Patent ID: 8689471

Claim:
An excavator having an excavator chassis pivotally mounted on an excavator undercarriage, a boom pivotally mounted on the excavator chassis, a dipper stick pivotally mounted on the boom, an excavator implement pivotally mounted on the dipper stick, a first hydraulic device for moving said implement with respect to the dipper stick, a first hydraulic control valve for controlling the application of hydraulic fluid to said first hydraulic device, a second hydraulic device for moving said dipper stick with respect to said boom, second hydraulic control valve for controlling the application of hydraulic fluid to said second hydraulic device, a third hydraulic device for moving said boom with respect to said excavator chassis, a third hydraulic control valve for controlling the application of hydraulic fluid to said third hydraulic device, a fourth hydraulic device for rotating said chassis with respect to said undercarriage, a fourth hydraulic control valve for controlling the application of hydraulic fluid to said fourth hydraulic device, and manually actuated joystick valves for supplying hydraulic fluid pressure to said first, second, third and fourth hydraulic control valves, to control the movement of said first, second, third and fourth hydraulic devices, respectively, further comprising: a plurality of sensors for sensing position, a memory storing the desired elevation of the worksite at the point being excavated, a processor, responsive to said sensors and to said memory, for determining the position of the implement, for comparing the implement position to the desired elevation of the worksite, and for supplying movement retarding signals when said implement approaches the desired elevation, and a manifold providing hydraulic fluid pressure from said manually actuated joystick valves to said first, second, third and fourth hydraulic control valves, to actuate said first, second, third and fourth hydraulic control valves, and for providing a portion of said hydraulic fluid pressure from said manually actuated joystick valves to said first, second, third and fourth hydraulic control valves in opposition to actuation of said first, second, third and fourth hydraulic control valves in response to said movement retarding signals from said processor when said implement approaches the desired elevation, whereby the movement of said implement below said desired elevation is opposed.