APPARATUS FOR CLEANING A CYLINDER

Abstract: A method of cleaning a cylinder (11) of a printing machine comprises the steps of pressing a cleaning cloth (18) onto the outer peripheral surface of the cylinder (11) while the cylinder (11) is rotating; forwardly feeding the cleaning cloth (18) so as to wipe off contaminant on the outer peri­ pheral surface of the cylinder (11); and partially feeding backwardly the portion of the cleaning cloth (18) which has been fed forwardly during the preceding cleaning operation, before the next cleaning operation is started, whereby the portion of the cleaning cloth (18) is partially used again for the cleaning in the next cleaning operation. The appara­ tus comprises a continous cleaning cloth (18) stretched be­ tween a cleaning cloth supply device (15) and a cleaning cloth take-up (16) rotatably supported by side plates, a take-up mechanism for rotating the cleaning cloth take-up roll (16) so as to take up the cleaning cloth (18); pressing device (20,21) for selectively pressing the cleaning cloth (18) into contact with the outer peripheral surface of the cylinder (11); and backward feeding device for backwardly feeding part of the cleaning cloth (18) taken up by the cleaning cloth take-up roll (16) during preceding cleaning operation towards the cleaning cloth supply device (15) after completion of the preceding cleaning operation.

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. The device according to the invention abandons the driving concept known in the art and follows a completely new constructive path. Although it is quite normal, as such, to use a step-by-step device for an intermittent transport of the cleaning cloth, the invention provides a conventional, and thus cheap, driving motor for the forward transport. This can be controlled in intervals thus enabling an intermittent cleaning cloth transport. The brake which is selectively activated with this driving motor further guarantees that very precise transport steps are made. The supply roll is, according to a further feature of the invention, also continuously coupled to a conventional driving motor, which is drivable in the rewinding direction. This driving motor remains continually energized while the machine is operating and thus fulfills two tasks namely, on the one hand, to keep the cleaning cloth stretched in standby mode and in cleaning mode and, on the other hand, to transport the cleaning cloth back in rewinding mode. 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. The take-up motor drivable in the feed direction enables, together with the brake, an intermittent drive of the cleaning cloth; it also enables a continuous drive of the cleaning cloth, should this be desired, as described. The motor coupled with the supply roll and driveable backwards serves to rewind the cleaning cloth; besides this it also helps to transport the cleaning cloth forward by holding it stretched. 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 front elevational view of a preferred embodiment of the present invention; Fig. 2 is a sectional view taken along the line I-I of Fig. 1; Fig. 3 is a sectional view taken along the line II-II of Fig. 1; Figs. 4 to 9 are illustrations of the operation of the embodiment; DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred 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 known printing cylinder cleaning apparatus 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. This known cylinder cleaning system 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 embodiments. First Embodiment A description will be made as to the first embodiment in which the cleaning cloth is fed backward by the power of a rewinding motor. The construction will be described with reference to Figs. 1 and 2. A timing pulley 45 is attached to one end of the shaft 151 of the cleaning cloth supply roll 15. A timing belt 44 is stretched between the timing pulley 45 and another timing pulley 43 which is attached to the shaft of a rewinding motor 41. The rewinding motor 41 is supplied with electric current such that it always produce an output torque in the direction of an arrow B ( see Fig. 2). A timing pulley 36 is attached to the end of the shaft 161 of the cleaning cloth take-up roll 16. A timing belt 35 is stretched between the timing pulley 36 and a timing pulley 34 which is attached to the output shaft of a take-up motor 31. An electromagnetic brake 37 is attached to the other end of the shaft 331 of the take-up motor 31 so as to brake the rotor of the take-up motor 31. 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. The sequence of operation of the respective parts will be explained hereinunder with reference to Figs. 4, 5, 6, 7, 8 and 9. State before cleaning (Cleaning system does not operate, see Fig. 4) The plenum chamber 21 on the back surface of the pressure pad 20 is not supplied with compressed air so that the pressure pad 20 is sufficiently spaced apart from the surface of the blanket 12. The rewinding motor 41 is supplied with electric power so that it produces a torque in the direction of the arrow B. On the other hand, the take-up motor 31 is not supplied with electric power, and its rotor is braked by the electromagnetic brake 37 which is supplied with the electric power. Therefore, the cleaning cloth 18 is not fed backward but is kept stationary under application of backward tension, i.e., in such a state that it is pulled towards the cleaning cloth supply roll, which is produced by the torque generated by the rewinding motor 41. State during cleaning (see Figs. 5 and 6) A cleaning start signal is given to the control system. In response to this signal, a cleaning liquid is supplied and sprayed from a spray nozzle. The spray is executed for a predetermined times at a set interval during the period of cleaning operation. Then, compressed air is supplied to the plenum chamber 21 so that the pressure pad 20 inflates so as to be pressed onto the contaminated surface of the blanket 12. Subsequently, the electromagnetic brake 37 of the take-up motor 31 is de-energized to allow the rotor of the take-up motor 31 to rotate in the direction of an arrow A. Namely, the cleaning cloth take-up roll 16 rotates in the direction of the arrow A thereby taking up the cleaning cloth 18. The rewinding motor 41 is kept energized to generate torque in the direction of the arrow B. The output torque of this motor 41, however, is smaller than the torque produced by the take-up motor 31 for taking up the cleaning cloth 18, so that the rotor of the rewinding motor 41 is reversed in the direction of the arrow A, thus allowing the cleaning cloth 18 to be fed forward in the direction of the arrow A. During the cleaning, the cleaning cloth 18 is taken-up intermittently at a suitable interval by a predetermined length in each take-up operation, or may be taken-up continuously such that a predetermined length of the cleaning cloth 18 is taken up in the period of the cleaning operation. In the case of a standard continuous take-up in an ordinary newspaper offset press, for example, about 450 mm of the cleaning cloth 18 is taken up in 4 minutes and 30 seconds. Therefore, the take-up motor 31 is set such that it provides a take-up speed of about 100 mm/min, through a reduction gear 32. The total length of feed of the cleaning cloth in each cleaning operation is about 450 mm also when the intermittent feed of cloth is adopted. The amount of feed of the cleaning cloth 18 is detected by an encoder 28 which detects the number of rotations of a rubber wheel 26 contacting the roll of the cleaning cloth 18. Completion of cleaning and subsequent operation (see Figs. 7, 8 and 9) The encode 28 produces a signal upon detection of a predetermined amount of the cleaning cloth 18 taken up. In response to this signal, the air is relieved from the plenum chamber 21 so that the pressure pad 20 is separated from the surface of the blanket 12. Then, the take-up motor 31 is de-energized with the electromagnetic brake 37 kept inoperative. Since the rewinding motor 41 is continuously energized to generate a torque in the direction of the arrow B, the cleaning cloth 18 is pulled by the cleaning cloth supply roll 15 in the direction of the arrow B, simultaneously with the extinction of the torque which has acted in the direction of the arrow A. In consequence, the cleaning cloth 18 is fed backward. The encoder 28 produces, upon detection of the backward feed of the cleaning cloth 18 by a predetermined amount, a signal which acts to put the electromagnetic brake 37 into effect thereby braking the rotor of the take-up motor 31. In consequence, the backward feed of the cleaning cloth 18 towards the cleaning cloth supply roll 15 is ceased.

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 (31, 35, 36) for rotating said cleaning cloth take-up roll (16) so as to take-up and transport forwardly said cleaning cloth (18), and pressing means (19, 20) 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 (41, 44, 45) 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 in that said take-up roll (16) is continuously coupled to a take-up motor (31) for forwardly driving said take-up roll (16), the take-up motor (31) further having a braking mechanism (37) for selectively braking or releasing the rotor of said motor, in that said supply roll (15) is continuously coupled to a rewind motor (41) for backwardly driving said supply roll (15), the torque output of said rewind motor being lower than that of said take-up motor (31), whereas in a stand-by mode the rewind motor (41) is energized and the take-up motor (31) is de-energized with the braking mechanism (37) being engaged, in a cleaning mode the rewind motor (41) is kept energized and at the same time the take-up motor (31) is energized with the braking mechanism being disengaged, and in a rewinding mode the rewind motor (41) is kept energized and at the same time the take-up motor (31) is de-energized with the braking mechanism (37) being disengaged. Apparatus according to claim 1, characterized in that the braking mechanism is an electromagnetic brake. Apparatus according to claim 1 or 2, characterized in that a control means is provided including detecting means (26 to 29) for determining a predetermined length of forwardly fed cleaning cloth (18), the control means at least controlling the action of the take-up motor (31) and of the braking mechanism (37) so as to rewind a predetermined amount of the forwardly fed length.

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