Abstract:
The present invention is for a modular, extensible software system for use with multi-modal, autonomous, or semi-autonomous vehicles. The design of the present invention involves the coherent integration of modules with responsibilities for human-interaction, training, path planning, mission execution, navigation, and safety to develop and complete missions. The present invention provides a modular software system that expresses vehicle behaviors through numerous small-grain elements to complete a mission. The system can be easily adapted or modified by adding new software modules or modifying existing modules as missions change or expand, with the smaller-grain modules being easier to adapt and reuse.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to a method and modular system for processing data for a vehicle control system.  
       BACKGROUND OF THE INVENTION  
       [0002]     As autonomous vehicle operation becomes more sophisticated, an increasing number of uses for such equipment is being identified. Demand for vehicles that can perform autonomously or semi-autonomously (i.e. with some human interface) is increasing, as is an interest in vehicles that can operate in more than one of manned, semi-autonomous or autonomous mode. Additionally, as more and more vehicles are being configured to operate autonomously or semi-autonomously, there is a desire to utilize software that can be easily and cost-effectively adapted, reused, and modified as an autonomous or semi-autonomous vehicle is utilized for new or additional tasks in order to reduce costs and streamline development of new uses.  
       SUMMARY OF THE INVENTION  
       [0003]     The invention described herein is a modular, extensible software system for use with multi-modal, autonomous, or semi-autonomous vehicles. The design of the present invention involves the coherent integration of modules with responsibilities for human-interaction, training, path planning, mission execution, navigation, and safety to develop and complete missions. The present invention provides a modular software system that can support multiple modes of operation (i.e. autonomous, semi-autonomous) to complete a mission. The system can be easily adapted or modified by adding new software modules or modifying existing modules as missions change or expand.  
         [0004]     When vehicles are used for autonomous operation, there are multiple functions that must be considered and controlled. An autonomous vehicle often cannot just be powered up and set to a task without there being prior work done to create software to help define the task, control the vehicle, and execute the task. Additionally, in most situations, the vehicle must be trained or learn certain things in order to execute the task. For example, if the vehicle is to perform a task within certain boundaries, the vehicle must learn the boundaries within which it is to perform the task.  
         [0005]     Additionally, if the vehicle is to be set up so that it can operate in multiple modes, such as autonomously, semi-autonomously, or under full control of a human, depending upon the situation, or if the operator wishes to have the ability to take over control of a vehicle operating autonomously or semi-autonomously, there must be an orderly sequence of steps that occur, often in a very short time frame, to transition the vehicle from autonomous to operator control, or vice-versa.  
         [0006]     The present invention comprises, in one arrangement, a method of controlling a vehicle comprising the steps of characterizing a vehicle operation as a series of missions; breaking each mission into one or more mission element sets that are necessary to accomplish the mission; breaking each mission element set into one or more mission element, each mission element consisting of a mission element entity and a mission element behavior; using a modular software system to create a software program defining the mission elements in each mission element set and the mission element sets in each mission in the operation; having a mission executor execute the software program to perform each mission, its defined mission element sets and the defined mission elements to provide input to the vehicle control unit; and having the vehicle control unit direct the vehicle to perform the vehicle operation.  
         [0007]     Another arrangement of the present invention is for a vehicle having a plurality of control modes, comprising a motorized vehicle capable of operating in at least one of autonomous, semi-autonomous or human-controlled control modes, the vehicle having a vehicle control unit capable of monitoring and controlling vehicle activity in at least one control mode; and a modular software system configured to control and direct the vehicle control unit in at least one operating mode by means of a mission executor which accepts commands from at least one mission element behavior in at least one mission element set in a software program, the commands issued by the mission element behavior providing commands to the mission executor for the vehicle control unit to direct vehicle activity.  
         [0008]     Yet another arrangement of the present invention is for a vehicle control system for a multi-modal vehicle, the system comprising a vehicle interface module, a mission planning module, a vehicle navigation module, a mission execution module and a perception module, each of the modules capable of accepting wired or wireless communications, by means of one or more ports, from a modular software system, the communications comprising commands from one or more mission element behavior components in the modular software system, the mission element behavior components directing one or more modules in the vehicle control system to perform one or more acts.  
         [0009]     In another arrangement of the present invention, a modular software system for controlling operations of a vehicle having a plurality of control modes via a vehicle control unit, by means of a mission executor comprises at least one mission comprising at least one mission element set, each at least one mission having an associated mission status; each at least one mission element set comprising a plurality of mission elements; each mission element comprising a mission element entity containing data about the mission element and an associated mission element behavior for controlling a structure and behavior of the associated mission element entity; and a mission executor for coordinating the mission element sets in a mission, performing the mission elements in each at least one mission element set in each at least one mission, and performing the missions in the operation sequentially.  
         [0010]     Another arrangement of the present invention is for a method of managing a vehicle having a vehicle control unit capable of controlling the vehicle, the method comprising the steps of identifying functional service modules associated vehicle navigation, mission execution, perception, mission planning and vehicle interface services; defining specifications associated with each service module; defining an operation for a vehicle, each operation comprising a plurality of missions, each mission comprising one or more mission element sets, each mission element set having one or more mission elements; defining at least one mission element as a mission driver capable of sending commands pertaining to vehicle mobility to the mission execution module for executing at least a portion of the mission element set containing the mission driver; and defining at least one mission element as a mission action capable of communicating with one or more functional service modules for executing the mission element sets of the operation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:  
         [0012]      FIG. 1  is a schematic core structural view of a software system for an autonomous vehicle control system of the present invention;  
         [0013]      FIG. 2  is a schematic view of an operation definition using a software system of the present invention;  
         [0014]      FIG. 3  is a schematic representation of the interrelationships of components of a Mission Element Set in the present invention;  
         [0015]      FIG. 4  is a schematic state machine view of a Mission Element Behavior of the present invention;  
         [0016]      FIG. 5  is a schematic state machine view of the Mission Executor of the present invention;  
         [0017]      FIG. 6  is a schematic structural view of the Mission Executor of the present invention; and  
         [0018]      FIG. 7  is a schematic view of the mission elements of a sample operation utilizing the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     In the discussion of the FIGURES the same reference numerals will be used throughout to refer to the same or similar components. In the interest of conciseness, various other components known to the art, such as computer processing and storage mechanisms and the like necessary for the operation of the invention, have not been shown or discussed, or are shown in block form.  
         [0020]     In the following, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be obvious to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known elements have been illustrated in schematic or block diagram form in order not to obscure the present invention in unnecessary detail. Additionally, for the most part, details concerning computer operation and the like have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the knowledge of persons of ordinary skill in the relevant art. While the preferred embodiments disclosed herein address land-based vehicles, it can be appreciated that those skilled in the art can extend the use of the invention to air or sea vehicles without departing from the scope of the invention disclosed herein.  
         [0021]     Various unique elements of the present invention are disclosed and described below in detail. The novelty in this invention is contained within the mechanisms for hierarchical expression of behavior through diverse numerous smaller-grain units known as “mission elements,” and the mission execution.  
         [0022]      FIG. 1  shows a core structural view of a sample software system for monitoring and controlling an autonomous motorized vehicle. The vehicle control system shown in  FIG. 1  is for a land-based vehicle. It can be appreciated that underwater or aerial vehicles would require additional components in order to meet all operating environment variables. A system  100  includes modules for vehicle interface  110 , mission planning  120 , vehicle navigation  130 , and mission execution  1240 . The system also includes a perception sub-module  150 . It can be appreciated that in a multi-mode vehicle (i.e. manual, autonomous, and semi-autonomous), when the vehicle is operating in manual or semi-autonomous mode, not all of the modules may be needed. Additionally, depending on the specific operation, it can be appreciated that additional modules might be needed, such as vehicle payload control.  
         [0023]     The vehicle interface module  110  allows for input to the vehicle (not shown) via the vehicle control unit  5 , and to and from the various other system modules. The vehicle control unit  5  is the microprocessor responsible for monitoring and controlling vehicle activity. Commands to operate the vehicle and information to the system  100  and from the vehicle are processed through the vehicle interface module  110 .  
         [0024]     The mission planning module  120  is used to develop and define a sequence of coupled mission drivers and mission actions needed to accomplish the desired mission. Mission drivers and mission actions are explained subsequently herein in greater detail. The scope of the mission and desired outcome(s), and anticipated problems are also defined as part of the mission plan. In practice, unexpected events occur which require dynamic adjustment of the planned mission. In some cases, this will require re-exercising the mission planning module  120 .  
         [0025]     Although it is some times treated as a separate entity, or part of the vehicle navigation module  130  or mission execution module  140 , vehicle training can also comprise a part of mission planning module  120 . The scope of vehicle training can vary, depending on the mission, and whether the mission is autonomous or semi-autonomous, but it essentially involves teaching the vehicle about the mission to be performed, including any parameters for the mission. This is typically done by a human operator teaching the system about parameters or behaviors, but it is appreciated that a variety of other training methods can also be used.  
         [0026]     The vehicle navigation module  130  provides information on (linear and angular) position of the vehicle, velocity, and acceleration relative to some fixed coordinate frame.  
         [0027]     The mission execution module. or mission executor (MX)  140  is used to carry out the missions created in the mission planning module  120 . The mission executor  140  activates the proper devices (motors, switches, etc.) in such a way that the vehicle is deployed according to the mission goals.  
         [0028]     The perception sub-system  150  is used to protect the vehicle and environment (including people, animals and property). The perception sub-system  150  perceives the environment and constructs occupancy and/or terrain maps. Based on these maps, adjustments in speed and direction of the vehicle may be necessary to maintain the required level of safety. The perception sub-system  150  operates in conjunction with various other modules or systems, whenever the vehicle is in motion, or preparing to go into motion.  
         [0029]     The autonomous platform software system  100  is complemented by an external application that provides high-level direction. The high-level direction is provided wirelessly or through wired connection. As can be seen in  FIG. 1 , these connections are accomplished through a series of ports  160  between the system  100  and various external applications and components. In one embodiment, the external application is driven by direct user input and supervision. The user has the ability to provide inputs to train the system about its environment, configure mission-specific parameters and launch or schedule mission executions. During execution, the user can monitor the feedback signals provided by the system  100  that contain pertinent information about the vehicle and mission status.  
         [0030]     A preferred embodiment of the present invention will utilize UML 2.0-based code generation tools, such as Rational Rose RealTime. Such tools allow for a definition of program structure through “capsules” with an expression of behavior by means of a “state machine”.  
         [0031]      FIG. 2  shows an arrangement of the hierarchical structure of the modular software system of the present invention. The present invention breaks down an operation  1  to be performed by the system into a collection of items called missions  10 . A mission  10  is a set of parameters and a sequence of tasks to be executed sequentially in order to perform an operation  1 . The allocation of tasks among the various missions  10  that comprise an operation  1  is configured to allow flexibility in the system. Each mission  10  has an associated mission status  12 , which represents the progress of the corresponding mission  10 , and is updated during execution of the mission  10 . At a minimum, this status would be an integer index that represents the active mission element set  20 .  
         [0032]     In the prior art, an operation was treated as one or more tasks, and the software program developed was based upon the tasks. However, in the present invention, an operation  1  is broken into a series of missions  10 , which are broken into a series of tasks, each referred to as a mission element set (MES)  20 . The MESs  20  in a mission  10  are executed in order to perform the mission  10 . Each MES  20  is composed of a collection of small-grain entities, called mission elements (ME)  50 , that execute concurrently to accomplish the specific mission element set  20 . By breaking an MES  20  into smaller-grain MEs  50 , all possible alternate flows can be included within the scope of an MES  20 . Also, by creating smaller units of behavior, the likelihood of future software reuse of at least some MEs  50  increases. The system component modules, such as those shown in  FIG. 1 , provide general functionalities to support the various missions  10 . These components provide services for the MEs  50 , and in turn the MEs  50  have the capacity to provide input to these modules. As shown in  FIG. 1 , the system contains interfaces to fundamental modules that provide general functionalities to support various missions  10 , such as navigation (positioning)  130 . An example would be a mission action  52  that controls implement deployment, such as a reactive chemical sprayer that determines when to spray chemicals by comparing information from the vehicle navigation module  130  to an priori map of the environment. The mission action  52  could also be configured for other functions, such as disengaging the sprayer if the vehicle speed was below a specific threshold, or if the vehicle perception module  160  determined there was a human in the vicinity of the sprayer. Furthermore, these modules are adorned with configurable attributes that provide run-time flexibility in terms of specifying parameter values and wholesale substitution of different versions of modules conforming to a specified, well-defined interface. An example would be various alternative navigation components  130 , based on different positioning technology, hardware or algorithms.  
         [0033]     Another novel feature of the present invention is the persistent mission element set (PMES)  25 , a special MES  20  that can optionally be added to each mission  1 , as shown in  FIG. 2 . The PMES  25  is special in that it is a set of mission elements  50  that are always active for the duration of the corresponding mission  10  during execution. The purpose of a PMES  25  is that it allows one to avoid duplicating an ME  50  that is needed throughout a mission  10 . As can be seen in  FIG. 2 , not every mission  10  in an operation  1  needs to have a PMES  25 .  
         [0034]     In the present invention, as shown in  FIGS. 2 and 3 , MEs  50  are further classified into two types: Mission Actions (MA)  52  and Mission Drivers (MD)  54 . An MD  54  can accept input from one or more MAs  52 .  
         [0035]      FIG. 3  shows the interactions of the MAs  52  and an MD  54  in an MES  20 . A valid MES  20  can have only (zero or) one MD  54  and zero or more MAs  52 . An MES  20  that has no MD  54  is one that does not exercise any active control over the mobility of the vehicle. Highly variable or application-specific aspects of operation are good candidates for MAs  52 . For example, the logic that dictates how to respond to an unexpected obstacle is well represented as an MA  52 . Another candidate for an MA  52  would be logic that provides for the evaluation of generic output from a perception component. Intentionally, the architecture is not overly stringent on how the system should be tailored for any given application or the precise definition of what can be allowed as an MA  52 .  
         [0036]     In some arrangements of the present invention, one or more MAs  52  may provide options or suggestions to the MD  54 , which in turn, issues the desired command to the vehicle for mobility via the vehicle interface module  110 . This structure of multiple MAs  52  providing input to an MD  54  provides the system with increased flexibility. The list of appropriate concurrent MAs  52  during different stages of execution of an operation would not be identical; by decomposing the problem this way, there is a natural way of expressing the MAs  52  that run in parallel during the mission  10 . A real-world analogy that demonstrates the interrelationship of MAs  52  and the MD  54  in situations where the MAs  52  provide suggestions to the MD  54  can be found in a car having a driver (the MD  54 ) and one or more passengers. When the car is approaching an intersection, the passengers can all provide input to the driver as to what action they think should be taken at the upcoming intersection, such as turning left, turning right, or going straight (the MAs  52 ). However, it is the driver (MD  54 ) that ultimately makes the decision and provides input to the car as to the action to take (i.e. going straight when there is no oncoming traffic).  
         [0037]     Each ME  50 , whether an MA  52  or MD  54 , is further broken down into a passive class, known as a Mission Element Entity (MEE)  500  and a corresponding behavioral element, known as a Mission Element Behavior (MEB)  510  that describes and controls the structure and behavior of the associated MEE  500 . In order for an ME  50  to function properly, it must have both an MEE  500  and an MEB  510 . The passive MEEs  500  have specific data associated with them, and that data is expressed as part of the mission  10  whenever such MEEs  500  are utilized. The MEEs  500  represent the overall description of how the class behaves as a function of time or events. The MEBs  510 , in contrast, perform the meaningful calculations. The base objects MEE  500  and MEB  510  are constructed with features that are anticipated to be common and useful. By using well-known objected-oriented programming techniques, it is possible to extract commonalities at several levels when defining various MEEs  500  (and MEBs  510 ) and specializing them to particular applications.  
         [0038]     When a new MES  20  in a mission  10  is to be performed, the system takes the following steps: 
        Any unnecessary mission elements  50  are deactivated (either stopped or destroyed, depending on the implementation). An ME  50  is unnecessary if it is neither contained in this new MES  20  or the PMES  25 . An active ME  50  that is obsolete according to a new MES  20  may or may not have its data saved for future potential usage, depending on the implementation.     The ME  50  belonging to the PMES  25  that are not yet active are activated.     If any needed ME  50  is already active, depending on the implementation, it will have its data updated rather than programmatically destroying and incarnating any new processes.     The ME  50  of the new MES  20  that are not yet active are activated.     The ME  50  of the new MES  20  take precedence over the ME  50  of the PMES  25  in the sense that: 
            If both the new MES  20  and PMES  25  contain a Mission Driver  54 , the Mission Driver  54  of the new MES  20  is used rather than that of the PMES  25 .     If the same ME  50  is contained in both the new MES  20  and PMES  25 , the data corresponding to the new MES  20  is used when launching the respective ME  50  rather than the data associated with the instance of the ME  50  contained in the PMES  25 .    
               
 
         [0046]     When a code generation tool that defines program structure through “capsules” is used, the Mission Element Behaviors  510  take the form of capsules. The capsule hierarchy mirrors class hierarchy, as in object-oriented programming so that each MEE  500  has a counterpart MEB  510 . Commonalities can be extracted down the inheritance tree by defining a base mission driving behavior (MDB)  540  and mission action behavior  520 , which correspond to an MD  54  and MA  52 , respectively. Similarly, the mission driving entity (MDE)  504  and mission action entity (MAE)  502  can also be defined with a base behavior. One implementation of the present invention utilizes a “factory of factories” design pattern allowing for easy run-time configuration and customization of the system. The system incorporates a top level factory that is aware of all the modules and specialized components for a particular operation  1 , and the interfaces between the modules, vehicle and software for performing the operation. The top level factory contains a mission factory that contains specific details on how the mission executor (MX)  140  operates for a given implementation. The top level factory also contains factories of MEEs and MEBs, which is essentially a collection of MEEs and MEBS that can be utilized in a specific implementation. The top level factory also contains a factory of client adapters, which include the special communication ports for the implementation, accommodating for the specific interactions between the vehicle and the client.  
         [0047]      FIG. 4  shows a “state machine” view of an MEB. The MEB  510  has the following commonalities: 
        Ability to set period of execution at runtime via a configuration file, of which there can be more than one.     Automatic creation of log files  512  for diagnostics and facilitating data playback.     Ports  511  for sending signals to the Mission Executor  140  (not shown), described below, as well as logging, timing and client messaging services.     Generic expression of initialization  514  and operational states  516  that are executed at the defined time. The operational state  516  is where meaningful specialization of the state machine is made. States for completion  518  and error conditions  519  are also present.     The MEB  510  makes calls to the respective ME  50  routines to accomplish work. Inside the Operational state  516  of the Mission Element Behavior  510 , a specific state diagram can be created that expresses how work is performed by the passive class MEE  500 , although the computations do not have to take place here, in order to provide for greater flexibility.     In an MES  20 , any MEB  510  can signal “Done” to the Mission Executor  140 , which will result in the execution of the next MES  20 .     If an MEB  510  will persist for more than one MES  20 , but is not part of a PMES  25 , the MEB  510  can be updated and brought forward to the next MES  20 .          
         [0055]     Another unique aspect of the present invention pertains to the execution of the mission.  FIG. 5  provides a “state machine” view of the mission executor (MX)  140 . The MX  140  is responsible for executing the operation  1  as expressed by MDs  54 , and coordinating the MES in each mission  10 . The MX  140  will, for an operation  1 , perform each MES  20  sequentially, including any PMES  25  where appropriate. When all the MES  20  of an operation  1  are exhausted, the system transitions to an idle state  710 . The nominal situation is that an ME  50  of a given MES  20  will signal “Done”  724  to the MX  140 , which triggers the update of the mission status  12  and the execution of the next MES  20  in the queue. A feature of this invention is that every MEB  510  has the ability to send the following signals to the MX  140 : 
        Error  722 —End the execution of the operation.     Done  724 —End the execution of the MES  20  to which they belong     Suspend  726 —Suspend the operation. In some cases, the mission  10  can be resumed later.     SideMission  728 —Create a new mission  10  that is executed, whereby the mission  10  to whom the ME  50  belongs is moved down to the second position in the queue of the MX  140 .     Replace  729 —Substitute the current mission  10  for one that the given ME  50  provides.     Insert  727 —Add a new mission  10  to an arbitrary location in the operation queue.        
 
         [0062]     Such capabilities provide the flexibility to accommodate many sets of requirements as necessitated by the application. Flexibility of expression is provided by allowing MEB  510  to alter the a priori operation  1  by modifying the operation queue, or the order or sequence of missions  10  in the operation  1 . By having flexibility at this very low-level, the system is more easily customizable than those found in prior art. The latter four signals above (suspend  726 , sidemission  728 , replace  729  and insert  727 ), empower an MEB  510  to create alternate flows of execution.  
         [0063]      FIG. 6  provides a view of the structural view of the MX  140  defined through capsules. As can be seen, the MDB  540  and MAB  520 , which have been defined using a capsule hierarchy, are activated by the MX  140  as needed. As was previously explained, communications between modules are accomplished through a series of ports  160 , with the MDB  540  or MAB  520  sending signals to a port  160  to signal deed status.  
         [0064]      FIG. 7  shows an example of one embodiment of the software of this invention, for the autonomous mowing of a sports turf field utilizing a mower capable of both autonomous and manual operation. The specific map of the area to be mowed and the mowing pattern must be defined as part of the mission planning phase. A processor called a Vehicle Control Unit (VCU)  5  is responsible for control of the mowing device and vehicle-specific sensors. Communications with the vehicle control unit  5  are achieved by means of the vehicle interface module  110 . A requirement for the system is that during autonomous mode operation, if an operator were to actuate the steering wheel or pedals, the vehicle will revert to manual mode and report an “override” condition. Additionally, the system is required to provide for the ability of operator-controlled transition back to autonomous operation and completion of the mission. Various other features and characteristics must be anticipated and planned for, such as obstacle avoidance. Also, in order for autonomous mowing to be possible, the vehicle has to be trained as to what areas to mow, in what direction, and whether or not to raise/lower the mowing device at any point or points during the mowing process, etc. Once the operation  1  has been planned and defined, and the vehicle trained, autonomous mowing is possible.  
         [0065]     In order for the defined mowing operation to occur, the first step is for the mower to be placed in the same location as when the mowing operation was originally defined during mission planning. For this reason, the first two missions  10  in the operation  1  are for initialization  1010  and location verification  1110 . The initialization mission  1010  ensures the vehicle is ready for autonomous control. Once it has been determined the vehicle is ready for autonomous control, the second mission, for location verification  1110 , is executed. The location verification mission  1110  evaluates whether a trajectory is needed from the vehicle&#39;s current location to the start of the mowing mission. If no such trajectory is necessary, as would be the case if the vehicle were sufficiently close to the desired pose, the location verification mission  1110  terminates, and the mowing mission  1210  will begin. On the other hand, if the location verification mission  1110  determines that a trajectory is needed to get to the desired pose, it creates a new mission  10 ′ for the location acquisition. The result of execution of the location acquisition mission  10 ′ is that the vehicle will, under nominal conditions, position the vehicle at the beginning pose for the next mission in the operation, the mowing mission  1210 , and the mission executor  140  will then begin the mowing mission  1210 . The mowing mission  1210  represents the main objective of mowing the sports turf field, while a fourth mission, the end operation mission  1210  embodies the application-specific requirements associated with completion of mowing.  
         [0066]     The missions of the operation are as set out below and in  FIG. 7 . Where applicable, those MEEs/MEBs that send important signals to the mission executor  140  are mentioned. 
        The Initialization Mission  1010  is for ensuring the vehicle is ready for entry into autonomous mode. The contents of the Initialization Mission  1010  are as follows:     Mission Element Set  20 : 
            VCUAutoInit  1050 : Gets mower into autonomous mode then sends the Done signal  724  to the Mission Executor  140 . If an error occurs, the Error signal  722  is sent to the mission executor  140 , which ends the operation    
            The Location Verification Mission  1110  is for comparing the current position of the vehicle, and if not in the correct position to begin mowing, get the vehicle moved to the proper position.     Mission Element Set  20  
            StopDriving  1150   a : Sends zero speed commands indefinitely.     LocationAcquirePlanningAction  1150   b : Checks to see if mower is close to start location. If the vehicle is close to the start pose, this Action sends the Done signal  724  to the mission executor  140 . If far from the start pose, the Replace signal  729  is sent to the mission executor  140 , to execute a point-to-point mission to maneuver the mower to the start location. The point-to-point mission  10 ′ is calculated by the mission planner  120 .    
            Mow stadium Mission  1210  includes the steps necessary for the goal of mowing the stadium.     Persistent Mission Element Set  1225  
            PauseAction  1225   a : Provides the service of allowing other components (other MEs  50 ) to ask the vehicle to temporarily stop moving. If excessive time elapses, it will send the Done signal  724  to the MX  140 .     NavigationMonitorAction  1225   b : Monitors the quality of the Navigation Interface  130  output. If appropriate, it will make vehicle slow down or pause/stop.     SegmentDrivingMonitorAction  1225   c : Monitors the quality of the path tracking behavior performance. If appropriate, it can also make vehicle slow down or pause/stop.     VCUAutoMonitorAction  1225   d  Interacts with vehicle interface module  110  to maintain auto mode and handle override conditions and errors appropriately. It may send Error  722  or Suspend  726  signal to the MX  140 .     SafeguardingAction  1225   e : provides safeguarding for vehicle when operating during the Mowing Mission  1210 .     ClientCommMonitorAction  1225   f : Receives signals indicating a loss of connectivity. It will pause the mower (PauseAction  1225   a ) if connection is lost for an excessive amount of time.    
            Mission Element Set  1220  (There is one MES like this for each segment of the mowing mission. 
            SegmentDriving  1220   a  drives the given segment at the given speed.     ReelSegmentAction  1220   b  keeps the mower reels in designated state.    
            End operation Mission  1310  includes the steps necessary to make the mower stop and wait for the operator to take over direct control of the vehicle. If a certain time elapses without attention, the vehicle will revert to manual mode, resulting in the engine turning off, due to safety interlocks.     Mission Element Set  1   1320  
            StopDriving  1320   a  sends zero speed to vehicle indefinitely.     ReelAction  1320   b  keeps reels up and not spinning indefinitely.     PauseAction  1320   c  a permanent pause state, signals Done to MX  140  when timer expires.    
            Mission Element Set  2   1320  
            VCUInitManualAction  1320   d  gets vehicle back into manual mode.    
               
 
         [0092]     It can be appreciated that the example provided could be easily modified as different needs arose. For example, suppose it was desired to add the capability of having the vehicle automatically follow an on-foot operator from a garage or depot onto the field as a precursor to the above operation. This could be mechanized by defining a Mission Element Set  20  that had a FollowPersonDrivingBehavior. This MES  20  would utilize perception data and generate appropriate mobility commands, and would signal “Done” to the MX  140  when the exit criteria was met, such as proximity to start location or specified area on the field. Such an MES  20  could be, for example, inserted after the Initialization mission  1010 , above.  
         [0093]     Other additions/modifications could also be made to the above operation. For example, another simple extension to the above operation would be to allow for cooperative driving with an operator, as well as the specified autonomous mowing operation. For example, if it was desired to allow, at any time, the operator to take control of the vehicle until a button was released or other input was activated, such an override could be configured in the program. One approach could be implemented by subclassing the SegmentDrivingBehavior  1220   a  to yield priority to such external inputs, for example. A second approach would be to add another Mission Element  1225   g  to the PMES  1225  that monitors for actuation of the joystick; when such actuation is detected, a side mission  10 ″ is created that is specifically tailored to embody the requirements of cooperative driving. Under this scenario, the transient side mission  10 ″ would remain active until the button or similar input was released.  
         [0094]     An example of a mission  10  for the above case would be for use with direct teleoperation. In this mode, the user is providing mobility commands, and has direct control over various actuators and peripheral devices. In one embodiment, this mission would have only a single MES  20 , whose elements  50  are Teleoperation Driving  54 , together with various MAs  52  to support control over the aforementioned actuators and devices. By partitioning the control into more than one MA  52 , better software reusability can be achieved, and a novel extension of direct teleoperation is more easily achieved, by simply adding or subtracting the appropriate mission elements  50 .  
         [0095]     Having described the preferred embodiment, it will become apparent that various modifications can be made without departing from the scope of the invention as defined in the accompanying claims.