US3497014A - Automatic blade bite control - Google Patents

Description

Feb. 24, 1970 T H. R. ASK 3,497,0

AUTOMATIC BLADE BITECONTROL Filed May 1, 1967 5 Sheets-Sheet l lo "X2 71 2O 30 I2 INVENTOR.

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Feb. 24, 1970 v H. R. ASK 3,4

AUTOMATIC BLADE BITE CONTROL Filed May 1, 1967 5 Sheets-Sheet 2 INVENTOR.

HENRY R. ASK

ATTORNEYS.

United States Patent O 3,497,014 AUTOMATIC BLADE BITE CONTROL Henry R. Ask, Wapping, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed May 1, 1967, Ser. No. 635,102 Int. Cl. E02f 3/ 76, 3/86 US. Cl. 1724.5 12 Claims ABSTRACT OF THE DISCLOSURE An automatic blade bite control for high speed earth contouring machinery; the control including a blade assembly mounted vertical accelerometer and associated circuitry for generating signals commensurate with short term vertical movements of the earth working blade, such signals being applied to the blade actuators to thereby isolate the blade from vertical movements of the machinery caused by irregularities in the terrain being worked. The control also includes means for comparing the actual fore and aft blade assembly angle with the desired blade assembly angle and providing a corrective signal in the case of discrepancies therebetween and means for sensing the actual forward speed of the machinery and generating a transient overload compensation signal.

BACKGROUND OF THE INVENTION Field of the invention The present invention relates to the control of earth working machinery. More particularly, the present invention is directed to the automatic control of machinery employed to work irregular terrain to a preselected grade. Accordingly, the general objects of the present invention are to provide new and improved methods and apparatus of such character.

Description of the prior art While not limited thereto in its utility, the present invention is particularly well suited for use on equipments, known generally in the art as dozers, which dislodge and move material by means of an adjustable, front mounted blade. By controlling blade assembly angle, it is possible to cut and/or fill in the establishment of a desired grade or contour. For many applications, there is a trend in the earth working machinery art to replace the conventional and relatively slow moving tracked equipment; commonly known as the bulldozer; with large, high speed, rubber tired apparatus. That is, for many jobs, it has been found to be more efficient to perform grading operations with the high speed, rubber tired dozers even though the blade bite of such equipment is generally less than that of the slower moving tracked equipment. Among the reasons for this trend are the improved maneuverability of rubber tired equipment and their increased versatility since the speed of operation of the equipment may be matched to the job requirements.

In the prior art, a grading operation has typically been performed with a slow speed, tracked vehicle making a rough cut and in the course thereof, removing or burying obstacles such as large rocks. Thereafter, in order to grade to the desired contour, scraper type equipment depth by some object. Further, since the finished grade Due to the slow speed and relatively stiff suspension systems on the tracked dozers, it has previously been deemed unnecessary to provide compensation for short term vertical blade movements in the control systems for such equipment. Restated, due to the slow forward speed of the prior art tracked dozers, the operator thereof could easily manually compensate for the situation where the vehicle and thus the blade was deflected from the desired cut depth by some object. Further, since the finished grade was generally produced by additional equipment brought to the construction site it was previously not deemed necessary to provide the dozer with automatic controls having the necessary sensing devices to provide compensation for such vertical movements.

However, automatic blade bite control equipment has been designed and occasionally utilized on earth working machinery to facilitate grading operations. Such control equipment is generally quite complex and thus both expensive and often lacking in reliability. Even more important, the prior art control schemes are not suitable for employment upon the high speed, rubber tired equipment. That is, the foregoing comments regarding the lack of compensation for vertical movements are true even in the case of relatively sophisticated dozer controls which provided for the maintaining of a pre-selected blade bite or grade angle. Such controls were capable of sensing the deviation from the desired grade and generating blade actuator control signals which would cause proper adjustment of the blade relative to the tractor so as to return to the desired grade. However, as a result of the relatively slow working speed of the tracked equipment, it was unnecessary to provide means to isolate the blade from short term vertical movements of the tractor. This, of course, is not true in the case of the high speed, rubber tired dozer. When one of the wheels of the latter equipment strikes an object at the normal or medium working speed, the blade will be deflected from the desired grade. In addition the rubber tire suspension causes an oscillatory pitching response in the vehicle not found in slow tracked vehicles. These responses are sensed as blade accelerations and largely taken out by this invention.

In addition to the above discussed deficiency of prior art blade controls, it should be noted that, while some of these prior art controls provided for maintaining of a pre-selected grade angle, the controls did not provide for automatic stepping of the equipment to a second elevation while continuing to grade at the desired grade angle. In a grading operation, it often happens that the dozer or other earth working machine will lose forward speed due to an excessive load of material ahead of the blade. In the prior art, when this situation occurred, the control system would oppose the equi-pments attempt to climb out of the cut and resume grading along the same angle but at a different level. Restated, in the prior art, when the earth working machine lost speed, it was necessary for the operator to disengage the automatic control and take over manual operation of the machine until a set of conditions was achieved where the automatic control could be reactivated.

SUMMARY OF THE INVENTION The present invention comprises an automatic blade bite control for earth moving machinery which overcomes the above-discussed disadvantages of the prior art and thus constitutes an improvement thereover. This improvement is precipitated by a control which employs means for sensing the onset of short term vertical accelerations of the earth working blade and for generating signals commensurate with such short term accelerations. Through suitable control circuitry, the signals commensurate with short term vertical blade accelerations are applied to the blade actuating mechanism thereby isolating the blade from short term vertical and rotational movements of the vehicle upon which it is mounted. The present invention also includes means for comparing the actual blade assembly angle with the desired blade assembly angle and for generating corrective signals for application to the blade actuators when the actual angle departs from the desired angle. The angle comparing means thus aids the operator in maintenance of a preselected grade slope. The present invention further comprises means for sensing the forward speed of the blade relative to the earth and for generating a signal which causes application of a transient blade up bias signal to the blade actuators when the forward speed of the blade drops below a pre-selected level. When the vehicle climbs out of the initial cut and begins moving forward on a different level, the disabling signal will automatically decay and the blade assembly angle will revert back to the commanded value.

BRIEF DESCRIPTION OF THE DRAWING The present invention may be better understood and its numerous advantages will become apparent to those skilled in the art by reference to the accompanying drawing wherein like reference numerals refer to like elements in the various figures and in which:

FIGURE 1 depicts a high speed, rubber tired, earth moving machine incorporating the present invention; the earth working blade of the apparatus of FIGURE 1 being partially broken away to show the placement of the sensors in a preferred embodiment of the present invention.

FIGURE 2 is a schematic representation of the earth moving apparatus of FIGURE 1 indicating the various angles which must be sensed and maintained during operation of the equipment.

FIGURE 3 consists of a block diagram of a preferred embodiment of the present invention.

FIGURE 4 represents a speed sensor of a type which may be employed on the present invention.

FIGURE 5 is an elevation view of terrain which depicts the operation of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGURE 1, a rubber-tired earth moving vehicle (dozer) is indicated generally at 10. Dozer has an earth working or moving blade assembly 12 mounted, by means of skids 14 and arms 16 and 18, from its front end. The angle of the blade assembly relative to the dozer will be controlled by a pair of hydraulic lift jacks 20, only one of which is shown. The lift jacks 20 will extend between opposite sides of blade 12 and the frame of dozer 10. Through control of the hydraulic lift jacks 20, the angle (bite) of blade 12 relative to the fore and aft axis of the vehicle may be adjusted thereby adjusting the finish grade angle of the terrain being worked. Dozer 10 is characterized by high maneuverability and the ability to operate at a relatively high speed while a cut is being made with blade 12.

The automatic blade bite control of the present invention includes a plurality of sensors which, with the exception to be described below, may be mounted on the apparatus at positions which, through trial and error, place the sensors where they are least susceptible to damage. In FIGURE 1, blade 12 has been partially broken away to show a plurality of these sensors.

A speed sensor, indicated generally at 22, is mounted behind blade 12 and preferably includes fifth wheel means, which contacts the terrain, and an associated tachometer generator, which provides a signal commensurate with the speed of rotation of the fifth wheel means and thus with the actual forward velocity of the dozer 10. A fifth or speed wheel which is in actual contact with the surface of the terrain over which dozer 10 is moving is necessary in order to measure the forward velocity of the apparatus. An ordinary speedometer connected to one of the wheels of dozer 10 would not provide an accurate measure of actual forward speed relative to the earth since the wheels of dozer 10 are generally all driven and always experience various amounts of slippage when blade 12 is loaded.

An angle sensing means 24 is shown in FIGURE 1 as mounted on a suitable bracket between blade 12 and the front end of dozer 10. Angle sensor 24 comprises means for sensing the angle a between the blade 12 and dozer 10.

It is also necessary to sense the angle p of the vehicle with respect to the earth. The angle ,6 is known as the vertical deviation angle and is measured by a sensor 26 which includes a vertical reference generator (see FIG- URE 3) conveniently located in or near the control box 28.

A linear accelerometer 30 is mounted on the rear of blade 12, as shown, with its sensitive axis aligned to sense local vertical motions of the blade. In accordance with the present invention, accelerometer 30 must be mounted on blade 12. While there is some flexibility, the primary consideration in the mounting of accelerometer 30 is, of course, that it be protected against damage from debris which falls or is otherwise forced between blade 12 and the front of dozer 10.

Considering briefly FIGURE 2, the three angles of interest in the operation of the present invention, as employed to cut and fill terrain to a desired grade angle, are shown. The angle a comprises the angle between the blade assembly and the fore-aft axis of the dozer. The angle 13 is the angle of the vehicle with respect to earth. That is, angle 5 is the angular deviation of dozer 10 with respect to earth or, restated, the fore and aft pitch angle of the dozer. The angle 0 is the desired grade angle in the direction of vehicle travel. In the normal control mode, the algebraic sum of the vertical deviation 3 and the blade assembly angle 0: is equivalent to the desired grade angle 0.

Referring now to FIGURE 3, a preferred embodiment of the control of the present invention is shown in block form. The means for computing the actual grade angle comprises, in the preferred embodiment, blade angle sensor 24 and vertical deviation angle sensor 26. The vertical deviation 5 angle sensor 26 may comprise a gyro slaved to the earth or a damped pendulum. The output of sensor 26 is, as previously noted, a signal commensurate with the angular deviation [3 of the dozer 10 with respect to the earth (the fore and aft pitching angle). The blade assembly angle sensor 24, which provides a signal commensurate with the angular rotation of the blade assembly with respect to dozer 10, will comprise a transducer mounted in such a manner as to pick ofl? said angular rotation.

The a and B signals, respectively from the blade angle transducer 24 and vertical position sensor 26, are applied to a summing circuit 32. Summing circuit 32 provides an output signal proportional to the algebraic sum of the vertical deviation 5 and the blade assembly angle a. As noted above, this sum is a signal proportional to the angle 0 between the blade reference axis and the earth which is, in the normal control mode, equivalent to the desired grade angle in the direction of vehicle travel. The 0 or grade angle signal from summing circuit 32 is passed through a lag or integrating circuit 34 to raise its low frequency gain level and hence improve its steady state position accuracy. The output signal from lag circuit 34 is amplified in a preamplifier 36 and applied to both a summing circuit 38 and a grade angle indicator 40.

A signal commensurate with vertical blade acceleration is generated by accelerometer 30. The acceleration signal from accelerometer 30 is summed with a gravity compensation signal in a summing circuit 42. The gravity compensation signal is obtained from the net blade assembly angle signal by passing the output signal from summing circuit 32 through a compensation circuit 44. Circuit 44 generates a signal commensurate with the magnitude of the 6 signal for application to summing circuit 42. The compensated vertical blade acceleration signals from summing circuit 42 are passed through a decoupler cihcuit 46 which eliminates steady state signal components due to imperfect gravity cancellation and/or null shifts in sensor 30. The output signals from decoupler circuit 46 are fed along two paths, being integrated in one path in approximate form by an integrator 48 to provide a short term velocity signal. The short term velocity and acceleration signals,

stabilization) signals from preamplifier 52 are applied directly to summing circuit 38.

As noted above in the discussion of FIGURE 1, the preferred embodiment of the present invention being described also includes means for sensing the forward speed of the dozer relative to the earth. While shown in FIGURES 1 and 4 as being mounted from the rear of blade 12, speed sensor 22 may be mounted from any suitable point on the apparatus. As may be seen most clearly from FIGURE 4, the speed sensing means 22 preferably comprises a speed wheel 54 and a tachometer generator 56. The speed sensor 22 is typically mounted from a bracket 58 on the rear of blade 12 and the speed wheel is urged into contact with the terrain being worked by a spring 60. The mechanical connection between speed wheel 54 and tachometer generator 56 will pass within the strut by which the speed wheel is suspended from the bracket. Raising of blade assembly 12 will lift speed wheel 54 out of contact with the earth.

The output of tachometer generator 56 is a signal commensurate with the actual speed of dozer 10. This speed signal is filtered in a filter circuit 62 to remove short term transients and is thereafter applied to a summing circuit 64. Also applied to summing circuit 64 is a speed trip adjustment signal commensurate with the desired minimum forward speed of dozer 10. The speed trip adjustment is made as required via a potentiometer 66 which will be physically located in the cab area of dozer 10.

Also added at summing circuit 64 is the forward-reverse lever lagged rate signal. The forward-reverse lever 68 actuates either forward switch 70 or reverse switch 72 depending upon its position. Switches 70 and 72 apply a fixed voltage of the proper polarity from power supply 74 to a derivative-lag circuit 76. When the operator moves the forward-reverse lever 68- from the forward to the reverse position, or vice-versa, one of switches 70 and 72 will be closed applying a steady state voltage to derivativelag circuit 76. Upon the removal and then reapplication of a steady state signal thereto, circuit 76 generates a transient artificial over-speed signal which is applied to summing circuit 64. This transient over-speed signal will, in the manner to be described below, prevent the blade assembly from raising when the operator changes the direction of vehicle travel. It is to be noted that the decay time of the transient over-speed signal generated by derivative-lag circuit 76 is commensurate with the time it takes for the dozer to come up to or resume speed upon start up or direction change under normal working conditions.

Under normal operating conditions, that is when the operator has not ordered a change in direction of travel, the actual speed signal from filter circuit 62 and the desired speed trip adjustment signal from potentiometer 66 are summed in summing circuit 64 to provide a speed error signal. The speed error signal from summing circuit 64 is applied to a preamplifier 78. The output of preamplifier 78 is applied to a speed relay 80. Preamplifier 78 will normally provide an output signal of sufficient magnitude to hold relay 80 in. With relay 80 held in, its contacts will be in the normally open position and no signal will appear at the output of the speed relay. However, when the forward speed of dozer 10 drops below a preselected value, such value being commensurate with the preselected speed trip adjustment signal, the speed error signal will increase in the proper direction to cause a reduction of the speed relay current supplied by preamplifier 78. When the signal from preamplifier 78 becomes insufficient to hold in relay 80, the relay will be unlatched, its contacts closed and a blade up bias signal from bias power supply 82 will be applied, through a decoupling circuit 84, to summing circuit 38. Decoupling circuit 84, in response to the application of a signal thereto from power supply 82 via the contacts of relay 80, generates a transient blade up signal. This transient blade up signal operates in the manner to be described below so as to cause the blade assembly to first rise and then, as the signal decays, to return to its original position and reengage the speed wheel. The decay time is sufiicient to allow the dozer to climb out of the cut and regain speed.

The blade assembly angle is initially set by the operator by means of adjusting the blade while observing grade angle indicator 54. The blade is adjusted by periodically closing a switch 86 to the up or down position. Each time the operator closes switch 86 in either direction, current of the proper polarity from a power supply 88 is delivered to a toggling motor 90. The output shaft of toggling motor 90 is connected through a gear reduction to the movable arm of a potentiometer 92 which is connected across power supply 82. The output signal as derived from the movable arm of potentiometer 92 will thus be a signal commensurate with the desired blade assembly angle. This blade assembly angle signal is applied to summing circuit 38.

During normal operation, after the speed trip potential at summing circuit 64 has been adjusted and the desired grade angle selected, the only signals applied to summing circuit 38 will be the desired grade angle signal from potentiometer 92, the actual grade angle 0 signal from preamplifier 36 and the transient stabilizing signals from preamplifier 52. When there is a discrepancy between the actual and desired grade angle signals or when a blade assembly vertical acceleration is sensed, a grade angle error signal will appear at the output of summing circuit 38. This grade angle error signal will be applied to a summing circuit 94 and thence to a power amplifier 96. The output of amplifier 96 is passed, via the normally closed contacts of a master automatic blade bite control cutout switch 98, to an actuator 100. Actuator 100 may be any well known electromechanical or electrohydraulic servo device which will control the operation of the lift jacks 20 on dozer 10 by means of regulating valves or other devices associated with the supply of motive power for the lift jacks. Movements of the output shaft of servo actuator 100 are sensed by a feedback transducer 102 which generates signals commensurate with such movements for application to summing circuit 94. Thus, the grade angle command signals from summing circuit 38 and blade actuator feedback signals are summed and the error signals feed a minor position loop; the minor feed back loop consisting of amplifier 96, servo actuator 100 7 and feedback transducer 102. As previously noted, the output of servo actuator 100 is mechanically coupled to the lift jack regulating means which are indicated schematically at 104.

Master cutout switch 98 may be controlled by the operator and is used when it is desired to disconnect the automatic blade bife control system of the present invention from the blade bite position controlling means on dozer 10. Regardless of the position of switch 98, the blade assembly may be manually adjusted by the operator through the operation of a control lever 106 located in the cab area. Control lever 106 is directly linked to regulating means 104.

In operation, through the manipulation of two-way switch 86, a signal commensurate with the desired grade angle is set into the system. During the setting of the desired grade angle signal, blade angle sensor 24 and vertical reference signal generator 26 will be operative to provide an actual grade angle signal to blade angle indicator 40. Thus, by watching indicator 40 and manipulating switch 86, the operator can ascertain when the proper blade angle for achieving the desired grade angle has been obtained. During the initial setting of the blade and thereafter during operation, the grade angle error signal provided by summing circuit 38 will control the operation of a feedback control system including a servo actuator 100 which positions the blade assembly lift jack regulating means. The desired speed trip point signal is also initially set into the system by adjusting potentiometer 66.

Once the desired grade angle and speed trip adjustment points have been set, the operator engages the forward-reverse lever 68 and the dozer begins to move forward. During the time that the dozer is coming up to speed, a transient simulated over-speed signal from lag circuit 76 is applied to speed relay preamplifier 78. This over-speed signal results in the holding in of the speed relay 80 and allows the blade assembly to assume the required angle even though the output from tachometer 56 is insufiicient to null out the speed trip signal from potentiometer 66.

Once the dozer has come up to speed, the speed sensing system comprising speed wheel 54 and tachometer generator 56 will provide an output signal which will oppose the desired speed signal established by speed trip adjustment potentiometer '66 and the speed error signal will be nulled. Speed relay 80 will accordingly be held in when the transient simulated over-speed signal from lag circuit 76 falls to zero. Operation of the dozer will continue with grade angle error signals being generated by summing circuit 38 and applied to the control loop. Should the dozer encounter an irregularity which results in vertical movement of dozer 10 and/or the blade assembly 12, vertical blade accelerometer 30 will sense such motion and; through the action of decoupler 46, integrator 48, summing circuit 50 and preamplifier 52; will provide a large amplitude output signal. This tran sient signal will be applied to summing circuit 38 and thence to the control loop. The acceleration signals and their integrated (velocity) values as applied to summing circuit 38 from preamplifier 52 will cause the servo actuator 100 to operate the blade lift jacks 20 in a direction opposite to the sensed motion of the blade. The response of the system is quite rapid and thus the blade assembly is effectively isolated from short term vertical movements of the dozer.

As grading continues, a load of material may build up in front of the blade 12 of dozer 10. This load of material will cause the dozer to slow down to a point where a speed error signal of sutficient magnitude to cause the dropping out of speed relay 80 will be generated. When this happens, a transient blade up bias signal will be applied to the control loop via decoupling circuit 84. The blade will then be raised, the dozer will proceed forward and will climb out of the cut while gaining speed, the transient blade up bias signal will decay to zero and the blade will be returned to the preset angle through the nulling of the grade angle error signal. Grading will then resume at a new initial elevation point and will proceed at the proper grade angle.

The above described operation may be more clearly seen from a consideration of FIGURE 5. In FIGURE 5, it is presumed that, starting at point a, the dozer is to grade the terrain to provide a grade at an angle 6 from point a to point i. The grade angle is set into the system by adjusting potentiometer 92 via control switch 86 and toggling motor 90. The throttle is then advanced, the forward-reverse lever engaged and the dozer proceeds forward (in a downhill direction) to point b. At point b, the load on the blade has become so great that the dozer loses speed. A transient blade up bias signal is thus applied to the system, the blade raised and the dozer again begins to proceed forward. As the dozer climbs out of the cut made by the blade between points a and b, it resumes speed, the blade up bias signal decays, the blade lowers and cutting is resumed. A new cut will thus be made at a different level but on the same angle 0 between point 0 and d. At point d, the blade is again loaded, the dozer slows down, the blade is raised, the dozer proceeds forward again and the blade is lowered thus grading along a third level but again at the same angle 0 between points e and f. The dozer will then be returned to point b and the operation will be repeated with the first cut being from point b to g, the blade then being raised and a second cut being from point d to point 11. The dozer then is returned to point g and finishes the grade to point i. The three passes required to contour the terrain to the grade angle 0, since they are performed with a piece of equipment operating at a relatively high speed and under automatic control, takes considerably less time than would be required using prior art equipment and techniques. Thus, the entire operation is speeded up thereby achieving higher equipment and manpower utilization. In addition, as a byproduct of the automatic control, the level of skill required by the operator to bring an excavation to grade and/ or to bring the excavation to grade more accurately using rough grading equipment is considerably reduced. This, in turn, reduces the job of finished grading where necessary. Operator fatigue is also reduced through the automatic control of equipment engaged in repetitious and/ or ordinary rough grading and excavating operations.

To summarize the results achieved through use of the present invention, the automatic blade bite control described above maintains a constant long term blade position with respect to earth. Because the dozer cuts its own path while maintaining a constant blade assembly angle, a constant grade slope results as long as material is available or as long as the bite does not cause the vehicle to significantly slow down. The acceleration and velocity feedback paths for the signal sensed by the blade vertical accelerometer (vertical deviations of the blade due either to blade and/or vehicle rotation and vertical translation of the entire vehicle) isolate the blade of the dozer from vehicle motions. By using an override signal to raise the dozer blade when the vehicle speed falls to near zero due to blade loading, the operator is released from making continuing blade adjustments due to blade resistance.

While a preferred embodiment has been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the present invention. Accordingly, it is to be understood that the present invention has been described by way of illustration rather than limitation.

What is claimed is:

1. An automatic blade control system for a vehicle having mounted thereon an adjustable blade, said vehicle being employed for moving material by means of said blade, the control system comprising:

an accelerometer mounted on the blade, said accelerometer comprising means for providing Signals commensurate with short-term vertical motions of the blade relative to the vehicle and to the earth;

means for generating a signal commensurate with the desired blade attitude;

means for sensing the actual blade attitude and for generating a signal commensurate therewith;

means responsive to said desired and actual bladeattitude signals and to said signals commensurate with vertical blade motions for generating blade adjustment control signals when the actual blade attitude deviates from the desired blade attitude and when a short-term vertical blade motion signal is present; and

means for applying said blade adjustment control signals to the blade positioning actuators on the Vehicle whereby the desired blade attitude may be maintained and the blade isolated from short-term vertical motions of the vehicle.

2. The apparatus of claim 1 wherein said means for sensing the actual blade attitude comprises:

means for sensing the angle of the blade with respect to the fore-aft axis of the vehicle and for generating a signal commensurate with said blade angle;

means for sensing the fore-aft pitch angle of the vehicle and for generating a signal commensurate with said pitch angle; and

summing means responsive to said signals commensurate with blade and pitch angle for providing a signal commensurate with the actual angular position of the blade.

3. The apparatus of claim 1 further comprising:

means for sensing the forward velocity of the vehicle and for generating a signal commensurate therewith;

means responsive to said vehicle velocity signal for generating a blade up bias signal when the vehicle velocity falls below a preselected level; and

means applying said blade up bias signal to said means for generating blade adjustment control signals whereby said blade will be raised when the load thereon causes the forward speed of the vehicle to fall below the preselected level.

4. The apparatus of claim 3 wherein said means for generating a blade up bias signal comprises:

means for generating a signal commensurate with a preselected minimum velocity;

means responsive to said signals commensurate with forward velocity and minimum velocity for generating a speed error signal; and

means responsive to said speed error signal for generating a transient blade up bias signal.

5. The apparatus of claim 4 wherein said means for generating a transient blade up bias signal comprises:

a source of steady state potential;

a decoupling circuit for generating a transient bias signal upon the application of a steady state signal thereto; and

means responsive to said speed error signal for applying a steady state signal from said potential source to said decoupling circuit.

6. The apparatus of claim 3 wherein said means for sensing the actual blade attitude comprises:

means for sensing the angle of the blade with respect to the fore-aft axis of the vehicle and for generating a signal commensurate with said blade angle;

means for sensing the fore-aft pitch angle of the vehicle and for generating a signal commensurate with said pitch angle; and

10 summing means responsive to said signals commensurate with blade and pitch angle for providing a signal commensurate with the actual angular position of the blade.

7. An automatic blade control system for a vehicle having mounted thereon an adjustable blade, said vehicle being employed for moving material by means of said blade, the control system comprising means for sensing vertical motions of the blade and for generating signals commensurate therewith;

means for generating a signal commensurate with the desired blade attitude;

means for sensing the actual blade attitude and for generating a signal commensurate therewith;

means for sensing the actual forward velocity of the vehicle and for generating a signal commensurate with therewith;

means for generating a signal commensurate with a preselected minimum forward velocity;

means responsive to said signal commensurate with actual and minimum forward velocity for generating a speed error signal;

means responsive to said speed error signal for generating a transient blade up bias signal;

means responsive to said desired and actual blade attitude signals and to said signals commensurate with said vertical blade motions for generating blade adjustment control signals when the actual blade attitude deviates from the desired blade attitude and when a vertical blade motion signal is present, said blade adjustment control signal generating means also being responsive to said transient blade up bias signals and generating blade adjustment control signals commensurate therewith; and

means for applying said blade adjustment control signals to the blade positioning actuators on the vehicle whereby the desired blade position may be maintained, the blade isolated from vertical movements of the vehicle and the blade momentarily unloaded in response to an unrequested decrease in vehicle speed greater than a preselected value.

8. The apparatus of claim 7 wherein said means for sensing vertical motions of the blade comprises:

an accelerometer mounted on the blade, said accelerometer providing signals commensurate with short term vertical motions of the blade relative to the vehicle and to the earth.

9. The apparatus of claim 7 wherein said means for generating a transient blade up bias signal comprises:

a source of steady-state potential;

a decoupling circuit for generating a transient bias signal upon the application of the steady-state signal thereto; and

means responsive to said speed error signal for applying a steady-state signal from said potential source to said decoupling circuit.

10. The apparatus of claim 9 wherein said means for sensing vertical motions of the blade comprises:

an accelerometer mounted on the blade, said accelerometer providing signals commensurate with short term vertical motions of the blade relative to the vehicle and to the earth.

11. The apparatus of claim 10 wherein said means for sensing the actual blade attitude comprises:

means for sensing the angle of the blade with respect to the fore-aft axis of the vehicle and for generating a signal commensurate with said blade angle;

means for sensing the fore-aft pitch angle of the vehicle and for generating a signal commensurate with said pitch angle; and

summing means responsive to said signals commensurate with blade and pitch angle for providing a signal commensurate with the actual angular position of the blade.

12. The apparatus of claim 11 further comprising:

means for generating a transient artificial over-speed signal in response to vehicle direction of motion change commands; and

means applying said transient over-speed signal to said speed error signal generating means whereby blade up bias signals will not be applied to said control signal generating means during start up or when the direction of movement of the vehicle is reversed.

References Cited UNITED STATES PATENTS Gurries et a1 1724.5 Ocnaschek 1724.5

Kutzler 172-2 X Small 1724.5 Taylor 1722 X Breitbarth et al 1724.5

Curlett 1724.5

ROBERT E. BAGWILL, lrimary Examiner A. E. KOPECKI, Assistant Examiner

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