OFFSET BOUNDARIES LIMIT FOR FALSE LASER STRIKES

Description

FIELD OF THE DISCLOSURE

The present disclosure relates generally to work machines such as excavators, and to grade control systems and methods for such work machines that operate using a laser plane as a reference.

BACKGROUND

Work machines within the scope of the present disclosure may for example include not only hydraulic excavators but loaders, crawlers, motor graders, backhoes, forestry machines, front shovel machines, and others. These work machines may typically have wheeled or tracked ground engaging units supporting a frame and/or undercarriage from the ground surface, but work machines within the scope of the present disclosure may also include stationary frames with one or more components moveable relative thereto. Work machines as disclosed herein may include for example a work implement, which includes one or more components, that is used to modify the terrain based on control signals from a controller of the work machine.

Such machines may include grade control systems which utilize a laser plane source located nearby on the work site as a reference for control of the working operation of the machine. One issue encountered in the use of such grade control systems is the possibility that the laser receiver may inadvertently detect an unintended laser strike from another laser source which has been set up elsewhere near the job site. There is a need for a system to detect such false laser strikes.

BRIEF SUMMARY

In one embodiment the present disclosure provides a work machine for working a terrain at a work site having multiple laser sources present on the work site. The work machine includes a laser receiver configured to receive laser plane reference signals from the laser sources, and at least one working implement configured to work the terrain. The work machine includes a controller configured to:

• • determine a position of a first laser plane reference signal from a first one of the laser sources relative to the work machine with the work machine positioned at a first location on the work site;
  • identify the first determined position as an expected position of the first laser plane reference signal relative to the work machine;
  • perform a working operation using the implement to work the terrain with the work machine positioned at the first location on the work site;
  • receive with the laser receiver a further laser plane reference signal during the working operation;
  • determine a position of the further laser plane reference signal relative to the work machine; and
  • determine whether the position of the further laser plane reference signal relative to the work machine is within a defined deviation of the expected position of the first laser plane reference signal relative to the work machine.

In a further embodiment a method is provided of operating a work machine including a laser receiver and at least one implement for working a terrain at a work site having multiple laser sources present on the work site. The method includes:

• • positioning the work machine at a first location on the work site;
  • receiving with the laser receiver a first laser plane reference signal from a designated one of the laser sources with the work machine positioned at the first location on the work site;
  • determining with an automatic controller a first determined position of the first laser plane reference signal relative to the work machine with the work machine positioned at the first location on the work site;
  • identifying the first determined position as an expected position of the first laser plane reference signal relative to the work machine;
  • performing a working operation using the implement to work the terrain;
  • receiving with the laser receiver a further laser plane reference signal during the working operation;
  • determining with the automatic controller a position of the further laser plane reference signal relative to the work machine; and
  • determining with the automatic controller whether the position of the further laser plane reference signal relative to the work machine is within a defined deviation of the expected position of the first laser plane reference signal relative to the work machine.

Numerous objects, features, and advantages of the embodiments set forth herein will be readily apparent to those skilled in the art upon reading of the following disclosure when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view representing an excavator as an exemplary work machine according to an embodiment of the present disclosure.

FIG. 2 is a side view representing the work machine of FIG. 1 in relation to a laser reference source according to an embodiment of the present disclosure.

FIG. 3 is another schematic side view representing the work machine of FIG. 1 on a work site at which multiple laser sources are present.

FIG. 3A is an enlarged view in the area of the laser receiver on FIG. 3.

FIG. 4 is a schematic drawing of a control system of the work machine of FIG. 1.

DETAILED DESCRIPTION

FIG. 1 depicts a representative self-propelled work machine 20 in the form of, for example, a tracked excavator machine. The work machine 20 includes an undercarriage 22 including first and second ground engaging units 24 including first and second travel motors (not shown) for driving the first and second ground engaging units 24, respectively. A main frame 32 is supported from the undercarriage 22 by a swing bearing 34 such that the main frame 32 is pivotable about a pivot axis 36 relative to the undercarriage 22. The pivot axis 36 is substantially vertical when a ground surface or terrain 38 engaged by the ground engaging units 24 is substantially horizontal. A swing motor (not shown) is configured to pivot the main frame 32 on the swing bearing 34 about the pivot axis 36 relative to the undercarriage 22.

In an embodiment, a swing angle sensor (not shown) may include an upper sensor part mounted on the main frame 32 and a lower sensor part mounted on the undercarriage 22. Such a swing angle sensor may be configured to provide a swing (or pivot) angle signal corresponding to a pivot position of the main frame 32 relative to the undercarriage 22 about the pivot axis 36. The swing angle sensor may for example be a Hall Effect rotational sensor including a Hall element, a rotating shaft, and a magnet, wherein as the angular position of the Hall element changes, the corresponding changes in the magnetic field result in a linear change in output voltage. Other suitable types of rotary position sensors include rotary potentiometers, resolvers, optical encoders, inductive sensors, and the like.

A work implement or working implement 42 in the context of the referenced work machine 20 is a boom assembly having numerous components in the form of a boom 44 pivotably connected to the main frame 32 at a linkage joint 105, an arm 46 pivotally connected to the boom 44 at a linkage joint 106, and a working tool 48. The boom 44 is pivotally attached to the main frame 32 to pivot about a generally horizontal axis relative to the main frame 32. The working tool 48 in this embodiment is an excavator shovel, which is pivotally connected to the arm 46 at a linkage joint 110. One end of a dogbone 47 is pivotally connected to the arm 46 at a linkage joint, and another end of the dogbone 47 is pivotally connected to a tool link 49. A tool link 49 in the context of the referenced work machine 20 is a bucket link 49.

The boom assembly 42 extends from the main frame 32 along a working direction of the boom assembly 42. The working direction can also be described as a working direction of the boom 44. As described herein, control of the work implement 42 may relate to control of any one or more of the associated components (e.g., boom 44, arm 46, tool 48). The working tool 48 may be described as a working implement 48 carried by the boom assembly 42.

Referring again to the embodiment of FIG. 1, the first and second ground engaging units 24 are tracked ground engaging units but in various embodiments may be wheels. Each of the tracked ground engaging units 24 includes a front idler 52, a drive sprocket 54, and a track chain 56 extending around the front idler 52 and the drive sprocket 54. The travel motor of each tracked ground engaging unit 24 drives its respective drive sprocket 54. Each tracked ground engaging unit 24 has a forward traveling direction 58 defined from the drive sprocket 54 toward the front idler 52. The forward traveling direction 58 of the tracked ground engaging units 24 also defines a forward traveling direction 58 of the undercarriage 22 and thus of the working machine 20.

An operator's cab 60 may be located on the main frame 32. The operator's cab 60 and the boom assembly 42 may both be mounted on the main frame 32 so that the operator's cab 60 faces in the working direction 58 of the boom assembly. A control station 62 may be located in the operator's cab 60.

Also mounted on the main frame 32 is an engine 64 for powering the working machine 20. The engine 64 may be a diesel internal combustion engine. The engine 64 may drive a hydraulic pump to provide hydraulic power to the various operating systems of the working machine 20. The engine 64 may also be an electric motor.

As schematically illustrated in FIG. 4, the work machine 20 may include a control system including a controller 112. The controller may be part of the machine control system of the working machine, or it may be a separate control module. The controller 112 may include a user interface 114 and optionally be mounted in the operator's cab 60 at the control station 62.

The controller 112 is configured to receive input signals from some or all of various sensors 102, 104, 108 as further described below. Various sensors 102, 104, 108 may typically be discrete in nature, but signals representative of more than one input parameter may be provided from the same sensor, and a sensor system 102, 104, 108 as disclosed herein may further include or otherwise refer to signals provided from the machine control system.

In an embodiment a set of inertial navigation system (INS) sensors 104 may be mounted on the work machine 20, as represented generally including multiple sensors 104a, 104b, 104c, 104d, 104e respectively mounted to the main frame 32, the boom 44, the arm 46, the dogbone 47, and the tool 48. The set of inertial navigation system (INS) sensors 104 may also be referred to as a plurality of position sensors mounted on the boom assembly 42 to track a position of the boom assembly 42 relative to the undercarriage 22 during the working operation. In another embodiment the plurality of position sensors could be or include rotary angle sensors associated with each of the pivot joints of the boom assembly 42.

In the embodiment represented in FIG. 1, which is intended as illustrative and non-limiting unless otherwise specifically noted herein, a sensor system 104 may include a sensor 104a mounted on the main frame 32; a sensor 104b mounted on the boom 44; a sensor 104c mounted on the arm 46; a sensor 104d mounted on the dogbone 47; and a sensor 104e mounted on the tool 48. Respective sensors may for example be mounted on opposing sides of at least one linkage joint. An opposing side of the at least one linkage joint may be ascertained by mounting or affixation of the sensor system 104 on either side of the at least one linkage joint, which is defined as a pivotal linkage joint connecting the one or more components of the work implement 42.

For example, the at least one linkage joint may be defined at a linkage joint 106, which constitutes a pivotal connection of the boom 44 and the arm 46. In this example, the sensor system 104 may be mounted in such a manner that the opposing sides of the at least one linkage joint are defined as follows: the sensor 104b mounted on the boom 44 opposing the sensor 104c mounted on the arm 46; the sensor 104b mounted on the boom 44 opposing the sensor 104d mounted on the dogbone 47; or the sensor 104b mounted on the boom 44 opposing the sensor 104e mounted on the tool 48.

As a further example, the at least one linkage joint may be defined at a pivotal connection of the arm 46 to the dogbone 47. In this example, the sensor system 104 may be mounted in such a manner that the opposing sides of the at least one linkage joint are defined as follows: the sensor 104c mounted on the arm 46 opposing the sensor 104d mounted on the dogbone 47; the sensor 104c mounted on the arm 46 opposing the sensor 104e mounted on the tool 48; the sensor 104b mounted on the boom 44 opposing the sensor 104d mounted on the dogbone 47; or the sensor 104b mounted on the boom 44 opposing the sensor 104e mounted on the tool 48.

As a further example, the at least one linkage joint may be defined at a linkage joint 110, which constitutes a pivotal connection between the arm 46 and the tool 48. In this example, the sensor system 104 may be mounted in such a manner that the opposing sides of the at least one linkage joint are defined as follows: the sensor 104d mounted on the dogbone 47 opposing the sensor 104e mounted on the tool 48; the sensor 104c mounted on the arm 46 opposing the sensor 104e mounted on the tool 48; or the sensor 104b mounted on the boom 44 opposing the sensor 104e mounted on the tool 48.

The sensor system 104 may be oriented in an x-, y-, and z-axis coordinate system. Using as one example the sensor 104c as mounted on the arm 46 and the sensor 104d as mounted on the dogbone 47, respective body frames of the sensors 104c and 104d (not shown) may be mounted such that the x-axes of the aforementioned body frames point along the direction of the work implement 42. Alternatively, the body frame of the sensor 104c and the body frame of the sensor 104d may be mounted in a manner such that the z-axes of the aforementioned body frames point in the direction of the main frame 32 of the work machine 20 (i.e., the excavator). Because an x-, y-, and z-axis coordinate system may be defined arbitrarily, the foregoing are not intended as limiting. The x-, y-, and z-axis coordinate system, though it may be defined arbitrarily, relates to the mechanical axes of rotation for roll (i.e., rotation about the x-axis), pitch (i.e., rotation about the y-axis), and yaw (i.e., rotation about the z-axis).

Some or all of the sensors 104 in the context of the referenced work machine 20 may include inertial measurement units (each, an IMU). IMUs are tools that capture a variety of motion-and position-based measurements, including, but not limited to, velocity, acceleration, angular velocity, and angular acceleration.

IMUs may include a number of sensors including, but not limited to, accelerometers, which measure (among other things) velocity and acceleration, gyroscopes, which measure (among other things) angular velocity and angular acceleration, and magnetometers, which measure (among other things) strength and direction of a magnetic field. Generally, an accelerometer provides measurements, with respect to (among other things) force due to gravity, while a gyroscope provides measurements, with respect to (among other things) rigid body motion. The magnetometer provides measurements of the strength and the direction of the magnetic field, with respect to (among other things) known internal constants, or with respect to a known, accurately measured magnetic field. The magnetometer provides measurements of a magnetic field to yield information on positional, or angular, orientation of the IMU; similarly to that of the magnetometer, the gyroscope yields information on a positional, or angular, orientation of the IMU. Accordingly, the magnetometer may be used in lieu of the gyroscope, or in combination with the gyroscope, and complementary to the accelerometer, in order to produce local information and coordinates on the position, motion, and orientation of the IMU.

As conventionally known in the art, an accelerometer is an electro-mechanical device or tool used to measure acceleration (m/s²), which is defined as the rate of change of velocity (m/s) of an object. Accelerometers sense either static forces (e.g., gravity) or dynamic forces of acceleration (e.g., vibration and movement). An accelerometer may receive sense elements measuring the force due to gravity. By measuring the quantity of static acceleration due to gravity of the Earth, an accelerometer may provide data as to the angle the object is tilted with respect to the Earth, the angle of which may be established in an x-, y-, and z-axis coordinate frame. However, where the object is accelerating in a particular direction, such that the acceleration is dynamic (as opposed to static), the accelerometer produces data which does not effectively distinguish the dynamic forces of motion from the force due to gravity by the Earth. Also as conventionally known in the art, a gyroscope is a device used to measure changes in orientation, based upon the object's angular velocity (rad/s) or angular acceleration (rad/s²). A gyroscope may constitute a mechanical gyroscope, a micro-electro-mechanical system (MEMS) gyroscope, a ring laser gyroscope, a fiber-optic gyroscope, and/or other gyroscopes as are known in the art. Principally, a gyroscope is employed to measure changes in angular position of an object in motion, the angular position of which may be established in an x-, y-, and z-axis coordinate frame.

In an embodiment, for each of at least one linkage joint as referenced above, sense elements from the received sensor output signals may be fused in an independent coordinate frame associated at least in part with the respective linkage joint, the independent coordinate frame of which is independent of a global navigation frame for the work machine 20, wherein for example measurements received by sensor system 104 may be merged to produce a desired output in the work implement 42 of the work machine 20.

One or more laser receivers 102 as are conventionally known in the art may further be mounted on the work machine 20 for catching a laser reference 200 as represented in FIG. 2. The laser reference 200 may be generated from a laser source 70 remotely positioned and in a stationary manner with respect to the work machine 20. A plane of the laser reference 200 may include a slope, direction, and height or predetermined/defined elevation offset 78 with respect to a target surface profile 76, the target surface profile 76 further corresponding to an amount of material to be graded away from an initial or current surface profile 74.

The controller 112 may be configured to produce outputs, as further described below, to a user interface 114 for display to the human operator or other appropriate user. The controller 112 may be configured to receive inputs from the user interface 114, such as user input provided via the user interface 114. Not specifically represented in FIG. 3, the controller 112 of the work machine 20 may in some embodiments further receive inputs from and generate outputs to remote devices associated with a user via a respective user interface, for example a display unit with touchscreen interface. Data transmission between for example a vehicle control system and a remote user interface may take the form of a wireless communications system and associated components as are conventionally known in the art. In certain embodiments, a remote user interface and vehicle control systems for respective work machines 20 may be further coordinated or otherwise interact with a remote server or other computing device for the performance of operations in a system as disclosed herein.

The controller 112 may further, or in the alternative, be configured to generate control signals for controlling the operation of respective actuators, or signals for indirect control via intermediate control units, associated with a machine steering control system 126, a machine implement control system 128, and/or an engine speed control system 130. The control systems 126, 128, 130 may be independent or otherwise integrated together or as part of a machine control unit in various manners as known in the art. The controller 112 may, for example, generate control signals for controlling the operation of various actuators, such as hydraulic motors or hydraulic piston-cylinder units 41, 43, 45, and electronic control signals from the controller 112 may actually be received by electro-hydraulic control valves associated with the actuators such that the electro-hydraulic control valves will control the flow of hydraulic fluid to and from the respective hydraulic actuators to control the actuation thereof in response to the control signal from the controller 112. In an embodiment, the controller 112 may in the context of a control operation further receive a pivot angle signal from a pivot angle sensor as described above and selectively drive a swing motor automatically to rotate the main frame 32 about the pivot axis 36 relative to the undercarriage 22 to a target pivot position of the main frame 32 relative to the undercarriage 22, as part of an aforementioned control unit 126, 128, 130 or optionally as a separate and/or integrated control unit within the scope of the present disclosure.

The controller 112 may include, or be associated with, a processor 150, a computer readable medium 152, a communication unit 154, data storage 156 such as for example a database network, and the aforementioned user interface 114 or control panel having a display 118. An input/output device, such as a keyboard, joystick or other user interface tool 116, is provided so that the human operator may input instructions to the controller 112. It is understood that the controller 112 described herein may be a single controller having all of the described functionality, or it may include multiple controllers wherein the described functionality is distributed among the multiple controllers.

Various “computer-implemented” operations, steps or algorithms as described in connection with the controller 112 or alternative but equivalent computing devices or systems can be embodied directly in hardware, in a computer program product such as a software module executed by the processor 150, or in a combination of the two. The computer program product can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, or any other form of computer-readable medium 152 known in the art. An exemplary computer-readable medium 152 can be coupled to the processor 150 such that the processor 150 can read information from, and write information to, the memory/storage medium 152. In the alternative, the medium 152 can be integral to the processor 150. The processor 150 and the medium 152 can reside in an application specific integrated circuit (ASIC). The ASIC can reside in a user terminal. In the alternative, the processor 150 and the medium 152 can reside as discrete components in a user terminal.

The term “processor” 150 as used herein may refer to at least general-purpose or specific-purpose processing devices and/or logic as may be understood by one of skill in the art, including but not limited to a microprocessor, a microcontroller, a state machine, and the like. A processor 150 can also be implemented as a combination of computing devices, e.g., a combination of a digital signal processor (DSP) and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The communication unit 154 may support or provide communications between the controller 112 and external systems or devices, and/or support or provide communication interface with respect to internal components of the self-propelled work machine 20. The communications unit 154 may include wireless communication system components (e.g., via cellular modem, WiFi, Bluetooth, or the like) and/or may include one or more wired communications terminals such as universal serial bus ports.

The data storage 156 as further described below may, unless otherwise stated, generally encompass hardware such as volatile or non-volatile storage devices, drives, memory, or other storage media, as well as one or more databases residing thereon.

The present disclosure is directed to a problem that is sometimes encountered when multiple laser sources 70 are present on the work site. In such a situation, as schematically shown in FIG. 3, the work machine 20 may be set up for a working operation using a first laser source 70A as the intended reference. But the machine may unintentionally also detect a signal from a second laser source 70B. This is sometimes referred to as a “false laser strike.” The present disclosure provides a system for detecting such a false laser strike and taking corrective action in response to detecting the false laser strike.

The operator of the work machine 20 may position the work machine 20 at a first location on the work site as shown in FIG. 3. If the first laser source 70A is not already in place the operator will place the first laser source 70A in an appropriate location to provide a first laser plane reference signal 200 to the area surrounding the first location on the work site.

As will be understood by those skilled in the art, the laser source 70A has a rotating head projecting a laser beam, so that the rotating beam defines a plane. That plane may be oriented horizontally or it may be sloped relative to horizontal. One typical practice is to orient the laser plane reference signal parallel to the desired target surface profile 76 (see FIG. 2) so that the work implement 42 may then be directed to cut to a certain distance below the laser plane reference signal. If the target surface profile 76 is sloped relative to horizontal the laser plane reference signal 200 may be similarly sloped relative to horizontal. A sloped laser reference plane signal 200 is generally defined as having a “mainfall” and a “cross slope.” The cross slope is perpendicular to the mainfall, so that by defining those two angles of slope relative to horizontal, and by defining a vertical position of one point of the plane, the entire reference plane is defined.

The mainfall and cross slope of the first laser plane reference signal 200 will be known from the set up of the first laser source 70A, and the operator may input that same data into the controller 112. Then when the work machine 20 is initially set up at the location on the work site as shown in FIG. 3, the longitudinal axis of the boom assembly 42 is preferably aligned with the defined mainfall of the first laser plane reference signal 200. Preferably both the longitudinal center axis of the undercarriage and the longitudinal axis of the boom assembly are aligned parallel to the mainfall of the first laser plane reference signal 200. With the boom assembly 42 so oriented, the controller 112 may determine a first determined position or elevation of the first laser plane reference signal 200 relative to the work machine 20. This first determined position may be identified by a point at which the first laser plane reference signal 200 strikes the laser receiver 102 with the boom assembly 42 in some identified position relative to the work machine 20. For example, as seen in FIG. 3 the boom assembly 42 may be positioned such that the bucket 48 is resting on the ground surface 38 with the longitudinal axis of the boom assembly 42 aligned parallel to the mainfall of the first laser plane reference signal 200.

As will be understood by those skilled in the art the laser receiver 102 detects the strike of the laser plane 200 with an array of photo diodes arranged along the length of the laser receiver 102. There may be a gap between diodes equal to the width of the beam. The receiver 102 detects which diode the first laser plane reference signal 200 strikes and generates a corresponding output signal 102S which is received by controller 112.

The controller 112 which already has the mainfall and cross slope data for the first laser plane reference signal 200 may then determine the location of the entire first laser plane reference signal 200 based on the one measured position represented by signal 102S. That determined position may then be identified in the controller 112 as an expected position of the first laser plane reference signal 200 relative to the work machine 20.

Then with the undercarriage 22 of the work machine 20 remaining fixed on the first location of the work site, the boom assembly 42 and main frame 32 may move relative to the undercarriage 22 to perform the working operation, i.e. excavating dirt from the work site. As the boom assembly 42 is manipulated and moved relative to the undercarriage 22 the controller 112 may track the position of the boom assembly 42 relative to the undercarriage 22 by monitoring the position signals from the plurality of position sensors 104. Since the controller 112 already knows the position of the first laser plane reference signal 200 relative to the undercarriage 22 it knows where the laser receiver 102 should intersect the first laser plane reference signal 200 for any position of the boom assembly 42.

As the work machine 20 proceeds with the working operation it may continually or periodically receive further laser plane reference signals with the laser receiver 102. At any given time the controller 112 can determine where the further laser plane reference signal is striking the laser receiver 102 and the controller 112 may compare that position to the expected position at which the first laser plane reference signal 200 should be striking the laser receiver 102.

The controller 112 may be programmed with a defined acceptable deviation to the position of the further laser plane reference signal from the expected position of the first laser plane reference signal. The operator of the machine 20 may be allowed to set or adjust the acceptable deviation by inputs to the user interface 114. If the detected position of the further laser plane reference signal is within the defined deviation from the expected position of the first laser plane reference signal, the controller may take no corrective action because it is presumed that the further laser plane reference signal is in fact the first laser plane reference signal. On the other hand, if the detected position of the further laser plane reference signal is not within the defined deviation from the expected position of the first laser plane reference signal, the controller may take corrective action.

In one embodiment the defined deviation may be no greater than plus or minus 0.040 meter. In another embodiment the defined deviation may be no greater than plus or minus 0.030 meter. In another embodiment the defined deviation may be no greater than plus or minus 0.020 meter.

During a typical working operation of the work machine 200 the controller 112 will be configured to control the digging action of the excavator tool 48 so that the ground surface is excavated to the level of the desired surface 76 shown in FIG. 2. To do this the controller 112 may continually monitor the position at which the first laser plane reference signal 200 strikes the laser receiver 102, and the controller 112 may correspondingly control the movement of the boom assembly 42.

Any laser signal detected after the initial set up of the machine may be referred to as a “further” laser plane reference signal. That “further” laser plane reference signal may in fact be the first laser plane reference signal 200, or it may be a false strike from another source. If the position of the further laser plane reference signal is determined to be within the defined deviation of the expected position of the first laser plane reference signal 200 relative to the work machine 20, the controller 112 may continue the working operation.

If the position of the further laser plane reference signal is determined not to be within the defined deviation of the expected position of the first laser plane reference signal 200 relative to the work machine 20, the controller 112 may provide a corresponding notice to an operator of the work machine, for example on the display 116.

If the position of the further laser plane reference signal is determined not to be within the defined deviation of the expected position of the first laser plane reference signal 200 relative to the work machine 20, the controller 112 may automatically stop the working operation.

If the position of the further laser plane reference signal is determined not to be within the defined deviation of the expected position of the first laser plane reference signal 200 relative to the work machine 20, the operator of the work machine may determine whether the further reference signal is a false laser strike from another laser source such as 70B other than the intended laser source 70A. In that situation the other laser source 70B may be removed from the line of sight of the laser receiver 102 of the work machine 20.

For example, as shown schematically in FIG. 3 there may be a second laser source 70B on the work site generating a second laser plane reference signal 202. The enlarged view 3A of the area adjacent the laser receiver 102 mounted on the arm 46 of boom assembly 42, schematically depicts the first laser plane reference signal 200 striking the laser receiver 102 at a first position 204 which the controller 112 may define as the expected position of the first laser plane reference signal 200. The controller 112 may then also be provided with a value of the acceptable deviation 206 about that expected position. As shown in FIG. 3A, the second laser plane reference signal 202 strikes the laser receiver 102 at a position 208 outside of that acceptable deviation. Although FIG. 3A is shown with the boom assembly in the set up position, it will be understood that the controller 112 tracks the movement of the boom assembly 42 and the laser receiver 102 during the working operation and the controller 112 may continuously compare the position of all received laser strikes to the expected position of the first laser plane reference signal 200. At any time during the working operation the controller 112 may detect a false laser strike from the second laser source 70B and take any of the corrective actions described above.

The operation of the controller 112 to detect false laser strikes as described above is described with regard to the work machine 20 remaining in the first location on the work site. That is, the undercarriage 22 of the work machine 22 does not move relative to the ground surface 38. If it is desired to move the work machine 20 to a second location on the work site, then the process of setting up the machine and the designated laser source 70A must be repeated at the second location. This may be described as receiving with the laser receiver 102 the first laser plane reference signal 200 from the designated one 70A of the laser sources with the work machine 20 positioned at the second location on the work site, determining with the automatic controller 112 a second determined position of the first laser plane reference signal 200 relative to the work machine 20 with the work machine 20 positioned at the second location on the work site, and identifying the second determined position as a second expected position of the first laser plane reference signal 200 relative to the work machine 20 with the work machine 20 positioned at the second location on the work site.

Thus, it is seen that the apparatus and methods of the present disclosure readily achieve the ends and advantages mentioned as well as those inherent therein. While certain preferred embodiments of the disclosure have been illustrated and described for present purposes, numerous changes in the arrangement and construction of parts and steps may be made by those skilled in the art, which changes are encompassed within the scope and spirit of the present disclosure as defined by the appended claims. Each disclosed feature or embodiment may be combined with any of the other disclosed features or embodiments.