US 5,102,196 · Granted 1992-04-07
The Dual-Shell Chair Design That Freed Office Furniture From Its Own Rigidity
Imagine a chair with two shells — one inside, one outside — that work together like a team. This patent unlocks the ability to make office chairs that are both strong and flexible at the same time, giving designers way more freedom to create comfortable, stable seats without sacrificing either quality.
The plain-English version
What it protects
The claim covers a chair structure built from two integral L-shaped shells (an inner and outer shell) that form both the seat and backrest as one connected piece. What's protected is the specific way these shells are positioned and supported — using brackets, special claws, and inclined bolts — so they can shift slightly relative to each other while staying bonded. The design also covers the fixed shell component that prevents gaps from forming and the balancing mechanism that lets the backrest flex without making the user feel unstable.
Why it matters
Before this patent, office chair designers faced a tough trade-off: make the inner shell alone do all the structural work, and you're limited in how flexible or stylish you can make it. Kokuyo's innovation splits the job between two shells, letting the outer shell contribute to both strength and aesthetic freedom while the inner shell handles support. This represented a significant advance in how office furniture could be engineered, giving manufacturers the tools to design chairs that were simultaneously durable, comfortable, and visually distinctive.
Real-world use
When you sit in an office chair and lean back, feeling it give slightly before settling into a firm position, you're experiencing the result of this dual-shell flexibility — the outer and inner shells moving in precise harmony to absorb your weight.
Original USPTO abstract
A chair provided with a backrest for use in offices, etc., comprising an inner shell (2) and an outer shell (3). Conventional chairs of this type have a problem that there is little freedom in design with respect to strength and flexibility since only the inner shell serves as a structural member. An object of this chair is to increase the freedom. To this end, in the chair of this invention, the outer shell (3) as well as the inner shell (2) are formed as an integral body L-shaped in side view and comprising a seat portion (31) and a backrest portion (32), so that a three-dimensional shell structure is formed. In this chair, various measures are taken to solve the problem caused by the outer shell which is formed into an integral body. First, a fixed shell (6) is adopted for preventing a gap from being formed. Also, to obtain a required resiliency the shells (2, 3) are of such a construction as to allow a positional shift between the shells, and the inner shell (2) is supported by two brackets (118, 119). In order not to make the user feel uneasy upon resilient deformation of the shells, they are so constructed that the brackrest point (d) can be suitably shifted. Moreover, to connect the shells properly claws, (302, 602) of a particular type and inclined bolts (355) are used. Also, to make a mechanism to be provided between the shells (2,3) as compact as possible, the balancing members (101) support a backrest support (104).
Patent details
- Publication number
- US 5,102,196
- Filing date
- 1988-10-24
- Grant date
- 1992-04-07
- Assignee
- Kokuyo Co., Ltd.
- Inventor(s)
- KANEDA; SHINICHI, SUZUKI; YOICHI, SUGANO; TAKAO, MIYASHITA; MASAMITU, ITO; TUNETARO, KATAGIRI; MIYOSHI
- CPC class
- A47C3/12
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