Patent Publication Number: US-2023132726-A1

Title: Systems and methods for surface milling

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to methods and systems for milling machines and, more particularly, to systems and methods for a milling machine having a rotor chamber. 
     BACKGROUND 
     Milling machines are useful in applications where it is desirable to remove material from a ground surface. Milling machines, which can include rotary mixers, cold planers, and other machines, are used for reclamation of asphalt or soil-based roadways for road rehabilitation, soil stabilization, surface mining, bio-remediation, agriculture, and other applications. Rotary mixers, cold planers, and similar machines include rotors with a drum and tool bits designed for removing and pulverizing material. The tool bits and rotor can be positioned within a partially-enclosed compartment with an open bottom surface and hydraulically-operated front and rear doors to facilitate mixing and homogenization of the material removed with the tool bits. 
     During operation of a milling machine that includes a rotor chamber, doors of the chamber are placed in a desired position, typically by an operator&#39;s manual interaction with an input device. In some machines, the rotor chamber doors are fully operator-controlled, such that the operator of the machine can place the doors in a specific desired position, such as fully closed, fully open, 50% open, etc. If the operator fails to select a condition-appropriate position for a front door, a rear door, or both, the doors can encounter material, such as asphalt, soil, rock, debris, etc., and even plow this material while the machine travels. Even when the doors are opened to an adequate degree, the door may encounter mounds of debris. Striking this material with a rotor chamber door can increase wear on the door, and on the hydraulic cylinders for raising and lowering the doors. In some circumstances, a door can plow material or strike a debris pile with sufficient force so as to damage the door, a component of the hydraulic system for the door, or both. This increased wear or damage can require increased maintenance, repair, and even replacement of the doors and/or mechanisms for opening and closing the doors. 
     A pavement planer including a tailgate lifting device with a pressure sensor is described in CN 102168401B (“the &#39;401 publication”) to Yongbiao Hu et al. The pavement planer described in the &#39;401 publication includes a control system that monitors pressure of a tailgate. When the pressure of the tailgate is above or below certain setpoints, the control system can adjust the pressure. While the pavement planer described in the &#39;401 publication may be useful in some circumstances, it may be unable to identify and remedy situations where a door encounters material before the material reaches the rotor, and may be unable to raise a door encountering this material in an automated manner. 
     The systems and methods of the present disclosure may solve one or more of the problems set forth above and/or other problems in the art. The scope of the current disclosure, however, is defined by the attached claims, and not by the ability to solve any specific problem. 
     SUMMARY 
     In one aspect, a method for monitoring a milling machine having a milling rotor and a rotor chamber surrounding the milling rotor may include propelling the milling machine in a direction of travel, positioning a door of the rotor chamber at a first position with an actuator, and receiving a signal indicative of a condition of the actuator for positioning the door of the rotor chamber. The method may further include determining that the door has encountered material based on the signal and opening the door of the chamber in response to determining that the door has encountered material. 
     In another aspect, a method for monitoring a milling machine having a milling rotor, a rotor chamber surrounding the milling rotor, a first door of the rotor chamber, and a second door of the rotor chamber may include determining a direction of travel of the milling machine and determining that the first door or the second door is a forward door that faces the direction of travel. The method may further include determining that the forward door has encountered material based on a signal generated with a sensor associated with the forward door and automatically opening the forward door in response to determining that the door has encountered material. 
     In yet another aspect, a milling system may include a frame, a rotor chamber connected to the frame, the rotor chamber having a first door and a second door opposite the first door, a first hydraulic cylinder configured to open and close the first door, and a sensor configured to output a signal that indicates when the first door has encountered material. The system may further include a controller configured to receive the signal from the sensor, determine that the signal indicates that the first door has encountered material, and cause the first door to open in response to determining that the first door has encountered material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  is a schematic diagram of a milling machine with doors in a closed position, according to aspects of the disclosure. 
         FIG.  1 B  is a schematic diagram of the milling machine of  FIG.  1 A  with doors in an open position, according to aspects of the disclosure. 
         FIG.  2    is a block diagram showing a rotor chamber door control system, according to aspects of the disclosure. 
         FIG.  3    is a flowchart depicting an exemplary method for automatic control of a rotor chamber door, according to aspects of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the features, as claimed. As used herein, the terms “comprises,” “comprising,” “having,” including,” or other variations thereof, are intended to cover a non-exclusive inclusion such that a method or apparatus that comprises a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such a method or apparatus. In this disclosure, relative terms, such as, for example, “about,” “substantially,” “generally,” and “approximately” are used to indicate a possible variation of ±10% in the stated value or characteristic. As used herein, “encountering material,” or “encountered material,” refers to one or more components that strike soil, rock, or other types of debris, or other material, this material being present outside of a chamber that encloses the rotor, with force sufficient to cause a measureable change in the position of the component (e.g., a door), a measureable change in a position of an actuator connected to the component (e.g., a hydraulic cylinder for opening and closing a door), and/or a measureable change in a pressure of hydraulic fluid supplied to the actuator. 
       FIGS.  1 A and  1 B  illustrate an exemplary machine system  10  that includes a machine  12  and an automatic door control system  14 . Machine  12  of system  10  may be a milling machine, such as a rotary mixer or a cold planer configured to remove surface materials. However, machine  12  may include one or more other types of machines. Machine  12  may include a cabin  16 , frame  20 , ground-engaging traction devices  22  such as wheels or tracks (wheels being shown in  FIGS.  1 A and  1 B ), and a rotor chamber  24  that surrounds a milling rotor  26 . Frame  20  may support rotor chamber  24  such that a front door  28  faces a front end of machine  12  (e.g., a direction an operator faces when present in cabin  16 ) and a rear door  30  faces a rear end of machine  12 . 
     As shown in  FIGS.  1 A and  1 B , machine  12  may be a rotary mixer in which milling rotor  26 , including a drum and a plurality of tool bits, is controllably (selectively and/or automatically) lowered to remove material from a ground surface. Rotor  26  may be rotatably mounted within rotor chamber  24  such that cutting bits secured to an outer periphery of rotor  26  engage the ground and/or pavement to remove and pulverize material when machine  12  is operated, as described below. Doors  28  and  30  may be movable between closed positions shown in  FIG.  1 A  and open positions shown in  FIG.  1 B . One or more control devices for selective operation of doors  28  and  30  may be present within cabin  16 . These controls may include a first control switch or button that opens door  28  (e.g., when pressed), a second control switch or button that closes door  28 , as well as third and fourth control switches that open and close door  30 . If desired, one or more control devices within cabin  16  may enable automatic monitoring of one or both doors  28  and  30  via automatic door control system  14 , such that the operator-set position of doors  28  or  30  are overridden when the door encounters material, as described below. Alternatively, automatic monitoring of doors  28  and/or  30  may be enabled with door control system  14  without the need to affirmatively enable automatic monitoring with a control device. 
     Automatic door control system  14  of machine system  10  may include hydraulic devices that together control the positions of doors  28  and  30 . These hydraulic devices may include a first actuator (front hydraulic cylinder  32 ), a second actuator (rear hydraulic cylinder  36 ), hydraulic valves  70  and  72 , one or more respective fluid lines  74  and  76  in communication with cylinders  32  and  36  and valves  70  and  72 , and other suitable hydraulic components, such as pumps, further valves, etc. Automatic door control system  14  may also include an electronic control module (ECM)  80  and one or more door sensors, two shown in  FIGS.  1 A and  1 B , door sensors  34  and  38 . ECM  80  may be in communication with door sensors  34  and  38  to detect a condition of hydraulic cylinders  32  and  36  connected to doors  28  and  30  based on the signals generated by these sensors  34  and  38 , as described below. 
     In an exemplary configuration, door sensors  34  and  38  may include one or more pressure sensors configured to sense a pressure of hydraulic fluid associated with hydraulic cylinders  32  and  36 . Additionally or alternatively, door sensors  34  and  38  may include one or more position sensors (e.g., hall-effect sensors) configured to detect a position of a movable member (e.g., a rod) of hydraulic cylinders  32  and  36 , respectively. While  FIGS.  1 A and  1 B  illustrate a single hydraulic fluid line  74  and  76 , respectively, for hydraulic cylinders  32  and  36 , as understood, hydraulic fluid lines  74  and  76  may each represent a plurality of hydraulic fluid lines, as described below and shown in  FIG.  2   . Moreover, while a single valve  70 ,  72 , is shown for each hydraulic fluid line  74 ,  76  and each cylinder  32 ,  36 , valves  70  and  72  may be part of a hydraulic system including one or more additional control valves, hydraulic pumps, motors, hydraulic fluid reservoirs, etc. Similarly, hydraulic cylinders  32  and  36  may represent a plurality of hydraulic cylinders, for example to distribute the load for opening, closing, and supporting a door across multiple actuators. 
     ECM  80  may be enabled, via programming, to monitor and control states of doors  28  and  30  based on one or more conditions of machine  12  and information received from a pressure sensor and/or a position sensor associated with an actuator for one of doors  28  and  30 . In particular, ECM  80  may be configured to control a position of doors  28  and  30  based on a calculated, requested, or detected travel direction of machine  12  and a detected condition of the door  28 , door  30 , or both detected with sensors  34  and  38 . In particular, ECM  80  may be configured to automatically open door  28 , door  30 , or both, in response to determining that the door facing a direction of travel of machine  12  is currently encountering material or encountered material recently. ECM  80  may be enabled to continuously monitor doors  28  and  30  in this manner, or may instead monitor doors  28  and  30  in response to a request initiated by an operator in cabin  16 . Such a request may be initiated by interacting with a switch, button, touchscreen, etc., to enable automatic monitoring in which ECM  80  monitors one or both of doors  28  and  30 . 
     In order to achieve these functions, ECM  80  may be programmed to implement an automatic door monitoring module  82  ( FIG.  2   ). ECM  80  may employ functions associated with automatic door monitoring module  82  to identify which door  28 ,  30 , faces a direction of travel and to automatically open this door after determining that the door has impacted material. If desired, ECM  80  may be in communication with one or more additional electronic control modules, including control modules for controlling a power source such as an internal combustion engine, a control module for a transmission system, additional hydraulic components, etc. Additionally or alternatively, ECM  80  may itself be programmed to control one or more aspects of system  10  in addition to the position of doors  28  and  30 . 
     ECM  80  may embody a single microprocessor or multiple microprocessors that receive inputs and generate outputs. ECM  80  may include a memory, a secondary storage device, a processor, such as a central processing unit or any other means for accomplishing a task consistent with the present disclosure. The memory or secondary storage device associated with ECM  80  may store data and software to allow ECM  80  to perform its functions including the functions described with respect to  FIG.  2    and method  300  described below. Numerous commercially available microprocessors can be configured to perform the functions of ECM  80 . Various other known circuits may be associated with ECM  80 , including signal-conditioning circuitry, communication circuitry, and other appropriate circuitry. 
       FIG.  2    is a block diagram of an exemplary configuration of ECM  80  that may enable monitoring functions for doors  28  and  30  of rotor chamber  24 . In some aspects, door monitoring functions performed with ECM  80  may identify a door  28  or  30  that faces a direction of travel of machine  12  and open the identified door to avoid or mitigate damage due to loose debris or other material impacting the door due to the travel of machine  12 . ECM  80  may receive a plurality of inputs  200 , such as a travel direction  201 , a rod end signal  202  and/or head end signal  204  associated with hydraulic cylinder  32 , and a head end signal  206  and rod end signal  208  associated with hydraulic cylinder  36 . Based on inputs  200 , ECM  80  may generate outputs  210  including commands for actuators of doors  28  and  30 , such as commands for hydraulic valves  70  and  72 . 
     When automatic door monitoring module  82  of ECM  80  is active or enabled, ECM  80  may identify when a door has been struck with debris, based on inputs  200 . In response to this determination, ECM  80  may generate one or more outputs  210  that cause the corresponding door to open by a greater degree. With reference to the exemplary configuration shown in  FIG.  2   , ECM  80  may receive travel direction  201 . Travel direction  201  may correspond to a direction of travel (e.g., forward or reverse) based on a request for propulsion from an operator. For example, an operator may select a travel direction such as forward or reverse with a lever or switch, the position of which is monitored with a position sensor that outputs travel direction  201  as a signal. Additionally or alternatively, travel direction  201  may be determined based on one or more speed sensors (e.g., a sensor associated with one or more traction devices  22 ), one or more accelerometers secured to frame  20  of machine  12 , etc. 
     ECM  80  may receive one or more inputs  200  in additional to travel direction  201  to allow automatic door monitoring module  82  to determine when a door that faces the direction indicated by travel direction signal  201  has encountered material, such as a pile of debris. As used herein, the “forward door” is the door that faces the direction indicated by direction of travel  201 . When the direction of travel  201  is reverse, for example, the “forward door” is door  30 , which is farther from cabin  16  as compared to door  28 . In the example illustrated in  FIG.  2   , door sensor  34  ( FIGS.  1 A and  1 B ) corresponds to a plurality of sensors, including a rod end pressure sensor  134  and a head end pressure sensor  136 . Similarly, door sensor  38  ( FIGS.  1 A and  1 B ) may represent a plurality of sensors, such as rod end pressure sensor  140  and head end pressure sensor  138 . However, in at least some configurations, door sensors  34  and  38  may represent a single sensor (e.g., rod end pressure sensor  134  and rod end pressure sensor  140 , respectively). 
     Rod end pressure sensor  134  may be configured to generate a pressure signal  202  that indicates or otherwise corresponds to the pressure of hydraulic fluid within a hydraulic fluid line connected to the rod end of hydraulic cylinder  32 . A rod end of a hydraulic cylinder may include a first chamber through which a rod extends, the first chamber having a variable volume that surrounds the rod. Head end pressure sensor  136  may be configured to generate a pressure signal  204  that is indicative of a pressure of fluid in a head end of hydraulic cylinder  32 . A head end of a hydraulic cylinder  32  may include a second chamber isolated from the first chamber by a piston, the second chamber having a variable volume whose size is inversely proportional to the size of the first chamber. Rod end pressure sensor  140  and head end pressure sensor  138  may operate in a manner analogous to pressure sensors  134  and  136 , respectively, and may generate a pressure signal  206  indicative of pressure of fluid in a head end of hydraulic cylinder  36  and a pressure signal  208  indicative of pressure in a rod end of hydraulic cylinder  36 . 
     Pressure sensors  134  and  136  may be associated with a door that has a higher likelihood of being the “front” door, door  28 , (e.g., the door that faces the travel direction when machine  12  moves in a direction indicated as “forward” by an in-cabin selector, a position faced by an operator when seated in cabin  16 , etc.). Pressure sensors  138  and  140  may be associated with a door that has a higher likelihood of being the “rear” door, door  30 , (e.g., the door that faces the travel direction when machine  12  moves in a direction indicated as “reverse” by an in-cabin selector). 
     While sensors  134 ,  136 ,  138 , and  140  have been described as being pressure sensors, inputs  200  may include one or more position sensors that are configured to detect a movement of the rod of a respective hydraulic cylinder  32  or  36 , as described above. Instead of or in addition to sensors  134 ,  136 ,  138 , and  140 , a load cell may be used as sensor  34  and/or  38 , the load cell being able to detect an amount of force applied to cylinders  32  and  36 . 
     Automatic door monitoring module  82  may be configured to evaluate at least one of signals  202 ,  204 ,  206 , and  208  to determine when a front-facing door  28  or  30  is encountering material, as described in more detail below. Automatic door monitoring module  82  may be configured to take action, by generating outputs  210 , to open the door that has encountered material. Outputs  210  may be generated by module  82 , for example, without operator intervention. For example, automatic door monitoring module  82  may be configured to generate a front door command signal  212  or a rear door command  214  to actuate the appropriate cylinder  32  or  36  based on travel direction  201  and information received by one or more of sensors  134 ,  136 ,  138 , and  140 , the information from the sensor being indicative that the door is encountering material from outside of rotor chamber  24 . Front door command  212  or rear door command  214 , when generated in this manner, may override the operator&#39;s setting. For example, if an operator has set front door  28  to a partially-open position (e.g., 50% open, or halfway between a fully-closed position and a fully-open position), front door command  212  may be generated to open door  28  by a greater degree in response to determining that door  28  has encountered material. 
     Automatic door monitoring module  82  may be selectively active, if desired. For example, automatic door monitoring module  82  may be perform monitoring and door control functions only when an automatic door monitoring mode is enabled by an operator (e.g., by manipulating a control within cabin  16 ). Alternatively, automatic door monitoring module  82  may be active whenever machine  12  is running, whenever rotor chamber  24  and/or rotor  26  are lowered to a working condition in which surface material can be removed, etc. 
     Automatic door monitoring module  82  may be configured to output a front door command  212  when the front door  28  of machine  12  is determined to face travel direction  201  and encounters material, overriding the position for door  28  set by an operator within cabin  16 . In a corresponding manner, when monitoring module  82  determines that rear door  30  faces travel direction  201  and encounters debris such as loose material, automatic door monitoring module  82  may output a command to rear door command  214  that opens door  30  by a greater degree than that set by an operator of machine  12 . 
     In at least some configurations, automatic door monitoring module  82  may be configured to perform automatic control on a door that faces away from the determined travel direction. For example, automatic door monitoring module  82  may be configured to cause the door facing away from travel direction  201  (e.g., front door  28  when direction  201  is reverse, rear door  30  when direction  201  is forward) to apply an approximately constant downpressure, enabling automatic control of this door independently of the control of the door that faces the direction of travel. In some aspects, the pressure may be determined based on head end pressure sensors  136  and  138 , and may enable closed-loop control over the downpressure of the door  28  or  30  that faces away from travel direction  201 . This pressure may be set, for example, by an operator to assist with gradation of material that exits chamber  24 . Thus, automatic control of doors  28  and  30 , and generated commands  212  and  214 , may be performed based on travel direction  201 , preventing material from striking the door facing direction of travel  201 , while allowing closed-loop control over the door that faces away from direction of travel  201 . 
     INDUSTRIAL APPLICABILITY 
     Machine system  10  may include any suitable machine  12  having a door that faces a direction of travel during at least some operating conditions of machine  12 . Machine  12  may therefore be a mobile machine, such as a milling machine, in which front and rear doors  28  and  30  are configured to provide control over a quantity of material within rotor chamber  24 . 
       FIG.  3    is a flowchart illustrating an exemplary method  300  for monitoring a milling machine such as machine  12 , according to aspects of the present disclosure. Method  300  may be performed while operating machine  12  to remove material from a paved surface, loose soil, hard-packed material, etc., to facilitate road production or rehabilitation, soil stabilization, mining, bio-remediation, agriculture, etc. During method  300 , one or more power-generating devices, such as an internal combustion engine, and power transferring devices, such as a transmission, may operate to generate power to propel machine  12  in a direction of travel (e.g., to the right in  FIGS.  1 A and  1 B ) and to provide energy for operating the hydraulic system of machine  12 . Method  300  may be performed continuously during the operation of machine  12 , or in response to a particular condition. This condition may include when an automatic operation mode is enabled (e.g., a mode for supervising a door that faces the direction of travel of machine  12 ). Additionally or alternatively, the condition for performing method  300  may include determining with ECM  80  that rotor chamber  24  and/or rotor  26  are in a suitable position for performing work on a ground surface (e.g., when rotor chamber  24  and rotor  26  are lowered to an appropriate height). 
     A step  302  of method  300  may include propelling machine  12  in a direction of travel. This direction of travel may be selected by an operator within cabin  16  and may be “forward” (e.g., to the right in  FIGS.  1 A and  1 B ). If machine  12  is autonomously or remotely operated, this direction may be received from a remote system, or generated with a control unit for facilitating autonomous control of machine  12 , such as ECM  80  or an additional electronic control unit. During step  302 , machine  12  may move in a forward direction or a reverse direction via ground-engaging traction devices  22 . 
     During a step  304 , which may be performed before and/or during step  302 , one or both of doors  28  and  30  for rotor chamber  24  may be set in a desired position. In an example where front door  28  faces the direction of travel of machine  12 , front door  28  may be in a fully-closed position or a nearly-closed position (e.g., less than 10% open). In other examples, doors  28  and/or  30  may be opened by a first amount (e.g., an amount set by an operator) that is greater than a 10% open position. An operator may set the position of doors  28  and/or  30  by interacting with one or more input devices within cabin  16 , such as a switch, button, joystick, etc. In response to this request, the position of doors  28  and  30  may be set by controlling the supply of hydraulic fluid via hydraulic valves  70 ,  72 , hydraulic lines  74 ,  76 , etc. While the position set in step  304  may be selected by an operator, the position may instead be automatically generated by ECM  80 . For example, ECM  80  may cause the door  28  or  30  facing the direction of travel to open by a first amount. 
     A step  306  may include receiving a rotor chamber door signal with ECM  80 . This may further including detecting a state of an actuator that opens door  28  or door  30  with ECM  80 . For example, ECM  80  may monitor a state of an actuator associated with the door  28  or  30  whose position was set in step  304 , this door facing the direction of travel of machine  12 . As described above, this may be performed by monitoring, via ECM  80 , a pressure of hydraulic fluid associated with one or more hydraulic cylinders  32  and  36  with sensors  34  and  38  (sensors  134 ,  136 ,  138 , and  140  in  FIG.  2   ). Step  306  may include monitoring a position of a rod of one or more hydraulic cylinders  32  and  36 , or a force placed on doors  28  and  30  (e.g., by placing one or more load cell sensors on doors  28  and  30 ), either in addition to or instead of monitoring hydraulic fluid pressure. 
     Step  308  may include determining when signals  202 ,  204 ,  206 , and/or  208 , that were received by ECM  80  during step  306  indicate that the door facing a direction of travel has encountered material. In an example where front door  28  is connected to a rod end of cylinder  32 , and material strikes door  28 , this material may tend to push door  28  inward toward rotor chamber  24 . This motion can, in turn, tend to extend the rod of hydraulic cylinder  32  by pulling the rod of cylinder  32  away from the head end of cylinder  32 . In some hydraulic systems, this may cause measureable movement of the rod of cylinder  32  and/or door  28 . Other hydraulic systems may resist movement of the rod of cylinder  32  and door  28  such that no measureable movement occurs. Regardless of whether a measureable amount of motion occurs, the pressure detected with sensor  34  may tend to fluctuate. The amount of this pressure change may be compared to a predetermined threshold to determine when the pressure change (a pressure increase or decrease) indicates that the door facing the direction of motion has struck material. 
     A pressure of hydraulic fluid detected for the rod end of cylinder  32 , e.g., with pressure sensor  134  ( FIG.  2   ), will tend to increase as door  28  is pushed inwardly. Thus, a pressure change detected with sensor  134 , such as a pressure increase, may be analyzed by automatic door monitoring module  82  to allow module  82  to determine that door  28  has encountered material. This pressure change may be compared to a predetermined threshold to determine when door  28  has encountered material. Additionally or alternatively, the value of pressure detected with sensor  134  may be compared to a predetermined threshold. For example, ECM  80  may determine, via automatic door monitoring module  82 , that door  28  has encountered material when the detected pressure exceeds a first predetermined threshold (e.g., 250 bar) and, in response to this determination, issue a command for opening door  28 , as described in further detail below with respect to step  310 . This pressure may be monitored such that, when ECM  80  determines that the pressure has dropped below a second predetermined threshold that is lower than the first threshold (e.g., 200 bar) for at least a predetermined period of time, ECM  80  may issue a command to return door  28  to the previous position (e.g., a position set by the operator). 
     ECM  80  may determine that door  28  has encountered material when pressure sensed with sensor  134  exceeds a predetermined threshold for any period of time. In other configurations, ECM  80  may determine that door  28  has encountered material when a value of pressure detected with sensor  134  exceeds a predetermined threshold for at least a predetermined set period of time. 
     In a corresponding manner, a pressure drop detected for the head end of cylinder  32  with sensor  136  may indicate that door  30  has encountered material. In some configurations, the pressure increase measured by sensor  134  may be compared to a predetermined pressure threshold that, when exceeded (or exceeded for a set period of time), allows module  82  of ECM  80  to automatically issue a command for opening the associated door. A similar analysis may be performed for comparing a pressure drop measured with sensor  136 . 
     ECM  80  may also perform the above-described analysis with sensors  138  and/or  140 . For example, an analysis for rod end pressure sensor  140  may performed in the manner described above with respect to rod end sensor  134 , and the analysis for head end pressure sensor  138  may be performed in the manner described above with respect to head end pressure sensor  136 . 
     As noted above, while step  308  may include detecting hydraulic fluid pressure, if desired, step  308  may be performed with one or more position sensors that sense movement of hydraulic cylinders  32 ,  36 , to determine when doors  28  and/or  30  are forced inwardly. For example, sensors  34  and/or  38  may be configured as one or more position sensors that output a signal that indicates when a cylinder associated with a door extends unexpectedly. 
     Based on the pressure(s) and/or position(s) detected with sensors  34  and  38 , automatic door monitoring module  82  of ECM  80  may determine that a door facing the direction of travel of machine  12  has impacted or is plowing material. In response to this determination, in a step  310 , module  82  may generate an output to increase the amount by which this door is opened. For example, module  82  of ECM  80  may generate front door command  212  or rear door command  214  that causes the hydraulic fluid system of automatic door control system  14  to actuate the appropriate hydraulic cylinder(s) to increase the amount by which door  28  or  30  is opened. In some aspects, step  310  may include opening door  28  or  30  by an additional predetermined amount (e.g., 25% farther with respect to the maximum range of motion of the door), opening door  28  or  30  to a predetermined minimum position (e.g., 50% open, 60% open, 70% open, etc.), opening door  28  or  30  by an amount based on the detected pressure (e.g., by opening door  28  or  30  by an amount that is determined as a function of the detected change in pressure), or opening door  28  or  30  to a fully-opened position. For example, step  310  may include opening door  28  or  30  by a first amount (e.g., a first amount in addition to the amount performed during step  304 ). By continuing to monitor doors  28  and  30 , method  300  may include repeating step  310  so as to open the same door by a second amount in addition to the first amount. If desired, step  310  may further include presenting a notification to the operator, such as a visual or audio warning via display and/or audio devices present within cabin  16 . 
     While method  300  may be performed to determine when a door facing direction of travel  201  has encountered (e.g., impacted) material, method  300  may also include performing closed-loop control over the door that faces away from the direction of travel  201 . As described above, this closed-loop control may enable an operator to set a desired downpressure for the door facing away from the direction of travel. Thus, the door (door  28  or  30 ) facing away from the direction of travel  201  may be controlled independently of the door that faces the direction of travel  201 . 
     While steps  302 ,  304 ,  306 ,  308 , and  310  have been described in an exemplary order, as understood, one or more of these steps may be performed and/or repeated in a different order. Moreover, any two or more of these steps may be performed simultaneously and/or at overlapping periods of time. 
     System  10  and method  300  may be useful for milling machines such as rotary mixers, cold planers, etc., to detect when a door has encountered material, or is continuing to encounter material, due to the motion of the machine. Thus, it may be possible to prevent plowing of material in worksites containing piles of loose material or other obstacles. Additionally, it may be possible to automatically open a door, by either opening a closed door or increasing the amount by which the door is open, preventing further wear and/or damage. By detecting or otherwise determining a direction of motion of the machine, it may also be possible to prevent damage to both front and rear doors, by monitoring the door that is currently acting as the “front” door that faces the direction of motion of the machine. The automatic monitoring and control over a “front” door may be performed in conjunction with automatic control over the opposite “rear” door, such as applying a predetermined pressure to facilitate accurate grading. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and method without departing from the scope of the disclosure. Other embodiments of the system and method will be apparent to those skilled in the art from consideration of the specification and system and method disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.