U.S. patent application number 09/766288 was filed with the patent office on 2002-09-12 for control system and method for controlling a screed head.
Invention is credited to Wray, Albert A., Yost, Jerald W., Zachman, Mark E..
Application Number | 20020127058 09/766288 |
Document ID | / |
Family ID | 25075984 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020127058 |
Kind Code |
A1 |
Zachman, Mark E. ; et
al. |
September 12, 2002 |
Control system and method for controlling a screed head
Abstract
A control system controls movement of individual hydraulically
moveable ends of a screed head carried by a boom of a machine so as
to maintain a selected elevational position between each end of the
screed head and a reference in a concrete paving application. One
of a pair of elevation receivers is mounted at each end of the
screed head, providing a first and second signals indicating the
position of the first and second ends of the screed head in
relation to the reference. A sensor, mounted on the screed head,
senses the orientation of the screed head along its length from the
first end to the second end and providing a third signal indicating
such orientation. A control circuit, responsive to the elevation
receivers and to the sensor, controls the hydraulically moveable
ends of the screed head using the first and second signals from the
elevation receivers when the first and second signals are
available, and controls the hydraulically movable ends of the
screed head using the third signal from the sensor and one of the
first and second signals from the elevation receivers when the
other of the first and second signals is not available.
Inventors: |
Zachman, Mark E.; (Dayton,
OH) ; Wray, Albert A.; (Sidney, OH) ; Yost,
Jerald W.; (Casstown, OH) |
Correspondence
Address: |
KILLWORTH GOTTMAN HAGAN & SCHAEFF, LLP
ONE DAYTON CENTRE, SUITE 500
ONE SOUTH MAIN STREET
DAYTON
OH
45402-2023
US
|
Family ID: |
25075984 |
Appl. No.: |
09/766288 |
Filed: |
January 19, 2001 |
Current U.S.
Class: |
404/84.5 ;
404/118; 404/75 |
Current CPC
Class: |
E01C 19/006
20130101 |
Class at
Publication: |
404/84.5 ;
404/75; 404/118 |
International
Class: |
E01C 023/07 |
Claims
What is claimed is:
1. A control system for controlling movement of individual
hydraulically moveable ends of a screed head carried by a boom of a
machine so as to maintain a selected elevational position between
each end of the screed head and a reference in a concrete paving
application as the screed head is moved toward the machine,
comprising: an elevation receiver, mounted on a first end of the
screed head, providing a first signal indicating the position of
the first end of the screed head in relation to the reference; an
elevation receiver, mounted on a second end of the screed head,
providing a second signal indicating the position of the second end
of the screed head in relation to the reference; a sensor, mounted
on the screed head, for sensing the orientation of the screed head
along its length from the first end to the second end and providing
a third signal indicating such orientation; and a control circuit,
responsive to the elevation receivers and to the sensor, for
controlling the hydraulically moveable ends of the screed head
using the first and second signals from the elevation receivers
when the first and second signals are available, and for
controlling the hydraulically movable ends of the screed head using
the third signal from the sensor and one of the first and second
signals from the elevation receivers when the other of the first
and second signals is not available.
2. The control system according to claim 1 for controlling movement
of individual hydraulically moveable ends of a screed head carried
by a boom of a machine so as to maintain a selected elevational
position between each end of the screed head and a reference in a
concrete paving application as the screed head is moved toward the
machine, in which the control circuit maintains the screed head in
an orientation such that the third signal remains substantially
constant when one of the first and second signals from the
elevation receivers is not available, whereby the orientation of
the screed head along its length from the first end to the second
end also is maintained substantially constant.
3. The control system according to claim 1 for controlling movement
of individual hydraulically moveable ends of a screed head carried
by a boom of a machine so as to maintain a selected elevational
position between each end of the screed head and a reference in a
concrete paving application as the screed head is moved toward the
machine, in which the sensor is an inclinometer mounted on the
screed head.
4. The control system according to claim 3 for controlling movement
of individual hydraulically moveable ends of a screed head carried
by a boom of a machine so as to maintain a selected elevational
position between each end of the screed head and a reference in a
concrete paving application as the screed head is moved toward the
machine, in which the inclinometer is a pendulum sensor with a low
pass filtered output.
5. The control system according to claim 1 for controlling movement
of individual hydraulically moveable ends of a screed head carried
by a boom of a machine so as to maintain a selected elevational
position between each end of the screed head and a reference in a
concrete paving application as the screed head is moved toward the
machine, in which the receivers are light detectors, and in which
the reference is established by a beam of light.
6. The control system according to claim 1 for controlling movement
of individual hydraulically moveable ends of a screed head carried
by a boom of a machine so as to maintain a selected elevational
position between each end of the screed head and a reference in a
concrete paving application as the screed head is moved toward the
machine, in which the receivers are laser light detectors and in
which the reference is established by a beam of laser light.
7. A control system for controlling movement of individual
hydraulically moveable ends of an elongated tool so as to maintain
a selected elevational position between each end of the tool and a
reference, comprising: an elevation receiver, mounted on a first
end of the tool, providing a first signal indicating the position
of the first end of the tool in relation to the reference; an
elevation receiver, mounted on a second end of the tool, providing
a second signal indicating the position of the second end of the
tool in relation to the reference; a sensor, mounted on the tool,
for sensing the orientation of the tool along its length from the
first end to the second end and providing a third signal indicating
such orientation; and a control circuit, responsive to the
elevation receivers and to the sensor, for controlling the
hydraulically moveable ends of the tool using the first and second
signals from the elevation receivers when the first and second
signals are available, and for controlling the hydraulically
movable ends of the tool using the third signal from the sensor and
one of the first and second signals from the elevation receivers
when the other of the first and second signals is not
available.
8. The control system for controlling movement of individual
hydraulically moveable ends of an elongated tool so as to maintain
a selected elevational position between each end of the tool and a
reference according to claim 7, in which the sensor is an
inclinometer mounted on the tool.
9. The control system for controlling movement of individual
hydraulically moveable ends of an elongated tool so as to maintain
a selected elevational position between each end of the tool and a
reference according to claim 7, in which the control circuit
maintains the tool in an orientation such that the third signal
remains substantially constant when one of the first and second
signals from the elevation receivers is not available, whereby the
slope of the tool along its length from the first end to the second
end also is maintained substantially constant.
10. The control system for controlling movement of individual
hydraulically moveable ends of an elongated tool so as to maintain
a selected elevational position between each end of the tool and a
reference according to claim 7, in which the inclinometer is a
pendulum sensor with a low pass filtered output.
11. A method of controlling the elevational position of
hydraulically moveable ends of a tool in relation to a reference
detected by elevation receivers attached to the ends of the tool,
when reception of one of the elevation receivers of the reference
is interrupted, comprising the steps of: (a) selecting a desired
elevational position of the tool with respect to the reference; (b)
sensing with the elevation receivers the position of the ends of
the tool in relation to the reference; (c) sensing the orientation
of the tool along its length from one end to the other; and (d)
controlling the elevational positions of the ends of the tool using
the sensed positions of the ends of the tool in relation to the
reference when such positions are both known, and controlling the
elevational positions of the ends of the tool using the sensed
position of one of the ends of the tool and the sensed orientation
of the tool along its length from one end to the other when such
positions are not both known.
12. The method of controlling the elevational position of
hydraulically moveable ends of a tool in relation to a reference
detected by elevation receivers attached to the ends of the tool,
when reception of one of the elevation receivers of the reference
is interrupted, according to claim 11, further comprising the steps
of: (e) detecting lateral movement of the tool generally in the
direction of the length of the tool; and (f) discontinuing
controlling the elevational positions of the ends of the tool using
the sensed orientation of the tool until the lateral movement of
the tool generally in the direction of the length of the tool is
terminated.
13. The method of controlling the elevational position of
hydraulically moveable ends of a tool in relation to a reference
detected by elevation receivers attached to the ends of the tool,
when reception of one of the elevation receivers of the reference
is interrupted, according to claim 11, in which the step of sensing
the orientation of the tool along its length includes the step of
sensing the orientation of the tool using an inclinometer.
14. The method of controlling the elevational position of
hydraulically moveable ends of a tool in relation to a reference
detected by elevation receivers attached to the ends of the tool,
when reception of one of the elevation receivers of the reference
is interrupted, according to claim 11, in which the elevation
receivers are light detectors and in which the reference is a
rotating beam of light.
15. The method of controlling the elevational position of
hydraulically moveable ends of a tool in relation to a reference
detected by elevation receivers attached to the ends of the tool,
when reception of one of the elevation receivers of the reference
is interrupted, according to claim 11, in which the elevation
receivers are laser light detectors and in which the reference is a
rotating beam of laser light.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a control system for
controlling movement of a tool carried by a machine and, more
specifically, to a control system for controlling movement of
individual hydraulically moveable ends of a tool which carries
laser receivers, even when one of the receivers does not receive
the transmitted plane of reference light.
[0002] In concrete paving operations, after concrete is poured, it
is commonly finished by drawing a tool, such as a screed head, over
the surface of the concrete. This smooths the surface of the
concrete before it cures. In asphalt paving operations, after
asphalt is laid, it is commonly leveled to a desired depth by
drawing a tool, such as also a screed head of a paver, over the
surface of the contour. Finally, in grading operations, a surface
is graded to a desired depth by drawing a tool, such as a blade of
a grader, over the surface of the contour. Thus, although the
physical configurations of the types of screed heads and the
grader's blade are not identical, the functions of these tools are
analogous.
[0003] Typically, hydraulic cylinders connected to each end of the
tool of the machine are used to raise and lower the ends of the
tool independently. It has been common to determine the elevational
positions of the ends of the tool by using a laser transmitter
which provides a rotating beam of laser light, effectively
producing a reference plane. The raising and lowering of the tool
are controlled by a control system that has a predetermined desired
elevational position for the surface.
[0004] A pair of laser receivers, one receiver mounted at each end
of the tool on an associated mast for vertical movement with the
tool, detects the reference plane and the relative elevation of the
ends of the tool with respect to the reference plane. A control
system of the machine then actuates hydraulic valves to supply
fluid to the hydraulic cylinders in response to these detected
levels. As a result, the elevation of each end of the tool can be
precisely controlled. Each of the receivers provides elevational
feedback to drive the hydraulics controlling the elevation of the
end of the tool with which it is associated.
[0005] A problem arises, however, if one the receivers is blocked
by something of an appreciable height, such as, for example, a
support column in a building. When a blockage occurs, there is a
need to maintain the relative elevation of the ends of the tool as
it is drawn toward the machine until the laser beam can be
reacquired by both receivers mounted at the ends of the tool.
[0006] One approach to this problem is to set up two laser
transmitters at the same elevation on opposite sides of the tool.
In this way, if a column blocks one of the transmitters, the other
transmitter is likely to be illuminating the receivers at the ends
of the tool, thereby compensating for the blockage. Essentially,
this eliminates all blind spots around the receivers. While
generally effective, this prior art method is disadvantageous in
that by requiring an additional transmitter, the cost of the
equipment is increased. Further, this method increases
significantly the time required to set up the equipment and
eliminate the possibility of a column block with the second laser
transmitter.
[0007] It is seen, therefore, that there is a need for a control
system and method for controlling movement of individually
hydraulically moveable ends of a tool, such as a screed head, to
maintain a selected elevational position between each end of the
tool and an elevation reference even when one of the elevation
receivers mounted on the ends of the tool fails to sense the
position of the end of the tool.
SUMMARY OF THE INVENTION
[0008] This need is met by a control system according to the
present invention for controlling movement of individual
hydraulically moveable ends of a tool, such as a screed head. The
screed head is carried by a boom of a machine in a concrete paving
application to maintain a selected elevational position between
each end of the screed head and a reference as the screed head is
moved toward the machine. The control system includes an elevation
receiver, mounted on a first end of the screed head, providing a
first signal indicating the position of the first end of the screed
head in relation to the reference, and an elevation receiver
mounted on a second end of the screed head, providing a second
signal indicating the position of the second end of the screed head
in relation to the reference. A sensor is mounted on the screed
head. The sensor senses the orientation of the screed head along
its length from the first end to the second end and provides a
third signal indicating this orientation. A control circuit is
responsive to the elevation receivers and to the sensor and
controls the hydraulically moveable ends of the screed head using
the signals. The control circuit uses the first and second signals
from the elevation receivers when the first and second signals are
available. The control circuit uses the third signal from the
sensor and one of the first and second signals from the elevation
receivers when the other of the first and second signals is not
available.
[0009] The control circuit preferably maintains the screed head in
an orientation such that the third signal remains substantially
constant when one of the first and second signals from the
elevation receivers is not available. In this manner, the
orientation of the screed head along its length from the first end
to the second end is maintained substantially constant.
[0010] The sensor may be an inclinometer mounted on the screed
head. Preferably, the inclinometer is a pendulum sensor with a low
pass filtered output.
[0011] Preferably, the receivers are light detectors, and the
reference is established by a beam of light. Even more preferably,
the receivers are laser light detectors and the reference is
established by a beam of laser light.
[0012] A method of controlling the elevational position of
hydraulically moveable ends of a tool according to the present
invention in relation to a reference detected by elevation
receivers attached to the ends of the tool, when reception of one
of the elevation receivers of the reference is interrupted,
includes the steps of: (a) selecting a desired elevational position
of the tool with respect to the reference; (b) sensing with the
elevation receivers the position of the ends of the tool in
relation to the reference; (c) sensing the orientation of the tool
along its length from one end to the other; and (d) controlling the
elevational positions of the ends of the tool using the sensed
positions of the ends of the tool in relation to the reference when
such positions are both known, and controlling the elevational
positions of the ends of the tool using the sensed position of one
of the ends of the tool and the sensed orientation of the tool
along its length from one end to the other when such positions are
not both known. The method may further include the steps of (e)
detecting lateral movement of the tool generally in the direction
of the length of the tool; and (f) discontinuing controlling the
elevational positions of the ends of the tool using the sensed
orientation of the tool until the lateral movement of the tool
generally in the direction of the length of the tool is
terminated.
[0013] The step of sensing the orientation of the tool along its
length may include the step of sensing the orientation of the tool
using an inclinometer. The elevation receivers preferably are light
detectors and the reference is preferably a rotating beam of light.
Even more preferably, the elevation receivers may be laser light
detectors and the reference may be a rotating beam of laser
light.
[0014] Other objects, features and advantages will appear more
fully in the course of the following discussion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates a screeding operation of a typical
concrete screed utilizing the control system of the present
invention;
[0016] FIG. 2 is an enlarged partial view of an inclinometer
mounted on the screed head;
[0017] FIG. 3 is a schematic representation of an inclinometer and
associated circuitry of the type incorporated in the present
invention;
[0018] FIG. 4 is a schematic representation of a screed head, and
elevation receivers, illustrating a technique for adjusting for
offsets in inclinometer mounting; and
[0019] FIG. 5 is a flow chart diagram illustrating operation of the
system of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0020] Referring to FIG. 1 of the drawings, the device implementing
the preferred embodiment of invention herein is a control system
for a machine 2, such as a concrete screed 4, that typically
incorporates a laser transmitter 10 mounted in a stationary
position. The transmitter 10 projects a rotating laser beam 12, in
order to provide a reference. A pair of elevation receivers, such
as laser receivers 14 and 15, and a control box 16 including a
control circuit are provided for controlling electro-hydraulic
control values (not shown) of the concrete screed 4. The concrete
screed 4 further includes a pair of masts 18, each carrying one of
the pair of laser receivers 14 and 15, attached with and moved
generally vertically, independently, with respective ends 20 and
21, respectively, of a tool or screed head 22. The screed head 22
is attached to the end of a hydraulic boom arm 23 which moves the
screed head 22 in longitudinal direction Y. During operation of the
screed, the control box 16 causes actuation of the hydraulic valves
such that hydraulic cylinders 24 and 25 at the ends 20 and 21,
respectively, independently raise or lower the ends 20 and 21 of
the screed head 22, as needed, as it is drawn in the direction Y
over the surface of uncured concrete 26. It is to be appreciated
that the raising and lowering of the screed head 22 in the vertical
direction are accomplished in response to reception of the
reference laser beam 12 by the pair of laser receivers 14 and 15.
The laser beam 12 rotates about an axis, as indicated at 28, so as
to define the reference as a reference plane of laser light. The
first and second receivers 14 provide respective first and second
signals indicating the position of the respective ends of the
screed head 22 in relation to the reference 12.
[0021] As discussed above, a difficulty arises with the
conventional control system of this type when the path of the laser
beam 12 to one of the pair of elevation receivers 14 is temporarily
blocked by a column or other obstruction at a work site. In the
present invention, this difficulty is addressed by the use of a
sensor 30, mounted on the screed head 22, for sensing the
orientation of the screed head 22 along its length from the first
end to the second end. The sensor 30 preferably is an inclinometer
that is mounted on the screed head as best shown in FIG. 2. The
sensor 30 provides a third signal that indicates the orientation of
the screed head. A control circuit in box 16 is responsive to the
elevation receivers 14 and 15 and to the sensor 30 for controlling
the hydraulically moveable ends 20 and 21 of the screed head 22
using the first and second signals from the elevation receivers 14
and 15 when the first and second signals are available, and for
controlling the hydraulically movable ends 20 and 21 of the screed
head 22 using the third signal from the sensor 30 and one of the
first and second signals from the elevation receivers 14 and 15
when the other of the first and second signals is not available.
The control circuit maintains the screed head 22 in an orientation
such that the third signal remains substantially constant when one
of the first and second signals from the elevation receivers 14 and
15 is not available. By this approach, the screed head is also
maintained in a substantially constant orientation along its length
from the first end to the second end.
[0022] As stated above, the sensor 30 is preferably an
inclinometer. An appropriate inclinometer 32 and associated
circuitry is shown in FIG. 3. As will be apparent, the inclinometer
32 is a pendulum sensor that incorporates a pendulum arm 34 which
pivots about axis 36, moving rotor 38. Rotor 38 includes a
plurality of windings 40 which rotate with the rotor and cooperate
with a permanent magnet stator 42. The output of the windings 40 is
supplied to with a low pass filter 44 and is then digitized in A-D
converter 46. As will be appreciated phototransistors 48 cooperate
with LED's 50 to determine when the inclinometer has been pivoted
sufficiently that the pendulum 34 does not prevent the light from
the LED's 50 from striking the transistors 48. When one of the
transistors 48 is illuminated, a signal is applied to amplifier 52
which then drives windings 40 until the pendulum 34 is brought back
into position to shield both of the phototransistors 48. The
amplitude of this driving current provides an indication of the
degree of inclination of the sensor 30.
[0023] It will be appreciated that the sensor 30 may not be mounted
in perfectly horizontal position on the screed head 22. If one were
to assume that when the receivers 14 and 15 were on grade, i.e., at
a position that indicates by appropriate receipt of the laser beam
12 that the screed head 22 is positioned at the correct height and
orientation, the inclinometer 30 would read zero slope, and the
algorithm of the slope control system would be relatively simple.
The controller would simply drive until the slope sensor read zero
whenever one of the laser receiver signals was lost. This
assumption is not always correct. Rather, the laser plane will have
some finite slope to it resulting in elevation offsets and the
slope sensor that is mounted to the screed head will also have some
slope offset to it (due to the mechanical mounting
characteristics). The following algorithm has been provided to deal
with these issues.
[0024] Variable Definitions:
[0025] All angles in the remainder of this document are expressed
in terms of slope (rise over run) and are referenced to
horizontally flat.
[0026] .DELTA..sub.LrLeft is the deviation from On-Grade point of
the laser receiver on the left side.
[0027] .DELTA..sub.LrRight is the deviation from On-Grade point of
the laser receiver on the right side.
[0028] .DELTA..sub.Lr is the total vertical error as measured by
the laser receivers. It is equivalent to
.DELTA..sub.LrRight-.DELTA..sub.LrLeft.
[0029] w is the width of the controlled item.
[0030] .theta..sub.measured is the angle that is measured by the
slope sensor mounted to the controlled item.
[0031] .theta..sub.sensor.sub..sub.--.sub.offset is the angular
offset of the slop sensor. It is equal to .theta..sub.measured when
the controlled item is perfectly flat.
[0032] w' is the length of the base of a right triangle created
from a hypotenuse w and the angle
(.theta..sub.measured-.theta..sub.sensor.sub..- sub.--.sub.offset).
This is in essence the horizontal component of the controlled item
when the controlled item is elevated on one end.
[0033] .theta..sub.grade is the angle generated from the slope
laser beam plane.
[0034]
.theta..sub.measured-.theta..sub.sensor.sub..sub.--.sub.offset is
equivalent to .theta..sub.grade when the implement is on-grade.
[0035] If .DELTA..sub.Lr is small compared to w, then the
approximation w.apprxeq.w' can be made.
[0036] When the laser strikes both laser receivers 14 and 15 at
approximately the same time, the data .theta..sub.measured,
.DELTA..sub.Lr, and w are available.
[0037] With this data, .theta..sub.offset can be calculated as
follows:
[0038]
.theta..sub.sensor.sub..sub.--.sub.offset=.theta..sub.measured-.the-
ta..sub.grade
[0039] but .theta..sub.grade is equivalent to 1 LR w .
[0040] This makes the assumption that the distance from On-Grade
point of the receivers to the cutting edge of the screed head is
equivalent on both sides. If this is not the case, an additional
offset is created which can be combined with
.theta..sub.sensor.sub..sub.--.sub.offset to produce a single
angular offset.
[0041] Therefore by substituting the following can be derived, 2
sensor_offset = measured - LR w
[0042] Now that .theta..sub.sensor.sub..sub.--.sub.offset is known,
if on the next laser sweep, one of the laser signals is missing,
the system can drive screed head 22 using a calculated
.DELTA..sub.LR as
.DELTA..sub.LR=.theta..sub.measured-.theta..sub.sensor.sub..sub.--.sub.of-
fset.
[0043] Reference is now made to FIG. 5, which is a flow chart
diagram illustrating the manner in which the operator smooths the
concrete surface as he repeatedly pulls the screed head 22 toward
the machine 4. The operator extends the boom 23 and toggles the
land switch on control box 16, as indicated at 54. A timer and a
lower valve drive are initiated. If either receiver 14 or 15 has
detected the laser reference 12 at 56, but not both, then the data
from the sensor 30 is used at 58 and 60 in place of the missing
data from the receivers. The valve drives for both sides of the
screed head are stopped at 62 when the screed head is one inch from
being at the correct height, i.e., "on grade." The system is then
placed in automatic mode, and the screed head is slowly lowered to
the on-grade height. The hydraulic boom arm 23 is then retracted
and the screed head smooths the concrete surface 26. If a signal
from one of the receivers 14 and 15 is not available during this
operation the control circuit maintains the screed head in an
orientation such that the third signal from the sensor 30 remains
constant. By this approach, the slope of the screed head along its
length from the first end to the second end also is maintained
substantially constant until the receiver 14 or 15 reacquires the
beam 12.
[0044] Depending upon the configuration of the structure around the
concrete surface being smoothed by the screed head, it may not be
possible to move the screed head in a straight line toward the
machine. It may, for example, be necessary for the operator to
shift the beam 23 from side to side to avoid columns and the like
as the screed is moved. This will, of course, induce an error in
the output of the sensor 30. To avoid this, the lateral movement of
the screed head generally in the direction of the length of the
screed head 22 is detected. Controlling the elevational positions
of the ends of the screed head using the sensed orientation of the
screed head is discontinuing until this lateral movement is
terminated. With many screed machines the operator must actuate a
switch to activate the hydraulic valves to rotate the screed head.
The control circuit senses actuation of this switch, and
discontinues use of the output of the sensor 30 until rotation of
the screed head 22 is terminated.
[0045] Having described the invention in detail and by reference to
preferred embodiments thereof, it will be apparent that
modifications and variations are possible without departing from
the scope of the invention defined in the appended claims.
* * * * *