Paper feed stoppage detection means in an electronic photocopying machine
United States Patent 1191 Kawai 1 51 Apr. 15, 1975 Primary ExaminerGlen R. Swann, III Attorney, Agent, or Firm-Wenderoth, Lind &amp; Ponack [75] Inventor: Yoshihisa Kawai, Aichi-ken, Japan [73] Assignee: Minolta Camera Kabushiki Kaisha, [57] ABSTRACT Osaka, 541, J a A plurality of sensors detect the passage of a sheet of copying paper through a copying machine. A plurality [22] Ffled&#39; 1973 of storage circuits having set and reset states are asso- [21] Appl. No; 402,051 ciated with the sensors. Each sensor, on detecting the paper, sets its associated storage circuit and resets the preceding storage circuit. Timers actuate an alarm if [30] Forelgn Apphcatmn Pnormy Data any storage circuit remains set longer than a predeter- OCt. 24, Japan mined and indicator how storage circuit is set. In order to allow for variable exposure U-S- e times one of the torage circuits is et dete tion of [5 Clr the paper at the exposure position and i reset the [58] Field of Search 340/259; 271/259 Start f the exposure The next Storage circuit is Set by the termination of the exposure and reset by detection [56] References Cited of the papers leaving the exposure position. Thus the UNITED STATES PATENTS paper may remain at the exposure position for any 2,003,336 6/1935 Braddon et al. 340/259 length of time Without Producing an alarm as long as 3,114,902 12/1963 Tanguy, Jr. 340/259 exposure is in P 3,6l8,936 ll/l97l Ziehm .r 27l/259 3,731,294 5/1973 Vass 340 259 6 Clams, 6 Drawmg Flgures Bl L. 4. w L Lam r- Lam Lump 22 amp l p 23b p 24 Li Paper l Paper Paper T Stops LStarts Tr I I2 2 l3a- T&#34; l I l3b 3 I4 I i J Ist Storage 2nd Storage, &#39;Start End Storage f 3rd Storage 4th Detector Circuit Detector Circuit I; Switch Sw&#39;tch Circuit Detector Circuit Detector q t O FF LS1 s2 1 OFF 4 Timer -32 Timer L330 Exposure Hl&#39;imer I330 Timer--34 l &#39;T&#39; T&#39; I OR Gate 40 Warning&#39; Signal PMENTECAPR I 5 sum 2 o 4 FIG. 2  
 FIG. 4  
 PMENTEBAPR I 1975 3&#39;, 878 540 sum u p {1 Dgl Ml PAPER FEED STOPPAGE DETECTION MEANS IN AN ELECTRONIC PHOTOCOPYING MACHINE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for the detection of stoppage of copy-paper feed in an electronic photocopying machine. and more particularly to an improved stoppage detection means, which not only accurately detects stoppages of paper feed, but also indicates the locations thereof in a photocopying machine.  
 2. Description of the Prior Art In a photocopying machine, the photoimage of an original document to be copied is transferred to sheets of copy-paper, which move through the machine. The main stages of the process are feeding sheets of copypaper from a hopper. exposure thereof to an image of an original document to be copied. development of the image. and fixing and delivery of the sheets to a delivery tray. The different stages of the process are effected in different parts of the photocopying machine, and normally, sheets of copy-paper are fed, one at a time, through the different stages by rollers, or similar means. A problem that can arise in the photocopying machine is that of stoppage of the feed of copy-paper sheets in some internal part of the machine. Conventionally, it has been known to provide a sheet detection element associated with a timer, as a means for the detection of such stoppages, The detection element is provided at the outlet of the photocopying machine, that is at the point of delivery into the delivery tray. and the timer is set to give a warning if a sheet of copypaper is not detected by the detection element a certain time after being fed into the photocopying machine from a hopper. The set time, after which the timer is to give a warning, is generally slightly longer than the time calculated to be necessary for sheet of copy-paper to travel from a hopper, through all the photocopying stages in a photocopying machine, and to a delivery tray. Such conventional means are simple. but have the disadvantage that when multiple copies of a document are required, and successive sheets of copy-paper are fed from a hopper, the sheets pass through the different stages and appear at the delivery tray at different intervals of time, and it is therefore necessary to employ two different timers, or to make the set time, after which a stoppage warning is to be given, slightly longer than the longest time anticipated to be required for completing one photocopying process. But in this case, considerable time may elapse between the actual occurrence of a stoppage and a warning thereof being given. Another disadvantage of such conventional stoppage detection means is that there is merely an indication that a stoppage in the feed of copy paper has occurred, and there is no indication of the location of the stoppage.  
  Although this problem can be resolved by a plurality of detectors located on the path of copy-paper through a photocopying machine, this has the disadvantage of making construction complicated.  
  Also, the times required for different stages in a photocopying process are not always the same. For example, in machines, in which photocopies are produced by exposing sheets of copy-paper to an image of an original document to form an electrostatic image thereon, adjustment of exposure is effected by varying the exposure time. In conventional means for detecting whether or not sheets of copy-paper are being fed at regular intervals through a photocopying machine. allowance for such variations of the intervals required at different stages must be made by compensating the set time of a stoppage detector, or by increasing the set time sufficiently to allow for the longest variation that may be required. But in this case also, it is obvious that there may be a considerable delay in the response of the detection means. and for machines into which sheets of copypaper are fed manually. such conventional detection means are completely inapplicable.  
 SUMMARY OF THE INVENTION It is accordingly an object of the present invention to provide an improved paper feed stoppage detection means which overcomes the defects inherent in conventional detection means.  
  It is another object of the present invention to provide an improved paper feed stoppage detection means which comprises a plurality of detectors located at various points on the path of travel of sheets of copy-paper through an electronic photocopying machine. whereby rapid indication is provided of both the occurrences and of the locations of stoppages of the feed of sheets of copy-paper.  
  It is a further object of the invention to provide a simple, and easily manufactured stoppage detection means, in which signals from detectors are transferred to indicating means and to warning means by a single structure comprising a number of identical cascadeconnected control circuits.  
  According to the present invention, one of the most important features resides in the provision of a paper feed stoppage detection means comprising a plurality of detectors provided on the feed path of sheets of paper, said detectors emitting output signals upon the detection of sheets of paper, a plurality of storage circuits, each of which produces output signals when set, and produces no output signals when reset, a 1st storage circuit being set by an input signal supplied thereto at the start of feed sheets of paper, and being reset by the first detector when a sheet of paper on said feed path reaches the first detector each subsequent storage circuit being set by one said detector and being reset by the succeeding detector on said feed path, a plurality of timers, each of which is actuated by one corresponding said storage circuit, and each of which produces an output signal if actuated longer than a certain time, and an alarm device actuated by an input signal from any one of said timers.  
 BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become apparent from the following description made, by way of example, in conjunction with preferred embodiments thereof with reference to the attached drawings, in which;  
  FIG. I is an electrical circuit block diagram of a paper feed stoppage detection means employed in an electronic photocopying machine according to one preferred embodiment of the present invention,  
  FIG. 2 is a cross-sectional view of the electronic photocopying machine provided with the paper feed stoppage detection means of FIG. 1, similar to FIG. 1, showing a portion of a paper feed stoppage detection means according to another embodiment of the present invention,  
  FIG. 4 is an electric circuit diagram applied to the paper feed stoppage detection means of FIG. 1 as a further embodiment of the present invention, and  
  FIGS. and 6 are respectively electric circuit diagrams similar to FIG. 4, showing a portion of a paper feed stoppage detection means according to other embodiments of the present invention.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Before the description of the present invention proceeds, it is to be noted that, for the sake of brevity, like parts are designated by like reference numerals throughout the several views of the accompanying drawings. It is also to be noted that the concept of the present invention as well as its paper feed stoppage detection means herein disclosed as preferred embodiments can be applied in any field of industry other than the electronic photocopying industry, for example, in connection with metallic foil, synthetic film, cloth or other like sheet materials if such article is arranged as herein disclosed.  
  FIG. 2 shows the concrete construction of the electronic photocopying machine employing the paper feed detecting means showing in FIG. 1. Referring first to FIG. 2, the housing structure 101 is ofa box-like shape having an upper glass plate 102 upon which an original document to be copied is placed and a hopper 103 to store sheets of copy-paper with a means including rollers 104 for feeding a sheet of copy-paper from the hopper 103 to the succeeding stages of process in a conventional known manner. In the housing structure 101 there is provided an exposure chamber 105 in which an image of the original document on the upper glass plate is exposed on the sheet of copy-paper fed from the feeding means through an optical means including lenses 106. Adjustment of exposure is effected by varying the exposure time. A developing chamber 107, in which the exposed sheet of copy-paper is developed to distinguish and to fix the image thereon by means of developing liquid for a certain period, and a drying chamber 108, in which the sheet of copy-paper developed is dried by means of heater 109, are also provided in the housing. The sheet of copy-paper having the image of the original document after passing through all the chambers is automatically led to and obtained on a delivery tray 110 provided at the lower portion of the housing structure 101.  
  Referring now to FIG. 1, a plurality of detectors 1, 2, 3, 4, 5 and 6 (detectors 3, 4 not shown), are provided and comprise micro-switches, photo-relays, or other elements, as described in further detail below. The detectors l 6 are for the purpose of detecting the passage, through an electronic photocopying machine, of sheets of paper used for the reproduction of original documents, and are disposed at various locations in the photocopying machine. As shown in FIG. 2, the detector 1 is located at the outlet of the hopper 103, the detector 2 at the entry to the exposure chamber 105, the detector 3 at the outlet of the exposure chamber 105, the detector 4 at the outlet of the development section 107, the detector 5 at the outlet of the drying section 108, and the detector 6 at the outlet of the photocopying machine, leading to the delivery tray 110. Each detector 1 6 produces output signals when a sheet of paper passes the location of the detector. That is, detector 1 produces output signals when a sheet of paper LII is fed into the photocopying machine from the hopper 103, detector 2 produces output signals when a sheet passes into the exposure chamber 105, detector 3 produces output signals when a sheet passes into the exposure chamber 105, detector 4 produces output signals when a sheet passes into the developing section 107, detector 5 produces output signals when a sheet passes into the drying section 108, and detector 6 produces output signals when a sheet is obtained into the delivery tray 110.  
  Needless to say, according to the invention, it is not essential that detectors be provided only in the abovedescribed locations, but detectors may be provided at any locations where important steps of the photocopying process take place, or where a stoppage in the travel of sheets is anticipated.  
  Associated with, and connected to the detectors 1, 2, 3, 4, 5 and 6 are provided storage circuits 11, l2, l3, l4, l5 and 16, respectively (storage circuits 13, l4, 15 not shown). Each storage circuit 11 16 comprises, for example a flip-flop having two stable states I and 0 of conventional type, and has a set input terminal IS, a reset input terminal IR, and output terminals 0. When a storage circuit l1, l2 15, or 16 receives a 1, input at its set input terminal IS, it stores I, and also produces a 1 output at each output terminal 0. A 1 input to the reset input terminal IR of a storage circuit resets the circuit, and, in this case, the circuits output goes to 0.  
  Input to the set input terminal IS of the storage circuit 11 is supplied in the form of a signal which is emitted from a feeding circuit F when sheets start being fed from the hopper of the photocopying machine. Input to the reset input terminal IR of circuit 11 is supplied by the detector 1, when a sheet reaches the location of the detector 1, and is detected thereby.  
  Input to the set input terminal IS of the other storage circuits 12, 13, 14, 15 and 16 is supplied by the detectors 1, 2, 3, 4 and 5, respectively, and in that order, when the detectors 1 5 detect sheets of paper passing their various locations. Input signals to the reset.-  
 input terminals IR of the storage circuits 12, 13, 14, 15 and 16 are supplied in the form of sheet detection signals from the detectors 2, 3, 4, 5 and 6, respectively, and in that order, when the detectors 2 6 detect sheets of paper passing their various locations.  
  Outputs from the storage circuits ll, 12, 16 are supplied to, and actuate pilot lamps 21, 22, 26 and timers 31, 32, 36. That is, the storage circuit 11 supplies an input signal to pilot lamp 21, and also to timer 31, and so on. The pilot lamps 21 26 are provided in any convenient, visible location, for example, on the operating panel of the photocopying machine, and light-up when receiving input signals from the corresponding storage circuits ll 16. Therefore, when sheets are being fed through the photocopying machine, from the hopper to the delivery tray, normally, the lamps 21 26 are turned on, and then off, in turn. Also, of course, since the lamps 21 26 are lit in response to a starting signal, or signals from the detectors 1 5, each lamp 21 26 gives an indication of the location of a sheet of copy-paper.  
  Each timer 31 36 is actuated by input from an 0 terminal of the corresponding storage circuit 11 16, as stated earlier, and if this input does not cease before a set time Ti, which is adjustable for each timer, the timer sends a signal to an OR gate 40. Upon receipt of an input signal from any of the timers 31 36, the OR gate actuates a device to give a warning that the normal time required for a sheet of copy-paper to travel between two detectors has been exceeded. in other words. that there is a stoppage.  
  The set time T1 for each timer 31 36 is the time required for a sheet of copy-paper to travel from one detector to the next, and is given by the formula:  
 in which, 11&#39; is the distance from a detector i to the next (1+1 Si is the speed of travel of a sheet of paper from detector (i+l and ai is a time allowance.  
  For photocopying stages in which a sheet of paper remains stationary between the locations of two detectors for a certain time, this interval also is included in the set time for the corresponding timer. For example during exposure, sheets of copy-paper must remain stationary for a certain time in the exposure chamber, and the time T23 required for a sheet of paper to travel from detector 2 to detector 3 is given by the formula;  
 in which 123 is the distance between detectors 2, 3, S23 is the speed of travel of a sheet of paper between detectors 2, 3, and t is exposure time. The time set for timer 33 is thus T23 =T23 +a23 A description of the operation of the abovedescribed equipment is given hereinbelow.  
  The photocopying process is started by actuation of a pushbutton swtich (not shown) in the feeding circuit F, which causes paper to be fed from the hopper, and at the same time supplies an input to the set input terminal of the storage circuit 11. The storage circuit 11, now being set, produces l outputs at its output terminals 0. Output from one output terminal 0 of the storage circuit 11 causes the pilot lamp 21 to light up, thus giving an indication that a sheet of paper has entered the photocopying machine from the hopper and is travelling towards the location of the detector 1. Output from the other output terminal 0 of the storage circuit l1 actuates the timer 3]. The set time for the timer 31 is slightly longer than the time calculated to be required for a sheet of paper to travel from the hopper outlet to the detector 1. lf, therefore, the photocopying machine is functioning normally, the sheet of copypaper reaches the detector 1 before the set time of the timer 31 elapses. Upon detection of the sheet of paper, the detector 1 supplies a reset input to the input terminal lR of the storage circuit 11. This resets the storage circuit 11, and output at both the output terminals 0 thereof goes to zero, thus turning off the pilot lamp 21, and stopping the timer 31. The detector 1 simultaneously supplies a set input to the storage circuit 12. The storage circuit 12, being set, supplies an output which actuates the timer 32, and an output which turns on the pilot lamp 22, thus giving an indication that the sheet of copy-paper is travelling between detectors 1 and 2.  
  When the photocopying machine is functioning normally, the above-described operation is repeated as the sheet (or sheets) of copy-paper comes to the locations of the different detectors. Successive storage circuits 13, 14, 15 and 16 are set and reset by detection signals from successive detectors 2, 3, 4 and 5, and the pilot lamps 23, 24 26 are turned on and turned off, in turn. When the sheet of paper reaches the outlet of the photocopying machine, the detector 6 resets the storage circuit 16. All the storage circuits 11-16 are therefore now reset, all the pilot lamps 21-26 and timers 31-36 are off, and this completes one photocopying cycle. During this cycle of normal operation, all the timers 3l36 are stopped before their various set times elapse, and so no signals are supplied to the OR gate 40, and there is no actuation of a stoppage warning device.  
  The description of the operation of the means of the invention will proceed hereinbelow. by way of example, with reference to the case in which a sheet of copypaper is blocked between the hopper outlet and the entry of the exposure chamber, that is between detector l and detector 2.  
  In this case, the pilot lamp 21 and timer 31 are switched on and then off, as described before. Also, the pilot lamp 22 and timer 32 are switched on by the storage circuit 12, which is actuated by a set input from the detector 1. Since, however, the sheet of paper being blocked before or in the exposure chamber does not reach the detector 2, there is no output from the detector 2, and no reset input to the storage circuit 12. The storage circuit 12 continues to supply output signals, the pilot lamp 22 remains on, and operation of the timer 32 continues. When the set time of the timer 32 elapses, the timer 32 supplies an input signal to the OR gate 40, and the OR gate 40 actuates a warning device. When the warning device is actuated, the pilot lamp is still on, and so it may be immediately determined that a sheet of copy-paper is blocked between the hopper outlet and the entry to the exposure chamber.  
  Similarly, if there is a stoppage in any other part of the photo-copying machine, a warning is given, and at the same time a particular pilot lamp is on, and gives an immediate indication of the location of the stoppage.  
  Referring now to FIG. 3, there is shown a block diagram of a 2nd embodiment of the present invention. In this 2nd embodiment, the circuits associated with the detectors 2, 3, at the entry and outlet of the exposure chamber, are divided into two blocks. One block B comprises a storage circuit 13a, pilot lamp 230, and timer 33a. The other block B comprises a storage circuit 13b, pilot lamp 23b, and timer 33b. The storage circuits 13a, 13b actuate their respective pilot lamps 23a, 23b and timers 33a, 33b in the same manner as the 33b supply input signals to the OR gate 40 if they are actuated continuously for longer than certain set times.  
  The storage circuit 13a is set by a set input from the detector 2, and is reset by an input signal which is supplied thereto from a start switch S, ofa exposure circuit E when a sheet of paper. after passing the detector 2, reaches&#39;and stops at the exposure position. and exposure thereof commences. The storage circuit 13b is set by an input signal supplied thereto from at end switch S of the exposure circuit E when exposure of the sheet has finished, and is reset by a reset input from the detector 3. In other words, the pilot lamp 234 and timer 33a are actuated from the time a sheet of copy-paper passes the detector 2 to the time the sheet reaches the position at which exposure thereof is to be effected. The pilot lamp 23b and timer 33b are actuated from the time the sheet leaves the exposure position to the time the sheet reaches the detector 3. During exposure of the sheet the lamps 23a, 23b and timers 33a, 33b are all off.  
 The set times T33u of the timer 33a and T 33b the timer 33b are as follows:  
 in which 123 is the distance between detector 2 and the exposure position, S23 is the speed of travel of a sheet of paper between the detector 2 and the exposure position, 133&#39; is the distance between the exposure position and the detector 3, S33 is the speed of travel of a sheet of paper between the exposure position and the detector 3, and (123, (133&#39; are time allowances.  
  This 2nd embodiment of the invention offers the advantage that even if exposure time is variable, the set times for the timers 33a, 33b may be-fixed.  
  In FIG. 4, there is shown an example of circuit assembly of the timer and pilotlamp circuits associated with the storage circuits shown in FIGS. 1, 3.  
  The push-button switch, and each detector which actuates a changeover switch, SWsl, SWal SWa6; are inserted in each circuit block L,, L L associated with successive pilot lamps and timers. These circuit blocks L are identical, and the description will proceed in reference to the operation of the circuit block L, associated with the pilot lamp 21, which is shown surrounded by a chain dot line in FIG. 4.  
  One terminal of the changeover switch SWSl connects to a capacitor C12,. The other terminal thereof normally connects to aresistor Ra, in parallel to the capacitor Cb,, and moves to a terminahconnecting one side of the lamp 21 through a re sistoriRb, when &#39;the&#39; switch SWs, is actuated by a start. signal of the pushtransistor Tal also is connected through a resistor Rel to the anode side of a diode Dal, and to a capacitor Ccl in series therewith. The emitter of the transistor Tal is connected, through a resistor Rfl, to the capacitor Cbl. The cathode side of the diode Dal is connected to an output terminal 01 which is connected to the timer 32. The anode side of the thyristor SCRl also is connected to a capacitor Cal, which is connected in series to the anode side ofa diode D01, and to a resistor Rhl in parallel to the diode Dcl. On their other sides, the diode DC] and resistor Rhl are connected in series to a capacitor Ca2, which forms part of the circuit block associated with the pilot lamp 22, and is connected to the anode side of a thyristor SC R2.  
  Subsequent circuit blocks L L L associated with subsequent pilot lamps and storage circuits are the same as the above-described circuit block, except that the last circuit block containing a thyristor SCR6 is not connected to a subsequent circuit block. The subsequent circuit blocks contain corresponding elements switches SWal, SWa2 SWa6 thyristors SCR2 SCR6, and so on.  
  When a sheet of paper is first delivered form the hopper, the changeover switch SWsl is actuated to connect the terminal of the resistor Rbl with the terminal of the capacitor Cbl, the thyristor SCRl is fired and conducts, and the pilot lamp 21 lights up. Conduction of the thyristor SCR] causes the base voltage of the NPN transistor Tal to be lowered, and the transistor Tal is cut off. When the transistor Tal is cut off, its collector voltage rises, and capacitor Ccl begins to be charged. The time required for the capacitor Ccl to be charged to its final voltage is set by suitable adjustment of the variable resistor VRal, and is made slightly longer than the time required for a sheet of paper to travel from the hopper outlet to the detector 1.  
  At the moment the sheet of paper reaches the detector 1, the changeover switch SWal is actuated to connect the terminal of the resistor Rb2 with the terminal of the capacitor Cb2. The thyristor SCR2 is therefore fired and conducts. Conduction of the thyristor SCR2 causes the pilot lamp 22 to light up. Also, because of the capacitor Cal, when the thyristor SCR2 conducts, the anode voltage of the thyristor SCRl drops, and thyristor SCRl is cut off. When SCRl is cut off, the base voltage of the NPN transistor Tal rises, and transistor Tal conducts. When transistor Tal conducts, its col-- lector voltage drops, and the previously charged capacitor Ccl discharges. Thyristor SCRl therefore does notconduct until the next gate input thereto, provided when the next sheet of paper is fed from the hopper and the changeover switch SWsl is actuated again, and the pilot lamp 21 is switched off.  
 If another sheet of paper is fed from the hopper, and  
  the thyristor SCRl is fired again while the thyristor button switch. The other side of the capacitor Cb, is  
 connected to the gate terminal of a thyristor SCRl, which is in series with the lamp 21. The lamp 21 is on the anode side of the thyristor SCRl through a resistor Rel. The cathode side of a diode Db, is connected to a point between the thyristor SCRl and lamp 21, the diode Dbl thus being in parallel to the lamp 21. The anode side of the diode Dbl is connected to the base of an NPN transistor Tal. A variable resistor VRal is provided in series with the collectorcircuit of the trancessive circuit blocks L L SCR2 is still conducting, the capacitor Cal is charged, in the reverse direction to that described-above, through resistor Rhl, and the thyristor SCR2 is unaffected.  
 The above-described circuit action is repeated in suc- L,,, as copy-paper is transported through the photocopying machine, comes to successive detectors, and actuates successive switches SWa2 SWa6. When the paper passes the switch SWa6, and comes to the last detector 6, the thyristor SCR6 is simply cut off, and no further&#39;circuit action takes place, thus completing one photocopying cycle.  
  In FIG. 5, there is shown a circuit diagram of control circuit blocks similar to those of FIG. 4 according to another embodiment of the invention.  
  The same-circuit blocks are provided in association with each pilot lamp and timer. The description will therefore proceed with reference to the first circuit block, it being understood that the other circuit blocks are the same.  
  Referring to FIG. 5, the first circuit block N may be seen to include a normally open switch SWsZ. One side of the switch is connected to a resistor RKl. This resistor is, in turn, coupled to the base of PNP transistor Tbl and to a resistor Rjl. Resistor Rjl is connected to a variable resistor VRal, to the emitter of the transistor Tbl and to one side of a resistor Rrl. The other side of the resistor Rrl is coupled to the cathode side of a diode DFl and to one side of the pilot lamp 21.  
  The other side of the switch SWs2 is connected to a capacitor Cdl; to the emitter of an NPN transistor TCl; to the emitter of an NPN transistor Tdl and to the base of the transistor through resistor Rrl; and to the other side of the lamp 21. The resistor Rrl is connected to the collector of PNP transistor Tbl through serially coupled resistors Rsl and Rgl. The capacitor Cdl is in series with a diode Ddl and an output terminal 01, which is connected with the timer 32, the output terminal 01 being on the cathode side of the diode Ddl. The anode side of the diode Ddl, and the resistor Rml are connected in series with the collector of the transistor T01, and in parallel to one another. The base of the transistor Tcl is connected to the collector of the transistor Tdl, through a diode Del, and to the base of the transistor Tbl, through the diode Del and resistor RPl, the transistor T cl being on the anode side of the diode Del. The base of the transistor Tdl is connected to the anode side of the diode Dfl and also to the anode side of a diode Dgl. The anode side of the diode Dfl is also connected to the collector of the transistor Tbl. The cathode side of the diode Dgl is connected to one side of a normally open contact SWbl, which closes a circuit associated with the pilot lamp 22.  
  When a sheet of copy-paper is fed from the hopper 103, the normally open switch SWs2 is closed, the base voltage of the PNP transistor Tbl drops, and transistor Tbl conducts. Current from the transistor Tbl is passed through diode Dfl, and is supplied to and lights up lamp 21. At the same time a voltage is applied to the base of the NPN transistor Tdl, and so transistor Tdl also conducts. The base current of the transistor Tbl flows also through the transistor Tdl, and so even after the contact SWs2 is opened, transistors Tbl, Tdl continue to conduct. The NPN transistor Tcl conducts prior to closure of the contact SWs2, but conduction of transistor Tdl lowers the transistor Tcl base voltage and cuts off the transistor Tcl. The collector voltage of transistor T01 therefore rises, and capacitor Cdl is charged.  
  When the sheet of paper reaches detector 1, contact SWbl is closed, and transistors Tb2, Td2 conduct. At the same time NPN transistor Tdl base voltage is lowered, and transistor Tdl is cut off. When transistor Tdl is cut off, base current of transistor Tbl also stops, transistor Tbl is cut off, and the lamp 21 is turned off, the first circuit block N1 thus returning to its original condition.  
  In the case where there is a stoppage, and contact SWbl is not closed, suitable adjustment of the variable resistor VRal keeps the transistor T01 cut off, and after a certain time, when the charge on the capacitor Cdl has reached a certain value, a signal indicating that there is a stoppage is supplied to the output terminal 01.  
  In the circuit shown in FIG. 5, the state of each circuit block has no effect on the action ofthe succeeding circuit block N N N and there are therefore no restrictions concerning the minimum distance between detectors.  
  In other words, if the distance between the detectors 1, 2, as shown in FIG. 2, is shorter than a sheet of copypaper, and both detectors 1, 2 are simultaneously actuated by a single sheet, the only result is that the pilot lamps 21, 22 are both on at the same time, and circuit operation for stoppage warning purposes is not affected. However, in the employment of cascadeconnected circuits as shown in FIG. 5, if the distance betwen two detectors, for example, detectors 1. 2 is such that both may be actuated simultaneously by a single sheet of copy-paper, in order to keep the related storage circuits set for a suitable time. the variable resistors should be adjusted so as to make the set time of the corresponding timers equal to the standard time required for the passage of a sheet of paper plus an additional allowance.  
  Some photocopying machines may employ copypaper sheets of different sizes, sheets of one size being large enough to actuate two detectors simultaneously, and sheets of another size actuating only one detector at a time. To effect rapid indication of a paper feed stoppage in such photocopying machines, the circuits are adjusted to keep the switches SWbl, SWb2 SWb6 closed only for the length of time necessary to keep the storage circuits set during the passage of sheets.  
  FIG. 6, shows a circuit, in which the detector contact switches SWbl, SWb2 SWb6 are made no-contact switches. The circuit may be seen to be similar to that shown in FIG. 5, except for a detector circuit M, which is surrounded by a one dot chain line. The detector circuit M, may be seen to comprise a photoconductive cell CdSl, PNP transistor Tel, NPN transistor Tfl, and zener diode Zdl. The base of the transistor Tel is connected to the photoconductive cell CdSl, the emitter thereof is connected to the anode side of the zener diode Zdl, and the collector thereof is connected to the base of the transistor Tfl through resistor RY I. On one side, the normally open contact SWs3 is connected to the photosensitive cell CdSl and to the cathode side of the zener diode Zdl through a pair of serially connected resistors RKl and RH. On the other side, the contact Sws3 is connected to the other side of the photosensitive cell CdSl through resistors VRcl and Rxl, to the base and to the collector of the transistor Tel through various resistors, and to the emitter of the transistor Tfl.  
  In the photocopying machine, a small lamp (not shown), or similar light source, is positioned opposite the photosensitive cell CdSl The small lamp normally illuminates the cell CdSl. In this case, the resistance of the cell CdSl is low, and the PNP transistor Te&#39;l is cut off. Transistor Tel being cut off, the NPN transistor Tfl also is cut off. When a sheet of paper comes between the small lamp and cell CdSl, illumination of the cell CdSl is cut. and the resistance thereof rises to a high value. Therefore. the base voltage of the PNP transistor Tel falls. base current flows. and transistors Tel. Tfl conduct. This has the same result as the closure of the switch SWbl in FIG. 5. and the pilot lamp 21 is switched on.  
  In the circuits of FIGS. 4. 5. 6. the output terminals 01. 02 06 are connected to the input of the OR gate shown in FIGS. 2. 3.  
  As is clear from the above description. the present invention provides a paper feed stoppage detection means for electronic photocopying machines. which gives an immediate warning upon the occurrence of a stoppage. and also gives an indication of the location of the stoppage. and is thus of great advantage in the operation of photocopying machines. Also. the means of the invention is compact in construction. since it is necessary to provide only a single warning device. which is actuated when there is a stoppage at any location. Timers employed in the means of the invention may be set to fixed times. and do not need to be adjusted in correspondence to changes in a photocopying process. and a circuit of the same structure may be used in association with each detector. The means of the invention is thus cheap. reliable. and maintenance thereof is easy. Lamps are provided to give an immediate indication of the locations of sheets of copy-paper. thereby making supervision of the copying machine easy. Also. the means of the invention accurately detects stoppages. even if sheets are fed through a machine at different intervals.  
  Needless to say. the detection means according to the present invention is not limited to detection of stoppage in the feed of paper through a photocopying machine. but may be employed for the detection of stoppage of any other articles carried over a set path.  
  Although the present invention has been fully disclosed by way of the preferred embodiment thereof shown in the accompanying drawings. it is to be noted that various changes and modifications. including those mentioned in the foregoing description. are apparent to those skilled in the art. Therefore. unless otherwise such changes and modifications depart from the true scope of the present invention. they should be construed as included therein.  
 What is claimed is:  
  l. A paperjam detecting means for use in an electrophotographic copying machine and the like. comprising:  
 a plurality of detectors located at various points along the path of travel of a sheet of copying paper through said machine. each of said detectors producing an output signal upon detection of passage of a sheet of copying paper;  
 a plurality of storage circuits. each having set and reset states and producing an output signal only when in the set state. a first of said plurality of storage circuits being set by an input signal supplied thereto at the start of feed ofa sheet of copying paper. a first of said plurality of detectors operatively coupled thereto. whereby said first storage circuit is reset by the output of said first detector. a second of said plurality of storage circuits operatively coupled to a detector located at the entrance to an exposure chamber andadapted to be reset by an input signal generated upon the commencement of exposure ofa sheetofcopying paper. a third of said plurality of storage circuits operatively coupled to a detector located at the exit of the exposure chamber and adapted to be set by a signal generated upon completion of exposure of the sheet of copying paper. the remaining ones of said plurality of storage circuits each operatively coupled to two successive detectors. one detector setting said storage circuit. thereby producing an output signal. the second detector resetting said storage circuit thereof:  
 a plurality of timers. each coupled to one of said storage circuits and activated by the output thereof. each of said timers producing an output if actuated for more than a predetermined time; and  
 alarm means coupled to all of said timers and adapted to be actuated by an output signal of any one of said timers.  
  2. A paper jam detection means as claimed in claim 1. further comprising a plurality of indicating means each associated with a respective one of said storage circuits. said indicating means adapted to be energized when a corresponding storage circuit is set and to be deenergized when reset. whereby indication is provided of an exact position where jamming has occurred.  
  3. A paper jam detection means in an electrophotographic copying machine and the like. comprising:  
 a plurality of detectors provided on a feed path of copying papers through said machine. at least one of said detectors located at the entrance of an exposure chamber and a second detector located at the exit of the exposure chamber. each of said detectors adapted to sense the arrival of a sheet of copying paper and producing an output responsive thereto;  
 a plurality of storage circuits associated with said detectors;  
 a plurality of timers. each associated with a respective one of said storage circuits. one of said storage circuits coupled to said detector located at the entrance of the exposure chamber and adapted to be set by a signal from said detector to actuate the associated timer and adapted to be reset by a signal indicating the commencement of exposure. another of said storage circuits coupled to the detector located at the exit of the exposure chamber and adapted to be set by a signal indicating the completion of exposure to actuate the associated timer and adapted to be reset by a signal from said detector; and  
 a warning means coupled to each of said timers. said means being actuated with any of said storage circuits fails to be reset within a time set by said timers.  
  4. A paper jam detection means as claimed in claim 3 wherein each of said storage circuits includes a set input terminal. a reset input terminal and a first output terminal. whereby each storage circuit may be set by the application of a signal to the set input terminal to actuate a corresponding one of the timers through the output terminal and whereby the circuit may be reset by the application of a signal to the reset input terminal.  
  5. A paper jam detection means as claimed in claim 4. wherein each of said storage circuits further includes a second output terminal connected to a lamp. said lamp being energized when said circuit is setand deenergized when said circuit is reset.  
 sociated with the storage circuit corresponding to the detector located at the exit of the exposure chamber and is determined by T (1 /S- a wherein T is the setting time. I- is the distance from the exposure position to said detector. S is the travelling speed of a copying paper for said distance 1-; and a: is a suitable time allowance.