Caterpillar Inc.

Charles A Robinson

Kenneth J Chlad

Timothy L Cooper

Ronald W Clutter

An apparatus and method for controlling a lifting magnet (12) of a materials handling machine (10) to eliminate arcing between contacts (70-80) within the magnet controller (26) as is well as is large voltage spikes. The controller (26) selectively excites the shunt field windings (66,68) of a direct current generator (22). The magnitude and direction of the current passing through the shunt field windings (66,68) is varied by the magnet controller (26) to control the magnitude and polarity of the voltage at the generator output (23). The armature (60) of the generator (22) is rotatably driven by a hydraulic motor at an essentially constant speed to minimize voltage variations at the output (23) of the generator (22). At least the drop cycle is controlled through use of a current transducer (200) that senses current flowing to the lifting magnet so that the electronic controller is able to control the flow of current to the lifting magnet based upon the sensed current in the magnet circuit.

Method and apparatus for controlling a lifting magnet of a materials

A hydraulic circuit (124) is defined in a manifold (130) which may be aluminum, steel, or any other suitable material. The circuit (124) regulates the flow of hydraulic fluid to the hydraulic motor (120) and thus ensures that the motor rotates at an essentially constant speed, independent of the speed of the hydraulic pump (122) supplying the circuit. The circuit includes a pressure compensated flow control valve assembly (140) with an adjustable flow control valve (142) that regulates the flow of hydraulic fluid to the motor (120). The assembly (140) also includes a balanced piston-type pressure compensator (144) that ensures a select pressure differential across the flow control valve (142) such that the flow through the valve (142) remains at least essentially constant. This constant flow through the pressure compensated flow control valve assembly (140) ensures an essentially constant rotational speed of the motor (120). A surge suppression/protection normally closed solenoid operated valve (180) is provided to prevent undesirable surges of hydraulic fluid during start-up of the motor.

Method and apparatus for controlling the flow of hydraulic fluid

An apparatus and method for controlling a lifting magnet (12) of a materials handling machine (10) to eliminate arcing between contacts (70-80) within the magnet controller (26) as well as large voltage spikes. The controller (26) selectively excites the shunt field windings (66,68) of a direct current generator (22). The magnitude and direction of the current passing through the shunt field windings (66,68) is varied by the magnet controller (26) to control the magnitude and polarity of the voltage at the generator output (23). The armature (60) of the generator (22) is rotatably driven by a hydraulic motor at an essentially constant speed to minimize voltage variations at the output (23) of the generator (22). The magnet controller (26) includes a programmable logic controller (40) which selectively opens and closes the contactors (70-80) within the controller (26). The programmable logic controller 40 is also connected to indicator lamps (L1-L5) within the operator's cab (14) of the materials handling machine (10), and selectively illuminates the lamps (L1-L5) to provide an operator of the apparatus with information regarding the status of the magnet control system (27) including the controller (26). A drop time adjustment control (81) is also positioned in the operator's cab (14) and operable to vary the drop time of the magnet controller (26).

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Galion, OH, United States of America

Charles A Robinson