Automatic leveling system for a grading blade

A hitching system for a tractor or similar vehicle which includes a parallelogram of four rigid members rotatably connected together at the ends of each of the members and in which the members are arranged to provide at least one member which is positioned vertically and moves essentially in the vertical direction despite variations in the surface of the terrain and the height to which the movable vertically positioned member is adjusted. This movable, vertically positioned member is connected to a blade, such as a box blade, to cause the blade to be held with its lower surface generally parallel to the desired final grade of the terrain. The blade is adjusted in the vertical direction as necessary to level the surface of the terrain by a hydraulic cylinder. A laser guidance system is included in a preferred embodiment to control this hydraulic cylinder and the height of the blade with respect to the terrain.

BACKGROUND 
1. Field 
The present invention relates to devices for grading terrain and more 
particularly to the improved control of tractor drawn blades, such as box 
blades. 
2. Prior Art 
There have been a number of prior art devices designed to produce level 
terrain by using different blades and different methods of attachment of 
the blade to the tractor. In particular, different methods have been used 
to actuate the blade to compensate for variations in the initial terrain. 
Roughness of the terrain and especially high and low areas in the initial 
terrain typically cause the tractor and the attached blade to move in a 
vertical and sometimes horizontal direction, making level grading 
difficult. Constant adjustments of the controls by the tractor operator 
are usually required to achieve the desired level terrain. To more clearly 
illustrate this problem, three prior art inventions designed to grade or 
contour terrain are listed below along with the difficulties encountered 
with each of these inventions. 
Generally box blade are connected to a tractor by way of what is referred 
to as a three point hitch such as hitch 2 shown in FIG. 1. The box blade 3 
is connected to the tractor 1 by the hitch 2. This hitch has three support 
members which extend from the tractor to the box blade. If it is necessary 
to raise or lower the box blade, an hydraulic cylinder 4 connected between 
the tractor and the hitch raises and lowers the hitch, but the hitch 
rotates about a point 2A and can place the lower surface of the blade 3A 
unintentionally at a pitch angle with the horizontal plane, as shown by 
the position of the blade shown in the dashed lines of FIG. 2. The pitch 
angle has been exaggerated in this Figure for illustrative purposes, but 
the problem it produces is real and significant even though the actual 
pitch angles may be small. This unintentionally produced pitch angle 
requires the tractor operator to supply constant corrections to 
compensate. In general, the production of the unintentional pitch angle 
makes grading for the operator more difficult and time consuming. 
U.S. Pat. No. 4,299,290 employs a set of wheels at the rear of a blade to 
aid in supporting the blade above the existing terrain. Hydraulic systems 
are used to further adjust the front and rear of the blade above the 
terrain. 
The problem encountered with this arrangement is the hydraulic system used 
to control the blade must be continuously controlled manually. A 
particular position for the box blade cannot be simply "found" and 
"locked" in place. It is difficult to hold the lower surface of the box 
blade in the horizontal plane and also hold it at a particular height of 
say one-fourth of an inch above the surface of the terrain. 
This system also suffers from the effects of an initially rough terrain 
because the blade does not instantaneously level the terrain before the 
trailing wheels pass over it. Consequently, the wheels follow the initial 
contours of the terrain and tend to move the blade away from its desired 
position. 
The blade shown in this patent is a box blade which includes sides and a 
partially open bottom that takes on soil taken when passing over high 
spots and empties soil when passing over low spots. These filling and 
emptying actions take place as long as the blade is held at a desired 
elevation and the lower surface of the blade remains generally parallel 
with the horizon plane so that the blade picks up the correct amount of 
fill and unloads it where it is needed. To keep the lower surface of the 
blade in this position is difficult because the movement of the wheels of 
both the tractor and the wheels attached to the blade can throw the blade 
off from its desired position. Also, the hydraulic systems used to correct 
the position of the blade does not ordinarily include controls designed to 
automatically compensate for such problems. As a result, the operator must 
continually adjust the controls to compensate for these problems. This 
system does not inherently tend to keep the lower surface of the box blade 
in a generally horizontal position, which would greatly reduce the 
complexity of control. An additional problem is the wheels at the rear of 
the blade prevent the tractor from coming close to a wall. This prevents 
this arrangement from being applied to complete many areas and thereby 
generally reduces its usefulness. 
U.S. Pat. No. 4,919,212 shows a method of connecting a dozer blade to the 
front of a tractor. There are two hydraulic controls used to position the 
blade; however, movement of one of the controls tips the blade either to 
the right and left and the other moves the blade up and down. There is no 
single control to keep the blade in the same relative position with 
respect to the terrain when the tractor runs over a high spot in the 
terrain. The lower surface of the blade is not inherently maintained in 
position to grade parallel to the horizon plane. 
U.S. Pat. No. 5,511,326 shows a ditcher which has a parallelogram-like 
linkage connecting the ditcher blade to the tractor. However, all the 
members of the parallelogram are not rigid. One member is an hydraulic 
cylinder which does not permit maintaining the lower surface of the blade 
in the horizontal plane because the movements in the hydraulic cylinder 
changes its length and destroys the normal functioning of the 
parallelogram. 
What is needed in this field to overcome these disadvantages is a system 
that permits level grading with a box blade without constant controlling 
and without the need for wheels on the rear of the box blade which 
restricts the usefulness of the system. 
SUMMARY 
It is an object of the present invention to provide a hitching system for a 
tractor, in which a movable, vertical hitch member remains vertically 
position despite the lowering or raising of the blade. 
It is an object of the present invention to provide for movement of the 
movable vertical hitch member only in the vertical direction. 
It is a object of the present invention to provide a hitching system for a 
box blade which maintains the lower surface of the box blade generally in 
the horizontal plane despite movement of the blade up or down during the 
grading operation. 
It is an object of the present invention to provide a means for inserting a 
box blade or similar blade into a space that is blocked because it is too 
narrow for the tractor to enter or because there is a low obstruction, 
such as a wall or a hedge, which cannot be reached by tractors with 
conventional hitching systems. 
It is an object of the present invention to automatically raise and lower 
the blade for grading by means of a laser leveling system while 
maintaining a constant pitch angle on the blade. 
The present invention is a hitching system designed to connect an earth 
moving blade to a vehicle such as a tractor. The hitching system includes 
a parallelogram arrangement of four shaft-like, rigid members in which 
each member has a longitudinal axis and each member is typically cut from 
heavy plate, as for example one-half inch thick steel plate. The four 
rigid members are connected together at the corners of the parallelogram 
by means of four rotary joints a first member of the parallelogram is 
connected to the vehicle and secured with its longitudinal axis held in a 
vertical position. A second member of the parallelogram, located opposite 
the first member, is also held with its longitudinal axis in the vertical 
position by virtue of its location in the parallelogram opposite the first 
rigid member, but unlike the first rigid member, which is held fixed in 
its position because of its fixed connection to the vehicle, the second 
rigid member is free to move in the vertical direction with respect to the 
vehicle. 
The second rigid member is connected to the earth moving blade with the 
lower surface of the blade positioned in the horizontal plane, which is 
orthogonal to the longitudinal axis of the second rigid member. This 
position of the lower surface of the blade is maintained in the horizontal 
plane despite changes in the height of the blade in the vertical direction 
which are usually necessary to effectively grade a surface. This is not 
the case with conventional hitching systems where the lower surface of the 
blade is unintentionally pitched at an angle with respect to the 
horizontal plane when the blade is moved in the vertical direction. The 
elimination of this unintentional pitching of the blade greatly simplifies 
the grading operation.

DETAILED DESCRIPTION OF THE INVENTION 
A prime objective of the present invention is to reduce the degree of 
manual control required to level terrain by maintaining the lower surface 
of a box blade generally parallel to the horizontal plane despite movement 
over unlevel terrain and despite the adjustment of the blade in the 
vertical direction. This objective is achieved in the present invention by 
using a parallelogram structure in the hitch between the blade and the 
tractor. This parallelogram 6 is shown in FIG. 3 and consists of four 
members 9A through 9D. Each of the members is typically a steel arm which 
is attached at its end to the adjacent members by rotating joints 10A 
through 10D. In FIG. 3, the members 9A through 9D are shown to be of equal 
length and are positioned to form a square at one setting of the hitch 
controls. In this position of the parallelogram, there are two rigid 
members that form the horizontal sides and two that form the vertical 
sides. 
Member 9A is a vertical member attached to the tractor while member 9D is 
also a vertical member but is located at the opposite side of the 
parallelogram. Member 9D is also free to move, but only in the vertical 
direction generally parallel to member 9A, which is held vertically by 
virtue of its attachment to the tractor. The lower end of member 9D is 
connected to the box blade, thereby causing the lower surface of the box 
blade to be held horizontally regardless of whether the blade is raised or 
lowered. This feature of the present invention overcomes the prior art 
problem of incurring unintentional pitching of the blade while the blade 
is moved to a desired height and consequently greatly reduces the need to 
constantly adjust the controls during a grading operation. 
Although it is usually desired to hold the lower surface of the blade in 
the horizontal plane, in some cases it is desired to intentionally pitch 
the blade at a controlled small angle, alpha, with respect to the 
horizontal plane. Two ways in which this can be accomplished are shown in 
FIGS. 5 and 6. 
In FIG. 5, a rigid member, such as member 9A, is rotatably connected at a 
point, such as the center of rotary joint 10B, to the vehicle. An end of 
this rigid member that is away from the rotary joint, such as the top end 
of member 9A, is moved by an hydraulic cylinder 4A, which is connected 
between this end and the tractor, to offset member 9A from the vertical 
axis by a small angle alpha. This causes member 9D to be similarly offset 
from the vertical axis by the angle alpha and the lower surface of the 
blade to be pitched by the same small angle alpha with respect to the 
horizontal plane. The parallelogram constrains member 9D to remain offset 
from the vertical by this small angle despite movement of this member and 
the movement of the blade in the vertical direction to adjust the height 
of the blade. 
The second method of adjusting the pitch of the lower surface of the blade 
is shown in FIG. 6. In this Figure, the blade is rotatably attached to 
member 9D by means of rotary joint 10E. The pitch is set by means of 
hydraulic cylinder 4C, which is connected between the second rigid member 
9D and the blade 3. Since member 9D is usually constrained to remain 
vertical, the lower surface of the blade will remain set at an angle alpha 
despite vertical movement of the member 9D to adjust the height of the 
blade above the terrain. 
Note that, although member 9D may be set at a small angle with respect to 
the vertical axis, its movement is essentially vertical because it is 
attached to the ends of members 9B and 9C which are extending generally 
horizontally. Members 9B and 9C rotate about fixed positions at there left 
end, as shown in FIG. 6, and their right ends can only move in arcs of 
circles with the center of the arcs located at their left ends. The 
tangent to these circular arcs at the point where these horizontal members 
9B and 9C meet vertical member 9D is in the vertical direction, causing 
the movement of member 9D to be essentially vertical for the typically 
small blade movements of a few inches needed to grade. 
A number of variations of the parallelogram are permissible without 
departing from the spirit and scope of the invention. For example, the 
same results can be achieved if the vertical members are of equal length 
and the horizontal members are of equal length, but the vertical members 
are not equal in length to the horizontal members. The sides of the 
parallelogram need not form a square, as long as opposite sides are 
parallel. Hydraulic cylinders are the most popular devices currently used 
to actuate component members of a hitching system, however they are not 
the only types of devices that can be used. Many different devices that 
constitute equivalents can be substituted, as for example an electrically 
or hydraulically driven mechanical worm gear or other reduction gear 
system. The point of connection of the hydraulic cylinder used to raise 
and lower the blade can be varied. For example the blade can be raised and 
lowered by connecting the hydraulic cylinder between the tractor and 
either the second or the third rigid member of the parallelogram. Twin 
parallelograms may be uses side by side with one supporting one side of 
the blade and the other supporting the opposite side of the blade. Other 
variations which also remain within the spirit and scope of the invention 
will be readily apparent to those skilled in the art. 
As noted above in the section on prior art, one of the difficulties 
encountered with a prior art arrangement was the location of wheels at the 
rear of the box blade which prevents the blade from coming close to a wall 
or other structure to complete a leveling operation. This does not present 
a problem for the present invention because there are no wheels employed 
at the rear of the box blade. However, there are areas which cannot be 
readily reached even with a box blade without wheels because of being 
blocked by an obstruction or blocked by the narrowness of an area which 
prevents the tractor from backing into such an area safely. This can be 
overcome with a variation of the present invention shown in FIG. 4. 
In FIG. 4, the parallelogram hitching system is not directly connected to 
box blade, but is connected to the blade via a boom 13. The boom is formed 
of a first boom section 13A and a second boom section 13B. The two 
sections of the boom allow the second section to slide within the first so 
that the boom can be locked at a desired length selected by the operator. 
The first section of the boom 13A is connected to the vertical member 9D 
of the parallelogram hitch while the box blade is connected to the far end 
of the second section of the boom 13B. Since here is a rigid connection 
between the movable vertical member of the parallelogram and the box 
blade, the lower surface of the box blade 3A will be maintained parallel 
to the horizontal plane and will gain all the benefits of this position 
even though it is located at the end of the boom. Grading can now be 
accomplished in areas that were previously inaccessible and can be done 
with much less difficulty. It is now possible with this embodiment of the 
invention to pass the boom over low obstructions, such as low walls or 
hedges, or place the boom in areas that are too narrow for the tractor to 
enter. 
The boom may be fabricated in several different ways and still accomplish 
the same results. For example the boom may be a single member or multiple 
members that fit within one another or slide past one another. The length 
of the boom may be adjusted from the tractor by means of an hydraulic 
cylinder connected between the sections of the boom. A collapsable, or 
multisection boom allows the boom to be drawn in towards the tractor for 
normal grading or extended for difficult to reach work. In this 
arrangement where the boom allows the blade to be drawn in close to the 
tractor for normal grading, the boom can remain connected to the tractor 
for all grading operations. 
A laser system is combined with the present invention to automatically and 
accurately produce a level grade. One embodiment of this system is shown 
in FIG. 3. In this Figure, a laser source generator 11 produces a beam 
which may be directed at the tractor or which rotate in a horizontal plane 
and strikes the tractor cyclically. This beam strikes a receiver 10 
located on a vertical extension 14 of vertical member 9D. The receiver 
detects whether its position in a horizontal plane lies above or below the 
beam and sends a signal to a computer 16 which sends a control signal to 
the hydraulic cylinder 12 to adjust the height of the box blade to keep 
the receiver nominally at the beam level and consequently the box blade at 
the desired height to produce a level grade parallel to the horizontal 
plane.