U.S. patent application number 10/545430 was filed with the patent office on 2006-10-12 for autonomous machine.
Invention is credited to Michael David Aldred, Alexander Philip Bommer, Thomas James Dunning Follows, Matthew Kitchin, Jonathan Paul Taylor.
Application Number | 20060229765 10/545430 |
Document ID | / |
Family ID | 9952986 |
Filed Date | 2006-10-12 |
United States Patent
Application |
20060229765 |
Kind Code |
A1 |
Bommer; Alexander Philip ;
et al. |
October 12, 2006 |
Autonomous machine
Abstract
An electric machine, such as an autonomous vacuum cleaner, is
powered through a cable and includes a means or device for
detecting the orientation of the cable with respect to the main
body of the machine that may be in the form of a pivotable member
such as pendulum, connected to a potentiometer. The potentiometer
provides an output signal proportional to the position of the free
end of the pendulum. Thus, the machine can detect the position of
the cable and thus can avoid it or else follow it. Microswitches
may also be provided to detect extreme positions of the cable.
Inventors: |
Bommer; Alexander Philip;
(Bristol, GB) ; Aldred; Michael David; (Wiltshire,
DE) ; Taylor; Jonathan Paul; (Bristol, GB) ;
Follows; Thomas James Dunning; (North Yorkshire, GB)
; Kitchin; Matthew; (Berkshire, GB) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
1650 TYSONS BOULEVARD
SUITE 300
MCLEAN
VA
22102
US
|
Family ID: |
9952986 |
Appl. No.: |
10/545430 |
Filed: |
February 13, 2004 |
PCT Filed: |
February 13, 2004 |
PCT NO: |
PCT/GB04/00601 |
371 Date: |
April 28, 2006 |
Current U.S.
Class: |
700/245 |
Current CPC
Class: |
G05D 1/0227 20130101;
G05D 2201/0215 20130101; B60L 2200/40 20130101; B60L 9/00 20130101;
G05D 1/0274 20130101; G05D 1/0219 20130101; G05D 1/0272 20130101;
A61L 2202/16 20130101 |
Class at
Publication: |
700/245 |
International
Class: |
G06F 19/00 20060101
G06F019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2003 |
GB |
0303368.5 |
Claims
1. An autonomous machine comprising a main body, a power cable and
a device for detecting the orientation of the cable with respect to
the main body.
2. An autonomous machine as claimed in claim 1, wherein the device
for detecting cable orientation comprises a first detecting device
arranged to detect the orientation of the cable within a first
predetermined range.
3. An autonomous machine as claimed in claim 2, wherein the device
for detecting cable orientation further comprises a second
detecting means device arranged to detect the orientation of the
cable within a second predetermined range.
4. An autonomous machine as claimed in claim 2 or 3, wherein the
first detecting device comprises a pivotable member associated with
a rotary encoder.
5. An autonomous machine as claimed in 4, in which the pivotable
member comprises a pendulum, one end portion of which is associated
with the cable, the other end portion of which is associated with
the rotary encoder.
6. An autonomous machine as claimed in claim 4, wherein the rotary
encoder comprises a potentiometer.
7. An autonomous machine as claimed in claim 3, wherein the second
detecting means device comprises a pressure switch arranged to
produce a signal when the cable pushes against it.
8. An autonomous machine as claimed in claim 3, wherein the second
detecting means device comprises two pressure switches located on
respective sides with respect to the cable, each switch being
arranged to produce a signal when the cable pushes against it.
9. An autonomous machine as claimed in claim 7 or 8, wherein the
cable is arranged to push against the or each switch via an
intermediary member.
10. An autonomous machine as claimed in claim 7 or 8, wherein the
pressure switch comprises a microswitch.
11. A vacuum cleaner comprising the autonomous machine of claim 1,
2, 3, 7 or 8.
12. (canceled)
13. A method of operating an autonomous machine comprising a main
body and a power cable, comprising detecting the orientation of the
cable with respect to the main body.
14. A method as claimed in claim 13, further comprising controlling
the machine to follow its own cable.
15. A method as claimed in claim 14, further comprising causing the
machine to collect the cable as it follows it.
16. A method as claimed in claim 15, in which the causing of the
machine to collect its cable comprises causing the cable to be
wound on a cable reel carried by the main body.
17. (canceled)
18. An autonomous machine as claimed in claim 5, wherein the rotary
encoder comprises a potentiometer.
19. An autonomous machine as claimed in claim 9, wherein the
pressure switch comprises a microswitch.
20. A vacuum cleaner comprising the autonomous machine of claim
4.
21. A vacuum cleaner comprising the autonomous machine of claim
5.
22. A vacuum cleaner comprising the autonomous machine of claim
6.
23. A vacuum cleaner comprising the autonomous machine of claim
9.
24. A vacuum cleaner comprising the autonomous machine of claim 10.
Description
[0001] This invention relates to an autonomous machine powered by a
power cable, for example a robotic vacuum cleaner.
[0002] There have been various proposals to provide autonomous or
robotic machines for performing duties such as cleaning or
polishing a floor area, or for mowing grass. Some autonomous
machines are capable of exploring the environment in which they are
placed without human supervision, and without advance knowledge
(e.g. a map) of the layout of the environment. The machine may
explore the environment during a learning phase and will
subsequently use this information during a working phase, or the
machine may begin working in the area immediately. Autonomous
machines of this type are particularly attractive to users as they
can be left to work with minimal human supervision.
[0003] It is also known to provide autonomous machines which derive
their power from a mains power supply and which carry a reel of
cable which is dispensed as the machine moves around the area. U.S.
Pat. No. 4,962,453 shows an example of this kind of machine, which
covers a working area by a complex series of fan-shaped coverage
patterns.
[0004] A problem which may be encountered with cable-powered
machines is that the cable itself can hamper the functioning of the
machine. For example, if an autonomous machine runs over its own
cable, it may experience odometry errors or may damage the
cable.
[0005] The invention provides an autonomous machine comprising a
main body, a power cable and means for detecting the orientation of
the cable with respect to the main body
[0006] The invention permits the machine to detect the position of
its own cable. The machine may therefore be controlled so as to
avoid or to follow its own cable.
[0007] Preferably, the means for detecting cable orientation
comprises a first detecting means arranged to detect the
orientation of the cable within a first predetermined range. A
second detecting means arranged to detect the orientation of the
cable within a second predetermined range may also be provided. The
first and second ranges may be separate or may overlap.
[0008] Advantageously, the first detecting means comprises a
rotatable member connected to a rotary encoder such as a
potentiometer. A suitable rotatable member is a pendulum, one end
portion of which is connected to the cable, the other end portion
of which is associated with the encoder.
[0009] The second detecting means may comprises one or more
pressure switches, such as microswitches, arranged adjacent the
cable, to produce a signal when the cable pushes against it.
Alternatively, an intermediary member such as a collar around the
cable may be arranged to push against the switches when the cable
is deflected.
[0010] The machine can take many forms: it can be a floor treating
machine such as a vacuum cleaner or floor polisher, a lawn mower or
a robotic machine which performs some other function.
Alternatively, it could be a general purpose robotic vehicle which
is capable of carrying or towing a work implement chosen by a
user.
[0011] The invention will now be described, by way of example, with
reference to the accompanying drawings, in which:--
[0012] FIG. 1 is a perspective view of an autonomous machine in the
form of a vacuum cleaner;
[0013] FIG. 2 shows the electrical systems of the machine of FIG.
1;
[0014] FIGS. 3A-3D (collectively "FIG. 3") are perspective views
showing a power cable management system of the machine of FIGS. 1
and 2 incorporating the present invention;
[0015] FIG. 4 is a flow chart of a navigation method used by the
machine;
[0016] FIGS. 5 and 6 are plan views showing the machine at work in
a working area, following the navigation method of FIG. 4;
[0017] FIGS. 7A, 713 and 7C (collectively "FIG. 7") are plan views
illustrating a movement carried out by the machine of FIG. 1 using
the navigation method of FIG. 4;
[0018] FIGS. 8 and 9 are plan views illustrating ways in which the
machine copes with large working areas;
[0019] FIGS. 10a-10d (collectively "FIG. 10") are perspective views
showing an alternative embodiment of the invention; and
[0020] FIGS. 11a-11c (collectively "FIG. 11") are perspective views
showing a further alternative embodiment of the invention.
[0021] FIG. 1 of the drawings shows a robotic, or autonomous, floor
cleaning machine in the form of a robotic vacuum cleaner 10. FIG. 2
shows the electrical systems incorporated into the vacuum cleaner
10.
[0022] The machine comprises a main body or supporting chassis 12,
two driven wheels 15, a cleaner head 40, a user interface with
buttons 60 and indicator lamps 65 and various sensors 20-26, 30 for
sensing the presence of objects around the machine. Also mounted on
the chassis 12 is apparatus 14 for separating dirt, dust and debris
from an incoming airflow and for collecting the separated material,
a reel for storing a length of power cable 95, and a system for
dispensing and rewinding the power cable. The machine 10 is
supported on the two driven wheels 15 and a castor wheel (not
shown) at the rear of the machine. The driven wheels 15 are
arranged at either end of a diameter of the chassis 12, the
diameter lying perpendicular to the longitudinal axis of the
cleaner 10. The driven wheels 15 are mounted independently of one
another via support bearings (not shown) and each driven wheel 15
is connected directly to a traction motor 16 which is capable of
driving the respective wheel 15 in either a forward direction or a
reverse direction. A full range of manoeuvres is possible by
independently controlling each of the traction motors 16.
[0023] Mounted on the underside of the chassis 12 is a cleaner head
40 which includes a suction opening facing the surface on which the
cleaner 10 is supported. A brush bar 45 is rotatably mounted in the
suction opening and a motor 48 is mounted on the cleaner head 40
for driving the brush bar 45. It will be appreciated that the brush
bar 45 could be omitted, if desired, so that the cleaner head 40
only has a suction opening and cleans by relying on suction alone.
For other types of surface treating machine, the cleaner head 40
could be replaced by a polishing pad, wax dispenser, squeegee
etc.
[0024] The chassis 12 of the machine 10 carries a plurality of
sensors 20-26, 30 which are positioned on the chassis 12 such that
the navigation system of the machine can sense obstacles in the
path of the machine 10 and also the proximity of the machine to a
wall or other boundary such as a piece of furniture. The sensors
shown here comprise several ultrasonic sensors 20-26 which are
capable of sensing the distance and angular position of walls and
objects from the sensors, and several passive infra red (PIR)
sensors 30 which can sense the presence of humans, animals and heat
sources such as a fire. There are forward-facing sensors 22, 23,
side-facing sensors 20, 21 and 24, 25, rear-facing sensors (not
shown) and high-level sensors 26. It will be appreciated that the
number of sensors, type of sensors and positioning of the sensors
on the machine 10 can take many different forms. For example, infra
red range-finding devices, also known as PSDs, may be used instead
of, or in addition to, the ultrasonic sensors 20-26. In an
alternative embodiment the machine may navigate by mechanically
sensing the boundary of the working area and boundaries of
obstacles placed within the area. One example of a mechanical
sensor which could be used on a machine of this type is a "bump"
sensor which detects movement of a moveable or resilient bumper
when the machine encounters an obstacle. "Bump" sensors can be used
in combination with the ultrasonic and PIR sensors described
above.
[0025] One or both sides of the vehicle can also have an odometry
wheel 18. This is a non-driven wheel which rotates as the machine
moves along a surface. Each odometry wheel 18 has an encoder
associated with it for monitoring the rotation of the odometry
wheel 18. By examining the information received from each odometry
wheel 18, the navigation system can determine both the distance
travelled by the machine and any change in angular direction of the
machine. It is preferred that the odometry wheel 18 is a non-driven
wheel as this increases the accuracy of the information obtained
from the wheel. However, in a simpler embodiment, the machine can
derive odometry information directly from the driven wheels 15, by
an encoder located on the wheel 15 or the motor 16 which drives the
wheel 15.
[0026] The machine 10 also includes a motor 52 and fan 50 unit
supported on the chassis 12 for drawing dirty air into the machine
via the suction opening in the cleaner head 40.
[0027] The electrical systems for the machine, shown in detail in
FIG. 2, will now be described. The navigation system comprises a
microprocessor 80 which operates according to control software
which is stored on a non-volatile memory 82, such as a ROM or FLASH
ROM. Another memory 84 is used during normal operation of the
machine to store data, such as odometry information and a map of
the working area (if required), and other operating parameters. The
navigation system receives inputs about the environment surrounding
the machine from the sensor array 20-26, 30 (including ultrasonic,
PIR and bump sensors) and inputs about movement of the machine from
odometry wheel movement sensors 18. The navigation system also
receives inputs from switches 60 on the user interface, such as
starting, pause, stop or a selection of operating speed or standard
of required cleanliness. The navigation system provides a plurality
of output control signals including signals for driving the
traction motors 16 of the wheels 15, a signal for operating the
suction motor 52 which drives the suction fan 50 and a signal for
operating the motor 48 which drives the brush bar 45. It also
provides outputs from illuminating indicator lamps 65 on the user
interface. Power is derived from a mains supply via a power cable.
The cleaner carries a cable reel 95 with a length of cable (e.g. 20
m) which is sufficient to allow the machine to circumnavigate a
typical room in which the machine will be used.
[0028] There are various ways of managing cable storage on the
machine. FIG. 3 shows one preferred scheme. Power cable 95 is
stored on a cable reel 71. The cable reel 71 is permanently biased,
by a spring, towards the wound up state. Cable 95 is drawn from the
reel 71 by a pair of pinch rollers 70, one of which is driven by a
motor 72, under the control of the navigation system, to dispense
cable from the reel 71, or to allow cable 95 to be rewound onto the
reel 71, as the machine moves around a working area.
[0029] In accordance with the invention, means are provided to
indicate the orientation of the cable with respect to the chassis.
After passing through the pinch rollers 70, the cable 95 passes
through an opening 75 in the free end of a pivotable member in the
form of a pendulum 74. The pendulum 74 is pivotable about a shaft
73, the pendulum 74 being movable in a vertical plane. Shaft 73
forms part of a rotary encoding device 76, such as a potentiometer,
which can provide an output signal proportional to movement of the
pendulum 74.
[0030] As shown in FIGS. 3B to 3D, the pendulum 74 tracks the
position of the cable 95 with respect to the cable reel 71. When
the cable 95 is under tension and is pulled out directly behind the
machine, the pendulum 74 will be approximately at the central
position of FIG. 3B. Thus the potentiometer signal will be small.
In FIG. 3C, the cable is to the left of the machine. Thus, the
pendulum 74 swings clockwise and the potentiometer 76 provides an
output signal indicative of the direction and angle of the cable 95
with respect to the chassis. This is particularly useful when the
machine is reversing along a path where cable 95 has been laid. The
control system can detect the position of the cable, and the
machine can be controlled to follow the path of the cable 95. This
technique will hereafter be referred to as `cable follow mode`.
[0031] In the situation shown in FIG. 3D, the cable is pulled out
to the extreme right, and so the pendulum 74 swings anti-clockwise
to the position shown. Depending on the sensitivity of the
potentiometer, this extreme may be outside the range of angular
positions detectable. Thus, a further detector may be provided to
detect such extremes. This may take the form of a so-called bump
sensor or pressure switch, such as a microswitch. In such a sensor,
a signal is output when a resilient part of the sensor is caused to
move. Thus, the machine may be arranged with two microswitches on
the chassis, either side of the cable. When the cable is to the
extreme left or right, it is urged against the resilient part of
one of the microswitches, which therefore produces a signal
indicative of the extreme position of the cable.
[0032] The operation of the machine will now be described with
reference to FIGS. 4 to 9. FIG. 4 is a flow chart of the general
process for navigating the machine around a working area.
[0033] FIGS. 5 to 9 show the machine 10 at work, in a room of a
house. The boundary of the working area for the machine is defined
by the walls of the room 301-304 and the edges of objects 305-308
placed within the room, such as articles of furniture (e.g. sofa,
table, chair). These figures also show the set of paths 320
traversed by the machine.
[0034] The machine 10 is placed in the room by a user. Ideally, the
machine is left near to a power socket 310 in the room, with the
plug inserted into the socket 310 and a short length of power cable
lying on the floor between the socket and the machine 10. Once the
machine has been switched on, it begins a short routine to discover
a starting or `home` position in the room (step 110). The power
socket 310 is a convenient home position for the mains powered
machine. The `home` position serves as a useful reference point for
determining, inter alia, when the machine has travelled around the
entire room. The machine determines the position of the power
socket 310 by winding the cable 95 onto its internal cable reel 71
as it reverses. The machine can find the socket 310 by mechanically
sensing that the cable 95 has been fully rewound, or by detecting a
marker 98 placed on the cable 95, near to the plug. The machine
then aligns its left hand side with the boundary of the area and
starts the suction motor 52 and brush bar motor 48. It waits until
the motors 48, 52 reach operating speed and then moves off. As the
cleaner moves forwards (step 115) it dispenses power cable 95 from
the cable reel so that the cable lies substantially along the path
taken by the machine 10. Due to the potential for odometry errors,
the cable 95 may be dispensed at a rate which is slightly higher
than the rate of movement of the machine 10.
[0035] The machine then begins a series of manoeuvres. The series
of manoeuvres may comprise, for example, random movements, a spiral
pattern, a so-called `spike` pattern, or any combination of
movement types. which in combination will be referred to as a
`spike`. The basic spike is shown in FIG. 7. The machine turns so
that it is pointing away from the boundary (wall), inwards into the
working area. It travels forwards on a path which is substantially
perpendicular to the boundary (step 120). The machine derives
information on the distance and direction of travel from the
odometry wheel sensors 18. As the cleaner moves forwards, along
path 331, it dispenses sufficient power cable 95 from the cable
reel 71 so that the cable 95 lies slackly along path 331. During
this movement, the machine continually monitors inputs from the
sensor array 20-26,30 to sense the presence of any obstacles in its
path. The machine continues to travel forwards until one of a
number of conditions are met. Should the machine sense the presence
of an obstacle (step 125) or the absence of a surface (e.g. a
staircase), or if the machine senses that it has dispensed all of
the power cable 95 from the reel 71, or if it senses some other
fault condition, it will immediately stop. If none of these
conditions are met, the machine will stop after a predetermined
distance has been travelled from the boundary. This distance will
depend on the type of working area where the vehicle is working. In
a domestic environment we have found that a maximum distance of 2-3
m works well.
[0036] Once the machine has stopped, having met one or more of the
conditions mentioned above, it reverses back towards the boundary
following a similar path 332 (step 135, FIG. 4). The machine
rewinds cable 95 during this return manoeuvre. For best cleaning
performance, the suction motor 52 and brush bar motor 48 are
operated during this return manoeuvre so as to treat the same area
of floor twice. This replicates the kind of `to and fro` cleaning
action that a human user performs when they use a vacuum cleaner.
As an alternative, during this return manoeuvre the suction motor
52 and brush bar motor 48 can be switched off. This would be a
useful way of increasing battery life for a battery powered
machine.
[0037] During the return manoeuvre, the machine can navigate
towards the boundary by using odometry information or it can follow
the cable 95 which was laid on the floor during the outward trip,
the process previously described as `cable follow mode`. Thus, the
machine detects the orientation of the cable with respect to the
chassis and follows the cable accordingly. This outward trip into
the working area and back again to the boundary constitutes the
previously mentioned `spike`.
[0038] As the length of the outward part of the spike increases,
the likelihood that the machine will drift from the intended path
also increases. Odometry errors, wheel slippage, changes of surface
material and the direction of carpet pile are some factors which
can cause the machine to drift from an intended path. In the
unlikely event that the outward and return paths of the spike are
spaced apart and an object lies between the paths, then there is a
risk that the power cable can become wrapped around the object. In
these circumstances, it is preferable for the machine to navigate
back to the boundary in the cable follow mode (steps 137, 138).
[0039] Once the machine has returned to the boundary, which it can
sense from its sensor array and odometry information, it turns so
that it is once again pointing in a clockwise direction, with its
left-hand side aligned with the boundary. It moves forwards for a
short distance which is sufficient to bring the machine next to the
strip of the floor which has just been treated. The cleaner then
turns so that it is again pointing away from the boundary, inwards
into the working area. The machine then travels forwards at an
angle which is substantially perpendicular to the boundary, as
before. The machine continues as previously described, traversing a
strip of the floor surface which is adjacent, or overlaps, the area
previously treated.
[0040] The machine repeats this sequence of steps so as to traverse
a plurality of paths extending into the working area from the
boundary, as can be seen in FIGS. 5 and 6. As the machine
progresses around the boundary it can be seen that the spikes
originating at different parts of the boundary can overlap one
another. This helps to ensure that as much of the working area as
possible is treated by the machine 10.
[0041] After completing each spike, the machine checks whether it
has covered the entire working area (step 140). This check can be
performed in various ways. In its simplest form, the machine can
use an on-board sensor to sense whether it has returned to a
starting position on the boundary. Preferably, a marker 98 is
provided on the power cable 95 at a position adjacent the plug so
that the machine can sense when it has returned to this position.
The marker 98 can be a magnetic marker and the machine can be
provided with a magnetic field sensor, such as a Hall-Effect
sensor, for sensing the marker. Alternatively, the machine
generates a map of the working area and updates this map so as to
record areas of floor visited by the machine. Thus, by using this
map, the machine can determine when it has completely covered the
working area. After each spike the machine also checks (step 145)
to ensure that it has sufficient cable 95 remaining on the cable
reel 71 to continue travelling around the boundary.
[0042] Step 145 requires the machine to have the capability to
detect the amount of cable 95 remaining on the cable reel 71. This
can be achieved by marking the cable 95 in a manner which indicates
the quantity of remaining cable 95 and providing the control system
with a sensor which can detect the markings. Alternatively, an
encoder on the pinch roller 70 can feed the control system with an
indication of the amount of cable 95 dispensed from the reel 71.
This is advantageous because the same mechanism can be used to
detect any jamming of the cable 95. In a simpler machine this step
can be omitted entirely and the machine can simply stop when all of
the cable 95 has been dispensed from the reel 71, wherever this may
be in the room.
[0043] If the machine determines that it has completely covered the
working area, it travels back to the starting position in the
working area. The machine can follow the boundary of the working
area, rewinding the cable 95 as it moves around the boundary.
Alternatively, the machine can operate in cable follow mode,
rewinding the cable 95 and following the path formed by the cable
95 on the surface of the working area. In the event that this
brings the machine near to an obstacle, the machine can revert to a
boundary following mode of operation until it is determined that
the cable 95 leads away from the obstacle, whereupon the machine
can once again operate in cable follow mode. The machine will
eventually return to the starting point near to the power socket
310.
[0044] In large working areas the machine may run out of cable
before it has completely covered the working area. In this case,
the machine proceeds to perform the same technique as has
previously been described in the opposite direction from the
starting point (step 170, FIG. 4). Thus, the cleaner follows the
boundary in an anti-clockwise direction, aligning the right-hand
side of the machine with the boundary of the area and performing a
series of spikes outwardly from the boundary of the working area.
FIG. 8 shows the same area as previously shown in FIG. 5. It is
assumed that during the initial clockwise trip around the area, the
cable was fully dispensed at point X. The machine has returned to
the start point at the socket 310 and has begun travelling
anti-clockwise around the boundary. The machine begins `spiking` as
soon as it returns to the start position. It will be appreciated
that the spike movements performed by the machine as it travels
anti-clockwise around the boundary are mirror images of the spike
movements illustrated in FIG. 7. The machine will continue in this
manner until either the cable 95 is again fully dispensed or the
navigation system detects that point X has been reached or
passed.
[0045] FIG. 9 shows an alternative scheme in which the machine,
once it has returned to the start point at the socket 310, begins
to travel around the boundary in the anti-clockwise direction.
However, instead of immediately beginning to spike into the area,
it simply travels around the boundary, dispensing cable, until the
navigation system detects that point X has been reached or passed.
The reason for this difference is because it may be easier for the
machine to detect when it reaches point X if the machine travels
there directly as there will then be fewer accumulated odometry
errors.
[0046] For the machine accurately to detect when it has returned to
a point where cleaning finished previously (such as point X), it
requires some form of mapping function. The machine needs to have
the capability to map the working area and record where it has
visited in the working area. The map can be constructed using
odometry information which is acquired from the odometry wheels 18
and/or information about features of the working area which is
acquired from the object detection sensors 20-26, 30 in a manner
which is known in the art. The machine can then use the map to
determine when it has returned to a point on the boundary which it
previously reached via a journey in the opposite direction around
the boundary. It is preferable to allow a good overlap region, as
accumulated odometry errors can cause some error between the actual
position of the machine, and the position of the machine as
determined by the map.
[0047] If the machine lacks any form of mapping function, then it
can simply continue to work in the opposite direction around the
working area until the cable has all been dispensed. This can
result in a considerable region where the surface is treated
twice.
[0048] Alternative embodiments of the invention are shown in FIGS.
10 and 11. In FIG. 10, the cable orientation detection mean
comprises a pivotable member 77 in communication with a
potentiometer 76, as before. However, in this embodiment, the
pivotable member 77 is arranged to pivot about a vertical axis 78.
The end portions of the member are co-incident with the axis 78,
with the central portion of the pivotable member protruding in a
horizontal direction. The central portion of the member has an
aperture 79, through which the cable 95 extends. Deviations of the
position of the cable 95 from the straight back position of FIG.
10b causes the member 77 to pivot about the axis 78 (FIG. 10c),
which motion is translated into an electrical signal by the
potentiometer 76. The signal is proportional to the extent of
deflection of the cable 95. This arrangement is suitable for
detecting slight deflections. A second cable detector for detecting
greater cable deflections is provided in the form of a collar 80
around the cable 95. The collar 80 is pivotable about a vertical
axis and is arranged adjacent two microswitches 81, 82, one either
side of the collar. As shown in FIG. 10d, when the cable 95 is
deflected to the extreme left with respect to the chassis, the
cable pushes against the collar 80 and urges it against the
left-hand microswitch 81. Thus, a signal is sent to the control
system of the machine indicating that the cable 95 is at an extreme
position. Similarly, if the cable 95 extends to the extreme right,
the collar 80 depresses the other microswitch 82.
[0049] A further alternative is shown in FIG. 11. This embodiment
employs a pivotable member 83, also pivotable about a vertical axis
84. The top end portion of the member is in direct communication
with a potentiometer 76, also aligned on the vertical axis 84. The
central portion of the pivotable member 83 protrudes further in a
horizontal direction than does the member of FIG. 10. An aperture
85 is provided for the cable 95. In this embodiment, the pivotable
member 83 translates deflection of the cable 95 into rotational
motion. This rotation causes the potentiometer 76 to output a
signal in dependence on the amount and direction of deflection of
the cable 95. It has been found that this embodiment provides
satisfactory results for all deflections of the cable, even at
extremes. Thus, microswitches are not required in this
arrangement.
[0050] Further variations may be made without departing from the
scope of the invention. For example, the machine need not employ a
cable-follow operation. Alternatively, or additionally, the machine
may employ signals from the rotary encoder and/or pressure switches
in order to avoid running over its own cable or somehow getting
tangled in the cable.
* * * * *