Laser beam level control with automatic override

Claim 1

In a laser beam level control system for an earth-moving machine having a variable height earth-moving blade, ground-contacting drive means and a motive engine, said level control system including receiver means for sensing a laser beam signal, which signal defines a reference plane, and for generating blade-up and blade-down command signals in response to the vertical displacement of said receiver means with respect to said reference plane, and blade operating means responsive to said blade command signals for raising and lowering the earth-moving blade of said machine to maintain the blade at a preselected elevation relative to said reference plane as said machine traverses terrain of variable elevation, the improvement in said control system which automatically prevents said blade being positioned such that the force required to drive said machine across said terrain exceeds the tractional force capability of said drive means or the available power of said motive engine, said improvement comprising: (a) means responsive to the force required to move said blade through said terrain, for automatically generating an override signal when said force exceeds a preselected value which does not exceed the tractional force capability of said ground-contacting drive means or the available horsepower of said motive engine; (b) means responsive to said automatic override signal which temporarily countermands a blade-down signal generated by said receiver means and applies a blade-up signal to said blade operating means; and (c) means to maintain said override signal as long as said force exceeds said preselected value and to return said blade to control by said laser beam signal as soon as said force no longer exceeds said preselected value.