US3893391A

US3893391A - Control circuit for master quantities in printing systems

Info

Publication number: US3893391A
Application number: US362370A
Authority: US
Inventors: Thomas J Borke; Donald W Macdonald
Original assignee: Multigraphics Inc
Current assignee: AB Dick Co
Priority date: 1973-05-21
Filing date: 1973-05-21
Publication date: 1975-07-08
Anticipated expiration: 1992-07-08
Also published as: JPS55171537U; DE2412366A1; DE2412366B2; JPS5015604A; JPS5726756Y2; GB1466942A; DE2412366C3

Abstract

A control circuit is described for governing the maximum quantity of planographic masters present in a printing system at all times. A device for producing planographic masters is coupled to a cyclically operable printing machine to produce predetermined quantities of printed copies correcponding to origianl documents inserted into the master making apparatus. The printing system, comprising the master maker and the printing machine, since it contains only a predetermined number of master rest positions, may malfunction if more than a predetermined quantity of planographic masters are present in the system at any one time. The control circuit assures that at the start of an operation no more than this predetermined quantity of masters enters the system and thereafter maintains this quantity by only allowing a master to enter the system as one is withdrawn from the system.

Description

United States Patent Borke et al.

CONTROL CIRCUIT FOR MASTER QUANTITIES IN PRINTING SYSTEMS Appl. No.: 362,370

1451 July 8,1975

Primary ExaminerEdgar S. Burr Assistant ExaminerWilliam Pieprz Attorney, Agent, or FirmRussell L. Root [57] ABSTRACT A control circuit is described for governing the maximum quantity of planographic masters present in a printing system at all times. A device for producing planographic masters is coupled to a cyclically operable printing machine to produce predetermined quantities of printed copies correcponding to origianl docu- [52] U.S. CI 101/141; 101/132 meats inserted into the master making apparatus, The [5 I] Int. Cl B4" 7/02 printing system, eomprising the master maker and the Field of Search 132.5, printing machine, since it contains only a predeter- I44 mined number of master rest positions, may malfunction if more than a predetermined quantity of piano- [56] Re er nlres Cited graphic masters are present in the system at any one UNITED STATES PATENTS time. The control circuit assures that at the start of an 3 426 678 2/1969 Carper et al 101/1325 than this predetermined quantity of 3:451:336 6/1969 Mignone ICU/1325 masters enters the system and thereafter maintains this 3,457,857 7/1969 Burger.............. 101/144 quantity by only allowing a master to enter the system 3,603,253 9/l96l Tonkin et al. [OI/132.5 as one is withdrawn from the system. 3,683,803 3/1972 Grey et al. 101/132 5 Claims, 3 Drawing Figures M45751? CONVERTER MASTER P/qy/Vfl/VG p/PGDUC/ll/G MAC/ 0V5 MACH/IVE l 1 24 l l msrm cauvmva L ----I-. AND PRODUCTION CONTROL MEANS l CONTROL CIRCUIT FOR MASTER QUANTITIES IN PRINTING SYSTEMS BACKGROUND OF THE INVENTION This invention relates in general to a planographic printing system and more particularly to the control of a system for producing ink image copies from original documents.

The master to be used in such a planographic printing system may be produced by any number of apparatuses presently being manufactured. One procedure for producing planographic masters includes photoelectrostatically copying the original document, and an example of such an apparatus is illustrated in U.S. Pat. No. 3,388,644. The use of such an apparatus in a planographic printing environment involves inserting an original document at a feed station and receiving the planographic master at the output of the master making device.

The master produced is then fed to a printing device, such as that shown in U.S. Pat. No. 3,056,346. Planographic master printing machines are generally cyclically operable devices, and the type shown in the aforesaid patent automatically takes masters fed to it and mounts them one at a time on the rotating cylinder in a removable manner. The master on the rotatable cylinder is then treated with moisture and ink and copies are printed therefrom in a known manner.

When the system is manually operated, the difference in operating speeds of the master producing de vice and the printing device give rise to no serious problems. Masters will collect at the output of the producing device until the operator is ready to use them.

But manual operation requiring the continuous attention of an operator is not desirable. If the planographic masters were fed from the master producing device to the printing device automatically, the total system could be programmed for the desired quantity of ink imaged copies for a number of original documents and operated continuously with only casual operator attention. Such systems have been developed using mechanical transports to couple the master producing device with the printing device.

A problem arises with the coupled system in that the existing interlocks normally permit one original to be inserted and a master to be made therefrom each time a printing operation is completed. However, before the first master reaches the master cylinder of the printing device, efficiency demands that several masters should be admitted to the system (four is the number currently provided for), and the system is set up to accept and hold these preliminary masters at predetermined locations until a master reaches the printing cylinder and generates a signal postponing further master making. Master making speeds are such, however, that if the operator is using short originals and works without delay between masters, there is the chance that extra masters (e.g. five or six) can be made and introduced into the system before master making is interdicted, and since there is no place for these extras to rest during the subsequent printing operation, a jam condition is apt to be created in the transport or master maker.

SUMMARY OF THE INVENTION The present invention concerns a simple low cost electrical circuit for controlling the movement of plano graphic masters into and within a planographic printing system. The system in this case comprises a planographic master producing apparatus and a planographic printing machine connected by a mechanical transport. Malfunction of the printing system is prevented by maintaining the number of planographic masters in the system at or below a predetermined maximum quantity while still allowing the initial preparatory batch of masters to enter the system.

It is therefore the primary object of this invention to produce inked image copies in a printing system and to prevent possible delay due to master jams by controlling the quantity of masters present within the printing system at all times.

Another object of this invention is to assure that at the initiation of operation of the printing system no more than the predetermined maximum quantity of masters are inserted into the system.

A further object of the present invention is to assure that no more than the predetermined maximum quantity of masters is present in the printing system, by allowing the masters to enter the system only in response to corresponding quantities of masters being withdrawn from the system, once the preparatory period is over.

IN THE DRAWINGS FIG. 1 is a block diagram ofa planographic printing system including a master making module;

FIG. 2 is an electrical schematic of the master counting circuit shown in FIG. 1;

FIG. 3 is a graph of the switch conditions produced by the cams of the impulse sequencing relay.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates, in block diagram form, a printing system indicated generally .as 10 including the master counting circuit of this invention. A master producing apparatus or master maker is shown generally as 16 in FIG. 1. The master producing apparatus in the preferred embodiment is a Model 2300 electrostatic copier. This machine is manufactured by Addressograph-Multigraph Corporation and is similar to the device further described in the above mentioned U.S. Pat. No. 3,388,644. The electrostatic copier in this case is capable of producing planographic masters by loading the machine with electrostatic master material. The machine thus supplied, prepares a master whenever an original is presented to the feed-in nip, providing the previous original has cleared and the printing machine signals its readiness to receive a master. Otherwise, the original waits at the nip until the acceptance conditions are satisfied and then the feed is automatically initiated.

A master converter, shown generally as 18 in FIG. 1, receives the masters produced by the electrostatic copy machine and may be similar to that shown in U.S. Pat. No. 3,630,776.

Finally, in the preferred embodiment, the masters are removed from the master converter and inserted onto a printing machine 20 similar in structure to that disclosed in U.S. Pat. No. 3,056,346. The printing system 10 is arranged so that either the master producing machine 16 or the printing machine 20 may be used independently of the other.

A master counting and production control means is indicated as 24 in FIG. 1. This means is associated with portions of the control circuitry of both printing machine and the master producing machine 16. The control circuitry for the printing machine 20 is more fully described in US. Pat. No. 3,457,857. The control circuitry for the master producing device is described in the corresponding above mentioned US. Pat. No. 3,056,346.

FIG. 2 illustrates the details of the master counting and production control means 24. An impulse sequencing relay indicated generally as is a major component in this means. A relay 32 connected with the impulse sequencing relay 30 controls circuits whereby an original document is accepted into the master producing apparatus each time relay 32 is activated, for example, in the conventional manner by activating a solenoid to trip a one revolution clutch at the usual infeed rollers. The relay 32 also includes contacts 320 to control pulsing of the impulse sequencing relay under certain circumstances as will hereinafter appear. The five relay contacts 340 through 34e are associated with one or more correlative relays of conventional construction which operate in a known manner substantially simultaneously in response to a signal indicating conditions related directly to the presence of a master on the printing cylinder of the printing machine. in other words all five sets of contacts 340 to 34c might be oper ated by a single relay mechanism to transfer whenever the relay is energized. Such a relay is illustrated schematically at 34 in FIG. 2. A preferred form of relay hav ing special utility for the present purpose would be a conventional locking or latching relay which would pull in and latch up (transferring all contacts to the nonillustrated position) in response to a signal pulse identifying the arrival of the first master at the master cylinder of the printing machine 20. A relay (or relays) of this type would remain latched until the secondary or release coil of each such relay is energized, This would occur in response to a signal pulse occurring when the immediate series of masters has been completed and the machine is shut down to an idling or off condition, at which time the five sets of contacts 340-34d would be restored to the initial position illustrated. Of course any other mechanism or circuitry accomplishing this function is also contemplated.

The impulse sequencing relay. indicated as 30, more specifically includes a relay coil 38. The relay coil is directly connected to a pawl 40, such that oscillatory motion is imparted to the pawl upon pulsed energization of the relay 38. The pawl is arranged to engage a ratchet wheel 42 in a manner to cause the ratchet wheel to rotate, stepwise, about its central axis. Firmly attached to the center of the ratchet wheel 42 is a drive shaft 44. The drive shaft 44 thus rotates about its central axis in concert with the ratchet wheel 42 and is subjected to frictional loading in any convenient manner, or provided with a conventional holding pawl, so that movement of the shaft 44 and wheel 42 will occur only in one direction upon activation of the relay coil 38, thus eliminating free wheeling rotation. An electrical switch contact 48 cooperating alternately with electri cal contacts 48a and 48b is operated by the movement of the cam 46. Also, drivingly mounted on the drive shaft 44 at a different position, is a second cam 50, and a second electrical switch having contacts 52 and 520, the former positioned to be activated by the cam 50.

In the preferred embodiment. the particular printing system used is capable of containing a maximum of four planographic masters at one time. That is, one

master would be on the rotatable cylinder of the printing machine, a second master would be at an input feed position on the printing machine, a third master would be on the mechanical transport just prior to the master converter and a fourth at the output of the master producing machine. Since the four positions described above are the only rest positions present in the printing system, any number of masters greater than four would produce an unstable condition and possibly result in a l() jam.

This wire connections to the master counting and production control means indicated in FIG. 2 are partly made to the master producing machiine l6 and partly to the printing machine 20. Leads 56, 58, 60 and 62 are connected to the printing machine 20, and leads 64 and 66 are connected to the master producing machine 16. Lead 56 is connected to the common side of AC power in the printing machine 20. Leads 58 and 62 are connected to AC power through a conventional cam operated switch arrangement to provide a train of pulses, one for each cylinder revolution, whenever the printing machine 20 is operating. AC power is connected to lead 60 at all times while the printing machine is on. Lead 64 is connected to the negative side of the DC power supply within the master producing machine 16. The positive side of the DC power supply in the master producing machine l6 is connected to lead 66 through a circuit which involves means to detect when both (a) the printing machine 20 is ready to accept a master onto the master cylinder (that is, ejection of a previous master, if any, has been completed), and (b) an original has been inserted into the master making machine 16, and which circuit thereupon becomes conductive.

The master counting and production control means 24 actually includes two electrical circuits, one associated with each of the

elements

16 and 20 of the printing system 10, the two circuits being interrelated mechanically. Thus, all of the elements in the master counting and production control means 24 which are connected to leads 56, 58, 60 and 62 comprise a first circuit cooperating with the mechanical elements 40-50 to provide a counting means. This first circuit includes the impulse sequencing relay coil 38, the contacts 48, 48a and 48b,

relay contacts

34a, 34b, 34c, and relay contacts 32a. The purpose of this first circuit is to control activation of the impulse sequencing relay coil 38 to step shaft 44 at appropriate times.

The remaining circuit elements related to the means 24, namely contacts 52 and 52a, and

relay contacts

34d and 34e, which are connected to leads 64 and 66, and

conductors

67 and 68, comprise another circuit which restrains activation of relay 32 to prevent initial insertion of new masters when a predetermined quantity of masters, in this case four, is present in printing system 10, and otherwise permits insertion of masters at special times programmed by operation of the printing machine. Of the latter circuit, the input conductor leading to switch contacts 34d, switch 34d, the conductor between 34d and 52a and conductor 57 may be designated a second circuit means controlled by the output of the impulse sequencing relay 30 at switch 52, 52a for defeating the acceptance of a master by the system when the impulse sequencing relay has attained its predetermined count. Relay coil 34 and its

contacts

34d and 34a together with the conductor 68 constitute a means responsive to initiation of printing by the printing machine for disabling the master counting action of the impulse sequencing relay, for bypassing the second circuit means immediately above mentioned, and for transferring control of the production of masters from the counting action of the impulse sequencing relay to the signals appearing on conductor 66 which are related to the departure of a used master from the printing machine.

The

cams

46 and 50 are constructed so that one revolution of the cam is equal to two operational cycles. That is, one-half of each cam is exactly identical to the other half of the same cam and each half performs the same function alternately. In an effort to use off-theshelf elements for the construction of the preferred embodiment, the impulse sequencing relay 30 was chosen to be capable of an even multiple of steps of the desired quantity and the twelve step version came closest to present requirements. Thus the only reasons for using repetitive cam profiles are convenience and economy in the manufacture of the device, and no limitation of the invention in this regard is intended.

FIG. 3 illustrates the switch positions produced by the cam arrangements of the impulse sequencing relay 30. The

first chart line

70, 71 is illustrative of the position of switches 48, 48a and 48, 48b as controlled by cam 46. Likewise, chart line 72 is illustrative of the position of switch 52, 520 as controlled by the cam 50.

The ratchet wheel 42 has twelve teeth to allow for 12 angular positions of the drive shaft 44 and the

cams

46 and 50. These 12 teeth and positions correspond to the 12 spaces along the base of the graphs in FIG. 3. Since the operation is repetitive, the relationships associated with the first seven positions only will be described.

Once the printing system has been started and the master counting and production control means 24 commences operation, the impulse sequencing relay coil 38 is energized by power from lead 58. FIG. indicates that, whenever a power pulse occurs on lead 58, it will energize coil 38 because, at start-up, relay contact 34a is closed and cam 46 when in its normal home position is maintaining the electrical switch contact 48 against contact 480. Step 1 in the graphs of FIG. 3, corresponds to the starting positions of the earns 46 and 50 in FIG. 2. The upper chart line 70, at Step 1 in FIG. 3 is indicative of the electrical switch contact 48 being held against contact 48a. As soon as the power pulse from lead 58 activates the relay coil 38, the pawl 40 causes the ratchet wheel 42 to step one notch, thereby telling the system to accept a master if available. The impulse sequencing relay 30 is now in its second position and, as indicated by the chart lines 70 and 71 in the FIG. 3, cam 46 has been rotated to allow the electrical switch contact 48 to return to contact 48b and switch 48, 48a is thus opened while switch 48, 48b is closed. Cam 50 has likewise been rotated to a sufficient degree to cause the electrical contact 52 to be held closed against contact 52a as shown by the chart line 72 in FIG. 3. As stated above, the relay contact 34d, when in its normal initial state, will-be closed and remain so until such time as the first master will have been introduced onto the master cylinder of the printing machine 20. Therefore, a pulse of power at lead 66 by means of closed contact 344' and the connection through contacts 52, 52a, will cause the relay 32 to be pulsed and thus to initiate feeding of a waiting original into the master producing machine 16; resulting in the production and forwarding of the first master.

Since switch contact 48 has returned to contact 48b at the start of the second position of impulse sequencing relay 30, and relay contact 34b remains closed until a master reaches the cylinder of the printing machine 20, pulsing of relay 32 will cause contacts 320 to momentarily connect lead 60 to the impulse sequencing relay coil 38. As before, the activation of relay coil 38 will cause the ratchet wheel 42 to advance to the next step.

Subsequent introductions of originals into the master producing machine will each produce a result similar to that just described, each causing a forwarding of the ratchet by one step and signalling the acceptability of another master.

When relay 32 is activated and the first original document is accepted by the master producing machine 16, a master is produced and appears at the output of the master producing machine and is moved towards the printing machine by the transport. This master continues to move through the printing system until reaching the master cylinder where it is then installed on the cylinder and copies are printed therefrom.

In the initial period before the first master reaches the rotatable cylinder of the printing machine 20, however, relay contact 34d remains closed. Also the cam 50 still maintains the electrical switch 52 at contact 52a. In this manner the relay 32 will again be repeatedly activated by the power at lead 66 as each new original is inserted into the master producing machine 16, the printing machine being at this time, of course, devoid of a master and hence constantly in an enabling aspect.

Let us assume for the moment that, it is still the initial period and no master has reached the cylinder of the printing machine, and the fourth master has been introduced into the system, causing the ratchet 42 to step to position 6, at which point it is desired that no further masters should be introduced into the path because of the danger of jamming. Looking at the lower chart line, it will be seen that the step from position 5 to position 6 caused switch 52, 52a to open, thus insuring that the relay 32 can no longer be pulsed by current through switch 34d and conductor 67. Consequently it is for the moment impossible to introduce a fifth original into the master maker to generate a fifth master, and since contacts 32a will consequently not be pulsed, no further stepping of the ratchet 42 will occur at this time.

The next change in system condition occurs when the first master reaches the master cylinder of the printing machine and its presence is sensed. At this time the correlative relay or relays cause all of the five switches 34a to 34: to transfer to the opposite condition. This means that no pulses will reach the relay coil 38 through now open swtiches 34a or 34b, whereby the counting function is effectively terminated. Pulses can now reach the relay coil 38 only through the now closed switch 34c, and, since a regular series of pulses is applied via the conductor 62, the ratchet 42 will be quickly stepped to its next home position, in this case step 7, thereby providing a resetting function. In the step 7 position, cam 46 will again place contact 48 against contact 480 in readiness for a new cycle of operation, and will open contacts 48, 48b to assure that stepping of the ratchet is terminated for the time being.

It is, of course, not necessary that four masters be produced before the first one reaches the master cylinder and printing is initiated, and in the case that only two or three masters have been entered. the resetting operation above described will occur whenever the signal that the first master has arrived at the master cylinder transfers all five of the switches 34a to 34e.

it will be noted that, at step 7, switch 52, 52a remains open, however, and the active line has now become conductor 68, for switch 34c is now closed due to the first master's having arrived at the master cylinder. in its closed condition, of course, 34c acts with conductor 68 to form a by-pass around switch 52, 520. Therefore, (as previously described) whenever (a) the printing machine 20 is ready to accept a master and (b) an original has been inserted into the master making machine 16, a pulse will appear on

conductive path

66, 34, 68 to activate relay coil 32 to feed in the original and start the production of a new master, and this type of operation will continue throughout the duration of the current printing operation until the current printing operation is completed.

Stepping of the impulse sequencing relay does not occur again until the immediate printing operation has been concluded and the printing system shut down. At that time a suitable signal given by the printing machine causes the contacts 34a to 34 transfer back to their original condition as previously described, and the entire system is ready for a new cycle of operation including another initial count control period whenever the system is started up again.

As can be seen from the foregoing detailed description, the apparatus of the present invention initially allows no more than the predetermined quantity of planographic masters to enter the printing system 10 and thereafter allows planographic masters to enter the printing system, one at a time, only as a master is released from the system. In the foregoing description the main function of the impulse sequencing relay has been identified as counting," and where this term, (or the related terms such as counting means") is used in this description and in the subjoined claims, it will be understood that the term is to be understood in its conventional sense which includes the concept of receiving a series of individual signals of a specific type, and accumulating a sensible record of the total of said signals, and then either registering the total as a legible display or, as in the present case, initiating some controlling function when the accumulated store reaches a predetermined value. Counting in the above sense is at the core of the present invention and is not to be confused with mere placement sensors or' escapement mechanisms.

While a particular embodi rn'nt of the invention has been described in detail, it will be understood that additions, eliminations and modifications may be made without departing from the ambit of the invention as defined in the subjoined claims.

What is claimed is:

1. in a printing system including a planographic master producing portion, a cyclically operable printing portion and a transport for causing movement of the planographic masters between the producing portion and the printing portion of said printing system, said printing portion and transport having the capability of successfully containing at predetermined detection locations only a predetermined plural number of masters at one time, and said master producing portion having a speed potential for introducing more than said predetermined number of masters before the presence of the excess is detectable at the predetermined locations, an improvement in controlling the number of planographic masters present in the printing system, comprising:

means operable during the initial startup of the system for counting the number of masters initially produced by said producing portion and producing a signal when said predetermined number has been counted; and

control means responsive to the signal provided by said counting means for so controlling operation of said master producing portion that no more than said predetermined number of planographic masters is ever present in said printing system,

said control means having a dual mode of operation allowing, during said initial production of masters and prior to the production of said signal, uninhibited production of masters until said predetermined number has been counted, and thereafter admitting a new master into the system upon the departure of a previous master therefrom.

2. A printing system as set forth in claim 1 in which:

there is also provided means to terminate the counting action of said counting means in response to initiation of printing operation by the printing portion; and

said control means includes:

means effective in response to initiation of printing operation by said printing portion, to condition the mechanism for preparation of one master only at the completion of each printing operation.

3. A printing system as set forth in claim 2 in which there is also provided means to restore said counting means to counting condition upon completion of printing operations and shutdown and restarting of said printing portion.

4. ln a printing system including a planographic master producing portion, a cyclically operable printing portion having a printing station, and a transport for causing movement of the planographic masters between the producing portion and the printing portion of said printing system, and embodying repositories for plural prepared masters between the master producing portion and the printing station, the improvement in controlling the number of planographic masters present in the printing system comprising:

means providing control of the operation of said master producing portion for normally triggering master production in dependence upon signals related to the absence at a predetermined location in the system of a previously produced master, and for otherwise inhibiting master production, but which permits free master production until such time as an initial master reaches said predetermined location;

means operative at the outset of a printing sequence for counting the number of masters initially produced by said producing portion and for giving a signal when a predetermined number has been counted; and

means responsive to said signal for preventing production of additional masters until normal operation of said control providing means has been established by the initial master's reaching said predetermined location.

S. In a printing system including a master introducing apparatus and a cyclically operable printing machine,

and including means for installing fresh masters in printing position and ejecting each master when printing therefrom is completed, the improvement in controlling the number of planographic masters present in said printing system comprising control means having a dual mode of operation allowing, during an initial period of introduction of masters at the startup of the system, uninhibited introduction of masters until a predetermined number is counted, and thereafter admitting a new master only upon departure of a previous master therefrom, said control means comprising:

an impulse sequencing relay;

a signal source giving signals each related to the completion of a printing run; first circuit means to step said impulse sequencing source.

Claims

1. In a printing system including a planographic master producing portion, a cyclically operable printing portion and a transport for causing movement of the planographic masters between the producing portion and the printing portion of said printing system, said printing portion and transport having the capability of successfully containing at predetermined detection locations only a predetermined plural number of masters at one time, and said master producing portion having a speed potential for introducing more than said predetermined number of masters before the presence of the excess is detectable at the predetermined locations, an improvement in controlling the number of planographic masters present in the printing system, comprising: means operable during the initial startup of the system for counting the number of masters initially produced by said producing portion and producing a signal when said predetermined number has been counted; and control means responsive to the signal provided by said counting means for so controlling operation of said master producing portion that no more than said predetermined number of planographic masters is ever present in said printing system, said control means having a dual mode of operation allowing, during said initial production of masters and prior to the production of said signal, uninhibited production of masters until said predetermined number has been counted, and thereafter admitting a new master into the system upon the departure of a previous master therefrom.

2. A printing system as set forth in claim 1 in which: there is also provided means to terminate the counting action of said counting means in response to initiation of printing operation by the printing portion; and said control means includes: means effective in response to initiation of printing operation by said printing portion, to condition the mechanism for preparation of one master only at the completion of each printing operation.

4. In a printing system including a planographic master producing portion, a cyclically operable printing portion having a printing station, and a transport for causing movement of the planographic masters between the producing portion and the printing portion of said printing System, and embodying repositories for plural prepared masters between the master producing portion and the printing station, the improvement in controlling the number of planographic masters present in the printing system comprising: means providing control of the operation of said master producing portion for normally triggering master production in dependence upon signals related to the absence at a predetermined location in the system of a previously produced master, and for otherwise inhibiting master production, but which permits free master production until such time as an initial master reaches said predetermined location; means operative at the outset of a printing sequence for counting the number of masters initially produced by said producing portion and for giving a signal when a predetermined number has been counted; and means responsive to said signal for preventing production of additional masters until normal operation of said control providing means has been established by the initial master''s reaching said predetermined location.

5. In a printing system including a master introducing apparatus and a cyclically operable printing machine, and including means for installing fresh masters in printing position and ejecting each master when printing therefrom is completed, the improvement in controlling the number of planographic masters present in said printing system comprising control means having a dual mode of operation allowing, during an initial period of introduction of masters at the startup of the system, uninhibited introduction of masters until a predetermined number is counted, and thereafter admitting a new master only upon departure of a previous master therefrom, said control means comprising: an impulse sequencing relay; a signal source giving signals each related to the completion of a printing run; first circuit means to step said impulse sequencing relay each time a master is introduced into the system to cause the same to count the number of masters initially introduced; and second circuit means controlled by the output of said impulse sequencing relay for defeating uninhibited introduction of masters into said system when the impulse sequencing relay has attained a predetermined count; and means responsive to the first master''s attaining printing position, for disabling the master counting action of said impulse sequencing relay, bypassing said second circuit means, and transferring introduction of masters to the control of said signal source.