(12) United States Patent
`Sehr
`
`USOO6916O7OB2
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,916,070 B2
`Jul. 12, 2005
`
`(54) LASER-BASED CONTROLLER FOR
`ADJUSTING THE HEIGHT OFA
`MACHINING TOOL OF A CONSTRUCTION
`MACHINE
`
`(*) Notice:
`
`(75) Inventor: Willibald Sehr, Hadamar/Steinbach
`(DE)
`(73) Assignee: MOBA-Mobile Automation GmbH,
`Elz (DE)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`(21) Appl. No.:
`10/433,863
`(22) PCT Filed:
`Nov. 28, 2001
`(86) PCT No.:
`PCT/EPO1/13912
`S371 (c)(1),
`(2), (4) Date: Nov. 13, 2003
`(87) PCT Pub. No.: WO02/46533
`PCT Pub. Date:Jun. 13, 2002
`Prior Publication Data
`US 2004/0068896 A1 Apr. 15, 2004
`Foreign Application Priority Data
`(30)
`Dec. 7, 2000 (DE) ......................................... 1OO 60903
`(51) Int. Cl." ................................................ EO1C 19/00
`(52) U.S. Cl. ....................... 299/15; 299/39.6; 404/84.1
`(58) Field of Search ................................. 299/1.05, 14,
`299/15, 39.6; 404/84.1–84.8; 356/3.03–3.08
`
`(65)
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,456.829 A * 6/1984 Fohey ................... 250/559.23
`4,796,998 A * 1/1989 Soma et al. ................ 356/608
`4,922,752 A
`5/1990 Kitazume et al. ............. 73/146
`
`
`
`7/1990 Zarniko et al. .............. 299/15
`4,943,119 A
`4,961,173 A * 10/1990 Sehr et al. .................... 367/96
`5,015,868 A
`5/1991 Park ...................... 250/559.08
`5,151,608 A * 9/1992 Torii et al. ............. 250/559.38
`5,163,319 A * 11/1992 Spies et al. ................... 73/146
`5,293,162 A * 3/1994 Bachalo .....
`... 340/905
`5,309.407 A * 5/1994 Sehr et al. .................... 367/96
`5,393,167 A * 2/1995 Fujita et al. ............... 404/84.1
`5,521,694. A * 5/1996 Osterwalder ............... 356/3.08
`5,753,808 A
`5/1998 Johnson ....................... 73/146
`5,837.997 A * 11/1998 Becket al.
`250/227.11
`6,371,566 B1 * 4/2002 Haehn .......
`... 299/15
`6,499,339 B1 12/2002 Hedstrom ...................... 73/81
`FOREIGN PATENT DOCUMENTS
`
`2/1990
`2/1990
`6/1992
`7/1995
`6/1993
`4/1995
`12/1999
`
`3827617 A1
`DE
`3827618 A1
`DE
`4038860
`DE
`4341894 C1
`DE
`O547378
`EP
`O542297
`EP
`WO9964681
`WO
`* cited by examiner
`Primary Examiner John Kreck
`(74) Attorney, Agent, or Firm-Glenn Patent Group;
`Michael A. Glenn
`ABSTRACT
`(57)
`A laser-regulating means for a construction machine for
`adjusting the height of a height-adjustable machining tool
`includes three laser measuring heads which are directed to
`three measuring points being Spaced from each other on a
`reference Surface, and an evaluating means, which, from the
`output signals of the laser measuring heads and from the
`known geometric arrangement of the laser measuring heads
`as regards the machining tool, determines the height of the
`machining tool relative to a reference Surface and, from this
`height and from a target height determines a control Signal
`for a height-adjustment of the machining tool. The construc
`tion machine is a road finisher with a height-adjustable plank
`or a cold planer with a height-adjustable milling drum.
`
`13 Claims, 4 Drawing Sheets
`
`Page 1 of 11
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`CATERPILLAR EXHIBIT 1013
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`U.S. Patent
`US. Patent
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`Jul. 12, 2005
`Jul. 12, 2005
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`Sheet 1 of 4
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`US 6,916,070 B2
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`FIG.1
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`U.S. Patent
`US. Patent
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`Jul. 12, 2005
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`US 6,916,070 B2
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`U.S. Patent
`US. Patent
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`Jul. 12, 2005
`Jul. 12, 2005
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`Sheet 3 of 4
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`US 6,916,070 B2
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`U.S. Patent
`US. Patent
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`Jul. 12, 2005
`Jul. 12, 2005
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`Sheet 4 of 4
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`US 6,916,070 B2
`US 6,916,070 B2
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`US 6,916,070 B2
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`1
`LASER-BASED CONTROLLER FOR
`ADJUSTING THE HEIGHT OFA
`MACHINING TOOL OF A CONSTRUCTION
`MACHINE
`
`2
`example, when finishing the Second track, a finished track of
`the road Surface is used as a reference plane for guiding the
`Scanning ski, and if the first track has a certain, undesired
`waviness, a Second track will inevitably comprise a structure
`with errors, which correspond to a reproduction of the errors
`of the road Surface in the area Scanned by the Scanning Ski.
`The mechanical Scanning by means of a Scanning Ski
`inevitably follows some sort of envelope curve over the
`respectively highest points of the reference Surface. If, there
`is, for example, an undesired obstacle in the form of a Stone
`on the reference Surface, the undesired deflection of the
`Scanning ski caused by this trouble spot results in a corre
`sponding height error of the finished track of the road
`Surface. A further problem is based on the mechanical
`Sensitivity of the Scanning ski, which may be easily damaged
`not only due to careleSS operating perSonnel, but also
`becomes quickly worn out during normal operation.
`From the U.S. Pat. No. 4,961,173 of the applicant, a
`control Sensor for a construction machine for generating
`height-control Signals and direction-control signals by Scan
`ning a reference cable or guide cable is known. The prior art
`control Sensor has a plurality of ultrasound transceivers
`which are arranged transversally to the direction of motion
`of the construction machine and which are arranged adjacent
`to each other, Such that their lobes overlap in the measuring
`plane in which the guide cable or the reference cable is
`located.
`The EP 0542297 B1 describes an alternative regulating
`means, in which at least three ultrasound Sensors are
`mounted at the plank essentially in the direction of motion
`of the road finisher and Spaced from each other, and in which
`an evaluating means uses the distance Signals of the ultra
`Sound Sensors for generating a height-control Signal for
`adjusting the plank. Among other things, this principle
`allows an averaging of the Surface in direction of travel and,
`in practice, leads to Satisfactory results. Yet, it has Some
`decisive practical disadvantages. Since the Sensors have to
`be arranged vertically above the respective measuring points
`on the floor, a stable construction needs to be built along the
`distance to be averaged in order to keep the Sensors in
`position. For delivering good accuracy, also the ultrasound
`Sensors have to be mounted as close as possible
`(approximately 30 cm) to the reference Surface. Disadvan
`tages of this ultrasound-regulating means include the high
`construction requirements, the hindering of workers during
`activities at or near the construction machine, and the danger
`of mechanically damaging the Sensors and the construction
`carrying the same in rough field conditions.
`The EP 0547378 E1 describes an ultrasound regulating
`means for a mobile planer. An evaluating means uses the
`Signals of at least three ultrasound Sensors to generate
`control Signals for the gear height-adjusting means depend
`ing on an adjustable target cutting depth. This apparatus
`provides the same disadvantages described above in con
`junction with the road finisher.
`The WO99/64681 A1 describes a laser-based, regulating
`means for a road finisher. A laser Scans the profile of the
`unfinished Surface before applying the paving material and
`of the Surface of the freshly applied paving material along a
`plane alongside the direction of motion of the road finisher
`and Vertical to the road Surface in a multitude of measuring
`points. From the thus obtained profile data, an evaluating
`means generates a control Signal for controlling the plank of
`the road finisher. The disadvantage of this System consists in
`the comparably complex and Sensitive mechanics of the
`laser Scanner used.
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to a laser-regulating means
`for a construction machine for adjusting the height of a
`height-adjustable machining tool.
`2. Description of the Related Art
`In the building trade, and, in particular, in underground
`engineering, various construction machines are employed to
`machine and/or generate large Surfaces, Such that the same
`comprise a desired, often approximately plane profile. In
`road construction, these machines include, for example, a
`road finisher, or paver, a cold planer for road use, a “motor
`grader', and others. The construction machines use
`mechanical or electronic regulating means to facilitate a
`quick and cost-efficient high-quality generation of a Surface
`with a desired profile. In the following the problems
`involved will be briefly discussed by means of a road
`finisher and a cold planer.
`Generally, a road finisher operates with a crawler track
`gear on a prepared underground, onto which is applied a
`road Surface, or road paving, or tarmac, yet to be finished.
`On the rear side of the road finisher, seen from the direction
`of travel, a height-adjustable plank is provided, on the front
`Side of which a Supply of paving material is piled up, which
`is distributed and tracked by means of a conveyor, which
`ensures that, on the front Side of the plank, there is always
`a Sufficient, yet not too great amount of paving material kept
`in Supply. The height of the rear edge of the plank relative
`to the Surface of the prepared underground, which may also
`be formed by a previously existing road Surface, establishes
`the thickness of the finished road Surface before the same is
`Subsequently further compacted by means of compactors.
`The plank is held at a traction arm, which is mounted in a
`height-adjustable manner around a traction point arranged in
`the central area of the road finisher, with the height of the
`plank being adjustable via hydraulics.
`In prior art road finishers, for controlling the height of the
`plank establishing the thickness of the paving to be finished,
`use is, for example, made of a mechanical Scanning device
`guided beside the road finisher along a reference Surface.
`Corresponding to a height of a Scanning ski detected by
`means of an evaluating, means, the plank will be re-adjusted
`in height.
`The reference plane, along which the Scanning ski is
`guided, depends on the current processing operation.
`Typically, the operating width of a road finisher is less than
`the width of the road surface to be finished. For establishing
`the height plane of the road Surface to be finished use is
`commonly made of a taut Steel cable as a reference height
`for a first track of the total road Surface to be finished. When
`laying the Second track, which is to follow the first track
`without any displacement in height, the Scanning ski is
`guided above the previously finished track, which then
`forms the reference surface. With prior art road finishers it
`is thus possible, through the use of a Scanning Ski, to use
`different objects as a reference plane, Such as, for example,
`the taut reference cables and/or the previously finished track
`of the road Surface.
`However, this prior art type of height-regulating the plank
`comprises Some System-related disadvantages. If, for
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`US 6,916,070 B2
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`The DE 3827617A1 describes a scanning sensor, which
`enables a track-like nominal plane recognition, for the
`purpose of which, for example, curbstones may be used. A
`distance, which is pre-adjustable over the Same, may serve
`to move the machining apparatus in a desired plane-height
`relative to the thus generated reference plane and to auto
`matically align the Same. The Scanning Sensor may be based
`on the use of ultrasound, a laser beam or other optical
`Scanning Systems.
`SUMMARY OF THE INVENTION
`It is the object of the present invention to provide a
`constructively simpler, mechanically more robust regulating
`means for a construction machine, which offers a higher
`degree of user friendliness at the construction site, for
`adjusting the height of a height-adjustable machining tool.
`The present invention provides a laser-regulating means
`for a construction machine for adjusting the height of a
`height-adjustable machining, tool comprising a first laser
`measuring head, a Second laser measuring head, and a third
`laser measuring head, which are arranged at the construction
`machine, with the first laser measuring head and the Second
`laser measuring head being arranged at a first angle to each
`other, with the first laser measuring head and the third laser
`measuring head being arranged at a Second angle to each
`other, with the first angle and the Second angle being
`Selected Such that a first measuring point of the first laser
`measuring head, a Second measuring point of the Second
`laser measuring head, and a third measuring point of the
`third laser measuring head are Spaced from each other on a
`reference Surface, with the first measuring point, the Second
`measuring point, and the third measuring point being
`arranged essentially behind each other in the direction of
`motion of the construction machine, and an evaluating
`means, which, depending on output Signals of the first laser
`measuring head, the Second laser measuring head, and the
`third laser measuring head, determines a first distance of the
`first laser measuring head from the reference Surface, a
`Second distance of the Second laser measuring head from the
`reference Surface, and a third distance of the third laser
`measuring head from the reference Surface, on the basis of
`the determined distances and the known geometric arrange
`ment of the first laser measuring head, the Second laser
`measuring head, and the third laser measuring head relative
`to the machining tool, calculates the height of the machining
`tool relative to the reference plane, and, depending on the
`calculated height and a target height, generates a height
`control Signal for the machining tool.
`An advantage of the inventive regulating means consists
`in that the arrangement of the laser measuring heads and the
`arrangement of the measuring point on a reference Surface
`are essentially independent of each other. On the one hand,
`therefore, the laser measuring heads may be mounted at a
`place, at or in the environment of the construction machine,
`where are no hindrance to certain jobs carried out or to
`workers working there, and where they are Safe from any
`damage, for example, at a height of Several meters. On the
`other hand, the position of the measuring points on the
`reference Surface is essentially freely adjustable to the
`practical requirements.
`The use of three laser measuring heads enables enhancing
`the regulating pcablerties of the laser-regulating means by
`recognizing artifacts using a simple plausibility control, the
`former, for example, resulting from objects on or holes in the
`reference Surface and not having any impact on the regula
`tion of the tool, as well as by compensating for any wavineSS
`of the reference Surface by means of averaging.
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`A preferred embodiment of the inventive laser-regulating
`means further includes a fourth laser measuring head and a
`fifth laser measuring head which are arranged on the con
`Struction machine with a third angle and/or under a fourth
`angle relative to the first laser measuring head, with the third
`angle and fourth angle being Selected Such that the first
`measuring point, the Second measuring point, the third
`measuring point, a fourth measuring point of the fourth laser
`measuring head and the fifth measuring point of the fifth
`laser measuring head are Spaced apart from each other on the
`reference Surface and that the measuring points are located
`essentially behind each other in the direction of motion of
`the construction machine, with the evaluating means calcu
`lating the height of the machining tool depending on a fourth
`distance of the fourth laser measuring head relative to the
`reference Surface, a fifth distance of the fifth laser measuring
`head relative to the reference Surface and the known geo
`metric arrangement of the fourth laser measuring head and
`fifth laser measuring head with respect to the machining
`tool.
`Preferably, the laser-regulating means determines the dif
`ferences of two distances each and classifies those distances
`as valid, the difference of which is Smaller than a limiting
`value, or discards one of the determined distances as invalid
`and does not use the same for generating the height-control
`Signal, if the distance involved ranges outside a predeter
`mined range. The predetermined range may be specified by
`a predetermined distance above/below a plane, with the
`plane being Specified by the remaining distances.
`Preferably, the evaluating means forms the mean value of
`the determined and, if necessary, not-discarded distances.
`Preferably, the laser measuring heads are further adjacent
`to each other in Spatial proximity, arranged essentially
`behind each other in the direction of motion and arranged
`essentially at equal distances to the machining tool. In this
`case, the total laser-regulating means may be arranged in a
`compact housing, Such that no mechanical or electrical
`connection to remotely arranged Sensors is required. AS a
`result of this, disadvantages in connection with interrupted
`or damaged Signal lines can be avoided, which occur in prior
`art construction machines owing to the required arrangement
`of the ultrasound Sensors.
`An advantage of the inventive laser-regulating means
`consists in that it does not contain any moveable or moved
`parts, Such that the same are especially robust, less error
`prone and easy to implement in terms of construction,
`manufacture, assembly, and maintenance. The Special
`robustneSS is especially important under the conditions at a
`construction machine (vibrations, a very high working tem
`perature range, humidity, etc.).
`The inventive laser-regulating means is, for example,
`attached to a road finisher or to a cold planer.
`Preferably, one of the laser measuring heads is aligned
`with the pertaining measuring point and the machining tool
`BRIEF DESCRIPTION OF THE DRAWINGS
`These and other objects and features of the present
`invention will become clear from the following description
`taken in conjunction with the accompanying drawings, in
`which:
`FIG. 1 shows a road finisher with the inventive laser
`regulating means in accordance with a first embodiment;
`FIG. 2 shows a schematic plan view of the road finisher
`from FIG. 1;
`FIG. 3 shows a block diagram of the inventive laser
`regulating means in accordance with a Second embodiment;
`and
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`FIG. 4 shows a cold planer with the laser-regulating
`means in accordance with the first embodiment.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`FIG. 1 shows a road finisher 2 having a crawler track gear
`4 on a prepared underground 6. At the rear end of the road
`finisher 2 opposing the driving direction, a height-adjustable
`plank 8 is arranged, which is mounted at a traction point 12
`at the road finisher 2 by means of a traction arm 10. In front
`of the plank 8, there is a Supply 14 of paving material kept
`essentially constant acroSS the total width area of the plank
`8 by a corresponding known regulation of the Speed of a
`Screw-like conveyor means 16.
`The plank 8 floats on the paving material of a road Surface
`18 to be finished. The thickness of the road Surface 18 to be
`finished prior to its final compaction by road compactors
`will be effected by regulating the height-position of the rear
`edge 20 of the plank 8. This height-regulation is induced by
`changing the blade angle of the plank 8 and is typically
`effected by controlling Setting cylinders engaging into the
`front end of the traction arms 10.
`The previously described road finisher 2 is in accordance
`with the road finishers in accordance with the state of the art
`Such that, in consideration of expert knowledge on the
`present technical field, it is not necessary to go into a
`detailed description.
`The road finisher 2 comprises a laser-regulating means in
`accordance with the present invention which is attached in
`a housing 30 via a mounting 32 at the traction arm 10. In the
`shown embodiment, the laser-regulating means includes
`three laser measuring heads not shown in FIG. 1, which
`direct three laser beams 40, 42 and 44 to three measuring
`points, 50, 52 and 54 on a reference surface 60 beside, in
`front of and/or behind the road finisher. As a result, the
`central laser measuring head is arranged vertically above the
`rear edge 20 of plank 8, Such that the pertaining measuring
`point 52 lies on a straight line with the rear edge 20 of the
`plank 8. The first laser beam 40 and the second laser beam
`42 include a first angle 70, the first laser beam 40 and the
`third laser beam 44 include a second angle 72. The reference
`Surface may, for example, be established by an existing or
`just finished track of the road Surface, an already finished
`kerb Strip of the road or any other Suitable Surface.
`FIG. 2 shows a schematic plan view of the road finisher
`2 from FIG.1. The laser beams 40, 42, and 44, respectively,
`of the laser measuring heads in housing 30, which are not
`shown, are directed to measuring points 50, 52, and 54,
`respectively. The first measuring point 50 and the second
`measuring point 52 lie on a reference Surface 60, which is
`Situated on the edge of the prepared underground 6 being
`provided with a road surface 18 while the road finisher is
`moving to the right. The third measuring point 54 lies on the
`edge of the finished road Surface 18 and on a Straight line
`with the first measuring point 50 and Second measuring
`point 52. Using several laser beams 40, 42, 44 of several
`laser measuring heads enables a flexible arrangement of the
`measuring points 50, 52, 54, which is adapted to the con
`ditions and requirements of the respective application field.
`In FIG. 3, an embodiment of the laser-regulating means is
`shown which, in contrast to the embodiment shown in FIG.
`1, includes five laser measuring heads 80, 82,84, 86, 88 each
`having one functionally related lens 90, 92,94, 96, and 98,
`respectively. The laser measuring heads 80, 82,84, 86, 88
`emit laser beams 40, 42, 44, 106, 107, which are directed to
`the respectively pertaining measuring points. The laser
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`regulating means further includes a number of transceiver
`circuits 110, 112, 114,116,118 corresponding to the number
`of laser measuring heads 80, 82, 84, 86, 88. These trans
`ceiver circuits 110, 112, 114, 116, 118 are in a respective
`electrical signal-connection to respectively one of the laser
`measuring heads 80, 82,84, 86,88. The transceiver circuits
`110, 112, 114, 116, 118 are further in an electrical signal
`connection to an evaluating means 120, which, for example,
`may comprise a microcomputer. AS is shown in FIG. 3, each
`of the transceiver circuits is connected to the evaluating
`means via two signal lines, with Signals being Sent to the
`transceiver circuit via one line and Signals being received
`from the transceiver circuit via the other line, as is shown in
`FIG. 3 by the arrows associated with the lines. Via an
`interface 122 and a first terminal 124, the evaluating means
`120 is connected to a non-illustrated apparatus for control
`ling the above mentioned Setting cylinders attacking the
`front ends of the traction arms 10 in order to influence the
`height position of the rear edge 20 of the plank and, thus, the
`thickness of the road Surface 18 to be finished. The connec
`tion between the evaluating means 120 and the interface 122
`is schematically shown by the arrow 125 in FIG. 3. Via a
`Second terminal 126, the evaluating means 120 is connected
`to a non-illustrated apparatus, where a user may first Set a
`target value for the height-adjustment of the plank. Via a
`non-illustrated terminal, the members of the laser-regulating
`means are Supplied with electrical power by a non-illustrated
`power Source.
`Each laser measuring head 80, 82, 84, 86, and 88,
`respectively, may be integrated with the respectively per
`taining transceiver circuit 110, 112, 114, 116, and 118,
`respectively, in a component (as illustrated) and/or with the
`pertaining lens 90, 92, 94, 96, and 96, respectively. The
`transceiver circuit 110, 112, 114, 116, and 118, respectively,
`the laser measuring head 80, 82, 84, 86, and 88, respectively,
`and the lens 90,92, 94, 96 and 98, respectively, cooperate to
`determine the distance of the laser measuring head 80, 82,
`84, 86, and 88, respectively, from the respective measuring
`point on the reference Surface 60 using the running time of
`the laser beam 40, 42, 44, 106, and 107, respectively, from
`the time of its emission by the laser measuring head 80, 82,
`84, 86 and 88, respectively, to the time of receiving the laser
`light reflected from the reference surface 60 in the pertaining
`measuring points by the measuring head 80, 82,84, 86, and
`88, respectively, and to Send an electrical signal correspond
`ing to this distance to the evaluating means 120. From the
`thus determined distance of the laser measuring head 80, 82,
`84, 86, and 88, respectively, and from its known geometric
`arrangement, the evaluating means 120 calculates its dis
`tance from the reference Surface.
`The classification of functionalities shown in FIG. 3
`within the laser height regulating means merely represents
`an embodiment and may be varied, for example, by inte
`grating various illustrated components in a component.
`Further, the laser height regulating means may comprise
`further, not-illustrated interfaces for exchanging data with
`other apparatuses, for example, other control and regulating
`apparatuses of the construction machine 2, with a central
`computer of the construction machine 2 or with an external
`computer for performing error diagnostics.
`Depending on the respective special area of application of
`the laser-regulating means and the conditions and circum
`stances related to the same, the laser measuring heads 80, 82,
`84, 86, 88, or the laser beams 40, 42, 44, 106, 107 emitted
`by the Same, are spatially aligned Such, that the respective
`measuring points are spaced from each other as far as
`possible, that is, that, for example, the first angle 17 between
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`the first laser beam 40 and the second laser beam 42, and the
`second angle 72 between the first laser beam 40 and the third
`laser beam 44 are chosen as great as possible.
`From the distances of the laser measuring heads 80, 82,
`84, 86, 88 relative to reference Surface 60 and the known
`geometric arrangement of the laser measuring heads 80, 82,
`84, 86, 88 with respect to the plank 8, the evaluating means
`120 determines the height of the plank 8 relative to the
`reference surface 60. From this height of the plank 8 relative
`to the reference Surface 60 as well as from a target height,
`which can be adjusted at the above-mentioned, not
`illustrated apparatus connected to the evaluating means 120
`via the terminal 122, the evaluating means 120 determines
`a height-control Signal for the plank 8. At the road finisher
`2, this height-control Signal Serves for controlling the Setting
`cylinders for adjusting the front traction points 12 of the
`traction arms 10 of the plank 8.
`In the following, preferred further processings of the
`detected signals from the laser measuring heads 80, 82,84,
`86, 88 by the evaluating means 120 for generating the
`height-control Signal will be described.
`From the distances of the laser measuring heads 80, 82,
`84, 86, 88 relative to the reference Surface 60, which have
`been determined from the output Signals of the laser mea
`Suring heads 80, 82.84, 86, 88, the evaluating means 120
`forms a mean value to determine the height of the plank 8
`relative to the reference Surface 60. By means of averaging,
`the influence of a waviness of the reference Surface 60 onto
`the height-control Signal is reduced and, thus, a better
`evenness, or Smoothness, of the just finished road Surface 18
`will be achieved. This averaging functions the better, the
`more laser measuring heads 80, 82, 84, 86, 88 or measuring
`points 50, 52, 54, 108, 109 are present on the reference
`surface 60 and the further the measuring points 50, 52, 54,
`108, 109 are spaced from each other on the reference surface
`60.
`Further, the evaluating means 120 may be implemented
`Such that the evaluating means 120 discards a distance of a
`laser measuring head 80, 82, 84, 86, 88 from the reference
`Surface 60 as invalid and does not use the same for gener
`ating the height-control Signal, if the distance involved lies
`outside a predetermined range. As a result, it is possible, for
`example, to SuppreSS the undesired transmission of various
`errors of the reference Surface 60 to the road Surface 18 to
`be finished. The predetermined range may be defined by a
`lower limiting value and an upper limiting value for the
`distance of a laser measuring head 80, 82,84, 86, 88 from
`the reference Surface 60. The errors of the reference Surface
`60 include, for example, holes, Stones or other objects lying
`on the reference Surface 60, and the influence of which onto
`the height-regulation of the plank 8 is mitigated, but not
`eliminated by the above-described averaging. The upper
`limiting value and the lower limiting value are Selected Such
`that a waviness of the reference Surface 60 is still within the
`range defined by the upper limiting value and the lower
`limiting value in order not to discard too many measuring
`points 50, 52,54, 108, 109 as invalid and such that the most
`objects and holes on or in the reference surface 60 or the
`distances generated by these ranges are outside the range in
`order not to have any influence on the height regulation of
`the plank 8. The precise values of both limiting values are
`dependent on the respective circumstance, for example, on
`the quality of the reference surface 60 or a longitudinal
`curvature of the reference Surface 60 or the road Surface 18
`to be finished as well as on the Spatial arrangement of the
`measuring point 50, 52, 54, and, during use, may be manu
`ally or automatically adapted to the respective circum
`StanceS.
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`The just described range, Outside of which one of the
`determined distances may be discarded or is not used for
`generating the height-control Signal, may be specified in a
`laser height-regulating means having at least three laser
`measuring heads 60, 82,84, 86, 88 by a range above/below
`the plane which is defined by the remaining distances. AS a
`result, even in the case of a longitudinal curvature of the
`reference Surface 60, the transfer of which to the road
`surface 18 to be finished is desired, a small predetermined
`range is adjusted, within which distances may be classified
`as valid and are not discarded.
`In a further embodiment, instead of the limiting values or
`the remaining distances, the difference between two dis
`tances each is determined, and those distances are discarded
`as invalid and not used for generating the height-control
`Signal, the differences of which exceed a predetermined
`limiting value as regards the distances of the other laser
`measuring heads 80, 82,84, 86, 88 relative to the reference
`surface 60. Thereby, errors at the reference surface 60 are
`also identified and their influence on the height-control
`Signal is eliminated.
`The advantage of the laser measuring heads 80, 82,84, 86,
`88 as against conventional approaches using ultrasound
`measuring heads consists in that, in contrast to ultrasound
`measuring heads, no vertical irradiation on the reference
`Surface 60 and no Small distance to the same is required.
`Under normal circumstances, that is, in case of a not too
`Strongly reflective reference Surface 60, the laser measuring
`heads 80, 82,84, 86, 88 may also be used at great angles to
`the perpendicular and at a great distance to the reference
`surface 60. Therefore, it is possible to arrange all laser
`measuring heads 80, 82, 84, 86, 88 largely independent of
`the arrangement of the pertaining measuring points on the
`reference surface 60. Especially, as is shown in FIG. 3, all
`laser measuring heads 80, 82, 84, 86, 88 may be arranged
`together with the evaluating means 120 and the interface 122
`in a common housing 30, which is mounted at the road
`finisher 2 at a h