Patent Application
20080084023
The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only, and are presented in order to provide what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.
In the drawings:
The present embodiments comprise a system and a method for gripper control, using a servo-driven cam. The principles and operation of a system and method according to the present invention may be better understood with reference to the drawings and accompanying description.
Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.
In one embodiment of the present invention, a gripper system for controlling the loading and unloading of sheets on a cylindrical sheet guide is disclosed. The gripper system comprises one or more grippers mounted on one axis, which is positioned at the outer edge of a cylindrical sheet guide. The gripper axis is coupled to a cam follower. The motion of the cam followers controls the elevation of the grippers. Accordingly, in order to elevate or lower the gripper axis, a cam is pivoted in the vicinity of the cam followers. A servomotor having an axle is adapted for steering the cam. A cam-gripper controller is configured for controlling the servomotor according to a certain printing profile and actual reading from the press main encoder. The printing profile may be chosen from a printing profile repository that comprises a number of printing profiles, each adapted for a printing-material with different boundary conditions, e.g., different thicknesses.
In another embodiment of the present invention a method for controlling loading and unloading of sheets from a cylindrical sheet guide is disclosed. During the first step, a gripper system operable for controlling the elevation of the grippers on the cylindrical sheet guide is provided. The gripper system is associated with a servomotor. Subsequently, a predefined elevation profile representing the elevation of the grippers during revolutions of the cylindrical sheet guide is received. The profile determines the elevation of the grippers during rotation of the cylindrical sheet guide. The servomotor actuates the gripper system, according to the predefined profile, for loading and unloading of sheets from the cylindrical sheet guide.
Reference is now made to
The gripper system is used, inter alia, for retaining sheets on the impression drum 7 and for transferring documents between the impression drum 7 and other assemblies of the printing press. Examples of such printing presses are those currently manufactured by Hewlett-Packard Development Company, L.P., under the designations “HP Indigo press 3050,” “HP Indigo press 1050” and “HP Indigo press s2000.”
In between each gripper and the impression drum 7 there is a sheet holding space. The width of the space is determined by the proximity of the gripper to the outer surface of the impression drum 7. In use, a sheet is fed towards the impression drum 7, and is held in place by grippers. As the impression drum rotates, an image is printed on the sheet. Other drums such as a storage drum or a perfecting cylinder may be used as well.
In order to ensure proper feeding of the sheet, the opening and closing operation of the grippers has to be synchronized with the rotation of the impression drum 7. For example, the grippers have to be opened for allowing loading of a sheet, as shown at 103, from a sheet loader onto the impression drum, and for allowing unloading of a sheet, as shown at 100, into a designated output tray or other systems. In order to allow processing of the sheets, the grippers have to be closed after loading and before unloading.
More complex opening and closing operations are also possible. For example, in one embodiment of the present invention only a portion of a certain printing job, such as one color of a printing job image, is printed on the gripped sheet during each cycle of the impression drum. In this case, the sheet remains gripped until all of the portions of the image that comprises different colors are printed. Thus, the grippers have to remain closed for a number of rotations of the impression drum, until the entire printing job image has been printed on the sheet.
In another embodiment, the grippers have to be synchronized with a perfector mechanism, which may be provided in a high speed, sheet-fed rotary printing press. A perfector mechanism allows the press to print on both sides of a sheet. The perfector mechanism is adjustably timed with respect to the impression drum such that, after printing on one side, the sheet is removed from the impression drum, turned over and transferred back thereto. The opening and the closing operation of the grippers has to be coordinated with the perfector mechanism. If the print job includes printing on only one side of the sheet (simplex printing), the sheet is released from the grippers and ejected into the output tray after one side of the sheet has been fully printed. If, however, the print job includes printing on two sides of the sheet (duplex printing), the sheet is first released from the grippers into a perfector 103, turned over, and then fed back onto the impression drum through the duplex system 102 for printing on the second side. The opening and the closing of the grippers has to be synchronized with the perfector 103 and duplex 102 such that a sheet may be transferred to the perfector 103 and returned to the impression drum after it has been turned over.
Reference is now made to
The rotary cam 9 has a non-uniformly shaped circumference that represents a profile, which determines the opening and the closing of the gripper axis 4. The cam gripper system 8 is configured to control the cam follower 11. The cam follower 11 maneuvers a gripper axis 4, therewith change the opening height which is formed in between the gripper blades 13 and the cylindrical sheet guide 7. In one embodiment the cylindrical sheet guide 7 is an impression drum. Individual grippers or groups of grippers on the edge of the cylindrical sheet guide are actuated either independently of one another, or simultaneously by the rotary cam 9, as described below.
The cam gripper system 8 may comprise more than one gripper and each gripper is associated with a corresponding cam follower. However, for the sake of simplicity, the description of the present embodiment will include mention of a single gripper 8 and cam follower 11.
The rotational positioning of the rotary cam 9 is controlled by the servomotor 1 as descried below. The cam follower positioning is controlled by the rotational positioning of the rotary cam 9. During the operation of the cylindrical sheet guide 7, the gripper axis 4 is moved by a cam follower 11, for example about a joint axis 5 which is disposed along the rotation axis of the impression drum 7. The rotational movement of the impression drum 7 in relation to the rotation of the rotary cam 9 causing the cam follower 11, to elevate the gripper axis 4 and the gripper blades 13. The rotational angle of the rotary cam 9 relative to the rotational angle of the impression drum 7 determines the points in time at which the gripper is closed and opened, as described below.
A bearing 12 may be positioned at each of the points of contact of the gear-wheel 2 and the servomotor 1, in order to reduce the friction therebetween, so that one may move freely relative to the other. There are numerous bearing mechanisms, which are capable of reducing friction, which are well known in the art and, hence, will not be described here in detail.
Reference is now made to
Reference is now made, once again, to
In order to coordinate opening and the closing of the gripper axis 4 with rotation of the impression drum, the rotational position of the rotary cam 9 and the rotational position of the impression drum 7 have to be coordinated, in order to correlate their rotational positions, the relative rotational angle between them has to be either maintained or changed during the printing process. In operation, the servomotor 1 may alter the rotational position of the rotary cam 9 such that their relative rotational positions are correlated. The servomotor 1 serves as a control device for controlling the rotational position of the rotary cam 9 in the servomechanism. The servomotor is designed to receive command signals, which are issued according to any of a number of printing profiles, from a cam-gripper controller (not shown). In one embodiment the command signals pass via an amplifier that amplifies the command signals to appropriate levels to result in movement of the servomotor axle that rotates gear-wheels 2 and 3 and, thus, the rotary cam 9. An alternating current (AC) may be supplied to the amplifier at a current level, which is adjusted to the required to torque of the servomotor's axle. The servomotor 1 is connected to the cam-gripper controller, which stores information about various printing profiles. In one embodiment the cam-gripper controller has been programmed to control the velocity and direction of rotation of the axle of the servomotor 1. By changing the velocity or direction, the rotational angle of the rotary cam 9 is changed in relation to the rotational angle of the impression drum 7.
Such an embodiment allows the cam-gripper controller to adjust the rotational position of the rotary cam 9 according to a number of different printing profiles, which are adjusted for different types of sheets. Since the rotary cam 9 has a nonuniform profile with projections of various sizes, as described below, one or more grippers 4 may be raised different amounts by the rotation of the rotary cam 9. The rotary cam 9 is designed to allow the positioning of the one or more grippers 13 such that the height which is formed in between the grippers blades 13 and the cylindrical sheet guide may vary accordingly.
Different types of sheets may have different thicknesses. As described above, the grippers are designed to be opened or closed during different stages of the printing process. Grippers are closed for allowing, inter alia, printing on the sheets during the pivoting of the impression drum 7, and are opened in order to enable the transferring of the sheets among different assemblies of the printing press. The height formed in between the gripper blades 13 and the cylindrical sheet guide 7 has to be adjusted for sheets with different thicknesses, since the printing press is used for printing on several types of sheets. The adjustment is important in order to achieve a better grip of each sheet and a smoother transfer of the sheets to and from the impression drum 7. An accurate adjustment of height which is formed in between the grippers blades 13 and the cylindrical sheet guide 7 during the printing process substantially reduces the probability of a sheet jam since the adjusted gripping improves the accuracy of the alignment of the sheets relative to the impression drum 7 and to the other assemblies of the printing press. Moreover, the adjusted gripping may reduce the velocity of angular change of the grippers during the opening or closing thereof, such that there is less jarring of the grippers 4. It should be noted that, by reducing the probability of a sheet jam, the rotation rate of the impression drum 7 may be accelerated, such that the printing rate may be increased without harming the continuity of the printing process.
The cam-gripper controller may be connected to a memory which is configured for storing a number of printing profiles. Each printing profile contains a series of synchronous activating orders, which are configured to instruct the servomotor to change the height which is formed in between the grippers blades 13 and the cylindrical sheet guide 7 by changing the rotational angle or the velocity of the rotary cam 9 during the printing process. During operation of the printing press, the movement of the cam during the rotation of the cylindrical sheet guide can readily be adapted to a change in boundary conditions, e.g., to different printing-material thicknesses. In one embodiment each printing profile corresponds to a particular thickness of a sheet such that, when each sheet is fed into the printing press, the height which is formed in between the grippers blades 13 and the cylindrical sheet guide 7 is adjusted accordingly, during the printing process.
In one embodiment of the present invention, the cam-gripper controller is connected to a sheet thickness identifier. The sheet thickness identifier is configured to detect the thickness of the sheets. In one embodiment the sheet thickness identifier comprises a sensor and an image-processing unit. In one embodiment the sensor is an image sensor complementary metal oxide semiconductor (CMOS) sensor or a charged coupled device (CCD) sensor. The image sensor is positioned in the printing press in a manner such that it measures the distance between the upper surface and the lower surface of the sheets which are conveyed within the printing press. In one embodiment the image-processing unit is used to process the images which are received from the image sensor to output the thickness of the conveyed sheet. In one embodiment the image processing unit outputs a control signal to a controller that chooses a printing profile which corresponds to the identified dimensions of the sheet. The method of identifying the thickness of a sheet by using image processing is well known in the art and, hence, will not be described here in detail.
In order to adjust the height which is formed in between the gripper blades 13 and the cylindrical sheet guide 7 according to a certain printing profile, the cam-gripper controller has to translate the synchronous activating orders into control signals that cause rotation of the axle of the servomotor 1 and pivoting of the rotary cam 9. The control signals determine the direction and the velocity of rotation of the axle of the servomotor 1. The servomotor 1 changes the rotational angle of the rotary cam 9 relative to the current rotational angle of the impression drum 7 such that one or more grippers 4 are elevated, depending on asynchronous activating order.
While
In one embodiment of the present invention the rotary cam 9 and the gripper system are positioned within the cylindrical sheet guide 7. Such an embodiment reduces the probability that a certain sheet may become entangled with parts of the gripper system.
Reference is now made to
Reference is now made to
In one embodiment a spring mechanism 504 for returning the cam follower 502 to its former position after it has been moved by the cam 501 is provided.
Reference is now made to
In one embodiment in order to maneuver the servomotor 1, the cam-gripper controller 202 receives feedback signals 203, 204 that represent the current rotational angle of the impression drum and the current rotational angle of the cam, respectively. The cam-gripper controller 202 further receives a certain printing profile 206. As described above, a number of printing profiles are stored in a memory which is connected to the cam-gripper controller. In one embodiment a profile generator 207 is used to generate the certain printing profile 206 according to a profile which is chosen from the memory. A servomotor feedback unit 201 coupled to the servomotor 1, outputs a feedback signal 204, which is sent back to the cam-gripper controller 202. The feedback signal 204 represents data regarding the current rotational angle of the axle of the servomotor 1. This data can easily be translated into data that represent the current rotational angle of the cam since, as described above, the cam and the servomotor have engaged gear-wheels.
A feedback unit 200 coupled to the cylindrical sheet guide outputs a feedback signal 203, which is sent back to the cam-gripper controller 202. The feedback signal 203 represents data regarding the current rotational angle of the cylindrical sheet guide.
In one embodiment each of the cylindrical sheet guide feedback unit 200 and the servomotor feedback unit 201 comprises a tachometer, which is configured to measure the RPM of the revolving axle of the servomotor. The readout of the RPM is in the form of an analog signal. In order to use the outputs of the tachometers as references for the control signals, the cam and the impression drum have to be synchronized, optionally as described below.
In one embodiment each of the cylindrical sheet guide feedback unit 200 and the servomotor feedback unit 201 comprises a resolver, which is an electrical transformer used for measuring the rotational angle of the cylindrical sheet guide or the axle of the servomotor. Each resolver comprises a primary winding, which is fixed to the cylindrical sheet guide or to the axle of the servomotor and is excited by a sinusoidal electric current. The sinusoidal electric current causes electromagnetic induction of a current flow in two secondary windings, which are coupled orthogonally to each other on a stationary part of the servomotor (the stator). The relative magnitudes of the two secondary currents are measured and used to determine the angle of the cylindrical sheet guide or the axle or the servomotor relative to the stationary part.
In one embodiment each of the cylindrical sheet guide feedback unit 200 and the servomotor feedback unit 201 comprises an encoder, which is used to encode a signal into a form that is acceptable for transmission. Either analog circuitry for analog encoding or digital circuitry for digital encoding may be used. The encoder, the resolver, and the tachometer are well known in the art and, hence, will not be described here in detail.
In one embodiment of the present invention the cam-gripper controller 202 uses the feedback signals to determine whether the servomotor moves the cam properly according to the received printing profile 206, and, if not, then the cam-gripper controller 202 transmits control signals 205 to the servomotor 1 to make appropriate adjustments. By reducing or increasing the voltage of the control signals 205 which are sent to the servomotor, the cam-gripper controller 202 adjusts the sheet holding space, as described above. The axle of the servomotor may be controlled in any other manner, inter alia, by changing its position, direction, or velocity. The control signals 205 represent changes in the velocity, the position, and direction of the axle of the servomotor 1, which result in adjustment of the gear-wheels 208 that maneuver the rotational angle of the cam that control the cam follower, as shown at 209. As described above, and shown at 210, the cam follower controls the cylindrical sheet guide's grippers.
Reference is now made to
As described above, the control signals, which are used to maneuver the cam during the printing process, may be generated according to the current rotational position of the cylindrical sheet guide and the cam. However, in order to utilize the control signals to affect pivoting of the rotary cam, the rotational positions of the cylindrical sheet guide and the cam have to be synchronized before they are analyzed.
The feedback signal represents the rotational force (torque) of the axle of the servomotor relative to different rotational positions of the cam. Since the cam's profile is nonuniform, the torque varies therealong. As commonly known, torque is a function of the force applied to a lever, multiplied by its distance from the point around which the lever rotates (fulcrum). This is true on condition that the force is in a direction at right angles to the lever. Since the gear-wheel of the cam and gear-wheel of the servomotor axle are engaged, the gear-wheel of the cam applies an opposing force to the gear-wheel of the servomotor axle. The applied force is a derivative of the radius of the rotary cam which is engaged with the cam follower. The longer the radius, the greater will be the applied force and, thus, the lower will be the torque of the axle of the servomotor. Accordingly, the amount of the torque at any point along the graph depends on the radius of the cam at a particular rotational position.
In one embodiment of the present invention, a sequence of torque levels of the axle of the servomotor during one rotation of the cam is recorded and stored in the memory of the cam-gripper controller as a reference pattern for synchronization. The recording of the reference pattern is a one-time event, which occurs during the calibration of the printing press. The recorded sequence of the torque levels is correlated with the cam's profile and a known initial rotational position is recorded. The sequence of torque levels is recorded when the rotational position of the cylindrical sheet guide is stable.
Since the torque levels of the reference pattern are correlated with known rotational positions of the cam, the deviation between the reference pattern and the current feedback signals may be used to identify an angular deviation between the current rotational position of the cam and its known initial rotational position. Based upon the identified deviation, the gripper system may be synchronized by rotating the cam to the known initial rotational position.
Reference is now made to
As shown at 403, after the revolution has been completed, the feedback signals are compared with the reference pattern. In one embodiment the recorded current feedback signals are smoothed and filtered in order to facilitate matching of the patterns. This may be done by comparing the recorded current feedback signals and the reference pattern, as described above. By comparing the patterns, a pattern deviation is identified. The deviation represents the angular deviation between the current rotational angle of the rotary cam and the known initial rotational position. Calculating pattern deviation is well known in the art and, hence, will not be described here in detail.
Based upon the pattern deviation, the angular deviation between the current rotational position and the known rotational position is calculated, as shown at step 404. During the subsequent step, as shown at 405, a control signal is sent to the servomotor in order to adjust the angle of rotation of the cam according to the calculated deviation.
Reference is now made to
However, as described above, the elevation of the grippers is a derivative of the cam profile. Accordingly, in order to improve the performance of the gripper system, the cam and the different profile of the servomotor have to be correlated.
In order to allow the opening of the grippers at more than one rotational angle, the servomotor may direct the rotary cam 700, as described above, to different rotational positions in relation to the rotation of the cylindrical sheet guide. This allows loading of a sheet onto an impression drum from a duplex tray, a perfector mechanism or a sheet loader.
As described above, during some printing processes, a sheet may remain gripped on the cylindrical sheet guide for more than one rotation thereof. For example, in some printing processes, only one color may be applied on the gripped sheet per rotation of the cylindrical sheet guide. Thus, in such printing processes, the grippers have to remain closed for a number of consecutive rotations until the image of the printing job has been fully printed on the sheet. In order to allow printing according to such a printing process, the servomotor may rotate the rotary cam at the same velocity as the cylindrical sheet guide during consecutive rotations in which the grippers have to remain closed. The rotary cam is rotated in order to keep the contact point between the rotary cam and the cam follower on an area 703 of the rotary cam profile, which is relativity close to the center of the cam 706.
By using such a cam, the servomotor may rotate the cam to control the elevation of the grippers during the printing process in a more accurate manner. By using such adjusted cams, the servomotor is able to maneuver the grippers to different elevations during each revolution of the cam. The cam may have a graded structure, which is adjusted to reduce the jarring which occurs during revolution of the cam.
Reference is now made to
Reference is now made to
It is expected that during the life of this patent many relevant devices and systems will be developed and the scope of the terms herein, particularly of the terms controller, circuitry, printing press, impression drum, and image sensor are intended to include all such new technologies a priori.
It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination.
Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. All publications, patents, and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention.
