GB2481709A

GB2481709A - Load sensitive safety device for an aerial lift

Info

Publication number: GB2481709A
Application number: GB201111049A
Authority: GB
Inventors: Paul CUMMINGS; Kevin Johnathan Gale; Allan Malcolm Starck
Original assignee: Blue Sky Access Ltd
Current assignee: Blue Sky Access Ltd
Priority date: 2010-07-02
Filing date: 2011-06-29
Publication date: 2012-01-04
Anticipated expiration: 2031-06-29
Also published as: GB201111049D0; GB2481709B; GB201011135D0

Abstract

A safety device for an aerial lift (10 fig. 1) having a basket or cage with operator controls 23 for manoeuvring the basket to a desired location and a foot operable safety switch 24 which provides a switch-closed signal to the controls 23 before the controls become operable, the safety device comprising a load sensitive bar 160 extending across the basket proximate to controls 23 and an auxiliary safety switch 26 connected in series with the foot switch 24 with its contacts (C1 fig. 4) normally in a closed condition (switch on) and in the event that the bar 160 is subject to a preset minimum load, the switch 26 is operated to change the contacts to a open condition (switch off) thereby cutting off the switch-closed signal. The minimum load may be preset for the load sensitive bar 160 by spring means (166 fig. 3). The load sensitive bar may be a fixed bar (173 fig. 6) having a pressure sensitive safety edge or bumper (175 fig. 6). Auxiliary safety switch 26 may be connected to an alarm such as a flashing beacon or an audible warning device. Auxiliary safety switch 26 may include a signal filter to prevent switch off of power until a desired time period has elapsed and thus prevent switch off due to inadvertent loads on the bar 160.

Description

An Aerial Lift with Safety Device

Field

This invention relates to an aerial lift with a safety device and in particular to an aerial lift having a cage or basket mounted on the end of an extendable boom.

Background of the Invention

Building construction sites for large buildings frequently employ aerial lift equipment for lifting operatives to elevated locations for, for example, the installation of overhead pipe work during the construction of a building.

A typical aerial lift may comprise a mobile elevated work platform (MEWP) having an extendable boom which has an elevator basket or cage for housing operatives secured to the end of the boom. The basket may contain a control panel which permits a user standing in the basket or cage to manoeuvre the cage to a raised location which facilitates the carrying out of work. The boom is typically raised by a powered hydraulic system on the vehicle.

The controls in elevator baskets typically include foot operable safety switch which needs to be closed before controls on the operator panel may be operated. If the safety device is released the movement of the basket ceases immediately. However in some situations, operators can become trapped between the MEWP basket and an overhead structure before they can either remove their foot from the foot operable safety switch or operate the emergency stop switch. Operators trapped in this way can be crushed sometimes fatally.

In EP-A-2096 078, the present applicant has described a safety device comprising a tensioned wire or cord arranged proximate to said controls and an auxiliary safety switch connected in series with the foot safety switch, the auxiliary switch having a set of contacts in use held in a closed condition (Switch on) by said tensioned cord or wire, and in the event that the cord is distorted the contacts are changed to a open condition (switch off) thereby cutting off the switch closed signal. This causes the movement of the basket to cease immediately.

The present invention provides an alternative safety device.

Statement of Invention

According to a first aspect of the present Invention there is provided a safety device for an aerial lift having a basket or cage with a control panel which permits an operator standing in the basket to manoeuvre the basket to a desired location, a foot operable safety switch which provides a switch-closed signal to a control means before controls on the control panel become operable, the safety device comprising a load sensitive bar extending across the basket proximate to the control panel and an auxiliary safety switch connected in series with the foot safety switch, the auxiliary switch having a first set of contacts in use held in a closed condition (Switch on) and in the event that the bar senses a load thereon the switch is caused to change the contacts to a open condition (switch oft) thereby cutting off the switch closed signal.

The auxiliary switch can be located in the power feed to the footswitch or in the electrical signal line between the footswitch and the control means.

Preferably, the auxiliary switch is located in the power feed to the foot safety switch upstream thereof.

The load sensitive bar may comprise a movable bar which operates the switch when subject to a transverse load. The moveable bar is biased to an equilibrium position by spring means so that the bar is moveable only when subject to a preset minimum load. Preferably the preset minimum load is

adjustable.

Alternatively the load sensitive bar may comprise a fixed bar having a pressure sensitive safety edge thereon, for example a Mayser IP 65. Safety Edges are sensors which may be offered as a normally closed contact. If a part that includes the safety edge or bumper strikes an operator (or vice versa) the flexible safety edge is depressed and will send a signal to the auxiliary switch to open and the automatic movement is stopped The auxiliary switch may include a second set of contacts that operate an alarm. The alarm may comprise a beacon and/or an audible warning device. The alarm may further include an RE' transmitter which sends a radio signal to at least one further alarm remote from the basket and which includes a co-operating receiver which operates said alarms.

The auxiliary switch may include a signal filter device which inhibits a change in signal from the first and/or second set of contacts until a desired time period has elapse so as to prevent the switch off of power to the foot safety switch due to inadvertent loads acting on the load sensitive bar.

The auxiliary safety switch and the alarm are connected to the safety foot switch through readily connectable and dis-connectable pin and socket connectors facilitating the assembly and dis-assembly of the safety device from the basket for testing, maintenance or re-placement.

A second aspect of the present invention provided for an aerial lift having a basket or cage having a control panel which permits an operator standing in the basket to manoeuvre the basket to a desired location, a foot operable safety switch which needs to be closed before controls on the operator panel become operable, and a safety device according to the first aspect of the invention.

The alarm may be mounted to the underside of the basket.

The basket may be mounted at one end of an extendable boom, which is typically raised by a powered hydraulic system on the vehicle.

Description of the Drawings

The invention will be described by way of example and with reference to the accompanying drawings in which:-FIG. 1 is a view of MEWP according to the present invention mounted on an extendible boom, Fig. 2 is an isometric view a basket or cage mounted on the extendible boom shown in Fig. 1 having an auxiliary safety switch with a load sensitive bar, Fig. 3 is an isometric view a portion of the basket of Fig 2 showing s first load sensitive bar Fig. 4 is a wiring diagram for incorporation of the safety switch into the circuit of the control panel in the basket and shown with auxiliary switch in a closed condition, Fig. 5 is a portion of the wiring diagram shown in Fig 3 showing the auxiliary switch having been activated, Fig. 6 shows an alternative load sensitive bar.

Fig. 7 is a schematic diagram showing an alternative embodiment of the invention including signal filters.

Detailed Description of the Inventi

With reference to Figs 1 of the drawings, there is shown a MEWP in the form of a self drive mobile lift of any suitable type. The MEWP has a drivable vehicle body 11 having wheels 12 and an extendable boom 14 mounted on a load carrying platform 13 at the rear of the vehicle body. StabiliserS 15 may be provided for steadying the vehicle on the ground G. A basket or cage 20 is mounted on the free end of the boom 14 and the basket, in use, can be raised or lowered and generally manoeuvred relative to the ground as is well known. The basket 20 is shown in a raised condition. The boom 14 is raised, lowered, extended, rotated etc. by any suitable means, typically operated by a powered hydraulic system provided on the vehicle body. The boom may be provided with a load sensor 18 which senses the total load on the boom.

The NEWF 10 shown is for example only and any type of aerial lift may be used and the present invention is applicable to any form of aerial lift, including scissor lifts, having a operator carrying basket, cage or platform which is provided with controls in the basket that allow the operator to manoeuvre the basket and sometimes the vehicle, utilising the MEWP power systems.

With reference to Figure 2, there is shown the lift or elevator basket 20 having a floor 21 surrounded by a safety barrier 22. The basket 20 is provided with a control including a control panel 23 and a foot switch 24 whereby an operator standing in the basket 20 can cause the basket to be moved to a desired location. The foot operated safety switch 24 must be depressed before an operator in the basket can cause the lift 10 to move the basket. In the event that the foot safety switch 24 is raised any movement of the basket will cease immediately. The foot switch 24 is typically connected to a control means V (see Fig. 3), usually a valve, which shuts off the vehicle's power supply to prevent movement of the basket in the absence of a switch-closed signal from the foot switch 24. An emergency stop 30 is also provided on the control panel 23. The general movement of the basket is controlled by a control lever 25. The control panel 23 may be partially protected by protection bars 36 and a back plate 37.

An auxiliary safety device comprising a switch 26, a load sensitive bar 160 and alarm 33 is also provided on the basket 20. The auxiliary switch 26 is mounted on or within the control panel 23. The switch 26 is connected via connector 31 and circuitry within the control 23 to the foot switch 24 and is operable to cut-off the power supply PWR to the foot switch 24 which has the same effect as the operators foot being removed from the foot switch 24. A suitable switch is a Guardmaster lifeline 4 available from Allen & Bradley. The switch 26 includes a first set of contacts Cl (see Fig.3) which are closed unless activated.

With reference to Fig. 2 and Fig 3, the auxiliary switch 26 is mounted on or within the control panel 23 and is operated by a load sensitive bar switch activation means 160. The contacts Cl C2 within the auxiliary switch 26 are preferably operated by a solenoid 27 (shown in Chain dotted outline in Fig.3) which receives an activation signal from the load sensitive bar 160 to operate the switch 26.

The switch activation means 160 comprises a support bar 161 mounted across the front of the control panel 23. The support bar 161 is mounted on the protection bars 36 by means of brackets 162. The support bar 161 has a pair of spaced apart cylindrical housings 164 thereon. Reciprocating pins or pistons 165 are guided and supported for movement in the housings 164 and a safety bar 163 is mounted on the pistons for relative movement of the safety bar 163 away from and towards the support bar 161. At least one of the two housings 164 includes a micro-switch 169 operated by inward movement of the respective piston 165.

The pistons 165 are spring loaded outwardly of the housing by for example coaxial springs 166 (shown schematically a double headed arrows) acting between the bar 163 and the respective housing 164. The load on the springs 166 may be adjusted by means of a screw adjuster ring 167 so that the bar 163 requires a pre-set minimal load before it is pushed inwardly towards the support bar 161 to activate the micro-switch(es) 169 and send a signal to the solenoid 27, to operate the auxiliary safety switch 26. A re-set button 168 is located on the support bar 161 for re-setting the auxiliary safety switch 26 after activation.

In an alternative arrangement (not shown) the switch may be operated 26 may be operated not by the solenoid but by direct mechanical linkage between the moveable safety bar 163 and the auxiliary switch With respect to Fig. 6 there is show yet another switch activation means 170. The switch activation means 170 has components in common with the switch activation means 160, and comprises a support bar 161 mounted across the front of the control panel 23. The support bar 161 is mounted on the protection bars 36 by means of brackets 162. The support bar 161 is connected to a rigid a safety bar 173 mounted on the support bar 161 by a pair of spaced apart supports 172.

A safety edge 175 or bump is mounted on the front of the safety bar 173. Safety edges are known A safety edge or safety bumper can be classified as a "trip" device. In general the safety edge and safety bumper and are particularly suitable for use on machines which stop immediately after removal of power. A complete safety edge consists of an aluminium rail, the safety contact, and the safety contact strip. The special shapes of the safety edges (rubber profile) protect the safety contact strip from damage. Safety bumpers operate in the same manner as the safety edge with the only construction difference being the addition of foam rubber covered in polyurethane to protect any object that comes in contact with the safety bumper. A signal from the safety edge causes the operation of the solenoid 27.

The auxiliary switch 26 also include a second contact set C2 (see Fig.4) which are connected via connector 32 to an emergency alarm 33 which is mounted on the basket 20 in a visible location, preferably on the underside of the floor 21. The alarm 33 may include an RF transmitter which send a radio signal to at least one further alarm (not shown) remote from the basket 20 and which includes a co-operating receiver which operates the second alarm.

Referring also to Fig 4, there is shown the electrical circuit for the safety device. The power feed line PWR to the foot switch 24 is diverted upstream thereof to a socket 41 within the socket part 31A of connector 31. A cooperating pin 51 of the plug part 31B of connector 31 is connected via electrical cable FL2 to contacts Cl and C2 in the auxiliary safety switch 26 in parallel. The other sides of contacts Cl and C2 are connected via electrical cable B and C to separate pins 52,53, respectively on the plug part 31B. The pins 52,53 are connectable with cooperating sockets 42 and 43 on the socket part 31A. The socket 42 is connected via electrical wire A and connection block 34 to the foot switch 24. The other socket 43 is connected by electrical cable D to a socket 63 of the socket part 32A of connector 32. A second socket 64 of the socket part 32A is connected by cable E to Earth or ground. The socket 63 is connectable with a co-operating pin 73 on the plug part 32B of connector 32. The pin 73 is connected by cable D2 to the alarm 33. The alarm 33 is grounded via cable F connected to pin 74 on the plug part 32B. The pin 74 co-operates with socket 64 for grounding the alarm 33.

As shown in Fig. 4, the auxiliary switch 26 is set with contacts Cl closed and contacts C2 open. In this condition, the power feed line PWR is connected through connector 31 to the contacts Cl to the foot switch 24. The contact C2 is open cutting off power to the alarm 33.

With reference to Fig. 5, when the solenoid 27 is activated, the contacts Cl and C2 within the auxiliary switch 26 are caused to move so that Cl becomes open and C2 closes. In this state, the power feed line FL2 is disconnected from the pin 52 of the connector 31 and the power feed line FL2 is connected to the pin 53 of the connector 31. In this state power is supplied to the alarm 33 and disconnected from the foot switch 24 and valve means V immediately imrnobilisiflg the movement of the basket 20.

The auxiliary switch 26 may include signal filter device T (shown in chain dot) downstream of Cl and C2 which inhibits a change in signal, i.e. power signal, from the first and/or second set of contacts until a desired time period has elapse so as to reduce or prevent triggering of the safety switch due to inadvertent loads acting on the tensioned cord.

With reference to Fig.7, there is shown a further embodiment of the safety device 80 in which the power feed line PWR to the emergency stop 30 is diverted to a connector 91 which serves to connect the device 80 to safety foot switch 24.

The safety device 80 includes an auxiliary safety switch 81 in the form of a relay 81. The relay 81 is connected to a control box 83 which can cause the contacts in the relays 81 to be closed to allow electricity to flow to the footswitch 24 or open thereby cutting the flow of electricity to the foot safety switch 24.

The control box 83 may include a programmable processor and is connected to a switch activation device 87, similar to the safety edge 170 described earlier, via a signal filter 86. The control box 83 is also connected to an alarm 84 via a pair of timers 88,89 and to a re-set device 85.

The control box 83 is also connected to the power input PWR.

The relay 81 is normally held in a closed condition allowing power to pass through the relay to the footswitch 24. In the event that the safety edge 87 is triggered, a signal S is sent to the control box 83 via a signal filter 86. The signal filter 86 removes signals having a time period less than a pre-determined limit, for example >0.6 seconds. If the signal S greater than the predetermined period, in this example 0.6 seconds or longer, the control box 83 operates the relay 81 to open and cut power to the foot switch 24 causing movement of the basket 20 to stop immediately. A signal S2 is also sent to the alarm 84 via the signal timer 88 to cause the alarm to "pulse" for a pre-set time period, say 10 seconds.

The control box 83 is connected to the reset button 85 and if the load has been removed from the safety edge 87, the operation of the re-set device stops the alarm and recluses the relay 81 allowing the controls 23 to again operate the lift.

After the pre-set time period as measured by timer 88 a further timer 89 causes the alarm the go into a continuous mode by for example operation of a relay and keeps the controls in an inactivate condition.

The controls cannot be operated until the pressure/load is removed from the safety edge and the re-set device 85 activated.

When the controls 23 are first switched on the control box can go through a self diagnostic routine and initially sound the alarm and opening the relay contacts 81. The re-set device 85 is then activated to close the relay contacts 81 and make the controls 23 ready for use.

Claims

Claims 1. a safety device for an aerial lift having a basket or cage with a control panel which permits an operator standing in the basket to manoeuvre the basket to a desired location, a foot operable safety switch which provides a switch-closed signal to a control means before controls on the control panel become operable, the safety device comprising a load sensitive bar extending across the basket proximate to the control panel and an auxiliary safety switch connected in series with the foot safety switch, the auxiliary switch having a first set of contacts in use held in a closed condition (Switch on) and in the event that the bar is subject to a preset minimum load operating the switch to change the contacts to a open condition (switch off) thereby cutting off the switch-closed signal.
2. A safety device as claimed in Claim 1, wherein the load sensitive bar comprises a movable bar which operates the switch when subject to a transverse load.
3. A safety device as claimed in Claim 2, wherein the moveable bar is biased to an equilibrium position by spring means so that the bar is moveable only when subject to said preset minimum load.
4. A safety device as claimed in Claim 3 wherein the preset minimum load is variable.
5. A safety device as claimed in Claim 1, wherein the load sensitive bar comprises a fixed bar having a pressure sensitive safety edge or bumper thereon which is in the form of a normally closed contact.
6. A safety device as claimed in any one of Claims 1 to 5, wherein the auxiliary switch is located in the power feed to the foot safety switch upstream thereof.
7. A safety device as claimed in any one of Claims 1 to 6, wherein the auxiliary switch includes a second set of contacts that operate an alarm.
8. A safety device as claimed in Claim 7, wherein the auxiliary switch includes a signal filter which inhibits the changes in signal from the first and/or second set of contacts until a desired time period has elapse so as to prevent the switch off of power due to inadvertent loads acting on the moveable bar.
9. A safety device as claimed in Claim 7 or Claim 8, wherein the alarm comprises a flashing beacon and/or an audible warning device.
10. A safety device as claimed in Claim 5 wherein the auxiliary safety switch is operated by a relay controlled by a control box which is connected to the pressure sensitive edge.
11. A safety device as claimed in any one of Claims 7 to 10, wherein the alarm includes an RF transmitter which send a radio signal to at least one further alarm remote from the basket and which includes a co-operating receiver which operates said remote alarms.
12. A safety device as claimed in Claim 10, wherein the control box is connected to the switch activation device via a signal filter that passes only signals having a predetermined minimum time period.
13. A safety device as claimed in Claim 12, an further including an alarm wherein the signal to the alarm passes through a timer so that the alarm is operated after a pre-set period
14. A safety device as claimed in Claim 13, wherein the timer is located between the control box and the alarm and permits the alarm to operate intermittently for said time period.

15. A safety device as claimed in Claim 114 wherein the control box is connected to a reset device allowing the alarm to be switched off.
15. A safety device as claimed in Claim 13 or Claim 14, wherein the control box is also connected to the alarm via a second timer which causes the alarm to operate continuously after said pre-set time period.
16. A safety device as claimed in any one of Claims 1 to 15, and further including readily connectable and disconnectable pin and socket connectors whereby the auxiliary safety switch and the alarm are connectable to the footswitch facilitating the assembly and dis-assernbly of the safety device from the basket.
17. An aerial lift comprising a basket or cage having a control panel which permits an operator standing in the basket to manoeuvre the basket to a desired location, a foot operable safety switch which needs to be closed before controls on the operator panel become operable, and a safety device as claimed in any one of Claims 1 to 16.*::r: INTELLECTUAL . ... PROPERTY OFFICE 19 Application No: GB 1111049.1 Examiner: Mr Karl Whitfield Claims searched: ito 17 Date of search: 24 October 2011 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims Y 1-11& GB2457908 A 15-17 (BLUE SKY) fig. 2 Y 1-4,6-11 US4362196 A & 15-17 (FERDINAND et al.) rail 16 & switch 18/19 X,Y X: 1-3, KRi02009O118467A Y: 4-u, (SHINHANGONDOLA CO LTD) fig. 3 15, i6 & i7 X,Y X: 1 & 5, KR 102009062779 A Y: 6-u (WOO JONG KIL) figs. 2 & 3 & i5-i7 X,Y X: i-3, KR i020090063626 A Y: 4-u (WOO JONG KIL) frame 140, switch i80 & 15-17 Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.same category.& Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB. EP, WO & US patent docjments classified in the following areas of the UKCX Worldwide search of patent documents classified in the following areas of the IPC B66F The following online and other databases have been used in the preparation of this search report WPI, EPODOC International Classification: Subclass Subgroup Valid From None Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk