Abstract:
The present disclosure is directed to a control system for a machine having first and second traction devices and a cabin. The control system has a first actuator driving the first traction device and a first interface device to generate a first input indicating a desired movement of the first actuator. The control system also has a second actuator driving the second traction device and a second interface device to generate a second input indicating a desired movement of the second actuator. The control system has a controller that causes the first actuator to operate according to the first input and the second actuator to operate according to the second input when the cabin faces a first direction. The controller also causes the first actuator to operate according to the second input and the second actuator to operate according to the first input when the cabin faces a second direction.

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to a control system, and more particularly, to a control system for switching traction device inputs. 
     BACKGROUND 
     Machines used in earth moving, mining, construction, forestry, or similar applications have an upper frame rotatably mounted to a lower frame. The lower frame of such a machine often includes a track assembly, which has a track on a left side and a track on a right side of the machine. An operator of the machine can independently control the left and right tracks, which cooperate to propel the machine in a desired direction. To propel the machine in the forward direction, the operator may use a right travel pedal to actuate the right track and a left travel pedal to actuate the left track. Specifically, the operator can use the right travel pedal to speed up or slow down the right track, and similarly use the left travel pedal to speed up or slow down the left track. 
     The operator can rotate the upper frame by 180° or more while maintaining the lower frame in its original position. In this configuration, the right track is located on the operator&#39;s left side and the left track is located on the right side of the operator. When the operator pushes on either of the pedals, an act intuitively associated with moving forward, the machine actually travels in the reverse direction. Operating the machine in this situation may become counter-intuitive and may pose mental strain on the operator. 
     One way to overcome this problem consists of rotating the lower frame of the machine without altering the relative positions of the upper and lower frame, effectively turning the whole machine around. In certain applications, however, geographic and/or space constraints may prevent the operator from turning the machine around. For example, in swamp logging operations, turning the whole machine can tear and damage the underlying surface due to the inherent instability of the terrain. In other situations, narrow and/or restricted workspaces may constrain the machine allowing it only to move in a forward or rearward direction. 
     One attempt to address some of the problems described above is disclosed in United States Patent Application Publication No. U.S. 2008/0119985 of Schubitzke that published on May 22, 2008 (“the &#39;985 publication”). In particular, the &#39;985 publication discloses a control system for a rotating turret vehicle having steering controls in the turret, wherein the steering controls may be reversed when the turret faces the rear of the vehicle. The disclosed system of the &#39;985 publication uses directional valves and valve matrices to reroute the hydraulic fluids from one side of the vehicle to the other in order to reverse the steering controls. 
     Although the &#39;985 publication discloses a system for reversing the steering controls based on a turret position, the system of the &#39;985 publication may still be problematic. For example, the disclosed system uses directional valves and valve matrices to route the hydraulic fluids. This configuration may involve increased cost of implementation and operation and longer reaction times due to the complexities of hydraulic fluid switching. 
     The control system for switching traction device inputs of the present disclosure solves one or more of the problems set forth above and/or other problems in the art. 
     SUMMARY 
     In one aspect, the present disclosure is directed to control system for a machine having first and second traction devices and a cabin capable of rotating relative to the first and second traction devices. The control system includes a first actuator configured to drive the first traction device and a first interface device configured to generate a first input indicative of a desired movement of the first actuator. The control system also includes a second actuator configured to drive the second traction device and a second interface device configured to generate a second input indicative of a desired movement of the second actuator. In addition, the control system includes a controller in communication with the first and second actuators and the first and second interface devices. The controller is configured to cause the first actuator to operate in accordance with the first input and the second actuator to operate in accordance with the second input when the cabin is facing a first direction. The controller is also configured to cause the first actuator to operate in accordance with the second input and the second actuator to operate in accordance with the first input when the cabin is facing a second direction. 
     In another aspect, the present disclosure is directed to a method of operating a machine having first and second traction devices, first and second interface devices, and a cabin capable of rotating relative to the first and second traction devices. The method includes receiving a first input from the first interface device, receiving a second input from the second interface device. The method also includes propelling the first traction device based on the first input and the second traction device based on the second input when the cabin faces a first direction. The method further includes propelling the first traction device based on the second input and the second traction device based on the first input when the cabin faces a second direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a pictorial illustration of an exemplary disclosed machine; 
         FIG. 2  is a schematic of an exemplary disclosed configuration of a control system for switching traction device inputs for the machine of  FIG. 1 ; 
         FIG. 3  is a schematic of another exemplary disclosed configuration of a control system for switching traction device inputs for the machine of  FIG. 1 ; and 
         FIG. 4  is a flow chart illustrating an exemplary disclosed method of switching traction device inputs performed by the control system configurations of  FIGS. 2 and 3 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary embodiment of a machine  10 . Machine  10  may be a mobile machine that performs some type of operation associated with an industry such as logging, mining, construction, farming, transportation, or another industry known in the art. For example, as shown in  FIG. 1 , machine  10  may be a forestry machine, feller buncher, or harvester equipped with grapples and heels and having multiple systems and components that cooperate to accomplish a task. 
     Machine  10  may include a lower frame  12  and an upper frame  14 . Lower frame  12  may include first traction device  16  and second traction device  18  that may be cooperatively operated to propel machine  10  in a desired direction. In one exemplary embodiment as illustrated in  FIG. 1 , first and second traction devices  16 ,  18  may be tracks. Upper frame  14  may include a cabin  20  and an arm  22  that includes a first member  24  operatively coupled to a second member  26 . Upper frame  14  may be rotated about an axis oriented vertically with respect to lower frame  12 . Specifically, upper frame  14  may be rotated by an angle ranging from about 0 to 360 degrees relative to lower frame  12 . 
     First member  24  and second member  26  may be supported and powered by hydraulic cylinders  28  and  30 , respectively. One or more tools  32 ,  34  may be attached to second member  26 . Tools  32 ,  34  may be cooperatively operated to perform a task, as desired by an operator (not shown) located in cabin  20 . First member  24 , second member  26 , and tools  32 ,  34  may also be rotated with upper frame  14 . It is contemplated that an operator may decide to rotate the entire machine  10 , and not just upper frame  14 . In other words, machine  10  may be operated to allow lower frame  12  and upper frame  14  to move together. 
     In one exemplary operating condition, cabin  20  may face a first direction  36 . In this operating condition, first traction device  16  may be located on the left side of an operator in cabin  20  and second traction device  18  may be located on the right side of the operator. In this operating condition, control of machine  10  may be intuitive because a first pedal (not shown) that the operator uses to control first traction device  16  may be on the left side of the operator, i.e. on the same side as first traction device  16 . Similarly, a second pedal (not shown) that the operator uses to control second traction device  18  may be on the right side of the operator, i.e. on the same side as second traction device  18 . 
     In another exemplary operating condition, upper frame  14  may be rotated by 180 degrees relative to lower frame  12  so that cabin  20  may face a second direction  38 . In this operating condition, first traction device  16  may be located on the right side of the operator in cabin  20  and second traction device  18  may be located on the left side of the operator in cabin  20 . In this operating condition, control of machine  10  may be counter-intuitive because the first pedal that controls first traction device  16  may no longer be on the same side as first traction device  16  and similarly, the second pedal that controls second traction device  18  may no longer be on the same side as second traction device  18 . 
       FIG. 2  illustrates a control system  50 , according to an exemplary embodiment. Control system  50  may include a fluid circulation system  60 , an actuator system  80  and an input switching system  100 . Fluid circulation system  60  may include a tank  62 , which may store hydraulic fluid. Fluid circulation system may also include a pump  64 , which may draw hydraulic fluid from tank  62 , pressurize the hydraulic fluid, and direct the pressurized hydraulic fluid to actuator system  80  via passageway  66 . A check valve  68  may be disposed in passageway  66  to prevent flow of pressurized hydraulic fluid back to pump  64 . Hydraulic fluid from actuator system  80  may be directed back to tank  62  via passageway  70 . Although,  FIG. 2  illustrates only one tank  62 , one pump  64  and one check valve  68 , fluid circulation system  60  may include any number of tanks  62 , pumps  64 , and/or check valves  68 . It is also contemplated that fluid circulation system  60  may include filters, control valves, relief valves, or any other components for circulating hydraulic fluid known in the art. 
     Actuator system  80  may include solenoid valves  82 ,  84 ,  86 ,  88 , directional valves  90 ,  92  and first and second actuators  94 ,  96 . As illustrated in  FIG. 2 , solenoid valves  82 ,  84 ,  86 , and  88  may be coupled to passageway  66  of fluid circulation system  60  to receive pressurized hydraulic fluid. Solenoid valves  82 ,  84 ,  86 , and  88  may also be coupled to passageway  70  to allow hydraulic fluid to return to tank  62 . Further, solenoid valves  82 ,  84  may be coupled to directional valve  90  that may be configured to drive first actuator  94 . Solenoid valves  86 ,  88  may be coupled to directional valve  92  that may be configured to drive second actuator  96 . In one exemplary embodiment, first actuator  94  may be used to propel first traction device  16  (see  FIG. 1 ) and second actuator  96  may be used to propel second traction device  18  (see  FIG. 1 ). 
     Solenoid valve  82  may be an independent metering valve configured to meter pressurized fluid into and out of directional control valve  90  based on a command from controller  110  (i.e., when energized by controller  110 ). In the disclosed embodiment, solenoid valve  82  may include a single valve element movable between a first position at which fluid from pump  64  may be directed into solenoid valve  82  via a supply passage connected to passageway  66 , and a second position at which fluid from solenoid valve  82  may return to tank  62  via passageway  70 . The valve element of solenoid valve  82  may be moved to the first position when solenoid valve  82  is energized by controller  110  (i.e. when an electrical current is directed to solenoid valve  82 ), and spring-biased to the second position when solenoid valve  82  is de-energized (i.e. when no current is supplied to solenoid valve  82 ). It is contemplated that solenoid valve  82  may alternatively include multiple valve elements that together or separately control the flows of fluid into and out of solenoid valve  82 , if desired. Although  FIG. 2  illustrates two solenoid valves  82 ,  84  controlling directional control valve  90 , it is contemplated that control system  50  may have only one solenoid valve  82  or  84  which may control first actuator  94 . Similarly, although  FIG. 2  illustrates two solenoid valves  86 ,  88  controlling directional control valve  92 , it is contemplated that control system  50  may have only one solenoid valve  86  or  88  which may control second actuator  96 . 
     First and second actuators  94 ,  96  may be hydraulic motors configured to rotate in the first and second angular directions. It is contemplated, however, that first and second actuators may be electric motors or any other type of rotational actuators known in the art. When solenoid valve  82  is energized, solenoid valve  82  may be configured to direct pressurized hydraulic fluid from passageway  66  to directional control valve  90 . Directional control valve  90  may direct the fluid to first actuator  94 , which may rotate in a first angular direction. By rotating in the first angular direction, first actuator  94  may cause first traction device  16  to be propelled in a forward direction. In one exemplary embodiment, as illustrated in  FIG. 1 , forward direction may be a direction collinear with first direction  36 . When solenoid valve  82  is de-energized, however, solenoid valve  82  may be configured to direct hydraulic fluid from directional control valve  90  to passageway  70 . Solenoid valves  84 ,  86 , and  88  may have a structure and function similar to that of solenoid valve  82 . 
     Solenoid valve  84  may be configured to provide drive power to actuator  94  in a manner similar to that of solenoid valve  82 . For example, when solenoid valve  84  is energized, solenoid valve  84  may be configured to direct pressurized hydraulic fluid from passageway  66  to directional control valve  90 . Directional control valve  90  may direct the fluid to first actuator  94 , which may rotate in a second angular direction opposite the first angular direction. By rotating in the second angular direction, first actuator  94  may cause first traction device  16  to be propelled in a rearward direction. In one exemplary embodiment, as illustrated in  FIG. 1 , the rearward direction may be a direction collinear with second direction  38 . 
     Solenoid valve  86  and directional valve  92  may be configured to provide drive power to actuator  96  in a manner similar to that discussed above with respect to solenoid valve  82 . Similarly, solenoid valve  88  and directional valve  92  may be configured to provide drive power to actuator  96  in a manner similar to that discussed above with respect to solenoid valve  84 . 
     Input switching system  100  may include controller  110 , selector  120 , first interface device  122 , second interface device  124 , and proximity sensor  126 . Controller  110  may include processor  112 , storage device  114 , and switch  116 . Various other known devices may be associated with controller  110 , including power supply circuitry, signal-conditioning circuitry, actuator driver circuitry (i.e., circuitry powering solenoids, motors, or piezo actuators), communication circuitry, and other appropriate circuitry. 
     Processor  112  of controller  110  may embody a single microprocessor or multiple microprocessors, field programmable gate arrays (FPGAs), digital signal processors (DSPs), etc. that include a means for receiving inputs from selector  120 , first interface device  122 , and second interface device  124  and for controlling the operation of solenoid valves  82 ,  84 ,  86 ,  88  and directional control valves  90 ,  92 . Numerous commercially available microprocessors can be configured to perform the functions of processor  112 . One skilled in the art would appreciate that processor  112  could readily embody a microprocessor separate from that controlling other machine functions, or that processor  112  could be integral with a general machine control system microprocessor and be capable of controlling numerous machine system functions and modes of operation. If separate from a machine control system microprocessor, processor  112  may communicate with the general machine control system microprocessor via data links or other methods. 
     Storage device  114  may include Random Access Memory (RAM) devices, NOR or NAND flash memory devices, Read Only Memory (ROM) devices, hard drives, solid state drives etc. Storage device  114  may be configured to store data or one or more instructions and/or software programs that perform functions or operations when executed by processor  112 . Furthermore, storage device  114  may be co-located with processor  112  or it may be communicatively coupled to controller  110  and/or processor  112  via wired and/or wireless networks. Although  FIG. 2  illustrates only one processor  112  and only one storage device  114 , controller  110  may include any number of processors  112  and storage devices  114 . 
     Switch  116  may be coupled to processor  112  and storage device  114  and may be configured to determine how controller  110  controls the operation of first and second actuators  94 ,  96 . Switch  116  may be a button, a knob, a slider, a lever, or a widget on a display or a touch-screen device. Switch  116  may be configured to be in an “OFF” (deactivated) state or in an “ON” (activated) state. Switch  116  may also be connected to a selector  120  which may be configured to activate or deactivate switch  116 . Selector  120  may be a joystick, lever, mouse pointer, keyboard, microphone, or any other type of input device known in the art. Although  FIG. 2  depicts switch  116  to be co-located with controller  110 , switch  116  may be disposed on selector  120  or anywhere else on machine  10 . 
     In one exemplary embodiment, when switch  116  is “OFF,” controller  110  may permit an operator to control first traction device  16  using first interface device  122  and to control second traction device  18  using second interface device  124 . When switch  116  is “ON,” controller may permit the operator to switch inputs to the first and second traction devices  16 ,  18 . That is, when switch  116  is “ON,” the operator may control first traction device  16  using second interface device  124  and control second traction device  18  using first interface device  122 . 
     Control system  50  may also include a proximity sensor  126 , which may be configured to sense an angular position of a reference portion of upper frame  14  relative to lower frame  12 . Proximity sensor  126  may be located on lower frame  12 , upper frame  14 , or any other portion of machine  10 . Proximity sensor  126  may be configured to send a signal to controller  110  upon detecting that upper frame and/or cabin  20  has rotated relative to lower frame  12  by an angle exceeding a threshold angle. Upon receiving the signal from proximity sensor  126 , controller  110  may be configured to switch inputs to the first and second traction devices  16 ,  18  in a manner similar to that discussed above with respect to switch  116 . In one exemplary embodiment, the threshold angle may be about 90 degrees. 
     First interface device  122  and second interface device  124  may be coupled to controller  110  and may be configured to control the operation of first and/or second traction devices  16 ,  18  via first and second actuators  94 ,  96 . In one exemplary embodiment, as illustrated in  FIG. 2 , first and second interface devices  122 ,  124  may be rocker pedals wherein the operator can push on the top of the pedals to propel first and second traction devices  16 ,  18  in the forward direction or on the bottom of the pedals to propel first and second traction devices  16 ,  18  in the forward direction. Further, when switch  116  is “ON,” the rocker pedal inputs may be switched so that operator may be able to push on the bottom of the pedals to propel first and second traction devices  16 ,  18  in the forward direction and push on the top of the pedals to propel first and second traction devices  16 ,  18  in the rearward direction. It is contemplated, however, that first and second interface devices may take other forms such as buttons, levers, knobs, or any other types of actuation devices known in the art. 
     First and second interface devices  122  and  124  may provide drive power to first and second actuators  94  and  96 . Activating first interface device  122 , for example, by pressing first interface device  122 , when first interface device  122  is a pedal, may generate a first input to controller  110 . In one exemplary embodiment, first input may be an electrical current  128 . Further, activating first interface device  122  may generate a first signal, which may indicate whether first actuator  94  may rotate in a first or second angular direction. Second interface device  124  may function in a manner similar to first interface device  122 . That is, activating second interface device  124  may generate a second input to controller  110 . In one exemplary embodiment, second input may be an electrical current  130 . Further, activating second interface device  124  may generate a second signal, which may indicate whether second actuator  96  may rotate in a first or second angular direction. 
     Controller  110  may be configured to direct electrical currents  128 ,  130  to one or more of solenoid valves  82 ,  84 ,  86 ,  88 . Controller  110  may be configured to select one or more of solenoid valves  82 ,  84 ,  86 ,  88  to energize with electrical currents  128 ,  130  based on whether switch  116  is “ON” or “OFF” and based on whether a first or second signal is generated. Controller  110  may cooperate with other electrical components (not shown) to direct electrical currents  128 ,  130  to one or more of solenoid valves  82 ,  84 ,  86 ,  88 . 
       FIG. 2  illustrates an exemplary configuration in which switch  116  is in the “OFF” position (deactivated state). When switch  116  is in the OFF position, first interface device  122  may be configured to control first traction device  16  and second interface device  124  may be configured to control second traction device  18 . In this configuration, for example, cabin  20  may face first direction  36 , first traction device  16  may be located on the left side of an operator in cabin  20 , and second traction device  18  may be located on the right side of the operator. Thus, for example, when first and second signals generated by first and second interface devices  122 ,  124  indicate that the operator desires to propel machine  10  in a forward direction, processor  112  may direct branch current  132  to solenoid valve  82  without energizing solenoid valve  84 . Processor  112  may similarly direct branch current  136  to solenoid valve  86  without energizing solenoid valve  88 . Upon receiving branch currents  132 ,  136 , solenoid valves  82  and  86 , respectively, may be configured to direct pressurized fluid to first and second actuators  94 ,  96 , which may rotate in a first angular direction causing first and second traction devices  16 ,  18  to be propelled in first direction  36 . Hydraulic fluid from first and second actuators  94 ,  96  may return to tank  62  via the de-energized solenoid valves  84 ,  88 , respectively. 
     Further, in the configuration of  FIG. 2 , when first and second signals indicated that the operator desires to move machine  10  in a rearward direction, processor  112  may direct branch current  134  to solenoid valve  84  without energizing solenoid valve  82 . Processor  112  may similarly direct branch current  138  to solenoid valve  88  without energizing solenoid valve  86 . Upon receiving branch currents  134 ,  138 , solenoid valves  84  and  88 , respectively, may be configured to direct pressurized fluid to first and second actuators  94 ,  96 , which may rotate in a second angular direction causing first and second traction devices  16 ,  18  to be propelled in second direction  38 . Hydraulic fluid from first and second actuators  94 ,  96  may return to tank  62  via de-energized solenoid valves  82 ,  86 , respectively. 
     It is contemplated that machine  10  may have additional controls for regulating the amplitude and/or any other parameters of electrical currents  128 ,  130  and branch currents  132 ,  134 ,  136 ,  138 . Regulating the amplitude or other parameters associated with electrical currents  128 ,  130  and/or branch currents  132 ,  134 ,  136 ,  138  may allow an operator to control a speed of first and second traction devices  16 ,  18 . In one exemplary embodiment, controller  110  may limit a magnitude of electrical currents  128 ,  130  from exceeding a threshold value, thereby limiting the maximum speed at which first and second traction devices  16 ,  18  may be propelled. In another exemplary embodiment, controller  110  may also limit a magnitude, amplitude, or other parameter associated with branch currents  132 ,  134 ,  136 ,  138  to inhibit first and second actuators  94 ,  96  from responding to actuation of first and second interface devices  122 ,  124 , when a speed of first and second traction devices  16 ,  18  exceeds a threshold speed. 
       FIG. 3  illustrates control system  50  according to an exemplary configuration in which switch  116  is “ON” (activated state). The components of control system  50  illustrated in  FIG. 3  are similar to those illustrated in  FIG. 2 . Therefore, in the following disclosure, only differences in the operating characteristics of control system  50  based on the activated state of switch  116  are described. 
     As illustrated in  FIG. 3 , when switch  116  is “ON” (activated state), inputs to the first and second actuators  94 ,  96  and, therefore, of first and second traction devices  16  and  18  may be switched (i.e. reversed) relative to the configuration of  FIG. 2 . That is, first interface device  122  may be configured to control second traction device  18  and second interface device  124  may be configured to control first traction device  16 . In this configuration, for example, cabin  20  may face second direction  38  (see  FIG. 1 ), first traction device  16  may be located on the right side of an operator in cabin  20  and second traction device  18  may be located on the left side of the operator. Thus, for example, when first and second signals generated by first and second interface devices  122 ,  124  indicate that the operator desires to propel machine  10  in a forward direction, processor  112  may direct branch current  134  to solenoid valve  84  without energizing solenoid valve  82 . Processor  112  may similarly direct branch current  138  to solenoid valve  88  without energizing solenoid valve  86 . Upon receiving branch currents  134 ,  138 , solenoid valves  84  and  88 , respectively, may be configured to direct pressurized fluid to first and second actuators  94 ,  96 , which may rotate in a second angular direction causing first and second traction devices  16 ,  18  to be propelled in second direction  38 . One of ordinary skill in the art would recognize that in this configuration, although travelling in second direction  38 , machine  10  would be moving in a forward direction relative to an operator located in cabin  20  because cabin  20  is facing second direction  38 . Hydraulic fluid from first and second actuators  94 ,  96  may return to tank  64  via the de-energized solenoid valves  82 ,  86 , respectively. 
     Further, in the configuration of  FIG. 3 , when first and second signals indicate that the operator desires to move machine  10  in a rearward direction, processor  112  may direct branch current  132  to solenoid valve  82  without energizing solenoid valve  84 . Processor  112  may similarly direct branch current  136  to solenoid valve  86  without energizing solenoid valve  88 . Upon receiving branch currents  132 ,  136 , solenoid valves  82  and  86 , respectively, may be configured to direct pressurized fluid to first and second actuators  94 ,  96 , which may rotate in a first angular direction causing first and second traction devices  16 ,  18  to be propelled in first direction  36 . One of ordinary skill in the art would recognize that in this configuration, although travelling in first direction  36 , machine  10  would be moving in a rearward direction relative to an operator located in cabin  20  because cabin  20  is facing second direction  38 . Hydraulic fluid from first and second actuators  94 ,  96  may return to tank  62  via de-energized solenoid valves  82 ,  86 , respectively. One of ordinary skill in the art would recognize that additional components such as filters, valves, passageways, sensors, etc. may be implemented the configurations of  FIGS. 2 and 3 . One of ordinary skill in the art would also recognize that  FIGS. 2 and 3  illustrate exemplary configurations and that the components illustrated in  FIGS. 2 and 3  could be arrange in alternative configurations to achieve the same results as described with respect to  FIGS. 2 and 3  above. 
     INDUSTRIAL APPLICABILITY 
     The disclosed control system may be applicable to any machine that includes an upper frame and a lower frame, wherein each of the upper and lower frames are independently rotatable with respect to one another. The disclosed control system may provide an intuitive control environment for an operator, irrespective of the orientation of the upper frame with respect to the lower frame. An exemplary operation of the disclosed system will now be explained. 
       FIG. 4  illustrates an exemplary disclosed method  140  of switching inputs to first and second traction devices  16 ,  18  of machine  10 . As illustrated in  FIG. 4 , controller  110  may receive a first input to propel first traction device  16  (Step  142 ). Further, controller  110  may receive a second input to propel second traction device  18  (Step  144 ). Controller  110  may determine whether it has received a signal to switch inputs (Step  146 ). Controller  110  may receive a signal to switch inputs from switch  116 , for example, when switch  116  is “ON.” For example, an operator may actuate switch  116  from the “OFF” position to the “ON” position using selector  120  when cabin  20  has rotated more than about 90 degrees relative to first direction  36 . In some exemplary embodiments, the signal to switch inputs may be generated automatically without operator intervention. For example, proximity sensor  126  may generate the signal to switch inputs when proximity sensor  126  detects that upper frame  14  has rotated relative to lower frame  12  by more than a threshold angle. In these exemplary embodiments, controller  110  may receive the signal to switch inputs from proximity sensor  126  without operator intervention. 
     When controller  110  determines that it has not received a signal to switch inputs (Step  146 : NO), controller  110  may proceed to step  148  of rotating first actuator  94  based on the first input received from first interface device  122  (Step  148 ). Controller  110  may also rotate second actuator  96  based on the second input received from second interface device  124  (Step  150 ). Controller may return to step  142 . 
     Returning to step  146 , when controller  110  determines, however, that it has received a signal to switch inputs (Step  146 : YES), controller  110  may proceed to step  152  of rotating the first actuator  94  based on the second input received from the second interface device  124  (Step  152 ). Controller  110  may also rotate the second actuator  96  based on the first input received from first interface device  122  (Step  154 ). Controller may return to step  142 . 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed control system for switching traction device inputs. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed control system for switching traction device inputs. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.