US2293521A - Electro-optical system - Google Patents

Description

ELECTRO-OPTICAL SYSTEM Filed Dec. 29. 1939 2 Sheets-Sheet 2 In venfor:

Patented Aug. 18, 1942 ELECTED-OPTICAL SYSTEM Kurt Thiim, Berlin-Lichterfelde, Germany, assignor to Fernseh G. m. b. IL, Berlin-Zehlendorf, Germany Application December 29, 1939, Serial No. 311,611

In Germany January 11, 1939 Claims.

I The invention relates to electro-optical systems and more particularly to a method of and means for producing synchronizing signals for television transmission.

It has been proposed to provide rotating discs with an appropriate number of radial slots so that at certain moments the light of a lamp will reach a photoelectric cell where an electrical signal will be generated.

For a high definition television system a great number of radial slots will be necessary, for example 441 slots for a television transmission according to the present U. S. A. and German rules. The light will pass through each of those 441 slots during the transmission of one picture, that is in sec. Therefore the disc usually is running with 1500 rev./min. It is very essential that the distance between adjacent radial slots is constant to prevent faulty synchronization.

The difiiculties connected with the construction and manufacture of the aforesaid disc will become apparent by the following example. To obtain a really good picture it is desirable that the beginning of each line is situated exactly below the beginning of the previous line with a tolerance of ti e the length of a picture point. On the other hand it is desirable that the diame ter of the rotating slotted disc is made not too large. Suppose the slots are arranged in a circle with a diameter of 200 mm. then the distance between the centre lines of two adjacent slots is about 1.5 mm. If the length of a line is equal to 500 picture points, corresponding to the present U. S. A. and German television system then the time interval required for the transmission of 500 picture points will correspond to a distance of 1.5 mm. on the disc. Therefore it is necessary to manufacture the disc so that the maximum tolerance of the distance between two adjacent slots is not more than Hitherto it has not been possible to manufacture discs with an aforesaid accuracy and therefore the edge of thetransmitted pictures was not a :i;0.0003 mm.

straight line but slightly notched owing to the tro-optical impulse generator which does notembody the disadvantages h'ereinbefore noted.

influence of a faulty location of the slots on the rotating disc by using an optical integrating device so that each electrical impulse will be generated not by a single optical impulse but by the sum of two or more simultaneous optical impulses, generated by different slots of the rotating disc.

Further objects of the invention will become apparent from the following description of embodiments of the invention.

The invention is illustrated in the attached drawings in which- Fig. 1 diagrammatically illustrates a system for generating electrical synchronizing impulses embodying the invention,

Fig. 2 illustrates a different form of the electro-optical system for generating electrical synchronizing pulses which may be used in place of that shown in Fig, 1,

Fig. 3 shows the form of slotted diaphragm used in the embodiment of Fig. 1,

Fig. 4 and Fig. 5 explain the principles of the optical integration.

Referring to Fig. 1 there is shown the basic plan of an electro-optical apparatus for carrying out the invention. The light of the light source I passes the condenser 2 and illuminates the slotted diaphragm 3. The diaphragm bears on the surface opposite to the light source a certain number of radial slots, for example 20. The slots are arranged in an arc of a circle. The light will fall through all slots of the diaphragm simultaneously on the rotating disc 5. The rotating disc bears 441 radial slots (corresponding to the present U. S. A. and German television rule of 441 lines per picture) which are arranged in a circle, so

that in certain positions of the rotating disc all slots ofthe diaphragm are in register with corresponding slots of the disc. If the slots of the diaphragm and of the rotating disc are in register then the light passing through the plurality of slots will be collected by means of an optical lens 6 on the photosensitive surface of the photoelectric cell 1. If the rotating disc moves further on, then the slots of the diaphragm and of the disc will not be'in register anymore and no light will reach the photoelectric cell, but when the rotating disc moves still further on, then at a certain position the slots of the diaphragm and of the disc will be in register and another optical impulse will reach the photoelectric cell and generate another electrical impulse.

Fig. 2 shows a section through another'embodiment of the invention. Corresponding parts in,

An object of the invention is to eliminate the Fig. 1 and Fig. 2 are characterized by the same numbers. The light from the light source I passes the condenser 2 and illuminates the slots on the diaphragm 3. The slots are arranged in three concentrical arcs of a circle and there are 20 radial slots in each are. An image of the illuminated slots is projected on the surface of the rotating disc 5 by means of an optical arrangement 8. The projected image of the slots may be larger or smaller than the actual size of the slots on the diaphragm. The slots on the diaphragm are so arranged, that at certain positions of the rotating disc their image is in register with the slots of the disc 5. Then the light from the source I will pass the disc 5 and will be integrated and collected by means of the optical lens 6 onto the surface of the photoelectric cell 1, thus gencrating an electrical signal in the associated circuits. According to the rotation of the disc, the slots will be alternately in register and not in register respectively and a series of electrical impulses will be generated.

Fig. 3 shows a plan elevation of the diaphragm 3, the radial slots 4 can be seen arranged. in an of the rotating disc.

neglected with reference to the width of the slots S1 and Si then the resulting common optical signal will be formed according to curve 0. The forefront of the signal illustrated by the curve c consists of two principal parts. The lower part will correspond to the signal generated by the leading edge'of the slot 81 and-the upper part of the aforesaid forefront will correspond with the signal generated by the leading edge of the slot S1.

Fig. 5 shows in a similar way the generated signals, when the width of the slot B: may not be neglected with reference to the width of-the slots S: and S2. It may be assumed that the slots S2 and S2 of the rotating disc are displaced by the same distance a as the slots S1 and S1 illustrated in Fig. 4. The leading edge of the slot S2 when passing over the slot B2 will cause a signal according to the curve d, whereas the leading e. By integrating these two signals-there will be obtained a resulting signal corresponding to the curve I. The middle part of the forefront of that signal is steeper than the upper or lower part of the forefront. For obtaining a maximum steepness in the middle part of the forefront it is essential that the width of the slot in the diaphragm is to some extent larger than the maximum faulty dislocation of the slots on the disc. Furthermore the signals generated in the photoelectric cell should be fed to an amplitude limiting device which becomes conductive when the amplitude of the electrical signal reaches about half the value of the maximum amplitude, thus obtaining the best possible accuracy of the derived electrical signals.

In an embodiment of the invention there is situated a diaphragm between the light source and the rotating disc very closelyto said disc. The diaphragm contains a certain number of holes which are shaped similar to the slots of the disc. These holes are arranged in the same edge-S2 will generate a signal according to curve way as the slots on the rotating disc, the number of the holes in the diaphragm corresponding with the number of the optical signals which are tobe generated simultaneously.

phragm (for example scratches in a silver layer) are situated on the'adjacent sides of the disc and the diaphragm respectively.

In a further embodiment of the invention there is used a light source, comprising a lamp with a ribbon-shaped filament. An image of that filament is projected by optical means on the slots In general it will be useful to provide such optical means, that the obtained image is larger than the actual size of the filament. The length and the breadth of the ribbon-shaped filament are chosen in accordance with the illuminated area on the slotted disc. The length of that area depends upon the radial length of the slots and the distance and number of the concentric circles and the breadth of that area depends upon the number and the distance of the simultaneously illuminated slots of each circle.

In a still further embodiment of the invention I the rotating disc also carries slots for gener ating the frame signals. The optical frame signals illuminate the same photoelectric cell as the line signals, so that the combined line and frame impulses are generated in the circuits connected with the output of said cell.-

What I claim is:

1. Electro-optical apparatus for generating periodical electrical signals comprising a light source, adiaphragm disposed in the path of light from said source and having a plurality of openings therein, a rotating disc having a series of slots therein, said disc being'so arranged that a plurality of said slots come intermittently in registry with said openings thereby to open a plurality of paths for light from said source and to produce a plurality of separate trains of optical signals, and photosensitive means disposed in said last-named light paths for transforming said trains of optical signals into a single train of electrical signals of improved timing accuracy by virtue of the integration of said plurality.

by to permit the light of said images to pass through said, disc and to produce a plurality of trains of optical signals, and photosensitive means adapted to receive the light from said images passing through said disc for transforming said trains of optical signals into a single train of electrical signals of improved timing accuracy by virtue of the integration of said plurality of optical signals.

3. Electro-optical apparatus for generating periodical electrical signals comprising a light source, a diaphragm disposed in the path of light from said source and having a plurality of openings therein, a rotating disc having a series of slots therein and arranged in close proximity to said diaphragm, said disc being so arranged that a plurality of said slots come intermittently in registry with said openings thereby to open a plurality of paths for light from said source and to produce a plurality of trains of optical signals, and photosensitive means disposed in said last-named light paths for transforming said trains of optical signals into a single train of electrical signals of improved timing accuracy by virtue of the integration of said plurality of optical signals.

4. Electro-optical apparatus for generating periodical electrical signals comprising a light source, a diaphragm disposed in the path of light from said source and having a plurality of openings therein arranged along concentric circles, a rotating disc having a series of slots therein arranged along a concentric circle, said disc being so arranged that a plurality of said slots come intermittently in registry with said openings thereby to open a plurality of paths for light from said source and to produce a plurality of trains of optical signals, and photosensitive means disposed in said last-named light paths for trans-'- forming said trains of optical signals into a single train of electrical signals of improved timing accuracy by virtue of the integration of said plurality of optical signals.

5. Electro-cptical apparatus for generating periodical electrical signals comprising a light source, a diaphragm disposed in the path of light from said source and having a plurality of openings therein, equal numbers of said openings being arranged in rows along concentric circles and corresponding openings being arranged along the same radii, a rotating disc having a series of slots therein, said disc being so arranged that a plurality of said slots come intermittently in registry with said openings thereby to open a plurality of paths for light from said source and to produce a plurality of trains of optical signals, and photosensitive means disposed in said lastnamed light paths for transforming said trains of optical signals into a single train of electrical signals oi! improved timing accuracy by virtue of the integration of said plurality of optical signals.

KURT THOM.

CERTIFICATE OF CORRECTION. Patent No. 2,295,521. August 1 19u2.

KURT 15311.

It is hereby certified. that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, sec- 0nd column, line 11;, for 'impulses" read '-pulses-; andthat the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 20th day of October, A. D. 19%.

Henry Van Arsdale, (Seal) Acting Conmiissioner of Patents.

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