Patent Number: 039375137
Section: summary

FIELD OF THE INVENTION The present invention relates to an apparatus for grabbing and lifting differently shaped elongated objects. More particularly this invention concerns an apparatus for inserting control rods and fuel elements into respective holes in a nuclear reactor and withdrawing them therefrom. BACKGROUND OF THE INVENTION In order to change the control rods and fuel elements in a nuclear reactor a device is known having a pair of side-by-side grabs, one adapted to fit and lock onto the top of the fuel element and the other adapted to lock onto the top of a group of control rods. This arrangement allows the adjustment of a reactor by remote control in that this double grab is mounted on the end of a traditional arm operated by remote control with various servo motors. The principal disadvantage of such a device is that it is extremely expensive. A separate set of controls, actuators, motors, sensors and the like is necessary for each of the grabs; thus the expense if elevated. In addition, such a device is relatively bulky and has a limited service life due to its extreme complexity. OBJECTS OF THE INVENTION It is therefore an object of the present invention to provide an improved apparatus for inserting differently shaped elongated objects into and withdrawing same from respective holes. Another object is the provision of an improved double grab usable both to pick up and to set down control rods and fuel elements in a nuclear reactor. Another object of this invention is the provision of such a double grab which is relatively simple and inexpensive to manufacture. A further object is to provide a double grab of the above-described general type which has a long service life. SUMMARY OF THE INVENTION These objects are attained according to the present invention in a grab having a head pivotally mounted on a vertically and horizontally displaceable support. This head has a pair of opposite sides on each of which is provided a respective grab, one adapted to engage and lock on the top of a fuel element and the other adapted to engage and lock on the top of a group of control rods. Means is provided for pivoting the head on the support between a pair of positions corresponding to alignment of a respective grab with a respective object. Thus the overall size of the device is reduced considerably, as the operator need merely turn the head of the grab over in order to change its function. In accordance with yet another object of this invention the pivotal head is provided with a single actuator displaceable against spring force in a single direction and connected to both of the grab means such taht on displacement in this direction against the spring force it opens both of these grabs. This single actuator therefore operates both of the grabs and the overall cost and complexity of the pickup device is considerably lessened. The operating element of this actuating means is according to the present invention a fluid-operated cylinder whose piston is displaceable in a direction which causes grab formations on the grabs to release the respecitve objects by means of fluid pressure and is urged constantly in the other direction by a spring. Thus any failure of fluid pressure cannot cause the grabs to drop their respective objects, a situation which could be extremely dangerous and costly in a nuclear reactor. In accordance with yet another feature of this invention the grab head is generally elongated, having one of the grabs on each of its ends, and is pivotal about a horizontal axis perpendicular to the longitudinal axis of the grab head. The grab is provided at its pivot with means for rotating it through 180.degree. so as to be able to bring either of its ends into a downwardly facing position for engagement of the complementary formation thereon with the top of a control rod assembly or a fuel element. This pivoting means comprises in accordance with the present invention a pinion carried on the grab head at the rotation axis thereof and a rack which is in mesh with the pinion and displaceable so as to rotate the head. According to yet another feature of this invention means is provided for locking the grab head in either of its two positions, that is in the position with one grab facing downwardly and the other upwardly and vice versa. This locking means comprises a locking element engageable with the upper ends of the grab head so as to lock this grab head pivotally. The locking element engages in a pair of slots and is normally urged downwardly toward the grab head into the upwardly directed slots that are provided on each end thereof. Fluid pressure can displace the locking element away from these slots so that once again a failure of fluid pressure will not cause the locking element to release so that the head can wobble and perhaps drop its load. In accordance with features of this invention sensors are provided to detect the position of the operating elements of both the locking mechanism and the actuating mechanism. These sensors give outputs which indicate that the grab head is locked pivotally in place and that the grabs are in the locking or closed positions. The pickup assembly according to the present invention is relatively compact and has a very simple mechanism. It is operated by remote control with relative ease, as only three controls need be provided; the orienting arrangement which determines which grab is facing downwardly toward the control rods or fuel elements, the pressurization apparatus for the operating member of these grabs, and the pressurization apparatus for the piston operating the locking mechanisms that holds the grab head rigidly in place. Otherwise this entire assembly is mounted on a support constituted by the end of the conventional pickup cat or arm of a nuclear power plant.