FR2718121A1 - Electromechanical overload protection for cable-type crane - Google Patents

Abstract

The cable (1), gripped by a thimble (4) between two pulleys (2,3), is deflected sideways by a spring-loaded (11) rod (5) carrying a cross-head (6). Adjustable screws (7, 8) in the latter are aligned with switch operating buttons. As the cable tension increases, the cross-head approaches the switches. One switch (9), set to operate first, closes an alarm circuit. If the overload increases, the second switch (10) opens the hoist motor circuit. The circuit enters this switch, which is pivoted bodily on the frame (13), via contacts on a stop (18) and a prop (16). A return spring (15) normally keeps these contacts closed, but if the switch contacts fail to separate, continued cross-head movement will tilt the switch body, separating prop and stop, so breaking the motor circuit.

Description

The present invention relates to mounted safety devices

  on rope lifting devices and machines of the kind of overhead cranes

  lants, cranes and the like, with a view to immediately stopping operation

  ment of the machine as soon as the weight of the maneuvered load exerts on the cable an axial force which exceeds the limit threshold. The invention relates more particularly to the security device which is the subject of Italian patent N 1,154,778 filed May 12, 1980 in the name of Daniel FOSSA. It will be recalled for the correct rule that the device

  envisaged incorporates a switch which is connected to the supply circuit

  ment of the hoist's electric motor, so that

  screw the said circuit by causing the lifting to stop immediately as soon as its

  mobile contact is controlled under the effect of an overload.

  Although it has been shown to be particularly effective, it has appeared that such a safety device can be subjected to damage,

  as a result particularly of the atmosphere in which it is dis-

  posed. Such damage can cause the moving contact of the switch to block, which then does not open the power circuit when

  the load to be maneuvered exceeds the safety threshold.

  It is understandable that such a risk is fraught with consequences since

  can cause very serious damage, sometimes irreparable.

  The object of the present invention is to remedy the disadvantage pre-

  cited, and by providing the device with additional mechanical safety which also ensures the opening of the electrical circuit

  power supply in case of accidental overload and which returns immediately

  diat in normal power as soon as the overload has disappeared.

  This additional security, which doubles that provided by the

  switch intended to open the electrical circuit supplying the lifting device when the maneuvered load exerts on the cable a

  axial force greater than the threshold provided, is constituted by a finger

  ductor which, carried by said switch, is applied against a contact-bearing abutment thereby defining a circuit connected in series with the circuit controlled by the aforementioned interceptor, the latter being provided movable against elastic return means so that its movement occurring in the event of non-operation of normal safety automatically ensures the opening of the supply circuit of

  the lifting device with which the safety device is associated.

  It is understood that the elastic means coupled to the switch or to the conductive finger carried by the latter return this switch to its normal position as soon as the overload has ceased, so that the finger

  contact returns itself by pressing against its contact carrier stop.

  The attached drawing, given by way of example, will allow better understanding

  take the invention, the characteristics which it presents and the advantages which it is capable of providing: FIG. 1 is a schematic side view of the device

security according to the invention.

  Fig. 2 is an elevational view from the front.

  Fig. 3 reproduced fig. 1 showing the pieces in position

  corresponding to an accidental overload.

  In fig. 1 and 2, the reference 1 designates the cable which ensures the

  lifting of the load on a lifting device such as a bridge

  traveling, crane or other. This cable 1 passes over two pulleys 2 and 3 and is fixed, between them, to a die 4 which a central rod 5 connects to a

  transverse bar 6, which carries two adjustable screws 7 and 8 des-

  tines to operate the actuation of two electrical switches 9 and 10. The switch 9 is connected to a pre-alarm circuit or the like, while the switch 10 is mounted on the circuit which supplies the motor which controls the cable 1 in order to interrupt this circuit

  when the screw 8 comes to bear against its operating button.

  To the assembly 5-6 is associated a spring 11 suitably calibrated for

setting the safety threshold.

  Under these conditions, when for any reason, the button 14 of the switch 10 fails to take off its movable contact from the corresponding fixed contact, under the effect of the overload which is exerted on the cable 1 the adjustable screw 8 continues its course and rotates in the direction of arrow 12 the aforementioned switch 10, which is mounted on a pivot 13 and is associated with a return spring 15. This switch carries at 17 a conductive finger 16 which is normally in support against a contact carrier stop 18, the circuit 16-18 being connected in series with that controlled by said switch; the pivoting of the latter under the effect of the screw 8 causes the mutual separation of the parts 16 and 18 in the manner illustrated in FIG. 3, so that the circuit

above is open.

  We therefore obtain the mechanical interruption of the supply circuit

  of the hoist motor, even in the event of a malfunction

  operation of the switch 10. In such a case, the intervention of the spring 15 implies only an overshoot, of the order of 4 to 5%, of the

normal security threshold.

  It goes without saying that the incorrect operation of the switch 10 can be detected during the normal operation of the

  lifting, causing the replacement of said switch.

  However, the correct functioning of the safety device remains unchanged: the additional safety provided by the device according to the invention only intervenes in the case where the internal contacts

  of the switches 10 are defective.

  It will be understood that, instead of being carried by a pivot 13, the switch is capable of being provided to move along guides against an appropriate return spring, in order to be able to carry out a translational movement ( rather than rotation) under the effect of the pursuit of

the stroke of the adjusting screw 8.

  It should also be understood that the above description has not

  given as an example and does not limit the area

  ne of the invention which we would not leave by replacing the details

  of execution described by all other equivalents.

Claims (4)

CLAIMS R E V E N D I C A T I O N S   1. Safety device for limiting the load on cable lifting devices, of the type incorporating a switch (10)   connected to the appliance's power circuit to open this circuit   baked when the force exerted on the cable (1) thereof exceeds a determined threshold, characterized in that the switch (10), provided movable against elastic return means (15), carries a conductive finger (16) that the elastic means (15) normally maintain in abutment against a contact-bearing stop (18), the circuit defined by these   parts (16 and 18) being connected in series to that controlled by the inter-   breaker (10) so that in the event of a malfunction of the latter, the finger (16) moves away from the stop (18) by opening the electrical circuit   above which closes immediately after the overload has ceased.   2. Device according to claim 1, characterized in that the operating fault of the switch (10) which is corrected by the conductive finger (16) is detectable during the normal operation of the lifting device.   3. Device according to any one of claims 1 and 2,   characterized in that the switch (10) is mounted on a pivot (13), in order to move angularly against a return spring (15).   4. Device according to any one of claims 1 and 2,   characterized in that the switch (10) is movable on guides against a return spring which maintains it in a position such that the finger (16) is normally applied against the contact-bearing stop (18) , said switch being able to move so as to distance one   on the other the two parts (16 and 18).