US3264959A

US3264959A - Paving machine slope control system

Info

Publication number: US3264959A
Application number: US300239A
Authority: US
Inventors: Reeford P Shea
Original assignee: Preco LLC
Current assignee: Preco LLC
Priority date: 1963-08-06
Filing date: 1963-08-06
Publication date: 1966-08-09
Anticipated expiration: 1983-08-09

Description

Aug. 9, 1966 R. P. SHEA 3,264,959

PAVING MACHINE SLOPE CONTROL SYSTEM Filed Aug. 1963 s Sheets-Sheet 1 REEFORD P. SHEA INVENTOR.

ATTORNEYS.

Aug. 9, 1966 R. PQSHEA v 3,264,959

- PAVING MACHINE SLOPE CONTROL SYSTEM Filed Aug. 1965 :5 Sheets-Sheet 2 REEFORD P. SHEA INVENTOR.

ATTORNEYS.

Aug. 9, 1966 r R. P. SHEA 3,254,959

PAVING MACHINE SLOPE CONTROL SYSTEM Filed Aug. 6, 1963 a Sheets-Sheet s REEFORD P SHEA INVENTOR.

He. 10 BY 5 V ATTORNEYS.

United States Patent 3,264,959 PAVING MACHINE SLQFE CONTROL SYSTEM Reeford P. Shea, Laguna Beach, Calif, assignor of one- This invention relates to paving machines of the type that deposit a continuous mat of paving material on a surface and, in particular, is directed to a system for controlling the transverse slope of the surface of the mat of paving material that is being deposited.

There are various types of conventional paving machines that employ a movably mounted screed having a flat surface that rides on top of the mat of freshly laid paving material and in this manner the screed levels off and smooths out the surface of the mat. As is well known to those skilled in the art, the paving material is deposited in front of the screed and the relatively fiat bottom surface of the screed is positioned at a slight vertical angle to the direction of travel of the screed so that the paving material is somewhat compacted by the screed and the resulting mat surface is longitudinally fiat although the bottom surface of the screed is actually positioned at an angle to the mat surface produced. It is also conventional to provide adjustable means on each transverse end of the screed for independently adjusting the angle of each end of the screed with respect to the surface of the mat that is being laid. Thus, the bottom surface of the screedis actually positioned at an adjustable angle to the direction of travel of the screed and this angle of attack may vary from one transverse end of the screed to the other transverse end of the screed.

As is well known, a transverse slope may be produced in the mat with respect to the surface on which the mat is being placed by setting the angle of attack of one end of the screed to a diifereut value than the angle of attack of the other end of the screed and generally speaking, the mat that is produced Will slope downwardly in the transverse direction toward that end of the screed which was set at the lesser angle of attack.

If the screed is set to certain angles of attack, then in theory, the screed should reach an equilibrium position where a continuous mat of unvarying transverse slope is produced. Any change in the setting of the angles of attack should result in the screed merely assuming a new equilibrium position. However, it has been found in laying a continuous mat of paving material with this type of paving machine, that it is not suflicient to merely adjust the angles of attack of the two ends of the screed until the desired transverse slope is produced and then to discontinue making adjustments since many varying conditions present will cause the transverse slope to vary from the desired slope although the screed adjustment is not modified.

Moreover, when it is desired to increase or decrease the transverse slope in the mat produced, it is near impossible to estimate and adjust the angles of attack of the screed so that the new equilibrium position that is reached does not produce a transverse slope less than or greater than the new desired slope. For these and other well known reasons there have been control systems developed, such as that described in my Patent No. 3,029,- 716, issued April 17, 1962, entitled, Paving Machine Control System, that are adapted for use with this type of paving machine for facilitating the adjustment of the angles of attack of the screed to produce a smooth and continuous mat surface of the desired transverse slope.

By this invention there is provided an improved control system for the described type of paving machine for anticipating and correcting error in transverse slope of the paving mat wherein means are provided for producing a value of transverse inclination corresponding to a combination of the transverse slope of the screed and the angles of attack of the two ends of the screed and for comparing the transverse slope of the mat surface produced and the aforementioned transverse inclination to produce a signal for adjusting the angles of attack of the screed to maintain the mat surface at the desired predetermined transverse slope. I

It is an object of this invention to provide a novel control system for paving machines which employs means for comparing actual transverse slope with a value of transverse inclination corresponding to a combination of transverse slope and the projected angles of attack of the screed and for producing a signal to modify the angles of attack of the screed to maintain the predetermined trans- Verse s-lope.

Another object of this invention is to provide such a control system wherein the means for measuring the transverse slope of the mat surface compares that meas-' ured slope with the desired transverse slope and modifies the actual value of said comparison of transverse inclination and desired slope to produce a signal for adjusting the angles of attack of the screed.

A further object of this invention is to provide a novel control system for the described type of paving machine wherein means are provided for producing a transverse inclination corresponding to a combination of transverse slope and the angles of attack of the screed and com paring this transverse inclination with the desired transverse slope to produce a signal for adjusting the angles of attack of the screed and wherein such comparison is continuously and cumulatively modified by comparisons between the actual and desired transverse slopes of the mat surface.

Still another object of this invention is to provide a novel control system for a screed type paving machine wherein the actual transverse slope of the mat surface is compared with the desired transverse slope and a value of transverse inclination corresponding to a projected value of transverse slope at some advanced location of the mat surface to automatically adjust the angles of attack of the screed to thereby anticipate variations in transverse slope and correct for such variations without over-correcting so as to unduly vary the transverse slope of the mat surface as it is laid.

Other and more detailed objects and advantages of this invention will appear from the following description and the accompanying drawings.

In the drawings:

FIGURE 1 is a side elevation of a paving machine of the type described incorporating the control system mechanism of this invention.

FIGURE 2 is a front elevation of the paving machine illustrated in FIGURE 1.

FIGURE 3 is a rear elevation of the paving machine illustrated in FIGURE 1.

FIGURE 4 is a fragmentary enlarged view of a portion of the control system mechanism illustrated in FIGURE 2.

FIGURE 5 is a schematic drawing of an illustrative electrical system for the control system of this invention.

FIGURE 6 is a schematic drawing of a modified form of electrical system for the control system of this invention.

FIGURE 7 is a schematic drawing of another modified electrical system for the control system of this invention.

FIGURE 8 is a schematic drawing of a modified electrical apparatus that may be substituted for portions of the electrical systems of FIGURES 5, 6 and 7.

FIGURE 9 is an enlarged fragmentary rear elevation similar to FIGURE 3 and illustrating'in further detail a portion of the control mechanism of this invention.

FIGURE is a sectional elevation taken substantially on the line 1010 as shown in FIGURE 9.

FIGURE 11 is an enlarged fragmentary side elevation of a portion of the screed apparatus shown in FIGURE 1.

FIGURE 12 is a perspective view of the apparatus for selecting the desired transverse slope including portions of the electrical systems illustrated in FIGURES 5, 6 and 7.

Referring now more particularly to FIGURES 1, 2 and 3, the control mechanism of this invention is adapted to be incorporated with a conventional paving machine, generally designated 20, which may be of any convenient type. The illustrated paving machine is supported on a pair of endless tractor treads 21 and may be selfpropelled by a motor unit 22 through appropriate drive means to the tractor treads 21.

In order to lay a mat 23 of paving material on the ground or any other surface 24, the bulk paving material 25 is deposited in the front of the paving machine 20 and then is appropriately distributed by means such as a powdered transverse screw conveyor 26 for tamping by appropriate tamping means 27 positioned on the front of the screed assembly 28. The screed assembly 28 has a screed 29 comprised of a plate positioned generally horizontally for riding on the surface 30 of the mat 23 of paving material for producing a smooth surface 30 and slightly compacting the mat. A pair of

draft arms

31 and 32 are rigidly connected to the screed assembly 28.

on each side of the paving machine 20 and each draft arm is independently pivotally connected by trunnions 33 to the frame of the paving machine 20. The screed assembly 28 is therefore capable of being raised or lowered by pivoting about the trunnions 33 and one lateral side of the screed assembly may be raised or lowered substantial amounts without affecting the position of the other lateral side of the screed assembly. All of the heretofore described apparatus is conventional for paving machines of this type although it is to be realized that certain of the apparatus may vary in detail of construction for various commercial embodiments of paving machines of this type.

In order to vary the thickness and transverse slope of the paving mat 23, the screed 29 is pivotally mounted to the remainder of the screed assembly 28 for pivoting about a horizontal transverse axis at point 34, whereby the bottom paving-engaging surface of the screed 29 may be pivoted to various positions relative to a horizontal plane. Any convenient means may be used for pivotally adjusting the position of the screed 29 such as a pair of

vertical screws

35 and 36 positioned on each lateral side of the screed assembly 28. The

screws

35 and 36 threadedly engage nuts 37 on the screed assembly and engage the screed 29 at a location spaced from the lateral horizontal axis through point 34. Threaded

screws

35 and 36 are independently adjustable whereby the bottom surface of the screed 29 at each lateral end is independently adjustable to varying angles of attack with respect to the direction of movement of the paving machine.

Thus, as is well known by those skilled in the art, by adjusting both of the

screws

35 and 36 to increase the angle of attack of both ends of the screed a mat of increased thickness will be produced, or by increasing the angle of attack of one end of the screed and decreasing the angle of attack of the other end of the screed a change in the transverse slope of the mat will be produced, or various other changes in the angles of attack will produce similar changes in the surface and thickness of the paving mat. When the angles of attack of the two lateral ends of the screed 29 are different there obviously will be a lateral twist in the bottom surface of the mat. Moreover, it is often conventional with this type of paving machine to provide means in the lateral center of the screed assembly 28 for bending or arching the screed 29 upwardly or downwardly to produce a mat surface 30 which is laterally humped or troughed, respectively, and it will readily hereinafter appear that such adjustment will not adversely affect the control system of this invention.

Since the screed assembly 28 is afiixed to the

draft arms

31 and 32 which are pivotally mounted on each side of the paving machine 20, it is apparent that any change in the elevation or transverse slope of the paving machine 20, at an axis passing through the trunnions 33, will result in a change in the position of the screed 29 even though no modification is made in the positions of adjusting

screws

35 and 36. Thus, for example, if the tread 21 on the same side of paving machine 20 as draft arm 31 were to encounter and ride up onto a bump in the surface 24, the angle of attack of the screed 29 on that side would be increased. Similarly, if the transverse slope of surface 24 were to change and yet it was desired that the transverse slope of surface 30 not be changed then it would be necessary to change the settings of one or both of the

screws

35 and 36 in order to compensate for this change in the transverse slope of the axis passing through the trunnions 33. Thus, the thickness and transverse slope of the mat 23 that will be produced at some subsequent location is a function of such factors as the present trans verse slope of the screed, the present angles of attack of the screed, and in what amount are these values of transverse slope and angles of attack changing or have been changing.

In order to produce a qualitative indication of a combination of the values of transverse slope and angles of attack of the screed 29, an apparatus, generally designated 40, is provided and may be substantially similar in mechanical structure as the like device described in my Patent No. 3,029,716 heretofore referred to. Apparatus 40 includes a pair of

arms

41 and 42 rigidly mounted on each lateral end of the screed 29 and extending forwardly and preferably upwardly as shown. A bracket 43 may be mounted on each of the

draft arms

31 and 32 for forming a guide slot between the draft arm and the bracket to receive and guide the associated

arm

41 or 42 without obstructing the vertical and longitudinal movement of such arms. A gantry beam 44 of any convenient shape to avoid interference with the operation of the paving machine 20 extends across the top of the paving machine and is pivotally connected at each end 45 to the

arms

41 and 42. A rigid link 46 extends between the gantry beam 44 and the paving machine for supporting the gantry beam and is pivotally connected at 47 to the paving machine and at 48 to the gantry beam for permitting vertical and lateral movement of the gantry beam. Thus, it may be seen that the transverse slope or inclination of gantry beam 44 is a function and combination of the actual transverse slope of the screed 29 and the difference between the angles of attack of the two lateral ends of the screed 29.

Referring now to FIGURE 4, means are provided for sensing the transverse inclination of the gantry beam 44 with respect to the horizontal and such means may include a weighted pendulum 50 pivotally mounted at 51 In a housing 52 that is in turn mounted on the gantry beam 44. The axis of the pivotal mounting of pendulum 50 is substantially parallel to the direction of movement of the paving machine 20 and therefore perpendicular to the gantry beam 44. Thus, as the transverse inclination of gantry beam 44 varies the position of pendulum 50 with respect to housing 52 will also vary. An appro priate scale may be provided on housing 52 for permitting visual observation of pendulum 50 and thereby producing a visual signal of the transverse inclination of gantry beam 44. However, for producing an electrical signal corresponding to this transverse inclination a Winding 53 may be mounted in housing 52 in insulating relationship and a brush 54 may be mounted on pendulum 50 in a manner for electrically contacting winding 53. The functron of these electrical means will become more apparent in the description of FIGURES 5, 6 and 7. The housing 52 may be rigidly or adjustably mounted on gantry beam 44. The specific mounting of housing 52 illustrated in FIGURE 4 incorporates the mechanism used with the electrical system of FIGURE 5, and is diiferen-t than that which is necessary with the electrical systems of FIG- URES 6 and 7. The housing 52 is pivotally mounted at one end 55 to a rigid bracket on gantry beam 44 and is pivotally mounted at the other end 56 to a threaded nut 57. Threaded nut 57 engages a threaded shaft 58 and shaft 58 may be rotated in either direction by reversible servo-motor 59. By this arrangement it may be seen that by rotating shaft 58 the physical position of housing 52 with respect to gantry beam 44 may be varied and therefore, a false or pseudo signal, visual or electrical, of the transverse inclination of gantry beam 44 will be produced by the pendulum 50 in its position with respect to housing 52. The purpose of producing such pseudo signal will be hereinafter disclosed more fully.

Referring now more particularly to FIGURES 3, 9, l0 and 11, an apparatus, generally designated 60, is provided on the screed 29 in order to produce a signal corresponding to the actual transverse slope of the mat surface 30 that is being produced at any given time. Apparatus 60 includes a transverse beam 61, a pair of

support columns

62 and 63 and a support link 64. The

support columns

62 and 63 are mounted on screed 29 for universal movement relative to the screed by any convenient means such as a ball-and-socket connection 65 between the screed and the lower end of the support columns. The

support columns

62 and 63 are preferably positioned directly above the trailing edge 29a of the screed. The ends of the transverse beam 61 are pivotally mounted on the upper ends of

support columns

62 and 63 by any convenient means such as a pin and clevis mounting 66. One end of the rigid link 64 is pivotally mounted to the transverse beam 61 and the other end of the link 64 is mounted on a portion 67 of the frame of the screed assembly 28 for universal movement relative to the screed assembly. In this manner transverse beam 61 is supported directly above the trailing edge 29a of the screed 29 and remains parallel to such edge without regard to differences in the angles of attack of the two ends of the screed or other factors. It is to be noted that if screed 29 is laterally arched upwardly or downwardly by the conventionally provided means for any desired purpose, as heretofore described, then transverse beam 61 remains substantially parallel to a line drawn between the two lateral ends of the screed at the trailing edge 29a of the screed which is equal to the overall transverse slope of the screed. A pendulum 68 is pivotally mounted at 68a in a housing 69 for pivotal movement about an axis substantially parallel to the direction of movement of the screed. Housing 69 is mounted on transverse beam 61 and therefore the transverse slope of beam 61 and in fact the transverse slope of the mat surface 30 being produced, will be indicated by the relative position of pendulum 68 with respect to housing 69. Appropriate means may be provided on the pendulum and housing for visual observation of such transverse slope and electrical means may be provided for producing an electrical signal corresponding to such transverse slope. Such electrical means may include a winding 73 mounted in insulated relationship to the housing 69 and a brush 74 mounted on pendulum 68 and adapted to electrically contact winding 73. The purpose of this electrical signal of transverse slope will become more apparent when considering the electrical systems of FIGURES 5, 6 and 7.

The adjusting screws 35 and 36 may be manually operated by crank wheels 70 to produce the desired settings of the angles of attack of the two lateral ends of the screed 29. In order to produce a powered operation of adjusting

screws

35 and 36 power means may be provided with each screw and, as shown in the drawings, these means may include a reversible electric motor 71 associated with each adjusting screw and provided with appropriate power transmission means 72 for rotating the 6 adjusting screws in either direction. FIGURES 5, 6 and 7 are directed to electrical systems for automatically operating motors 71 to produce the desired adjustments of the angles of attack of the screed.

Referring now to FIGURE 5, an electrical system is shown which incorporates the adjustable pendulum hous ing arrangement shown in FIGURE 4. As previously described, the pendulum 50 has a brush 54 for making an electrical contact with winding 53 to form a potentiometer. A second potentiometer is provided having a winding with a brush contact 101 which is adjustable along the winding 100 by any convenient mechanical means. The two ends of the

windings

53 and 100 are connected by two

adjustable resistors

102 and 103 and a power source 104, shown as a battery, is connected across winding 100 to form a bridge circuit. A master switch 105 is provided in series with the power source 104 for controlling the operation of the circuit. The voltage signal tapped by brush 54 and the voltage signal tapped by brush 101 are supplied through

lines

106 and 107 respectively, to a servo-amplifier 108 which is in turn supplied with power to operate the motors 71 in response to the signals supplied by

lines

106 and 107. A meter 109 may be provided for producing a visual indication of the voltage signals from

lines

106 and 107. The mechanical means for adjusting brush 101 may be provided with an appropriate scale and dial having readings corresponding to degrees of slope or the like so that the desired transverse slope of the mat surface 30 may be set on this potentiometer formed by winding 100 and brush 101. The electrical system thus far described is balanced such that when the slope indicated by pendulum 50 is equal to the desired slope set by brush 101, no signal will be produced on

lines

106 and 107 and therefore motors 71 will not be operated. When the slope of pendulum 50 differs from the slope set by brush 101 then the signal produced on

lines

106 and 107 will operate motors 71 to change the angles of attack of the screed 29 in a direction to tend to change the position of the gantry beam 44 so as to bring the slope indication of pendulum 50 into agreement with the slope setting by brush 101. Appropriate switching may be provided for operating one or the other of the motors 71 as desired, to operate

screw

35 or 36 or even operating both motors 71 simultaneously in opposite directions to produce the necessary change in screed angles. However, since the transverse inclination or slope .of gantry beam 44 is a function of the combination of the transverse slope of the screed 29 and the angles of attack of the two ends of the screed, as previously described, the slope indicated by pendulum 50 will not always be equal to the transverse slope of the mat surface 30 and in fact is more of an indication as to what the transverse slope of the mat 30 will be at some future location. In order to monitor the actual transverse slope of the mat surface 30 which is being produced at any one time and to induce appropriate changes in the screed angles of attack to correct any difference between actual transverse slope and desired transverse slope, a control system, generally designated 110, is provided and functions to appropriately modify the control signal produced by the electrical control system, generally designated 111, heretofore described. Control system 110 includes the potentiometer formed by the pendulum 68 having a brush 74 for electrically contacting the winding 73. A second potentiometer is provided in control system 110 comprised of a winding 112 with a brush 113 having convenient means for adjusting the location of the contact of the brush 113 with winding 112. The two ends of

windings

73 and 112 are connected by a pair of

adjustable resistors

114 and 115 to form a bridge circuit. An electrical power source indicated as battery 116 is connected across winding 112 with a switch 117 in series therewith for selectively supplying power to the bridge circuit. It is to be noted that while

batteries

104 and 116 and

switches

105 and 117 have been illustrated as separate components, they may be the same physical components with only one battery and one switch provided. The brush 113 is set to the desired transverse slope of the mat surface 30 by any convenient means having indicating means for selecting such slope.

Whenever the pendulum 68 indicates a transverse slope differing from the predetermined desired slope set by brush 113, a voltage signal will be produced on

lines

118 and 119 to the input of a servo-amplifier 120. A meter 121 may be provided for visually indicating the input signal to the amplifier 12%. Amplifier 120 is provided with an appropriate power supply and the output of amplifier 120 through lines 122 operates the servo-motor 59. As previously described with respect to FIGURE 4, servo-motor 59 functions to change the position of pendulum housing 52 with respect to gantry beam 44 thereby producing a pseudo indication by pendulum 50 of the actual transverse inclination of gantry beam 44. The output of amplifier 120 operates the reversible servo-motor 59 in the appropriate direction to modify the slope indication by pendulum 50 in the same direction as the difference in actual transverse slope and desired transverse slope indicated by the control system 110. For example, at a given moment, if the bridge circuit of control system 111 is balanced so as to not produce a signal for operating adjusting screw motors 71 and yet the bridge circuit of control system 110 produces a signal indicating that the actual transverse slope of the mat 33] is less than the desired transverse slope as set by brush 113, then motor 59 will operate to change the position of pendulum housing 52 to produce a reading on the potentiometer formed by pendulum 50 and winding 53 that also indicates that the transverse slope is less than the desired transverse slope. Thus, in this example, the bridge circuit of control system 111 will no longer be balanced and a signal will be produced on

lines

106 and 107 to amplifier 108 to operate motors 71 and adjust the screed angles to increase the transverse slope, thereby tending to bring the actual transverse slope of the mat surface 30 back to the desired transverse slope. It is to be noted that since the position of pendulum housing 52 is changed by motor 59 there is actually a cumulative effect produced on the bridge circuit of control system 111 in that even when a zero signal is produced by control system 110, the pendulum housing 52 will remain in its changed position with respect to gantry beam 44 thereby continuing the pseudo transverse slope indication produced by the potentiometer of pendulum 50 and winding 53.

Thus, again by way of example only, certain conditions may exist wherein the desired transverse slope, as set by

brushes

101 and 113 of the two control systems, is two degrees and an equilibrium position might be reached where pendulum 68 indicates the desired two degrees but gantry beam 44 has an actual slope of three degrees and yet due to the positioning of pendulum housing 52, no signal will be produced for operating motors 71. Thus, in this example, this equilibrium condition will be maintained and the desired slope will be produced.

In order to provide only intermittent operation of motor 59 in response to the signal produced by control system 110, an apparatus, generally designated 125, is provided for operating a switch 126 in the lines 122 to the motor 59. The apparatus 125 may be of any convenient type for prefenably closing the switch 126 for a short interval of time and opening the switch for a longer period of time. In this manner, the signal produced by control system 110 operates motor 59 to slightly modify the position of pendulum housing 52 and then the operation of motor 59 is discontinued for a period of time to permit the screed 29 to approach or reach a new equilibrium position before the signal produced by control system 110 is again imposed on the control system 111 by modifying the position of housing 52. Apparatus 125 may take many forms such as a timer for opening and closing switch 126 for specific periods of time or an odometer mechanism appropriately coupled to the driving mechanism of the paving machine 20 to open and close the switch 126 at predetermined distances of movement of the paving machine.

As previously described, the

brushes

101 and 113 are set to the desired transverse slope for the two control systems 111 and 110 respectively, and such settings may be made by mechanical means. Such mechanical means may take any convenient form such as that illustrated in FIGURE 12, including a control box 127 mounted at an appropriate location on the paving machine. A shaft 128 is rotatably mounted in control box 127 and may be rotated by means of knob 129. A pointer 130 on knob 129 sweeps a dial face 131 having appropriate indicia for indicating transverse slope in degrees or the like. The brushes 191 and 113 are mounted on shaft 128 in insulated relationship thereto for contacting the windings and 112 respectively, which are in turn mounted in insulated relationship with respect to the control box 127.

Referring now to FIGURE 6, a modified form of electrical control system is illustnated having essentially two control systems, generally designated a and 111a similar in function although dilfering in detail to the heretofore described control systems 110 and 111 respectively. Control system 111a includes a pendulum 50a substantially similar to pendulum 50 except that the housing mounting pendulum 50a is not movable by a servo-motor as was housing 52 movable by servo-motor 59. Pendulum 50a indicates the transverse slope of gantry beam 44. A brush 54a mounted on pendulum 50a contacts a winding 53a to form a potentiometer and a second potentiometer is formed by winding 100a and brush 101a similar in function and operation to the two otentiometers of heretofore described control system 111, A power supply is connected across winding 100a and the two ends of windings 53a and 106a are connected by an adjustable resistor 103a and a variable resistor 140. The setting of variable resistor 140 is controlled and appropriately modified by servo-motor 141 in a manner hereinafter described. As with control system 111, control system 111a functions to produce an input signal to amplifier 108a which in turn appropriately operates adjusting screw motors 71 in a direction to reduce the signal produced by the bridge circuit. Control system 110a may be identical to heretofore described control system 110 and have a potentiometer formed by pendulum 68, winding 73 and brush 74, a second potentiometer formed by winding 112 and adjustable brush 113, a power source across winding 112, and a pair of

adjustable resistors

114 and 115 to form a bridge circuit to produce an input signal to amplifier 120. The output of amplifier through lines 122 operates the reversible servo-motor 141 in an appropriate direction to change the resistance of variable resistor 140 and thereby modify the voltage signal to amplifier 108a which is produced by the bridge circuit of control system 111a. Variable resistor 140 is adjusted in the direction to tend to produce a signal to amplifier 108a which corresponds to the difference in actual and desired transverse slope detected by control system 110a to thereby operate motors 71 to tend to correct this difference. Thus, in effect, the resistance of variable resistor 140 is modified to electrically imbalance the bridge circuit to accomplish the same function as is accomplished by the control system of FIGURE 5 wherein the position of pendulum housing 52 was modified to produce a pseudo indication of the actual transverse slope of gantry beam 44. Again, an apparatus 125 may be provided for intermittently operating a switch 126 to produce only intermittent operation of servo-motor 141.

Referring now to FIGURE 7, a control system is illustnated that performs substantially the same functions as the control systems of FIGURES 5 and 6, but wherein certain dilferent components are provided for accomplishing these functions. The system of FIGURE 7 is comprised of two control systems, generally designated 1113b and 111b corresponding in function to the control systems 110 and 111 respectively, heretofore described. Control system 111b includes a potentiometer formed by pendulum brush 54b, and Winding 53b and a second potentiometer formed by winding 10017 and brush 1131b. The brush 101b of the second potentiometer is adjustable to the desired slope by any convenient means such as that illustrated in FIGURE 12.

A power supply is provided across winding and the two ends of

windings

53b and 10% are connected by variable resistors 103i) and 14% to complete a bridge circuit for producing an input signal to amplifier ltlSb to operate the motors 71. A servo-motor 141k is provided for adjusting the variable resistor 1401) in response to a signal from control system 1101) in an identical manner to the operation of servo-motor 141 in adjusting resistor 140 in response to a signal from control system 110a heretofore described with respect to FIGURE 6. Control system 11% is substantially identical to heretofore described

control system

110 and 110a and has a bridge circuit formed by the pendulum mounted brush 74, winding 73,

adjustable resistors

114 and 115, a potentiometer form by winding 112 and brush 113, and a power source across winding 112 to produce an input signal to amplifier 120. In addition to operating servo-motor 141b, the output of amplifier 120 through lines 122 operates a bidirectional relay 150 or equivalent type device for producing switch movement in two directions. Relay 150 operates switch 151 which has one pole connected by line 152 to one of the input lines 1137b to the amplifier 10%. Upon an output signal from amplifier 120, relay 150 operates to move the switch 151 from a neutral position, wherein no circuit is formed by switch 151, to one of two positions whereby a resistance 153 is connected from line 152 to the juncture between winding ltifib and variable resistor 140b or a resistance 154 is connected from line 152 to the juncture between winding 16% and variable resistor 10311. By connecting

resistor

153 or 154, in the bridge circuit in this manner, a substantial change in the input signal on lines 106b and 107k to amplifier 1081) is produced. The operation of relay 150 is oriented so that this change in the signal to amplifier 1138b is actually an increase in the signal in the same direction over that signal which would be produced if

resistor

153 or 154 were not connected into the circuit. In this manner, the temporary correcting signal from control system 1105 which is imposed on control system 111]) to operate motors 71 is greater than the semi-permanent change that is made in resistor 14% by servo-motor 1411).

FIGURE 8 illustrates a modified form of control system that may be substituted for each of the

control systems

110, 110a, 11% or 111 and in particular is a substitution for the described bridge circuits of those control systems. This control system, generally designated 160, includes a pendulum 161 similar to

pendulums

50 and 68 having an electrical contact member 162 for contacting one or the other of electrical contact points 163 and 164 as the pendulum pivots. Contact points 163 and 164 are mechanically adjustable to the desired transverse slope and therefore when the transverse slope measured by pendulum 161 differs from the desired transverse slope the contract 162 will engage

contact point

163 or 164, depending on the direction of such difference between actual and desired transverse slope. The contact points 163 and 164 are connected to an amplifier 165 and a power source 166 is connected between pendulum 161 and amplifier 165. The output of amplifier 165 operates a motor 167 which may be equivalent to motors 71 -or 59 or 141 or 141b, depending upon which of the abovedescribed control systems is being replaced by this control system 160. It is to be noted that with this control system 160, a control signal is produced which only indicates needed correction in one direction or another where as in the previously described control systems, a quantitative value of the needed correction was produced by the bridge circuits as the control signal.

Thus, it may be seen that by the control system of this invention, through its various embodiments, the adjustments of the screed angles of attack in response to the control signal produced by comparing the transverse slope of gantry beam 44 with the desired transverse slope is monitored and modified by inducing control signals produced by comparing the actual transverse slope of the mat surface 30 being produced and the desired transverse slope. While it has been found beneficial in anticipating and correcting errors in transverse slope to use the mechanism 41; for producing a transverse inclination of a gantry beam 44 corresponding to a combination of the actual transverse slope of the screed and the dilference between the angles of attack of the two ends of the screed, it has also been found that even under equilibrium conditions the transverse slope of the gantry beam may not equal the actual transverse slope of the mat. Thus, with previous control systems it has often been necessary to set the desired transverse slope at an amount differing from the actual desired transverse slope in order to produce the actual desired transverse slope, thereby introducing guess-work into controlling the transverse slope of the surface 30 that was intended to be eliminated by the previous control systems.

Having fully described my invention, it is to be understood that I do not wish to be limited to the details of the embodiments herein set forth or to the details illustrated in the drawings, but rather my invention is of the full scope of the appended claims.

I claim:

1. In a slope control apparatus for a paving machine having a screed movably connected to a prime mover and operable means for independently varying the angle of attack of each lateral end portion of the screed, the combination of: first sensing means operatively connected to the screed for registering a value of transverse inclination corresponding to a combination of the actual transverse inclination of the screed and the angles of attack of both end portions of the screed, second sensing means operatively connected to the trailing edge of the screed for registering a value of transverse inclination equal to the transverse inclination of the trailing edge of the screed, means responsive to said first sensing means and a preselected value of desired transverse slope for producing a signal for adjusting said operable means to modify the angle of attack of said screed in a manner to reduce the difference between registered transverse inclination and desired transverse slope, control means for modifying the said first inclination-slope difference,

and second means responsive to said second sensing means and the preselected value of desired transverse slope for producing a second signal of this second inclination-slope difference between registered transverse inclination and desired transverse slope for adjusting said control means to modify the first inclination-slope difference in the direction of said second inclination-slope difference.

2. In a slope control apparatus for a paving machine having a screed movably connected to a prime mover and operable means for independently varying the angle of attack of each lateral end portion of the screed, the combination of: first sensing means operatively connected to the screed for registering a value of transverse inclination corresponding to a combination of the actual transverse inclination of the screed and the angles of attack of both end portions of the screed, second sensing means operatively connected to the trailing edge of the screed for registering :a value of transverse inclination equal to the transverse inclination of the trailing edge of the screed, adjustable means operatively connected with each said sensing means for selecting the predetermined desired transverse slope, means responsive to said first sensing means and the desired transverse slope selected on the associated said adjustable means for producing a signal of the difference between registered transverse inclination and desired transverse slope for adjusting said operable means and modifying the angle of attack of the screed in a manner to reduce such first inclinationslope difference, control means for modifying the value of said first inclination-slope difference, and second means responsive to said second sensing means and the desired transverse slope selected on the associated said adjutable means for producing a second signal of this second inclination-slope difference vbetween registered transverse inclination and desired transverse slope for adjusting said control means to modify the first inclination-slope difference in the direction of said second inclination-slope difference.

3. In a slope control apparatus for a paving machine that has a screed attached to its lateral end portions to draft arms that are pivotally connected to a prime mover and operable means for independently varying the angle of attack of each lateral end portion of the screed, the combination of: first sensing means operatively connected to the screed for registering a value of transverse inclination corresponding to a combination of the actual transverse inclination of the screed and the angles of attack of both end portions of the screed, second sensing means operatively connected to the trailing edge of the screed for registering a value of transverse inclination equal to the transverse inclination of the trailing edge of the screed, adjustable means operatively connected with each said sensing means for selecting the predetermined desired transverse slope, power means for operating the said operable means for independently varying the angle of attack of the end portions of the screed, means responsive to said first sensing means and the desired transverse slope selected by the associated said adjutable means for producing a signal and operating said power means to modify the angle of attack of the screed end portions in a manner to reduce the difference between registered transverse inclination and desired transverse slope, control means for modifying the said inclinationslope difference signal produced by said responsive means, and second means responsive to said second sensing means and the desired transverse slope selected by the associated said adjustable means for producing a second signal of this second inclination-slope difference between registered transverse inclination and desired transverse slope and operate said control means to modify the first inclination-slope difference signal in the direction of said second inclination-slope difference signal.

4. In a slope control apparatus for a paving machine that has a screed attached by its lateral end portions to draft arms that are pivotally connected to a prime mover and operable means for independently varying the angle of attack of each lateral end portion of the screed, the combination of: first sensing means operatively connected to the screed for registering a value of transverse inclination corresponding to a combination of the actual transverse inclination of the screed and the angles of attack of 'both end portions of the screed, second sensing means operatively connected to the trailing edge of the screed for registering a value of transverse inclination equal to the transverse inclination of the trailing edge of the screed, adjustable means operatively connected with each sensing means for selecting the predetermined desired transverse slope, power means for operating the said operable means for independently varying the angle of attack of the end portions of the screed, means responsive to said first sensing means and the desired transverse slope selected on the associated said adjustable means for producing a signal of the difference between registered transverse inclination and desired transverse slope to selectively operate said power means and modify the screed angle of attack in a manner to reduce such inclination-slope difference, control means for modifying the value of said inclination-slope difference signal produced by said responsive means, second means responsive to said second sensing means and the desired transverse slope selected on the associated said adjustable means for producing a second signal of this second inclinationslope difference between registered transverse inclination and desired transverse slope and for operating said control means to modify the first inclination-slope difference signal in the direction of said second inclination-slope difference signal, and means operatively connected to said control means for selectively operating said control means in response to said second signal only at predetermined intervals.

5. In a slope control apparatus for a paving machine that has a screed attached by its lateral end portions to draft arms that are pivotally connected to a prime mover and operable means for independently varying the angle of attack of each lateral end portion of the screed, the combination of: first sensing means operatively connected to the screed for registering a value of transverse inclination corresponding to a combination of the actual transverse inclination of the screed and the angles of attack of both end portions of the screed, second sensing means operatively connected to the trailing edge of the screed for registering a value of transverse inclination equal to the transverse inclination of the trailing edge of the screed, adjustable means operatively connected with each said sensing means for selecting the predetermined desired transverse slope, means responsive to said first sensing means and the desired transverse slope selected on the associated said adjustable means for producing a first signal of the difference between registered transverse inclination and desired transverse slope for adjusting the operable means to modify the screed angle of attack in a manner to reduce such inclination-slope difference, control means operatively connected to said responsive means for modifying said responsive means for producing a pseudo value of said inclination-slope difference and of said first signal, said pseudo values continuing until further modified by said control means, and second means responsive to said second sensing means and the desired transverse slope selected on the associated said adjustable means for producing a second signal of this second inclination-slope difference between registered transverse inclination and desired transverse slope for operating said control means to modify the first inclination-slope difference and induce said pseudo values in the same qualitative direction as said second inclination-slope difference.

6. In a slope control apparatus for a paving machine of the type having a movably mounted screed assembly with a screed adjustable by operable means at each lateral end to various angles of attack and a gantry beam extending laterally between, two forwardly projecting members attached to the screed whereby the gantry beam is transversely inclined in response to a combination of the transverse inclination of the screed and the angles of attack of the lateral ends of the screed, the combination of: first sensing means for measuring the transverse inclination of the gantry beam, means responsive to said first sensing means and a setting of desired transverse slope for adjusting the operable means to vary the screed angles of attack and reduce any difference to zero, second sensing means operatively connected to the trailing edge of the screed for measuring the transverse slope of the surface of the paving mat being produced, means responsive to said second sensing means and a setting of desired transverse slope for producing a signal of the difference between the measured and desired slopes, control means operated in response to said signal fOl imposing a psuedo difference on the actual difference of transverse inclination of the gantry beam with desired transverse slope, said pseudo difference imposed in the same qualitative direction as the difference between desired transverse slope and transverse slope measured by said second sensing means producing said signal, and means for operating said control means only at spaced intervals and for a limited duration for imposing the same said pseudo difference throughout said interval and modifying that pseudo diiierence during said limited duration in response to said signal as then produced.

7. In a slope control apparatus for a paving machine of the type having a movably mounted screed assembly with a screed adjustable by operable means at each lateral end to various angles of attack and a gantry beam extending laterally between two forwardly projecting members attached to the screed whereby the gantry beam is transversely inclined in response to a combination of the transverse inclination of the screed and the angles of attack of the lateral ends of the screed, the combination of: first sensing means for measuring the transverse inclination of the gantry beam, means responsive to said first sensing means and a setting of desired transverse slope for adjusting the operable means to vary the screed angles of attack and reduce such difference to zero, second sensing means including pendulum means mounted on the trailing edge of the screed for measuring the transverse slope of the paving mat surface being produced at the trailing edge of the screed, an electrical bridge circuit including a potentiometer responsive to the transverse slope measured by said pendulum means and a second potentiometer selectively set to the desired transverse slope for said potentiometers to produce a direction-oriented signal, control means operated in response to said signal for imposing a pseudo difierence on the actual difference between transverse inclination of the gantry beam and desired transverse slope, and said pseudo diiierence imposed in the same qualitative direction as the dilference between desired transverse slope and transverse slope measured by said sensing means producing said signal.

8. In a slope control apparatus for a paving machine of the type having a movably mounted screed assembly with a screed adjustable by operable means at each lateral end to various angles of attack and a gantry beam extending laterally between two forwardly projecting members attached to the screed whereby the gantry beam is transversely inclined in response to a combination of the transverse inclination of the screed and the angles of attack of the lateral ends of the screed, the combination of: first sensing means for measuring the transverse inclination of the gantry beam including a housing movably mounted on the gantry beam and a pendulum pivotally mounted in said housing, a servo-motor for pivoting said housing relative to said beam, means responsive to said first sensing means for producing a signal of the deviation of the transverse inclination of the gantry beam as measured by the position of said pendulum in said housing from the desired transverse slope for adjusting the operable means to vary the screed angles of attack and reduce such difference toward zero, second sensing means mounted above the trailing edge of the screed for measuring the transverse slope of the surface of the paving mat being produced, means responsive to said second sensing means and the value of the said transverse slope measured by said second sensing means and a setting of desired transverse slope for producing a signal of the difference in said slopes, means for operating said servo-motor in response to said signal for changing the position of said housing relative to said gantry beam to produce a pseudo difference in the actual difference comparison of desired transverse slope with transverse inclination of the gantry beam, and said pseudo difference imposed in the same qualitative direction as the difference between desired transverse slope and transverse slope measured by said second sensing means producing said signal.

9. In a slope control apparatus for a paving machine of the type having a movably mounted screed assembly with a screed adjustable by operable means at each lateral end to various angles of attack and a gantry beam extending laterally between two forwardly projecting members attached to the screed whereby the gantry beam is transversely inclined in response to a combination of the transverse inclination of the screed and the angles of attack of the lateral ends of the screed, the combination of: first sensing means for measuring the transverse inclination of the gantry beam, means responsive to said first sensing means and a preselected desired transverse slope for adjusting the operable means to vary the screed angles of attack and reduce the difference between measured transverse inclination and desired transverse slope to zero, said responsive means including an electrical bridge circuit having a variable resistor, servo-motor means for adjusting the setting of said variable resistor, second sensing means mounted above the trailing edge of the screed for measuring the transverse slope of the surface of the paving mat being produced, means responsive to said second sensing means and a preselected desired transverse slope for producing a signal of the difference in said slopes, means for operating said servo-motor in response to said signal for adjuusting said variable resistor to produce a pseudo ditference in said bridge circuit of the actual difierence between desired transverse slope and transverse inclination of the gantry beam, and said pseudo difierence imposed in the same qualitative direction as the difierence between desired transverse slope and transverse slope measured by said second sensing means producing said signal.

10. The combination of claim 9 wherein means are provided for imposing a resistance on the said electrical bridge circuit during the duration of said signal for further producing a pseudo difference on the bridge circuit that is oriented in the same manner as the pseudo difference imposed by said variable resistor.

11. A paving machine slope control system comprising a pair of traction arms pivoted on the paving machine and rigidly connected to a screed structure, a flexible screed plate pivotally supported by said screed structure, a pair of arms rigidly connected to said screed plate and extending forwardly and upwardly thereof, a gantry beam having its ends operatively connected to said forwardly and upwardly extending pair of arms, sensing means intermediate the ends of said gantry beam to indicate the relative position of the points of connection of said arms to said screed plate thereby indicating the relative elevation and relative angle of attack at the two ends of the screed plate, power means responsive to said sensing means to change the relative inclination at opposite ends of the screed plate, a second sensing means supported intermediate the ends of the screed above the trailing edge of the screed plate to measure the actual transverse slope of said screed plate, and motor means actuated by said second sensing means to change the inclination of said first sensing means relative to said gantry beam to bring the actual transverse slop of the screed plate back to the desired transverse slope.

References Cited by the Examiner UNITED STATES PATENTS 3,029,716 4/1962 Shea 94-46 JACOB L. NACKENOFF, Primary Examiner.

Claims

1. IN A SLOPE CONTROL APPARATUS FOR A PAVING MACHINE HAVING A SCREED MOVABLY CONNECTED TO A PRIME MOVER AND OPERABLE MEANS FOR INDEPENDENTLY VARYING THE ANGLE OF ATTACK OF EACH LATERAL END PORTION OF THE SCREED, THE COMBINATION OF: FIRST SENSING MEANS OPERATIVELY CONNECTED TO THE SCREED FOR REGISTERING A VALUE OF TRANSVERSE INCLINATION CORRESPONDING TO A COMBINATION OF THE ACTUAL TRANSVERSE INCLINATION OF THE SCREED AND THE ANGLES OF ATTACK OF BOTH END PORTIONS OF THE SCREED, SECOND SENSING MEANS OPERATIVELY CONNECTED TO THE TRAILING EDGE OF THE SCREED FOR REGISTERING A VALUE OF TRANSVERSE INCLINATION EQUAL TO THE TRANSVERSE INCLINATION OF THE TRAILING EDGE OF THE SCREED, MEANS RESPONSIVE TO SAID FIRST SENSING MEANS AND A PRESELECTED VALUE OF DESIRED TRANSVERSE SLOPE FOR PRODUCING A SIGNAL FOR ADJUSTING SAID OPERABLE MEANS TO MODIFY THE ANGLE OF ATTACK OF SAID SCREED IN A MANNER TO REDUCE THE DIFFERENCE BETWEEN REGISTERED TRANSVERSE INCLINATION AND DESIRED TRANSVERSE SLOPE, CONTROL MEANS FOR MODIFYING THE SAID FIRST INCLINATION-SLOPE DIFFERENCE, AND SECOND MEANS RESPONSIVE TO SAID SECOND SENSING MEANS AND THE PRESELECTED VALUE OF DESIRED TRANSVERSE SLOPE FOR PRODUCING A SECOND SIGNAL OF THIS SECOND INCLINATION-SLOPE DIFFERENCE BETWEEN REGISTERED TRANSVERSE INCLINATION AND DESIRED TRANSVERSE SLOPE FOR ADJUSTING SAID CONTROL MEANS TO MODIFY THE FIRST INCLINATION-SLOPE DIFFERENCE IN THE DIRECTION OF SAID SECOND INCLINATION-SLOPE DIFFERENCE.