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As described in Kellett, U.S. Ser. No. 08/645,747, titled MATERIALS USEFUL IN LITHOGRAPHIC PRINTING PLATES, filed May 14, 1996, incorporated by reference herein, a continuous jet printer can be used to prepare a printing plates for offset printing. Typically in offset printing, four separate aluminum plates are used to produce a single color image. Each of the four plates is engraved with a partial image used to print one of four colors: cyan, magenta, yellow and black. Because four plates are used to produce a single image, the partial images must be precisely aligned on the drum and on the printing press.57219
SUMMARY OF THE INVENTION
According to one aspect of the invention, a printer drum includes a leading edge assembly for holding a first end of a substrate, and a trailing edge assembly for holding a second end of the substrate. The leading edge assembly includes a first plurality of interconnected disks, and the trailing edge assembly includes a second plurality of inter¬connected disks. The disks of the two assemblies are inter¬leaved such that the disks of the trailing edge assembly are rotatable relative to the disks of the leading edge assembly about the axis of rotation of the drum.
Embodiments of this aspect of the invention may include one or more of the following features.
The axis of rotation of the drum is a common central axis of the disks of both assemblies. Each disk defines a centric hole and an axle extends along the axis of rotation and through each centric hole. The axle is fixedly connected to the leading edge assembly such that rotation of the axle causes rotation of the leading edge assembly. A rotation lock prevents the disks of the trailing edge assembly from rotat¬ing with respect to the disks of the leading edge assembly.
Each disk defines a through hole located between a center of the disk and a circumference of the disk for containing a balancing weight such that a center of mass of the leading edge assembly and a center of mass of the trailing edge assembly lie along the axis of rotation.
In certain embodiments, a balancing disk is interleaved with the disks. The balancing disk includes an adjustably positioned balancing weight for compensating for the weight of a printing plate attached to the drum. The balancing disk is a disk of the leading edge assembly. The balancing disk includes a central member, a first ring rotatably mounted to a first side of the central member, and a second ring rotatably mounted to a second side of the central member. The balancing weight includes a weight fixedly mounted to the first ring and a weight fixedly mounted to the second ring.
A leading edge clamp interconnects the first plurality of disks, and a trailing edge clamp interconnects the second 55
plurality of disks. The disks are generally circular in shape and each disk defines a relieved section along a portion of
the circumference of the disk. The relieved section provides clearance for the clamps during rotation of the leading edge
clamp relative to the trailing edge clamp. 60
The disks define a continuous printing plate support surface. The disks of both assemblies are substantially
identical. Each disk has a first side and an opposing second side. When interleaved the disks of the second plurality are reversed with respect to the disks of the first plurality such 65 that the first side of a disk of the first plurality faces the first side of a disk of the second plurality.
The leading edge assembly includes a third plurality of disks. A second trailing edge assembly has a fourth plurality of disks interleaved with the third plurality of disks and rotatable relative to the leading edge assembly about the axis of rotation.
According to another aspect of the invention, a clamp for holding a substrate includes a base, a clamping member elastically deformable between a clamping position and a non-clamping position, and an actuator movable between a first position and a second position. The base supports a first side of the substrate, and the clamping member in the clamping position presses against a second side of the substrate. The actuator is in contact with the clamping member when the actuator is in the second position such that the clamping member is elastically deformed from the clamping position to the non-clamping position. The clamp¬ing member resiliently returns to the clamping position when the actuator is moved to its first position.