AU603483B2 - Automatic control of work platforms - Google Patents

Description

ATNhTRADT-MARKS COMMONWEALTH OF AUISTHA\A IA T; A$.ALI om1 PATENTS ACT 1G15 2 COMPLETE SPECIFICATION (ORIGINAL) 7 FOR OFFICE USE: Application Number: Class Int. Class Lodged: Complete Specification Lodged: 0 Accepted, 0 Pu blished: P-riority, Relate'd Art:

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Name of Applicant: Add ress of Applicant: Adtjiai Jkiventor: Address for Service' TO BE~ COMPLETED BY APPLICANT FREDERICK PETER FITZGERALD 9 Osterley Avenue, Bridgewaterr State of South Australia, Commonwealth of Australia FREDERICK PETER FITZGERALD Care of R.K. MADDERN ASSOCIATESt 345 King William Street, Adelaide, State of South Australia, Commonwealth of Australia Com~iete Specification for the invention entitled:, "AUTOMATIC, CONTROL OF WORK PLATFORMS" The following statement is a full description of this invention, Including the best method of performing It known to me.

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1 111 lj This invention relates to the automatic control of work plat~forms and in particular to a circuit means ,that provides safe operation and automatic relevelling of a work platform -that is being raised and lower-ed by hoists Common use is made off work platforms that are raised and lowered by hoists (where hoist is equivalent to winch) wherein the work plahforms are suspended by cables from a fixed elevated point. Movement of the work platform up and 10 down the cables enables the work platform to access areas such as the external surfaces of high rise buildings, and are useful in many other applications where access is required to otherwise inaccessible surfaces.

Presently a hoist is affixed to each end of a work platformr whereupon two persons are used to control the upward or downward control of those hoists. With this configuration either the different speeds of the hoist motors or the different operation of each of the hoists by the operators results in the platform becoming more than substantially out of level.

A further problem encountered is the oscillations created by the stopping and starting at either of the sides of the platform of the hoist motors by their respective operator~s. This process places a large amount of strain on the suspension cables and incizeaseq the wear and tear on the hoist motors when starting and stopping during oscillation periods.

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-2- There exists control means which allow a single operator to control both hoist motors simultaneously, however the different hoisting speeds of these motors often results in the platform moving from a substantially level position to an unsafe inclined position. Under manual control it is not uncommon that once the hoist motor is switched off to correct this situation, the inertia of the work olatform will continue to cause oscillations of the platform as the suspension cables 10 extend and contract. Obviously, if a hoist motor is e a O O Sswitched on under such circumstances, quite excessive loadings on the hoist and motor can result.

a Should a working platform become unlevel, then in order to prevent any worsening of the situation, it is essential that all of the hoist motors be prevented from *I0 continued operation. Some of the prior art automatic ccntrol systems, function by allowing the hoist at the lower end of the work platform to continue operating while the high side hoist remains stationary, and once the platform is level the de-energised hoist is once again turned on. Obviously, it is preferable that if a work platform were to become inclined, then both hoist motors should be de-energised, and the work platform then p levelled. Also the turning off and then on of the hoist motor creates, as it is mentioned above, a great deal of oscillating motion, which may result in the malfunction of the inclination sensing means, in addition to the increased wear and tear upon the hoist motors.

-3- L^ It is also vitally important that all the normal control commands i.e. UP, DOWN and EMNERGENCY STOP he unaffected in their operation and safety aspects.

It is an object of this invention to inte,-'facoQ to the existing controls and operation of commercially available hoists and ensure that their operation is unchanged from normal operating procedures and additionally introduce safety features to enhance the operation of the platforms which are integral to the embodiment of the invention.

o Therefore, it is an object of this invention to provide an automatic levelling control means 04 (incorporating desired safety features) and that overcomes the abovementioned problems and allows a single operator: to control the motion of the platform upwards and 444 downwards along the suspension cables.

00 In its broadest form, the invention comprises a work 4..:,platform control means for maintaining the platform in a substantially level position when being raised or lowered by two or more electrically powered hoists comprising an inclination sensing means that provide a signal 441 should the platform be in an out of level position, and a cficuit means that, senses the signal of the inclination sensing means, and stops operation of said hoists when the platform is out of level, 4- 6-T (ii) causes a C.irst delay period, (iii) after said first delay period operates the hoist on the low side of the platform until the platform is substantially level, where upon the operation of the hoist is stopped, (iv) causes a second delay period, and after said second delay period recommences operation of all said hoists to continue raising or lowering the platform.

said pair of hoists, a circuit means providing a first

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delay period after which the hoist on the low side of the S*.oO platform is operated until the platform is level, and then oI a 0 stops operation of that hoist, a further circuit mens providing a second delay period after which the pair of hoists are operated to continue raising or loworing the platform.

0 In a further aspect of this invention, the automtticj control means is provided with a de-bounce circuiit where the output from the inclination sensing means is p'ovided 20 with hysteresis to ensure that the threshold inclination 4 0 I angles have occurred. These threshold angles represent a oi limits of what is considered not substantially level. The i f. de-bounce circuit is used to filter the inclination li ~sensing device output so as to provide definite indication to the hoist controller that these thresholds have been achieved. This de-bounce circuit ensures that any oscillations caused by the stopping or starting of the hoist in an upward or downward motion are interpreted correctly.

-1 The automatic control means is preferably located between the two hoist motors and interfaces the external power supply to the hoist control relays hoists. This enables the control means to be fitted to existing work platforms without major electrical wiring changes.

Miniaturisation of this preferred embodiment could be such that the level control means may be incorporated into the respective hoist housings with integral or external inclination sensing devices and suitable connections between hoists at each side of the working 0 0 o platform.

Sr oAdditionally, this invention could be used to allow the joining of like working platforms and thus allow O o0 0* the movement of a number of platforms in concert with 0 *0 each other, for example a number of platforms interlinked to move up and down together.

Qo* Further, the invention could be used to control the automatic control of level of the platform in the transverse axis, by incorporating pairs of inclination sensing devices orthogonal to the existing pairs of 4 °*0o inclination sensing devices and using the existing or an 00 additional circuit to sense their output at ptaset angles.

A still further application of this invention would be the control of the hydraulic levelling legs of vehicle chassis which support cranes and the like while stationary to stabilise the chassis of the vehicle during crane operation.

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A preferred embodiment of the invention will now be described, but it will be understood that th:e invention need not be limited to any one or combination of the following features.

In this embodiment, an automatic control means is provided to maintain a platform that is being operated by hoists in a level position. A pair of hoists is preferably attached at each end of the longitudinal axis of the work platform. The control system is preferably positioned in the centre of the work platform along one of its faces and the power supply input to both hoists is I t directed via the automatic level control means and associated safety control means.

"tooIn order that the invention may be more clearly understood, reference will now be made to the accompanying drawings, wherein: 0 4 Fig. 1 shows a schematic of the logic of the automatic levelling controller; Fig. 2 shows a circuit diagram of the automatic levelling controller when used with an ASTRO winch; Fig. 2a shows a circuit diagr'am of the changes required for the automatic level con~troller when used with an ASTRO winch; and Fig. 3 shows the do-bounce circuit wliich interEaces the inclination sensing device with the automatic level controller; -7-

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4* *4 4 44 4 *4 4 4* q* 4 *4 4 *4 #4 4 4 4* 4 #4 44 4 o 4* *4 *4 *4 p *4 4 *4 4 Fig. 4 shows a further circuit diagram of the automatic levelling controller when used with an ALPHA winch device; Fig. 5 shows a circuit embodiment of Fig. 1.

The preferred automatic level control means embodiment comprises Up/Down and Emergency Stop buttons which are hand-held or integrated into each hoist housing; a control card comprising an inclination sensing device which in this embocdiment is a pair of mercury switches, 2,0 switch de-bounce circuits; main circuit breaker; control, latch and main contactor relays circuit; an overload current sense circuit and a logic controller circuit.

The automatic level control means is interposed between the A.C. single phase power supply and the left and right hand hoists and acts upon control signals fromi the controllers..In further embodiments a single controller can provide the necessary control signals.

In addition to the above, a changeover switch is available to direct the incoming A.C. supply to General Purpose Outlet.0 via an Earth Leakage Circuit Breaker (EL!CB) for use while the working platform is in a stationary position. The hoists cannot be operated while the General Purpose Outlets (GPO's) are in use. This is forced upon the operator for Safety reasons and additionally reduces the power requirements to the working platform. Lighting upon the working platform would require a separate A.C. supply.

di A variey oE features are incorporated in this device which includes a maximum de~ad and live load detection device and circuit, which provides automatic cut-out of hoist operation, while preset limits are exceeded.

In this preferred embodiment the operator or operators select an upward mode of travel by selecting "UP" on the remote hand controls. One operator can operate the platform since the "UP" and "DOWN" controls are not momentary contact type switches. Both hoists travel in the upward direction until one hoist becomes out of level If ~approximately 50 When this occurs, both hoists stop.

6 6 After 1.8 seconds, the lower of the two winches climbs until the platform is no longer greater than 50 out of level and then stops. Both hoists remain static for 3 seconds, then both continue in the upward direction until one person releases the selector switch or presses the o emergency stop button.

In this embodiment it is a characteristic of the mercury switches that iv-.s signal is only available at the predetermined angle and the combination of the dc-bounce 41 circuit hysteresis and winch mot~or overrun ensure that the out of level return prorcess provides a platform angle of approximately 00 to the horizontal. Alternat~ive embodiments utilizing a range of angle sensing signals will allow greater accuracy of level posi.6tioning.

Alternatively, the operator or operators select a downward mode of travel by selecting "DOWN" on the remote hand coptrols. Both hoists travel in the downward direction until one hoist becomes out of level by approximately When this occurs, both hoists stop.

After 1.8 seconds, b'e lower of the two hoists climbs until the platform is no longer greater than 5° out of level and then stops. Both hois':.s remain static for 3 seconds, then both continue in the downward direction 04 4 i until one person releases the selector switch or presses o 9 o the emergency stop button.

10 This embodiment provides aircuits for control of 0 0 an 'ASTRO' winch as manufactured by POWER CLIMBER N.V., o a Smallestraat 28, B2008, ANTWERPEN, BFLGIE 03-2314856 but a further embodiment for control of an 'ALPHA' winch manufactured by SKY CLIMBER ANTWERPEN, BELGIE, 03-2314856 is also given.

SIn this embodiment, the inclination sensing device comprises a pair of mercury switches. In use it has been 0'found necessary to encapsulate the switches to lesson the .0 likelihood of damage. An arcuate shaped mercury switch is best employed, known as a banana switch, which is designed in this embodiment to become an open switch when inclined to horizontal at 5° or more. A first pair (one for each angle either side of the perpendicular) of mercury switches is used to detect the out of level condition i.e.

greater than or equal to 5° and a second pair of mercury switches is used to detect the extreme out of level condition i.e. greater than or equal to The second 0 0 C

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pair of mercury switches, if activated, ceases operation of the hoists until a reset procedure is undertaken which includes manual correction of the platform level and will not allow resumption of normal operation until the platform is substantially level. These mercury switches are mounted within the equipment enclosure which itself is designed to be mounted on a rail parallel to the longitudinal axis. It can be seen that a similar arrangement, of inclination sensing devices could be 10 located within or outside the equipment enclosure to detect inclination orthogonal to the transverse axis of the working platform.

Both mercury switches will make and break contact through their oircuit while in the vicinity of their 15 trip angles, and more particularly a rapid make and break occurs if the platform is oscillating while at the vioinity of the trip angle. Therefore, circuitry is provided to de-bounoe or add a hysteresis to the contact brake action. Fig. 3 shows the conditioning circuit that achieves this function. With the values of components shown, the time taken to switch off the conditioning circuit is 0.67 seconds; when the mercury switch is closed and the time taken to switch on the output whon the switch opens again is 0.39 seconds. As shown the output of the conditioning circuit is fed to a transistor which energises a relay and its contactors switch the 240V to the logic controller, and operate an indicator LED. This -11-

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foregoing circuit is associated with the fi':st pair of mercury switches which are set to detect the tilt of the platform equal to or greater than Hoist operation is controlled via the automatic level control device which includes a logic controller.

A representation of the logic which controls the various operations is provided in Fig. 1. This logic is powered ,uvp upon the switching of the master control switch to 0 9 "WINCH" and the MAXIMUM TILT level cosense safety circuit is brought into circuit to ensure a substantially level 0 00 o D platform exists prior to allowance of the operation of the a S° "hoists. Additionally, if the hoists are not plugged into hand controllers and in turn the hand controllers are not 0 00 O plugged into the control box, no operation of the hoists oan be effocted. If both controllers are ON, then they 0o0 must as forced by the logic, select the same direction of travel or no operation of the hoist can be affected.

0* °As shown in Fig. 2, the current drawn by the two i hoists is monitored by the Ovor Current Protector devico I 20 and when a preset quantity is reached, all hoist ofraion I is ceased. The preset quantity is detormiod from manufacturers' recommendations and safe working practices k-i in relation to dead and livo loading of the platform.

"ii Different platform sizes and loadings require different settings.

This overload signal and the 8° maximum tilt signal are detected by a latching relay and in turn actuate the -12ii main contactor to cease the operation of the hoists. This trip function will not automatically reset. A manual reset procedure must be initiated, either after a lessening of loading, or manual re-levelling of the platform.

The implementation of this invention is shown ,n but one way and there will exist to the skilled addressee numerous other suitable circuits. However, the functions, performed in this embodiment by relays, are an integral requirement of the operational and safety features of this invention.

POWER UP Referri. i to Fig. 2, with the actuation of the 16 Amp Double Pole Miolature Circuit Breaker power is I I! supplied to the 20 Amp Double Pole Two Position 0 1F switch, and (b the 2 Amp Control Miriaature Circuit Breaker (positioned within the device and is not capable of bing activated unless the device is opened).

The 20 Amp switch allows selection of either WINCH t X operation or GPO usage. In the GPO position, A.C. supply is fed via an Earth Leakage Circuit Breaker to a pair of Amp Weatherproof GPO's. In this mode, as is clear from the circuit, the WINCHES cannot be operated.

In the WINCH position, both the Active and Neutral of the A.C. supply are fed via Auxilliary Contacts MT3 and M14 of the Main Contactor relay to the Control Platform 1. Automatic Level-Printed Circuit Card (CPI-AL- PC Card) has ultimate control of the A.C. source to -13the winches via pin 1 cable I\ for the left hand side winch and pin 5 cable IA to the right hand side winch.

A.C. supply for the remainder of the device is sourced via the 2 Amp M.C.B. The over curent protectors at pin Al are first followed by the first of two pairs of inclination sense devices. A prior descri)tion provides details as to their operation. This first pair is the Maximum Tilt Sense Device 80 preset). A- will become clear after explanation of the circuit, if either 1 of this pair of switches is opened as a result of the platform tipping greater than or equal tr) 80, the o 44 platform will totally stop and a manual reset procedure will need to be conducted prior to resumption of operation. This Maximum Tilt Sense Device is also in 15 series with the Emergency 9TOP Button (located on the til ASTRO winches) referred to in Fig. 2a, and has the same effect and consequences when they are operated. The circuit for this interconnection begins at the output side of the Normally Closed Tilt Sense Device and via cable 5 connects to pin 3 of the 10 pin connect/ disconnect device associated with the left hand side (LHS) winch. Continuing via cable 5 of the 10 core plus earth mm Multi-Core PVC Flex cable to pin 3 of the LHS pin winch disconnect female.

Via the internal cable 5 of the winch to the N/C Emergency STOP Button and return via pin 10 cable of the Multi-Core cable, pin 10 cable 10 of the -14- Jz'I' 4, 00 o 04 0 0 0 0 0 G4 0 4 0 04~~q 0 0 0 4 connect/disconnect device associated with the LHS winch and via cable 10 (link) to the Right Hand Side (RHS) connect/disconnect pin 10. Continuing via cable 10 to pin 10 of the RHS winch, via the N/C Emergency STOP Button on the RHS 'ASTRO' winch. Thus via pin 5 cable 5 the circuit follows via cable 5 through the RHS connect/ disconnect device and onto pins 8 and 9 of the device via a link.

The following description involves the operation of three relays referred to as the Control Relay (RI), Latch Relay (LR) and Main Contactor They are interrelated via their auxilliary contactors and ultimately via the Main Contactor Auxilliary contacts which control the supply of A.C. on both the Active and Neutral sides to the CP1-AL-PC card.

It is these contacts which bring about the cessation of winch operation.

At power up, assuming that the circuit switches thus far described Max Tilt, Emergency STOP switches) are closed and an Over Current condition does not exist the following will applIy.

R1 is energised and since its coil and its contactors react more quickly than the MI contactor coil and contacts, the RI Auxilliary contact opens and rohiai-s open while RI is energised. Therefore LR, which is a momentary latching relay, is not energised from the source Active via R1 or the open MIAuxl. MAuxl is open since MI has not 1 yet fully energised, but, when it does via the closed LRAux, MI will then close MIAuxl contact.

Thus the LIVE condition of the relays (O=open, C=closed E=energised, NE=not energised) is as follows.

RI R1 Aux LR LRAux MI MIAuxl, 2, 3, 4 LIVE E O NE C E C O C C EMERGENCY BUTTON/MAX TILT DEVICE OPERATION :o 1 Since these devices are N/C and in series when any S t one of them are operated, Rl is de-energised for an 10 equivalent time, which closes R1 Aux and LR is energised %(pulsed) for that short period as well, via the momentarily closed R1 Aux contact and also closed MIAuxl contact. With 1,R momentarily energised LRAux opens and de-energises the MI coil. This in turn operates the MIuxl 15 to open, thus closing off the supply to the LR coil.

S, Concurrently, with the MI coil de-energised the MIAux3 and 4 coi.hact open and A.C. supply is ceased to the CP1-AL-PC .o Card.

S: R1 R1 Aux LR LRAux MI MIAuxl, 2, 3, 4 Momentary NE C O NE C

EME/TILT

Note that the LRAux contact is a mechanically latched relay and requires a pulse to operate 'ON' and a pulse to a1 operate 'OFF'.

R1 Rl Aux LR LRAux MI MIAuxl, 2, 3, 4 Post E 0 NE 0 NE O C 0 0 Momentary

EME/TILT

-16- \Fi~ An Over Current Protector is associated with each of the winches. A DOLD type MK9053 current protector relay manufactured by E. DOLD SONS, Posfach 60, D-7743 Furtwayen, Schwartzwald, WEST GERMANY, is used. This relay measures the arithmetic average of the rectified measuring current.

The auxilliary voltages required are provided via an Active to the Al terminal and Neutral to the A2 S 10 terminal. External control is provided for setting of a e 9 response/trip valve and a release/reset valve via an 9 externally adjustable hysteresis potentiometer. These 0 o settings are made using test loads and different settings are required for various platform sizes and loadings.

15 When the predetermined trip current is sensed the auxilliary contact provided within the relay is closed and the Active via its own pin 11 is shunted to the coil of LR via its own pin 14 output.

This initiates the shut-off process as described 20 for the Max Tilt/Emergency STOP sequence. The current protector relay auxilliary contact is operated open again, Safter the hysteresis period has elapsed and the protector relay is reset for' normal monitoring operation. The hysteresis period is preferably less than 5 seconds otherwise the LR relay coil will burn out.

-17- .P "I After manually correcting the cause of the 'STOP' the respective relays will have the following condition.

R1 R1 Aux LR LRAux MI MIAuxl, 2, 3, 4 Pre RESET E 0 NE O NE O C O O When the Reset Switch is pressed and mode A.C. active is available via the closed Max Tilt Device circuit via the Emergency STOP buttons on the winches to the RESET switch. Since MIAux2 contactor is closed the reset switch *00<*0 S« 10 allows the LR coil to be energised which mechanically 0 a resets LRAux to the closed position thus allowing Active 0 to the MT coil. MIAux2 opens thus negating the RESET a o 6 S, switch function and MIAux's 3 and 4 are then closed restoring A.C. to CPl-AL-PC card.

15 Rl Rl AUX LR LRAux MI MIAuxl, 2, 3, 4 °"Post RESET E 0 NE C B C O C C o w0l S* 0 0 1 UP AND DOWN CONTROL In this ombodiment UP and DOWN controls are available S 20 on the ASTRO winch housings or on separate hand controllers in the ALPHA winch configuration. A further J iembodiment would be to link across these control switches ,and splice the control wires and place buttons in series *to the appropriate control lines and provide alternative UP and DOWN control switches. The Emergency STOP buttons could be replaced in a similar manner.

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controls into the enclosure of the automatic levelling device and thus allow a neater and more convenient device and enable one occupant to control all the operations of the platform.

Fig. 4 displays a schematic of the logic which controls the UP and DOWN function of the Automatic Level Control device. This logic is contained in the CPl-AL-PC card circuit. Fig. 5 shows a circuit embodiment of this logic.

UP SIGNAL INPUT This signal to the CPl-AL-PC card is generated as a consequence of the operation of the UP switches on both the winches (Astro embodiment). A.C. is sourced from pin 8 15 of *the RIUS connect/disconnect device. This AC is communicated via the Maximum Tilt device and1 Emergency STO1? switches, via cable 8 to pin 8 of the RHS winch, the circuit is taken via the Rope Sot switch and the RHS winch UP switch which is integral to a two position UP, DOWN 20 selector switch. The switch can only be set up or down, and as will be apparent both switches in both winches must be of the same selection. Via cable 6 to pin 4 of the winch the circuit is taken to pin 4 of the connect/disconnect device via cable 6. The circuit carries along cable 6 to the LHS connect/disconnect device pin 4 and continues along cable 6 to pin 4 of the LHS winch connector. Via cable 6 to the UP switch and when made to the Rope Set Switch then via cable 8 to pin 8 of the a, a a at a.

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II I I I It through the LHS connect/ disconnect to cable 8 connected to pin 10 of the CP1-AL-PC card. This pin is designated the UP input. An A.C. signal present on this input denotes an UP command for both winches.

UP SIGNAL OUTPUT This signal is generated after the CP1-AL-PC card receives the UP signal input.

Both winches simultaneously receive UP energisation 10 current. Pin 2 of the CP1-AL-PC card provides UP energisation to the LHS winch via cable 3, pin 5 of the LHS connect/disconnect device, to pin 5 of the LHS winch, then via cable 3 of the ASTRO winch, which then drives the LHS of the platform upward.

15 Pin 6 of the CPl-AL-PC card provides UP energisation to the RHS winch via cable 3, pin 5 of the RHS connect/disconnect device, to pin 5 of the RHS winch, then via cable 3 to the ASTRO winch then drives the RHS of the platform upward.

20 A much abbreviated description of the DOWN SIGNAL follows since the operation is the same as for the UP SIGNAL albeit on different circuits.

DOWN SIGNAL IMPUT This signal to the CP1-Ati-PC card is generated as a consequence of the operation of both the DOWN switches I II I I I I It C It I I I It 1*41 a a IC I I I

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A.C. is sourced from pin 8 of the RHS connect/disconnect device. Via cable 9 to pin 9 of the RHS winch, via the Rope Set switch, the DOWN switch via cable 7 to pin 7 of the RHS winch and then via cable 7, across to the LHS connect/disconnect to pin 7 of the LHS winch, via the DOWN switch, the Rope Set switch via cable 9 to pin 9 of the LHS winch and to cable 9 leading to pin 9 of the CP1-AL-PC card. This pin is the INPUT DOWN pin and is activated when A.C. is impressed on pin 9.

DOWN SIGNAL OUTPUT St f This signal is generated after the CP1-AL-PC card S. receives the DOWN signal input. Both winches 4 44 simultaneously receive DOWN energisation curreit.

15 Pin 4 of the CPl-AL-PC card, via cable 4 to, pin 6 of 0 0• Soo, the LHS connect/disconnect device, via cable 4 to pin 6 of 4 the LHS winch, then via cable 4 of the ASTRO winch, which 0 0 then drives the LHS of the platform downward.

Pin 8 of the CPl-AL-PC card, vio cable 4 to, pin a44 20 6 of the RHS connect/disconnect device, via cable 4 to "pin 6 of the RHS winch, then via cable 4 of the ASTRO winch, which then drives the RHS platform downward.

WINCH ACTIVE ~While power is available to the relay circuits, MIAux's 3 and 4 are closed. In particular MIAUx3 is conneching A.C. Active to the CP1-AL-PC card. Terminals 1 and 5 of the CPI-AL-PC card via cables 1A, via inputs -21- 4 .J.

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44 ft 4 t t *4 4 44 4 44 at #4 4 4 4 44 44 44 .4 4 o 0@ 0 4* 0 44 00 4 4 44 4 40 4 o 44 4444 o a.

a, 4 cable number 1, pin 1, cable 1 to pins 1 on both the LHS and RHS winches.

WINCH NEUTRAL In particular MIAux4 is connecting A.C. Neutral to the CPI-AL-PC card. Terminals 3 and 7 of the CPI-AL-PC card via cable 2, via pin 2 of both the connect/disconnect device, and to pin 2 of the RHIS and LHS winches.

CPI-AL-PC Card 10 This card contains a circuit which mimics the logic provided in schematic form in Fig. 1 and shown in detail in Fig. The platform out of substantial level signals are provided by inclination sensing switches, comprising, in 15 this embodiment, mercury switches designed to go open circuit when an angle o£ 5° or greater is achieved. If the platform was proceeding upwards or downwards and the LHS winch becomes higher than the RHS winch and the platform is at an angle of 5° or greater to the 20 horizontal, then the mercury switch connected between terminals 13 and 14 of the CP1-AL-PC card go open circuit, Both winches stop. A 1.8 second time delay takes place allowing any winch cable bounce to cease. The lower RHS winch will then continue upwards until the platform is level as determined by the level sense devices becoming closed circuit. Both winches stop and a 3 second delay takes place allowing any winch cable bounce to cease. Both winches then travel in their given direction of travel.

*440 4 4444 44«

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4-i ,from the lef t hand or right hand angle sense device initiates via the OR gate the first 1.8 second time delay before the right or left hand up control signal is generated. The next signal from the left or right hand angle sense device indicates a return to an inclination of less than 50 and the timning device initiates a 3 second time delay before recommencing the combined left and right up or down movement of the platform.

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Claims (7)

1. A work platform control means for maintaining the platform in a substantially level position when being raised or lowered by two or more electrically powered hoists comprising an inclination sensing means that provide a signal should the platform be in an out of level position, and a circuit means that, senses the signal of the inclination sensing means: and stops operation of said hoists when the 10 platform is out of level, (ii) causes a first delay period, (iii) after said first delay period operates the hoist on the low side of the platform until the platform is substantially level, whore upon the operation of the 15 hoist is stopped, (iv) causes a svcond delay period, and after said second delay period recommences operation of all said hoists to continue raising or lowering the platform.

2. A work platform control moans according to claim 1 furthoer comprising an inclination sensing moans being provided in reolation to each said hoist wherein when the platform is oi, of level an inclination sensing means indicates which hoist is to bo oporated to roturn the platform to a substantially levol position. -24-

3. A work platform control means according to claim 2 wherein said inclination sensing means comprise mercury switches having tubes with an arcuat.e shape and a pair of contacts at one end which provide a normally closed circuit until inclined to an angle or 50 or greater.

4. A work platform control means according to claim 3 wherein each said mercury switch is connected to a do- 46 64 bounce circuit which provides a hysteresis delay t the opening or closing of the inclination sensing means. a A work platform control moans according to any a 0preceding claim wherein there is provided a second 0 69 inclination sensing means as a fail safo.

6. A work platform control means according to claim 8 4wherein the said second inclination sensing device provides a signal when inolined at an angle of So or a: greater.

7. A work platform control means according to any preceding claim whereain said inclination sensing means snses inclination about a transvorse horizontal. axmi of the work platform, and who 'oin a further pair of inclination sensing moans is provided to sense inclination about a longitudinal horizontal axis of the work platform. 7; 8. A work platform control means according to any precoding cicim further comprising an over cuCrent circouit breakor and an emorgoncy stop button wherein said circuit, means, current circuit broaker and emergency stop b'tton are in sarias and operation of oither oC them halts movement of the work platform. ii

9. A work platform control means according to claim 8 wherein the power source may bb switched from the control means to provide earth leakage protected general purpose outlets. A work platform control means substantially as hereinbefore claimed and described with reference to the accompanying figures. 0 @0 0 0 0 00 00f 00 0 O0 0 oe 0 a0 00 40 a 4 B 0 0 04 Dated this 20th day of September, 1988. FREDERICK PETER FITZGERALD, By his Patent Attorneys, R.K. MADDERN ASSOCIATES 0 04 9 6« 0 a0 -26- 1 A