Brakes – Operators – Electric
Reexamination Certificate
1997-10-29
2001-02-13
Graham, Matthew C. (Department: 3613)
Brakes
Operators
Electric
C188S161000
Reexamination Certificate
active
06186290
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the area of braking, resistance generating, and motion control devices. Specifically, it relates to devices employing a controllable medium for motion resistance generation in rotating mechanisms.
BACKGROUND OF THE INVENTION
Magnetorheological (MR) devices for damping and controlling vibration and shock are known. MR devices may be of the “rotary-acting” or “linear-acting” variety, and can advantageously provide variable controlled torques or forces, as the case may be. Known MR devices include linear dampers, rotary brakes, and rotary clutches.
MR fluid devices, for example, typically include a housing or chamber that contains a quantity of magnetically controllable fluid, with a movable member, a piston or rotor, mounted for movement through the fluid in the housing. The housing and the movable member both include a magnetically permeable pole piece. A magnetic field generator (a coil or permanent magnet) produces a magnetic field across both pole pieces for directing the magnetic flux to desired regions of the controllable fluid.
MR fluid devices employ a Magnetorheological (MR) fluid comprised of soft-magnetic particles dispersed within a liquid carrier. Typical particles include carbonyl iron, and the like, having various shapes, but which are preferably spherical and have mean diameters of between about 0.1 &mgr;m to about 500 &mgr;m. The carrier fluids include low viscosity hydraulic oils, and the like. In operation, these MR fluids exhibit a thickening behavior (a rheology change) upon being exposed to a magnetic field. The higher the magnetic field strength in the fluid, the higher the damping/restraining force or torque that can be achieved within the MR device.
MR fluid devices are disclosed in U.S. patent application Ser. No. 08/304,005 entitled “Magnetorheological Fluid Devices And Process Of Controlling Force In Exercise Equipment Utilizing Same”, U.S. patent application Ser. No. 08/613,704 entitled “Portable Controllable Fluid Rehabilitation Devices”, U.S. application Ser. No. 08/674,371 entitled “Controllable Brake”, U.S. patent application Ser. No. 08/674,179 entitled “Controllable Vibration Apparatus” and U.S. Pat. Nos. 5,547,049, 5,492,312, 5,398,917, 5,284,330, and 5,277,281, all of which are commonly assigned to the assignee of the present invention.
U.S. Pat. No. 3,962,595 to Eddens discloses a “Magnetic Particle Brake”, commonly referred to as “Dry Particle Brakes” that includes a rotating member that is disposed in an annular space in a stationary member. A field-generating coil is mounted in an outer part of the stationary member. Magnetic particles are disposed in a space between the inner part of the stationary member and the rotating member. Other magnetic particle brakes are disclosed in U.S. Pat. No. 4,350,913 to Eddens and U.S. Pat. No. 4,575,103 to Pedu.
Exercise machines such as stationary bicycles, rowers, stair climbers, and ski machines, typically rely on some kind of resistance generating device to provide adjustable resistance to the exercise movements of the user. Conventional resistance systems used in exercise machines, for example, friction devices, have deficiencies in providing reliable control of the resistance setting and in duration over repeated use of the machine. Before the present invention, however, there has been no resistance device for exercise machines using MR technology to replace conventional resistance devices and provide improved performance, reliability and endurance characteristics.
The foregoing illustrates limitations known to existing present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.
SUMMARY OF THE INVENTION
The present invention provides a Magnetorheological (MR) device which combines a rotary brake with a flywheel thereby providing both resistance and rotational inertia, and can be used in an exercise apparatus and/or as a brake for rotating equipment and vehicles.
According to a preferred embodiment of the invention, a rotary brake device comprises an outer rotating member having a hollow interior space and an inner stationary member disposed in the hollow space. The rotating member, or rotor, rotates around the stationary member, or stator, an arrangement contrary to conventional practice. The stator is sized so that a small working space exists between the inner wall of the rotor and the peripheral surface(s) of the stator. The stator supports a field generating device, preferably a magnetic field producing coil. A controllable medium (a MR fluid or dry powder) is disposed in the working space so that the medium can be acted upon by the field generating device. In addition, each of the rotor and the stator is made to include a magnetically permeable portion that acts as a pole piece. Rotation of the rotor distributes the controllable medium about the inner circumference of the rotor.
Thus, according to the invention, resistance to rotation can be generated and preferably controlled by applying a magnetic field to the pole pieces and to the controllable medium in the working space. The field causes the controllable medium to thicken (a rheology change), which produces the resistance to rotation of the rotor relative to the stator.
The inventor has discovered that a controllable medium of dry powder of magnetically permeable material, such as carbonyl iron, provides a significantly high resistance force. A controllable medium formed of 410 stainless steel powder of 325 mesh particles (less than 45 microns in diameter) has been found to be particularly effective in a brake according to the invention, and has endured a test program of sixteen million cycles without failure.
The controllable medium optionally can be formed of soft-magnetic material particles included in a low-viscosity carrier of hydraulic oil.
The flywheel resistance device of the invention can be incorporated in exercise devices, such as bicycles, rowing machines, step machines, and ski machines to provide controllable, variable resistance, or in other devices/apparatus where it is desirable to have combinations of rotational inertia and resistance.
Alternatively, a device in accordance with the invention may be formed as a stationary shaft disposed in a tubular outer member, which may be useful as a brake for a conveyor system or a resistance device for a ski machine, for example.
The above-mentioned and further features, advantages, and characteristics of the present invention will become apparent from the accompanying descriptions of the preferred embodiments and attached drawings.
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Magnetic Power Systems, Inc.'s Brochure re: FASTEP Magnetic Particle Clutche
Gnibus Michael M.
Graham Matthew C.
Lord Corporation
Wayland Randall S.
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