The present invention relates to magnetically actuated motion control device. In particular the present invention relates to magnetically actuated motion control devices that vary contact pressure between a first member and a second member in accordance with a generated magnetic field.
Magnetically actuated motion control devices such as magnetically controlled dampers or struts provide motion control, e.g., damping that is controlled by the magnitude of an applied magnetic field. Much of the work in the area of magnetically controlled dampers has focused on either electrorheological (ER) or magnetorheological (MR) dampers. The principle underlying both of these types of damping devices is that particular fluids change viscosity in proportion to an applied electric or magnetic field. Thus, the damping force achievable with the fluid can be controlled by controlling the applied field. Examples of ER and MR dampers are discussed in U.S. Pat. Nos. 5,018,606 and 5,384,330, respectively.
MR fluids have high yield strengths and viscosities, and therefore are capable of generating greater damping forces than ER fluids. In addition, MR fluids are activated by easily produced magnetic fields with simple low voltage electromagnetic coils. As a result, dampers employing MR fluids have become preferred over ER dampers.
Because ER and MR fluid dampers still involve fluid damping, the dampers must be manufactured with precise valving and seals. In particular, such dampers typically require a dynamic seal and a compliant containment member which are not particularly easy to manufacture and assemble. Further, the fluid type dampers can have significant xe2x80x9coff-statexe2x80x9d forces which can further complicate manufacture and assembly. Off-state forces refer to those forces at work in the damper when the damper is not energized.
The foregoing illustrates limitations known to exist in 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.
According to one aspect of the invention, a magnetically actuated motion control device is provided. The magnetically actuated motion control device includes a housing, and movable member and a magnetic field generator located on either the housing or the movable member. The housing defines a cavity in which the movable member is located and includes at least one slot. A magnetic field applied by the field generator causes the housing to press against the movable member and thereby provide friction damping.
According to another aspect of the invention, a sensor for sensing the position of a movable member relative to a housing of a magnetically controlled damper is provided. The sensor includes a first member secured to the housing, a second member, such as a slide, that is coupled to the movable member so that the relative position of the first member and the second member relates the position of the movable member within the housing. According to an exemplary embodiment, the movable member can include a depression for receiving an extension on the second member of the sensor. The extension of the second member fits through a slot in the housing and into the depression to couple the second member of the sensor to the movable member. In another embodiment, the second portion of the sensor can be configured so as to be in rolling contact with the movable member. In this embodiment, relative rotation between the first member and the second member indicates relative motion between the movable member and the housing.
The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawing figures.