US2285593A - Scanning method and device - Google Patents

Description

June 9, 1942 R. D. LEMERT v 2,285,593

v SCANNING METHOD AND DEVICE Filed July 24, 193'? 2 Sheets-Shea*l l Il l I IHIIIIIIJIII June 49, 1942. R D. .I EMERT 2,285,593

SCANNING METHOD AND DEVICE Filed July 24, 193'? 2 Sheets-Sheet 2 Patented June 9, 1942 UNITED STATES PATENT OFFICE scANNING METHon'AND DEVICE Ralph D. Lemert, Los Angeles, Calif. Application July 24, 1937, serial No. 155,542

s claims. `(c1. 17a-.7.6) f

My invention relates to scanning methods anddevices applicable to television systems.

In the scanning of an object or anY image in a visual field at a sending station, or in scanning a eld at a receiving station to develop the corresponding image, important problems involved relateto illumination of the eld by the projected light, to definition of the image,'and to the mechanics of the scanning device. The general object of my invention is to achieve relatively intense eld illumination and exceptional image definitionV with means having several mechanical advantages over prior art devices.

The present invention provides a television scamiing apparatus characterized by means for concentrating light from a source into a beam small enough in cross-section for scanning with the required definition, means for displacing on the eld each successive line of a pattern in spaced relation to its predecessor without intersecting its predecessor, and means for rotating each successive path of a pattern with respect to the preceding path.

The present invention further provides a method of scanning a field for television and the like, characterized by concentrating -light from a source into a beam small enough in crosssection for scanning with the required definition, displacing on the eld each successive line of a pattern in spaced relation to its predecessor Without intersecting its predecessor, and rotating each successive path of a pattern with respect to the preceding path.

In addition to rotating and offsetting the successive paths on the scanning field, I have the further object in the preferred form of my invention of causing the scanning lines to skip over the eld instead of progressively scanning the field in a minute manner. More specifically,l it is my purpose in my preferred practice to scan the field systematically with relatively widely spaced lines several times within the usual frame period for the purpose of reducing the actual scanning rate without causing flickering, there being no definite points dividing the scan-- ning process into the usual definite frames. In fact, the employment of skip scanning with progressive rotation and osetting of the successive scanning lines producing multiple scanning intersections reduces the scanning .rate necessary for effective transmission to such an extent that my device mayrbe used for television at frequencies too low to be operative in prior art practices. It has been demonstratedthat the frequency enough to eliminate the various diiliculties associated with high frequency transmission that have handicapped the development of television.

- The frequency may be low enough, for example,

to' eliminate the necessity for co-axial cables and to permit transcontinental broadcasting from a. single transmitter.

Each pattern that spansfthe field comprises a series of spaced non-intersecting lines in which each line is both rotated and shifted laterally with respect to its predecessor. In my preferred practice I also rotate each of the patterns of lines relative to the preceding pattern and thereby produce numerous intersections with the lines of the preceding pattern and scan areas missed by the preceding pattern.

An important feature of my scanning method is that it may be carried out by means continuously rotating in continuous directions about two axes at uniform rates of rotation.

Other objects and advantages of my invention will be apparent in the detailed description and claims to follow, taken with the accompanying drawings, in which:

Fig. 1 is a diagrammatic `.representation of one form of my scanning arrangement, the scanning mechanism and the plane of the scanning field being shown in perspective.

Fig. '2 is a similar view shown in plan.

Figs. 3 to 5 indicate how the mirrors on the rotary scanning means may be progressively inclined to provide lateral displacement of lines.

Fig. 6 schematically indicates the method of scanning achieved by progressively inclining the mirrors in the manner indicated in Figs. 3 to 5.

Fig. 7 is a side elevation of a second form of scanning mechanism.

Fig. l8 is a fragmentary side View, partly in section, of the same mechanism with certain parts rotated from the positions of Fig. 7, and

Fig. 9 is a fragmentary section taken as indicated by the line 9 9 of Fig. 8.

ithrough a mask means 22 positioned to In the arrangement shown in Figs. 1 and 2, a converging beam of lightl 20 from a light source, conventionally shown at 2|, passes cut off stray rays of light, strikes the periphery of an annular series of mirror units 23, and is reflected therefrom as a beam 24 that converges to form a flying light spot 25 on a screen 26.

The mirror units 23 are mounted face outward on the periphery of a.mirror body 29 thatV ro.-

tates about a primary axis A-A, lthe body roof operation of my system may be low tating on bearingsv` concealed in a bracket 30. The bracket 30, having arms 3|,

is carried by a base 32 that is revolvably mounted on a gear box 33,'the base being adapted to rotate about a secondary axis B-B intersecting the primary axis AA. It is important to note that the secondary axis also intersects the annular series of mirror umts 23 and that the light beam 20 is directed to the area on the periphery of the mirror body 29 that includes the intersection. By virtue of such disposition, the light beam continuously bears on the periphery of the annular series of mirrors even though the mirrors simultaneously rotate about two axes.

A drive shaft 35 driven by external means (not shown) actuates mechanism within the gear box 33 for rotating the base member 32 about the secondary axis, and actuates additional mechanism in the gear box, as well as in the base member 32 and in the bracket 30, for simultaneously driving the mirror body 29 about the primary axis, the details of which mechanism being omitted for the sake of clarity.

The mirror units 23 will be of equal size and preferably arranged in a contiguous series. For the purpose of progressively displacing laterally the succeeding lines of a scanning frame, I incline the successive individual mirrors progressively with respect to the primary axis. Figs. 3 to indicate in an exaggerated manner the inclination of the mirrors. The angles of the mirrors vary in a uniformly graduated manner from one extreme indicated bythe inclination of Fig. 3 to an opposite extreme indicated by Fig. 5, Fig. 4 representing the middle point of the series. Preferably, the mirrors of the series will be successively inclined to progress in the manner stated so that if there are forty-five mirrors, Fig. 3 represents mirror No. 1, Fig. 4 represents mirror No. 23, and Fig. 5 represents No. 45. The mirrors may, however, be arranged vin other than progressive order.

The continuous light beam 20 will be reflected from the annular series of mirrors as a series of successive beams, each beam sweeping across the screen 26. Since it is contemplated that no two successive spots will appear simultaneously on the screen, the angle of separation of each mirror with respect to the succeeding mirror must' be taken into consideration in the spacing of the screen from the scanning device. Preferably, the spacing will be such that a spot will enter one margin of the screen substantially instantaneously after the preceding spot disappears from the opposite margin of the screen. Since in a square or rectangular screen the longest scanning path will be across a diagonal of the screen, the angle from the series of mirrors subtended by the diagonal will be the preferred angle of separation of the successive reected beams.

The general direction of movement across the screen of a flying spot will be determined primarily by the instantaneous plane of rotation of the annular series of mirrors. Since the plane of the mirrors is rotating about the secondary axis while the mirrors are simultaneously rotating about the primary axis, the path of the flying spot will be the resultant of two components of motion, the successive paths forming a series of curves each of which is both offset and rotated with respect to its predecessor. The degree of curvature of each of the lines will depend upon the ratio A B in which A represents the speed of rotation about the primary axis, and B represents the speed of rotation about the secondary axis. If this ratio is raised, the curvature of the line decreases and at a relatively high ratio of A to B the lines will have the appearance of straight lines. L

gli 2B If there are forty-ve mirrors in the annular series and the mirrors rotate 120 times per second about the primary axis and '7.5 times about the secondary axis, there will be three hundred and sixty lines to a frame. The number of frames per second will be twice B, or, for the values.

given, fteen frames per second. The time for scanning one line will equal mA second, or 541W) second for the assumed values. If the total mirror area' and the size of the screen are constant, and if the size of the flying spot varies inversely to the number of lines, the screen illumination, I, will equal Am lc being some constant.

It is` apparent from the foregoing equations that decreasing B relatively; to A will increase the number of lines to a frame with sacrifice of screen illumination, and reducing the number of mirrors without changing the total of the mirror areas will increase'the intensity of the screen illumination at the cost of reducing the number of lines to a frame. It is important to note, however, that decreasing m increases I to a relatively great extent. Thus, if B is decreased 75%, and m is decreased 50%, the net result will be that the number of lines will be increased and I, the intensity of the screen illumination, will be quadrupled. These statements bring out an important feature of my invention, the elciency of screen illumination inherent in themethod of scanning.

In such a scanning arrangement, it is contemplated that mirror No. 1 will cause a scanning spot to sweep across the screen near one edge of the field, and the mirror No. 45 will cause a spot to sweep across the field at an opposite edge, with the intervening mirrors sweeping the screen along the paths successively displaced laterally towards said opposite edge.

If there were no rotation about the secondary axis, the successive scanning lines could be represented by a true rectangle. Rotation about the secondary axis, however, results in a traversing pattern that may be regarded as a distortion of a rectangle, the degree of distortion varying inversely with the ratio of A to B. Fig. 6 shows diagrammatically two successive traversing patterns 31 and 38 respectively, produced by two successive complete rotations of the inclined mirrors about the primary axis, each traverse being composed of lines progressively rotated and additionally progressively displaced laterally to shift across the screen, the dotted lines being used to indicate one complete traverse and the full lines indicating the succeeding traverse partially completed.

The line 39 represents the sweep occasioned by the mirror No. 1; the line i8 represents the sweep occasioned by the mirror 45 in a single rotation of the mirror body about the primary axis; and the line 4| represents the sweep occasioned by the mirror No. 1 in the succeeding rotation about the primary axis. Itwill be noted that the lines are progressively inclined or' rotated from the disposition of the line 39 at the beginning of one traverse to the line 4l at the beginning of the next traverse, and that the lines described in each succeeding rotation of the mirrors about the primary axis intersect at several points all of the lines produced by the previous complete rotation about the primary axis. y

Since the number of mirrors is limited, the lines of one traverse will be spaced relatively far apart, too far to adequately define an image; but

since succeeding traversing series of the lines are both rotated and displaced laterally, each succeeding series will cover additional portions of the image and define the image with progressive,

neness of detail. It is apparent that no definite number of traverses constitute a frame, since there is no one point at which it may be said that one complete scanning of the image leaves oif and a second complete scanning begins. An important feature of this form of my invention, as will be understood by those familiar with the art, is that since there is no apparent division between scanning frames, an image may be scanned without icker at relatively low speeds. It may be desirable that the image be traversed a suicient number of times to define the image adequately in the time interval allotted to the conventional frame; i. e., a period not greater than one-tenth of a second, but in contradistinction to other systems, it is not fatally necessary to completely define the image in the usual frame period because the scanning pattern of one frame period supplements rather than merely repeats the scanning pattern of the preceding frameperiod, and the observer will unconsciously integrate patterns, even when separated by intervals substantially greater than that of visual sensory retention.

The general direction in which a pattern of lines traverses the field depends upon the mean position of the circular series of mirrors with respect to the B axis of the mechanism during the period of traverse. During one revolution about the B axis the field will be scanned by a number of patterns equal to and the direction of traverse will shift progressively through 360; If B is commensurate with A in the sense of being an even divisor of A, the patterns of lines described in one complete rotation of the direction of traverse, i. e., one complete rotation of the mechanism about the B axis, will register exactly with the corresponding patterns of lines during the preceding complete rotation of the direction of traverse. It will be apparent to those skilled in the art that the ratio of A to B may be such that the initial entering point `of the rst frame or pattern at the beginning of one rotation of the mechanism about the B axis may be advanced around the periphery of the field with respect to the initial i entering point of the first frame of the preceding rotation of the mechanism about the B axis.

The mechanism may be so arranged, then, that during one rotation about the B axis the scanvThe shaft 81 is mounted in the casing 65, and carries on its opposite ends yning beam explores areas -not traversed `during the preceding rotation of the mechanism about the B axis. The result, of course, is better image definition.

vWhile the description of my method of scanning has been directed primarily to the development of an image on a screen, it will be readily understood that the same principles apply to the scanning of a scene or other visual field at a transmitting station, and, further,` it will be understood that the principles of the method may be applied to scanning problems outside of television. l

Figs. 7, 8, and 9 show a second embodiment of the mechanical means for carrying out my method of scanning. In this form of the device, the mechanism is mounted on a base plate 45 carried by a pair of rings 46. the rings being rotatably embraced by complementary supporting rings 41 having legs 48. In the particular construction shown, the supporting rings 41 have removable annular flanges 49 secured by screws 58. Preferably, the supporting rings 41 will carry radially disposed thumb screws 5| (Fig. 7) for releasably securing the rings 41 at selected positions.

A forward end plate 54 and a rear end plate 55`are mounted on the base plate 45 in spaced relation thereto by suitable legs 56. The legs may be in the form of rods, as shownweach leg having a reduced lower end 51 inserted in a complementary bore 58 in the base plate 45, the reduced end being secured by a nut 59. To pro-v vide for adjustment in the spacing of `the end plates relative to the base plate 45, `the rods may slidingly extend through complementary apertures (not shown) in the end plates, the rods being provided with nuts 69 and 6| engaging the upper and lower edges respectively of the end plates. Preferably, the end plates Will be tied together by interconnecting rods 63 having nuts 6d.

A casng 65, which may be cylindrical in configuration, is revolvably carried by the two end plates, the casing being supported by a bearing 66 in the forward end plate 54 and by a second bearingY 61 in the rear end plate 55.

A motor 68 having a base 69 mounted on the base plate 45 has a drive shaft 10 connected by a suitable coupling 1I to a driven shaft 12, the driven shaft passing through an aperture 13 in the rear end plate 55 and extending axially into the interior of the casing 65. The shaft 12 has an enlarged portion 15, at the opposite ends of which thrust bearings 16 for the shaft are mounted in the casing. Rearwardly from the end plate 55 a relatively small sheave 11 is keyed to the shaft 12, and forwardly from the end plate 55 a relatively large sheave 18 is keyed to the periphery of the casing 65. Below the end plate 55 are diagonally disposed sheaves 19 carried by brackets 8 0, the brackets being secured to the base plate by suitable bolts 8|. A belt 84 passing from the sheave 11 around the sheaves 19 to the sheave 18 causes the casing 65 to be .driven in the opposite direction from the shaft 12.

A beveled gear 85, mounted on the linner end of the shaft 12, meshes with a second beveled gear 86 that is keyed to a transverse shaft 81. in suitable bearings 88 exteriorof the casing a pair of relatively large sheaves 90. By means of belts 9| the sheaves 90 drive complementary relatively small sheaves 92 mounted on the exterior of the ca sing on the opposite ends of a second transverse shaft 93. The shaft 93 is mounted in suitable bearings 84.

Mounted on the shaft 93 and non-rotatably related thereto by a suitable key 95 is a circular mirror body 96 extending through longitudinal apertures 91 of the Wall of the casing 65, the mirror body being provided with an annular series of mirror units 23a on its periphery, as previously described. The forward end plate 54 is provided with a suitable aperture, 98 communicating with the interior of the casing 65 to permit light to be received and reflected on the periphery of the mirror body 96 in the manner and for the purposespreviously described.

The mirror body will be rotated at a relatively high speed about the shaft 93 as its primary axis and will simultaneously be rotatedY at a lower speed about the axis of the casing 65 as its secondary axis. A train of gears may be employed, if desired, instead of sheaves interconnected by belts.

In the transmission of an image by such an arrangement, the image developed on the screen at the receiving station will be rotated from its proper vertical disposition if the annular series of mirrors at the receiving station are not in syn'- chronism with the corresponding annular series of mirrors at the broadcasting station. The received image may be readily corrected in disposition by simply loosening the thumb-screw i and rotating the whole assembly in the supporting rings 41.

The specic mechanisms and procedures described in detail for the purpose of illustrating the principles of my conception suggest a substantial range of change and modication without departing from the spirit of my invention. I reserve the right to all such changes and modifications that properly come within the scope of my appended claims.

I claim as my invention:

1. A television system, including: a series of mirrors arranged in substantially a circle; means to rotate said series of mirrors about the axis of said circle; means to rotate the series of mirrors simultaneously about a secondary axis intersecting said series of mirrors; and means to direct light against the rotating series of mirrors in the vicinity of the intersection thereof with said secondary axis, thereby producing reflected beams successively sweepinga field at progressively inclined angles, said mirrors being in planes disposed at various angles relative to the direction of said first axis, whereby the series of sweeping beams produced by one rotation about the rst axis will traverse the field from side to side, the direction of traverse changing with each successive series to produce intersection of the paths of sweep.

2. A television system, including: a series of mirrors arranged in substantially a circle, all of said mirrors intersecting a common plane perpendicular to the axis of said circle; means to rotate said mirrors simultaneously about two axes, the rst axis being the axis of the circle of mirrors, the second axis being perpendicular to the rst axis and intersecting both the first axis and said circle of mirrors; and means directing light continuously onto the periphery of said circle of mirrors to strike each mirror in turn at the intersectionthereof with said second axis.

3. A television system, including: a source of light; means for concentrating light from the source into a beam small enough in cross-section for scanning with the required denition; and

means for deflecting the beam in successive scanning sweeps to produce a scanning pattern in which successive lines are progressively rotated i in' disposition, each successive line of a pattern being displaced laterally on the eld from its predecessor without intersecting its predecessor.

rand in which the time interval between successive sweeps is substantially less than the time required l for one sweep.

4. A method of scanning a field for television and the like, .said method being characterized by concentrating light from a source into a single beam small enough in cross-section for scanning with the required denition and deflecting the single beam in successive scanning sweeps across the field from one edge of the eld to another to produce a scanning pattern in which successive lines produced by said successive sweeps are progressively rotated in disposition and progressively displaced laterally without intersection.

5. A method as set forth in claim 4 in which the eld is scanned by successively rotated patterns of relatively few lines a sufiicient number of times to achieve image definition within the usual frame period.

6. A method as set forth in claim 4 in-which entering points of initial scanning lines of the successive scanning patterns are advanced progressively around the periphery of the eld.

7. A method as set forth in claim 4 in which entering points of initial scanning lines of the successive scanning patterns are advanced progressively around the periphery of the field, the advance of each successive entering point being less than of the circumference of the field.

8. A television system, including: a series of mirrors arranged in substantially a circle, all of said mirrors intersecting a common plane perpendicular to the axis of said circle, most of said mirrors lying in planes cutting said axis in a graduated series of angles; means to rotate said mirrors abouty said axis of the circle; means to rotate said mirrors simultaneously about a second axis perpendicular to said first axis in said perpendicular plane; and means directing light continuously onto the periphery of said circle of mirrors at the intersection thereof with said seconcl axis. I

RALPH D. LEMERT.

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