Patent Publication Number: US-9896306-B2

Title: Apparatus and method for dampening oscillations of an elevator car

Description:
This application claims priority from U.S. Provisional Patent Application Ser. No. 61/055,794, filed on May 23, 2008 for Active Guiding And Balance System For An Elevator, and from U.S. patent application Ser. No. 12/471,052, filed on May 22, 2009 for Active Guiding And Balance System For An Elevator, the content of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates, in general, to elevators and, in particular, to an active guiding and balance system for an elevator. 
     BACKGROUND OF THE INVENTION 
     Elevators are generally guided in an elevator shaft by guide rails that are affixed to the building structure. The elevator generally includes a sling that is hoisted by cables and a cabin that is mounted within the sling. The elevator cabin is normally isolated from the sling by elastomeric dampers, springs, or a combination of springs and elastomeric dampers. 
     Typically, an elevator car is guided by guide rails in such a manner that guide elements of guide devices provided in the elevator car come into contact with the guide rails, which are vertically arranged on side walls of a hoistway. However, errors frequently occur in the installation of the guide rails such that they are misaligned, and further deflection is often caused in the guide rail by a load given to the car, and a small level difference and winding may be caused in the guide rail with age. Accordingly, the elevator may be vibrated in the up and down direction (elevating direction) and/or the side to side direction (direction perpendicular to the elevating direction). Guide rails are likely never to be perfectly aligned. The misalignment of the guide rails can additionally be caused, for example, by installation errors, building settlement, or building movement, such as occurs in tall buildings during windy conditions. It is not uncommon to find that the misalignment of the guide rails is caused by all of these factors. Additionally, vertical vibrations caused by such things as torque ripple in the drive system may be transmitted to the sling and therefore to the elevator cabin via the ropes. The characteristics of ropes as string resonators are often such that vertical vibrations quickly manifest themselves as horizontal vibrations that are sensed in the cabin. Aerodynamic buffering may also create vibrations in the elevator cabin. 
     Misalignment of the guide rails and other factors frequently result in vibration that is felt by passengers. Such vibrations are often uncomfortable and may be anxiety inducing to passengers. In addition to being uncomfortable and a psychological stressor, the vibrations also may have a real effect on the life expectancy of various elevator components due to inconsistent wear and/or consistent or frequent detrimental vibratory stress. 
     Conventionally, in order to reduce the longitudinal and the lateral vibration, an elastically supporting member or a vibration isolating member for reducing an input of displacement given by the guide rail is arranged between the cage and the car frame or between the car frame and the guide element. In such situations, generally, to provide significant isolation of vibration, it is necessary to reduce the rigidity of the elastically supporting member and the vibration isolating member. On the other hand, in order to prevent the occurrence of interference of the cage with other components when an unbalanced load is given to the cage, it may be necessary to somewhat increase the rigidity. For the above reasons, it may be difficult to design an elevator for which a sufficiently high vibration isolating effect can be provided where, concomitantly, no problems are caused even if an unbalanced load is given to the cabin. 
     Numerous systems have been developed in attempts to attenuate longitudinal and lateral vibrations. Many of such systems are based on the sky hook dampener concept. U.S. Pat. No. 6,474,449, the disclosure of which is incorporated herein by reference, teaches such a system that uses an approach that produces a constant vibration correcting force regardless of the position of the actuator, the asymmetric load in the car, or the disturbing force. In such systems, attention is generally given to an active vibration isolating method, in which a force to suppress vibration is given from the outside, instead of a passive vibration isolating method such as a damper. In the &#39;449 patent, an active vibration isolating method is disclosed in which an electric current is made to flow in a coil so as to generate a magnetic field at the center (axial center) of the coil. Also, vibration is reduced by a magnetic force when a reaction bar made of magnetic body is arranged at a position opposed to the magnetic field. 
     In addition to reducing vertical and horizontal vibration, numerous elevator safety systems have been developed to protect passengers and components in the event of a mechanical failure or environmental event. Roller guides are generally equipped with stops that limit their travel. For example, if excessive travel exists, then the braking shoes of the associated safety gear will contact the rails of the elevator and may then engage the brake shoes bringing the cabin to an emergency stop. 
     In seismic areas, auxiliary guiding means may be provided at each guide shoe to continue to guide the elevator cabin even if the normal guide shoes have failed such as, for example, during an earthquake. However, the auxiliary guide rails are often simply notched steel plates, where the contact between the steel plates and the rails may produce an uncomfortable ride for passengers. 
     Elevator cabins are normally loaded in such a way that the center of gravity of the cabin does not coincide with the center of suspension. These circumstances may cause the cabin to tilt and also may cause the springs or the roller guide to be compressed unequally. While this condition exists routinely with passive roller guides, it can create special problems for active systems. In order to prevent these conditions, roller guides may be provided with mechanical stops that limit their travel. If a cabin is asymmetrically loaded in an extreme condition an active roller guide may be dictated to move in a direction that will cause impact with one of the stops. Such an impact may be uncomfortable to the elevator passengers and may start or exacerbate an unstable condition in which the active damping system goes into resonance. Such a condition may be anxiety producing, damaging to the elevator system, or dangerous for the passengers. 
     An actuator described in U.S. Pat. No. 6,474,449 has an almost linear force profile over its displacement range, such as shown in  FIG. 1 . While such a system may be easy to control under normal operating conditions, it may not prevent or control runaway instability or resonance. 
     European Patent Application EP-01547955A1 teaches that all closed loop drive systems can become unstable and oscillate to resonance. This is particularly true of elevator active guidance systems. The described system disconnects the active guidance system when it becomes unstable. Although this approach may stop the instability, it may also eliminate the ride quality that an active system attempts to achieve. Additionally, such a system may not be cost effective. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and, together with the general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention. 
         FIG. 1  illustrates an almost linear force profile over its displacement range of an actuator described in U.S. Pat. No. 6,474,449. 
         FIG. 2  is a perspective view of an active guiding and balance device constructed in accordance with the teachings of the present invention. 
         FIG. 3  is a first side view of the active guiding and balance device of  FIG. 2 . 
         FIG. 4  is a second side view of the active guiding and balance device of  FIG. 2 . 
         FIG. 5  is a diagrammatic perspective view of a version of the actuator of  FIG. 2 . 
         FIG. 6  is a right-side view of the actuator of  FIG. 5 . 
         FIG. 7  is a top view of the actuator of  FIG. 5 . 
         FIG. 8  is a front view of the actuator of  FIG. 8 . 
         FIG. 9  is a diagrammatic cross-section taken along line  9 - 9  of  FIG. 8 . 
         FIGS. 9A and 9B  are a fragmentary enlarged view of a portion of  FIG. 9  diagrammatically illustrating movement of the coil between the magnetic pairs. 
         FIG. 10  diagrammatically illustrates lines of magnetic flux between magnets supported by mounting blocks. 
         FIG. 11  is a perspective photograph of an embodiment of the coil of the actuator of  FIG. 7 . 
         FIG. 12  is a schematic diagram illustrating a signal flow diagram of the active guiding and balance control system constructed according to the teachings of the present invention. 
         FIG. 12A  illustrates is a diagrammatic illustration of an alternate embodiment of the active guiding and balance control system. 
         FIG. 13  is a graph depicting a first version of a non-linear relationship between displacement and Lorentz force in the active guiding and balance device. 
         FIG. 13A  is a graph depicting a second version of a linear relationship between displacement and Lorentz force in the active guiding and balance device. 
     
    
    
     Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail, wherein like numerals indicate the same elements throughout the views,  FIGS. 2, 3 and 4  are views of an active guiding and balancing device constructed according to the present invention. An active guide system is one equipped with actuators such as motors or solenoids that augment or diminish the spring force on the guiding devices of the active guide system in response to a control system that determines the dampening requirements of the system to counteract the accelerations of the elevator system to create zero acceleration in the car. The control system may use sensors, such as accelerometers to detect acceleration of the elevator car and actuators to effect the dampening requirements. 
     As seen in  FIGS. 2-4 , there is shown roller guide assembly indicated generally at  2 . As is known, a plurality of roller guide assemblies  2  are used on an elevator car at spaced apart locations to engage guide rails (not shown in  FIGS. 2-4 ), similar to that depicted in FIG. 1 of U.S. Pat. No. 6,474,449, the disclosure of which is incorporated herein by reference. Roller guide assembly  2  includes two spaced apart rollers  4  and  6  lying in the XZ plane, and roller  8  lying in the YZ plane. The construction of rollers  4 ,  6  and  8  are similar, with rollers  4  and  6  mirroring each other. Roller guide assembly  2  includes base  10  which is mounted directly or indirectly to the elevator car (not shown) and which carries rollers  4 ,  6  and  8 . Each roller  4 ,  6  includes respective lever arms  12 ,  14 , depicted in  FIGS. 2-4  as a respective assembly of lower lever arm  12   a ,  14   a  and upper lever arm  12   b ,  14   b . Each lower lever arm  12   a ,  14   a , is bearingly carried by base  10 , pivotable about a respective pivot axis  12   c  and  14   c . Each lever arm  12 ,  14 , rotatably carries rollers  4 ,  6 , respectively, bearingly supported thereby about respective roller shafts  12   d ,  14   d  (not seen completely). Each upper lever arm  12   b ,  14   b , is resiliently urged inwardly in the direction toward the guide rail (not shown) and therefore toward each other by respective biasing members  16 ,  18  carried by respective cantilevered shafts  20 ,  22 , supported by base  10 , which extend through respective openings of upper lever arms  12   b ,  14   b . Although biasing members  16 ,  18  are illustrated as springs, any suitable biasing device may be used. In the embodiment depicted, the force exerted by biasing members  16 ,  18 , against upper lever arms  12   b ,  14   b  (and resisted by the guide rail through rollers  4  and  6 ) may be adjusted by the position of members  24 ,  26 . Outward movement of lever arms  12 ,  14 , is limited by restraints  28 ,  30 , respectively. Each respective restraint  28 ,  30 , includes cantilevered shaft  28   a ,  30   a  extending from base  10 , and rubber bumper  28   b ,  30   b , the positions of which can be adjusted by positioning retainers  28   c ,  30   c , illustrated as nut pairs. Restraints  28 ,  30  may be of any suitable construction or components. At the respective distal ends of lever arms  12 ,  14 , are disposed respective actuators generally indicated at  32 ,  34 , the details of which will be discussed later. Although in the embodiment depicted each roller  4 ,  6  has a respective actuator  32 ,  34  which function independent of each other, the movement of rollers  4 ,  6  could be made interdependent, with a single actuator disposed to dampen the oscillations acting on the frame. 
     Still referring to  FIGS. 2-4 , the configuration of the supporting structure for roller guide  8  is similar to that described above. Roller guide  8  is supported on either side by two spaced apart lever arms  36 ,  38 , depicted in  FIGS. 2-4  as a respective assembly of lower lever arm  36   a ,  38   a , and upper lever arm  36   b ,  38   b . Each lower lever arm  36   a ,  38   a , is bearingly carried by base  10 , pivotable about a respective pivot axis  36   c  and  38   c . Each lever arm  36 ,  38 , cooperatively rotatably carries roller  8 , bearingly supported thereby about roller shaft  40 , with roller shaft  40  being bearingly supported at each end by lever arms  36 ,  38 , respectively. Each upper lever arm  36   b ,  38   b , is resiliently urged inwardly in the direction toward the guide rail (not shown) by respective biasing members  42 ,  44  carried by respective cantilevered shafts  46 ,  48 , supported by base  10 , which extend through respective openings of upper lever arms  36   b ,  38   b . Although biasing members  42 ,  44  are illustrated as springs, any suitable biasing device may be used. In the embodiment depicted, the force exerted by biasing members  42 ,  44 , against upper lever arms  36   b ,  38   b  (and resisted by the guide rail through roller  8 ) may be adjusted by the position of members  50 ,  52 . Outward and inward movement of lever arms  36 ,  38 , is limited by restraints  54 ,  56 , respectively. Each respective restraint  54 ,  56 , includes cantilevered shaft  54   a ,  56   a  extending from base  10 , and rubber bumpers  54   b ,  56   b  on the outside the positions of which can be adjusted by positioning retainers  54   c ,  56   c , illustrated as nut pairs, and  54   d ,  56   d  on the inside the positions of which can be adjusted by positioning retainers  54   e ,  56   e , illustrated as nut pairs. Restraints  54 ,  56  may be of any suitable construction or components. The respective distal ends of lever arms  36 ,  38 , are connected to each other through cross member  60 , causing each lever arm  36 ,  38  to remained in proper alignment with the other. Actuator  62  is disposed at cross member  60 . 
     Since, in the embodiment depicted, the construction of actuators  32 ,  34  and  62  is substantially the same, only actuator  32  will be described in detail, it being understood that the same description applies to actuators  34  and  62 , and that there are other suitable configurations for actuators  32 ,  34  and  62 . Referring to  FIGS. 5-8 , actuator  32  is diagrammatically illustrated. In the embodiment depicted, actuator  32  includes moveable member  76 , which as depicted in the embodiment illustrated may be a coli  76 , and includes first mount  64  and a second mount  66  constructed from steel SAE 1020, or any other suitable material. First mount  64  may be associated with first magnet  68  and second magnet  70  and second mount  66  may be associated with third magnet  72  and fourth magnet  74 . Magnets  68 ,  70 ,  72 ,  74  may be integral with, or attached in any suitable manner, to first mount  64  and second mount  66 , respectively. With reference also to  FIGS. 2-4 , mounts  64  and  66  are carried by base  10 . 
     Magnets  68 ,  70 ,  72 ,  74  may be constructed from any suitable material and/or alloy such as, for example, NdFeB 40 MGOe, or any other suitable material such as other NdFeB alloys. Actuator  32  may be configured such that first magnet  68  and second magnet  70  are positioned adjacent one another in-line perpendicular to the vertical axis of the elevator shaft, having opposite polarity, and third magnet  72  and fourth magnet  74  are positioned adjacent one another in-line perpendicular to the vertical axis of the elevator shaft, having opposite polarity. 
     Referring to  FIG. 9 , which is a diagrammatic cross-section (with cross hatching omitted for clarity) taken along line  9 - 9  of  FIG. 8 , the direction of North for each magnet  68 ,  70 ,  72 ,  74  is shown. In the embodiment depicted, third magnet  72  and fourth magnet  74  are configured such that they each face inward from second mount  66  and interact magnetically with first magnet  68  and second magnet  70 . As seen, mounts  64 ,  66  and magnets  68 ,  70 ,  72 ,  74  may be configured such that first magnet  68  faces third magnet  72  creating a first magnetic pair with the north pole of first magnet  68  facing and spaced apart from the south pole of third magnet  72 . Similarly, a second magnetic pair is created by second magnet  70  and fourth magnet  74 , with the north pole of second magnet  70  facing and spaced apart from the south pole of fourth magnet  74 . Mounts  64 ,  66  may be of any suitable shape configured to provide the desired magnetic flux field and density. For example, as seen in  FIG. 7 , ends  64   a ,  64   b ,  66   a ,  66   b  of mounts  64 ,  66  may have a trapezoidal shape as illustrated by phantom lines. These edges of mounts  64 ,  66  may, for example, be ½ inch to 1 inch longer at each end. The shape of ends  64   a ,  64   b ,  66   a ,  66   b  may affect the roll off of the force generated on coil  76  as coil  76  moves away from its center position, without affecting the force on coil  76  while at its center position. 
     Still referring to  FIGS. 5-10 , coil  76  is disposed between first mount  64  and second mount  66 , which is operably configured to magnetically interact with magnets  68 ,  70 ,  72 ,  74 . Coil  76  is carried by upper lever arm  12   b , such that magnetic forces acting upon coil  76  produces force on upper lever arm  12   b  in a direction which adds to or opposes the force exerted by resilient member  16  on upper lever arm  12   b . Coil  76  may be of any suitable construction. With reference also to  FIG. 11 , in the embodiment depicted, coil  76  comprises a plurality of turns of insulated wire formed in a toroidal shape, although any suitable shape may be used. For example, in the embodiment depicted, coil  76  is configured from 250 feet of 23 American Wire Gauge (AWG), is insulated with a thin layer of resin or the like. Coil  76  is depicted as containing central region  78 , dividing coil  76  into first region  80  positioned between first magnet  68  and third magnet  72  of the first magnetic pair and second region  82  positioned between second magnet  70  and fourth magnet  74  of the second magnetic pair. The current flows in the same direction through the wires which make up first region  80 , such as into the page as indicated at  80   a . The current flows in the same direction through the wires which make up second region  82 , such as out of the page as indicated at  82   a . Since coil  76  is a continuous loop, as can be seen in  FIG. 11 , the direction of current flow in region  80  is opposite the direction of flow in region  82 . 
     In the embodiment depicted, the first magnetic pair has a polarity opposite that of the second magnetic pair, concentrating the magnetic lines of flux as seen in  FIG. 10 , which illustrates lines of magnetic flux between magnets supported by mounting blocks (with coil  76  not energized), such that stability of the elevator system is improved. As seen in  FIG. 9 , in the embodiment depicted, the magnetic pairs extend beyond each side of regions  80  and  82 . As coil  76  initially moves in either direction of arrows A and B, regions  80  and  82  remain within the respective gaps defined by each magnetic pair.  FIG. 9A  illustrates regions  80 ,  82  disposed at respective edges of the gaps defined by each magnetic pair. With reference to  FIG. 10 , the lines of magnetic flux are relatively uniform to the edges of the gaps defined by each magnetic pair. Since each magnetic pair is arranged in opposite polarity, the current flow through coil  76  produces a force on coil  76  which is in the same direction (such as a center seeking restoring force in the direction of arrow B to provide dampening) on each region  80 ,  82  due to the opposite direction of current flow through each region  80 ,  82 . 
     As the edge of each region  80 ,  82  moves beyond the respective ends of the gaps defined by the respective magnetic pairs, the effect of the magnetic pair begins to diminish or roll off. For the edge of either region  80  or  82  which moves into and through central region  78 , and into the gap defined by the other magnetic pair, the direction of the force on that region  80  or  82  changes. For example, referring to  FIG. 9B , edge  80   b  is illustrated disposed aligned with the edges of magnets  70 ,  74 , and will enter the gap defined by that magnetic pair with any further movement in the direction of arrow A. As edge  80   b  moved through transition area  78   a , the effect of the magnetic flux between the first magnetic pair of magnets  68  and  72  decreased while the effect of the magnetic flux between the second magnetic pair of magnets  70  and  74  increased. Because of the direction of current through region  80 , the force exerted by the second magnetic pair on region  80  is in the direction of arrow A, opposite from the direction of the force exerted on region  80  by the first magnetic pair. As edge  80   b  advances further into the gap defined by the second magnetic pair, the magnitude of the force increases. The force and flux density provided by this configuration of actuator  32  (as well as actuators  34  and  64 ) results in increased elevator stability, using fewer magnets than conventional devices, and by providing a reduced mass coil. Such features may benefit the stability of the elevator system cost effectively. 
     Within the teachings of the present invention, the air gap flux between magnetic pairs is configured by utilizing shaped magnetic shunts (e.g., mounts  64 ,  66 ) at its extremes in such a manner as to create the force pattern desired. The magnetic shunts may enable actuator force changes to be inherent in the actuator design and thus do not rely on actuator driver filters, tuning, response, and/or position limiters of a control system. This version may result in improved response capabilities and may limit damper activations that can lower ride quality. 
     The shape of actuator  32  may also be modified to create the force pattern desired. It will be appreciated that actuator  32  may be constructed from any suitable material, may contain any suitable number of magnets, coils, and/or mounts, and may be configured with any suitable shape or dimensions to facilitate elevator system stability. 
     Unevenness in the guide rails, lateral components of traction forces originated from the traction cables, positional changes of the load during travel, and aerodynamic forces, for example, may cause oscillation of the car frame and the elevator car, and thus impair travel comfort. Position sensors may be used with each roller guide to continually monitor the position of the lever arms. Accelerometers may be utilized to measure transverse oscillations or accelerations acting on the car frame. 
     Referring to  FIG. 12  is a schematic diagram illustrating a signal flow diagram of an active guiding and balance control system constructed according to the teachings of the present invention. A signal flow diagram of the active ride control system incorporating instability detection signals derived from position sensors  84  and/or accelerometers  86  may be fed into a controller box mounted on the elevator car. The controller box may contain the power electronics to drive the actuators  32 ,  34 ,  36  and closed loop feedback controller  88  processing the signals from sensors  84  and  88  to operate actuators  32 ,  34 ,  60  in directions such to oppose the sensed oscillations. Thereby, damping the oscillations acting on the frame and the elevator car may be achieved. Oscillations may be reduced to the extent that they are imperceptible to the elevator passenger. 
     External disturbances act on the elevator car and car frame as they travel along the guide rails. These external disturbances may comprise high frequency vibrations due mainly to the unevenness of the guide rails and relatively low frequency forces produced by asymmetrical loading of the elevator car, lateral forces from the traction cable, and air disturbances or wind forces. The disturbances may be sensed by the position sensors  84  and/or accelerometers  86 , where the position sensors  84  and/or accelerometers  86  may produce signals that are fed into controller  88 . 
     In controller  88 , the sensed position signals may be compared with reference values P ref  at summation point  92  to produce position error signals e p . The position error signals e p  may then be fed into a position feedback controller  94  which produces an output signal F p  which may be fed into a displacement algorithm  96 . The displacement algorithm  96  may compare, for example, the F p  to a pre-programmed non-linear measurement plot such that a signal is sent to the actuator  32  to diminish or vary the Lorenz force associated with the active system. It will be appreciated that the displacement algorithm  96  may combine, compare, and/or analyze any suitable number of conditions or factors to provide a desirable balance between active system control, stability, and passenger comfort to the elevator system. It is contemplated that an output signal F p , or a command from the displacement algorithm  96 , may be transmitted directly to the actuator  32  in the absence of accelerometers  86 . 
     Still referring to  FIG. 12 , should accelerometers  86  be provided, the signals from accelerometers  86  may be inverted at summation point  98  and fed into an acceleration feedback controller  100  as acceleration error signals e s . The output F s  from the acceleration controller  100  may be combined with the output F pl  from the displacement algorithm  96  at summation point  102 . The resulting output control signals F, F p , and/or F pl  may be used as the input for a power amplifier (not shown) to produce current for the actuators  32 ,  34 ,  60  to counteract the disturbance forces and thus reduce vibrations on the car. 
     The output F s  of the acceleration controller  100  may contain a broad band of frequencies and the amplitude of the higher frequency signals may be relatively large. To detect instability, time duration may also be evaluated. A good measurement of stability may be the root means square or RMS value. It is a measure for the energy or power that is contained in a signal and time duration weighting can be chosen freely. The moving RMS value can be compared with a maximum admissible value and if it exceeds the admissible value, an error flag may be set true. The error signal may not fully deactivate the active control system, which provides a comfortable ride for passengers, but may, rather, vary the Lorentz force developed by the first actuator. The Lorentz force may be varied by the first actuator depending upon the degree of displacement. For example, controller  88  may be programmed such that a threshold measurement of displacement of 6 or −6 triggers a reduction of the Lorentz force to a level lower than that provided during normal operation. Applied Lorentz force may be varied along at least a partially non-linear continuum relative to displacement. It will be appreciated that actuator  32  may be provided with adaptive multi-band vibration suppression based on when, how much, and which frequency needs to be suppressed. Sensors operably configured to monitor a frequency range may send an indication of a detected frequency, for example, to the displacement algorithm, such that action may be taken specific to vibration caused by that particular frequency. 
     The level of reduction of the Lorentz force of the active control system may be reduced to a greater degree as the displacement increases. Controller  88  may be pre-programmed with a continuum, such as with a displacement algorithm  96  such that an identified level of displacement is associated with a particular level of applied Lorentz force. Such a continuum is illustrated by the non-linear portions of the measurement plot. It will be appreciated that any suitable relationship between Lorentz force and displacement may be provided so as to balance passenger comfort and vibration reduction. Rather than deactivating the active control system entirely, a graduated relationship between displacement and Lorentz force may provide a comfortable passenger ride while maintaining active control of the elevator system. 
       FIGS. 13 and 13A  illustrate two versions of the Lorentz force that may be created by actuators  32 ,  34 ,  62 . Plots  104 ,  104   a  illustrate one example of the relationship between displacement, as measured along the x axis, and force, as measured along the y axis, of an elevator system. Actuators  32 ,  34 ,  62  may be configured as a linear motor as described, with at least one fixed magnet and a moving coil having a low mass such that it may respond to frequencies of between 2 and 200 Hz. As discussed above, when the moving coil is energized with an electric current, the coil may move relative to the permanent magnet creating a force that may be used to dampen vibration. In one version, the Lorentz force created by the first actuator is non-linear relative to displacement at high levels of displacement such as, for example, at a displacement of greater than 7 mm in either direction. In  FIG. 13 , region  108  is illustrated as nearly linear, and in  FIG. 13A , region  108   a  is illustrated as linear, each at 7 mm or less of displacement. In  FIG. 13 , high displacement regions  106  and  110  may be nearly linear as illustrated, or as seen in  FIG. 12A , high displacement regions  106   a  and  110   a  may be linear, wherein the application of Lorentz force is diminished, but not stopped, to dampen vibrations while still retaining at least partial active control of an elevator system. 
     It will be appreciated that any suitable level of displacement may be associated with any suitable level of Lorentz force, or any other suitable force, to maintain active control of an elevator system at high levels of displacement. Actuator  32 , or any other suitable actuator, may be configured such that any portion of plot  104 ,  104   a  may be linear or non-linear. For example, the linear regions as seen in  FIG. 13A  may range from a displacement of from about −20 mm to about 20 mm displacement, from about −7 mm to about 7 mm displacement, from about −5 mm to about 5 mm displacement, from about −10 mm to about 10 mm displacement, from about −20 to about 20 mm displacement, from about −7 mm displacement to about 3 mm displacement, and/or from about −3 mm to about 7 mm displacement. It will be appreciated that actuator  32  may be configured such that plot  104  is asymmetrical with respect to the y-axis. 
     Still referring to  FIG. 13 , one version of a maximum force and flux density graph at the linear zone is shown. The force refers to the quantity of magnetic field force, or “push.” The flux density refers to the amount of magnetic field flux concentrated in a given area, where the field flux is the quantity of total field effect, or “substance” of the field. As moving coil  76  approaches the limits of travel, less force is produced. This force profile is advantageous because a full force impact into a physical stop can cause the system to become unstable. The fact that the force is reduced and working against spring that the force, gives the control system time to develop and implement an improved solution. Vibration dampening such as this, requires extremely fast processing of solutions. 
     In one embodiment, in the event of a loss of power or driver faults, power to the actuators is disconnected and a shunt resistor is connected across the coil of the actuator. Referring to  FIG. 12A , control signal L may be directed into a relay or solid state device S, which when there is power, allows the signal L to be directed to coil  76 . In the event of a power failure, device S would cause resistor R to be placed in series with coil  76 . This allows coil  76  to function as a dynamically stronger virtual spring. Resistor R is selected based on the size of coil  76  and the elevator car characteristics. Resistor R may be adjustable to allow tuning to a particular elevator car while on site. Coil  76  moving through magnets produces electricity, which is applied across the shunt resistor R. Resistor R dissipates energy as heat, stiffening the dampening to add to the springs, therefore not just mechanical springs are in the passive mode, but as a generator providing damping at midpoints. 
     In summary, numerous benefits have been described which result from employing the concepts of the invention. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiment was chosen and described in order to best illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.