Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F33/00—Indicating, counting, warning, control or safety devices
  • B41F33/0072—Devices for measuring the pressure between cylinders or bearer rings

Definitions

• the present invention relates to a printing press and in particular to an offset printing press.
• the object of the invention is an offset printing press which comprises a support structure on which first and second print rolls are mounted for rotation, the print rolls being superimposed one above the other and counter-rotating in operation, and between which, in operation, is passed the substrate intended to receive the print .
• Offset printing presses currently used in the art include a support structure constituted by a single base, which bears the print rolls and associated pressure cylinders.
• the ink used in offset printing is typically very viscous and the pressure between the print rolls must be calibrated very accurately in order to achieve an optimum result. This is currently achieved in an empirical manner, involving repeated attempts at adjusting the so-called “penetration" of the print rolls, that is their relative position, and then observing the resulting print. Calibration is carried out without the operator actually knowing the value of the pressure that has been selected.
• the pressure value determined between the print rolls can in fact be disrupted by a variety of causes.
• the thickness and/or the smoothness of the sheet or web of paper can vary, for example.
• the rubber covering of the print rolls can vary in thickness, while the gap or space between the print rolls and the associated pressure cylinders can also alter.
• the diameter of the rolls can also vary in operation, since heat can cause them to expand.
• the object of the present invention is to provide an offset printing press which enables the printing pressure to be accurately calibrated initially and which allows for any alterations in printing pressure owing to the above causes to be compensated for in operation.
• an offset printing press of the type described above, characterised in that the aforesaid support structure includes a movable upper portion and a stationary lower portion; each portion supporting a respective print roll, the following means being associated with structure sensor means able to emit electrical signals indicating the pressure exchanged between the two print rolls; and means for obtaining controlled movement of the upper portion relative to the lower portion, in order to achieve a corresponding change in the relative position of, and in the pressure exchanged between, the said print rolls.
• Figure 1 is a schematic illustration of an offset printing press according to the invention.
• FIGS 2a, 2b and 2c are partial views showing part of an offset printing press of the invention in three different conditions during the initial calibration of printing pressure.
• an offset printing press according to the invention is generally indicated 1.
• This machine has a support structure which comprises a movable upper portion 2 and a stationary lower portion 3, pivoted to each other about a pin 4 arranged with its axis essentially horizontal .
• the upper portion 2 of the machine 1 carries a print roll 5, with a rubber outer covering 5a, and an associated pressure cylinder 6.
• the stationary lower portion 3 of the machine supports a stationary print roll 7, with a rubber outer covering 7a and an associated pressure cylinder 8.
• At least one load cell 9 is fixed to the upper portion 2 of the press 1 so as to face a corresponding actuator 10 fixed to the stationary lower portion 3 of the machine.
• An actuator rod 11 extends from the top end of this actuator 10 and bears against the load cell 9.
• a device for defining a reference relative position between portions 2 and 3 of the press 1 is indicated 12.
• this device includes a stop member 13, fixed to the upper portion 2 of the press, and a screw 14, screwed into a threaded hole through a lug 15 fixed to the lower portion 3 of the press so as to be aligned facing the stop member 13 (see Figures 2a to 2c) .
• the load cell 9 is connected to an electronic control unit ECU which controls movement of the rod 11 of the actuator 10 by means of interface devices 16.
• the electronic control unit ECU is also connected to a personal computer PC with a control keyboard K and a visual display screen S .
• the actuator 10, 11 is operable under the control of the unit ECU, to cause controlled movements of the upper portion 2 of the press relative to the lower portion 3 thereof about the axis of the pin 4, thereby correspondingly adjusting the relative position of, and the pressure exchanged between, the aforesaid print rolls 5 and 7.
• the initial calibration or setting of the printing pressure can be carried out as follows .
• the calibration operation begins with the respective rubber sleeves removed from the print rolls 5 and 7.
• the upper portion 2 of the press is then raised, by means of the actuator 10, 11 so that the print rolls 5 and 7 are moved away from each other, as shown in Figure 2a.
• the weight of the upper portion 2 of the press bears on the pin 4 and on the load cell and actuator 9, 10, 11.
• the load cell 9 supplies a measurement to the electronic control unit ECU: equal to 6.5 tonnes, for example.
• the unit ECU controls the actuator 10, 11 slowly to lower the upper portion 2 of the press.
• the print rolls 5 and 7 start partly to bear the weight of the upper portion 2 of the press and correspondingly reduce the load on the cell 9, which immediately signals a slightly lower weight to the unit ECU: 6.499 tonnes, for example.
• the electronic control unit ECU then stops the actuator 10, 11 in whatever position it is in.
• the corresponding position of the upper portion 2 of the press is taken as the "zero" or reference position.
• the screw 14 of the device 12 is tightened until the upper end thereof bears against the stop member 13 of the upper portion 2 of the press.
• the screw 14 is then locked, by a method known per se, into this position which is taken as the reference position (see Figure 2b) .
• the control unit ECU then reactivates the actuator 10, 11 in order to raise the upper portion 2 of the press once again, thereby returning the print rolls 5 and 7 to their spaced configuration.
• the respective rubber sleeves 5a and 7a are then placed back on the print rolls.
• the actuator 10, 11 is then used to lower the upper portion 2 of the press once again.
• the load cell 9 will indicate a reduction in the load registered (indicating a condition in which the print rolls, with their respective sleeves, are in contact and exchanging pressure) , this occurring before the so-called "zero" or reference position is reached.
• the data supplied by the load cell is unequivocally linked to the pressure exchanged between the print rolls 5 and 7.
• the display screen S it is thus possible, by means of the display screen S, to provide the operator of the press with a visual display of value of the pressure exchanged between the print rolls 5 and 7.
• the operator is therefore able to use the keyboard K to stop the descent of the upper portion 2 of the press once a predetermined pressure value has been reached (value determined in dependence on the thickness of the print substrate, indicated P in Figure 1, for example) .
• the load cell 9 enables any changes in pressure exchanged between the print rolls 5 and 7, owing to any of the various causes described earlier, to be displayed on the screen. This enables the control unit ECU to control the actuator 10, 11 in such a way as to compensate for any variations in pressure which may occur.

Landscapes

• Impact Printers (AREA)
• Diaphragms For Electromechanical Transducers (AREA)
• Inking, Control Or Cleaning Of Printing Machines (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=11459274

Family Applications (1)

Country Status (2)

Cited By (3)

Citations (3)

• 2001
  • 2001-10-24 IT ITTO20011012 patent/ITTO20011012A1/it unknown
• 2002
  • 2002-10-23 WO PCT/EP2002/011816 patent/WO2003035398A1/en not_active Application Discontinuation

Patent Citations (3)

Non-Patent Citations (1)

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