Method & apparatus for providing low speed safety braking for a hoist system
AssigneeEderer Incorporated
InventorsFred E. Langford, Roger A. Johnson
Life of this patent
Estimating the term…
Abstract
At predetermined low speeds, a safety brake is applied directly to the hoisting drum at a setting sufficiently high to stop the load from falling should drive line failure occur. The load can be lowered or raised by applying sufficient torque to the drum to overcome the braking force and thus lower or raise the load. If drive train failure occurs, the brake will instantaneously stop the load without further uncontrolled movement.
Claims8
A hoist system comprising:
- a drum,
- a wire rope wrapped about said drum, said rope being secured to said drum and being connected to a load, the load applying a force to the wire rope tending to unwind the rope from the drum,
- a prime mover and a drive train coupling said prime mover to said drum for bidirectional rotation of said drum in a winding and an unwinding direction, said prime mover being capable of providing sufficient torque in a winding direction to wind wire rope onto said drum when a load is connected to said rope,
- a primary brake associated with the drive train and being capable of selectively stopping rotation of the drive train to hold the load at a predetermined position,
- a secondary brake coupled directly to said drum and being capable of applying a braking force to said drum that will counter the unwinding force exerted on said drum by said load to stop the load,
- a sensor for sensing the rotational speed of the drum, and
- a brake control for applying said secondary brake with sufficient braking force to stop the unwinding of said rope when no unwinding torque is being supplied by said prime mover, said brake control applying said secondary brake only at and below a predetermined speed of said drum, said prime mover being capable of supplying sufficient unwinding torque to said drum in an unwinding direction at and below said predetermined speed to overcome the braking force of said secondary brake and thereby unwind said rope and lower said load, said secondary brake being capable of stopping the unwinding of said rope in the event of drive train failure.
A method for preventing a load suspended from a hoist system from dropping uncontrollably in the event of drive train failure, the hoist system including a drum, a wire rope wrapped about said drum, said rope being secured to said drum and being connected to a load, the load applying a force to the wire rope the drum, a prime mover and a drive train coupling said prime mover to said drum for bidirectional rotation of said drum in a winding and an unwinding direction, a primary brake associated with the drive train and being capable of selectively stopping rotation of the drive train to hold the load at a predetermined position, said prime mover being capable of providing sufficient torque in a winding direction to wind wire rope onto said drum when a load is coupled thereto, and a secondary brake coupled to said drum and being capable of applying a braking force to said drum that will counteract the unwinding force exerted on said drum by said load to stop the load, comprising the steps of:
- applying the secondary brake to the drum with sufficient force to stop the unwinding of the rope when a load is coupled thereto only at and below a predetermined speed, and
- when lowering the load as said secondary brake is applied, applying sufficient torque to said drum from said prime mover in the unwinding direction to overcome the resistance of said secondary brake and thus slowly lowering the load, said secondary brake stopping the load immediately upon drive train failure.
Dependencies are inferred from the claim text.