Abstract:
A machine employing controllable mounts and a method for controlling such mounts based on operator input are disclosed. The controllable mount may include a housing, a pin, rheological fluid within the housing and coils provided proximate to the rheological fluid. As current is applied to the coils, the apparent viscosity of the rheological fluid is increased, and in so doing so is the stiffness and damping of the controllable mount. Depending on various factors, the operator may want a particular level of feedback. For example, when fine grading, the operator may want to feel every vibration and thus the controllable mounts should be as stiff as possible. The present disclosure therefore provides the operator with the ability to select the desired level of feedback. This can be done through an operator interface that enables an operator to specifically set the current to each mount, or enter other information whereupon a processor of the control system executes the necessary algorithm to provide the operator with the optimum level of feedback.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a non-provisional application claiming priority under 35 USC 119(e) to U.S. Provisional Patent Application Ser. No. 61/122,490 filed on Dec. 15, 2008. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to cab mounts and, more particularly, relates to machines employing cab mounts and methods for controlling cab mounts. 
     BACKGROUND 
     In many different heavy equipment machines, an operator cab is supported by a frame of the machine with cab mounts. Cab mounts are available in many different forms and configurations and generally try to isolate the cab from the undercarriage of the machine so as to limit the vibrational impact experienced by the operator when the machine moves or performs work. For example, with a loader traveling over rocky terrain, the chassis, undercarriage, and wheels/track of the loader may be jostled and bounced around considerably, but as the cab is not fixedly mounted to the frame, the play afforded by the cab mounts lessens the effect of that motion on the operator. 
     Such mounts can be as simple as a mechanical spring or an elastomeric shock absorber offering a fixed level of vibration damping. Other types of mounts are fluid or electro-chemical in nature. Magneto-Rheological (MR) and Electro-Rheological (ER) mounts are two examples of such mounts. Taking a MR mount as an example, generally it includes a housing containing MR fluid, a structure that moves through the MR fluid, and a coil for providing a magnetic field across the MR fluid. By directing current to the coils, not only is the magnetic field created through the MR fluid, but the apparent viscosity of the MR fluid is increased as well. As the structure moves through the MR fluid, increasing the apparent viscosity of the MR fluid makes the mount more rigid. 
     One example of a MR mount is disclosed in U.S. Pat. No. 7,063,191. The &#39;191 patent discloses a hydraulic mount that includes a decoupler sub-assembly, a body filled with MR fluid, a pumping chamber and a diaphragm chamber. The body may be formed from a flexible, molded elastomer, such that vibrational inputs from the engine elastically deform the pumping chamber to cause fluid transfer between the pumping chamber and the diaphragm chamber through the decoupler sub-assembly for viscous damping. While somewhat effective, such a mount provides no feedback 
     Another example of a MR mount is disclosed in US Patent Application Publication No. 2007/0257408, published Nov. 8, 207 to Kenneth Alan St. Clair. et al. The &#39;408 publication discloses a strut with a magneto-rheological fluid damper that includes a tubular housing filled with magneto-rheological fluid and a piston head movable within the tubular housing along its longitudinal length. 
     SUMMARY OF THE DISCLOSURE 
     In accordance with one aspect of the disclosure, a machine is therefore disclosed which comprises a frame, an operator cab supported by the frame, at least one movable implement operatively associated with the frame, a controllable mount operatively connecting the operator cab to the frame and including a housing, a pin mounted within the housing, a rheological fluid within the housing, and coils positioned relative to the housing to generate a field through the rheological fluid, and a controller operatively associated with the coils and adapted to change a level of current applied to the coils to adjust an apparent viscosity of the rheological fluid based on operator input. 
     In accordance with another aspect of the disclosure a method of controlling a cab mount is disclosed wherein the method comprises connecting a cab to a machine using a cab mount, the machine including at least one movable implement, the cab mount having a housing and a pin movable relative to the housing, receiving an input from an operator via an operator interface of the cab, and adjusting current flow to the coils based on the input received from the operator. 
     In accordance with yet another aspect of the disclosure a control system for controlling a mount operatively connecting an operator cab to a frame of a machine having at least one movable implement is disclosed, wherein the control system comprises a controllable mount including a housing, a pin movable within the housing, a volume of rheological fluid within the housing, and coils mounted proximate to the rheological fluid, an operator interface in the cab enabling an operator in input a desired level of feedback, and a processor adapted to receive the desired level of feedback from the operator interface and adjust a level of current directed to the coils based on the desired level of feedback. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a machine constructed in accordance with the teachings of this disclosure; 
         FIG. 2  is a sectional view of a controllable mount constructed in accordance with the teachings of this disclosure; 
         FIG. 3  a chart depicting creep in an elastomeric member of the controllable mount during initial use, over time, and as corrected; 
         FIG. 4  is a schematic representation of a control system constructed in accordance with the teachings of this disclosure; 
         FIGS. 5   a - d  are schematic representations of alternative embodiments for sensing mount displacement; 
         FIG. 6  is a block diagram of an operator interface constructed in accordance with the teachings of this disclosure; 
         FIG. 7  is a graph plotting frequency vs. spectral density, depicting historical data associated with a controllable mount, and identifying when a mount should be replaced or repaired; 
         FIG. 8  is a graph plotting frequency vs. amplitude, and depicting stacked algorithms controlling same in accordance with the teachings of this disclosure; 
         FIGS. 9   a - e  are schematic representations of different mount location embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, and with specific reference to  FIG. 1 , a machine constructed in accordance with the teachings of this disclosure is generally referred to by reference numeral  100 . The machine  100  includes a frame  102  supporting an operator cab  104 . As shown, the machine  100  is depicted as a track-type tractor, but is to be understood that the teachings of this disclosure can be employed with equal efficacy with other heavy industry and construction machines such as, but not limited to, backhoe loaders, wheel loaders, tracked loaders, articulated trucks, off-highway trucks, excavators, motor graders, fork-lifts, skid steers, or any other machine known in the art that includes a cab mounted to a frame. 
     Referring now to  FIG. 2 , a cross-sectional view illustrates an example of one embodiment of a controllable mount  106  for use with the machine  100  and method disclosed herein. As shown, the controllable mount  106  may include a housing  108  that may be mounted to the frame  102  (see  FIG. 1 ) via a mounting flange  110 . The housing  108  may include a first chamber  112  and a second chamber  114 . As will be described in further detail herein, the first chamber  112  may be filled with a rheological fluid  116  such as a magneto-rheological (MR) fluid or an electro-rheological (ER) fluid. The second chamber  114  may be filled with a compressed fluid  118  such as compressed gas including compressed air. 
     The controllable mount  106  may also include a pin  120  that is partially disposed with the housing  108  and may be attached to the cab  104  at a mounting end  122 . The pin  120  may be attached to the housing  108  by an elastomeric member  124  that permits the pin  120  limited axial movement along axis  126  and radial movement perpendicular to the axis  126 . The elastomeric member  124  may dampen axial as well as radial motion between the pin  120  and the housing  108 . 
     As shown, a damping plate  128  may be attached to the pin  120  and be disposed within the rheological fluid  116  of the first chamber  112 . The damping plate  128  may include a plurality of apertures  130  to permit the rheological fluid  116  to pass through the damping plate  128 . As the damping plate  128  is moved through the rheological fluid  116 , the relative motion between the housing  108  and the pin  120  is damped. The level of damping may be adjusted by applying a magnetic or electric field to the rheological fluid  116 . Moreover, by changing the strength of the magnetic or electric field, the apparent viscosity of the rheological fluid  116  is proportionally changed thereby providing a mechanism by which the degree of damping afforded by the controllable mount  106  can be tailored to the needs of the operator. 
     In order to generate the magnetic or electric field, coils  131  are provided proximate the rheological fluid  116 . More specifically, the coils  131  may be mounted on the housing  108  laterally adjacent the first chamber  112 . Leads  132  may extend from the coils  131  for connection to a controllable power supply  134 . Alternatively, or additionally, the coils  131  may be mounted on the pin  120  and/or the damping plate  128 . 
     The pin  120  may also include a plunger  136  that separates the first chamber  112  from the second chamber  114 . The plunger  136  may include a seal  138  that seals against a shaft  140  of the housing  108 . In such a configuration, the plunger  136  and the second chamber  114  act as a gas spring  142  for positioning the pin  120  at an ideal snubbing height  144 , the importance of which will be described in further detail herein. The pressure of the compressed fluid  118  within the gas spring  142  may be adjusted by way of a valve  146 . By adjusting the pressure of the compressed fluid  118 , the biasing force of the gas spring  142  applied to the plunger  136  is adjusted as well. A first hose or tube  148  may be connected to the valve  146  to supply pressurized fluid  118  to the second chamber  114 . The valve  146  may also include a second hose or tube  150  to return the pressurized fluid  118  within the second chamber  114  to a storage tank  152 , or to be vented to atmosphere. 
     To assist in biasing the plunger  136  toward the ideal snubbing height  144 , a mechanical spring  154  may also be used. The spring  154  may be disposed about a guide extension  156  of the pin  120  and extend between the guide extension  156  and a base  158  of the housing  108 . The guide extension  156  may be positioned to contact the housing  108  and act as a first end stop for the controllable mount  106 . 
     The controllable mount  106  may also include a sensor  160  for generating a signal indicative of the relative displacement between the cab  104  and the frame  102 . In the current embodiment, it does so by determining the relative displacement between the housing  108  and the pin  120 . The sensor  160  may include a strain gauge (not shown) disposed in a channel  162  provided in the elastomeric member  124 . Alternatively, the channel  162  may be filled with a conductive elastomer  164  having an electrical conductivity and resistance that changes with elongation and contraction. More specifically, the strain placed on the conductive elastomer  164  may be correlated to the resistance exhibited by the conductive elastomer  164 . Thus, as the resistance is measured, the relative displacement between the housing  108  and the pin  120  may be calculated. Leads  166  may be used to communicate data from the sensor  160  to an electronic control unit  168  (see  FIG. 4 ). 
     The controllable mount  106  may also include a sensor  170  to monitor the pressure of fluid  118  within the second chamber  114 . The pressure sensor  170  may be connected to the electronic control unit  168  as well with leads  172 . In general, the pressure sensor  170  may be used to measure pressure spikes and thus wear on the elastomeric member  124 . In so doing, the remaining life and serviceability of the controllable mount  106  can be calculated. In addition, failure of either sensor  160  or  170  may indicate that the controllable mount  106  needs replacement or repair. 
     As an alternative or addition to the sensor  160  within the elastomeric member  124 , the pressure sensor  170  may also be used to determine the displacement of the pin  120  relative to the housing  108 . More specifically, the displacement may be determined using the formula:
 
 V   n   =P   i   *V   i   /P   n  
         wherein:
           V n  is the new volume;   P i  is the initial pressure;   V i  is the initial volume; and   P n  is the new pressure.
 
Initial pressure and initial volume could be initially calibrated from a known position of the pin  120  and could correspond to the volume and pressure of the second chamber  114 . New pressure and new volume could correspond to the displacement from the initial position. The new position may be determined from the new volume using the formula:
 
 D =( V   n   −V   i )/(π *R   2 )
   
           wherein:
           D is the change in displacement;   R is the radius of the shaft  140 ;   V i  is again the initial volume; and   V n  is again the new volume.
 
Temperature compensation may also be used to increase the accuracy of the displacement measurement. Alternatively, the displacement may be determined through stored tables where these calculations have already been determined.
   
               

     This calculated displacement may then be used to provide feedback in a control algorithm executed by the electronic control unit  168  controlling the mount  106 . More specifically, the calculated displacement data may be used to adjust the current applied to the coils  130  of the controllable mount  106  and hence adjust the apparent viscosity of the controllable mount  106  to provide improved performance. 
     In one embodiment, the apparent viscosity of the rheological fluid  116  is changed in direct relation to the displacement of the mount  106 . Thus, as the pin  120  moves away from the ideal snubbing height  144 , more current is applied to the coil and the apparent viscosity of the rheological fluid  116  increases to bias the pin  120  away from engagement with the housing  108 . In so doing, the pin  120  and damping plate  128  encounter greater resistance to movement and thus this feedback control may be used to minimize occurrences where the pin  120  reaches an endstop, also known as bottoming or topping out. 
     In another embodiment, statistical analysis of the data from one or more sensors  160 ,  170  may be used to interpret the displacement of the controllable mount  106  over time and adapt the control of the controllable mount  106  to changes in weight in the cab, i.e., the weight of different operators, their tools and accessories, and the like. Initial pressure and initial volume may be determined and calibrated at the factory and during machine servicing. 
     This displacement data may also be statistically analyzed and kept for long term storage. The historical data may include average displacements, frequency domain, and power spectral density data. The historical statistical displacement data may be used to determine when to replace a specific mount. For example, if the controllable mount is operating outside of its historical average, the controllable mount would be deemed to need replacement. Additionally, the history may be taken over the life of the controllable mount to develop a long historical average. The long historical average may be compared to a medium history and a short history to provide a total error or a point by point error to look for problems in performance. 
     By tracking and maintaining a historical statistical average of displacement, the set and creep of the elastomeric member  124  may also be determined. As used herein, the “set” and “creep” of the elastomeric member  124  refers to changes in the elasticity of the elastomer. Initially, the elastomer will deform predictability and return to the same shape and strength. Over time and repetitive motion, however, the elastomer may begin to change at the molecular level so as not to exhibit the same elasticity. In the present application this can cause the elastomeric member  124  to begin to sag over time. 
     In graphical form, this means that as the elastomeric member  124  sags, sets, and begins to creep, the elastomeric member  124  may begin to behave nonlinearly as shown in  FIG. 3 . As shown, the elastomeric member  124  may initially behave in a generally linear fashion as indicated by line  174  between the end stops  176 . However, over time, the elastomeric member  124  may take on a set and begin to creep as shown by line  178 . 
     The electronic control unit  168  may be used to compensate for this change in the material properties, as well as, minimize the effects of creep. For example, the electronic control unit  168  may be used to adjust the current applied to the coils  130  and thereby correct for the change in the material properties of the elastomeric member  124 , which is shown as dotted line  180 . Thus more current may be applied to the coils  130  when negative displacement is determined and less where positive displacement is determined. In configurations where a pneumatic system is available to increase the gas pressure within the gas spring  142 , the increased gas pressure may be used to compensate further and bias the pin  120  toward the ideal snubbing height  144 . 
     Referring now to  FIG. 4 , a schematic diagram illustrates a control system  182  for a machine  100  on which the controllable mounts  106  may be used. As shown, the system  182  includes the electronic control unit  168  that is in electrical communication with machine sensors  186 , an operator interface  188 , and a power source  190 . The electronic control unit  168  may include a processor  192  and a computer readable media or memory  194  for storing instructions. Machine sensors  186  may include a wide variety of sensors including accelerometers, inclinometers, temperature sensors, pressure transducers, and other sensors known in the art for use on the machine  100 . The operator interfaces  188  may include joysticks, pedals, switches, buttons, touch screens, keypads, and other devices known in the art for receiving operator input. 
     The electronic control unit  168  may also be in electrical communication with a plurality of controllable mounts  106  used to mount the cab  104  to a machine frame  102 . Such mounts  106  may include a right front controllable mount  198 , a right rear controllable mount  200 , a left rear controllable mount  202 , and a left front controllable mount  204 . The right front controllable mount  198 , right rear controllable mount  200 , left rear controllable mount  202 , and left front controllable mount  204  may each include the features of controllable mount  106  described above, as well as other features of controllable mounts known in the art. 
     In one embodiment, the controllable mounts  106  may be identical. However, their physical positions on the machine frame  102  and cab  104  may be different and known via a wiring harness  206  provided between the controllable mounts  106  and the electronic control unit  168 . For example, a series of switches  208  may be coded to indicate the position of each controllable mount  106  on the machine frame  102 . If four mounts  106  are used, for example, the following codes of TABLE 1 may be used: 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Position 
                 Switch 1 
                 Switch 2 
               
               
                   
                   
               
             
             
               
                   
                 Cab, forward, right 
                 0 
                 0 
               
               
                   
                 Cab, forward, left 
                 0 
                 1 
               
               
                   
                 Cab, rear, right 
                 1 
                 0 
               
               
                   
                 Cab, rear, left 
                 1 
                 1 
               
               
                   
                   
               
             
          
         
       
     
     The harness codes may provide the switch functionality through two wires and a ground line (not shown) being run to each mount location as part of the wiring harness  206 . The switches  208  of the above table are then provided for in each connector by connecting a respective wire to ground to provide a 1 and left open for a 0. This may be routed through the connector to the controllable mount  106  so that the controllable mount  106  can identify its position on the machine frame  102 . This positional information may be used to tune and more precisely control the controllable mounts  106  on the machine frame  102 . 
     In another embodiment, the controllable mounts  106  may be distinct and be configured to receive a specific connector from the wiring harness  206 . Alternatively, a generic wiring harness  206  may be used and each controllable mount  106  may be given its address by a technician to communicate its position to the electronic control unit  168 . 
     Optionally and as shown, the controllable mounts  106  may each include the gas spring  142  as discussed above in relation to  FIG. 2 . Each gas spring  142  may be pneumatically connected to a source of pressurized gas, such as a pump  210 , and a source of low pressure gas, such as the tank  152 . In the depicted embodiment, the electronic control unit  168  is shown as being in communication with the pump  210 , but the control need not be electronic. For example a mechanical valve arrangement can be used. With the electronic embodiment, however, if the pressure of gas within the gas spring  142  of the right front controllable mount  198  is determined to be too low, for example, the electronic control unit  168  may command the pump  210  to provide pressurized gas and command a pneumatic valve (not shown) of the right front controllable mount  198  to open and receive the pressurized gas to increase the gas pressure within the gas spring  142 . When the pressure of the gas spring  142  is sufficient, the electronic control unit  168  may close the valve and shut down the pump  210 . Alternatively, in situations where the pressure is too high in the gas spring  142 , the electronic control unit  168  may open the valve to the tank  152  and close the valve when the pressure has been sufficiently reduced. 
     Accurate mount displacement measurement permits the controllable mounts  106  to be maintained at or near the ideal snubbing height  144  for maximum effectiveness of the controllable mounts  106 . By maintaining each mount at their ideal snubbing height  144  throughout their useful life, excessive loading and bottoming out/topping out of the mount  106  during machine operation may be minimized or prevented. Consequently, fewer replacement parts of the cab  104  and mounts  106  may be needed over the life of the machine  100 . The present disclosure and its accommodating of different static loads of the cab  104  may permit different systems and options to be installed at different times without having to replace the mounts  106 , thus providing a high degree of modularity and tailoring of the machine  100  to specific applications over the entire machine life while retaining the same mount package. 
     Referring now to  FIGS. 5   a - d , in addition to the methods and systems discussed above, controllable mount displacement measurement can be achieved with other sensors including through the use of a Hall-effect sensor  214 . For example, as shown in  FIG. 5   a , a permanent magnet  216  may be positioned on the housing  108  of the controllable mount  106 . A sensor chip  218  may be connected to the cab  104  and positioned to sense the relative position of the magnet  216 . In another embodiment ( FIG. 5   b ), an expandable chamber  220  may house a laser  222  in one end and a receiver  224  in the other end. Each end may be attached to one of the cab  104  and the machine frame  102 . As the chamber  220  expands and contracts with the relative movement of the cab  104  and frame  102 , accurate mount displacement measurement may be achieved. In another embodiment, a bar code reader  226  may be positioned to read a stainless steel or other corrosion-resistant material bar code display  228 , as depicted in  FIG. 5   c . The display  228  may be attached to the frame  102  and the bar code reader  226  attached to the cab  104 . In yet another embodiment, a rotary sensor  230  with a gear  232  disposed to move up and down a rack  234  (see  FIG. 5   d ) may also be used to determine the displacement. 
     In addition to diagnosing and correcting for creep or set in the elastomeric member  124 , the controllable mounts  106  of the present disclosure also provide a mechanism by which machine feedback may be provided to the operator. For example, the controllable mounts  106  can be hardened and thereby selectively lower damping so as to pass more of the vibration and impact loads to the cab  104  from the machine frame  102 . As indicated above, hardening the controllable mounts  106  occurs when an electrical current is provided to coils  131  and the apparent viscosity of the rheological fluid  116  is increased. Conversely, when machine feedback is not as desirable as comfort of the operator, the controllable mount  106  may be softened by removing or reducing the current to thereby decrease damping. The level of damping may be manually selected by the operator, programmed to change during specific intervals of machine operation, and/or based on sensor inputs as described in greater detail below. 
     Another feature of the present disclosure is that the operator interface  188  may permit the operator significant control over the controllable mounts  106 . For example, as shown schematically in  FIG. 6 , the operator interface  188  may include an on/off switch  236  to enable an operator to turn the controllable mounts  106  off and thereby provide the softest ride at all times. In such a situation, the controllable mounts  106  would function simply as a viscous mount. Alternatively, an operator may adjust the control algorithm via an incremented switch  238 , a touch screen  240 , or a keypad  242  to scale the current flow provided by a control algorithm through the controllable mount  106 . For example, the operator may scale the control algorithm to fifty percent (or other) in order to obtain a softer ride, which may result in a different dynamic rate and damping characteristics of the control system  182 . 
     In another embodiment, the operator interface  188  may permit the operator to have to direct control over the current being applied to each controllable mount  106 . For example, four slider bars  244  (or a different number if a different number of controllable mounts are used) may respectively represent the four respective mounts  106  and allow the operator to move the slider  244  on the operator interface  188  to fit his or her personal preferences. The operator interface  188  may be the touch screen  240  to allow direct control, or a mouse  246  or joystick  248  may be used to move a cursor over the screen  240  to make the desired changes to the controllable mount settings. 
     Further, the control of the controllable mounts  106  may be accessible through the menu or operating system  250  of the machine  100 . In some embodiments, control of the controllable mounts  106  may be accessible only to a service technician via password protection or may be preprogrammed as part of an operator identification device  252  that would adjust settings to the specific operator. This may be achieved through the use of an RFID identification card  254 , or operator information stored on such items as a cell phone  256 , flash drive  258 , personal digital assistant  260 , or other computer readable media or device. 
     The operator interface  188  may also permit the operator to input or automatically input the geographical location of the machine  100  as well as road and worksite material conditions. Consequently, the electronic control unit  168  may adjust or implement a control algorithm to best compensate for the individual terrain characteristics of the worksite and thereby provide for the best ride. For example, if a rocky worksite is being traversed, the electronic control unit  168  may increase the current flow to the coils  131  to a higher level in each controllable mount  106  in order to provide the more damping to the cab  104  and operator. In one example, the machine  100  may operate at fifty percent of maximum current while traveling over the rocky terrain, and zero percent over a smooth worksite. 
     In a different configuration, and operator may also specify the type of machine task being performed, in which case different control algorithms  262  programmed to best damp vibrations when appropriate and allow feedback at other times may take over. For example, if the selected task is loading trucks from a pile of material, a loading algorithm  264  may be selected. The loading algorithm  264  may provide the controllable mounts  106  with fifty percent (or other) maximum current while moving between the truck and the pile, but during bucket loading and when the bucket is raised above a predetermined height, the electronic control unit  168  may increase the current flow to one hundred percent in order to provide machine feedback and thus provide better operator control. 
     In another example, an operator may indicate that the machine  100  is a motor grader and the task to be performed is fine grading. The electronic control unit  168  may then cause the controllable mounts  106  to be hard while the transmission of the machine  100  is in a forward gear, and soft while in a reverse gear. During fine grading, operators desire as much feedback as possible in order to more quickly complete the job within specified tolerances. Additionally, or alternatively, the controllable mounts  106  may be tuned to the desire of the operator for selected operational settings. For example, the operator may direct the electronic control unit  168  to pass one hundred percent current during fine grading, zero percent doing roading, and fifty percent during snow removal. 
     In other example, a wheel loader may keep the controllable mounts  106  soft during roading and moving around a worksite, but harden the controllable mounts  106  when the bucket is raised so that the operator can better feel the operation of the machine. In yet another example, the controllable mounts of a track-type tractor may be kept as soft as possible with zero current being passed through the coils  131  while the machine  100  is being moved with the bucket and ripper up. The same machine  100  may be programmed to pass the maximum current when either of those implements is performing a task. 
     Similarly, if the machine  100  is an excavator, when a large load is being placed, the controllable mounts  106  may be hardened so as to provide the operator with valuable feedback. In contrast, when the excavator is being moved, zero current can be passed through the controllable mounts  106  to provide a softer, more comfortable ride to the operator. Commonly with excavators, the controllable mounts  106  may always be soft, except when transients occur during dumping, digging or other events. 
     The teachings of the present disclosure can also be employed for detecting track slippage in a track-type tractor. By setting the controllable mounts  106  to a high current setting, the operator is provided with increased feedback. This feedback may indicate to the operator that track slippage is occurring. In such an event, the operator may choose to cease operations so that maintenance can be performed and thus minimize undercarriage wear. 
     The control system  182  of the present disclosure may also employ any of the control algorithms  262  to most effectively and expeditiously balance feedback and comfort. In addition to the loading algorithm  264  mentioned above, a predictive algorithm  266  may be used by the electronic control unit  168  to control the controllable mounts  106 . The controllable mounts  106  may be tuned to the specific machine use and task being performed, such as dozing, ripping, grading, or excavating, or to the desired setting such as improved ride, noise reduction or operator comfort. Specific machine use and task may be entered by the operator as indicated above, or may be determined from the position of a blade, ripper, bucket or other implements  268  of the machine  100  as sensed by an implement position sensor  269 . Alternatively, they may be inferred from the operator interface  188 , hydraulic pressures gauges  270 , worksite maps  272 , global positioning system information  274 , laser grading inputs  276 , topographical maps  278 , inclinometers  280 , determined pitch rates  282 , steering signals  284 , altimeters  285 , articulation joint position  286 , and thermometers  287 . For example, shock loads may be anticipated from the position of a truck in a loading zone and thus the controllable mount  106  may be adjusted accordingly to absorb as much of the impact from loading as possible. 
     Alternatively, when the bucket of a wheel loader, tracked loader, excavator or other machine using buckets is lowered and positioned for engagement with a pile, the controllable mounts  106  may be initially softened and then hardened when the hydraulic cylinder pressures exceed a predetermined threshold to provide feedback to the operator while minimizing the impact of the bucket engaging the pile. In addition, speed of the machine  100  can be used to predict the desired settings for the controllable mounts  106 . For example, at higher speeds, as sensed by a speedometer  288 , the controllable mounts  106  may be softer and then hardened when the machine slows  100 . This hardening and softening may also be dependent on a transmission  289  of the machine ( 100 ), specifically a gear in which the machine  100  is operating. In first gear a fifty percent (or other) current may be passed through the coils  131  and in a second gear forty percent may be passed. In third gear, twenty five percent current may be passed and in fourth gear zero percent may be passed. Harder mounts at lower speeds would provide the operator with a better feedback, while higher speeds would provide greater comfort. 
     The predictive algorithm  266  may also use the sensed speed of the implement to control the controllable mounts  106 . For example, when a blade is lowered the initial contact with the ground can jar the operator. Thus, when the blade is being dropped, the controllable mounts  106  may be softened in anticipation of the impact and hardened after contact has been made to improve feedback and control. Generally, the control algorithm  262  may also be set up to control the vibrational, heave, pitch, roll and yaw modes as well. The predictive algorithm  266  may also be used to predict that when an implement  268  is not in use and the machine  100  is moving at a relatively high rate of speed, this may mean that roading is taking place and the controllable mounts  106  should be adjusted for maximum comfort. 
     A historical algorithm  290  may also be used. More specifically, a histogram of the performance of each controllable mount  106  may be obtained from the sensors associated with each controllable mount  106 . The histogram may be used to continuously tune each individual controllable mount  106  to current conditions. In other words, the electronic control unit  168  uses the sensor histories to adapt the controllable mount  106  to current performance, thus providing improved performance over time and use. For example, peak pressure and frequency may be kept to develop a history of performance to identify when to harden and soften with decay rate. If the controllable mount  106  undergoes very little movement over a past history, it can soften itself up to avoid unnecessary harshness and wasting of energy. As more motion is seen, the controllable mount  106  can then increase damping. For example, if while the machine is roading, high frequency small displacement vibration is sensed, the controllable mounts  106  can soften up to minimize noise, increase comfort, and save energy. When the machine  100  begins encountering rough terrain, the electronic control unit  168  may increase current to change the damping of the controllable mount  106  to compensate for the larger low frequency displacement. 
     In order to prevent failure of one of the controllable mounts  106  from causing damage to the other controllable mounts  106  and/or other machine systems through continued use, the sensor data collected from sensors associated with the controllable mount  106  may be collected and used by the historical algorithm  290  to provide a history of operation which may then be used to determine operating tolerances. The current sensor data may be used to provide the power spectral density of the controllable mount  106  and determine if the controllable mount  106  should be replaced. For example, and referring to  FIG. 7 , the dotted lines  292  may represent the tolerances for acceptable operation for the controllable mount  106  and the solid line  294  may represent the actual running power spectral density. A spike  296  outside of a tolerance zone  298  or an average error which exceeds the tolerance zone  298  may indicate that the controllable mount  106  should be replaced. In an alternative, the displacement and acceleration of the cab  104  relative to the mount  106  or the exact displacement of the mount components could be used to follow the life of the controllable mount  106  and feed the historical algorithm  290  to control the stiffness of the controllable mount  106 . 
     These control algorithms  262  and the others discussed herein may be implemented as stacked algorithms  300  as well. For example, the electronic control unit  168  may use a default algorithm  302 , an end stop algorithm  304 , and a resonant control algorithm  306 . The default algorithm  302  may use the controllable mount history to adjust the current to performance needs. All three algorithms may be calculated together and priority may be given to the algorithm that provides the highest force control over the controllable mount  106  under the current circumstances. For example, and referring to  FIG. 8 , the machine  100  may be roading during which the default algorithm  302  may be used to control the controllable mount  106 . If the machine  100  moves over a pothole, that will provide an impulse to the control system  182  which if undamped is represented by line  308 . Line  310  represents the effect produced by the stacked algorithms  300  in response to the impulse. The default algorithm  302  may control until the endstop algorithm  304  may then be given priority to control the controllable mount  106 . After the endstop algorithm  304  has acted, the resonant control algorithm  306  may be given priority to dampen out a resonance caused by the impact with the pothole. The default algorithm  302  may resume control of the controllable mount  106  once the resonance has been controlled. 
     In addition to operator selected control and the control to provide operator feedback, the electronic control unit  168  may be used to provide cab  104  leveling and adjustment. Specifically, static load adjustment and ride height adjustment may be attained by adjusting the gas spring  142  to bias the pin  120  of each mount  106  away from engagement with the housing  108  and toward its ideal snubbing height  144 . This therefore avoids having the pin  120  engage the housing  108  in “topping out” or “bottoming out” fashion. The electronic control unit  168  may monitor the relative displacement and adjust the gas spring  142  by adding or releasing gas. If the sensors  160 ,  170  indicates that the mount  106  is at or near the ideal snubbing height  144 , no action is taken by the electronic control unit  168  to adjust the pressure within the gas spring  142 . 
     This adjustment of the controllable mount  106  may be beneficial to compensate for different sized operators who may or may not be carrying tools, food and other equipment in the cab  104 . The different loads may move the controllable mounts  106  away from the ideal snubbing height  144 . In some applications, the machine  100  may be operating on a slope and thus the downside controllable mounts may bear a larger portion of the load. Thus, the downside controllable mounts may not be located at their ideal snubbing heights  144 . The pneumatic chamber  114  of each mount  106  may thus be individually adjusted to return each mount  106  to the ideal snubbing height  144 . 
     Changes in altitude and ambient temperature may also move the controllable mounts  106  from their ideal snubbing heights  144 . For example, a machine  100  that has been operating in zero degree temperatures at sea level and then taken into the mountains and used at six thousand feet above sea level in fifty degree temperatures may have mounts that are no longer disposed at their ideal snubbing heights  144 . The present disclosure may therefore adjust for this change in altitude and ambient temperature to return the mounts  106  to their ideal snubbing heights  144 . 
     A mixed mount arrangement may also be used to provide reduced cost and complexity while providing many of the benefits associated with controllable mounts. For example, as shown in  FIGS. 9   a - e , controllable mounts  106  may be used at some locations to provide controllability to the cab response while using lower cost mounts to help support/attach the cab  104  at other locations. In one embodiment (see  FIG. 9   a ), where pitching of the cab  104  is desired to be controlled, two passive mounts  312  may be positioned at a front  314  of the cab  104  and two controllable mounts  106  may be positioned at rear locations  316 . Thus, through selective hardening of the controllable mounts  106 , the pitch and roll motion may be controlled. The configuration may also be reversed as in  FIG. 9   b  with two passive mounts  312  positioned at the rear  316  of the cab  104  and two controllable mounts  106  positioned at the front  314  of the cab  104 . As used herein, passive mounts have dampening characteristics that cannot be altered during operation and include, for example, viscous and rubber mounts. 
     Alternatively, a three-point system may also be possible with a single passive mount  312  in front  314  and two controllable mounts  106  positioned at the rear  316  of the cab  104 , as shown in  FIG. 9   c , so that the structure is less expensive and easier to manufacture for plane and positional alignment. In yet another embodiment (see  FIG. 9   d ), two passive mounts  312  may be mounted near an inertial roll axis  318  with a third controllable mount  106  being mounted away from the axis  318 . 
     Another cab mounting arrangement may be used with machines  100  that include an external roll-over protection structure  320 . For example, as shown in  FIG. 9   e ), passive mounts  312  may be mounted between the cab  104  and the frame  102  of the machine  100 . One or more controllable mounts  106  may be disposed above the cab  104  and mounted between the cab  104  and the external roll-over protection structure  320 . In this configuration, the passive mounts  312  provide noise reduction and the overhead controllable mounts  106  may provide ride control. 
     INDUSTRIAL APPLICABILITY 
     From the foregoing, it can be seen that the teachings of this disclosure have applicability in a variety of industrial situations, particularly with machines to which operator cabs are mounted. Such machines may include, but are not limited to, track-type tractors, wheel loaders, track loaders, excavators, motor graders, articulated trucks, off-highway trucks, skid steers, skidders, and the like. The machines may employ a controllable mount so as to isolate the vibrations generated by the undercarriage and engine of the machine from the cab and thus the operator within the cab. 
     In addition, by providing a mount such as that disclosed herein, the ideal snubbing height of the pin within the housing can be maintained. In so doing, excessive loading and bottoming out or topping out of the mount during machine operation can be minimized or eliminated. This in turn can help to extend the serviceable life of the mount. Moreover, by monitoring the relative displacement of the pin with regard to the housing, a diagnostic can be generated indicating when an elastomeric member of the mount, or the mount itself, should be replaced. 
     The teachings of the present disclosure may also be used to construct a machine that provides increased feedback to the operator. By stiffening the mounts, the operator will more acutely feel vibrations which can prove valuable in performing tasks, such as fine grading, plowing, or excavating, or sensing conditions such as track slippage. Conversely, when roading the mounts can be relaxed to decrease feedback and thus provide better operator comfort. 
     The present disclosure also has applicability in providing a machine mount control system wherein an operator can select a desired hardness or feedback level through an appropriate operator interface. Such an operator interface can also allow the operator to select the type of task being performed and the control system can then set the mount accordingly. 
     Sensors can also monitor the positions or speeds of the machine or implements to then predict the type of task being performed. Once predicted, the appropriate mount settings can be used. Such a predictive algorithm approach can not only use machine sensed parameters, but utilize global positioning satellite and other mapping technology as well to predict the task and desired mount settings.