US2638500A - Process and apparatus for photoelectric engraving - Google Patents

Description

May 12, 1953 c. E. ERNST 2,638,500

PROCESS AND APPARATUS FOR PHOTOELECTRIC ENGRAVING Filed June 28, 1951 Sheets-Sheet l 5' 28 T 43 1 1' ii i 22 T 2 L q) 75 E 1 I 86 V F 134 74 o o 74 A: /g 87 '73 a 89 I To: Clare E.Ern5t 63 I g 1 .INVENTOR ATTORNEY C. E. ERNST May 12, 1953 PROCESS AND APPARATUS FOR PHOTOELECTRIC ENGRAVING 5 SheetsSheet 2 Filed June 28, 1951 Clare ELErnS't INVENTOR W ATTORNEY C. E. ERNST May 12, 1953 PROCESS AND APPARATUS FOR PHOTOELECTRIC ENGRAVING' 5 SheetsSheet 5 Filed June 28, 1951 Ciai'eE.ErnsZ INVENTOR 4 BY ATTORNEY y 2, 1953 c. E. ERNST 2,638,500

PROCESS AND APPARATUS FOR PHOTOELECTRIC ENGRAVING Filed June 28, 1951 5 SheetsSheet 4 (Za re E. E rnsi lNVENTOR ATTORNEY y '12, 1953 c. E. ERNST 2,638,500

PROCESS AND APPARATUS FOR PHOTOELECTRIC ENGRAVING Filed June 28, 1951 5 Sheets-Sheet 5 INVENTOR ATTORNEY Patented May 12, 1953 UNITED" STATES PATENT OFFICE PROCESS AND APPARATUSFOR PHOTO- ELECTR'IC ENGRAVING 5' Claims.

This invention relates to methods and apparatuses for photoelectrically engravinghalf-tone plates, having particular reference to automatic mechanical removal of printing surface from pfates according to graduati'ons of tone of images being reproduced.

Half-tone plates made according to the customary photoengraving method wherein acid is used for attacking areas of the plate have not proven satisfactory as acid cannot be properly controlled and often results in uneven contours and undercuts. Furthermore, the cost of producing half-tone plates by this method is very expensive due to time requirements and the necessity of employing highly skilled labor.

Efiorts have previously been made to intermittently and individually remove or displace surface areas from half-tone plates of varying sizes in accordance with the density of tone in pictures by prick-punching, etching, and drilling processes with the use oi pointed tools that are controlled as to their depth of engagement into the plate during each individual removal or displacement operation. For different reasons, such mechanical dispersement of surface areas of plates have not produced half-tone plates acceptable to the trade.

It is therefore the primary object of this invention to provide a novel and improved method and apparatu for eficiently and accurately producing from pictures half-tone plates for use either in the making of stereotype mats or for printing directly from the plates.

Another object of the invention is to provide an apparatus of the above-indicated character wherein a photoelectric tube and picture-refleeting lenses are encased by a telescopic tube and aligned. with a restricted aperture therebetween located on the focal plane of an image reflected from a picture by said lenses, said telescopic tube being provided to prevent outside light from entering through the aperture to the photoelectric tube and to permit variations in the spacing of the lenses relative to the picture and restricted aperture for varying the size of the reflected image from which a half-tone plate is produced and for movement of the photoelectric tube relative to the lenses and picture during scanning operation.

A further object of the invention is to provide a photoelectric engraving apparatus wherein the voltage and current from a picture-scanning photo-electric tube that controls depths of engagement of a cutter into a half-tone plate can be varied at different intensities of illumia nation of the photoelectric tube for lightening gray'portionswithout changing black or darkened portions when producing a half-tone platefrom a picture, thereby obtaining greater con trast between; light and dark tones in pictures produced with the half-tone plate than the tone contrast of the original picture.

A further object of the invention; is to: pro videa novel manner or" obtaining a screeneffect with a mechanically produced half-tone plate whereincuts of adjacent rows of cuts in the surface of a plate are in staggered relation to one another;

It is also an object of the invention to provide an apparatus as set" forth having a highspeed, air-operated rotor attached; directly to the shankof a cutting tool; both being of extremely lightweight" construction and rotatably mounted as a unit on a sensitive, flexible support which is magnetically flexed according to tonegraduations of apicture being reproduced to move'. the cutting tool intoand out of a half-tone plate being produced, said air rotor being of a width that air pressure directed thereto substantially tangent to its diameter continually actuates said rotor' independent of the position of the cutting tool. relative to the plate and without influencing the position of the cutting tool These, together with various auxiliary features and objects of the invention which will later become apparent as the following description proceeds, are attained by the present invention, preferred embodiments of which have been illustrated, by way of examples only, in the accompanying drawings, wherein:

Figure 1 is a side elevation, with parts broken away and shown in section, of the scanning unit;

Figure 2 is a side elevation of the engraving unit;

Figure 3 is a fragmentary rear elevation of the engraving unit shown in Figure 2;

Figure 4 is an end elevation of the scanning uni Figure 5 is a fragmentary plan view showing the rear portion of the scanning unit;

Figure '6 is a plan view of the engraving unit;

Figure 7 is an end elevation of the engraving unit with the forward portion thereof broken away;

Figure 8 is a horizontal section taken on line 8-8 of Figure 7;

Figure 9 is a vertical section taken on line 9-9' of Figure 8;

Figure 10 is a vertical section taken on line I 0'--Hl-- of Figure 9;

Figure 11 is a. horizontal section taken on line II-H of Figure 9;

Figure 12 is an enlarged sectional View through a half-tone plate in the process of being made, showing the cutting end of a tool relative to said plate;

Figure 13 is a plan view of fragments of a half-tone plate made with the apparatus;

Figure 14 is a diagrammatic view of both the scanning and the engraving units showing electrical symbols and wire connections to various elements of the apparatus;

Figure 15 is a diagram of the picture-reflecting mechanism;

Figure 16 is a side elevation of a modified form of engraving unit;

Figure 1'7 is a vertical section on line I 1-H of Figure 16 showing a face view of the transducer;

Figure 18 is a vertical section taken on line l8|8 of Figure 17; and

the purpose of illustration, separate from the engraving unit, and being connected thereto only by electric wires.

The scanning unit has a base 20 with a track 2| on which a copyboard 22 and focusing lenses 23 are slid towards and away from each other and adjusted relative to a photoelectric cell 24 on a frame 25 fixed to said base. Different adjusted positions of the copyboard and focusing lenses along the track for reflecting an image of a picture attached to the copyboard on a, focal plane relative to the photoelectric cell permit the making of enlarged and reduced reproductions, as well as reproductions of the same size.

Mounted in horizontally extending dovetailed guide members 26 of the frame 25 are slides 21 at both the upper and lower ends of a transversely movable member 28 which is threadably engaged by a horizontal feed screw 29 mounted in bearings 30 on the frame and rotated by a synchronous motor 3! which is operated in opposite directions for imparting reciprocal motion to said member 23. J ournaled in upper and lower bearings 32 on the member 28 are the opposite end portions of another feed screw 33 arranged at right angles to the screw 29 and threaded through a lug 34 on a vertical, movable carriage 35 guided in its vertical movement by a beveled way 36 formed in the member 28. On the lower end of the feed screw 33 below the lower bearing 32 is secured a ratchet 37 engaged by a pawl 38 mounted on an end of a bell crank lever 39 which is also connected to a solenoid 40 by a link 4|. An end of a spring 42 engages the teeth of the ratchet to prevent turning of the ratchet upon return of the pawl 38 to engage the next tooth of the ratchet. Thus, it can be seen that each time the solenoid is energized, the feed screw will lower the carriage a slight distance.

' On a rearwardly projecting platform of the carriage 25 is secured a bracket 43 of universal movement construction which is connected to a casing 44 that houses the photoelectric cell 24. Opening into the casing 44 and aligned with the photoelectric tube is the smaller end section 45 of a telescopic tube 46 that has its larger opposite end section 41 formed with an enlarged socket 48 which receives and is turned about a substantially ball-shaped casing 49 that houses the focusing lenses 23, there being oppositely arranged openings in the ball-shaped casing at the focusing lenses and an opening from the socket into the section 41 through which light enters the telescopic tube. The casing 49 is flanged, as at 50, where it is attached to a bracket 5| that slides on the track 2! which provides the previously mentioned slidable connection for the focusing lenses 23 along the track.

In the smaller tube section 45 of the telescopic tube 46 is a closed off wall 52 with a small, square opening 53 centrally of the tube section for restricting the amount and shape of light rays from the focusing lenses that are permitted to pass said closed oil wall. Between the closed off wall 52 and the photoelectric cell 24 and also arranged in the tube section 45 is a small lens 54 which reflects light passing through the opening 53 to the photoelectric cell.

The controlling of the direction of rotation of a synchronized motor 3| and the energizing of the solenoid 40 for turning the horizontal and vertical feed screws 29 and 33, respectively, for moving the carriage 35 on which is supported the photoelectric cell 24 that scans during such movement a picture on the copyboard will be described as the description proceeds. However, it can be assumed that the synchronized motor reciprocates the carriage horizontally and that the solenoid lowers the carriage slightly at the end of each stroke of reciprocal motion, thereby scanning the entire surface area of a picture. The telescopic tube, while shuttin off outside light to the photoelectric cell, pivots at its opposite ends about the housing of the focusing lenses and on the carriage and compensates for lengthening and shortening of the distance between the focusing lenses and the photoelectric cell during scanning movement of the carriage. Also, the use of a telescopic tube permits adjustment of the distance between the focusing lenses and the photoelectric cell when reducing or enlarging a reproduction of a picture, as it is essential that the focusing lenses be adjusted relative to the picture on the copyboard and the opening 53 in the closed off wall 52 so that the focal plane on an image reflected from the picture is at the opening 53 in the closed off wall 52. In Figures 1 and 15, the dash and double-dot line 55, centrally of the focusing lenses 23, telescopic tube, 48, and photoelectric cell 24, and extended to the copyboard 22, indicates the portion of a picture refiected to the photoelectric cell, while the crosseddash and dot lines 55 and 51 indicate extreme positions the photoelectric cell is capable of moving during a scanning movement. The vertical dash and dot line 53 represents the focal plane of a picture reflected by the focusing lenses as being directly on the restricted opening 53 in the closed off wall 52.

Attention is now directed to Figures 2, 3, 6, and '7 illustrating the engraving unit of the apparatus wherein the number fill indicates the upper portion of a cabinet on which a rectangular base frame *6! constructed of channel members rests. Secured t0 the base frame are spaced uprights 62 and 53, a motor seat 64 on the upright 62, and ppwfiin plate 65 across one end of said base frame. Attached to and extending between the uprights 52 and 63 is a pair of guide rods 65 that slidably supports a carriage 31, while mounted on the base frame and extending at right angles to the pair of guide rods 68 is another pair of spaced guide rods 68 that slidably supports a table 59 to which is clamped the plate to be made into a half-tone plate. A feed screw H rotatably mounted adjacent opposite ends thereof on the uprights 62 and 63, extending parallel to the guide rods '66 and threadably engageable with the carriage 61, as at 12, reciprocates said carriage on said guide rods when rotated in opposite directions by a synchronous motor 13 mounted on the motor seat 64.

Adjustable extensions H on opposite sides of the carriage 61 are adapted to engage limit switches attached to the inner sides of the uprights at the ends of desired movement of the carriage in both directions. The limit switches 15 are connected to a reversible motor l3 mounted on the plate 65 of the base frame 61 and reverse the direction of rotation of the motorupon each actuation of either switch. The reversible motor 13 is connected by a belt and pulley drive 13 to the synchronous motor 13 which is electrically connected to the synchronous motor 3| for reversing the direction of rotation of the synv chronized motors 3i and 13 to move the carriages and 81, respectively, in directions opposite to that previously moved.

Another feed screw 16, mounted at its opposite ends in bearings Tl attached to the forward and rear sides of the base frame Bl, as shown in Figure 6, and threadably engageable with the table 59, slides the table on the guide rods 68 upon turning movement of said feed screw. On the forward end of the feed screw 15 is attached a ratchet 10 which is engaged by a pawl 19 mounted on one arm of a bell crank lever 89 that has its other arm connected to a solenoid 8! by a link 82. A spring 33 returns the pawl to engage the next tooth of the ratchet after each time the solenoid is energized, while a free end of a leaf spring 84 prevents turning of the ratchet in the wrong direction during return of the pawl to an operative position.

The solenoid 8| and the solenoid on the scanning unit have circuits closed thereto by actuation of the limit switches 75 during the period of reversing the directions of reciprocal motions of the carriages 57 and 35. Thus, when the table :69 and photoelectric cell 24 have reached an end of a stroke of their reciprocal motion, the table and the photoelectric cell are slightly moved at right angles to their reciprocal motion for cutting and scanning along other adjacent areas of the plate and picture, respectively.

On the end of the feed screw "H that is rotatably mounted on the upright 63 is secured a disk 95 with a pair of parallel and oppositely spaced lugs 85 which project outwardly therefrom for engaging a cross bar 3? at opposite sides of a pivotal connection of said bar to the feed screw H to cause said bar to be rotated with said feed screw. Secured to each end of the cross bar 81 is a permanent magnet 88 arranged so that the path of movement of both magnets will place said magnets at predetermined spaced intervals of time in close proximity to a pulse generator coil 89 stationary on the upright 63 for exciting said pulse generator coil. The width of the magnets determines the length of time of each impulse, while the space between the two magnets determines the time between impulses, thus; by using magnets of greater or lesser widths, length of time of each impulse may be increased or decreased. The purpose of the impulses will be set forth as the description proceeds. The locations 6 of the lugs 86 relative to the cross bar 81 are such that a lost motion of ninety degrees of rotation of the cross bar with respect to the feed screw II is present upon the reversing of the direction of rotation of the feed screw, which, together with i the locating of the permanent magnets 88 one hundred eighty degrees apart, causes an even staggering of the spaced intervals of the time of excitement of the pulse generator coil 89 during reciprocal motion of the carriage 6'! in opposite directions.

In guide ways '90 on the carriage 51, and movable by an adjusting screw 91, is a bracket 52 that supports an engraving head, generally indicated by the numeral 93. Said support consists of a right-angled, projecting, forked portion 94 between which are pivotally connected, as at 95, parts 96 of the head 93, while an adjusting screw 91 on the bracket engages a part 98 of the head and determines the position of the head on its pivotal connection relative to the bracket.

The engraving head 93, shown more in detail in Figures 9, 10, and 11, has a horseshoe-type permanent magnet which is the part 93 previously referred to and which has connected to its ends pole pieces and on that are forked and directed towards one another for receiving in the combined forks of both a pair of spaced coils HM and I02 between which is a flexible blade I93 that supports for slight rotary movement an armature 104 that extends through openings in the coils and between the push and pull ends of the pole pieces 99 and Hill, said armature being normally held by said flexible blade in a position contrary to its position of actuation by said pole pieces upon current impulses of said pulse generator.

To one end of the armature I04 a yoke I05 is mounted by a laterally flexible leaf connection I06 and is provided with inturned ends that engage in holes in opposite sides of a collar H31 rotatably connected against end movement on an arbor I08 which holds a cutting tool 109. The shank of the cutting tool IE9 is supported for rotation and endwise movement in V-shaped notches in the free ends of a pair of oppositely directed and telescoping U-shaped brackets H0 and l H supported by the lower pole piece 109 and insulated therefrom by a block H2. The attaching screws H3 that retain the U-shaped bracket Ill in place have coil springs Ihl under the heads thereof which engage the bracket H l for yieldably forcing said bracket in position with bearing surfaces of the V-shaped notches of both brackets in engagement with the shank of the cutting tool.

Mounted on the parts that pivotally connect the head 93 to the bracket 92 are the lower ends of a pair of angled arms H5 that extend upwardly and then forwardly. To said forward ends are attached the opposite ends of one of a pair of clamping members H6 and ii! that engage about a stub extension H8 on the casing of a lightweight, high speed air motor He of the 75,000 to 100,000 R. P. M. type. The drive shaft 920, to which is attached the rotor of the motor, depends from the motor casing, and besides having a central bore [2| extending upwardly from its lower end to slidably receive the upper end of the arbor I08, has slots I2 2 therein into which extend the ends of a cross pin !23 on the arbor for forming a slidable drive connection between the air motor and the arbor. The point 124 of the cutting tool I09, which is substantially in the form of a drill point for cutting tapered holes of varying depths in the 7 plate 10 according to the value of the current which flows through the photoelectric cell 24, is adjusted relative to the plate I by the adjusting screws 9| and 91; but in order to further retain proper relationship of such parts, a shoe I25, adjustable on the head 93, rides over the plate in during cutting operation in advance of the area of the plate being cut for slightly raising the head on the pivot 95 should higher areas in the plate be encountered.

Figures 12 and 13 show tapered holes I26 of varying diameters cut into the upper surfaces of the plate for removing areas from the plate surfaces to obtain light and dark tones in a picture printed either directly or indirectly from said plate.

Arrows I21 indicate the direction of travel of the cutting tool produced by the coordination of rotation of the feed screws. Also shown is the staggered relation of adjacent rows of holes cut in the plate produced by the lost motion in the connection of the cross bar 81 to the feed screw TI when rotating said feed screw in op posite directions. It will be observed that in the removal of surface from the plate, some of the individual, circularly out holes are of such large diameter that they coalesce, leaving small, substantially rectangular, unconnected surface areas in the form of islands which are indicated by the numeral I28.

Referring now to Figure 14 which shows an electric Wiring diagram of the entire apparatus and diagrammatic illustrations of certain elements of the apparatus, there is indicated both an alternating current circuit and a direct current circuit. The alternating current circuit, which times and coordinates movement of the photoelectric cell 24, engraving head 93, plate I0, and pulse generator magnets 88, has a source of current, indicated at I29, with wires I30 lead- V ing therefrom to a reversing switch relay I3I from which the usual three-line connection I32 is made to the reversing motor 13 Also from the reversing switch relay I 3|, wires I33 connect to the two limit switches 15, while other wires I34 connect to the solenoids and 8|. The synchronous motors 3I and I3 are connected together by the usual five-wire connection I35, while the synchronous motor I3 receives current through the wires I36 from the source I29.

The direct current circuit, which supplies pulses of varying currents to the mechanism which actuates the cutting tool, consists of the scanning photoelectric cell 24 for producing varying currents according to the density of tone of pictures, the coil 89 of a pulse generator for producing timed electrical pulses, an adjustable mixer for receiving current variations from the photoelectric cell and timed pulses from the coil of the pulse generator, an amplifier for amplifying timed pulses mixed with varying currents, and the mechanism which actuates the cutting tool that is operated according to the value of pulses from the amplifier.

I The adjustable mixer has therein a 6L7 mixer tube I31 with a potentiometer I38 adjustably connected through a IOO-megohm resistor I39 by a wire I40 to a control grid of the mixer tube and connected by Wire IM to the cathode of the photoelectric cell 24 for varying the bias voltage of the grid and for partially varying the sensitivity of the photoelectric cell. The other con trol grid of the mixer tube is connected by a wire I42 to one end of another potentiometer I43 which has the adjustable connection thereof wired,'as at I 44, to the pulse generator coil 89, while the other ends of the potentiometer and pulse generator coil are grounded. A 250-volt battery I45 with the negative terminal grounded is tapped at 90- volts for connection by a wire I46 to the plate of the photoelectric cell 24, at 100 volts by a wire I41 through a resistor I48 to the screen grid of the mixer tube, and at 250 volts by a wire I49 through a resistor I59 to the plate of the tube. The cathode-heating filament of the tube is supplied with current from a 6-volt battery l5l, while the cathode is groundedby a wire I52. To the lead I49 between the resistor I50 and the plate of the mixer tube a wire I53 is connected and leads through a condenser I54 and an amplifier I55 after which said wire is grounded.

Connected to the output of the amplifier I 55 are a pair of wires I56 and I5! which lead to opposite ends of the series-connected coils I M and I02 of the mechanism which actuates the cutting tool. The pulses of varying current from the amplifier I55 to the coils IM and I02 cause magnetism to be set up in the armature I04 which then repells itself from the magnetic pole of the permanent magnet of the same polarity causing the armature to swing on its flexible support I03 according to the values of current impulses.

When reproducing a picture on a plate that does not have sufficient contrast between light and dark tones, and it is desired to lighten gray portions of the picture Without changing black or darker portions, the bias voltage on the control grids of the mixer tube I31 can be varied by adjusting the two separate potentiometers I38 and I43 to allow more current to flow from the cathode to the plate in the mixer tube. The potentiometer I43 on the second control grid is adjusted for dark or black tones, while the potentiometer I38 on the first control grid is adjusted for'lightening gray tones.

Figures 16, 1'7, 18, and 19 show a modified form of engraving unit wherein a different type of engraving head, generally indicated by the numeral I53, is used, and other parts of the unit are turned ninety degrees on the cabinet 60, thereby arranging some elements that were in vertical positions on horizontal planes and other elements that were in horizontal positions on vertical planes. By turning the unit on its side, both the plate 10 that is acted upon by the engraving head I58 and the right-angled projecting forked portion 94 that supports the engraving head I58 are arranged vertically instead of horizontally.

In this case, the permanent magnet I59 is of a circular type with a core pole I60 projecting through and spaced from an opening in an end plate I6I- which constitutes the other pole. Attached to the end plate I6I of the permanent magnet I59 is a supporting bracket I62 provided with pivot holes I63 into which the pointed ends of trunnions I64 on the ends of the forked portion 94 of the adjustable bracket 92 extend. An offset leg I65 depends from the bracket I62 and is engaged by the adjusting screw 91 of the bracket portion 94 for limiting movement of the head I58 towards the plate I0, while coil springs I66 attached to said leg, as at I61, and to the bracket by pins I68 yieldably hold the head in position with the leg I65 in contact with the adjusting screw 91.

The bracket I62 has a circular opening I69 therein aligned with and of greater diameter than the opening in the end plate I6I of the magnet. Around said opening, the bracket is annularly recessed, as at I'IO, to provide a seat for the marginal portion of the diaphragm HI and to receive a clamping ring I'I2. Spaced from and aligned with the daiphragm I'II is another diaphragm H3 that is supported by pins I'M which also attach the bracket IE2, diaphragm HI, and ring M2 to the plate It: of the magnet by extending said pins through all of said parts. The pins lit have one of each of their ends threaded into the plate lGI, have spacer sleeves I15 thereabout between the ring I72 and diaphragm I13, and have nuts I16 threaded on their other or outer ends.

Attached to and arranged centrally of the diaphragm lit, by brazing or the like, and extending towards the center of the diaphragm Ill is a small, sleevelike housing IT. containing in each end thereof bearings I78 and 579 that rotatably receive a cutting tool Iii-c that projects forwardly through holes in the ends of the housing l1! and diaphragm lit. The end of the housing I'l'I adjacent the diaphragm l'lI is threaded into a flanged socket IBI riveted or otherwise attached to the forward side of the diaphragm I1 I. These same rivets attach the bottom of a thin-walled, cup-shaped armature I82 to the rear side of said diaphragm with the annular Wall thereof reposed in the space between the pole pieces I59 and ISI of the magnet I53 and out of engagement with said pole pieces. Wound around and insulated from the annular wall of the cup-shaped armature N52 is a coil I83 with leads I84 extending through holes in the diaphragm l'lI to terminal blocks its supported and insulated from the ring I '12. Connected to the leads I84 at the terminal blocks are the wires I53 and I91 that lead to the armature W shown in the other form of engraving unit illustrated in Figure 14.

On the forward portion of the shank of the cutting tool I80 projecting through the diaphragm I73 is detachably secured an air wheel or rotor I86 by a set screw I81 in a collar thereof. A Venturi-type nozzle I88 is shown as being supported by a hanger I89 from one of the pins I14 and is directed substantiallytangent to the outer ends of radial vanes I90 of the rotor, as best shown in Figure 17. The vanes I90 are slightly arced, being undercut on their faces that are engaged by a blast of air from the nozzle and are of a width across their faces sufficient to remain in contact with said blast of air in all endwise positioning of the rotor and cutting tool.

Extending across the engraving head forward of the rotor lfifi and offset, as at I9I, for permitting the cutting tool to pass thereby is a bar I92 ivoted at one end to an arm I93 on the bracket .182 and detachably connected to another arm I94 on the bracket IE2 at its opposite end. Below the point of the cutting tool and at the offset I9I, the bar I92 has thereon a rounded end shoe I95 that engages the surfaces of the plate III along an area thereof in advance of the cutting apparatus to said plate for properly positioning the head relative to the surface of the plate being cut. The end of the bar I92 detachably connected to the arm I94 is also adjustable on said arm for properly locating the shoe I95 with respect to the depth of engagement of the point of the cutting tool into the plate upon difierent endwise motion of the cutting tool. Said adjustment consists of an adjusting screw I96 on the arm against which the bar I92 is held by a coil spring I9'I, the end of said arm I94 being slotted,

10 as at I98, for supporting the detachable end of the bar against up and down movement.

It will be observed that the two diaphragms Ill and H3 support a high-speed, rotatable cutting mechanism of extremely light Weight for sensitive end movement produced by pulses varying current to the coil H33. As the permanent magnet I99 has a constant magnetic field of constant polarity, impulses or polarity from the transformer in the amplifier 555 through the coil I83 repel each other, thereby pushing the coil out or away from the magnet to engage the cutting tool into the plate according to the value of each pulse. When pulses through the coil are of opposite polarity which attract the coil to the magnet, and when there is no current through the coil and the coil is returned to the position held by the diaphragms I'I'I and 3'53, the cutting tool is out of engagement with the plate.

Due to the lightweight and high-speed requirements of the cutting mechanism, the small precision ball bearings ill} and H9 used for rotatabiy supporting the shank of the cutting tool must be lubricated. Therefore, the sleevelike housing I71 is also used as an oil reservoir and is supplied with oil through the filler cap I99.

While there are shown and described separately a scanning and an engraving unit for the purpose of locating the units a distance from each other, it is to be understood that certain elements of the apparatus may be eliminated, and parts of both the scanning and the engraving unit maybe mounted on the same movable members for movement in unison.

In view of the foregoing description taken in conjunction with the accompanying drawings, it is believed that a clear understanding of the con struction, operation and advantages of the apparatus will be quite apparent to those skilled in this art. A more detailed description is accordingly deemed unnecessary.

It is to be understood, however, that even though there are herein shown and described preferred embodiments of the invention,- various changes may be made without departing from the spirit and full intendment of the invention.

What is claimed is:

1. A plate-engraving apparatus comprising a photoelectric cell for scanning a picture, a cutting tool, a plate positioned for engagement of said cutting tool therewith, means for imparting reciprocal motion and movement at right angles to said reciprocal motion at the end of each stroke of reciprocal motion to said photoelectric cell relative to the picture and to said cutting tool relative to said plate in unison, said means for imparting reciprocal motion including a feed screw rotatably mounted and reversed in its directions of rotation, a pulse generator including a stationary pulse generator coil and at least one permanent magnet connected to said feed screw and rotatably moved in close proximity past the coil for producing electrical impulses, said permanent magnet having a lost motion in its connection to the feed screw upon rotation of the feed screw in opposite directions for producing impulses staggered relative to reciprocal motion in opposite directions, a mixer tube receiving cur rent variations from said photoelectric cell and timed pulses from said pulse generator, an amplifier receiving timed pulses of varying currents from said mixer tube, and a cutting tool activating mechanism for moving said tool into said 11 plate according to the value of the pulses from said amplifier.

2. A plate-engraving apparatus including a scanning unit and an engraving unit, each of which is comprised of a support, and a carriage slidable on said support; means for synchronized reciprocal motion of said carriages on said supports; a picture-reflecting member on said scanning unit adjustable for varying the size of an image reflected from a picture; an encased photoelectric tube on the carriage of said scanning unit, said encasement having an aperture therein arranged on the focal plane of an image reflected from a picture; means for moving the carriage with the photoelectric cell relative to said reflected image and at a direction at right angles to said reciprocal motion of the carriage at the end of each stroke of the reciprocal motion for progressively scanning the image along spaced, parallel, imaginary lines; a work plate on said engraving unit; a high speed, power-driven cutter supported on the carriage of said engraving unit and mounted for movement into and out of engagement with said work plate; means for mov-. ing the carriage of said engraving unit relative to said work plate in a direction at right angles to the reciprocal motion of said carriage at the end of each stroke of the reciprocal motion for progressively moving the cutter along spaced, parallel rows over the surface of the plate; means for varying the amplitude of movement of said cutter into said plate in accordance with variations in the intensity of illumination of said photoelectric tube; and means intermittently actuating said means of variable movement at constant intervals during both directions of reciprocal motion of the engraving carriage and at intervals staggered relative to movement of the carriage in opposite directions.

3. A plate-engraving apparatus including a scanning unit and an engraving unit, each of which is comprised of a support, a carriage slidable on said support, and a threaded shaft rotatably mounted on said support and threadably engageable with said carriage; reversible, synchronized motors connected to said threaded shafts for sliding said carriages on said supports, limit switches on one of said supports operated by the carriage supported thereby for reversing said synchronized motors for reciprocating the carriages in unison; a picture-reflecting member on said scanning unit adjustable for varying the size of an image reflected from a picture; a photoelectric cell on the carriage of said scanning unit; a casing enclosing said photoelectric tube with an aperture therein arranged on the focal plane of an image reflected from a picture; means for movement of the carriage with the photoelectric cell relative to said reflected image in a direction at right angles to said reciprocal motion of the carriage at the end of each stroke of the reciprocal motion for progressively scanning the image along spaced, parallel, imaginary lines; a work plate on said engraving unit; a high speed, power-driven cutter supported on said carriage of said engraving unit and mounted for movement into and out of engagement with said work plate; means for movement of the carriage of said engraving unit relative to said work plate in a direction at right angles to the reciprocal motion of the carriage at the end of each stroke of the reciprocal motion for progressively moving the cutter along spaced, parallel rows-over the surface of the plate; means for varying the amplitude of movement of ,said cutter into said 12 plate in accordance with variations in the intensity of illumination of said photoelectric cell; a permanent magnet on one of said threaded shafts and rotated therewith; and a pulse generator coil fixed to one of said supports and arranged in close proximity to the path of movement of said permanent magnet and electrically connected to said means of variable movement for intermittently actuating said means of variable movement at constant intervals upon continued passing of said permanent magnet thereby in each direction of reciprocal motion of said carriage. 1 4. A plate-engraving apparatus including scanning unit and an engraving unit, each of which is comprised of a support, a carriage slidable on said support, and a threaded shaft rotatably mounted on said support and threadably engageable with said carriage; reversible, synchronized motors connected to said threaded shafts for sliding said carriages on said supports, limit switches on one of said supports operated by the carriage supported thereby for reversing said synchronized motors for reciprocating the carriages in unison; a picture-reflecting member on said scanning unit adjustable for varying the size of an image reflected from a picture; a photoelectric cell on the carriage of said scanning unit; a casing enclosing said photoelectric tube with an aperture therein arranged on the focal plane of an image reflected from a picture; means for movement of the carriage with the photoelectric cell relative to said reflected image in a direction at right angles to said reciprocal motion of the carriage at the end of each stroke of the reciprocal motion for progressively scanning the image along spaced, parallel, imaginary lines; a work plate on said engraving unit; a high speed, power-driven cutter supported on said carriage of said engraving unit and mounted for movement into and out of engagement with said work plate; means for movement of the carriage of said engraving unit relative to said work plate in a direction at right angles to the reciprocal motion of the carriage at the end of each stroke of the reciprocal motion for progressively moving the cutter along spaced, parallel rows over the surface of the plate; means for varying the amplitude of movement of said cutter into said plate in accordance with variations in the intensity of illumination of said photoelectric cell; a permanent magnet on one of said threaded shafts and rotated therewith; and a pulse generator coil fixed to one of said supports and arranged in close proximity to the path of movement of said permanent magnet and electrically connected to said means of variable movement for intermittently actuating said means of variable movement at constant intervals upon continued passing of said permanent magnet thereby in each direction of reciprocal motion of said carriage, said permanent magnet having lost motion in its connection to said rotatable shaft for staggering the constant intervals of actuation of said means of variable movement relative to travel of the carriages in opposite directions.

5. A plate-engraving apparatus comprising a picture-reflecting member adjustable for varying the size of an image reflected from a picture, a photoelectric cell for scanning the image, a cutting tool, a plate positioned for engagement of said cutting tool therewith, means for imparting reciprocal motion and movement at right angles to said reciprocal motion at the end of each stroke of reciprocal motion to said photoelectric cell with variations in the intensity of illumination of said photoelectric cell.

CLARE E. ERNST References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,719,621 Pearne July 2, 1929 10 2,076,220 Bennett Apr. 6, 1937 2,127,160 Cook Aug. 16, 1938 2,315,361 Wise et al. Mar. 30, 1943

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