BACKGROUND OF THE INVENTION Printing problems are often encountered after the start of a press-run of a lithographic printing press.

Some such problems are caused by temperature changes in the press. For example, after start-up, the ink temperature and dampening fluid evaporation rate associated with the press begin rising until the press reaches a warm press equilibrium. These increases in temperature and evaporation rate cause the printing plates of the press to gradually move into a too-dry condition wherein undesirable ink scum appears in non- image areas of the print. More dampening fluid is needed to prevent this too-dry, scum-producing condition.

Starting a print run from a cold start using dampening settings used when the press was previously running or warm does not solve this problem. Such an approach causes too much dampening fluid to be applied to the printing plates until the warm press equilibrium is reached. This excess of dampening fluid results in a loss of print density for a corresponding length of time.

In the past, press operators have attempted to address these problems by manually adjusting the amount of dampening fluid delivered by the dampener to a level where these undesired effects are eliminated. Such manual adjustment, however, suffers from certain disadvantages. For example, manual adjustment requires the press operator to identify the problem, typically while poor quality, tinted/scummed prints are being produced. Until the problem is recognized and corrected, poor quality prints will be produced. Moreover, dampener adjustments can be frequently needed. In one such example 35 adjustments were needed in a run of 200,000 impressions.

SUMMARY OF THE INVENTION In accordance with an aspect of the invention, an apparatus for controlling a dampener delivering dampening fluid to a printing press is provided. The apparatus includes a temperature sensor mounted on the frame of the printing press for measuring the temperature thereof. It also includes a dampening control unit which is associated with the dampener and which is in communication with the temperature sensor. The dampening control unit adjusts the quantity of dampening fluid delivered by the dampener to the printing press in response to temperature changes detected by the temperature sensor.

In accordance with another aspect of the invention, a method is provided for controlling the amount of

dampening fluid delivered by a dampener to a printing press having a frame. The method comprising the steps of: sensing the temperature of the frame of the printing press; and adjusting the amount of dampening fluid delivered by the dampener to compensate for sensed temperature changes.

In some embodiments, the method further comprises the steps of: determining a difference between the sensed frame temperature and a baseline temperature; and developing a temperature modification factor by multiplying the difference by a first constant.

Optionally, the method may also comprise the steps of: sensing a current humidity; determining a humidity difference between the current humidity and a baseline humidity; developing a humidity modification factor by multiplying the humidity difference by a second constant; and multiplying the temperature modification factor and the humidity modification factor to develop a control signal for adjusting the dampener.

Other features and advantages are inherent in the method and apparatus claimed and disclosed or will become apparent to those skilled in the art from the following detailed description and its accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of an apparatus constructed in accordance with the teachings of the invention.

FIG. 2 is a schematic illustration of one possible environment of use for the apparatus of FIG. 1.

FIG. 3 is a schematic illustration of a four high printing press stack employing four independent dampener control units.

FIG. 4 is a schematic illustration of a spray nozzle dampener which may optionally be controlled by the apparatus of FIG. 1.

FIG. 5 is a side view of a brush dampener which may optionally be controlled by the apparatus of FIG. 1.

FIG. 6 is a front view of the brush dampener of FIG.

5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An apparatus 10 constructed in accordance with the teachings of the instant invention is shown in FIG. 1.

Although in the following discussion, the apparatus 10 is described as being used to control the output of one or more dampeners on a particular lithographic printing press, persons of ordinary skill in the art will appreciate that the present invention is not limited to use with any particular type of lithographic press. On the contrary, the apparatus 10 can be utilized with any lithographic printing press which would benefit from regulating dampener fluid flow in response to temperature change.

An example of a single unit 1 of a lithographic printing press which might benefit from the teachings of the present invention is shown schematically in FIG. 2.

The illustrated press is adapted for simultaneously printing two sides of a web of paper 3. Thus, it includes a pair of blanket cylinders 2 between which the web of paper 3 passes. The blanket cylinders 2 act as backing cylinders for each other as is conventional in the art. Each of the blanket cylinders 2 forms a couple with a plate cylinder 4. Each of the plate cylinders 4 carry a printing plate, as is well known in the art.

For purposes of illustration, different dampening and inking systems are shown in the left and right sides of FIG. 2. However, persons of ordinary skill in the art will readily appreciate that such an approach would not ordinarily be employed in the field. On the contrary,

the same types of dampening and inking mechanisms would typically be used on both sides of the printing unit 1.

Turning first to the left side of FIG. 2, the printing unit 1 is provided with a train of rollers 5 for delivering ink to the leftmost plate cylinder 4 in a conventional manner. It is also provided with a dampener 6 implemented by a pan roller 51, a high speed brush 52 and a dampener roller train 53. The pan roller 51 lifts dampening fluid from a reservoir. The high speed brush 52 propels the lifted fluid from the surface of the pan roller 51 onto the dampener roller train 53 which delivers the dampener fluid to the plate cylinder 4.

Turning to the right side of FIG. 2, the printing unit 1 is provided with a train of rollers 7 for delivering both ink and dampening fluid to the rightmost plate cylinder 4. While the ink delivery system is similar on both the left and right sides of the unit 1, the right side of the unit delivers dampening fluid differently than the left side. In particular, on the right side of the unit 1, a dampener implemented as a spray bar 8 is utilized to spray dampening fluid onto the roller train delivering ink to the plate cylinder 4.

Thus, both ink and dampening fluid are delivered to the plate cylinder 4 via the same train of delivery rollers.

Returning to FIG. 1, for the purpose of detecting changes in the temperature of the serviced printing press, the apparatus 10 is provided with a temperature sensor 14. Preferably, the temperature sensor 14 is implemented as a thermocouple sensor mounted on the frame

of the printing press. Although other locations would also be acceptable, one preferred location for mounting the temperature sensor is on the press frame in the vicinity of the blanket cylinders 2 as shown in FIG. 2.

Alternatively, in lithographic printing presses which utilize a mixture or emulsion of ink and dampening fluid as the means of dampening such as the Adopt"press of Goss Graphics, the temperature sensor 14 may optionally be located within the flow path of the mixture (e. g., within a reservoir holding the mixture, within a conduit carrying the mixture from the reservoir to the press, etc.) and can optionally sense the temperature of the mixture.

Although other sensors could be employed in this role, in the illustrated embodiment the temperature sensor 14 is implemented by a sensor sold by Omega Engineering Inc. under the product name Omega Dual Magnet Probe Thermocouple.

In order to control the operation of the dampener 12 supplying dampening fluid to the printing press, the apparatus 10 is further provided with a dampening control unit 18. As shown in FIG. 1, the dampening control unit 18 is associated with the dampener 12 and is in communication with the temperature sensor 14. The dampener control unit 18 which, in the illustrated embodiment, is implemented by a microprocessor such as the MC68HC11 which is commercially available from Motorola, Inc. is programmed to adjust the quantity of dampening fluid output by the dampener in response to

temperature changes detected by the temperature sensor 14. In particular, in the preferred embodiment, the dampening control unit 18 is programmed to calculate the appropriate, thermally compensated setting for the dampener 12 in accordance with the following equation: wherein Tc = current temperature in Fahrenheit as measured on the printing press frame; Tn = a baseline temperature in Fahrenheit (typically, a default value stored in memory which may optionally be user adjustable to account for local climate conditions); Dn = the operator's original dampener setting; Dc = the dampener setting as thermally compensated; and Kl = an adjustable gain factor specifying the dampener adjustment increment per degree Fahrenheit.

In order to enable setting of the adjustable gain factor K1 and, thus, the increments at which the apparatus 10 will adjust the output of the dampener 12, the apparatus 10 is preferably provided with an input device 22 such as a keyboard, a touch screen, a mouse, or the like. A user can, thus, input the factor Kl via suitable manipulation of the provided input device. In the preferred embodiment, the adjustable gain factor K defaults to a value of one. Thus, unless the user adjusts this value via the input device, the apparatus 10 responds to a one degree Fahrenheit increase in temperature by increasing the output of the dampener 12

by one percent In the preferred embodiment, the apparatus 10 accepts K1 factor values of between 0 and 5 in 0.1 increments. However, persons of ordinary skill in the art will readily appreciate that other values and/or increments (including, but not limited to, no fixed increments or continuous control) could be utilized without departing from the scope of the invention.

In the preferred embodiment, the input device 22 is also used to accept other user inputs. For example, when the press is initially set-up, the input device 22 is used to input a curve mapping dampening quantity to press speed. As is well known in the art, an increase in press speed (e. g., from 20,000 impressions per hour to 70,000 impressions per hour) requires a corresponding increase in dampening fluid. This relationship, which is typically not linear, is programmed into the dampener control unit 18, and is taken into account in a conventional manner by the control unit 18 when selecting an appropriate level of dampening fluid to be delivered to the press (i. e., when controlling the dampener 12).

To enable such control, the apparatus 10 is provided with a conventional speed sensor 70 for sensing a rotational speed of the printing press. The speed sensor 70 is in communication with the dampener control unit 18.

By way of another example, the input device 22 may also be used to input an operator's original dampener setting Dnwhich is utilized to automatically control the dampener 12 as discussed below. The user may optionally influence the automatic operation of the dampener control

unit 18 by adjusting the original dampener setting Dn. If desired, the operator can effectively deactivate the automatic temperature compensation feature of the control unit 18 by setting K1 to zero and manually adjusting the Dn factor to manually react to temperature changes. In embodiments employing the humidity control feature discussed below, the K2 factor (explained below) can be entered or set to zero to effectively deactivate the automatic humidity compensation feature of control unit 18.

In operation, the dampener control unit 18 monitors the readings developed by the frame temperature sensor 14 and the speed sensor 70, and periodically calculates the optimal amount of dampening fluid to be supplied to the press under the current conditions using the adjustable gain factor K1 and the baseline temperature Tn stored in memory. The calculated dampening fluid amount is converted to a control signal in a known manner which is output to the dampener 12. Preferably, the dampener 12 responds by adjusting its output to the indicated level.

Persons of ordinary skill in the art will readily appreciate that either open loop or closed loop control could be used to control the dampener 12 without departing from the scope of the invention. If closed loop control is employed, the dampener control unit 18 is preferably provided with a comparator for comparing the current setting of the dampener to the desired setting calculated by the control unit 18. Under such an approach, the difference signal developed by the

comparator is used to adjust the setting of the dampener 12.

For the purpose of compensating the dampener output for humidity changes, the apparatus 10 may optionally be further provided with a humidity sensor 30. In the illustrated embodiment, the humidity sensor 30 is implemented by the sensor sold by Rotronic Instrument Corp. under the product name Rotronic F3 Humidity Transmitter.

In embodiments employing a humidity sensor 30, the dampener control unit 18 is preferably programmed to perform the following calculation: wherein the new terms are defined as follows: Hc = current humidity near the printing press (preferably inside the printing unit guards); Hn = baseline humidity (for example, set to 100); K1 = the previously discussed adjustable gain factor for temperature; and K2 = an adjustable gain factor for humidity.

All other terms are as defined in connection with the previous equation discussed above.

In this embodiment, the apparatus 10 senses the temperature of the press frame, the press speed 70, and the current humidity using the sensors 14,30,70. The dampening control unit 18 then develops a temperature modification factor by determining a difference between the sensed frame temperature and the baseline

temperature, and then multiplies the calculated difference with the adjustable gain factor K1 stored in memory for temperature. The dampening control unit 18 then determines a humidity difference between the current humidity and the baseline humidity. It then develops a humidity modification factor by multiplying the humidity difference by the adjustable gain factor K2 for humidity stored in memory. Then, after separately adding one to both the humidity modification factor and to the temperature modification factor, the dampening control unit 18 multiplies the temperature modification factor with the humidity modification factor and with the operator's original dampener setting to arrive at the new dampener setting. The new dampener setting is saved in memory and the dampener 12 is adjusted accordingly.

As shown in FIG. 3, a four color lithographic printing press often includes four units 80,82,84,86 such as that illustrated in FIG. 2. Each of these units 80,82,84,86 typically prints only a single color of ink on the web of paper 3 (illustrated by a dashed line in FIG. 3) passing therethrough. For example, unit 80 might print black ink, unit 82 might print yellow ink, unit 84 might print magenta ink, and unit 86 might print cyan ink. In the illustrated embodiment, each of the units 80,82,84,86 includes two blanket cylinders 2, two plate cylinders 4, and two ink and dampener fluid delivery systems 5,6 or 7,8. For simplicity of illustration, the ink and dampening fluid delivery systems 5,6 or 7,8 have each been illustrated by a

single circle in FIG. 3. However, persons of ordinary skill in the art will readily appreciate that multiple rollers such as those illustrated in FIG. 2 will typically be utilized in these roles. Also, although each unit 80,82,84,86 has been illustrated as including two different types of ink/dampening fluid delivery systems 5,6 or 7,8, as explained above each unit will typically employ only one type of these systems 5,6 or 7,8, and the same type of system 5,6 or 7,8, will usually be employed in all of the units 80,82,84, 86.

In the embodiment shown in FIG. 3, each unit 80,82, 84,86 is preferably provided with its own dampener control unit 18 and its own temperature sensor 14. Each of the temperature sensors 14 is preferably mounted on the press frame in proximity to the blanket cylinders 2 of the serviced unit 80,82,84,86. If the humidity control option is implemented, each unit 80,82,84,86 is preferably provided with its own humidity sensor 30 (not shown). In the embodiment shown in FIG. 3, each control unit 18 controls at least two dampeners 6,8.

Although for simplicity of illustration, the dampening control units 18 have been illustrated as located within the individual press units 80,82,84,86, persons of ordinary skill in the art will readily appreciate that the control units 18 will preferably be located external to the printing units 80,82,84,86.

In addition, although in the embodiment illustrated in FIG. 3, each unit 80,82,84,86 has its own control unit

18, persons of ordinary skill in the art will appreciate that, if desired, all of the printing units 80,82,84, 86 may be controlled (independently or otherwise) by a single dampener control unit 18 having suitable computing ability without departing from the scope or spirit of the invention.

As will be appreciated by persons of ordinary skill in the art and as briefly discussed above, dampeners 12 of various constructions can be controlled by the apparatus 10 without departing from the scope or spirit of the invention. For example, as shown in FIG. 4, the dampener 12 could be implemented as a spray bar 40 having a plurality of spray nozzles 42 (typical 8 nozzles). The spray nozzles 42 are located to spray dampening fluid onto a roller train which feeds fluid to the plate cylinder 4 of the printing press.

When the dampener 12 is implemented as a spray bar 40, the amount of fluid delivered by the dampener can be adjusted in two ways, namely, by controlling the"on time"or the spraying frequency of the nozzles 42.

Pursuant to the time method, the nozzles 42 are turned on at the same frequency (e. g., every 200 msec), but the duration of the on-period is adjusted (e. g., from 5 msec to 10 msec) to adjust the amount of dampening fluid delivered by the dampener 12. An increase in the on- period results in more fluid being delivered to the press.

When the frequency method is used, the on-periods of the nozzles have fixed duration (e. g., 5 msec), but the

frequency at which these on-periods occur are adjusted (e. g., every 150 msec, or every 200 msec, etc.). The more frequently the nozzles 42 are turned"on", the more dampening fluid will be delivered to the press.

Optionally, the spray nozzles 42 may be independently controlled by the dampener control unit 18.

If such an approach is taken, the on-times or the frequencies of the nozzles 42 can be separately controlled to control the amount of dampening fluid delivered by the dampener 12. Independent control of the nozzles 42 is advantageous when some region (s) of a print (such as at the edges of a cylinder) generate more heat than others. The nozzle (s) 42 corresponding to the warmer region (s) can be adjusted to supply more dampening fluid than the other nozzles to correct for this effect. Of course, persons of ordinary skill in the art will appreciate that independent control is optional, and that the nozzles 42 can be controlled in unison if desired.

As shown in FIG. 4, control of the nozzles 42 is effected by selectively energizing solenoids 43 to magnetically move plungers 45 associated with the nozzles 42 between open and closed positions. When the plungers are in the open position, fluid can flow through the nozzles 42. Conversely, when the plungers 45, which are typically spring biased towards their closed positions, are in the closed position, fluid is precluded from exiting the nozzles 42.

By way of another example, the dampener 12 may optionally be implemented as a pan roller 51 which lifts

dampening fluid 54 from a pan 56 and a high speed brush 52 which propels the fluid from the pan roller 51 to a roller train 53 of the press. As shown in FIGS. 5 and 6, the pan roller 51 is preferably implemented as a roller which rotates through the fluid 54 in the pan 56. The brush 52 rotates against the pan roller. In this embodiment, the dampener control unit 18 controls the amount of dampener fluid delivered to the press by adjusting the speed of rotation of the pan roller 51.

The speed of rotation of the brush roller 52 is typically constant.

Numerous modifications and alternate embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure may be varied substantially without departing from the spirit of the invention and the exclusive use of all modifications which are within the scope of the appended claims is reserved.