Laser beam level control with automatic override

Claim 1

In a level control system for an earth-working machine having variable height, earth-working implement, ground-contacting drive means, and a motive engine, said level control system including means for sensing a reference signal which signal defines a selected absolute reference height for said earth-moving implement, and means for generating implement-up and implement-down command signals in response to a vertical displacement of said earth-working implement from said selected absolute reference height, and implement operating means responsive to said implement command signals for raising and lowering the earth-working implement of said machine so as to maintain said implement at said absolute reference height despite the unevenness of the terrain traversed by said machine, the improvement in said control system which automatically prevents said earth-working implement being driven into the earth such that the force required to drive said machine across said terrain exceeds the tractional capability of said ground-contacting drive means or the available power of said motive engine, comprising: (a) means responsive to the force required to move said blade through said terrain for automatically generating an implement-command override-signal when said force exceeds a preselected value selected to be less than the available drive power of said motive engine or the tractional capability of said ground-contacting drive means; (b) means responsive to said automatically generated override signal which temporarily countermands said implement-down command signal generated in response to a vertical displacement of said earth-working implement from said selected absolute reference height and applies instead an overriding implement-up signal to said implement operating means; and (c) means to maintain said override-signal as long as said force exceeds said preselected value and to return said earthworking implement to control by said level control system implement command signals when said force no longer exceeds said preselected value.