US3471194A - Electric grab - Google Patents

Description

Oct. 7, 1969 J. A. MARTIN ET 3,471,194

ELECTRIC GRAB Filed Dec. 26, 1967 2 Sheets-Sheet 1 Oct. 7, 1969 J. A. MARTIN ETAI- 3,

ELECTRIC GRAB Filed Dec. 26, 1967 2 Sheets-Sheet 9 United States 3,471,194 Patented Oct. 7, 1969 3,471,194 ELECTRIC GRAB Jean Antoine Martin, Bagneux, Pierre Mauguen, Montfermeil, and Jacques Pinault, Paris, France, assignors to Groupement Atomique Alsacienne Atlantique, Le

Plessis-Robinson, France Filed Dec. 26, 1967, Ser. No. 693,344 Claims priority, applicatignlltrance, Dec. 29, 1966,

Int. Cl. I566c 1/06 US. Cl. 294-88 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an electric grab and is more specifically concerned with the means which are associated with the handling tongs or grab jaws in order to carry out the controlled locking of said jaws and to ensure operational safety and reliability of the grab.

It is already a known practice to make use of electric grabs of the type comprising a body on which an electromagnet is supported axially, two holding jaws which are freely mounted inside said body on each side of the electromagnet and each rigidly fixed to a member formed of non-magnetic material and a slightly curved flexible strip which serves to interconnect the two jaws so that said jaws are attracted simultaneously as and when the electromagnet is energized and are thus caused to pivot laterally by deformation of the flexible strip.

Moreover, arrangements which have already been contemplated in a grab of this type consist in mounting a locking device which makes it possible to lock the jaws in their rest position in order to prevent any unexpected movement of these latter during the different operations involving transfer of an object which is being carried by said jaws. For this purpose, a grab of this type comprises a second electromagnet and a magnetic pallet supported by the extremity of a leaf spring which is rigidly fixed at the extremity thereof so that, when no voltage is applied to the electromagnet, said pallet serves to maintain the jaws in outwardly displaced relation by engagement of these latter within a recess formed between two shouldered portions respectively formed on each jaw. When the second electromagnet is energized, the pallet is withdrawn from its recess and the grab jaws are consequently released.

However, it is essential to ensure that a grab of this type should afford full reliability of operation without any danger of accidental opening or closure of its jaws during handling operations. In point of fact, operational reliability may not be fully ensured by means of the locking system of the type considered above, in particular when axial shocks occur and tend to dislodge the locking pallet from its recess.

In fact, in order that a pallet having a weight M which is subjected to a restoring force F by its spring and which has an unlocking travel C should not be accidentally released under the action of an impact whilst the grab is endowed with a velocity V, the relation:

must be satisfied. However, this inequality cannot be satisfied in all cases, 1n particular at high velocities. In fact, the force developed by the electromagnet must be greater than the force F in order to initiate a grab release and this is not always possible, especially for reasons of permissible size of said electromagnet.

The aim of the present invention is to circumvent the above-noted disadvantage and is more especially concerned with an improved locking device whose operation is no longer dependent on the relation stated above, said device being characterized in that it comprises jaw-locking means which are insensitive to axial accelerations of said grab, said means being maintained in the locking position by a spring-loaded member whose action is exerted in a plane at right angles to the longitudinal axis of the grab and being brought into the unlocking position by means of an electromagnet which produces a set of forces in opposition to the action of said member.

In a first alternative embodiment, said locking means comprise a pallet formed of magnetic material and rotatably mounted between the armatures of the electromagnet, said pallet being rigidly fixed to a shaft located at right angles to its plane and coupled to a second pallet having dimensions such that the extremities thereof are engageable in the jaw-locking position within a circular recess formed in a shoulder which is provided on each grab jaw, and a spring mounted in coaxial relation with said shaft so as to work under torsional stress and to maintain said second pallet in the locking posi ion, the unlocking of said jaws being obtained by energizing said clectromagnet which produces the limited rotational motion of said pallets in opposition to the action of said spring.

The movement of rotation of the shaft which interconnects said pallets can be carried out on roller-bearings, on plain bearings, by means of flexible articulations, knife-edge articulations and so forth.

In another alternative embodiment, said locking means comprise at least two arms which are symmetrical with respect to the center-line of said grab and pivotally mounted in their plane about pivot-pins which are carried by said grab, a spring which is adapted to initiate in the locking position a radial displacement of said arms towards the periphery of said grab, and an electromagnet which is adapted to effect the unlocking of the grab jaws by attracting said arms in the opposite direction in opposition to the action of said spring.

The different features of the invention will now be explained in detail in the following description of two exemplified embodiments which are given solely by way of indication and not in any limiting sense, reference being had to the accompanying drawings, in which:

FIG. 1 is a vertical sectional View taken along line 1-1 of FIG. 2 and showing a locking device comprising a rotary pallet in a first form of execution;

FIGS. 2 and 3 are horizontal sectional views taken respectively along lines 11-11 and HI-IH of FIG. 1;

FIG. 4 is a vertical sectional view taken along line IV-IV of FIG. 6 and showing a second alternative embodiment of the locking device;

FIG. 5 is a vertical sectional view taken along line V-V of FIG. 6;

FIG. 6 is a horizontal sectional view taken along line VI-VI of FIG. 4.

In FIG. 1, the grab which is illustrated comprises a body 1 of substantially cylindrical shape inside which is fixed axially an electromagnet 2 composed of a former 3 and coil 4. The former 3 is made up of two identical parts of mild steel separated from each other by a nonmagnetic plate 5. A second electromagnet 7 is attached to said electromagnet 2, a non-magnetic partition plate 6 being advantageously provided between said electromagnets in order to isolate their respective circuits. The electromagnet 7 also comprises a core 8 and a coil 9.

The two grappling tongs or grab jaws which are designated respectively by the reference numerals 10 and 11 are mounted within the body 1 on each side of the electromagnet 2. Each jaw is provided at the lower end thereof with a nose 10a or 11a, thereby enabling the grab to grip any object (not shown in the drawings) by engagement of its two noses in a circular channel formed in said object. The jaws 10 and 11 are provided respectively at the upper ends thereof with extensions in the form of two members 12 and 13 which are made of nonmagnetic material and which are applied against the top face of the electromagnet 2. These two members 12 and 13 are interconnected by means of a metallic strip 14 which is secured at each extremity. Said strip has a very slightly curved profile which makes it possible to exert an upwardly directed force on each of its extremities and, in fact, on the members 12 and 13 to which said extremities are rigidly fixed, thereby producing a lateral movement of separation of the jaws when the electromagnet 2 is not energized. In the central portion thereof, the strip 14 is maintained applied against a block 16 which is rigidly fixed to the top face of the electromagnet 2 by means of a fixing screw 17 having an extended length which penetrates into the partition plate 5.

In this grab, which is of a type already known per se, it is the electromagnet 2 which controls the movement of separation or of closure of the jaws in combination with the fiexible strip 14. However, by reason of the very flexibility of said strip, it is apparent that the jaws must be instantaneously arrested or locked in position in order to prevent any maloperation or accidental detachment of loads, especially when the grab is liable to be subjected to shocks or accelerations.

For the purpose aforesaid and in the form of execution which is illustrated in FIGS. 1, 2 and 3, the coil unit 9 of the electromagnet 7 is placed around the central core 8 and surrounded by a hollow cylinder 50 which is screwed onto said core. Said cylinder 50 is provided at the lower end with two abutment shoulders 51 and 52, the profile of which is shown in the sectional view of FIG. 2. Between the cylinder 50 and the lower end of the central core 8, there is fitted a first pallet 53, the plane of which is located at right angles to the center-line of the grab 1. Said pallet is rigidly fixed at its center to a shaft 54 carried by a stationary bearing support 55 in which said shaft is capable of rotating freely on ball bearings 56 or the like. The shaft 54 is rigidly fixed at the lower end thereof to a second pallet 57 which is parallel to the first and has slightly larger diametrical dimensions. The extremities 58 and 59 of said second pallet are capable of engaging in suitable shoulders formed on the corresponding faces of the jaws 10 and 11. A helical spring 60 is mounted around the shaft 54, said spring being secured at one end to the stationary bearing support 55 and at the other end to the second pallet 57, with the result that said spring continuously tends to place said pallet in the position shown in FIG. 3 in which its extremities 58 and 59 lock the jaws 10 and 11 in position. Under these conditions, the device herein described locks said jaws and maintains these latter in the open position. In this position, as shown in FIG. 2, the first pallet 53 is in turn placed in such a manner that the extremities thereof cooperate with the abutment shoulders 51 and 52 of the hollow cylinder 50.

In order to carry out the unlocking operation, the electromagnet 7 is energized; the electromagnetic driving torque thus produced causes the pallet 53 to pivot about its axis until it is brought into contact with a stop 61 carried by the grab body. The second pallet 57 follows the pallet 53 in its rotational motion and its extremities 58 and 59 are freed from the corresponding shoulders, thereby freeing the grab jaws 10 and 11 which can then be caused to close by energizing the main electromagnet 2 of the grab.

Referring now to the form of execution which is illustrated in FIGS. 4 to 6, it can be seen that the locking device essentially comprises two arms 70 and 71 disposed symmetrically with respect to the center-line of the grab in a plane substantially parallel to that of each of the jaws 10 and 11. Said arms 70 and 71 are pivoted respectively on the grab body about pins 72 and 73 and are associated with two small plates 74 and 75 of magnetic material which are mounted opposite to the poles of the locking electromagnet 7. As in the embodiment of FIGS. 1 to 3, said electromagnet comprises a central core 8 and a coil 9. The lower portions of the arms 70 and 71 are curved and joined together by means of a spring 76 which continuously urges the arms outwards by causing them to pivot in their plane. In this position, the arms 70 and 71 are adapted to cooperate with two segments 77 and 78 of generally circular shape which are rigidly fixed to the jaws 10 and 11 in such a manner that the central portion of said arms comes into engagement between said segments, thereby maintaining the jaws in their open position, the outward displacement of the arms being limited by stops 79 which are carried by these latter and which come up against the corresponding edges of the segments. When the electromagnet 7 is energized, the small magnetic plates 74 and 75 are attracted by the electromagnet and initiate the pivotal motion of the arms about their pivot- pins 72 and 73 in opposition to the action of the spring 76. Said arms then move away from the segments 77 and 78 and towards each other, thereby permitting operation of the jaws by means of the main electromagnet 2.

As is readily understood, the invention is not limited solely to the examples herein described and illustrated but extends, on the contrary to all alternative forms. In particular, the two forms of construction which have been more specifically described could be employed in combination in order to endow the grab with even greater safety and reliability despite any mechanical stresses to which it may be subjected.

What is claimed is:

1. An electric grab fitted with two jaws which are controlled both for opening and closure, wherein said grab comprises jaw-locking means which are insensitive to axial accelerations of said grab, said means being maintained in the locking position by a spring-loaded member whose action is exerted in a plane at right angles to the longitundinal axis of the grab and being brought into the unlocking position by means of an electromagnet which produces a set for forces in opposition to the action of said member.

2. An electric grab as claimed in claim 1, wherein said locking means comprise a pallet formed of magnetic material and rotatably mounted between the armatures of the electromagnet, said pallet being rigidly fixed to a shaft located at right angles to its plane and coupled to a second pallet having dimensions such that the extremities thereof are engageable in the jaw-locking position within a circular recess formed in a shoulder which is provided on each grab jaw, and a spring mounted in coaxial relation with said shaft so as to work under torsional stress and to maintain said second pallet in the locking position, the unlocking of said jaws being obtained by energizing said electromagnet which produces the limited rotational motion of said pallets in opposition to the action of said spring.

3. An electric grab as claimed in claim 1, wherein said locking means comprise at least two arms which are symmetrical with respect to the center-line of said grab and pivotally mounted in their plane on pivot-pins which are carried by said grab, a spring which is adapted to initiate in the locking position a radial displacement of said arms towards the periphery of said grab, and an electromagnet which is adapted to elfect the unlocking of the grab jaws by attracting said arms in the opposite direction in opposition to the action of said spring.

4. An electric grab as claimed in claim 3, wherein said arms comprise small attraction plates of magnetic material which are placed in oppositely-facing relation to the poles of the electromagnet.

References Cited UNITED STATES PATENTS 3,253,853 5/1966 Loyer et. al. 29488 FOREIGN PATENTS 1,329,072 4/1963 France.

10 ANDRES H. NIELSEN, Primary Examiner

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