Patent Application
20160289916
The present disclosure relates to a control system associated with an implement of a machine and more specifically, a control system for controlling a position of an implement of a machine.
Earthmoving or geography altering machines such as track type tractors, motor graders, scrapers, and/or backhoe loaders, have an implement such as a dozer blade or bucket, which is used on a worksite in order to alter a geography or terrain of a section of earth. The implement may be controlled by an operator or by an autonomous grade control system to perform work on the worksite. For example, the operator may move an operator input device that controls the movement or positioning of the implement using one or more hydraulic actuators. To achieve a final surface contour or a final grade, the implement may be adjusted to various positions by the operator or the grade control system.
Positioning the implement, however, is a complex and time-consuming task that requires expert skill and diligence if the operator is controlling the movement. Conventional machines deploy proportional (P), proportional-derivative (PD), proportional-integral (PI), and/or proportional-integral-derivative (PID) controllers to attain position control of various machine implements. Such controllers may be deployed in combination with a Global Positioning System (GPS) receiver on the machine.
U.S. Pat. No. 9,234,329 describes an adaptive control system for a machine implement. The adaptive control system includes an adaptive controller coupled to the machine implement. The adaptive controller includes a processor configured to receive a position of the machine implement relative to a terrain from at least one position detection system, receive data regarding operating conditions of the terrain, compare the position with a target position stored in a memory, compare the data regarding the operating conditions with data stored in a reference model of the terrain stored in the memory, and adjust the position of the machine implement based upon the comparisons and based upon an updated reference model of the operating conditions of the terrain.
However, conventional P/PD/PI/PID controllers require frequent retuning of control gain parameters. Further, such controllers rely on feedback corresponding to input parameters such as position of the machine etc. and control position of an implement based on reference models causing an inherent delay in the control process. Hence, an improved control system is required.
In an aspect of the present disclosure, a control system for controlling a position of an implement of a machine operating on a terrain is provided. The control system includes a controller which generates a signal indicative of a desired cylinder velocity of an actuator associated with the implement of the machine. The control system includes an operating mode sensor which generates a signal indicative of an operating mode of the machine. The controller includes an instability detection module communicably coupled to the controller and the operating mode sensor. The instability detection module receives the signal indicative of the desired cylinder velocity of the actuator from the controller and the signal indicative of the operating mode of the machine from the operating mode sensor. Thereafter, the instability detection module detects an instability condition based on the signal indicative of the desired cylinder velocity of the actuator and selectively adjusts a controller gain associated with the desired cylinder velocity based at least in part on the instability condition and the operating mode of the machine.
Wherever possible, the same reference numbers will be used throughout the drawings to refer to same or like parts.
As shown, the machine 10 includes a power source 12 and an operator's station or cab 13. The machine 10 further includes a machine implement 14 (hereinafter interchangeably referred to as an implement 14). Examples of the implement 14 may include a blade or a shovel for moving earth in a worksite 16. The cab 13 may include a user interface (not shown) necessary to operate the machine 10. The user interface may be provided along with or may include, for example, one or more displays. The user interface may be configured to propel the machine 10 and/or to control other machine components. The user interface may include one or more joysticks provided within the cab 13, and adapted to receive an input from an operator indicative of a desired movement of the implement 14. The display may be configured to convey information to the operator and may include a keyboard, touch screen, or any suitable mechanism for receiving input from the operator to control and/or operate the machine 10, the implement 14, and/or the other machine components.
The implement 14 may be adapted to engage, penetrate, or cut the surface of the worksite 16 and may be further adapted to move the earth to accomplish a predetermined task. The worksite 16 may include, for example, a mine site, a landfill, a quarry, a construction site, a golf course, or any other type of worksite having an associated terrain. Moving the earth may be associated with altering the geography at the worksite 16 and may include, for example, a grading operation, a scraping operation, a leveling operation, a material removal operation, or any other type of geography altering operation at the worksite 16. In one aspect, the terrain of the worksite 16 has operating conditions associated therewith. Such operating conditions may be described using parameters such as a type of material making the terrain, a dryness factor of the terrain, one or more disturbances present in the terrain (e.g., waves, undulations, or uneven surfaces), and/or other geographical patterns of the terrain of the worksite 16, and the like.
In the illustrated embodiment, the implement 14 includes a cutting edge 18 that extends between a first end 20 and a second end 22. The first end 20, of the cutting edge 18 of the implement 14, may represent a right tip or right edge of the implement 14 and the second end 22, of the cutting edge 18 of the implement 14, may represent a left tip or left edge of the implement 14. In one aspect, the implement 14 may be moveable by one or more hydraulic mechanisms operatively connected to the user interface provided in the cab 13.
The hydraulic mechanisms may include one or more hydraulic lift actuators 24 and one or more hydraulic tilt actuators 26, for moving the implement 14 to various positions, such as, for example, lifting the implement 14 up or lowering the implement 14 down, and tilting the implement 14 left or right. In the illustrated embodiment, the machine 10 includes one hydraulic lift actuator 24 and two hydraulic tilt actuators 26, one on each side of the implement 14. Only one of the two hydraulic tilt actuators 26 is shown (only one side shown). Moreover, the hydraulic mechanism may also include one or more hydraulic push cylinders (not shown) for pitching the implement 14 in forward or backward direction. In one aspect, the hydraulic lift actuators 24 and the one or more hydraulic tilt actuators 26 may be configured to swivel the machine implement 14. Alternatively, the machine 10 may include additional hydraulic actuators to swivel the machine implement 14 over a range of solid angles.
The power source 12 may be an engine that provides power to a ground engaging mechanism 28 adapted to support, steer, and propel the machine 10. In one embodiment, the power source 12 may provide power to actuate the hydraulic mechanism to move or position the machine implement 14. The power source 12 may embody an engine such as, for example, a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or any other type of combustion engine known in the art. It is contemplated that the power source 12 may alternatively embody a non-combustion source of power not shown such as, for example, a fuel cell, a power storage device, or another suitable source of power. The power source 12 may produce a mechanical or electrical power output that may be converted to hydraulic power for providing power to the ground engaging mechanism 28, the implement 14, the hydraulic lift actuator 24, the one or more hydraulic tilt actuators 26, and other machine components.
The machine 10 may include other known components such as vehicular parts including tires, wheels, transmission, engine, motor, hydraulic systems, suspension systems, cooling systems, fuel systems, exhaust systems, chassis, ground engaging tools, imaging systems, and the like. The machine 10 also includes various sensors for sensing various parameters related to the machine 10. The machine 10 may be movable along different directions for the machine implement 14 to implement a predetermined grade on the terrain of the worksite 16.
The machine 10 includes an operating mode sensor 30 which may provide information about an operating mode of the machine 10. The machine 10 may operate in different operating modes such as moving forward, moving reverse, the implement 14 in an engaged position, the implement 14 in a stowage position etc. The operating mode sensor 30 may generate a signal indicative of the current operating mode of the machine 10. The operating mode sensor 30 may be a steering sensor which may provide information about an angle of steering. The operating mode sensor 30 may provide information about a direction of travel of the machine 10 indicating if the machine 10 is travelling in a forward direction or a reverse direction. The operating mode sensor 30 may also provide information about a speed at which the machine 10 is travelling on the surface of the worksite 16. In an embodiment, the operating mode sensor 30 may provide information about command history from an operator input device such as a joystick etc. or a control algorithm to determine the operating mode of the machine 10. For exemplary purposes, if the operator has not provided a blade position change request for a prolonged period of time even though the machine 10 is moving forward, the operating mode sensor 30 would output the operating mode as ‘not grading’ and there may be no control actions taken afterwards. The operating mode sensor 30 may provide any other such information suitable to the present disclosure which indicates the operating mode of the machine 10.
The machine 10 further includes a control system 32 as illustrated in
The terrain map may he a database containing previously-gathered points defining the terrain. The terrain map may, for example, store the previously-gathered points in a matrix form. Each point may include a location (e.g., Cartesian, polar, or spherical coordinate data) and/or other attributes e.g., a grade) about the particular point on the surface of the worksite 16. It is to be appreciated that as the worksite 16 undergoes geographic alteration (e.g., excavation), the surface may change with time. Accordingly, the terrain map stores a matrix containing points defining the most recently scanned and stored surface of the worksite 16. In one embodiment, the points may be previously-gathered by sensors. Alternatively or additionally, the points may be previously-gathered by satellite imagery, aerial mapping, surveys, and/or other terrain mapping means known in the art.
The controller 34 may store terrain maps corresponding to a current state of the worksite 16 and a desired state of the worksite 16. The current terrain map may include information about various parameters defining the present condition of the surface of the worksite 16 and the desired terrain map may include information about a final state of the worksite 16 required after undergoing geographic alterations.
The controller 34 may control the implement 14 considering all the stored information about the machine 10 and the worksite 16 in the memory. The controller 34 controls the position of the implement 14 by controlling a cylinder velocity of the hydraulic actuators of the implement 14. The hydraulic actuator is generally a cylinder having a piston translating inside the cylinder under the effect of a hydraulic force applied by a hydraulic fluid. The cylinder velocity may be defined as a velocity of the piston in the hydraulic cylinder. The cylinder velocity may he associated with either the hydraulic lift actuator 24 or the hydraulic tilt actuator 26. The cylinder velocity may also be associated with a combination of both the hydraulic lift actuator 24 and the hydraulic tilt actuator 26. The cylinder velocity may be associated to a rate of the hydraulic fluid being supplied to the hydraulic cylinder. A valve (not shown) may control the rate of hydraulic fluid being supplied to the hydraulic cylinder. The controller 34 may actuate the valve so as to control the cylinder velocity and in turn the position of the implement 14.
The cylinder velocity is indicative of the position of the implement 14. The controller 34 determines the cylinder velocity on the basis of the position of the implement 14 to be maintained in order to achieve the desired grade of the surface of the worksite 16. The controller 34 takes into account various parameters such as, including but not limited to, terrain maps, operational parameters of the machine 10, desired final grade of the surface of the worksite 16 etc. Based on the various parameters, the controller 34 determines a desired cylinder velocity. The desired cylinder velocity is the cylinder velocity for which the position of the implement 14 would be such as to impart the desired grade to the surface of the worksite 16. The controller 34 generates a desired cylinder velocity signal 36. The desired cylinder velocity signal 36 may be provided by the controller 34 in mm/s. Any other units may also be used to provide the desired cylinder velocity signal 36 so as to suit the need of the present disclosure.
The control system 32 further includes a filter module 38 which receives the desired cylinder velocity signal 36. The filter module 38 may be a separate module or the filter module 38 may also be an integral part of the controller 32. The filter module 38 may include a single or multiple filters to process the desired cylinder velocity signal 36. The filter module 38 may process the desired cylinder velocity signal 36 with a band pass filter 40. The band pass filter 40 only allows a range of frequencies of the signal being processed to pass through. The band pass filter 40 filters out the frequencies outside a pre-determined range of the band pass filter 40. The range of the band pass filter 40 may be set in accordance with a constant value provided to the band pass filter 40. The constant value may be a hydraulic natural frequency of the hydraulic lift actuator 24 or the hydraulic tilt actuator 26. The hydraulic natural frequency remains same for a particular model of the machine 10. For example, a Caterpillar® D5 Track Type Tractor has a hydraulic natural frequency of 3 Hz. The range of the band pass filter 40 may be set according to the hydraulic natural frequency of the model of the machine 10. The hydraulic natural frequency provides the band pass filter 40 with a reference point to set the range of frequencies allowed after the signal passes the band pass filter 40.
The band pass filter 40 processes the desired cylinder velocity signal 36 so as to remove any inconsistent data which may arise from any unforeseen circumstances. Example of such a situation may bean operating mode detected by the controller 34 as ‘not grading’ based on inputs provided by the operating mode sensor 30. In such a scenario, the control system 32 may not take any action at all and reject the data corresponding to such operating modes. The band pass filter 40 filters out any such inconsistencies from the desired cylinder velocity signal 36. The band pass filter 40 processes the desired cylinder velocity signal 36 and outputs a first filtered signal 42. The first filtered signal 42 may further pass through a low pass filter 44.
The low pass filter 44 filters out frequencies lower than a pre-determined cutoff frequency. The cutoff frequency depends upon a constant value provided to the low pass filter 44. The constant value may be a roll off frequency of the low pass filter 44. The roll off frequency determines a response time of the low pass filter 44. The low pass filter 44 should not take too much time to filter the first filtered signal 42. Also, the response should not be too quick for the control system 32 to handle. The roll off frequency determines how quickly the low pass filter 44 would react.
The constant value may depend upon the model of the machine 10 and varies across different models and operating conditions. The low pass filter 44 processes the first filtered signal 42 and outputs a second filtered signal 46. Although the filter module 38 is described as having the band pass filter 40 and the low pass filter 44, it should be contemplated that the filter module 38 may include any other filters as well to process the desired cylinder velocity signal 36. The filter module 38 may include only low pass filters, or only band pass filters or any other combination of the band pass and low pass filters. The filter module 38 generates a signal corresponding to the second filtered signal 46. An instability detection module 48 receives the second filtered signal 46.
The instability detection module 48 determines whether an instability condition exists corresponding to the operation of the implement 14 of the machine 10. The instability condition is defined as an operating condition of the machine 10 where the position of the implement 14 is such as the implement 14 is not able to impart desired characteristics to the surface of the worksite 16. The characteristics may include a grade, a contour etc. The instability detection module 48 may either be a separate module or the instability detection module 48 may also be an integral part of the controller 34.
The instability detection module 48 may have pre-stored range of value of the second filtered signal 46 to determine the instability condition. The instability detection module 48 may have historical data models of machine operation corresponding to previous instability conditions which may be used to identify the instability condition. The instability detection module 48 may include an artificial neural network which may determine an existing or upcoming instability condition based on the second filtered signal 46. The instability detection module 48 may have any other means to detect the instability condition based on the second filtered signal 46. The instability detection module 48 generates an instability signal indicative of the instability condition.
The instability detection module 48 may have means to convert the instability signal into a controller gain. Generally, the controller gain is a measure of responsiveness of a system. In context of the present disclosure, the controller gain indicates how much the position of the implement 14 would change in response to a particular value of the desired cylinder velocity. The controller 34 may have a value of the controller gain associated with the controller 34 according to initial operating conditions. In an embodiment, the controller gain may he a proportional gain of the controller 34. The instability detection module 48 may include a look-up table having values of the controller gain corresponding to the values of the instability signal. The instability detection module 48 may include an expression or a formula which can be used to derive the controller gain based on the instability signal. The instability detection 48 module may have any other such means to derive the controller gain based on the instability signal.
The instability detection module 48 also receives signals from the operating mode sensor 30 indicative of the operating mode of the machine 10. The operating mode of the machine 10 provides information about the operating conditions of the machine 10 and enhances logic behind detecting the instability condition. For example, if the machine 10 may be operating in a relatively higher speed range, the desired cylinder velocity signal 36 may have more fluctuations compared to when the machine 10 is operating in relatively lower speed range. There may be some operating modes where the control system 32 is not applicable. For example, if the machine 10 is reversing, the control system 32 may not adjust the position of the machine implement 14 at all. Another example may be when the machine 10 is undergoing very steep steering angles.
The instability detection module 48 determines an adjustment required in the value of the controller gain based on the instability signal and the operating mode of the machine 10. The instability detection module 48 provides the controller gain adjustment signal 50 to the controller 34. The controller gain adjustment signal 50 is indicative of a change in existing value of the controller gain. The instability detection module 48 may alternatively provide a revised value of the controller gain considering the controller gain adjustment signal 50.
The controller gain is adjusted in case of an instability condition. The controller gain adjustment signal 50 may be an increase or decrease in the existing value of the controller gain. The controller gain adjustment signal 50 may be an adjustment in a proportional gain of the controller 34. Increasing or decreasing the controller gain may be referred to as tuning the position of the implement 14. Increasing the controller gain corresponds to the implement 14 responding at a faster rate to the desired cylinder velocity signal 36 and improving performance of the machine 10. Decreasing the controller gain corresponds to the implement 14 responding at a relatively slow rate to the desired cylinder velocity signal 36 and improving stability of the position of the implement 14. Tuning of the machine 10 is always done to strike off an optimal balance between performance and stability. It may also be contemplated that the desired cylinder velocity may be so as no adjustment is needed in the controller gain. In such cases, the value controller gain may remain same as previous conditions.
The increase or decrease in the controller gain is performed at a particular rate. The rate of decrease in the controller gain is typically greater than the rate of increase in the controller gain. In an embodiment, the rate of decrease in the controller gain is greater than or equal to at least five times the rate of increase in the controller gain. For example, the controller gain is decreased in case the machine 10 has encountered an obstacle or the machine 10 is going through a rough terrain. Such a condition may correspond to an instability condition and the controller gain adjustment signal 50 may be such as to decrease the controller gain quickly. However, after such a condition ceases to exist, the controller gain may not be increased at the same rate. The controller gain is scaled up relatively slowly as compared to the rate of decreasing the controller gain. This offers the control system 32 ample time to adjust to new operating parameters and ensures optimum performance and stability.
The instability detection module 48 may also include means to limit the rate of adjustment of the controller gain. The instability detection module 48 may include a rate limiter block. The rate limiter block limits the rate of controller gain adjustment. The rate limiter block may set an upper limit and lower limit to the rate of increasing and the rate of decreasing the controller gain. The rate limiter block may receive an input signal corresponding to an operating condition of the machine. The input signal may be received from the operating mode sensor 30. The input signal may also be received from the controller 34. The input signal may also be received from any other such sensor suitable to the need of the present disclosure. The rate limiter block may set separate upper and lower limits for rate of increasing and decreasing the controller gain based on the input signal. The limits set by the rate limiter block may change and adjust dynamically according to the operating conditions.
An aspect of the present disclosure is applicable generally to control systems and methods and, more particularly, to a control method for controlling positioning of machine implements (e.g., the machine implement 14). Conventionally, control systems use the classical PD (Proportional Derivative) controller, or other types of proportional controllers. These conventional controllers require frequent tuning when the operating conditions change for different terrains. Also, frequent use of filters slows down the system and delays response times. The aspects of the present disclosure overcome these drawbacks.
The low pass filter 44 processes the first filtered signal 42 and outputs the second filtered signal 46 represented by the third curve 56. As illustrated, the low pass filter 44 filters out any frequencies above a pre-determined frequency. The pre-determined frequency may be set based on the model of the machine 10 as well as the operating conditions. The second filtered signal 46 is passed to the instability detection module 48. The instability detection module 48 processes the second filtered signal 46 and determines the instability condition. The instability detection module 48 includes means to further process the instability condition and determine the controller gain corresponding to the instability condition.
An exemplary representation of the controller gain for the controller 34 determined by the instability detection module 48 is depicted by the fourth curve 58. The instability detection module 48 also receives machine operating mode signal from the operating mode sensor 30. Thereafter, the instability detection module 48 determines the adjustments to be made to the value of controller gain to make sure that the implement 14 of the machine 10 maintains the desired position so as to impart a desired characteristic such as grade, to the surface of the worksite 16. As illustrated, the instability condition is detected and shown in the second curve 54. The fourth curve 58 represents the controller gain signal before the controller gain signal is processed by the rate limiter block. The controller gain adjustment signal 50 is reflected in a fifth curve 60 which illustrates new values of the controller gain after applying the controller gain adjustment signal 50. The new values of the controller gain are used to maintain the desired position of the implement 14 of the machine 10.
The control system 32 controls the position of the implement 14 of the machine 10 by analyzing and processing the desired cylinder velocity signal 36 provided by the controller 34 as opposed to prior art systems working with input signals such as terrain data, machine speed, blade angle etc. The control system 32 offers considerable reduction in response times as the control system 32 eliminates feedback delays for the input signals occurring due to filtering various signals to get relevant data.
Although the control system 32 is explained in context with controlling the position of the implement 14 of the machine 10, the present disclosure is equally applicable to various other domains as well. Examples may include controlling a steering system, joystick commands for various purposes, driveline control etc.
While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.
