Open loop control with velocity threshold for pneumatic hoist
AssigneeWilmington Research and Development Corporation
InventorDouglas A. Johnson
Life of this patent
Estimating the term…
Abstract
A control system for a pneumatic hoist limits the velocity or acceleration of a load attached to the hoist. The control system includes a controller and a valve. The controller provides a variable gain between an actuator, which controls the speed of the hoist, and the valve, which controls fluid flow into the hoist, thereby controlling the velocity or acceleration of the load. As the velocity or the acceleration of the load reaches a predetermined maximum value, the control system proportionally reduces the gain between the actuator and the valve, thereby closing the valve and reducing the velocity or acceleration of the hoist.
Claims16
A hoist comprising:
- a housing having a first end wall and a second end wall, the housing, first end wall and second end wall forming a chamber,
- an inlet mechanism attached to the housing the inlet mechanism allowing the passage of a fluid into the chamber;
- a slidable piston mounted within the chamber;
- a cable wrapped on the piston for attachment to a load;
- a valve connected to the inlet mechanism, the valve controlling the amount of fluid entering the chamber;
- a pressure sensor attached to the chamber and in fluid communication with a fluid within the chamber;
- a position measuring device connected to the housing and in positional communication with the piston;
- an actuator in electrical communication with the valve, the actuator controlling the positioning of the valve;
- and
- a control system in electrical communication with the valve, the pressure sensor, the position measuring device and the actuator, the control system having a variable gain between the actuator and the valve, the gain being reduced as the velocity or acceleration of a load attached to the piston approaches a preset maximum value.
A method for adjusting the velocity of a load attached to a pneumatic hoist comprising the steps of:
- providing a control system for a pneumatic hoist having a maximum allowed velocity value and a maximum allowed acceleration value for a load attached to the hoist;
- measuring a velocity or acceleration of the load attached to the hoist;
- comparing the measured velocity or acceleration of the load against the maximum allowed velocity value or maximum allowed acceleration value;
- and
- adjusting a gain between an actuator and a valve of the control system in response to the results of the comparison in order to adjust the velocity or acceleration of the load, such that the gain of the control system is reduced as the measured velocity or acceleration of the load approaches the preset maximum allowed velocity value or the maximum allowed acceleration value.
A method for stopping the motion of a load attached to a hoist comprising the steps of:
- providing a hoist having a piston, a valve and an actuator, the actuator having a plurality of piston directional control inputs and a deadband input;
- engaging a piston directional control input, thereby causing the piston to rotate in a chosen direction and causing the valve to pulse in a first direction;
- engaging the deadband input, thereby causing the valve to pulse in a direction opposite to the first direction;
- scaling a magnitude of the pulse from the valve to correspond with the velocity of the piston;
- reversing the direction of rotation of the piston;
- and
- stopping the motion of the load.
A method for stopping the motion of a load attached to a hoist comprising the steps of:
- providing a hoist having a piston, a valve and an actuator, the actuator having a plurality of piston directional control inputs and a deadband input;
- engaging a piston directional control input, thereby causing the piston to rotate in a chosen direction and causing the valve to pulse in a first direction;
- engaging the deadband input, thereby causing the valve to pulse in a direction opposite to the first direction;
- scaling a duration of the pulse from the valve to correspond to the moving average of a valve magnitude based upon the first direction of the valve;
- reversing the direction of rotation of the piston;
- and
- stopping the motion of the load.
Dependencies are inferred from the claim text.