Automatic Slope Controller

Abstract

A controller for a road finishing machine which is adapted to match the slope of the surface presently being prepared to the slope of an adjacent surface previously prepared embodying a first means for sensing the slope of the previously prepared surface, a second means for sensing the slope of the surface currently being prepared and control means for comparing the outputs of the two sensors and for providing an error signal indicative of the difference of the two slopes.

Description

In the finishing of adjacent passes of a road surface or road bed, it is sometimes difficult to match the slope of adjacent passes. This difficulty is especially manifest in the finishing of curves where, in the preparation of the curve in the road, it is sometimes desirable to provide for a banking angle which may continuously change around the curve.

Heretofore, the manner in which the slope angle was controlled or continuously made to change was by manually adjusting the road finishing machine. Whereas it was relatively simple to match the slopes of adjacent passes in a straightaway, it was many times more difficult to match the slope angle of the current pass to the continuously changing slope angle of a previous pass forming part of the curve. Due to the human element injected into the manual control of the slope, the error between the slope angles of the two passes could sometimes be large.

This invention is designed to eliminate that error by providing for the automatic control of the slope of the surface prepared by the machine. This automatic control is accomplished by providing a traveling ski dragged behind or along the side of the road finishing machine. Mounted on the ski is a gravity sensing device which gives an output indicative of the slope angle of the previously prepared surface. A second gravity sensing device is mounted on the road finishing machine to indicate the slope angle of the machine as it makes its current pass. The outputs of these two sensors are then compared to indicate the difference between the actual slope angle of the machine and the desired slope angle. This difference in slope angles of the two adjacent passes results in an error signal which is used to adjust the machine in a manner tending to eliminate the error signal.

It is, therefore, an object of this invention to eliminate the necessity of manually controlling the slope of a road being prepared by a road finishing machine.

It is a further object to eliminate this manual control by providing a completely automatic slope controller.

It is yet a further object to provide for automatic control by sensing the slope angles of a previously prepared pass and the slope angle of a road finishing machine and using the error signal that results to control that machine.

These and other objects will become apparent as the description of the invention progresses.

IN THE DRAWING

FIG. 1 is a diagrammatic representation of a machine as it makes its current pass.

FIG. 2 is a simplified circuit diagram of the automatic control.

FIG. 3 is a detailed schematic drawing of the automatic controller for the road finishing machine.

In FIG. 1, a machine M is shown performing its road finishing operations. The machine, traveling into the drawing for example, either drags behind or alongside a traveling ski upon which the reference pendulum is mounted. The traveling ski rides over the surface previously prepared and the reference pendulum is used to measure the slope angle of that surface. Mounted upon the machine is a second pendulum utilized to indicate the slope angle of the machine as it makes its current pass. Because pendulums are used, they have for their reference the gravity of the earth. The outputs of these two pendulums will then be compared and the error signal that results will indicate the difference by which the slope angle of the surface prepared by the machine in making its current pass has deviated from the slope angle of the surface prepared in the previous pass. This error signal is then used to adjust the slope of the machine in its current pass. As the machine makes its future passes, the traveling ski will always ride over the previously prepared surface of the machine to provide a uniform slope angle over all of the prepared surfaces.

This automatic control of the machine makes the finishing of curves much easier than was previously known in the art. Until now, the slope angle of all of the passes of the machine had to be non-automatically, continuously varied. Such non-automatic control made it extremely difficult, if not impossible, to adequately match the slope angle of the current pass to the slope angle of the previous pass. With this invention, the slope angle of the first pass is manually controlled; thereafter, the slope angles of succeeding passes may be completely, automatically controlled.

FIG. 2 is a brief schematic diagram of the automatic controller. The automatic controller comprises essentially three elements: a machine mounted pendulum to indicate the current slope angle of the machine; a reference pendulum to indicate the desired slope angle of the machine; and, a comparator to produce an error signal representative of the deviation of the slope angles of the machine between the actual and desired values. The machine mounted pendulum comprises a structure D upon which a weight W1 is mounted. The weight causes the structure D to seek a gravity reference. The structure D is mounted on one end of the shaft at the other end of which is mounted a core C which will rotate in accordance with the rotation of structure D. The core cooperates with a transformer having a primary P and two secondaries, S1 and S2, which are connected to a comparator.

The reference pendulum comprises an arm which is weighted by W2 causing the arm to seek a gravity reference and, in so doing, sweeps across the potentiometer P2. A manual set point comprising a potentiometer P1 is provided for controlling the machine whenever manual operation is desired. The ends of the potentiometer of the reference pendulum and the set point potentiometer are connected together and to a comparator, and the arms of the two potentiometers are connected to a switch S. The switch S has a movable contact, a manual contact M connected to the arm of P1, and an automatic contact A connected to the arm of P2. The movable contact of the switch S will thus connect either P1 or P2 to the comparator to provide either manual or automatic control.

Offset potentiometers P3 and P4 are included to facilitate an initial adjustment of the reference potentiometer to insure that the traveling ski will have a predetermined angle with respect to the machine. With potentiometers P3 and P4 ganged together, an increase in resistance of one will result in a decrease in resistance of the other. Thus, as the potentiometers P3 and P4 are adjusted, the resistances on either side of the arm of P2 will change. The machine will see this change as though there had been a change in slope angle of the travelling ski. The machine, therefore, will adjust its slope angle. As examples of some uses of this adjustment, a crown in the road can be programed into the automatic controller or an initial alignment of the machine and traveling ski can be made.

The comparator compares the outputs of the two secondaries with either the reference pendulum or the set point potentiometer, depending upon the state of switch S, and produces an error signal representative of the deviation of the machine pendulum from the reference pendulum or the set point potentiometer, whichever is used. This error signal is then amplified by the amplifier used to control the machine.

FIG. 3 is a more detailed description of the circuit controller and shows, by way of example only, the contents of the comparator. Secondary S1 is connected across the input of a full wave bridge rectifier comprising diodes D1, D2, D3, and D4, and secondary S2 is connected across the inputs of a full wave bridge rectifier comprising diodes D5, D6, D7, and D8. These two full wave bridge rectifiers are connected in series additive fashion. The output of these two rectifiers is taken across three terminals, 14, 15 and 16. Terminal 14 is connected to the movable contact of switch SW1 and terminal 16 is connected to the movable contact of switch SW2. Contact A1 of switch SW1 is connected to one side of the reference pendulum potentiometer P2 while contact A2 of switch SW2 is connected to the other side of potentiometer P2. The movable arm of P2 is connected to the automatic contact, A3, of switch SW3. The manual contact, M1, of switch SW1 is connected to one side of the set point potentiometer P1 whereas the contact M2 of switch SW2 is connected to the other side of this potentiometer. The movable arm of potentiometer P1 is connected to the manual contact M3 of switch SW3. The movable contact of switches SW1, SW2 and SW3 are ganged together for simultaneous operation, and operate to connect either P1 or P2 to the comparator to provide either manual or automatic control of the machine.

The machine pendulum is designed such that when the core is in a neutral position with respect to both of the secondaries, the outputs across the two bridge rectifier circuits will be equal and if the reference pendulum, used when automatic operation is desired, senses a level slope of the previous pass, the movable arm of potentiometer P2 will be at its mid point position such that the voltage impressed on either side of the arm will be equal. Thus, the voltages on the arm of the reference pendulum potentiometer will equal the voltage at terminal 15, and the output taken across 12 and 13 will be zero indicating that no correction is needed. However, when the reference potentiometer arm is moved due to a change in the slope angle in the previous pass, such movement of the potentiometer arm will cause an unbalance of the voltage across that potentiometer and, therefore, an output will result across terminals 12 and 13. This output is used to adjust the slope angle of the machine such that core C will be moved in a manner to alter the voltages across the two rectifier bridges to equal their respective voltages across potentiometer P2 thus reducing the voltage across terminals 12 and 13 to zero.

Output terminals 12 and 13 are connected across a differential amplifier consisting of transistors Q1, Q2, Q3 and Q4 and biasing resistors R2, R3, R4 and R5. Resistor R1, diodes D9, D10 and D11 and transistor Q5 are included to provide a temperature-compensated bias for the differential amplifier transistors. Output terminal 12 is connected to the base of transistor Q4, and transistor Q3 is connected to transistor Q4 in emitter follower fashion. Output terminal 13 is connected to transistor Q1, and transistor Q2 is connected to transistor Q1 in emitter follower fashion. The output of the differential amplifier is taken across the collectors of transistors Q2 and Q3, and these outputs are amplified by suitable transistor power amplifiers to provide outputs at terminals 10 and 11.

A triangular wave form generator is connected to the junction of terminal 13 and the base of Q1 to provide time base proportioning operation of the differential amplifier and the transistors of the power amplifier stages. The reason for using such time base proportioning is to operate the transistors in a fully on or fully off condition. In a DC proportioning system, i.e., where no additional voltage is added to the base of Q1, the transistors are operated in a partly on state thus increasing the wattage on the transistors which raises their temperature. By operating the transistors either fully on or fully off, the wattage is decreased and, therefore, the temperature is decreased. By decreasing the temperature, smaller and less expensive transistors may be used.

The transistors of the differential amplifier are biased such that they fully saturate just after an input is received from the triangular wave form generator; thus, although the input is a triangular wave form, the output of the differential amplifier is a square wave. Under quiescent conditions with the output across terminals 12 and 13 zero, the outputs of the terminals 10 and 11 are equal but 180.degree. out of phase such that the total effect on the output as seen by terminals 10 and 11 is essentially zero. As an output is received across terminals 12 and 13, this output, in the form of a DC voltage, offsets the biasing of the differential amplifier causing the square wave output to shift. This shifting of the output will result in an average output across terminals 10 and 11 indicating the necessity of adjusting the slope angle of the machine. An example of a device which can be used to adjust this slope angle is a servo valve.

As changes can be made in the above-described construction and many apparently different embodiments of this invention can be made without parting from the scope thereof, it is intended that all matter contained in the above description is shown on the accompanying drawings be interpreted as illustrative only and not in a limiting sense.

Claims

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. A device for automatically controlling a road finishing machine, wherein the machine makes several consecutive parallel passes in its road finishing operations and wherein it is desired to match the slope of the current pass of the machine to the slope of the surface prepared by the previous pass, comprising:

first sensing means for producing an output indicative of the slope angle of the surface prepared by the road finishing machine in making its previous pass,

second sensing means for producing an output indicative of the slope angle of the current pass of the road finishing machine, and

comparison means connected to said first and second sensing means for comparing the outputs of the first and second sensing means and producing an error signal, said error signal representing the difference in the slope angles of the current pass and of the surface prepared by the previous pass.

2. A device as set forth in claim 1 wherein said first sensing means comprises a pendulum gravity sensor.

3. A device as set forth in claim 1 wherein said second sensing means comprises a pendulum gravity sensor.

4. A device as set forth in claim 3 wherein said pendulum gravity sensor comprises:

a weighted structure which seeks a gravity reference,

a primary coil adapted to receive an alternating current signal,

at least two secondary coils connected to said comparison means, and

a core connected to and movable by said weighted structure whereby movement of said core produces a change in the output signals across said secondary coils.

5. A device as set forth in claim 4 wherein said comparison means comprises:

a full wave rectifying bridge for each of said secondary coils, each secondary coil being connected across its respective bridge, said bridges being interconnected so as to be series additive so that the bridge has two end junctions and a midpoint, and means connecting said first sensing means across the two end points of the bridge.

6. A device as set forth in claim 5 further comprising, a manually adjustable reference means, and switching means for selectively connecting either the first sensing means or the manually adjustable reference means across the end junctions of the bridges.

7. A device as set forth in claim 1 wherein said device further comprises a manually adjustable reference means, and switching means for selectively connecting either the first sensing means or the manually adjustable reference means to the comparison means.

8. A device as set forth in claim 1 wherein each of said first and second sensing means comprises a pendulum gravity sensor.

9. A device as set forth in claim 1 wherein offset means are connected to the first sensing means for adjusting the output of said first sensing means.

10. A device as set forth in claim 1 wherein said first sensing means comprises a traveling ski adapted to be mechanically connected to said machine, said ski extending over a substantial transverse portion of said previously prepared surface, and a pendulum gravity sensor mounted upon said ski to sense the slope thereof, said sensor being connected to said comparison means.