Patent Publication Number: US-3876116-A

Title: Electronic photocopying machine

Description:
United States Patent Kushima et al. 1 Apr. 8, 1975 ELECTRONIC PHOTOCOPYING MACHINE 3.698.356 10/i972 DuBois et al. .i ll8/DlGi 23 [75] Inventors: Teizo Kushima; Susumu Tanaka;  
 Masaya Ogawa1 a of Osaka Japan Primary ExaminerMorris Kaplan [73] Assignee: Minolta Camera Kabushiki Kaisha.  
 Osaka Japan [57] ABSTRACT [22] Filed: Jan. 3 1973 An automatic adjusting device for the concentration of a developing solution in a photocopy machine PP 328357 comprising a concentration detecting and measuring Rained Application Data system. an electronic circuit, and a system for operat- [60] continuatiommpan of SN No 270 8 Jul, H ing a valve of an inverted bottle containing a concen- 1972 which is a division l N0 i trated developing solution and located above a devel- 18 [966 PM NO 3190759 oping solution tank. The systems and circuit are so arranged that the operation of opening the valve to in- [52] CL H 222/70; 1 18/7; 118/602 troduce the concentrated developing solution into the 51 Int. Cl .i G03g 13/10 tank can automatically be made with and [58] Field of Search 118/7 8 4 DIG 23; constant time interval by a photoelectric current gen- 355/3; 222/57 70; H-HDIG 2 37 LE erated in response to the variation of concentration of the developing solution which flows between a light [56] Rderences Cited source and a photoelectric element the operation UNITED STATES PATENTS being stopped when the concentration of the develop ing solution reaches a predetermined level. $369,524 2/1968 Fuhrer [Hi/637 1494328 2/l970 Maloney Hit/637 10 Claims, 24 Drawing Figures FIG. 9  
 ill!!! FIG. IO  
  ELECTRONIC PHOTOCOIYING MACHINE This application is a continuation-impart of Ser. No. 270,83I filed July I I, I972, which in turn is a division of application Ser. No. 543,226 filed Apr. 18, 1966 and issued as U.S. Pat. No. 3,690,759 on Sept. 2, I972.  
 BRIEF SUMMARY OF THE INVENTION The present invention relates to a copying machine of the type, wherein zinc oxide powders (ZnO) or equivalent materials are applied to surfaces of paper to produce sensitive papers which can used by being exposed to rays of light after being negatively electrified. and which are then developed and fixed to complete a copying operation.  
  Particularly, the invention relates to a device for automatically adjusting the concentration of a developing solution for electronic photocopying, by detecting the concentration of the developing solution, effecting strengthening of the developing solution by selectively adding concentrated solution whenever the concentration is lowered below a certain predetermined value and repeating the addition operations in a certain time interval, whereby the concentration of the developing solution can automatically be retained at a certain level.  
  In general, a developing solution for photocopying machines consists essentially of a strengthening solution wherein a pigment or fine carbon powder is dissolved in a solvent to form a concentrated solution and of a solvent for diluting said strengthening solution. The concentration of the developing solution varies with use and in particular where dark figure portions are abundant in the copy, the carbon or pigment content is rapidly transferred or removed and thus the developing solution is quickly diluted.  
  In conventional photocopying machines, the concentration of the developing solution has been adjusted by manual operation ofa valve to drop concentrated solution therein, but such operation has the disadvantages that correct maintenance of the concentration is quite difficult and the hands of the operator are liable to be stained with the concentrated developing solution.  
  According to the present invention, there is provided an automatically operating arrangement in which the above disadvantages are completely eliminated by combining a simple electronic circuit, an electric valve and photoelectric sensing means thereby enabling an appropriate concentration ofthe developing solution to be automatically maintained.  
 BRIEF DESCRIPTION OF THE DRAWING FIG. I is a perspective view of an electronic photocopying machine according to the present invention;  
  FIG. 2 is a side sectional view illustrating the essential parts of said electronic photocopying machine of the present invention;  
  FIG. 3 is a side sectional view of a lens exchange device for said electronic photocopying machine;  
  FIG. 4 is an oblique view of a sensitive paper feeding device;  
  FIG. 5 is a partial plan of a belt for a sensitive paper feeding belt;  
 FIG. 6 is a side sectional view thereof;  
  FIG. 7 is a side sectional view of said sensitive paper feeding device;  
  FIG. 8 is an oblique view ofa sensitive paper separating hook;  
  FIG. 9 is a diagram showing the displacement of focal distance due to the movement of lenses;  
  FIG. 10 is a partial perspective view showing a practical example of FIG. 9;  
  FIG. 11 is an exploded fragmentary view in perspective of a stopping device for lens fixtures;  
  FIG. 12 is a diagram of an electric circuit for driving and controlling the electronic photocopying machine according to FIGS. 1 and 2;  
  FIG. 13 and FIG. 14 are respectively an electric circuit diagram and perspective view ofa dial counter for sheet numbers of sensitive paper;  
  FIG. 15 is a partial perspective view of an electrification device and an exposure frame in said electronic photocopying machine;  
  FIG. 16 is a fragmentary and exploded perspective view showing a roller-supporting position;  
  FIG. 17 is a perspective view of said exposure frame and of an exposure frame body accompanied with driving rollers;  
  FIG. 18 is an explanatory sectional view of an intermittent sensitive paper feeding device for said electronic photocopying machine;  
  FIG. 19 is a diagrammatic illustration ofa system adjusting the concentration of the developing solution:  
  FIG. 20 is an enlarged sectional view showing the valve at the bottom of the vessel containing concentrated developing solution;  
  FIGS. 21a, 21b and 216 are diagrammatic illustrations showing respective concentration detecting parts of the concentration adjusting device; and  
  FIG. 22 is an electronic wiring circuit for the concentration adjusting device.  
 DETAILED DESCRIPTION In FIGS. 1 and 2 is shown a general construction of the electronic photocopying machine ofthe present invention and therein 1 denotes an outer casing and 2 denotes a glass plate on which an original 3 is loaded; 4 denotes a soft plate to push down said original; 5 and 6 denote illuminating lamps for the original; 7 is an illuminating box with a cooling fan for illuminating the surface of the original with the aid of the lamps; 8 is a re flecting plate to reflect the image from the original; 9 denotes a projecting lens means; 10 denotes a transpar ent focusing glass for making the sensitive paper 20 even. A clearance of approximately I mm is provided between said transparent focusing glass and plane rear plate 10&#39;, and said sensitive paper is fed into said clearance.  
  Two projecting lenses 9, 9 are used as shown in FIG. 3 of which, for instance, lens 9 is a projecting lens for equimultiple photographing and lens 9&#39; is a projecting lens for contraction photographing. In this case, the equimultiple and contraction photographings are performed by various lenses mentioned above, of varying focal lenths. As illustrated in FIG. 3 and 11, a lens fitting 19 is provided with a knob 13 which protrudes outside the machine through a hole 14 formed in the outercasing and a lever shank is provided on a pin 11, as a lens-exchanging means. Furthermore, a stopping mechanism (see FIG. 11) comprising a ball 16, a spring 17 and a pushing screw 18 is provided on a front panel 12 ofa photographing box 15. When either of the two lens comes to the optical axis. the ball 16 enters a re cess 38 of the lens fitting member 19, said fitting member being thereby stopped. In such a way, with even two or three lenses, similar operation can be conducted. Further as in said embodiment of the present invention, the distance between the original 3 and sensitive paper may be changed. The means therefor are shown in FIG. 9, wherein the glass plate 2 on which the original is loaded and the lens 9 are placed respectively at the position shown by solid lines for the equimultiple photographing and the contraction photographing is performed by displacing said glass plate 2 and said lens 9 to the dotted line positions. This is easily understood from the fundamental calculation regarding the optical system and the carrying out means is shown in FIG. 10.  
  Namely, in FIG. 10, a frame 2&#39; joined with the circumference of glass plate 2 for loading the original 3 is formed with a plurality of holes H, H Each middle hole H, engages a pin P, provided in the outer casing l of the copying machine proper, for the purpose of positioning while the other pairs of holes H and H, are spaced respectively by distances A and B to engage P and P, on the outer casing I. If the frame 2 is taken off the pins and turned around through 180 horizontally, and then if the frame is engaged with the pins again, pin P, is sufficiently long to fit with the hole H,. But since pins P,, P, can not be respectively inserted in holes H H said frame is raised by the heights of pins P P Accordingly, if the heights of pins P P are assumed to be the length ofthe abovementioned objects can be accomplished and the lens can be advanced by well known means, such as a helicod or like means.  
  In connection with FIG. 1, FIG. 2 and FIG. 4, the sen sitive paper 20 of sheet formed and cut in regular sizes is piled up on the upper portion of machine, with the sensitive surface facing downward. It is pulled out, sheet by sheet, by paper feeding rollers 25, when a print switch button 36 is pushed. In order to prevent the sheets of sensitive paper 20 from being sent out more than two sheets at a time, friction plates 21 made of sponge, rubber or the like are used and guide plates 22, 23 and 24 which prevent meandering of said sensitive paper are also used for changing the advancing direction of the sensitive paper. Further, the paper feeding rollers 25 are rotated through a transmission gear com prising a motor 27, sprocket wheels 28, 29 pulleys 26 and 30, a chain 31, a belt 33 and a shaft 32, until the front end of sensitive paper 20 reaches a microswitch 34 whereby said microswitch is opened and motor 27 is stopped (see FIG. 12), so that two sheets of sensitive paper are not transported. During this time, a sheet of sensitive paper 20 is taken between rollers 41 and 41 and fed continuously between corona electrification device 37 to become sensitive to light and then fed to the exposure surface through rollers 42 and 42&#39;.  
  A movable contact of the other microswitch 35 provided in parallel with the microswitch 34 is initially in contact with a terminal towhich a resistor R,, neon lamp Ne and resistor R,, are connected, as illustrated in FIG. 12, and moves so as to contact the other terminal to charge a condenser C, through a rectifier 39 when an actuator thereof is pushed by the front side or edge of said sensitive paper 20 passing across the same. However, the actuator of said microswitch returns to unactuated position to return the movable contact to said initial position when the rear side or edge of the sensitive paper is passed completely across the actuator and thus the condenser C, discharges charged current through the resistor R,, neon lamp Ne and resistor R,  
 and illuminate the lamp Ne. Accordingly, the collector current of a transistor TR is increased and as relay RY, is operated to close-circuit the contact point RY,A, relay RY, is operated to change contact point RY A over to contact point RY B. Therefore, the main motor 40 and related rollers are all stopped, while the sensitive paper 20 is stopped at exposure position and simultaneously the lamps 5 and 6 are lit and the exposure is commenced. However, the charge charged into the condenser C, is gradually discharged according to a time constant as established by R,, R VR and C,, the collector current of TR being thereby decreased and RY, and RY, being recovered after several seconds. In consequence, illuminating lamps 5 and 6 are extinguished and again the main motor 40 is rotated and the sensitive paper 20 is fed out of the exposure frame. Further, a variable resistor VR is used for adjusting the operational time for the timer.  
  In FIG. 15 showing construction details in the neighborhood of the exposure frame, rollers on the side of sensitive film (opposite the flat transparent plate 10, and also on the side oflenses) of sensitive paper 20 are all driven rollers, and the bearings of all other 41&#39;, 42, 43, 45 and so arranged as to be pushed to the counter driving rollers by spring pressure slidably as shown in FIG. 16. Namely, in FIG. 16 a bearing 92 slidable along a notched groove ofa holding plate 91 and a spindle 97 of driven roller 41&#39; is inserted in said bearing and a metallic stopper 93 is provided for avoiding dropping-off of said hearing. A spring 94 is held with two pins to push down bearing 92. The abovementioned construction is a mere example, and other equivalent constructions may be as well used. Further, the driven roller 43 as illustrated in FIG. 15 is pushed by one end of a lever 44&#39; which is tensioned by a spring 29 and pivoted on a pin 44 suitably secured to the copying machine body and thus said driven roller always urged to a driving rol ler 43&#39;.  
  On the other hand, each of driving rollers 41, 42, 43&#39; and 45&#39; possesses a sprocket wheel 46 respectively as shown in FIG. 15 and is connected with chain 47 through sprocket 48 and idle pulley 49 and rotated by main motor 40 through electromagnetic clutch 40&#39;.  
  As apparent from the foregoing descriptions, consideration will now be given to the film surface side and rear surface side of sensitive paper 20 separately. Between both sides, since there is no power transmission mechanism on the roller surface excepting the frictional transmission on said surface, said construction can be incorporated with the film surface side and with rear surface side respectively. Thus, the rear surface side can be alone separated, opened and closed, and moreover when opened, all the driven rollers can be stopped. Therefore, the sensitive paper 20 can be easily taken out, or focusing can be performed easily. If, on the contrary, the film surface side of sensitive paper 20 is operated for driving the roller instead of as in the construction of the present embodiment, it is very difficult to design a construction wherein the said driven roller shaft does not project and it is obvious that such a construction can not be realized. Further, when both driving rollers and driven rollers are presented, the situation will become even more difficult.  
  Further. as a means for feeding sensitive paper 20 in the abovementioned copying machine, the belt conveyor shown in FIGS. 5 to 8 is recommended. More particularly, an endless belt 57 is incorporated with or separately secured with a large number of flexible sucking discs 58; said belt being hung over rollers 59 and 79 either of which rollers for instance, one of the rollers 59 is set as the driving roller and opposed to a roller which imparts suction to the suctioning discs, while the other 79 is opposed to a hook means 108 for separating sensitive paper from the sucking discs. A pair of rollers 109 and 109&#39; is provided at the near downward portion to said hook so as to feed the sensitive paper. In addition, when sensitive paper is introduced in a space between rollers 59 and 107, the sucker 58 of belt 57 will be compressed with said two rollers and will be passed through said rollers with said sensitive paper, while the interior air is forced out. Therefore, the suckers 58 passing through said two rollers advances with said sensitive paper being sucked thereagainst and the paper thus approaches the stopping position for exposure. Then, the exposure is completed with images of original figures being projected onto the sensitive paper through lens 9 and again belt 57 proceeds accompanied by the sensitive paper. As it passes along the curve of roller 79 the outside length becomes large and suckers 58 are deformed correspondingly. Sensitive paper can not correspond thereto and air is lost due to the deformation. Automatically, the sensitive paper is peeled off separately and said paper is guided to feeding rollers 109 and 109&#39; by the separating hook 108 which serves also as a guiding member to proceed downward to the following step.  
  According to the present embodiment since the sensitive paper is fed between rollers together with flexible sucking discs incorporated or separately provided in a transporting endless belt, the sensitive paper cannot slide but is firmly and closely kept in position due to the sucking action of many sucking discs. Moreover, shadows from the previously employed clipping bars and hooks are avoided and do not appear on the copying surface. Further high priced and complicated means for vacuum suction purposes is not required.  
  Next, FIG. 17 is a perspective view of an exposure frame and driving rollers according to the present invention. All references in FIG. 17 correspond to those of FIG. 2. 50 denotes the machine bed of the present copying machine; 51 denotes a pair of supporting brackets; 52 denotes a pin mounted on said supporting bracket, said pin being engaged with holes 53 formed in the plate 98&#39; and being so composed as to rotate a driving system block as represented by two point-chain lines, and when closed, a recess groove 56 of lever 55 is engaged with pin 54 secured to exposure frame body 98 thereby retaining a clearance between the flat transparent plate 10 and rear plate 10&#39;. Furthermore, 60 denotes a developing vessel for developing the sensitive paper 20 already exposed.  
  One of the features of the copying machine according to the present invention lies in that a next sensitive paper 20 is drawn into an exposure position, i.e. into clearance between the transparent focusing glass 10 and rear plate 10 for commencing the next exposure, while the sensitive paper 20 already exposed is continuously pulled in the developing vessel 60 thereby providing a continuous copying velocity capable of being abruptly increased.  
  Generally, in the automatic copying machine, the sensitive paper is usually fed at a predetermined veloc ity through all the steps excepting the stationary period during said exposure stage. For instance, in the elec- 6 tronic copying machine, the sensitive paper is fed in order through all the steps from the feeding-in of sensitive paper through charging, exposing and drying fixing) or the like at constant velocity excepting the exposure.  
  Furthermore, in order to manufacture a plurality of copies continuously from the same manuscript (objects) each time the sensitive paper is stopped, the distance between the sensitive paper advanced during the time and that just stopped is extended and it is reasonable that the copying velocity per minute is decreased. During the steps of electrification, development, drying and so forth, the velocity of movement is required to be rather uniform or else in the finishing of the figures there occur troubles such as uneveness in electrification and the finish of figures, uneveness in the development and uneveness in drying all of which damages the quality of the pictures.  
  An object of the present invention is to continuously effect the copying operation at highest effeciency within the required limitation of paper feeding velocity in the development and drying stages by possibly shortening the distance between sheets of sensitive paper during the exposure. In order to accomplish such as object, according to the present invention, an intermittent feeding device for sensitive paper as shown in FIG. 18 can be proposed. The object or original 3 is put on the stand glass plate 2 so as to contact images on the object to be copied with the plate 2. When the surface of the object is illuminated bby a suitable light source, the optical path from the object is bent by means of the plane reflecting mirror 8 and the image on the object is projected onto the sensitive paper 20 through the lens assembly 9 and the flat transparent plate 10 and copies onto the sensitive paper which is fed prior to the exposure in position between the flat transparent plate 10 and the rear plate 10&#39; located in parallel with the trans parent plate and closely thereto. Further, another means, for instance, a plane rear plate 10&#39; formed with a number of small holes, without using the flat transparent plate 10, the air existing between the sensitive paper and plane rear plate is evacuated by a suctioning device (not illustrated) so that said sensitive paper is sucked to the surface of said plane and back plate and simultaneously transported. Furthermore, when the distance from rollers 42 and 42&#39;, 4S and 45&#39; are longer than thhe sensitive paper, rollers 43 and 43&#39; for transporting said sensitive paper with only ear portions thereof being clamped are used. The reference letters a e show the sensitive papers occupying the drying, developing position, a position between exposing and developing positions, exposing and awaiting position, respectively.  
  In the abovementioned construction, all the rollers driven by the motor 40 are stopped, when the sensitive paper is fed into the exposing position, by means of the microswitches 34, 35 and the related mechanism as described hereinbefore, the lamps 5 and 6 (FIG. 2) illuminating to commence the exposure. When the circuit recovers after an appropriate period of time has elapsed, by means ofa timer in the circuit, the abovementioned illuminating lamps are extinguished, said rollers begin to rotate and the sensitive paper after exposure is discharged by rollers 45 and 45&#39;. When the front side of the exposed sensitive paper abuts and presses the actuators of microswitches 34&#39;, 35 at the lower end of the exposing position, this actuates the microswitches so as to commence the feeding of the next sensitive paper to the exposing position through rollers 42 and 42. On the other hand, the preceding exposed sensitive paper is guided by a guide plate 61, and introduced into a developing vessel 60 by rollers 62 and 62&#39;, and developed by developing solution 64. After a squeezing out of the excess amount of solution by rollers 63 and 63&#39; the developed wet sensitive paper is transferred by a conveyor belt to a heater 82 to dry the same, and the paper is discharged from the machine. The development vessel illustrated is a single bath type but a two-or-more bath type vessel can, of course, be worked out similarly. Moreover, any dry type developing means may be used for the present copying machine in lieu of the wet one.  
  In the abovementioned construction, the features of this embodiment of the present invention which are useful for shortening the distance between each of the sensitive papers include that the feeding velocity for the sensitive papers, i.e. circumferential velocity of rollers 25, 41, 42, 43&#39; and 45&#39;, is increased to several times the feeding velocity for rollers subsequent to the roller 62 and simultaneously the resulting deflection of the sensitive paper is temporarily taken out of the regular passage to avoid effect on the velocity of feeding sensitive paper for the developing and drying (fixing) stages.  
  This will further be explained in connection with FIG. 18 wherein C is the sennsitive paper which is entering the developing vessel 60 after the exposure finished, the front end of said sensitive paper approaching the vessels from rollers 45, 45&#39; to 62, 62&#39; along the shortest course. However, since the feeding velocity of rollers 45, 45&#39; is higher than that of rollers 61, 62, the later half of the sensitive paper forms a loop outside the passage as apparent in FIG. 18 and the tail of the sensitive paper passing through rollers 45, 45 turns as shown and assumes an arc like shape as shown in the thick dotted lines. Meanwhile, the next sensitive paper d is drawn into the exposure position and it is arranged that 4. may pass through rollers 62. 62&#39; completely until the exposure is finished.  
  As apparent from the foregoing operations, the continuous copying capacity N in a fixed period of time is shown substantially as in the following formula:  
 S: distance (cm) between the sensitive papers, re-  
 spectively at waiting and exposing positions W: length of sensitive paper (cm) v: sensitive paper feeding velocity (cm/sec) until the paper entering the developing vessel i.e. circumferential velocity of rollers 25, 41, 41, 42, 42, 43, 43&#39;, 45, 45  
 1: exposure time.  
  The above-shown S.W. r are constant according to each copying machine, and can not be altered abruptly but u can be changed relatively easily.  
  As described above. since the capacity of copying machines is limited according to the developing and fixing usually it is limited to approximately 3cm/sec, while. on the contrary, according to the present invention, the velocity can be increased to approximately cm/sec. The practical examples for both cases will be described as follows:  
  Assuming that S 9cm, W 21cm (Japanese Standard Paper Sizes: A4), and r =4 sec, when v 3 cm/sec, N 4.3 sheet/min; when v 10 cm/sec, N 8.6 sheet/min. Namely, the copying velocity can be doubled.  
  As ahead running sensitive paper passes through rollers 62, 62&#39; in (S w/v T) seconds 7 seconds, copying can be contained without overlapping.  
  Next, the sensitive paper enters the developing vessel 60 as described above. Driving rollers 62, 63 and driving pulley 77 possess sprocket wheel 73 respectively, and rotate by the transmission mechanism of chain 76 through motor 72, sprocket wheel 75 and idle pulley 74; and a conveyor belt 81 is rotated by driving pulley 77 and driven pulley 78. Furthermore, the developing vessel 60 is provided with a guide plate 65 for guiding passage of sensitive paper and withh a developing electrode 66 adjacent the sensitive plane. Sensitive paper is advanced through the clearance. Further, as shown in FIG. 1, 67 denotes a jet pipe for developing solution; 68 denotes a solution supplying pipe; 69 denotes a drain hole; 70 denotes a liquid delivery pipe for discharging a liquid to the developing tank. The surfaces of liquid-squeezing rollers 63 and 63&#39;0 are cleaned by a cleaner 71. On the other hand, a dryer is located at the middle of the conveyor belt 81, heat light rays issued by a drying heater 82 are collected by a reflecting cap 83 to illuminate the dried surface and simultaneously heat particularly between the bottom plate 84 and top plate 85 at high temperature. Further, 86 denotes a fan for accelerating the drying; 87 denotes insulating plates for protecting the reflecting mirror 8 and lens 9 or the like from heat, and the sensitive papers completely dried are gathered in a paper receiving member 89. Further, 90 is a fan for dispersing the heat accumulated in the upper portion outside the machine.  
  Referring now to FIG. 19, a suitable amount of developing solution is always kept in a tank 201 and stirred therein with a stirrer 203. The developing solution is continuously pumped by a pump 204 through pipe 68 to developing vessel 60 and stored therein for passage of the photosensitive paper only in a certain amount. The remaining developing solution is removed from the developing vessel 60 and returned to the tank 201 through pipe 70. The stirrer 203 may be dispensed with and the tank 201 and developing vessel 60 may be constructed as an integral member. A stregthening or concentrated developing solution 209 is accommodated in an inverted bottle 210 mounted on a lid 201&#39; of the tank 201 and is supplied to the developing solution in the tank 201 to increase the concentration thereof, by pressing one end 212&#39; of a lever 212 the other end of which rotates about pivot 213 to press upwardly a valve shaft 211 ofa valve provided at the mouth of the bottle 210 to open the valve. Hitherto, the lever 212 has been manually operated by an operator, but according to the present invention. the lever 212 is automatically operated, as will be shown hereinafter. The valve structure mounted on the mouth of the bottle is generally known but an embodiment thereof which may be used in the invention shall be explained by referring to FIG. 20, by way of example. A threaded cap 220 of the bottle 210 comprises a packing 225 and is provided with a central opening 220&#39; through which the valve shaft 211 extends. The cap is supported by a frame like member 221 secured to the central portion of the cap 220. On the valve shaft 211, two valve elements 223 and 224 are fixedly mounted in opposed relation and the valve shaft 211 is urged downward by a spring 222. With such valve arrangement, the concentrated solution in the bottle will be discharged by pressing the valve shaft toward the inside of the bottle with the aid of lever 212, but if the valve shaft is pressed further in the same direction the valve element 223 will block the central bore 220&#39; f the cap 220 to stop the outflow. If the pressing of the valve shaft 211 is then released, the discharge will again occur but is immediately stopped. since the valve element is urged by the spring 222 and returns to its initial position as shown in FIG. 20. A valve structure, wherein the valve elements 223 is omitted, may of course be employed for the device according to the present invention.  
  The present invention is characterized by further providing as shown in FIG. 19, a means 214 for measuring the concentration of the developing solution, an electronic circuit 215 and a valve opening and closing solenoid or motor 216, thereby automatically detecting and measuring the concentration of the developing solution, adding concentrated solution to the developing solution, and stopping the addition when the concentration reaches a predetermined value, the addition being repeated and stopped automatically at suitable and constant time intervals.  
  FIGS. 21a, 21b and 21c show embodiments of the concentration measuring means. In all the embodimennts, light beam from a source 230 reaches a photoelectric element 231 through the developing solution along a suitable light path.  
  FIG. 21a shows a light path from a lens 232 and reflecting mirrors 233 and 233&#39;, wherein the light beam reflected by the mirror 233 passes through a closed window 234 and reaches the mirror 233 through another closed window 234&#39; which is spaced from the window 234 by the distance d as shown, the light path passing through the developing solution. FIGS. 21!; and 210 show other light paths which are respectively formed from optical fibers and optical material having high refractive indices (n 1.8 or more) so as to prevent refractive scattering of the light beam in the devel oping solution.  
  FIG. 22 shows an electronic circuit, wherein L and CdS represent respectively a lamp as the light source and a photoelectric element which correspond to the members 230 and 231 in FIGS. 21a 210. In this cir cuit, the internal resistance of C115 and a variable resistance R,-, form a potential divider for a DC voltage stored in a condenser C so that, in normal periods (the concentration of the developing solution being at a desired level and the amount of light beam reaching to CdS not being large), the bias voltage of a transistor TR is kept at a lower value relative to its base voltage. When the concentration of a developing solution lowers, the potential at point e gradually raises to increase the collector current of the transistor TR and then actuate a relay RY Since a contact of switch SW will move from its initial position as shown in FIG. 22 upon the actuation of the relay RY,, the charge stored in condenser C is discharged through a coil in a relay RY; to actuate switches SW and SW for keeping the relay RY, in its operational state. A movable contact of a switch SW, will move from its initial position as shown in FIG. 22 with the start of discharge in the condenser C3 and is kept in its moved position during the discharging period, so that a condenser C can discharge to actuate solenoid 216 for attracting the lever 212 which acts on the valve shaft 211 for discharging strengthening solution. When the discharge of the condenser C is completed, the switches SW, and SW open, and the movable contact in the switch SW4 returns to its initial position. as respectively shown in FIG. 22 to interrupt the current flowing to the solenoid 216. The feature of this circuit lies in that a time delay defined by the condenser C and resistance r of the relay RY is set for several to 10 seconds (this period is called T), so that the above operation is repeated in required times when the movable contact in the switch SW returns to its initial position. This time delays is set to provide sufficient mixing time in which the strengthening solution is sufficiently stirred with the developing solution in the tank. If there is not provided any time delay circuit, the concentration of the developing solution where the strengthening solution has dropped is too high at one place but at another place, particularly where the photoelectric element CdS is arranged is low and thus the solenoid continuously actuates to increase the concentration by introducing the strengthening solution. If there is not provided any repeating system, the device can not detect whether or not the concentration reaches the predetermined level with one supplying operation of the strengthening solution.  
  The solenoid may be a simple plunger type as illustrated in FIG. 22, but it may also be a combination of a gear motor and a cam.  
  The concentration control device has the advantage that the concentration of the developing solution can automatically be controlled and there is no fear that the concentration of the developing solution can become too high. The operation is easy and stable, and constant concentration solution can be fed to the developing portion.  
  FIGS. 13 and 14 represent a sheet number dial count ing device which records the number of sheets copied wherein 110 denotes a rotary solenoid, 111 denotes a rectifier and 112 denotes a sheet number dial. Another exposure device may also be made so as to disconnect the feeding rollers within the exposure range of sensi V tive paper sucked to the casing through action ofa solenoid. Moreover, in an optical device the projection is made on the surface of said object through a lens system, a transparent flexible belt and cloth or rubber or the like flexible belt are provided in contact with each other, and said contact surface is made to be coincident with the focal plane of said optical device and the trans parent belt is arranged at the lens side and sensitive paper is put between both belts and exposed by projection through the transparent belt. Simultaneously the transportion of said sensitive paper is stopped by the interlocking of those belts. Further, as another embodiment of the sensitve paper feeding devices, a transport member having an insulating resistor is used to attract and transfer the sensitive paper electrostatically.  
 What is claimed is:  
  1. An automatic adjusting device for the concentration of a developing solution in a developing solution tank of a photocopy machine, said device comprising a supply of concentrated developing solution, valve means for controlling the feed of the concentrated developing solution from said supply to the developing tank, photoelectric sensing means including a light source arranged outside the developing tank, a photoelectric receiver also arranged outside the developing tank and light guide means to guide the light beam from the light source to the photoelectric receiver through the solution in the developing tank, and electric means coupled to the photoelectric receiver and to said valve means for opening said valve means for a predetermined interval when the concentration of the solution in the developing tank reaches a minimum level and thereafter to hold said valve means closed for another predetermined interval before re-opening to allow the concentrated solution from said supply to be dispersed into the solution in the developing tank.  
  2. A device as claimed in claim 1 wherein said circuit means includes electromagnet means for operating said valve means.  
  3. A device as claimed in claim 1 wherein said supply is an inverted vessel having a bottom opening with said valve means in said opening.  
  4. A device as claimed in claim 3 comprising lever means for opening and closing said valve means, said circuit means including an electromagnet operatively coupled to said lever means to cause the latter to open and close the valve means.  
  5. A device as claimed in claim 1 comprising a stirring means to disperse the concentrated developing solution in the solution in the developing tank.  
  6. A device as claimed in claim 5, wherein said stirring means is arranged between said supply and said photoelectric sensing means.  
  7. A device as claimed in claim 1, wherein said light guide means comprises two hollow members having. respectively, a closed window arranged opposite one another at a given distance, one of said hollow members having a reflecting mirror to reflect the light beam from the light source to the photoelectric receiver through the closed windows and another reflecting mirror arranged in the other hollow member.  
  8. A device as claimed in claim 1, wherein said light guide means comprises two bundles of optical fibers, one of the bundles having one end arranged near the light source another other end arranged in the solution in the developing tank and opposite one end of the other bundle which has another end arranged near the photoelectric receiver.  
  9. A device as claimed in claim 1, wherein said light guide means comprises two rods spaced from one another and made of an optical material other than optical fiber having a regractive index of at least n 1.8 and having respectively. a free end cut obliquely and arranged in the solution in the developing tank to reflect the light beam from the light source to the photoelectric receiver through the slanted ends.  
  10. A device as claimed in claim 2, wherein said circuit means includes a first switch means controlling the operation of the electromagnet means, means for effecting time delay in the closing operation of the first switch means after any previous opening operation of the valve means and comprising an RC circuit, said first switch means being a relay coupled to said R-C circuit to be opened during discharge of a condenser of said R-C circuit, another condensor in said circuit means in series with said first switch means, and a second switch means in said R-C circuit having one operative state to actuate the R-C circuit when the concentration of the solution in the developing tank reaches a minimum level and another operative state in which the condensor of the R-C circuit will be charged.