Curl spring shoe based window balance system
CA 2119506 C · Owner: Westfall, Norman R. · Inventors: Westfall, Norman R.
Overview
Its claims, description and drawings are in the Canadian Patents Database.
Open the CIPO recordAbstract From the Canadian patent
A window balance system for a tilt sash uses a pair of constant force curl springs having curled convolutions carried by sash shoes and free end regions mounted in sash shoe channels above the region of travel of the shoes. The recurl tendency of the springs imparts a lift to the curled spring convolutions and the shoes transmit the lift to the sash. The springs recurl into the convolutions as the shoes rise and uncurl from the shoes into the shoe channels when the shoes move downward and neither movement requires the springs to slide frictionally within the shoe channels. Each shoe is preferably formed of two identical halves that are assembled to trap the curl spring along with a cam that …
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Listed from its CIPO record in Patent Yard's archive of Canadian patents past their term. Its claims, description and drawings are in the CIPO record and on Google Patents, and the Claude kit works from them.
Why it's free to use
- Filed March 21, 1994 and granted February 4, 1997. A Canadian patent filed from October 1, 1989 lasts 20 years from filing, so its term ended March 21, 2014.
- A certificate of supplementary protection adds at most two years for a drug, so even that would have ended by March 21, 2016.
- We check Canadian rights only. A patent in its family in another country could still be in force: check its family on Google Patents.
Timeline
Timeline From CIPO dates
Sources & verification
Official CIPO records
Everything on this page comes from the CIPO record linked above. Contains information licensed under the Open Government Licence – Canada.