US008308395B2
`
`(12) United States Patent
`US 8,308,395 B2
`(10) Patent No.:
`Jurasz et al.
`(45) Date of Patent:
`*Nov. 13, 2012
`
`(54)
`
`ROAD CONSTRUCTION MACHINE,
`LEVELING DEVICE, AS WELL AS METHOD
`FOR CONTROLLING THE MILLING DEPTH
`OR MILLING SLOPE IN A ROAD
`CONSTRUCTION MACHINE
`
`4,186,968 A
`
`2/1980 Barton
`
`(Continued)
`
`DE
`
`FOREIGN PATENT DOCUMENTS
`9204614 U1
`7/1992
`
`(75)
`
`Inventors: Jaroslaw Jurasz, Windhagen (DE);
`Giinter Hahn, Konigswinter (DE);
`Giinter Tewes, Unkel (DE)
`
`(73)
`
`( * )
`
`Assignee:
`Notice:
`
`Wirtgen GmbH (DE)
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`This patent is subject to a terminal dis-
`claimer.
`
`(21)
`
`(22)
`
`(65)
`
`(63)
`
`(30)
`
`Appl. No.: 13/098,798
`
`Filed:
`
`May 2, 2011
`Prior Publication Data
`
`US 2011/0206456A1
`
`Aug. 25,2011
`
`Related US. Application Data
`
`Continuation of application No. 12/225,792, filed as
`application No. PCT/EP2007/053590 on Apr. 12,
`2007, now Pat. No. 7,946,788.
`
`Foreign Application Priority Data
`
`Apr. 27, 2006
`Int. Cl.
`
`(51)
`
`(DE) ......................... 10 2006 020 293
`
`(52)
`
`(58)
`
`(56)
`
`(2006.01)
`E01C 23/08
`US. Cl.
`..... 404/84.8; 404/83; 404/84.05; 404/84.2;
`404/94; 404/96
`Field of Classification Search ............... 404/83796
`
`See application file for complete search history.
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,140,420 A
`
`2/1979 Swisher, Jr. et a1.
`
`(Continued)
`
`OTHER PUBLICATIONS
`
`English translation ofWritten Opinion ofthe International Searching
`Authority, PCT/EP2007/053590, Dec. 10, 2008. (not prior art).
`
`Primary Examiner 7 Raymond W Addie
`(74) Attorney, Agent, or Firm 7 Waddey & Patterson, P.C.;
`Lucian Wayne Beavers
`
`(57)
`
`ABSTRACT
`
`In a road construction machine (1) for the treatment of road
`surfaces with a milling drum (3) height-adjustable with
`regard to the milling depth, with a leveling device (4) with at
`least one controller (611, 60) which receives set values for the
`milling depth and/or the slope of the milling drum (3), and
`with at least one exchangeable sensor (A, B, C) or with
`several switchable sensors for registering the current actual
`value ofthe milling depth and/or the slope ofthe milling drum
`(3) relative to a reference surface, where the controller (6a,
`60) effects a milling depth control and/or a slope control for
`the milling drum (3) conditional on pre-determined set values
`and the currently measured actual values of the at least one
`sensor (A, B, C) by returning an adjustment value for achiev-
`ing or maintaining the set value during the milling operation,
`where the leveling device (4) is provided with an indication
`and setting device (2) for indicating and setting operating
`parameters for the at least one sensor (A, B, C), it is provided
`that the indication and setting device (2) ofthe leveling device
`(4), in addition to an indication and setting unit (2a, 20)
`provided for the at least one sensor (A, C) currently in use, is
`provided with an additional indication and setting unit (2b)
`for a selectable sensor (B) that is to be exchanged for the
`sensor (A, C) currently in use.
`
`27 Claims, 8 Drawing Sheets
`
`
`
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`Page 1 of 15
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`CATERPILLAR EXHIBIT 1001
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`Page 1 of 15
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`CATERPILLAR EXHIBIT 1001
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`

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`US 8,308,395 B2
` Page2
`
`U.S. PATENT DOCUMENTS
`
`7,510,347 B2*
`*
`
`3/2009 Lemke ......................... 404/84.5
`
`4,270,801A
`4,929,121 A
`
`6/1981 Swisherahem.
`5/1990 Lentetal.
`
`5,318,378 A
`5,378,081 A
`5,533,790 A
`5,556,226 A *
`5,984,420 A
`7,422,391 B2
`
`6/1994 Lem
`1/1995 Sw1sher, Jr.
`7/ 1996 We11and
`9/1996 Hohmann, Jr.
`11/1999 Murray etal.
`9/2008 H011 et a1.
`
`............... 404/84.1
`
`12/2002 Johnson
`2002/0192025 A1
`7/2009 Zachmanetal.
`7,559,718 B2
`12/2004 Lloyd
`2004/0247388 A1
`6/2008 Berning
`2008/0152428 A1
`FOREIGN PATENT DOCUMENTS
`
`............ 404/84.5
`
`1154075 A2
`EP
`* cited by examiner
`
`“/2001
`
`Page 2 of 15
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`Nov. 13, 2012
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`US 8,308,395 B2
`
`1
`ROAD CONSTRUCTION MACHINE,
`LEVELING DEVICE, AS WELL AS METHOD
`FOR CONTROLLING THE MILLING DEPTH
`OR MILLING SLOPE IN A ROAD
`CONSTRUCTION MACHINE
`
`BACKGROUND OF THE INVENTION
`
`The invention relates to a road construction machine, a
`leveling device, and a method.
`It is already known for road milling machines to integrate
`a leveling device by means ofwhich it is to be ensured that an
`even milled surface can be produced.
`The milling depth control system is designed in such a
`fashion that different sensors can be connected. Among oth-
`ers, the sensors used include, for example, wire-rope sensors,
`ultrasonic sensors and slope sensors.
`A wire-rope sensor is mounted at the side plates (edge
`protection) next to the milling drum and thus scans the refer-
`ence surface, in this case the road surface, very precisely. The
`ultrasonic sensor operates in a non-contact fashion and is
`therefore not subject to any mechanical wear and tear. It can
`be used in a variety of ways as it can be attached in different
`positions on the machine.
`Ifa defined cross slope is to be produced, a slope sensor can
`also be used which is integrated into the road milling
`machine.
`
`The known milling depth control system can be provided
`with two independent control loops. A controller is provided
`in each control loop to which the sensors canbe connected via
`plug-in connectors. For example, either two height sensors
`are provided, or one height sensor in combination with one
`slope sensor.
`It is unfavorable in the state of the art that the frequent
`change between the many different sensors, which is neces-
`sary for application-related reasons, is not possible without an
`interruption of the milling operation and without negative
`influences on the work result. To change the current sensor,
`the automatic mode of the control system needs to be left first
`as there is merely one controller, or merely one indication and
`setting device for set values and actual values per controller
`respectively. The new sensor can then be selected, and the
`desired set value canbe set before it is possible to change back
`into the automatic mode of the control system. If the road
`milling machine continued milling during changing of the
`sensor, faults in the work result could occur because no con-
`trol is effected during that time. The machine therefore needs
`to be stopped for a change of the sensor, which leads to a
`significant time loss. An adverse effect on the work result
`ensues even if the road milling machine is stopped during
`change of the sensor because the milling drum cuts clear
`when standing. This is an unwelcome effect, in particular
`during fine milling.
`It is therefore the object of the invention to specify a road
`construction machine, as well as a leveling device and a
`method for controlling the milling depth and/or the milling
`slope, in which it is possible to change the sensors without any
`interruption of the milling operation.
`
`SUMMARY OF THE INVENTION
`
`The invention provides in a favorable manner that the indi-
`cation and setting device of the leveling device, in addition to
`an indication and setting unit provided for the at least one
`sensor currently in use, is provided with an additional indi-
`cation and setting unit for a selectable sensor which is to be
`exchanged for the sensor currently in use. Providing a further
`
`10
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`15
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`20
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`25
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`30
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`35
`
`40
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`45
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`50
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`60
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`65
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`2
`
`indication and setting unit offers the advantage that the new
`sensor, which is to be exchanged for a sensor currently in use,
`can be prepared for the time of switchover in terms of its
`actual and set values while the operation continues. At the
`time of switchover, the sensor can therefore be changed with-
`out any alteration of the currently applicable adjustment
`value. The leveling device is provided with a device for the
`switchover of sensors which, upon activation of a switchover
`command, effects switchover of the leveling device from the
`at least one current sensor to at least one pre-selected other
`sensor without interruption ofthe milling operation and with-
`out any erratic alteration of the current adjustment value for
`the setting of the milling depth and/or for the setting of the
`slope of the milling drum.
`The switchover device, with the indication and setting
`device, enables a pre-selection of the other sensor and the
`pre-setting of operating parameters (set values and actual
`values) of the other pre-selected sensor.
`In this way, a machine operator can already prepare the
`switchover of the sensors during the milling operation so that
`switchover of the sensors is possible at the push of a button
`without any time loss and without an interruption of the
`milling operation.
`For this purpose, the leveling device is provided with an
`indication and setting device which is capable of indicating
`and altering the data of the current sensor and the data of the
`pre-selected sensor. By means of the switchover device,
`switching over from the current sensor to the pre-selected
`sensor can be effected during the milling operation without
`any repercussion on the work result.
`One embodiment of the invention provides that the cur-
`rently measured actual value for the milling depth and/or for
`the slope of the milling drum of the at least one pre-selected
`other sensor can be set, latest at the time of switchover, to the
`same, last measured actual value for the milling depth and/or
`for the slope of the previously used sensor.
`It is therefore possible, when changing the sensor, to apply
`the actual value of the sensor last used, so that the adjustment
`value for the setting ofthe milling depth and/or for the setting
`ofthe slope ofthe milling drum is not altered on account ofthe
`change, and that the evenness ofthe milled road surface is not
`adversely affected by the change of the sensor.
`An alternative embodiment provides that the set value for
`the milling depth and/or for the slope of the milling drum can
`be set, latest at the time of switchover, to the currently mea-
`sured actual value for the milling depth of the at least one
`pre-selected sensor.
`Equating the set value to the currently measured actual
`value of the pre-selected sensor which will replace the previ-
`ous sensor ensures that no alteration of the adjustment value
`for the setting of the milling depth and/or the slope will be
`made at the time of switchover.
`
`A third embodiment provides that, in case of a deviation of
`the measured actual values of the selected other sensor from
`
`the previously used sensor, the adjustment value for the set-
`ting of the milling depth and/or the setting ofthe slope can be
`altered by means of a pre-seeable transition function.
`According to a further alternative, it is therefore provided
`that, in case that an alteration of the current adjustment value
`results on account of the switchover of the sensors, said
`alteration follows a pre-setable transition function starting
`from an adjustment value of 0. It is thereby achieved that the
`alteration of the adjustment value is not effected in an erratic
`fashion, so that the evenness of the milled road surface is not
`adversely affected and adaptation to the adjustment value
`resulting on account of the switchover is effected over a
`longer distance, for example, over 10 m or more.
`
`Page 11 of 15
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`US 8,308,395 B2
`
`3
`It is preferably provided that the leveling device is provided
`with two controllers, the sensors of which are arranged par-
`allel to the rotating axis of the milling drum at a lateral
`distance to one another, and which preferably control the
`milling depth independently of one another on the left and
`right side of the machine.
`According to the method for controlling the milling depth
`or the milling slope ofthe milling drum of a road construction
`machine by registering the current actual value of the milling
`depth and/or of the slope of the milling drum relative to a
`reference surface using at least one exchangeable or switch-
`able sensor, where a milling depth control and/or a slope
`control of the milling drum is effected conditional on pre-
`determined set values and currently measured actual values
`during the milling operation by returning an adjustment value
`for achieving or maintaining the set value, it is provided that,
`when exchanging a currently used sensor for a pre-selected
`other sensor, control of the milling depth and/or the slope is
`effected without interruption of the milling operation by set-
`ting the set values and actual values of the sensor, prior to
`switchover, by means of an additional indication and setting
`unit in such a fashion that the current adjustment value for the
`setting of the milling depth and/or for the setting of the slope
`of the milling drum is not altered in an erratic fashion.
`Upon activation of a switchover command for the switcho-
`ver of sensors, the control is effected without an interruption
`of the milling operation and without an erratic alteration of
`the current adjustment value for the setting of the milling
`depth and/or for the setting of the slope of the milling drum.
`The road surface or a defined horizontal plane pre-deter-
`mined, for instance, by a laser, or any other freely definable
`pre-selected surface can be used as reference surface, which
`may show a different slope or gradient (positive or negative)
`in the course of the road surface.
`
`In the following, embodiments of the invention are
`explained in more detail with reference to the drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a road construction machine.
`
`FIG. 2 shows a leveling device.
`FIG. 3 shows an indication and setting device.
`FIG. 4 shows a matching of the actual values of different
`sensors at switchover.
`
`FIG. 5 shows a matching ofthe set value to the actual value
`of a new sensor at switchover.
`
`FIG. 6a and FIG. 6b shows the change from a milling depth
`control to a milling slope control.
`FIG. 7a through FIG. 70 shows the switchover procedure
`with matching of the set values.
`FIG. 8a to FIG. 8d shows a switchover with matching ofthe
`actual and set values.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS OF THE DRAWINGS
`
`FIG. 1 shows a road machine 1 for the treatment of road
`
`surfaces with a milling drum 3 height-adjustable with regard
`to the milling depth. The front travel drive unit supports itself
`on, for instance, the road surface 12, which can serve as
`reference surface for a milling depth control or slope control.
`For this purpose, the road machine 1 is provided with a
`leveling device 4 with at least one controller 611, 60 which
`receives set values for the milling depth and/or the slope ofthe
`milling drum 3. Exchangeable sensors A, B, C can be con-
`nected to the controllers 611, 6c of the leveling device 4. The
`sensors A, B, C serve the purpose of registering the current
`
`4
`
`actual value of the milling depth and/or the slope of the
`milling drum 3 relative to a reference surface, which may
`consist in the road surface 12, a pre-determined horizontal
`plane or a freely definable, for instance, mathematically pre-
`determined plane or surface.
`The at least one controller 611, 60 effects a milling depth
`control and/or a slope control for the milling drum 3 condi-
`tional on pre-determined set values and the currently mea-
`sured actual values of the at least one sensor A, B, C, with an
`adjustment value being returned for achieving or maintaining
`the set value in the milling operation. As follows from FIG. 2,
`the leveling device 4 is provided with an indication and set-
`ting device which is divided into three nearly identical indi-
`cation and setting units 211, 2b, 2c. The indication and setting
`device 2 serves the purpose of setting operating parameters
`for the sensors A, B, C. Set values and actual values of the
`sensors A, B, C can be set in each indication and setting unit
`211, 2b, 2c. The indication and setting units 2a and 20 right and
`left are each connected to a controller 611, 60 which can be
`activated by means of an automatic button to effect the cor-
`responding control automatically. The controllers remain in
`automatic mode during switchover. The adjustment value of
`the controllers 611, 60 resulting from the difference of the set
`value and actual value is indicated qualitatively by arrows 14,
`with the indication unit being capable of indicating the verti-
`cal traverse speed of the machine proportionally, meaning
`quantitatively, as well. The pre-determined set values and
`actual values of the central indication and setting unit 2b,
`which is coupled to a selectable sensor B that is to be
`exchanged for the currently used sensor A or C, can be inter-
`changed, by means of a switchover device 1011 or 10b, with
`the set values and actual values of the sensorA or C that is to
`
`10
`
`15
`
`20
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`25
`
`30
`
`35
`
`be exchanged for a selectable other sensor B.
`The embodiment shows a version in which one controller
`
`each 611, 6c is provided for one side of the road construction
`machine 1. It is understood that the indication and setting
`device 2 may also be provided with merely two indication and
`setting units if merely one controller is present, where one
`sensor is exchanged for another selectable sensor.
`The number of indication and setting units provided is
`therefore always larger by one than the number ofthe sensors
`in use.
`FIG. 2 shows the connection of sensors A, B, C to the
`leveling device 4 with two controllers 6a, 60, where the lev-
`eling device is provided with an indication and setting device
`2 with three indication and setting units 2a, 2b, 20.
`FIG. 3 shows an embodiment of the indication and setting
`device 2, wherein setting buttons 16 (up and down) for the
`setting of set values, as well as setting buttons 18 (up and
`down) for the adjustment of measured actual values are
`present for each indication and setting unit 211, 2b, 2c.
`The currently adjusted set values and the currently mea-
`sured actual values of the sensors A, B, C are indicated on the
`displays 20 of the indication and setting units 211, 2b, 2c. The
`direction of a possibly set slope of the milling drum can also
`be indicated on the displays 20. Furthermore, units are indi-
`cated, for example, in inch or cm, or percentages in % relating
`to the value indicated.
`A choice of sensors is indicated at the lower end 22 of the
`
`display 20, enabling a machine operator to determine by
`means of the current indication as to which type of sensor is
`currently indicated on the indication and setting unit 211, 2b,
`2c. The symbols represent, from left to right, a wire-rope
`sensor, a slope sensor, an ultrasonic sensor, a multiplex sen-
`sor, a total station, as well as a laser for pre-determining the
`reference surface.
`
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`US 8,308,395 B2
`
`5
`Above the displays 20, one button each is provided for the
`automatic mode and for the setting mode to set the controller
`parameters. A horn 24, as well as buttons 26 for adjusting the
`height of the travel drive unit may also be provided on the
`indication and setting device 2. Two memory buttons M1, M2
`for memorizing set values are additionally provided below
`the display 20 on the central indication and setting unit 2b.
`Various possibilities ofhow to avoid an erratic alteration of
`the current adjustment value are explained in FIGS. 4 to 6.
`In the embodiment of FIG. 4, the measured actual value of
`the pre-selected sensor B is equated to the last measured
`current actual value of the previously used sensor A at the
`time of switchover.
`
`In FIG. 5, the pre-determined set value is adapted to the
`currently measured actual value of the pre-selected sensor B
`so that, also in this case, there is no alteration of the adjust-
`ment value.
`In case of a deviation of the measured actual values of the
`
`previously used sensorA from the pre-selected new sensor B,
`the adjustment value can, as an alternative to the embodi-
`ments of FIGS. 4 and 5, also change into the adjustment value
`that results on account of the differences in the actual values
`
`by means of a transition function. A temporal transition there-
`fore takes place by means ofwhich no erratic alteration of the
`adjustment value can occur.
`FIGS. 6a and 6b show a switchover procedure in compen-
`sated condition. FIG. 6a shows the initial situation in which
`
`the indication and setting unit 20, which is linked to the
`controller 60, is to be switched over from the operating mode
`milling depth (set value 10.0 cm) to the operating mode
`milling slope (set value 2%). Switchover takes place in com-
`pensated condition. This means that the respective actual
`value on both sides of the machine corresponds to the set
`value, and that the adjustment value is therefore 0 on both
`sides. The compensated condition is indicated by the indica-
`tion and setting device 14a, 140 through a horizontal bar. It is
`evident from FIG. 6b that, when actuating the switchover
`button 10b of the switchover device 10, the pre-selected set
`values and actual values are interchanged from the indication
`and setting unit 2b to the indication unit 20, and are taken as
`the basis in continued automatic mode for a mixed milling
`depth and milling slope control.
`FIGS. 7a to 70 show the switchover procedure with match-
`ing of the set values.
`In this example, the adjustment values on both sides of the
`machine are unequal 0. The indication and setting unit 20 of
`the controller 60 is switched over from milling depth control
`to milling slope control. The set value of the slope is adapted
`manually in FIG. 7b by actuating the buttons 16, so that no
`erratic alteration of the adjustment value will occur. It is
`assumed in this example that the adjustment value is propor-
`tional to the control deviation (P controller), and that the
`proportionality factor for the milling depth and milling slopes
`is equal numerically. The control deviation is 0.3 cm for the
`milling depth (indication and setting unit 20 in FIG. 7a), and
`0.6% for the milling slope (indication and setting unit 2b in
`FIG. 711) so that the adjustment value would therefore double
`in terms of value after switchover. In order to match the
`
`control deviation, the set value of the slope is reduced to 2.0,
`which results in an equal control deviation numerically. This
`can be effected manually via the button 16 “reduce set value”,
`or automatically, for example, via the button combination 16,
`18 “increase actual value and reduce set value” (FIG. 7b).
`By actuating the switchover button 10b in the illustration
`according to FIG. 70, the set value and actual value of the
`milling slope is applied, as indicated by arrows in FIG. 70. In
`this process, the adjustment value remains unchanged.
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`An additional embodiment not shown may provide auto-
`matic matching of the set values. In such an embodiment, the
`alteration of the set values in the embodiment of FIGS. 7a to
`
`70 mentioned before is effected automatically when the
`switchover button 10b (or 1011) is actuated in automatic mode.
`The first step of the manual alteration of the values in the
`central indication and setting unit 2b (FIG. 7) can then be
`dispensed with as it is effected automatically.
`A further variant not shown consists in altering, in case of
`a deviation of the actual values, the adjustment value by
`means of a pre-set transition function, starting from the cur-
`rent adjustment value.
`FIGS. 8a and 8d show an embodiment with matching ofthe
`actual values and set values.
`
`The initial situation shown in FIG. 8a indicates, with
`regard to the controller 60 on the right side, the values of a
`milling depth sensor C, for example, a wire-rope sensor
`mounted at the edge protection, while the central indication
`and setting unit 2b indicates the values of a milling depth
`sensor B, for example, an ultrasonic sensor with scanning
`point in front of the milling drum.
`The milling depth sensor C is to be replaced by the milling
`depth sensor B, where the set values and actual values of the
`two sensors B, C do not match. However, the current adjust-
`ment value equals 0, as is evident from the indication device
`1411, 140.
`As sensor B is adjusted differently, its actual value does not
`match the actual value of sensor C. It can be equated to the
`actual value of sensor A by means of the actual value setting
`buttons 18 either manually or automatically, for example, by
`keeping the two actual value setting buttons 18 pressed for an
`extended period of time.
`FIGS. 80 and 8d show the matching procedure of the set
`values. As the set value of the two sensors B, C relates to the
`milling depth on the right, the set value of sensor B is to be
`adapted to the set value of sensor C. This can be effected via
`set value setting buttons or automatically, for example, by
`keeping the two set value setting buttons pressed for an
`extended period of time.
`Following actuation of the right switchover button 10b, the
`set value and actual value of sensor B are applied. The adjust-
`ment value remains 0 and is thus unchanged.
`All embodiments indicate the set values and actual values
`
`of the pre-selected sensor B, which is to be exchanged for a
`previously used sensor C, in the indication and setting unit 2b.
`It is possible in this way to pre-set all setting values (set values
`and actual values) of the pre-selected sensor B, and to adapt
`them to the previously used sensors A, C or their set values or
`actual values respectively even prior to entering a switchover
`command via the switchover buttons 1011 or 10b. Upon actua-
`tion ofthe switchover button 10a ofthe switchover device 10,
`the pre-selected sensor is exchanged with the sensorA that is
`currently used on the left side of the road construction
`machine 1.
`
`As already explained before in connection with the
`embodiment ofFIG. 7, instead ofeffecting equalization ofthe
`set values manually, equalization of the set values can also be
`effected automatically when actuating the switchover button
`10b (or 1011) in automatic mode.
`Although a preferred embodiment of the invention has
`been specifically illustrated and described herein, it is to be
`understood that minor variations may be made in the appara-
`tus without departing from the spirit and scope of the inven-
`tion, as defined by the appended claims.
`
`Page 13 of 15
`
`Page 13 of 15
`
`

`

`US 8,308,395 B2
`
`7
`
`What is claimed is:
`1. A road construction machine for the treatment of road
`
`surfaces, comprising:
`a milling drum, the milling drum being position adjustable
`with regard to at
`least one position characteristic
`selected from the group consisting of milling depth of
`the drum and slope of the drum; and
`a leveling system configured to control the at least one
`position characteristic, the leveling system including:
`a plurality of selectable sensors, each sensor configured to
`sense a current actual value of an operating parameter
`corresponding to at least one of the milling depth of the
`drum and the slope of the drum;
`a plurality of indication and setting devices, each of the
`indication and setting devices being associatable with at
`least one of the plurality of selectable sensors, each
`indication and setting device being operable to indicate
`the current actual value of and to set a set value for each
`
`operating parameter sensed by its associated sensor or
`sensors;
`
`a controller and switchover system configured to control
`the at least one position characteristic conditioned on set
`value or values and sensed current actual value or values
`
`of the operating parameter or parameters sensed by a
`selected subset of the plurality of selectable sensors by
`returning at least one adjustment value to adjust the at
`least one position characteristic so that the sensed cur-
`rent actual value or values of the operating parameter or
`parameters approach the set value or values for the
`selected subset ofthe plurality of selectable sensors; and
`the controller and switchover system being configured to
`switch over from control based upon a first selected
`subset of the plurality of selectable sensors to control
`based upon a second selected subset during milling
`operation without interruption of the milling operation
`and without any erratic alteration of the at least one
`adjustment value, the second selected subset exchanging
`at least one replacement sensor not in the first subset for
`at least one replaced sensor that was in the first subset.
`2. The road construction machine of claim 1, wherein:
`the controller and switchover system is operable to set a
`current actual value for an operating parameter for the
`replacement sensor to a last measured actual value for
`the operating parameter of the replaced sensor.
`3. The road construction machine of claim 1, wherein:
`the controller and switchover system is operable to set a set
`value for an operating parameter for the replacement
`sensor to the current actual value for the operating
`parameter of the replacement sensor.
`4. The road construction machine of claim 1, wherein:
`the controller and switchover system is operable, in the
`case of a difference between a current actual value of an
`
`operating parameter for the replacement sensor and the
`current actual value of the operating parameter of the
`replaced sensor, to alter the at least one adjustment value
`in accordance with a pre-settable transition function.
`5. The road construction machine of claim 1, wherein:
`the controller and switchover system includes a manually
`operable switchover device; and
`the manually operable switchover device and the one ofthe
`indication and setting devices associated with the
`replacement sensor are operable so that a human opera-
`tor may manually pre-select the replacement sensor and
`manually pre-set the operating parameter ofthe replace-
`ment sensor prior to effecting the switchover.
`
`8
`6. The road construction machine of claim 1, wherein:
`the controller and switchover system includes first and
`second control units operably associated with first and
`second sensors, respectively, of the plurality of select-
`able sensors, the first and second sensors being arranged
`parallel to a rotational axis of the milling drum, the first
`and second control units being operable to control mill-
`ing depth of the milling drum independently of one
`another on left and right sides, respectively, of the road
`construction machine.
`7. The road construction machine of claim 1, wherein:
`the plurality of selectable sensors includes:
`a first sensor being a left side depth sensor;
`a second sensor being a right side depth sensor; and
`a third sensor being a third depth sensor;
`the first subset of sensors includes only two of the first,
`second and third sensors; and
`the second subset of sensors includes the other one of the
`first, second and third sensors not in the first subset, and
`the second subset of sensors includes only one ofthe two
`sensors of the first subset of sensors.
`8. The road construction machine of claim 1, wherein:
`the plurality of selectable sensors includes a first sensor
`and a second sensor;
`the first subset of sensors includes the first sensor but not
`the second sensor; and
`the second subset of sensors includes the second sensor but
`not the first sensor.
`9. The road construction machine of claim 8, wherein:
`the plurality of selectable sensors includes only the first
`and second sensors.
`10. The road construction machine of claim 8, wherein:
`the plurality of selectable sensors further includes a third
`sensor.
`
`1 1 . A leveling device for a position adjustable milling drum
`of a road construction machine, the milling drum being posi-
`tion adjustable with regard to at least one position character-
`istic selected from the group consisting ofmilling depth ofthe
`drum and slope of the drum, th