WO1995008677A1 - Multi-variable control of multi-degree of freedom linkages - Google Patents
Multi-variable control of multi-degree of freedom linkages Download PDFInfo
- Publication number
- WO1995008677A1 WO1995008677A1 PCT/US1994/004888 US9404888W WO9508677A1 WO 1995008677 A1 WO1995008677 A1 WO 1995008677A1 US 9404888 W US9404888 W US 9404888W WO 9508677 A1 WO9508677 A1 WO 9508677A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- velocity
- signals
- signal
- linkage
- producing
- Prior art date
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
- F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
- F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
- F15B21/008—Reduction of noise or vibration
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02F—DREDGING; SOIL-SHIFTING
- E02F3/00—Dredgers; Soil-shifting machines
- E02F3/04—Dredgers; Soil-shifting machines mechanically-driven
- E02F3/28—Dredgers; Soil-shifting machines mechanically-driven with digging tools mounted on a dipper- or bucket-arm, i.e. there is either one arm or a pair of arms, e.g. dippers, buckets
- E02F3/36—Component parts
- E02F3/42—Drives for dippers, buckets, dipper-arms or bucket-arms
- E02F3/43—Control of dipper or bucket position; Control of sequence of drive operations
- E02F3/431—Control of dipper or bucket position; Control of sequence of drive operations for bucket-arms, front-end loaders, dumpers or the like
- E02F3/434—Control of dipper or bucket position; Control of sequence of drive operations for bucket-arms, front-end loaders, dumpers or the like providing automatic sequences of movements, e.g. automatic dumping or loading, automatic return-to-dig
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02F—DREDGING; SOIL-SHIFTING
- E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
- E02F9/20—Drives; Control devices
- E02F9/2025—Particular purposes of control systems not otherwise provided for
- E02F9/2037—Coordinating the movements of the implement and of the frame
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02F—DREDGING; SOIL-SHIFTING
- E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
- E02F9/20—Drives; Control devices
- E02F9/22—Hydraulic or pneumatic drives
- E02F9/2203—Arrangements for controlling the attitude of actuators, e.g. speed, floating function
-
- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02F—DREDGING; SOIL-SHIFTING
- E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
- E02F9/20—Drives; Control devices
- E02F9/22—Hydraulic or pneumatic drives
- E02F9/2221—Control of flow rate; Load sensing arrangements
Definitions
- This invention relates generally to a control system for a work implement and more particularly to a control system for a work implement having a plurality of multi-degree of freedom linkages.
- a front end loader utilizes a work implement for digging, loading and dumping a bucket.
- the work implement includes at least two linkages, a boom and a bucket.
- Each linkage is actuated by at least one hydraulic cylinder for controlled movement.
- the hydraulic excavator is another example.
- the HE'S work implement typically has three linkages: a boom, a stick, and a bucket. Furthermore, rotary motion of the implement itself is provided hydraulically either by rotation of the implement about a pivot point or rotation of the HE , s cab.
- actuation of the hydraulic cylinders is typically provided through movement of a series of mechanical levers.
- Each mechanical lever is mechanically coupled to a hydraulic directional control valve which controllably provides a flow of hydraulic fluid to the respective hydraulic cylinder(s).
- each circuit would contain at least one directional control valve.
- the directional control valve may be either directly coupled to a control lever or hydraulically coupled through a hydraulic pilot system.
- An operator in order to affect movement of a particular linkage would controllably operate one of the control levers. Movement of a control lever along a particular axis would result in responsive movement of a specified linkage.
- four separate levers may be provided, each movable along a single axis. Movement of a particular lever may effect movement of a respective linkage.
- levers movable along two perpendicular axes may provide control of two linkages.
- a controller typically microprocessor based, interprets the electronic signals and controllably actuates an electrohydraulic direction control valve or a pilot control valve for providing hydraulic fluid flow to the cylinders.
- the dynamic effects are a result of the oil- mass resonances associated with each implement circuit.
- the resonant frequency of each circuit is different and varies as a function of the forces exerted on each linkage and the oil column lengths of the individual circuits (as defined by the linear extension of the respective cylinder and line volumes) .
- the forces exerted on the linkage are a function of the load on the implement and the individual forces exerted on the linkage from each of the hydraulic cylinders.
- each resonant frequency is dynamic, i.e., it continuously varies.
- the problem lies in the fact that as each hydraulic cylinder is extended or retracted, the force exerted by the respective cylinder on the linkage may force the hydraulic cylinders corresponding to the other circuits into an oscillatory mode resulting in a severe degradation of desired path accuracy. This is known as dynamic coupling or "cross-talk" among the implement circuits.
- Each hydraulic circuit has the potential for adversely exciting the other circuits. As a result, whenever one hydraulic circuit is being utilized on a multi linkage implement, the potential for cross-talk and a degradation in system response accuracy exists.
- the present invention is directed to overcoming one or more of the problems, as set forth above.
- an apparatus for controllably actuating a work implement has at least a first linkage and a second linkage.
- the apparatus produces a control signal and senses the position and velocity of the first and second linkages.
- the apparatus produces a command signal as a function of the control signal and the position and velocity signals.
- the command signal controls actuation of the first linkage such that cross-talk between the first and second linkages is minimized.
- Fig. 1 is a stylized representation of a work implement having first, second and third linkages, respective actuating means, and a controlling means, according to an embodiment of the present invention
- Fig. 2 is a block diagram of the controlling means of Fig. 1 and position and velocity input sensors;
- Fig. 3 is a detailed block diagram of the controlling means of Fig. 1 including a multivariable controlling means;
- Fig. 4 is an equation used in the multivariable controlling means of Fig. 3;
- Fig. 5 is a stylized representation of a serial hydraulic circuit and the controlling means of Fig. 1, according to am embodiment of the present invention
- Fig. 6 is a stylized representation of a parallel hydraulic circuit and the controlling means of Fig. 1, according to am embodiment of the present invention
- Fig. 7 is a stylized representation of one of the actuating means of Fig. 1, including an open center directional control valve and an electrohydraulic pilot valve;
- Fig. 8 is a stylized representation of one of the actuating means of Fig. 1, including a closed center pressure compensated directional control valve and an electrohydraulic pilot valve;
- Fig. 9 is a stylized representation of one of the actuating means of Fig. 1, including an electrohydraulic open center directional control valve; and.
- Fig. 10 is a stylized representation of one of the actuating means of Fig. 1, including an electrohydraulic closed center directional control valve.
- the present invention or apparatus 102 is adapted to control the work implement 104 of an earthmoving vehicle.
- the work implement 104 shown is that of a hydraulic excavator.
- the present invention is applicable to the work implements of various other earthmoving vehicles, e.g., a front end loader or motorgrader.
- the work implement 104 of the hydraulic excavator has first, second and third linkages 106,108,110 (the boom, stick and bucket).
- first, second and third linkages 106,108,110 the boom, stick and bucket.
- the present invention provides advantages for various other arrangements, for example, work implements having as few as two linkages and work implements having as many as N linkages.
- the following discussion is concerned with a hydraulic excavator, i.e., a work implement having 3 linkages.
- the present invention is equally applicable to a work implement having as few as 2 and as many as N linkages.
- a means 124 produces at least one control signal.
- the control signal producing means 124 includes first and second control handles 126,128.
- the control handles 126,128 are electronic joysticks which generate electronic signals in response to movement of the joysticks along or about suitable axes.
- a controlling means 130 receives the control signal(s), the first, second, and third position signals, the first, second, and third velocity signals and produces a first command signal (C ⁇ ) as a function of the control signal(s), the first, second, and third position signals and the first, second, and third velocity signals.
- the controlling means 130 also produces a second command signal (C 2 ) as a function of the control signal(s), the first, second, and third position signals and the first, second, and third velocity signals and produces a third command signal (C 3 ) as a function of the control signal(s), the first, second, and third position signals and the first, second, and third velocity signals.
- a means 202 senses the position and velocity of the first linkage 106 and responsively produces a first position signal and a first velocity signal.
- a means 204 senses the position and velocity of the second linkage 108 and responsively produces a second position signal and a second velocity signal.
- a means 206 senses the position and velocity of the third linkage 110 and responsively produces a third position signal and a third velocity signal.
- the means 202,204,206 may sense either linear and angular positions and velocities.
- each position and velocity sensing means 202,204,206 includes a RF linear position sensor.
- the RF position sensor senses the linear extension of the cylinders.
- the RF sensor also senses the linear velocity of the cylinder.
- a separate velocity sensor for example, a DC rotary generator connected to the cylinder which generates an electrical signal responsive to the speed of rotation.
- the controlling means 130 estimates the individual velocities as the derivative of the position signals.
- each position and velocity sensing means 202,204,206 includes a rotary encoder which generates signals indicated of the movement of the individual linkages 106,108,110 about a respective pivot point.
- a means 112 receives the first command signal (C ⁇ ) and responsively actuates the first linkage 106 as a function thereof.
- a means 114 receives the first command signal (C 2 ) and responsively actuates the second linkage 108 as a function thereof.
- a means 116 receives the first command signal (C 3 ) and responsively actuates the third linkage 110 as a function thereof.
- the first, second, and third actuating means 112,114,116 includes two hydraulic cylinders 118, one hydraulic cylinder 120 and one hydraulic cylinder 122, respectively.
- the first command signal is adapted to minimize the cross-talk between the first actuating means 112 and the second and third linkages 108,110 and actuating means 114,116.
- the second command signal is adapted to minimize the cross-talk between the second actuating means 114 and the first and third linkages 106,110 and actuating means 112,116.
- the third command signal is adapted to minimize the cross-talk between the third actuating means 116 and the first and second linkages 106,108 and actuating means 112,114.
- cross-talk refers to the effect actuation of one hydraulic circuit has on the other hydraulic circuits.
- Each hydraulic circuit (including the linkage and the respective cylinder) has a dynamic oil-mass resonant frequency.
- the dynamic behavior of each linkage i.e., the oil-mass resonant frequency
- the oil mass resonant frequencies of the linkages overlap.
- the inertial load e.g., material in the bucket, also affects the individual oil-mass resonance frequencies and provides a forcing function for excitation.
- the present invention compensates for the cross-talk between the hydraulic circuits thereby reducing the dynamic coupling.
- the actuating means 112,114 are parallelly connected in a hydraulic circuit 502.
- a pump 504 provides pressurized hydraulic fluid to the actuating means 112,114.
- a feedback control valve 506 provides load compensation to the pump 504.
- each actuating means 112,114 are serially connected in a hydraulic circuit 602.
- a pump 602 (shown here as being uncompensated) provides pressurized hydraulic fluid to the actuating means 112,114.
- each actuating means 112,114,116 includes an open center directional control valve 902 and a pilot control valve 704.
- each actuating means 112,114,116 includes a closed center pressure compensated directional control valve 802 and a pilot control valve 804.
- each actuating means 112,114,116 includes an electrohydraulic open center directional control valve 902.
- each actuating means 112,114,116 includes an electrohydraulic closed center pressure compensated directional control valve 1002.
- the controlling means 130 includes a controller 208.
- the controller 208 is a digital controller which receives the sensor information and controllably operates the individual actuating means.
- the controller 210 is micro-processor based.
- One suitable microprocessor is MC68332 which is available from Motorola Corp. of Schaumburg, IL.
- the controlling means 130 includes a means 302 for receiving the control signal(s) and responsively producing first desired position and velocity signals, second desired position and velocity signals, and third desired position and velocity signals.
- the present invention is flexibly suitable to work with a multitude of control systems, i.e., manual, automatic, or semi ⁇ automatic.
- a single control signal indicates the desired position and/or velocity of the point.
- the desired position and velocity signal producing means 302 receives the control signal(s) and according to the current mode of the control system, determines the desired position and velocity signals corresponding to the desired position and velocity of the respective linkages.
- the controlling means 130 further includes a means 304 for receiving the desired position and velocity signals and the position and velocity signals, compares the respective signals, and responsively produces velocity and position error signals.
- the controlling means 130 also includes a means 306 for receiving the position and velocity error signals and responsively determining the command signals.
- the command signal determining means 306 includes a means for multiplying the position error signal by a first position transfer function, multiplying the first velocity error signal by a first velocity transfer function, multiplying the second position error signal by a second position transfer function, multiplying the second velocity error signal by a second velocity transfer function, and multiplying the third position error signal by a third position transfer function, and multiplying the third velocity error signal by a third velocity transfer function.
- the first command signal (C ⁇ ) is a function of the sum of the above products.
- command signals for a work implement having n linkages are determined by the equation, which is also shown in Fig. 4:
- PE- the first position error signal
- PE 2 the second position error signal
- PE n the nth position error signal
- VE X the first velocity error signal
- VE 2 the second velocity error signal
- VE n the nth velocity error signal
- H p ii' ⁇ 11 the fi rst position and velocity transfer functions for command c 1# H pl2
- H p2n ,H v . 3n the nth position and velocity transfer functions for command C 2
- H pn i'H v ni the first position and velocity transfer functions for command C n
- H p n 2 ' H vn2 the sec °nd position and velocity transfer functions for command C n
- H pnn ,H vnn the nth position and velocity transfer functions for command C n .
- the transfer functions are dependent upon the linkage arrangement/specifications of the work implement and are synthesized based on empirical measurements of the linkage dynamics.
- the control matrix (H) is derived from a system model consisting of: l. linear transfer function models of the implement circuits's dynamic behavior; 2. linear transfer function models describing the error or inaccuracy of the implement circuit models as the linkage geometry changes; 3. performance models describing the gain and bandwidth necessary to meet the required tracking accuracy performance; and
- linear transfer function models describing the frequency characteristics of the (position and velocity) sensor noise.
- the linear transfer models are based on empirical data and include coupling terms.
- the linear transfer models are derived using a dynamic signal analyzer.
- One suitable dynamic signal analyzer is the HP 3566A
- the system model defined by the above models is transformed to a state-space representation using standard conversion techniques.
- the state-space system (P) is partitioned as follows:
- the control matrix H is derived such that the tracking error between the commanded implement circuit hydraulic cylinder positions and velocities and actual cylinder positions and velocities.
- the control matrix H is derived using the following procedure: 1. derive system model P;
- H is synthesized using an H-infinity method.
- the H- infinity method is summarized in "State-space Solutions to Standard H2 and H-infinity Control Problems," by Doyle, J.C. et al., IEEE Transactions on Automatic Control, VI. 34, No. 8, August 1989, which is herein incorporated by reference.
- the state-space system P is scaled by matrices obtained using an mu- analysis method.
- the mu-analysis method is disclosed in "Performance and Robustness Analysis for Structured Uncertainty," by Doyle, J.C. et al, IEEE Conference on Decision and Control, Dec. 1982, pp. 629-636, which is herein incorporated by reference.
- the present invention 102 is adapted to provide more stable and accurate control of the linkages comprising the work implement.
- the present invention is described in relation to a hydraulic excavator.
- the present invention has equal applicability to a wide range of work implements.
- the present invention is not expressly limited to any such vehicle or linkage arrangement.
- the present invention works equally well in a wide range of work implement control modes.
- the work implement may be operated in a manual, semi-automatic or automatic mode.
- a manual mode an operator preferably requests movement of the linkages through a pair of electronic joysticks.
- the controlling means 130 receives the signals and the feedback signals. According to a set of rules defining the desired response characteristics (position, velocity) of the individual linkages the controlling means determines desired positions and velocities and subsequently position and velocity errors.
- the controlling means 130 filters the required error signals and determines individual command signals for each individual hydraulic circuit.
- the individual commands are functions of the position and velocity errors respective to all of the individual circuits. This allows the controlling means through the position and velocity transfer functions to effect the required movement and simultaneously to minimize the effect of cross-talk between the hydraulic circuits.
- the present invention also works during semi-automatic or automatic modes. For example, linear motion of a point on the work implement, typically the end point of the bucket linkage, is provided in a semi-automatic mode controllable by an operator through a single control lever. Desired position and velocity signals for each linkage in the work implement are determined as a function of the control signal. Thereafter, the controller works similarly to that described above.
- the transfer functions implemented by the controller are dependent upon the specifications of the work implement.
- the transfer functions are based on empirical measurements as discussed above.
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP50422695A JP3614171B2 (en) | 1993-06-28 | 1994-05-02 | Multivariate control of multistage free link mechanism |
DE4497127T DE4497127T1 (en) | 1993-06-28 | 1994-05-02 | Control with multiple variables for connections or connecting links with several degrees of freedom |
SE9501220A SE506338C2 (en) | 1993-06-28 | 1995-04-04 | Multivariate control of link systems with multiple degrees of freedom |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/082,644 US5383390A (en) | 1993-06-28 | 1993-06-28 | Multi-variable control of multi-degree of freedom linkages |
US08/082,644 | 1993-09-23 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1995008677A1 true WO1995008677A1 (en) | 1995-03-30 |
Family
ID=22172477
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1994/004888 WO1995008677A1 (en) | 1993-06-28 | 1994-05-02 | Multi-variable control of multi-degree of freedom linkages |
Country Status (5)
Country | Link |
---|---|
US (1) | US5383390A (en) |
JP (1) | JP3614171B2 (en) |
DE (1) | DE4497127T1 (en) |
SE (1) | SE506338C2 (en) |
WO (1) | WO1995008677A1 (en) |
Families Citing this family (22)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH07268897A (en) * | 1994-03-23 | 1995-10-17 | Caterpillar Inc | Self-adaptable excavation control system and method thereof |
JP2972530B2 (en) * | 1994-11-16 | 1999-11-08 | 新キャタピラー三菱株式会社 | Work machine control device for construction machinery |
KR100328218B1 (en) * | 1996-04-30 | 2002-06-26 | 볼보 컨스트럭션 이키프먼트 홀딩 스웨덴 에이비 | Operation method selection device and method of hydraulic construction machine |
US6050090A (en) * | 1996-06-11 | 2000-04-18 | Kabushiki Kaisha Kobe Seiko Sho | Control apparatus for hydraulic excavator |
US6025686A (en) * | 1997-07-23 | 2000-02-15 | Harnischfeger Corporation | Method and system for controlling movement of a digging dipper |
DE19743801A1 (en) * | 1997-10-02 | 1999-04-08 | Claas Selbstfahr Erntemasch | Device for controlling a hydraulic cylinder in a self-propelled harvesting machine |
US6115660A (en) * | 1997-11-26 | 2000-09-05 | Case Corporation | Electronic coordinated control for a two-axis work implement |
US6233511B1 (en) | 1997-11-26 | 2001-05-15 | Case Corporation | Electronic control for a two-axis work implement |
US5953977A (en) * | 1997-12-19 | 1999-09-21 | Carnegie Mellon University | Simulation modeling of non-linear hydraulic actuator response |
ATE203488T1 (en) * | 1998-09-08 | 2001-08-15 | Palfinger Ag | CRANE |
US6129155A (en) * | 1998-12-02 | 2000-10-10 | Caterpillar Inc. | Method and apparatus for controlling a work implement having multiple degrees of freedom |
US6257118B1 (en) | 1999-05-17 | 2001-07-10 | Caterpillar Inc. | Method and apparatus for controlling the actuation of a hydraulic cylinder |
DE10040395A1 (en) | 1999-09-14 | 2001-03-22 | Caterpillar Inc | Hydraulic control system for improving pump response and dynamic match of pump and valve has control unit for controlling rate of change of cross-section of main flow control valve |
FR2822483B1 (en) * | 2001-03-22 | 2003-07-18 | Volvo Compact Equipment Sa | LOADER-TYPE PUBLIC WORKS MACHINE |
US20030196434A1 (en) * | 2001-12-11 | 2003-10-23 | Brown Bryan D. | Multi-circuit flow ratio control |
EP1416095B1 (en) * | 2002-10-31 | 2011-10-12 | Deere & Company | Work vehicle, in particular a backhoe and/or a vehicle with a front loader |
US8069772B1 (en) * | 2008-06-18 | 2011-12-06 | Arnold Peterson | Systems and methods for controlling hydraulic actuators |
US8109197B1 (en) * | 2008-06-18 | 2012-02-07 | Arnold Peterson | Hydraulic control system and method |
US20120253609A1 (en) * | 2011-03-31 | 2012-10-04 | Caterpillar Inc. | Proportional control using state space based scheduling |
EP3535458B1 (en) | 2016-11-02 | 2023-07-12 | Clark Equipment Company | System and method for defining a zone of operation for a lift arm |
US20180252243A1 (en) * | 2017-03-03 | 2018-09-06 | Husco International, Inc. | Systems and methods for dynamic response on mobile machines |
US10634442B2 (en) * | 2018-01-17 | 2020-04-28 | Cubic Corporation | Light gun breech position detector |
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EP0361666A1 (en) * | 1988-09-08 | 1990-04-04 | Caterpillar Inc. | Intuitive joystick control for a work implement |
FR2671118A1 (en) * | 1990-12-31 | 1992-07-03 | Samsung Heavy Ind | SYSTEM AND METHODS FOR AUTOMATICALLY CONTROLLING THE OPERATION OF PUBLIC WORKS ENGINES. |
EP0532195A2 (en) * | 1991-09-13 | 1993-03-17 | Caterpillar Inc. | Method and apparatus for controlling an implement |
FR2691186A1 (en) * | 1990-10-31 | 1993-11-19 | Samsung Heavy Ind | Control system to automatically control an excavator based on control levers or pedals. |
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-
1993
- 1993-06-28 US US08/082,644 patent/US5383390A/en not_active Expired - Fee Related
-
1994
- 1994-05-02 DE DE4497127T patent/DE4497127T1/en not_active Withdrawn
- 1994-05-02 WO PCT/US1994/004888 patent/WO1995008677A1/en active Application Filing
- 1994-05-02 JP JP50422695A patent/JP3614171B2/en not_active Expired - Fee Related
-
1995
- 1995-04-04 SE SE9501220A patent/SE506338C2/en not_active IP Right Cessation
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0361666A1 (en) * | 1988-09-08 | 1990-04-04 | Caterpillar Inc. | Intuitive joystick control for a work implement |
FR2691186A1 (en) * | 1990-10-31 | 1993-11-19 | Samsung Heavy Ind | Control system to automatically control an excavator based on control levers or pedals. |
FR2671118A1 (en) * | 1990-12-31 | 1992-07-03 | Samsung Heavy Ind | SYSTEM AND METHODS FOR AUTOMATICALLY CONTROLLING THE OPERATION OF PUBLIC WORKS ENGINES. |
EP0532195A2 (en) * | 1991-09-13 | 1993-03-17 | Caterpillar Inc. | Method and apparatus for controlling an implement |
Also Published As
Publication number | Publication date |
---|---|
SE506338C2 (en) | 1997-12-08 |
JPH08504909A (en) | 1996-05-28 |
US5383390A (en) | 1995-01-24 |
SE9501220L (en) | 1995-07-25 |
JP3614171B2 (en) | 2005-01-26 |
SE9501220D0 (en) | 1995-04-04 |
DE4497127T1 (en) | 1995-11-23 |
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