You can freely build on How Laser Printers Use Rotating Mirrors to Write Information
This patent expired in 1992. Every claim — 0 independent, 1 dependent — is now unenforceable. Anyone can use, reproduce, manufacture, sell, or offer for sale this technology without a license.
Original assignee
Xerox Corp
Patent granted
1975
Expired
1992
Forward citations
22
What this patent covers
This system uses a laser to project a tiny, high-intensity spot of light onto a light-sensitive surface, like a drum in a printer. A multifaceted rotating polygon mirror reflects this beam, sweeping it across the surface to create a line of information. Because the beam moves faster in the middle of a scan than at the edges, the system uses a function generator to speed up or slow down the data transmission rate (the bit rate) to match the spot's velocity. This ensures the printed image remains uniform and does not look stretched or distorted.
What is now free to use
All 1 claims of US 3867571 are in the public domain. Specifically:
The 1 dependent claim add narrowing limitations and are also free.
What is NOT covered
Patent expiry frees this specific invention. Separately-patented improvements made after expiry may still be protected.
Does not cover non-laser light sources that lack collimated, uniform intensity.
Does not cover scanning systems that use a fixed data rate regardless of the spot's velocity.
Does not cover systems that lack a multifaceted rotating polygon for beam deflection.
Does not cover digital image processing or software-based image correction.
Who is building on this today
Xerox pioneered this, but the technology was quickly adopted and refined by companies like HP, Canon, and Brother, who dominated the office printer market for decades. Today, the core principles remain in use for high-end industrial laser marking and specialized printing hardware.
Products built on expired version of this technology
Early Xerox laser printers
Standard office laser printers
Laser-based barcode scanners
Laser-based phototypesetting equipment
How to cite this patent in your documentation
Xerox Corp. US Patent 3867571. Flying spot scanner. Granted 1975, expired 1992. Now in the public domain.
Note: This is a convenience citation. Consult a patent attorney for formal freedom-to-operate analysis.
PatentBrief is an educational resource and does not provide legal advice. Patent expiration information is derived from USPTO records and may not reflect continuation patents, divisional filings, or separately-patented improvements. For commercial use or production decisions, obtain a formal freedom-to-operate (FTO) opinion from a registered patent attorney.