Patent Application
20090249971
The present invention relates to a printing machine and in particular to a color-printing machine with devices for its calibration, i.e. for positioning of the printing units with respect to a central drum or roller.
Printing machines comprise a central drum or roller around which the web material to be printed is fed. Printing units, in the same number as the number of colors used, are arranged in various angular positions around the central drum or roller. The printing units each comprise a cliché roller, which receives ink from an application or distribution system and transfers it to the web material to be printed. In general, the ink is distributed on the cliché roller by means of an anilox roller, which in turn receives it from an ink dispenser, which can have various configurations. The cliché roller has a raised pattern, which receives the ink and transfers it to produce a corresponding printed pattern on the web material. For correct printing it is necessary to position the cliché roller precisely with respect to the central roller so that there is complete contact at the correct pressure between the web material to be printed and the surface of the selected roller. Similar adjustments are often required to adjust the position of the anilox roller with respect to the cliché roller.
Various calibration or adjustment systems are used for this purpose, which allow identification of the initial position of the printing unit with respect to the central drum or roller and retrieval of this position each time a machine is operated by moving the printing units towards the central roller. This calibration method and the relative devices present on currently known machines are not satisfactory, as they require long and complex operations with a considerable amount of manpower.
In particular, in known machines a system is typically used to move the cliché roller towards the central roller with interposition of a known feeler gauge, typically of one tenth of millimeter, interposed between the cliché roller and the central roller. This movement is performed manually operating each of the two motors or actuators with which each cliché roller is equipped at its ends. In a four-color machine this means making eight adjustments. Similar adjustments are required for the anilox roller of each printing unit, also by means of two respective actuators for a total of sixteen manual adjustments. The position taken by each roller through manual positioning and use of the aforesaid feeler gauge is stored and subsequently used to return the printing unit to its correct position.
These adjustments are performed with the cliché roller not fitted with the outer sleeve, which carries the respective pattern to be printed. When the machine must be operated after the initial calibration step and with the sleeves fitted on the single cliché rollers, positioning is performed taking into account the thickness of each sleeve fitted on each cliché roller and therefore taking the cliché rollers and respective anilox rollers to the calibration position previously identified with the manual operations described above, minus the thickness of the sleeve.
According to one aspect the invention provides a machine, which allows a simpler, more precise and/or more rapid calibration with respect to what is can currently be achieved with prior art machines.
In substance, the invention relates to a printing machine comprising: a central roller; at least one printing unit with a cliché roller and means for applying an ink to said cliché roller, said cliché roller cooperating with said central roller; a control unit interfaced with at least one actuator to move the printing unit towards the central roller. Advantageously, the printing unit comprises at least one load sensor and at least one position transducer associated with the cliché roller, interfaced with the control unit. Moreover, the control unit can be programmed to perform a calibration of the printing unit with a first step to move the printing unit towards the central roller until reaching a zero position defined on the basis of a signal of said at least one load sensor. In this manner, the subsequent operations to move the printing unit towards the central roller are performed using said at least one position transducer and said zero position. With a device of this type initial calibration takes place simply by setting the value that the load sensor must detect when the cliché roller has reached its zero position. This position is then stored and retrieved each time the machine is brought into operation by means of the position transducer. Load sensor is intended in general as a sensor capable of detecting a force or a pressure, and which therefore allows identification of the zero position of the cliché roller through a value which is a function of the stress exerted on the roller by the constraints with which it is supported and therefore, in substance, which allows the pressure between the cliché roller and the central roller to be measured.
A sensor of this type can typically be a load cell which, for example, detects a load on a bearing, or a pressure sensor inside a hydraulic actuator which moves the cliché roller with respect to the central roller.
Further advantageous features and embodiments of the invention are indicated in the dependent claims and will be described hereunder with reference to the drawing, which shows a non-limiting embodiment of the invention.
The invention will be better understood by following the description and accompanying drawing, which shows a non-limiting practical embodiment of the invention. More in particular, in the drawing:
The present invention can be applied to printing machines with a variable number of printing units. The example (
The printing unit 5 of
The cliché roller 7 is carried by side panels 15 mounted on respective slides 17 guided by sliding blocks 19 on a pair of guide systems 21 positioned at the sides of the machine. The section of
Each slide 17 is provided with second guide systems 27, engaging in which are sliding blocks 29 constrained to further slides 31, which carry side panels 33 to support the anilox roller 11. The section of
In some embodiments movement of the slides 17 according to the double arrow f17 towards and away from the central roller 3, and therefore movement of the entire printing unit 5 towards and away from the central roller, is controlled by a pair of hydraulic piston-cylinder actuators 35. The latter are engaged at one end to the fixed structure 25 and at the opposite end to the slides 17. With a similar arrangement, it is possible to obtain movement of the unit carrying the anilox roller 11 according to the double arrow f9 towards and away from the cliché roller 7. In this case, two hydraulic piston-cylinder actuators 37 are provided, each constrained at one end to the respective slide 17 and at the opposite end to the respective slide 31.
To perform calibration and correct positioning of each printing unit 5 each time the machine is operated, for example after having replaced the sleeve 7A of one or more cliché rollers 7, load sensors and position transducers are associated with the various actuators associated with the single printing units 5, 5A-5D. More in particular, according to some embodiments, a load sensor and a position transducer are associated with each of the actuators 35, 37. In the drawing, these members are represented schematically with 41 and 43 for the hydraulic piston-cylinder actuators 35 and with 45 and 47 for the hydraulic piston-cylinder actuators 37. In some embodiments the load sensor can be formed of a load cell positioned inside the chamber of each hydraulic piston-cylinder actuator to detect the pressure of the hydraulic liquid inside. In other embodiments the load sensor can instead be positioned on the support of each bearing of the respective rollers 7 and 11. What is important is that the load sensor detects a measurement linked to the stresses exerted on the respective cliché roller 7 or on the anilox roller 11 respectively. In a preferred modified embodiment, the load sensor can be formed of a pressure switch, installed on the piping connected to the piston-cylinder actuators, or directly on the bottom of these cylinders.
Similarly, the position transducer can be of different type and can be incorporated inside the piston cylinder actuator 35 or 37, or can be fitted on the fixed part or on the moving part of the relative support system of the roller 7 or of the roller 11. What is important is only to detect the position of a member constrained to the respective cliché roller 7 or anilox roller 1 to allow correct and precise identification of its position with respect to the fixed structure 25, in the case of the cliché roller 7, or with respect to the fixed structure 25 or with respect to the slide 17 in the case of the roller 11.
In the configuration shown sixteen piston-cylinder actuators are therefore provided, two for each cliché roller 7 and two for each anilox roller 11, with respective sixteen position transducers and sixteen load transducers or load sensors. These members are connected to a central control unit schematically shown at 50 (
The machine described above can perform a calibration cycle according to the method described below. Normally, calibration is performed with the cliché roller 7 not fitted with the sleeve 7A, as sleeves 7A can vary in thickness and the calibration step is instead performed to identify a zero position for subsequent positioning of the rollers, which will take account of the dimensions of the sleeves 7A inserted or fitted on the cliché rollers 7 each time.
In a first calibration step, the slides 17 of the single printing unit 5 are moved towards the central roller 3 carrying the cliché roller 7 not fitted with a sleeve 7A to press against this central roller. The load transducers or load sensors 41 detect a signal proportional to the pressure with which the cliché rollers 7 are pressed against the central roller 3. A contact pressure at which the slides 17 are stopped is set using an appropriate user interface 52. The position reached by each of the slides 17, detected by the position transducers 43 associated with the actuators 35, is stored as zero position.
A similar procedure can be performed for each of the cliché rollers 11 using the actuators 37 for movement of these rollers and identifying the zero position through the pressure or load sensors 54 and storing the zero position with the position transducers 47.
As each roller 7, 9 is carried by a pair of slides 17, 31, in this manner it is possible to correctly position each roller acting independently on the two ends thereof.
After storing the zero position of each cliché roller 7 and of each anilox roller 11 in this manner, it is possible to rapidly return the machine to the correct operating position each time it has been stopped and must be restarted, for example after having replaced the sleeves 7A on the cliché rollers 7. It will be sufficient to command, through the control unit 50 using the interface 52, movement of the cliché rollers 7 and of the anilox rollers 11 to operating positions which are determined on the basis of the zero position set with the calibration cycle described above and modified with the thickness values of the sleeve 7A inserted on the cliché roller 7 each time, said thickness being known to the operator and communicated to the control unit 50 using the interface 52.
It is understood that the drawing shows just one example, provided merely as a practical demonstration of the invention, which can vary in its forms and arrangements, without however departing from the scope of the concept underlying the invention. Any reference numbers in the appended claims are provided to facilitate reading of the claims with reference to the description and to the drawing, and do not limit the scope of protection represented by the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| FI2008A000064 | Apr 2008 | IT | national |
