Cleaning system for a printing press

Abstract: A cleaning device for cleaning a cylinder (6) of an offset sheet-fed press has a support (ll) provided with a blade member (8) having a relatively sharp edge pressing a cleaning cloth (l) against the cylinder (6). The cylinder (6) is an impression cylinder provided with sheet holding grippers (l3) projecting over the outer peripheral surface of the impression cylinder (6). The grippers (l3) are protected so as not to directly contact the cleaning cloth (l) under the pressed condition by locating cam members (l2) to shield the grippers (l3). Alternatively a device controlled by a cam on the shaft of cylinder (6) moves the support (ll) carry blade member (8) such that when the grippers (l3) approach the blade member (8) during the rotation of the impression cylinder (6), the blade member (8) is moved away therefrom.

Description: BACKGROUND OF THE INVENTION This invention relates to a cleaning system for a printing press and more particularly to a combination of an impression cylinder and a cleaning unit therefor for an offset sheet-fed press. An offset printing press of general type comprises in combination a plate cylinder, a blanket cylinder, an impression cylinder and intermediate cylinder which are arranged to be mutually rotatable in contacting conditions, a printed paper recovery unit, an inking unit, a cleaning unit and the like. With the offset printing press of the character described above, in an actual printing operation, printing liquid such as ink is transferred on an outer peripheral surface of the respective cylinders, for example, impression cylinder through the blanket cylinder, and dirt or paper dust or the like will be adversely stuck thereon during the printing operation. The dirt or dust thus stuck on the impression cylinder surface will form protrusions thereon which obstruct precise printing operation and make it impossible to obtain clearly printed materials. Under these circumstances, several kinds of cleaning devices for cleaning the respective cylinders, for example, for the blanket cylinder has been developed, and a typical type of these cleaning devices or units comprises a magazine roll around which a cleaning cloth or the like is wound, a used cleaning cloth take-up roll, a cleaning liquid supply means for applying the cleaning liquid to the cleaning cloth, and a pressing member such as pneumatic pad for pressing the cleaning cloth against the outer peripheral surface of the cylinder. In the actual cleaning, the cylinder is rotated and the cleaning cloth is stepwisely drawn out under the pressed condition against the cylinder by suitable means. The cleaning operation involves the following disadvantages or drawbacks. (a) The draw-out of the cleaning cloth under the pressed condition requires much force for drawing out the same and it is also required for the cleaning cloth to apply a considerably large tension. This requires some strengthening means for a drive system and hence the whole structure of the press to impart the stiffness thereto, which results in enlargement and heavy weight of the whole structure of the press, thus being complicated and noneconomical. (b) In a case where it is required to remove the cleaning cloth from the impression cylinder, the cleaning cloth pressing means has to be everytime moved in a direction apart from the cylinder, so that the pressing means and hence the press itself will be complicated. In another aspect, however, regarding the cleaning of the impression cylinder which are generally provided with hook-shaped grippers for gripping a paper sheet in a condition of projecting outwardly from the outer peripheral surface of the impression cylinder, the location of these grippers may provide the following defects or drawbacks in the cleaning operation. (c) Because of the projection of the grippers, it is considerably difficult to clean the area of the impression cylinder near the projecting grippers. (d) The projecting grippers may damage the cleaning cloth during the rotation thereof under the pressed condition by means of such as pressing pad. (e) The grippers may themselves be damaged during the rotation of the impression cylinder, which results in the damage of the offset press. Taking the above-mentioned defects or drawbacks into consideration, the cleaning of the respective cylinders, particularly impression cylinder, is often carried out manually. Such manual cleaning working is however undertaken in a narrow space between the respective cylinders and various printing units under the rotating condition of the cylinders, thus being dangerous and desirable cleaning effect was not expected. These drawbacks require as a consequence long cleaning time and result in the reduction of the production efficiency of the offset printing press. The following documents form part of the state of the art: DE-A-2538105 (US-A-4058059) discloses a device for cleaning a cylinder of an offset printing press in which a frame supports a magazine roll around which a cleaning cloth is wound and a take-up roll around which used cleaning cloth is taken up.. A roller supported in the frame at a portion between the magazine roll and the take-up roll acts as means for pressing the cleaning cloth against the cylinder to be cleaned. Also provided are means for supplying cleaning liquid to the cleaning cloth and means for moving the support frame away from the cylinder. The XEROX DISCLOSURE JOURNAL Vol.4, No.2, March/April 1979 pages 263 and 264 discloses a similar system for cleaning cylindrical photoreceptors and other surfaces in which a blade is used to press the cleaning cloth against the surface to be cleaned. In US-A-4270450 and EP-A-0004605 an impression cylinder is cleaned by a washing roller. To prevent the roller falling into a gap on the impression cylinder and contacting sheet gripper arcuate bridging pieces are secured to the ends of the cylinder in the path of the roller and spanning elements mounted in the gap, the gap. DE-C-3005469 and US-A-4344361 propose a cylinder cleaning system similar to that of DE-A-2538105/US-A-4058059 but in which the cleaning cloth is pressed against the cylinder by an inflatable bladder, which can be deflated to allow the cloth to move away from the cylinder. SUMMARY OF THE INVENTION The present invention provides means for overcoming defects and drawbacks outlined above in prior art cleaning techniques. With respect to the disclosure of DE-A-2538105, this invention is characterised in that said cylinder is an impression cylinder having sheet holding grippers projecting over its peripheral surface and that a rotary encoder, proximity switch, photoelectric switch, mark sensor, photointeractor, or limit sensor is located near the impression cylinder to detect by means of a voltage or current variation a predetermined angular position of said impression cylinder where said pressing means is adjacent to said sheet holding grippers, to cause said moving means to raise said support frame or said pressing means away from the impression cylinder to prevent said gripper from directly contacting said cleaning cloth. Preferably the pressing means is a blade member, typically having a longitudinal length substantially equal to the width of the cleaning cloth contacting the cylinder. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings; Fig. 1 is a schematic illustration of an arrangement of respective cylinders of an offset sheet-fed press; Fig. 2 is a cross sectional side view of a cleaning device for cleaning a cylinder of the press shown in Fig. 1; Fig. 3 is a perspective view, partially broken away, of the cleaning device shown in Fig. 2; Fig. 4 is a side view showing a pneumatic cylinder assembly for moving the cleaning device such as shown in Fig. 2; Fig. 5 is a cross sectional side view showing the arrangement of the combination of the cleaning device and an impression cylinder to be cleaned; Fig. 6 is a brief cross sectional side view showing grippers located in the impression cylinder; Fig. 7 is a cross sectional side view of a cleaning device according to prior art for cleaning a cylinder of an offset press. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before the disclosures of preferred embodiments of this invention, for clear understanding of the nature and character of the invention, the background art or the like will first be described here-under in conjunction with accompanying drawings. Fig. 1 shows a brief arrangement of an offset printing press of one kind which comprises a plate cylinder 101, a blanket cylinder 102 in rotatable engagement with the plate cylinder 101, an impression cylinder 103 in rotatable engagement with the blanket cylinder 102, and intermediate cylinders 104a and 104b, which are mutually rotatable in directions as shown by arrows in Fig. 1. The offset press further comprises an inking device, not shown, a sheet-fed apparatus, not shown, an impression cylinder cleaning device 105 etc. which are operatively associated with the cylinders described above. With the arrangement of the typical offset press described above, although only the impression cylinder cleaning device is illustrated with the reference numeral 105, other cleaning devices are usually provided for the respective cylinders, and for example, roller-type, brush-type and cleaning-cloth-type cleaning device for the blanket cylinder have widely been known and developed. The cleaning operation for the impression cylinder 103, however, has not effectively carried out manually because of the reason described hereinbefore. Fig. 7 is a brief illustration of an impression cylinder cleaning device of one prior type, i.e. cleaning-cloth-type, which has been used for eliminating the manual cleaning operation for the impression cylinder. Referring to Fig. 7, a cleaning cloth 1 wound around a magazine roll 2 is fed for cleaning the outer peripheral surface of an impression cylinder 6 and then wound up around a take-up roll 3. A cleaning device 9 is located between the magazine roll 2 and the take-up roll 3 and comprises a cleaning liquid supply pipe 4 provided with nozzles 5 through which a cleaning liquid is supplied to the cleaning cloth 1 and a pressing means 7 such as a pneumatic pad 7 in Fig. 7 for pressing the cleaning cloth 1 against the outer peripheral surface of the impression cylinder 6. Under the pressed condition of the cleaning cloth 1, the impression cylinder 6 is rotated and the cleaning cloth 1 is stepwisely fed by drive means. not shown. As the pressing means 7 is utilized a cushion such as sponge, a pressing roller or the like instead of pneumatic pad. With the cleaning device of the character described above, however, in use of any type of pressing means described above, a pressed or pressing area between the cleaning cloth 1 and the impression cylinder 6 is likely made wide in accordance with the nip width, and this fact exposes drawbacks or disadvantages described hereinbefore. Namely, the movement of the cleaning cloth 1 under the pressed condition requires a considerably large driving force, which results in the enlargement of the driving mechanism and hence the whole structure of the printing press. The tension applied to the cloth also requires the mechanical strength of the whole structure. Moreover, it is troublesome to move or shift the pressing means at a time when the cleaning cloth is removed from the impression cylinder. In addition, since the impression cylinder of an offset sheet-fed press is usually provided with hook-shaped sheet grippers projecting outwardly from the outer peripheral surface of the impression cylinder, the existance of the projecting grippers makes it difficult to effectively clean the area near the projections of the impression cylinder. Figs. 2 and 3 are illustrations of a cleaning device for cleaning cylinder, particularly an impression cylinder, of an offset printing press, and like reference numerals are added to elements corresponding to those shown in Fig. 10. Referring to Figs. 2 and 3 respectively as a cross sectional side view and a perspective view of the cleaning device, the cleaning cloth 1 wound up around the magazine roll 2 is stepwisely drawn out by operation of driving means, not shown, and taken up by the take-up roll 3 and these rolls 2 and 3 are rotated by driving means operatively connected to shafts of the respective rolls these shafts being supported by a frame 11. A support member 10 also supported by the frame 11 is located between the respective rolls 2 and 3 and supports the cleaning liquid supply pipe 4 having nozzles 5 for jetting the cleaning liquid towards the cleaning cloth near the impression cylinder 6. The support member 10 further supports a blade 8 as a pressing means for pressing the cleaning cloth 1 against the impression cylinder 6. The use of the blade 8 having a longitudinal length substantially equal to the width of a cleaning cloth to be used and a sharp edge contacting the rear surface of the cleaning cloth 1 at an angle of about 45° eliminates the contacting area there-between in comparison with the use of the other pressing means such as pneumatic pressing pad used in the prior technique to thereby improve the cleaning effect. In addition, it is of course desired to use the blade made of a material not to be affected with a liquid or solvent used as the cleaning liquid. It is to be noted that although the cleaning device according to this invention is further provided with a pneumatic cylinder means as a unit for moving the cleaning device from the impression cylinder for preventing the device from contacting the impression cylinder during the high speed rotation thereof and a one-way clutch and air cylinder means for stepwisely drawing out and taking up the cleaning cloth, these units and mechanisms are per so well known in this art of field, so that the details thereof are substantially eliminated herein, and one example of only the pneumatic cylinder assembly for moving the cleaning device will be described herein in conjunction with Fig. 4. Referring to Fig. 4, a cylinder portion of a pneumatic cylinder assembly 30 is attached to a printing machine frame, not shown, and a plunger head 31 of the assembly is in turn secured to the frame 11 of the cleaning device. The pneumatic cylinder 30 lifts pivotably the cleaning device, when it is extended, to move the device away from the impression cylinder 6 and lowers the same by the self-gravity to contact the cylinder to be cleaned. The frame 11 is usually constructed to be rotatable about a pivot, not shown, in association with the operation of the pneumatic cylinder 30. In one preferred embodiment according to this invention, the respective constructional means or elements have characters and natures such as follows. Cleaning Cloth The cleaning cloth 1 is of the thickness of about 0.3mm and possessed with a solvent, as cleaning liquid, resisting ability, and is made of a non-woven cloth provided with lipophilic and hydrophilic characters. Magazine Roll The magazine roll 2 is provided with a mechanism for easily mounting the rolled cloth as it is and a brake means capable of preventing the cleaning cloth from loosening when the cleaning cloth is stepwisely drawn out from the magazine roll shaft. Take-up Roll The take-up roll 3 is provided with a mechanism for easily removing the used rolled cloth as it is and is rotated in a direction reverse to the rotating direction of the impression cylinder to be cleaned. Pressing Blade The pressing means, which may be in the shape of a blade 8 having an edge, possesses a nature not to be affected by the solvent used as the cleaning liquid such as aluminum. The blade has a thickness of about 5mm and is pressed against the impression cylinder with the pressure of about 350g/cm 2 to 700g/cm 2 . The blade is also provided with a front edge having an inclination angle of about 20° to 60° for effectively pressing the cleaning cloth against the impression cylinder. Cleaning Liquid Supply Device The cleaning liquid supply pipe 4 is generally provided with a plurality of nozzles 5 for respectively jetting the solvent and the water so as to supply the cleaning liquid evently to the cleaning cloth throughout the axial length of the impression cylinder. It is desired for the jetting amount of the cleaning liquid to be sufficient for wetting the cleaning cloth (for example, in this embodiment, about 20 ml to 50 ml per one jetting operation with respect to the blade having a width of 1362 mm). Support Member The support member 10 positively supports the blade 8 so that the blade can always press the cleaning cloth with a constant pressure and at a constant angle. The support member 10 also supports the cleaning liquid supply device so that the cleaning liquid can be jetted to the cleaning cloth always at a constant angle of the nozzles. As described hereinbefore, according to one preferred embodiment of this invention, the use of the blade as a cleaning cloth pressing means reduces the contacting area between the cleaning cloth and the cylinder, whereby the friction force caused therebetween can be effectively reduced, and moreover, the cleaning cloth can be taken up by the take-up roll without applying large tension to the cloth, thus simplifying the take-up mechanism. The construction in which the cleaning cloth can be drawn out by rotating the take-up roll in the direction reverse to the rotating direction of the cylinder to be cleaned can highly improve the cleaning efficiency. The fact that there is no need for removing the pressing blade from the cylinder in case of winding up the used cleaning cloth makes it possible to considerably reduce the cleaning time. In addition, the use of the blade as the pressing means makes compact the structure thereof in comparison with the conventional one such as pneumatic pressing pad, thus being economical. Furthermore, in case of cleaning the impression cylinder, since the pressing blade is provided with a relatively narrow front edge, the area of the outer peripheral surface near the projecting grippers of the impression cylinder can be effectively cleaned. In the foregoing descriptions, although the use of the blade means as the cleaning cloth pressing means is referred to for effectively improving the cleaning effects of the cylinder, particularly the impression cylinder, of an offset press, this cleaning effect will be more increased, by providing an improved structure of a gripping mechanism of the impression cylinder of an offset sheet-fed press. Fig. 5 shows a cross sectional side view of the cleaning device shown in Fig. 2 in operative association with an impression cylinder provided with an improved sheet gripping mechanism and Fig. 6 is also a cross sectional side view showing the gripping mechanism of Fig. 5, in which like reference numerals are added to elements or means corresponding to those shown in Figs. 1 through 3. Referring to Figs. 5 and 6, a recess 6a is formed in the impression cylinder 6 along the axial direction therof for accommodating hook-shaped grippers 13 mounted on a gripper shaft 14. In this invention, there is provided an improved mechanism capable of shifting the pressing means or cleaning device for pressing the cleaning cloth against the impression cylinder of the offset sheet-fed press when the grippers located in the impression cylinder approaches the pressing means of the character described hereinbefore during the rotation thereof to prevent the grippers, pressing means and cleaning cloth from being damaged mutually. As a shifting mechanism or method for shifting the cleaning device inclusive of the pressing means from the grippers of the impression cylinder, is considered a mechanism or method for shifting the whole cleaning device and only the pressing means, but since the shifting principles of both the cases are substantially the same, the mechanism or method for shifting only the whole cleaning device will be described hereunder in conjunction with Figure 5. The cleaning device is shifted at the gripper portion while detecting the rotation of the impression cylinder 6 is detected and then converted into electric current or voltage, whereby the position of the grippers 13 of the rotating impression cylinder 6 is obtained as an angular information by detecting the voltage (or current) variation by means of a rotary encoder, a proximity switch, a photoelectric switch, a mark sensor, a photointeracter or a limit sensor. The position of the grippers 13 is detected directly by locating the switch or sensor near the impression cylinder 6. According to this invention the damage of the cleaning device in direct contact with the grippers of the impression cylinder can be effectively avoided, the cleaning operation can be automatically and substantially completely performed without dangerous manual operation. This results in the reduction of the working time and the improvement of the production efficiency of the offset sheet-fed press. The invention has been described in detail with particular reference to the preferred embodiments thereof, but it will be understood by those skilled in the art that various variations and modifications can be effected within the scope of the invention as described hereinabove and as defined in the appended claims.

Claims: A device for cleaning a cylinder (6) of an offset printing press comprising a support frame (11), a magazine roll (2) around which a cleaning cloth (1) is wound and having a rotation shaft supported by said support frame (11), . . a take-up roll (3) around which a used cleaning cloth (1) is taken up and having a rotation shaft supported by said support frame (11), a pressing means (8) attached to said support frame (11) at a portion between said magazine roll (2) and said take-up roll (3) and adapted to press said cleaning cloth (1) against the cylinder (6) to be cleaned, means (4) for supplying cleaning liquid to said cleaning cloth (1) and means (30) for moving said support frame (11) away from said cylinder (6), characterised in that said cylinder is an impression cylinder (6) having sheet holding grippers (13) projecting over its peripheral surface and that a rotary encoder, proximity switch, photoelectric switch, mark sensor, photointeractor, or limit sensor is located near the impression cylinder to detect by means of a voltage or current variation a predetermined angular position of said impression cylinder (6) where said pressing means (8) is adjacent to said sheet holding grippers (13), to cause said moving means (30) to raise said support frame (11) or said pressing means (8) away from the impression cylinder (6) to prevent said grippers (13) from directly contacting said cleaning cloth (1). A device as claimed in claim 1, in which the pressing means is a blade (8) having a longitudinal length substantially equal to the width of the cleaning cloth (1) contacting the cylinder (6). A device as claimed in claim 2, characterised in that the pressing means is a blade (8) having a sharp edge contacting the rear surface of the cleaning cloth (1) at an angle of about 45°. A device as claimed in claim 3, characterised in that the pressing means is a blade (8) having a front edge with an angle of inclination of about 20° to 60°.

Inventors: KATSUTA TETSURO, MIYAMA HIROSHI, NOZAKA YOSHIKI, KATSUTA, TETSURO, MIYAMA, HIROSHI, NOZAKA, YOSHIKI
Applicants: DAINIPPON PRINTING CO LTD, DAI NIPPON INSATSU KABUSHIKI KAISHA
Application year: 1987
Main classification: B41F35
IPC codes: B41F35