Semantics of the Wheelchair interface commands

Micheal Hewett and Emilio Remolina
25 June 2000

Assumptions

We assume that the navigator (planner + plan-executor + location-manager) has a queue of tasks to execute. Tasks are removed from the queue when they are finished, when a new plan is created or when the user explicitly directs that they should be removed. A task can be initiated, stopped, suspended, continued or removed. The current navigation task is the first task in the queue (if any). The semantics of the different user commands are defined in terms of the how they modifiy the execution of the tasks in the navigator's queue.

When there is indecision as to whether the robot should continue moving after executing a task, we assume that the robot should continue moving if possible. Thus, in some cases a command will add more than one task to the queue, to ensure that the robot will continue moving after the first task is finished.

In the following table, "current task" means the first task on the navigation task queue. A task has five possible states:

Ready - Initialized and ready to run.
Running - In progress.
Paused - Stopped, but resumable.
Done - Successfully completed.
Killed - Halted before completion.

Stop and Go commands

Command	Meaning
`Go`	If there is a current task, perform Continue, otherwise, choose the most appropriate travel control law and perform it.
`Continue`	If there is a current task that is either Ready or Paused, execute it.
`Stop`	Halt the wheelchair. Pause the current task.
`Reset`	Perform Stop. Clear the task queue.
`Forget it`	Synonym for Reset
`Keep going`	Synonym for Go
`Go [to [the]] place name`	Generate a navigation plan. If a plan exists, perform Stop, Reset and start the new plan.
`Take me [to [the]] place name`	Synonym for Go to the ....

Control Law execution

These commands allow the user to initiate a control law without a specific destination in mind. The control law will terminate when its built-in termination conditions are satisfied, or when the user causes a "Stop" command to be generated.

Command	Meaning
`FOLLOW WALL \| MIDLINE`	Moves forward maintaining a setpoint from the wall or walls.
`ALIGN [with [the]] FRONT\|LEFT\|RIGHT WALL`	Aligns the robot with the specified wall.
`ALIGN [with [the]] DOORWAY\|CORNER`	Points the robot toward the doorway or corner.
`ENTER [the] DOORWAY`	If the robot perceives a doorway, pass through it.
`TURN AROUND\|LEFT\|RIGHT`	Performs either a 180-degree turn, or an open-loop turn.
`BACK UP`	Perform an open loop movement backwards.

General communication

`WHAT ARE YOU DOING?`	Displays robot's current action and control law.
`WHERE ARE YOU?`	Displays the robot's current location information.
`WHERE ARE YOU GOING?`	Displays the robot's current goal location.
`SHOW ME THE MAP [OF SOMETHING]`	Displays a map.
`YOU ARE [at \| on] location`	Tell the robot where it is. `Location` can be a coordinate, a place, a view or a path. Normally it is a view.
`HELP`	List the available commands

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