Printing – Flexible-sheet-securing devices
Reexamination Certificate
2000-02-15
2002-02-26
Evanisko, Leslie J. (Department: 2854)
Printing
Flexible-sheet-securing devices
C101S378000
Reexamination Certificate
active
06349646
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a blanket-mounting mechanism for mounting a blanket onto a blanket cylinder of an offset press, as well as to a blanket.
2. Description of the Related Art
Conventionally, by means of a blanket-mounting mechanism, a blanket is mounted onto a blanket cylinder in the following manner. One end of the blanket is appropriately attached to the blanket cylinder. The blanket is wound onto the outer circumferential surface of the blanket cylinder. The other end of the blanket is inserted into a groove formed in a single dragging shaft disposed within the blanket cylinder. The dragging shaft is rotated so as to windingly drag the blanket into the blanket cylinder, thereby mounting the blanket onto the blanket cylinder. Such a blanket-mounting mechanism and a blanket are disclosed in, for example, Japanese Utility Model Application Laid-Open (kokai) No. 61-133332 and Japanese Patent Application Laid-Open (kokai) No. 7-285214.
The blanket-mounting mechanism disclosed in Japanese Utility Model Application Laid-Open No. 61-133332 includes a hollow dragging shaft, a torsion bar, and an adjustment mechanism. The dragging shaft is disposed in a groove which extends axially in the blanket cylinder and opens at the circumferential surface of the blanket cylinder. The opposite ends of the dragging shaft are rotatably supported by the opposite end portions of the blanket cylinder. The torsion bar is coaxially disposed within a hollow portion of the dragging shaft. One end of the torsion bar is connected to one end of the dragging shaft. The other end of the torsion bar projects from the other end of the dragging shaft. Via the adjustment mechanism, the projecting end of the torsion bar is attached to the corresponding end portion of the blanket cylinder, which end portion rotatably supports the other end of the dragging shaft. The adjustment mechanism is adapted to adjust the angular displacement of the torsion bar.
One end of the dragging shaft projects from the corresponding end portion of the blanket cylinder, which end portion rotatably supports the one end of the dragging shaft. A worm wheel is attached to the projecting end of the dragging shaft. A removable handled worm can be engaged with the worm wheel.
The blanket is mounted onto the blanket cylinder in the following manner. One end of the blanket is fixedly fitted into a groove which is axially formed in the circumferential surface of the blanket cylinder. The blanket cylinder is rotated so as to wind the blanket onto the outer circumferential surface of the blanket cylinder. The handled worm is set in a predetermined position so as to be engaged with the worm wheel and is rotated manually to thereby rotate the worm wheel. As the worm wheel rotates, the dragging shaft rotates to thereby twist the torsion bar, since one end of the torsion bar is connected to the dragging shaft. Thus, a restoration force is accumulated. When a blanket attachment portion of the dragging shaft reaches an appropriate position through rotation of the dragging shaft, the other end of the blanket is attached to the blanket attachment portion.
Next, the handled worm is rotated in the reverse direction so that the dragging shaft windingly drags in the other end of the blanket. When the tension exerted by the blanket and the restoration force accumulated in the torsion bar balance with each other, the worm wheel stops rotating. When the handled worm is rotated further in the reverse direction, the handled worm is disengaged from the halted worm wheel.
Thus, mounting of the blanket onto the blanket cylinder is completed.
In the blanket-mounting mechanism disclosed in Japanese Patent Application Laid-Open No. 7-285214, the opposite ends of a dragging shaft project from the corresponding end faces of a blanket cylinder. Rotating means composed of a worm and a worm wheel is disposed at each end of the dragging shaft.
Further, Japanese Patent Application Laid-Open No. 7-285214 states that some blanket-mounting mechanisms employ a structure in which rotating means comprising a lever and a latch mechanism is provided. The publication also discloses a structure such that a blanket to be attached to a blanket cylinder is provided with a thin band sheet attached to opposite end portions of the blanket cylinder to be located on a single side thereof.
The above-mentioned conventional techniques involve the following problems.
In the blanket-mounting mechanism disclosed in Utility Model Application Laid-Open (kokai) No. 133332/1986, a torque exerted by the torsion bar is transmitted to the dragging shaft through one end thereof to thereby rotate the dragging shaft. The blanket is windingly dragged into the blanket cylinder and is thus wound onto the blanket.
However, in the case of a long dragging shaft, the other end of the dragging shaft to which a torque exerted by the torsion bar is not directly transmitted exhibits a smaller angular displacement than does the opposite end, because of the action of a frictional force. As a result, the dragging shaft is twisted.
Since a central portion of the dragging shaft is not supported, the dragging shaft deflects at the central portion due to the tension exerted by the blanket.
Thus, the blanket mounted on the blanket cylinder is not subjected to uniform tension. The blanket is mounted on the blanket cylinder while being pulled at a constant tension and remaining in close contact with the surface of the blanket cylinder. Since the blanket is stretched, the thickness thereof varies slightly.
Moreover, if a nonuniform tension is exerted on the blanket, the thickness of the blanket becomes nonuniform, causing nonuniform contact pressure between the blanket and a printing cylinder or between the blanket and printing paper. As a result, a certain portion may not be printed under an appropriate pressure, with a resultant impairment in printing quality.
In the blanket-mounting mechanism disclosed in Japanese Patent Application Laid-Open No. 7-285214, when the blanket is to be windingly dragged into the blanket cylinder, the opposite ends of the dragging shaft must be alternatingly rotated. Dragging work is both labor consuming and time consuming.
In the case of the rotating means composed of a lever and a latch mechanism, one end of the dragging shaft is rotated so as to windingly drag the blanket into the blanket cylinder, and then the other end of the dragging shaft is rotated so as to compensate a torsion of the dragging shaft. Since the angular displacement of the dragging shaft, or the degree of drag of the blanket, and the reverse angular displacement of the dragging shaft for compensation of a torsion of the dragging shaft are in units directly related to the tooth pitch of the latch mechanism, the tension exerted by the mounted blanket cannot be adjusted optimally for the thickness and physical characteristics of the blanket.
As a result, the tension exerted by the blanket mounted on the blanket cylinder may be slightly weak or strong with respect to an optimum level, resulting in a failure to obtain desired printing quality. Also, the life of the blanket is shortened.
Further, since the deflection of the dragging shaft cannot be prevented, the blanket cannot be mounted onto the blanket cylinder while being subjected to uniform tension. Therefore, as in the case of the blanket-mounting mechanism disclosed in Utility Model Application Laid-Open No. 61-133332, good printing quality is not provided.
The blanket disclosed in Japanese Patent Application Laid-Open No. 7-285214 has a band sheet attached to opposite end portions located on a single side. The band sheet serves as a reinforcing member and is long and narrow. When a worker handles the band sheet, an external force may be exerted thereon, potentially causing a slight warpage or torsion thereof. Particularly, in the case of a deformation of the band sheet to be attached to an end portion of the blanket which is to be inserted into a groove formed in the dragging shaft, insertion of the end port
Hasegawa Toshio
Kusunoki Kenji
Takahashi Yukitoshi
Armstrong Westerman & Hattori, LLP
Evanisko Leslie J.
Tokyo Kikai Seisakusho Ltd.
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