Method and apparatus for precision control of linear motors and the like employing a closed loop technique

A method for operating a dual axis linear motor along the surface of a platen having mutually perpendicular sets Serial No. 077,112 of grid lines for forming an orthogonal matrix of teeth cooperating with the first and second mutually perpendicular forcer means of said linear motor, said method comprising the steps of:

• providing one of said sets of grid lines with a reflectivity characteristic which is different from the reflectivity characteristic of the remaining one of said sets of grid lines and so that the directions of the light beams are substantially orthogonal to one another;
• directing first and second light beams from said linear motor toward the surface of said platen containing said grid lines;
• receiving the light beams reflected from said platen surface at two independent locations;
• and
• generating a grid line passage signal for each light beam only when the reflected light falls within a predetermined range of signal strength for each light source, said threshhold ranges being non-overlapping to differentiate between the two sets of orthogonal grid lines.

Apparatus for accurately verifying the movement of linear motors and the like, said linear motors having first and second forcer means, said controlling means comprising:

• a platen formed of a magnetic material and having first and second sets of parallel, uniformly spaced grooves formed in the platen surface for defining an orthogonal matrix of teeth;
• first sensor means arranged on said linear motor for detecting said grid lines and including means for generating a signal indicative of the presence of a grid line of only one of said sets of grid lines to the exclusion of the remaining one of said sets;
• second sensor means for generating a signal representing the passage of only the remaining ones of said grid lines to the exclusion of said first set of said grid lines;
• Serial No. 077,112
• a transparent sheet having first and second sets of uniformly spaced parallel grid lines formed on one surface of said transparent sheet and being perpendicular to one another, the spacing between the grid lines of said first and second sets being respectively substantially equal to the spacing between the grooves provided in said platen;
• said first set of grid lines being of a different color than said second set of grid lines;
• said sheet being provided with openings each bound by a pair of said first set of grid lines and a pair of said second set of grid lines, each opening being of a shape and size sufficient to each receive an associated one of said platen teeth so that the top surfaces of said teeth as well as the exposed surface of said transparent sheet collectively form the top surface of said platen assembly.

A platen for use with linear motors formed of a magnetic material and having first and second sets of parallel, uniformly spaced grooves formed in the platen surface for defining an orthogonal matrix of teeth;

• Serial No. 077,112
• a transparent sheet having first and second sets of uniformly spaced parallel grid lines formed on one surface of said transparent sheet and being perpendicular to one another, the spacing between the grid lines of said first and second sets being respectively substantially equal to the spacing between the grooves provided in said platen;
• said first set of grid lines being of a different color than said second set of grid lines;
• said sheet being provided with openings each bound by a pair of said first grid line and a pair of said second set of grid lines, each opening being of a shape and size sufficient to each receive an associated one of said platen teeth so that the top surfaces of said teeth as well as the exposed surface of said transparent sheet collectively form the top surface of said platen assembly.