Damping devices are widely used (e.g., in airplane landing gear, automobile suspension systems, earthquake-proof buildings, and optical tables) to reduce vibration and noise, thus improving comfortableness, prolonging machine lives, increasing production quality, and even avoiding catastrophes. People are developing various dampers that can be electronically-controlled for the sake of improved performance.
There is a family of damping devices that utilizes electrorhoelogical (ER) fluids. When exposed to an electric field, an ER fluid changes its rheological properties, most noticeably its viscosity, with a fast response time. ER damping devices can be classified into flow-mode, mixed-mode, and shear-mode dampers according to the source of damping force. The source of damping force is a flow-induced pressure drop for a flow-mode damper, shearing forces on relatively-shearing surfaces for a shear-mode damper, and a mixture of a pressure drop and shearing forces for a mixed-mode damper.
Among the three modes, the ER flow-mode design is most similar to the design of a traditional shock absorber of a vehicle suspension system except that it replaces the conventional orifice with an ER valve. To achieve the same performance, an ER flow-mode damper is believed to be not as compact and not as efficient as an ER shear-mode damper. To achieve the same ER damping force, an ER mixed-mode damper is believed to be more compact than an ER shear-mode damper. However, the ER mixed-mode damper is believed to be not as effective in control as the ER shear-mode damper.
Shear-mode dampers can be further divided into rotary and translational types, either of which can have its own variations in the way electrodes are arranged. The translational type of shear-mode dampers, for example, can have either a plurality of coaxial cylinders or a plurality of parallel perforated-disk-shaped plates as electrodes. Because of the stroke of the translational motion, not all surface area of the electrodes is engaged to generate damping forces, resulting in an inefficiency in design.
The rotary type of shear-mode dampers can have a plurality of perforated-disk-shaped electrodes arranged along the rotational axis or have a plurality of coaxial cylinders. These dampers are able to rotate in complete circles, and the entire surface area of the electrodes is engaged for the damping force generation. One may call them complete-circle rotary-type shear-mode dampers. A rotary-type shear-mode damper may also consist of a plurality of fan- or blade-shaped (instead of perforated-disk-shaped) electrodes, and the electrodes can rotate less than a complete circle. For the sake of distinction, one may call this kind of dampers incomplete-circle rotary-type shear-mode dampers. With a rotary-type damper, a translation-to-rotation conversion mechanism is needed if the vibration to be damped is translational.
Several ER flow-mode damping devices are disclosed in U.S. Pat. No. 4,720,087, U.S. Pat. No. 4,858,733, U.S. Pat. No. 5,000,299, U.S. Pat. No. 5,029,677, U.S. Pat. No. 5,100,166, U.S. Pat. No. 5,014,829, U.S. Pat. No. 5,161,653, and U.S. Pat. No. 5,259,487. Also disclosed in U.S. Pat. No. 5,029,677 is an ER mixed-mode damping device. They are all different from the present invention, which has a shear-mode design.
A family of rotary damping devices that utilize electrorheological magnetic (ERM), also called magnetorheological (MR), fluids are disclosed in U.S. Pat. No. 4,942,947 and U.S. Pat. No. 5,257,681. They are also different from the present invention. ERM or MR fluids respond to a magnetic field while ER fluids respond to an electric field. ERM or MR dampers need relatively complicated magnetic coils while ER dampers need only simple electrodes. The ERM or MR dampers disclosed in U.S. Pat. No. 4,942,947 and U.S. Pat. No. 5,257,681 have an incomplete-circle rotary mixed-mode design, while the present invention uses a complete-circle rotary shear-mode design.
There are also several known ER full-circle rotary shear-mode damping devices. Carlson and Duclos (Carlson, J. D., and Duclos, T. G., 1990, "ER fluid clutches and brakes-fluid property and mechanical design considerations," Electrorheological Fluids, Proceedings of the Second International Conference on ER Fluids-1989, Carlson, J. D., Sprecher, A. F., and Conrad, H., ed., Technomic Pub. Co., Inc., Lancaster, pp.353-367.) disclosed a screwdriver that includes an ER full-circle rotary shear-mode clutch and a magnetic rotation-to-rotation coupling. Stangroom (Stangroom, J. E., 1990, "Tension control using ER fluids--a case study," Electrorheological Fluids, Proceedings of the Second International Conference on ER Fluids--1989, Carlson, J. D., Sprecher, A. F., and Conrad, H., ed., Technomic Pub. Co., Inc., Lancaster, pp.419-425.) disclosed a tension control device that includes an ER full-circle rotary shear-mode clutch. Colvin and Carlson (Colvin, D. P., and Carlson, J. D., 1990, "Control of a fall safe tether using an ER fluid brake," Electrorheological Fluids, Proceedings of the Second International Conference on ER Fluids-1989, Carlson, J. D., Sprecher, A. F., and Conrad, H., ed., Technomic Pub. Co., Inc., Lancaster, pp.426-436.) disclosed a fall-safe tether that includes an ER full-circle rotary shear-mode clutch. None of the just mentioned ER full-circle rotary shear-mode damping devices is intended/designed to reduce translational vibration, which a vehicle suspension system or aircraft landing gear has to deal with. None of the just mentioned ER full-circle rotary shear-mode damping devices, therefore, has an integrated spring element and the mechanism for the motion conversion between rotation and translation, which are included in the present invention.