Clover-shaped stamping offers precise positioning

DN Staff

September 18, 2000

3 Min Read
Clover-shaped stamping offers precise positioning

Able to generate a linear stroke as large as 25% of its outer diameter, the Clover/ Disc(TM)will accurately position any attached components or mechanism. Designing it into hydraulic or pneumatic controls will cause valves to snap open or closed at a precise value or pressure.

Three interconnected elements, spaced 120 degrees about a center aperture, comprise the flat stamping. When the stamping, or disc, is pushed onto a cylindrical shaft or bearing, the elements stress equally to form a dome. Mechanical interference between shaft diameter and center aperture determines spring characteristics, while a V-shaped groove in the shaft positions the assembly.

Clover/Disc, say its developers, provides both radial and longitudinal spring characteristics difficult to achieve in conventional disc-spring technology. The combination of high radial and low longitudinal spring rates offers a wide range of potential applications for switches, valves, fasteners, motors, and pumps. Other performance characteristics include:

Choice of materials. While 17-7 PH stainless steel or BeCu alloys are used in most applications, the disc can be stamped from almost any material.

Low spring rates. The Clover/Disc is said to be capable of deflecting six to eight times more than a Belville washer. Spring ratio is 10 to 15 times that of a comparable size Belville washer.

Linear force/displacement. Force vs displacement gradually increases until the point of snap, where the curve abruptly reverses to an equal negative value with little or no hysteresis.

Monostable operation. Applying bias to the hub portion makes the Clover/Disc snap back after it snaps over center.

Long life .In simple back-and-forth flexing applications such as a linear bearing, mechanical life can exceed millions of cycles.

Production uniformity. After stressing to become snap acting, force values measured at 75% deflection repeat within a few percent part-to-part. Material thickness tolerance and dimensional accuracy of the disc aperture/shaft diameter are the limiting factors.

Clover/Disc technology is available for license from Schwab-Koplin Associates, e-mail THGMeade@ mindspring.com.

Tracing the technology

Clover/Disc has its origins in the M-blade snap-action switch, configured here as a circuit breaker. Also stamped from a flat thin sheet of metal, the M-blade responds to mechanical stressing for bistable operation.

Clover/Disc Configurations -- Three basic Clover/Disc styles accommodate the boradest range of application. The Full Disc -- good for fasteners and latching components, as well as inexpensive force or pressure sensors -- has a diameter which expands and contracts with every over-center snap action. The Involute and Knee Disc configurations allow Clover/Disc expansion/contraction when mounted line-to-line or with a light interference fit. These styles are used when concentricity between center and OD is critical, as in motor or solenoid armatures. The Involute Disc offers a higher spring rate than the Knee Disc for an equal amount of throw or compression.

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