US3181441A

US3181441A - Control apparatus

Info

Publication number: US3181441A
Application number: US144667A
Authority: US
Inventors: Richard C Flom
Original assignee: Honeywell Inc
Current assignee: Sundstrand Corp
Priority date: 1961-10-12
Filing date: 1961-10-12
Publication date: 1965-05-04
Anticipated expiration: 1982-05-04

Description

y 4, 1965 R. c. FLOM 3,181,441

CONTROL APPARATUS Filed Oct. 12, 1961 2 Sheets-Sheet 1 INVENTOR. RIQ ARD L. 1.

ATTORNEY May 4, 1965 c, FLOM CONTROL APPARATUS 2 Sheets-Sheet 2 Filed Oct. 12. 1961 LAN-1|- A ,m :m

INVENTOR. RICHARD C JZQ Z BY flTTORA/E) United States Patent 3,181,441 CONTROL APPARATUS Richard C. Flom, Minneapolis, Minn., assignor t0 Honeywell Inc., a corporation of Delaware Filed Oct. 12, 1961, Ser. No. 144,667 14 Claims. (Cl. 94-46) The present invention is concerned with an improved control apparatus particularly adapted for use with road paving machines of the floated screed type.

Many roads are surfaced with a bituminous material to form what is commonly called a blacktop road. Such roads may be produced by machines including a hopper into which the bituminous material is deposited and out of which the bituminous material is fed, immediately in front of the screed, to be deposited on the surface to be paved, the screed compacting the bituminous material to form the paved road surface. Thus, the screed is effective to control the height or grade of the resulting paved road as well as the slope of the road, it being recognized that such a road is normally crowned at the center and sloped toward the outer edges, and is also sloped at curves which are formed in the road.

A type of paving machine of this general construction utilizes a floating screed which freely rests upon the paved surface by virtue of the weight of the screed and in which the angle of attack, that is the attitude of the bottom surface of the screed, determines the height of the resulting paved surface. More specifically, such a paving machine is provided with a propulsion unit which includes a pair of crawler treads or wheels disposed at each side of the propulsion unit, to move the unit. The forward end of the propulsion unit is provided with a hopper to receive the bituminous material. This bituminous material is fed out of the rear portion of the propulsion unit onto the surface to be paved. This operation is provided as the propulsion unit moves along the roadway to be paved. Positioned behind the propulsion unit is a floating screed which is attached to the propulsion unit and towed thereby by means of a pair of beams, the forward ends of which are freely pivoted to the propulsion unit at each side of the unit. The rear ends of the beams are rigidly attached to the screed. Thus, as the paving machine moves, the bituminous material is supplied from the hopper to the roadway to be paved immediately in front of the screed, and the screed compacts this materialas the paver moves. The height of the resulting road surface is normally controlled by controlling the attitude of the screed by means of screed adjusting screws located at the rear end of the beams. However, should the forward ends of the beams be moved in an upward direction, the angle of attack of the screed is changed (the forward edge is tilted up) and a thicker road is produced to increase the height of the road as the screed climbs on top of the bituminous material deposited in front of the screed. Should the forward end of the beams be lowered, the angle of attack of the screed is again changed (the forward edge is tilted down) and the screed tends to dig into the bituminous material, as the paving machine moves, to thus form a thinner layer of bituminous material and to lower the height of the resulting road surface. Furthermore, if the forward end of one of the beams is raised as the forward end of the other beam either remains stationary or is lowered, then the transverse slope of the screed is changed and the resulting slope of the paved road surface is likewise changed.

The present invention is concerned with an improved automatic control apparatus for automatically controlling the attitude of the screed to thus provide a road surface having a height established by a predetermined height datum means which has been disposed along the ice surface to be paved, and likewise having a slope which is manually selected and automatically controlled.

My invention provides a pair of sensors including transducers in the form of potentiometers whose wipers are controlled by sensors, one of the wipers being controlled by a height sensor disposed on one of the beams, and the other wiper being controlled by a pendulum sen.- sor. These potentiometers constitute portions of two A.C. bridge circuits, each bridge circuit including a further manually controllable potentiometer. The first bridge circuit associated with the height sensor (called the Follower Sensor) is provided with a vernier adjustment potentiometer such that the output of this bridge circuit may be nulled as the paving machine is initially brought into engagement with the height sensor contacting or cooperating with the height datum means. Thus, the paving machine is initially adjusted to produce the desired height and thickness of paved surfaces. The second A.C. bridge circuit is associated with the floated pendulum and is provided with a slope adjustment potentiometer which is calibrated so as to allow the operator of the paving machine to manually adjust the slope of the screed and to change this slope as certain conditions are met, such as the forming of a curve in the road.

A further feature of my invention is the provision of a pair of indicating meter circuits which are connected one to each of the two A.C. bridge circuits to thus provide an indication of the operaiton of the control apparatus, indicating respectively the grade or height error and the slope error.

The output of each of the bridge circuits is also fed to first and second motor control circuits, respectively. These motor control circuits are phase-sensitive circuits having silicon controlled rectifier output circuits to provide reversible polarity D.C. voltage output.

In the preferred embodiment of my invention the position of each of the beams is controlled by a reversible .C. motor which is operatively connected thereto. It is within the teachings of my invention to selectively control either of these beams by the pendulum or by the height sensor. This is accomplished by a manual switch which selectively connects the output of the first or second motor control circuits to one or the other of the D.C. motors which are associated with the beams. Thus, my apparatus provides a means whereby the pendulum may be switched to control one or the other of the beams, the height sensor also being switched to control the beam which is at that time not being controlled by the pendulum, A more desirable arrangement of the switching provides transfer of low power signals in the electronics instead of switching motor loads.

A further feature of my invention is the provision of further pair of manual switches having a manual and an automatic position, one of these switches being connected with the pendulum and the other of the switches being connected with the height sensor. Thus, the operator of the paving machine may selectively control the paving machine automatically or may control the machine manually utilizing a switch which may be pulsed or momentarily closed to control the positions of the beams manually. The above mentioned indicating meter circuits are at all times connected to one of the sensing means (the pendulum or the height sensor) and thus the indicating meters indicate to the operator the nature of the manual control which he is maintaining.

While the present description deals with an electrical system having electric motors, it is within the teachings of my invention to provide means to control hydraulic motive means, such as hydraulic rams.

The preferred embodiment of my invention will be ap-v parent to those skilled in the art upon reference to the following specification, claims, and drawings, of which:

FIGURE 1 is a view of a paving machine of the floating screed type, showing portions constituting elements of my invention,

FIGURE 2 is a simplified showing of portions of the paving machine of FIGURE 1, showing the screed in diagrammatic form, the beams which are attached, one to each side of the screed, and showing the pendulum sensor and following sensor, as well as the reversible DC. motors which are operative to control the vertical position of the pivots of the beams, and

FIGURE 3 is a schematic representation of my electronic control system whereby the slope and grade of the resulting road surface is selectively automatically controlled or manually controlled, in accordance with the mode of operation of my invention which is selected by the operator of the paving machine.

Referring specifically to FIGURE 1, reference numeral identifies generally a paving machine having a propulsion unit 11 including a hopper 12 and crawler type treads '13. This propulsion unit 10 includes a motor connected to drive the treads 13, one of which is disposed at each side of the paving machine 10. The hopper 12 of the paving machine is adapted to receive bituminous material, usually dumped into the hopper by a truck which hauls the bituminous material between the roadbed to be paved and the plant which is producing the bituminous material. The paving machine 10 is adapted to be operated by an operator positioned on the paving machine, and reference numeral 14 identifies a control box whereby the operator may selectively automatically or manually control the road surface which is being produced by paving machine 10. The method of achieving automatic or manual control will be evident from the following description.

Reference numeral 15 identifies a roadbed which is to be paved and along which a height reference datum 16 is provided, this height reference datum consisting of a wire, string, or the like which has been previously placed in position alongside the roadbed 15 at a predetermined height. Reference numeral 17 designates a finished road surface which has been produced by the paving machine as it moves in a forward direction, that is to the right as shown in FIGURE 1.

The height datum may also be obtained from a previously produced roadbed mat, for purposes of matching one mat to another.

Reference numeral 20 identifies generally a screed construction which is rigidly attached to a beam 21, pivoted to the propulsion unit at a forward pivot 22. The paving machine 10 of FIGURE 1 is provided with a pair of beams, one of which is positioned at each side of the propulsion unit. Each of the beams is pivoted at its forward end. The attitude of the screed, that is the angle of attack of the lower surface 23 thereof, may be initially manually controlled by means of a pair of screeded adjusting

screws

24 and 25 which can be turned by the operator of the paving machine to control the angle of attack of the screed. Bituminous material is fed from hopper 12 to a spreader type mechanism 26 which is effective to spread the bituminous material on the roadbed 15 immediately in front of screed 20, where the material is compacted by the screed into the finished road 17. The screed assembly 20 may include a vibrating mechanism or tamping mechanism as well as a means for heating the bituminous material deposited under and in front of the screed.

My invention is concerned with an improved control apparatus for automatically controlling the screed 29 in a manner to produce a predetermined desired finished road 17. This is accomplished by means including a follower sensor 27 cooperating with the height datum 16, and by means of a pendulum sensor 30.

Referring now to FIGURE 2, in this figure I have shown a simplified view of the screed, its supporting beams, their pivot points, and the follower sensor and pendulum sensor. As in FIGURE 1, the screed assembly is identified by the reference numeral 20 having a bottom surface 23. Beam 21 having pivot 22 is shown as is the other beam disposed at the back side of the paving machine as shown in FIGURE 1. This beam is identified by reference numeral 31 and is provided with a pivot 32. Follower sensor 27 is shown adjustably positioned on beam 21 and in engagement with the height datum 16. Pendulum 30 is supported on a transverse beam 33 which is pivotally mounted at a pair of upright supports 34 and 35 associated with the

beams

21 and 31 respectively. Thus, as the pivot points of

beams

21 and 31 move up and down, the beam 33 is maintained in transverse alignment with the pivot points 22 and 32. Pendulum 30, responsive to gravity, thus assumes a position indicative of the slope of the transverse beam 33. The height of the

pivots

22 and 32 is controlled by a pair of pivot adjusting screws 36 and 37 whose positions are controlled by a pair of reversible D.C. motors 40 and 41.

As mentioned, screed assembly 20 floats on the bituminous material deposited thereunder and is attached to the propulsion unit 11 by means of the

pivots

22 and 32. Thus, the angle of attack of the bottom surface 23 of this screed is controlled by the vertical movement of these pivot points. Should the pivot points 22 and 32 be driven in an upward direction, the bottom surface 23 of the screed assembly is tilted in an upward direction and thus the screed climbs up on top of a greater thickness of hituminous material which is deposited under the screed. Thus, the height of the finished road surface 17 is increased. Should the pivot points 22 and 32 be lowered, the bottom surface 23 of the screed assembly is tilted in a downward direction and the screed tends to dig into the bituminous material deposited in front of the screed and thus the finished road surface 17 is reduced in thickness, that is the height is decreased. Furthermore, the transverse slope of the finished road surface 17 may be controlled by raising or lowering the

pivots

22 and 32 in a differential fashion. Thus, if pivot 22 is lowered while pivot 32 is raised, screed assembly 20 is tilted to raise the right hand end as seen in FIGURE 2 while lowering the left hand end. Thus, the resulting road surface 17 is sloped toward the height datum 16.

During the paving operation there are several input disturbances that can upset the screed setting and the ability of the machine to lay the desired smooth mat. These disturbances are: (l) roughness of the subbase, or surface being pave-d, which causes vertical motion of the machine 10 and hence the pivot points 22 and 32; (2) variations in compaction of the bituminous material which results in a change in vertical displacement of the screed 20 for a given ski angle setting of the screed bottom 23 as the machine 11 travels forward; and (3) a change of the setting of the screed adjusting screws 24 and 25 which results in a change of the attitude of the screed bottom 23 relative to the

pivot point heights

22 and 32.

Mounting of the follower sensor 27 between the pivot point 22 and the screed 20 will cause the control system to compensate for all of these above mentioned disturbances. Placement of the sensor 27 closer to the pivot point 22 will result in favoring item (1) above. Moving the sensor 27 horizontally toward the screed 21) will result in favoring correction for items (2) and (3) above. In essence correction to a step disturbance will occur in a shorter distance of travel for the aforementioned conditions.

The same arguments are true for the transverse or slope control and apply to the attachment points 34 and 35 of the transverse beam 33 to the screed tow beams 21 and 31.

Since the control system maintains the transverse beam 33 at a preselected angle with respect to gravity by means of pendulum 3f), the final mat surface 17 will be parallel to the transverse beam 33 only if the screed adjusting screws 24 and 25 are at the same setting such that both sides of the screed bottom 23 are at the same angle with respect to the tow beams 21 and 31. This is not a necessary condition to laying the desired mat surface 17, but unless the condition is met external calibration means are required.

Referring now to FIGURE 3, in this figure I disclose a schematic diagram of an electronic circuit by which the paving machine and thus the finished road surface may be manually or automatically controlled at the option of the operator of the paving machine. In this figure I disclose two channels, one of which is operative with the pendulum sensor and the other of which is operative with the follower sensor. The outputs of each of these channels may be selectively connected to control the DC. reversible motors 40 and 41 under the control of manually operable switch means 42.

The basic components of my control system constitute

A.C. bridge circuits

43 and 44,

meter drive circuits

45 and 46 connected to indicating

meters

47 and 48 respectively, and motor drive circuits 5i and 51 which provide a reversible polarity DC voltage across output resistors 52 and 53 respectively. As will be apparent, the output resistors 52 and 53 may be selectively connected to either of the motors 40 and 41, depending upon the position of the manual switch 42.

To avoid the switching of high magnitude motor currents, resistors 52 and 53 may be directly connected to motors 41 and 46 respectively and switch 42 may be connected to switch the control signals at the primary windings of

transformers

104 and 112, For example, in one position of switch 42, when so connected, unijunction transistor 111 is connected to silicon controlled rectifier 113 and unijunction transistor 193 is connected to silicon controlled rectifier 105. The other position of switch 42 reverses this interconnection of the unijunction transistors I and silicon controlled rectifiers. As disclosed in FIGURE 3, the output of the channel connected to the wire follower, that is resistor 53, is connected to control motor 40 and thus control pivot point 22 of beam 21. The output of the motor drive circuit connected to be controlled by the pendulum sensor, that is resistor 53, is connected to control motor 41 and thus to control pivot point 32 of beam 31.

It is within the teachings of this invention to not only provide switch 42 to reverse the control of motors 40 and 41 but by this means provide means whereby the wire follower sensor 27 may be mounted on the other side of the paving machine from that shown in FIGURE 1, namely on beam 31 rather than on beam 21 as shown in FIGURE 2. The follower sensor must control the motor on the side the sensor is mounted by proper selection of switch 42s position.

Considering the schematic diagram of FIGURE 3 in greater detail, the lower portion of the figure will first be considered, that being the portion controlled by the follower sensor. The follower 27 of FIGURES l and 2 is mechanically connected by means identified by reference numeral 54 to control the position of wiper 55 of potentiometer 56 having a resistance element 57. Potentiometer 56 constitutes a portion of the A.C. bridge circuit 44 whose input voltage is supplied by means of a transformer 60 having a primary connected to a source of alternating voltage, not shown. This A.C. bridge circuit 44 includes a further potentiometer 61 designated a Vernier adjustment potentiometer having a resistance element 62 and a manually adjustable Wiper 63. A.C. bridge circuit 44 also includes a pair of

resistors

64 and 65 which are connected in series, the series connected resistors being connected in parallel with the resistance elements 57 and 62 of potentiometers 56 and 61 to the supply voltage for the bridge. Reference numeral 66 identifies a manual switch having a normal open position and having a pair of closed positions to which the switch may be moved and held, the switch returning to its center position upon being released.

The input of meter drive circuit 46 is connected to bridge 44 at a terminal 67 and at a manually adjustable potentiometer wiper 7d. The resistance element "1'1 cooperating with potentiometer wiper 70 has one terminal connected to the wiper 63 of the Vernier adjustment potentiometer and the other terminal connected to the wiper 55 which is controlled by the wire follower sensor 27.

The input of the motor drive circuit 51 consists of a grounded terminal 72 and a further terminal 73 which is connected to the movable blade of manual switch means identified generally by means of reference numeral 74. This manual switch means 74 constitutes the automatic and manual switch of my apparatus whereby the operator of the paving machine 10 may select automatic or manual control of the pivot points 22 and 32 of

beams

21 and 31. Switch means 74 includes a pair of

movable switch blades

75 and 76 which cooperate with stationary contacts 77 and 7 8 in the automatic position of the switch means and which cooperate with stationary contacts 89 and 81 in the manual position of the switch means. With switch means 74 positioned in the automatic position, as shown in FIGURE 3, input terminal 72 of the motor drive circuit 51 is connected through switch blade 75 and contact 77 to potentiometer wiper 55, the position of which is controlled by the wire follower sensor 27. The other input terminal 73 of the motor drive circuit 51 is connected by switch blade 76 and contact 78 to the wiper 63 of the Vernier adjustment potentiometer 61.

Should the switch means 74 be positioned in the manual position, then the input terminal 72 of motor drive circuit 51 is connected by switch blade 75 and contact 8% to a terminal 82 connected between

resistors

64 and 65. Thus, the input terminal 72 of the motor drive circuit 51 is effectively connected to a fixed A.C. potential level. The input terminal '73 of motor drive circuit 51 is connected by means of switch blade 76 and contact 81 to the manual switch means 66. Thus, when the manual switch 66 is moved in an upward direction, a contact 83 and a resistor 84 connect terminal 73 to an A.C. potential of a first level, whereas when switch 66 is moved in a downward direction to engage contact 85, input terminal 73 is connected through a resistor 86 to a second A.C. potential level. Thus, with switch 74 in the manual position switch 66 may be pulsed to engage either contacts 83 or to achieve the desired direction control of the motor connected to the output 53 of motor drive circuit 51.

Thus far, the explanation of my invention has concerned itself primarily with the description of the operation of A.C. bridge circuit 44. This description of operation can be readily applied to bridge circuit 43 wherein a potentiometer wiper 87 has its position controlled by the pendulum sensor 30. A slope adjustment potentiometer 90 having a manually adjustable wiper 91 is connected to form a portion of A.C. bridge circuit 43 in much the same manner as the Vernier adjustment potentiometer 61 of bridge circuit 44, above described.

Resistors

92 and 93 are provided, corresponding to

resistors

64 and 65 of bridge circuit 44. Reference numeral 94 identifies a manual switch having an automatic and a manual position to control the input to motor drive circuit 56) at

terminals

97 and 98, in much the same manner as described in connection with motor drive circuit 51.

In normal operation of the paving machine 16 of FIG- URE 1 the operator first activates the automatic control system with the switch means 74 and 94 in the manual position. By means of manual switch 66 the pivot screw 36 is controlled to position pivot point 20 at its approximate midpoint position. The slope adjustment potentiometer 9t) is set at the desired slope setting and switch 94 set to the Auto position. This will result in the screw 37 driving the pivot point 32 to a vertical position that will maintain the angle of the transverse beam 33 at the desired slope angle. The propulsion unit 11 is then activated to start the paving operation, and the screed screw 24 is controlled to produce the desired mat thickness of 7 bituminous material on the right side of screed 20. The screed screw 25 must be adjusted the same as screed screw 24- to keep the two sides of the screed synchronized.

This initial manual control is necessary because of the fact that the bituminous material compacts under the screed assembly 20 and this compaction varies with the mix being received from the hopper 12. When this desired bituminous mat thickness has been achieved, the propulsion unit 11 is stopped and the height of the follower 27 is adjusted on beam 21 such that the grade error meter 48 is near its null position as shown in FIGURE 3. The grade error meter 40 is then brought to the absolute null position by manual movement of the Vernier adjustment potentiometer wiper 63.

Switches

94 and 74 are now set to their automatic position and the propulsion unit 11 moves in a forward direction to produce the finished road surface 17 at the height selected by the height datum 16 and at the slope controlled by the slope adjustment potentiometer wiper 91.

In unusual situations of large slope requirements or large deviations of the existing surface (to be repaved) from the desired slope, the procedure outlined above may not be satisfactory due to limitations in the mechanical travel of pivot point screws 36 and 37. Such a case may require initial differential setting of screed adjusting screws 24 and 2 so as to keep the pivot points 22 and 32 reasonably close to the center of travel of pivot screws 36 and 37 when the desired mat thickness and mat slope are achieved during initial manual operation. When this is done, the slope potentiometer 90 calibration will not correspond to mat slope. There will exist a constant offset angle that can be readily measured and the slope potentiometer 90 offset by the required amount.

Switches

74 and 94 can now be set to their automatic position and the paving operation started.

Once the calibration has been obtained, the screed adjusting screws 24 and 25 should not be changed. Small variations in mat thickness can be obtained by changing the setting of the Vernier adjustment potentiometer 61 and slope variations obtained by changing the setting of the slope adjustment potentiometer 90.

As the paving progresses, the operator may change the slope of the resulting roadbed, for example as the paving machine rounds a curve to be formed in the road. Furthermore, the degree of automatic control being achieved by my invention may at all times be observed by reference to the slope error meter 47 and the grade error meter 48, these meters being contained within the control box 14 as shown in FIGURE 1.

Referring now specifically to the motor drive circuit 51, the trigger amplifier of the motor drive circuit receives its energizing voltage from a full wave rectifier, unfiltered, and clipped source 101. As a result of this circuit, the supply voltage present at terminal 200 (and terminal 201 for motor drive circuit 50) consists of a series of trapezoid shaped pulses, having a steep leading edge, a flat top portion, and a steep trailing edge joining the leading edge of the next pulse. Capacitor 202 charges through resistor 203when terminal 200 is positive. Conduction of transistor 102 modifies the charging rate by means of forming a shunt path around capacitor 202. In the absence of an input signal potentiometer 204 is adjusted to provide conduction of transistor 102 such that the voltage across capacitor 202 is not sufficient to cause firing of unijunction transistor 103 during the flat top portion of the voltage wave form at terminal 200. As the voltage falls on the trailing edge of the wave form at 200, the unijunction transistor 103 will fire. Thus the capacitor 202 is discharged at the end of each half cycle and therefore is synchronized to line frequency.

As an A.C. control signal is derived from bridge 44, transistor 102 is rendered less conductive for a particular half cycle, depending upon the phase of this control signal. With transistor 102 less conductive, capacitor 202 now charges more rapidly (its shunt path has been at least partially removed) to the firing voltage of unijunction transistor 103. The rate of charging of capacitor 200 depends upon the state of conduction of transistor 102, this in turn being controlled by the magnitude of the control signal, the greater the magnitude of the control signal, the less the conduction of transistor 102. As a result, the unijunction transistor 103 is rendered conductive during the flat portion of its supply voltage pulse. When unijunction transistor 103 fires, capacitor 202 is discharged through the primary of transformer 104, generating a secondary pulse from transformer 104 which fires silicon controlled rectifier 105, resulting in a D.C. voltage developed across resistor 53. Larger magnitude control signals produce earlier firing of the silicon controlled rectifier 105 during the particular half cycle, resulting in a greater average D.C. across resistor 53. Reversal of the phase of bridge 44 control signal causes firing of the silicon controlled rectifier 105 during the opposite half cycle resulting in a reversal of the D.C. voltage across resistor 53. Thus, depending upon the phase and magnitude of the input voltage applied from the A.C. bridge circuit 44 to transistor 102, unijunction transistor 103 is effective to control the conduction of silicon controlled rectifier 105 and produce a D.C. voltage of a polarity which is reversible with the phase of the A.C. signal voltage applied from bridge circuit 44 and of a magnitude corresponding to the magnitude of bridge voltage. Thus, reversible control of motor 40 is achieved.

By way of a specific example, if it is assumed that the propulsion until 11 drops into a hole which exists in roadbed 15, then the pivot points 22 and 32 of

beams

21 and 31 will drop in a downward direction and wire follower 27 will also be lowered. As wire follower 27 lowers, the position of potentiometer wiper 55 is altered and an input signal is applied to not only the input of meter drive circuit 46 but also to the input of motor drive circuit 51. The phase of the A.C. voltage applied to the input of motor drive circuit 51 is such as to control the conduction of silicon controlled rectifier 105 to produce a D.C. voltage across resistor 53 of a polarity which causes rotation of motor 40 to drive the pivot point 22 of beam 21 in an upward direction to thus restore the relative position of sensor 27 and height datum 16. Further, since pendulum 30 is responsive to the relative positions of the

beams

21 and 31, the raising of pivot point 22 causes the transverse attitude of beam 33 to also change. This change in attitude of beam 30 is sensed by pendulum 30 to affect a corresponding control of its motor 41 to thus change the attitude of the bottom surface 23 of the screed, causing a thicker mat of bituminous material to be laid at this portion of the roadbed, thus compensating for the hole which is present in the roadbed and manitaining the finished road surface 17 at the reference datum 16 and at the slope which has been selected by means of the slope adjustment potentiometer wiper 91.

The above description has concerned itself with the motor drive circuit 51. Motor drive circuit 50, cooperat ing with A.C. bridge circuit 43 corresponds to motor drive circuit 51 and is provided with a transistor controlling a unijunction transistor 111, the output of unijunction transistor 111 being provided at a transformer 112 whose secondary is connected to control the conduction of a silicon controlled rectifier 113 constituting a portion of a bridge rectifier 114 whose supply voltage is derived from a transformer 115 connected to the source of alternating voltage. Thus, as above described in connection with the wire follower 27, should the paving machine 10 tilt in a transverse direction, again due to irregularities in the roadbed 15, this tilting of the paving machine is sensed by pendulum 30 to adjust the position of wiper 87. An A.C. input signal of a given phase is then applied to the input of motor drive circuit 50 to control transistor 110 and in turn to control unijunction transistor 111. Unijunction transitsor 111 is effective to control the conduction of silicon controlled rectifier 113 to provide a D.C.

voltage at resistor 52 having a polarity to affect operation of motor 41 to restore pendulum 3t), and thus screed assembly 29 to its desired slope. For example, if it is assumed that the propulsion unit 11 of the paving machine tilts so as to lower the pivot point 32, pendulum 30 is effective to sense this resulting change in attitude of beam 33 and potentiometer wiper 8'7 associated with the pendulum is moved to provide an A.C. input signal to motor drive circuit 50 to produce control of silicon controlled rectifier 113 resulting in a DC voltage present across resistor 52 which is of a polarity to drive motor 41 to effect an upward movement of pivot point 32 of beam 31 to restore the desired attitude of beam 33 and thus the desired slope attitude of screed assembly 20.

Referring noW specifically to the meter drive circuit 46 associated with the A.C. bridge circuit 44, this meter drive circuit transsistor 124 derives its energizing voltage from a pair of diodes 120 and 121 connected to the secondary Winding of a transformer 122 whose primary is connected to the source of alternating voltage. The DC. voltage resulting from diodes 121) and 121 is supplied across a resistor 123, which voltage is effective to supply operating voltage to a first transistor 124. This first transistor is connected in controlling relation to a second transistor 125, the second transistor receiving its supply voltage from the secondary of transformer 122 by way of a further pair of

diodes

126 and 127, these diodes being connected to the collector electrode of transistor 125 through

resistors

128 and 129. The output of meter drive circuit 46 consists of a capacitor 130 which is connected to the grade error meter 48, this meter being a DC. meter of the center position null type. The A.C. signal present at input terminals 67 and 70 of meter drive circuit 46 is amplified by transistor 124 and is applied to the input electrode of transistor 125 to cause this transistor to conduct such that one half cycle of conduction is greater than the other half cycle of conduction, depending upon the polarity of the A.C. voltage present at input terminals 67 and 70. The voltages developed across resistors 128 and 129 (during the alternate half cycle above mentioned) will be of unequal magnitude, one voltage being larger than the other, corresponding to that half cycle during which transistor 125 conducts to a greater degree than it does on the other half cycle. Thus, capacitor 130 is charged as a result of the voltage differential across

resistors

128 and 129 and a voltage of one polarity or another is applied to meter 48, depending upon the phase of the A.C. input voltage applied at terminals 67 and 70. It of course follows that with the relative position of the wire follower 27 and height datum 16 as desired, the output of bridge circuit 44 is at a null position and likewise meter 48 is nulled to indicate that the roadbed 17 is being produced at the desired height. Potentiometer 131 provides an A.C. signal to the electrode of transistor 124 to null the meter under the conditions of zero signal at terminals 67 and 70.

The meter drive circuit 45 associated with A.C. bridge circuit 43 corresponds to meter drive circuit 46 above described. Here again, a transistor 141i is connected to control .a transistor 141. Transistor 141 in conjunction with

resistors

142 and 143 and diodes 144 and 145, is effective to control the charge on a capacitor 146 which is connected to the slope error meter 47, this meter being of the null reading D.C. type. In this case, so long as the roadb ed 17 is being formed at the slope which has been selected by adjustment of the slope adjustment potentiometer wiper 91, the A.C. output of bridge 43 is at a null and the slope error meter 47 is likewise at a null position.

A further feature of my invention resides in the fact that my meter drive circuits 45 and 4d are at all times connected to the output of the

respective bridges

43 and 44 and thus the slope error meter 47 and the grade error meter 48 are effective to indicate to the operator of the paving machine the degree of correlation between the resuiting road surface 17 and that which has been selected by the slope adjustment potentiometer wiper 91 and the height datum 16. This is true even though the switch means 74 or 94 are switched to the manual position wherein control of either or both of the pivot points 22 and 32 of the

beams

21 and 31 may be manually controlled .by the manual switches 66 and 1%. Thus, the paver may be manually controlled by means of switches 66 and and the

meters

47 and 48 may be observed by the operator todetermine the degree of control which he is efiecting by manual means.

While the description has dealt with the position of manual switch 42 wherein motor 41 is connected to be controlled by motor drive circuit 51 and thus by means of wire follower 27, it is within the teachings of this invention to reverse the control of the motors 4t) and 41 such that motor 41 is now controlled by follower sensor 27 and motor 41) is controlled by pendulum 30, when the sensor 27 is moved to beam 31.

It is recognized that further embodiments of my invention will be apparent to those skilled in the art and it is thus intended that the scope of the present invention be limited solely by the scope of the appended claims.

I claim as my invention:

1. Control apparatus for use with a paving machine of the floated screed type wherein the screed rests upon the paved surface being formed and is towed by a propulsion unit to which it is pivotally attached by means of a pair of forwardly extending beams, the rear ends of the beams being rigidly fixed to the screed, the control apparatus functioning to automatically control the angle of attack of the two ends of the screed in relation to the paved surface to thereby vary the height and slope of the surface as the machine moves to deposit paving material under the screed, with the height being established by a height datum disposed along the route to be paved, the apparatus comprising; a pair of electric motors, one of which is associated with each of the beams to independently move the same uipon energization of its motor and thereby independently change the angle of attack of the two ends of the screed; height sensing means mounted on one of the beams to move therewith and to cooperate with the height datum, said height sensing means including a :potentiometer having a resistance element and a wiper whose position is controlled by the relative spacing of said height sensing means and the height datum; a Vernier adjustment potentiometer having a resistance element and a manually movable wiper; a first source of voltage, means connecting the resistance elements of said height sensing means potentiometer and said Vernier adjustment potentiometer in parallel to said first source of voltage, first motor control means having an output and having an input which is connected to the Wipers of said height sensing means potentiometer and said Vernier potentiometer; slope sensing means mounted on the beams and having a potentiometer with a resistance element and a wiper controlled by a pendulum, the position of said wiper being indicative of the slope of the screed and the angle of attack of the two ends of the screed; a slope adjustment potentiometer having a resistance element and a manually movable wiper; a second source of voltage, means connecting the resistance elements of said slope sensing means potentiometer and said slope adjustment potentiometer in parallel to said second source of voltage, second motor control means having an output and having an input which is connected to the wipers of said slope sensing means potentiometer and said slope adjustment potentiometer; and manually operable switch means selectively operable to connect the outputs of said first and second motor control means each to one or the other of said pair of electric motors.

2. In combination, a paving machine having a propulsion unit and a floated screed, a pair of beams pivotally attached at their forward end to said propulsion unit and rigidly attached at the rear ends to said screed, said pav- '11. 1 ing machine being constructed and arranged to deposit paving material beneath said screed such that the angle of attack of the two ends of the screed in relation to the paved surface varies the height of the surface as the paving machine moves to deposit the paving material under the screed, height datum means disposed along the route to be paved, a pair of reversible DC. motors, means operatively connecting one of said pair of motors to each of said beams to thereby independently move the same and to independently change the angle of attack of the two ends of said screed upon energization of said motors, height sensing means mounted on one of said beams and movable therewith, said height sensing means cooperating with said height datum means and including a potentiometer having a resistance element and a wiper whose position is controlled by the relative spacing of said height sensing means and said height datum means, a vernier adjustment potentiometer having a resistance element and a manually movable wiper, a first source of A.C.

voltage, means connecting the resistance elements of said height sensing means potentiometer and said vernier adjustment potentiometer in parallel to said first source ct A.C. voltage, first phase sensitive motor control means having .a reversible polarity DC. output and an input which is connected to the wipers of said height sensing means potentiometer and said vernier potentiometer, slope sensing means cooperatively associated with each of said beams and having a potentiometer with a resistance element .and a wiper controlled by a pendusum, the position of said wiper being indicative of the slope of said screed and the angle of attack of the two ends thereof,

a slope adjustment potentiometer having a resistance element and a manually movable wiper, a second source of A.C. voltage, means connecting the resistance elements of said slope sensing means potentiometer and said slope adjustment potentiometer in parallel to said second source of A.C. voltage, second phase sensitive motor control means having a reversible polarity DC. output and an input which is connected to the wipers of said slope sensing means potentiometer and said slope adjustment potentiometer, manually operable switch means selectively operable to connect the outputs of said first and second motor control means to one or the other of said pair of electric motors, first and second indicating means including first and second electrical meters disposed to indicate grade error and slope error respectively, and

means connecting said first and second indicating means in parallel with the input of said first and second motor control means.

3. Control apparatus for use with a paving machine of the floating, screed type wherein it is desired to produce a paved surface of a height as controlled by height datum means positioned adjacent the surface to be paved, wherein the paving machine is constructed and arranged with a propulsion unit connected to the floating screed by a pair of beams which are rigidly attached to the screed and loosely pivotally attached to the propulsion unit, the apparatus comprising: motive means operatively connected to the beams to change the angle of attack of the screed, height sensing means mounted on one of the beams and movable therewith, said height sensing means including a potentiometer having a resistance element and a movable wiper whose position is controlled in accordance with the relative spacing of said height sensing means and the height datum means, a vernier adjustment potentiometer having a resistance element and a manually movable wiper, a source of voltage, circuit means connecting the resistance elements of said height sensing means potentiometer and said vernier adjustment potentiometer in parallel to said source of voltage, indicating meter means having an input connected to the wipers of said height sensing means potentiometer and said vernier adjustment potentiometer, further resistance means having a tap and end terminals, means connecting said end terminals to said source of voltage, control means having an output connected to said motive means, manually operable switch means having an automatic position and a manual position, circuit means including said last-named switch means in the automatic position connecting the input of said control means to the potentiometer wipers of said height sensing means potentiometer and said vernier adjustment potentiometer, and further circuit means including said switch means in said manual position connecting the input of said control means to the tap of said further resistance means and selectively to one or the other of the end terminals of said further resistance means.

4. In combination, a paving machine having a propulsion unit, a floating screed, and a pair of beams having one end rigidly connected to said floating screed and the other end pivotally connected to said propulsion unit, said propulsion unit being adapted to tow said floating screed such that paving material may be deposited in front of said screed and said screed rides on the paving material to form a paved surface, the height of the paved surface being determined by the angle of attack of said screed; height datum means disposed along the surface to be paved, height sensing means mounted on one of said beams and movable therewith, said height sensing means including a member cooperating with said height datum means, a height sensing means potentiometer having a resistance element and a movable wiper whose position is controlled by the member of said height sensing means, a vernier adjustment potentiometer having a resistance element and a manually movable wiper, a source of A.C. voltage, circuit means connecting the resistance elements of said height sensing means potentiometer and said vernier adjustment potentiometer in parallel to said source of voltage; motive means operatively connected to said one of said beams to control the angle of attack of one end of said screed, said motive means having an input including a first and a second terminal, circuit means connecting said first terminal to a reference potential; first manually operable switch means having an automatic and a manual position, circuit means including said first manual switch means in said automatic position connecting the potentiometer wiper of said height sensing means potentiometer to said reference potential and connecting the other input terminal of said motive means to the potentiometer wiper of said vernier adjustment potentiometer; a resistance element having a pair of end terminals and a tap, circuit means connecting said end terminals to said source of voltage; second manually operable switch means having a normally open position and a first and second closed position, circuit means including said first switch means in said manual position connecting the tap of said resistance element to said reference potential, and further circuit means including said first switch means in said manual position connecting the other input terminal of said motive means selectively through said second switch means to one of the end terminals of said resistance element.

5. In combination, a paving machine of the floated screed type having a propulsion unit and a floated screed which is towed behind the propulsion unit by means of a pair of beams which are pivoted at their forward end to the propulsion unit and which are rigidly attached to the floated screed, the paving machine including means adapted to deposit paving material under the floated screed, first and second reversible DC. motors, means connecting said motors one to each of said beams to vary the position of its beam and change the angle of attack of the ends of said screed; datum means establishing a height reference along the route to be paved, height sensing means disposed on one of said beams and movable therewith, said heightvsensing means including means cooperating with said height datum means and including a potentiometer having a wiper whose position is controlled by said height sensing means to provide an indication of the relative position of said height sensing means and said height datum means; a pendulum supported by said beams and including a potentiometer whose resistance element is moved by said pendulum such that the position of said wiper is indicative of the slope of said screen and the angle of attack of the ends of said screed; a first A.C. bridge circuit including a first source of A.C. voltage, said height sensing means potentiometer, and an adjustment potentiometer having a manually movable wiper; first indicating meter means having an input connected to the wipers of said height sensing means potentiometer and said adjustment potentiometer; a first impedance element having a tap and end terminals connected to said first source of voltage; a first phase sensitive motor control circuit providing a reversible polarity DC. output and having a pair of input terminals, one of which is connected to a reference potential; first manually operable switch means having an automatic and a manual position, said first switch means in said automatic position connecting the wiper of said height sensing means potentiometer to said reference potential and connecting the second input terminal of said first motor control circuit to the wiper of said adjustment potentiometer; second manually operable switch means having a normally open condition and a first and a second closed condition, said first switch means in said manual position connecting the tap of said first impedance element to said reference potential and connecting the second input terminal of said first motor control circuit to said second switch means, circuit means including said second switch means connecting said second input terminal of said first motor control circuit selectively to one of said end terminals of said first impedance element; a second A.C. bridge circuit including a second source of A.C. voltage, said pendulum potentiometer, and a slope adjustment potentiometer having a manually movable wiper; second indicating meter means having an input connected to the wipers of said pendulum potentiometer and said slope adjustment potentiometer; a second impedance element having a tap and end terminals connected to said second source of voltage; a second phase sensitive motor control circuit providing a reversible polarity DC. output and having a pair of input terminals, one of which is connected to said reference potential; third manually operable switch means having an automatic and a manual position; said third switch means in said automatic position connecting the wiper of said pendulum potentiometer to said reference potential and connecting the second input terminal of said second motor control circuit to the wiper of said slope adjustment potentiometer; fourth manually operable switch means having a normally open condition and a first and a second closed condition, said third switch means in said manual position connecting the tap of said second impedance element to said reference potential and connecting the second input terminal of said second motor control means to said fourth switch means, circuit means including said fourth switch means connecting said second input terminal of said second motor control circuit selectively to one of the said terminals of said second impedance element; and further manually operable switch means selectively operable to connect the outputs of said first and second motor control means to one or the other of said first or second motors.

6. Control apparatus for use with a floating screed paving machine, in which the screed is towed behind a propulsion unit and the height and slope profile of a resulting road surface is controlled by independently controlling the angle of attack of the opposite ends of the screed, the apparatus comprising; height sensing means vertically movably mounted in relation to the paving machine and carried thereby, control means having an input connected to be controlled by said height sensing means and having an output connected to control the angle of attack of one end of the screed and to concurrently move said height sensing means vertically relative to the paving machine; slope sensing means mounted in relation to the screed to be responsive to the transverse slope of the screed and to the angle of attack of the opposite ends of the screed, and control means having an input connected to be controlled by said slope sensing means and having an output connected to control the angle of attack of the other end of the screed.

7. Control apparatus for use with a floating screed paving machine, in which a transversely extending screed is towed behind a propulsion unit by means of a pair of beams, one of which is attached to each end of the screed and is also pivoted to the propulsion unit at the forward end of the beams, and the height and slope profile of a resulting road surface is controlled by independently controlling the angle of attack of the opposite ends of the screed by vertical movement of the beams, the apparatus comprising; height datum sensing means, means adapted to mount said sensing means on one of the beams such that movement of that one of the beams causes vertical movement of said sensing means as the angle of attack of one end of the screed is changed; slope attitude responsive means adapted to be mounted on both of the beams to sense the slope of the screed and the angle of attack of each end of the screed; and control means having input means connected to be controlled by said sensing means and by said responsive means, and having output means adapted to affect independent vertical movement of said one of the beams by said sensing means and the other of the beams by said responsive means,

8. Control apparatus for use with a paving machine of the floating screed type to automatically control the angle of attack of one end of the screed thereof in accordance with a predetermined height reference datum and thus control the surface of the road being produced as the paving machine moves, comprising: height datum sensing means mounted with reference to said one end of the screed and having movable control means adapted to cooperate with the height reference datum, said sensing means being vertically movable as the angle of attack of said one end of the screed is varied and having an electrical transducer whose control element is moved by movement of said control means; a control electrical transducer having a manually movable control element, a source of voltage, means connecting said sensing means transducer and said control transducer to said source of voltage; motive means connected to the screed to control the angle of attack of said one end thereof upon actuation of said motive means, to thereby produce a subsequent change in vertical position of said sensing means relative to the reference datum as the screed angle of attack changes; and electrical control means for said motive means, said electrical control means having an input connected to said sensing means transducer and said control transducer and having an output connected to said motive means.

9. In combination, a paving machine of the floated screed type having a propulsion unit including motive means to move the paving machine, a floating screed, said screed being attached to said propulsion unit by a pair of spaced beams which are pivoted to the propulsion unit at the forward end of the beams and are rigidly attached to the screed at the rear end of the beams so that vertical movement of the beams changes the angle of attack of spaced portions of the screed, grade reference means establishing a grade reference for the paved surface, grade sensing means mounted on one of said beams to be vertically movable therewith and cooperating with said grade reference means, said sensing means including a potentiometer whose wiper is moved in accordance with deviations in relative position of said sensing means and said grade reference means, a further potentiometer having a manually movable wiper, a source of voltage, circuit means connecting the resistance elements of said sensing means potentiometer and said further potentiometer to said source of voltage, motive means connected in cooperating relation to said one of said beams to move said one beam and thereby vary the angle of attack of one portion of the screed, control means having an output connected to said motive means and having an input connected to the wipers of said sensing means potentiometer and said further potentiometer to apply an error signal thereto upon a variation in the relative position of said sensing means and said grade reference means, indicating means, and means connecting said indicating means to the Wipers of said sensing means potentiometer and said further potentiometer to apply an input thereto to thus provide an indication of such variation.

10. Control apparatus for use with a paving machine of the floating screed type wherein the screed is towed behind a propulsion unit, the floating screed resting on the resulting paved surface by virtue of the weight of the screed and the thickness and slope of the paved surface being determined by the angle of attack of the two ends of the screed, the control apparatus comprising: a pair of motive means, a first of which is associated with one end of the screed and a second of which is associated with the other end of the screed, to independently control the angle of attack of the ends of the screed; grade sensing means mounted ahead of said one end of the screed and adapted to cooperate with grade datum means which forms a predetermined grade; slope sensing means associated with each end of the screed and responsive to the slope of the screed and to the angle of attack of the ends of the screed; a first potentiometer having a resistance element and a wiper whose position is controlled by said grade sensing means; a second potentiometer having a resistance element and a wiper whose position is controlled by said slope sensing means; a Vernier adjustment potentiometer having a manually movable wiper, a first bridge network including a source of voltage connected to said first potentiometer and to said vernier adjustment potentiometer; a slope adjustment potentiometer having a manually movable wiper, a second bridge circuit including a source of voltage connected to said second potentiometer and to said slope adjustment potentiometer; first and second control means each having an input and an output, means connecting the output of said first control means to said first motive means, means connecting the output of said second control means to said second motive means; means connecting the input of said first control means to the potentiometer wipers of said first bridge circuit to thus automatically control the angle of attack of said one end of the screed in accordance with the grade sensing means; and means connecting the input of said second control means to the potentiometer wipers of said second bridge circuit to thus automatically control the angle of attack of the other end of the screed in accordance with the slope sensing means.

11. Control apparatus for use in automatically controlling the angle of attack of the screed of a floated screed paving machine, to maintain a predetermined grade and slope road profile, the floated screed being towed by means of first and second spaced beams which are rigidly attached to first and second ends respectively of the floated screed at the rear end of the beams, said paving machine being adapted to cooperate with grade datum means establishing the grade for a resultant paved surface, the control apparatus comprising: first and second motive means each of which is cooperatively associated with the first and second beams respectively to control the position of its beam and thus vary the angle of attack of said first and'second ends of the fioated screed; grade sensing means movably positioned forward said first end of the screed and having a potentiometer whose wiper is adjusted by means cooperating with the grade datum means, the relative position of said grade sensing means and the grade datum means varying by virtue of unevenness of the surface to be paved by the paving machine and by virtue of movement of said one beam by operation of its associated motive means; a pendulum supported on said beams and responsive to the slope of the scIeed and 1 .0 the angle of attack of said first id and second ends of the screed, a second potentiometer having a wiper whose position is determined by said pendulum; a Vernier adjustment potentiometer having a manually movable wiper, a first bridge circuit including a tion of said grade sensing means; a slope adjustment potentiometer having a manually movable wiper which is manually moved to produce the desired slope to the resulting paved surface, and second control means having an input connected to the potentiometer wipers of said pendulum potentiometer and said slope adjustment potentiometer and having an output connected to said second motive means.

12. Control apparatus for use in automatically controlling the angle of attack of one end of the screed of a floating screed road paving machine to maintain a predetermined grade profile as established by a grade datum, the control apparatus comprising: grade datum sensing means adapted to be mounted to move vertically as the angle of attack of the one end of the screed is varied, and

p as irregularities in the surface to be paved are encountered, a first potentiometer whose wiper moves as said sensing means is moved vertically; a Vernier adjustment potentiometer having a manually movable wiper; a source of voltage, means connecting said first potentiometer and said adjustment potentiometer to said source of voltage to form a bridge network; voltage responsive motive means adapted to be placed in controlling relation to control the angle of attack of the one end of the screed; a switch having a manual and an automatic position, means controlled by said switch in said automatic position connecting said motive means to the wipers of said first potentiometer and said adjustment potentiometer to be controlled by the bridge voltage at said wipers to achieve automatic control of the angle of attack of the one end of the screed, and means controlled by said switch in said manual position adapted to selectively connect said motive means to a source of voltage to achieve manual control of the angle of attack of the one end of the screed.

13. Control apparatus for use in automatically controlling the angle of attack of one end of the screed of a floating screed road paving machine to maintain a predetermined slope profile, the control apparatus comprising: slope sensing means adapted to be mounted to sense the slope and the angle of attack of the one end of the screed, which factors vary as the angle of attack of the one end of the screed is varied and as irregularities in the surface to be paved are encountered, a first potentiometer whose wiper moves as said sensing means senses a change in said factors; a slope adjustment potentiometer having a manually movable wiper; a source of voltage, means connecting said first potentiometer and said adjustment potentiometer to said source of voltage to form a bridge network; voltage responsive motive means adapted to control the angle of attack of the one end of the screed; a switch having a manual and an automatic position, means controlled by said switch in said automatic position connecting said motive means to the wipers of said first potentiometer and said adjustment potentiometer to be controlled by the bridge voltage at said wipers to achieve automatic control of the angle of attack of the one end of the screed, and means controlled by said switch in said manual position adapted to selectively connect said motive means to a source of voltage to achieve manual control of the angle of attack of the one end of the screed.

14. Control apparatus for use to stabilize a movable elongated member both as to slope and height, the apparatus comprising: a slope sensor adapted to be connected to the member to sense the transverse slope thereof, control means having an input connected to be controlled by said slope sensor, motive means connected to be controlled by the output of said control means and adapted to move one end of the member to maintain a desired slope; a height sensor adapted to be connected to the member at a position spaced from said one end to sense the height of said position, second control means having an input connected to be controlled by said height sensor and second motive means connected to be controlled by the output of said second control means and adapted 2,295,519 9/ 42 Millikin 9446 2,491,275 12/49 Millikin 9446 2,922,345 1/ 60 Mentes 9446 3,029,715 4/ 62 Bowen 9446 3,029,716 4/62 Shea 9446 3,111,070 11/63 Pollitz 9446 JACOB L. NACKENOFF, Primary Examiner.

Claims

6. CONTROL APPARATUS FOR USE WITH A FLOATING SCREED PAVING MACHINE, IN WHICH THE SCREED IS TOWED BEHIND A PROPULSION UNIT AND THE HEIGHT AND SLOPE PROFILE OF A RESULTING ROAD SURFACE IS CONTROLLED BY INDEPENDENTLY CONTROLLING THE ANGLE OF ATTACK OF THE OPPOSITE ENDS OF THE SCREED, THE APPARATUS COMPRISING; HEIGHT SENSING MEANS VERTICALLY MOVABLY MOUNTED IN RELATION TO THE PAVING MACHINE AND CARRIED THEREBY, CONTROL MEANS HAVING AN INPUT CONNECTED TO BE CONTROLLED BY SAID HEIGHT SENSING MEANS AND HAVING AN OUTPUT CONNECTED TO CONTROL THE ANGLE AT ATTACK OF ONE END OF THE SCREED AND TO CONCURRENTLY MOVE SAID HEIGHT SENSING MEANS VERTICALLY RELATIVE TO THE PAVING MACHINE; SLOPE SENSING MEANS MOUNTED IN RELATION TO THE SCREED TO BE RESPONSIVE TO THE TRANSVERSE SLOPE OF THE SCREED AND TO THE ANGLE OF ATTACK OF THE OPPOSITE ENDS OF THE SCREED, AND CONTROL MEANS HAVING AN INPUT CONNECTED TO BE CONTROLLED BY SAID SLOPE SENSING MEANS AND HAVING AN OUTPUT CONNECTED TO CONTROL THE ANGLE OF ATTACK OF THE OTHER END OF THE SCREED.