U.S. patent application number 14/001266 was filed with the patent office on 2014-03-13 for positive and negative obstacle avoidance system and method for a mobile robot.
This patent application is currently assigned to Adept Technology, Inc.. The applicant listed for this patent is Adept Technology, Inc.. Invention is credited to Matthew LaFary, George Paul.
Application Number | 20140074287 14/001266 |
Document ID | / |
Family ID | 48873949 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140074287 |
Kind Code |
A1 |
LaFary; Matthew ; et
al. |
March 13, 2014 |
POSITIVE AND NEGATIVE OBSTACLE AVOIDANCE SYSTEM AND METHOD FOR A
MOBILE ROBOT
Abstract
Embodiments of the present invention provide methods and systems
for ensuring that mobile robots are able to detect and avoid
positive obstacles in a physical environment that are typically
hard to detect because the obstacles do not exist in the same plane
or planes as the mobile robot's horizontally-oriented obstacle
detecting lasers. Embodiments of the present invention also help to
ensure that mobile robots are able to detect and avoid driving into
negative obstacles, such as gaps or holes in the floor, or a flight
of stairs. Thus, the invention provides positive and negative
obstacle avoidance systems for mobile robots.
Inventors: |
LaFary; Matthew;
(Peterborough, NH) ; Paul; George; (Merrimack,
NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Adept Technology, Inc. |
Pleasanton |
CA |
US |
|
|
Assignee: |
Adept Technology, Inc.
Pleasanton
CA
|
Family ID: |
48873949 |
Appl. No.: |
14/001266 |
Filed: |
January 25, 2013 |
PCT Filed: |
January 25, 2013 |
PCT NO: |
PCT/US13/23154 |
371 Date: |
August 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61596685 |
Feb 8, 2012 |
|
|
|
61590806 |
Jan 25, 2012 |
|
|
|
Current U.S.
Class: |
700/253 |
Current CPC
Class: |
B25J 9/1676 20130101;
Y10S 901/01 20130101; Y10S 901/46 20130101; G05D 1/024 20130101;
G06N 3/008 20130101; G05B 2219/40202 20130101; G05B 19/4061
20130101; Y10S 901/50 20130101; G05B 2219/39082 20130101; G05D
1/0274 20130101 |
Class at
Publication: |
700/253 |
International
Class: |
B25J 9/16 20060101
B25J009/16 |
Claims
1. In a mobile robot comprising a memory and a propulsion system, a
method for avoiding positive obstacles in a physical environment,
the method comprising: a) storing in the memory (i) a map defining
a floor plan representing the physical environment and a two
dimensional coordinate system delineating the floor plan, (ii) a
first data structure of two-dimensional coordinates from the floor
plan, the two-dimensional coordinates in the first data structure
representing locations in the physical environment to be avoided by
the mobile robot, (iii) first laser placement information for a
first laser attached to the mobile robot, said first laser being
oriented to scan the physical environment in a first plane that is
not parallel to the floor of the physical environment, wherein said
first laser placement information includes a first laser position
and a first laser tilt, and (iv) a tolerance profile comprising a
ceiling offset, a floor offset, a ceiling adjustment angle and a
floor adjustment angle, b) receiving a set of laser readings from
said first laser, each laser reading corresponding to a location in
the physical environment where said first laser detects a physical
obstacle in said first plane, and each laser reading comprising a
first plane angle and a first plane distance from a given site on
the mobile robot; c) for each laser reading in said set of laser
readings (i) converting said each laser reading into a
three-dimensional coordinate based on said first plane angle, said
first plane distance, said first laser position and said first
laser tilt, wherein said three-dimensional coordinate comprises an
x-component, a y-component and a z-component, (ii) determining a
minimum ceiling height and a maximum floor height for the three
dimensional coordinate based on the x-component, they-component and
the tolerance profile, and (iii) if the z-component is between the
minimum ceiling height and the maximum floor height, adding the
x-component and they-component to the first data structure of
two-dimensional coordinates to represent a new location in the
physical environment to be avoided by the mobile robot; and d)
causing the propulsion system to drive the mobile robot in the
physical environment under control of the first data structure,
wherein the propulsion system prevents the mobile robot from
passing into the locations in the physical environment represented
by the two-dimensional coordinates in the first data structure.
2. The method of claim 1, further comprising: a) receiving on the
mobile robot a command to move from a current position to a
specified location in the physical environment; b) calculating on
the mobile robot, in accordance with the floor plan, a path between
said current position and said specified location, said path
avoiding the locations in the physical environment represented by
the first data structure of two-dimensional coordinates; and c)
activating the propulsion system to automatically drive the mobile
robot along the path.
3. The method of claim 1, wherein said first plane is perpendicular
to the floor of the physical environment.
4. The method of claim 1, wherein said maximum floor height is
calculated by using the formula: maximum floor height=floor
offset+A*sin(floor adjustment angle), wherein, A=the distance from
the current position to the coordinate (x-component, y-component)
in the two-dimensional coordinate system.
5. The method of claim 1, wherein said minimum ceiling height is
calculated according to the formula: minimum ceiling height=ceiling
offset+A*sin(ceiling adjustment angle), wherein, A=the distance
from the current position to the coordinate (x-component,
y-component) in the two-dimensional coordinate system.
6. The method of claim 1, further comprising: a) storing in the
memory (i) a second data structure of two-dimensional coordinates
from the floor plan, the two dimensional coordinates in the second
data structure representing locations in the physical environment
to be avoided by the mobile robot, (ii) second laser placement
information for a second laser attached to the mobile robot, said
second laser being oriented to scan the physical environment in a
second plane that is not parallel to the floor of the physical
environment, wherein said second laser placement information
includes a second laser position and a second laser tilt, and (iii)
receiving a second set of laser readings from said second laser,
each laser reading corresponding to a location in the physical
environment where said second laser detects a physical obstacle in
said second plane, and each laser reading comprising a second plane
angle and a second plane distance from a given site on the mobile
robot; b) for each laser reading in said second set of laser
readings (i) converting said each laser reading into a second
three-dimensional coordinate based on said second plane angle, said
second plane distance, said second laser position and said second
laser tilt, wherein said second three-dimensional coordinate
comprises a second x-component, a second y-component and a second
z-component, (ii) determining a minimum ceiling height and a
maximum floor height for the second three-dimensional coordinate
based on the second x-component, the second y-component and the
tolerance profile, and (iii) if the second z-component is between
the maximum floor height and the minimum ceiling height, adding the
second x-component and the second y-component to the second data
structure of two-dimensional coordinates to represent another
location in the physical environment to be avoided by the mobile
robot; and c) causing the propulsion system to drive the mobile
robot in the physical environment under control of the first data
structure and the second data structure, wherein the propulsion
system prevents the mobile robot from passing into the locations in
the physical environment represented by the two-dimensional
coordinates in both the first data structure and the second data
structure.
7. The method of claim 6, further comprising: a) receiving on the
mobile robot a command to move from a current position to a
specified location in the physical environment; b) calculating on
the mobile robot, in accordance with the floor plan, a path between
said current position and said specified location, said path
avoiding the locations in the physical environment represented by
the first data structure of two-dimensional coordinates and the
second data structure of two-dimensional coordinates; and c)
activating the propulsion system to automatically drive the mobile
robot along the path.
8. The method of claim 6, wherein said second plane is
perpendicular to the floor of the physical environment.
9. In a mobile robot comprising a memory and a propulsion system, a
method for avoiding negative obstacles in a physical environment,
the method comprising: a) storing in the memory (i) a map defining
a floor plan representing the physical environment and a two
dimensional coordinate system delineating the floor plan, (ii) a
first data structure of two-dimensional coordinates from the floor
plan, the two dimensional coordinates in the first data structure
representing locations in the physical environment to be avoided by
the mobile robot, (iii) first laser placement information for a
first laser attached to the mobile robot, said first laser being
oriented to scan the physical environment in a first plane that is
not parallel to the floor of the physical environment, wherein said
first laser placement information includes a first laser position
and a first laser tilt, and (iv) a tolerance profile comprising a
maximum floor offset, a minimum floor offset, a maximum floor
adjustment angle, a minimum floor adjustment angle and a maximum
allowable floor gap, b) receiving a set of laser readings from said
first laser, each laser reading corresponding to a location in the
physical environment within said first plane, and each laser
reading comprising a first plane angle and a first plane distance
from a given site on the mobile robot; c) for each laser reading in
said set of laser readings (i) converting said each laser reading
into a three-dimensional coordinate based on said first plane
angle, said first plane distance, said first laser position and
said first laser tilt, wherein said three-dimensional coordinate
comprises an x-component, a y-component and a z-component, (ii)
determining a maximum floor height and a minimum floor height for
the three-dimensional coordinate based on the x-component,
they-component and the tolerance profile, and (iii) if the
z-component is between the maximum floor height and the minimum
floor/height, changing an indicator in the memory to designate the
x-component and the y-component of the three-dimensional coordinate
as the last good floor reading, (iv) if the z-component is not
between the maximum floor height and the minimum floor height,
determining whether the distance G between the last good floor
reading and the location in the two-dimensional coordinate system
defined by the x-component and they-component exceeds the maximum
allowable floor gap, and (v) if the distance G exceeds the maximum
allowable floor gap, adding the x-component, the y-component and
the last good floor reading to the first data structure of
two-dimensional coordinates to represent a new location in the
physical environment to be avoided by the mobile robot; d) causing
the propulsion system to drive the mobile robot in the physical
environment under control of the first data structure, wherein the
propulsion system prevents the mobile robot from passing into the
locations in the physical environment represented by the
two-dimensional coordinates in the first data structure.
10. The method of claim 9, further comprising: a) receiving on the
mobile robot a command to move from a current position to a
specified location in the physical environment; b) calculating on
the mobile robot, in accordance with the floor plan, a path between
said current position and said specified location, said path
avoiding the locations in the physical environment represented by
the first data structure of two-dimensional coordinates; and c)
activating the propulsion system to automatically drive the mobile
robot along the path.
11. The method of claim 9, wherein said first plane is
perpendicular to the floor of the physical environment.
12. The method of claim 9, wherein said maximum floor height is
calculated by using the formula: maximum floor height=floor
offset+A*sin(floor adjustment angle), wherein, A=the distance from
the current position to the coordinate (x-component, y-component)
in the two-dimensional coordinate system.
13. The method of claim 9, wherein said minimum floor height is
calculated according to the formula: minimum floor height=floor
offset-A*sin(floor adjustment angle), wherein, A=the distance from
the current position to the coordinate (x-component, y-component)
in the two-dimensional coordinate system.
14. A positive obstacle avoidance system for use with a mobile
robot in a physical environment, comprising: a) a first laser
attached to the mobile robot, said first laser being oriented to
scan the physical environment in a first plane that is not parallel
to the floor of the physical environment; b) a memory for storing
(i) a map defining a floor plan representing the physical
environment and a two dimensional coordinate system delineating the
floor plan, (ii) a first data structure of two-dimensional
coordinates from the floor plan, each two dimensional coordinate in
the first data structure representing a location in the physical
environment to be avoided by the mobile robot, (iii) first laser
placement information for said first laser, said first laser
placement information including a first laser position and a first
laser tilt, and (iv) a tolerance profile comprising a ceiling
offset, a floor offset, a ceiling adjustment angle and a floor
adjustment angle, c) a laser controller for receiving a set of
laser readings from said first laser, each laser reading
corresponding to a location in the physical environment where said
first laser detects a physical obstacle in said first plane, and
each laser reading comprising a first plane angle and a first plane
distance from a given site on the mobile robot; d) a positive
obstacle avoidance engine that, for each laser reading in said set
of laser readings (i) converts said each laser reading into a
three-dimensional coordinate based on said first plane angle, said
first plane distance, said first laser position and said first
laser tilt, wherein said three-dimensional coordinate comprises an
x-component, a y-component and a z-component, (ii) determines a
minimum ceiling height and a maximum floor height for the three
dimensional coordinate based on the x-component, they-component and
the tolerance profile, and (iii) if the z-component is between the
minimum ceiling height and the maximum floor height, adds the
x-component and they-component to the first data structure of
two-dimensional coordinates to represent a new location in the
physical environment to be avoided by the mobile robot; and e) a
propulsion system that drives the mobile robot in the physical
environment under control of the first data structure, the
propulsion system being configured to prevent the mobile robot from
passing into the locations in the physical environment represented
by the two-dimensional coordinates in the first data structure.
15. The system of claim 14, further comprising: a) a communication
interface that receives a command to move from a current position
to a specified location in the physical environment; and b) a path
planning engine that calculates, in accordance with the floor plan,
a path between said current position and said specified location,
said path avoiding the locations in the physical environment
represented by the first data structure of two-dimensional
coordinates; c) wherein the propulsion system is further configured
to automatically drive the mobile robot along the path.
16. The system of claim 14, wherein said first plane is
perpendicular to the floor of the physical environment.
17. The system of claim 14, wherein said positive obstacle
avoidance engine calculates the maximum floor height according to
the formula: maximum floor height=floor offset+A*sin(floor
adjustment angle), wherein, A=the distance from the current
position to the coordinate (x-component, y-component) in the
two-dimensional coordinate system.
18. The system of claim 14, wherein said positive obstacle
avoidance engine calculates the minimum ceiling height according to
the formula: minimum ceiling height=ceiling offset+A*sin(ceiling
adjustment angle), wherein, A=the distance from the current
position to the coordinate (x-component, y-component) in the
two-dimensional coordinate system.
19. The system of claim 14, wherein: a) a second laser is attached
to the mobile robot, said second laser being oriented to scan the
physical environment in a second plane that is not parallel to the
floor of the physical environment; b) the memory further comprises
(i) a second data structure of two-dimensional coordinates from the
floor plan, each two dimensional coordinate in the second data
structure representing another location in the physical environment
to be avoided by the mobile robot, (ii) second laser placement
information for said second laser, said second laser placement
information including a second laser position and a second laser
tilt, and c) the laser controller receives a second set of laser
readings from said second laser, each laser reading corresponding
to a location in the physical environment where said second laser
detects a physical obstacle in said second plane, and each laser
reading comprising a second plane angle and a second plane distance
from a given site on the mobile robot; d) the positive obstacle
avoidance engine, for each laser reading in said second set of
laser readings (iii) converts said each laser reading into a second
three-dimensional coordinate based on said second plane angle, said
second plane distance, said second laser position and said second
laser tilt, wherein said second three-dimensional coordinate
comprises a second x-component, a second y-component and a second z
component, (iv) determines a minimum ceiling height and a maximum
floor height for the second three-dimensional coordinate based on
the second x-component, the second y component and the tolerance
profile, and (v) if the second z-component is between the maximum
floor height and the minimum ceiling height, adds the second
x-component and the second y-component to the second data structure
of two-dimensional coordinates to represent another location in the
physical environment to be avoided by the mobile robot; and e) the
propulsion system drives the mobile robot in the physical
environment under control of the first data structure and the
second data structure, whereby the propulsion system prevents the
mobile robot from passing into the locations in the physical
environment represented by the two-dimensional coordinates in both
the first data structure and the second data structure.
20. The system of claim 19, further comprising: a) a communication
interface that receives a command to move from a current position
to a specified location in the physical environment; and b) a path
planning engine that calculates, in accordance with the floor plan,
a path between said current position and said specified location,
said path avoiding the locations in the physical environment
represented by the first data structure of two-dimensional
coordinates; c) wherein the propulsion system is further configured
to automatically drive the mobile robot along the path.
21. The system of claim 19, wherein said second plane is
perpendicular to the floor of the physical environment.
22. A negative obstacle avoidance system for use with a mobile
robot in a physical environment, comprising: a) a first laser
attached to the mobile robot, said first laser being oriented to
scan the physical environment in a first plane that is not parallel
to the floor of the physical environment; b) a memory for storing
(i) a map defining a floor plan representing the physical
environment and a two dimensional coordinate system delineating the
floor plan, (ii) a first data structure of two-dimensional
coordinates from the floor plan, the two dimensional coordinates in
the first data structure representing locations in the physical
environment to be avoided by the mobile robot, (iii) first laser
placement information for said first laser, the first laser
placement information including a first laser position and a first
laser tilt, and (iv) a tolerance profile comprising a maximum floor
offset, a minimum floor offset, a maximum floor adjustment angle, a
minimum floor adjustment angle and a maximum allowable floor gap,
c) a laser controller for receiving a set of laser readings from
said first laser, each laser reading corresponding to a location in
the physical environment within said first plane, and each laser
reading comprising a first plane angle and a first plane distance
from a given site on the mobile robot; and d) a negative obstacle
avoidance engine that, for each laser reading in said set of laser
readings (i) converts said each laser reading into a
three-dimensional coordinate based on said first plane angle, said
first plane distance, said first laser position and said first
laser tilt, wherein said three-dimensional coordinate comprises an
x-component, a y-component and a z-component, (ii) determines a
maximum floor height and a minimum floor height for the three
dimensional coordinate based on the x-component, they-component and
the tolerance profile, and (iii) if the z-component is between the
maximum floor height and the minimum floor height, changes an
indicator in the memory to designate the x-component and the
y-component of the three-dimensional coordinate as the last good
floor reading coordinate, (iv) if the z-component is not between
the maximum floor height and the minimum floor height, determines
whether the distance G between the last good floor reading
coordinate and the location in the two-dimensional coordinate
system defined by the x-component and they-component exceeds the
maximum allowable floor gap, and (v) if the distance G exceeds the
maximum allowable floor gap, adds the x-component, the y-component
and the last good floor reading coordinate to the first data
structure of two-dimensional coordinates to represent another
location in the physical environment to be avoided by the mobile
robot; and e) a propulsion system that drives the mobile robot in
the physical environment under control of the first data structure,
the propulsion system being configured to prevent the mobile robot
from passing into the locations in the physical environment
represented by the two-dimensional coordinates in the first data
structure.
23. The system of claim 22, further comprising: a) a communication
interface that receives a command to move from a current position
to a specified location in the physical environment; and b) a path
planning engine that calculates, in accordance with the floor plan,
a path between said current position and said specified location,
said path avoiding the locations in the physical environment
represented by the first data structure of two-dimensional
coordinates; c) wherein the propulsion system is further configured
to automatically drive the mobile robot along the path.
24. The system of claim 22, wherein said first plane is
perpendicular to the floor of the physical environment.
25. The system of claim 22, wherein the negative obstacle avoidance
engine calculates said maximum floor height by using the formula:
maximum floor height=floor offset+A*sin(floor adjustment angle),
wherein, A=the distance from the current position to the coordinate
(x-component, y-component) in the two-dimensional coordinate
system.
26. The system of claim 22, wherein the negative obstacle avoidance
engine calculates said minimum floor height according to the
formula: minimum floor height=floor offset-A*sin(floor adjustment
angle), wherein, A=the distance from the current position to the
coordinate (x-component, y-component) in the two-dimensional
coordinate system.
Description
FIELD OF ART
[0001] This invention generally relates to mobile robots. More
specifically, the invention is directed to systems and methods for
detecting positive and negative obstacles in physical environments
through which mobile robots move and preventing the mobile robots
from driving into those obstacles.
BACKGROUND ART
[0002] Mobile robots, including autonomously-navigating mobile
robots, inertially-guided robots, remote-controlled mobile robots,
and robots guided by laser targeting, vision systems, roadmaps and
beacons, to name a few examples, normally use horizontally-oriented
laser sensors to scan the area in the mobile robot's direction of
travel and to detect potential obstacles in the mobile robot's
path. The horizontally-oriented lasers, which typically scan in
two-dimensional planes roughly parallel with floor, work reasonably
well for detecting objects that extend from the floor in a
substantially perpendicular direction, so long as the obstacle
intersects the horizontally-oriented scanning plane. However, they
do not work well for detecting positive physical obstacles in the
mobile robot's path that are parallel to the floor and/or obstacles
that are not at the same height as the horizontally-oriented
scanning plane. This means the mobile robots frequently have no way
of detecting and avoiding positive obstacles, such as long tables
with legs at the ends (and no legs in the middle), objects
suspended from a ceiling or other structure, and obstacles that
stick out from the edge of another object, like a keyboard tray.
Mobile robots that use horizontally-oriented lasers for detecting
obstacles also have problems detecting and avoiding unexpected
negative obstacles, such as a hole in the floor, a descending
flight of stairs, the end of a loading dock or the edge of a
cliff.
[0003] Previous attempts to solve these problems have included, for
example, attaching a plurality of vertically-oriented or
randomly-oriented lasers to the mobile robots and using the
vertical or randomly-oriented lasers to detect obstacles parallel
to the floor, as well as holes or drop-offs in the floor. However,
there have been a number of significant disadvantages associated
with such solutions, including prohibitively-high cost associated
with installing, using and maintaining a multiplicity of expensive
lasers, and an unacceptably high number of false positives arising,
for example, from gratings in the floor, which do not necessarily
need to be avoided by the mobile robot.
SUMMARY OF THE INVENTION
[0004] Embodiments of the present invention provide methods and
systems for ensuring that mobile robots are able to detect and
avoid positive obstacles in a physical environment that are
typically hard to detect because the obstacles do not extend
vertically from the floor. Embodiments of the present invention
also help to ensure that mobile robots are able to detect and avoid
driving into negative obstacles, such as gaps or holes in the
floor, or a flight of stairs. In general, embodiments of the
present invention include a positive obstacle avoidance system for
use with mobile robots, a negative obstacle avoidance system for
use with mobile robots, or both a positive and negative obstacle
avoidance system operating in the same mobile robot. The inventive
systems and methods work for a variety of different types of mobile
robots (also known as "automated guided vehicles" or "AGVs"),
including without limitation autonomously-navigating mobile robots,
visually-guided robots, telepresence robots, haptic input-guided
robots and laser- or beacon-following robots.
[0005] In one aspect of the invention, there is provided a positive
obstacle avoidance system for use with a mobile robot in a physical
environment, comprising a first laser attached to the mobile robot,
a memory, a laser controller, a positive obstacle avoidance engine
and a propulsion system. The first laser attached to the mobile
robot is oriented to scan the physical environment in a first plane
that is not parallel to the floor of the physical environment. The
memory stores initial operating parameters and preferences for the
positive obstacle avoidance engine, including: (1) a map defining a
floor plan representing the physical environment and a two
dimensional coordinate system delineating the floor plan, (2) a
first data structure of two-dimensional coordinates from the floor
plan, each two dimensional coordinate in the first data structure
representing a location in the physical environment to be avoided
by the mobile robot, (3) first laser placement information for the
first laser, including the first laser's position on the mobile
robot and the first laser's orientation (or tilt angle), and (4) a
tolerance profile for the obstacle avoidance system. The tolerance
profile typically includes a ceiling offset, a floor offset, a
ceiling adjustment angle and a floor adjustment angle. Using a
tolerance profile in the positive obstacle avoidance engine
calculations reduces the number of false positives that might
otherwise result if, for example, the floor or the ceiling is not
exactly horizontal, or if the laser is not installed at exactly the
right height or orientation relative to the floor, the ceiling or
the direction of travel. The initial operating parameters may be
received from a remote system via a wired or wireless communication
interface on the mobile robot, stored in a database onboard the
mobile robot, or hard-coded into the program instructions
comprising the positive obstacle avoidance engine. The data
structure used to store the two-dimensional coordinates
representing locations in the physical environment that the mobile
robot should avoid may comprise any suitable data structure for
organizing and managing two-dimensional coordinate data, as would
be known by those skilled in the computer arts, including without
limitation, a collection of database records, a linked list, a
table, an array, a tree, a heap, or a stack. In some embodiments
and applications, the data structure of two-dimensional coordinates
describes what is known in the art as an "occupancy grid" for the
floor plan for the physical environment.
[0006] The laser controller receives a set of laser readings from
the first laser, each laser reading corresponding to a location in
the physical environment where the first laser detects a physical
obstacle that may or may not need to be avoided by the mobile
robot, depending, for example, on whether the object at the
location is truly a physical object existing in the path of the
mobile robot, or merely a spot on a distant part of the floor or
the ceiling of the physical environment. Typically, the laser
provides laser readings in polar coordinates (angle and distance to
the detected obstacle), but other types of laser readings may be
suitably used without departing from the scope of the invention.
Thus, the laser readings received by the laser controller include a
first plane angle (theta) and a first plane distance (radius=r)
from a given site on the mobile robot.
[0007] For each reading in the set of laser readings received from
the first laser, the positive obstacle avoidance engine, typically
comprising computer software instructions executable on a
microprocessor on board the mobile robot, determines whether the
reading represents a spot on the floor or the ceiling of the
physical environment, or otherwise represents an object existing
between the floor and the ceiling that should be avoided by the
mobile robot. If the reading identifies an obstacle, rather than a
spot on the ceiling or the floor, the positive obstacle avoidance
engine stores the x and y coordinates of the laser reading in the
first data structure in order to "remember" that location, in
accordance with the floor plan, as a location to be avoided. The
positive obstacle avoidance engine accomplishes this by first
converting the laser reading (theta and r) into a three-dimensional
coordinate based on the first plane angle (theta), the first plane
distance (r), the first laser position and said first laser tilt in
the memory. The three-dimensional coordinate includes an
x-component, a y-component and a z-component. Because the first
laser may be attached to the mobile robot in a variety of different
orientations, so long as its scanning plane is not horizontal
(i.e., not parallel to the floor), the formula used to calculate
the three-dimensional coordinate depends on the angle of the
scanning plane relative to the floor and the direction of travel
for the mobile robot. So, for example, when the first laser's
scanning plane is perpendicular to the floor and parallel to the
direction of the mobile robot's direction of travel, the positive
obstacle avoidance engine may be programmed to convert the laser
readings into a three-dimensional coordinate (x, y, z) using the
formulas:
x-component=first laser x position+first plane
distance*cosine(first plane angle),
y-component=first laser y position, and
z-component=first laser z position+first plane distance*sin(first
plane angle).
[0008] Next, the positive obstacle avoidance engine determines a
minimum ceiling height and a maximum floor height for the
three-dimensional coordinate based on the x-component, the
y-component and the tolerance profile. The maximum floor height may
be calculated, for example, by using the formula:
maximum floor height=floor offset+A*sin(floor adjustment
angle),
wherein, A=the distance from the current position to the coordinate
(x-component, y-component) in the two-dimensional coordinate
system. The minimum ceiling height may be calculated according to
the formula:
minimum ceiling height=ceiling offset+A*sin(ceiling adjustment
angle),
wherein, A=the distance from the current position to the coordinate
(x-component, y-component) in the two-dimensional coordinate
system.
[0009] If the z-component is between the minimum ceiling height and
the maximum floor height, then the positive obstacle avoidance
engine is considered to have detected a positive obstacle suspended
above the floor and below the ceiling. This obstacle could be the
horizontal part of a table, a keyboard tray sticking out of a desk
or workstation, or some other cantilevered object. In this case,
the positive obstacle avoidance engine will add the x-component and
the y-component of the three-dimensional coordinate (representing
the two-dimensional locations on the floor plan beneath the table,
keyboard tray or other object) to the first data structure of
two-dimensional coordinates to represent a new location in the
physical environment to be avoided by the mobile robot. In this
fashion, the positive obstacle avoidance engine builds a data
structure of two-dimensional coordinates (or adds new
two-dimensional coordinates to a previously-existing data
structure) that identifies all of the locations on the floor plan
where a positive obstacle has been found.
[0010] The propulsion system typically comprises a collection of
hardware and software components that cause the mobile robot to
drive about the physical environment under control of the first
data structure. This means the propulsion system prevents the
mobile robot from passing into the locations in the physical
environment represented by the two-dimensional coordinates in the
first data structure by plotting a path around the locations, if
possible, or bringing the mobile robot to a stop if no path around
the obstacle is available. In some embodiments, the mobile robot
receives a command from another computer system to move the mobile
robot from its current position to a specified location in the
physical environment. In such cases, the mobile robot may include a
wired or wireless communication interface to enable receiving such
commands, and the propulsion system may encompass a path planning
engine that calculates, in accordance with the floor plan, a path
between the current position and the specified location, wherein
the path is calculated so as to avoid the locations in the physical
environment represented by the first data structure of
two-dimensional coordinates. Then the propulsion system, which may
include navigation and locomotion components (e.g., motors and
wheels and a microcontroller to operate the motors and wheels)
automatically drives the mobile robot along the calculated path,
thereby avoiding the obstacle.
[0011] Multiple non-horizontal lasers oriented to scan the physical
environment in non-horizontal planes may be used to enhance the
mobile robot's ability to detect and avoid positive obstacles that
do not extend vertically from the floor or intersect the mobile
robot's horizontal scanning planes, and are therefore undetected by
the mobile robot's horizontal lasers. Thus, in addition to the
first non-horizontal laser scanning in the first plane, a second
non-horizontal laser may be attached to the mobile robot and
oriented to scan the physical environment in a second plane that is
also not parallel to the floor of the physical environment. In such
embodiments, the memory stores a second set of initial operating
parameters and preferences for use by the positive obstacle
avoidance engine in processing the laser readings from the second
non-horizontal laser, including: (1) a second data structure of
two-dimensional coordinates from the floor plan, each two
dimensional coordinate in the second data structure representing
another location in the physical environment to be avoided by the
mobile robot, and (2) placement information for the second laser,
including a second laser position and a second laser tilt. In this
case, the laser controller receives a second set of laser readings
from the second laser, each laser reading corresponding to a
location in the physical environment where the second laser detects
a physical obstacle in the second plane. The positive obstacle
avoidance engine performs the same calculations for each laser
reading received from the second set of laser readings in order to
determine whether the detected obstacle represents the expected
floor or ceiling, based on distance and angle from the robot, or
otherwise represents some obstacle located between the floor and
the ceiling in the physical environment that needs to be avoided.
Thus, the positive obstacle avoidance engine converts each laser
reading into a second three-dimensional coordinate based on the
second plane angle (theta), the second plane distance (r), the
second laser position and the second laser tilt. The positive
obstacle avoidance engine then determines an minimum allowable
ceiling height and a maximum allowable floor height for the second
three-dimensional coordinate based on the x-component of the second
three-dimensional coordinate, the y-component of the second
three-dimensional coordinate and the tolerance profile. Then the
engine determines whether the second z-component lies between the
allowable floor height and the allowable ceiling height based on
the z-component's distance from the robot. If so, the positive
obstacle avoidance engine adds the x-component and the y-component
of the second three-dimensional coordinate to the second data
structure of two-dimensional coordinates to represent another
location in the physical environment to be avoided by the mobile
robot. In this manner, the positive obstacle avoidance engine
builds and populates a second collection or list of two-dimensional
coordinates from the floor plan that the mobile robot should avoid
while driving about the physical environment. The propulsion system
drives the mobile robot about the physical environment under
control or influence of the first data structure and the second
data structure, while preventing the mobile robot from passing into
the locations in the physical environment represented by the
two-dimensional coordinates in both the first data structure and
the second data structure. It will be understood by those skilled
in the art that embodiments of the present invention may in fact
store all of the two-dimensional coordinates for both the first
laser and the second laser in a single data structure, or a
multiplicity of different data structures, instead of two discreet
data structures, without departing from the scope of the claimed
invention. Any number of data structures may be used, so long as
the propulsion system accesses the stored two-dimensional
coordinate data to determine which parts of the floor plan should
not be driven into by the mobile robot.
[0012] In another aspect, embodiments of the present invention also
provide a negative obstacle avoidance system for use with a mobile
robot in a physical environment. The negative obstacle avoidance
system operates to prevent the mobile robot from driving into a
hole or ditch, driving off the edge of a cliff, or driving across
an unacceptably large gap in the floor. In essence, the negative
obstacle avoidance system does this by comparing currently-received
floor distance readings from one or more non-horizontally-oriented
lasers with a tolerance profile, which defines, among other things,
the largest gap in the floor (i.e., a "gap profile") that the
mobile robot will be permitted to traverse. Embodiments of the
present invention, however, also use the tolerance profile settings
to avoid recognizing too many false positives in the data, which
could arise, for example, when the mobile robot is approaching a
relatively safe grating, small bump or small gap in the floor. The
tolerance profile settings also reduce the number of false
positives that arise when the laser data readings are less than
perfect. This might occur, for example, when the laser light coming
from the mobile robot strikes something too reflective and at an
angle that prevents the light from returning to the sensor, or when
the laser light coming from the mobile robot strikes something that
is not reflective enough, and therefore absorbs too much of the
light for any of it to return to the mobile robot.
[0013] In general, the negative obstacle avoidance system comprises
a first laser attached to the mobile robot, a memory, a laser
controller, a negative obstacle avoidance engine and a propulsion
system. The first laser is oriented to scan the physical
environment in a first plane that is not parallel to the floor of
the physical environment. The memory stores a set of initial
operating parameters and preferences for use by the negative
obstacle avoidance engine, including: (1) a map defining a floor
plan representing the physical environment and a two dimensional
coordinate system delineating the floor plan, (2) a first data
structure of two-dimensional coordinates from the floor plan, each
two dimensional coordinate in the first data structure representing
locations in the physical environment to be avoided by the mobile
robot, (3) first laser placement information for the first laser,
including a first laser position and a first laser tilt, and (4) a
tolerance profile comprising a maximum floor offset, a minimum
floor offset, a maximum floor adjustment angle, a minimum floor
adjustment angle and a maximum allowable floor gap.
[0014] The laser controller receives a set of laser readings from
said first laser, each laser reading corresponding to a location in
the physical environment within said first plane, and each laser
reading comprising a first plane angle and a first plane distance
from a given site on the mobile robot. The negative obstacle
avoidance engine first converts each laser reading into a
three-dimensional coordinate based on the first plane angle, the
first plane distance, the first laser position and the first laser
tilt. Next, the negative obstacle avoidance engine determines a
maximum allowable floor height and a minimum allowable floor height
for the three-dimensional coordinate based on the x-component, the
y-component and the tolerance profile. The engine then determines
if the z-component falls between the maximum allowable floor height
and the minimum allowable floor height. If it does, the negative
obstacle avoidance system changes an indicator, such as a flag in
the memory to designate the x-component and the y-component of the
three-dimensional coordinate as the coordinate corresponding to the
last good floor reading. If the z-component does not fall between
the maximum allowable floor height and the minimum allowable floor
height, then the negative obstacle avoidance engine determines
whether the distance G between the last good floor reading
coordinate and the location in the two-dimensional coordinate
system defined by the x-component and the y-component exceeds the
maximum allowable floor gap stored in the memory. If the distance G
exceeds the maximum allowable floor gap, the negative obstacle
avoidance engine adds the x-component, the y-component and the last
good floor reading coordinates to the first data structure of
two-dimensional coordinates to represent another location in the
physical environment to be avoided by the mobile robot. The
propulsion system then drives the mobile robot in the physical
environment under control of the first data structure, so as to
prevent the mobile robot from passing into the locations in the
physical environment represented by the two-dimensional coordinates
in the first data structure. Thus, the mobile robot, operating
under the control of the propulsion system, which itself operates
under the influence of the first data structure of two-dimensional
coordinates identifying all of the two-dimensional coordinates in
the floor plan to be avoided, avoids driving into the gap, ditch or
hole, or off of a cliff.
[0015] In yet another aspect there is provided a method for
avoiding positive obstacles in a mobile robot comprising a memory
and a propulsion system. The first step in the method comprises
storing the map, the first data structure of two-dimensional
coordinates, the first laser placement information and the
tolerance profile in the memory. In the next step, a set of laser
readings from the first laser are received, each laser reading
corresponding to a location in the physical environment where said
first laser detects a physical obstacle in the first plane, and
each laser reading having a first plane angle (theta) and a first
plane distance (radius=r) from a given spot on the mobile robot.
Next, each laser reading in the set of laser readings is
automatically processed by the mobile robot by: (1) converting each
laser reading into a three-dimensional coordinate based on the
first plane angle (theta), said first plane distance (r), the first
laser position and the first laser tilt. The three-dimensional
coordinate includes an x-component, a y-component and a
z-component. Then, a minimum ceiling height and a maximum floor
height for the three-dimensional coordinates are determined based
on the x-component, the y-component and the tolerance profile. If
the z-component falls between the minimum ceiling height and the
maximum floor height, then the laser reading is considered to have
detected an obstacle that (such as a table surface or overhang)
that should be avoided, and the x-component and the y-component of
the three-dimensional coordinate (which point to the spot on the
floor below the table or overhang) are added to the first data
structure of two-dimensional coordinates to represent a new
location in the physical environment to be avoided by the mobile
robot. In the final step, the propulsion system drives the mobile
robot in the physical environment under the influence or control of
the first data structure. As previously stated, this means the
propulsion system periodically checks the data in the first data
structure of two-dimensional coordinates and prevents the mobile
robot from passing into the locations in the physical environment
represented by the two-dimensional coordinates in the first data
structure. By avoiding the spots on the floor below the table or
overhang, the mobile robot also avoids driving into the table or
overhang. In some embodiments, the mobile robot does its own path
planning and navigation. In these embodiments, the method further
includes the steps of: (1) receiving on the mobile robot a command
to move from a current position to a specified location in the
physical environment, (2) calculating on the mobile robot, in
accordance with the floor plan, a path between the mobile robot's
current position and the specified location that avoids the
locations in the physical environment represented by the
coordinates in the first data structure of two-dimensional
coordinates, and (3) activating the propulsion system to
automatically drive the mobile robot along the path.
[0016] In still another aspect, the present invention provides a
method for avoiding negative obstacles in a physical environment
using a mobile robot comprising a memory and a propulsion system.
In this aspect, the method begins by storing in the memory a map
defining the floor plan representing the physical environment and a
two dimensional coordinate system delineating the floor plan, a
first data structure of two-dimensional coordinates from the floor
plan, the two dimensional coordinates in the first data structure
representing locations in the physical environment to be avoided by
the mobile robot, first laser placement information for a first
laser attached to the mobile robot, the first laser being oriented
to scan the physical environment in a first plane that is not
parallel to the floor of the physical environment. The first laser
placement information includes a first laser position and a first
laser tilt, and a tolerance profile comprising a maximum floor
offset, a minimum floor offset, a maximum floor adjustment angle, a
minimum floor adjustment angle and a maximum allowable floor gap.
The next step comprises receiving a set of laser readings from the
first laser, each laser reading corresponding to a location in the
physical environment within the first plane, and each laser reading
comprising a first plane angle and a first plane distance from a
given site on the mobile robot. Then, each laser reading in the set
of laser readings is converted into a three-dimensional coordinate
based on the first plane angle (theta), said first plane distance
(r), the first laser position and the first laser tilt. The
three-dimensional coordinate has an x-component, a y-component and
a z-component. In the next step, the mobile robot determines a
maximum allowable floor height and a minimum allowable floor height
for the three-dimensional coordinate based on the x-component, the
y-component and the tolerance profile. If the z-component falls
between the maximum allowable floor height and the minimum
allowable floor height, the mobile robot changes an indicator, such
as flag in the memory to designate the x-component and the
y-component of the three-dimensional coordinate as the last good
floor reading. However, if the z-component does not fall between
the maximum allowable floor height and the minimum allowable floor
height, the mobile robot next determines whether the distance G
between the last good floor reading and the location in the
two-dimensional coordinate system defined by the x-component and
the y-component exceeds the maximum allowable floor gap. If it
does, then the system has found a gap in the floor that the mobile
robot cannot safely traverse, in which case the system adds the
x-component, the y-component and the last good floor reading to the
first data structure of two-dimensional coordinates to represent a
new location in the physical environment to be avoided by the
mobile robot. In the final step of the method, the system causes
the propulsion system to drive the mobile robot in the physical
environment under the influence or control of the first data
structure, the propulsion system preventing the mobile robot from
passing into the locations in the physical environment represented
by the two-dimensional coordinates in the first data structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The present invention and various aspects, features and
advantages thereof are explained in more detail below with
reference to exemplary and therefore non-limiting embodiments and
with the aid of the drawings, which constitute a part of this
specification and include depictions of the exemplary embodiments.
In these drawings:
[0018] FIGS. 1A and 1B together illustrate, by way of example, one
of the disadvantages of conventional laser-based obstacle avoidance
systems for mobile robots.
[0019] FIG. 2 illustrates, by way of non-limiting example, the
placement and orientation of an additional scanning laser in
accordance with an exemplary embodiment of the present
invention.
[0020] FIG. 3 contains a schematic diagram that illustrates, by way
of non-limiting example, how a scanning laser attached to a mobile
robot, and oriented to operate in accordance with exemplary
embodiments of a positive obstacle avoidance system of the present
invention, detects horizontally-oriented objects in the physical
environment where the mobile robot operates.
[0021] FIG. 4 contains a schematic diagram illustrating, by way of
example, how a scanning laser attached to a mobile robot, and
oriented to operate in accordance with embodiments of the present
invention, detects an unacceptably large gap in the floor of the
physical environment.
[0022] FIG. 5 shows a high-level block diagram illustrating the
major physical and logical components of a mobile robot with a
positive and negative obstacle avoidance system in accordance with
exemplary embodiments of the present invention.
[0023] FIG. 6 shows, in printed form, an example of the coordinate
data in the data structure of two-dimensional coordinates in some
embodiments of the present invention.
[0024] FIG. 7 shows a high-level flow diagram illustrating steps
that may be performed by a positive and negative obstacle avoidance
system, like the one shown in FIG. 5, operating in accordance with
embodiments of the present invention to determine the locations of
positive obstacles in the physical environment.
[0025] FIG. 8 shows a high-level flow diagram illustrating steps
that may be performed by a positive and negative obstacle avoidance
system, like the one shown in FIG. 5, operating in accordance with
embodiments of the present invention to determine the locations of
negative obstacles in the physical environment.
[0026] FIG. 9 illustrates, by way of example only, a known
algorithm a mobile robot might use to plan a path between the
mobile robot's current position and a particular location in
accordance with a map.
[0027] FIG. 10 illustrates, by way of example, some of the data
content of a map file defining a floor plan for the physical
environment. The map file is stored in the memory of the mobile
robot according to embodiments of the invention.
[0028] FIG. 11 shows a graphical representation of the map file
illustrated in FIG. 10.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0029] FIGS. 1A and 1B together illustrate, by way of non-limiting
example, one of the disadvantages of conventional laser-based
obstacle avoidance systems for mobile robots. As shown in FIGS. 1A
and 1B, mobile robot 10 is equipped with a horizontally-oriented
scanning laser (not shown), which emits laser light rays 15 that
fan out in front of the robot in a substantially horizontal plane
that is roughly parallel to the floor or other surface upon which
the mobile robot travels. When mobile robot 10 approaches an
obstacle that is resting on the floor of the physical environment,
or very near the floor, such as obstacle 20 in FIG. 1A, the laser
light rays 15 strike the obstacle 20 and are reflected back to the
mobile robot 10. Sensors in the laser detect and process the
reflections, thereby informing the mobile robot 10 that there is an
obstacle 20 in its path that needs to be avoided. Thus, the
obstacle avoidance and locomotion controllers on board mobile robot
10, if any, cause mobile robot 10 to go around obstacle 20 or
otherwise brake to come to a stop before mobile robot 10 can
collide with the obstacle 20. This process is sometimes called
"laser localization," or "Monte Carlo localization with a laser."
However, as shown in FIG. 1B, when mobile robot 10 approaches an
obstacle 25 suspended above the floor or travel surface in such a
way that obstacle 25 does not lie in the same plane as the laser
light rays 15 emanating from the horizontally-oriented laser on
mobile robot 10, then the laser light rays 15 will not strike and
thus will not be reflected back from obstacle 25. Since mobile
robot 10 does not detect light bouncing back at it from the
distance corresponding to the location of obstacle 25, it does not
"know" that there is an obstacle 25 in its path and, consequently,
collides with obstacle 25, potentially causing severe damage to
mobile robot 10, obstacle 25, cargo 12, or all of them.
[0030] Although it would be possible to detect obstacle 25 by
raising the scanning laser to a higher position on mobile robot 10,
this solution would only lead to mobile robot 10 not being able to
detect and avoid colliding with obstacles closer to the floor, such
as obstacle 20 shown in FIG. 1A. Depending on the height of the
mobile robot, as well as the physical environment where the mobile
robot operates, adding a multiplicity of horizontally-oriented
scanning lasers to mobile robot 10 in order to account for every
possible obstacle may be impractical due to the expense and the
trouble of purchasing, installing and maintaining a large number of
lasers for every mobile robot in an organization, as well as
managing, crunching and using all of the data that such a
multiplicity of installed lasers would produce.
[0031] FIG. 2 illustrates, by way of non-limiting example, the
placement and orientation of an additional scanning laser in
accordance with an exemplary embodiment of the present invention.
As shown in FIG. 2, scanning laser 27 is attached to mobile robot
10 and oriented so that it emits laser light rays 30 in a plane
that is not parallel to the floor of the physical environment. In
this orientation, scanning laser 27 emits laser light rays 30 in a
plane that is much more likely to intersect with and be reflected
from any obstacle, including obstacle 35, in mobile robot 10's
path. Thus laser light rays 30 are much more likely to be reflected
back to mobile robot 10 when mobile robot 10 approaches tables with
legs at the ends, protruding keyboard trays, obstacles suspended
from the ceiling or suspended from other objects, and the like.
Although the scanning laser 27 may be installed so that the laser
light rays 30 emanating from scanning laser 27 fall into a plane
that is substantially perpendicular to the floor, scanning the
physical environment in a plane that is perpendicular to floor is
not required. Orienting the lasers to scan other planes will work
just as well or better, depending on the lasers used and the
physical environment, so long as the lasers are installed so that
they scan in planes that are not parallel to the floor, or more
accurately, parallel with the objects that are most likely to form
obstacles that the mobile robot needs to avoid, such as tables and
keyboard trays.
[0032] FIG. 3 contains a schematic diagram that illustrates, by way
of non-limiting example, how a scanning laser 315 attached to a
mobile robot 310, and oriented to operate in accordance with
exemplary embodiments of a positive obstacle avoidance system of
the present invention, detects horizontally-oriented objects in
mobile robot 10's path of travel. As shown in FIG. 3, scanning
laser 315 produces laser light rays that intersect with a
horizontally-oriented obstacle 320 in mobile robot 310's path of
travel. As illustrated by FIG. 3, a multiplicity of laser light
rays may strike and be reflected back toward mobile robot 310,
depending on the relative heights of scanning laser 315 and
obstacle 320. It should be understood that, even if scanning laser
315 and obstacle 320 are at exactly the same height, the
non-horizontal orientation of the plane of laser light produced by
scanning laser 315 ensures that at least some of the laser light
rays will strike the obstacle 320. Thus, while mobile robot 310 may
not be capable of "seeing" multiple spots on the top surface of
obstacle 320 (as shown in FIG. 3), because the obstacle 320 is at
the same height as the scanning laser 315, it will still "see" the
nearest edge of the horizontally-oriented obstacle as the mobile
robot 310 approaches the obstacle 320, and therefore take steps to
avoid it, as will be described in more detail below.
[0033] In accordance with embodiments of the present invention,
FIG. 3 also illustrates the locations of the minimum allowable
ceiling height 330 and maximum allowable floor height 335
calculated and used by the positive obstacle avoidance engine, as
described herein. The slope in the minimum allowed ceiling height
330 and the maximum allowable floor height 335, as well as their
offsets from the real ceiling 331 and real floor 332, respectively,
permits mobile robots operating according to embodiments of the
invention to function properly even though the ceiling or the
floor, or both of them, may not be exactly horizontal. Thus, the
mobile robot 310 will not determine, erroneously, that the floor or
the ceiling is an obstacle in its path that must be avoided merely
because the floor happens to rise a little, or because the ceiling
happens to fall a little, as the distance from the robot increases,
so long as the laser readings received by the mobile robot 310
indicate that the object detected is at or below the maximum
allowable floor height 335, or at or above the minimum allowable
ceiling height 330.
[0034] FIG. 4 contains a schematic diagram illustrating, by way of
example, how a scanning laser 415 attached to a mobile robot 410,
and oriented to operate in accordance with embodiments of the
present invention, detects an unacceptably large gap 420 in the
floor 405 of the physical environment. As shown in FIG. 4, scanning
laser 415 is attached to mobile robot 410 and oriented to scan the
physical environment in a plane that intersects the floor 405. As
explained herein, mobile robot 410 has a negative obstacle
avoidance engine that is configured to remember the last good floor
reading obtained by the engine and constantly compares that last
good floor reading with current readings in order to determine if
it is safe for the mobile robot 410 to traverse the gap 420. If the
gaps are small, for example, such as would be the case when the gap
is one of the holes in a screen or grate, then embodiments of the
present invention are typically configured to permit the mobile
robot to continue driving over the gaps in the screen or grate
because such screens or grates will not pose a risk or danger to
the mobile robot 410.
[0035] FIG. 5 shows a high-level block diagram illustrating the
major physical and logical components of a mobile robot 501 having
a positive and negative obstacle avoidance system in accordance
with exemplary embodiments of the present invention. As shown in
FIG. 5, the mobile robot 501 includes a non-horizontal laser (or
"first laser") 505, a non-horizontal laser controller 510, a
positive and negative obstacle avoidance engine 515, a memory 503
and a propulsion system 550. The non-horizontal laser 505 on the
mobile robot 501 is oriented to scan the physical environment in a
first plane (not shown) that is not parallel to the floor of the
physical environment. The non-horizontal laser is programmatically
coupled to a non-horizontal laser controller 510, that receives the
non-horizontal laser's readings are passes that information along
to the positive and negative obstacle avoidance engine 515.
Suitable lasers and laser controllers to use for these purposes may
be obtained, for example, from Hokuyo Urg, of Japan (Part Nos.
URG-04LX and URG-04LX-UG01).
[0036] Typically, but not necessarily, mobile robots operating
according embodiments of the present invention will also have one
or more other range devices 580, including another scanning laser,
that the mobile robot 501 uses, for example, to scan in a
horizontal plane that is parallel to the floor. The
horizontally-oriented laser and other range devices 580 send
readings to one or more range device controllers 585, which uses
the data to populate the data structure of two-dimensional
coordinates 520 with two-dimensional (x,y) coordinates representing
locations in the physical environment that the mobile robot 501
should avoid. The other range devices 580 may be very useful, for
example, for detecting vertically-oriented objects extending from
the floor of the physical environment, which may not be easy to
detect with the non-horizontal laser 505, especially if the
non-horizontal laser 505 happens to be oriented to scan in a plane
that is perpendicular to floor. Notably, although shown as separate
controllers in FIG. 5, it will be recognized by those skilled in
the art, upon reading this disclosure, that embodiments of the
present invention may use a single range device controller to
receive readings from both the horizontally-oriented lasers and the
non-horizontally-oriented laser.
[0037] The memory 503 stores initial operating parameters and
preferences for the positive obstacle avoidance engine 515,
including a map 530 defining a floor plan 535 representing the
physical environment and a two dimensional coordinate system
delineating the floor plan 535. Exemplary data content for a
computer file comprising the map 530 is shown in FIG. 10. FIG. 11
shows a graphical representation of the map 530. The initial
operating parameters stored in the memory 503 also include a data
structure of two dimensional coordinates 520. Each two dimensional
coordinate in the data structure 520 represents a location in the
physical environment to be avoided by the mobile robot 501 because
some obstacle has been detected at that location. In some
embodiments, coordinates for virtual obstacles 525, including
things like forbidden zones, need to enter zones, single robot
zones, robot avoidance zones, one-way zones, and the like, may be
defined by the system operator and added to the data structure of
two-dimensional coordinates to control where mobile robots can and
cannot go in the physical environment, even though no physical
obstacles exist in those locations. FIG. 6 shows, in printed form,
an example of the coordinate data stored in the data structure of
two-dimensional coordinates 520 in some embodiments of the present
invention.
[0038] Returning to FIG. 5, the memory 503 also includes laser
placement information 540 for the non-horizontal laser 505,
including the non-horizontal laser 505's position on the mobile
robot 501 and the first laser's tilt angle (both values being
relative to the center of the robot, for example). The memory 503
also holds a tolerance profile 545 for use with the positive and
negative obstacle avoidance engine 515. As previously stated, the
tolerance profile 545 typically includes a ceiling offset, a floor
offset, a ceiling adjustment angle and a floor adjustment angle to
be used by the positive and negative obstacle avoidance engine 515
to avoid generating too many false positives caused by sloping
ceilings or floors, or variations in the position and tilt of the
installed laser.
[0039] The propulsion system 550 may comprise a combination of
hardware, such as motors and wheels 570, and software processors
and/or controllers, such as path planning engine 555 and locomotion
controller 560, that when executed by a microprocessor on board the
mobile robot 501 (the microprocessor is not shown), cause the
mobile robot 501 to avoid driving into the locations in the
physical environment represented by the coordinates in the data
structure of two dimensional coordinates 520. In other words, the
propulsion system 550 is typically configured to periodically check
the coordinates in the data structure 520 in order to ensure, for
example, that no coordinates from the data structure 520 will be
used in a path planned by the path planning engine 565. In some
embodiments, avoiding the locations in the physical environment
represented by the coordinates in the data structure 520 will mean
calculating paths around the prohibited locations. In other
embodiments, the mobile robot 501 may slow down and/or come to a
complete stop if the path to the current destination is blocked by
a prohibited location or because proceeding along the intended path
would cause the mobile robot 510 to drive into a gap in the
floor.
[0040] As shown in FIG. 5, the propulsion system 550 may optionally
include a path planning engine 565, which determines, in accordance
with the map 530 and the floor plan 535 for the physical
environment, an optimum path the mobile robot 501 should take to
travel from its current position in the physical environment to a
specified location. A variety of different path planning techniques
are known and used by those skilled in the art to accomplish such
path planning for mobile robots. FIG. 9, discussed below, shows a
high-level flow diagram illustrating, by way of example, the steps
that might be performed by one such path planning engine
encompassed by the propulsion system 550. Another path planning
technique is discussed in detail in Chapter 7 of the book
"Artificial Intelligence and Mobile Robots," First Edition,
published in 1998 by AAAI Press, and edited by David Kortenkamp, R.
Peter Bonnaso and Robin Murphy. For purposes of the present
invention, the path planning engine 555 plans a path that avoids
all of the locations that have been identified by the positive and
negative obstacle avoidance engine 515 as containing obstacles.
[0041] FIG. 7 shows a high-level flow diagram illustrating steps
that may be performed by a positive and negative obstacle avoidance
system, like the one shown in FIG. 5, operating in accordance with
embodiments of the present invention to determine the locations of
positive obstacles in the physical environment. As shown in FIG. 7,
the first step, step 705, comprises receiving angle and distance
information (theta and r) from the non-horizontal laser 505 and
non-horizontal laser controller 510. Step 705 in FIG. 7 also
includes initializing certain operating parameters for the positive
and negative obstacle avoidance engine 515. The remaining steps 710
through 725 are performed by the positive and negative obstacle
avoidance engine 515 to populate the data structure of
two-dimensional coordinates 520 with two-dimensional coordinates
representing locations in the physical environment that need to be
avoided.
[0042] More specifically, in step 710, the positive and negative
obstacle avoidance engine 515 converts the laser reading (theta and
r) obtained in step 705 into a three-dimensional coordinate (x, y,
z) based on the first plane angle (theta), the first plane distance
(r), the first laser position and said first laser tilt stored in
the memory 503 at step 705. The three-dimensional coordinate
includes an x-component, a y-component and a z-component. As
discussed above, the first laser may be attached to the mobile
robot in a variety of different orientations. But when the first
laser's scanning plane is perpendicular to the floor and parallel
to the direction of the mobile robot's direction of travel, the
positive obstacle avoidance engine is programmed to convert the
laser readings into a three-dimensional coordinate (x, y, z) using
the formulas:
x-component=first laser x position+first plane
distance*cosine(first plane angle),
y-component=first laser y position, and
z-component=first laser z position+first plane distance*sin(first
plane angle).
[0043] Next, at step 715, the positive obstacle avoidance engine
515 determines a maximum floor height and a minimum ceiling height
for the three-dimensional coordinate based on the x-component, the
y-component and the tolerance profile 545 stored in the memory 503.
As previously stated, the maximum floor height may be calculated
according to the formula:
maximum floor height=floor offset+A*sin(floor adjustment
angle),
where A=the distance from the current position to the coordinate
(x-component, y-component) in the two-dimensional coordinate
system. The minimum ceiling height may be calculated according to
the formula:
minimum ceiling height=ceiling offset+A*sin(ceiling adjustment
angle),
where A=the distance from the current position to the coordinate
(x-component, y-component) in the two-dimensional coordinate
system.
[0044] Next, at step 720, the positive and negative obstacle
avoidance engine 515 determines whether the z-component is between
the minimum ceiling height and the maximum floor height. If it is,
then the positive and negative obstacle avoidance engine construes
this as an indication that the location is occupied by a positive
obstacle suspended above the floor, such as the horizontal
component of a table, a keyboard tray extending out of a desk or
workstation, or possibly some other cantilevered object.
Accordingly, at step 725, the positive obstacle avoidance engine
515 will then add the x-component and the y-component of the
three-dimensional coordinate (representing the spot on the floor
below the table, keyboard tray or other object) to the first data
structure of two-dimensional coordinates to represent a new
location in the physical environment to be avoided by the mobile
robot. If there are more distance and angle readings from the
non-horizontal laser, then execution returns to step 710, upon
which the next three-dimensional coordinate is processed. In this
fashion, the positive obstacle avoidance engine builds the data
structure of two-dimensional coordinates (or adds new
two-dimensional coordinates to a previously-existing data
structure) that identifies all of the locations on the floor plan
where a positive obstacle has been found. Notably, the data
structure of two dimensional coordinates built by the positive and
negative obstacle avoidance system may also contain coordinates for
obstacles that were found, or could also be found, by a
horizontally-oriented laser on the mobile robot. In other words,
the positive and negative obstacle avoidance system may be
configured to operate completely independently from the operation
of other obstacle avoidance systems tied, for example, to a
horizontally-oriented later on the mobile robot.
[0045] FIG. 8 shows a high-level flow diagram illustrating steps
that may be performed by a positive and negative obstacle avoidance
system, like the one shown in FIG. 5, operating in accordance with
embodiments of the present invention to determine the locations of
negative obstacles in the physical environment. First, in step 805,
laser readings are received from the non-horizontal laser 505 and
the non-horizontal laser controller 510. Also in this step, a set
of initial operating parameters and preferences for use by the
positive and negative obstacle avoidance engine 515 is stored in
the memory, including laser placement information for the
non-horizontal laser, including a first laser position and a first
laser tilt, and a tolerance profile 545 comprising a maximum floor
offset, a minimum floor offset, a maximum floor adjustment angle, a
minimum floor adjustment angle and a maximum allowable floor
gap.
[0046] Then, in step 810, the positive and negative obstacle
avoidance engine converts each laser reading into a
three-dimensional coordinate based on the first plane angle, the
first plane distance, the first laser position and the first laser
tilt. Next, at step 815, the negative obstacle avoidance engine
determines a maximum allowable floor height and a minimum allowable
floor height for the three-dimensional coordinate based on the
x-component, the y-component and the tolerance profile, and
determines in step 820 whether the z-component falls between the
maximum allowable floor height and the minimum allowable floor
height. If it does, the positive and negative obstacle avoidance
engine 515 changes an indicator, such as a flag, in the memory to
designate the x-component and the y-component of the
three-dimensional coordinate as the coordinate corresponding to the
last good floor reading (step 825). On the other hand, if the
z-component does not fall between the maximum allowable floor
height and the minimum allowable floor height, then, in steps 830
and 835, the positive and negative obstacle avoidance engine 515
determines whether the distance G between the last good floor
reading coordinate and the location in the two-dimensional
coordinate system defined by the x-component and the y-component
exceeds the maximum allowable floor gap stored in the memory 503.
If the distance G exceeds the maximum allowable floor gap, the
positive and negative obstacle avoidance engine 515 adds the
x-component, the y-component and the last good floor reading
coordinate to the data structure 520 of two-dimensional coordinates
to represent another location in the physical environment to be
avoided by the mobile robot 501 (step 840). When all of the
non-horizontal laser readings are processed, positive and negative
obstacle avoidance engine will have populated the data structure
520 with a list of coordinates that need to be avoided. This
information may then be used by a path planning engine, an
autonavigation engine, or both.
[0047] FIG. 9 illustrates, by way of example only, a known
algorithm a mobile robot might use to plan a path between the
mobile robot's current position and a particular location in
accordance with a map and a floor plan delineated by a
two-dimensional coordinate system. In general, the steps of the
path planning algorithm include receiving the job location (step
905), planning a global path to the job location (step 910),
planning a local path around detected and remembered obstacles
(step 915), finding an allowable set of movement commands for the
mobile robot in order to follow the path (step 925) and sending the
movement commands to a locomotion controller or motors (step
930).
[0048] Although the exemplary embodiments, uses and advantages of
the invention have been disclosed above with a certain degree of
particularity, it will be apparent to those skilled in the art upon
consideration of this specification and practice of the invention
as disclosed herein that alterations and modifications can be made
without departing from the spirit or the scope of the invention,
which are intended to be limited only by the following claims and
equivalents thereof.
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