1. Field of the Invention
This invention relates to engraving devices and more particularly, to a method and apparatus for determining a cylinder characteristic, such as cylinder diameter and a cylinder run-out, and adjusting an engraver in response thereto.
2. Description of Related Art
Prior art devices of the type shown in U.S. Pat. Nos. 4,450,486; 5,424,846; 5,438,422; 5,424,845; 5,329,215 typically comprised an engraving head having an engraving device, such as a diamond stylus, and a guide shoe. The guide shoe bore against a surface of a cylinder and provided a reference for the engraving process. An electromagnetic driver mounted within the engraving head caused the engraving device to oscillate into engraving contact with the cylinder as the cylinder rotated about its cylindrical axis, thereby causing either a helical or cylindrical tract of engraved areas or cells to be engraved on the surface of the cylinder.
The cylinders engraved were oftentimes not concentric about their axis or if they comprised support shafts, it was not uncommon that the axis of the support shafts was not coaxial with the rotational axis of the cylinder, thereby causing the cylinder to not rotate about its rotational axis.
Still another problem with engravers of the past related to registration. The cylinder typically had two end support shafts which were received in chucks located on the engraver. Sometimes one or more of the support shafts were not properly registered or aligned in the chuck in which they were mounted.
These problems were sometimes called "run out". In engraving devices of the past, run-out caused the engraving device or stylus to engrave areas which were not of the proper density. For example, if the cylinder comprised an eccentric, then on the high areas, the engraving device would engrave areas having larger densities, whereas on "low" areas, the engraving device would engrave areas having lower densities due to the proximity of the engraving device relative to the surface of the cylinder. In the past, an operator would attempt to adjust the engraver to eliminate the mis-registration by manually determining the "run out" associated with a cylinder and then manually adjusting one or more jaws on a chuck to account for that run out. Typically, an operator would place a gauge in contact with the surface of the engraver and attempt to measure the run out associated with that cylinder. Thereafter, the operator may attempt to adjust the engraver to eliminate the run-out by manually loosening and retightening one more jaws on one or both chucks which supported an end shaft of the cylinder in order to attempt to eliminate the run out.
These processes were oftentimes inaccurate and time consuming and required manual intervention.
What is need, therefore, is a method and apparatus for automatically measuring the run-out associated with a cylinder and then automatically adjusting the engraver to reducer or eliminate such run-out.