Methods and systems for automated transportation of items between variable endpoints

Abstract

An automated system for transporting items between variable endpoints includes a guidance system for identifying the endpoints and at least one autonomous mobile robot interacting with the guidance system for automatically moving items between the endpoints. The at least one robot is configured to (a) collect an item to be transported at a source end point, (b) travel to a destination endpoint utilizing the guidance system to locate the destination endpoint, (c) deliver the item to the destination endpoint, and (d) repeat (a) through (c) for a given set of items. The guidance system is dynamically reconfigurable to identify new endpoints.

Description

BACKGROUND

The present application relates generally to transportation of items and, more particularly, to automated methods and systems for transporting items between variable endpoints.

BRIEF SUMMARY

An automated system for transporting items between variable endpoints in accordance with one or more embodiments includes a guidance system for identifying the endpoints and at least one autonomous mobile robot interacting with the guidance system for automatically moving items between the endpoints. The at least one robot is configured to (a) collect an item to be transported at a source endpoint, (b) travel to a destination endpoint utilizing the guidance system to locate the destination endpoint, (c) deliver the item to the destination endpoint, and (d) repeat (a) through (c) for a given set of items. The guidance system is dynamically reconfigurable to identify new endpoints.

A method of transporting items between endpoints in accordance with one or more embodiments includes the steps of: establishing a source endpoint and a destination endpoint; activating at least one autonomous mobile robot to automatically (a) travel to a source endpoint, (b) collect an item to be transported, (c) travel to the destination endpoint with the item, (d) deliver the item to the destination endpoint, and (e) repeat (a) through (d) for a given set of items; and changing the location of one or both of the source and destination endpoints, wherein the at least one robot dynamically adapts to changed endpoints to repeat steps (a)-(e).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram illustrating use of a navigation system by robots to locate endpoints in accordance with one or more embodiments.

FIG. 2 is a simplified diagram illustrating use of beacons or passive tags by robots to locate endpoints in accordance with one or more embodiments.

FIG. 3 is a simplified diagram illustrating use of beacons and markers by robots to locate endpoints in accordance with one or more embodiments.

FIG. 4 is a simplified diagram illustrating use of markers by robots to locate endpoints in accordance with one or more embodiments.

FIG. 5 is a block diagram of various components of an exemplary robot in accordance with one or more embodiments.

Like or identical reference numbers are used to identify common or similar elements.

DETAILED DESCRIPTION

Various embodiments disclosed herein are generally directed to material handling methods and systems. In particular, automated methods and systems are provided for transporting items between variable endpoints. An automated system in accordance with one or more embodiments includes a guidance system for identifying the endpoints and one or more autonomous mobile robots or platforms interacting with the guidance system for automatically moving items between the endpoints. Each robot is configured to (a) collect an item to be transported at a source end point, (b) travel to a destination endpoint utilizing the guidance system to locate the destination endpoint, (c) deliver the item to the destination endpoint, and (d) repeat (a) through (c) for a given set of items. The guidance system is dynamically reconfigurable to identify new endpoints. The guidance system can mark a complete route or just the end points of a route for the robot.

Advantages of automated systems in accordance with various embodiments can include flexibility, minimal infrastructure, no programming needed, and adaptability to unstructured environments.

The automated system can be used across broad market segments. Automated systems in accordance with various embodiments can also be operated under a variety of conditions including the following. (1) The terrain is rough, e.g., outdoor environments where conventional material handling systems are difficult to use. (2) The surface over which material must travel cannot support heavy weight, e.g., the weight of trucks, forklifts or other mechanized solutions. (3) The workspace is unstructured and dynamic. In addition to most outdoor spaces, this description includes indoor spaces, where the workflow changes frequently or large objects (e.g., pallets) are often repositioned. (4) The pickup point or the drop off point or both, change during operations. (5) Obstruction of the workspace created by a fixed conveyor system is unacceptable. (6) Material must be moved long distances and system utilization is low to moderate. (7) The initial cost of the material-handling system is required to be low.

Platform

The form of an autonomous robot in a particular implementation can vary depending on payload and environmental factors. By way of example, if the robot operates on a flat surface inside a building, it can use a two-wheeled, differential drive mobility system. If it operates on a rough terrain, e.g., a construction site, it may use a tracked platform able to traverse inclines and loose soil.

Behaviors

The autonomous robots move items from a source or load point to a sink or unload point. The robot's basic behaviors depend on its relationship to the source and sink points and whether it is carrying a load. The following table describes some exemplary behaviors triggered by position and load status:

	Position	Load status	Behavior
	Source	Loaded	Move toward sink
		Empty	Stop, wait to be loaded
	Intermediate	[Don't care]	Proceed along the route until an
			endpoint is reached
	Sink	Loaded	Stop, wait to be unloaded
		Empty	Move toward source

Beyond the basic behaviors outlined in the table, autonomous robots in accordance with various embodiments may have additional behaviors that are activated at intermediate positions along the route. These behaviors deal with obstacles (including other robots) discovered along the way.

Queuing

In accordance with one or more embodiments, each autonomous robot includes a sensor or other mechanism for detecting the presence of other nearby robots. If a robot encounters an obstacle along its route, it either stops or attempts to go around the obstacle. However, if the obstacle is another robot then the robot stops, thus forming a queue. Queues develop near endpoints of the route when robots wait to be loaded or unloaded.

Avoidance

If a robot encounters an obstacle along a route that is not another robot, the robot may attempt to continue toward its destination by skirting the object. The robot can include a wide-angle range sensor (see below) to provide it knowledge of obstructions on and near its route. This may make it possible for the robot to depart from a direct route and then return once the obstacle has been passed. However, whether the robot attempts to go around an obstacle or wait for the obstacle to move is a user choice. In generally uncluttered environments, it will be safe for a robot to search for an alternate route by itself. In more complex environments—especially those with non-geometric hazards—finding a safe alternative to the marked route may not be safe. Thus the user can instruct the robot whether to wait when the route is blocked.

Sensing

Route: In accordance with one or more embodiments, robots can navigate between source and sink using a guidance system such as a beacon marking the route's endpoints or a continuous route marker.

The beacon can be active (e.g., an IR emitter) or passive (e.g., a pattern recognized by an onboard camera). If a beacon is used, each robot should maintain a line of sight between the beacons, i.e., both beacons should be visible to the robot at nearly all times. The robot moves directly from one beacon toward the other unless an obstacle intervenes as described above.

The beacons can establish a coordinate system, where the beacon is the origin of the system. Angular encoding can be used to specify the axes of the coordinate system. The coordinate system enables robots to queue along a particular ray whose origin is the beacon. Angle encoding can also enable other useful properties.

A route marker indicating a robot's path may be used in situations where either a line of sight between beacons does not exist or traveling in a straight path between beacons is not desired. For example, a route marker might enable a robot to avoid a ditch at a construction site.

The route marker can be a worker-positioned tape or line, e.g., comprising a retro-reflective material that enables the robot to acquire it at a distance. The tape or line need not be permanently installed on the floor.

The robot can illuminate the tape or line using, e.g., conventional IR LEDs. In one or more embodiments, the robot detects the tape or line using a position-sensitive detector composed of discrete components (i.e., not a camera) to servo on the tape or line. The detector measures the degree of retro-reflectivity in view to eliminate false positives.

In some embodiments, the robots servo on the line directly. In other embodiments, the robots can servo at any selected offset with respect to the line. Offset servoing enables two important properties. When placing the line to mark the robot's path, workers need not allow space between line and objects. Any time the robot finds its path partially blocked by an object, it will increase its offset from the line so that it can follow the line without colliding with the object. A second feature enabled by offset following allows two robots that meet while traveling along the line in opposite directions to avoid collision. When the robots determine that a collision is imminent, each can offset its position relative to the line. They can thus pass without obstructing each other.

Obstacles: In order to move safely along its route, each robot is equipped with a sensor such as a wide-angle range sensor.

Robot: Each robot can be equipped with a sensor able to distinguish between obstacles and other robots at relatively short range. By way of example, this sensor can be an active IR emitter on one robot that is detected by a receiver on the other robot. The components of this system on the two robots can be arranged such that the following robot detects the robot in front only when the two are physically close.

Load: To allow autonomous operation, each robot can further include a sensor capable of detecting when the robot carries a load. The robot uses the output from this sensor to decide whether to wait at an end point or traverse to the opposite endpoint (see table above).

Manipulation: Robots may optionally include a mechanism enabling a robot to load and unload itself.

User interface: The interface for each robot is preferably simple and intuitive such that the workers themselves are able to setup material handling system wherever necessary. In one or more embodiments, no programming is required.

Implementation Examples:

Automated material handling systems can have a wide range of applications, including, by way of example, the following:

Application	Current Practice	Automated Solution	System Advantages
Produce picker	Laborers in the field	Workers establish	The automated system
conveyor	pick produce and place	routes for one or more	eliminates the time
	it in a basket or sling.	autonomous robots.	workers spend in transit
	Periodically, they carry	The robots travel along	and eliminates the need
	the produce from the	crop rows and stop at	to carry heavy loads.
	field to a truck or other	the collection point.
	collection point.	Periodically a robot
		arrives at the place
		where a worker is
		picking. The worker
		places just-picked
		produce on the robot
		then continues picking.
Truck Loading	Trucks back up to the	Robots move products	The automated system
	loading dock. Workers	into the trucks. A	reduces the time and
	move items from a	worker in the loading	number of workers
	warehouse or other	area places items onto a	needed to load a truck.
	facility into the loading	robot and dispatches it	Reduced loading time
	area. There the items	to the correct truck. A	translates directly into
	may be staged into	worker in the truck	cost savings especially
	orders or loaded	packs the truck.	in situations where
	directly onto the trucks.		customers must pay the
	In either case, workers		trucking company for
	make a large number of		idle time while trucks
	back and forth trips to		are loaded.
	move items into trucks.
Baggage	At small airports ticket	Ticket agents place	The automated system
Handling	agents collect luggage	luggage on robots	enables more timely
	onto a tray or pull cart	queued in the ticket	departures by reducing
	as passengers check in.	area. Bags then move	the loading bottleneck.
	Eventually, a batch of	immediately to the	It also makes more
	bags is hauled out to the	aircraft loading area.	efficient use of airline
	airplane. Loading		personnel. Bags can be
	cannot begin until the		loaded onto the airplane
	batch arrives.		as passengers arrive and
			need not be loaded en
			mass just before
			takeoff.
Contract	Work is typically	When a new contract	The automated system
Manufacturing	performed on the	job begins routes are	improves the efficiency
	subassemblies of a	established between the	of low-volume
	product at several	various stations where	manufacturing by
	different assembly	the work will be done.	providing the benefits
	stations. The particular	The robots	of automatic conveyor
	stations involved and	automatically carry	systems where they
	the flow of work pieces	subassemblies from	cannot now be used.
	among them may	each station to the next.
	change with each
	contract job. Because
	workflow is frequently
	scrambled, fixed
	conveyor systems
	cannot be used.
Stocking	Workers place	Workers mark the start	The automated system
shelves in	merchandise on	and end points of a	eliminates multiple
stores	stocking carts then push	route. A worker in the	round trips. Workers
	the carts to the correct	store's storage area	need set up a route only
	area of the store.	loads robots with the	once, then the robot
	Popular items or items	proper items. After the	will follow it however
	that do not stack well	robots have delivered	many times necessary.
	may require many trips.	their cargo to the proper
		areas (using an optional
		AutoOffLoad feature)
		workers can stock the
		shelves.
Construction	Obstructions or soft	Workers set up a route	The automated system
site material	surfaces at construction	for robots to follow. A	saves time by relieving
delivery	sites often prevent	worker at one end of	workers of the need to
	trucks from delivering	the route loads robots	manually cart material
	material to the place	with material, and a	from the delivery truck
	where it will be used.	worker at the work	to the work point.
	In these cases workers	point unloads them.
	may need to make
	repeated trips to carry
	or cart item from the
	delivery point to the
	work area.
Landscaping	Trucks filled with	A route is established	The automated system
site material	plants and other items	with drop off points	reduces the time needed
delivery	arrive at a landscaping	indicated. The robots	to distribute plants at
	site. Because trucks	are loaded at the truck	landscaping sites.
	cannot drive on the	then automatically carry
	lawn all materials must	plants to the proper
	be carried or hand-	point and drop them
	carted to the places	off.
	where they will be
	installed.
Debris removal	Workers tear out walls,	Robots continuously	The automated system
	fixtures, and other items	carry debris away from	eliminates the time
	in preparation for new	the work area as it is	workers spend in transit
	construction. The work	generated.	hauling debris.
	area becomes filled		Because the work area
	with debris. Carts are		never becomes cluttered
	brought in, loaded with		with debris demolition
	debris, and it is moved		proceeds more
	to a dumpster, usually		efficiently.
	located outdoors.
Consumer leaf	Removing fallen leaves	The homeowner places	The automated system
collection	typically involves	a beacon at the point	makes raking faster and
	raking the leaves into a	where the leaves are to	easier.
	pile, placing the pile on	be deposited. An
	a wheelbarrow or tarp,	automated robot
	then moving the	repeatedly travels
	wheelbarrow or tarp to	between the leaf deposit
	a collection point.	point and the place
		where the owner is
		raking. The robot
		dumps the leaves using
		an optional dumping
		mechanism.

FIGS. 1-4 illustrate various possible guidance systems that can be used by robots to locate endpoints in accordance with one or more embodiments. In FIG. 1, the guidance system comprises a SLAM navigation system that gives robots 10 a global coordinate frame. In this formulation destinations are coordinates, thus no physical markers are necessary.

As shown in FIG. 2, beacons or passive tags 12 visible from a large distance mark each possible destination. This method allows the robot to reach any inbox or outbox without the need of a global frame.

FIG. 3 shows a guidance system combining shorter-range beacons 12 with “highways” established by markers 14 attached to the floor to give the robots a rough global frame. This arrangement simplifies range sensor requirements compared to SLAM.

In FIG. 4, robots are guided by marker 16 laid on the ground, in some cases temporarily.

FIG. 5 is a block diagram of various components of an exemplary robot 10. The robot 10 includes a chassis and a drive subsystem 52 for maneuvering the chassis. It further includes a guidance subsystem 54 on the chassis for interacting with the guidance system. In some embodiments, the subsystem 54 includes one or more marker detecting sensors able to detect the position of a marker such as a retro-reflective tape laid on the ground. By way of example, the marker detecting sensors can each comprise a photodiode-based sensor and one or more radiation sources (e.g., LEDs) to servo on the marker.

In some embodiments, the guidance subsystem 54 comprises a plurality of beacons, each having a radio frequency or other (e.g., infrared) beacon transmitter. In this case, the guidance subsystem 54 includes one or more sensors for detecting signals from beacons.

The robot includes an obstacle detection subsystem 56 for detecting other robots and obstacles.

The robot includes a microprocessor-based controller subsystem 58 for controlling operation of the robot in performing programmed behaviors. A power supply 50 for all the subsystems can include one or more rechargeable batteries.

In some embodiments, the drive subsystem 52 takes the form of a differential drive comprising two coaxial wheels and a roller for balance. The wheels are driven together or independently by one or more motors and a drive train controlled by the controller subsystem 58.

The obstacle detection subsystem 56 can include one or more range sensors to detect other robots and obstacles. In some embodiments, the range sensor is a wide-angle (120 degree) range sensor. Raw range sensor data (in the form of a list of angle and range readings) supplied by the sensor is processed by a computer processor (e.g., a processor in the controller subsystem 58) to return the position of other robots and obstacles.

The controller subsystem 58 is configured (e.g., programmed) to perform various functions, including transporting items between endpoints. The controller subsystem 58 is responsive to the output of guidance subsystem 54 and the output of obstacle detection subsystem 56. The controller subsystem 58 controls the drive subsystem 52 to maneuver the robot to prescribed endpoint locations.

Having thus described several illustrative embodiments, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to form a part of this disclosure, and are intended to be within the spirit and scope of this disclosure. While some examples presented herein involve specific combinations of functions or structural elements, it should be understood that those functions and elements may be combined in other ways according to the present disclosure to accomplish the same or different objectives. In particular, acts, elements, and features discussed in connection with one embodiment are not intended to be excluded from similar or other roles in other embodiments. Additionally, elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same functions.

The processes the robots are programmed to perform as described above may be implemented in software, hardware, firmware, or any combination thereof. The processes are preferably implemented in one or more computer programs executing on the programmable controller subsystem, which includes a processor, a storage medium readable by the processor (including, e.g., volatile and non-volatile memory and/or storage elements), and input and output devices. Each computer program can be a set of instructions (program code) in a code module resident in a random access memory. Until required, the set of instructions may be stored in another computer memory (e.g., in a hard disk drive, or in a removable memory such as an optical disk, external hard drive, memory card, or flash drive) or stored on another computer system and downloaded via the Internet or other network.

Accordingly, the foregoing description and attached drawings are by way of example only, and are not intended to be limiting.

Claims

1. An automated material handling system comprising: a reconfigurable guidance system configured to dynamically identify a changeable source endpoint and a changeable destination endpoint; andat least one autonomous mobile robot interacting with the guidance system for automatically moving items between the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint;wherein the at least one autonomous mobile robot is configured to automatically and dynamically adapt to an identified dynamic change of the dynamically identified changeable source endpoint or the dynamically identified changeable destination endpoint, which identified dynamic change to the dynamically identified changeable source endpoint or the dynamically identified changeable destination endpoint is effected while the at least one autonomous mobile robot is in autonomous operation.

2. The automated material handling system of claim 1, wherein the at least one autonomous mobile robot is configured to: collect an item to be transported at a dynamically identified source endpoint;travel to a dynamically identified destination endpoint utilizing the reconfigurable guidance system to locate the dynamically identified destination endpoint; anddeliver the item to the dynamically identified destination endpoint.

3. The automated material handling system of claim 1, wherein the reconfigurable guidance system defines a route to the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint, comprising route markers that are detectable by the at least one autonomous mobile robot to guide the at least one autonomous mobile robot to the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint.

4. The automated material handling system of claim 3, wherein the at least one autonomous mobile robot is configured to servo on each marker at an offset position relative to the marker, wherein the offset position can be automatically changed to avoid colliding with another robot servoing on the marker.

5. The automated material handling system of claim 1, wherein the reconfigurable guidance system comprises a plurality of beacons, each beacon identifying a different endpoint.

6. The automated material handling system of claim 1, wherein the reconfigurable guidance system comprises a plurality of beacons, each beacon identifying a series of intermediate locations leading to an endpoint.

7. The automated material handling system of claim 1, wherein the at least one autonomous mobile robot includes a range sensor configured to detect obstacles or other robots in its travel path.

8. The automated material handling system of claim 7, wherein the at least one autonomous mobile robot is configured to change its travel path to avoid the obstacle or other robot blocking its travel path or to wait until the travel path is unblocked.

9. The automated material handling system of claim 7, wherein the range sensor is configured to distinguish between the detected obstacles and the detected robots.

10. The automated material handling system of claim 1, wherein the at least one autonomous mobile robot includes a plurality of robots, each robot being configured to detect a presence of other robots and form a queue when another robot is detected in its travel path at an endpoint.

11. The automated material handling system of claim 1, wherein the at least one autonomous mobile robot includes a mechanism to load or unload the items at the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint.

12. The automated material handling system of claim 1, wherein the at least one autonomous mobile robot is configured for manual loading and unloading of items to and from the at least one autonomous mobile robot.

13. The automated material handling system of claim 1, wherein each of the at least one autonomous mobile robot comprises: a chassis;an apparatus on the chassis for carrying an item;a drive subsystem for maneuvering the chassis;a subsystem on the chassis for interacting with the reconfigurable guidance system;an obstacle detection subsystem on the chassis; anda controller on the chassis responsive to the subsystem for interacting with the reconfigurable guidance system and the obstacle detection subsystem and being configured to control the drive subsystem to travel between the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint.

14. An automated material handling system comprising: a reconfigurable guidance system configured to dynamically identify a changeable source endpoint and a changeable destination endpoint;an undeterministic travel surface along which the changeable source endpoint and the changeable destination endpoint are located; andat least one autonomous mobile robot configured totraverse the undeterministic travel surface, andinteract with the guidance system for automatically moving items between the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint along the undeterministic travel surface;wherein the at least one autonomous mobile robot is configured so that the undeterministic travel surface provides holonomic selectable paths for the at least one autonomous mobile robot substantially everywhere on the undeterministic travel surface, each of the paths being freely selectable by the at least one autonomous mobile robot for traversing along the undeterministic travel surface upon identification of a dynamic change of one or more of the changeable source endpoint and the changeable destination endpoint, where the identification of the dynamic change of one or more of the changeable source endpoint and the changeable destination endpoint is effected while the at least one autonomous mobile robot is in autonomous operation.

15. The automated material handling system of claim 14, wherein the reconfigurable guidance system is configured to change a location of one or more of the changeable source endpoint and the changeable destination endpoint and the at least one autonomous mobile robot is configured to dynamically adapt to the changed locations.

16. The automated material handling system of claim 15, wherein the at least one autonomous mobile robot is configured to dynamically adapt to the changed locations free from operation intervention.

17. The automated material handling system of claim 15, wherein the reconfigurable guidance system defines a route to the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint, comprising route markers that are detectable by the at least one autonomous mobile robot to guide the at least one autonomous mobile robot to the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint.

18. The automated material handling system of claim 17, wherein each marker comprises a retro-reflective material and each of the at least one autonomous mobile robot includes a marker detecting sensor for detecting the retro-reflective material.

19. The automated material handling system of claim 15, wherein the reconfigurable guidance system comprises a plurality of beacons, each beacon identifying a different endpoint.

20. The automated material handling system of claim 15, wherein the reconfigurable guidance system comprises a plurality of beacons, each beacon identifying a series of intermediate locations leading to an endpoint.

21. A method for automated material handling using an autonomous mobile robot, said method implemented in a microprocessor-based controller of the autonomous mobile robot comprising the steps of: (a) controlling the autonomous mobile robot to interact with a reconfigurable guidance system that can dynamically identify a changeable source endpoint and a changeable destination endpoint;(b) controlling the autonomous mobile robot to automatically move items between the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint; and(c) controlling the autonomous mobile robot to automatically and dynamically adapt to an identified dynamic change of the dynamically identified changeable source endpoint or the dynamically identified changeable destination endpoint, which identified dynamic change to the dynamically identified changeable source endpoint or the dynamically identified changeable destination endpoint is effected while the autonomous mobile robot is in autonomous operation.

22. The method of claim 21, wherein step (b) comprises: controlling the autonomous mobile robot to collect an item to be transported at a dynamically identified source endpoint;controlling the autonomous mobile robot to travel to a dynamically identified destination endpoint utilizing the reconfigurable guidance system to locate the dynamically identified destination endpoint; andcontrolling the autonomous mobile robot to deliver the item to the dynamically identified destination endpoint.

23. The method of claim 21, wherein the reconfigurable guidance system defines a route to the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint, comprising route markers that are detectable by the autonomous mobile robot to guide the autonomous mobile robot to the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint.

24. The method of claim 23, further comprising controlling the autonomous mobile robot to servo on each marker at an offset position relative to the marker, wherein the offset position can be automatically changed to avoid colliding with another robot servoing on the marker.

25. The method of claim 21, wherein the reconfigurable guidance system comprises a plurality of beacons, each beacon identifying a different endpoint.

26. The method of claim 21, wherein the reconfigurable guidance system comprises a plurality of beacons, each beacon identifying a series of intermediate locations leading to an endpoint.

27. The method of claim 21, further comprising controlling the autonomous mobile robot to detect obstacles or other robots in its travel path.

28. The method of claim 27, further comprising controlling the autonomous mobile robot to change its travel path to avoid the obstacle or other robot blocking its travel path or to wait until the travel path is unblocked.

29. The method of claim 21, further comprising controlling the autonomous mobile robot to detect a presence of other robots and form a queue when another robot is detected in its travel path at an endpoint.

30. The method of claim 21, further comprising controlling the autonomous mobile robot to load or unload the items at the dynamically identified changeable source endpoint and the dynamically identified changeable destination endpoint.