Method and apparatus for registration control during processing of a workpiece particularly during producing images on substrates in preparing printed circuit boards

A method of controlling the imaging operation of an imaging machine for producing an image on a substrate according to an image file, comprising the following steps:

• (a) determining the nominal locations of at least two sensible reference marks on said substrate in terms of the coordinates of the substrate;
• (b) mounting the substrate on the imaging machine having a plotting head;
• (c) sensing, and measuring the actual locations of, said reference marks on the mounted substrate in terms of the coordinates of the imaging machine;
• (d) determining at least one geometrical transformation needed to transform the substrate coordinates of the nominal locations of said reference marks to the imaging machine coordinates of the sensed locations of said reference marks;
• (e) and controlling said plotting head to produce an image on said substrate in accordance with the determined geometrical transformation.

Apparatus for controlling a processing operation on a workpiece carrying sensible reference marks at nominal locations on the workpiece in terms of the coordinates of the workpiece, comprising:

• a mounting device for mounting the workpiece to the apparatus;
• a processing head movable with respect to a workpiece when mounted on said mounting device;
• a sensing device carried by said processing head so as to move therewith with respect to a mounted workpiece, said sensing device being capable of sensing said workpiece reference marks and having a reference point which is at a known location with respect to a reference point on the processing head;
• and
• a data processor system processing the output of said sensing device for:
• (a) determining the locations of said reference marks on the workpiece in terms of the coordinates of the processing head;
• (b) determining the geometrical transformations needed to transform the workpiece coordinates of the nominal locations of said reference marks to said processing head coordinates of the sensed locations of said reference marks;
• and
• (c) controlling said processing operation in accordance with at least one of said geometrical transformations.