Electronic Ink Flow Control for Printing

1. Field of the Invention

This invention relates to a method and apparatus for controlling the amount of ink transferred to the ink train in a printing press, which utilizes an electronic control for precisely regulating the ink transfer in accordance with a user input even when press speed is varied.

2. Description of the Prior Art

In a typical commercial-type offset printing press, ink is deposited on the plate cylinder from an ink train having a plurality of interengaging rollers. Typically, a fountain ball or roller is mounted in contact with an ink supply and a ductor roller is shiftably mounted to cycle back and forth between the fountain roller and the ink train. When the ductor roller is in contact with the fountain roller and the fountain roller is rotated, ink is transferred to the ductor roller. The ductor roller then cycles into contact with the ink train for transfer of ink to the ink train roller while the latter is in rolling contact with the ductor roller. It will be appreciated that the interval or "dwell angle" during which the ductor roller is in contact with the fountain roller and the rollers are rotated, largely determines the amount of ink transferred to the ductor roller. In a conventional printing press, a mechanically controlled, pneumatically actuated piston and cylinder mechanism is typically connected to the ductor roller. Such mechanically controlled mechanisms are usually adjustable to regulate the interval the ductor roller is in ink transferring relation with the fountain roller. Since the shifting mechanism is driven by the main press drive, the rest of cycle reciprocation of the ductor ideally would be directly proportional to press speed. In actual fact though inherent delays in shifting of the ductor by the pneumatic mechanism introduces non-linear relationship between press speed and ductor cycling.

In web-fed commercial-type printing, particularly multi-color printing, it is essential that the amount of ink transferred to the ink train be precisely controlled to assure consistent print quality. For example, the color density of the printed image is heavily dependent upon the amount of ink deposited to the ink train. In a conventional printing press having a mechanically controlled system for shifting the ductor rollers, the press operator establishes a particular press speed for set-up purposes and adjusts the amount of ink transferred to the ink train on each individual printing tower until the final end product exhibits the desired print quality.

Several problems exist with such mechanically controlled ink transfer systems and their method of operation. First, the make-ready for such a mechanically controlled system requires a substantial amount of time for the press operator to adjust all of the printing towers to achieve the desired print quality. Thus, until the desired print quality is achieved, the press output is waste and undesirable. Furthermore, where the operator speeds up the press to its normal velocity, then the print quality degrades because of insufficient ink being supplied to the web. As those skilled in the art will appreciate, press speed is also varied in many instances during a job run and it is then necessary either to readjust the individual offset towers or to accept a lower quality print product. Thus, the provision of a control system which reduces makeready costs and assures high print quality regardless of press operating speed variations represents a significant advance in the printing art, particularly where the desired result is obtained without modifications of existing technology relating to ink trains, ink fountain supplies and drive mechanisms.

The present invention is concerned with a method and apparatus for controlling the amount of ink transferred to the ink train in a printing press which substantially eliminates the problems associated with conventional ink flow control devices where press speed is varied from set up to run or during the run. The method and apparatus hereof easily and accurately allows the press operator to initially set up the press so that minimum adjustment of the press ink flow is necessary. This feature substantially reduces the waste associated with conventional ink transfer regulating systems, and is helpful to press operators of all skill levels. Further, the method and apparatus hereof accurately controls the amount of ink transferred to the press ink train even when press speed is varied. For example, when the press is accelerated to a faster operating speed than that used during the press set-up, the method and apparatus hereof consistently transfers the desired amount of ink during the acceleration and at the elevated velocity to yield a high quality print notwithstanding change of the press speed.

The ink flow control of the present invention includes a fountain roller operably associated with an ink supply and a shiftably mounted ductor roller. The ductor roller picks up ink from the fountain roller during the interval of time that contact is established between the ductor and fountain rollers and the rollers are rotated. A sensor provides a signal representative of the amount of ink transferred as a result of rotational movement of the fountain roller during such ink transfer interval. A micro processor is provided which receives the signal from the sensor. The press operator provides an instruction input to the processor indicative of the desired amount of ink to be transferred. The processor compares the representative signal with the operating instruction input and is programmed to control shifting of the ductor roller in a manner to regulate the ink transfer interval in correlated relationship with the input instruction. The fountain roller operates in a duty cycle of rotation and non-rotation and preferably, the ductor roller is shifted into contact with the fountain roller before the fountain roller begins ink transferring rotation. Thus, control of the amount of ink transferred to the ductor roller is largely a function of the timing of disconnect of the duct roller from engagement with the fountain roller. The processor operates to initiate disengagement of the ductor roller when a programmed relationship exists between the operating instruction input and the signal provided from the sensor. It will be appreciated that the programmed relationships established in the processor allow for any one of a number of operating instruction inputs, with the programmed relationships being operable to maintain a high print quality at all print speeds including normal run velocities.

In a preferred form of the invention, the ink flow control includes a feed back mechanism which determines when the ductor roller actually disengages from contact with the fountain roller and supplies an indication of the disengagement to the processor. The processor operates to compare the delay between the initiation of ductor roller disengagement and the indication received from the feed back mechanism. The processor adjusts the programmed relationship currently in use to account for the delay to assure high quality printing regardless of any such actuation delay.

Preferably, the control is provided with a transmission mechanism which causes intermittent rotational movement of the fountain roller in a duty cycle of rotation and non-rotation. The transmission includes a rotatable gear interconnected to the fountain roller. The gear has a plurality of spaced apart markings thereon and a detection mechanism which senses passage of the markings therepast. The detection mechanism generates a signal for each mark and feeds the signals to the microprocessors. Because the transmission rotates the fountain roller, the number of markings detected correlates to the amount of rotational movement of the fountain roller. The processor operates to count the signals and initiates the disconnect of the ductor roller from the fountain roller when the programmed relationship is reached.

FIG. 1 is a schematic view of the ink flow control of the present invention;

FIG. 2 is a block diagram of the microprocessor used in the present invention, and the relation of input and output sources thereto;

FIG. 3 is a flow chart for the main operating program of the microprocessor illustrated in FIG. 2;

FIG. 4 is a flow chart depicting the external interrupt program;

FIG. 5 is a flow chart of the counter-interrupt program;

FIGS. 6 and 7 are graphs of press ductor operating characteristics with the ordinate of each graph being ductor position and the abscissa machine displacement (web feet of travel through the press), wherein:

FIG. 6 illustrates the operating characteristics of a prior art ductor control, and

FIG. 7 is a graph illustrating the operating characteristics of ductor control in accordance with the present invention.

Turning now to the drawings, FIG. 1 illustrates schematically an ink flow control 10 for transferring ink to an ink train 12 in a printing press. The ink train 12 (illustrated only schematically as a series of interengaging rollers the number of which varies from press to press) includes an uppermost vibrator roller 14 which serves as the initial point of ink pick-up. The ink is transferred from roller to roller in the ink train 12 for deposit on the plate cylinder (not shown) of the printing press.

Broadly speaking, the ink flow control 10 include a ductor roller 16, ductor shifting mechanism 18, a fountain roller 20, a fountain drive transmission 22, and an electronic control assembly 24. As shown in FIG. 1, the fountain roller 20 is rotatably associated with an ink fountain 26 of conventional design. The ink fountain 26 receives the viscous ink 28 and includes a plurality of ink keys (not shown) which regulate the amount of ink 28 deposited on the fountain roller 20. The fountain roller 20 is also conventional in the sense that upon rotation thereof, the ink 28 adheres to the outer surface. The drive transmission 22 includes a unidirectional clutch 30 which serves to impart an axial rotation to the fountain roller 20.

The fountain drive transmission 22 has a first link 32 connected to the unidirectional clutch 30 and a second link 34 pivotally connected to the link 32. The link 34 is pivotally joined at its distal end to an axially rotatable gear 36 driven by the main press drive. The gear 36, which has a magnet 38 thereon and presents a plurality of equidistant, circumferentially spaced apart, peripheral teeth 40. The gear 36 is operatively coupled to the main press deive at a suitable reduction ratio, and under normal conditions, continuously rotates when the press is operated. Rotation of the gear 36 in turn imparts a reciprocating movement to the link 32 via the link 34. The unidirectional clutch 30 translates the reciprocating movement received from the link 32 into a intermittent rotational movement of the fountain roller 20. Thus, the fountain roller 20 axially rotates in one direction in a repetitive duty cycle of rotation and non-rotation.

The rubber covered ductor roller 16 is mounted for intermittent shiftable movement between the fountain roller 20 and vibrator roller 14 under the control of the shifting mechanism 18. For purposes of simplicity, only one mechanism 18 is illustrated. It is to be understood though that a pair of such assemblies operating in tandem may be employed if desired to avoid application of asymmetrical forces to the ductor roller 16 during reciprocal movement thereof. The ductor shifting mechanism 18 as shown includes an elongated arm 42 having one end rotatably mounting the ductor roller 16 while the other end is mounted for pivotal movement about a fixed point. A piston 44 of a multi-positional air cylinder 46 is operatively coupled to the arm 42 and controls the shifting thereof as shown at FIG. 1. Piston 44 has mounted thereon a second magnet 48 while the air cylinder 46 has a position sensor 50 which detects movement of the magnet 48 therepast when the piston 44 moves. A multi-positional air solenoid 52 controls supply of air to the air cylinder 46 and is connected to an air supply (not shown) by pneumatic line 54.

The electronic control assembly 24 illustrated in FIG. 1 includes a computer control board 60 which operates to control the solenoid valve 52 and receives inputs from a number of sources. One input to the board 60 is from the two digit thumb wheel switch assembly 62 which supplies a press operator furnished ink flow control operating instruction input to the board 60. The input number set in the thumb wheel switch 62 is indicative of the desired amount of ink to be transferred from the fountain roller 20 to the ductor roller 16. The number set in thumb wheel switch 62 is preferably passed to the board 60 as an 8-bit Binary Coded Decimal (BCD) value.

Another input to the board 60 is from the cycle initiation sensor 64. Preferably, the sensor 64 is a Hall effect-type position sensor disposed adjacent the gear 36 which operates to supply a 12 volt electrical signal indication to the board 60 when the magnet 38 travels therepast. A Hall effect sensor such as a Series 200SR manufactured by Microswitch, Inc. has proven operable in this regard. Preferably, the output signal from the sensor 64 is passed through an optoisolator (not shown) for input to the computer control board 60 as a 5 volt logic voltage signal. In this regard, isolator model H11L1 made by General Electric incorporates a microprocessor compatible Schmitt trigger and has proven effective in passing a digital signal from the sensor 64 to the board 60.

Another input into the computer control board 60 is from the machine displacement sensor 66. The sensor 66 is disposed adjacent the gear 36 and essentially counts the number of gear teeth travelling therepast. A Photoswitch, Inc. type 51 inductive sensor has proven effective in counting the teeth 40 of the gear 36. The 12 volt output from the machine displacement sensor 66 is preferably passed through an optoisolator, such as General Electric's Model H11L1, for inputting a logic voltage signal to the board 60.

It is also to be seen from the schematic diagram of FIG. 2 that another input to the control board 60 is the signal generated by position sensor 50 when activated by magnet 48.

A final input to the computer control board 60 is the ductor system control switch 68 which functions to regulate the operation of the ductor roller 16. Preferably, the ductor control switch 68 is a three pole, five position rotary switch having the following modes--on, auto, free, vibrator, and fountain. In the on mode, the ductor shifting mechanism 18 operates normally to shift the ductor roller 16 between the ink train 12 and fountain roller 20, regardless of whether or not the the ink form rollers of the printing press are being rotated. In the auto mode, the ductor shifting mechanism 18 operates normally only if the ink forms are activated. In the free mode, the ductor shifting mechanism 18 disrupts the air pressure to the air cylinder 46, taking the pressure off of the ductor roller 16 and effectively disabling the operation thereof. In the vibrator mode, the ductor shifting mechanism 18 operates to move the the ductor roller 16 into contact with the vibrator roller 14 of the ink train 12. The vibrator mode is particularly useful in clean-up operations to extract most of the ink from the ductor roller 16. Finally, in the fountain mode, the ductor shifting mechanism 18 moves the ductor roller 16 into contact with the fountain roller 20 and retains the ductor roller in that position. The fountain mode is useful during makeready of the press, for example to set the individual ink keys of the ink fountain 26.

Turning now to FIG. 2, the computer control board 60 and the input and output devices coupled thereto are illustrated in block diagram form. A 12 volt DC power supply 70 provides power to the computer control board 60 and preferably has a voltage regulator coupled thereto for supplying logic voltage to the board 60 (a voltage regulator such as National Semiconductor Model LM7805 has proven operable). The control board 60 includes an input buffer 72, a single chip microcomputer 74, an output buffer 76, and a pair of relays 78, 80 operatively connecting the output buffer with the solenoid air valve 52.

Those skilled in the art will appreciate that the microcomputer 74 could comprise a wide variety of different types of digital processors with either on chip or external memory. In the preferred embodiment, the microcomputer 74 is an Intel Corporation Model 8748 having an eight bit CPU and a single level interrupt. The microcomputer 74 contains a 1K .times.8 erasable, user-programable program memory (EPROM), a 64 word data memory (RAM), 27 I/O lines, and an eight bit timer/counter. The position of the ductor control switch 68 is fed directly to the microcomputer 74 (pins P10-P12). The appropriate signal indicative of the setting in the two digit thumb wheel switch 62 is also fed directly to the microcomputer 74 (pins P20-P27). Cycle initiation sensor 64, machine displacement sensor 66 and air cylinder position sensor 50 feed directly to the input buffer 72 (via appropriate optoisolators). In this regard, it is noted that the signal generated from the cycle initiation sensor 64 is fed to the interrupt pin of the microcomputer 74 and initiates an external interrupt, assuming the interrupt feature is enabled. Further, the signal generated from the machine displacement sensor 66 is fed to the timer/counter function of the microcomputer 74 (pin T1) and designated a counter input using the appropriate mnemonic. The counter portion of the microcomputer 74 is labelled 82 in FIG. 2, it being understood that the counter function operates to count from 0 to 255 and generates an internal interrupt upon rollover from 255 to 0.

Operation of the ink flow control 10 in accordance with the present invention is most easily understood from the control sequence depicted in the flow charts of FIGS. 3, 4, 5. In this regard, the program listing included herein sets forth in detail the control sequence. The program listing includes source statements and comments for the main program (FIG. 3), for the trigger or external interrupt program (FIG. 4) and for the counter interrupt program illustrated in FIG. 5. In addition to the main, external interrupt and counter interrupt programs, the program memory (EPROM) of the microcomputer 74 includes the look-up table contained on page 5 of the program listing. The look-up table represents a programmed relationship between the number of gear teeth 40 expected to be counted by the sensor 66 and the ink flow input set on the thumb wheels of the switch 62.

Turning to the flow chart of the main program depicted in FIG. 3, after power up, program execution moves to the beginning of program memory and enters an initialization sequence which clears the internal registers of the microcomputer 74 and initiates a signal to the output buffer 76 to move the ductor roller 16 into contact with the vibrator roller 14 while the rest of the main program is executed. This signal causes the solid state relay 78 to close and actuates the solenoid air valve 52. Actuation of the solenoid valve 52 in turn causes air under pressure to be directed to air cylinder 46 thus extending piston 44 and effecting shifting of the ductor roller 16 into contact with vibrator roller 14.

The next step in the main program flow chart of FIG. 3 involves loading of the ink flow control number from the thumb wheel switch 62 (scan routine in the attached program listing). In this routine, the computer simply reads in the two digit (3 bit BCD valve) ink flow input number and stores the number in a temporary register. The computer uses the ink flow input as a pointer in the look-up table to find the number of gear teeth 40 programmed to correspond to the ink flow input number. If the ink flow input number read from the thumb wheel switch 62 is the same as the input number previously used and stored in the register, then it is not necessary to enter the look-up table as no change in the number of gear teeth is needed.

The next step in the main program is concerned with loading of switch position of the ductor system control mode set switch 68 into the microcomputer 74. The final step is configuration of the ink flow control 10 according to the position of the ductor control switch 68. That is, the selected one of the five modes (on, auto, free, vibrator, and fountain) which has been selected on the control switch 68 must be known by the microprocessor 60. In the free, vibrator, and fountain modes, the external (or trigger) program interrupt (FIG. 4) is disabled. In the auto mode, the external program interrupt is disabled unless the form rollers are activated on the press. In the auto mode with the form rollers activated and in the on mode, the external program interrupt is enabled. It should be noted that the ductor system control switch 68 for normal operation is placed in either the on or auto mode settings.

After the ink flow control 10 is configured as defined by the ductor control switch 68, the program jumps back to the "load ink flow control number" step in the flow chart of FIG. 3. Essentially, the program operates in a continuous loop to continually monitor the settings of the thumb wheel switch 62 and ductor control switch 68 for any changes made by the operator.

Turning to FIG. 4, the flow chart for the trigger or external interrupt program is illustrated. Assuming the press is in normal operation, the external interrupt is enabled (the "on" mode or "auto" mode with forms enabled). The external interrupt routine of FIG. 4 is entered when the sensor 64 detects passage of the magnet 36 therepast. The signal generated by the sensor 64 is directed to the interrupt pin of the microcomputer 74 (via optoisolator and input buffer 72) interrupting the main program of FIG. 3 and entering the external interrupt program of FIG. 4. In the first step in the interrupt program the ductor roller 16 is moved into contact with the fountain roller 20. To effectuate the move, the microcomputer 74 generates a signal to the output buffer 76 which activates the relay 80 and solenoid air valve 52. Air valve 52 causes the air to be directed to air cylinder 46 in a direction to effect retraction of the piston 44, forcing the ductor roller 16 into contact with the fountain roller 20. It has been found preferable to move the ductor roller 16 into contact with the fountain roller 20 before the fountain roller begins rotation. Therefore, magnet 38 is located on gear 36 in disposition such that even at maximum press operating speed, the sensor 64 will generate a signal which ultimately moves the ductor roller 16 into contact with the fountain roller 20 while the fountain roller 20 is still in the non-rotation stage of its duty cycle.

The next step in the external interupt program of FIG. 4 involves loading of the gear tooth number found from the look-up table into the counter portion 82 of the microcomputer 74. With the counter 82 enabled, the counter counts the pulses generated by the air cylinder position sensor 50 in accordance with the gear teeth displaced therepast. The external interrupt program enables the counter interrupt function allowing the counter 82 to signal the microcomputer 74 when the required number of gear teeth are counted. Preferably, the look-up table contains the 2's complement of the gear teeth number such that the counter interrupt occurs on rollover from 255 to 0. After the counter interrupt feature is enabled, program execution then returns to the main program of FIG. 3 to monitor any changes to the thumb wheel switch 62 or ductor control switch 68 while the counter 82 operates.

As soon as the ductor roller 16 is brought into contact with the fountain roller 20, the ductor roller 16 and fountain roller 20 are in a position for ink transfer. However, effective ink transfer does not begin until the fountain roller 20 begins rotation. The "interval" (also referred to as "dwell angle") during which the rollers 16, 20 are in contact and rotating is determinative of the amount of ink transferred to the ductor roller 16. Therefore, for the amount of ink transferred to the ductor roller 16 to be accurate for high quality printing, it is necessary that the ductor roller 16 disengage from contact with the fountain roller 20 at the appropriate time, and most especially in the preferred embodiment of the present invention in accordance with the ink flow operating instruction input set on the thumb wheel switch 62. The programmed relationship of the operating instruction input to gear tooth count found in the look-up table is established to give an initial, near optimum disconnect of the ductor roller 16 from the fountain roller 20. As a tooth 40 passes the inductive sensor 66, a pulse signal is generated which ultimately causes the counter to be incremented for each tooth 40 sensed. When the counter rolls over to zero, an internal interrupt is generated which causes program execution to jump from the main program to the counter interrupt program shown in FIG. 5.

Turning now to FIG. 5, the counter interrupt program first causes the ductor roller 16 to move from a position in contact with the fountain roller 20 to a position in contact with the vibrator roller 14. To accomplish this, the microcomputer 74 outputs a signal through the output buffer 76 to the relay 78 actuating the solenoid air valve 52. The air valve 52 causes actuation of the air cylinder 46, with piston 44 being displaced to push the ductor roller 16 into contact with the vibrator roller 14 (shifting right to left as shown in FIG. 1).

Even after the counter interrupt program is entered, the counter 82 continues to count gear teeth sensed by the inductive sensor 66. The counter 82 stops when the microcomputer 74 indicates that the ductor roller 16 has actually disengaged from the fountain roller 20. In the preferred embodiment, the actual disengagement of the rollers 16, 20 is determined inferentially by disposition of magnet 48 on the piston 44 in a location such that the position sensor 50 generates a signal at the moment of disengagement. The signal from the position sensor 50 is supplied to the microcomputer 74 which stops the counter.

On power-up, the gear tooth number from the look-up table is placed in a temporary register as the "active" gear tooth number in the counter 82. The "active" gear tooth number is then either incremented, decremented, or left unchanged dependent upon the delay between initiation of disengagement by the microcomputer and the time when the microcomputer 74 receives the disengage signal from the position sensor 50. That is, the number of gear teeth counted by the counter 22 during the delay (counter overflow) is added to the active gear tooth number and the sum compared with the original look-up table tooth number. If the sum is less than the look-up table number, the "active" gear tooth number is decremented. If the sum is equal to the look-up number no change is made. If the sum is greater than the look-up number, the "active" number is incremented. It should be appreciated that this feature provides compensation for changes in press speed. After modification of the gear tooth number is made, the execution returns to the main program. The ductor roller 16 remains in contact with the vibrator roller 14 and the microcomputer 74 executes the main progress until the magnet 38 is again sensed by the Hall Effect sensor 64. As previously described, the sensor 64 initiates a signal which generates an external interrupt, and program execution jumps to the external interrupt program (FIG. 4). Thus, another ductor cycle begins as previously described.

The ductor cycle operating characteristics of a typical prior art press is graphically depicted in FIG. 6, while FIG. 7 illustrates the ductor cycle operating characteristics of the ink flow control 10 of the present invention. Both FIGS. 6 and 7 present ductor roller position as the ordinate plot versus machine displacement as the abscissa. Machine displacement is usually expressed in terms of surface feet of web travel through the printing press. On both graphs, the angular displacement of fountain roller rotation is depicted along the uppermost margin thereof. The lowermost margin of the graphs is used to denote the position of the ductor roller 16 which it is in contact with the vibrator roller 14. The uppermost margin of each graph is the position of the ductor roller 16 while it is in contact with the fountain roller 20. For comparison purposes, position of a ductor roller under ideal conditions (e.g. instantaneous constant velocity) is labeled as ideal line 90 in both FIGS. 6 and 7.

Starting from left to right in FIGS. 6, and 7, it is seen that an ideal ductor roller (line 90) would be operated to break contact with the vibrator roller and without actuation delay, then travel at an instantaneous, constant velocity until the ductor roller contacts the fountain roller. The point labeled in 92 in FIGS. 6 and 7 is the point at which the ideal ductor roller first contacts the fountain roller. Optimally, the ideal ductor roller will contact the fountain roller at the instant the fountain roller begins to rotate, as illustrated in the drawing. The point labelled in 94 in the drawings is the point at which the ideal ductor roller would break contact with the fountain roller. It will be appreciated that the interval (dwell angle) between points 92 and 94 denotes the ink pick-up phase; that is, the ductor roller and the fountain roller are in ink transferring relation when in contact during fountain roller rotation.

In FIG. 6, the inverted U-shaped line labeled 96 graphically denotes the path of travel of the ductor roller from the time of engagement with the fountain roller until contact therewith is broken in a conventional printing press at press set-up speed. In a conventional printing press, the press operator adjusts the dwell angle of the ductor roller until the optimum print quality at set-up speed is achieved. For optimum print quality to occur, line 96 intersects ideal points 92, 94.

Inverted U-shaped line 98 of FIG. 6 is a depiction of the position at any instant of time of a prior art ductor roller at a press speed slower than initial press set-up speed. Slowing a printing press down from the initial set-up speed is common, for example to pass a web splice through the printing press. The primary difficulty in slow speed press operation as illustrated by line 98, is that the ductor roller disengages from the fountain roller before the ideal break point 94. Thus, the interval of ink transfer from point 92 to contact break point, is less than the ideal ink transfer interval established at press set-up speed. The amount of ink transferred to the ductor roller, and hence to the ink train, is less than ideal and either print quality is sacrificed or the press operator must recalibrate the movement of the ductor roller to achieve the ideal ink transfer interval.

Finally, inverted U-shaped line 100 graphically illustrates the positions on a time basis of a conventionally controlled ductor roller at a press speed greater than the initial press set speed. Hereagain, this is a common occurence, in that a press operator normally uses a moderate press speed for set-up purposes to reduce the amount of waste occuring during set-up, and the operator then generally increases press speed for the job run. As illustrated in FIG. 6, the position of line 100 deviates sufficiently from the ideal line 90 to make it difficult if not impossible possible for the operator to continue press operation at a particular speed without readjustment of the ductor roller dwell angle against the fountain roller 20. In FIG. 6, the point of contact of the ductor roller with the fountain roller 20 under the high speed conditions of line 100 is labeled 102, and the point of disengagement is labeled 104. It is seen that the deviation of point 102 from the ideal point 92 is substantially different from the deviation of point 104 from point 94, with the result that the ink transferring interval between point 102 and 104 deviates from the ideal. A wide variety of factors are involved in contributing to these deviations. For example, the rate of change of ductor shifting is not proportional to changes in machine displacement, with the end result being that when a conventional printing press is operated at other than press set up speed, ink transfer deviates from the ideal. Ink transfer is a significant factor in print quality. This is one reason that in a conventional printing press, ductor roller shifting must be either readjusted or print quality sacrificed when press speed is changed.

Turning now to FIG. 7, the operating characteristics of ink flow control 10 of the present invention is graphically shown in a format similar to FIG. 6. The inverted U-shaped line labeled 106 is a plot of the positions of the ductor roller 16 versus machine displacement at initial press set-up speed. During set-up, the press operator inputs a predetermined, initial ink flow setting into the thumb wheel switch 62 suitable for the job run. In this regard, the look-up table has been established to give a programmed relationship between ink flow input and gear tooth count number to yield a good print quality during makeready. Thus, waste during makeready using the ink flow control 10 of the present invention is reduced when compared with conventional printing presses.

Inverted U-shaped line 108 is a plot of the positions of the ductor roller 16 at a press speed lower than initial set-up speed, while inverted U-shaped line 110 represents a plot of ductor roller positions at the maximum press operating speed. Significantly, at all press operating speeds, the ductor roller 16 engages the fountain roller 20 before the fountain roller begins rotation. Thus, even at maximum press operating speed (line 110) ductor roller 16 is in contact with the fountain roller ready for ink transfer as soon as the fountain roller begins the rotation phase of its duty cycle (approximately point 92 in FIG. 7). Because the counter interrupt program modifies the gear tooth number count to acommodate actuation delays in the ductor roller, the ductor roller 16 disengages from the fountain roller at approximately the ideal break point 94, regardless of press operating speed. That is, during acceleration and deceleration of the press and at different press operating speeds, the ink flow control system 10 constantly modifies the ductor dwell angel, if necessary, to approach an ideal ink transfer interval. Those skilled in the art will appreciate that the method and apparatus of the present invention represents a significant advance in the art in reducing problems associated with press makeready and ensuring a high print quality notwithstanding changes in press operating speed. ##SPC1##