Patent Publication Number: US-2020299930-A1

Title: Selectable velocity-based or position-based work vehicle operator control system

Description:
STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     FIELD OF THE DISCLOSURE 
     This disclosure generally relates to work vehicles, and more specifically to operator control systems of work vehicles. 
     BACKGROUND OF THE DISCLOSURE 
     Heavy equipment operators often operate large work vehicles using an operator control system with a variety of operator control devices. Such devices may include joysticks, dials, buttons, switches, wheels, pedals, and the like. In complex vehicles, such as motor graders or wheel loaders, the operator may be required to manipulate a large number of operator control devices in succession or simultaneously to operate numerous independent or interdependent sub-systems of the vehicle, including a steering system for directing the heading rate and direction of the vehicle, as well as systems that operate the tools or implements carried by the vehicle. 
     Effective and efficient operation of the vehicle and its implements may require the operator to perform intricate hand and arm gestures in order to manipulate the control devices required to actuate these systems timely and accurately. Such effective and efficient operation may be complicated by operator control strategies that differ from vehicle to vehicle and/or from manufacturer to manufacturer. 
     SUMMARY OF THE DISCLOSURE 
     The disclosure provides a control system for a work vehicle that enables the operator to selectively operate under a position-based control strategy or velocity-based control strategy for operating an actuation device on the work vehicle. 
     The disclosure provides a control system for a work vehicle that includes one or more actuation devices. The control system includes an operator input device configured to receive operator input from an operator of the work vehicle and a controller operatively connected to the operator input device and to the one or more actuation devices. The controller is configured to: receive a control mode selection input including a position control mode selection input or a velocity control mode selection input; receive an actuation request input from the operator input device; determine an operating command corresponding to the actuation request input from the operator input device according to the control mode selection input; and issue the operating command to the one or more actuation devices. 
     In one aspect, the disclosure provides a control system for a work vehicle having one or more actuation devices. The control system includes an operator input device configured to receive operator input from an operator of the work vehicle and a controller operatively connected to the operator input device and to the one or more actuation devices. The controller is configured to: receive a control mode selection input including a mode selection input as a position control mode or a velocity control mode; receive an actuation request input from the operator input device; determine an operating command corresponding to the actuation request input from the operator input device according to the control mode selection input; and issue the operating command to the one or more actuation devices. In the position control mode, the operating command includes an instruction to move the one or more actuation devices to a position corresponding to a position corresponding to the actuation request input from the operator input device. In the velocity control mode, the operating command includes an instruction to move the one or more actuation devices at a rate of change corresponding to a rate of change of the actuation request input from the operator input device. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a work vehicle in the form of a motor grader in which the operator control system of this disclosure may be incorporated; 
         FIG. 1B  is a perspective view of a work vehicle in the form of a wheel loader in which the operator control system of this disclosure may be incorporated; 
         FIG. 2  is simplified view inside an operator cabin of the motor grader of  FIG. 1A  or the wheel loader of  FIG. 1B  showing example operator input devices; 
         FIG. 3  is a functional block diagram depicting dataflows of an operator control system on an example embodiment; 
         FIG. 4  is a perspective view of an active feedback force joystick device that may be implemented in the operator control system of  FIG. 3  according to an embodiment; 
         FIGS. 5A and 5B  are schematic views of a passive feedback force joystick device that may be implemented in the operator control system of  FIG. 3  according to an embodiment; 
         FIGS. 6A-6C  are cross-sectional views of a portion of the joystick device of  FIG. 5A  through line  6 - 6 ; and 
         FIGS. 7A-7C  are cross-sectional views of a portion of the joystick device of  FIG. 5A  through line  7 - 7 . 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The following describes one or more example embodiments of the disclosed operator control system, as shown in the accompanying figures of the drawings described briefly above. Various modifications to the example embodiments may be contemplated by one of skill in the art. 
     Generally, the disclosed operator control systems and methods (and work vehicles in which they are implemented) provide for improved operator experience to perform steering tasks as compared to conventional systems by enabling the operator to select between a velocity-based control strategy and a position-based control strategy for steering or other actuation devices, thereby simplifying steering and/or improving operation of the work vehicle for each operator. 
     Work vehicles used in various industries, such as the agriculture, construction and forestry industries, may include systems, tools, or implements used to maneuver and carry out various functions for which the work vehicle was designed. Typically, this requires the vehicle operator to be familiar with the vehicle devices for controlling the vehicle heading and speed and operating the implement. Certain work vehicles, such as those with a number of implements having multiple degrees of freedom in movement, may be rather complex to operate and require the operator to have considerable related skill and experience. Suboptimal operation of the vehicle or the implements may result in inefficient or imprecise performance at the work site or generally discourage potential operators from attempting to operate unfamiliar or different vehicles. 
     One particularly complex work vehicle is the motor grader, which is generally used in the construction industry to set grade. Modern motor graders are typically large machines with a lengthy articulated chassis formed by a front frame with steered wheels pivotally connected to a rear frame with drive wheels. Motor graders may also have the capability to tilt the steered wheels. These features thus provide for an improved (i.e., shorter) turning radius, thereby making the large machine nimbler than otherwise possible. Beyond the heading and speed control, motor graders may have rather complex implements. The primary tool on motor graders is the moldboard or blade, which is mounted to a turntable known in the industry as a circle. The circle is adjustably mounted to the vehicle frame, and the blade in turn is adjustably mounted to the circle, thus giving the blade a wide-range of possible movements. Other types of vehicles, such as wheel loaders, may present similar operational complexities. 
     To perform the aforementioned functions and operations, the motor graders and other types of vehicles may be outfitted with a relatively large number of joysticks, control levers, buttons, switches, knobs, and other devices that may each control operation of a single, discrete operation or motion. As examples, one arrangement includes a dual joystick control system with left and right multi-axis joystick devices that, in addition to multiple inputs by manipulation of the joystick grip interfaces, each carry a large number of other input devices. In one example, manipulation of one of the joystick devices along one axis may control the steering system (e.g., pivoting the steered wheels to the right and left). Such steering must be performed along with numerous other possible control functions. Even though the steering control is already challenging while undertaking the numerous other tasks, steering control issues may be compounded by the multiple control strategies that may vary from vehicle to vehicle. Certain operators may have a control strategy preference and/or unfamiliar operation may result in inefficiencies. Potential steering control strategies may include a velocity-based steering control strategy and a position-based steering control strategy. Additionally, although the steering system is discussed below, the control strategies may also be applicable to other actuation devices on the work vehicle, including implement actuation devices, such as booms, buckets, blades, and the like. 
     In a velocity-based steering (or other actuation) control strategy, an operator control system generates velocity-based commands in response to velocity-based operator inputs to control the associated actuation devices of the work vehicle. Generally, in the velocity-based steering control strategy, the position (e.g., the absolute position or angle relative to neutral) of the actuation request input at the operator input device is interpreted to request a command to move an actuation device at a corresponding rate of change. As such, a relatively small amount of movement by the operator input device to a particular position may thus correspond to a relatively slower movement of the associated actuation device as long as the position of the operator input device is maintained, as compared to a larger movement by the operator input device, which results in a relatively faster movement of the associated actuation device. As such, the controller may thus receive velocity-based input commands corresponding to a desired movement of the machine or implement, and the controller may resolve the velocity-based inputs, possibly in conjunction with inputs from sensors or other position-indicating devices, and command one or more target actuation device velocities (e.g., depending on the number of actuation devices required to effectuate the desired end movement). The joystick device additionally provides a feedback force in accordance with the velocity-based steering control strategy. In particular, in the velocity-based steering control strategy, the operator makes the intended control input (e.g., joystick device movement) and then lets the control input return to a neutral position without continuing to hold the joystick grip interface until the actuation device movement cycle time is completed, as may be required in a position-based steering control strategy. Typically, the velocity-based steering control strategy implements a feedback force opposing the direction of input that increases as the joystick grip interface moves away from the neutral position and decreases as the joystick grip interface moves towards the neutral position. As an example, a curve the depicts feedback force in view of joystick grip interface angle according to the velocity-based steering control strategy may have a V-shaped appearance that is centered about the neutral position. 
     In a position-based steering (or other actuation) control strategy, an operator control system generates position-based commands in response to position-based operator inputs to control the associated actuation devices of the work vehicle. Generally, in the example of a joystick, the position of an actuation request at the operator input device relative to a neutral position is interpreted by the controller to represent the desired corresponding position (e.g., angle) of the steering system in the designated direction. Moreover, rate at which the joystick grip interface is moved may be considered by the controller to represent the desired speed at which to implement the command. As such, the controller may thus receive position-based input commands corresponding to a desired movement of the machine or implement, and the controller may resolve the position-based inputs, possibly in conjunction with inputs from sensors or other position-indicating devices, and command one or more target actuation device positions (e.g., depending on the number of actuation devices required to effectuate the desired end movement). The operator input device additionally provides a feedback force in accordance with the position-based steering control strategy. In particular, in the position-based scheme, the operator makes the intended control input (e.g., joystick movement) and then the joystick grip interface generally stays in that position until adjusted by the operator, thereby providing a stabilizing feedback force. In addition to this aspect of the feedback force, the position-based steering control strategy typically implements a further feedback force opposing the direction of input that increases as the joystick moves away from an initial position, which may or may not be the neutral position. In this instance, the feedback force represents an overspeed response corresponding to the reaction of the steering system. In other words, as the joystick grip interface is moved quickly from a neutral position, the feedback force will be relatively high to, in effect, enable implementation of the corresponding command, while if the joystick is moved slowly from a neutral position, the feedback force will be relatively low since the steering system has time to react appropriately. In position-based steering control strategies, this feedback force function is also applicable to initial positions other than the neutral position. As an example, the feedback force-angle curve of a position-based steering control strategy may have a V-shaped appearance that is centered about the current position that is lagged based on steering system articulation. 
     Now with reference to the drawings, one or more example implementations of the operator control system for use on a work vehicle will now be described. While a motor grader is illustrated and described herein as an example work vehicle, one skilled in the art will recognize that principles of the operator control system disclosed herein may be readily adapted for use in other types of work vehicles, including, for example, various crawler dozer, loader, backhoe and skid steer machines used in the construction industry, as well as various other machines used in the agriculture and forestry industries. As such, the present disclosure should not be limited to applications associated with motor graders or the particular example motor grader shown and described. Similarly, the operator control systems are discussed below with respect to the steering system. However, other systems may implement corresponding operator control systems in which velocity-based and position-based control strategies may be applicable. 
     As shown in  FIG. 1 , a motor grader  100  includes an operator control system  110  that controls various functions associated with the motor grader  100 , including a steering function based on manual inputs from an operator and other inputs, as discussed in greater detail below. The operator control system  110  is implemented with a controller  120  and may further be considered to include one or more operator input devices  130  and/or a steering system  140 . Generally, as described in greater detail below, the operator input devices  130  may include one or more operator control apparatuses  132 ,  134  (e.g., as joystick-type or other types of controls) to receive operator inputs that control various aspects of the motor grader  100  and a steering mode selection switch  136  to receive operator inputs that select a mode associated with a control strategy. Additional details about the operator control system  110  will be provided below after a more general description of the motor grader  100 . 
     In the depicted example, the motor grader  100  is formed by a front frame  150  and a rear frame  152  that are pivotably connected to each other via an articulation joint  154 . The front frame  150  and the rear frame  152  are respectively supported by front wheels  156  and rear wheels  158 . In other embodiments, the motor grader  100  may include other ground-engaging devices for propelling the machine, such as track assemblies, for example, as known in the art. 
     The motor grader  100  further includes a drive system  160  adapted to drive or power the motor grader  100  and collectively formed by an engine or other type of power source  162 , and a transmission  164  supported, in this example, by the rear frame  152 . The engine  162  may be any suitable type of engine, including a diesel engine, a gasoline engine, a gaseous fuel powered engine such as a natural gas engine, or any other type of engine apparent to one skilled in the art. Other power sources may alternatively embody a non-combustion source of power such as a fuel cell, a power storage device, an electric motor, or other similar mechanism. Although not shown in detail, the transmission  164  includes a plurality of forward and reverse gears and a neutral gear and is connected to a differential axle for driving one or more of the rear wheels  158  based on torque from the engine  162 . In some embodiments, the motor grader  100  may include an all-wheel drive system in which one or more of the front wheels  156  are also driven. 
     An operator cab  170  is mounted to the front frame  150 . The operator cab  170  may contain many controls of the motor grader  100 , including operator input devices  130  described in greater detail below, used to steer and otherwise operate the motor grader  100 . The operator cab  170  may also include a display device  172  adapted to convey information to the operator concerning the operation of the motor grader  100 . In some examples, the display device  172  may accept operator inputs (e.g., as a touchscreen display) such that the display device  172  may also be considered to be one of the operator input devices  130 . 
     As introduced above, the motor grader  100  includes the steering system  140  to maneuver the motor grader  100  during operation based on signals from the controller  120  and/or operator input devices  130  according to a selected steering control strategy, described in greater detail below. As is generally known, the steering system  140  includes various linkages, levers, joins, gears, pins, rods, and the like to position one or more driven wheels  156 ,  158  to orient the motor grader  100  in the desired direction. In one example and as schematically shown in  FIG. 1 , the steering system  140  includes one or more steering actuation devices, such as one or more steering cylinders  142  (schematically shown) coupled to the front or rear wheels  156 ,  158  configured to be hydraulically operated to articulate or reposition of the wheels  156 ,  158  (e.g., pivoting about a vertical axis) to steer the motor grader  100 . Additional steering mechanisms may be provided, including one or more lean cylinders  144  (schematically shown) coupled to the front or rear wheels  156 ,  158  configured to be hydraulically operated to control the position of the wheels  156 ,  158  (e.g., pivoting about a horizontal axis). Further, the steering system  140  may include one or more articulation cylinders  146  (schematically shown) mounted to one or both of the frames  150 ,  152  to rotate the front frame  150  relative to the rear frame  152  about the articulation joint  154 . The components of the steering system  140  introduced above are merely examples, and any number of additional components or systems may be provided. For example, the steering system  140  may further incorporate various types of circuits, including a hydraulic circuit and/or an electrical circuit for facilitating and controlling operation of the cylinders  142 ,  144 ,  146  and other actuation devices of the steering system  140 . Although not shown, such a hydraulic circuit may include hoses, pumps, tanks, valves, and the like. 
     The motor grader  100  includes one or more implements  180 ,  182  for performing work functions. As examples, the motor grader  100  includes a circle  180  and blade assembly  182  are mounted to the front frame  150  in front of the operator cab  170 . Various types of actuators (as well as brackets, couplings, motors, hydraulic and electric components, etc.) are provided to manipulate the circle  180  and/or blade assembly  182 , including lifting, tilting, rotating, shifting, repositioning, and the like to advantageously perform the functions of the motor grader  100 . Other implements may be provided. 
     As noted above, the controller  120  is provided to control various operational aspects of the motor grader  100 . Generally, the controller  120  may receive inputs from a number of sources, including the operator via the operator input devices  130  and from various sensors, units, and systems onboard or remote from the motor grader; and in response, the controller  120  generates one or more types of commands for implementation by the various systems of motor grader  100 . As one example discussed in greater detail below, the controller  120  may facilitate operation of the operator control system  110 , particularly with respect to receiving steering or other actuation request inputs from the operator via the operator input devices  130  and generating associated steering or other actuation device commands for the steering system  140  based on a selected mode associated with a respective control strategy. 
     Broadly, the controller  120  may be configured as a computing device with associated processor devices and memory architectures, as a hard-wired computing circuit (or circuits), as a programmable circuit, as a hydraulic, electrical or electro-hydraulic controller, or otherwise. As such, the controller  120  may be configured to execute various computational and control functionality with respect to the motor grader  100  (or other machinery). In some embodiments, the controller  120  may be configured to receive input signals in various formats (e.g., as hydraulic signals, voltage signals, current signals, and so on), and to output command signals in various formats (e.g., as hydraulic signals, voltage signals, current signals, mechanical movements, and so on). In some embodiments, the controller  120  (or a portion thereof) may be configured as an assembly of hydraulic components (e.g., valves, flow lines, pistons and cylinders, and so on), such that control of various devices (e.g., pumps or motors) may be implemented with, and based upon, hydraulic, mechanical, or other signals and movements. 
     The controller  120  may be in electronic, hydraulic, mechanical, or other communication with various other systems or devices of the motor grader  100  (or other machinery). For example, the controller  120  may be in electronic or hydraulic communication with various actuators, sensors, and other devices within (or outside of) the motor grader  100 , including various devices associated with pumps, control valves, and so on. The controller  120  may communicate with other systems or devices (including other controllers) in various known ways, including via a CAN bus (not shown) of the motor grader  100 , via wireless or hydraulic communication means, or otherwise. An example location for the controller  120  is depicted in  FIG. 1 . It will be understood, however, that other locations are possible including other locations on the controller  120 , or various remote locations. 
     In some embodiments, the controller  120  may be configured to receive input commands and to interact with an operator via the operator input devices  130 , which may be disposed inside an operator cab  170  of the motor grader  100  for easy access by the operator. The operator input devices  130  may be configured in a variety of ways. In some embodiments, the operator input devices  130  may include one or more joystick devices, various switches or levers, one or more buttons, a touchscreen interface that may be overlaid on a display, a keyboard, an audible device, a microphone associated with a speech recognition system, or various other human-machine interface devices. In one example, the one or more switches (e.g., switch  136 ) may receive an input associated with a steering mode selection and a joystick (or other) device (e.g., apparatuses  132 ,  136 ) may receive steering requests associated with the steering system  140  according to a selected steering mode to implement an associated steering control strategy. More specific examples of operator input devices  130  are provided below with reference to  FIG. 2 . 
     Various sensors (not shown) may also be provided to observe various conditions and other parameters associated with the motor grader  100 . For example, various sensors may be associated with the steering system  140 , drive system  160 , and/or the implements  180 ,  182 . Example sensors include sensors for measuring the articulation angle at the articulation joint  154 ; pressure and/or position sensors to evaluate the positions of the various cylinders, pumps, and valves; travel speed sensors; steering feedback angle sensors; and steering velocity sensors. One or more sensors may also be incorporated into the operator input devices  130 , discussed below. 
     As shown in  FIG. 1B , a wheel loader  100 ′ includes an operator control system  110 ′ that controls various functions associated with the wheel loader  100 ′ in a similar manner to the motor grader  100  discussed in reference to  FIG. 1A , including steering or other actuation functions based on manual inputs from an operator and other inputs, as discussed in greater detail below. As above, the operator control system  110 ′ is implemented with a controller  120 ′ and may further be considered to include one or more operator input devices  130 ′ and/or a steering system  140 ′. Generally, the operator input devices  130 ′ may include one or more operator control apparatuses  132 ′,  134 ′ (e.g., as joystick-type or other types of controls) to receive operator inputs that control various aspects of the wheel loader  100 ′ and a mode selection switch  136 ′ to receive operator ii inputs that select a mode associated with a control strategy (e.g., a steering or other actuation control mode). Additional details about the operator control system  110 ′ will be provided below after a more general description of the loader  100 ′. 
     In the depicted example, the wheel loader  100 ′is formed by a chassis or frame  150 ′ supported by front wheels  156 ′ and rear wheels  158 ′. In other embodiments, the wheel loader  100 ′ may include other ground-engaging devices for propelling the machine, such as track assemblies, for example, as known in the art. The wheel loader  100 ′ further includes a drive system  160 ′ adapted to drive or power the wheel loader  100 ′ and collectively formed by an engine or other type of power source  162 ′ and a transmission  164 ′, as generally described above. 
     An operator cab  170 ′ is mounted to the frame  150 ′. The operator cab  170 ′ may contain many controls of the wheel loader  100 ′, including operator input devices  130 ′ described in greater detail below, used to steer and otherwise operate the wheel loader  100 ′. The operator cab  170 ′ may also include a display device  172 ′ adapted to convey information to the operator concerning the operation of the wheel loader  100 ′. In some examples, the display device  172 ′ may accept operator inputs (e.g., as a touchscreen display) such that the display device  172 ′ may also be considered to be one of the operator input devices  130 ′. 
     As introduced above, the wheel loader  100 ′ includes the steering system  140 ′ to maneuver the wheel loader  100 ′ during operation based on signals from the controller  120 ′ and/or operator input devices  130 ′ according to a selected steering control strategy, described in greater detail below as one example. As is generally known, the steering system  140 ′ includes various linkages, levers, joins, gears, pins, rods, and the like to position one or more driven wheels  156 ′,  158 ′ to orient the wheel loader  100 ′ in the desired direction. In one example and as schematically shown in  FIG. 1B , the steering system  140 ′ includes one or more steering actuation devices, such as one or more steering cylinders  142 ′ (schematically shown) coupled to the front or rear wheels  156 ′,  158 ′ configured to be hydraulically operated to articulate or reposition of the wheels  156 ′,  158 ′ (e.g., pivoting about a vertical axis) to steer the wheel loader  100 ′. Additional steering mechanisms may be provided. The components of the steering system  140 ′ introduced above are merely examples, and any number of additional components or systems may be provided. For example, the steering system  140 ′ may further incorporate various types of circuits, including a hydraulic circuit and/or an electrical circuit for facilitating and controlling operation of the cylinders  142 ′ and other actuation devices of the steering system  140 ′. Although not shown, such a hydraulic circuit may include hoses, pumps, tanks, valves, and the like. 
     The wheel loader  100 ′ further includes a work implement, such as a bucket  180 ′, positioned at a front of the wheel loader  100 ′ and attached to the wheel loader  100 ′ through one or more linkage arms  182 ′ that include a series of pinned joints, structural members, and at least one hydraulic actuator  184 ′. This configuration allows the bucket  180 ′ to be moved up and down relative to the ground, and rotate around a lateral axis of the work vehicle  100 ′. Other implements may be provided. 
     Generally, the controller  120 ′ of the wheel loader  100 ′ operates in a manner similar to that described above with respect to the controller  120  of the motor grader  100  to control various operational aspects of the motor grader  100 . In particular, the controller  120 ′ may receive inputs from a number of sources, including the operator via the operator input devices  130 ′ and from various sensors, units, and systems onboard or remote from the wheel loader  100 ′; and in response, the controller  120 ′ generates one or more types of commands for implementation by the various systems of wheel loader  100 ′. As one example discussed in greater detail below, the controller  120 ′ may facilitate operation of the operator control system  110 ′, particularly with respect to receiving steering request inputs from the operator via the operator input devices  130 ′ and generating associated steering actuation device commands for the steering system  140 ′ based on a selected mode associated with a respective control strategy. 
     Reference is briefly made to  FIG. 2 , which depicts the interior cabin of the operator cab  170  of the motor grader  100 , although the cab  170  and description below may also refer to the wheel loader  100 ′. As shown, the operator cab  170  provides an enclosure for the operator to access a number of different operator input devices  130 , including a steering wheel, accelerator, and brake pedals. The operator cab  170  may further house the display device  172 . In this example, the operator input devices  130  include operator control apparatuses  132 ,  134  as a left operator control apparatus  132  and a right operator control apparatus  134  mounted to each side of the operator seat. 
     The operator control apparatuses  132 ,  134  are joystick-type controls with a grip interface and various types of inputs, such as buttons, switches, and dials, mounted on the grip interface. In one example, the left operator control apparatus  132  may include input mechanisms for lifting, lowering, and adjusting the pitch of the blade assembly  182 ; rotating the circle  180 ; shifting the transmission  164 ; and certain auxiliary functions. As a further example, the right operator control apparatus  134  may include input mechanisms for shifting the circle  180  and the blade assembly  182 ; adjusting the lean of the wheels  156 ,  158 ; adjusting the articulation of the frames  150 ,  152 ; and locking the differential axle. 
     According to one embodiment of the operator control system  110  with respect to the steering system  140 , the left operator control apparatus  132  includes a joystick grip interface that may be pivoted to the left and right as a steering request to steer the front wheels  156  via the steering system  140 . In particular, the operator provides manual operator steering inputs by pivoting the joystick grip interface, and the controller  120 , upon receiving the steering inputs, generates appropriate steering actuation device commands to the steering system  140 . Although the steering function is discussed below with respect to the joystick device, the steering function may be implemented into other operator input devices  130 , such as the right operator control apparatus  134 , steering wheel, and/or the other buttons, dials, and the like. Additional details about example implementations of a joystick device will be provided below. 
     As also depicted in  FIG. 2 , the operator input devices  130  further include the steering mode selection switch  136  that may form part of the operator control system  110 . The steering mode selection switch  136  may take any form. In one example, the steering mode selection switch  136  is a mechanical, physical, and/or virtual switch that enables an operator to select between a velocity-based steering control strategy (e.g., as a velocity control mode) and a position-based steering control strategy (e.g., as steering control mode), as will be discussed in greater detail below. In one example, the steering mode selection switch  136  may have visual indicia reflecting the potential strategies of the system  110  such that the operator may position the switch  136  according to the desired strategy. As introduced above, switch  136  of the motor grader  100  may be analogous to the switch  136 ′ of the wheel loader  100 ′. 
     Reference is now made to  FIG. 3 , which is a functional block dataflow diagram of portions of the operator control system  110  (and operator control system  110 ′) according to an embodiment. As noted above, the operator control system  110 ,  110 ′ may be considered to include the controller  120 ,  120 ′, the steering system  140 ,  140 ′ with one or more actuation devices  142 ,  142 ′, and one or more operator input devices  130 ,  130 ′. Generally, the actuation devices  142 ,  142 ′ discussed below may refer to any individual or combination of actuation devices and associated components that may be utilized to steer the motor grader  100  or wheel loader  100 ′, In this example, the operator input devices  130 ,  130 ′ include a joystick device  350  and the steering mode selection switch  136 ,  136 ′ (such as the steering mode selection switches  136 ,  136 ′ of  FIG. 1A or 1B ). The display device  172 ,  172 ′ (such as the display device  172 ,  172 ′ of  FIG. 1A or 1B ) may also form part of the operator control system  110 ,  110 ′. 
     In one example, the joystick device  350  may be incorporated into a larger operator control apparatus, such as one of the operator control apparatuses  132 ,  132 ′,  134 ,  134 ′, with numerous operator input mechanisms. However, for the purpose of steering the front wheels of the steering system  140 ,  140 ′ as part of the operator control system  110 ,  110 ′, the joystick device  350  is a single-axis joystick unit that may be pivoted to the left and right by the operator in order to steer the motor grader  100  ( FIG. 1A ) or the wheel loader  100 ′ ( FIG. 1B ). Generally, the joystick device  350  described below in reference to  FIG. 3  may be implemented in any suitable manner; however, more specific example implementations are described below with reference to  FIGS. 4, 5A, 5B, 6A-6C, and 7A-7C . 
     As shown, the joystick device  350  includes a joystick grip interface  352  mounted to a base or housing  354 . The joystick grip interface  352  is a lever-type or shaft element with a first end engageable by an operator and a second end secured to pivot within the housing  354  about a pivot axis. The operator engages the joystick grip interface  352  along a range of motion to implement a desired steering or other actuation function of the motor grader  100  or the wheel loader  100 ′ as an operator steering input  370 , as described below. 
     A feedback unit  356  is coupled to the joystick grip interface  352  or the base  354  in order to impart a feedback force in response to the operator manipulation of the joystick grip interface  352 . As used herein, the term “feedback” refers to a force imparted on the joystick grip interface  352  in any form or for any purpose, including a force to counteract or resist operator manipulation or external forces, a force to maintain a position of the grip interface  352  in the absence of operator manipulation, or a force to center or reposition the grip interface  352  (e.g., to a neutral position or otherwise) in the absence of operator manipulation. In general, the feedback unit  356  applies the haptic feedback force or “feel” responsive to operator movements. The feedback force may be linear or non-linear and proportional to the force required to move the grip interface  352 . As described below, the feedback unit  356  is commanded to apply the force in view of the steering control strategy. 
     The joystick device  350  further includes at least one control interface sensor  358  configured to collect various types of information associated with the operator steering input  370 . In particular, with respect to the joystick grip interface  352 , the control interface sensor  358  is configured to collect data associated with the position or displacement angle relative to a neutral position and the speed or angular velocity of the displacement (or derivations thereof), and in response, the control interface sensor  358  generates a corresponding signal in the form of an actuation request input  382 . The actuation request input  382  is provided to the controller  120 ,  120 ′. 
     As introduced above, the operator input devices  130 ,  130 ′ further include the steering mode selection switch  136 ,  136 ′. The steering mode selection switch  136 ,  136 ′ is configured to receive an operator mode input  372  in which the operator selects between a velocity control mode implementing the velocity-based steering control strategy and a position control mode implementing the position-based steering control strategy. In response to the operator mode input  372 , the steering mode selection switch  136 ,  136 ′ generates a corresponding signal in the form of a control mode selection input  380 . The control mode selection input  380  is provided to the controller  120 ,  120 ′. 
     As such, the controller  120 ,  120 ′ may receive the control mode selection input  380  and actuation request input  382 . With respect to the operator control system  110 ,  110 ′ of  FIG. 3 , the controller  120 ,  120 ′ may be organized as one or more functional units or modules  310 ,  320 , and  330  (e.g., software, hardware, or combinations thereof). As can be appreciated, the modules  310 ,  320 ,  330  shown in  FIG. 3  may be combined and/or further partitioned to carry out similar functions to those described herein. As an example, each of the modules  310 ,  320 ,  330  may be implemented with processing architecture such as a processor  302  and memory  304 , as well as suitable communication interfaces. For example, the controller  120 ,  120 ′ may implement the modules  310 ,  320 ,  330  with the processor  302  based on programs or instructions stored in memory  304 . In this example, the controller  120 ,  120 ′ includes a mode module  310 , an actuation module  320 , and a feedback module  330 . In some embodiments, the feedback module  330  may be omitted, as described below. 
     As introduced above, the controller  120 ,  120 ′ is configured to receive the actuation request input  382  and the control mode selection input  380 . In one embodiment, the mode module  310  receives the control mode selection input  380 . The mode module  310  evaluates the control mode selection input  380 , and in response, generates a control mode determination  312  that identifies the selected control mode represented in the control mode selection input  380 . The control mode determination  312  is provided to the actuation module  320  and feedback module  330 . 
     The actuation module  320  receives the actuation request input  382  and the control mode determination  312 . The actuation module  320  evaluates the actuation request input  382  in view of the control mode determination  312 . The actuation module  320  may access stored information that maps the actuation request input  382  to a work device operating command  390  according to the current control mode determination  312 . Specifically, an actuation request input  382 , when in the velocity control mode, is mapped to one or more work device operating commands  390  in order to implement a particular velocity; and an actuation request input  382 , when in the position control mode, is mapped to a work device operating command  390  in order to implement a particular position. For example, in the velocity control mode, the actuation request input  382  is interpreted as a joystick grip interface input, and in response, the actuation module  320  may reference a stored map to determine a corresponding velocity command for one or more of the steering actuation devices  142 ,  142 ′ that results in an operator desired steering velocity. Such reference maps may include a collection of data in the form of tables, graphs, and/or equations. Similarly, in the position control mode, the actuation request input  382  based on the operator steering input  370  is interpreted as a joystick grip interface (or other operator interface) position input, and in response, the actuation module  320  may reference a stored map to determine a corresponding position command for one or more of the steering actuation devices  142 ,  142 ′ that results in an operator desired steering position. 
     The work device operating command  390  generated by the actuation module  320  is provided to the steering system  140 ,  140 ′, such as one or more of the steering actuation devices  142 ,  142 ′, as introduced above. For example, the work device operating command  390  may correspond to valve positions to operate the actuation devices  142 ,  142 ′ to a specified position or velocity. Accordingly, the steering system  140 ,  140 ′ implements the work device operating command  390  for the control mode determination  312 , thereby enabling steering operation with steering inputs  370  according to a desired or preferred steering control strategy. 
     In some embodiments, the actuation module  320  may receive additional input data (not shown) from various sensors, systems, or other modules on-board or off-board of the motor grader  100  or wheel loader  100 ′. Such additional input may include information associated with the actuation devices  142 ,  142 ′ (e.g., cylinder positions, tank volumes, fluid pressures, etc.). The actuation module  320  may further evaluate the actuation request input  382  in view of the additional input to provide an appropriate operating command  390 . 
     In some examples, the mode module  310  may further provide the control mode determination  312  to the display device  172 ,  172 ′. This enables a visual indication to the operator of the present steering control mode. 
     The mode module  310  further provides the control mode determination  312  to the feedback module  330 . The feedback module  330  also receives the actuation request input  382 . In turn, the feedback module  330  may actively generate an appropriate feedback command  392  in response to the actuation request input  382  according to the control mode determination  312  for the feedback unit  356  of the joystick device  350 . In one example, the feedback module  330  may access stored information that maps the actuation request input  382  in view of the control mode determination  312  to an associated feedback force response as a feedback command  392 . Specifically, an actuation request input  382 , when in the velocity control mode, is mapped to one or more feedback commands  392  in order to implement a particular feedback force according to a velocity-based steering control strategy; and an actuation request input  382 , when in the position control mode, is mapped to one or more feedback commands  392  in order to implement a particular feedback force according to a position-based steering control strategy. Such reference maps may include a collection of data in the form of tables, graphs, and/or equations. 
     Upon receipt, the feedback unit  356  applies a force to the joystick grip interface  352  according to the feedback command  392 . As a result, the steering control mode dictates the nature of the feedback force generated by the feedback unit  356  on the joystick grip interface  352 . 
     In some examples, the feedback module  330  may be omitted. In those embodiments, the feedback force may be applied passively to the joystick device  350 , e.g., without active control. Additional details regarding the feedback unit  356 , including example mechanisms for applying the feedback force, are provided below. 
     In this manner, the operator control system  110 ,  110 ′ enables the operator to select a steering mode and provide steering inputs, and in response, the controller  120 ,  120 ′ implements these inputs to appropriately control the steering system  140 ,  140 ′. The controller  120 ,  120 ′ may additionally generate the appropriate feedback force at the joystick device  350  according to the selected mode. 
     In various embodiments of the operator control system  110 ,  110 ′ described above, the velocity-based and position-based steering control strategies may be implemented according to various types of operator input devices and associated feedback responses. For example, the operator input devices may be implemented in an active system in which a motor generates an appropriate feedback response; a passive system in which mechanical components generate the feedback response; and a semi-active system that includes implementation characteristics of a passive system and an active system. Examples are provided below with reference to  FIGS. 4, 5A, 5B, 6A-6C, and 7A-7C . Additionally, as noted above, although the operator control system  110 ,  110 ′ is primarily described in the context of steering, corresponding strategies may be utilized with other actuation operations. 
     Reference is made to  FIG. 4 , which is an active (or full-active) feedback force joystick device  400 . In one embodiment, the joystick device  400  is an electromechanical joystick device. The joystick device  400  of  FIG. 4  may be considered one of the operator input devices  130  of the operator control system  110 ,  110 ′ discussed above with reference to  FIGS. 1A, 1B, 2, and 3 . 
     The joystick device  400  includes a joystick grip interface (or joystick shaft)  410  that extends between a first end  412  configured for engagement by the operator to a second end within a housing or base member. Although not shown, the second end of the joystick grip interface  410  is pivotally coupled to a positioning motor  430  via any suitable linkage arrangement, such as gimbal arm, pivot bearing, bearing mount, gear arrangements, and the like. 
     A positioning motor  430 , such as a servo motor, is operatively coupled to the joystick grip interface  410  via various mechanisms such that a desired force and/or velocity can be applied to the control joystick grip interface  410  having a magnitude that is a function of the torque and/or velocity of a motor drive shaft (not shown). 
     One or more electromechanical or optical position sensors  440  (schematically shown) are operatively coupled to the joystick grip interface  410  to determine the position of the joystick grip interface  410 . Examples of such sensors  440  include rotary or linear potentiometers, optical encoders, and linear displacement voltage transducers (LDVTs). 
     In  FIG. 4 , the joystick grip interface  410  is in a neutral or center position. During operation, a force applied by the operator pivots the joystick grip interface  410  relative to the steering axis, and thus pivots a linkage arrangement to cause rotation of the drive shaft of the motor  430 . The amount of rotation imparted to drive shaft may be sensed by sensors  440  that output a corresponding signal representing an actuation request signals (e.g., actuation request input  382  of  FIG. 3 ). 
     Additionally, the motor  430  is configured to generate a feedback force applied to the joystick grip interface  410  in response according to command signals (e.g., feedback command  392  of  FIG. 3 ). In particular, the motor  430  applies a feedback force in order to move or resist movement of the joystick grip interface  410 . The motor  430  may implement the variable feedback force according to the selected control mode, e.g., either the velocity-based steering control strategy in the velocity control mode or the position-based steering control strategy in the position control mode. 
     As examples, in the velocity control mode, the feedback force curve remains centered, regardless of the position of the joystick grip interface  410 . As such, as the joystick grip interface  410  is moved further from the center, the motor  430  applies an increasing feedback force to the joystick grip interface  410  in an opposing direction, although typically less than the force required to move the joystick grip interface  410 . Moreover, the feedback force from the motor  430  functions to re-center the joystick grip interface  410  after the operator releases the joystick grip interface  410 . Based on the feedback commands, the feedback force may be linearly or non-linearly proportional to the force required to move the joystick grip interface  410 . 
     In the position control mode, the feedback force curve follows the position of the joystick grip interface  410 . As such, as the joystick grip interface  410  completes a movement, the feedback force applied by the motor  430  operates to maintain the position of the joystick grip interface  410  associated with the operator input. As introduced above, the motor  430  may additionally provide a feedback force in view of the speed of the operator input according to the reaction time of the steering system (e.g., steering system  140  of  FIG. 1A , as well as steering system  140 ′ of  FIG. 1B ). In particular, if the joystick grip interface  410  is moved quickly, the motor  430  may apply a relatively strong resisting feedback force to the joystick grip interface  410 . The resisting feedback force reflects the ability of the steering system to implement the actuation request input. Otherwise, the steering system may not be able to “keep up” with the inputs at the joystick grip interface  410 . 
     In some examples, the feedback force applied by the motor  430  may have characteristics of both the velocity-based steering command strategy and the position-based steering command strategy regardless of the current steering control mode in order to improve the function of the joystick device  400 . For example, in the velocity control mode, the motor  430  operates to provide some stabilizing feedback force to the joystick grip interface  410  upon returning to the neutral position. Otherwise, the joystick grip interface  410  may undesirably oscillate upon returning to the neutral position. Similarly, in the position control mode, the motor  430  operates to provide some stabilizing feedback force on the joystick grip interface  410 , even when the joystick grip interface  410  has been released by the operator. Otherwise, the weight of the joystick grip interface  410  may cause unwanted movement. Instead, the feedback force of the motor  430  may automatically account for the weight of the joystick grip interface  410  such that when the interface  410  is released, it stays in the position. However, the selected mode designates which strategy dominates the applicable feedback force. 
     Reference is now made to  FIGS. 5A-5B, 6A-6C, and 7A-7C , which are different views of a passive (or full-passive) feedback force joystick device  500 . The joystick device  500  may be considered one of the operator input devices  130 ,  130 ′ of the operator control system  110 ,  110 ′ discussed above with reference to  FIGS. 1A, 1B, 2, and 3 . In this example, the joystick device  500  is incorporated with a steering mode selection switch  510 , which may correspond to the steering mode selection switch  136  also discussed above with reference to  FIGS. 1A, 1B, 2, and 3 . 
     Initially referring to  FIG. 5A , the joystick device  500  includes a joystick grip interface  530  that extends between a first end  532  configured for engagement by the operator to a second end  534  within a housing or base member  536 . The second end  534  of the joystick grip interface  530  is pivotally coupled to a pivot collar  540  to pivot about a pivot axis  542 . 
     The joystick device  500  further includes a feedback unit  550  that functions to provide velocity-based feedback force and position-based feedback force on the joystick grip interface  530  based on operator selections from the steering mode selection switch  510 . In particular, the feedback unit  550  includes a velocity-based feedback pack  560  and a position-based feedback pack  570 , as described in greater detail below. The feedback packs  560 ,  570  discussed below are merely examples on the numerous types of feedback mechanisms that may be implemented according to the embodiments discussed herein. 
     The joystick device  500  additionally includes one or more sensors  580 . As the joystick grip interface  530  pivots about the pivot axis  542 , the sensor  580  collects information associated with one or more of the position and velocity of the joystick grip interface  530 , including the position and the velocity resulting from the operator input on the joystick grip interface  530 , which results in the actuation request input (e.g., input  382  of  FIG. 3 ). As described in greater detail below, the sensor  580  additionally collects information associated with the operator mode selection on the steering mode selection switch  510 . The sensor  580  provides the actuation request input and the operator strategy selection input to an operator system controller (e.g., the controller  120 ,  120 ′), as described above. In one example, the sensor  580  includes one or more of a rotary hall effect sensor, a reed switch, or a hall effect sensor. 
     The steering mode selection switch  510  includes an operator engagement interface, such as a knob  512 , coupled to a rod  514  terminating at a cam  516 . The cam  516  has a gear engagement that is coupled to an engagement rod  520 . As a result of this arrangement, twisting of the knob  512  operates to shift the engagement rod  520  along the pivot axis  542  back and forth (i.e., to the left and right in  FIG. 5A ). In effect, the engagement rod  520  is a link between the switch  510  and the velocity-based feedback pack  560  and the position-based feedback pack  570 . As noted above, the knob  512  may be surrounded by indicia reflecting knob positions corresponding the respective modes 
     The engagement rod  520  has a first end  522  coupled to a cam  516 , a center portion  524  that extends through the housing  536  of the joystick device  500 , and an end portion  526  positioned in one of the velocity-based feedback pack  560  or the position-based feedback pack  570 , depending on the position of the steering mode selection switch  510 . As described below, the engagement rod  520  may have at least two positions corresponding to the position of the steering mode selection switch  510 , including: a first position (as shown in  FIG. 5A ) in which the end portion  526  is positioned in the velocity-based feedback pack  560 ; and a second position (as shown in  FIG. 5B ) in which the end portion  526  is positioned in the position-based feedback pack  570 . 
     The engagement rod  520  has a first set of splines (or teeth)  525  arranged on the center portion  524  that extend through the pivot collar  540 . The pivot collar  540  has internal splines or teeth  544  that engage the splines  525  of the engagement rod  520 . Regardless of the position of the engagement rod  520 , the splines  525  of the engagement rod  520  mesh with the splines  544  of the pivot collar  540 . As a result, when the interface  530  pivots about the pivot axis  542 , the engagement rod  520  pivots with the interface  530 . The splined arrangement enables the engagement rod  520  to slide relative to the pivot collar  540  while maintaining the pivoting engagement. 
     The engagement rod  520  has a set of teeth (or splines)  527  (as shown in  FIGS. 6A-6C, 7A-7C ) on the end portion  526 . The other portions of the engagement rod  520 , including the center portion  524  immediately proximate to the end portion  526 , may be cylindrical or other cross-sectional shapes that have smaller cross-sectional areas than the teeth  527  on the end portion  526 . As described below, the teeth  527  of the end portion  526  of the engagement rod  520  selectively engage the velocity-based feedback pack  560  or the position-based feedback pack  570  such that the selected pack  560 ,  570  may impose a force on the joystick grip interface  530  via the engagement rod  520  and the pivot collar  540 . 
     Reference is now made to  FIGS. 6A-6C , which are cross-sectional views of the joystick device  500  through line  6 - 6  of  FIG. 5A , particularly through the velocity-based feedback pack  560 . In  FIG. 6A , the joystick grip interface  530  is in a neutral position; in  FIG. 6B , the joystick grip interface  530  has been moved leftward; and in  FIG. 6C , the joystick grip interface  530  has been moved rightward. 
     As shown, the velocity-based feedback pack  560  is a centering spring pack and includes a centering spring  610  on a pivot bracket  630  pivotally mounted on a planar rear wall  632  within a housing  602  and a stationary bracket  670  fixedly mounted to the housing  602 . In this example, the pivot bracket  630  includes a first (or cylindrical) wall element  640  and second (or U-shaped) wall element  650 . 
     The cylindrical wall element  640  of the pivot bracket  630  is pivotally coupled to the rear wall  632  and generally cylindrical to define a passageway  642  therethrough that aligns with a corresponding passageway through the rear wall  632 . The cylindrical wall element  640  includes a plurality of internal teeth (or splines)  644  that circumscribe the passageway  642 . As shown, when the mode selection switch  510  is in the position corresponding to the velocity control mode, the teeth  527  on the engagement rod  520  engage the teeth  644  of the cylindrical wall element  640  for rotational engagement, as discussed in greater detail below. 
     The U-shaped wall element  650  of pivot bracket  630  is pivotally coupled to the rear wall  632  and is formed with a curved section  652 , a first wall leg  654 , and a second wall leg  656 . The curved section  652  surrounds, but is spaced apart from, a portion of the cylindrical wall element  640 . The first wall leg  654  extends linearly from one end of the curved section  652  and the second wall leg  656  extends linearly from the other end of the curved section  652 . The first and second wall legs  654 ,  656  are parallel to each other. The U-shaped wall element  650  is fixed to the cylindrical wall element  640  to pivot therewith. 
     In this embodiment, the stationary bracket  670  extends between side walls  604 ,  606  of the housing  602 . The stationary bracket  670  is generally parallel to the rear wall  632  and spaced axially apart from the wall elements  640 ,  650 ,  660  of the pivot bracket  630 . The stationary bracket  670  include pins or stops  672 ,  674  that extend axially toward the rear wall  632  on either side of the centering spring  610 . 
     The centering spring  610  is formed by a center coil  612 , a first spring leg  614  extending linearly from a first end of the center coil  612 , and second spring leg  616  extending linearly from a second end of the center coil  612 . As shown, the center coil  612  is wrapped around the cylindrical wall element  640 , in between the cylindrical wall element  640  and the U-shaped wall element  650 . The spring  610  is fixedly engaged to the cylindrical wall element  640 . In the neutral position, the first and second spring legs  614 ,  616  extend parallel to one another, along the first and second wall legs  654 ,  656 , respectively. 
     Accordingly, when the operator desires to implement a steering function in a velocity control mode, the operator rotates the knob  512  to a position representing the velocity control mode. When the knob  512  is rotated into the position corresponding to the velocity control mode, the engagement rod  520  is translated by the rod  514  and cam  516 . Upon movement or repositioning of the engagement rod  520 , the sensor  580  determines the position of the engagement rod  520  and sends a control mode selection input (e.g., input  380 ) to the controller  120 ,  120 ′, as discussed above. Upon the linear translation of the engagement rod  520  into the position reflected by the knob  512  for the velocity control mode, the teeth  527  at the end portion  526  of the engagement rod  520  mesh with the teeth  644  in the cylindrical wall element  640  of the pivot bracket  630  of the velocity-based feedback pack  560 . In this position, the center portion  524  ( FIG. 5 ) of the engagement rod  520  extends through a passageway (discussed below) in the position-based feedback pack  570  such that the engagement rod  520  is not engaged with the position-based feedback pack  570 . 
     Because the engagement rod  520  is engaged with the velocity-based feedback pack  560 , the joystick device  500  behaves in an operator-accustomed manner for a velocity-based steering control strategy, as discussed below. As shown in  FIG. 6A , in a neutral position, the joystick grip interface  530  is positioned in a vertical orientation, although the neutral position may correspond to other angles relative to the ground plane in other embodiments based on the shape of the interface  530 , ergonomics, or other considerations. As noted above, when the joystick grip interface  530  and thus the velocity-based feedback pack  560  are in the neutral position, the first and second spring legs  614 ,  616  of the spring  610  are parallel to one another and respectively engage the stops  672 ,  674  of the stationary bracket  670 , which maintain the spring  610  and thus, the pivot bracket  630 , engagement rod  520 , pivot collar  540 , and joystick grip interface  530  in the generally neutral position according to a centering equilibrium of the spring force. 
     During an operator steering input in a leftward direction, the force applied by the operator moves the joystick grip interface  530  to an angle offset from the vertical, as shown in  FIG. 6B . During this pivoting movement, the splined connection between the pivot collar  540  and the engagement rod  520  causes the engagement rod  520  to rotate. As noted above, movement of the engagement rod  520  is sensed by the sensor  580  for the generation of a corresponding actuation request input (e.g., input  382  of  FIG. 3 ) to the controller  120 . In response and since the velocity control mode has been selected, the controller  120  generates an operating command (e.g., command  390  of  FIG. 3 ) that moves the steering actuation devices (e.g., devices  142 ,  142 ′) at a rate of change corresponding to a rate of change of the actuation request input (e.g., input  370 ) on the joystick device  500 . 
     Moreover, as discussed above, movement of the joystick grip interface  530  results in corresponding movement within the velocity-based feedback pack  560 . In particular, pivoting of the joystick grip interface  530  results in the pivoting of the pivot bracket  630  (e.g., via the pivot collar  540  and engagement rod  520 ). As the pivot bracket  630  pivots, the first wall leg  654  of the U-shaped wall element  650  presses the first spring leg  614  of the spring  610  in the pivoting direction on the other side of the pivot axis  542  (e.g., to the right in  FIG. 6B ), while the first stop  672  maintains the position of the second spring leg  616  of the spring  610 . This results in the spring  610  being placed under compression, thereby generating a resistance force in the direction opposite to the pivoting direction. The resistance force is transferred through the pivot bracket  630 , through the splined connection to the engagement rod  520 , and through the collar  540  to the joystick grip interface  530 , such that the resistance force provides a feedback force to the operator. Typically, the feedback force is consistent with the feel of the joystick grip interface  530  in a velocity-based steering control strategy. 
     When operator pressure is no longer being applied to the joystick grip interface  520 , the force of the spring  610  at the first spring leg  614  of the spring  610  presses the first wall leg  654  of the U-shaped wall element  650  such that the pivot bracket  630  returns to the neutral position. As a result, the engagement rod  520  rotates, which in turn pivots the joystick grip interface  530  back into the neutral position. 
     Referring briefly to  FIG. 6C , a similar operation occurs in the opposite direction when then joystick grip interface  530  is moved by the operator in the right direction. Movement of the joystick grip interface  530  is interpreted according to the velocity control mode and the spring  610  imparts an appropriate feedback force. Subsequently, upon release, the spring  610  returns the pivot bracket  630  and thus the joystick grip interface  530  back into the neutral position. 
     Accordingly, the configuration of the velocity-based feedback pack  560  with the spring  610  provides haptic behavior is consistent with the velocity-based steering control strategy. Elements other than the coil spring  610  may be provided, such as gas springs, air springs, or similar elements. 
     Reference is now made to  FIGS. 7A-7C , which are cross-sectional views of the joystick device  500  through line  7 - 7  of  FIG. 5A , particularly through the position-based feedback pack  570 . In  FIG. 7A , the joystick grip interface  530  is in a neutral position; in  FIG. 7B , the joystick grip interface  530  has been moved leftward; and in  FIG. 7C , the joystick grip interface  530  has been moved rightward. 
     As shown, the position-based feedback pack  570  is a friction damping pack and includes a position-maintaining, friction-based dampening device formed by one or more fixed plates  710  and one or more pivot plates  720 , each mounted on a housing  702 . The plates  710 ,  720  may be arranged in a stacked and/or abutting configuration such that adjacent planar surfaces of the plates  710 ,  720  abut against and frictionally engage one another. Each plate  710 ,  720  defines a passageway  722  (one of which is shown) respectively aligned with one another. The passageways  722  through the pivot plates  720  includes a plurality of internally extending teeth or splines  724 , and the passageways (not shown) through the fixed plates  710  are larger than the passageways  722  through the pivot plates  720 . As a result, the teeth  527  on the engagement rod  520  are configured to engage the teeth  724  of the pivot plates  720  for rotational engagement, while the engagement rod  520  passes through the fixed plates  710  unencumbered. 
     Accordingly, when an operator desires to implement a steering function in a position control mode, the operator rotates the knob  512  to a position representing the position control mode. When the knob  512  is rotated into the position corresponding to the position control mode, the engagement rod  520  is translated by the rod  514  and cam  516 . Upon movement or repositioning of the engagement rod  520 , the sensor  580  determines the position of the engagement rod  520  and sends a control mode selection input (e.g., input  380 ) to the controller  120 ,  120 ′, as discussed above. Upon the linear translation of the engagement rod  520  into the position reflected by the knob  512  for the position control mode, the teeth  527  at the end the end portion  526  of the engagement rod  520  mesh with the teeth  724  of the pivot plates  720  of the position-based feedback pack  570 , as depicted in  FIGS. 7A-7C . 
     Because the engagement rod  520  is engaged with the position-based feedback pack  570 , the joystick device  500  behaves in an operator-accustomed manner for position-based steering control strategies. As shown in  FIG. 7A , in a neutral position, the joystick grip interface  530  is positioned in a vertical orientation, although the neutral position may correspond to other angles relative to the ground plane in other embodiments. 
     Regardless of the position of the joystick grip interface  530 , the plates  710 ,  720  abut one another and apply a mutual friction force to resist movement. When the joystick grip interface  530  is moved (e.g., from neutral in  FIG. 7A  to the left as shown in  FIG. 7B  or to the right as shown in  FIG. 7C ), the engagement rod  520  also pivots. 
     As noted above, movement of the engagement rod  520  is sensed by the sensor  580  for the generation of a corresponding actuation request input (e.g., input  382  of  FIG. 3 ) to the controller  120 . In response and since the position control mode has been selected, the controller  120  generates an operating command (e.g., command  390  of  FIG. 3 ) that that moves the steering actuation devices (e.g., devices  142 ,  142 ′) into a position corresponding to a position of the actuation request input (e.g., input  370 ) on the joystick device  500 . 
     Moreover, as discussed above, movement of the joystick grip interface  530  results in corresponding movement within the position-based feedback pack  570 . In particular, pivoting of the joystick grip interface  530  results in a force imparted on the pivot plates  720  via engagement of the engagement rod  520  and the pivot plates  720 . When sufficient force is placed on the joystick grip interface  530 , the friction force between the abutting plates  710 ,  720  is overcome and the pivot plates  720  move relative to the fixed plates  710 . The friction force from abutting plates  710 ,  720  provides resistance as a feedback force for the operator at the joystick grip interface  530  (e.g., through the engagement rod  520  and collar  540 ). Typically, the feedback force is consistent with the feel of the joystick grip interface  530  in a position-based steering control strategy. When operator pressure is no longer being applied to the joystick grip interface  530 , the friction force between abutting plates  710 ,  720  maintains this position, and thus, the position of the joystick grip interface  530 . 
     In some examples, a detent arrangement  726  may be implemented to provide a haptic indication of a center or neutral position. For example, a detent arrangement  726  may be cooperating detents on one or more of the plates  710 ,  720  such that a “click” or neutral position may be sensed by the operator. Other mechanisms indicating the neutral position may be provided, including spring arrangements, ball arrangements, and the like. 
     Accordingly, the configuration of the position-based feedback pack  570  with the friction plates  710 ,  720  provides haptic behavior is consistent with the position-based steering control strategy. Position-maintaining elements other than the plates  710 ,  720  may be provided in other embodiments. 
     Generally, the joystick device  400  of  FIG. 4  may be considered an active system in which the motor (e.g., motor  430 ) generates the feedback response, and the joystick device  500  of  FIGS. 5A, 5B, 6A-6C, and 7A-7C  may be considered a passive system in which passive elements (e.g., the spring  610  and plates  710 ,  720 ) generate the feedback response. However, in some embodiments, a joystick device may be provided as a semi-active system that includes characteristics of both active systems and passive systems. 
     In one such semi-active embodiment, the joystick device may include a partial electro-mechanical joystick device with a positioning motor and a centering spring, each coupled to a joystick grip interface. For example, the positioning motor may be similar to the motor  430  described above with reference to  FIG. 4  and the centering spring may be similar to the positioning spring  610  described above with reference  FIGS. 5A, 5B, and 6A-6C . As such, the positioning spring may be coupled to a pivot bracket that engages an engagement rod coupled to the joystick grip interface, as described above, and the pivot bracket may further have teeth that engage a drive shaft of a motor. As above, a steering mode selection switch may be provided to indicate the desired mode to the controller and the actuation request inputs from the joystick device are interpreted accordingly. 
     Regarding application of a feedback force, typically in such an arrangement according to a velocity control mode, the motor is not used and the device operates such as described above with the device of  FIG. 4  utilizing the feedback force of the coil spring. In effect, the positioning motor may be locked in a center position. In the position control mode, the motor is actively controlled according to position-based position control strategy such that a feedback force is applied to the joystick grip interface through the pivot bracket or housing. When the operator releases the joystick grip interface, the motor may maintain the position of the joystick grip interface. Moreover, the motor may be actively controlled to resist movement of the joystick grip interface at too fast a speed that would overtax the steering system, thereby providing a haptic feel to the operator that the joystick grip interface is being moved too fast. 
     Accordingly, the operator control system may selectively implement one of two operator control strategies for steering a work vehicle, namely, a velocity-based steering control strategy and a position-based steering control strategy. In response to the operator selection that the velocity-based steering control strategy is to be used, the joystick device acts in accordance with how the operator is accustomed to a joystick device operating under the velocity-based steering control strategy and the work vehicle responds accordingly. In response to the operator selection that the position-based steering control strategy is to be used, the joystick device acts in accordance with how the operator is accustomed to a joystick device operating under the position-based steering control strategy and the work vehicle responds accordingly. 
     Also, the following examples are provided, which are numbered for easier reference: 
     1. A control system for a work vehicle having one or more actuation devices, the control system comprising: an operator input device configured to receive operator input from an operator of the work vehicle; and a controller operatively connected to the operator input device and to the one or more actuation devices, the controller configured to: receive a control mode selection input including a position control mode selection input or a velocity control mode selection input; receive an actuation request input from the operator input device; determine an operating command corresponding to the actuation request input from the operator input device according to the control mode selection input; and issue the operating command to the one or more actuation devices. 
     2. The control system of example 1, wherein, in the position control mode, the operating command includes an instruction to move the one or more actuation devices to a position corresponding to a position corresponding to the actuation request input from the operator input device; and wherein, in the velocity control mode, the operating command includes an instruction to move the one or more actuation devices at a rate of change corresponding to the position of the actuation request input from the operator input device. 
     3. The control system of example 1, wherein the operator input device includes a grip interface having a range of motion for transmitting the operator input to the operator input device. 
     4. The control system of example 3, wherein the operator input device is an electro-mechanical joystick device having a feedback motor coupled to the grip interface; and wherein the controller is further configured to: determine a feedback command corresponding to movement of the grip interface associated with the actuation request according to the control mode selection input; and issue the feedback command to the feedback motor. 
     5. The control system of example 4, wherein, in the position control mode, the feedback command includes an instruction to the feedback motor to maintain a position of the grip interface associated with at least one of the actuation request input and the position of the one or more actuation devices; and wherein, in the velocity control mode, the feedback command includes an instruction to the feedback motor to re-center the grip interface following the actuation request input. 
     6. The control system of example 5, wherein, in the velocity control mode, the feedback command includes an instruction to the feedback motor to provide a counteracting force resisting movement of the grip interface that is less than or equal to a force required to move the grip interface, wherein the counteracting force is linearly or non-linearly proportional to the force required to move the grip interface. 
     7. The control system of example 3, wherein the operator input device is a partial electro-mechanical joystick device having a positioning motor and a centering spring both coupled to the grip interface; wherein, in the position control mode, the controller is further configured to determine a position command corresponding to movement of the grip interface associated with the actuation request input; and wherein, in the velocity mode, the positioning motor is locked in a center position. 
     8. The control system of example 3, wherein the operator input device is a mechanical joystick having a position-maintaining device, a centering device or both the position-maintaining device and the centering device; wherein the position-maintaining device is configured to maintain a position of the grip interface after movement associated with the actuation request input; and wherein the centering device is configured to center the grip interface after movement associated with the actuation request input. 
     9. The control system of example 8, wherein the position-maintaining device is a friction and damper device; and wherein the centering device is a centering spring. 
     10. The control system of example 10, wherein the operator input device includes a selection switch; and further comprising: a sensor configured to detect a position of the selection switch and provide the control mode selection input to the controller. 
     11. The control system of example 10, wherein the operator input device includes a link coupled to the selection switch and to either the position-maintaining device or the centering device. 
     12. The control system of example 11, wherein the operator input device includes both the position-maintaining device and the centering device; and wherein movement of the selection switch causes movement of the link to selectively couple to either the position-maintaining device or the centering device. 
     13. A control system for a work vehicle having one or more actuation devices, the control system comprising: an operator input device configured to receive operator input from an operator of the work vehicle, wherein the operator input device includes a grip interface having a range of motion for transmitting the operator input to the operator input device; a controller operatively connected to the operator input device and to the one or more actuation devices, the controller configured to: receive a control mode selection input including a mode selection input as a position control mode or a velocity control mode; receive an actuation request input from the operator input device; determine an operating command corresponding to the actuation request input from the operator input device according to the control mode selection input; and issue the operating command to the one or more actuation devices; wherein, in the position control mode, the operating command includes an instruction to move the one or more actuation devices to a position corresponding to a position corresponding to the actuation request input from the operator input device; and wherein, in the velocity control mode, the operating command includes an instruction to move the one or more actuation devices at a rate of change corresponding to the position of the actuation request input from the operator input device. 
     14. The control system of example 13, wherein the operator input device is an electro-mechanical joystick having a feedback motor coupled to the grip interface; and wherein the controller is further configured to: determine a feedback command corresponding to movement of the grip interface associated with the actuation request input according to the control mode selection input; and issue the feedback command to the feedback motor, wherein, in the position control mode, the feedback command includes an instruction to the feedback motor to maintain a position of the grip interface associated with the actuation request input; and wherein, in the velocity control mode, the feedback command includes an instruction to the feedback motor to re-center the grip interface following the actuation request input and to provide a counteracting force resisting movement of the grip interface that is less than a force required to move the grip interface, wherein the counteracting force is linearly or non-linearly proportional to the force required to move the grip interface. 
     15. The control system of example 13, wherein the operator input device includes a mode selection switch; and wherein the control system further comprises a sensor configured to detect a position of the mode selection switch and provide the control mode selection input to the controller, wherein the operator input device is a mechanical joystick having a friction dampening device and a spring centering device; wherein the friction dampening device is configured to maintain a position of the grip interface after movement associated with the actuator request; and wherein the spring centering device is configured to center the grip interface after movement associated with the actuator request, and wherein movement of the mode selection switch causes movement of the link to selectively couple to either the position-maintaining device or the centering device. 
     As used herein, unless otherwise limited or modified, lists with elements that are separated by conjunctive terms (e.g., “and”) and that are also preceded by the phrase “one or more of” or “at least one of” indicate configurations or arrangements that potentially include individual elements of the list, or any combination thereof. For example, “at least one of A, B, and C” or “one or more of A, B, and C” indicates the possibilities of only A, only B, only C, or any combination of two or more of A, B, and C (e.g., A and B; B and C; A and C; or A, B, and C). 
     As used herein, the term module refers to any hardware, software, firmware, electronic control component, processing logic, and/or processor device, individually or in any combination, including without limitation: application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Embodiments of the present disclosure may be described herein in terms of functional and/or logical block components and various processing steps. It should be appreciated that such block components may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. For example, an embodiment of the present disclosure may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, or the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that embodiments of the present disclosure may be practiced in conjunction with any number of systems, and that the loader described herein is merely one example embodiment of the present disclosure. 
     For the sake of brevity, conventional techniques related to signal processing, data transmission, signaling, control, and other functional aspects of the systems (and the individual operating components of the systems) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent example functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in an embodiment of the present disclosure. 
     As will be appreciated by one skilled in the art, certain aspects of the disclosed subject matter can be embodied as a method, system (e.g., a work vehicle control system included in a work vehicle), or computer program product. Accordingly, certain embodiments can be implemented entirely as hardware, entirely as software (including firmware, resident software, micro-code, etc.) or as a combination of software and hardware (and other) aspects. Furthermore, certain embodiments can take the form of a computer program product on a computer-usable storage medium having computer-usable program code embodied in the medium. Any suitable computer usable or computer readable storage or signal medium can be utilized. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. Explicitly referenced embodiments herein were chosen and described in order to best explain the principles of the disclosure and their practical application, and to enable others of ordinary skill in the art to understand the disclosure and recognize many alternatives, modifications, and variations on the described example(s). Accordingly, various embodiments and implementations other than those explicitly described are within the scope of the following claims.