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Self-cleaning litter box
U.S. Patent 6,055,910 · 2000
From the abstract
A self-cleaning litter box including a generally spherical chamber rotatably mounted to a base, the chamber containing litter and being rotatable about a horizontal axis to separate clumped waste from clean litter through internal screening structures.
Note
Prior art for what eventually became the Litter-Robot, the spherical rotating cat toilet that costs $700 and that millions of cat-owners now consider non-negotiable. The mechanical idea — a rotating sphere with internal screens that separate clumps from clean substrate — is essentially unchanged in modern products. The patent's drawings, especially Figure 4, are minor masterpieces of cross-sectional engineering art.