U.S. patent number 3,879,149 [Application Number 05/290,237] was granted by the patent office on 1975-04-22 for method and apparatus for providing grade control for the screed of a paver or the like.
This patent grant is currently assigned to Barber-Greene Company. Invention is credited to Harry A. Barber, Ronald W. Beaty, Donald W. Smith.
United States Patent |
3,879,149 |
Smith , et al. |
April 22, 1975 |
METHOD AND APPARATUS FOR PROVIDING GRADE CONTROL FOR THE SCREED OF
A PAVER OR THE LIKE
Abstract
A mobile grade reference device includes first means for sensing
the vertical distance between successive points along a
predetermined path on the subgrade and a grade reference point on
such grade reference device. Second means are provided for
continuously generating and storing first intelligence
representative of the successive vertical distances sensed by such
first means as the grade reference device travels over the
subgrade. Third means on the paver senses the vertical distance
between successive points along said predetermined path on the
subgrade and a point on the screed. Fourth means continuously
generate second intelligence representative of the successive
vertical distances sensed by the third means as the paver travels
along the aforesaid predetermined path. Fifth means compare the
first and second intelligence as the latter is generated and
produce grade control signals representative of the differences
between the vertical distances sensed by the first and third means
at the same points on the subgrade. A control mechanism for the
screed is actuated by these grade control signals.
Inventors: |
Smith; Donald W. (Aurora,
IL), Beaty; Ronald W. (Aurora, IL), Barber; Harry A.
(Aurora, IL) |
Assignee: |
Barber-Greene Company (Aurora,
IL)
|
Family
ID: |
23115098 |
Appl.
No.: |
05/290,237 |
Filed: |
September 18, 1972 |
Current U.S.
Class: |
404/72;
404/84.1 |
Current CPC
Class: |
E01C
19/008 (20130101) |
Current International
Class: |
E01C
19/00 (20060101); E01c 019/00 () |
Field of
Search: |
;404/84,83,72
;37/DIG.20 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Byers, Jr.; Nile C.
Attorney, Agent or Firm: McDougall, Hersh & Scott
Claims
We claim:
1. The method of controlling a traveling roadway surface
preparation machine for making a continuous roadway surface, which
machine has a grade control element controllable in response to a
grade control signal, said method comprising the steps of:
a. moving a mobile grade reference device over the subgrade along a
predetermined path and continuously generating grade control
intelligence having a horizontal control data factor and a factor
representative of the vertical distances between successive points
on the subgrade and an averaged grade reference point on said
device;
b. storing said grade control intelligence;
c. moving the roadway surface preparation machine over the subgrade
along said predetermined path and continuously generating grade
profile intelligence representative of the vertical distances
between a point on said grade control element and successive points
on the subgrade corresponding to said first mentioned successive
points;
d. integrating said grade control intelligence with said grade
profile intelligence and generating grade control signals
representative of the differences between the respective vertical
distances of the former and the latter at corresponding ones of
said points on the subgrade; and
e. controlling said grade control element in response to said grade
control signals.
2. The method according to claim 1 wherein a fixed horizontal
distance is maintained between said grade reference device and said
machine and wherein the step of storing said grade control
intelligence includes moving a member along an endless path at
least a portion of which is representative of the horizontal
distance between said grade reference point and said point on the
machine.
3. The method according to claim 1 wherein the step of storing said
grade control intelligence includes continuously recording the same
on a medium representative of the progressive horizontal distances
from a fixed point to said first mentioned points on the
subgrade.
4. The method according to claim 1 wherein the step of storing said
grade control intelligence includes continuously recording the
latter by the use of a tangible medium and depositing the same on
the subgrade according to a pattern corresponding to said
predetermined path.
5. The method according to claim 1 wherein the step of storing said
grade control intelligence includes continuously recording the
latter by the use of a tangible medium in the form of a strip
having vertical distance information thereon and depositing the
strip on the subgrade along a line corresponding to said
predetermined path.
6. The method of providing grade control for the screed of a paver
comprising the steps of:
a. moving a mobile grade reference device over the subgrade along a
predetermined path and generating first grade profile information
having a horizontal control data factor and a factor representative
of the vertical distances between successive points along the
subgrade and an average grade reference point on the grade
reference device;
b. storing said first grade profile information;
c. moving the paver over the subgrade along said predetermined path
and generating second grade profile information representative of
the vertical distances between an element on the screed and
successive points along the subgrade corresponding to said first
mentioned successive points;
d. comparing said second grade profile information with said first
grade profile information at the time the former is generated and
thereby generating error signals representative of the difference
between the corresponding vertical distances of respective first
and second grade profile information; and
e. operating said screed in response to said error signals.
7. The method according to claim 6 wherein a fixed horizontal
distance is maintained between said grade reference device and said
paver and wherein the step of storing said first grade profile
information includes moving a member along an endless path at least
a portion of which is representative of the horizontal distance
between said grade reference element and said elment on the
machine.
8. The method according to claim 6 wherein the step of storing said
first grade profile information includes continuously recording the
same on a medium representative of the progressive horizontal
distances from a fixed point to said first mentioned points on the
subgrade.
9. The method according to claim 6 wherein the step of storing said
first grade profile information includes continuously recording the
latter by the use of a tangible medium and depositing the same on
the subgrade according to a pattern corresponding to said
predetermined path.
10. The method according to claim 6 wherein the step of storing
said first grade profile information includes continuously
recording the latter by the use of a tangible medium in the form of
a strip having vertical distance information thereon and depositing
the strip on the subgrade along a line corresponding to said
predetermined path.
11. The method of providing grade control for the screed of a paver
comprising the steps of:
a. moving a mobile grade reference device over the subgrade along a
predetermined path and generating first information having a
horizontal control data factor and a factor representative of the
vertical distances between successive first points on the subgrade
and corresponding second points along the path described by
movement of a grade reference element on the grade reference device
as the latter moves laong said predetermined path;
b. storing said first information;
c. moving the paver over the subgrade and along said predetermined
path and generating second information representative of the
vertical distances between successive points on the subgrade
corresponding to said first points and third points along the path
described by movement of an element on the screed as the latter
moves along said predetermined path;
d. comparing said first information with said second information as
the latter is generated and thereby generating error signals
representative of the differences between the corresponding
vertical distances of said first and second information,
respectively; and
e. operating screed grade control mechanism in response to said
error signals such that said element on the screed describes a path
as it travels over the subgrade corresponding to the path described
by said grade reference element as the latter moves over the
subgrade.
12. The method according to claim 11 wherein the step of storing
said information includes recording the latter on a medium
representative of the progressive horizontal distances said first
points bear with respect to a fixed point on the subgrade.
13. The method according to claim 11 wherein the step of storing
said first information includes continuously recording the latter
by the use of a tangible medium and depositing the same on the
subgrade longitudinally thereof.
14. The method acording to claim 11 wherein the step of storing
said first information includes continuously recording the latter
by the use of a tangible medium in the form of a strip having
vertical distance information thereon and depositing the strip on
the subgrade longitudinally thereof.
15. The method of making a roadway comprising the steps of:
a. moving a mobile grade reference device over the subgrade and
along a predetermined path;
b. continouously sensing, during movement of said grade reference
device, the vertical distances between the subgrade and a grade
reference point on said grade reference device thereby to generate
successive first bits of vertical distance information:
c. continously sensing, during movement of said grade reference
device, the progressive horizontal distances between said grade
reference point and a fixed reference point on the subgrade;
d. correlating and storing said first bits of information with said
horizontal distance information;
e. moving roadway making machinery over the subgrade and along a
predetermined path, which machinery includes a propulsion unit and
grade control equipment movable vertically relative thereto;
f. continuously sensing, during such movement of the machinery, the
vertical distances between the subgrade and a point on the grade
control equipment thereby to generate successive second bits of
vertical distance information;
g. comparing said second bits of information with the corresponding
first bits of information as a determined by said horizontal
distance information to generate successive error signals
representative of the differences between corresponding first and
second bits of information; and
h. operating said grade control equipment on said machinery in
response to the generation of said error signals thereby to make a
roadway having a surface defining a grade profile corresponding to
the path of movement described by said grade reference point.
16. In a mobile roadway making apparatus of the type which deposits
a layer of roadway material on the subgrade and which includes
vertically movable mechanism for controlling the grade profile
defined by the surface of said layer of material in response to
grade control signals, the improvement comprising:
a. a mobile grade reference device and means for moving the same
over the subgrade along a predetermined path;
b. first means on said grade reference device for sensing the
vertical distance between a point on the subgrade and a grade
reference point on said grade reference device;
c. second means for
1. continuously generating first intelligence having a horizontal
control data factor and a factor representative of the successive
vertical distances sensed by said first means as it travels along
said predetermined path; and
2. storing said first intelligence;
d. third means on said mobile apparatus for sensing the vertical
distance between a point on the subgrade and a point on said
vertically movable mechanism;
e. fourth means for continuously generating second intelligence
representative of the successive vertical distances sensed by said
third means as it travels along said predetermined path; and
f. fifth means for comparing said first intelligence with said
second intelligence as the latter is generated thereby to produce
grade control signals representative of the differences between the
corresponding vertical distances sensed by said first and third
means, respectively.
17. The improvement according to claim 16 further defined by:
a. said mobile grade reference device including a plurality of
subgrade engaging members which are spaced apart longitudinally of
said predetermined path;
b. linkage means connecting said members;
c. said linkage means including a generally horizontally disposed
linear element which is moved vertically in response to vertical
movements of said subgrade engaging members, which linear element
has a point therealong defining said grade reference point; and
d. said first means including a subgrade engaging element and
transducing means engaged with the latter and said linear element
at said grade reference point for supplying information to said
second means.
18. The improvement according to claim 16 further defined by, other
means connecting said mobile grade reference device with said
mobile apparatus forwardly of the latter and at a fixed distance
with respect thereto such that movement of the mobile apparatus
imparts corresponding movement to the mobile grade reference
device.
19. The improvement according to claim 18 further defined by, said
second means including a subgrade engaging member and means
mounting the same for movement with said mobile grade reference
device and along an endless path at least a portion of which is
representative of the horizontal distance between said grade
reference point and said point on said vertically movable
mechanism.
20. In a mobile roadway making apparatus of the type which deposits
a layer of roadway material on the subgrade and which includes
vertically movable mechanism for controlling the grade profile
defined by the surface of said layer of material in response to
grade control signals, the improvement comprising:
a. a mobile grade reference device and means for moving the same
over the subgrade along a predetermined path;
b. first means on said grade reference device for sensing the
vertical distance between a point on the subgrade and a grade
reference point on said grade reference device;
c. second means for
1. continuously generating first intelligence representative of the
successive vertical distances sensed by said first means as it
travels along said predetermined path; and
2. storing said first intelligence;
d. third means on said mobile apparatus for sensing the vertical
distance between a point on the subgrade and a point on said
vertically movable mechanism;
e. fourth means for continuously generating second intelligence
representative of the successive vertical distances sensed by said
third means as it travels along said predetermined path;
f. fith means for comparing said first intelligence with said
second intelligence as the latter is generated thereby to produce
grade control signals representative of the differences between the
corresponding vertical distances sensed by said first and third
means, respectively;
g. said mobile grade reference device being separate from said
mobile apparatus; and
h. powered mobile means engaged with said mobile grade reference
device for moving the same along said predetermined path
independently of said mobile apparatus.
21. The improvement according to claim 20 further defined by, said
second means including a subgrade engaging member and means
mounting the same for movement with said mobile grade reference
device and along an endless path at least a portion of which is
representative of the progressive horizontal distances between a
fixed point on the subgrade and said grade reference point.
22. The improvement according to claim 16 wherein said mobile
apparatus is a paver and wherein said vertically movable mechanism
is a screed.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention relates to control systems for
roadway making machinery, and more particularly to systems for
providing grade control for a mobile apparatus of the type which
forms a roadway by applying a layer of roadway material to the
subgrade. Specifically, the invention concerns a method and
apparatus for providing grade control to the screed of a paver.
2. The Prior Art
In the use of an asphalt paving machine, for example, an external
grade reference device, from which grade sensings are taken, is
preferably provided. As is known to those skilled in the art, an
asphalt paving machine for use with an external grade reference
device includes an automatic screed control system. Such a system
includes a feeler or sensor which engages the external reference
wire or stringline; this external reference establishes a reference
plane independently of the paving machine. The feeler or sensor
activates a control mechanism, usually hydraulically or
electrically operated, to change the screed level; this may be
achieved by raising or lowering the pivot points of the draft arms
which mount the screed or by pivoting the screed with respect to
the draft arms.
The external reference may be provided by erecting a wire
stringline supported in parallel relation to the desired gradeline.
This is disadvantageous in that erection of such stringline is time
consuming. Further, the stringline interferes with the free
movement of men and equipment along the subgrade.
In some instances, an existing curb or adjacent pavement surface
parallel to the desired grade may be used as the external reference
device. Quite often, such a curb or pavement surface is not
available; in such a situation, a mobile grade reference device is
frequently employed. Such a mobile grade reference device is
connected to the paver for movement therewith. This mobile grade
reference device, which usually mounts a stringline defining the
external reference plane, includes plural shoes or skids which ride
over the subgrade during movement of the paving machine. As used
herein, the term "subgrade" has reference to the surface which is
to receive the material being laid by the roadway making machine,
whether bituminous material, graded earth, or a layer of aggregate
placed on the earth.
As is known to those skilled in the art, a mobile grade reference
device of the type under consideration provides optimum results
when the device is of substantial length, say at least thirty feet,
and is preferably provided with a considerable number of
longitudinally spaced subgrade engaging shoes or skids. In this
regard, reference is made to the copending application of Munyon
and Beaty, Ser. No. 202,127, filed Nov. 26, 1971, now Pat. No.
3,771,882, and assigned to the assignee of the present invention. A
linkage system connects the various subgrade engaging members and
supports the stringline which is engaged by the sensor of the
automatic screed control mechanism. The most accurate sensings are
obtained by having the sensor engage the stringline adjacent the
longitudinal midpoint of the mobile grade reference device. As
explained in Munyon Pat. 3,285,148, assigned to the assignee of the
present application, optimum results are obtained when the sensor
is mounted forwardly of the forward portion of the screed,
preferably adjacent such forward portion. With these last two
mentioned requirements in mind, it necessarily follows that the
mobile grade reference device must be mounted adjacent one side of
the paver with the longitudinal midpoint of the grade reference
device located just forwardly of the forward portion of the
screed.
In many instances, the mobile grade reference device cannot be
mounted adjacent one side of the paver for movement therewith
because the surface adjacent the subgrade is unsuitable for
movement of the mobile grade reference devices. For example, the
area adjacent and to one side of the subgrade may have a grade
profile which does not correspond to the grade profile of the
subgrade; or, obstructions may be located on such area adjacent the
subgrade.
When such conditions have been encountered, one practical
alternative is to mount the mobile grade reference device forwardly
of the screed and within the lateral extremities thereof using the
linkage mechanism shown in the copending application of Beaty and
Martenson, Ser. NO. 278,299, filed Aug. 7, 1972, now Pat. No.
3,811,787, and assigned to the assignee of the present application.
The mechanism described and claimed in the aforementioned Beaty and
Martenson application provides quite satisfactory results; however,
such mechanism does require special means for attaching the grade
reference device to the screed and also requires that the grade
reference device be limited to an effective length of twenty feet
or so.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention has to do with methods and apparatus whereby
a mobile grade reference device, which may be of any desired
length, is moved over the subgrade in advance of the roadway making
machinery. According to one embodiment of the apparatus of the
invention, the mobile grade reference device is attached to the
paver forwardly thereof and is moved or pushed ahead of the paver.
The mobile grade reference device includes means for sensing the
vertical distance between successive points along a predetermined
path on the subgrade and a grade reference point on the
longitudinal midpoint of the grade reference device. Means are
provided for continuously generating and storing first intelligence
representative of the successive vertical distances sensed by the
mobile grade reference device as it travels along the subgrade. The
paver includes sensing means adjacent the forward portion of the
screed for sensing the vertical distance between a reference point
on the screed and successive points on the subgrade along said
predetermined path. Means are provided for continuously generating
second intelligence representative of the successive vertical
distances sensed at the screed as the paver moves along the same
predetermined path. The mobile grade reference device carries a
subgrade engaging wheel. Rotation of this wheel provides
information representative of the horizontal distance between the
grade reference sensing points on the grade reference device and on
the screed. This information is used for comparing the first
intelligence with the second intelligence as the latter is
generated thereby to produce grade control signals representative
of the differences between vertical distances sensed at the grade
reference device and at the screed for each of the same points on
the subgrade. These grade control signals operate the automatic
screed level control mechanism.
In another embodiment of the invention, the mobile grade reference
device is not connected with the paver and is propelled
independently over the subgrade by powered means separate from the
power or motive means of the paver. In this embodiment, the first
intelligence generated and stored by the mobile grade reference
device is correlated with horizontal position identification data
representative of the progressive horizontal distances between the
grade reference point on the mobile grade reference device and a
fixed point adjacent the subgrade. This first intelligence is
retrieved as the second intelligence is generated at the screed
thereby to provide the aforementioned grade control signals
representative of the differences between the corresponding
vertical distances sensed at the mobile grade reference device and
at the screed.
A primary object of the present invention is the provision of a new
and improved method and apparatus for providing grade control for a
roadway making apparatus wherein a mobile grade reference device is
moved over the subgrade in advance of the roadway making
machinery.
Another object of the present invention is the provision of a
method for controlling the screed of a paver or the like which
includes the steps of moving the mobile grade reference device over
the subgrade in advance of the paver, storing the grade profile
reference data generated by sensing means on the mobile grade
reference device, and then retrieving this data when the paver is
moved over the subgrade.
Another object of the present invention is the provision of a
method for controlling the screed of a paver or the like which
includes the steps of advancing a mobile grade reference device
over the subgrade along a predetermined path in advance of the
paver, generating and storing first intelligence representative of
the successive vertical distances between the subgrade and a
reference point on the mobile grade reference device, moving the
paver along said path over the subgrade and generating second
intelligence representative of the successive vertical distances
between the subgrade and a grade reference point on the screed and
then comparing the first intelligence with the second intelligence
as the latter is generated thereby to produce grade control signals
representative of the differences between corresponding vertical
distances sensed by the grade reference device and the paver,
respectively.
Still another object of the present invention is the provision of a
new and improved apparatus for carrying out the aforesaid method,
which apparatus includes, a mobile grade reference device which may
be connected to the paver forwardly thereof or which may be
independent of the paver and moved over the subgrade by separate
powered means, first means on the grade reference device for
sensing the vertical distance between a point on the subgrade and a
grade reference point on the mobile grade reference device, second
means for continuously generating and storing first intelligence
representative of the successive vertical distances sensed by such
first means as the mobile grade reference device travels along a
predetermined path over the subgrade, third means on the paver for
sensing the vertical distances between a point on the subgrade and
a reference point on the screed, fourth means for continuously
generating second intelligence representative of the successive
vertical distances sensed by said third means as the paver travels
along said predetermined path over the subgrade, and fifth means
for comparing the first intelligence with the second intelligence
as the latter is generated thereby to produce grade control signals
representative of the differences between the corresponding
vertical distances sensed by said first and third means,
respectively.
These and other objects and advantages of the present invention
will become apparent from the following specification disclosing a
preferred embodiment shown in the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view, largely schematic in form, of
one embodiment of the apparatus of the present invention;
FIG. 2 is a reduced top plan view of the apparatus of FIG. 1
showing the same positioned on a subgrade;
FIG. 3 is an enlarged side view of the vertical distance sensing
means attached to the screed;
FIG. 4 is an enlarged side view of the vertical distance sensing
means attached to the mobile grade reference device;
FIG. 5 is a block diagram of a system for generating and storing
the profile grade reference data sensed at the mobile grade
reference device and for comparing such data with the profile grade
reference data sensed at the screed of the paver; and
FIG. 6 is a side view, largely schematic in form, of another
embodiment of the apparatus of the present invention.
DESCRIPTION OF THE METHOD AND PREFERRED EMBODIMENTS OF THE
INVENTION
The method and apparatus of the present invention is herein
described and illustrated within the context of an asphalt paving
machine. However, the invention is not to be limited for use with
such a machine as the invention has broader applicability. For
example, the present invention may be used with other roadway
making equipment of the type adapted to apply roadway material in
the form of a layer to an existing subgrade, concrete finishing
machines and certain types of graders being representative of this
type of equipment.
Referring now to FIGS. 1 and 2, an asphalt paver, generally
designated 10, of the type well known to those skilled in the art
includes a screed 11 towed behind the paver by a pair of draft arms
12 and 14. These draft arms are pivotally mounted at their forward
ends to the paver. Powered means, hydraulically or electrically
operated, are provided for raising or lowering the forward ends of
the draft arms to vary the angle of attack of the screed for
decreasing or increasing the thickness of the asphalt layer so as
to provide grade control. The angle of attack of the screed may
also be varied by pivoting the screed with respect to the draft
arms in which case the forward ends of the latter are secured to
the paver by fixed pivots.
The paver 10 is preferably provided with an automatic screed
control system of the type shown in the aformentioned Munyon Pat.
No. 3,285,148. According to the automatic system disclosed in this
Munyon patent, a sensor mounted adjacent one side of the paver
engages the external reference device and supplies signals of the
appropriate direction and magnitude for actuating the powered means
for one of the draft arms. Transverse slope control means are
provided to raise and lower the pivot axis of the other draft arm
thereby to maintain the predetermined slope. Reference should be
had to the Munyon patent for a detailed explanation of the
automatic screed control system.
A sensing device, generally designated 15, is mounted to the screed
for movement in unison therewith, as by means of a bracket 16. The
sensing device includes a rotary transducer 18 (FIG. 3) including a
shaft 19 mounting an arm 20. This arm is pivotally engaged with a
shoe or skid 21, the latter being adapted to engage the subgrade
just forwardly of the forward portion of the screed 11. As will be
explained hereinbelow, the transducer 16 produces an electrical
signal which varies in proportion to the amount of rotation of the
shaft 19 thereby producing a signal representative of the vertical
distance sensed between the subgrade and a given reference point on
the screed. Of course, other forms of transducers, such as a linear
transducer, could be provided to produce the appropriate vertical
distance signal.
Referring again to FIGS. 1 and 2, a mobile grade reference device
is generally designated 24. The mobile grade reference device
includes plural pairs of subgrade engaging shoes or skids 25 each
pivotally engaged with arms or links 26. The arms 26 are pivotally
engaged with other linkage 27 which supports a stringline or wire
28. A preferred form of mobile grade reference device is disclosed
and claimed in the aforementioned application of Munyon and Beaty,
Ser. No. 202,127, now Pat. No. 3,771,892, reference should be had
to that application for a detailed description of the mobile grade
reference device.
A sensing device, generally designated 30, is connected with the
mobile grade reference device 24 adjacent the longitudinal midpoint
of the latter. This sensing device includes a rotary transducer 31
including a shaft 32 mounting an arm 33. A follower element 34 is
mounted on the distal end of the arm 33, which follower engages the
stringline 28. The transducer 31 is mounted on a subgrade engaging
skid or shoe 36, which shoe is pivotally connected with a link 37,
the latter being pivotally connected to the linkage 27 forming part
of the mobile grade reference device.
It will be apparent that the sensing device 30 will continuously
sense or measure the vertical distance between the stringline 28
and the subgrade at the shoe 36. The rotary transducer 31, as will
be explained hereinbelow, produces an electrical signal which
varies in proportion to the vertical distance between the subgrade
and the stringline.
In the embodiment of the present invention now being described, the
grade reference device 24 is moved along the path over the subgrade
by a powered wheel apparatus 40 of any suitable form, this
apparatus being connected with the mobile grade reference device by
a bracket or arm 41. Thus, it is seen that the mobile grade
reference device 24 is independent of the paver and is propelled
over the subgrade by powered means separate from the motive or
power means of the paver 10. At this time it should be mentioned
that the mobile grade reference device, since it is separate from
the paver, may be of any desired length, say forty or fifty feet or
even longer, to provide the optimum trace approximating the means
profile grade of an undulating or otherwise uneven surface to be
paved.
A subgrade engaging wheel 44 is connected to the linkage 27 of the
mobile grade reference device by appropriate pivotally mounted arms
or links 45, 46. Such wheel is rotated by reason of its engagement
with the subgrade as the mobile grade reference device is moved
over the subgrade thereby to provide the necessary horizontal
control data which is correlated with the vertical sensings taken
by the sensing device 30. The wheel 44 may be fitted with
mechanical or magnetic switches, for example, to provide electrical
pulse signals for each unit of length of travel along the subgrade,
which unit may be a single revolution of the wheel 44 as well as a
fraction or multiple thereof. Since an unacceptable accumulation of
errors would result if the wheel 44 were to measure horizontal
distances of substantial length along the roadway subgrade,
preferably horizontal distance control points in the form of stakes
or the like are longitudinally spaced apart along the path of
travel of the mobile grade reference device at predetermined
locations, say 50 to 100 foot intervals, such that the component
(to be referred to hereinbelow) which accepts the horizontal
distance data accumulated by the wheel 44 may be reset to "zero" as
the mobile grade reference device passes each such stake.
Reference should now be had to FIG. 5 which illustrates, in block
form, a suitable solid-state memory system for use with the
embodiment of the apparatus just described. The rotary transducer
31 of the sensing device 30 on the mobile grade reference device
may be in the form of an optical encoder, whereby two trains of
pulses are transmitted representing clockwise or counterclockwise
rotation of the encoder shaft 32. The time relationship of these
pulses, as determined by a pulse circuit 48, will cause an up or
down pulse to be generated and supplied to a pulse dividing circuit
49. This last mentioned circuit, depending upon information
supplied by a selector switch (not shown), will divide these pulses
by 1, 2, or 3, thereby establishing three ranges of elevation
sensing, e.g., .+-. 1 inch, .+-. 2 inches, or .+-. 3 inches,
respectively. Pulses from the dividing circuit 49 are then fed to
an encoder-follower counter 50 which maintains a running tally of
the present state of the optical encoder 31 relative to an initial
null or zero position which may be preset. The counter 50 not only
maintains this information on the position of the encoder shaft,
but also converts this position information into parallel format
for further processing.
A data latch 51, upon command, accepts new data from the
encoder-follower 50 and retains this data regardless of subsequent
changes in the counter data. An over-range latch 52 will be
activated whenever a specific (hardwired) count is reached and will
inhibit new data from entering the data latch until the count is
reduced below this present maximum.
A comparator 53 receives data from the data latch and a compare
counter 54 detects any difference between such data and enables a
main clock 55 to drive the compare counter 54 either up or down
until a match is obtained. The number of counts required to match
the compare counter are fed to a difference counter 56 and
represent the difference between the last vertical distance sensed
or measured by the device 30 and the current vertical distance
sensed; this function represents the change in vertical distance
between successive points measured or sensed as the mobile grade
reference device is moved over the subgrade.
This vertical distance change information is supplied to a shift
register memory 57. This shift register memory retains the vertical
distance change data as a group of six binary bits and sequentially
moves this information one position further back with each command
of the distance clock 58, which clock is actuated by the distance
wheel 44. The ouput of the shift register memory 57 is used to
preset a drive pulse counter 59; presetting this drive pulse
counter causes the same to start counting down to zero, thereby
converting the parallel vertical distance change data into serial
data once again.
This serial vertical distance change data from the drive pulse
counter 59 is supplied to a motor pulse sequencer 60 which converts
the single-line serial data into four-line sequential pulses
required to drive a stepper motor which constitutes the rotary
transducer 18 of the sensing device 15 attached to the screed of
the paver. The motor drive pulses are fed to the stepper motor
through a current amplifier 61 where they are converted from low
power logic pulses to high power pulses capable of driving the
stepper motor 18.
The motor pulse sequencer 60 also receives up and down commands
directly from the shift register memory 57 and uses this data to
determine the count sequence, i.e., 1, 2, 3, 4 or 4, 3, 2, 1. This
sequence determines the direction of rotation of the stepper motor
shaft 19.
A sub-routine generator 62 and the main clock 55 serve as part of
the over-all memory system and perform a variety of the necessary
tasks. For example, these components are used to drive the counters
and sequence the comparator 53 through a fixed series of
operations.
Summarizing the operation of the embodiment of the invention
heretofore described, the mobile grade reference device 24 is
advanced longitudinally over the subgrade along a predetermined
path. This path may be determined by a steering stringline or by an
existing reference device, such as a curb. The sensing device 30
continuously senses the successive vertical distances between the
stringline 28 and points on the subgrade over which the shoe 36
travels. This varying vertical distance information is programmed,
i.e., this information is generated and stored along with
correlated horizontal distance information resulting from rotation
of the distance measuring wheel 44.
This vertical distance information or intelligence along with the
horizontal information may be stored on tape or wire in a reel or
cassette. Since this grade profile information is recorded and
stored, it is apparent that such information may be generated well
in advance of the paving operation. For example, this vertical
distance information may be generated and stored a day or even
weeks in advance of the paving operation, the only requirement
being that there be no appreciable change in the profile of the
subgrade between the time it is traversed by the mobile grade
reference device and the paver.
When the paver is advanced over the subgrade along the same path
followed by the mobile grade reference device, the sensing device
15 on the screed senses the successive vertical distances between a
given point on the screed and the successive points on the subgrade
over which the shoe 21 rides. As this vertical distance information
is continuously generated, it is compared with the retrieved
vertical distance information generated by the mobile grade
reference device for corresponding, i.e., the same, points on the
subgrade as determined by the horizontal position information. In
essence, these corresponding sensed vertical distances are compared
and the differences, if any, can be considered as error signals
which are supplied as inputs to the automatic screed control
system. It will be appreciated that by the system just described,
any given reference point on the screed will follow the path of
travel of the grade reference point on the mobile grade reference
device, which last mentioned point may be assumed, for purposes of
this discussion and by way of illustration, as the point of
engagement between the follower 34 and the stringline 28; in other
words, the grade reference point on the screed will follow the
grade profile defined by the path of movement of the grade
reference point on the mobile grade reference device.
It will be appreciated that systems other than the one shown in
block diagram form in FIG. 5 may be used in practicing the present
invention. By way of example, the grade profile data generated by
the sensing device 30 may be recorded and stored, along with the
horizontal position control data, using magnetic tape or wire,
punched paper tape or multiple shift registers. If such data are
recorded on tape or wire, the latter might be deposited directly on
the subgrade along the path of travel of the mobile grade reference
device. The paver would then subsequently be moved along the same
path described by the mobile grade reference device, and the
sensing means on the paver would pick up the recorded vertical data
on the tape or wire. Correlation of grade control data and
horizontal control data would be automatically accomplished using
this system.
In lieu of appling such tape or wire directly to the subgrade, a
magnetic type of paint could also be applied to the subgrade, the
amount of paint being proportional to the vertical distance between
the subgrade and the grade reference point of the mobile grade
reference device. When applying either the tape or wire or magnetic
paint directly to the subgrade, the latter would act as a memory
and would obviate storage of the vertical grade data and horizontal
control data in the manner described in connection with the
explanation of the system shown in FIG. 5.
As an alternative to the use of the horizontal distance measuring
wheel 44, it is contemplated that the horizontal control data could
also be developed by means of a wire antenna deposited along one
side of the subgrade and through which radio frequency signals
would be transmitted. The horizontal distance along such antenna
could be determined by measuring the time for a signal to travel
from a transmitter to a transponder or other target.
Another embodiment of the apparatus of the present invention is
illustrated in FIG. 6. Here, a screed 65 of an asphalt paving
machine is disposed behind a transverse auger 66 and supported from
the rearward ends of the usual draft arms, one such arm being
illustrated and designated 67. The forward end of the draft arm 67
is pivotally mounted to the ram 68 of a hydraulic cylinder 69,
which cylinder is pivotally engaged with the frame 70 of the paving
machine. The other draft arm is of course mounted to the paver in
the same manner, the fluid cylinder 69 and the fluid cylinder for
the other draft arm being controlled by an automatic screed control
system of the type referred to in the aforementioned Munyon
patent.
A mobile grade reference device, generally designated 72 is
disposed forwardly of the screed and within the lateral extremities
thereof. This mobile grade reference device includes a beam 73
having downwardly inclined legs 74, 75 pivotally engaged with
subgrade engaging shoes or skids 76, 77 respectively. A bracket 78
is connected to the beam 73, which bracket is pivotally engaged
with a link 79. The link 79 is pivotally connected to a bracket 80,
the latter being connected to the frame 70 of the paver. In other
words, the mobile grade reference device 72 is connected to the
paver and is propelled over the subgrade thereby.
A distance measuring wheel 82 is connected to an arm 83, which arm
is pivotally engaged with another arm 84 mounted from the beam 73.
The wheel 82 drives a belt 85 which in turn rotates the input shaft
of a suitable rotary transducer 86 for accumulating the horizontal
position information.
A subbeam 88 has downwardly and outwardly inclined legs 89, 90. The
leg 89 is pivotally connected with both the beam 73 and the shoe
77. The leg 90 is pivotally connected with a shoe 92.
A bracket 94 depending from the draft arm 67 mounts a rotary
transducer 95, the rotary shaft of which mounts a sensing arm 96.
This sensing arm is engaged by an upright member 97, the latter
being connected to the shoe 77. It is apparent that the transducer
95 will continuously sense vertical distances between the subgrade
and a given reference point on the screed or draft arm.
Another rotary transducer 99 is mounted on the beam 73. This
transducer includes a sensing arm 100 engaged by an upstanding
member 101, the latter being connected to the shoe 92. It is
apparent that the transducer 99 will sense the vertical distance
between the subgrade at the shoe 92 and a grade reference point on
the mobile grade reference device 72, which point may be considered
for purposes of illustration as defined by the engagement between
the arm 100 and the upstanding member 101.
Since the mobile grade reference device 72, according to the
embodiment of the invention shown in FIG. 6, is attached to the
paver, there is a constant horizontal distance between the point
where vertical measurements are sensed by the transducer 95 and the
point wherein the vertical distances are sensed by the transducer
99. When using this embodiment of the invention, a multiple shift
register may be conveniently employed. The vertical grade control
data generated by the transducer 99 would be entered as incremental
"bits"in a shifting digital register. The entry of this data to the
register would be controlled by signals from the horizontal
distance transducer 86. Each bit of such data is shifted down the
register one step as a new bit is entered and the last bit drops
out of the register as an input to the automatic screed control
system. In essence, such a multiple shift register provides that
the vertical distance measured at the shoe 77 is compared with the
vertical distance which was sensed by the shoe 92 when the latter
occupied the position along the subgrade occupied by the shoe
77.
It will be apparent that the mobile grade reference device 24 in
the embodiment of the invention illustrated in FIGS. 1 through 4
could be directly connected to the paver for movement in unison
with the latter in which case the separate powered means 40 would
not be required. With such an arrangement, the distance measuring
wheel 44 could supply the input information to a multiple shift
register of the type just mentioned to correlate the vertical
distances sensed by the sensing devices 15 and 30. It should also
be understood that the mobile grade reference device 72 of the FIG.
6 embodiment might be considerably greater in length than
illustrated and provided with additional subgrade engaging shoes
along with appropriate linkage to provide an optimum trace
approximating the mean profile grade.
* * * * *