US2258994A - Photographic printing apparatus - Google Patents

Description

Oct. 1941- w. E. MERRIMAN ET AL 2,253,994

PHOTOGRAPHI C PRINT ING APPARATUS Filed Dec. 14, 1939 2 Sheets-Sheet 1 MLL/AM f. MfRR/MAN 5RAw/1Aw5uR/v/1AM INVENTORJ I ma G l ATTORNEYS Oct. 14, 194 w. E. MERRIMAN ET AL 2,253,994

.PHOTOGRAPHIC PRINTING APPARATUS 2 Sheets-Sheet 2 Filed Dec. 14, 1959 Mu. MM ENERR/MA/y BRADJHA A/BUR/YHAM IN VEN TOR 3514. xauzz ATTORNEYS results condensers discharge path conductive after the Patented O ct..14, 1941 UNITED STATES PATENT OFFICE lrno'rooaarmc ranv'rnvo msns'ms Williaml. lerrhnan and Bradshaw Burnlmn, 'lhehestenmYcalllgnontoEastmanxodak New Jersey N. I, a corporation of Application December 14), 1939, Serial No. 309,222

The present invention relates to phot graphic apparatus and 'more particularly to that class of apparatus in which the exposure interval is determined by the rate of change in the charge I ,of an energy storage device, such as a condenser,

as controlled by the intensity of the exposing light.

vide a time delay apparatus which will give accurate results over a long range of photographic exposures.

A further object of the invention is to provide a photosensitive time delay apparatus which is particularly adapted for the accm'ate control of exposure intervals in photographic printing. v

A number oi. arrangements are known for controlling a printing interval by varying the charge One of the objects of the-invention is to prop in connection with-the accompanying drawings.

on a condenser at a rate determined by the different may be obtained 1 adjusting the starting charge oi the condenser.

by terminating the printing interval at a difl'erent charge on the condenser, by employing diilerent condensers, by adjusting the characteristics of the charge or discharge path, or many other well brown way, adjusting some factor or factors whereby a predetermined printing intensity will be translated into a different time interval.

7 In accordance with this invention 'a light sensitive cell subjected to a known proportion of the printing light regulates the rate of discharge of a condenser which previously had been provided with a predetermined charge, the value of which was selected in accordance with the sensitivity or printing requirements of the paper employed A vacuum tube relay circuit is employed for obtaining accurate and' rapid response and since such a circuit can and should be made verysensitive it isdesirable to forestall a repeat exposure by some arrangement for carrying the discharge beyond the critical point at which the exposure is terminated. This-is dcnebymaintaining the termination of the printing interval.

4 Claims. (,c1. "-20 The novel features which are believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and mode of operation, will best-be understood by reference to the following description taken in which Figure 1 represents an embodiment of the invention as applied to a photographic printer of the projection type; Figure 2 shows in perspective a schematic arrangement of a circuit similar to that shown in Figure 1; and Figure 3 shows a similar arrangement as modified for use with a direct current source of power.

Referring to the drawings, there is shown diagrammatically a printing apparatus comprisinga source of light II for illuminating a record v II to be printed and which is imaged on a sensitive'sheet I! by a suitable lens IS. The starting and stopping of a printing interval is brought about in any well known manner and is here shown as being accomplished by a shutter vane ll which is biased by a spring I! to light blocking position and is adapted to be' moved to ht position (shown in broken lines in Figure 2) by a solenoid IO.

For energizing the automatic control arrangement of the invention, a light sensitive cell I1 is positioned to be activated in strict accordance with the intensity of a printing exposure and as shown in the drawings this is accomplished by-arranging in the light path a semi-transparent reflector II for directing onto the cell ll acertain cathode of an electric valve 2. will be'charged proportion oi'the light transmitted by the record I I being Printed.

With the plug is connected to a source of power (the circuit illustrated in Figs. 1 and 2 is designed for operation on volt, 60 cycle alternating current) an energy storage device shown as a condenser C1 connected in series with a potentiometer network P across the grid and to the peak value of the A. C. potential at E-as shown in Fig. l. This potential 1! is of course determined 'by the setting of the potentiometer Fund is preferably variable and full line voltage. The photocell I1 is in the discharge path of the condenser C1 and this path is kept conduct ing by providing an auxiliary lamp II which is made non-actinic by shielding its rays fromthe sensitive sheet I! or, preferably, restricting its light to a wave length to which the sensitive material I! is insensitive but to which the cell II is sensitive. The cell ll is preferably red between about 7 volts red light. Thus, with the 1 stantially the instant it reaches its final 2 sensitive and, accordingly, the lamp 2! may emit discharge path always conducting the rectifying action of the grid of tube will balance the charging and discharging condition which produces a very stable initial D. C. voltage across the condenser C1. A mercury switch 22, when closed, completes the circuit through the printing lamp it and a micro switch 23 which, in operation of the printer, is operated after the switch 22, disconnects the A. C. poten' tial from the grid of tube 2t and connects the a cathode of a second tube 241 to the line. The

removal of the A. C. potential from the grid of the tube 2t leaves the potential on this grid at a high negative value determined by the charge on the condenser 01 and thus blocks the passage of plate current in the first tube 2@. The plate current of the tube 28) serves to bias the grid of the second tube 2% by reason oi the drop across resstance R2 and, when this plate current stops, the tube it becomes conducting and its plate current energizes a coil 25 to close a relay 2% which shunts the red lamp 2E.

The shunting of the red lamp 2i throws full line voltage upon the solenoid it which removes the shutter vane M from the light beam and a printing exposure starts. Upon the starting of this exposure a portion of the light transmitted by. the record H is directed by the reflector it upon the cell ii and the charge on the condenser C1 begins to drain on at a rate determined by the intensity of the light transmitted by the record ll. As the condenser C1 discharges, the potential on the grid of the'tube 28 becomes; more positive and finally reaches a value at which the tube 20 again becomes conducting and its plate current through the resistance R2 impresses a v biasing potential upon the grid of the second tube 24 to block its plate current, thereby releasing condenser C1 was not drained below the critical value.

The switches 22 and 23 are preferably arranged to be actuated in the desired sequence upon the movement of a platen 21 to a position at which it holds flat the sensitive material E2 in any well known manner. As shown in Fig. l, the switch 22 is arranged to be actuated'by the platen just prior to its clamping position and the switch 23 is" arranged to be actuated by the platen 21 at subposition. This sequential operation of the switches 22 and 23 insures that the-lamp It will reach its lull brilliancy before a printing exposure is started.

A diode section of the second tube 24 is employed to supply direct current for the plate circuit of the tube 24 and also to supply direct current for the anode of the photocell l1. Thus, al-

though the tube 26 and the cell II have returns to the opposite sides of the A. C. line, a single clear from the drawing that this is accomplished scription that the apparatus of the present invention, in addition to providing an accurately timed exposure, possesses many refinements without sacrificing simplicity. For instance, the auxiliary lamp 2i shining on the photocell ll prevents repeat exposures by, in effect, locking the automatic exposure mechanism in the released condition. This lamp it also functions to stabilize the initial charge of the condenser C1 by establishing equilibrium between the cell current caused by the lamp 2! and the grid current of the tube 26. Due to this arrangement, if the voltage of the supply side of the condenser C1 is changed in order to print photographic material of diii'erent sensitivity, a momentary unbalance of the grid and photocell currents which occurs is quickly restored by the relatively large photocell current. This-insures that the proper exposure will be obtained after each sensitivity level' change. By arranging the red lamp 2! so that it is visible to the operator, it functions as an indicator of when the exposure has terminated. In the circuit of the lamp it there is preferably provided a slide rheostat 28 and a resistance 29 which resistance may be shunted by a switch 30, which switch may be positioned so that it may be convenient for operation by the knee of the operator. With these two means of adjusting the current through the lamp it, its temperature changes and, of course, a corresponding change takes place in the ratio between the actinic and red light emitted by the lamp it. Since the photocell H is preferably red sensitive, and the sensitive material it is generally sensitive in' the blue end of the spectrum, a change in the apparent printing level is obtained even though the energy required to discharge the condenser remains constant. Thus, by adjusting the rheostat 28 or shunting the resistance 29, the print density may be altered without adjustment of the automatic control circuit.

In general, if difierent prints are made at different optical magnifications, it would normally give different photographic results unless the automatic exposure circuit was adjusted. Since any adjustments of t l tsxposure circuit would-be difilcult to provide in advance, without knowing the focal length of lenses which were to be employed in printing, it is believed preferable to insert in the different lenses a red diaphragm in, order to alter the red to actinic light transmission ratio and thereby equalize'any number of lenses so that the exposure control system will print properly for all without further adjustment.

It is frequently desirable to print difierent types otnegatives upon difierent types of printing paper and, accordingly, the potentiometer netwoi P is provided with three separate adjustments so that any one of three switches S, M, ,or H, which may correspond; respectively, to so called soft,

- medium, and hard papers, may be closed to alter the exposure control circuit in accordance with the sensitivity of these papers. The arrangement illustrated in Figures 1 and 2 is adapted for operation from alternating current source of supply and if it is desired to operate from direct current,

the circuit arrangement of Figure 3 may be 8111- ployed. In Fig. 3 the parts corresponding to equivalent parts in Figs. 1 and 2 are given corresponding labels and it is believed that inspection by the arrangement of the resistance R: and the condensers C3 and C5, whereby the condensers Ca and C charge to the same direct current voltage.

of Fig. 3 will enable. anyone skilled in the art to build the control arrangement of the invention for operation on direct current.

In one arrangement constructed in accordance Therefore, the rela asusaccs with Fig, 3, the following values or the several nu .s. I were Ohm;

megohmfih, 100,000 ohms; and R4, 10,000 ohms:

The capacities employed'were as follows:

It will be understood that these values are given merely as an example 0% one circuit arrangement andarenottobeconstruedaslimitingJ While we have described the preferred embodiments oi. our invention, it will be obvious that it is not limited to the exact iormsillustratedand that many variations may in the particular connections be used without departing from the scope oi. the invention as set forth in the appended claims.

If manual rather than automatic operation (1 aswitch Ilconnectedinthe'mainlead i'rom the'plug ll may be moved to contact 32 without breaking its engagement with contact 31. With the switch 8| both contacts flandflthegridoithesecondtubeflisre-' turned to the line through a resistor R4 (10,000 ohms) in parallel with the resistor R: (1 megohm) in the plate circuit oifthe first tube 3|. This'resistance' is so low that the potential drop due'to the plate current of the first tube 20 is too small to bias the tube 24 suiiiciel .ly to allow thcrelaycoilfltoreieaseitsarmaturefl. 25 and the solenoid It are energized as long as the operator holds down theplaten 21.

We claim:

1. In photographic printing apparatus in which the discharge of a condenser determines the printing exposure interval, alight sensitive cell activated in accordance with the printing in- I I tensity for governing the discharge or the condenser, means for terminating the exposure when the condenser has been discharged to a predetermined value, and means actuated by the exposure terminating means for discharging the condenser below said predetermined value, whereby surges arising upon the sudden termination or the exposure will not bring about a repeat 2. In photographic printing apparatus in which the discharge of a condenser through a predenected directly to one plate oi the condenserand havinga cathode and an anode, means'ior'impressing an alternating potential bettsan the cathode and grid so that the rectifying action of the grid charges the condenser, a light sensitive cell connected for discharging the condenser in accordance with the conductance 01' said cell, an

auxiliary lamp for illuminating said cell with non-actinic light oi'suflicient intensity to provide said cell with a conductance such that the discharge current substantially equals the charging currnt thereby providing a stable and repeatable initial charge for the condenser, means for removing the alternating potential from the grid of said tube, whereby said tube becomes nonconducting, means controlled by the stopp e of current through said tube for starting a printing exposure and extinguishing said auxiliary lamp,

termined range andunder the control or a light sensitive cell determines the exposure period, a

condenser, an electronic tube having a grid conmeans for activating said cell in accordance with the intensity of the printing exposure, thereby discharging the condenser and raising the grid potential at a corresponding rate, means controlled by current through said tube when the grid potential reaches a predetermined value for terminating the printing exposure and energizing said auxiliary lamp, whereby the cell is maintained sufliciently conductive to assure that the potential on the grid does not drop below said predetermined value. 7

3. In photographic printing apparatus, means for translating-the average intensity of the printing light into an inversely corresponding time interval, said means including a condenser, a light sensitive cell for governing the rate of variation of a charge on the condenser and means ior terminating the time interval when the charge on the condenser has been varied through a predetermined range, and means-operative upon t'ermination of the time interval for continuing the variation of the condenser charge to a value substantially beyond'said predetermined range.

4. In apparatus for controlling a photographic exposure, means ior regulating the exposure interval comprising a condenser, means for varying the charge on the condenser at a rate strictly proportional to the intensity of the exposure, means responsive .to a predetermined variation in the charge on the condenser for terminating the exposure, and means operative upon termination or the exposure Ior activating said condenser charge varying means, whereby the variation of the charge on the condenser is carried beyond said predetermined variation.

BRADSHAW BURNEAM.

CERTIFICATE OF CORRECTION. Q

' Octobe'r 111 1911.1.

Patent No. 2,258,991

WILLIAM HERRINAN, ET AL.

It i; hereby c ertifie'd that error appeang in the printed speofiicatiqn. of the above numbered. patent requiring oorrecti'onas folQLows: Page}, flnst column, line 9, for C (in and C read --C Ch and'C line 10, for "0 read c gnci th at the said Letters Patent shoulcibe read with this correction therein that the 'sememay conform tothe record of the 00.51; in the Patent office. 4 I

Signed and sealed. this 2nd day of December, A. 191 1.

7 Henry Van Arsdaie, Acting Commissioner of Patents.

. a 4 CERTIFICATE OF CORRECTION. 1 Patent No. 2,258,9914..- October 114 19,41.

" wmim 1:, nERRI R. ET A It is hereby certified that errbr appeal rs: in the printed speoificatiqn. of the above numbered patent requiring correction as folZLdws: Page}, firet; column, line 9, for 6 (5) and C read "0 Ch and 0 line 10, for 3 read Crz"-; that the said Letters Patent shouldbe read with this correotion therein that the same-may conform tothe record of the case in the Patent Office.

Signed and sealed this 2nd day of December, A. D

. Henry Van Arsdal e, a v Acting com-1831 1181 of Patents;

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