US2775172A - Photographic type composing apparatus - Google Patents

Description

Dec. 25, 1956 R. HIGONNET ETAL PHOTOGRAPHIC TYPE COMPOSING APEARATUS Filed Aug. 26, 1952 READER REG1STER KEYBOARD 3 Sheets-Sheet l COUNTER FOUR-STAGE BINARY COUNTER ATTORNEYS INVENTORS RENE HIGONNET YRO Dec. 25, 1956 R. HIGONNET ET AL PHOTOGRAPHIC TYPE COMPOSING APPARATUS 3 Sheets-Sheet 2 Filed Aug. 26, 1952 Fig. 2

INVENTORS RENE HIGONNET LOUIS MOYROUD BY ATTORNEYS Dec. 25, 1956 R. HIGONNET ET AL PHOTOGRAPHIC TYPE COMPOSING APPARATUS 3 Sheets-Sheet 3 Filed Aug. 26, 1952 INVENTORS RENE HIGONNET LOUIS MOYROUD M irim ATTORNEYS United States Patent PHOTOGRAPHIC TYPE COMPOSING APPARATUS Ren Higonnet and Louis Moyroud, Cambridge, Mass., assignors to Graphic Arts Research Foundation, Inc., Cambridge, Mass., a corporation of Delaware Application August 26, 1952, Serial No. 306,462

Claims priority, application Great Britain August 27, 1951 6 Claims. (Cl. 95-.4.5)

This invention relates generally to photographic type composing apparatus, and more particularly to apparatus for projection of characters while in motion with respect to an optical system by means of light flashes of extremely brief duration.

in our copending application, Serial No. 770,320, filed August 23, 1947, We have described a complete photographic composing apparatus in which a matrix of characters is disposed upon a continuously rotating character carrier, which may be for example a disk or drum. Selected characters in a line of type are stored in a register for purposes of justification. The register causes successive projections of the characters by actuating timing means to trigger an intermittent discharge tube or similar device at the precise moments when the selected characters are located in a projection position.

The timing means in the above application includes a coarse control device, either in the form of a rotary switch with a contact corresponding to each of the characters, or in the form of a decoder or commutator device having a coded arrangement of conducting and non-conducting areas or segments. In either case, the coarse control device serves as a means for gating a flash control circuit so that no flash can occur except during the interval of time in which the selected character is located in the projection position.

A trigger impulse for the flash control circuit is produced by a second part of the timing means, called a fine or precise control device. The gating signal from the coarse control device is of relatively long duration, while the trigger impulse is extremely brief and extremely accurate, occuring just as the character reaches a precise location with respect to the optical axis of the projection lens.

According to the above application, the precision of the fine control is brought about by a photoelectric apparatus, including control slits or apertures disposed on the matrix support, which either block out or admit a beam of light to a photocell to generate the trigger impulses. There is a slit or aperture in precise spatial relation to each character in the matrix. The apertures are identical in dimensions, and the trigger impulses which they generate do not distinguish between the characters. The flash control circuit receives all of the trigger impulses, but energizes the flash device only when gated.

In our copending application, Serial No. 150,024, filed March 16, 1950, now Patent No. 2,652,755, we have described a related type of character projection apparatus in which We employ control slits or apertures which are each divided into a number of coded segments. Each character has a unique code, represented by a combination of opaque and translucent segments in the corresponding aperture. A continuous source of light directed to a photocell is obstructed by the apertures successively, and also by a stationary multiple shutter-device actuated by the register. When substantially; all of the lightis obturated by the combination of an apertureand 'ice the shutter device, a flash is produced to project the character corresponding to the particular aperture. By this means the coarse control of our earlier application is dispensed with, but the control slits or apertures are required to be uniquely coded for each character.

A principal object of this invention is to provide character projection apparatus having not only the advantages of precise projection which result from using these slits or apertures mounted on the character carrier, but also the advantage of using identical slits, as in our abovementioned application, Serial No. 770,320, while yet dispensing with a coarse control device of the type therein described.

With the above object in vie-w, one feature of this invention is the employment of counting means to count the trigger impulses, and means actuated according to a selected character to preset a number into the counter. This causes a carry-over signal to be generated by the counter on the impulse generated by the aperture corresponding to the selected character. The carry-over signal triggers the flash circuit, which energizes the discharge device to project the character.

Another feature of the invention is the simplicity of construction of the matrix with its control apertures. These apertures may be of identical size and shape, and may also be restricted to a relatively narrow band upon the matrix support in view of the simplicity of the optical trigger arrangement. In one embodiment there is only a single beam of light directed to the photocell, rather than a plurality of separate or contiguous beams.

Another feature is the increase in the life of the apparatus which results from dispensing With rotary switches, cornmutators, or similar devices such as are used in our abovementioned application, Serial No. 770,320. Such devices are subject to Wear, pitting and other deteriorating action, resulting in accumulations of dust and dirt and consequent loss of reliability. Both the maintenance and initial cost of such devices are considerable, and they add to the size, complexity and cost of the mechanism which is provided to rotate the character carrier. In contrast, the counter device which is used in the present invention is not mechanical, and is not coupled with the character carrier. It may be readily removed as a unit from the composing machine and replaced in the event of a breakdown. Thus, inexperienced personnel provided with replacement counters may put the composing machine back into operation after a failure of the counter, while only skilled mechanics could repair a rotary switch or decoder if the same should become loose upon its shaft, or develop trouble with its brushes or other similar failure.

Other objects of the invention and other features not heretofore mentioned Will become evident from the description to follow. The invention is described with reference to two illustrative embodiments, and is further and more particularly defined in the claims.

' In the drawings,

Fig. 1 is a pictorial view, partly in schematic form, of a first embodiment of the photographic composing apparatus;

Fig. 2 is a view of a matrix support showing the characters and related apertures;

Fig. 3 is a pictorial view, partly in schematic form, of a second embodiment of the photographic composing apparatus which is adapted to use a matrix support of the type illustrated in Fig. 2; and

Fig. 4 is a schematic diagram of the reader and counter circuits.

Referring to Fig. l, the invention will first be described with reference to a simplified form of photographic composing apparatus.

Text matter is composed upon a keyboard 2 which,

cooperates with permutation bars to record the selected characters successively in a register 4. A full line of text is recorded in the register before photography of the characters begins so as to permit the computations necessary for justification. The keyboard 2 and register 4 may take the form described in our above-mentioned copending application, Serial No. 770,320. The register there shown includes a field of depressable pins arranged in columns with each column being devoted to a single character. Hammer means adjacent to the pins advance from column to column, depressing or setting the combination of pins in each column which corresponds to a selected character. Thus, each character is recorded in the register.

A reader 6 moves from column to column of the pins after the line has been recorded to sense the characters. This device is also shown and fully described in our above-mentioned application Serial No. 770,320.

A matrix support 8, preferably made of a transparent material such as glass covered by an opaque coating, supports character transparencies 10 and corresponding "control means in the form of transparent apertures 12 in two circles concentric with the axis of rotation of the support. The support is continuously rotated by a motor 14.

In this simplified version of the invention, it is assumed that each character in the matrix is given a number, starting with l and increasing in the order that the char acters move past a fixed projection position. matrix, counting lower case and upper case letters, punctuations and other special marks used in composition, there are 88 characters.

Each aperture 12 is in precise spatial relation with its corresponding character. Thus, when a particular character such as the c in the drawing is located in the projection position in front of a projection lens 16, its corresponding aperture 12 is in position to trigger a photocell 20. The precise location of the characters and apertures to accomplish this result, which is more fully described below in connection with Figs. 2 and 3, is such that when each aperture has reached the triggering position its corresponding character is properly located in the optical axis of the lens 16 and may be projected at that moment upon a sensitive film 22 by a discharge device 24. If this character has been selected for projection the photoelectric trigger impulse generated in the photocell by the aperture is transmitted to a flash circuit 26 which energizes the discharge device.

An optical condenser 28 is interposed between the discharge device 24 and the matrix support to concentrate the light upon the character to be projected. As already indicated, it is assumed that the characters and apertures are transparencies upon an opaque background.

An opaque shield 30 is provided with windows 32 and 34, whereby only one character at a time can be pro jected upon the film 22, and whereby the precise moment when a transparent aperture 12 admits light to the photocell 20 can be accurately controlled. A continuous source of light 36, through an optical condenser 38, continuously illuminates the window 34 so as to cause each and every aperture 12 to send a light impulse to the photocell 20. it will be understood that the object is to project upon the disk a very thin stationary slit of light which will he suddenly shuttered by each moving aperture as it passes, or a slit of light having a very sharp edge coinciding at successive moments with an edge of each of the apertures. Optical arrangements which dispense with the window 34 entirely are also satisfactory for this purpose. These are well known in the art of motion picture sound reproduction. A common arrangement of this type uses in place of the condenser 38 an optical condenser or microscope for projecting a very thin luminous line directly upon the disk.

As stated above, each character is given a number to distinguish it from the other characters in the matrix.

In a typical The permutation bars of the keyboard 2 record this number, less 1, in the register 4. The recording is preferably accomplished in the binary form of notation, in which each pin in the register 4 has assigned to it a particular order in the binary system of numeration, such as 2, 2 2 etc., as is well known in the art of computing devices. The hammer means of the register are arranged to depress the pins which are to represent the coefiicient l in the recorded binary number.

As shown in Fig. 4, the sensing contacts of the reader 6 are each connected to a stage of a binary counter 40. The counter may be made up of standard electronic flipflop or trigger stages according to any of the many suitable variants of the Eccles-Iordan multivibrator type. We show a form of circuit essentially like that described in Electronics, Experimental Techniques by Elmore and Sands, at pages 111 to 114 (McGraw-Hill, 1949). Any number of substitute circuits will suggest themselves to those skilled in the electronic arts.

The counter 40 must have sufficient stages to permit the counting of all of the characters in the given matrix. Each stage is connected to the succeeding stage by a carry-over lead such as 37. It is also provided with resetting means including a reset cam 39 which closes contacts to turn on the 0 tubes in each stage at some time prior to the passage of character number 1 past the projection position, and with presetting means, including a cam 41 timed to close its contacts immediately after the cam 39, and the sensing contacts of the reader 6. These contacts are normally closed, but are opened when a depressed pin representing a 1 is sensed.

The preset circuit is connected to the 1 tubes of the counter, so that each counter stage is left in the reset condition 0 if the corresponding register pin represents 1 (as in the case of the 2 stage of the drawing), and is preset to 1 if the corresponding pin represents 0 (as in the case of the 2 stage of the drawing).

It may be readily verified mathematically that the number in the counter in each case may be found by subtracting the number in the register from the highest number that the given number of counter stages can record. The net result is that the counter reads a number equal to the maximum value that it can represent, minus the number of the character, plus 1.

For example, for the letter a which has the number 1," the register stores a O. In the case of a matrix of 88 characters, the number of stages in the binary counter 40 which would be necessary to count all of the characters would be seven. For a, the register would therefore read 0000000, and the reader would preset the counter 40 with the binary number 1 111111, which is 127. Similarly, the character c has the number 3. The register would store this character as a 2" or 0000010, and the counter would be preset with the number 1111101, which is 125.

It also follows in each case that the counter 40 sends over a line 42 which is the carry-over lead for the last stage corresponding to the lead 37 for the first stage, a carry-over signal which is generated by the aperture corresponding to the character to be projected. in the case of the letter c, the third photoelectric impulse would generate a carry-over signal on the lead 42 connected with the highest order stage of the counter 40, which signal would energize the flash circuit 26 to project the character.

The technique of fiash projection of characters, including the specific construction of the flash circuit 26 and the optical elements associated therewith, is more fully described in our above-mentioned copending application, Serial No. 770,320.

A detailed description of the operation of the counter circuit is not given here, but reference to the above-mentioned publication may be had for specific descriptive data.

An alternative embodiment of the invention will next be described with-reference to Figs. 2. and 3. Referring to Fig. 2, the matrix is' mounted upon a circular matrix support 44 as in the preceding embodiment. The control means or apertures are arranged in two circles, an outer circle of apertures such as 46 and an inner circle of apertures such as 48. The outer apertures are used to trigger the light flashes for projection, there being one of these apertures for each character such as 50. Each of these apertures is in precise spatial relation to a character in the matrix. For example, the aperture 46 is in precise relation to the character e, being on the same radius line with the leading edge of the character as it moves in the direction indicated by the arrow in Fig. 2, passing eventually through a projection position opposite a window 52 in an opaque shield 54. It will be obvious that the particular spatial relationship herein described is not the only one possible. in fact, it may be desirable to displace the apertures and characters angularly as well as radially to provide more room for the photoelectric and character projection apparatus, but this would have no effect upon their precision.

The shield 54 is also provided with a window 56 which is of sufficient length to include both circles of apertures. As shown in the drawing, the right edge of the window 56 coincides with a radius line 58 of the disk 44. However, as in the embodiment of Fig. 1, the window 56 may be dispensed with if an appropriate means for pro jecting a thin luminous slit upon the line 58 is substituted therefor.

In Fig. 2, the character i is shown in a position referred to herein as the projection position. This position is defined as follows: A projection lens 60 (see also Fig. 3) has an optical "axis intersecting the radius line 58 of the disk. The character is located in the first quadrant of the lens; that is, its left edge rests upon the radius line 58 and its bottom edge rests substantially upon a circle having its center in the axis of the disk and passing through the point of intersection of the optical axis and the radius line 58. The corresponding aperture 62 for the character i is located substantially at the right edge of the window 56, that is, upon the line 58, so that it just opens the light path to a photocell 64 at the described instant. A continuous light source 66 such as an incandescent lamp illuminates the window 56 through an optical condenser 68 in the same manner as in the preceding embodiment.

The purpose of having the characters located in the indicated position with respect to the optical axis of the lens 60 relates to the feature described in our abovementioned copending application, Serial No. 150,024, whereby the lens 60 may be interchanged with other lenses of different magnifications for the purpose of changing the magnification or point sizes of the projected characters. Since it is assumed in that application and in the present application that the film is to be spaced the appropriate distance for each character after it is projected, it will be apparent that if the next character is to be of a larger point size it should not be enlarged in such a manner as to encroach upon the space thus pro vided. The described arrangement avoids this diificulty.

A second photocell 70 is actuated by the inner circle of apertures in the same manner as that which is hereto fore described with reference to the outer circle of apertures.

As in the preceding embodiment, a keyboard 72 and register 74 are provided for recording the line of characters. In this embodiment, however, it is further assumed that for each character nine storage pins, or devices of similar nature, are provided in the register. These are divided into two groups, a group of five pins by which the width of the particular character is recorded in the form of a binary number, and a group of four pins by means of which the particular character is distinguished from other characters of like width by another binary number. Thus, as in the preceding embodiment, each character in the matrix has a distinctcode combination of pins which are depresesd or actuated when thecharacter is recorded.

In this embodiment two counters are provided, a five stage binary counter 76 and a four stage binary counter 78. A reader 80 similar to the reader 6 in the preceding embodiment has nine sensing contacts, divided into two sets. The sensing contacts reading the character width storage pins are connected to the five stages of the counter 76 in the same manner as shown in Fig. 4, so as to preset the counter 76 with a number equal to the capacity of the counter, which is 31, minus the width of the particular character. Similarly, the sensing contacts reading the other set of storage pins are connected to the four stages of the counter 78 to preset the counter 78 with a number equal to the capacity of that counter, which is 15, minus the number which is stored in the corresponding pins of the register.

The photocell 70 is connected by a wire 82 to the lowest order stage of the counter 76. A wire 84 is connected to the counter 78 from the highest order stage of the counter 76. This wire receives a signal representing a carry-over from the highest order stage of the counter 76. The carry-over occurs on the next impulse appearing on the lead 82 following the impulse which causes the counter to read its maximum capacity of 31.

The carry-over signal on the lead 84 activates the counter 78 to permit it to count the photoelectric impulses directed to its lowest order stage from the photocell 64. Prior to the carry-over signal the counter 78 is not sensitive to the photoelectric impulses of the photocell 64. Thereafter, however, the counter 78 begins to count the outer circle of apertures, and finally sends a carry-over signal from its highest order stage over a lead 86 to a flash circuit 88 which energizes a flash tube 90 to project the character through the lens 60 upon the sensitive film 92.

The operation of the apparatus of Figs. 2 and 3 may best be described with reference to a specific example. Suppose that it is desired to project the character e. For the matrix of Fig. 2, the character e would be represented by the binary code combination 01000 0101, that is, 8-5, meaning that the character has a width of eight units and that it is the fifth character in the group of characters having eight units of width. Characters of like width are disposed consecutively upon the disk 44, there being a total of twelve width groups separated from one another by the apertures of the inner circle.

At some moment while a dead space 94 (Fig. 2) is in the projection position the counters are reset and the reader 80 then presets the counter 76 with the number 23, i. e., 31 minus 8, and the counter 78 with 10, i. e., 15 minus 5. The reset and preset circuits are identical with those shown in Fig. 4.

After the counters are preset, the aperture 48 on the inner circle is the first to reach the window 56, thereby sending an impulse from the photocell 70 to the counter 76. In all, six such impulses are sent to the counter 76 before the first impulse from the outer ring of apertures reaches the photocell 64.

The first impulse from the photocell 64 and those immediately following it do not advance the counter 78, since the impulses received by the photocell 70 have not yet. advanced the counter 76 to the point where it sends a carry-over signal to the wire 84. However, when the aperture 96, being the ninth aperture to actuate the photocell 70, finds the counter 76 already reading its maximum capacity of 3 1, it causes a carry-over signal to reach the counter 78. Thereafter, each of the apertures in the outer circle sending an impulse to the photocell 64 also advances the counter 7 8. The sixth such impulse, which is produced by the aperture corresponding to the character e, finds the counter 78 reading its maximum capacity of 15, and therefore sends out the trigger impulse to the flash circuit 88.

Thus, the counter 76 may be referred to as a width counter since it starts from an initial position, or count, corresponding to the width of the selected character, and advances under the control of the inner circle of apertures until it carries over on an impulse generated by the aperture which appears immediately ahead of the group of characters having the width of the selected character. Similarly, the counter 78 may be referred to as a character counter since it starts at an initial count corresponding to the desired character in the selected Width group and advances one count for each character in that group until it reaches the selected character. The precision of the projection is ultimately determined by one of the apertures in the outer circle, which must obviously be the one which is in precise spatial relation to the character whose projection it initiates.

It will be apparent that the matrix support does not need to be in the form of a disk, but may be a drum as described in our copending application, Serial No. 770,320, mentioned above. It will also be apparent that the counters in either of the described embodiments may be of other than the binary form.

As stated above, it is assumed that the counters 76 and 78 are reset to zero and then preset by the reader 80 at some time While the dead space 94 is in the projection position. While the specific synchronizing means have not been described, any well-known cam device mounted upon the same shaft with the disk 44, such as is described in our copending application, Serial No. 770,320, mentioned above, may be used. It will be obvious that timing means of this type will also be necessary to cause the spacing of the film 92 between the successive character projections according to the width of the character which has just been projected. The spacing means are conveniently energized by the same sensing contacts of the reader 80 which are used to preset the counter 76.

It will be noted that since the apertures of the inner circle do not actuate the discharge device 90, it is not necessary to locate them with the same precision as the apertures of the outer circle. If desired, they may be replaced with some other form of device having less precision than the photoelectric device herein described.

It will be evident that the invention is not limited to the use of translucent apertures in either of the described embodiments. Thus, the apertures may be replaced with any other form of control means capable of a similar function, such as locally magnetized areas in a magnetic coating disposed upon the matrix support.

It will be apparent to those skilled in this art that other modifications, improvements and variations of the described apparatus may also be made without departing from the scope of the invention.

Having thus described our invention, we claim:

1. Photographic type composing apparatus comprising, in combination, a matrix support bearing a number of characters to be projected and marks each in precise relation to a corresponding character, a continuously rotating mechanism for moving the characters successively through a projection position and the corresponding marks simultaneously through a trigger position, an intermittent discharge device to illuminate a character in the projection position, means for projecting an image of said character upon a sensitized sheet, sensing means operable by each mark in the trigger position to generate an impulse, a multistage counter comprised of seriesconnected elements each adapted for a plurality of stable conditions and connected for cumulative addition of impulses from the sensing means, said counter also hav-- ing a circuit connected with one of the stages to be energized by one of said impulses received when the counter represents a fixed sum, presetting means to in troduce to the counter a sum corresponding to the number of marks intermediate the marl: corresponding to the selected character and a predetermined mark, said preset sum being such that said circuit of the counter is energized when the selected character is in the projection position, and means actuated by said circuit to energize the discharge device.

2. Photographic type composing apparatus comprising, in combination, a matrix support bearing a number of characters to be projected and apertures each in precise relation to a corresponding character, a continuously rotating mechanism for moving the characters successively through a projection position and the apertures successively through a trigger position, an intermittent discharge device to illuminate a character in the projection position, means for projecting an image of said character upon a sensitized sheet, a continuous light source to illuminate the apertures, a photocell adapted to produce an impulse at the instant each aperture passes through the trigger position, a multistage counter comprised of series-connected elements each adapted for a plurality of stable conditions and connected for cumulative addition of impulses from the photocell, said counter also having a circuit connected with one of the stages to be energized by one of said impulses received when the counter represents a fixed sum, presetting means to introduce to the counter a sum corresponding to the number of apertures intermediate the aperture corresponding to the selected character and a predetermined aperture, said preset sum being such that said circuit of the counter is energized when the selected character is in the projection position, and means actuated by said circuit to energize the discharge device.

3. In type composing apparatus, the combination of a rotatable support bearing in consecutive annular arrangement the characters to be photographed and a number of marks each in precise spatial relation to a corresponding character, a register to store digital information corresponding to the position in said arrangement of each selected character in a line of type, means to rotate the support continuously to bring the characters successively through a projection position, each corresponding mark being simultaneously brought through a trigger position, optical means to focus a character in the projection position on to a sensitized sheet, means operable by each mark in the trigger position to generate an impulse, a digital impulse counter adapted to advance on receiving each impulse, means to remove the count in the counter at a fixed time in the cycle of said support, means operated by the register after said removal to advance the counter to a preset count corresponding to said information for a selected character, said counter having a circuit to produce a trigger signal when it is advanced to a predetermined count, a flash device to illuminate a character in the projection position, and means operated by said trigger signal to energize the flash device, said preset count having a value whereby the counter produces said trigger signal when it receives a number of impulses measured by the difference between said predetermined and preset counts.

4. In type composing apparatus, the combination of a rotatable support bearing in consecutive annular arrangement a number of groups of characters to be photographed, each group having characters of like width and the groups being arranged consecutively by width, said support also having a first set of marks each in precise spatial relation to a corresponding character and a second set of marks spaced according to said groups, a register to store digital information corresponding to the width of each selected character in a line of type and its position in a width group, means to rotate the support continuously to bring the characters successively through a projection position, each corresponding mark of the first set being simultaneously brought through a trigger position, optical means to focus a character in the projection position onto a sensitized sheet, means operable by each mark in the trigger position to generate an impulse, means operable by each mark in the second set to generate an impulse, a pair of digital impulse counters adapted to advance on receiving each impulse from the first and second sets of marks, respectively, means to remove the count in each counter at a fixed time in the cycle of said support, means operated by the register after said removal to advance the counters to preset counts corresponding, respectively, to the width and position of a selected character, said counters each having a circuit to produce a trigger signal when it is advanced to a predetermined count, said circuit for the counter corresponding to the second set of marks being adapted to initiate the counting of the other counter, a flash device to illuminate a character in the projection position, and means operated by said trigger signal from said other counter to energize the flash device, said preset counts having values wehreby said other counter produces its trigger signal when it receives a number of impulses measured by the difference between its predetermined and preset counts.

5. Photographic type composing apparatus having, in combination, a matrix support bearing a number of characters to be projected and marks each in precise relation to a corresponding character, said relation being identical for all characters and their corresponding marks, a continuously rotating mechanism for moving the characters successively through a projection position and the corresponding marks simultaneously through a trigger position, an intermittent discharge device to illuminate a character in the projection position, means for projecting an image of said character upon a sensitized sheet, sensing means operable by each mark in the trigger position to generate an impulse, a counter connected with the sensing means, adapted for counting the impulses and provided with a circuit to energize the intermittent discharge device upon reaching a first sum, and preset means operating in timed relation to said rotating mechanism to put a second sum in the counter corresponding to the difference between said first sum and the number of succeeding impulses to be received before the impulse generated by the mark corresponding to a selected charaeter.

6. Photographic type composing apparatus having, in combination, a matrix support bearing a number of characters to be projected and marks each in precise relation to a corresponding character, the characters being of difi erent widths, a continuously rotating mechanism for moving the characters successively through a projection position, each mark being brought through a trigger position simultaneously as its corresponding character passes through said projection position, an intermittent discharge device to illuminate a character in the projection position, a support for a sensitized sheet, means for projecting an image of said character upon the sensitized sheet, a movable carriage to cause projection of successive characters on different portions of the sensitized sheet, said carriage being stationary at the moment the intermittent discharge device is energized, sensing means operable by each mark in the trigger position to generate an impulse, a counter connected with the sensing means, adapted for counting the impulses and pro vided with a, circuit to energize the intermittent discharge device upon reaching a first sum, and preset means operating in timed relation to said rotating mechanism to put a second sum in the counter corresponding to the difference between said first sum and the number of succeeding impulses to be received before the impulse generated by the mark corresponding to a selected character.

References Cited in the file of this patent UNITED STATES PATENTS 2,203,437 Levy June 4, 1940 2,257,763 Petterson Oct. 7, 1941 2,475,497 Harrold July 5, 1949 2,600,168 Klyce June 10, 1952 2,641,976 Bryce June 16, 1953

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