1. Field of the Invention
The present invention relates to a printing plate mounted on a surface plate which is a stage for exposure and the like, and a method and a device for positioning the printing plate at a position relative to the surface plate.
2. Description of the Related Art
Technology (printing plate automatic exposure devices) has been developed whereby an image is recorded onto a printing plate. The printing plate (e.g., a presensitized plate, a thermal plate, a photopolymer plate or the like) is provided with a recording layer on top of a base layer. The image is recorded at a printing plate""s photopolymerization layer with a direct laser beam or the like.
With this sort of technology, images can be recorded onto printing plates quickly. Therefore, sequential feeding of the printing plates is required. A plurality of printing plates are prepared in a stacked state at a predetermined position beforehand. The printing plates are automatically taken one at a time, positioned on the surface plate, and fed into an exposure portion. In some cases, punched holes are provided for positioning the printing plates at the plate cylinder of the printing machine before or after feeding to the exposure portion. Therefore, positioning each of the printing plates on the surface plate is an important operation.
Conventionally, in cases in which the printing plate is placed on the surface plate and then positioned, pins that can abut against the face of the surface plate are provided at the rim of the face of the surface plate (at two adjacent sides). These pins push the printing plate at the corresponding two sides. The pins apply force and thereby effect positioning of the printing plate.
However, in the aforementioned conventional positioning method, the displacement of the printing plate is large, and a corresponding amount of space must be guaranteed.
When the printing plate is placed on the surface plate, if it is placed in an angled state, displacement for positioning is particularly great, and positioning cannot be done quickly.
Moreover, positioning pins and displacement mechanisms for pushing from the two directions are needed. Hence, the number of components increases. Moreover, such displacement mechanisms are attached to the surface plate. Therefore, the surface plate""s weight increases and the torque required to move the surface plate must increase.
In view of the aforementioned, an object of the present invention is to provide a method and a device for positioning a printing plate wherein highly accurate positioning of the printing plate at a position relative to a surface plate can be done with a short stroke, the surface plate can be lightened by reducing the number of components in the surface plate, and the torque for displacement can be reduced.
A first aspect of the present invention is a method for positioning a printing plate, which has been placed on a surface plate, relative to the surface plate, including the step of rotating the printing plate by pushing an edge thereof for thereby substantially eliminating an angular error.
In the first aspect of the present invention the printing plate is pushed, for example, by a plate movable along a predetermined direction. The printing plate is pushed from only one edge. Thus, the printing plate rotates and the angular error can be substantially eliminated.
A second aspect of the present invention is a method for positioning a printing plate, which has been disposed on a surface plate, relative to the surface plate wherein the printing plate and surface plate are movable in a first direction relative to one another, the method including the step of rotating the printing plate, while holding the printing plate at a point, about the point by pushing an edge of the printing plate for thereby substantially eliminating an angular error with respect to the surface plate.
In the second aspect of the present invention, while one side of the printing plate is being pushed, one point of the printing plate""s surface is held. The means of holding may be suction at a small hole provided at the surface plate, which suction holds the one point, or the means of holding may be a spherical body and the like above the printing plate, which body presses with a non-sharp-cornered member and holds by gripping the printing plate between this member and the surface plate. Such a member should be free of sharp corners, so as to prevent damage to the printing plate.
When the printing plate is held at one point and pushed from one side, if the printing plate is oblique, it adjusts by rotating about the one point. Thus, obliqueness is substantially eliminated with little displacement in X and Y directions relative to the surface plate. Hence, obliqueness can be substantially eliminated in a small space.
A third aspect of the present invention is a method for positioning a printing plate, which has been disposed on a surface plate, relative to the surface plate wherein the printing plate and surface plate are movable along a first direction relative to one another, the method including the steps of: (a) rotating the printing plate, while holding the printing plate at a point, about the point by pushing an edge of the printing plate for thereby substantially eliminating an angular error with respect to the surface plate; (b) continuing the pushing, thereby positioning the printing plate in a second direction substantially orthogonal to the first direction; (c) subsequently moving the surface plate in the first direction, thereby positioning the printing plate in the first direction using a plurality of printing plate detection sensors; and (d) setting a resultant position of the surface plate as an initial position.
In the third aspect of the present invention, when substantial elimination of obliqueness, as in the second aspect, is complete, the printing plate is positioned in the X direction, which is orthogonal to the Y direction (a direction in which the surface plate can be moved).
When positioning in the X direction is complete, positioning in the Y direction is carried out. In the third aspect, the positioning in the Y direction is not done by altering the position of the printing plate relative to the surface plate, but by moving the surface plate itself in the Y direction. This movement is monitored by a plurality of sensors. When the printing plate reaches a predetermined position, the movement stops.
When at this position, the printing plate has been properly positioned. However, the surface plate has moved from an original position thereof. Therefore, the position of the surface plate after the movement is recognized as being an initial position.
Hence, the printing plate and surface plate are effectively positioned at an appropriate position and operations such as, for example, punching of punch holes and exposure processing can be performed accurately.
A fourth aspect of the present invention is a printing plate positioning device for positioning a printing plate relative to a surface place, wherein the printing plate has been moved onto the surface plate from a predetermined transport path, the device including: (a) a movable body disposed proximate a side of the surface plate, the movable body being movable towards and away from the surface plate; (b) a plurality of sensors operable for detecting the printing plate presence at predetermined positions; and (c) a first holding portion and a second holding portion provided at the surface plate, for holding the printing plate.
A fifth aspect of the present invention is a printing plate positioning device for positioning a printing plate relative to a surface plate, wherein the printing plate has been moved onto the surface plate from a predetermined transport path, the device including: a holding device provided at a surface of the surface plate, the holding device holding the printing plate on the surface plate such that the printing plate is rotatable with respect to the surface plate about one point of the printing plate; and a pushing device disposed proximate a side of the surface plate, the pushing device pushing an edge of the printing plate while the printing plate is held by the holding device and thereby rotating the printing plate about the one point of the printing plate for thereby substantially eliminating an angular error with respect to the surface plate in a direction of rotation.
A sixth aspect of the present invention is a printing plate positioning device for positioning a printing plate, which has been disposed on a surface plate, relative to the surface plate wherein the surface plate is movable along a certain direction, the device including: a holding device provided at a surface of the surface plate, the holding device holding the printing plate on the surface plate such that the printing plate is rotatable with respect to the surface plate about one point of the printing plate; a first pushing device disposed proximate a side of the surface plate, the first pushing device pushing an edge of the printing plate while the printing plate is held by the holding device and thereby rotating the printing plate about the one point of the printing plate for thereby substantially eliminating in a direction of rotation an angular error with respect to the surface plate; a second pushing device disposed proximate a side of the surface plate, the second pushing device pushing an edge of the printing plate after the first pushing device has substantially eliminated the angular error, for thereby positioning the printing plate along a first direction substantially orthogonal to the certain direction; and a detection portion operable for detecting a position along a second direction of the printing plate at a time when the printing plate is moved along the certain direction by movement of the surface plate after the printing plate has been positioned along the first direction, wherein the printing plate is positioned in accordance with the detection portion, and a resultant position of the surface plate is set as an initial position.
In the sixth aspect of the present invention, the first pushing device and the second pushing device are preferably consitituted by a single pushing device which performs substantial elimination of the angular error and positioning along the first direction in a continuous manner.
If a single pushing device is used in the sixth aspect of the present invention, the printing plate positioning device can be made smaller. Also, the printing plate can be positioned in a shorter time.
In the fifth and sixth aspects of the present invention, it is preferable for the printing plate positioning device to further include a punching device proximate a transport direction back end edge of the printing plate for punching punch holes along an edge portion of the printing plate after the printing plate has been positioned along the first direction and the second direction.
Consequently, when the printing plate and the surface plate have been positioned at a suitable position, punch holes can be provided in the printing plate with high accuracy.