Apparatus for cleaning a cylinder

Abstract: 1. An apparatus for cleaning a cylinder (11) of a printing machine has a continuous cleaning cloth (18) stretched between a cleaning cloth supply means (15) and a cleaning cloth take-up roll (16) rotatably supported by side plates, and pressing means for selectively pressing said cleaning cloth (18) into contact with the outer peripheral surface (12) of said cylinder (11). Said apparatus comprises backward feeding means (86, 89, 90, 93, 99) for backwardly feeding part of the cleaning cloth (18) fed during preceding cleaning operation towards said cleaning cloth supply means (15) after completion of said preceding cleaning operation. The backward feeding means comprise a single drive motor (86) operable in one rotating direction and a reversible power transmitting mechanism connected to said motor, said mechanism comprising means for selectively coupling the take-up roll (16) for rotation in a take-up rotating direction, or the supply roll (15) for rotation in a backward feeding rotation direction, respectively, with said motor (86), and at the same time disconnecting the respective other roll (15, 16).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for cleaning a cylinder and a roller of a printing machine. More particularly, the present invention is concerned with an apparatus for cleaning a cylinder of an offset printing machine by pressing a cleaning cloth onto the outer peripheral surface of the blanket by means of a pressure pad. Still more particularly, the present invention pertains to an apparatus for backward feeding the cleaning cloth in a cleaning system of the type mentioned above. 2. Description of the Prior Art A typical known printing cylinder cleaning apparatus will be described hereinunder. Although the following description is concentrated specifically on an apparatus for cleaning a blanket cylinder of an offset printing machine, it is to be understood that the same printing cylinder cleaning apparatus can be used for cleaning other types of cylinders. An offset printing machine usually has three cylinders, namely, a plate cylinder, a blanket cylinder and an impression cylinder. These cylinders are arranged such that their axes extend in parallel with one another and such that they can be brought into mutual contact. A printing plate made of, for example, a type alloy or aluminum is wound on the plate cylinder, while a sheet-like blanket such as of rubber is wound on the blanket cylinder. The printing plate has a grained surface and is provided with a water repellent layer carrying an image of characters or a picture. The surface of the printing plate other than portions having images of characters or picture is dampened as water is supplied to the surface of the printing plate by means of dampening device. An oily ink is applied to the surface of the printing plate by means of an inking device. The ink will attach to the portion of the plate surface carrying the image because this area is not dampened, but will be repelled by other portions of the plate surface due to the water content held by the grained surface. The ink thus held on the plate cylinder is transferred to the blanket cylinder and is further transferred to a printing paper which passes through the nip between the blanket cylinder and the impression cylinder. This is the principle of offset printing. As the offset printing machine operates long, the blanket surface is contaminated due to accumulation of residual ink. In order to obviate this problem, an apparatus has been developed which is capable of cleaning the blanket cylinder. This apparatus has a cleaning cloth supply roll and a cleaning cloth take-up roll arranged in a pair on a pair of side plates which are mounted on the frame of the printing machine. A continuous cleaning cloth is wound at its both ends on these rolls and are suitably tensed between these rolls. The cleaning cloth take-up roll is driven by a driving device to rotate at a predetermined speed and intermittently, e.g., once every 3 seconds. A stay having a substantially T-shaped cross-section is provided to extend in the direction of axes of these rolls. Both ends of the stay are fixed to the adjacent side plates. The portion of the stay opposing to the blanket cylinder is made hollow, and the surface facing the blanket cylinder is hermetically lined with a pressure pad made of an elastic member. A plenum chamber which is defined by the end of the stay and the pressure pad is communicated with an external air compressor. As the air compressor operates, compressed air is supplied to the plenum chamber so that the pressure pad is expanded, whereby the cleaning cloth sliding on the outer surface of the pressure pad is pressed against the blanket cylinder so as to wipe off contaminant on the blanket wound on the blanket cylinder thereby cleaning the blanket surface. The pressure pad is made of an elastic resin or a rubber so that it elastically presses the cleaning cloth onto the surface of the blanket cylinder. In the standard sheet offset printing machine, the cleaning cloth is fed intermittently, e.g. once for every three rotations of the blanket cylinder, by about 5 mm in each feeding cycle. Each cleaning cycle usually has, for example, 20 cycles of feed on the cleaning cloth. This means that about 100 mm of the cleaning cloth is consumed in each cycle of cleaning operation. In case of a newspaper offset printing press, about 450 mm of cleaning cloth is consumed in each cleaning cycle, tough detailed numerical data is not shown. The cleaning cloth has to meet various requirements such as high tensile strength, dimensional precision and wettability and, therefore, is usually made of an expensive material such as a non-woven fabric. This undesirably raises the running cost of the printing machine. FR-A-2 285 997 already describes an apparatus according to the preamble of claim 1 for partly feeding backwardly the portion of the cleaning cloth which has been fed forwardly during the preceding cleaning operation in order to repeatedly use the less contaminated portion of the cleaning cloth and thereby reduce the consumption of the costly cleaning material. The length to be rewound has to be determined by the person operating the machine and the rewinding procedure is performed manually. For that purpose the driving mechanism for the cloth feeding apparatus has to be disconnected and a handle has to be mounted. For this reason the apparatus as known by the French Patent Application cannot be used in modern automatically operated machine plants. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an apparatus for cleaning a cylinder of a printing machine, wherein used portion of the cleaning cloth is fed backwards partially so as to be used repeatedly, thereby reducing the consumption of the cleaning cloth, in such a way that it is suitable for automatic operation in modern, fast-working machines so as numerical controlled printing plants. This problem is solved in the invention by the features described in claim 1. According to the invention, only one single drive motor rotating in one rotating direction is needed to effect both the forward and the backward feeding of the cleaning cloth by simply switching the power transmission mechanism. The drive motor enables an intermittent operation for forward feeding and for backward feeding. According to another aspect of the invention, the backwardly feeding means comprise a detecting means for detecting a predetermined length of forwardly fed cleaning cloth and enabling said driving motor to rewind said predetermined length. The device according to the invention is structured simply and cheaply and can, nevertheless, be completely integrated in the automatic operation of modern, fast-working printing machines. Thus, a predetermined length of the cleaning cloth is fed during one cleaning cycle. The portion of this length of the cleaning cloth, which was made to contact with the cylinder in the beginning part of the cleaning cycle, is usually heavily contaminated, i.e., saturated with contaminant, but the contamination becomes less heavy towards the trailing end of the cleaning cloth. Thus, the portion of the cleaning cloth which was brought into contact with the cylinder in later part of the cleaning cycle, e.g., the trailing half portion of the cleaning cloth fed in each cleaning cycle, still has a substantial capability for wiping off the contaminant. According to the invention, the cleaning cloth is fed backward by a length which, for example, corresponds to half the length fed during the preceding cleaning cycle, so as to be used again for the cleaning purpose. The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments when the same is read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a developed front elevational view of a preferred embodiment during the cleaning; Fig. 2 is a developed front elevational view of the embodiment during reversing of the cleaning cloth; Fig. 3 is a sectional view taken along the line II-II of Fig. 1; Fig. 4 is a sectional view taken along the line I-I of Fig. 1; Fig. 5 is a partial view showing the detecting means. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the invention, suitable for cleaning the blanket cylinder of an offset printing machine, will be described hereinunder with reference to the drawings. An offset printing machine has three cylinders, namely, a plate cylinder, a blanket cylinder and an impression cylinder. These cylinders are arranged such that their axes extend in parallel with one another and such that they can be brought into mutual contact. A printing plate is wound on the plate cylinder, while a sheet-like blanket is wound on the blanket cylinder. In operation, an ink is applied to the surface of the printing plate and is transferred to the blanket cylinder and is further transferred to a printing paper whereby the printing is executed. Referring now to Figs. 1 and 3, a printing cylinder cleaning apparatus normally has a cleaning cloth supply roll 15 and a cleaning cloth take-up roll 16 carried by shafts 151 and 161 arranged in a pair on a pair of side plates 13 which are mounted on the frame 25 of the printing machine. These rolls 15 and 16 are disposed in parallel with each other and are mounted rotatably on the shafts 151 and 161. A continuous cleaning cloth 18 is wound at its both ends on these rolls 15 and 16 and is suitably tensed between these rolls. The shaft 161 of the cleaning cloth take-up roll is driven by a driving device to rotate at a predetermined speed and intermittently once every 3 seconds. A stay 19 having a substantially T-shaped cross-section is provided to extend in the direction of axis of these rolls 15 and 16. Both ends of the stay 19 are fixed to the adjacent side plates 13. The portion of the stay 19 opposing to the blanket cylinder 11 is made hollow, and the surface facing the blanket cylinder 11 is hermetically lined with a pressure pad 20 made of an elastic member. A plenum chamber 21 which is defined by the end of the stay and the pressure pad 20 is communicated with an external air compressor (not shown). As the air compressor operates, compressed air is supplied to the plenum chamber 21 so that the pressure pad 20 is expanded, whereby the cleaning cloth 18 sliding on the outer surface of the pressure pad 20 is pressed against the blanket cylinder 11 so as to wipe off contaminant on the blanket 12 wound on the blanket cylinder 11 thereby cleaning the blanket surface. A cylinder cleaning system of this type suffers from a problem in that the running cost is raised due to large amount of consumption of the cleaning cloth which is superior in quality and, accordingly, expensive. This problem, however, can be overcome by the present invention as will be understood from the following description of the preferred embodiment. A description will be made hereinunder with reference to Figs. 1 and 2 as to a preferred embodiment of the present invention in which the backward feed of the cleaning cloth is effected by reversing the cleaning cloth supply roll by the power of a single motor transmitted through a reversible power transmitting mechanism. The construction of this embodiment will be described with reference to Figs. 1, 2 and 4. The driving and stopping of the cleaning cloth take-up roll shaft 161 is effected by bringing the shift gear 93 into and cut of engagement therewith. The forward rotation of the cleaning cloth supply roll 15 is caused by the force transmitted through the cleaning cloth 18 produced as a result of the forward rotation of the cleaning cloth take-up roll 16. The reversing of the cleaning cloth supply roll 15 is effected by bringing the shift gear 93 into and out of engagement therewith. The spine shaft 90 of the shift gear 93 is rotatable only in the direction of the arrow A because it is supported by one-way clutch 92. The amount or length of forward feed of the cleaning cloth 18 is detected by a detector composed of a rubber wheel 26 and an encoder 28 both of which are shown. in Fig. 5. The sequence of operation of this embodiment will be described with reference to Figs. 1 and 2. Cleaning (see Fig. 1) The shift gear 93 is shifted in the direction of the arrow X so as to become able to drive the gear 98 on the cleaning cloth take-up roll shaft through the intermediate gear 96. Thus, the cleaning cloth take-up roll 16 is intermittently driven in the direction of the arrow A. The gear on the cleaning cloth supply roll does not engage with the shift gear 93 so that it can rotate freely. Therefore, the cleaning cloth supply roll 15 pays away the cleaning cloth 18 in the direction of the arrow A. Meanwhile, the cleaning cloth take-up roll shaft 161 is engaged with the shift gear 93 which has a reversing prevention mechanism, so that the cleaning cloth 18 on the cleaning cloth take-up roll 16 is never extracted therefrom. The amount or length of feed of the cleaning cloth 18 is detected and controlled by a rubber wheel 26 and an encoder 28. Backward feed of the cleaning cloth (see Fig. 2) The shift gear 93 is shifted in the direction of the arrow Y so as to drive the gear 99 on the shaft of the cleaning cloth supply roll 15 thereby reversing the latter in the direction of the arrow B. Meanwhile, the gear 98 on the shaft of the cleaning cloth take-up roll 16 is disengaged from the shift gear 93 so that the shaft 161 of the cleaning cloth take-up roll is allowed to rotate freely. Therefore, as the cleaning cloth supply roll 15 rotates in the direction of the arrow B, the cleaning cloth 18 is fed in the direction of the arrow B so as to be fed backwardly and rewound and taken-up by the cleaning cloth supply roll 15. The amount or length of the backward feed of the cleaning cloth is detected by the detecting device composed of the rubber wheel 26 and the encoder 28. A rubber wheel 26 carried by the shaft 27 of the encoder 28 is pressed onto the outer peripheral surface of the roll of the cleaning cloth 18 on the cleaning cloth supply roll 15. The rubber wheel 26 is resiliently pressed onto the cleaning cloth by a suitable pressing means (not shown) such as a spring, so that it rotates as the cleaning cloth 18 is fed forward, thereby to detect the length of forward feed of the cleaning cloth 18. Although the invention has been described through its preferred forms, it is to be understood that the described embodiments are only illustrative and various changes and modifications may be imparted thereto. As has been described, according to the present invention, the cleaning cloth which has been forwardly fed for cleaning a cylinder of a printing machine is fed backward partially so as to be used again for the purpose of cleaning the cylinder, whereby the consumption of expensive cleaning cloth is reduced to provide a remarkable effect from the economical point of view. Pulley 91 on shaft 90 is drivingly connected to the pulley 88 on shaft 87 of the drive motor 86 by an endless belt 89. Drive motor 86 is supported by a bracket 85 mounted to the side wall 25.

Claims: An apparatus for cleaning a cylinder (11) of a printing machine having a continuous cleaning cloth (18) stretched between a cleaning cloth supply means (15) and a cleaning cloth take-up roll (16) rotatably supported by side plates, a take-up mechanism (86, 89, 90, 93, 96, 98) for rotating said cleaning cloth take-up roll (16) so as to take-up and transport forwardly said cleaning cloth (18), and pressing means for selectively pressing said cleaning cloth (18) into contact with the outer peripheral surface (12) of said cylinder (11), said apparatus comprising backward feeding means (86, 89, 90, 93, 99) for backwardly feeding part of the cleaning cloth (18) fed during preceding cleaning operation towards said cleaning cloth supply means (15) after completion of said preceding cleaning operation, characterised by a single drive motor (86) operable in one rotating direction and a reversible power transmitting mechanism connected to said motor, said mechanism comprising means for selectively coupling the take-up roll (16) for rotation in a take-up rotating direction, or the supply roll (15) for rotation in a backward feeding rotation direction, respectively, with said motor (86), and at the same time disconnecting the respective other roll (15, 16). An apparatus as claimed in claim 1, characterized in that the power transmitting mechanism comprises a shift gear (93) adapted to be selectively coupled with a first gear train (96, 98) connected to said take-up roll (16) or with a second gear train (99) connected to said supply roll (15). An apparatus as claimed in claim 1 or 2, characterized in that coupling means (92) are provided between said drive motor (86) and said power transmitting mechanism. An apparatus as claimed in any one of claims 1 to 3, characterized in that said backwardly feeding means includes detecting means (26, 28) for detecting a predetermined length of forwardly fed cleaning cloth and enabling said driving motor (86) to rewind said predetermined length of cleaning cloth. An apparatus as claimed in claim 4, characterized in that said detecting means comprise a rubber wheel (26) pressed to the peripheral surface of the roll of the cleaning cloth (18) and connected to a rotating encoder (28).

Inventors: HARA AKIRA, HARA, AKIRA
Applicants: B J TRADING KK, B-J TRADING LIMITED
Application year: 1988
Main classification: B41F35
IPC codes: B41F35