US20180171799A1

US20180171799A1 - Control system for machine having rotary cutting head

Info

Publication number: US20180171799A1
Application number: US15/380,772
Authority: US
Inventors: Carl Moberg; Brent Michael Duppong; Justin Philip Pahl; Matthew Thomas Palmer; Frank Karl Kuehnemund; Thomas Temmann
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2016-12-15
Filing date: 2016-12-15
Publication date: 2018-06-21
Also published as: WO2018112332A1

Abstract

A control system may be provided for operating a machine having a rotary cutting head. The control system may include a wrist capable of rotating about a wrist axis, a gear mechanism capable of driving rotation of the wrist. A cutting head may be attached to the wrist and capable of rotating about a cutter axis that is substantially perpendicular to the wrist axis. The control system may also include primary and redundant angular sensors capable of generating signals indicative of angular orientations of the wrist. The control system may additionally include a controller, capable of controlling operation of the wrist and the cutting head, comparing an actual angular orientation of the wrist to a target angular orientation, as indicated by the primary and secondary signals, and selectively inhibiting the cutting head from operating when the actual angular orientation differs from the target angular orientation by an operation threshold.

Description

TECHNICAL FIELD

The present disclosure relates generally to a machine having a rotary cutting head, and more particularly, to a system for controlling the position of the rotary cutting head.

BACKGROUND

One manner of milling tunnels into rock is to repetitively pass a cutting head across a vertical face of the rock. An overall efficiency of a operation of this type may be governed by a cutting depth and a speed of movement of the cutting head. These variables are often constrained by the nature of the milled material and the orientation of the cutting head. For example, milling coal and hard rock often requires different techniques, cutting depths, speed of movements, and cutting head orientations.
Existing cutting methods may be inefficient when milling hard rock at comparatively deep cutting depths because the cutting head is not maintained in an optimal cutting orientation relative to the vertical face of the rock. Although this problem is not as prevalent when mining soft materials, such as, for example, coal, the very nature of hard rock may require specialized cutting heads and techniques.
Additionally, misalignment of the cutting head relative to the vertical rock face may damage a positioning member. Misalignment may damage the cutting head and other portions of a machine because of uneven feedback and force transfer between the cutting head and the wrist. Such uneven feedback may result in excessive wear and possibly significant damage to the mining machine. Even relatively small misalignment of the cutting head may be detrimental when milling extremely hard rock.
One attempt to address these problems is disclosed in U.S. Pat. No. 6,062,650 (“the '650 patent”). The '650 patent discloses an angular encoder for measuring the rotation angle of a turret (attached to a cutting head) with reference to a predetermined line, usually a vertical axis of the turret. The encoder sends signals to an onboard computer, which processes the signals according to a computer program. The computer program assists a controller, which controls proportional valves, hydraulic cylinders, and the speed of rotation of the turret, to cut a preselected profile at a predetermined cut depth and rate of advance.
Although the encoder system of the '650 patent may help in cutting preselected milling profiles, the '650 patent may be prone to error as it may be possible for the encoder to fail without indication or warning. This can lead to misalignment of the cutting head. Further, the '650 patent fails to account for potential misalignment of the cutting head. In particular, the control system of the '650 patent relies on the output of a single encoder without a reliable way to ensure that the cutting head remains in proper alignment relative to a rock face and throughout extended use.
The machine, discussed herein, is directed at overcoming one or more of the problems set forth above and/or other problems in the prior art.

SUMMARY

One aspect of the present disclosure is directed to a control system for a machine. The control system may include a wrist capable of rotating about a wrist axis, a gear mechanism capable of driving rotation of the wrist, and a cutting head attached to the wrist and capable of rotating about a cutter axis that is substantially perpendicular to the wrist axis. The control system may additionally include a primary angular sensor capable of generating primary signals indicative of angular orientations of the wrist, and at least one redundant angular sensor capable of generating secondary signals indicative of angular orientations of the wrist. The control system may further include a controller capable of controlling operation of the wrist and the cutting head, and comparing an actual angular orientation of the wrist, as indicated by one or more of the primary signals or the secondary signals, to a target angular orientation. The controller may also selectively inhibit the cutting head from operating when the controller determines that the actual angular orientation differs from the target angular orientation by an operation threshold.
Another aspect of the present disclosure is directed to a method for operating a cutting head of a machine. The method may include determining a target angular orientation of the cutting head. The method may also include generating a primary angular orientation output associated with the cutting head, and generating a redundant angular orientation output associated with the cutting head. The method may additionally include making a first comparison of the primary angular orientation output to the target angular orientation, and selectively inhibiting the cutting head from operating based on the first comparison when the primary angular orientation output and the target angular orientation differs by an operation threshold.
Another aspect of the present disclosure is directed to a machine. The mining machine may include a wrist capable of rotating about a wrist axis, a gear mechanism capable of driving rotation of the wrist and having an exposed surface with angular markings, and a stationary surface adjacent the gear mechanism and having a reference marking. The mining machine may also include a cutting head attached to the wrist and capable of rotating about a cutter axis that is substantially perpendicular to the wrist axis. The mining machine may additionally include a primary encoder disposed in the gear mechanism and capable of generating primary signals indicative of angular orientations of the wrist, and a redundant encoder disposed in the gear mechanism and capable of generating secondary signals indicative of the angular orientations of the wrist. The mining machine may further include a controller that is capable of controlling operation of the wrist and the cutting head, comparing an actual angular orientation of the wrist, as indicated by one or more of the primary signals or the secondary signals, to a target angular orientation, and comparing the primary signals to the secondary signals. The controller may also be capable of selectively inhibiting the cutting head from operating when the controller determines that the actual angular orientation differs from the target angular orientation by an operation threshold, and when the controller determines that the primary signals differ from the secondary signals by the operation threshold. Additionally, the controller may be capable of selectively causing a calibration instruction to be shown on a display when the controller determines the primary signals differ from the secondary signals by a signal threshold, and selectively causing a warning to be shown on the display when the controller determines the actual angular orientation differs from the target angular orientation by a warning threshold that is lower than the operation threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a machine;

FIG. 2 is a top plan view of the machine of FIG. 1;

FIG. 3 is a diagrammatic illustration of a portion of the machine of FIGS. 1 and 2; and

FIG. 4 is an exemplary flowchart depicting a method of operating the machine of FIGS. 1 and 2.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, an exemplary machine 10 such as, for example, a machine for creating tunnels, roadways, or shafts in material (such as rock, for example), is depicted. In this regard, machine 10 may be any machine associated with various industrial applications, including, but not limited to, mining, agriculture, forestry, construction, and/or other industrial applications. Machine 10 may include a cutting head 12 configured to mill the material by rotating about a cutter axis 13. Machine 10 may also include a frame 14 equipped with ground engaging drive mechanisms, such as tracks 16. In one embodiment, machine 10 may further include one or more motors that are operatively connected to a remote power source (not shown), which supplies electric power to the machine via one or more tethered cables (not shown). Alternatively, machine 10 may have a localized power source, such as an engine (not shown). The power source(s) may be used to produce mechanical and electrical power outputs for driving and controlling the numerous components of machine 10.
Cutting tools 18 may be mounted on cutting head 12 such that cutting tools 18 collectively rotate about cutter axis 13. Cutting tools 18 may also be capable of individually rotating a plurality of cutting edges about respective cutting tool axes (not shown) that are substantially perpendicular to cutter axis 13. Cutting head 12 and cutting tools 18 may be moved to engage with a target cutting surface at any orientation by adjusting an angle of reproach of cutter axis 13. However, in order to ensure efficient and damage free operation, cutting head 12 may follow a cutting plane aligned with cutter axis 13. That is, cutting head 12 should engage material in a direction perpendicular to the axial end face of cutting head 12. Additionally, when cutting head 12 is moving along a particular milling path, the major axis (i.e., an amount equal to the diameter of cutting head 12) of cutting head 12 may be aligned perpendicular to the line of travel in order to mill the maximum amount of material. In at least one embodiment, a preferred cutting orientation may be defined as an orientation in which cutter axis 13 is substantially parallel to a target cutting surface, cutting edges of cutting tools 18 are substantially perpendicular to the target cutting surface, and the major axis of cutting head 12 is substantially perpendicular to a target trajectory line of travel.
Wrist 19 may be configured to rotate cutting head 12 about a wrist axis 20 to maintain cutting head 12 in a preferred cutting orientation. Positioning drum 22 may be configured to move wrist 19 vertically up and down by pivoting about a lift axis 23. Boom 24 may be configured to swing cutting head 12, wrist 19, and positioning drum 22 about a swing axis 25. Additionally, boom 24 may also be configured to extend and retract cutting head 12, wrist 19, and positioning drum 22 along an extension axis 26. Movement of boom 24 along extension axis 26 and swing axis 25 may result in corresponding movements of positioning drum 22, wrist 19, and cutting head 12. Movement of positioning drum 22 along lift axis 23 may result in corresponding movement of wrist 19 and cutting head 12. Rotational movement of wrist 19 may result in rotational movement of cutting head 12. Boom 24 may be configured to move with the assistance of extension actuators 30 and swing actuators 31. Positioning drum 22 may be configured to move with the assistance of lift actuators 32. Rotation of wrist 19 may be achieved by operation of a gear mechanism 33. Gear mechanism 33 may be driven by a hydraulic motor (not shown) or other similarly situated actuator.
As shown in FIG. 3, a controller 40 may be in communication with extension actuators 30, swing actuators 31, lift actuators 32, and gear mechanism 33. Controller 40 may be capable of causing actuators 30-32 and gear mechanism 33 to move (e.g., electric or hydraulic circuitry). In this way, controller 40 may direct the rotating, swinging, lifting, pivoting, extending, and retracting movements of machine 10 and components of machine 10. Controller 40 may be an electronic controller that operates in a logical fashion to perform operations, execute control algorithms, store and retrieve data and other desired operations. Controller 40 may include or access memory, secondary storage devices, processors, and any other components for running an application. Various other circuits may be associated with controller 40 such as power supply circuitry, signal conditioning circuitry, driver circuitry, and other types of sensory circuitry.
The term “controller” is meant to be used in its broadest sense to include one or more controllers and/or microprocessors that may be associated with the machine 10 and that may cooperate in controlling various functions and operations of machine 10. Controller 40 may utilize one or more data maps relating to the kinematics of machine 10 and the operating environment of which machine 10 may operate in.
Controller 40 may be in communication with a display interface 41, as shown in FIG. 3. In at least one embodiment, display interface 41 may also have an associated input device for communicating inputs that may be stored on the memory of controller 40. Display interface 41 may display information concerning the state of machine 10 (e.g., the angular orientation of cutting head 12). Controller 40 and display interface 41 may be located on machine 10 and/or may be distributed with components located remotely off-board machine 10.
Machine 10 may be equipped with a plurality of sensors that provide data indicative of various operating parameters of machine 10 and/or aspects of the environment in which machine 10 may be operating in. The term “sensor” is meant to be used in its broadest sense to include one or more sensors and related components associated with machine 10 that cooperate to sense various functions, operations, and operating characteristics.
In the example shown in FIG. 3, an environment sensor 43 and/or a position sensor 46 may be included within a control system 47 that also includes controller 40 and display interface 41. Sensors 43, 46 may sense a position and/or orientation (e.g., a heading, pitch, roll or tilt, and yaw) of machine 10. Controller 40 may process information from sensors 43, 46 and use the information to control the motions of machine 10. Sensors 43, 46 may take the form of numerous embodiments, some of which will be explained now.
Environment sensor 43 may include one or more sensing elements that interact with the working environment of machine 10. For example, machine 10 may utilize lasers and prisms with the assistance of field engineering and surveying equipment. Based upon a known position of the lasers and reflected light from the prisms, a pose of machine 10, and more particularly a pose of cutting head 12, may be determined. In other embodiments, environment sensor 43 may be a RADAR sensor (radio detection and ranging), a SONAR sensor (sound navigation and ranging), a LIDAR (light detection and ranging) sensor, and/or a camera vision sensor. Environment sensor 43 may generate data that is received by controller 40 and used to determine the position and orientation of cutting surfaces shown in FIGS. 1 and 2. Such surfaces may include a floor face 50, a lower cutting face 52, upper cutting face 53, and a ceiling face 54.
Position sensor 46 may include one or more sensing elements that cooperate to generate and provide an actual position and/or orientation of machine 10 to controller 40. In some embodiments, position sensor 46 may detect the actual position and/or orientation of cutting head 12 relative to a reference location by utilizing a database of maps consisting of known kinematics of machine 10. In other embodiments, position sensor 46 may include a slope sensing element, an inclination sensing element, a pitch angle sensing element, an accelerometer, a strain gauge, etc. Position sensor 46 may be disposed on or adjacent to cutting head 12 for improved accuracy. For example, the sensing elements may be associated with gear mechanism 33 for directly detecting an angular orientation of cutting head 12 relative to frame 14.
FIG. 3, in addition to showing control system 47, also illustrates an internal cross-section of gear mechanism 33. It should be noted that FIG. 3 is exemplary in nature and is not drawn to scale, and certain parts may be removed and/or exaggerated for ease of understanding. As shown in FIG. 3, gear mechanism 33 may include a stationary platform 58 on which a plurality of pinion gears 60 are rotatably supported. Pinion gears 60 may be capable of rotating about pinion gear axes 61. Pinion gears 60 may be driven, for example, by independent hydraulic motors (not shown) located behind platform 58, and/or by a common gear (e.g., a sun gear). Pinion gears 60 may engage a common ring gear 62, such that rotation of pinion gears 60 about their respective pinion gear axes 61 translates into rotation of ring gear 62 about axis 20. Cutting head 12 may be operatively connected to ring gear 62, such that a rotation of ring gear 62 results in a corresponding rotation of cutting head 12.
Control system 47 may further include a primary angular sensor 63 and a redundant angular sensor 64 associated with gear mechanism 33. Although the exemplary control system 47 is shown with two sensors 63, 64 it is contemplated that some embodiments may have more than two sensors 63, 64. For example, a primary angular sensor 63 and at least one redundant angular sensor 64. Sensors 63, 64 may be configured to detect an angular orientation of wrist 19, (e.g., relative to platform 58 and/or frame 14) by detecting a rotation of ring gear 62. Sensors 63, 64 may be optical, magnetic, capacitive, or geared sensors. For example, sensors 63, 64 may be rotary encoders that convert the angular position of ring gear 62 to an analog or digital signal for use by controller 40. The signals may indicate an angular orientation of wrist 19 and cutting head 12.
As encoders, sensors 63, 64 may engage ring gear 62 via gear teeth in the same way that pinion gears 60 engage ring gear 62. Sensors 63 and 64 may also include a sensing element that detects when each tooth, or a particular tooth, passes by the sensing element (e.g., an optical sensor). Each time a tooth movement is detected a signal associated with the detection may be generated. Alternatively, a sensing element could detect a portion of a shaft connected to the gear teeth. Other methods may be available as would be understood by a person having ordinary skill in the art.
In some embodiments, a portion of gear mechanism 33 (e.g., an axial end face of ring gear 62) may have an exposed surface along its perimeter that is marked with a plurality of angular markings 65. Angular markings 65 may be evenly spaced around the circumference or perimeter of gear mechanism 33. For example, angular markings 65 may be evenly distributed around the circumference at every 2 degrees. A reference marking 66 (See FIG. 1) may be provided along a non-rotatable surface adjacent to gear mechanism 33. For example, reference marking 66 may be located on positioning drum 22. Reference marking 66 may be configured to align with angular markings 65 to mechanically indicate an angular orientation of wrist 19. Angular markings 65 and reference marking 66 may be viewable from a ground position or any other external vantage location.
FIG. 4 is an exemplary flowchart depicting a positioning method that may be implemented by controller 40 during operation of the mining machine 10 of FIGS. 1 and 2.
FIG. 4 will be disclosed in more detail in the next section to further illustrate the disclosed concepts.

INDUSTRIAL APPLICABILITY

The disclosed control system may be applicable to any machine having a rotatable cutting head, and more particularly applicable to machines having rotatable cutting heads that move three dimensionally and must maintain angular alignment in relation to a dynamically modified surface. The disclosed control system may improve efficiency and prevent unnecessary wear and tear of cutting head 12 by maintaining cutting head 12 in a preferred orientation relative to a target cutting surface.
FIG. 4 is an exemplary flowchart illustrating operation of control system 47, which will now be explained with reference to components of FIGS. 1-3. When performing an operation, such as an operation controller 40 may determine a target angular orientation of cutting head 12 (Step 100).
The target angular orientation may be a preferred cutting orientation that allows material to be milled during engagement with cutting faces 52 and 53. In at least one embodiment, the target angular orientation may be defined as a wrist 19 orientation that maintains the cutter axis 13 of cutting head 12 substantially parallel to a cutting face 52 during movement in a direction aligned with cutter axis 13. In other words an axial end face of cutting head 12 should be generally perpendicular to the trajectory of cutting head 12 during milling. Additionally, the target angular orientation may dynamically change throughout operation of a milling process, based on a change in the trajectory, and may be continuously updated during operation. Determining the target angular orientation may consist of establishing a wrist angle that ranges from 0 degrees to 360 degrees for a particular cutting segment.
Controller 40 may be in communication with a plurality of sensors (e.g, environment sensor 43, position sensor 46, and sensors 63, 64) and receive signals from these sensors (Step 102). These signals may include a primary signal generated by primary angular sensor 63, a secondary signal generated by redundant angular sensor 64, and an environment signal generated by environment sensor 43 and/or position sensor 46.
Controller 40 may then determine whether the primary signal is available (Step 104). If the primary signal is unavailable (e.g., when primary angular sensor 63 has failed or when the signal from primary angular sensor 63 is out of range), controller 40 may cause display interface 41 to show a warning, and continue operation by using only the secondary signals generated by redundant angular sensor 64 (Step 106). The warning may be a graphic image, textual indication, and may appropriately indicate whether the primary angular sensor 63 has failed or if the signals from primary angular sensor 63 are out of range. As long as controller 40 determines that the primary signal is available (Step 104: Yes), controller 40 may then compare the primary signals to the secondary signals. That is, controller 40 may determine if a difference between the primary and redundant sensors 63, 64 is greater than an operation threshold and/or a signal comparison threshold (Step 108). For example, controller 40 may process the primary signals into a primary value and process the secondary signals into a secondary value (e.g., each ranging from 0 degrees to 360 degrees). Controller 40 may then calculate a difference between the primary value and the secondary value and determine if the difference is greater than an operation threshold amount and/or a signal comparison threshold. When the difference is greater than the operation threshold (Step 108: Yes) controller 40 may inhibit milling of cutting head 12 (Step 116). When the difference is greater than the signal comparison threshold (Step 108: Yes) controller 40 may cause display interface device 41 to show an instruction to calibrate sensors 63, 64 (Step 110). When the difference is less than the signal comparison threshold (Step 108: No) controller 40 may continue operation by using only the primary signals (Step 112).
Controller 40 may perform a comparison of the actual angular orientation of wrist 19 to the target angular orientation of wrist 19 (Step 114). The actual angular orientation may be established by determining an actual angular orientation value based on the primary or secondary signals, depending on completion of step 106 or step 112. The actual angular orientation value may range from 0 degrees to 360 degrees. Controller 40 may also use the environment signals to determine the target angular orientation of wrist 19. For example, controller 40 may use information received from environment sensor 43 to dynamically map a surface plane of cutting face 52 and/or 53. Controller 40 may then determine the target angular orientation based on the map of the surface plane and the preferred orientation requirements for efficient and damage free milling. Controller 40 may then compare a difference between the actual angular orientation and target angular orientation to an operation threshold.
If the difference between the actual angular orientation and target angular orientations is greater than an operation threshold (Step 114: Yes), controller 40 may inhibit milling of cutting head 12 (Step 116). Inhibiting milling may consist of powering down cutting head 12 and cutting tools 18 or it may consist of decelerating the movement of cutting head 12 and cutting tools 18. Operation of machine 10 may remain inhibited until the difference between the actual angular orientation and target angular orientations is less than the operation threshold. In some instances re-orientating of boom 24, positioning drum 22, and/or wrist 19 may be required. If the difference determined at step 114 is less than the operation threshold (Step 114: No), controller 40 may then compare the difference to a lower warning threshold (Step 118). If the difference is greater than the lower warning threshold (Step 118: Yes), controller 40 may cause display interface 41 to show a warning (Step 120). Controller 40 may allow milling to occur following steps 118 and 120 (Step 122).
In some embodiments, a machine operator may be able to visually verify the actual angular orientation of wrist 19 by comparing alignment of angular marking 65 with reference marking 66. Additionally, the machine operator may use angular marking 65 and reference marking 66 to calibrate or re-calibrate primary angular sensor 63 and/or redundant angular sensor 64. In order to do this, the machine operator may incrementally rotate wrist 19 about wrist axis 20 until angular marking 65 aligns with reference marking 66. Then the machine operator may use display interface 41 to electronically zero out the signals from sensors 63 and 64.
In some embodiments, a machine operator may perform manual movement of wrist 19 in order to determine if a specific sensor has failed and/or is out of range. For example, controller 40 may cause display interface 41 to display a calibration instruction (Step: 110) and further prompt the machine operator to select a specific sensor to disable and/or a specific sensor to rely on. In other embodiments, control system 40 may execute an intelligent calibration that is performed automatically. For example, when controller 40 determines that the difference between primary and secondary signals is greater than the operation threshold (Step 108: Yes) controller 40 may inhibit milling of cutting head 12 (Step 116) and execute an automatic intelligent calibration. The automatic intelligent calibration may rotate wrist 19 counter-clockwise and verify that sensors 63,64 are generating signal outputs that are expected for the degree of counter-clockwise rotation (i.e., compare the signal output values to the expected output values). The automatic intelligent calibration may additionally rotate wrist 19 clockwise and verify that sensors 63,64 are generating signal outputs as expected for the degree of clockwise rotation (i.e., compare the signal output values to the expected output values). If Controller 40 determines that the difference between the signal outputs and expected outputs is greater than an expectation threshold controller 40 may cause a specific sensor warning to be shown on display interface 41.
Several benefits may be associated with the disclosed control system. Specifically, the disclosed control system may reduce unnecessary wear and tear by maintaining cutting head 12 in a preferred orientation relative to a target cutting surface during an operation. By maintaining cutting head 12 in the preferred orientation, the longevity and production capability of machine 10 may be increased. Additionally, the disclosed control system may inhibit operation when cutting head 12 is significantly misaligned, thereby avoiding catastrophic damage.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed control system. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed control system. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. As used herein, the articles “a” and “an” are intended to include one or more items, and may be used interchangeably with “one or more.” Where only one item is intended, the term “one” or similar language is used. Also, as used herein, the terms “has,” “have,” “having,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.

Claims

What is claimed is:

1. A control system for a machine, the control system comprising:

a wrist configured to rotate about a wrist axis;

a gear mechanism configured to drive rotation of the wrist;

a cutting head coupled to the wrist and configured to rotate about a cutter axis that is substantially perpendicular to the wrist axis;

a primary angular sensor configured to generate primary signals indicative of angular orientations of the wrist;

at least one redundant angular sensor configured to generate secondary signals indicative of angular orientations of the wrist; and

a controller configured to:

control operation of the wrist and the cutting head;

compare an actual angular orientation of the wrist, as indicated by one or more of the primary signals or the secondary signals, to a target angular orientation; and

selectively inhibit the cutting head from operating when the controller determines that the actual angular orientation differs from the target angular orientation by an operation threshold.

2. The control system of claim 1, wherein the controller is further configured to control operation of the wrist based on only one or more of the primary signals.

3. The control system of claim 1, wherein the controller is further configured to control operation of the wrist based on only the secondary signals when the primary signals are unavailable and when the primary signals are out of range.

4. The control system of claim 1, further including a display in communication with the controller, wherein the controller is configured to:

compare the primary signals and the secondary signals to an expectation value, and

selectively cause a specific sensor warning to be shown on the display when the controller determines that at least one of the primary signals or the secondary signals differs from the expectation value by an expectation threshold.

5. The control system of claim 1, further including a display in communication with the controller, wherein the controller is configured to selectively cause a signal warning to be shown on the display when the controller determines the primary signals are unavailable and when the controller determines the primary signals are out of range.

6. The control system of claim 1, further including a display in communication with the controller, wherein the controller is configured to:

compare the primary signals to the secondary signals;

selectively inhibit the cutting head from operating when the controller determines that the primary signals differ from the secondary signals by the operation threshold; and

selectively cause a calibration instruction to be shown on the display when the controller determines that the primary signals differ from the secondary signals by a signal threshold.

7. The control system of claim 1, further including a display in communication with the controller, wherein the controller is configured to selectively cause a warning to be shown on the display when the controller determines that the actual angular orientation differs from the target angular orientation by a warning threshold that is lower than the operation threshold.

8. The control system of claim 1, further including an environment sensor in communication with the controller and configured to generate environment signals, wherein the controller is further configured to:

compare an actual angular orientation of the wrist, as provided via the environment signals, to the target angular orientation; and

selectively inhibit the cutting head from operating when the controller determines that the actual angular orientation differs from the target angular orientation by the operation threshold.

9. The control system of claim 1, wherein the target angular orientation is a preferred orientation in which an axial end face of the cutting head is perpendicular to an operation milling direction.

10. A method for operating a cutting head of a machine, the method comprising:

determining a target angular orientation of the cutting head;

generating a primary angular orientation output associated with the cutting head;

generating a redundant angular orientation output associated with the cutting head;

making a first comparison of the primary angular orientation output to the target angular orientation; and

selectively inhibiting the cutting head from operating based on the first comparison when the primary angular orientation output and the target angular orientation differ by an operation threshold.

11. The method of claim 10, further including:

making a second comparison of the redundant angular orientation output to the target angular orientation only when the primary angular orientation output is unavailable and when the primary angular orientation output is out of range; and

selectively inhibiting the cutting head from operating based on the second comparison when the redundant angular orientation output and the target angular orientation differs by the operation threshold.

12. The method of claim 11, further including displaying a second warning when the redundant angular orientation output and the target angular orientation differs by a warning threshold that is lower than the operation threshold.

13. The method of claim 10, further including:

generating an environment angular orientation output associated with the cutting head;

making a third comparison of the environment angular orientation output to the target angular orientation; and

selectively inhibiting the cutting head from operating based on the third comparison when the environment angular orientation output and the target angular orientation differs by the operation threshold.

14. The method of claim 10, further including displaying a signal warning when the primary orientation output is unavailable and when the primary orientation output is out of range.

15. The method of claim 10, further including:

comparing the primary angular orientation output to the redundant angular orientation output;

selectively inhibiting the cutting head from operating based on the third comparison when the environment angular orientation output and the target angular orientation differs by the operation threshold; and

displaying a calibration instruction when the primary orientation output and the redundant orientation output differs by a signal threshold.

16. The method of claim 10, further including:

comparing the primary angular orientation output to the redundant angular orientation output; and

displaying a second warning when the primary angular orientation output and the target angular orientation differs by a warning threshold that is lower than the operation threshold

17. A machine, comprising:

a wrist configured to rotate about a wrist axis;

a gear mechanism configured to drive rotation of the wrist and having an exposed surface with a plurality of angular markings;

a stationary surface adjacent the gear mechanism and having a reference marking;

a primary encoder disposed in the gear mechanism and configured to generate primary signals indicative of angular orientations of the wrist;

at least one redundant encoder disposed in the gear mechanism and configured to generate secondary signals indicative of the angular orientations of the wrist; and

a controller configured to:

control operation of the wrist and the cutting head;

compare an actual angular orientation of the wrist, as indicated by one or more of the primary signals or the secondary signals, to a target angular orientation;

compare the primary signals to the secondary signals;

selectively inhibit the cutting head from operating when the controller determines that the actual angular orientation differs from the target angular orientation by an operation threshold and when the controller determines that the primary signals differ from the secondary signals by the operation threshold;

selectively cause a calibration instruction to be shown on a display when the controller determines the primary signals differ from the secondary signals by a signal threshold; and

selectively cause a warning to be shown on the display when the controller determines the actual angular orientation differs from the target angular orientation by a warning threshold that is lower than the operation threshold.

18. The control system of claim 17, wherein the controller is further configured to control operation of the wrist based on only the primary signals as long as the primary signals are available and within range.

19. The control system of claim 18, wherein the controller is further configured to control operation of the wrist based on only the secondary signals when the controller determines the primary signals are unavailable and when the controller determines the primary signals are out of range.

20. The control system of claim 17, further including an environment sensor in communication with the controller and configured to generate environment signals, wherein the controller is further configured to: