U.S. patent application number 11/109832 was filed with the patent office on 2005-10-06 for debris sensor for cleaning apparatus.
Invention is credited to Cohen, David A., Landry, Gregg W., Ozick, Daniel.
Application Number | 20050218852 11/109832 |
Document ID | / |
Family ID | 34795633 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050218852 |
Kind Code |
A1 |
Landry, Gregg W. ; et
al. |
October 6, 2005 |
Debris sensor for cleaning apparatus
Abstract
A piezoelectric debris sensor and associated signal processor
responsive to debris strikes enable an autonomous or non-autonomous
cleaning device to detect the presence of debris and in response,
to select a behavioral mode, operational condition or pattern of
movement, such as spot coverage or the like. Multiple sensor
channels (e.g., left and right) can be used to enable the detection
or generation of differential left/right debris signals and thereby
enable an autonomous device to steer in the direction of
debris.
Inventors: |
Landry, Gregg W.;
(Gloucester, MA) ; Cohen, David A.; (Brookline,
MA) ; Ozick, Daniel; (Newton, MA) |
Correspondence
Address: |
LUCASH, GESMER & UPDEGROVE, LLP
40 BROAD ST
SUITE 300
BOSTON
MA
02109
US
|
Family ID: |
34795633 |
Appl. No.: |
11/109832 |
Filed: |
April 19, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11109832 |
Apr 19, 2005 |
|
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10766303 |
Jan 28, 2004 |
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Current U.S.
Class: |
318/580 |
Current CPC
Class: |
A47L 2201/04 20130101;
G05D 1/0272 20130101; Y10S 901/01 20130101; A47L 11/4066 20130101;
A47L 2201/06 20130101; A47L 9/2831 20130101; A47L 11/4005 20130101;
A47L 9/2852 20130101; G05D 1/0227 20130101; A47L 9/0466 20130101;
A47L 5/362 20130101; A47L 9/2857 20130101; A47L 11/4008 20130101;
G05D 1/021 20130101; A47L 9/281 20130101; G05D 2201/0203 20130101;
A47L 11/4011 20130101; Y10S 901/46 20130101; A47L 9/0488 20130101;
A47L 9/2805 20130101; A47L 9/2889 20130101; G05D 1/0242 20130101;
G05D 2201/0215 20130101; A47L 9/2842 20130101; A47L 9/2884
20130101; A47L 9/2894 20130101; A47L 11/4061 20130101; G05D 1/0238
20130101 |
Class at
Publication: |
318/580 |
International
Class: |
G05D 001/00 |
Claims
1. An autonomous cleaning apparatus, comprising: a drive system
operable to enable movement of the cleaning apparatus; a controller
in communication with the drive system, the controller including a
processor operable to control the drive system to provide at least
one pattern of movement of the cleaning apparatus; and a debris
sensor for generating a debris signal indicating that the cleaning
apparatus has encountered debris; wherein the processor is
responsive to the debris signal to select a pattern of movement of
the cleaning apparatus.
2. The apparatus of claim 1 wherein the pattern of movement
comprises spot coverage of an area containing debris.
3-5. (canceled)
6. An autonomous cleaning apparatus, comprising: a drive system
operable to enable movement of the cleaning apparatus; a controller
in communication with the drive system, the controller including a
processor operable to control the drive system to provide at least
one pattern of movement of the cleaning apparatus; and a debris
sensor for generating a debris signal indicating that the cleaning
apparatus has encountered debris; wherein the processor is
responsive to the debris signal to select an operative mode from
among predetermined operative modes of the cleaning apparatus.
7. The apparatus of claim 6 wherein selection of an operative mode
comprises selecting a pattern of movement.
8. The apparatus of claim 7 wherein the pattern of movement
comprises spot coverage of an area containing debris.
9. The apparatus of claim 7 wherein the pattern of movement
comprises steering the cleaning apparatus toward an area containing
debris.
10. The apparatus as in one of claims 6-9 wherein the debris sensor
comprises spaced-apart first and second debris sensing elements
respectively operable to generate first and second debris signals;
and wherein the processor is responsive to the first and second
debris signals to select a pattern of movement.
11. The apparatus of claim 10 further wherein the processor is
responsive to differences in the first and second debris signals to
steer the cleaning apparatus in a direction of debris.
12. The apparatus as in one of claims 6-11 wherein the debris
sensor comprises a piezoelectric sensor element located proximate a
cleaning pathway of the cleaning apparatus and responsive to a
debris strike to generate a signal indicative of such strike.
13. A cleaning apparatus comprising: a cleaning pathway for
transporting debris; a piezoelectric sensor located proximate to
the cleaning pathway and responsive to a debris strike to generate
a debris signal indicative of such strike; and a processor
responsive to the debris signal to change an operative mode of the
cleaning apparatus.
14. The apparatus of claim 13 wherein the change in operative mode
comprises illuminating a user-perceptible indicator light.
15. The apparatus of claim 13 wherein the change in operative mode
comprises changing a power setting.
16. The apparatus of claim 13 wherein the change in operative mode
comprises reducing a movement speed of the apparatus.
17. A debris sensor for a cleaning apparatus, the debris sensor
comprising: a piezoelectric element located proximate to a cleaning
pathway of the cleaning apparatus and responsive to a debris strike
to generate a first signal indicative of such strike; and a
processor operable to process the first signal to generate a second
signal representative of a characteristic of debris being
encountered by the cleaning apparatus.
18. The sensor of claim 17 wherein the characteristic is relative
quantity of debris.
19. The sensor of claim 17 wherein the characteristic is a vector
from a present location of the cleaning apparatus to an area
containing debris.
20. The sensor of claim 17 wherein the processor is further
operable, in response to the second signal, to change an operative
mode of the cleaning apparatus.
21. The sensor of claim 20 wherein the change of operative mode
comprises changing a power setting.
22. The sensor of claim 20 wherein the change of operative mode
comprises illuminating a user-perceptible indicator light.
23. The sensor of claim 20 wherein the change of operative mode
comprises reducing a movement speed of the cleaning apparatus.
24. The sensor of claim 17 wherein: the piezoelectric element is
mounted proximate to the cleaning pathway by mounting elements, and
the mounting elements comprise at least one mounting screw and
associated elastomer mounting grommet.
25. The sensor of claim 24 wherein the elastomer mounting grommet
receives the mounting screw and provides vibration dampening for
the piezoelectric element mounted proximate to the cleaning pathway
by the mounting screw.
26-28. (canceled)
29. The sensor of claim 17 wherein the piezoelectric element
comprises a flexible piezoelectric film.
30. The apparatus of claim 13 wherein the piezoelectric sensor
element comprises a flexible piezoelectric film having multiple
electrically isolated sections.
31. The sensor of claim 29 wherein the piezoelectric element
comprises a flexible piezoelectric film.
32. A method of operating an autonomous cleaning apparatus, the
method comprising: using a processor to control a drive system of
the cleaning apparatus to provide at least one pattern of movement
of the cleaning apparatus; using a debris sensor in communication
with the processor to generate a debris signal indicating that the
cleaning apparatus has encountered debris; and using the processor
to select a pattern of movement of the cleaning apparatus in
response to the debris signal.
33. The method of claim 32 wherein the pattern of movement
comprises spot coverage of an area containing debris.
34-36. (canceled)
37. A method of operating an autonomous cleaning apparatus, the
method comprising: using a processor to control a drive system of
the cleaning apparatus to provide at least one pattern of movement
of the cleaning apparatus; using a debris sensor in communication
with the processor to generate a debris signal indicating that the
cleaning apparatus has encountered debris; and using the processor
to select, responsive to the debris signal, an operative mode from
among predetermined operative modes of the cleaning apparatus.
38. The method of claim 37 wherein selection of an operative mode
comprises selecting a pattern of movement.
39. The method of claim 38 wherein the pattern of movement
comprises spot coverage of an area containing debris.
40. The method of claim 39 wherein the pattern of movement
comprises steering the cleaning apparatus toward an area containing
debris.
41. The method as in one of claims 37-40 wherein the debris sensor
comprises spaced-apart first and second debris sensing elements
respectively operable to generate first and second debris signals;
and wherein the processor is responsive to the first and second
debris signals to select a pattern of movement.
42. The method of claim 41 further wherein the processor is
responsive to differences in the first and second debris signals to
steer the cleaning apparatus in a direction of debris.
43. The method as in one of claims 37-42 wherein the debris sensor
comprises a piezoelectric sensor element located proximate a
cleaning pathway of the cleaning apparatus and responsive to a
debris strike to generate a signal indicative of such strike.
44. A method of operating a cleaning apparatus, the method
comprising: using a piezoelectric sensor located proximate to a
cleaning pathway of the cleaning apparatus and responsive to a
debris strike to generate a debris signal indicative of such
strike; and using a processor in communication with the
piezoelectric sensor and responsive to the debris signal to change
an operative mode of the cleaning apparatus.
45. The method of claim 44 wherein the change in operative mode
comprises illuminating a user-perceptible indicator light.
46. The method of claim 44 wherein the change in operative mode
comprises changing a power setting.
47. The apparatus of claim 44 wherein the change in operative mode
comprises reducing a movement speed of the apparatus.
48. A method of operating a cleaning apparatus, the method
comprising: using a piezoelectric element located proximate to a
cleaning pathway of the cleaning apparatus and responsive to a
debris strike to generate a first signal indicative of such strike;
and using a processor in communication with the piezoelectric
element and operable to process the first signal to generate a
second signal representative of a characteristic of debris being
encountered by the cleaning apparatus.
49. The method of claim 48 wherein the characteristic is relative
quantity of debris.
50. The method of claim 48 wherein the characteristic is a vector
from a present location of the cleaning apparatus to an area
containing debris.
51. The method of claim 48 wherein the processor is further
operable, in response to the second signal, to change an operative
mode of the cleaning apparatus.
52. The method of claim 51 wherein the change of operative mode
comprises changing a power setting.
53. The method of claim 51 wherein the change of operative mode
comprises illuminating a user-perceptible indicator light.
54. The method of claim 51 wherein the change of operative mode
comprises reducing a movement speed of the cleaning apparatus.
55. The method of claim 48 further comprising: mounting the
piezoelectric element proximate to the cleaning pathway using at
least one mounting screw and associated elastomer mounting
grommet.
56. The method of claim 55 wherein the elastomer mounting grommet
receives the mounting screw and provides vibration dampening for
the piezoelectric element mounted proximate to the cleaning pathway
by the mounting screw.
57-59. (canceled)
60. The method of claim 48 wherein the piezoelectric element
comprises a flexible piezoelectric film.
61. The method of claim 44 wherein the piezoelectric sensor element
comprises a flexible piezoelectric film having multiple
electrically isolated sections.
62. The method of claim 60 wherein the piezoelectric element
comprises a flexible piezoelectric film.
Description
CROSS-REFERENCE TO RELATED PATENT DOCUMENTS
[0001] The present application for patent is related to the
following commonly-owned U.S. patent applications or patents,
incorporated by reference as if fully set forth herein:
[0002] U.S. patent application Ser. No. 09/768,773 filed Jan. 24,
2001, now U.S. Pat. No. 6,594,844, entitled Robot Obstacle
Detection System (Atty. Dkt. DP-4);
[0003] U.S. Provisional Patent Application Ser. No. 60/345,764
filed Jan. 3, 2002, entitled Cleaning Mechanisms for Autonomous
Robot;
[0004] U.S. patent application Ser. No. 10/056,804, filed Jan. 24,
2002, entitled Method and System for Robot Localization and
Confinement (Atty Dkt. DP-6);
[0005] U.S. patent application Ser. No. 10/167,851 filed Jun. 12,
2002, entitled Method and System for Multi-Mode Coverage for an
Autonomous Robot (Atty Dkt. DP-5);
[0006] U.S. patent application Ser. No. 10/320,729 filed Dec. 16,
2002, entitled Autonomous Floor-Cleaning Robot (Atty Dkt.
DP-10);
[0007] U.S. patent application Ser. No. 10/661,835 filed Sep. 12,
2003, entitled Navigational Control System for Robotic Device (Atty
Dkt. DP-9).
FIELD OF THE INVENTION
[0008] The present invention relates generally to cleaning
apparatus, and, more particularly, to a debris sensor for sensing
instantaneous strikes by debris in a cleaning path of a cleaning
apparatus, and for enabling control of an operational mode of the
cleaning apparatus. The term "debris" is used herein to
collectively denote dirt, dust, and/or other particulates or
objects that might be collected by a vacuum cleaner or other
cleaning apparatus, whether autonomous or non-autonomous.
BACKGROUND OF THE INVENTION
[0009] Debris sensors, including some suitable for cleaning
apparatus, are known in the art. Debris sensors can be useful in
autonomous cleaning devices like those disclosed in the
above-referenced patent applications, and can also be useful in
non-autonomous cleaning devices, whether to indicate to the user
that a particularly dirty area is being entered, to increase a
power setting in response to detection of debris, or to modify some
other operational setting.
[0010] Examples of debris sensors are disclosed in the
following:
1 DeBrey 3,674,316 DeBrey 3,989,311 DeBrey 4,175,892 Kurz 4,601,082
Westergren 4,733,430 Martin 4,733,431 Harkonen 4,829,626 Takashima
5,105,502 Takashima 5,136,750 Kawakami 5,163,202 Yang 5,319,827 Kim
5,440,216 Gordon 5,608,944 Imamura 5,815,884 Imamura 6,023,814
Kasper 6,446,302 Gordon 6,571,422
[0011] Among the examples disclosed therein, many such debris
sensors are optical in nature, using a light emitter and detector.
In typical designs used in, e.g., a vacuum cleaner, the light
transmitter and the light receiver of the optical sensor are
positioned such that they are exposed into the suction passage or
cleaning pathway through which dust flows. During usage of the
vacuum cleaner, therefore, dust particles tend to adhere to the
exposed surfaces of the light transmitter and the light receiver,
through which light is emitted and detected, eventually degrading
the performance of the optical sensor.
[0012] Accordingly, it would be desirable to provide a debris
sensor that is not subject to degradation by accretion of
debris.
[0013] In addition, debris sensors typical of the prior art are
sensitive to a level of built-up debris in a reservoir or cleaning
pathway, but not particularly sensitive to instantaneous debris
strikes or encounters.
[0014] It would therefore be desirable to provide a debris sensor
that is capable of instantaneously sensing and responding to debris
strikes, and which is immediately responsive to debris on a floor
or other surface to be cleaned, with reduced sensitivity to
variations in airflow, instantaneous power, or other operational
conditions of the cleaning device.
[0015] It would be also be useful to provide an autonomous cleaning
device having operational modes, patterns of movement or behaviors
responsive to detected debris, for example, by steering the device
toward "dirtier" areas based on signals generated by a debris
sensor.
[0016] In addition, it would be desirable to provide a debris
sensor that could be used to control, select or vary operational
modes of either an autonomous or non-autonomous cleaning
apparatus.
SUMMARY OF THE INVENTION
[0017] The present invention provides a debris sensor, and
apparatus utilizing such a debris sensor, wherein the sensor is
instantaneously responsive to debris strikes, and can be used to
control, select or vary the operational mode of an autonomous or
non-autonomous cleaning apparatus containing such a sensor.
[0018] One aspect of the invention is an autonomous cleaning
apparatus including a drive system operable to enable movement of
the cleaning apparatus; a controller in communication with the
drive system, the controller including a processor operable to
control the drive system to provide at least one pattern of
movement of the cleaning apparatus; and a debris sensor for
generating a debris signal indicating that the cleaning apparatus
has encountered debris; wherein the processor is responsive to the
debris signal to select an operative mode from among predetermined
operative modes of the cleaning apparatus.
[0019] The selection of operative mode could include selecting a
pattern of movement of the cleaning apparatus.
[0020] The pattern of movement can include spot coverage of an area
containing debris, or steering the cleaning apparatus toward an
area containing debris. The debris sensor could include
spaced-apart first and second debris sensing elements respectively
operable to generate first and second debris signals; and the
processor can be responsive to the respective first and second
debris signals to select a pattern of movement, such as steering
toward a side (e.g., left or right side) with more debris.
[0021] The debris sensor can include a piezoelectric sensor element
located proximate to a cleaning pathway of the cleaning apparatus
and responsive to a debris strike to generate a signal indicative
of such strike.
[0022] The debris sensor of the invention can also be incorporated
into a non-autonomous cleaning apparatus. This aspect of the
invention can include a piezoelectric sensor located proximate to a
cleaning pathway and responsive to a debris strike to generate a
debris signal indicative of such strike; and a processor responsive
to the debris signal to change an operative mode of the cleaning
apparatus. The change in operative mode could include illuminating
a user-perceptible indicator light, changing a power setting (e.g.,
higher power setting when more debris is encountered), or slowing
or reducing a movement speed of the apparatus.
[0023] A further aspect of the invention is a debris sensor,
including a piezoelectric element located proximate to or within a
cleaning pathway of the cleaning apparatus and responsive to a
debris strike to generate a first signal indicative of such strike;
and a processor operable to process the first signal to generate a
second signal representative of a characteristic of debris being
encountered by the cleaning apparatus. That characteristic could
be, for example, a quantity or volumetric parameter of the debris,
or a vector from a present location of the cleaning apparatus to an
area containing debris.
[0024] Another aspect of the invention takes advantage of the
motion of an autonomous cleaning device across a floor or other
surface, processing the debris signal in conjunction with knowledge
of the cleaning device's movement to calculate a debris gradient.
The debris gradient is representative of changes in debris strikes
count as the autonomous cleaning apparatus moves along a surface.
By examining the sign of the gradient (positive or negative,
associated with increasing or decreasing debris), an autonomous
cleaning device controller can continuously adjust the path or
pattern of movement of the device to clean a debris field most
effectively.
[0025] These and other aspects, features and advantages of the
invention will become more apparent from the following description,
in conjunction with the accompanying drawings, in which embodiments
of the invention are shown and described by way of illustrative
example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] A more complete understanding of the present invention and
the attendant features and advantages thereof may be had by
reference to the following detailed description of the invention
when considered in conjunction with the accompanying drawings
wherein:
[0027] FIG. 1 is a top-view schematic of an exemplary autonomous
cleaning device in which the debris sensor of the invention can be
employed.
[0028] FIG. 2 is a block diagram of exemplary hardware elements of
the robotic device of FIG. 1, including a debris sensor subsystem
of the invention.
[0029] FIG. 3 is a side view of the robotic device of FIG. 1,
showing a debris sensor according to the invention situated in a
cleaning or vacuum pathway, where it will be struck by debris
upswept by the main cleaning brush element.
[0030] FIG. 4 is an exploded diagram of a piezoelectric debris
sensor in accordance with the invention.
[0031] FIG. 5 is a schematic diagram of a debris sensor signal
processing architecture according to the present invention.
[0032] FIG. 6 is a schematic diagram of signal processing circuitry
for the debris sensor architecture of FIG. 5.
[0033] FIG. 7 is a schematic diagram showing the debris sensor in a
non-autonomous cleaning apparatus.
[0034] FIG. 8 is a flowchart of a method according to one practice
of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] While the debris sensor of the present invention can be
incorporated into a wide range of autonomous cleaning devices (and
indeed, into non-autonomous cleaning devices as shown by way of
example in FIG. 7), it will first be described in the context of an
exemplary autonomous cleaning device shown in FIGS. 1-3. Further
details of the structure, function and behavioral modes of such an
autonomous cleaning device are set forth in the patent applications
cited above in the Cross-Reference section, each of which is
incorporated herein by reference. Accordingly, the following
detailed description is organized into the following sections:
[0036] I. Exemplary Autonomous Cleaning Device
[0037] II. Behavioral Modes of an Autonomous Cleaning Device
[0038] III. Debris Sensor Structure
[0039] IV. Signal Processing
[0040] V. Conclusions
[0041] I. Autonomous Cleaning Device
[0042] Referring now to the drawings wherein like reference
numerals identify corresponding or similar elements throughout the
several views, FIG. 1 is a top-view schematic of an exemplary
autonomous cleaning device 100 in which a debris sensor according
to the present invention may be incorporated. FIG. 2 is a block
diagram of the hardware of the robot device 100 of FIG. 1.
[0043] Examples of hardware and behavioral modes (coverage
behaviors or patterns of movement for cleaning operations; escape
behaviors for transitory movement patterns; and safety behaviors
for emergency conditions) of an autonomous cleaning device 100
marketed by the iRobot Corporation of Burlington, Mass. under the
ROOMBA trademark, will next be described to provide a more complete
understanding of how the debris sensing system of the present
invention may be employed. However, the invention can also be
employed in non-autonomous cleaning devices, and an example is
described below in connection with FIG. 7.
[0044] In the following description, the terms "forward" and "fore"
are used to refer to the primary direction of motion (forward) of
the robotic device (see arrow identified by reference character
"FM" in FIG. 1). The fore/aft axis FA.sub.x of the robotic device
100 coincides with the medial diameter of the robotic device 100
that divides the robotic device 100 into generally symmetrical
right and left halves, which are defined as the dominant and
non-dominant sides, respectively.
[0045] An example of such a robotic cleaning device 100 has a
generally disk-like housing infrastructure that includes a chassis
102 and an outer shell 104 secured to the chassis 102 that define a
structural envelope of minimal height (to facilitate movement under
furniture). The hardware comprising the robotic device 100 can be
generally categorized as the functional elements of a power system,
a motive power system (also referred to herein as a "drive
system"), a sensor system, a control module, a side brush assembly,
or a self-adjusting cleaning head system, respectively, all of
which are integrated in combination with the housing
infrastructure. In addition to such categorized hardware, the
robotic device 100 further includes a forward bumper 106 having a
generally arcuate configuration and a nose-wheel assembly 108.
[0046] The forward bumper 106 (illustrated as a single component;
alternatively, a two-segment component) is integrated in movable
combination with the chassis 102 (by means of displaceable support
members pairs) to extend outwardly therefrom. Whenever the robotic
device 100 impacts an obstacle (e.g., wall, furniture) during
movement thereof, the bumper 106 is displaced (compressed) towards
the chassis 102 and returns to its extended (operating) position
when contact with the obstacle is terminated.
[0047] The nose-wheel assembly 108 is mounted in biased combination
with the chassis 102 so that the nose-wheel subassembly 108 is in a
retracted position (due to the weight of the robotic device 100)
during cleaning operations wherein it rotates freely over the
surface being cleaned. When the nose-wheel subassembly 108
encounters a drop-off during operation (e.g., descending stairs,
split-level floors), the nose-wheel assembly 108 is biased to an
extended position.
[0048] The hardware of the power system, which provides the energy
to power the electrically-operated hardware of the robotic device
100, comprises a rechargeable battery pack 110 (and associated
conduction lines, not shown) that is integrated in combination with
the chassis 102.
[0049] As shown in FIG. 1, the motive power system provides the
means that propels the robotic device 100 and operates the cleaning
mechanisms, e.g., side brush assembly and the self-adjusting
cleaning head system, during movement of the robotic device 100.
The motive power system comprises left and right main drive wheel
assemblies 112L, 112R, their associated independent electric motors
114L, 114R, and electric motors 116, 118 for operation of the side
brush assembly and the self-adjusting cleaning head subsystem,
respectively.
[0050] The electric motors 114L, 114R are mechanically coupled to
the main drive wheel assemblies 112L, 112R, respectively, and
independently operated by control signals generated by the control
module as a response to the implementation of a behavioral mode,
or, as discussed in greater detail below, in response to debris
signals generated by left and right debris sensors 125L, 125R shown
in FIG. 1.
[0051] Independent operation of the electric motors 114L, 114R
allows the main wheel assemblies 112L, 112R to be: (1) rotated at
the same speed in the same direction to propel the robotic device
100 in a straight line, forward or aft; (2) differentially rotated
(including the condition wherein one wheel assembly is not rotated)
to effect a variety of right and/or left turning patterns (over a
spectrum of sharp to shallow turns) for the robotic device 100; and
(3) rotated at the same speed in opposite directions to cause the
robotic device 100 to turn in place, i.e., "spin on a dime", to
provide an extensive repertoire of movement capability for the
robotic device 100.
[0052] As shown in FIG. 1, the sensor system comprises a variety of
different sensor units that are operative to generate signals that
control the behavioral mode operations of the robotic device 100.
The described robotic device 100 includes obstacle detection units
120, cliff detection units 122, wheel drop sensors 124, an
obstacle-following unit 126, a virtual wall omnidirectional
detector 128, stall-sensor units 130, main wheel encoder units 132,
and, in accordance with the present invention, left and right
debris sensors 125L and 125R described in greater detail below.
[0053] In the illustrated embodiment, the obstacle ("bump")
detection units 120 can be IR break beam sensors mounted in
combination with the displaceable support member pairs of the
forward bumper 106. These detection units 120 are operative to
generate one or more signals indicating relative displacement
between one or more support member pairs whenever the robotic
device 100 impacts an obstacle such that the forward bumper 106 is
compressed. These signals are processed by the control module to
determine an approximate point of contact with the obstacle
relative to the fore-aft axis FAX of the robotic device 100 (and
the behavioral mode(s) to be implemented).
[0054] The cliff detection units 122 are mounted in combination
with the forward bumper 106. Each cliff detection unit 122
comprises an IR emitter-detector pair configured and operative to
establish a focal point such that radiation emitted downwardly by
the emitter is reflected from the surface being traversed and
detected by the detector. If reflected radiation is not detected by
the detector, i.e., a drop-off is encountered, the cliff detection
unit 122 transmits a signal to the control module (which causes one
or more behavioral modes to be implemented).
[0055] A wheel drop sensor 124 such as a contact switch is
integrated in combination with each of the main drive wheel
assemblies 112L, 112R and the nose wheel assembly 108 and is
operative to generate a signal whenever any of the wheel assemblies
is in an extended position, i.e., not in contact with the surface
being traversed, (which causes the control module to implement one
ore more behavioral modes).
[0056] The obstacle-following unit 126 for the described embodiment
is an IR emitter-detector pair mounted on the `dominant` side
(right hand side of FIG. 1) of the robotic device 100. The
emitter-detector pair is similar in configuration to the cliff
detection units 112, but is positioned so that the emitter emits
radiation laterally from the dominant side of the robotic device
100. The unit 126 is operative to transmit a signal to the control
module whenever an obstacle is detected as a result of radiation
reflected from the obstacle and detected by the detector. The
control module, in response to this signal, causes one or more
behavioral modes to be implemented.
[0057] A virtual wall detection system for use in conjunction with
the described embodiment of the robotic device 100 comprises an
omnidirectional detector 128 mounted atop the outer shell 104 and a
stand-alone transmitting unit (not shown) that transmits an
axially-directed confinement beam. The stand-alone transmitting
unit is positioned so that the emitted confinement beam blocks an
accessway to a defined working area, thereby restricting the
robotic device 100 to operations within the defined working area
(e.g., in a doorway to confine the robotic device 100 within a
specific room to be cleaned). Upon detection of the confinement
beam, the omnidirectional detector 128 transmits a signal to the
control module (which causes one or more behavioral modes to be
implemented to move the robotic device 100 away from the
confinement beam generated by the stand-alone transmitting
unit).
[0058] A stall sensor unit 130 is integrated in combination with
each electric motor 114L, 114R, 116, 118 and operative to transmit
a signal to the control module when a change in current is detected
in the associated electric motor (which is indicative of a
dysfunctional condition in the corresponding driven hardware). The
control module is operative in response to such a signal to
implement one or more behavioral modes.
[0059] An IR encoder unit 132 (see FIG. 2) is integrated in
combination with each main wheel assembly 112L, 112R and operative
to detect the rotation of the corresponding wheel and transmit
signals corresponding thereto the control module (wheel rotation
can be used to provide an estimate of distance traveled for the
robotic device 100).
[0060] Control Module: Referring now to FIG. 2, the control module
comprises the microprocessing unit 135 that includes I/O ports
connected to the sensors and controllable hardware of the robotic
device 100, a microcontroller (such as a Motorola MC9512E128CPV
16-bit controller), and ROM and RAM memory. The I/O ports function
as the interface between the microcontroller and the sensor units
(including left and right debris sensors 125 discussed in greater
detail below) and controllable hardware, transferring signals
generated by the sensor units to the microcontroller and
transferring control (instruction) signals generated by the
microcontroller to the controllable hardware to implement a
specific behavioral mode.
[0061] The microcontroller is operative to execute instruction sets
for processing sensor signals, implementing specific behavioral
modes based upon such processed signals, and generating control
(instruction) signals for the controllable hardware based upon
implemented behavioral modes for the robotic device 100. The
cleaning coverage and control programs for the robotic device 100
are stored in the ROM of the microprocessing unit 135, which
includes the behavioral modes, sensor processing algorithms,
control signal generation algorithms and a prioritization algorithm
for determining which behavioral mode or modes are to be given
control of the robotic device 100. The RAM of the microprocessing
unit 135 is used to store the active state of the robotic device
100, including the ID of the behavioral mode(s) under which the
robotic device 100 is currently being operated and the hardware
commands associated therewith.
[0062] Referring again to FIG. 1, there is shown a brush assembly
140, configured and operative to entrain particulates outside the
periphery of the housing infrastructure and to direct such
particulates towards the self-adjusting cleaning head system. The
side brush assembly 140 provides the robotic device 100 with the
capability of cleaning surfaces adjacent to base-boards when the
robotic device is operated in an Obstacle-Following behavioral
mode. As shown in FIG. 1, the side brush assembly 140 is preferably
mounted in combination with the chassis 102 in the forward quadrant
on the dominant side of the robotic device 100.
[0063] The self-adjusting cleaning head system 145 for the
described robotic device 100 comprises a dual-stage brush assembly
and a vacuum assembly, each of which is independently powered by an
electric motor (reference numeral 118 in FIG. 1 actually identifies
two independent electric motors--one for the brush assembly and one
for the vacuum assembly). The cleaning capability of the robotic
device 100 is commonly characterized in terms of the width of the
cleaning head system 145 (see reference character W in FIG. 1).
[0064] Referring now to FIG. 3, in one embodiment of a robotic
cleaning device, the cleaning brush assembly comprises asymmetric,
counter-rotating flapper and main brush elements 92 and 94,
respectively, that are positioned forward of the vacuum assembly
inlet 84, and operative to direct particulate debris 127 into a
removable dust cartridge 86. As shown in FIG. 3, the autonomous
cleaning apparatus can also include left and right debris sensor
elements 125PS, which can be piezoelectric sensor elements, as
described in detail below. The piezoelectric debris sensor elements
125PS can be situated in a cleaning pathway of the cleaning device,
mounted, for example, in the roof of the cleaning head, so that
when struck by particles 127 swept up by the brush elements and/or
pulled up by vacuum, the debris sensor elements 125PS generate
electrical pulses representative of debris impacts and thus, of the
presence of debris in an area in which the autonomous cleaning
device is operating.
[0065] More particularly, in the arrangement shown in FIG. 3, the
sensor elements 125PS are located substantially at an axis AX along
which main and flapper brushes 94, 92 meet, so that particles
strike the sensor elements 125PS with maximum force.
[0066] As shown in FIG. 1, and described in greater detail below,
the robotic cleaning device can be fitted with left and right side
piezoelectric debris sensors, to generate separate left and right
side debris signals that can be processed to signal the robotic
device to turn in the direction of a "dirty" area.
[0067] The operation of the piezoelectric debris sensors, as well
as signal processing and selection of behavioral modes based on the
debris signals they generate, will be discussed below following a
brief discussion of general aspects of behavioral modes for the
cleaning device.
II. Behavioral Modes
[0068] The robotic device 100 can employ a variety of behavioral
modes to effectively clean a defined working area where behavioral
modes are layers of control systems that can be operated in
parallel. The microprocessor unit 135 is operative to execute a
prioritized arbitration scheme to identify and implement one or
more dominant behavioral modes for any given scenario based upon
inputs from the sensor system.
[0069] The behavioral modes for the described robotic device 100
can be characterized as: (1) coverage behavioral modes; (2) escape
behavioral modes; and (3) safety behavioral modes. Coverage
behavioral modes are primarily designed to allow the robotic device
100 to perform its cleaning operations in an efficient and
effective manner and the escape and safety behavioral modes are
priority behavioral modes implemented when a signal from the sensor
system indicates that normal operation of the robotic device 100 is
impaired, e.g., obstacle encountered, or is likely to be impaired,
e.g., drop-off detected.
[0070] Representative and illustrative coverage behavioral
(cleaning) modes for the robotic device 100 include: (1) a Spot
Coverage pattern; (2) an Obstacle-Following (or Edge-Cleaning)
Coverage pattern, and (3) a Room Coverage pattern. The Spot
Coverage pattern causes the robotic device 100 to clean a limited
area within the defined working area, e.g., a high-traffic area. In
a preferred embodiment the Spot Coverage pattern is implemented by
means of a spiral algorithm (but other types of self-bounded area
algorithms, e.g., polygonal, can be used). The spiral algorithm,
which causes outward spiraling (preferred) or inward spiraling
movement of the robotic device 100, is implemented by control
signals from the microprocessing unit 135 to the main wheel
assemblies 112L, 112R to change the turn radius/radii thereof as a
function of time (thereby increasing/decreasing the spiral movement
pattern of the robotic device 100).
[0071] The robotic device 100 is operated in the Spot Coverage
pattern for a predetermined or random period of time, for a
predetermined or random distance (e.g., a maximum spiral distance)
and/or until the occurrence of a specified event, e.g., activation
of one or more of the obstacle detection units 120 (collectively a
transition condition). Once a transition condition occurs, the
robotic device 100 can implement or transition to a different
behavioral mode, e.g., a Straight Line behavioral mode (in a
preferred embodiment of the robotic device 100, the Straight Line
behavioral mode is a low priority, default behavior that propels
the robot in an approximately straight line at a preset velocity of
approximately 0.306 m/s) or a Bounce behavioral mode in combination
with a Straight Line behavioral mode.
[0072] If the transition condition is the result of the robotic
device 100 encountering an obstacle, the robotic device 100 can
take other actions in lieu of transitioning to a different
behavioral mode. The robotic device 100 can momentarily implement a
behavioral mode to avoid or escape the obstacle and resume
operation under control of the spiral algorithm (i.e., continue
spiraling in the same direction). Alternatively, the robotic device
100 can momentarily implement a behavioral mode to avoid or escape
the obstacle and resume operation under control of the spiral
algorithm (but in the opposite direction-reflective spiraling).
[0073] The Obstacle-Following Coverage pattern causes the robotic
device 100 to clean the perimeter of the defined working area,
e.g., a room bounded by walls, and/or the perimeter of an obstacle
(e.g., furniture) within the defined working area. Preferably the
robotic device 100 of FIG. 1 utilizes obstacle-following unit 126
(see FIG. 1) to continuously maintain its position with respect to
an obstacle, e.g., wall, furniture, so that the motion of the
robotic device 100 causes it to travel adjacent to and
concomitantly clean along the perimeter of the obstacle. Different
embodiments of the obstacle-following unit 126 can be used to
implement the Obstacle-Following behavioral pattern.
[0074] In a first embodiment, the obstacle-following unit 126 is
operated to detect the presence or absence of the obstacle. In an
alternative embodiment, the obstacle-following unit 126 is operated
to detect an obstacle and then maintain a predetermined distance
between the obstacle and the robotic device 100. In the first
embodiment, the microprocessing unit 135 is operative, in response
to signals from the obstacle-following unit, to implement small CW
or CCW turns to maintain its position with respect to the obstacle.
The robotic device 100 implements a small CW when the robotic
device 100 transitions from obstacle detection to non-detection
(reflection to non-reflection) or to implement a small CCW turn
when the robotic device 100 transitions from non-detection to
detection (non-reflection to reflection). Similar turning behaviors
are implemented by the robotic device 100 to maintain the
predetermined distance from the obstacle.
[0075] The robotic device 100 is operated in the Obstacle-Following
behavioral mode for a predetermined or random period of time, for a
predetermined or random distance (e.g., a maximum or minimum
distance) and/or until the occurrence of a specified event, e.g.,
activation of one or more of the obstacle detection units 120 a
predetermined number of times (collectively a transition
condition). In certain embodiments, the microprocessor 135 will
cause the robotic device to implement an Align behavioral mode upon
activation of the obstacle-detection units 120 in the
Obstacle-Following behavioral mode wherein the implements a minimum
angle CCW turn to align the robotic device 100 with the
obstacle.
[0076] The Room Coverage pattern can be used by the robotic device
100 to clean any defined working area that is bounded by walls,
stairs, obstacles or other barriers (e.g., a virtual wall unit). A
preferred embodiment for the Room Coverage pattern comprises the
Random-Bounce behavioral mode in combination with the Straight Line
behavioral mode. Initially, the robotic device 100 travels under
control of the Straight-Line behavioral mode, i.e., straight-line
algorithm (main drive wheel assemblies 112L, 112R operating at the
same rotational speed in the same direction) until an obstacle is
encountered. Upon activation of one or more of the obstacle
detection units 120, the microprocessing unit 135 is operative to
compute an acceptable range of new directions based upon the
obstacle detection unit(s) 126 activated. The microprocessing unit
135 selects a new heading from within the acceptable range and
implements a CW or CCW turn to achieve the new heading with minimal
movement. In some embodiments, the new turn heading may be followed
by forward movement to increase the cleaning efficiency of the
robotic device 100. The new heading may be randomly selected across
the acceptable range of headings, or based upon some statistical
selection scheme, e.g., Gaussian distribution. In other embodiments
of the Room Coverage behavioral mode, the microprocessing unit 135
can be programmed to change headings randomly or at predetermined
times, without input from the sensor system.
[0077] The robotic device 100 is operated in the Room Coverage
behavioral mode for a predetermined or random period of time, for a
predetermined or random distance (e.g., a maximum or minimum
distance) and/or until the occurrence of a specified event, e.g.,
activation of the obstacle-detection units 120 a predetermined
number of times (collectively a transition condition).
[0078] By way of example, the robotic device 100 can include four
escape behavioral modes: a Turn behavioral mode, an Edge behavioral
mode, a Wheel Drop behavioral mode, and a Slow behavioral mode. One
skilled in the art will appreciate that other behavioral modes can
be utilized by the robotic device 100. One or more of these
behavioral modes may be implemented, for example, in response to a
current rise in one of the electric motors 116, 118 of the side
brush assembly 140 or dual-stage brush assembly above a low or high
stall threshold, forward bumper 106 in compressed position for
determined time period, detection of a wheel-drop event.
[0079] In the Turn behavioral mode, the robotic device 100 turns in
place in a random direction, starting at higher velocity (e.g.,
twice normal turning velocity) and decreasing to a lower velocity
(one-half normal turning velocity), i.e., small panic turns and
large panic turns, respectively. Low panic turns are preferably in
the range of 45.degree. to 90.degree., large panic turns are
preferably in the range of 90.degree. to 270.degree.. The Turn
behavioral mode prevents the robotic device 100 from becoming stuck
on room impediments, e.g., high spot in carpet, ramped lamp base,
from becoming stuck under room impediments, e.g., under a sofa, or
from becoming trapped in a confined area.
[0080] In the Edge behavioral mode follows the edge of an obstacle
unit it has turned through a predetermined number of degrees, e.g.,
60.degree., without activation of any of the obstacle detection
units 120, or until the robotic device has turned through a
predetermined number of degrees, e.g., 170.degree., since
initiation of the Edge behavioral mode. The Edge behavioral mode
allows the robotic device 100 to move through the smallest possible
openings to escape from confined areas.
[0081] In the Wheel Drop behavioral mode, the microprocessor 135
reverses the direction of the main wheel drive assemblies 112L,
112R momentarily, then stops them. If the activated wheel drop
sensor 124 deactivates within a predetermined time, the
microprocessor 135 then reimplements the behavioral mode that was
being executed prior to the activation of the wheel drop sensor
124.
[0082] In response to certain events, e.g., activation of a wheel
drop sensor 124 or a cliff detector 122, the Slow behavioral mode
is implemented to slowed down the robotic device 100 for a
predetermined distance and then ramped back up to its normal
operating speed.
[0083] When a safety condition is detected by the sensor subsystem,
e.g., a series of brush or wheel stalls that cause the
corresponding electric motors to be temporarily cycled off, wheel
drop sensor 124 or a cliff detection sensor 122 activated for
greater that a predetermined period of time, the robotic device 100
is generally cycled to an off state. In addition, an audible alarm
may be generated.
[0084] The foregoing description of behavioral modes for the
robotic device 100 is merely representative of the types of
operating modes that can be implemented by the robotic device 100.
One skilled in the art will appreciate that the behavioral modes
described above can be implemented in other combinations and/or
circumstances, and other behavioral modes and patterns of movement
are also possible.
III. Debris Sensor Structure and Operation
[0085] As shown in FIGS. 1-3, in accordance with the present
invention, an autonomous cleaning device (and similarly, a
non-autonomous cleaning device as shown by way of example in FIG.
7) can be improved by incorporation of a debris sensor. In the
embodiment illustrated in FIGS. 1 and 3, the debris sensor
subsystem comprises left and right piezoelectric sensing elements
125L, 125R situated proximate to or within a cleaning pathway of a
cleaning device, and electronics for processing the debris signal
from the sensor for forwarding to a microprocessor 135 or other
controller.
[0086] When employed in an autonomous, robot cleaning device, the
debris signal from the debris sensor can be used to select a
behavioral mode (such as entering into a spot cleaning mode),
change an operational condition (such as speed, power or other),
steer in the direction of debris (particularly when spaced-apart
left and right debris sensors are used to create a differential
signal), or take other actions.
[0087] A debris sensor according to the present invention can also
be incorporated into a non-autonomous cleaning device. When
employed in a non-autonomous cleaning device such as, for example,
an otherwise relatively conventional vacuum cleaner 700 like that
shown in FIG. 7, the debris signal 706 generated by a piezoelectric
debris sensor 704PS situated within a cleaning or vacuum pathway of
the device can be employed by a controlling microprocessor 708 in
the body of the vacuum cleaner 702 to generate a user-perceptible
signal (such as by lighting a light 710), to increase power from
the power system 703, or take some combination of actions (such as
lighting a "high power" light and simultaneously increasing
power).
[0088] The algorithmic aspects of the operation of the debris
sensor subsystem are summarized in FIG. 8. As shown therein, a
method according to the invention can include detecting left and
right debris signals representative of debris strikes, and thus, of
the presence, quantity or volume, and direction of debris (802);
selecting an operational mode or pattern of movement (such as Spot
Coverage) based on the debris signal values (804); selecting a
direction of movement based on differential left/right debris
signals (e.g., steering toward the side with more debris) (806);
generating a user-perceptible signal representative of the presence
of debris or other characteristic (e.g., by illuminating a
user-perceptible LED) (808); or otherwise varying or controlling an
operational condition, such as power (810).
[0089] A further practice of the invention takes advantage of the
motion of an autonomous cleaning device across a floor or other
surface, processing the debris signal in conjunction with knowledge
of the cleaning device's movement to calculate a debris gradient
(812 in FIG. 8). The debris gradient is representative of changes
in debris strikes count as the autonomous cleaning apparatus moves
along a surface. By examining the sign of the gradient (positive or
negative, associated with increasing or decreasing debris), an
autonomous cleaning device controller can continuously adjust the
path or pattern of movement of the device to clean a debris field
most effectively (812).
[0090] Piezoelectric Sensor: As noted above, a piezoelectric
transducer element can be used in the debris sensor subsystem of
the invention. Piezoelectric sensors provide instantaneous response
to debris strikes and are relatively immune to accretion that would
degrade the performance of an optical debris sensor typical of the
prior art.
[0091] An example of a piezoelectric transducer 125PS is shown in
FIG. 4. Referring now to FIG. 4, the piezoelectric sensor element
125PS can include one or more 0.20 millimeter thick, 20 millimeter
diameter brass disks 402 with the piezoelectric material and
electrodes bonded to the topside (with a total thickness of 0.51
mm), mounted to an elastomer pad 404, a plastic dirt sensor cap
406, a debris sensor PC board with associated electronics 408,
grounded metal shield 410, and retained by mounting screws (or
bolts or the like) 412 and elastomer grommets 414. The elastomer
grommets provide a degree of vibration dampening or isolation
between the piezoelectric sensor element 125PS and the cleaning
device.
[0092] In the example shown in FIG. 4, a rigid piezoelectric disk,
of the type typically used as inexpensive sounders, can be used.
However, flexible piezoelectric film can also be advantageously
employed. Since the film can be produced in arbitrary shapes, its
use affords the possibility of sensitivity to debris across the
entire cleaning width of the cleaning device, rather than
sensitivity in selected areas where, for example, the disks may be
located. Conversely, however, film is at present substantially more
expensive and is subject to degradation over time. In contrast,
brass disks have proven to be extremely robust.
[0093] The exemplary mounting configuration shown in FIG. 4 is
substantially optimized for use within a platform that is
mechanically quite noisy, such as an autonomous vacuum cleaner like
that shown in FIG. 3. In such a device, vibration dampening or
isolation of the sensor is extremely useful. However, in an
application involving a non-autonomous cleaning device such as a
canister-type vacuum cleaner like that shown in FIG. 7, the
dampening aspects of the mounting system of FIG. 4 may not be
necessary. In a non-autonomous cleaning apparatus, an alternative
mounting system may involve heat staking the piezoelectric element
directly to its housing. In either case, a key consideration for
achieving enhanced performance is the reduction of the surface area
required to clamp, bolt, or otherwise maintain the piezoelectric
element in place. The smaller the footprint of this clamped "dead
zone", the more sensitive the piezoelectric element will be.
[0094] In operation, debris thrown up by the cleaning brush
assembly (e.g., brush 94 of FIG. 3), or otherwise flowing through a
cleaning pathway within the cleaning device (e.g., vacuum
compartment 104 of FIG. 3) can strike the bottom, all-brass side of
the sensor 125PS (see FIG. 3). In an autonomous cleaning device, as
shown in FIG. 3, the debris sensor 125PS can be located
substantially at an axis AX along which main brush 94 and flapper
brush 92 meet, so that the particles 127 are thrown up and strike
the sensor 125PS with maximum force.
[0095] As is well known, a piezoelectric sensor converts mechanical
energy (e.g., the kinetic energy of a debris strike and vibration
of the brass disk) into electrical energy--in this case, generating
an electrical pulse each time it is struck by debris--and it is
this electrical pulse that can be processed and transmitted to a
system controller (e.g., controller 135 of FIGS. 1 and 2 or 708 of
FIG. 8) to control or cause a change in operational mode, in
accordance with the invention. Piezoelectric elements are typically
designed for use as audio transducers, for example, to generate
beep tones. When an AC voltage is applied, they vibrate
mechanically in step with the AC waveform, and generate an audible
output. Conversely, if they are mechanically vibrated, they produce
an AC voltage output. This is the manner in which they are employed
in the present invention. In particular, when an object first
strikes the brass face of the sensor, it causes the disk to flex
inward, which produces a voltage pulse.
[0096] Filtering: However, since the sensor element 125PS is in
direct or indirect contact with the cleaning device chassis or body
through its mounting system (see FIGS. 3 and 4), it is subject to
the mechanical vibrations normally produced by motors, brushes,
fans and other moving parts when the cleaning device is
functioning. This mechanical vibration can cause the sensor to
output an undesirable noise signal that can be larger in amplitude
than the signal created by small, low mass debris (such as crushed
black pepper) striking the sensor. The end result is that the
sensor would output a composite signal composed of lower frequency
noise components (up to approximately 16 kHz) and higher frequency,
possibly lower amplitude, debris-strike components (greater than 30
kHz, up to hundreds of kHz). Thus, it is useful to provide a way to
filter out extraneous signals.
[0097] Accordingly, as described below, an electronic filter is
used to greatly attenuate the lower frequency signal components to
improve signal-to-noise performance. Examples of the architecture
and circuitry of such filtering and signal processing elements will
next be described in connection with FIGS. 5 and 6.
IV. Signal Processing
[0098] FIG. 5 is a schematic diagram of the signal processing
elements of a debris sensor subsystem in one practice of the
invention.
[0099] As noted above, one purpose of a debris sensor is to enable
an autonomous cleaning apparatus to sense when it is picking up
debris or otherwise encountering a debris field. This information
can be used as an input to effect a change in the cleaning behavior
or cause the apparatus to enter a selected operational or
behavioral mode, such as, for example, the spot cleaning mode
described above when debris is encountered. In an non-autonomous
cleaning apparatus like that shown in FIG. 7, the debris signal 706
from the debris sensor 704PS can be used to cause a
user-perceptible light 710 to be illuminated (e.g., to signal to
the user that debris is being encountered), to raise power output
from the power until 703 to the cleaning systems, or to cause some
other operational change or combination of changes (e.g., lighting
a user-perceptible "high power" light and simultaneously raising
power).
[0100] Moreover, as noted above, two debris sensor circuit modules
(i.e., left and right channels like 125L and 125R of FIG. 1) can be
used to enable an autonomous cleaning device to sense the
difference between the amounts of debris picked up on the right and
left sides of the cleaning head assembly. For example, if the robot
encounters a field of dirt off to its left side, the left side
debris sensor may indicate debris hits, while the right side sensor
indicates no (or a low rate of) debris hits. This differential
output could be used by the microprocessor controller of an
autonomous cleaning device (such as controller 135 of FIGS. 1 and
2) to steer the device in the direction of the debris (e.g., to
steer left if the left-side debris sensor is generating higher
signal values than the right-side debris sensor); to otherwise
choose a vector in the direction of the debris; or to otherwise
select a pattern of movement or behavior pattern such as spot
coverage or other.
[0101] Thus, FIG. 5 illustrates one channel (for example, the
left-side channel) of a debris sensor subsystem that can contain
both left and right side channels. The right side channel is
substantially identical, and its structure and operation will
therefore be understood from the following discussion.
[0102] As shown in FIG. 5, the left channel consists of a sensor
element (piezoelectric disk) 402, an acoustic vibration filter/RFI
filter module 502, a signal amplifier 504, a reference level
generator 506, an attenuator 508, a comparator 510 for comparing
the outputs of the attenuator and reference level generator, and a
pulse stretcher 512. The output of the pulse stretcher is a logic
level output signal to a system controller like the processor 135
shown in FIG. 2; i.e., a controller suitable for use in selecting
an operational behavior.
[0103] The Acoustic Vibration Filter/RFI Filter block 502 can be
designed to provide significant attenuation (in one embodiment,
better than 45 dB Volts), and to block most of the lower frequency,
slow rate of change mechanical vibration signals, while permitting
higher frequency, fast rate of change debris-strike signals to
pass. However, even though these higher frequency signals get
through the filter, they are attenuated, and thus require
amplification by the Signal Amplifier block 504.
[0104] In addition to amplifying the desired higher frequency
debris strike signals, the very small residual mechanical noise
signals that do pass through the filter also get amplified, along
with electrical noise generated by the amplifier itself, and any
radio frequency interference (RFI) components generated by the
motors and radiated through the air, or picked up by the sensor and
its conducting wires. The signal amplifier's high frequency
response is designed to minimize the amplification of very high
frequency RFI. This constant background noise signal, which has
much lower frequency components than the desired debris strike
signals, is fed into the Reference Level Generator block 506. The
purpose of module 506 is to create a reference signal that follows
the instantaneous peak value, or envelope, of the noise signal. It
can be seen in FIG. 5 that the signal of interest, i.e., the signal
that results when debris strikes the sensor, is also fed into this
block. Thus, the Reference Level Generator block circuitry is
designed so that it does not respond quickly enough to high
frequency, fast rate of change debris-strike signals to be able to
track the instantaneous peak value of these signals. The resulting
reference signal will be used to make a comparison as described
below.
[0105] Referring again to FIG. 5, it will be seen that the signal
from amplifier 504 is also fed into the Attenuator block. This is
the same signal that goes to the Reference Level Generator 506, so
it is a composite signal containing both the high frequency signal
of interest (i.e., when debris strikes the sensor) and the lower
frequency noise. The Attenuator 508 reduces the amplitude of this
signal so that it normally is below the amplitude of the signal
from the Reference Level Generator 506 when no debris is striking
the sensor element.
[0106] The Comparator 510 compares the instantaneous voltage
amplitude value of the signal from the Attenuator 508 to the signal
from the Reference Level Generator 506. Normally, when the cleaning
device operating is running and debris are not striking the sensor
element, the instantaneous voltage coming out of the Reference
Level Generator 506 will be higher than the voltage coming out of
the Attenuator block 508. This causes the Comparator block 510 to
output a high logic level signal (logic one), which is then
inverted by the Pulse Stretcher block 512 to create a low logic
level (logic zero).
[0107] However, when debris strikes the sensor, the voltage from
the Attenuator 508 exceeds the voltage from the Reference Level
Generator 506 (since this circuit cannot track the high frequency,
fast rate of change signal component from the Amplifier 504) and
the signal produced by a debris strike is higher in voltage
amplitude than the constant background mechanical noise signal
which is more severely attenuated by the Acoustic Vibration Filter
502. This causes the comparator to momentarily change state to a
logic level zero. The Pulse Stretcher block 512 extends this very
brief (typically under 10-microsecond) event to a constant 1
millisecond (+0.3 mS, -0 mS) event, so as to provide the system
controller (e.g., controller 135 of FIG. 2) sufficient time to
sample the signal.
[0108] When the system controller "sees" this 1-millisecond logic
zero pulse, it interprets the event as a debris strike.
[0109] Referring now to the RFI Filter portion of the Acoustic
Vibration Filter/RFI Filter block 502, this filter serves to
attenuate the very high frequency radiated electrical noise (RFI),
which is generated by the motors and motor driver circuits.
[0110] In summary, the illustrated circuitry connected to the
sensor element uses both amplitude and frequency information to
discriminate a debris strike (representative of the cleaning device
picking up debris) from the normal background mechanical noise also
picked up by the sensor element, and the radiated radio frequency
electrical noise produced by the motors and motor driver circuits.
The normal, though undesirable, constant background noise is used
to establish a dynamic reference that prevents false debris-strike
indications while maintaining a good signal-to-noise ratio.
[0111] In practice, the mechanical mounting system for the sensor
element (see FIG. 4) is also designed to help minimize the
mechanical acoustic noise vibration coupling that affects the
sensor element.
[0112] Signal Processing Circuitry: FIG. 6 is a detailed schematic
diagram of exemplary debris sensor circuitry. Those skilled in the
art will understand that in other embodiments, the signal
processing can be partially or entirely contained and executed
within the software of the microcontroller 135. With reference to
FIG. 6, the illustrated example of suitable signal processing
circuitry contains the following elements, operating in accordance
with the following description:
[0113] The ground referenced, composite signal from the
piezoelectric sensor disk (see piezoelectric disk 402 of FIG. 4) is
fed into the capacitor C1, which is the input to the 5-pole, high
pass, passive R-C filter designed to attenuate the low frequency,
acoustic mechanical vibrations conducted into the sensor through
the mounting system. This filter has a 21.5 kHz, -3 dB corner
frequency rolling off at -100 dB/Decade. The output of this filter
is fed to a signal pole, low pass, passive R-C filter designed to
attenuate any very high frequency RFI. This filter has a 1.06 MHz,
-3 dB corner frequency rolling off at -20 dB/Decade. The output of
this filter is diode clamped by D1 and D2 in order to protect U1
from high voltage transients in the event the sensor element
sustains a severe strike that generates a voltage pulse greater
than the amplifier's supply rails. The DC biasing required for
signal-supply operation for the amplifier chain and subsequent
comparator circuitry is created by R5 and R6. These two resistor
values are selected such that their thevenin impedance works with
C5 to maintain the filter's fifth pole frequency response
correctly.
[0114] U1A, U1B and their associated components form a two stage,
ac-coupled, non-inverting amplifier with a theoretical AC gain of
441. C9 and C10 serve to minimize gain at low frequencies while C7
and C8 work to roll the gain off at RFI frequencies. The net
theoretical frequency response from the filter input to the
amplifier output is a single pole high pass response with -3 dB at
32.5 kHz, -100 dB/Decade, and a 2-pole low pass response with break
frequencies at 100 kHz, -32 dB/Decade, and 5.4 MHz, -100 dB/Decade,
together forming a band-pass filter.
[0115] The output from the amplifier is split, with one output
going into R14, and the other to the non-inverting input of U1C.
The signal going into R14 is attenuated by the R14-R15 voltage
divider, and then fed into the inverting input of comparator U2A.
The other signal branch from the output of U1B is fed into the
non-inverting input of amplifier U1C. U1C along with U1D and the
components therebetween (as shown in FIG. 2) form a half-wave,
positive peak detector. The attack and decay times are set by R13
and R12, respectively. The output from this circuit is fed to the
non-inverting input of U2A through R16. R16 along with R19 provide
hysteresis to improve switching time and noise immunity. U2A
functions to compare the instantaneous value between the output of
the peak detector to the output of the R14-R15 attenuator.
[0116] Normally, when debris is not striking the sensor, the output
of the peak detector will be greater in amplitude than the output
of the attenuator network. When debris strikes the sensor, a high
frequency pulse is created that has a higher amplitude coming out
of the front-end high pass filter going into U1A than the lower
frequency mechanical noise signal component. This signal will be
larger in amplitude, even after coming out of the R14-R15
attenuator network, than the signal coming out of the peak
detector, because the peak detector cannot track high-speed pulses
due to the component values in the R13, C11, R12 network. The
comparator then changes state from high to low for as long as the
amplitude of the debris-strike pulse stays above the dynamic, noise
generated, reference-level signal coming out of the peak detector.
Since this comparator output pulse can be too short for the system
controller to see, a pulse stretcher is used.
[0117] The pulse stretcher is a one-shot monostable design with a
lockout mechanism to prevent re-triggering until the end of the
timeout period. The output from U2A is fed into the junction of C13
and Q1. C13 couples the signal into the monostable formed by U2C
and its associated components. Q1 functions as the lockout by
holding the output of U2A low until the monostable times out. The
timeout period is set by the time constant formed by R22, C12 and
R18, and the reference level set by the R20-R21 voltage divider.
This time can adjusted for 1 mS, +0.3 mS, -0.00 mS as dictated by
the requirements of the software used by the
controller/processor.
[0118] Power for the debris sensor circuit is provided by U3 and
associated components. U3 is a low power linear regulator that
provides a 5-volt output. The unregulated voltage from the robot's
onboard battery provides the power input.
[0119] When required, circuit adjustments can be set by R14 and
R12. These adjustments will allow the circuit response to be tuned
in a short period of time
[0120] In a production device of this kind, it is expected that
power into, and signal out of the debris sensor circuit printed
circuit board (PCB) will be transferred to the main board via
shielded cable. Alternatively, noise filters may be substituted for
the use of shielded cable, reducing the cost of wiring. The cable
shield drain wire can be grounded at the sensor circuit PCB side
only. The shield is not to carry any ground current. A separate
conductor inside the cable will carry power ground. To reduce
noise, the production sensor PCB should have all components on the
topside with solid ground plane on the bottom side. The sensor PCB
should be housed in a mounting assembly that has a grounded metal
shield that covers the topside of the board to shield the
components from radiated noise pick up from the robot's motors. The
piezoelectric sensor disk can be mounted under the sensor circuit
PCB on a suitable mechanical mounting system, such as that shown in
FIG. 4, in order to keep the connecting leads as short as possible
for noise immunity.
V. CONCLUSIONS
[0121] The invention provides a debris sensor that is not subject
to degradation by accretion of debris, but is capable of
instantaneously sensing and responding to debris strikes, and thus
immediately responsive to debris on a floor or other surface to be
cleaned, with reduced sensitivity to variations in airflow,
instantaneous power, or other operational conditions of the
cleaning device.
[0122] When employed as described herein, the invention enables an
autonomous cleaning device to control its operation or select from
among operational modes, patterns of movement or behaviors
responsive to detected debris, for example, by steering the device
toward "dirtier" areas based on signals generated by the debris
sensor.
[0123] The debris sensor can also be employed in non-autonomous
cleaning devices to control, select or vary operational modes of
either an autonomous or non-autonomous cleaning apparatus.
[0124] In addition, the disclosed signal processing architecture
and circuitry is particularly useful in conjunction with a
piezoelectric debris sensor to provide high signal to noise
ratios.
[0125] Those skilled in the art will appreciate that a wide range
of modifications and variations of the present invention are
possible and within the scope of the invention. The debris sensor
can also be employed for purposes, and in devices, other than those
described herein. Accordingly, the foregoing is presented solely by
way of example, and the scope of the invention is limited solely by
the appended claims.
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