Patent Number: 047611073
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to apparatus for the mechanized transfer of objects to and from containers, and particularly to apparatus which enables such operations to be controlled from a distance. In many industrial situations, objects must be transferred from one location to another in a precisely controlled manner by means of power operated conveying devices either because of the size and/or weight of the objects or because the objects constitute a hazard to operating personnel. All of these considerations exist when it is necessary to replace or transfer large components of a nuclear reactor. A particular case of this type involves the exchange of rod control cluster (RCC) elements in a fuel assembly for a reactor core. Specifically, a reactor core includes a plurality of fuel assemblies each of which contains an RCC element which must be replaced from time to time. Such replacement involves lifting out of the RCC element previously installed therein, transfer of that RCC element to a holding position, and then installation of a new RCC element. The movements involved in each of these operations must be precisely controlled by an operator who can view the operation while being isolated from the radioactive material of the elements and fuel assembly. SUMMARY OF THE INVENTION It is an object of the present invention to enable such operations to be carried out in a precisely controlled and reliable manner. Another object of the invention is to permit accurate positioning of one or more fuel assemblies and accurate transfer of RCC elements to and from such assemblies. These and other objects are achieved, according to the invention, by a novel apparatus for transferring components to and from containers therefor, which apparatus includes: a stationary support frame defining a pathway; a carriage movable along the pathway and having at least one first container compartment for receiving and holding a container and at least one first component compartment for receiving and holding a component, said container compartment being spaced from said component compartment along the pathway; two stationary stops located to delimit first and second ends of the pathway; a movable stop located along the pathway between said stationary stops; abutment means carried by said carriage, and disposed to cooperate with said stops so that contact between said abutment means and said stationary stops defines respective first and second end operating positions of said carriage along said pathway and contact between said abutment means and said movable stop defines at least one further operating position of said carriage along said pathway, which further position is spaced from said second end position by a distance equal to the spacing between said container compartment and said component compartment; component transfer means for transferring a component vertically to and from a respective one of said compartments when said carriage is in a respective one of said second end and further operating positions; signal controllable drive means connected to said carriage for moving said carriage to a selected operating position along said pathway; signal controllable movable stop displacing means coupled to said movable stop for displacing said movable stop between a raised position in which said movable stop can be contacted by said abutment means and a lowered position in which said movable stop can not be contacted by said abutment means; and electronic data processing means connected to receive signals indicative of the desired operating position of said carriage and connected to said drive means and movable stop displacing means for operating said drive means and said movable stop displacing means for automatically displacing said carriage to the desired operating position. According to preferred embodiments of the invention, the containers are nuclear reactor core fuel assemblies and the components are RCC elements. The carriage includes two container compartments each arranged to hold a respective fuel assembly and one first component compartment for receiving and temporatily holding an RCC element, the latter compartment being located between the fuel assembly compartments. Preferably, the abutment means include two abutments spaced apart along the path of travel of the carriage and each arranged to cooperate with the movable stop to define a respective further operating position of the carriage. The component transfer means includes a hoist supporting a pneumatically operated gripper, the hoist including a cable supporting the gripper and a motor-driven drum about which the cable is wound. An air hose is coupled between the gripper and a pressurized air source through the intermediary of an electrically controlled valve. The carriage is driven by a motor via cables connected between respective ends of the carriage and respective ends of a chain which passes around a toothed wheel driven by the motor. To avoid damage to the various motors as a result of overloads, the drum and the toothed wheel are coupled to their respective motors via slip clutches. Displacement of the movable stop is effected by means of a lever pivoted by a solenoid controlled, pneumatic piston-cylinder assembly and coupled to the movable stop by a cable. Rotation of the drum is monitored by a multi-position geared limit switch, while rotation of the toothed wheel which displaces the carriage is monitored by a position transducer which undergoes one cycle of rotation in response to movement of the carriage between the ends of its pathway. Limit switches associated with the piston-cylinder assembly indicate the position of the movable stop, while the state of the valve controlling the supply of air to the gripper is monitored in any suitable manner. All of the monitoring indications are supplied to the electronic data processing means, along with signals supplied by the operator to indicate the operation to be performed. According to a further feature of the invention, the operation of the system is controlled from a station which is connected to the electronic data processing means via a disconnectable cable. The station can be of the pendant type and is provided with a plurality of pushbuttons and a trigger switch, the pushbuttons indicating each operation to be performed and the trigger switch instructing the system to carry out the presently indicated operation. Preferably, in accordance with the invention, each pushbutton is transparent and houses an indicator lamp which is connected to the data processing means in such a manner that depression of the pushbutton produces a signal sequence such that the associated lamp initially produces a blinking light signal which changes to a steady light signal when the appropriate monitoring means indicates that the operation indicated by that pushbutton has been completed. Once an operation has been indicated by depression of a particular pushbutton, it is necessary to close the trigger switch in order to cause the operation to begin. During the course of the operation, the trigger switch condition is repeatedly interrogated so that if the trigger switch should be released, the operation is immediately halted. The pushbuttons are arranged in groups, a first group controlling carriage displacement, a second group controlling hoist movement and a third group controlling gripper operation. Only one pushbutton can be effective at a time and all of the pushbuttons are interconnected, either electrically or mechanically, so that depression of one pushbutton, when the trigger switch is open, will deactuate the previously pressed pushbutton. However, if the trigger switch is closed, pressing of a pushbutton will not halt the operation indicated by the previously pressed pushbutton. The movable stop is provided in order to enable the carriage to be halted at one or more further operating positions located between the ends of the carriage pathway. The movability of this stop allows the carriage to move past the position or positions defined thereby, when desired. The movable stop is pivotable between a raised position, in which it will engage a carriage abutment, and a lowered position, in which it permits movement of the carriage abutments past the location of the movable stop. To assure accurate and reliable positioning of the carriage by means of the movable stop, the movable stop is associated with a fixed abutment member against which the movable stop bears when in its raised position and the operating positions defined by the movable stop are created when a respective abutment on the carriage presses against the movable stop from the side opposite the abutment member associated with the movable stop. Therefore, before the movable stop can be moved to its lowered position, the carriage must be moved to a position at which such movement of the movable stop is not prevented by a carriage abutment. For this purpose, the control system according to the present invention provides a respective intermediate position for each carriage position which is defined by the movable stop, each intermediate position being located to assure that the carriage abutment or abutments are clear of the movable stop before it is lowered. Accurate positioning of the movable carriage at each of its operating positions is achieved, according to the present invention, by configuring the electronic control in such a manner that a carriage abutment will come into contact with an associated stop slightly before the data processing system indicates that the carriage has arrived at that position. Therefore, the motor driving the carriage continues to rotate through a small angle until the carriage position sensor produces an indication that the carriage has arrived at the desired position. This small additional rotation of the carriage drive motor thus occurs while the carriage is stationary and is absorbed by the ability of each cable connected to the carriage to undergo a small amount of elastic elongation. According to a further feature of the invention, the station carrying the controls to be actuated by the operator is also provided with display members which are connected to indicate the load being supported by the hoist and/or the hoist vertical position. Information for these displays can be provided by a load cell operatively associated with the hoist and a position transducer driven by the hoist cable drum. The display members can be of the LED or LCD type and can be installed as an integral part of the station housing or as a separate device clamped to the cable which connects the station to the data processing system. The latter possibility enables such a display member to be retrofitted to an existing system. In either embodiment, a single display device can be provided and can be programmed to alternately display the two parameters.