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Walking Phases
Walking Phases
WALKING MACHINERY CONTROL
The Drag-Propel Switch, located in the drag-propel cabinet, connects the drag motors or the propel motors, depending on what machine control mode the operator selects. In the DIG mode, the drag (left) controller in the cab controls the drag motors for digging. In the PROPEL mode, this same lever controls the propel motors for walking.
The walking shoes at each side of the machine are not mechanically connected. The position of the two shoes is electrically monitored to keep them in time/synchronized. This timing system detects when one shoe gets ahead of the other and generates an error signal to slow down the leading shoe. This timing system functions to align the shoes through the complete step. This provides a smooth, shock-free propel movement. The propel portion of the step will be completed. The encoders in this timing system are also used to detect when the shoes are at their “top dead center” (TDC) or PARK position.
AUTO PARK
Auto park is the method of bringing both shoes to top dead center (TDC) and setting the brakes. The operator can initiate auto park any time. The operator must pull the joystick back in the propel direction. When either shoe reaches 340 degrees, the shoe synchronization is turned off; reference is clamped to 15%. When each shoe reaches 350 degrees their references are linearly reduced to about 2%. When each shoe reaches 359 degrees, their brakes are told to set. When both brakes are set, the propel motion is turned off.
WALKING
Some preparations are required before moving the dragline. Its travel path must be adequately prepared. See the previous subsection GROUND PREPARATION. The bucket must be positioned to suit the ground conditions. The machine must be rotated so its rear faces the desired direction of travel. Provision must be made for safely and correctly handling the trail cable during the move. DO NOT USE A WALKING SHOE TO PULL OR MOVE THE TRAIL CABLE to avoid damaging the trail cable.
The position at which the bucket is carried when the machine is propelled contributes considerably to the walking operation and is dependent upon the condition of the ground. When traversing firm, level surfaces, the bucket should be suspended from the boom point approximately 1/3 the dump radius of the machine. The same position is used when propelling up a ramp. When propelling down a ramp, carry the bucket below the boom point. In all cases, the bucket should be high enough so that it will not touch the ground during a walking step.
“Heeling” the bucket while walking is done by letting the rear of the bucket contact the ground during the step and slide along when the tub slides rearward in the direction of travel. As the tub is lowered to the ground, the bucket is picked up as the boom point raises. THE BUCKET SHOULD NOT BE JERKED OFF THE GROUND. Heeling is useful while traversing dry, sandy, or powdery soil conditions to reduce the ground pressure under the sliding area of the tub and stop soil build up behind the tub’s front edge or to avoid shoe slippage on the ground.
Each operator will learn through experience where to carry the bucket while propelling to suit the ground conditions encountered. The above are general guidelines for any operator to follow initially for positioning the bucket for walking.
When all is ready for the machine to be moved, transfer the machine control from DIG to PROPEL mode. Refer to CHANGING TO PROPEL MODE in this section for the procedure. Sound the signal horns to indicate the machine will propel.
Move the left controller rearward and hold it there during the entire propel period.
