U.S. patent application number 16/496602 was filed with the patent office on 2021-01-07 for a robotic work tool and a method for use in a robotic work tool comprising a lift and collision detection.
The applicant listed for this patent is Husqvarna AB. Invention is credited to Jonathan Bjorn, Anders Hjalmarsson, Fredrik Kallstrom, Mats Svensson, Par-Ola Svensson.
Application Number | 20210000008 16/496602 |
Document ID | / |
Family ID | |
Filed Date | 2021-01-07 |
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United States Patent
Application |
20210000008 |
Kind Code |
A1 |
Svensson; Mats ; et
al. |
January 7, 2021 |
A Robotic Work Tool and a Method for Use in a Robotic Work Tool
Comprising a Lift and Collision Detection
Abstract
A robotic work tool (100) comprising a chassis (110), a body
(120) and a controller (400) for controlling operation of the
robotic work tool (100) and at least one three-dimensional sensor
arrangement (200) for detecting relative movement of the body (100)
and the chassis (110), wherein the sensor arrangement (200)
comprises a sensor element (210) arranged in one of the body (120)
and the chassis (110) and a detection element (220) arranged in the
other of the body (120) and the chassis (110), wherein the
controller (400) is configured to: receive sensor input indicating
relative movement of the sensor element (210) and the detection
element (220) and; determine, from the sensor input, whether a
collision or a lift has been detected.
Inventors: |
Svensson; Mats; (Huskvarna,
SE) ; Svensson; Par-Ola; (Foreserum, SE) ;
Kallstrom; Fredrik; (Huskvarna, SE) ; Bjorn;
Jonathan; (Jonkoping, SE) ; Hjalmarsson; Anders;
(Granna, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Husqvarna AB |
Huskvarna |
|
SE |
|
|
Appl. No.: |
16/496602 |
Filed: |
March 13, 2018 |
PCT Filed: |
March 13, 2018 |
PCT NO: |
PCT/SE2018/050240 |
371 Date: |
September 23, 2019 |
Current U.S.
Class: |
1/1 |
International
Class: |
A01D 34/00 20060101
A01D034/00; A01D 75/18 20060101 A01D075/18 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2017 |
SE |
1750347-5 |
Aug 23, 2017 |
SE |
1751013-2 |
Claims
1. A robotic work tool comprising a chassis, a body and a
controller for controlling operation of the robotic work tool and
at least one three-dimensional sensor arrangement for detecting
relative movement of the body and the chassis, wherein the sensor
arrangement comprises a sensor element arranged in one of the body
and the chassis and a detection element arranged in the other of
the body and the chassis, wherein the controller is configured to:
receive sensor input indicating relative movement of the sensor
element and the detection element; and determine, from the sensor
input, whether a collision or a lift has been detected.
2. The robotic work tool according to claim 1, wherein said sensor
element is configured to sense the position of the detection
element in three dimensions.
3. The robotic work tool according to claim 1, wherein the
detection element is a magnet and the sensor element is a
three-dimensional sensor configured to detect magnetic field in a
plane and in a direction, which is normal to the plane.
4. The robotic work tool according to claim 1, wherein the
detection element is a magnet and the sensor element is configured
to detect the magnitude and direction in three-dimensional space of
the magnetic field of the magnet, and wherein the sensor element
comprises a Hall sensor.
5. (canceled)
6. The robotic work tool according to claim 2, wherein the sensor
element is configured as an integrated unit encapsulated in a
single integrated circuit package.
7. The robotic work tool according to claim 1, wherein the
three-dimensional sensor arrangement is positioned, as seen from
above, at a distance from a geometrical center of the robotic work
tool.
8. The robotic work tool according to claim 1, wherein the
controller is configured to receive sensor input indicating lateral
movement of the sensor element and the detection element relative
each other, and in response thereto, determine that the collision
has been detected.
9. The robotic work tool according to claim 1, wherein said at
least one three-dimensional sensor arrangement comprises a first
and a second three-dimensional sensor arrangement, each of said
first and second three-dimensional sensor arrangements comprising a
respective sensor element arranged in one of the body and the
chassis and a respective detection element arranged in the other of
the body and the chassis.
10. The robotic work tool according to claim 1, wherein the
controller is configured to determine, from the sensor input, the
direction of the collision.
11. The robotic work tool according to claim 1, wherein the
controller is configured to receive sensor input indicating
vertical movement of a sensor element and the detection element
relative each other, and in response thereto, determine that the
lift has been detected.
12. The robotic work tool according to claim 1, wherein the
controller is configured to receive sensor input indicating lateral
and vertical movement of the sensor element and the detection
element relative each other and, in response thereto, determine
whether collision or lift has been detected by comparing the sensor
input with a threshold value.
13. The robotic work tool according to claim 1, comprising at least
one suspension device for movably supporting the body on the
chassis, the suspension device comprising an elongate, rigid
support member having a first end that is supported on the chassis
and a second end that supports the body, wherein the elongate
support member is extendable and pivotal such that the body is
movable laterally and vertically relative to the chassis.
14. The robotic work tool according to claim 13, wherein the first
end of the elongate support member is configured to be pivotally
supported on the chassis and the second end of the elongate support
member is joined to the body.
15. The robotic work tool according to claim 13, wherein the
elongate support member comprises a base member and a lift member,
respectively configured such that at least a portion of one of the
base member and the lift member is slidably receivable in the other
of the base member and the lift member, so that the elongate
support member is telescopically extendable.
16. The robotic work tool according to claim 15, wherein the
elongate support member comprises a first biasing element arranged
to bias the lift member towards the base member.
17. The robotic work tool according to claim 16, wherein the base
member comprises an elongate guide opening and wherein the first
biasing element is arranged in the base member and comprises a
guide element that extends through the elongate guide opening and
is attached to the lift member.
18. The robotic work tool according to claim 13, wherein the
suspension device comprises a second biasing element arranged to
bias the elongate support member from a pivoted position to an
upright position, or wherein the three-dimensional sensor
arrangement and the at least one suspension device are arranged
laterally separated from each other.
19. (canceled)
20. The robotic work tool according to claim 13, comprising at
least a first and a second suspension device, wherein a number of
the suspension devices is greater than a number of the
three-dimensional sensor arrangements.
21. (canceled)
22. The robotic work tool according to claim 13, comprising at
least a first and a second suspension device and wherein a three
dimensional sensor arrangement is arranged between the first and
the second suspension devices, and wherein the robotic work tool
comprises a robotic lawnmower.
23. (canceled)
24. A method for use in a robotic work tool comprising a chassis; a
body; a controller for controlling operation of the robotic work
tool and at least one three-dimensional sensor arrangement for
detecting relative movement of the body and the chassis, wherein
the sensor arrangement comprises a sensor element arranged in one
of the body and the chassis and a detection element arranged in the
other of the body and the chassis, the method comprising: receiving
sensor input indicating relative movement of the sensor element and
the detection element; and determining, from the sensor input, that
a collision or a lift has been detected.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a robotic work tool, such
a lawn mower and to a method for improved lift and collision
detection to be executed by a robotic work tool.
BACKGROUND ART
[0002] Automated or robotic power tools such as robotic lawnmowers
are becoming increasingly more popular. In a typical deployment the
robotic work tool may not be aware of objects in the work area,
stationary or movable, that the robotic work tool may collide with.
Therefore, collision detection is necessary in order to enable the
robotic work tool to adapt its operation when a collision is
detected, to avoid the robotic work tool from simply stopping in
front of the object by trying to push through it.
[0003] Likewise, it is important also from a safety perspective to
detect that a robotic work tool is lifted, so that the operating
member or tool, typically a rotating knife of a robotic lawnmower
may be turned off to prevent risk of injuring an operator. The lift
and collision detection is usually achieved by arranging the cover
of the robotic work tool from being movable in relation to the
chassis or main body of the robotic work tool. Such arrangements
usually comprise a movable or slidable member which movements are
monitored and if a movement in an XY plane (the same as that of the
surface being worked) is detected a collision is detected. If a
movement in a Z direction (normal to the XY plane), a lift is
detected.
[0004] However, in these type of conventional arrangements a
collision with an object may also give rise to a movement in a Z
direction, whereby a lift may be falsely detected.
[0005] As a lift detection usually turns off any active member or
tool of the robotic work tool, a falsely detected lift will impair
the operation of the robotic work tool, which is of course
unwanted.
[0006] A further drawback of the conventional arrangements is that,
in a collision situation, the robotic work tool may respond to a
detected collision in a manner that does not improve the situation.
Thus, there is a need for improved lift and collision detection for
a robotic work tool.
SUMMARY OF THE DISCLOSURE
[0007] It is therefore an object of the present disclosure to
provide a robotic work tool that solves or at least mitigates one
of the problems of the prior-art. In particular, it is an object of
the present disclosure to provide a robotic work tool with accurate
determination of lift and collision. A further object of the
present disclosure is provide a robotic work tool with improved
determination of the orientation of the robotic work tool relative
a collision object. Yet a further object of the present disclosure
is to provide a robotic work tool that may be realized with few
parts and at low cost.
[0008] According to a first aspect of the present disclosure, at
least one of these objects are met by a robotic work tool
comprising a chassis, a body and a controller for controlling
operation of the robotic work tool. The robotic work tool comprises
at least one three-dimensional sensor arrangement for detecting
relative movement of the body and the chassis. The sensor
arrangement comprises a sensor element arranged in one of the body
and the chassis and a detection element arranged in the other of
the body and the chassis. Advantageously the controller is
configured to receive sensor input indicating relative movement of
the sensor element and the detection element and to determine, from
the sensor input, whether a collision or a lift has been
detected.
[0009] A three-dimensional sensor arrangement may differentiate a
change in relative position of the detection element and the sensor
element in lateral direction from a changes of their relative
position in vertical direction. The use of a three-dimensional
sensor in the robotic work tool according to the present disclosure
therefore results in that the controller may be configured to
accurately determine from the sensor output whether the robotic
work tool has been subjected to a collision (lateral movement of
the body) or a lift (vertical movement of the body). This in, turn
results in effective operation of the robotic work tool since false
alarms essentially are avoided. The robotic work tool may further
be produced at a low cost since only one sensor arrangement is
necessary for detection of collision or lift.
[0010] According to an embodiment, said sensor element may be
configured to sense the position of the detection element in three
dimensions.
[0011] According to an embodiment, the detection element may be a
magnet and the sensor element may be a three-dimensional sensor
configured to detect magnetic field in a plane, and in a direction
which is normal to the plane.
[0012] According to an embodiment, said detection element may be a
magnet and the sensor element may be configured to detect the
magnitude and direction in three-dimensional space of the magnetic
field of the magnet. By way of example, the sensor element may be a
three-dimensional Hall sensor.
[0013] According to an embodiment, said the sensor element may be
configured as an integrated unit, and preferably encapsulated in a
single integrated circuit package. Such an integrated circuit
package may be soldered to a printed circuit board.
[0014] According to an embodiment, the three-dimensional sensor
arrangement may be positioned, as seen from above, at a distance
from a geometrical centre of the robotic work tool, and preferably
adjacent to a lateral side of the robotic tool. Thereby, a
particularly efficient collision detection may be obtained in
situations when the robotic work tool does not collide head-on.
[0015] According to an embodiment, the controller may be configured
to receive sensor input indicating lateral movement of the sensor
element and the detection element relative each other, and in
response thereto, determine that a collision has been detected.
[0016] According to an embodiment, said at least one
three-dimensional sensor arrangement may comprise a first and a
second three-dimensional sensor arrangement, each of said sensor
arrangements comprising a respective sensor element arranged in one
of the body and the chassis and a respective detection element
arranged in the other of the body and the chassis. Also in this
case, a particularly efficient collision detection may be obtained
in situations when the robotic work tool does not collide head-on.
Each of said first and second three-dimensional sensor arrangements
may optionally be configured in accordance with any of the
embodiments hereinabove.
[0017] According to an embodiment, the controller may be configured
to determine, from the sensor input, the direction of the
collision.
[0018] According to an embodiment, the controller may be configured
to receive sensor input indicating vertical movement of a sensor
element and a detection element relative each other, and in
response thereto, determine that a lift has been detected.
[0019] According to an embodiment, the controller may be configured
to receive sensor input indicating lateral and vertical movement of
a sensor element and a detection element relative each other and,
in response thereto, determine whether collision or lift has been
detected by comparing sensor input with a threshold value.
[0020] According to an embodiment, the robotic work tool may
comprising at least one suspension device for movably supporting
the body on the chassis. The suspension device may comprise an
elongate, optionally rigid, support member having a first end that
is supported on the chassis and a second end that supports the
body. The elongate support member may be extendable and pivotal
such that the body may move laterally and vertically relative the
chassis.
[0021] According to an embodiment, the first end of the elongate
support member may be configured to be pivotally supported on the
chassis. The second end of the elongate support member may be
joined to the body.
[0022] According to an embodiment, the elongate support member may
comprise a base member and a lift member, respectively configured
such that at least a portion of one of the base member and the lift
member is slidably receivable in the other of the base member and
the lift member, so that the elongate support member may be
extended telescopically.
[0023] According to an embodiment, the elongate support member may
comprise a first biasing element arranged to bias the lift member
towards the base member.
[0024] According to an embodiment, the base member may comprise an
elongate guide opening. The first biasing element may be arranged
in the base member, and may comprise a guide element that extends
through the elongate guide opening and is attached to the lift
member.
[0025] According to an embodiment, the suspension device may
comprise a second biasing element arranged to bias the elongate
support member from a pivoted position to an upright position.
[0026] According to an embodiment, said three-dimensional sensor
arrangement or arrangements, as the case may be, and the at least
one suspension device, may be arranged laterally separated from
each other.
[0027] According to an embodiment, the robotic work tool may
comprise at least a first and a second suspension device.
[0028] According to an embodiment, the number of suspension devices
may be greater than the number of three-dimensional sensor
arrangements.
[0029] According to an embodiment, the robotic work tool may
comprise at least a first and a second suspension device. A three
dimensional sensor arrangement according to any of the embodiments
defined hereinabove may be arranged between the first and the
second suspension device.
[0030] According to an embodiment, the robotic work tool may be a
robotic lawnmower.
[0031] According to a second aspect, there is provided a method for
use in a robotic work tool comprising a chassis; a body; a
controller for controlling operation of the robotic work tool and
at least one three-dimensional sensor arrangement for detecting
relative movement of the body and the chassis, wherein the sensor
arrangement comprises a sensor element arranged in one of the body
and the chassis and a detection element arranged in the other of
the body and the chassis. The method may comprise:
[0032] receiving sensor input indicating relative movement of the
sensor element and the detection element; and
[0033] determining, from the sensor input, that a collision or a
lift has been detected.
[0034] Further embodiments of the method are provided by combining,
wherever possible, the method with features of any of the
embodiments defined hereinabove with reference to a robotic work
tool.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1: A schematic drawing of a robotic work tool according
to an embodiment of the present disclosure.
[0036] FIG. 2: A schematic drawing of a robotic work tool system
according to an embodiment of the present disclosure.
[0037] FIG. 3: A schematic perspective drawing of a robotic work
tool according to an embodiment of the present disclosure.
[0038] FIG. 4: A cross-sectional view of a portion of the robotic
work tool of FIG. 3.
[0039] FIG. 5a, 5b: Schematic drawings showing the
three-dimensional sensor arrangement of the robotic work tool
according to the present disclosure during collision and lift,
respectively.
[0040] FIG. 6: A flowchart for a method according to the present
disclosure.
[0041] FIG. 7a-7c: Schematic, cross-sectional drawings of a
suspension device of the robotic work tool according to the present
disclosure.
[0042] FIG. 8: A schematic drawing of an arrangement of suspension
devices and three-dimensional sensor arrangements in a robotic work
tool according to the present disclosure.
DETAILED DESCRIPTION OF EMBODIMENTS
[0043] The robotic work tool according to the present disclosure
will now be described more fully hereinafter. The robotic work tool
according to the present disclosure may however be embodied in many
different forms and should not be construed as limited to the
embodiments set forth herein. Rather, these embodiments are
provided by way of example so that this disclosure will be thorough
and complete, and will fully convey the scope of the present
disclosure to those persons skilled in the art. Same reference
numbers refer to same elements throughout the description.
[0044] It is appreciated that while the description given herein
will be focused on robotic lawnmowers, the teachings herein may
also be applied to robotic cleaners such as robotic vacuum cleaners
and/or robotic floor cleaners, robotic ball collectors, robotic
mine sweepers, robotic farming equipment, or other robotic work
tools to be employed in a work area defined by a boundary
cable.
[0045] FIG. 1 shows a schematic overview of the robotic working
tool 100, which is exemplified by a robotic lawnmower 100, having a
front carriage 101' and a rear carriage 101''. The robotic
lawnmower 100 comprises a chassis 110 which in the embodiment shown
in FIG. 1 comprises a front chassis 110' of the front carriage 101'
and a rear chassis 110'' of the rear carriage 101''. The robotic
lawnmower 100 further comprises a body (not shown) which may
comprise a front body (not shown) of the front carriage 101' and a
rear body (not shown) of the rear carriage 101''. The robotic
lawnmower 100 comprises two pair of wheels 150. One pair of front
wheels 150 is arranged in the front carriage 101' and one pair of
rear wheels 150 is arranged in the rear carriage 101''. At least
some of the wheels 150 are drivably connected to at least one
electric motor 450. It is appreciated that while the description
herein is focused on electric motors, combustion engines may
alternatively be used possibly in combination with an electric
motor.
[0046] In the example of FIG. 1, each of the rear wheels 150 is
connected to a respective electric motor 450. This allows for
driving the rear wheels 150 independently of one another which, for
example, enables steep turning.
[0047] The robotic lawnmower 100 also comprises a controller 400,
which may be arranged in the rear carriage 101'' as shown in FIG.
1. The controller 400 may be implemented using instructions that
enable hardware functionality, for example, by using executable
computer program instructions in a general-purpose or
special-purpose processor that may be stored on a computer readable
storage medium (disk, memory etc.) 410 to be executed by such a
processor. The controller 400 is configured to read instructions
from the memory 410 and execute these instructions to control the
operation of the robotic lawnmower 100 including, but not being
limited to, the propulsion of the robotic lawnmower. The controller
400 may be implemented using any suitable, publically available
processor or Programmable Logic Circuit (PLC). The memory 410 may
be implemented using any commonly known technology for
computer-readable memories such as ROM, RAM, SRAM, DRAM, FLASH,
DDR, SDRAM or some other memory technology.
[0048] The robotic work tool 100 may further have at least one
boundary sensor 470. In the example of FIG. 1 there are four
boundary sensors 470. Two boundary sensors 470 are arranged in the
front part of the front carriage 101' and two boundary sensors 470
are arranged in the rear part of the rear carriage 101''. The
boundary sensors 470 are configured to detect a magnetic field (not
shown) and for detecting a boundary cable and/or for receiving (and
possibly also sending) information from a signal generator (will be
discussed with reference to FIG. 2).
[0049] In some embodiments, the boundary sensors 470 may be
connected to the controller 400, and the controller 400 may be
configured to process and evaluate any signals received from the
boundary sensor 470. The sensor signals may be caused by the
magnetic field being generated by a control signal being
transmitted through a boundary cable. This enables the controller
400 to determine whether the robotic lawnmower 100 is close to or
crossing a boundary cable, or inside or outside an area enclosed by
the boundary cable. This also enables the robotic lawnmower 100 to
receive (and possibly send) information from the control
signal.
[0050] The robotic lawnmower 100, may comprise a grass cutting
device 460, such as a rotating blade driven by a cutter motor 465.
The grass cutting device 460 being an example of a work tool 460
for a robotic work tool 100. In the embodiment of FIG. 1 the grass
cutting device 460 and the cutter motor 465 are arranged in the
front carriage 101. The cutter motor 465 is connected to the
controller 400 which enables the controller 400 to control the
operation of the cutter motor 465. The controller 400 may also be
configured to determine the load exerted on the rotating blade, by
for example measure the power delivered to the cutter motor 465 or
by measuring the axle torque exerted by the rotating blade. The
robotic lawnmower 100 also has (at least) one battery 480 for
providing power to the motors 450 and the cutter motor 465.
[0051] The robotic lawnmower 100 is also arranged with at least one
suspension device 300 which will be described in greater detail
with reference to FIGS. 7a-7c. In the example of FIG. 1, both the
front carriage 101' and the rear carriage 101'' are provided with
suspension devices 300, e.g. four suspension devices 300
respectively. The robotic lawnmower 100 is also arranged with at
least one three-dimensional sensor arrangement 200, which will be
described in detail under FIG. 4. In FIG. 1 at least one
three-dimensional sensor arrangement is provided in each of the
front carriage 101 and the rear carriage 101'. The
three-dimensional sensor arrangement 200 is connected to the
controller 400, and the controller 400 may be configured to process
and evaluate any signals received from the three-dimensional sensor
arrangement 200.
[0052] FIG. 2 shows a schematic view of a robotic work tool system
50 in one embodiment. The schematic view is not to scale. The
robotic work tool system 50 comprises a charging station 51 and a
boundary cable 56 arranged to enclose a work area 57, in which the
robotic work tool e.g. a robotic lawnmower 100 is supposed to
serve.
[0053] As in FIG. 1, the robotic work tool 100 is exemplified by a
robotic lawnmower, but the teachings herein may also be applied to
other robotic work tools adapted to operate within a work area.
[0054] The charging station 51 may have a base plate (not shown)
for enabling the robotic lawnmower to enter the charging station 51
in a clean environment and for providing stability to the charging
station 51.
[0055] The charging station 51 has a charger 52, that may be
coupled to two charging plates 53. The charging plates 53 are
arranged to co-operate with corresponding charging plates (not
shown) of the robotic lawnmower 100 for charging the battery 480 of
the robotic lawnmower 100.
[0056] The charging station 51 also has, or may be coupled to, a
signal generator 54 for providing a control signal 55 to be
transmitted through the boundary cable 56. The signal generator
thus comprises a controller for generating the control signal. The
control signal 55 comprises an alternating current, such as a
continuously or regularly repeated current signal. The control
signal may be a CDMA signal (CDMA--Code Division Multiple Access).
The control signal may also or alternatively be a pulsed control
signal, the control signal thus comprising one or more current
pulses being transmitted periodically. The control signal may also
or alternatively be a continuous sinusoidal wave. As is known in
the art, the current signal will generate a magnetic field around
the boundary cable 56 which the boundary sensors 470 of the robotic
lawnmower 100 will detect. As the robotic lawnmower 100 (or more
accurately, the boundary sensor 470) crosses the boundary cable 56
the direction of the magnetic field will change. The robotic
lawnmower 100 will thus be able to determine that the boundary
cable has been crossed, and take appropriate action by controlling
the driving of the rear wheels 150 to cause the robotic lawnmower
100 to turn a certain angular amount and return into the work area
57. For its operation within the work area 57, in the embodiment of
FIG. 2, the robotic lawnmower 100 may alternatively or additionally
use the satellite navigation device 490, supported by the deduced
reckoning navigation sensor 495 to navigate the work area 57.
[0057] As can be seen in FIG. 2, there is one example of an object
exemplified as a tree (trunk) 58.
[0058] FIG. 3 shows a robotic work tool 100 according to an
embodiment of the present disclosure in a perspective side view.
The robotic work tool 100 comprises a front carriage 101' and a
rear carriage 101'' which are coupled by a shaft 140 that is
rotationally attached to the rear carriage 101'' and fixedly
attached to the front carriage 101'. The robotic work tool 100
further comprise a body 120 which in the described embodiment is
embodied in a front body 120' and a rear body 120'' of the
respective front carriage 101' and the rear carriage 101''. The
body 120, which may be made of plastic or metal, forms a protective
outer cover or housing of the robotic work tool 100 and protects
components, such as the aforementioned motors and controller, that
are located within the body 120 or on the chassis 110.
[0059] It is appreciated that the present disclosure is not limited
to a robotic work tool 100 having separate front and rear carriages
101', 101'' as described above. Rather, the robotic work tool 100
may also be of type that comprises one single integral chassis and
one single integral body. Therefore, in the following description,
when it is not necessary to differentiate between a front and rear
carriage, reference will only be made to "chassis 110" or "body
120".
[0060] FIG. 4 shows a view of a cross-section of the robotic work
tool 100 along the line A-A in FIG. 3. The body 120 is movably
supported on the chassis 110 by suspension devices 300 that will be
described more in detail under FIGS. 7a-7c. The body 120 may
therefore move laterally relative the chassis 110 when subjected to
a collision with an object (not shown) in the surroundings of the
robotic work tool. The body may 120 may also move vertically
relative the chassis 110 subjected to lift. For example when a
person grabs hold of the body 120 and lifts it upwards.
[0061] According to the present disclosure, the robotic work tool
100 comprises at least one three-dimensional sensor arrangement 200
for detecting relative movement of the body 120 and the chassis
110. The three-dimensional sensor arrangement 200 comprises a
sensor element 210 and a detection element 220. The sensor element
210 may be arranged on, or in, one of the body 120 and the chassis
110. The detection element 220 may be arranged in, or on, the other
of the body 120 and the chassis 110. In the embodiment shown in
FIG. 4, the detection element 220 is arranged in the body 120 and
the sensor element 210 is arranged in the chassis 110. Preferably,
the sensor element 210 is arranged in a water sealed space 112 of
the chassis 110 so that it is protected from moisture and
contamination. The sensor arrangement 200 is preferably arranged
such that the detection element 220 and the sensor element 210 are
facing each other in a predetermined default lateral position
XY.sub.0 (see FIG. 5a) when the robotic work tool 100 is not
subjected to a collision. The sensor arrangement 200 is further
arranged such that detection element 220 and the sensor element 210
are in the predetermined default vertical default position Z.sub.0
(see FIG. 5b) when the robotic work tool 100 is not subjected to a
lift. In the predetermined default vertical default position
Z.sub.0, the detection element 220 and the sensor element may be in
contact with each other. However preferably, the detection element
220 and the sensor element 210 are spaced apart a predetermined
distance from each other in order to reduce wear.
[0062] By "relative movement" between sensor element and detection
element is meant that either the detection element 220 moves
relative the sensor element 210 or that the sensor element 220
moves relative the detection element 210.
[0063] The sensor element 210 is configured to sense i.e. detect
the position of the detection element 220 in three dimensions. That
is, in three spatial dimensions. In detail, the sensor element 210
is configured to sense the lateral position of the detection
element 220 relative the sensor element 210. That is, the position
of the detection element 220 in a plane XY which is parallel to the
sensor element 210. Additionally, the sensor element 210 is
configured to sense the vertical position of the detection element
220 relative the sensor element 210. That is, the position of the
detection element 220 along a normal between the detection element
220 and the sensor element 210. The sensor element 210 senses
continuously or intermittently the position of detection element
220 during operation of the robotic work tool 100, and may thus
detect any movement of the detection element 220 relative the
sensor element 210.
[0064] It is appreciated that the three-dimensional sensor
arrangement 200 is integrated. That is, the three-dimensional
sensor arrangement 200 is an integrated unit comprising, or
consisting of, one sensor element 210 and one detection element
220. It is further appreciated that the sensor element 210 is
integrated. Thus, the sensor element 210 is an integrated,
preferably single, physical unit configured to detect the position
of the detection element 220 in three dimensions. Analogous, also
the detection element 220 is an integrated, preferably single,
physical unit.
[0065] FIG. 5a shows schematically the sensor arrangement 200 of
FIG. 4 in view from above. The solid central circle 210 indicates
the sensor element 210 and the solid dashed circle 210 indicates
the detection element 220 in a lateral default position XY.sub.0 in
which the detection element 220 is centred over the sensor element
210. The dashed circle 220 indicates a situation in which the
detection element 220 has moved laterally in a plane XY relative
sensor element 210. The arrow B indicate the direction of the
lateral movement of the detection element 220 relative the sensor
element 210. Thus, FIG. 5a shows a situation in which the body 120
(not shown) of the robotic work tool 100 has been subjected to
collision at location 130 on the body 120 and moved laterally in
the XY-plane in direction of arrow B away from the location of the
collision 130.
[0066] FIG. 5b shows schematically the sensor arrangement 220 of
FIG. 4 in a side view. The solid box 220 indicates the detection
element 220 in a vertical default position Z.sub.0 relative the
sensor element 210. The dashed box 220 indicates a situation in
which the detection element 220 has moved vertically relative the
sensor element 210 along the normal Z due to lifting of body 120
(not shown) of the robotic work tool 100.
[0067] The sensor element 210 is preferably a three-dimensional
sensor that is configured to detect a magnetic field in a plane or
in a direction (e.g. an axis) which is normal to the plane. The
three-dimensional sensor element 210 may be a three-dimensional
Hall-sensor. For example, the three-dimensional sensor 210 may be
TLV493 three-dimensional sensor which is commercially available
from the company Infineon Technologies AG. An example of a
detection element 220 is a magnet, for example a permanent
magnet.
[0068] Movement of the detection element 220 relative the sensor
element 210 is detected by the three-dimensional sensor element 210
as a change in the magnetic field that is produced by the detection
element 220.
[0069] The sensor element 210 may detect changes in the magnetic
field when the detection element 220 moves laterally, i.e. in the
XY-plane relative the sensor element 210.
[0070] The sensor element 210 may further detect changes in the
magnetic field when the detection element 220 moves vertically
relative the sensor element 210, i.e. along the normal Z.
[0071] Thus, specific and different changes in the magnetic field
produced by the detection element 220 may be detected by sensor
element 210 when the detection element 220 moves laterally,
respectively vertically, relative the sensor element 210. Specific
changes in the magnetic field may for example be changes in the
magnitude of the magnetic field. Other specific changes in the
magnetic field that may be detected by the sensor element are for
example changes in direction or orientation of the magnetic
field.
[0072] In the following description, the three-dimensional sensor
arrangement 200 is exemplified by a three-dimensional sensor 210
that is configured to detect a magnetic field and the detection
element 220 is exemplified in the form of a magnet. However, the
present disclosure is not limited to three-dimensional sensors that
are configured to detect a magnetic field. Rather, other
three-dimensional sensor element may be utilized, for example
capacitive sensors or force resistance sensors (FSR).
[0073] The controller 400 (see FIG. 1) is connected to the sensor
arrangement 200 and configured to receive sensor input indicating
movement of the detection element 220 relative the sensor element
210. Thus, as described above, the sensor element 210 continuously
or intermittently senses the magnetic field produced by the
detection element 220 and outputs a corresponding sensor signal as
sensor input to the controller 400.
[0074] The controller 400 is further configured to determine from
the sensor input whether a collision or a lift has been detected.
The controller 400 may thereby be configured to determine from
specific changes in the magnetic field produced by the detection
element 220 that a collision, respectively a lift, has been
detected. The controller 400 may thereby be configured to determine
that specific changes in the magnetic field indicates that the
detection element 220 has moved laterally relative the sensor
element 210 and based thereon determine that a collision is
detected. The controller 400 may also be configured to determine
that specific changes in the magnetic field indicates that the
detection element 220 has moved vertically relative the sensor
element 210 and based thereon determine that a lift is detected.
The controller 400 may further be configured to operate the robotic
work tool (not shown) in dependency of a detected collision or a
detected lift. For example, if a collision has been detected, the
controller may change the driving path of the robotic work tool.
Alternatively, if a lift has been detected, the controller may be
configured to switch off the work tool (e.g. the cutter) of the
robotic work tool.
[0075] The controller 400 may further be configured to determine
the direction of movement of the detection element 220 in the
XY-plane relative the sensor element 210. In the described
embodiment, the controller 400 may thereby be configured to
determine that specific changes in the magnetic field indicate that
the detection element 220 has moved laterally relative the sensor
element 210 in a specific direction. This is advantageous since it
allows the controller 400 to operate the robotic work tool very
effectively in view of an object in the close surroundings of the
robotic work tool.
[0076] Namely, the controller 400 may from the collision direction
determine the position of the object with which the robotic work
tool has collided and change the driving path of the robotic work
tool so that the robotic work tool moves away or around the object.
In a simple example, the controller 400 may be configured to, in
response to a detected collision, steer the robotic work tool 200
in the direction of movement of the detection element 220 and thus
away from the object.
[0077] The controller 400 may further be configured to determine
the amount of lateral and vertical movement of the detection
element 220 relative the sensor element 210. In the described
embodiment the controller 400 may thereby be configured to
determine that specific changes in the magnetic field indicates
that the detection element 220 has moved a specific distance
laterally away from the lateral default position or vertical away
from the vertical default position.
[0078] This is advantageous in a situation where the body 120 of
the robotic work tool 100 is subjected to simultaneous collision
and lift since it makes possible for the controller to prioritize
operation of the robotic tool with regards to e.g. a large vertical
movement of the body and ignore a small lateral movement of the
body. The controller 400 may thereby be configured to compare the
amount of lateral and vertical movement of the detection element
220 relative the sensor element 210 with lateral and vertical
movement threshold values. The controller 400 may further be
configured to determine whether the movement of the detection
element 220 relative the sensor element 210 is predominately
vertical or predominately lateral. For example, the controller 400
may be configured to determine that movement of the detection
element 220 is predominately lateral when the amount of lateral
movement of the detection element 220 approximates or exceeds a
lateral movement threshold value. Accordingly, the controller 400
may be configured to determine that movement of the detection
element 220 is predominately vertical when the amount of lateral
movement of the detection element 220 approximates or exceeds a
vertical movement threshold value. The controller 400 may further
be configured to determine, when the movement of the detection
element 220 is predominately vertical, that a lift is detected.
Accordingly, the controller 400 may be configured to determine,
when the movement of the detection element 220 is predominately
lateral, that a collision is detected.
[0079] FIG. 6 shows a flowchart for a general method according to
the present disclosure where the controller 400 receives 610 sensor
input from the three-dimensional sensor arrangement indicating
relative movement of the sensor element 210 and the detection
element 220 and; determines 620, from the control input, whether a
collision or a lift has been detected.
[0080] Returning to FIG. 4. The robotic work tool 100 comprises at
least one extendable and pivotal suspension device 300 for movably
supporting the body 120 on the chassis 110 so that the body 120 may
move laterally and vertically relative the chassis 110.
[0081] FIG. 7a shows the suspension device 300 in detail. Thus, the
suspension device 300 comprises an elongate support member 310
which may have rotational symmetric form and that comprises a base
member 320 and a lift member 330.
[0082] The base member 320 is elongate and has a first end 311,
which forms the first end 311 of the elongate support member 310.
The base member 320 has further a second end 323 and a stem portion
321 that extends from the second end 323 to a base portion 322
which extends to the first end 311 of the base member 320. The stem
portion 321 may have generally uniform cross-section. In the
embodiment of FIG. 7a, the stem portion 321 is hollow and of
cylindrical cross-section. The base portion 322 may have a
cross-section that widens towards the first end 311. The first end
311 is configured to be pivotally supported on a support surface
111 of the chassis 110. The first end 311 may thereby have a flat
end surface which is supported on a corresponding flat support
surface 111 on the chassis 110. It appreciated that the first end
311 of the elongated support member 310 is freely supported on the
chassis 110. That is, the first end 311 is not permanently joined
to the chassis 120. As shown in FIG. 7b, the flat end surface of
the first end 311 allows the elongate support member 310 to pivot
when the body 120 of the robotic work tool is subjected to a
collision. Instead of a flat end surface, the first end 311 may
have a concave or convex end surface which is configured to be
pivotally supported on a corresponding convex or concave support
surface 111 of the chassis (not shown). The stem portion 321
further comprises at least one elongate guide opening 324 for
receiving a guide pin 341 of a biasing element 340 which will be
described further hereinafter. In FIG. 7a only one elongate guide
opening 324 is visible. However, two elongate guide openings 324
may be provided opposite to each other in the stem portion 323. The
at least one elongate guide opening 324 extends in direction from
the base portion 322 towards the second end 323 of the base member
320.
[0083] The lift member 330 is also elongate and hollow and
comprises a first end 331 with an opening 332 for receiving the
stem portion 321 of the base member 320. The lift member 330
further comprises a second end 312, forming the second end 312 of
the elongate support member 310. The second end 312 may be
supported on the inner surface of the body 120 of the robotic work
tool. Preferably, the second end 312 is joined to the body 120. For
example by formfitting.
[0084] The base member 320 and the lift member 330 are configured
such that at least a portion of the base member 320 may be slidably
received in the hollow lift member 330. Thus, at least a part of
the stem portion 321 of the base member 320 may be received through
the opening 332 in the first end 331 in the lift member 330 and
thus extend within the hollow lift member 330. The elongate support
member 310 may thereby be extended and retracted telescopically by
sliding of the lift member 330 on the base member 320 in vertical
direction towards or away from the chassis 110 (see FIG. 7c).
[0085] Configuration of the lift member 330 and the base member 320
may be achieved by appropriate selection of geometrical dimensions,
such as shape, length and inner- and outer diameter of the base
member 320 and the lift member 330. Preferably, at least a part of
the stem portion 321 of the base member 320 is cylindrical and at
least a portion of the hollow lift member 330 is of corresponding
hollow cylindrical cross-section.
[0086] The suspension member 300 may further comprise a first
biasing element 340 which is arranged to bias, i.e. force, the lift
member 330 towards the base member 310. The first biasing element
340 is a resilient member for example a spring, such as helical
coil spring, or a helical pressure coil spring. Alternatively, the
first biasing element 340 is a resilient member manufactured by
elastic material such as a rubber or elastomer. In the embodiment
of FIG. 7a, the biasing element 340 is a helical coil pressure
spring and is inserted into the stem portion 321 of the base member
320. A first end of the biasing member 340 is supported onto the
second end 323 of the stem portion 321. The second end of the
biasing member 340 comprises a guide element 341, for example in
the form of a guide pin, that extends through the at least
elongated guide opening 324 in the stem portion 321 of the base
member 320 and into the lift member 330. The guide element 340 is
further fixedly attached to the lift member 330. For example, the
end of the guide element 341 (in the form of guide pin) is received
in a circular opening in the base member 330 (not shown).
[0087] The biasing element 340 and the elongated guide opening 324
in the base member 320 as well as the position of attachment of the
guide pin 341 to the lift member 330 are configured such that the
biasing element 340 forces the lift member 330, in vertical
direction, towards the base member 320 when the suspension device
300 is in a vertical default position. That is, when no lift force
is exerted on the lift member 330. Thus, when the suspension device
is in a vertical default position, as shown in FIG. 7a, the biasing
element 340 (in the form of a coil pressure spring) is slightly
compressed.
[0088] This configuration of the suspension device 300 is
advantageous since the pre-biased biasing element 340 ensures that
the body 120 of the robotic work tool does not move in vertical
direction when the robotic work tool runs down a slope. This is
further advantageous since any movement of the body 120 of the
robotic work tool in vertical direction may be detected as a lift
by the controller 400 and result in deactivation of the cutter. An
advantage of the elongate guide opening 324 in the base member 320
is that the upper end of the elongated guide opening 324 provides a
predetermined stop for movement of the guide element 341 and thus a
predetermined stop for lifting of the body 120 of the robotic work
tool.
[0089] Turning to FIG. 7c, which show a situation in which the body
120 (not shown) of the robotic work tool is subjected to a lift.
This causes the lift member 330 to be pulled vertically upwards
away from the base member 320. The guide element 341 thereby runs
in the elongated guide opening 324 in the base member 320 and the
biasing element 340 is compressed against the second end 323 of the
base member 320. When the lifting force on the lift member 330 is
released, the biasing element 340 expands, i.e. springs back and
forces the lift member 330 in vertical direction towards the base
member 320.
[0090] The suspension device 300 may further comprise a second
biasing element 350 which is arranged to bias, i.e. force, the
elongate support member 310 from a pivoted position (as shown in
FIG. 7b) towards an upright position (as shown in FIG. 7a). The
second biasing element 350 may also be a resilient element such as
a helical coil spring or a helical pressure coil spring. The second
biasing element 350, preferably in the form of a helical coil
spring, may be arranged around the outer periphery of the base
member 320 and attached by one end to the support surface 111 of
the chassis 110.
[0091] FIG. 8 shows schematically an arrangement of
three-dimensional sensor arrangement 200 and suspension devices 300
in a robotic work tool 100. Preferably, the three-dimensional
sensor arrangements 200 are arranged laterally separated from the
suspension devices 300. This makes possible to reduce the number of
three-dimensional arrangements 200 in the robotic work tool.
Typically, the suspension devices 300 are arranged in the corners
of the robotic work tool 100 (as shown in FIG. 8). However, the
corners of the robotic work tool 100, and thus the suspension
devices 300, may be so far spaced apart that lifting of one corner
of the robotic work tool not necessarily result in detectable
vertical displacement of another corner of body of the robotic work
tool. Therefore, if the sensor arrangements 200 are arranged
within, or directly above, the suspension devices 300 it may be
necessary to have one sensor arrangement in each suspension device
300 to ensure lift detection over the entire robotic work tool.
Therefore, by arranging the sensor arrangements 200 laterally
spaced apart from the suspension devices 300 it is possible to
place at least one or at least two sensor arrangements 200 in
positions on the robotic tool 100 that allows lift to be detected
regardless which part of the robotic work tool that has been
subjected to the lift.
[0092] In FIG. 8 the robotic work tool 100 one three-dimensional
sensor arrangement 200 and a first and a second suspension device
300 are arranged in a row. Two such rows are arranged on opposite
sides of the robotic work tool and in each row one three
dimensional sensor arrangement 200 is arranged between the first
and second suspension device 300. This arrangement is advantageous
since it allows for a stable collision signal when the body 120 of
the robotic work tool is subjected to a collision 130 in diagonal
collision direction (as indicated by arrow B). When subjected to a
diagonal collision, the body of the robotic work tool 100 may twist
which in turn may result in only small movement of the body of the
robotic work tool in the XY-plane. However, when the robotic work
tool comprises at least two horizontally separated sensors 200,
e.g. arranged as in FIG. 8, at least one sensor 200 will detect the
collision even if the movement of the body is small. The
arrangement of FIG. 8 also provides very reliable detection of lift
over the entire body of the robotic work tool 100.
* * * * *