Register control means for web processing apparatus

In combination:

• web processing apparatus comprising:
• an impression cylinder (10) for forming a succession of impressions (52) and associated register marks (54) on a web (W);
• a cutter mechanism (26) having a cutting zone (27) wherein blanks containing said impressions (52) are cut from said web (W);
• a rotatable metering roll (18) for continuously feeding said web (W) from said impression cylinder (10) to said cutter mechanism (26);
• an adjustable speed register control motor (30) for rotatably driving said metering roll (18);
• a movable dancer (12) engaged with said web (W) at a location between said impression cylinder (10) and said metering roll (18), said dancer (12) assuming a predetermined dancer position when said register control motor (30) operates at a speed at which said impressions (52) are in registry with said cutting zone (27);
• and selectively operable dancer position adjustment means (15) for moving said dancer (12) when the latter is disengaged from said web (W);
• and register control means comprising:
• a dancer position sensor (36) for providing dancer position signals;
• a register mark scanner (38) for sensing register mark positions at a location upstream of said metering roll (18) and for providing register mark position signals;
• a metering roll encoder (40) driven by said metering roll (18);
• a tachometer (46) driven by said register control motor (30);
• a cut-stroke signal generator (44) driven by said cutter mechanism (26);
• a control panel (60) comprising a digital visual display (62) and manually operable switches for providing switch signals and including an automatic/manual selector switch (68), a setup switch (70), a web advance switch (64) and a web retard switch (66);
• and an electronic controller (80) comprising circuits for receiving and processing said switch signals, and signals from said sensor, scanner, encoder, tachometer, and signal generator, said circuits including:
• base speed circuit means (I) responsive to switch signals from said set-up switch (70) to provide a base speed control signal to effect operation of said register control motor (30) at a selected base speed and to effect a numeric display of said selected base speed on said digital display (62);
• circuit means to receive and process signals from said metering roll encoder (40) and said tachometer (46) and to provide a correction control signal to said base speed control signal to maintain a predetermined fixed speed ratio between said output signals from said metering roll encoder (40) and said tachometer (46);
• circuit means (J) for counting the number of metering roll encoder pulses provided by said metering roll encoder (40) which occur in an interval of time between a cut-stroke signal representing the arrival of a register mark (54) at said register mark sensor (38) and the subsequent occurrence of a signal from said cut-stroke signal generator (44) representing an operation of said cutter mechanism (26);
• memory circuit means (A) for storing a predetermined number representing said predetermined repeat length;
• circuit means (K) for comparing the number of metering roll encoder pulses occurring during said interval of time to said predetermined number stored in said memory circuit (A) to provide a digital error count signal representing the direction and magnitude of misregistration error and to effect display of said error count signal;
• a digital-to-analog converter circuit (G) to convert said digital error count signal to an analog error signal;
• a circuit (J) for counting the number of said error correction signals which were applied to effect elimination of said register error, a circuit (M) for transmitting said count, a circuit (F) for adding those error correction signals which are positive and for subtracting those error correction signals which are negative, and a circuit (H) to provide an analog DC voltage error signal which is to be added to or subtracted from said base speed control signal to effect a change in the rotational speed of said register control motor (30);
• the PID circuit (H,G,E,F and K) to receive said analog voltage DC error signal and to ascertain the trend and average magnitude of said error over a fixed period of time and to thereby provide an error correction signal which is momentarily applied by circuit (H) to base speed control signal for said register control motor (30) to thereby adjust the speed of said metering roll (18) to the speed of said printing cylinder (10);
• circuit means (B) to sense the position of said dancer (12) and to provide a dancer position signal whose value relates to dancer position;
• memory circuit means (A) to store the value of said dancer position signal which represents dancer null position which is provided when said analog error correction signal is eliminated;
• and circuit means (K) to compare the value of a dancer position signal, which is provided when a corrected base speed signal is being provided, to the stored null position signal value and for providing a dancer control signal for said dancer adjustment means (15) to adjust the position of said dancer (12) in accordance with said stored position signal when said web (W) is not engaged with said dancer (12).