3, 3' and 3" to the rotatable electrodes 6, 6' 
and 6". 
In the present invention, it is also possible to transmit a plurality of 
light modulating signals by a set of the stationary electrode and the 
rotatable electrode by employing high frequency signals having frequencies 
different from one another for the respective light modulating signals. 
FIG. 8 shows an embodiment of the electric circuit for transmitting three 
light modulating signals different from one another by a set of the 
stationary electrode and the rotatable electrode. In FIG. 8, light 
modulating signals f1, f2 and f3 are respectively entered into 
high-frequency oscillators G1, G2 and G3 which generate high frequency 
signals having frequencies different from one another. The high frequency 
signals modulated with the light modulating signals f1, f2 and f3 are then 
combined by a signal combining circuit M, and a combined signal obtained 
therefrom is sent to the stationary electrode 3. The combined signal is 
transmitted from the stationary electrode 3 to the rotatable electrode 6 
via the dielectric layer or the air layer intervening therebetween of 
capacitive coupler 20, and then separated into the respective high 
frequency signals by band-pass filters F1, F2 and F3. The high frequency 
signals separated from one another are then detected by detecting circuits 
D1, D2 and D3 to remove high-frequency components from the signals, and 
demodulated into light modulating signals f1, f2 and f3. The light 
modulating signals f1, f2 and f3 thus demodulated are then amplified by 
amplifiers A1, A2 and A3 respectively and used to modulate the light 
intensities of three light sources such as semiconductor laser sources 
independently from one another. Electric power necessary for the circuits 
in the rotating body may be supplied by another means such as rotary 
transformer. 
The system in accordance with the present invention has been described with 
reference to amplitude modulation. However, it should be understood that 
any other modulation method, for example, frequency modulation or pulse 
code modulation, can be employed in the system in accordance with the 
present invention by changing the demodulating circuit.