[0001] This invention relates to a control system for an elevatable and extendible structure
and is especially but not exclusively applicable to the control of a turntable extending
ladder mounted on a fire engine.
[0002] Turntable ladders are usually mounted on fire engines so that they can be taken rapidly
to the scene of a fire or other disaster for the purpose of rescuing trapped people.
A difficulty which arises in the operation of a turntable ladder is that the ladder
is often extended transversely of the vehicle and the weight of an additional person
at the top of the ladder can produce a sufficiently large moment to overturn the vehicle
even if it is supported by stabilising jacks. The operators of such a ladder are aware
of the limitations of its use, but as rescues are frequently carried out in emergency
conditions the stresses of such conditions can cloud the judgment of the operator.
In order to avoid having too great dependence on the operator's judgment of the extended
length of a ladder and its angle of inclination indicators of these values are sometimes
provided in association with an indication as to whether the use of the ladder will
be safe with one, two or more persons on it. Whilst such indications would enable
the ladder to be used safely at all times, it is possible that the operator could
be distracted at a crucial instant and permit the configuration of the ladder to become
dangerous for its intended use.
[0003] It is an object of the present invention to provide a control system which would
enable the ladder to be used up to the limits of its safe operation without the need
for the operator to keep a close eye on the indications of its length and elevation.
[0004] According to one aspect of the present invention there is provided a control system
for an elevatable and extendible structure in which a limit, dependent on the load
on the structure and the actual extended length of the structure, is imposed on the
elevation, and a limit, dependent on the load on the structure and the actual elevation
angle of the structure, is imposed on the extended length of the structure.
[0005] According to a second aspect of the present invention there is provided a control
system for an elevatable and extendible structure having first means responsive to
an elevation angle of the structure to produce an indication of the angle and second
means responsive to the extended length of the structure to produce an indication
of the length, wherein the system includes means for entering a proposed mode of use
of the structure and is responsive to the indications produced by the first and second
means and to the r proposed mode of use to impose limits on the elevation angle and
extended length of the structure.
[0006] The modes of use of the structure may include indications of the loadings to be applied
to the structure and the limits may be determined by the likelihood of the structure
being overturned by the loading applied to it.
[0007] The structure may be a turntable ladder which may be mounted on a suitable vehicle
to form a fire engine or fire appliance. Alternatively, the structure may be a cage
or platform on an elevatable telescopic boom mounted on a vehicle for rescue and maintenance
applications.
[0008] Control signals for the structure may be applied to it through the system from manually
operable input devices. The system may be arranged so that as the elevation or extension
approaches the limit value the maximum rate of change of the variable is limited to
a lower speed.
[0009] The system may include numerical displays of the elevation angle and the extended
length, a display of the selected mode of operation, and means for indicating when
the limits are reached. A graphical display of the disposition of the structure may
also be provided.
[0010] Where the structure is to be mounted on a vehicle it may be provided with means for
preventing the structure from colliding with the cab or other part of the vehicle
by inhibiting movements likely to cause a collision. The system may also be used to
monitor the correct operation of stabilising jacks on the vehicle where such are provided.
[0011] If the structure is a ladder it may be provided with sensing means producing an indication
of the inclination of the rounds (rungs) of the ladder to the horizontal, and the
system may be responsive to that indication automatically to produce output signals
for correcting the inclination. In addition, the extension may be adjusted to values
such that the rounds on adjacent ladder sections are aligned.
[0012] The structure may be provided with a load cell responsive to bending forces on the
structure, for example due to the structure striking part of a building in performing
a required movement. The system may respond to signals from the load cell to inhibit
such movement of the structure as would increase the bending forces.
[0013] The system may be provided with an override switch allowing slow movement of the
structure under manual control outside the limits imposed by the system. The system
may include tests on the operational state of the various monitoring devices and may
permit manual control only where a device is suspect.
[0014] In order that the invention may be fully understood and readily carried into effect
it will now be described with reference to the accompanying drawings, of which:-
FIGURE 1 shows a fire engine with a turntable ladder suitable for control by a system
according to the present invention;
FIGURE 2 is a block diagram of one example of a system according to the present invention
based on the information flow in the system;
FIGURE 3 is a flow diagram showing part of the operation of the ladder control system;
FIGURE 4 is a flow diagram showing the initialisation and error detection of the operation
of the system;
FIGURE 5 is a diagram of the system shown in Figure 2 but divided in accordance with
the structural components of the system; and
FIGURE 6 shows the detail of the graphic display produced by the system.
[0015] The fire engine shown in Figure 1 consists of a vehicle chassis having a cab 1
-with an extending ladder 2 mounted on a turret 3 on a turntable 4 on the platform
4A of the chassis. The ladder 2 is supported by a gimbal, not shown, and is elevated
by a single dual concentric hydraulic ram 5 extending between the turret 3 and brackets
6 on the underside of the ladder 2. The plumbing of the ladder, that is to say the
levelling of its rounds or rungs which is necessary when the engine is standing on
an inclined surface, is effected by two hydraulic rams one on each side of the ladder
of which that on the left-hand side has the reference number 7. Further details of
the mounting of the ladder on the turret are given in British Published Patent Application
No. 2 105 298A.
[0016] The ladder 2 is extended by means of a wire rope system which may be as described
in British Published Patent Application No. 2 105 398A, the wire system being operated
by a drum, not shown, and an hydraulic motor driving the drum. The operator of the
ladder is provided with a seat 8 and has controls and display equipment on a console
9.
[0017] For accommodating the ladder 2 whilst the engine is being driven there is provided
a cradle 10 just behind the cab 1 and on the chassis of the engine there are provided
four jacks of which two having the references 11 and 12 are shown, which jacks can
be extended diagonally downwards for the purpose of stabilising the engine when the
ladder 2 is erected.
[0018] Figure 2 shows in block diagrammatic form a control system for the operation of the
turntable ladder shown in Figure 1 and includes a control processor 20 which is connected
to receive inputs from the ladder 2 representing its disposition and the loads on
it. These inputs are included in the broken rectangle 21 and include a digital shaft
encoder 22 connected to the rope drum driving the reeving system for extending and
retracting the ladder 2 and a second shaft encoder 23 connected by a parallelogram
or similar linkage between the ladder 2 and the turret 3 so as to produce a digital
output representing the elevation angle of the ladder 2 relative to the turret 3.
In addition, the ladder is provided with an electromagnetic sensor (Tilt unit 2) which
produces an analogue output representing the inclination to the horizontal of the
rounds of the ladder 2; this sensor is represented by the block 24. An analogue to
digital converter is included in the processor 20 to convert the analogue output to
digital form to represent the inclination of the rounds of the ladder. On the turret
3 are mounted further sensors represented by the block 25 which detect whether the
inclination of the turret is too great for the plumbing movement provided to level
the rounds of the ladder 2; these limits are typically 7
0 in either sense. The block 26 represents a switch on the ladder 2 which is operated
when the ladder is fully retracted or housed. Block 27 represents a combination of
load cells which are built into the ladder on the main ladder stringers just forward
of the junction between the stringers and the ladder frame to produce outputs representing
the loads up and down and from one side to the other on the ladder so as to detect
when the ladder is fouling on the building, for example.
[0019] The turntable 4 has other sensors included in the broken rectangle 30 in Figure 2.
Two of the sensors, 31 and 32, are electromagnetic tilt sensors which produce analogue
outputs which are converted to digital signals representing the fore and aft tilt
and the left and right tilt of the platform respectively. The two other sensors, 33
and 34, respond to the orientation of the turntable 4 on the platform 4A and produce
signals which are used as described below to prevent the ladder 2 colliding with the
cab 1 and to assist in parking the ladder on the cradle 10. The cradle itself has
a switch or other means for detecting when the ladder 2 is resting on it and this
is shown as block 35 in Figure 2.
[0020] The stabilising jacks of which two, 11 and 12, are shown in Figure 1 are extended
and retracted hydraulically in response to a manual control lever (not shown). The
position of this lever is fed to the control processor 20, Figure 2, from switches
represented by the block 36. The jacks themselves also have switches which are operated
when the jacks are sufficiently extended, and these switches are represented by the
block 37. Obviously all the jacks or must be secured/locked in the extended position,
before the ladder 2 can be used safely up to its operational limits.
[0021] The operator's console 9 (Figure 1) has various controls, display devices and warning
lamps which are used as described below to cause the ladder 2 to be moved to the required
position and to provide monitoring information to assist the operator in controlling
the ladder. The console is represented in Figure 2 by the block 38.
[0022] The control of the ladder itself and the other parts of the fire engine is performed
in response to outputs from the processor 20 using electric motors, electromagnetic
devices and solenoid valves to manipulate mechanical and hydraulic equipment. These
are represented by the block 39. The nature of the controlling devices and the ways
in which they are controlled will become apparent from the following description of
the system in operation.
[0023] From a consideration of Figure 2 it will be apparent that the control processor receives
two sets of inputs - those set manually from controls on the console and those monitoring
the status and disposition of the mechanisms under control - and produces two sets
of outputs - those applied to devices regulating the application of power to the controlled
mechanisms and those producing displays to the operator of the status and dispositions
of the controlled mechanisms. The manually set inputs are:-
1. System on/off
2. Ladder extend
3. Ladder retract
4. Ladder rotate left
5. Ladder rotate right
6. Ladder rounds alignment
7. Jacks extend
8. Jacks retract
9. Ladder elevate
10. Ladder depress
11. Intended ladder loading
12. Manual override switch - processor off-switch
[0024] The pairs of inputs 2 and 3, 4 and 5, and 7 and 8 may each be provided by three position
controls having an off position to which the control is spring loaded between the
two active positions.
[0025] The monitoring inputs are:-
1. Ladder length
2. Ladder elevation
3. Angle of ladder rounds to horizontal (Tilt unit 2)
4. Orientation of the ladder relative to the cab
5. The loading on the ladder - up/down forces
6. The loading on the ladder - sideways forces
7. "Inclination of ladder too great to permit complete plumbing" switches
8. Turntable tilt - fore-aft (Tilt unit 1)
9. Turntable tilt - left-right (Tilt unit 3)
10. "Ladder fully retracted" switch
11. Ladder cradle switch
12. "Jacks extended and locked" switches
13. "Jacks retracted" switches
[0026] Of these inputs, numbers 1, 2, 3, 5, 6, 8 and 9 are digital and are either derived
directly from shaft encoders or similar devices or from analogue signals by analogue
to digital converters. All the other inputs except number 4 are two-state ones being
derived from switches. The orientation of the ladder relative to the cab has four
states: away from the cab, too near the left, too near the right, and centrally disposed
over it. These signals may be generated by a combination of switches or by two electromagnetic
sensors resposive to elements on the turntable.
[0027] The outputs from the control processor which are applied to devices for regulating
the power applied to controlled mechanisms are all electrical signals which are amplified
sufficiently to perform the tasks allotted to them, which depend on the nature of
the regulating device. For example, the ladder extension and retraction is effected
by a wire rope system using a drum driven by an hydraulic motor, whereas the ladder
elevation and plumbing are effected by hydraulic rams. A motor speed control circuit
could be used for the hydraulic motor and solenoid operated hydraulic valves could
be used to control the ladder extension. The control outputs are as follows:-
1. Ladder extension
2. Ladder retraction
3. Ladder elevate
4. Ladder depress
5. Ladder plumbing (and to docking angle when low over the cab)
6. Turntable rotate - left and right
7. Jacks - down
8. Jacks - up
[0028] A half speed operation of numbers 1, 2, 3 and 4 is provided, which is used as the
parameter approaches the required value. Half speed operation is also possible under
manual control with the processor switched off.
[0029] The displays on the console, which are provided by the other outputs of the control
processor, are as follows:-
1. Numerical display of ladder length
2. Numerical display of ladder elevation
3. Graphic display of ladder disposition and stability limits of intended loading
4. Stability zone warning lamps: green, amber, red.
5. Plumbing indicators (lamps)
6. Normal and excessive loads on the ladder (lamps) and audible warning devices including
an indication'of the direction in which the load acts
7. Round alignment completed
--8. Jacks - extended and locked
[0030] In addition indications of error conditions are displayed and details of these will
become apparent from the description of the system in operation. The graphic display
may be substantially as described in British Published Patent Application No. 2 108
746A and as shown in Figure 6 of this application.
[0031] The purpose of the system is to prevent the ladder being inadvertently used outside
its stability limit. When the system is first switched on the control processor checks
that all of the inputs to it are reasonable, that the ladder length and elevation
correspond to it being parked on the cradle and that a valid expected man-loading
of 1, 2 or 8 is entered. Ladder operation is inhibited until the jacks are extended
and locked - this could include a check that all four are set firmly on the ground.
The system may also indicate other pre-conditions for operation which are not satisfied,
such as low fuel for the engine supplying electrical and hydraulic power or a fault
withe the engine itself. The fault indication may involve flashing of a lamp and identification
of the nature of the fault on one of the numerical displays, for example, which may
be adapted to display alphabetic and numeric characters. If a fault has occurred the
operator may override the system and use full manual control at half speed.
[0032] If all of the pre-conditions are satisfied and the "jacks set" signal is received,
the green stability lamp is lit and the disposition of the ladder is displayed numerically
and on the graphic display. The ladder can then be raised from the cradle and rotated,
elevated and extended as required. As soon as the ladder has left the cradle plumbing
is automatic and continuous. As the ladder approaches the stability limit for the
intended loading the green lamp goes out and the amber lamp is flashed until the limit
is reached when the red lamp is lit and the ladder movement is stopped. Further movement
of the ladder under control of the system is only possible in directions away from
the limit, i.e. retraction or elevation.
[0033] Impact of the ladder with the cab is prevented by the system, with the result that
the ladder can be brought over the cab only if the elevation angle is sufficient to
give clearance. When the ladder is central over the cab it can be lowered on to the
cradle to park it.
[0034] As mentioned above, shaft encoders are used to provide digital coding relative to
angular movement for elevation and ladder length. The elevation shaft encoder is mounted
at the side of the turret and is operated by a parallelogram type mechanical linkage
attached to the gimbal beam. The ladder length encoder is driven by a rear shaft from
a gear box located at the left hand end of winch drum and is in synchronism with the
mechanical output shaft for the mechanical ladder length indicator. The 'rounds aligned'
out put is also derived from the shaft encoder output for ladder extension in that
'rounds aligned' shaft codes are identified by the processor and signalled accordingly
when 'round alignment is selected by the operator.
[0035] The elevation shaft encoder is orientated to the turret and corrections are necessary
to ensure that the angular datums, with the exception of parking on the ladder cradle,
are referenced to the true vertical irrespective of attitude of platform. The data
for the necessary correction is applied to the processor by inclinometer type Tilt
Units. Tilt Unit 1 is located within the console and senses gimbal frame tilt in the
fore and aft axis. Tilt Unit 2 is located on the gimbal beam and controls plumbing
by sensing tilt in relation to the horizontal. Tilt Unit 3 is located within the console
at 90 degrees to the fore and aft axis of the ladder and is used exclusively to sense
deviation between the plumbing datum and the ladder cradle angular datum when making
up the ladder to the headrest.
[0036] The Tilt Units generate analogue voltages related to angle of tilt in one plane only.
The analogue voltages are converted into a digital code. In the case of the Tilt Unit
1 the voltages are converted to a digital code and by summation with shaft encoder
information within the processor, results in an output of true angular reference about
the horizontal. The true reference is used by the processor as the basis for comparison
with the preprogrammed operational envelope limitations and'the ladder loading selection
made by the operator. Both the true reference and operational envelope are displayed
on the graphic display.
[0037] When parking the ladder on the cradle because the inclinometer mounted on the gimbal
beam will plumb to the vertical at 90 degrees to the fore and aft axis of the ladder
it will invariably be necessary to correct the angle of the plumbing beam so that
it is parallel to the cradle when the ladder is parked. Tilt Unit 3 is mounted on
the gimbal frame and will sense the tilt on the gimbal frame, which with the ladder
central will provide the datum for comparison of the difference between the cradle
and plumbing beam. The signals from Tilt Unit 3 are inhibited until the ladder is
detected by the processor to be central with the headrest and moving through 10 degrees
of elevation towards the cradle. At this point the processor will compare the angular
difference between Tilt Unit 3 and the gimbal beam inclinometer inputs. The processor
will then initiate the appropriate plumbing control which will cause the rounds to
move into parallel alignment with the ladder cradle. Plumbing is not influenced by
Tilt Unit 3 except during the first 10 degrees of ladder movement with the ladder
central.
[0038] Certain aspects of processor programming are under direct control of the operator
and this is in the selection of the 1 man, 2 man, and 8 man loads which set the operational
limits for loading and stability. When the selected program is exceeded, i.e. the
processor system detects that the ladder position and speed is about to exceed the
selected operating envelope limitations, the processor will automatically initiate
slow and stop signals as required.
[0039] Ladder normal and side loads are derived from circuits within a 'Load Cell' unit
which accepts and interprets signals from two transducer strain detectors and associated
amplifiers, mounted on the main ladder stringers just forward of the junction between
stringers and ladder frame. The Load Cell converts amplified transducer outputs into
continuous down load and side load inputs which are used to drive the load indicator
meters. In addition the Load Cell detects maximum left, right and down strain outputs
from the transducers and provides the necessary signals as additional inputs to the
processor so that corrective control may be initiated. An overload situation is also
detected and signalled to the processor and to the operator both audibly and by lamp.
[0040] Ladder side impact is detected as an abnormal loading and is applied to the processor
by the Load Cell. The processor initiates STOP outputs to relays controlling hydraulic
solenoid operated valves when rotation load limits are reached. As there is no SLOW
control for the rotation operation a STOP signal only is initiated. The processor
will allow rotation away from the STOP in the normal way.
[0041] For control of the ladder close to the cab the processor receives control signals
from two proximity detectors as follows:
The two detectors are mounted on the turntable of the gimbal frame and are used to
centralise the ladder and also prevent rotation of the ladder at below 6° elevation
within a 45 degree arc of the base frame forward centre line to prevent collision
with the vehicle cab. A metal target is centred on the base frame and provides a segment
45 degrees either side of the turntable base so that with the ladder in line with
the cradle each detector is just within the operating arc of the target. Any movement
from the centre line will result in the appropriate detector (left or right) not sensing
the target and providing an output to the processor. It follows that with no signals
from either detector the ladder is outside the 45 degree quadrant either side of the
base frame centre line. In this case the processor will permit the ladder to be moved
to the maximum depression limits for ladder bridging operations. During-the ladder
parking operation the processor will automatically align the ladder to the cradle
by reference to the two tilt units, before the ladder reaches the cradle.
[0042] In addition, two detectors mounted to detect targets attached to the gimbal beam
are set to sense the 7 degrees maximum plumbing limits. A signal from either sensor
may cause the processor to inhibit control to the plumbing hydraulic circuits. At
the same time the ladder plumbed indicator will also be inhibited. The system may
be arranged to carry out the automatic plumbing as far as it can whilst producing
an indication that the ladder is not fully plumbed.
[0043] A flow diagram, shown in Figure 3, represents the sequence of operations performed
by the processor unit.
[0044] Faults may be present in the system before commencement of ladder operation or may
occur during system operation. At start-up the control processor checks the validity
of the following system transducers:
(1) "Jacks extended and locked" and jack lever input circuits
(2) Left and right cab protection proximity detectors
(3) Elevation and extension shaft encoders
(4) Tilt Units 1 to 3 (i.e. Gimbal beam, Gimbal frame fore and aft, Gimbal frame left
and right)
(5) Load cell inputs
(6) Maximum plumbing detectors
(7) Ladder fully retracted switch
(8) Man loading switch settings
[0045] Once the processor has checked the validity of the above transducer inputs, it will
assume that the transducers and the respective circuits are serviceable and the inputs
are correct for ladder operation.
[0046] All ladder operations are inhibited until a "Jacks extended and locked" signal is
received by the processor. The ladder may be manually operated without the processor
by switching OFF all electrical circuits or by switching OFF the processor unit power
supply at the switch on the side of the unit. The ladder may then be operated at half
speed, but there would be no stability limit cut-out and no 'stops' except the.ladder
fully retracted stop. The load cell and its indicators will remain functional if the
processor unit only is turned OFF.
[0047] The "Jacks retract" signal is an immediate cancellation of the "Jacks extended and
locked" signal and inhibits normal ladder control in the same manner as if a "Jacks
extended and locked" signal was not received. The fault is indicated by flashing stability
lamps and display of the appropriate fault on the digital display. The ladder may
be operated manually provided the jacks are firmly on the operating surface.
[0048] The left and right cab proximity detectors should both be active with the ladder
central at start-up but if one or both are inactive then a fault will be assumed and
once the ladder has been elevated above eight degrees it cannot be depressed below
eight degrees. The processor will not permit depression below eight degrees until
the manual override switch is operated and it will then allow depression below 8 degrees
while causing the CENTRAL indicator lamp to illuminate and the stability lamps to
flash ON and OFF. If a detector fault occurs during ladder operation the processor
cannot recognise the fault.
[0049] The elevation and extension shaft encoders are essential for the correct control
of the ladder by the processor. At start-up the processor checks validity codes approximating
zero to +2.5 degrees elevation and 30ft +1/0.lft in ladder length. If either of these
checks is incorrect the processor cannot accurately control the ladder within the
correct operational limits and should indicate the fault and stop operation of the
ladder. It can then be switched OFF thus removing stability limit control.
[0050] The Tilt Units 1 to 3 provide analogue outputs and the only fault that the processor
will recognise is an invalid voltage input in which case the appropriate fault condition
will be displayed.
[0051] If the load cell signals are detected active by the processor on start-up the processor
will cause the stability lamps to flash and will display the appropriate error code
on the digital display until the load cell reverts to normal inputs or the load cell
system is switched off. If the signals are activated during ladder operation the processor
assumes them to be valid and reacts accordingly. If excess side load is signalled
the processor inhibits rotation towards the load and only enables rotation away from
the side loading. If excess downloading is signalled the processor inhibits all ladder
operation except retraction, and monitors the override switch. When the override switch
is operated depression, elevation and rotation is enabled so that the fault may be
cleared by the operator.
[0052] If either of the two maximum plumbing detectors is active at the initial condition
of start-up it will either by due to an electrical fault or the ladder is located
seven degrees out of true with the cradle. The appropriate fault code would be displayed
and manual override would be available. Normal ladder operation using manual plumbing
control will be possible but on return to the cradle the processor will display an
error coding to indicate that inspection/maintenance is required. Maximum plumbing
will be limited by the mechanical stops.
[0053] The initiation of and fault detection in the ladder control circuits is summarised
in the flow diagram shown in Figure 4.
[0054] The ladder fully retracted switch is normally active at start-up but if not the processor
will permit normal ladder operation and the invalid check will be held in memory.
When the ladder is subsequently approaching the fully retracted position a stop will
be initiated at, say, 31 ft preventing further movement. The stability lamps will
flash and the appropriate error code will be displayed. The manual override switch
may be operated to permit further retraction of the ladder. If the fully retracted
switch is active at start-up and is active when the ladder extension circuits show
that the ladder has moved awar from the fully retracted position no fault is displayed.
The HOUSED indicator lamp will remain illuminated clearly indicating the fault.
[0055] The man loading switch is monitored by the processor for valid inputs which are applied
to the appropriate stability limits for the selected operating envelope. If an invalid
input is detected by the processor the operating envelope for the 1 man scale is reverted
to. The reversion can be checked by comparing the load scale lamps and the LCD display.
[0056] Figure 5 shows in block form the circuit of the system shown in Figure 2 divided
in structural units instead of in accordance with their functions. In Figure 3 the
processor unjt50 is connected directly to the ladder units 51, the console display
cabinet 52, the load cell 53 and the three tilt units 54, 55 and 56. The processor
unit 50 is also connected through circuit box 57 to console panel 58 and fulcrum frame
junction box 59. The console panel 58 is connected to telephone unit 60 and engine
control unit 61 controlling engine 62. The telephone enables the operator to communicate
with a man up the ladder. In general, the engine 62 is not the unit which propels
the vehicle but provides the hydraulic and electrical power for the ladder and its
turntable.
[0057] The fulcrum frame junction box 59 is connected through slip rings 63 between the
turntable 4 and the platform 4A to the engine control unit 61 and through cab circuit
64 to chassis circuit 65 and battery 66.
[0058] The processor unit 50 may be a conventional microcomputer with a microprocessor connected
through data and address busses to random access memory and read-only memory storing
the program data. The busses will also be connected to input/output interface devices
to receive and transmit the signals.
[0059] The circuit box 57, fulcrum frame junction box 59 and slip rings 63 merely provide
interconnections connecting the processor unit 50, which is located in the console
9 (Fig.l), to the ladder (for certain signals only), to the telephone unit and the
engine which are also carried on the turntable, and through the slip rings to the
chassis circuit and the cab circuit.
[0060] The ladder units 51 include the elevation and extension shaft encoders each of which
provides a 12 bit parallel input connected directly to the processor unit 50. An indication
of the stability state of the ladder is provided at its head in the form of 3 lamps,
one red, one amber and one green, which are lit in the same way as the corresponding
stability lamps on the console. The energisation for the stability lamps on the ladder
is fed through the circuit box 57 as are the power supplies for the shaft encoders.
The'ladder housed" status output indicating that it is fully retracted is returned
to the processor unit 50 through the circuit box 57 as well.
[0061] Each of the three tilt units 54, 55 and 56 receives its power supply from the processor
unit 50 and selectively returns high and low output signals to the unit 50 indicating
the amount of tilt. The polarity of the low output indicates the sense of the tilt.
[0062] The load cell 53 receives its energisation from the processor unit 50 and produces
as inputs to that unit down load and side load signals as well as signals indicating
that a predetermined maximum down load, left load and right load have been reached.
In addition an overload signal is produced.
[0063] Since the console display cabinet 52 produces indications of the status of the system
as outlined above it only receives inputs, mostly from the processor unit 50 but also
from the ladder units 51 (the housed signal), the console panel 58 (e.g. the number
of men to be on the ladder) and the chassis circuit 65 (indicating the position of
the jacks and whether the ladder is parked). As mentioned above the display includes
numeric indications of the elevation and length of the ladder as well as the graphic
display shown in Figure 6, together with indicator lamps. In addition the processor
unit 50 produces indications of faults and breakdowns in the form of error numbers
on the numeric displays. The display cabinet may include alphanumeric display means
enabling error codes to be displayed. Indications other than those provided by the
control system of the invention may be produced on the cabinet 51, e.g. an indication
that the hydraulic pressure for elevating the ladder is satisfactory.
[0064] The console panel 58 has the control switches for the system and also includes controls
for the engine 62 and for the telephone 60. As mentioned above, the chassis circuit
65 monitors the jacks and the ladder parked status; it feeds corresponding signals
into the system and the cab circuit 64 transmits them.
[0065] Figure 6 shows some details of the graphic display produced by the system which as
mentioned above is substantially the same as the display described in published British
Patent Application No. 2 108 746A. As shown in Figure 6, the display 70 consists of
a plurality of selectively energisable liquid crystal or light emitting diode elements
arranged to form sectors radiating from a centre, the sectors being divided into approximately
rectangular elements by circumferential lines about the same centre. The sectors represent
5° intervals in the ladder elevation in a range from 10° below horizontal (indicated
as -10°) to 80
0 with a lowermost sector representing from -10 to -15°. The operation of the display
is such that a line of elements in a sector is energised if the actual elevation angle
lies between the limits defining the sector, the length of the line representing the
extended length of the ladder in a range from 30 rounds to 99 rounds and each element
corresponding to an interval of 3 rounds, this being the minimum length difference
usable with a 4-section ladder, intermediate values not permitting round alignment.
In Figure 6, a line 71 of elements is shown energised indicating that the ladder elevation
is between 25° and 30° and its length is 87 rounds. The ranges of values include their
upper limits. At the centre from which the sectors radiate are an 80° sector 72 and
a 17
0 sector 73. The sector 72 is energised to produce a colour red if the ladder is elevated
to an angle in excess of 76°. The sector 73 is energised whenever the ladder is below
-15°. Three vertical lines 74, 75 and 76 are marked over the elements representing
the disposition of the ladder and these represent the maximum horizontal reach of
the ladder when carrying 1, 2 or 3 men respectively. The display includes a diagram
77 for showing the intended loading on the ladder, which may be 1 man, 2 men, 3 men
or 8 men. The diagram 77 is energised in such a way as to show the appropriate number
of pin-man figures. Eight-man working is only permissible when the ladder is bridged
to a wall or building.
[0066] The display 70 is operated by the processor unit 50 (Figure 5) in response to the
digital values representing the elevation and length of the ladder. These are represented
by the blocks 78 and 79 and are connected through a decoder 80 to display drivers
81 energising the display 70. A stop condition detector 82 is connected to respond
to the elevation and length values to produce outputs representing the stability status
of the ladder in its intended mode of use entered via a line 83. Since the ground
on which the vehicle is standing may not be level and the stability status of the
ladder depends on its true angle of elevation it is necessary to correct the elevation
value obtained from the shaft encoder 23 (Figure 2) by adding to it (in the correct
sense) the tilt of the turntable obtained from the sensor 31 (Figure 2), which is
also referred to as tilt unit 1. The tilt value represented by block 84 is an analogue
signal and is converted to digital form by converter 85 and added to the elevation
value. This addition would in practice be performed by the processor unit. A round
alignment signal represented by block 86 is combined with the ladder length value
79 to provide an indication when the length is correct.
[0067] In a modification, the display may be arranged so that instead of only a single line
of elements being energised, a block of elements filling the sector from the horizontal
line to the ladder elevation angle is energised up to the length of the ladder.
[0068] The display 70 is constructed using conventional light emitting diode or liquid crystal
display techniques.
[0069] In the system described the movements of the ladder are decided upon by the operator
who uses levers and switches to set the orientation, elevation and length of the ladder
to the values he thinks are required, and the system slows down such movements as
the ladder approaches its stability limits for the intended use and stops movement
beyond the limits. The system could be arranged to have further control on the ladder
movement so that it can be brought to a required position as quickly as possible within
the constraints of the stability limits.
[0070] The system may be modified by the omission of any of the described features or the
addition of extra features.
1. A control system for an elevatable and extendible structure in which a limit, dependent
on the load on the structure and the actual extended length of the structure, is imposed
on the elevation, and a limit, dependent on the load on the structure and the actual
elevation angle of the structure, is imposed on the extended length of the structure.
2. A control system according to claim 1 in which the limits are used to restrict
the moment of the load on the structure about the mounting of the structure.
3. A control system according to claim 2 in which manual control at full speeds of
the elevation and extension of the structure is provided within ranges of values subject
to the limits, and manual control at reduced speeds is possible outside the ranges.
4. A control system according to claim 1, 2 or 3 including a further manual control
input for indicating a mode of use for the structure, thereby defining an expected
load which is used as a basis for deriving the limits.
5. A control system according to claim 4 wherein the structure is a turntable ladder
mounted on a suitable vehicle to form a fire appliance.
6. A control system according to claim 4 wherein the structure is a cage or platform
on an elevatable telescopic boom mounted on a vehicle.
7. A control system for an elevatable and extendible structure having first means
responsive to an elevation angle of the structure to produce an indication of the
angle and second means responsive to the extended length of the structure to produce
an indication of the length, wherein the system includes means for entering a proposed
mode of use of the structure and is responsive to the indications produced by the
first and second means and to the proposed mode of use to impose limits on the elevation
angle and extended length of the structure.
8. A control system according to claim 7, wherein the indication of the extended length
is used in combination with the proposed mode of use to derive a limit on the elevation
angle, the indication of the elevation angle is used in combination with the proposed
mode of use to derive a limit on the extended length, and the proposed modes of use
indicate probable loadings on the structure, whereby the limits are determined to
restrict the likelihood of the moment of the loading about the mounting of the structure
exceeding a particular value.
9. A control system according to claim 8 including manual input means for setting
required values of the extension of the structure and its elevation angle, the system
producing control outputs for control elements for the structure until the first and
second means indicate that the required values have been attained or one or more limits
are reached.
10. A control system according to claim 8 or 9 including numerical displays of the
elevation angle and the extended length of the structure, a display of the selected
mode of operation and means for indicating when the limits are reached.
11. A control system according to clain 8, 9 or 10 including a graphical display representing
the disposition of the structure.
12. A control system according to any of claims 7 to 11 wherein the structure is a
cage or platform on an elevatable telescopic boom mounted on a vehicle.
13. A control system according to any of claims 7 to 11 wherein the structure is a
turntable ladder with sensing means producing an indication of the inclination of
the rounds of the ladder to the horizontal, the system being automatically responsive
to that inclination to produce output signals for correcting the inclination, and
to realign the rounds with a cradle as the ladder is returned to a rest position on
it.
14. A control system according to claim 13 in which the extension of the structure
is automatically adjusted to a value at which the rounds of adjacent sections of the
ladder are aligned.
15. A control system according to claim 12, 13 or 14 in which the rate of change of
the extension and/or the elevation angle is restricted as the or each limit value
is approached.
16. A control system according to claim 16 having a throttle value which is actuated
to restrict the flow of hydraulic oil for adjusting extension or elevation angle as
the or each limit value is approached.
17. A control system according to claim 12, 13, 14 or 15 including digital processor
means responsive to control signals from different sources in digital form to produce
digital control output signals in accordance with the required operation of the system.
18. A control system according to claim 17 in which the structure is mounted on a
vehicle with stabilising jacks, wherein the system includes means for monitoring the
position of the jacks and is arranged to inhibit normal operation if the jacks are
not extended and locked.
19. A control system according to claim 17 or 18 including load cell means responsive
to bending forces on the structure, the system being arranged to inhibit such movement
of the structure as would tend to increase the bending forces.
20. A control system according to claim 17, 18 or 19 including override switch means
permitting movement of the structure at restricted speeds outside the limits imposed
by the system.
21. A control system according to claim 17, 18, 19 or 20 wherein initially tests are
performed on the operational state of parts of the system and indications are produced
of those parts whose operational state is not satisfactory, and the system being arranged
to permit manual control at reduced speed of any operations involving a part whose
operational state is not satisfactory.
22. A control system for a truntable ladder mounted on a vehicle substantially as
described herein with reference to the accompanying drawings.