Patent Publication Number: US-6340080-B1

Title: Apparatus including a matrix structure and apparatus

Description:
RELATED APPLICATIONS 
     The present invention is a continuation-in-part of U.S. application Ser. No. 08/959,775 to J. David Carlson entitled “CONTROLLABLE MEDIUM DEVICE AND APPARATUS UTILIZING SAME” filed Oct. 29, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     Dampers and shock-absorbers are known which use a hydraulic fluid as the working medium to create damping forces to control or minimize shock and/or vibration. Typically, the damping forces are generated by a pressures resisting movement between operative components of the damper or shock absorber. One class of these devices includes magnetorheological (MR) fluid devices. MR devices may be of the “rotary-acting” or “linear-acting” variety. Known MR devices include linear dampers, rotary brakes and rotary clutches. Each MR device employs a Magnetorheological (MR) fluid comprised of soft-magnetic particles dispersed within a liquid carrier. Typical particles include carbonyl iron, and the like, having various shapes, but which are preferably spherical and have mean diameters of between about 0.1 μm to about 500 μm. The carrier fluids include low viscosity hydraulic oils, and the like. In operation, these MR fluids exhibit a thickening behavior (a rheology change) upon being exposed to a magnetic field. The higher the magnetic field strength exposed to the fluid, the higher the damping/restraining force or torque that can be achieved within the MR device. 
     MR fluid devices are disclosed in U.S. Pat. No. 5,816,372 entitled “Magnetorheological Fluid Devices And Process Of Controlling Force In Exercise Equipment Utilizing Same”, U.S. Pat. No. 5,711,746 entitled “Portable Controllable Fluid Rehabilitation Devices”, U.S. Pat. No. 5,842,547 entitled “Controllable Brake”, U.S. patent application Ser. No. 08/674,179 now U.S. Pat. No. 5,878,871 entitled “Controllable Vibration Apparatus” and U.S. Pat. Nos. 5,547,049, 5,492,312, 5,398,917, 5,284,330, and 5,277,281, all of which are commonly assigned to the assignee of the present invention. 
     Known MR devices advantageously can provide controllable forces or torques, as the case may be, but, as currently designed, such devices are comparatively expensive to manufacture. These devices typically include a housing or chamber that contains a quantity magnetically controllable fluid, with a movable member, a piston or rotor, mounted for movement through the fluid in the housing. The housing and the movable member both include a magnetically permeable pole piece. A magnetic field generator produces a magnetic field across both pole pieces for directing the magnetic flux to desired regions of the controllable fluid. Such devices require precisely toleranced components, expensive seals, expensive bearings, and relatively large volumes of magnetically controllable fluid. The costs associated with such devices may be prohibitive to their use in certain applications, for example, washing machines and home exercise devices. Therefore, there is a long felt, and unmet, need for a simple and cost effective MR fluid device for providing variable forces and/or torques. 
     RELATED APPLICATIONS 
     The present invention is a continuation-in-part of U.S. application Ser. No. 08/959,775 to J. David Carlson entitled “CONTROLLABLE MEDIUM DEVICE AND APPARATUS UTILIZING SAME” filed Oct. 29, 1997. 
     SUMMARY OF THE INVENTION 
     The present invention provides a controllable medium device which uses a vastly reduced quantity of controllable rheological medium as compared to prior art devices, and which eliminates the need for expensive seals, bearings, and precisely toleranced components. As a result, the cost to manufacture such devices is dramatically reduced. 
     According to the invention, a small amount of controllable medium, preferably in fluid form, is entirely contained in a working space between relatively movable members subjected to the magnetic field by a fluid-retaining means, for example, an absorbent matrix (preferably an open cell foam or the like) or a wicking member. The inventor herein discovered that an absorbent member can hold a sufficient amount of fluid to produce a significant rheological effect between a first pole member and a relatively movable second pole member. The invention may be incorporated in various physical embodiments such as linear dampers, rotary dampers such as brakes, mountings, pneumatic devices and applications therefor. 
     In particular, the present invention is a magnetorheological medium device which comprises first and second members coupled for relative movement and having a working space therebetween, means for producing a magnetic field that acts on the first and second members and the working space and a field controllable medium contained substantially entirely in the working space. 
     A working space is provided by spacing the first and second members using structural supporting means. In a piston and cylinder device, for example, a working space is provided by selecting a piston head to have an outer dimension that is smaller than an inner dimension of the cylinder by a predetermined amount. The difference in size provides the working space when the piston head is assembled in the cylinder. In a piston and cylinder device, the structural support to maintain the spacing may conveniently be provided by a fluid retaining material surrounding and preferably fixed to the piston head. In a disk brake device, the working space is provided by mounting the rotor and caliper yoke in such a way as to space apart the surface of the rotor and the inner surfaces of the calipers. In other devices, spacing means for maintaining a constant gap dimension of the working space are positioned at a first and second end of the matrix structure. Preferably, the spacing means comprises at least one disc and may be integral with a first member. 
     According to a preferred embodiment of the invention, a controllable fluid is contained in the working space by a material providing an absorbent matrix disposed in the working space. Absorbent matrix is used here to indicate a material that has the ability to pick up and hold a fluid by wicking or capillary action. In a particularly preferred embodiment, the absorbent matrix is a sponge-like material, for example, an open-celled or partly open-celled foam. Polyurethane foam and rubber foam are examples of particularly suitable materials. Foams made of other materials are also suitable, and examples include silicone rubber, polyamide, viton rubber, neoprene, Ioner rubber, melamine, a polyimide high temperature foam and metal foams. 
     An absorbent matrix can also be formed of other material structures, such as an unwoven material (e.g. a mineral wool), or a felt, for example, Nomex brand aramid fiber felt or a compressed carbon fiber felt. In addition, a woven fabric could be used, made from materials such as Kevlar brand fiber, graphite, silica, Nomex brand aramid fiber, polybenzimadazole, Teflon brand fiber and Gore-Tex brand fiber. Alternatively, a mesh material, such as a metal mesh, could be used. 
     Other structures that can contain a fluid, for example, brushes, flocked surface materials, wipers, and gaskets are also suitable. 
     The absorbent matrix need not entirely fill the working space, as long as the field controllable medium is contained in the working space. Thus, the absorbent matrix may be formed as a structure having a plurality of cavities, such as a honeycomb or other network structure, to contain the medium in the working space. 
     By containing an effective amount of controllable medium only in the working space of the device, no expensive seals are needed to contain the controllable medium as in the prior art. 
     According to another aspect, the invention comprises an apparatus, such as a controllable damper, having a transmission that converts relative linear motion between a first and second component into rotational motion of the second member. Further, the transmission may increase the relative motion and speed between the first and second members. Such transmission means preferably causes a mechanical amplification which multiplies the force produced by the apparatus by a predetermined factor. 
     In particular, the apparatus comprises a disc rotably mounted to a housing, a pole unit mounted stationarily relative to the housing, and a field generator. The disc is coupled to the first component (e.g., including a rod or rack) by means of a friction drive or pinion gear. The working space between the rotor disc and pole unit is filled by a fluid retaining matrix structure. This embodiment of the invention substantially reduces the amount of high-permeability steel required in the device for any given force capacity. Except for the electromagnetic coil and matrix filled structure retaining the field responsive medium (e.g., magnetorheological fluid), all other components may be made from low permeability, non-magnetic materials such as plastic or aluminum. 
     According to another aspect, the invention is an apparatus, comprising: a first component, a second component including; a housing, a first member mounted stationarily relative to the housing, and a second member spaced from the first member to form a working space therebetween, the second member rotatable relative to the first member, a matrix structure disposed in the working space, a field responsive medium retained in the matrix structure, and a field generator for generating a flux in said members thereby producing a field in the working space to change the rheology of said medium and resultantly produce a resistance to relative motion between said members, and a transmission converting linear motion of the first component to rotary motion of the second member. 
     According to another aspect, the invention comprises a first component, a second component including a first member, a second member spaced from the first member to form a working space therebetween, means for mounting the second member such that the second member may rotate relative to the first member, a matrix disposed in the working space, a field responsive medium retained in the matrix structure, and means for producing a magnetic field in the working space to change the rheology of the medium and resultantly produce a resistance to relative motion between the members, and means converting linear motion of the first component to rotary motion of the second member. 
     According to another aspect, the invention is an apparatus, comprising: a first component, and a second component that is moveable relative to the first component, the second component including; a housing, a first member mounted stationary in the housing, a second member spaced from the first member to form a working space therebetween, means for rotatably mounting the second member in the housing such that the second member may rotate relative to the first member, means for retaining a field responsive medium in the working space, and means for producing a field in the working space to change a rheology of the medium and resultantly produce a resistance to relative motion between said members, and a transmission converting linear motion of the first component to rotary motion of the second member. 
     It is another advantage of the invention that the amount of controllable medium needed to accomplish the rheology-based resistance effect is dramatically reduced to only the amount contained in the working space. 
     Another advantage of the invention, is providing a linear damper that requires no seals or bearings. 
     Another advantage of the invention, is providing a linear damper that doesn&#39;t require precisely toleranced components, i.e., non-ground piston rods and loosely toleranced outer member tubes and pistons. 
     According to the invention, means for generating a field in the first and second member and the working space is mounted to either of the first or second members in proximity with the working space. For example, in a piston/cylinder damper, the generating means can be at least one coil circumferentially wrapped on the piston head. In a rotary damper, the generating means can be at least one coil mounted to a yoke having arms between which the rotor turns. 
     A damping device in accordance with the invention can be incorporated in a number of apparatuses where it previously was cost-prohibitive to use controllable dampers. For example, the dampers of the invention can be used in washing machines to control vibration during various cycles. A resistance device of the invention can also be incorporated in exercise devices, such as bicycles, step machines, and treadmills to provide variable resistance. 
     The above-mentioned and further features, advantages and characteristics of the present invention will become apparent from the accompanying descriptions of the preferred embodiments and attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings which form a part of the specification, illustrate several key embodiments of the present invention. The drawings and description together, serve to fully explain the invention. In the drawings, 
     FIG. 1 is a schematic side view of a magnetorheological linear resistance device in accordance with the present invention, 
     FIG. 2 is a partial isometric view of an absorbent matrix material for the resistive device, 
     FIG. 3 is a cross sectional view of a damper having an alternative fluid retaining structure, 
     FIG. 4 is a cross sectional side view of a passive linear damper, 
     FIG. 5 is a cross-sectioned side view of a controllable linear damper, 
     FIG. 6 illustrates an alternative embodiment of the damper of FIG. 5 having a multiple coil field generator, 
     FIG. 7 a cross-sectioned side view of a linear rod damper embodiment of MR device, 
     FIG. 8 is a perspective side view of a controllable linear damper having a movable strip and a stationary yoke, 
     FIG. 9 is a perspective side view of an alternative yoke member for the device of FIG. 8, 
     FIG. 10 a  is a perspective cross-sectioned view from the front of an alternative linear strip damper or brake, 
     FIG. 10 b  illustrates a field generating coil for the linear strip damper of FIG. 10 a,    
     FIG. 10 c  is a pole piece used in connection with the linear strip damper of FIG. 10 a,    
     FIG. 11 is a front view of a brake device for a continuous belt, 
     FIG. 12 is a side perspective view of a brake device for a rotor disc, 
     FIG. 13 illustrates a device for replenishing controllable medium to a device as in FIG. 12, 
     FIG. 14 illustrates a nipple arrangement for supplying or replenishing controllable medium to a device, 
     FIG. 15 is a perspective view from the side of a pivoting damper arrangement, 
     FIG. 16 is a perspective, cross-sectioned view of a two rotor brake system, 
     FIG. 17 is an alternative structure for the brake elements with a rotor, 
     FIG. 18 is an exploded view of the brake elements of FIG. 17, 
     FIG. 19 is a front sectional view of a front loading washing machine including controllable dampers, 
     FIG. 20 is a graph of rotation speed of a washing machine tub during a washing cycle, 
     FIG. 21 is a graph of transmitted forces from a washing machine tub during a spin cycle, 
     FIG. 22 is a side sectional view of a damper with an integrated spring; 
     FIG. 23 is a side sectional view of a top loading washing machine include a damper with an integrated spring; 
     FIG. 24 is a side sectional view of a damper incorporated in an air spring supported leveling table for providing vertical damping; 
     FIG. 25 is a side view of a step machine incorporating a resistance device, 
     FIG. 26 is a side view of a stationary exercise bicycle incorporating a resistance device, 
     FIG. 27 is a side sectional view of a treadmill having a damper in accordance with the invention to control the impact conditions at the deck, 
     FIG. 28 is a side sectional view of a rotary brake in accordance with the invention, 
     FIG. 29 is a perspective view of another embodiment of the controllable apparatus in accordance with the invention, 
     FIG. 30 a  is a top view of the lower half of the housing of the controllable device of FIG. 29, 
     FIG. 30 b  is a is a bottom view of the housing of the controllable apparatus of FIG. 29, 
     FIG. 31 is a bottom view of the second half of the housing of FIG. 29, 
     FIG. 32 is an enlarged perspective view of the field generator and pole unit in accordance with the invention, 
     FIG. 33 is a perspective view of the first component of the controllable device of FIG. 29, 
     FIG. 34 is an enlarged perspective view of the second member, shaft and friction member in accordance with the invention, 
     FIG. 35 a  is a cross-sectional end view of the apparatus of FIG. 29 along line  35 — 35  thereof, 
     FIG. 35 b  is a cross-sectional side view of the apparatus of FIG. 29 along line  35 — 35  thereof, 
     FIG. 36 is a is a top view of the apparatus of FIG. 29 with the top half of the housing removed for clarity, 
     FIG. 37 is a partial perspective view of an alternate friction member for the controllable apparatus in accordance with the invention, 
     FIG. 38 is a cross-sectioned side view of another embodiment of controllable apparatus showing the disc, field generator, pole unit, matrix, and transmission, all positioned in the housing in accordance with the invention, 
     FIG. 39 is a is a perspective view of another embodiment of the controllable device in accordance with the invention shown in a assembly including a vibration sensor and control electronics, 
     FIG. 40 is a top view of yet another embodiment of the invention, 
     FIG. 41 is a cross-sectional side view of the apparatus of FIG. 40 along line  41 — 41 , 
     FIG. 42 is a top view of yet another embodiment of the invention, 
     FIG. 43 is a side view of the apparatus of FIG. 42, and 
     FIG. 44 is a cross-sectional side view of the apparatus of FIG. 43 along line  43 — 43 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the Drawings where like numerals denote like elements, in FIG. 1, shown generally at  20 , is a schematic illustration of a device for providing preferably controllable resistance between two relatively movable structures (not shown). The device  20  includes a first member  22  and a second member  24  that are disposed in spaced relation or coupled for relative movement along the mating surfaces. A working space  26  is provided between the coupled portions by spacing the mating surfaces apart. Means for generating a field, indicated by the vertical arrows, produces a field that preferably acts on the first member  22  and the second member  24  and (generally across) the working space  26 . 
     According to the invention, the field generating means can be an electric field generator or a magnetic field generator. For reasons relating to cost, power requirements, and field strength, it is preferred to use a magnetic field generating means. The first  22  and second  24  members each preferably include magnetically permeable material (such as a soft magnetic steel), which can be done by forming each of the members  22 ,  24  entirely from such a material, or including such material as a component part or integrated portion of the member  22 ,  24 . A field responsive controllable medium  28 , such as a controllable fluid, compatible with the field generating means is contained in the working space  26  by fluid retaining means  30 . Magnetorheological controllable fluids as contemplated for the present invention are disclosed in, for example, U.S. Pat. No. 5,382,373 to Carlson et al. and U.S. Pat. No. 5,578,238 to Weiss et al. 
     For use with an electric field generator (not illustrated), an electrical conducting material, such as aluminum, is incorporated in the first  22  and second  24  members, and is used with an Electrorheological (ER) fluid. 
     The field generating means alters the rheology of the controllable medium  28  in proportion to the strength of the field. The controllable medium  28  becomes increasingly viscous with increasing field strength, and provides a shear force to resist movement between the members  22 ,  24 . The members  22 ,  24  are preferably fixedly secured to relatively moveable structures (not shown) to provide resistance to movement therebetween. 
     The inventor has discovered that a significant shear force for resisting relative movement can be obtained with a small amount of controllable medium  28 , such as MR fluid, contained in the working space between the movable members. Thus, a variety of relative movements, rotational, linear, pivoting, that include shear movement between two structural members can be controlled by a device according to the invention. By containing substantially the entire amount of controllable medium or fluid at the working space, the present invention avoids the need to provide a large quantity of medium or fluid, and the associated seals and containing devices of the prior art, and accordingly reduces the tight tolerances formerly needed on all components. 
     Any suitable means for containing the medium or fluid at the working space can be used. According to a preferred embodiment of the invention, means for containing the controllable medium in the working space comprises an absorbent matrix material, that is, a material that can take up and hold the controllable medium by wicking or capillary action. The absorbent matrix preferably provides a structure having open spaces for containing the medium, and the material forming the matrix may or may not be absorbent itself. A particularly preferred absorbent material is a sponge-like material, for example, an open-celled or partly open-celled foam. Examples of materials suitable for making a foam are polyurethane, rubber, silicone rubber, polyamide, neoprene, Ioner, melamine, polyimide high temperature foam, and metal foam. By way of example, if the absorbent material is, for example, a foam, it is desirable to have the foam compressed between about 30% and 50% from a resting state in its installed state. 
     In addition, other exemplary absorbent matrix materials include felts, including felts made of materials such as Nomex brand aramid fiber, compressed carbon fiber, or other materials, loose weave fabrics, mineral wool, cloths made from graphite, silica, Nomex brand aramid fiber, polybenzimadazole fiber, Teflon brand fiber, and Gore-Tex brand fiber, fiberglass wicking, and woven brake or clutch lining material. Other materials and structures are also suitable, for example, a metal mesh, a brush, or a flocked surface material. 
     The medium or fluid retaining means  30  is preferably fixed to one of the relatively moving members to ensure that it remains disposed in the working space  26 . According to a preferred embodiment, a fluid retaining means is adhesively bonded to one member, for example, by a pressure sensitive adhesive. A preferred material is a polyurethane foam having a pressure sensitive adhesive on one side. The foam may be readily attached to one member by the adhesive. Alternatively, the fluid retaining means can be shaped so that it is held in place by the structure of the member, for example, a tubular shaped foam material may be fitted on a piston head as a sleeve. 
     The retaining means need not fill the working space. An absorbent matrix such as that illustrated in FIG. 2, having a plurality of cavities  32  for holding the controllable medium may be placed in the working space. 
     In a linearly acting damper, for example, a piston and cylinder arrangement as illustrated in FIG. 3, the medium or fluid retaining means  30  alternatively can be formed as dams  34  at the boundaries of the working space  26 , either inside or outside the working space  26 , to trap the medium or fluid in the space  26  in proximity to the magnetic poles  54 ,  54 ′. As may be understood, in a piston  50  and cylinder  40  arrangement, the working space  26  are defined between cylindrical portions of the of the piston  50 , and localized portions of the inner wall of the cylinder  40 . As the piston  50  slides in the cylinder  40 , the working space  26  moves with the piston  50 . The field generating means  80  is conveniently carried and mounted on the piston  50 . The dams  34  slide with the piston head  50  as it slides relative to the cylinder  40  to retain controllable fluid  28  in the moving working space  26  and in proximity the field generating means. Thus, when the poles  54 ,  54 ′ are energized, the controllable fluid  28  changes rheology in the space  26 . The dams  34  can be formed of elastomer, felt, or foam materials, as is convenient. Alternatively, packing material or gasket material could be used to form the dams. Other structures that may occur to those skilled in the art could also be used. 
     As will be understood by those skilled in the art, any suitable fluid retaining means could be used in the embodiments described below, and the embodiments are not limited to the particular, preferred fluid retaining means described. 
     A controllable fluid made from a suspension of iron alloy particles suspended in a carrier, as disclosed in, for example, U.S. Pat. No. 5,382,373 to Carlson et al. and U.S. Pat. No. 5,578,238 Weiss et al. may be used in the present invention. Preferably, the controllable fluid for the present invention has the consistency of a grease or paste to aid in containing the fluid in the retaining means. One such grease is described in PCT/US97/02743, entitled “Magnetorheological Fluid Seismic Damper.” 
     The invention can be incorporated in a wide range of devices for resisting relative movement between members, including linear dampers, rotary dampers, resistance devices for exercise equipment, braking devices, and others, as will be understood from the following descriptions. 
     FIG. 4 illustrates a passive linear damper  38  in the form of a piston and cylinder arrangement. The damper of FIG. 4 includes a cylinder  40  and a piston  50  disposed in the cylinder for sliding movement. The piston  50  is preferably supported in the cylinder  40  by fluid retaining means, here, an absorbent matrix material  30 , for example, an open cell foam. The absorbent matrix material  30  is wrapped around circumference of the piston  50 , and is fastened to the piston  50  by pressure sensitive adhesive. The absorbent matrix material  30  spaces and supports the piston  50  from the inner surface  42  of the cylinder  40 , thus providing a working space  26  between the piston  50  and cylinder  40 . The absorbent matrix material  30  also eliminates the need for bearings to support the piston  50 , which reduces the cost of the damper. A controllable fluid  28  is contained in the absorbent matrix material  30 . To prevent an air spring effect, the cylinder  40  is preferably provided with vents  44  to relieve air pressure during movement of the piston  50 . 
     The cylinder  40  and the piston  50  include pole pieces  54 ,  54 ′, which are parts formed of soft-magnetic, magnetically permeable material. The cylinder  40  can be formed entirely out of a magnetically permeable metal or formed with an inner metallic sleeve as the pole piece  54 ′. The piston  50  may similarly be formed entirely out of metal or, as illustrated, to have end pole pieces  54  formed of magnetically permeable material. 
     In this embodiment, a permanent magnet  60  including axially directed north n and south s poles is carried on the piston  50  and produces a magnetic field, indicated by the flux lines  62 . The magnetic field acts on the pole pieces  54  of the piston  50 , the pole piece  54 ′ of the adjacent portion of the cylinder  40 , and the working space  26 . By selecting the field strength of the magnet  60 , the force resisting movement of the piston  50  in the cylinder  40  can be selected. Those skilled in the art will recognize that the magnetic field and controllable fluid will resist linear, that is sliding, movement of the piston, and also rotation of the piston about the shaft axis. A piston rod  56  is fixedly secured to the piston  50 . Suitable means for connecting to the relatively moveable structures (not shown) are provided, such as rod end  51  and bushing  52 . 
     A controllable linear damper  70  in the form of a piston and cylinder is illustrated in FIG.  5 . The damper  70  includes a piston  50  disposed in a cylinder  40 . Each of the piston  50  and the cylinder  40  includes a pole piece  54 ,  54 ′, the cylinder  40  in this case being formed entirely of a magnetically permeable material, and the piston  50  having a core of magnetically permeable material. The piston head is wrapped with an absorbent matrix material  30  which functions as the means for containing a controllable fluid  28  in the working space  26 . Magnetic field generating means in the form of a coil  80  is mounted on the piston  50 , and is connected to a controller and power supply (not shown) by wires  82  (shown graphically as a single line) that preferably pass through a hollow interior of the piston rod  56 . The resistive force produced can be varied by changing the magnetic field strength which is controlled by the amount of current supplied to the coil  80  by the controller (not shown). The controllable damper  70  may be adjusted from low resistance to high resistance to restrain relative movement between the piston  50  and the cylinder  40 . 
     FIG. 6 illustrates an alternative embodiment of the damper of FIG. 5, in which a plurality of coils  80   a,    80   b,  and  80   c  are wound on the piston  50 . The cylinder  40  includes a sleeve  46  of magnetically permeable material to serve as the cylinder pole piece. Multiple coils are advantageous in situations where the cylinder pole is subject to magnetic saturation, such as where the cylinder wall is thin or a sleeve  46 , as illustrated, is used as the magnetically permeable member. As in the damper of FIG. 5, wires  82  connect the field generating coils  80   a,    80   b,  and  80   c  to a controller. The coils  80   a,    80   b,  and  80   c  are alternately wound so that the fields produced are additive. Elastomer bushings  52  may be added as the means to attach to the structural members (not shown), the elastomer helping to reduce the harshness in any control algorithm utilized. 
     The device of FIG. 7 is useful for motion control or guide mechanisms, or in a braking device. Pole pieces  54  are supported on a shaft  56  by an absorbent matrix material  30  for sliding and/or rotational movement, as illustrated by arrows A and B, respectively. The absorbent matrix material  30  supports the pole pieces  54  relative to shaft  56  and at a distance to provide the working space  26 . Thus, in this embodiment, no bearings are necessary to support relative movement of the pole pieces  54  relative to shaft  56 . The pole pieces  54  may be part of a moving component  49  and the shaft  56  may be part of a fixed frame  48 . Alternatively, the pole pieces  54  may be the fixed element. A controllable fluid medium  28  is contained in the absorbent matrix material  30 . A coil  80  is circumferentially wound and generates a magnetic field acting on the shaft  56 , the pole pieces  54  and the working space  26  as indicated by the dotted field lines shown. 
     Other linear movement devices could advantageously incorporate the resistance device of the invention. FIG. 8 illustrates a device  120  in which a strip  100  is coupled for linear movement in a yoke member  110 . The yoke  110  is C-shaped and includes two opposed jaws  112 ,  114  defining a working space  26  in which the strip  100  is disposed for sliding movement. Fluid retaining means  30 , such as an absorbent matrix, is carried on the jaws  112 ,  114  in the working space  26  to hold the controllable fluid  28 . A coil  80  is mounted on a shoulder  116  of the yoke  110  between the jaws  112 ,  114  to generate a magnetic field that acts on the yoke jaws  112 ,  114 , and across the strip  100  and the working space  26 . Fittings  166  as shown in FIG. 14 allow controllable fluid to be replenished in the working space  26  and absorbent matrix  30 . As shown in FIG. 9, the yoke  110  may be alternatively formed from a stack of magnetically permeable layers laminated together. The strip  100  and yoke  110  are preferably formed of a soft magnetic ferrous metals. Bracket  115  attaches the yoke  110  to a stationary structure  148 . Means such as bolt hole  152  shown are used for attaching strip  100  to a movable structure (not shown). 
     An alternative linear strip device  120 ′ is illustrated in FIG. 10 a.  In this embodiment, a strip  100  is disposed between the opposed walls  122  of a U-shaped yoke  110 . Fluid medium retaining means  30  is disposed in the working space  26  between the walls  122  and the strip  100 . In this embodiment, a field generating means in the form of a square-shaped coil  80 , illustrated separately in FIG. 10 b,  is disposed to surround a magnetically soft pole piece  124 , illustrated separately in FIG. 10 c,  mounted between the walls. 
     A linear acting brake is illustrated in FIG.  11 . In this device an endless metal belt  130 , for example, a drive belt, of a soft magnetic/magnetically permeable material is driven by one or more of the rollers  132 . The belt  130  passes through working space  26  provided between an upper pole  134  and a lower pole  136  of the brake. An absorbent material  30  is disposed in the working space  26  on both sides of the belt  130 . Field generating means  80  (shown in back of the belt  130 ) is provided as a coil that surrounds a shoulder member (not shown) interconnecting the poles  134 ,  136 . The field generating means  80  creates a magnetic field (indicated by the arrows) that acts on the plates, the belt  130 , and controllable fluid  28  in the working space  26 . The device acts at the maximum radius of the rollers  132 , which provides very effective braking. The device could also readily be used as a brake for a metal cable or wire, or other like drive member, as will readily understood, by replacing the endless belt with a cable, wire or other like drive member. Notably, in the case of a metal belt the brake only need act on a small lateral (into and out of the paper) portion of the belt  130 , thus leaving the majority of the belt free from a medium film. Appropriate shrouding may be added to cover the portion of belt including a film on its surface. 
     FIG. 12 illustrates a rotary braking device. A rotor element  140 , which could be a flywheel of an exercise machine, for example a stationary bicycle (see FIG.  26 ), is mounted for rotation on a shaft  142 . The rotor element  140  is preferably formed entirely of a magnetically permeable material. A yoke  110 , similar to that shown and described in FIG. 8 or  9 , is mounted so that the outer portion of the rotor element  140  passes between the jaws  112 ,  114  of the yoke  110 . The fluid retaining means  30 , in this embodiment formed of an absorbent matrix material, is carried in a working space  26  between the jaws  112 ,  114  to retain the controllable fluid  28  in the working space. A coil  80  for generating a magnetic field is mounted on the yoke  110 . The device may be variably activated to provide adjustable resistance to rotation of the rotor  140 . 
     The device of FIG. 12 may be used for large diameter rotors. In addition, the rotor  140  may be formed with sufficient inertial mass to act as a flywheel, as may be used in an exercise bicycle, ski machine, or step machine. Additional brake devices may be provided to increase the braking force. 
     The controllable fluid  28  is retained, for the most part, in the absorbent matrix material  30 , and a small amount will form a thin layer on the surface of the contacting outer portion of the rotor element  140 . Under normal conditions, the controllable fluid  28  is not consumed, and spreading of a thin layer on the rotor  140  presents no problem. Should the use conditions require that the controllable fluid  28  be replenished, for example, at high rotation speed where the fluid film on the rotor  140  is spun off by centrifugal effects, a device as shown in FIG. 13 provides a controllable fluid replenishment source  150 , a pan container, in communication with the outer portion of the rotor element  140 . As the rotor element  140  turns through the pan  150 , controllable fluid is picked up on the outer portion of the rotor element  140  and carried into the working space  26  to be absorbed by the absorbent matrix material  30 . Appropriate shrouding may be used. 
     FIG. 14 illustrates an alternative embodiment for supplying and replenishing a controllable fluid medium  28  to the working spaces  26 . A moving element  153  (plate, strip, disc, etc.) is positioned in working spaces  26  between two pole piece jaws  160 ,  162  which carry magnetic flux therein. Fluid retaining means  30  is disposed in the working spaces  26 . This structure can be included within a linear or rotary acting device, as will be readily understood. The pole jaws  160 ,  162  have passages  164  that communicate with the working space  26 , and fittings  166  (similar to grease fittings) are mounted to the passages  164  to allow controllable fluid  28  to be introduced to the working space  26 . Although not shown, the fittings  166  may include means to prevent escape of the medium from the fitting  166  once filled, i.e., spring-loaded ball mechanisms or caps. 
     The yoke  110  as previously described can also be used for other apparatuses, for example, a reciprocating pivot apparatus as shown in FIG. 15, in which a pivoting element  170  mounted with a shaft  172  has an outer portion that moves between the jaws  112 ,  114  of the yoke  110 . Shaft  172  is interconnected to a machine (not shown). Other applications will be apparent to those of ordinary skill in the art. 
     FIG. 16 illustrates, in perspective sectional view, a device in which two parallel disc-like rotors  180 ,  182  are mounted for rotation with a shaft  184 . The shaft  184  being rotatably attached to other rotating componentry of a machine (not shown). A U-shaped pole bracket  190  having a center spacing piece  192  is positioned adjacent to and straddling a radially outer portion of the rotors  180 ,  182 . Multiple working spaces  26  are provided between legs  194 ,  196  of the bracket and the center piece  192 . The rotors  180 ,  182  are positioned so that a portion rotates through the working spaces  26 . Fluid retaining means  30  includes an absorbent material disposed in the working spaces  26 . Field generating means includes a single annular coil  80  mounted in the center piece  192 , which produced a field which acts on the pole bracket  190  and the working spaces  26 . A puck-shaped center pole  154  having disc-like end poles  154 ′ in contact therewith focus the magnetic field across the working spaces  26 . 
     FIG.  17  and FIG. 18 illustrate another braking device  200 . FIG. 17 is a sectional view of a rotor  140  mounted for rotation with a shaft  142 . Shaft  142  being rotatably mounted relative to stationary frame  148 . Rigidly connected to shaft  142  is pulley  265 . Pulley  265  is interconnected to a machine (not shown), such as an exercise machine, in this embodiment by cable  267  doubled about pulley  265 . The braking device  200 , shown in exploded view in FIG. 18, includes a U-shaped pole bracket  202  that defines a space for receiving the rotor  140 . Mounted to both inner surfaces of the legs of the pole bracket  202  are annular wound coils  80 , soft magnetic puck-shaped core  204  which supports the coils  80 , disc-shaped pole pieces  206  and a fluid retaining member  30 , such as a molded foam absorber. Each of the coils  80  generates a field that acts on the pole bracket  202 , pole pieces  206 , cores  204 , and fluid retaining member  30  and across the working spaces  26 . The coils  80  are wound in the same directions so that the generated magnetic fields are aligned. The approximate magnetic field lines are illustrated by the dotted line in FIG.  17 . 
     One particularly advantageous application for a linear damper of the invention is in washing machines. FIG. 19 illustrates controllable linear dampers  70 , such as those described with reference to FIG. 6, mounted in a front loading washing machine  210  as components of the suspension and damping system. The front loading machine  210  has a horizontally-mounted drum  212  including a rotational portion  213  rotationally fixed and drivable relative to drum  212  by a motor (not shown). The drum  212  (and rotational portion  213 ) are flexibly suspended relative to a cabinet  214  by flexible springs  216 . Dampers  70  provide control of radial vibrations of the drum  212 . 
     Controllable dampers according to the invention can be used in top-loading washing machines also to superior advantage, as illustrated in FIG. 23. A damper  70 ′ with an integrated spring  47 , such as a coil spring, is illustrated in sectional view in FIG.  22 . The damper  70 ′ is similar to that shown in FIG. 6, and includes a soft magnetic cylinder  40  in which is mounted a piston  50  for relative axial sliding movement. The piston  50  carries a circumferentially wound annular coil  80 , soft magnetic piston head including poles  54 , and a fluid retaining absorbent matrix material  30 , such as a open-celled polyurethane foam is wrapped around the piston head. The spring  47  acts between the piston  50  and the cylinder  40  to provide vertical and radial support to the drum  212 ′ (FIG.  23 ). Suitable means for securing to the drum  212 ′ and cabinet  214 ′ are provided such as rod end  51  and bushing  52 . 
     FIG. 23 illustrates a plurality (preferably four) of the dampers  70 ′ of FIG. 22 mounted in a top-loading washing machine  220 . Dampers  70 ′ including integral springs  47  are used to suspend the drum  212 ′ from the washing machine cabinet  214 ′. 
     Controllable dampers (ex.  70 ,  70 ′) allow for adjusting the damping of the washing machine system to the different washing cycles. A typical wash cycle for a front loading machine is illustrated in FIG. 20 in terms of drum rotational speed in Revolutions Per Minute (RPM) over time. The cycle from T 1  to T 2  represents an agitation/wash cycle in which the rotating member  213 ,  213 ′ executes reciprocal rotations. As the rotation accelerates into the spin cycle, represented by the period T 3  to T 4 , the drum assembly  213 ,  213 ′ passes through a resonance condition, which is shown in FIG. 21 between speed points A and B. By activating the damper  70 ,  70 ′ during this acceleration period T 3  to T 4 , damping can be imparted to the system and the transmitted force can be reduced. The washing machine cycle includes a second agitation T 6  to T 7  during the rinse cycle, and a second spin T 9  to T 10 , which includes a second resonance condition during the associated acceleration T 8  to T 9 . The damper  70 ,  70 ′ would be activated during this time also. The damper  70 ,  70 ′ is also preferably used at the end of the spin cycles when the drum decelerates through the resonance condition. 
     From FIG. 21, it can be seen that while increased damping is advantageous during the resonance condition between spin speeds A and B, increased damping will cause more force to be transmitted after the drum reaches spin speed than will low damping. Thus, the controllable dampers are preferably turned off after the drum leaves the resonance condition. The system of the invention advantageously allows damping to be adjusted for minimal force transmission throughout the washing machine cycle, which is a vast improvement over passive systems, in which a single, constant damping value must be chosen for all conditions. 
     Control of the dampers  70 ,  70 ′ may be through a timer coordinated with the washing machine control timer, or through a speed sensor monitoring the drum rotation and set to activate the dampers  70 ,  70 ′ at predetermined speeds, or through a vibration sensor  218 ,  218 ′ (FIG. 19,  23 ), for example, an accelerometer, monitoring drum vibration. Alternatively, vibration in the cabinet  214 ,  214 ′ may be monitored. 
     FIG. 24 illustrates another application for damper in accordance with the invention, in a air-spring leveling table. A table  240  is illustrated in part, and one supporting leg  242  (one of four) of the table is shown in the figure. The leg  242  encloses an air chamber  244  divided by a wall  246  having vents  248 . A damper  70 ″ includes a soft magnetic cylinder  40  mounted to the wall  246  by weldments or the like, and a piston  50  having a rod  56  connected to the table  240 . A bellows or rolling diaphragm  250  closes the upper portion of the chamber  244  and allows the table  240  to be supported and levitated by the air in the chamber  244 . The rod  56  is connected to pole  241  having permanent magnet  242  secured thereto. A field produced by the magnet  243  causes the pole  241  to be attracted to the table piston  247  made form a ferromagnetic material. This avoids having to cut a hole in bellows  250 . 
     The damper  70 ″ helps control the motion of the table  240  when air is added to or removed from the chamber  244 , by quickly damping the transient motions which cause the table  240  to oscillate. 
     Dampers and resistance devices in accordance with the invention can also be advantageously incorporated in exercise apparatus, as previously mentioned. FIG. 25 shows a simplified step machine  260  which includes a flywheel  140  and a resistance device  220  as described in connection with FIGS. 12,  16 , or FIG.  17 . The resistance device  220  may be controlled to adjust the resistance to rotation of the flywheel according to the user&#39;s preference. The device  220  according to the invention can generate high torque with a relatively small flywheel. 
     A similar rotary resistance device  220 ′, such as described in connection with FIGS. 12,  16  and  17 , can be mounted in an exercise bicycle  270 , shown in FIG.  26 . The resistance device  220 ′ is mounted on the bicycle flywheel  140 . 
     FIG. 27 shows a treadmill  280  having a damper  220 ″ including a linear strip  100  and a yoke  110  mounted between the deck  282  and frame. Alternatively, a linear piston and cylinder damper as in FIG. 5,  6 , or  22  can be used. The damper  220 ″ can be controlled to provide a stiffer or softer running surface. For example, for slow running, that is, low foot strike frequency, a runner may prefer a softer, springier surface, and for fast running, a stiffer surface. The damper can also adjust the damping of the deck surface  282  for the weight of the user, to increase damping for heavier users and decrease it for lighter weight users. FIG. 28 illustrates a rotary brake  300  in accordance with the invention. 
     The brake  300  includes a fixed member, or stator  302 , which forms an outer member. The stator  302  is formed of magnetically permeable material to act as a pole piece, and includes an interior space  304 . A disc-shaped rotor  306  is disposed in the interior space  304 , and is rigidly connected to a shaft  310  for rotation in the interior space  304 . The rotor  306  is spaced from the inner surfaces of the stator  302  that define the interior space  304 , which provides a working space  26  between the stator  302  and the rotor  306 . An absorbent material  30  is disposed in the working space  26  to surround the radially outer portion of the rotor  306 . A controllable medium  28  is contained by the absorbent material  30 . A circumferentially wound field generating coil  80  is mounted between halves  303  of the stator  302  and preferably radially surrounds the rotor  306 . The coil  80  is connected by wires  82  to a controller and power source (not shown). 
     As shown by the field lines  312 , the coil  80  produces a field that acts on the stator  302 , the rotor  306  and across the working space  26 . Activation of the field causes resistance to rotation of the rotor  306 . The absorbent material  30  eliminates the need to seal the interior space  304  of the stator. Further, no bearings are required. 
     FIGS. 29-44 illustrate several other embodiments of controllable apparatus  470  in accordance with the present invention. With reference to FIGS. 29-36, a first embodiment of the apparatus is described. The device  470  includes a first component  72  that is relatively moveable (linearly reciprocatable) along a linear axis in relation to a second component  76 . 
     The first component  72 , as best shown in FIG. 33, preferably comprises an attachment member  51 , such as a plastic rod end, and a preferably hollow rod-shaped shaft element  74  extending therefrom. The rod end  51  is secured to the shaft  74  via suitable adhesive and/or mechanical locking means, such as a press fit. The rod is preferably steel or aluminum and may have a roughened surface, such as by knurling. Alternatively, the rod  74  and rod end  51  may be provided in an integral plastic unit. 
     The second component  76  comprises a preferably plastic housing  78 , a first member  22  mounted stationarily relative to the housing  78 , and a second member  140  spaced from the first member  22  to form a working space  26  therebetween; the second member  140  being rotatable relative to the first member  22 . In addition, the second component  76  also includes a matrix structure  30  disposed in the working space  26 , a field responsive medium  28  retained in the matrix structure  30 , and a field generator  80  for generating a magnetic flux in the members  22 ,  140  thereby producing a magnetic field in the working space  26 . Exposure of the medium  28  to a field changes the rheology of the medium  28  (apparent viscosity) which, in turn, generates a resistance to relative motion (a resistance or damping force) between the members  22 ,  140 , and thus, also between the components  72 ,  76 . The apparatus  470  also includes a transmission  94  for converting linear motion of the first component  72  into rotary motion of the second member  140 . 
     According to a preferred embodiment, the housing  78  comprises first and second halves  78   a,    78   b  that are interconnected by fasteners  86  or other suitable fastening means, such as adhesive or ultrasonic welding. Most preferably, the housing  78  is formed of a low friction material, such as Nylon or other suitable plastic or rigid material. A first member  22 , such as included in a pole unit  90 , is mounted in the housing  78 . At least one, and most preferably both, halves  78   a,    78   b  of the housing  78  includes an appropriately shaped recess  79  (FIGS. 30-31) formed therein for receiving a portion of the pole unit  90 . These recesses  79  confine and position the unit  90  such that it is immovable relative to the housing  78 . Further, the first component  72  is guided in a guideway  85  formed in the housing  78  (FIGS. 30,  35   a ). 
     As best shown in FIG. 32, the pole unit  90  includes first and second halves  90   a,    90   b  (which are preferably identical) which are in contact with each other at a first end thereof. The pole unit  90  is preferably manufactured from a highly magnetically permeable, soft-magnetic material, such as 12L-14 steel. In the embodiment shown, the halves  78   a,    78   b  are secured together by fasteners  71 . However, as shown in FIG. 38, the halves  78   a,    78   b  need only be in intimate contact with each other and may, for example, be stamped and bent plates. Most preferably, the pole unit  90  generally comprises a U-shape. Received over one leg of the unit is the field generator  80 . The pole unit  90  may include a tapered portion  73  (FIGS. 32,  36 ) formed at a terminal end adjacent to the second member  140 . The apparatus may also include a radiused portion  75  of radius R 2  formed at a terminal end of pole unit  90  at a position adjacent to the second member  140 ; the radiused portion  75  having a center which generally corresponds (coincident) to a center of a radius R 1  of the second member  140 . The radius R 2  of the pole unit  90  is smaller that the radius R 1  of the disc  140  such that there is overlapping portion  67  of the pole unit  90 . 
     The generator  80  includes a non-magnetic (e.g., plastic) bobbin  89  having a generally rectangular shape, a pocket (not shown) formed therethrough, end walls  89   a,    89   b,  and a tab  89   c.  Molded into the tab  89   c  are spade connectors thereby forming an electrical connector  97 . A coil  92  of electrically insulated, copper magnet wire of approximately 33 gage and approximately 700 turns is mounted on the bobbin  89 . Respective ends of the coils  92  are wound about, connected to, and soldered to, the respective spade connectors of an electrical connector  97 . The electrical connector  97  passes through a hole  77  formed in the housing  78 . The coil  92  is disposed about, and surrounds, either one of the first and second pole pieces  90   a,    90   b.  Energization of the generator  80  with appropriate electrical current (approx. 200 milliamps) produces a magnetic flux in the pole unit  90  and, in particular, within the overlapping portion  67  thereof. 
     Preferably, the second member  140  comprises a disc that is mounted to a shaft  142 , such as by press fitting, welding, adhesive, screws, or the like. Highly magnetically permeable soft-magnetic material such as 12L-14 steel makes up the working portion (in the area of overlap) of the disc  140 . 
     In between the disc  140  and each respective leg  90   a,    90   b  of the pole unit  90  is interposed a matrix structure  30  which retains (preferably absorbing) a field responsive medium  28  (e.g., a magnetorheological fluid—liquid or grease). The matrix structure  30  preferably comprises a ether-or ester-based, reticulated, open-cell polyurethane foam having between about 40 and about 80 pores per inch (about 1.6 to 3.1 pores/mm). Most preferably, the foam is formed (by a dinking die) into a washer-shaped element which may be adhered to the top and bottom surface of the disc  140  via suitable pressure sensitive adhesive. Alternatively, the structure  30  may be attached (glued) to, and substantially fill, the space in the housing  78 . In this option, the medium  28  may be retained only in the area adjacent to the pole unit  90 . Alternatively, the matrix  30  may be located only at the overlap area and adhered to the inside faces of the pole arms  90   a,    90   b  at the overlap area  67 . 
     The shaft  142  comprises small diameter pilots  88  formed at the ends thereof. The pilots  88  are rotatably received in bearing recesses  81  formed in halves  78   a,    78   b  of the housing  78 , thus the disc  140  is free to rotate within the housing  78 . The second member disc  140  is received between the halves  90   a,    90   b  of the pole unit  90  and extends almost to the field generator  80  (See FIGS. 35 a,    35   b ). Mounted on an end portion of the shaft  142  offset from the disc  140  is a friction member  83  (FIGS. 34,  35   a,  and  35   b ). The friction member  83  contacts the surface  84  of the shaft  74  of the first component  72 . 
     Thus, it should be apparent, that the friction member  83  and shaft  142  mounted in housing  78  collectively function as a transmission mechanism for converting linear motion of the rod  74  of the first component  72  into rotary motion of the disc  140 . In the preferred embodiment, the friction member  83  is at least one, and more preferably, a plurality of annular resilient members (e.g., a plurality of elastomeric o-rings). The o-rings are mounted in spaced-apart grooves formed in the shaft  142  and frictionally engage the rod  74  thereby interconnecting the shaft and rod. Alternatively, as shown in FIGS. 37 and 38, the friction member  83  may be an annular member of compliant material, such as elastomer (e.g., natural rubber, synthetic elastomer or blends thereof). Any other suitable material which exhibits some degree of flexibility and good surface friction characteristics may be employed, as well. An embodiment employing the alternative annular rubber friction element  83  and a stamped and bent pole unit  90  is shown in FIG.  38 . 
     The transmission  94  functions to convert liner to rotary motion. But also, the transmission  94  functions as a means for increasing the speed of the relative motion between the first component  22  (included in the pole assembly  90 ) and the second component  140 . By way of example, and not to be considered limiting, the transmission Amplification Ratio (AR) is approximately AR=6:1, where AR=Ravg/Rcontact. Ravg is approximately equal to (R 1 +R 2 )/2 whereas Rcontact is approximate radius where contact occurs with the shaft  74  of the first component. Including a transmission  94  allows for amplification of the force produced by the assembly including disc  140  and pole unit  90 . 
     In FIGS. 39-43, the apparatus  470  according to the invention is shown in an assembly interconnected between first  91  and second  93  relatively vibrating members. The members  91 ,  93  may include any relatively moving components where it is desired to produce a force, such as to damp motion or for controlling forces between the members. For example, the apparatus may comprise a damper to be included in a washing machine assembly to damp vibration between the frame and the tub thereof, or between any two relatively moving components of a machine. In the illustrated embodiment of FIG. 39, the apparatus  470  is controlled responsive to a vibration of the second member  93  detected by a sensor  95 , such as an accelerometer. The vibration may be compared to a preset threshold value by a control system  95   b  and current supplied to the apparatus  470  upon exceeding such threshold. 
     FIGS. 40-41 illustrates yet another embodiment of the apparatus  470 . In this embodiment, the first component  72  comprises a shaft extending through the body of the housing  78 . By way of example, the shaft may be part of a stationary component  93  in a positioning system and the housing  78  may be attached to a moving component  91  thereof. In FIG. 40, the apparatus  470  is shown with the top cover removed for clarity, thereby exposing the generator  80  including coil  92 , pole unit  90 , and disc  140 . It should be apparent that in this embodiment, the pole unit  90  is formed from a strap bent over upon itself forming a U-shape. 
     FIGS. 42-44 are directed to an embodiment of the apparatus  470  including a first component  72  having a rod  74  in the form of a rack having teeth  98  formed on the exterior thereof. The teeth  98  mesh with like teeth formed on the pinion gear  99  secured to shaft  142 . Longitudinal motion of the rod via motion of the moving component  91  causes rotation of the pinion gear  99  which rotates the interconnected shaft  142  and which, in turn, rotates the first disc-shaped member  140  relative to the second member  24 . Thus this embodiment also includes a transmission  94  for converting motion from linear to rotary form. The motion may be advantageously amplified via making the pinion gear  99  smaller than the average working diameter of the disc  140 . Although not shown, in this embodiment, the internal components (generator, pole unit, and matrix) may be identical to those described in any of the previous embodiments. It should be apparent from the foregoing, that the shape of the rod member  74  may be altered to suit the application. 
     In summary, it should be apparent from the foregoing that the present invention comprises a novel controllable device (either rotary or linear acting) which includes a controllable medium retaining means for holding medium (ex. a magnetically controllable fluid) in a working space between relatively moving components. The invention provides controllable devices and apparatus that are simpler to design and manufacture, and less costly, than prior devices. 
     While several embodiments including the preferred embodiment of the present invention have been described in detail, various modifications, alterations, changes, and adaptations to the aforementioned may be made without departing from the spirit and scope of the present invention defined in the appended claims. It is intended that all such modifications, alterations, and changes be considered part of the present invention.