US 3638540 A
In a paving machine having a tractor and a screed means extending transversely across the rear end and connected to the tractor pulling arms on each side thereof, a control system automatically maintains the grade and slope of the screed as the tractor moves over an irregular surface. A photoelectric sensing means measures vertical deviation from a reference plane, produces a signal that is amplified to actuate an electrically operated valve means actuating a power means that controls the grade of one side of the screed. A second photoelectric sensing means measures the vertical movement of the opposite side relative to the first side, and produces a signal that is amplified to control a second electrically operated valve means that controls a second power means and said opposite side of the screed, thereby maintaining the screed at a constant slope.
Claims available in
Description (OCR text may contain errors)
United States Patent Williams 1 Feb. 1,1970
 PHOTOCELL GRADE SENSOR AND BUOYANCY SLOPE SENSOR 211 App]. No.: 888,672
3,210,710 lO/l965 3,264,958 8/1966 3,349,785 10/1967 Duffy..... ...318/326X 3,511,949 5/1970 Hanson ..94/46 Primary Examiner-Nile C. Byers, Jr. Att0meyMandeville & Schweitzer [5 7] ABSTRACT In a paving machine having a tractor and a screed means extending transversely across the rear end and connected to the tractor pulling arms on each side thereof, a control system automatically maintains the grade and slope of the screed as the tractor moves over an irregular surface. A photoelectric sensing means measures vertical deviation from a reference plane, produces a signal that is amplified to actuate an electrically operated valve means actuating a power means that controls the grade of one side of the screed. A second photoelectric sensing means measures the vertical movement of the opposite side relative to the first side, and produces a signal that is amplified to control a second electrically operated valve means that controls a second power means and said opposite side of the screed, thereby maintaining the screed at a constant slope.
3 Claims, 8 Drawing Figures PAIENIEBrm mrz 3.638.540
SHEET 1 BF 3 PATENTEB FEB 1.872
sum 2 or 53' PHOTOCELL GRADE SENSOR AND BUOYANCY SLOPE SENSOR SUMMARY OF THE INVENTION This invention is in the field of paving machines and particularly relates to the control of the elevation and slope of a screed associated with paving machines, although it could be used for control of elevation and slope of other types of construction equipment that utilize a blade, screed or similar device.
The laying of a paving material on a base by a paving machine is a very critical operation because it is necessary to have pavement with an upper surface as smooth as possible. Driving an automobile over paved surfaces that contain humps, dips and bumps is not only aggravating for many drivers, but many be dangerous as well. Accordingly, a paving machine that automatically maintains its screed at a constant grade and slope relative to a reference grade, even though the tractor may be travelling over an irregular or bumpy base, is necessary if a smooth paved surface is to result.
The elevation and slope of the screed is a function of the elevation of the forward ends of pulling arms that are attached to the tractor as well as the screed. Vertical adjustment of the forward ends of the pulling arms where they are attached to the tractor controls the grade and slope. For a more complete disclosure of the mechanics of operation of the screed, consult U.S. Pat. No. 3,236,163.
A primary object of the invention is a control system that automatically maintains a constant grade and slope of a screed relative to a reference grade, regardless of vertical movement of the tractor as it travels over a base.
Another object is a control system that will be sufficiently sensitive to monitor and correct for minor deviations in the grade and slope of a screed.
Another object is a control system that has sensing means that are not susceptible to excessive wear caused by frictional contact between moving parts therewithin.
Another object is sensing means that utilize photoelectric circuits to measure deviation from a nominal or preset value.
Other objects will hereafter appear in the specification, drawings and claims.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view ofa paving machine.
FIG. 2 is a perspective view of a part of the paving machine shown in FIG. 1.
FIG. 3 is a schematic diagram of the grade control portion of the control means.
FIG. 4 is an end view of the grade-sensing means, partially cut away,
FIG. 5 is a section taken along line 55 of FIG. 4.
FIG. 6 is a schematic diagram of the slope control portion of the control means.
FIG. 7 is a sectional front view of the sensor means of the slope control portion.
FIG. 8 is a sectional top view of the slope sensor shown in FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENT referring to the drawings, a paving machine which may be of well-known design is shown generally at 10 in FIG. 1. It comprises a self-propelled tractor 12 mounted upon pneumatic tires 14 and rubber wheels 16 for forward movement. The paver moves over a base 18 which may be a layer of previously laid paving material or graded earth or the like. Paving material is placed into the hopper 20 positioned at the forward end of the paver, conveyed rearwardly by a conveyor (not shown) to a position immediately forward of a screed 22 where an auger mechanism (not shown) distributes the paving material received from the conveyor along the entire width of the screed 22. Thereafter, the material falls to the base and the screed acts to strike off and compact the paving material as the paver moves forwardly, thereby forming pavement having a smooth upper surface. As is clearly shown in FIG. I, the screed 22 extends transversely across the rear of the tractor. Various forms of screeds are well known in the art, and for that reason the screed 22 need not be described in detail here.
The screed 22 may having pulling arms 24, 26 attached thereto and extending forwardly on each side of the tractor 12, where they are attached to .the tractor at their forward ends. This attachment to the tractor is of a conventional nature and is not described in detail here, except that the forward ends are free to move in.a vertical direction, but are limited in any horizontal movement relative to the tractor. As the tractor moves forwardly along the base, the screed moves also, but the elevation of the screed may be varied relative to the tractor because of the vertical movement capability of the forward ends of the pulling arms-24, 26 relative to the tractor 12. As was mentioned previously, the detailed disclosure of the mechanics of operation of the screed is contained in US. Pat. No. 3,236,163.
Referring to FIG. 2, an external reference grade is established by placing a taut wire.28 or the like adjacent to the base to be paved. Attached to the pulling arm 24 is a grade sensor, indicated generally at 30, to which is attached a feelcr arm 32 extending downwardly and then outwardly, enabling it to maintain contact with the wire 28. The grade sensor 30 has rotatable shaft 34 to which the feeler arm is fixedly attached by set screw 36 or the like, so that vertical movement of the tractor relative to the reference grade defined by the wire 28, will cause the feeler arm to rotate the shaft 34 to the sensor 30.
Referring to FIGS. 4 ad 5, the sensor 30 has a housing 38 which includes a portion 40 that forms a seat for bearings 42 in which shaft 34 is free to rotate. Also contained therein is a lamp 44, void 46 and photoelectric receivers 48, 50 which produce an electric signal proportional to the amount of light received. Near the inward end of shafts 34 is a light-masking disc 52 having a generally wedge-shaped portion cut away at its periphery. As can be seen in FIG. 4, movement ofthc fcelcr arm 32 rotates shaft 34 and disc 52, which simultaneously varies the amount of light received by photoelectric receiver 50 from the lamp 44. Similarly, threaded adjustment screw 54 can be rotated to vary the amount of light received by photoelectric receiver 48 from the lamp 44.
Referring to the schematic diagram of FIG. 3, the two photoelectric receivers are connected to have opposite polarities. In an electrically balanced condition the signal produced by the grade sensor 30 would be zero or null. Movement of the disc 52 or the adjustment screw 54 would produce an unbalanced condition thereby producing an error signal from the grade sensor 30 through conductor 56 to differential amplifier 58 where it is amplified and sent through conductor 60 to an electrically controlled directional valve 62 which communicates with a pump 64 and a hydraulic cylinder 66. The hydraulic cylinder 66 has its upper end connected to the tractor in a conventional manner and its piston rod 68 connected to the forward end of the pulling arm 24. As best seen in FIG. 2, actuation of the cylinder will vertically move the forward end of the pulling arm 24 relative to the tractor as well as the reference grade defined by wire 28. The amount of fluid passing through the valve 62 being proportional to the electric signal controlling it, the cylinder will operate only when an error signal is produced by the sensor and that actuation of the cylinder will move the forward end of the pulling arm 24 and feeler arm 30 relative to the reference grade, thereby rotating the shaft 34 and mask 52 to again produce a null signal which closes the valve and deactivates the cylinder. In this manner the side of the screed near the reference grade remains substantially constant regardless of vertical changes made by the tractor while moving over an irregular base.
The slope of the screed 22 refers to the angle of the screed relative to horizontal when viewed from the rear of the paving machine. This angle could also be expressed as a function of the elevation of one side of the screed relative to the other. Referring to FIG. 2, if the side near the pulling arm 26 has the same elevation as the side near the pulling arm 24, the slope of the screed would be zero.
The slope sensor portion of the control system measures the difference in elevational of the forward end of pulling arm 26 relative to the forward end of pulling arm 24 to measure the slope of the screed.
Referring to FIG. 2, linkages 69 and 70 are attached to the forward ends of pulling arms 26 and 24 respectively, and are rotatably connected to a crossbar 72 in a conventional manner at 74 and 76. It is seen that vertical movement of the forward end of pulling arm 26 relative to the forward end of pulling arm 24 would change the angular position of crossbar 72.
around pivot point 76. Since the grade control is associated with pulling arm 24, the slope control maintains pulling arm 26 and therefore the slope of the screed, relative to the arm 24. The slope sensor 78 is fixedly attached to the crossbar 72 near the center of the bar as shown.
Referring to FIGS. 7 and 8, the slope sensor 78 has a watertight enclosure 80 which is filled with a substantially transparent fluid 82, such as silicone oil, which is placed in the enclosure through an opening sealed by filling cap 84. An inflatable bladder 86 may be inflated by forcing air or other gaseous mixture through valve stem 88, one way valve 90 and conduit 92 to prevent sloshing of the fluid within the enclosure in the event that some fluid 82 is lost. If fluid is lost, the bladder will expand because of its greater internal pressure, keeping the electrically full of fluid. The sensor 78 has lamps 94, 96 and photoelectric receivers 98, 100 which form two separate photoelectric circuits. The photoelectric receivers produce a signal proportional to the amount of light received in each of them. Contained within the enclosure and immersed in the fluid is a sealed buoyant float 102 which is connected to the bottom of the enclosure 80 by a flexible strap 104. The float 102 has a specific gravity less than that of the fluid 82 so that the float is buoyed upwardly at all times, being held in place by the flexible strap 104. lt is seen that if the enclosure is tipped or rotated, the float will pivot around the strap 104 to seek to maintain its vertical orientation. In this way it is seen that the top surface of buoy 102 will remain horizontal while the enclosure is rotated from side to side as viewed in FIG. 7.
Referring to the schematic diagram of HO. 6, the photoelectric circuits within the slope sensor have opposite polarities which are then added to result in the signal from the slope sensor. If the enclosure 80 is horizontal, the float 102 will mask the same quantity of light from each of the photoelectric receivers, thereby producing an electrically balanced condition which will result in a zero or null signal from the sensor. [f the enclosure is not horizontal, but is positioned at an angle, perhaps because cross bar 72 has tilted, the float 102 will mask one of the receivers 98 or 100 and expose the other, producing an electrically unbalanced condition and an error signal. This signal is fed through conductor 106 to differential amplifier 108 where it is amplified and sent through conductor 110 to an electrically controlled directional valve 112, which communicates with pump 114 and a hydraulic cylinder 116. The hydraulic cylinder 116 has its upper end connected to the tractor in a conventional manner and its piston rod 118 connected to the forward end of pulling arm 26. Actuation of the cylinder will vertically move the forward end of he pulling arm 26 relative to the tractor 10. The amount of fluid passing through the valve 112 being proportional to the electric'signal controlling it, the cylinder will operate only when an error signal is produced by the sensor and actuation of the cylinder 116 will move the forward end of the pulling arm 26 and therefore the end of crossbar 72 near pulling arm 26 to change the angle of the crossbar 72 relative to the pivot point 76 when viewed from the rear of the screed. As the crossbar 72 returns to a horizontal position, the float within the sensor 78 returns to a horizontal position, thereby balancing he photoelectric circuits to again produce a null signal which deactivates the cylinder 116.
Assuming that operator wishes the slope to be other than horizontal, a manually variable signal cari be produced by potentiometer 120 which is fed into amplifier 108 by conductor 122 where it is compared with the signal received form the sensor 78. In this way varying degrees of slope may be maintained by offsetting the signal received from sensor 78.
Although two photoelectric circuits have been utilized in FIGS. 6, 7 and 8, the slope sensor may be modified to employ only one photoelectric circuit by use of only ordinary skill in the art. I
lt would also be possible to add a second potentiometer, similar to potentiometer 120, to the amplifier 58 and thereby produce a manually variable signal which may be compared to the signal from the grade sensor 30. This would enable a master grade and slope control to be located near the operator of the machine, thereby requiring only electrical connections to the respective amplifiers 58 and 108.
The use, operation and function of the invention are as follows:
Assuming that the paving machine is in position to place paving material upon the base, that the line 28 has been established, that the feeler arm 32 is in contact with the line and the sensor 30 is producing a null signal, then the paver will produce a smooth layer of pavement as it moves forwardly over the base. If, however, the right tires 14 of the tractor l2 encounter a depression or hole, the right side of the pave will then dip down. This will cause the feeler arm32 to rotate the shaft 34 because of contact by the wire 28. Clockwise rotation of the shaft 34 rotates the mask 52 thereby diminishing the light received by receiver 50 so that the signal produced by receiver 48 is greater than that of receiver 50. The resultant positive signal is amplified by amplifier 58 to actuate the valve 62 permitting hydraulic fluid to operate the cylinder 66 which will move the forward end of pulling arm 24 upwardly until the feeler arm 32 returns to its original position whereby the two receivers are again balanced producing a null signal which closes the valve 62 deactivating the cylinder 66. Because this complete operation occurs in a very small amount of time, the level of the side of the screed nearer the wire 28 does not appreciably change even though the right wheel of the tractor has encountered the depression.
Assuming that the screed is intended to be horizontal, the crossbar 72 will also be horizontal. If the left wheel 14 of the tractor l2 encounters a depression, the left side of the tractor and screed will dip down causing the left side of the crossbar 72 to be lower than the right side. The angular change of the crossbar around pivot point 76 rotates the sensor 78 and the float 102 will maintain its vertical orientation thereby masking more of the light received by receiver from lamp 96 and exposing more light to receiver 98 from lamp 94. This produces an unbalanced condition and an error signal transmitted through conductor 106 to the amplifier, where the signal is amplified and sent to the electrically operated valve 112 which opens to actuate the cylinder 116. The cylinder will operate to raise the forward end of pulling arm 26, the left side of crossbar 72 until the crossbar returns to a level, horizontal position. When the crossbar is again level, the float 102 will mask equal amounts of light in the respective photoelectric circuits, producing an electrically balanced condition and an null signal which in turn closes the valve deactivating the cylinder.
It is seen that the operation of either the slope or grade control would be opposite if the tractor encountered a bump or hump in the base, as a negative error signal would then be produced which causes the electrically operated valves to operate the hydraulic cylinder in an opposite direction.
For purposes of clarification, neither the electric wires nor the hydraulic connecting lines have been shown except in the schematic diagrams of FIGS. 3 and 6.
While the preferred embodiment of the invention has been illustrated and described, it is understood that suitable additional modifications, substitutions and alternations may be made by one skilled in the art without departing from the invention's fundamental theme.
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 slope-sensing 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.
2. Apparatus as described in claim I, in which said slopesensing means includes a housing adapted to contain a quantity of fluid, a quantity of generally transparent fluid substantially filling said housing, at least one lamp located within said housing, at least one photoelectric-receiving means located within said housing and producing a signal proportional to the amount of light received from said lamp, buoyant float masking means flexibly attached to said housing having a specific gravity less than that of said fluid and being located in said fluid between said lamp and receiving means, and being movable relative to said lamp and receiving means to vary said signal produced by said receiving means.
3. Apparatus as described in claim 2, in which said slopesensing means includes an inflatable pressurized bladder located within said housing which expands when a quantity of said fluid is lost.