HEAD BRAKE RELEASE WITH MEMORY

摘要

In accordance with the invention, a control is provided for a drill head mounted on a drill mast that includes a hydraulic motor to raise and lower the drill head and a hydraulically releasable brake that holds the drill head in position on the mast. The control includes a hoist line connecting the hydraulic motor to a source of hydraulic fluid under pressure, a brake release line connected to the brake, a brake release valve normally connecting the brake release line to tank and electrically actuated to connect the brake release line to a source of hydraulic fluid under pressure to release the brake, a programmable logic controller with a memory storage for controlling the actuation of the brake release valve, and a pressure transducer connected to the hoist line and the controller for providing a signal to the controller representative of the hoist line pressure which is storable in the memory. The controller will actuate the brake release valve only after the hoist line pressure sensed by the transducer is as great as the pressure stored in memory. Preferably, the control includes a brake switch connected to the controller and actuated to set and release the brake. A timer in the controller is turned on for a predetermined time when the brake switch is actuated to set the brake. The timer prevents the controller from actuating the brake release valve to set the brake until the timer is turned off. While the timer is on, the existing hoist line pressure signals are stored in the memory.