Abstract: A braiding machine of the maypole form having co-acting horngear assemblies positioned in a cylindrical housing and arranged to drive spool carriers along a double undulating and intersecting drive track groove as groups in opposed directions. The form of the groove is such as to avoid discontinuities both in normal and in tangential components of acceleration forces on the spool carriers. Drive is transmitted from the horngear assemblies to the spool carriers by drive forks each carried on a pivot shaft mounted for oscillating rotation through restricted arc on the respective horngear assembly. Oscillating rotation of the drive forks is effected by a cam follower arrangement engaging a cam track such that the drive forks propel the spool carriers along the guide track groove with constant or substantially constant linear velocity.

Abstract: A method and apparatus is described for performing automatic overlay measurements on wafers utilized in semiconductor manufacturing. The overlay measurements are made at selected sites on a given wafer where a single bar pattern has been overlaid over a double bar pattern. The position of the single bar center line with respect to the center line between the double bars is a direct indication of the overlay error of the two patterns. The overlay error is measured in both the X and Y dimensions and is utilized to monitor the overlay error or to produce statistics and correlations to system parameters so that the sources of overlay errors may be identified and the errors eliminated or minimized on subsequent wafers being processed.