Patent Publication Number: US-2010122881-A1

Title: System comprising magnetically actuated motion control device

Description:
This application is a divisional of pending U.S. patent application Ser. No. 10/809,084, filed Mar. 25, 2004, which is a continuation-in-part of U.S. patent application Ser. No. 10/647,554, filed Aug. 25, 2003, now U.S. Pat. No. 7,243,763, which is a divisional of U.S. patent application Ser. No. 10/080,293, filed Feb. 20, 2002, now U.S. Pat. No. 6,640,940, which was a divisional of U.S. patent application Ser. No. 09/537,365, filed Mar. 29, 2000 now U.S. Pat. No. 6,378,671, all of which the benefit is claimed herein and incorporated by reference. 
    
    
     FIELD OF THE INVENTION  
     The present invention relates to magnetically actuated motion control devices. 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. 
     BACKGROUND AND RELATED ART 
     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 “off-state” 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. 
     SUMMARY OF THE DISCLOSURE 
     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. 
     The invention includes a magnetically actuated motion control device. The magnetically actuated motion control device is preferably comprised of a first housing member defining a cavity with the first housing member including a movable flexible finger. The magnetically actuated motion control device is preferably comprised of a second member positioned within the first housing member cavity with the first housing member movable relative to the second member with a magnetic field generator located on the second member. The magnetic field generator causes the movable flexible finger to press against the second member to produce frictional damping. In a preferred embodiment the second member is a stator having a center axis with the stator and the first housing being relatively rotatable around the central axis. Preferably the housing encircles the second member with the housing relatively rotatable around the second member. 
     The invention includes a magnetically actuated motion control device. The magnetically actuated motion control device is preferably comprised of a first housing member defining a cavity with the first housing member including a movable flexible finger. The magnetically actuated motion control device is preferably comprised of a second member positioned within the first housing member cavity. The second member is movable relative to the first member with a magnetic field generator located on the second member. The magnetic field generator causes the movable flexible finger to press against the second member to produce frictional damping. In a preferred embodiment the second member is a stator having a center axis with the stator and the first housing being relatively rotatable around the central axis. Preferably the housing encircles the second member with the second member relatively rotatable within the stationary housing. Preferably the first housing member and its movable flexible finger are rotationally stationary with the second inner member stator rotating within the first housing member and its movable flexible finger. 
     The invention includes a magnetically actuated motion control device comprised of a first housing member including a cavity formed therein and including a movable finger; and a second member disposed in the cavity; and at least one magnetic field generator mounted to cause the movable finger to be displaced toward the second member and thereby squeeze the second member. In a preferred embodiment the first housing member has an outer perimeter and includes a shaft, with the cavity for receiving the second member between the outer perimeter and the shaft. 
     The invention includes a method of controlling relative motion between a housing and a second member. The housing has a finger, with the housing and finger movable relative to the second member, and the housing defining a cavity in which the second member is located. The invention includes generating a magnetic field and pressing the finger against the second member in accordance with the generated magnetic field. 
     The invention includes a method of controlling relative motion between a housing and a rotating second member. The housing has a finger, with the housing and finger rotationally stationary. Preferably the second member is rotatably movable relative to the housing and finger, with the housing defining a cavity in which the second member is located. The invention includes generating a magnetic field and pressing the finger against the rotating second member in accordance with the generated magnetic field. 
     The invention includes a system with a magnetically actuated motion control device. The motion control device of the system has a finger that frictionally engages a circular stator to control a rotational motion of the system. Preferably the magnetically actuated motion control device is coupled to a shaft with a wheel, with the circular stator or the housing being rotatable relative to the shaft. In a preferred embodiment the wheel and is comprised of a control knob. Preferably the system includes a rotational sensor that tracks rotation and a magnetic field generated by the stator moves the finger to make a rotational end stop. 
     The invention includes a vehicle with a body and a door. The door is attached by a hinge to the body frame. The invention includes a magnetically actuated motion control device housing mounted between the door and the body to magnetically control a movement of the door relative to the body. A second member stator is received in a cavity inside the housing. A rotary position sensor is mounted with the housing to sense rotational movement of the device and the hinge. The second member stator has a center axis, with the stator and the housing being relatively rotatable around the central axis. Preferably the housing includes a shaft oriented with the central axis, with the shaft directly coupled to a rotating shaft of the hinge. In a preferred alternative the housing includes a shaft oriented with the central axis, with the shaft indirectly coupled to a rotating shaft of the hinge. In a preferred embodiment the housing and its movable finger are rotationally stationary with the second member stator rotationally received within the housing cavity such that the second member inner stator rotates relative to the stationary housing with the movable finger magnetically actuated into contact with the rotating second member inner stator to control rotation of the second member inner stator and the motion of the door relative to the vehicle body. 
     The invention includes a body frame and a door with the door being attached by a hinge to the body frame and a magnetically actuated motion control device with a first housing member defining a cavity. The first housing member includes a movable finger and a second member positioned within said first housing member cavity, with the second member movable relative to the first housing member. The second member includes a magnetic field generator with the magnetic field generator causing the movable finger to press against the second member to produce frictional damping with the magnetically actuated motion control device mounted to control a positioning of the door relative to the body frame. In a preferred embodiment the housing and its movable finger are rotationally stationary with the second member stator rotationally received within the housing cavity such that the second member inner stator rotates relative to the stationary housing with the motion on the door relative to the body frame at the hinge, with the movable finger magnetically actuated into contact with the rotating second member inner stator to control rotation of the second member inner stator and the motion of the door relative to the vehicle body frame. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The objects and advantages of the invention will be understood by reading the following detailed description in conjunction with the drawings in which: 
         FIG. 1  is a cutaway side sectional view of a first exemplary embodiment of the present invention. 
         FIG. 2  is an end sectional view taken along section  2 - 2  in  FIG. 1 . 
         FIG. 3A  is a side view of a housing according to a second exemplary embodiment of the present invention. 
         FIG. 3B  is an end sectional view taken along section  3 - 3  in  FIG. 3A . 
         FIG. 4A  is a side view of a housing according to a third exemplary embodiment of the present invention. 
         FIG. 4B  is an end sectional view taken along section  4 - 4  in  FIG. 4A . 
         FIG. 5A  is a side view of a housing according to a fourth exemplary embodiment of the present invention. 
         FIG. 5B  is an end sectional view taken along section  5 - 5  in  FIG. 5A . 
         FIG. 6  is a cutaway side sectional view of a fifth exemplary embodiment of the present invention. 
         FIG. 7  is a cutaway sectional view of a sixth exemplary embodiment according to the present invention. 
         FIG. 8  is a cutaway side sectional view of a seventh exemplary embodiment according to the present invention. 
         FIG. 9  is a side cutaway sectional view of an eighth exemplary embodiment of the present invention. 
         FIG. 10  is a cutaway side sectional view of a ninth exemplary embodiment of the present invention. 
         FIG. 11  is a graph showing the relationship between damping force and current for a damper constructed in accordance with the present invention. 
         FIG. 12  is a perspective view of a tenth exemplary embodiment of the present invention. 
         FIG. 13  is a perspective exploded view of the embodiment shown in  FIG. 12 . 
         FIG. 14  is a side view of an embodiment of the present invention including an outer layer of acoustically insulating material. 
         FIG. 15  is a cutaway side sectional view of an eleventh embodiment of the present invention. 
         FIG. 16  is an end sectional view taken along section  17 - 17  in  FIG. 15 . 
         FIG. 17  is an exploded perspective view of the embodiment shown in  FIGS. 15 and 16 . 
         FIG. 18  is a cutaway side sectional view of a twelfth exemplary embodiment according to the present invention. 
         FIG. 19  is a cutaway side sectional view of a thirteenth exemplary embodiment according to the present invention. 
         FIG. 20  is a cutaway side sectional view of a fourteenth exemplary embodiment according to the present invention. 
         FIG. 21  is a cutaway side sectional view of a fifteenth exemplary embodiment according to the present invention. 
         FIG. 22  is an end sectional view taken along section  23 - 23  in  FIG. 21 . 
         FIG. 23  is a schematic illustration of a washing machine employing an embodiment of the present invention. 
         FIG. 24  is a schematic illustration of an embodiment of the present invention used in an automobile, truck, or other vehicle. 
         FIG. 25A  is a schematic illustration of an embodiment of the present invention used as a damper in a chair. 
         FIG. 25B  is a schematic illustration of an embodiment of the present invention being used to control the tilt of the chair shown in  FIG. 25A . 
         FIG. 26  is a schematic illustration of a height adjustable table employing an embodiment of the present invention. 
         FIG. 27A  is a schematic illustration of an embodiment of the present invention used for locking a tilting door. 
         FIG. 27B  is a schematic illustration of an embodiment the present invention used for locking a tilting work surface. 
         FIG. 28  is a side schematic illustration of an embodiment of the present invention used as a rotary brake in a force feedback steering wheel. 
         FIG. 29  is a schematic side sectional illustration of a computer pointing device employing an embodiment of the present invention as rotary brakes. 
         FIG. 30  is a schematic side sectional illustration of an active force feedback steering wheel employing an embodiment of the present invention as a brake. 
         FIG. 31  is a schematic illustration of a device for holding irregular objects employing an embodiment of the present invention. 
         FIG. 32  is a cutaway side sectional view of a sixteenth exemplary embodiment according to the present invention. 
         FIG. 33  is a cutaway side sectional view of a seventeenth exemplary embodiment according to the present invention. 
         FIG. 34  is a cutaway side sectional view of an eighteenth exemplary embodiment according to the present invention. 
         FIG. 35A  is a schematic side sectional view of a nineteenth exemplary embodiment according to the present invention. 
         FIG. 35B  is a sectional view taken along section  36 - 36  in  FIG. 35A . 
         FIG. 36A  is a side view of the housing according to the embodiment shown in  FIG. 35A . 
         FIG. 36B  is an end view of the housing shown in  FIG. 36B . 
         FIG. 37A  is a side view of a housing according to a twentieth exemplary embodiment according to the present invention. 
         FIG. 37B  is an end view of the housing shown in  FIG. 37A . 
         FIG. 38  is a side sectional view of a twenty-first exemplary embodiment of the present invention. 
         FIG. 38A  is a partial view of the housing of  FIG. 38 . 
         FIG. 39  is a side sectional view of the embodiment shown in  FIG. 38  in an on-state. 
         FIG. 39A  is a partial view of the housing of  FIG. 39 . 
         FIG. 40A  is a sectional view taken along section  41 - 41  in  FIG. 39 . 
         FIG. 40B  is a perspective view of a spring in the embodiment shown in  FIG. 40A . 
         FIG. 40C  is a perspective view of a bearing in the embodiment shown in  FIG. 40A . 
         FIG. 41  is a cutaway side sectional view of a twenty-second exemplary embodiment according to the present invention. 
         FIG. 42  is a cutaway side sectional view of a twenty-third embodiment according to the present invention. 
         FIG. 43  is a schematic view of the embodiment shown in  FIG. 38  employed in a car door. 
         FIG. 44A-C  show embodiments of the invention. 
         FIG. 45A-D  show embodiments of the invention. 
         FIG. 46A-C  show embodiments of the invention. 
         FIG. 47A-B  show embodiments of the invention. 
         FIG. 48A-B  show embodiments of the invention. 
         FIG. 49A-C  show embodiments of the invention. 
         FIG. 50A-D  show embodiments of the invention. 
         FIG. 51A-F  show embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     For a better understanding of the invention, the following detailed description refers to the accompanying drawings, wherein exemplary embodiments of the present invention are illustrated and described. 
     The present invention relates to a magnetically actuated alternative to traditional MR fluid motion control devices. A magnetically actuated motion control device according to the present invention can be embodied as linear or rotary dampers, brakes, lockable struts or position holding devices. The invention contains no MR fluid, yet provides a variable level of coulombic or friction damping that is controlled by the magnitude of the applied magnetic field. 
     In contrast to MR or ER fluid devices, a magnetically actuated motion control device according to the present invention is simple to manufacture and relatively low cost. A magnetically actuated motion control device according to the present invention also allows for very loose mechanical tolerances and fit between components. In addition, a magnetically actuated motion control device according to the present invention does not require a dynamic seal or a compliant containment member as does a fluid type damper, and is therefore relatively easy to manufacture and assemble. Further, a magnetically actuated motion control device according to the present invention has particularly low off-state forces which provide for a wide dynamic range between the off-state and a maximum damping force. 
     An example of a magnetically actuated motion control device according to the present invention includes a magnetically permeable tubular housing that moves relative to an electromagnetic piston and includes one or more coils, an associated magnetically permeable core or core pieces and associated pole regions. Although the housing in this example is tubular, a housing can be of any suitable cross section, including, but not limited to a rectangular cross section. The pole regions are located near an interface between the piston and the housing and carry magnetic flux in a generally radial direction with respect to a longitudinal axis running along the housing. The housing includes at least one slot but typically includes an array of slots. The housing slots allow the housing to flex and constrict radially when a magnetic field is applied by directing current through the coils. In so doing, the inner surface of the housing squeezes against the outer surface of the piston with a normal force that is approximately proportional to the magnitude of the applied magnetic field. Thus, the housing acts like a magnetically actuated collet that squeezes the piston to resist relative movement between the housing and the piston. Generally, the magnitude of the applied magnetic field is proportional to the electric current supplied to the coil. The damping force thus depends on the coefficient of friction between the inner surface of the housing and the outer surface of the piston and the normal force between these surfaces, which is dependent on the magnetic field produced by running current through the coils. 
     The invention allows for the accommodation of very loose mechanical tolerances or fit between the housing and the piston. Because the present invention does not require a dynamic seal or compliant containment member, it offers particularly low off-state forces and is simple to manufacture and assemble. 
     The present invention is particularly suitable for making low-cost, high-volume linear dampers for use in household appliances such as washing machines. Other applications for magnetically actuated motion control devices according to the present invention include simple rotary or linear brakes for controlling mechanical motions inside office equipment such as copiers or printers, e.g., paper feed mechanisms. Additional applications for magnetically actuated motion control devices according to the present invention include dampers for use as semi-active control elements in conjunction with ultra-low vibration tables and platforms. Magnetically actuated motion control devices according to the present invention can also be used as latching or locking mechanisms in office furniture, e.g., props and latches for doors, drawers, etc. Still other applications include exercise equipment, rehabilitation equipment, joysticks, control knob wheels, seismic structural control dampers, avionics semi-active control devices, machine tool fixturing devices, ventilation system flaps and doors in automobiles, door hinges and sliding doors in vehicles, etc. 
     Magnetically actuated motion control devices according to the present invention can also be used in the area of haptics. The field of haptics includes devices used in computer peripherals such as force-feedback steering wheels, control knobs, programmable detents, programmable endstops, computer pointing devices and joysticks used with games and other software. This field also includes industrial force feedback mechanisms such as steering wheels on steer-by-wire vehicles and rotating instrument control knobs. 
     Yet another application is to use either linear or rotary embodiments of the invention in conjunction with pneumatic and hydraulic actuators to enable precision position and velocity control. 
     Turning to the drawings, a first exemplary embodiment of a magnetically actuated motion control device according to the present invention is shown in  FIGS. 1 and 2 . The first embodiment motion control device is a damper  101  and includes a housing  103  defining a cavity  105  in which a piston  107  is located. The housing  103  includes a least one longitudinal slot  109  (five of eight such slots can be seen in  FIG. 1 ). The housing shown in  FIG. 1  includes a plurality of slots that pass through the housing wall to define flexible bands, tabs, or fingers  111 . The slots  109  extend through the wall of the housing  103  and extend nearly the entire length of the housing  103 . Although narrow slots are illustrated in the Figures, it should be understood that a suitable wide slot could also be provided in the housing. 
     The piston  107  includes a shaft  112  having a magnetically active portion  113  made up of at least one, and preferably two electromagnetic coils  115  set in a magnetically permeable core  117 . Although here the magnetically permeable core  117  is hollow, the core can alternatively be a solid bobbin. A hollow core allows space for connecting wires or for an axial screw or rivet. However, a solid core is preferable because magnetic saturation of the core is reduced. 
     In addition, the core can be made up of a plurality of core pieces. A current source  118  supplies current to the coils  115  through wires  119 . Each end of the damper preferably includes a structure which facilitates attaching damper  101  to other structures, such as clevis eye  121  for attaching the end to a portion of a damped component. 
     Current flowing through the coils  115  creates a magnetic field that draws the housing  103  in toward the piston  107 . For this purpose, the housing  103  is formed of a material which will be attracted by the magnetic field. Examples include, but are not limited to, steels and other iron alloys. The amount of current flowing through the coils  115  is generally directly proportional to the magnitude of the magnetic field generated. Thus, control of the electric current flowing through the coils  115  can be used to control the normal or pressing force between the inner surface of the housing  103  and the outer surface of the piston  107 , thereby controlling the damping effect of the damper  101 . 
     An illustration of the damping effect can be seen in the end sectional view shown in  FIG. 2 , which shows the relationship of the slotted housing  103  with respect to the piston  107 . When no magnetic field is applied, the piston  107 , and particularly the active portion  113 , fits loosely within the housing  103  to define a small radial clearance  123  between the housing  103  and the magnetically active portion  113  of the piston  107 . That is, the housing  103  is relaxed and does not press against the piston  107 . When current is supplied to the coils  115  the magnetic field generated causes the flexible fingers  111  in the housing  103  to be attracted radially inward as indicated by the arrows  125  such that the housing  103  squeezes the piston  107  with a force proportional to the applied magnetic field, and therefore the applied current. 
     The slotted housing  103  and the core  117  of the piston  107  are preferably made from low carbon, high permeability steel, although other magnetically permeable materials can be used. The slots  109  are preferably evenly spaced around the circumference of the housing  103  so that axial-periodic symmetry is maintained. The pair of coils  115  is preferably wired such that they produce magnetic fields in opposite directions. This configuration allows the magnetic field produced by each coil  115  to add rather than cancel in an area between the coils  115 . 
     The configuration of the slots in the housing of the damper can be varied to tune the flexibility of a housing.  FIGS. 3A and 3B  illustrate a housing  127  that includes fewer longitudinal slots  109 , and therefore has less flexibility than a comparable housing having a larger number of slots. Longitudinal slots  109  may also be carried through to an open end  129  of a housing  131  as shown in  FIGS. 4A and 4B . Slots  109  carried through to the end  129  create a flexible housing  131  which promotes full contact between the housing  131  and the piston when the magnetic field is applied. Such a slot configuration may be particularly useful when the housing  131  is made from a thick-wall tubing. Greater housing flexibility can also be obtained by connecting pairs of slots  109  in a housing  133  with a cross-slot  135  to form flexible fingers  137  having free ends  138  as shown in  FIGS. 5A and 5B . 
     Depending on the thickness of the housing material and its consequent ability to carry magnetic flux (permeability), and also on the magnitude of the desired damping force, the number of coils  115  can vary from the embodiment shown in  FIGS. 1 and 2 . For example, a single-coil embodiment  139  is shown in  FIG. 6  and a 4-coil embodiment  141  is shown in  FIG. 7 . Except for the number of coils  115 , and a solid core  143  rather than the hollow core described above, the embodiments shown in  FIGS. 6 and 7  are identical to the embodiment shown in  FIGS. 1 and 2 . More coils  115  are preferable when the thickness of the housing is small in order to avoid magnetic saturation of the housing. Magnetic saturation refers to the maximum amount of magnetization a material can attain, as will be readily appreciated by one of ordinary skill in the art. The thickness of the housing limits the amount of magnetization that can be induced in the portion of the housing adjacent to the coils. 
     In some applications of the invention it is desirable to have the magnetic field, and therefore the damping force, applied most of the time with only short instances of turning the damping off. This can be accomplished by adding one or more permanent magnets to the system. A permanent magnet can be used in the damper so that the damper is in its on-state and the housing pressing against the piston when no current is applied to the electromagnetic coil. The electro-magnetic coil serves to cancel the field of the permanent magnet as current is applied to progressively turn the damper off 
     A seventh exemplary embodiment of the motion control device of the present invention is illustrated in  FIG. 8 . As seen in  FIG. 8 , two axially polarized (i.e., the opposite faces of the disks are the opposite poles of the magnets) disk magnets  143  are positioned and oriented to bias a damper  145  into an on-state, i.e., a condition in which the housing is magnetically attracted to the piston. A magnetically active portion  147  of a piston  149  includes three core pieces  151  between which the disk magnets  143  are located. The disk magnets  143  are located immediately radially inward of the coils  115 . The disk magnets  143  pull the housing  103  and the piston  149  together. In order to turn the damping off, the magnetic fields produced by the permanent disk magnets  143  are at least in part, and preferably completely canceled by applying current to the pair of coils  115 , which each generate magnetic fields that oppose those of the permanent magnets  143 . 
     An eighth exemplary embodiment of the motion control device of the present invention is illustrated in  FIG. 9 . In this case the electromagnets do not cancel the magnetic field in all directions. Rather, the electromagnets cause the field of the permanent magnet to be redirected to a different path. 
     Like the embodiment shown in  FIG. 8 , the embodiment of a damper  150  according to the present invention shown in  FIG. 9  includes the housing  103  having the same structure as that shown in  FIGS. 1 and 2 . According to the embodiment shown in  FIG. 9 , a magnetically active portion  152  of a piston  153  includes axially-polarized permanent ring magnets  155  located immediately radially inward of the coils  115 . The coils and ring magnets are located between magnetically permeable core pieces  157  so as to define non-magnetic gaps  159  in the center of each ring magnet  155 . Gaps  159  are less magnetically permeable than core pieces  157 , and therefore cause less magnetic flux through the center of the magnetically active portion  152 . The core pieces  157  and ring magnets  155  are held together by a non-magnetic connector  161 . The connector  161  is non-magnetic to prevent the generated magnetic field from being shunted away from the interface between the housing  103  and the magnetically active portion  152 . Alternatively, the core pieces  157  can be held together by an adhesive. Any suitable adhesive can be used, including but not limited to epoxys and cyanoacrylates. 
     As shown in  FIG. 9 , the non-magnetic gaps  159  at the center of the ring magnets  155  allow very little magnetic flux to follow flanking paths through the non-magnetic gaps  159  at the center of the ring magnets  155 . As a result, a magnetic field through the housing  103  has a much lower reluctance (resistance to carrying a magnetic field) than the flux path through the center of each of the ring magnets  155  and therefore radially draws the housing  103  and the piston together, as described above. In order to reduce the damping force, current is applied to the electromagnetic coils  115  which produce a magnetic field. The current can be adjusted such that the magnitude of the field produced by the coils is equal to, but opposite, that of the ring magnets  155  where the field paths cross into the housing  103 . 
     A ninth exemplary embodiment of the motion control device of the present invention is illustrated in  FIG. 10 . As shown in  FIG. 10 , a spring  167  can be added to an end of a damper according to the present invention to form a strut  169 . The damper shown in  FIG. 10  is identical in structure to that shown in  FIGS. 1 and 2 , except that the spring  167  is provided between the end  171  of the piston  107  and closed end  173  of the housing  103 . In a mechanical system the strut  169  provides the desired spring stiffness in addition to a controllable level of damping force. In addition, as schematically shown in  FIG. 10 , a mechanical stop  175  is added to the end of the housing  103  to hold the piston  107  in the housing  103  and allow the spring  167  to be preloaded. The mechanical stop  175  can optionally be included with damper embodiments as well. 
     Measured performance of a damper constructed according to the present invention is shown in the graph comprising  FIG. 11 . For purposes of plotting the performance graph, the damper housing was constructed from low-carbon steel tubing having a 1.125 inch (28.58 mm) outer diameter and 1.000 inch (25.40 mm) inner diameter. The steel part of the housing was 5.0 inches (127 mm) long. Four lengthwise slits each approximately 0.040 inches (1 mm) wide 4.25 inches (108 mm) long were formed in the housing. The piston included two coils wound onto a low carbon steel double bobbin having an overall length of 1.0 inches (25.4 mm) The diameter of the steel poles of the piston was 0.990 inches (25.15 mm) The axial length of the two outer pole sections were each 0.145 inches (3.68 mm) The center pole section was 0.290 inches (7.37 mm) long. The diameter of the solid center core of the piston was 0.689 inches (17.5 mm) The two coils were each wound with 350 turns of 35 AWG magnet wire and were connected in series. The total resistance of the two coils was approximately 48 ohms The total usable stroke of the damper was about 3 inches (76 mm) 
     Turning now to the graph, initially, at low current, the example damper displays a proportionate, nearly linear behavior which then rolls off as magnetic saturation effects begin to dominate as can be seen in  FIG. 11 . The damping force that is produced is almost perfectly coulombic with little or no velocity dependence. That is, the damping force is almost directly dependent on the current supplied to the coils. The data shown are peak forces obtained with the damper undergoing sinusoidal excitation with a ±0.5 inches (12.7 mm) amplitude and a peak speed of 4 inches/sec (102 mm/s) A curve obtained with a peak speed of 1 inch/sec (25.4 mm/sec) appeared to be nearly identical. 
     Although axial motion of the piston relative to the housing is what has been discussed thus far, a damper according to the present invention will also function as a rotary damper with the piston rotating relative to the housing. A tenth exemplary embodiment of the motion control device of the present invention is illustrated in  FIGS. 12 and 13 .  FIG. 12  shows an assembled example of a rotational embodiment according to the present invention, with portions broken away to show some interior elements.  FIG. 13  shows the embodiment shown in  FIG. 12  partially disassembled. In this embodiment a coil  177  wound around a center steel bobbin  179  form a circular stator  181 . The stator  181  is positioned within a cavity defined by, and for rotation relative to, a slotted housing  183 . Slots  185  are connected by cross-slots  186  to define fingers  187 , which impart a high degree of flexibility to the housing  183 . The highly flexible finger  187  of highly flexible housing  183  allow contact between the stator  181  and the housing  183  when the magnetic field is energized. Bearings  188  are included in the stator  181  to support a shaft  190  with which the housing  183  rotates. Bearings  188  allow the circular housing and shaft  190  to rotate around circular stator  181 . As shown in  FIG. 13  second member circular stator  181  is received in the cavity between the outer perimeter of the first housing member and the inner shaft  190 . As shown in  FIG. 12 , the housing encircles the stator  181  received in the cavity around the shaft  190 . The flexible finger  187  is movable into frictional contact with the outer circumference surface of circular stator  181  when a current from current source  118  generates a magnetic field with coil  177 . The magnetic field generator of the circular stator  181  with the bobbin and wound coil generates a magnetic field that pulls the finger  187  inward and into frictional contact to produce frictional damping of the relative rotation between the housing and the stator. 
     A damper according to the present invention generates strong coulombic pressing forces when the outer surface of the magnetically active portion of the piston or stator makes direct contact with the inner surface of the steel housing finger. In fact, the inventor herein has found that damper performance actually improves after being initially operated due to an apparent “wearing-in” process. During the wearing-in process friction between the surfaces of the housing and the piston causes some wear to occur which effectively laps or burnishes the contacting surfaces such that “high spots” (large surface features) are removed and the housing and piston (or stator) contact more intimately. This improves the efficiency of the magnetic circuit and increases total contact surface area so that the overall damping force is increased. 
     In some applications of the present invention, it is desirable to place a layer of damping material or acoustic foam  189  around the outside of the housing as seen on the exemplary damper shown in  FIG. 14 . The components of the damper shown in  FIG. 14  are identical to the exemplary dampers discussed with respect to  FIGS. 1-13 . Such an acoustically insulating material will serve to attenuate any high frequency squeaking, rubbing or clanking sounds that may occur due to a metal housing moving against a metal piston. The desirability of such added acoustic material depends on a number of factors, including: the actual thickness of the housing; the resonant characteristics of the housing; the looseness of the fit between the housing and the piston, the alignment of the parts during application of the damper; and the presence of elastomeric bushings in the clevis eyes used to mount the damper. Lubricant (grease or oil) can also be added so that the parts of the damper slide smoothly relative to each other in the off-state. Suitable acoustic material will be readily apparent to one of ordinary skill in the art. 
     A similar quieting effect can be achieved by adding an intermediary friction increasing layer to the rubbing surfaces of the piston or stator, or the inner surfaces of the housing. Examples of such materials may be a thin polymeric layer such as polyethylene or nylon, or a composite friction material such as that typically used in vehicle clutches and brakes. Such a friction layer eliminates metal to metal contact and reduces long term wear. However, the presence of such layer of friction material will in general make the magnetic circuit less efficient. Unless the friction material has a high permeability like low carbon steel it increases the reluctance of the magnetic circuit dramatically and lowers the amount of damping force when the damper is in the on-state. 
     According to yet another embodiment of the present invention, a magnetically controlled damper can further include an integrated position sensor. Exemplary embodiments of a damper including a position sensor according to the present invention are shown in  FIGS. 15-22  and  49 . Preferably, a magnetic friction damper  191  includes sensor  193 , such as a linear potentiometer, including a first portion  194  and a slider  196 . The first portion is attached to the housing  103  by brackets  198 . The slider  196  is coupled to the damper piston  195  by a small engagement pin  197  that passes through one of a plurality of slots  109  in the housing  103  of the magnetic friction damper  191 . Preferably in rotational embodiments of the invention a rotary position sensor is utilized, such as a rotary potentiometer. 
     An eleventh exemplary embodiment of the motion control device of the present invention is illustrated in  FIGS. 15-17 .  FIGS. 15-17  show a damper similar to the damper shown in  FIGS. 1 and 2 . Otherwise identical to the piston shown in  FIGS. 1 and 2 , the piston  195  includes a circumferential groove  199  between electromagnetic coils  115 . The sensor  193  is mounted along the side of the damper housing with brackets  198  such that an extension, such as the pin  197  of the slider  196  on the potentiometer  193 , can pass through one of the longitudinal slots  109  in the damper housing  103 . The groove  199  in the damper piston  195  accepts the pin  197  and causes the slider  196  to move longitudinally in concert with the piston  195  while permitting relative rotational movement between the piston and the housing. Thus, for example, electrical resistance of a potentiometer varies in proportion to the piston displacement in the housing, thereby indicating the relative position of the housing  103  and the piston  195 . 
     Alternatively or in addition to measuring linear displacement with the sensor  193 , the sensor can be used to measure the relative velocity or acceleration of the housing  103  and the piston  195 . Furthermore, sensor  193  can be a velocity sensor or an accelerometer, which are readily commercially available and with which one of ordinary skill in the art is well acquainted. A device for interpreting the signal from sensor  193 , such as a general purpose computer  200  having a memory  201 , is in electrical communication with electrical connections  202  on the sensor  193 . Computer  200  can further be provided with logic in the memory  201  which can determine relative position, velocity, or acceleration based on the electrical signals sent by the sensor  193 , and can store data representative of one or more of these parameters. Because one of ordinary skill in the art readily appreciates the details of the use of such a computer  200  and logic usable with sensor  193 , further details will not be provided herein. 
     A circumferential groove  199  rather than a hole in the piston  195  is preferred because the circumferential groove  199  does not inhibit rotational motion of the piston  195 . Allowing free rotational motion of the piston  195  relative to the housing  103  is important so that the clevis eyes  121  at the ends of the damper  191 , when provided, can be easily properly aligned with the mounting pins in the components to which the damper  191  is attached so that the damper  191  does not bind during use. 
     Twelfth, thirteenth and fourteenth exemplary embodiments of the motion control device are illustrated in  FIGS. 18 ,  19  and  20  respectively. As seen in  FIGS. 18-20 , a circumferential groove can be located on other parts of the piston  195  as well. For example, as seen in the embodiment shown in  FIG. 18 , a groove  203  is formed into the shaft of the piston  195  just behind a magnetically active portion  205  of the piston. In the embodiment shown in  FIG. 19 , a groove  207  is formed between a lip  209  formed into the piston  195  and a rear end  211  of the magnetically active portion  205  of the piston  195 . In the embodiment shown in  FIG. 20 , a disk-shaped member  213  is attached to a free end  215  of the piston  195  to define a groove  217 . Other than the arrangement of the circumferential groove the embodiments shown in  FIGS. 18-20  are identical to the embodiment shown in  FIGS. 15-17 . 
     An experimental example of a damper including a position sensor was tested by the inventor herein. The prototype utilized a Panasonic potentiometer (part number EVA-JQLR15B14, Matsushita Electric (Panasonic U.S.A.), New York, N.Y., U.S. distributors include DigiKey and Newark Electronics) with a working stroke of 3.94 inches (100 mm) Electrical resistance varied linearly from 0 to 10 Kohms. The potentiometer was mounted to the damper housing using hot-melt adhesive. The original rectangular extension on the slider was modified into the form of a small diameter pin to fit through one of the longitudinal slots in the magnetic friction damper housing. In the example, the groove in the piston was made by adding a small, spaced plastic disk to the end of an existing piston as shown in  FIG. 20 . The final result was an integrated variable resistance sensor whose output varied linearly with the position of the damper piston. Further, the pin and groove geometry allowed free rotational motion of the piston within the housing, a feature that allowed for proper alignment of the clevis eyes during damper installation and use. 
     A fifteenth exemplary embodiment of the motion control device of the present invention is illustrated in  FIGS. 21 and 22 . Another exemplary embodiment of a damper including a position sensor is shown if  FIGS. 21 and 22 . In this embodiment a rotary sensor  219  (e.g., a rotary potentiometer) is used in the position sensor. Alternatively, a rotary optical encoder can be used in the position sensor. The rotary sensor  219  is mounted to the housing by a bracket  220  and is coupled to the motion of a piston  221  by means of the integrated rack and pinion system  223 . A pinion gear  225  is coupled to the rotary sensor  219  (or optical encoder) by an axle  227 . The piston  221  includes a shaft  228  that is molded (of, e.g., plastic) or otherwise formed to include a rack  229 . It is preferable to allow relative rotation between the piston and the pinion gear. Therefore, it is preferable that the rack  229  is formed around the entire circumference of the piston  221 . 
     In addition to the variable resistance sensors discussed above, other sensing devices may alternatively be used, including variable inductance or variable capacitance sensors, optical encoders, flex or bend sensors etc. and are all within the spirit and scope of the present invention. As discussed in reference to  FIGS. 15-22  a sensor can be used to measure relative velocity or acceleration as well as relative position between a piston and a housing. 
     Further, although the magnetic damper including a position sensor has been described in the context of collet type dampers, the same position sensors may be included with MR or ER dampers. Examples of such MR or ER dampers are described in U.S. Pat. Nos. 5,284,330, 5,277,281 and 5,018,606, which are herein incorporated by reference in their entireties. 
     Magnetically actuated motion control devices according to the present invention, including those described herein, are useful in many applications.  FIGS. 23-31  illustrate a number of exemplary applications for the present invention device. For example,  FIG. 23  shows the use of magnetically controllable dampers according to the present invention  230  in a washing machine  231 . Magnetically controllable friction dampers can provide a high level of damping when the washing machine  231  passes during a resonance cycle and can be turned off during high speed spin to provide optimum isolation of the spinning basket or drum  232 . 
       FIG. 24  shows several possible uses of the present invention in an automobile, truck, or other vehicle. Magnetically actuated motion control devices according to the present invention can be used as a semi-active seat suspension when located between a seat  233  and an associated base  235 . Dampers according to the present invention can also be used as a locking element  237  in a steering column  239  including tilt and telescope mechanisms  241 ,  243 . A magnetically actuated motion control device  230  in its on-state locks the steering column  239  in place. In its off-state, the damper allows the steering wheel to tilt and telescope into a desired position. Other applications in motor vehicles include the use of a damper as an interlock mechanism in gearshift mechanisms (not illustrated). 
     Another application for the invention is as a locking member  245  for various types of furniture such as office chairs, for example.  FIG. 25A  illustrates the use of a magnetically actuated motion control device  230  in a height adjustor  245  of an office chair  247 .  FIG. 25B  illustrates the use of a magnetically actuated motion control device  230  as a locking mechanism  249  for the back tilt motion of the chair  247  and as a locking mechanism  250  for a height adjustable armrest  252  of the chair  247 , and which can be connected between the armrest  252  and either a seat  254  or a backrest  256  of the chair  247 . An electrical control  251  is used by an operator to selectively turn off the magnetically actuated motion control device  230 , thereby allowing the chair  247  to tilt. 
       FIG. 26  illustrates the use of magnetically actuated motion control device  230  as a locking mechanism  253  for an adjustable height table  255 . The adjustable height table  255  also includes a control  258  wired to the locking mechanism  253 . The control  258  selectively allows selective locking of the adjustable table  255  by alternatively turning the dampers on and off. 
       FIGS. 27A and 27B  show a magnetically actuated motion control device  230  according to the present invention used as a locking mechanism for a tilting work surface  257  into position ( FIG. 27B ) or for locking a flipper door  259  into place (FIG.  27 AA). 
     Another area of application for the motion control device of the present invention is the area of haptics, where a linear or rotary embodiment of the invention may be used to provide tactile force feedback to an operator.  FIG. 28  illustrates a force-feedback steering wheel  261  that uses a rotary damper  263 , such as that described in reference to  FIGS. 12 and 13 . Such a device can also be used in “steer-by-wire” mechanisms on vehicles such as cars, trucks or industrial jitneys and forklifts. The present invention can also be used in computer games as a force-feedback steering wheel that is responsive to virtual action in a game. In the example shown in  FIG. 28 , the damper  263  is coupled to a rotary position sensor  265  so that the damping can be coupled to the position of the steering wheel. Similarly a control knob wheel  261  can be provided with programmable end stops, with a rotary position sensor sensing the position of the rotor and an end stop then being generated by generating a magnetic field to stop further rotation in the rotating direction. 
     The present invention can also be used as a small controllable friction brake inside computer pointing devices, such as a computer mouse  267  as shown in  FIG. 29 . The mouse  267  includes a mouse ball  269  that is in rolling contact with a y-drive pinion  271  and an x-drive pinion  273 . The drive pinions  271 ,  273  are each respectively coupled to a y-encoder wheel  275  and an x-encoder wheel  277  with a rotary brake  279  of the type described in reference to  FIGS. 12 and 13 , for example. Each encoder wheel  275 ,  277  is positioned so as to rotate through an encoder sensor  280 . The rotation of an encoder wheel is sensed by a respective encoder which sends an electrical signal representing the movement of the mouse ball  273  in an x-y plane which passes through pinions  271 ,  273 . 
     The invention can also be used to provide an active force feedback steering wheel  281  as shown in  FIG. 30 . In this application a pair of clutches  283 ,  285 , similar in structure to the rotary damper described with reference to  FIGS. 12 and 13 , are used to selectively couple the steering wheel  281  to either clockwise or counter-clockwise rotating housings  287 ,  289 . In a clutch arrangement, the stator and the housing are each rotatable, and are rotatable relative to one another. A motor  291  is coupled to clockwise and counter-clockwise housings  287 ,  289  by a pinion drive  293 . A shaft  295  extending from the steering wheel passes through the housing  289  and is coupled to stators  297 ,  299  of the clutches  283 ,  285 , respectively. The shaft  295  can include bearings or other similar structures where the shaft passes through the housings  287 ,  289 , to permit relative rotational movement between the shaft and the housings. A rotary position sensor  298  is coupled to the end of shaft  295  to detect the rotation of the steering wheel  281 . The stators  297 ,  299 , provide friction damping in the clockwise and counter-clockwise directions as in the manner described with reference to  FIGS. 12 and 13  with contact surfaces  301 ,  303 . Thus, the steering wheel  281  can actually be forced to turn with a prescribed amount of force in either direction with the ultimate driving source being a simple single direction motor  291 . 
     The invention can also be used in flexible fixturing systems such as the fixturing system  305 , schematically illustrated in  FIG. 31 . In this example, an array of struts  307 , like those described in reference to  FIG.10 , are each coupled to extensions  309  and are used to hold an irregularly shaped object  311  in position for machining or gauging of the object  311 . Each of the struts  307  can selectively lock or release an extension  309  so that objects of various sizes and shapes can be accommodated and held in place. 
     In addition to the embodiments of the present invention shown in  FIGS. 1-22  and described hereinabove, other embodiments of the present invention shown in  FIGS. 32-49  can be interchanged for the exemplary magnetically actuated control devices illustrated in the applications described with reference to  FIGS. 23-31 . 
     The sixteenth preferred embodiment of the motion control device is illustrated in  FIG. 32 . As seen in  FIG. 32 , the motion control device is comprised of a damper  313  that includes a housing  103  having slots  109  and a piston  315  having a magnetically active portion  317  that includes a permanent disk magnet  319  sandwiched between core pieces  321 . The core pieces  321  are held together by the magnetic field generated by the permanent magnet  319 , eliminating the need for connectors or adhesives in the magnetically active portion of the piston  315 . Thus, the assembly of the damper  313  is greatly simplified. Because the magnetic field generated by the permanent magnet  319  cannot be varied, the damper  313  is always in an on-state. That is, the housing  103  always squeezes the piston  315  with the same force. 
     Seventeenth and eighteenth exemplary embodiments of the motion control device of the present invention are illustrated in  FIGS. 33 and 34 . However, as seen in  FIGS. 33 and 34 , the squeezing force between the housing and the magnetically active portion of the piston can be varied by introducing a variable width gap into the magnetically active portion of the damper. As seen in  FIG. 33 , a damper  323  of this type includes a housing  103  including a plurality of slots  109 , within which a hollow piston  325  is located. A magnetically active portion  326  of the piston  325  includes an end  327  connected to a control rod  329 . The end  327  includes an axially polarized disk magnet  330  that is sandwiched between a cap piece  332  and a first pole piece  331 . The control rod  329  is attached to the cap piece  332 . 
     According to an exemplary embodiment shown in  FIG. 33 , a second pole piece  333  is attached to the hollow piston  325 . A clearance  335  between the control rod  329  and the second pole piece  333  allows the second pole piece  333  to slide relative to the control rod  329 . A lever  337  located on the outer surface of the piston  325  is connected to the control rod  329  through an opening  338  in the piston  325  so that as the lever  337  is turned, the control rod  329  pushes the end  327  of the magnetically active portion  326  toward or away from the second pole piece  333  attached to the hollow piston  325 . In this way, an air gap  339  of variable size is introduced into the magnetically active portion  326 . The gap  339  increases the reluctance within the magnetically active portion  326 , thereby diminishing both the force with which the housing  103  squeezes the piston  325 , and also the frictional damping force produced by the damper. 
     Alternatively, as seen in  FIG. 34 , a damper  341  according to the present invention can include a control rod  343  having a threaded end  345  that threads into a tapped second pole piece  347  that is attached to the hollow piston  325 . Like the embodiment shown in  FIG. 33 , the control rod  343  is attached (at the threaded end  345 ) to a cap piece  349  that sandwiches an axially polarized disk magnet  350  with a first pole piece  351 . The control rod  343  is connected to a knob  353  that is exposed through an opening  355  in the hollow piston  325 . Rotating the knob  353  rotates the control rod  343  and causes the tapped second pole piece  347  to move relative to the cap piece  349 . In this way, a variable air gap  357  is introduced into the magnetically active portion. As discussed in reference to the embodiment shown in  FIG. 33 , the variable gap  357  can be used to control (diminish) the damping force produced by the damper. 
     Nineteenth and twentieth exemplary embodiments of the motion control device of the present invention are illustrated by  FIGS. 35A-36B , and  37 A- 37 B respectively. As seen in  FIGS. 35A-37B , according to the present invention the components of a magnetically actuated motion control device can be reversed with respect to the other exemplary embodiments discussed thus far. For example, as seen in  FIGS. 35A and 35B , a damper  359  includes a housing  361  that defines a cavity  363  in which a piston  365  is located. The piston  365  includes four slots  367  that extend from an open end  369  of the piston  365 . Although the piston  365  is tubular, a piston can have any suitable cross-sectional area such as square, cylindrical etc. A magnetic field generator, such as coils  371  (shown schematically), is located in a magnetically permeable assembly  373  having pole pieces  375 . At least a portion of the slotted piston  365  is magnetically permeable so that when a magnetic field is generated by the coils  371 , the piston flexes and presses outward against the pole pieces  375  of the magnetic assembly  371  located on the housing  361 . Accordingly, the friction damping force can be controlled by controlling the magnetic field generated by the coils  371 . 
     As seen in  FIG. 36A and 36B , the piston  365  is hollow. A hollow piston is preferred because a hollow piston can easily flex outward in response to an applied magnetic field. However, according to an embodiment shown in  FIGS. 37A and 37B , a piston  377  can be solid. Slots  379  extend through the solid piston  377  to define bands, sections, tabs, or fingers  381 . The fingers  381  flex outward in response to an applied magnetic field to produce a frictional damping force. An advantage of having a solid piston is that magnetic saturation of the piston can be mitigated. 
     Other embodiments of a magnetically actuated motion control device according to the present invention include bearing components that contact the components of the magnetically controlled motion control device, e.g., a housing and a piston, and provide smooth relative motion between the components when the motion control device is in its off-state. 
     For example, a twenty-first exemplary embodiment of the motion control device of the present invention is illustrated in FIGS.  20  and  38 - 40 C. A magnetically actuated motion control device  383  includes a piston  385  which fits within a housing  387 . The piston  385  includes one or more longitudinal slots  388  which extend through an end  389  of the piston  385  to define one or more fingers  390 . The housing  387  includes magnetic field generators, such as coils  391 , mounted between pole pieces  393 . The housing  387  defines a cavity  395  connecting opposing open ends  397 ,  399  of the housing  387 . In this way, the piston  385  can pass through both open ends  397 ,  399  of the housing  387  during its stroke. Accordingly, the axial length of the housing  387  can be much shorter than the axial length of the piston  385 , thereby providing a compact device. Trunnion mounts  401 , which extend from the housing  387 , allow the open ended housing  387  to be mounted to a separate device. 
     Turning to a partial view  38 A, a bearing assembly  403  is located radially inward of each of the coils  391  and within radial grooves  404  defined by the pole pieces  393  of the housing  387 . Each bearing assembly  403  includes an annular spring  405  (see also,  FIG. 40B ) located between a coil  391  and an expandable bearing  407 . Preferably, the spring is a band of compliant, elastomeric material, e.g., a sponge material or an O-ring. 
     The expandable bearing  407  contacts the surface of the piston  385  and is biased by the spring  405  radially inward toward the outer surface of the piston  385 . As a result, a small gap  409  is maintained between the housing  387  and the piston  385  when the coils  391  are not energized. Preferably, the radial thickness of each bearing  407  is greater than the thickness of the gap  409  so that the bearing remains captured within the respective radial groove  404 . Preferably, only the bearings  407  contact the outer surface of the piston  385  when the magnetically actuated motion control device is in its off-state. By spacing a plurality of bearings  407  axially along the housing  387 , the piston  385  and the housing  387  are prevented from binding, or moving out of axial alignment relative to one another (also referred to as “cocking”) when the device is in an off-state. 
     Energizing the coils  391  causes the fingers  390  to flex in a radially outward direction and press against the inner surface of the housing  387 . At the same time, each bearing  407  is pressed outward by the fingers  390 , thereby compressing the spring  405 . Thus, when the motion control device  383  is in its on-state, the gap  409  between the housing  387  and the piston  385  is eliminated as seen in  FIGS. 39 ,  39 A and  40 A as the magnetic field generated by the coils  391  causes the housing  387  and the piston  385  to press firmly against one another. 
     In order to provide firm contact between the housing  387  and the piston  385 , the bearing  407  must expand radially as the fingers  390  flex toward the housing  387  in response to a magnetic field generated by the coils  391 . As seen in  FIG. 40C , one embodiment of the annular bearing includes a split  411  to allow for radial expansion. Optionally, split  411  can be eliminated by forming bearing  407  of a material flexible enough to permit its radial expansion. Preferably, the bearing is made from a strip of flexible, low friction material. Examples of suitable bearing materials include nylon materials, e.g., molybdenum disulfide filled nylon fibers, Hydlar HF (A.C. Hyde Company, Grenloch, N.J.), which is a material including nylon reinforced with Kevlar fibers, polytetrafluorethylene materials, e.g., Teflon®, Derlin AF® (E.I. Dupont Nemours and Co., Wilmington, Del.), which is teflon filled with an acetal homopolymer, and Rulon® (Dixon Industries, Bristol, R.I.), which is a material including Teflon® reinforced Kevlar® fibers, Vespel® (E.I. Dupont Nemours and Co., Wilmington, Del.), which is a polyimide material, Ryton® (Philips Petroleum Co., Battlesville, Okla.), which is a material including polyphenylene sulfide filled with carbon fiber, or brass. The preceding list is not exhaustive, and other suitable materials will be apparent to one with ordinary skill in the art. 
     As explained earlier, the magnetic field generators, e.g., coils can be mounted to either the housing or the piston with the other of the housing or the piston being split into one or more flexible fingers.  FIG. 41  shows a twenty-second embodiment of the present invention including a piston  413  having two magnetic coils  391  located within a core  414  and a slotted housing  415  in which the piston  413  is located. Like the embodiments discussed in reference to  FIGS. 1 and 2 , the housing  415  includes one or more longitudinal slots  417  that define one or more flexible fingers  419 . 
     The piston  413  slides within the housing  415  on bearing assemblies  421 , which are each located radially inward of the coils  391  and bear against the inner surface of the housing  415 . Each bearing assembly includes an annular spring  425 , which is located between an annular bearing  427  and one of the respective coils  391 . The spring  425  biases the bearing  427  radially outward and away from the magnetically active portion of the piston to create a gap  428  between the outer surface of the piston  413  and the inner surface of the housing  415 . Preferably, each bearing  427  and spring  425  are of the same structures and materials as those discussed in reference to  FIGS. 38-40 . 
     According to a twenty-third exemplary embodiment shown in  FIG. 42 , bearing assemblies are located axially spaced from coils  391 . In this embodiment a piston  429  is located within a housing  430  having structure such as that described in reference to  FIG. 41 , including slots  432  defining one or more fingers  434 . The piston  429  includes a main body  431  having a shoulder  433  at one end, an end cap  435  including a shoulder  436  that opposes the shoulder  433  and two steel cores  437  sandwiched between the end cap  435  and the main body  431 . 
     A first bearing assembly  439  is located between the cores  437  and the shoulder  433  in the cores  437 . A second bearing assembly  441  is located between the shoulder  436  and the main body  431 . Each bearing includes a spring  438  that biases a bearing  440  against the inner surface of the housing  430 . Preferably, the spring  438  and bearing  440  are constructed in the same manner as described with respect to the previous embodiments. The bearings  440  are biased against the inner surface of the housing  430  to create a gap  442  between the cores  437  and the inner surface of the housing  430  when the coils are not energized, i.e., the magnetically actuated motion control device is in an off-state. 
     The cores  437  are secured to the main body of the piston  429  by an interference fit between the outer surface of the cores  437  and the inner surface of the piston  429 . The cores  437  and end cap  435  are secured to one another by a bolt  443  and a nut  445 . The bolt  443  passes through aligned bores in the cores  437  and the end cap  435 . Accordingly, as exemplified by this embodiment, the bearing assemblies need not be located between the magnetic field generator (e.g., coils  391 ) and the opposing slotted member. 
     While two magnetic field generators, e.g., coils  391 , are illustrated in  FIGS. 38-41 , one of ordinary skill in the art will readily appreciate that one, or three or more, magnetic field generators may alternatively be used within the spirit and scope of the invention. Similarly, although two bearing assemblies are illustrated in  FIGS. 38-41  one or more bearing assemblies may be used within the spirit and scope of the invention. 
     Advantages of using bearing assemblies in a magnetically actuated motion control device in order to create a gap between the housing and the piston include maintaining the piston and the housing in axial alignment and creating smooth, fluid-like, relative movement between the housing and the piston while the damper is in its off-state. An example of a situation in which it may be important to provide smooth movement between the housing and the piston is when an embodiment of the present invention is used as a locking mechanism in a hinged vehicle door. In the example shown in  FIG. 43 , a car  447  includes a body  449  and a door  451  that swings on a hinge  453  relative to the body  449 . The housing  387  of a motion control device  383  (shown in  FIGS. 39-40C ) is mounted in the door  451  of the car  447 . Because the door  451  has limited space in which to fit extra components, the housing  387  is preferably short relative to the length of the piston  385 . The slotted piston  385  is attached at one end to the body of the car. As the door is swung open and closed, the piston  385  moves within the housing  387 . An operator can lock the door  451  into any position by activating a switch  455  which energizes the magnetic field generator to cause the piston and the housing to press against one another together, thus holding the door in position. Similarly the rotational embodiments of the present invention are utilized to hold the vehicle door in position and control the motion of the door relative to the vehicle body with magnetic actuation of the finger towards the stator. The rotational embodiments of the invention are utilized to control the rotating motion of a hinge. The shaft  190  can be directly coupled and connected to the rotating hinge members or indirectly coupled, such as with meshing gears. A rotary position sensor is preferably utilized to sense the rotating motion of the hinge and the control device. 
     The invention includes a magnetically actuated motion control device. The magnetically actuated motion control device is preferably comprised of a first housing member defining a cavity with the first housing member including a movable flexible finger. The magnetically actuated motion control device is preferably comprised of a second member positioned within the first housing member cavity with the first housing member movable relative to the second member with a magnetic field generator located on the second member. The magnetic field generator causes the movable flexible finger to press against the second member to produce frictional damping. In a preferred embodiment the second member is a stator having a center axis with the stator and the first housing being relatively rotatable around the central axis. Preferably the housing encircles the second member with the housing relatively rotatable around the second member. Preferably the movable flexible finger has a tab end for attachment with the first housing member. In an embodiment the movable flexible finger has a free end and a distal attached end which is attached to the first housing member, preferably with the distal attached end comprised of a tab end. In an embodiment the movable flexible finger has a first tab end and a distal second tab end. 
       FIGS. 12-13  and  44 - 51  show rotational embodiments of the magnetically actuated motion control device. The magnetically actuated motion control device is preferably comprised of a first housing member  183  defining a cavity  184  with the first housing member including a movable flexible finger  187 . The magnetically actuated motion control device is preferably comprised of a second member  181  positioned within the first housing member cavity  184  with the first housing member  183  movable relative to the second member with a magnetic field generator  177  located on the second member. Preferably the second member  181  is a magnetic field generator stator formed from a center bobbin  179  and a coil  177  wrapped around the bobbin to produce a magnetic field when a current is supplied to the coil from a current source  118 . The magnetic field generator causes the movable flexible finger  187  to press against the second member  181  to produce frictional damping. In a preferred embodiment the second member  181  is a stator having a center axis  182  with the stator and the first housing being relatively rotatable around the central axis. Preferably the housing  183  encircles the second member  181  with the housing rotatable around the second member. In an embodiment the movable flexible finger  187  has a free end  501  and a distal attached end  503  which is attached to the first housing member  183 . Preferably the first housing member includes a slot opening  185 . In a preferred embodiment the movable finger  187  extends through first housing member opening  185  with at least one tab end  503 . Preferably the movable finger is a circular finger band  187  that encircles the stator  181 . In an embodiment the movable circular band finger  187  has a free end  501  and a distal second end  503 . Preferably the distal second end  503  is comprised of a tab, with the distal second end tab extending through the opening slot  185 . As shown in  FIGS. 47A and 48A  such a motion control device with a free end  501  and a tab end  503  is preferred when the motion control device is intended to control motion in one direction of rotation. As shown in  FIGS. 47B and 48B  such a motion control device with a first tab end  503  and a second tab end  503  is preferred when the motion control device is intended to control motion in two directions of rotation. Preferably the end tab is contained in the opening slot in which it is movable. The finger  187  rotates along with the housing  183 . Preferably the circular band finger  187  rotates with the circular cup housing  183 , with the finger band pulled around by the housing slot  185 . In preferred embodiments the band finger  187  is magnetic and the rotor cup housing and the rotor shaft  190  is preferably nonmagnetic. Preferably the band finger encircles at least 70%, more preferably at least 80%, more preferably at least 90%, most preferably at least 95% of the outer circumference of stator  181 . An air gap between the movable finger  187  and the second member  181  when a magnetic field is not generated by the magnetic field generator allows for relative movement between the first housing  183  and the second member  181  without frictional damping and contact between the housing finger and the second member. Preferably the movable finger  187  encircles the second member  181  with a gap  505  between the movable finger and the second member when a magnetic field is not generated by magnetic field generator stator coil. Preferably the first housing member is comprised of a rotor cup having a rotor cup outer perimeter  507  and a rotor cup inner shaft  190 , with the second member  181  received in cavity  184  between the rotor cup outer perimeter  507  and the rotor cup inner shaft  190 . Preferably the first housing member  183  has an inner shaft  190  and a cavity  184  for receiving the second member  181  with the second member stator received in the cavity between the finger  187  and the inner shaft. Preferably the first housing member inner shaft  190  is separated from the second member  181  with a bearing  188 . Preferably the movable finger  187  is a circular band that substantially encircles the outer circumference stator  181 . The second member circular stator outer circumference provides for contact with the finger  187  of housing  183 . 
     The invention includes a magnetically actuated motion control device comprised of a first housing member including a cavity formed therein and including a movable finger; and a second member disposed in the cavity; and at least one magnetic field generator mounted to cause the movable finger to be displaced toward the second member and thereby squeeze the second member. In a preferred embodiment the first housing member has an outer perimeter and includes a shaft, with the cavity for receiving the second member between the outer perimeter and the shaft. 
     As shown in  FIGS. 12-13  and  44 - 48  first housing member  183  has an outer perimeter  507  and an inner shaft  190  that provides a cavity  184  for receiving second member circular stator  181 . A movable finger  187  frictionally engages the second member stator  181  when it is magnetically attracted by the magnetic field generated by the stator. Preferably the first housing member is a rotor cup having a rotor cup with a rotor cup inner shaft. Preferably the first housing member inner shaft  190  is separated from the second member stator  181  with at least one bearing  188 . The stator  181  has a center axis  182  and includes a center steel bobbin  179  and a wound coil  177  for generating the magnetic field. The generated magnetic field pulls the finger  187  into contact with the circular stator outer circumference. 
     The invention includes a method of controlling relative motion between a first housing and a second member, with the housing having a finger movable relative to the second member, and the housing defining a cavity in which the second member is located. The invention includes generating a magnetic field and pressing the finger against the second member in accordance with the generated magnetic field. 
     The invention includes a method of controlling relative motion between a housing  183  having a finger  187  and a second member  181 , with the second member movable relative to the housing and finger, and the housing  183  defining a cavity  184  in which the second member is located. The invention includes generating a magnetic field and pressing the finger  187  against the second member  181  in accordance with the generated magnetic field. Preferably the second member  181  is a circular stator including a bobbin  179  and a coil  177  and said housing  183  includes a shaft  190  and the finger  187  is magnetically permeable wherein generating a magnetic field includes supplying a current from a current source  118  to the coil to attract the finger towards the circular stator. Preferably the finger  187  is formed from a material attracted by magnetic fields, and is able to carry a magnetic flux. Preferably the method includes rotating the circular stator relative to the housing with a bearing between the stator and the shaft. Pressing the finger  187  against the second member includes collapsing the finger around the circular stator. Preferably the finger  187  is a circular band, more preferably a notched circular band with flex link notches  509  along its outer circumference, preferably with the finger flex link notches  509  in parallel alignment with the central axis  182  and normal to the direction of rotation. As shown in  FIG. 45A-B , finger  187  includes outer circumference flex link notches  509  in parallel alignment with central axis  182  and normal to the direction of rotational motion to provide for finger flexibility and frictional engagement of the finger with the second member upon generation of the magnetic field. In a preferred embodiment the invention includes providing a finger  187  with a plurality of flex links  509  spaced along the circumference of finger  187 . In embodiments as shown in  FIG. 45C-D , the circular band finger  187  includes flex links  509  between magnetic finger segments  511 . Magnetic finger segments  511  are preferably steel segments that are drawn inward toward the second member upon generation of the magnetic field, with the plurality of magnetic finger segments  511  linked together with the flex links  509  to form the magnetically actuatable movable finger  187 . As shown in the view of magnetically actuatable movable finger  187  in  FIG. 45D , the flex links  509  form a web belt to contain and position the plurality of magnetic finger segments  511 , such as the circular band finger formed from an a flexible plastic belt with magnetically attractable steel magnetic finger segments  511  attached thereto between flex links  509 , such as with the finger segments  511  adhered thereto, snapped into place, or molded into the belt. In an embodiment the finger links  509  comprise a molded plastic belt with sockets that accept the magnetic finger segments  511  and contain and position the magnetic steel finger segments  511  around the finger  187  to form the magnetically actuatable movable finger which frictionally engages the second member upon generation of the magnetic field. 
     The invention includes a system with a magnetically actuated motion control device with a finger  187  frictionally engaging a circular stator  181  to control a rotational motion of the system. The magnetically actuated motion control device is coupled to a shaft with a wheel, with the circular stator or the housing being rotatable relative to the shaft. In a preferred embodiment the wheel and shaft is comprised of a control knob. Preferably the system includes a rotational sensor  193  that tracks rotation. Based on the sensor output a magnetic field is generated by the stator  181  to move finger  187  to make a rotation end stop. 
     The invention includes a vehicle  447  including a body  449  and a door  451 . The door  451  is attached by hinge  453  to the body frame  449 . The invention includes a magnetically actuated motion control device housing  183  mounted between the door  451  and the body  449  to magnetically control a movement of the door  451  relative to the body  451 . A second member stator  181  is received in a cavity  184  inside housing  183 . Rotary position sensor  193  is mounted with the housing  183  to sense rotation movement of the device and the hinge. The second member stator  181  has a center axis  182 , with the stator and said first housing  183  being relatively rotatable around the central axis. 
     The invention includes a vehicle  447  a body frame  449  and a door  451 . The door  451  is attached by a hinge  453  to the body. The invention includes a magnetically actuated motion control device comprising a first housing member  183  defining a cavity  184 . The first housing member  183  includes a movable finger  187  and a second member  181  is positioned within the first housing member cavity  184 , with the second member  181  movable relative to the first housing member  183  and includes a magnetic field generator which causes the movable finger  187  to press against the second member  181  to produce frictional damping with said magnetically actuated motion control device mounted to control a positioning of the door  451  relative to the body  449 . Preferably the movable finger  187  is a circular band that encircles the second member. Preferably the second member is a stator having a center axis  182 , and includes a bobbin  179  and a coil  177 , preferably with the stator being a circular stator with an outer circumference. 
     The invention includes a body frame  449  and a door  451  with the door being attached by a hinge  453  to the body frame  449  and a magnetically actuated motion control device with a first housing member  183  defining a cavity  184 . The first housing member  183  includes a movable finger  187  and a second member  181  positioned within said first housing member cavity  184 , with the second member movable relative to said first housing member. The second member  181  includes a magnetic field generator with the magnetic field generator causing the movable finger  187  to press against the second member  181  to produce frictional damping with the magnetically actuated motion control device mounted to control a positioning of the door  451  relative to the body frame  449 . 
     The invention includes a magnetically actuated rotary motion control device comprising a first housing member  183  including a cavity  184  formed therein and including a movable finger  187  with a plurality of flex links  509 . The magnetically actuated rotary motion control device includes a second member  181  disposed in the cavity  184  and at least one magnetic field generator mounted to cause said movable finger  187  to be displaced toward said second member  181  and thereby squeeze said second member. Preferably the second member  181  is comprised of a stator that includes the at least one magnetic field generator, with the stator  181  having a coil  177  wound around a center bobbin  179  such that a current through the coil  177  generates the magnetic field that attracts movable finger  187  toward second member stator  181 . Preferably the movable finger  187  with flex links  509  is a circular band finger. Preferably the stator  181  is a circular stator with the stator having an outer circumference and the movable finger  187  is a circular band and encircles at least seventy percent of the second member stator outer circumference. 
     The invention includes a magnetically actuated rotary motion control device comprising a first housing member  183  including a cavity  184  formed therein and including a movable finger  187 . The magnetically actuated rotary motion control device includes a second member  181  having an outer circumference and is disposed in the cavity  184  with the movable finger  187  encircling at least seventy percent of the second member outer circumference. The magnetically actuated rotary motion control device includes at least one magnetic field generator mounted to cause said movable finger  187  to be displaced toward said second member outer circumference and thereby squeeze said second member  181 . Preferably the second member  181  is comprised of a stator that includes the at least one magnetic field generator, with the stator  181  having a coil  177  wound around a center bobbin  179  such that a current through the coil  177  generates the magnetic field that attracts movable finger  187  toward second member stator  181 . Preferably the movable finger encircles at least eighty percent of the second member outer circumference. Preferably the movable finger encircles at least ninety percent of the second member outer circumference. Preferably the movable finger encircles at least ninety five percent of the second member outer circumference. Preferably the movable finger  187  is a circular band finger, preferably with flex links  509 . 
     The invention includes a haptic system comprising a control knob  261  that provides tactile force feedback to an operator with programmable virtual hard end stops. As shown in  FIG. 50A-D  the magnetically actuated rotary motion control device provides a haptic control knob  261  with tactile force feedback of the rotating control wheel knob including programmable virtual hard stops. The control knob system includes a first member circular band movable finger  187  and a second member base  515  with said control knob  261  rotatable relative to the base. The control knob system includes a rotational sensor  265  positioned to sense a positional characteristic of said rotatable control knob  261  relative to the base  515 . The base  515  includes a circular stator  181  for generating a magnetic field to cause the movable finger  187  to press against the second member stator base to produce frictional damping to inhibit rotation of the control knob  261  relative to the stationary base. Preferably the stator generates the magnetic field based on a positional characteristic of the rotating control knob  261  sensed by sensor  265 . Preferably the sensor  265  is comprised of an optical encoder, preferably a high resolution optical encoder with a resolution of at least 100 code positions per rotation (complete turn of 360 degrees), preferably at least 150 code positions per rotation, such as high resolution miniature optical encoders Grayhill Inc. Series 63Q and 63T. As shown in  FIG. 50 , the sensor  265  senses the rotational position and rotational motion of the control knob  261 , with a current controllably supplied to the coil  177  to generate a magnetic field that draws the first member finger  187  into contact with the second member stator  181  in order to provide haptic feedback relating to the rotation of the control knob  261  relative to the base, including detents and hard stops of the control knob. 
     The invention includes a magnetically actuated rotary motion control device. As shown in  FIG. 51 , the magnetically actuated rotary motion control device includes a first housing member  183  including a cavity  184  formed therein and including a circular band movable finger  187 . The magnetically actuated rotary motion control device includes a second member  181  disposed in the cavity  184 . The second member  181  including a permanent magnet  330  as a magnetic field generator. The permanent magnet generates an attractive magnetic field for attracting said circular band movable finger  187  into frictional contact with said second member  181  to inhibit rotation between said first member  183  and said second member  181 . The magnetically actuated rotary motion control device preferably includes an adjustable magnetic field generating coil  177 , with the adjustable magnetic field generating coil  177  generating an adjustable coil magnetic field that cancels the permanent magnet attractive magnetic field to provide for retraction of the circular band movable finger  187  and inhibiting its frictional contact with said second member  181 . Permanent disk magnets  330  provide for having the attractive magnetic field, and therefore the damping force, applied most of the time with only short instances of turning the damping off. The permanent magnets are positioned and utilized in the rotary motion control damper so that the damper is in its on-state with the first member housing circular band movable finger  187  pressing against the second member  181  when no current is applied to the electromagnetic coil  177  such as shown in  FIGS. 51A and 51D . As shown in  FIG. 51F  the electro-magnetic coil  177  serves to cancel the field of the permanent magnets as current is applied to progressively turn the damper off.  FIG. 51D  shows the magnetic field and magnetic flux due to the permanent magnets only.  FIG. 51E  shows a magnetic flux due to the electro-magnetic coil only.  FIG. 51F  shows the net magnetic flux with the permanent magnet flux and the coil magnetic flux through the circular band movable finger  187  cancelled. Preferably the second member  181  is a circular stator with the stator having an outer circumference and the movable finger  187  is a circular band and encircles at least seventy percent of the second member stator outer circumference. In a preferred embodiment the circular band movable finger  187  includes a plurality of flex links  509 . As shown in  FIG. 51 , the second member  181  includes a steel core, a steel pole, a secondary gap non-magnetic spacer. The first member housing  183  includes a non-magnetic rotor cup and shaft, with the first member housing  183  and the second member  181  relatively rotatable about a center axis  182  with a sleeve bearing, with the assembly retained together with an outer large circumference wire retaining ring and an inner small circumference retaining ring. The permanent magnet  330  is preferably a plurality of permanent disk magnets positioned in a non-magnetic spacer disk, with plurality of spaced apart permanent magnets generating the attractive magnetic field for attracting said circular band movable finger  187  into frictional contact with said second member  181 . In an alternatively preferred embodiment the permanent magnet  330  is a permanent ring magnet which generates the attractive magnetic field for attracting said circular band movable finger  187  into frictional contact with said second member  181 . The permanent magnet  330  attracts the movable finger  187  into frictional contact to inhibit rotation between the first member housing  183  and the second member  181 . The coil  177  provides a means for canceling this attraction of the movable finger  187  to allow for rotation between the first member housing  183  and the second member  181 . 
     The present invention has been described with reference to exemplary embodiments. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than as described above without departing from the spirit of the invention. The exemplary embodiments are illustrative and should not be considered restrictive in any way. The scope of the invention is given by the appended claims, rather than the preceding description, and all variations and equivalents which fall within the range of the claims are intended to be embraced therein.