Abstract:
A safety device for an aerial lift ( 10 ) having a basket ( 20 ) with controls ( 23 ) which permit an operator to manoeuvre the basket ( 20 ), and a foot operable safety switch ( 24 ) which activates the controls ( 23 ), the safety device comprising an auxiliary safety switch ( 24 ) operated by a trip cord ( 27 ) arranged proximate to the controls ( 23 ) and which is connected in series with the foot safety switch ( 24 ) so that in the event that the cord is distorted the auxiliary switch ( 26 ) prevents activation of the control panel ( 23 ) and may additionally operate an alarm.

Description:
FIELD OF THE INVENTION 
       [0001]    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 
       [0002]    Building construction sites for large buildings frequently employ aerial lift equipment for lifting operatives to elevated locations for, for example, the installation of overhead pipework during the construction of a building. 
         [0003]    A typical aerial lift may comprise a mobile self drive lift having an extendable boom which has an elevator basket or cage for housing operatives secured to the end of the boom. The basket may contains a control panel which permits a user standing 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. 
         [0004]    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, it has been known for some operators to cut out safety procedures by jamming the switch into a closed position by the use of a foreign body such a piece of wood. In such a situation if the operator standing at the controls is disabled by accident when the basket is in a raised condition, if the operator is caused to releases the movement control lever, the movement of the basket ceases gradually. If the operator had become accidentally trapped between the basket and some other object, this extra movement may give rise to serious injury or may even be fatal to the operator. In some circumstance, operators have not always been hit the emergency stop provided on the control panel. A similar situation may arise when the operator is disabled but their foot remains trapped on the safety switch. 
         [0005]    In the event that the operator is being asphyxiated and is working on their own, their predicament may not be known to others in the vicinity, then the operator may not be freed within the critical time period which is up to four minutes of the operator being unable to breathe. 
         [0006]    The present invention provide a safety device which will help prevent death or serious injury in the event of the foot safety switch remaining closed when an operator is disabled and will warn others in the vicinity that a serious incident has occurred. 
       STATEMENT OF THE INVENTION 
       [0007]    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 controls, typically 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 further control means before said controls on the operator panel become operable, the 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 first 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. 
         [0008]    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 downstream thereof. 
         [0009]    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 RF 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. 
         [0010]    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 tensioned cord. 
         [0011]    The cord may be routed adjacent the control panel as is desired so as to tripped by a disabled operator during for example a collapse. 
         [0012]    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. 
         [0013]    A second aspect of the present invention provided for an aerial lift having a basket or cage having a controls 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 said controls become operable, and a safety device according to the first aspect of the invention. 
         [0014]    An alarm may be mounted to the underside of the basket. 
         [0015]    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 
         [0016]    The invention will be described by way of example and with reference to the accompanying drawings in which:— 
           [0017]      FIG. 1  is a view of a fork vehicle having aerial lift according to the present invention mounted on an extendible boom, 
           [0018]      FIG. 2  is an isometric view a basket or cage mounted on the extendible boom shown in  FIG. 1  having an auxiliary safety switch and trip wire, 
           [0019]      FIG. 3  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 held with the trip wire under tension, 
           [0020]      FIG. 4  is a portion of the wiring diagram shown in  FIG. 3  showing the auxiliary switch having been activated, and 
           [0021]      FIG. 5  is an isometric view a basket of  FIG. 2  with an alternatively routed trip wire. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    With reference to  FIG. 1  of the drawings, there is shown a vehicle  10  in the form of a self drive mobile lift of any suitable type. The vehicle  10  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. Stabilisers  15  are 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. 
         [0023]    The aerial lift  10  is shown by example only and any type of aerial lift may be used and the present invention is applicable to any form of aerial lift having a operator carrying basket, cage or platform which is provided with controls in the basket that allow the operator to manoeuvre the basket utilising the vehicle&#39;s power systems. 
         [0024]    With reference to  FIGS. 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 controls  23  whereby an operator standing in the basket  20  can cause the basket to be moved to a desired location. The controls  23 , shown as a control panel, further include a foot operated safety switch  24  which 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&#39;s power supply to prevent movement of the basket in the absence of a switch-closed signal from the foot switch. An emergency stop  30  may also be provided on the control panel. The general movement of the basket is controlled by a control lever  25 . 
         [0025]    An auxiliary safety device comprising a switch  26 , trip cord  27  and alarm  33  is also provided on the basket  20 . The auxiliary switch  26  is mounted on the safety barrier  22  to one side of the control  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 to the foot switch  26  which has the same effect as the safety switch  24  being raised. A suitable switch is a Guardmaster lifeline  4  available from Allen &amp; Bradley. The switch  26  includes a first set on contacts C 1  (see  FIG. 3 ) which are closed when under a tension load. 
         [0026]    The tension load is applied by the tensioned trip wire or cord  27  which extends across the front of the control  23  and is fixed to a support  28  mounted on the safety barrier  22  on the far side of the control  23 . The cord  27  may be held in tension by an adjustable tensioner  29 . The trip cord  27  must be positioned so to allow normal operation of the control  23  but be tripped by an operator in the event that the operation is disabled and falls or collapses within the basket. In this example the wire runs across the front of the control from which it is spaced by a suitable distance. 
         [0027]    The auxiliary switch  26  also include a second contact set C 2  (see  FIG. 3 ) 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. 
         [0028]    Referring also to  FIG. 3 , there is shown the electrical circuit for the safety device. The power feed line FL to the foot safety switch  24  is diverted to a socket  41  within the socket part  31 A of connector  31 . A cooperating pin  51  of the plug part  31 B of connector  31  is connected via electrical cable FL 2  to contacts C 1  and C 2  in parallel. The other sides of contacts C 1  and C 2  are connected via electrical cable B and C to separate pins  52 , 53 , respectively on the plug part  31 B. The pins  52 , 53  are connectable with cooperating sockets  42  and  43  on the socket part  31 A. 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  32 A of connector  32 . A second socket  64  of the socket part  32 A is connected to Earth or ground . The socket  63  is connectable with a co-operating pin  73  on the plug part  32 B of connector  32 . The pin  73  is connected by cable D 2  to the alarm  33 . The alarm  33  is grounded via cable F connected to pin  74  on the plug part  32 B. The pin  74  co-operates with socket  64  for grounding the alarm  33 . 
         [0029]    As shown in  FIG. 3 , the trip cord  27  (represented by dotted lines) is under tension and the auxiliary switch is set with contacts C 1  closed and contacts C 2  open. In  15  this condition, the power feed line FL is connected through connector  31  and contacts C 1  to the safety foot switch  24 . The contact C 2  is open cutting off power to the alarm  33 . 
         [0030]    With reference to  FIG. 4 , when the trip wire  27  is activated, the contacts C 1  and C 2  within the auxiliary switch  26  are caused to move so that C 1  becomes open and C 2  closes. In this state, the power feed line FL 2  is disconnected from the pin  52  of the connector  31  and the power feed line FL 2  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  thus immediately immobilising the movement of the basket  20 . 
         [0031]    The circuitry in  FIG. 3  could alternatively be adapted for insertion into the signal line from the switch  24  to the control means V. 
         [0032]    With reference to  FIG. 5 , there is shown a basket  20  in which the trip cord  27  is routed across the rear of the control panel  23 . The routing of the trip cord is facilitated by the use of freely rotating pulley wheels  35  which accommodate changes in direction of the cord. 
         [0033]    The auxiliary switch  26  may include a signal filter device T (shown in chain dotted outline) downstream of C 1  and C 2  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.