1
Steven H Drucker: Method and apparatus for self-referencing and self-focusing a bar-code reader. Quential, A C Smith, April 4, 1989: US04818886 (64 worldwide citation)

A scanning device and method for reading bar code or other contrasting marks from a surface at a variable distance from the scanning device operates by modulating the focal point of the optical system to yield pulse responses on detected code bars while in focus, and average background response leve ...


2
Steven H Drucker: Method and means for self-referencing and self-focusing a bar-code reader. Quential, A C Smith, May 16, 1989: US04831275 (53 worldwide citation)

A scanning device and method for reading bar-code or other contrasting marks from a surface at variable distance from the scanning device operates by modulating the focal point of the optical system to yield pulse responses on detected code bars while in focus, and average background response levels ...


3
Drucker Steven H: Improved method and means for self-referencing and self-focusing a bar-code reader.. Quential, May 18, 1988: EP0267549-A2 (9 worldwide citation)

A scanning device and method for reading bar code or other contrasting marks from a surface (2) at a variable distance from the scanning device (11, 9) operates by modulating the focal point of the optical system (9) to yield pulse responses on detected code bars while in focus, and average backgrou ...


4
Drucker Steven H: Methode et dispositif dauto-etalonnage et dautofocalisation pour lectuer de codes a barres, Method and means for self-referencing and self-focusing a bar-code reader. Drucker Steven H, Quential, SIM & MCBURNEY, November 12, 1991: CA1292069

Abstract of the Disclosure A scanning device and method for reading bar code or other contrasting marks from a surface at a variable distance from the scanning device operates by modulating the focal point of the optical system to yield pulse responses on detected code bars while in focus, and avera ...