Photocell grade sensor and buoyancy slope sensor

Claim 1

In a paving machine having tractor means adapted to move along an irregular base and deposit paving material thereon, screed means disposed on the rear end of said tractor means and extending transversely thereof for leveling and smoothing said material; a first pulling means connected to said screed and extending forwardly; a second pulling means connected to said screed at the side thereof opposite said first pulling means and extending forwardly; first power means disposed between the forward end of said first pulling means and said tractor means for effecting relative vertical movement therebetween; second power means disposed between the forward end of said second pulling means and said tractor for effecting relative vertical movement therebetween; and feeler means associated with said first pulling means for measuring the vertical movement thereof relative to a reference; the combination which comprises grade control means associated with said first power means for the actuation thereof in response to said feeler means measuring vertical movement of said first pulling means relative to said reference plane; said grade control means including a housing, a rotatable shaft disposed in said housing and connected to said feeler means, a lamp disposed in said housing, photoelectric receiving means contained within said housing for producing a signal proportional to the amount of light received, and a disc disposed on said shaft and having a generally wedge-shaped portion cut away at its periphery for varying the amount of light received by said photoelectric-receiving means; a first amplifier means electrically connected to said grade control means; electrically actuated valve means disposed between said first amplifier means and said first power means; a crossbar member pivotally disposed between said first and second pulling means; a slope control including a slope-sensing means disposed on said crossbar member; second amplifier means electrically connected to said slope-sensing means; second electrically actuated valve means disposed between said second amplifier means and said second power means; whereby when said grade control means produces a signal that is amplified by said first amplifier means, said first valve means is actuated and when said slopesensing means produces a signal that is amplified by said second amplifier means, said second valve means is actuated for maintaining the vertical distance between said forward end of said first pulling means and said reference grade substantially constant and the vertical distance between the forward ends of said first and second pulling means substantially constant.