US2185139A - Scanning apparatus - Google Patents

Description

Dec. 26, 1939. F. L. WURZBURG. JR 2,185, 39

SCANNING APPARATUS Filed April 23, 1937 4 Sheets-Sheet 1 W A \w Linn Jim? i= Fm \NVENTOR firm as lav/.5- li uizw/ng 72 Dec. 26, 1939. F. L. WURZBURG. JR 39 SCANNING APPARATUS Filed April 23, 193'! 4 Sheets-Sheet 2 //////L// ///////%/Zl ATTORN SCANNING APPARATUS Filed April 23, 1937 4 Shee'ts-Sheet 3 7% w m Q N m R liil Dec. 26, 1939. F. 1.. WURZBURG, JR

SCANNING APPARATUS Filed April 23, 1937 4 Sheets-Sheet 4 Patented Dec. 26, 1939 UNITED STATES PATENT OFFICE SCANNING APPARATUS poration of Ohio Application April 23,

3 Claims.

This invention relates to electro-mechanical scanning apparatus and provides an apparatus of this character which is particularly adapted for use in making color printing plates.

In the co-pending application of Arthur C. Hardy, Serial No. 126,110, filed February 17, 1937 (and assigned to the assignee of the present application) on which Patent No. 2,136,340 was issued on Nov. 8, 1938, there is disclosed a method in which photo-electric scanning mechanism is employed for making a contrast image of a picture on a photo-sensitive surface. .This method produces superior contrast images, which are particularly advantageous for controlling the etching of half-tone plates for printing. It possesses a number of other advantages. For instance, half-tone plates can be made without the use of screens, thus eliminating the screen lines in the image. However, when three or more plates, for use in color printing, are made from contrast images produced by the electro-mechanical scanning method, the prints produced are apt to present moir effects, even though no screen has been employed in the method.

According to the present invention, I provide an improved scanning apparatus, which avoids these moir efl'ects. More particularly, the apparatus provides for producing three contrast images, or color separation images, of the same subject, the apparatus being so constructed that both the subject to be scanned and the photosensitive image surface can be readily turned through the same angle, so that the scanning lines on each of the color separation images lie at an angle of, say, 60 to the scanning lines on other images. By scanning lines I mean the lines which the recording light makes in its movement over the photographic plate. More particularly, the present apparatus comprises a rectilinear scanning apparatus in which both the subject to be scanned and the photographic plate can be rotated through given, equal angles.

The scanning apparatus which I have invented is of especial value when used for carrying out the method described in Arthur C. Hardy application Serial No. 121,466, filed January 21, 1937 (which has been assigned to the assignee of this application) on which Patent No. 2,165,168 was issued on July 4, 1939. In that method, a color-separation image is made by the additive and subtractive combining of three master images and the combination is effected by means of an electro-mechanical scanning apparatus. When that method is carried out by means of the scanning apparatus which I have 1937, Serial No. 138,520

invented, the combining of the three master images and the production 01' a contrast image to be used for engraving may be efiected simultaneously in a. single scanning operation.

The present scanning apparatus has a number oi other important advantages which will appear from a detailed description of an illustrative apparatus embodying my invention which is shown in the accompanying drawings:

Fig. l is a top view 01. the apparatus;

Fig. 2 is a plan view of the bed plate of the carriage for the optical parts:

Fig. 3 is a transverse section of the apparatus on the line 3'3 of Fig. 1;

Fig. 4 is a transverse section on the line 4-4 of Fig. 2 showing the means for traversing the optical apparatus:

Fig. 5 is a detailed top view oi one of the prisms of the optical apparatus showing the supporting tube section on the line 55 of Fig. 3;

Fig. 5A shows a detail of modified optical systern;

Fig. 6 is a. partial end elevation of the apparatus;

Fig. '7 is a partial section on the line 1l of Fig. 1, showing the mechanism for traversing the carrier;

Fig. 8 is a transverse section on the line 8-8 of Fig. 6;

Fig. 9 is an enlarged and broken section on the line 9-9 of Fig. 2 showing the supporting rails for the bed plate carrying the optical apparatus, and

Fig. 101s a diagram 01' the electric circuits.

The apparatus illustrated consists of a picture carrier A and an optical carrier B slidably mounted for straight line movement in directions at right angles to one another. The picture carrier has a frame consisting of two rods Al secured together by cross-pieces A2 and slidably mounted in standards ll secured to the table Ill. The optical carriage B consists of a bed plate Bl located below and partly under the picture carriage A and a number of U-shaped arms B2, extending over the picture carriage A. The bed plate Bl of the optical carriage is slldably mounted on rails II which are secured to the table "I and extend at right angles to the rods Al of the picture carriage.

Automatic means are provided for reciprocating the picture carriage in the direction of the rods Al and for giving the optical carriage a short movement in a rearward direction along the rails I! at the end of each traversing movement of the picture carriage. These means provide for movement oi the picture carriage at a uniform rate throughout its traversing movements in each direction.

The means for moving the picture carriage include a worm A3 having an unthreaded end Al fixed in a detent A5 on one of the cross-pieces A2. The worm A3 meshes with an internally threaded nut i3 which is rotatably mounted in one 01' the standards II by means of bearings l3a, which are arranged to take the thrust in both directions. Nut l3 may be driven from a constant speed, reversing motor (not shown), connected to the picture carriage A in any suitable, conventional manner for reversing the motor at each end oi the travel of the carriage. In the form of apparatus shown in Fig. 7, the nut i3 is secured to a pulley I4 which is driven from the motor by belt l5. However, suitable gearing may be employed instead.

The means for moving the optical carriage B are actuated by the movement of the picture carriage A. At the end of each traversing movement of the picture carriage A, one or the other of two adjustable stops Alli (Fig. 6) strikes one or the other of two arms 20, one of which is rotatably mounted on a shaft 2i journalled in a standard 22 at the front of the table and carrying a worm 23 meshing with a nut B3 carried by the bed plate Bi of the optical carriage. The arms 20 are connected by gear segments 24 and one of them carries a pawl 25 engaging a ratchet 26 fixed on the shaft 2i. The arms 20 are normally held in the position shown in Fig. 5 by a spring 21, but, when either of them is struck by one of the stops All], the pawl turns the ratchet to cause a slight rotation of the shaft 2| and a small rearward movement of the optical carriage B.

As shown in Fig. l, the picture carriage A has four circular picture-supporting tables Al i, which may comprise metal rims and glass centers. These tables are set in arcuate recesses in the cross-pieces oi the carriage A. Each table has six equally spaced holes Alt formed in its rim, any diametrically opposite pair of these holes being adapted to engage cooperating pins mounted on the cross-bars of the carriage. At least one of the tables, and, in the form shown, for use in the method described in Patent No. 2,165,168, each of the three tables at the left supports a continuous-tone transparency Ali which is adapted to be scanned. The table at the right, in Fig. 1, supports a photo-sensitive film or plate Alli. The transparencies and the photo-sensitive film are all of the same size and shape.

As bestshown in Fig. 3, at least one of the arms B2 of the optical carriage B, and, in the form shown. each of the three arms B2 at the left in Fig. 1, carries an optical system including a lamp 2I2, a tube B4, a prism B1 and a vertical lens system BB, for directing light of fixed intensity through a small, sharply defined area oi the transparency located beneath the lens system. Instead of employing the tube B4 and the prism B1, an electric lamp 2|2X, having a small filament, may be mounted directly above the lens system B8 as shown in Fig. 5A. Beneath each of the transparencies .there is mounted, an optical carriage B, a photo-electric cell 2. In the optical system of the right-hand table in Fig. i, there is mounted, in place of the lamp 2i2, a recording lamp H6, hereafter described, for forming the image on the photo-sensitive film or plate. Obviously, no photo-electric cell is used beneath this right-hand table.

when three transparencies are to be employed for making a composite or master image, for color work, these may be prepared as described in aforesaid Patent No. 2,165,168. In this case, an electrical circuit is provided, also as described in said application, for adding or subtracting the tones in the transparencies which represent the color values to be combined in making the master image on the photo-sensitive film or plate Alli. This circuit is shown in the lower part of Fig. 10.

Three scanning lights 2l2A, U23 and 2I2C are connected in parallel in a circuit 2H. Connected with the three lights are three rheostats 2I4A, H413 and MIC which control the intensity of the three lights. Suitable dials (not shown) are provided for indicating the setting of the rheostats.

The three photo-electric cells 2|IA, 2IIB and H10 are connected in parallel in an electric circuit 218 containing a source of electro-motive force 2i9. These photo-electric cells are connected into the circuit IIB through three reversing switches MIA, 2MB and IZIC, which may be set so as to oppose the current passing through any one photo-electric cell to that passing through the others. The symbols an are indicated on the switches. When all three switches are thrown to the position, the currents through all three of the photo-electric cells are passed through the circuit 2" in the same direction (that is, the direction indicated by the arrows on Fig. 10), so that they are added. The throwing or any one of the switches to the position opposes the current controlled by this switch to the current flowing through the switches which are in the positions. As the separate current through each photo-cell varies proportionately to the amount of light falling upon that photo-cell and the resultant current in the circuit H8 is the algebraic sum of the separate currents through the cells. the variations in the resultant current are proportional to the sum 01' the variations in the transparency of the images controlling the photo-cells whose switches are in the position less the corresponding variations in the transparency of the image controlling the photo-cell whose switch is in the position; or, if two of the switches are in the position, the variations in the resultant current are proportional to the variations in the transparency of the image controlling the photo-cell whose switch is in the position less the sum of the corresponding variations in the transparency of the images controlling the photo-cells whose switches are in the position. This resultant current in the circuit 2l8 is employed to flash the lamp H6 which forms the image on the photo-sensitive surface Alli (Fig. 1).

It will be understood that instead of employing the variable recording lamp I IS, a fixed light provided with a suitable light valve, or similar inertialess recording device may be used, as an equivalent.

When recording lamp H5 is used, it illuminates a shield I I1 containing a long narrow slit or aperture. A lens system B8 focuses an image of the slit on a recording film Ali. The lamp is a gasdischarge lamp having no afterglow. The length of the image of the slit is equal to the distance that the optical carriage B is moved rearward each time carriage A reaches one end of its travel, so that, as the mechanism operates, the image of the slit scans the entire area of the recording film without any overlap. The length of the image or the slit on the recording film determines the width of the elemental areas of the contrast image produced on the recording him. In this connection, it should be noted that the elemental areas are all of the same width. The lengths of the elemental areas are determined by the time length of the cycle of the recording lamp H8: and the proportion of black and white which each elemental area contains is determined by the time during which the recording lamp H6 is lighted and the time periods during which it is extinguished during one cycle. These time periods are controlled by the light passing through the originals to the photo-electric cells 2" by means of inter-connecting electric circuits between the photo-electric cells 2" and the recording lamp Hi.

This may be accomplished to particular advantage by means of the electrical circuit described in Patent No. 2,136,340, mentioned above.

The interconnected electric circuits, as shown in Fig. 10, include a photo-cell circuit which charges a condenser I35, a constant current circuit which discharges the condenser I35, a trigger circuit actuated by the voltage across the condenser I35, and a control circuit for the recording lamp IIG actuated by the trigger circuit. The circuits are so interconnected that the condenser I35 is alternately charged and discharged in a cycle controlled by the resultant current in the circuit 2l8 and controlling the cycle of the recording lamp I I6 and thus the length and character of the elemental areas of the contrast image.

The photo-cell circuit contains the circuit 2I8 and a resistance I42, and is connected to the plate I35a of the condenser so that a positive potential is built up on this plate when the current flows in the circuit 2 I 8 in the direction of the arrow. The current or rate of charge of this condenser in this circuit is proportional to the resultant current in circuit in 2I8.

The discharging circuit is connected to the plate l35a of the condenser and contains a source of electro-motive force I28 opposed to the source of electro-motive force 2H] in the photo-cell circuit. The discharging circuit also contains means for maintaining the flow of current constant and means for stopping and starting the flow of current. These means consist of a vacuum tube I2I whose plate circuit constitutes a part of the discharging circuit. The tube I2I contains a grid I2Ia maintained at a constant potential and holding the flow of current in the plate circuit at a constant value greater than the greatest resultant current in the photo-cell resultant circuit. While greater than the current in the photo-cell circuit, the discharging current should be of the same order as that in the photocell circuit which requires that the tube I2I be operated at very low voltage. The strength of the discharging current may be regulated by a potentiometer I53 connected to the grid I2 Ia and spanning the source of electro-motive force I28. The tube I2I also contains a control grid I2Ib which permits the plate current to flow when it is neutral with respect to the cathode of the tube and cuts oil the flow of current when it is at a certain negative bias with respect to the cathode of the tube. This grid is connected by a variable tap I49 to the resistor I38 of the trigger circuit hereinafter described. When the current is flowing in the discharging circuit, it reduces the positive charge on the plate I35a, because the current in this circuit is greater than the resultant current in the photo-cell circuit by which it is opposed.

In addition to the charging and discharging circuits connected to the plate I350; of the con denser, a means for varying the condenser charge is connected with its other plate I35b. This means is the resistor I38 to which the plate I35b is connected by a variable tap I so that the existence of a voltage drop in the resistor I38 applies a negative potential to the plate I35b equal to the voltage drop between the high end I38a of the resistor I38 and the variable tap I50, while the absence of a voltage drop in the resistor I38 eliminates this negative charge on the plate I351: of the condenser.

The trigger circuit is actuated by the voltage across the condenser I35 in such manner as to cause a drop in potential in the resistor I38 only when the condenser voltage is below a predetermined value (which, for convenience. I shall term the trigger value). The trigger circuit includes a vacuum tube I22 whose grid is connected to the plate I35a of the condenser and whose plate circuit is connected to cause a flow of current through a resistor I31. The resistor I31 is connected through an oscillator and detector (enclosed in dotted lines in Fig. 10) to the resistor I38. The operation of this oscillator and detector (hereinafter described in detail) is such that it causes a flow of uni-directional current through the resistor I38 only when the flow of current through the resistor I3! is such as occurs in the plate circuit of the tube I22 when its grid is below the trigger value.

tial in the resistor I 38 or only when there is no drop in potent al across this resistor, according to the setting of a reversing switch Ill). The control circuit includes a source of electro-motive force I34, the recording lamp II6, and the plate circuit of the tube I28. Current flows in this circuit only when the grid of the tube I26 is neutral. The grid of the tube I26 is connected directly to the low end of the resistor I38 when the reversing switch is in the position marked Neg." on Fig. 10, so that current flows through the recording lamp IIB only when there is no potential drop in the resistor I38. This results in making a negative contrast image of a positive subject. When the switch Hill is thrown to the position marked Pos. in Fig. 10, the grid circuit of the tube I 26 is connected across a resistor I39 in the plate circuit of a tube I25 whose grid is then connected to the low end of the resistor I38. In this case. the current in the plate circuit of the tube I26 and the recording lamp IIB flows only when there is no current in the plate circuit of the tube I25, that is, when there is a potential drop in the resistor I38. In this case, a positive contrast image is made.

The operation of the interconnected circuits which have been described is cyclic and may conveniently be described by beginning at the end of the discharge of the condenser I35. At this time, there is a potential drop in the resistor I38, as the condenser voltage is below the trigger value; if the reversing switch is in the positive position, the recording lamp is on and no current is flowing in the discharge circuit which includes the plate circuit of the tube I2I. The condenser, therefore, becomes charged by the current flowing through the photo-cell circuit, and the charge continues to increase until it reaches the trigger value. At this point, the trigger circuit operates to stop the flow of current in the resistor I38 eliminating the potential drop in this resistor.

The elimination of the potential drop in the re sistor I38 causes three effects: (1) It increases the charge of the condenser by a predetermined value depending upon the setting of the variable tap I50. (2) It eliminates the negative bias on the control grid I2Ib of the tube III and starts the flow of current in the discharge circuit. (3) It operates the control circuit to extinguish the recording lamp II6. After these three efiects of the elimination of the voltage drop in the resistor I88, which take place simultaneously, the condenser voltage decreases, since the current in the discharging circuit is greater than the current in the photo-electric circuit which is opposing it. The discharge of the condenser continues until its voltage reaches the trigger value. The trigger circuit then starts a fiow of current through the resistor I38, causing a potential drop in this resistor. The potential drop in the resistor I38 has three effects: (1) It decreases the charge in the condenser by the same amount as this charge was increased by the elimination of the voltage drop in the resistor I38. (2) It produces a negative bias on the control grid IZIb of the tube I2I sufiicient to stop the flow of current in the discharge circuit. (3) It lights the recording light Hi. This completes the cycle and the charging of the condenser by thecurrent in the photo-cell circuit begins again.

To facilitate the description of the operation of the interconnected circuits which have been described, their operation will first be described on the assumption that the switch 22IA is in position and the switches 22IB and 22IC are open, so that the current in the circuit 2I8 is simply the current through the photo-cell 2I'IA. Under these circumstances the rate at which the condenser is charged is proportional to the amount of light reaching the photo cell ZIIA, as this determines the strength of the current in the photo-cell circuit. The rate at which the condenser is discharged is an inverse function 01' the amount of light reaching the photo-cell, since the photo-cell current opposes the constant current in the discharging circuit. The amount of time required for the discharging and charging of the condenser depends upon the discharging and charging rates and upon a fixed capacity of the condenser and the fixed voltage by which the condenser voltage is raised above and dropped below the trigger value by the voltage drop in the resistor I38 applied to the plate I35b of the condenser through the variable tap I50. Since the time for charging and discharging of the condenser determines the length oi the black and white portions of each elemental area of the contrast image, the device which has been described operates to produce a positive contrast image when the switch I40 is in Pos. position.

When a dark-tone area of the original is between the scanning lamp and the photo-cell, the photo-cell current is weak, so that the charging of the condenser to the trigger value takes a long period of time making a long black area on the contrast image, and the discharge of the condenser is rapid making a short white area. Because of the slowness of the charging, the whole cycle is long, and consequently the elemental area is long.

When a light-tone area of the original lies between the scanning lamp and the photo-cell, the photo-cell current is large, charging the condenser rapidly and opposing the discharging current so that the discharge is slow. This also rearcane sults in a long cycle producing a long elemental area which, in this case, contains a long white area and a short black area.

When a middle-tone of the original is between the scanning lamp and the photo-cell, the current in the photo-cell circuit is approximately half the current in the discharge circuit, so that both the charging and discharging of the condenser are comparatively rapid, giving a short cycle producing a short elemental area which is half black and half white.

No black area of the contrast image can be less than a predetermined length, which is determined by the time required for the maximum photo-cell current to charge the condenser to the trigger value. At the same time, no white area can be less than a predetermined length, which is determined by the time required for the constant current in the discharge circuit to discharge the condenser when the photo-cell current is at its lowest value.

Adjustments may be made to determine the size of the elemental areas in the middle tones and the minimum sizes of the black and white areas as desired in the making of contrast images for etching printing plates. Best results are secured when the discharging current is made equal to the maximum photo-cell current plus the minimum photo-cell current. This or other desired adjustment of the discharging current may be made as follows:

The proportion of black area in the contrast image is indicated by a milliammeter I46 which is connected in the recording lamp circuit and provided with a variable shunt I48 which is adjusted so that the milliammeter reads 100 when the recording light H5 is lighted without interruption, a condition which may be attained by closing the switch I5I to maintain a constant potential on the grid 01' tube I26. The switch I5I is then opened and the indications of the milliammeter I46 are then used as a guide in adjusting the photo-cell current and the discharging current. The adjustment is made after a positive continuous-tone image AIS has been placed on one of tables in Fig. 1. The darkest tone of this image is moved between the scanning lamp 2I2A and the photo-cell 2IIA with the reversing switch I40 in positive position. The strength of the photo-cell current is then adjusted by adjusting the brightness of the scanning lamp 2I2A, for example by a. rheostat 2I4A, until the reading of the milliammeter I46 equals the percentage of black area desired to represent the darkest tone of the original, for example 95%. The lightest portion of the continuous-tone original is then moved between the scanning lamp 2I2A and the photo-cell 2IIA, and the discharging current is adjusted by means of the potentiometer I53 until the reading of the milliammeter I46 is equal to the percentage of. black desired to represent the lightest tone of the original, for example 5%. It is desirable to select the percentages so that 100 minus the percentage selected for the darkest tone equals the percentage selected for the lightest tone, as this results in making the discharging current equal to the sum of the maximum and minimum photo-cell currents. After the relation of the minimum size white and black areas to the size of the elemental area has been adjusted in this manner, the size of the elemental areas is adjusted by varying the position of the variable tap I50 on the resistor I38 to control the frequency of the charging and discharging of the cycle of the condenser I35. The adjustment is most desirably such as makes the elemental areas in the middle tones about equal in size to the elemental areas of an ordinary half-tone contrast image used for the sort of plate for which the contrast image made on the apparatus is to be used.

A further feature of the apparatus illustrated consists in a means for indicating the total amount of black area in a contrast image produced by the apparatus. This is of value since it enables a printer using a plate made from such an image to know the area of the printed plate which must be covered with ink without the experimentation necessary to determine this as in using ordinary printing plates. The means for indicating the total black area consists of an ampere hour meter I50 connected in the circuit of a recording lamp H6. The number of ampere hours indicated by this meter during the making of a positive contrast image on the apparatus, when divided by the number of amperehours which would be required to burn the recording lamp H6 for the same length of time gives the proportion of black area in the contrast image.

In describing the operation of the device, I have referred to placing a positive continuoustone image on the table and producing a positive contrast image when the reversing switch I40 is in "Pas." position and a negative contrast image when the reversing switch I40 is in "Neg. position. It should, of course, be understood that, if desired, a negative continuous-tone image may be placed upon the table and that, in this case, a positive contrast image will be obtained by placing the reversing switch I40 in the Neg. position and a negative contrast image by placing the reversing switch I46 in the Pos." position.

The operation of the oscillator and detector enclosed in dotted line in Fig. 10 is as follows:

When suflicient current flows through resistor I31, the grid of tube I23 is held at a negative potential suflicient to prevent a current in the plate circuit of this tube. When the current through resistor I31 decreases, there is a corresponding increase in the potential of the grid of tube I23. This causes the plate current of this tube to increase. The plate current flows through the primary of transformer III. This induces a voltage in the secondary of the transformer which causes the grid of tube I23 to become more positive by virtue of the potential induced on one plate of condenser I36. This results in a further increase in the plate current and a correspondingly further increase in the grid voltage until saturation conditions are attained. At this point, the current through the primary of transformer Ill becomes momentarily constant and the secondary voltage drops to zero. This causes a decrease in the potential of the grid of tube I23, which produces a corresponding reduction in the current through the primary of transformer Ill. This induces in the secondary of the transformer a voltage of the opposite sign and tends to make the grid of tube I23 even more negative. This process continues until the grid of tube I23 becomes so negative that the plate current ceases. Current then flows through the resistor I in such a direction as toagain cause the potential of the grid of tube I23 to increase. These oscillations continue so long as the voltage drop across resistor I3'I biases the grid of tube I23 above the cut-oi! potential of this tube.

Tube I2 is operated as a detector, its grid being biased normally slightly below the cut-off potential. During one-half of the oscillation period of tube I23, the voltage induced in the secondary of transformer III causes the grid of tube I24 to become positive allowing current to flow in the plate circuit through the resistor I33. Since the oscillations of tube I23 are at a radio frequency, the oscillations of this tube result in a pulsating uni-directional through resistor I33 which to all intent and purpose may be regarded and treated as a direct current. It is obvious to one skilled in the art that this oscillator and detector might be replaced by a direct current amplifier containing an odd number of stages.

From this description of the operation 01 the circuits when only one photo-electric cell is connected and from the description of the circuit 2 I 3 on page 2, it is apparent that, when the three photo-cells are placed in operation by closing all the switches 22IA, 22IB and 22IC with one or more of them in the position and one or more of them in the position, the operation of the circuits will be the same except that the charging of the condenser I35 will be controlled by the resultant current in the circuit 2 III which is the algebraic sum of the separate currents through the photo-cells and is, therefore, proportional to an additive and subtractive combination of the point-to-point variation in density of the three master images placed on the three tables over the three photo-cells 2|IA, 2IIB and 2I'IC.

In using the present apparatus, it is merely necessary to place one or more pictures to be scanned on the appropriate tables above one or more of the photo-electric cells 2I1A, ZIIB, 2I'IC, adjust the electrical circuits, and start the reciprocating mechanism to produce the image on the right-hand table in Fig, 1. This image, when made by the use of the radio frequency circuit last described, includes a large number of minute elemental areas faithfully representing the lighttone, middle-tone, and dark-tone portions of a continuous-tone original, and is particularly adapted for making half-tone printing plates. Moreover, when three master images arecombined to make a color-separation image, from which superior color printing plates are produced. How ever, it will be understood that mechanical fea tures of the present invention are useful and ad vantageous in connection with other types of scanning devices. The arrangement of the parts shown in Fig. 5 is not essential as other forms of scanning apparatus, including those designed to scan an opaque original, may he used in carrying out my invention.

In the use of my apparatus, for making images for the three-color process, one image is made with the tables in the positions shown, after which the tables are turned 60 and locked in place, and the second image is made. The tables are then turned another 60, and the third image is made. It will be appreciated that the tables may be rotated through other angles, for instance 30 in each case. In making a set of colorseparation contrast images from a set of continuous-tone color-separation originals, the rotation of the tables serves to locate the scanning lines in the images at large angles to one another. A set of printing plates made from these images does not produce moir effects. Moreover, the

apparatus is so constructed that the adjustments (5 can be readily and quickly made, while the scanning is accomplished by a rectilinear movement.

What I claim is:

1. In an electro-mechanical scanning apparatus, a flat transparent member adapted to support a picture to be scanned, a photo-sensitive plate, a frame for supporting said picture and plate in the same plane and in a plurality of positions at fixed, equal angles to a line joining their centers, a scanning lamp and a photo-electric cell at opposite sides of said transparent memher, a recording lamp adjacent said plate, a U- shaped frame for supporting said lamps and cell, means for reciprocating one oi said frames at a uniform rate of motion, and means for causing a step-by-step movement of the other frame at each reversal of movement of the reciprocated frame.

2. An electro-mechanical scanning apparatus for producing a composite contrast image from a plurality of continuous-tone master images, comprising a reciprocating carriage, tables for supporting the master images on said carriage, a table for supporting a photographic plate on said carriage, a scanning lamp and a photo-electric cell associated with each of said master image supports, a circuit connecting said photo-electric cells so as to produce a. resultant current equal to the algebraic sum of the separate currents through the cells, a recording light associated with said photographic platecarriage, a circuit connecting said resultant current with said recording light and arranged to light and extinguish said light for periods corresponding in length to variations in said resultant current, and means for making corresponding angular adjustments of said master image tables and said photographic plate tables.

3. In an electro-mechanical scanning apparatus, a flat, transparent member adapted to support a picture to be scanned, a photo-sensitive plate, a reciprocatably mounted carriage supporting said transparent member and said plate, a scanning lamp and a photo-electric cell at opposite sides of said transparent member, a recording lamp at one side of said plate, a U-shaped frame having arms extending at opposite sides of the first frame and mounted for reciprocatory movement at right angles to the movement of the first frame, means for reciprocating one of said frames at a uniform rate of motion, and means for causing a step-by-step movement 01 the other frame at each reversal of movement of the reciprocated frame.

FRANCIS LEWIS WURZBURG, JR.

CERTIFICATE OF CORRECTION.

Patent no 2, 1 5, 1 9.

December 26, 1959 FRANCIS LEWIS W'URZBURG, JR. It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 67, for an optical" read on optical; page 5, first column,

lines 52 and 55, for

current;

"photo-cell resultant circuit, while greater than the current read photo-cell circuit.

while greater than the resultant and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of February, A. D. l91l0.

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

can be readily and quickly made, while the scanning is accomplished by a rectilinear movement.

What I claim is:

1. In an electro-mechanical scanning apparatus, a flat transparent member adapted to support a picture to be scanned, a photo-sensitive plate, a frame for supporting said picture and plate in the same plane and in a plurality of positions at fixed, equal angles to a line joining their centers, a scanning lamp and a photo-electric cell at opposite sides of said transparent memher, a recording lamp adjacent said plate, a U- shaped frame for supporting said lamps and cell, means for reciprocating one oi said frames at a uniform rate of motion, and means for causing a step-by-step movement of the other frame at each reversal of movement of the reciprocated frame.

2. An electro-mechanical scanning apparatus for producing a composite contrast image from a plurality of continuous-tone master images, comprising a reciprocating carriage, tables for supporting the master images on said carriage, a table for supporting a photographic plate on said carriage, a scanning lamp and a photo-electric cell associated with each of said master image supports, a circuit connecting said photo-electric cells so as to produce a. resultant current equal to the algebraic sum of the separate currents through the cells, a recording light associated with said photographic platecarriage, a circuit connecting said resultant current with said recording light and arranged to light and extinguish said light for periods corresponding in length to variations in said resultant current, and means for making corresponding angular adjustments of said master image tables and said photographic plate tables.

3. In an electro-mechanical scanning apparatus, a flat, transparent member adapted to support a picture to be scanned, a photo-sensitive plate, a reciprocatably mounted carriage supporting said transparent member and said plate, a scanning lamp and a photo-electric cell at opposite sides of said transparent member, a recording lamp at one side of said plate, a U-shaped frame having arms extending at opposite sides of the first frame and mounted for reciprocatory movement at right angles to the movement of the first frame, means for reciprocating one of said frames at a uniform rate of motion, and means for causing a step-by-step movement 01 the other frame at each reversal of movement of the reciprocated frame.

FRANCIS LEWIS WURZBURG, JR.

CERTIFICATE OF CORRECTION.

Patent no 2, 1 5, 1 9.

December 26, 1959 FRANCIS LEWIS W'URZBURG, JR. It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 67, for an optical" read on optical; page 5, first column,

lines 52 and 55, for

current;

"photo-cell resultant circuit, while greater than the current read photo-cell circuit.

while greater than the resultant and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of February, A. D. l91l0.

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

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