Adaptive position determining system for hydraulic cylinder

A position determining system may include a hydraulic cylinder and a flow control device operatively connected to the hydraulic cylinder. A controller may be configured to supply an actuating signal to the flow control device. The controller may be configured to monitor a characteristic associated with the actuating signal, determine a hydraulic fluid flow rate in the hydraulic cylinder based on stored information relating the hydraulic fluid flow rate to the characteristic associated with the actuating signal, calculate a position of a component associated with the hydraulic cylinder based on the hydraulic fluid flow rate, and update the stored information when the determined position deviates from an actual position of the component.

TECHNICAL FIELD

The present disclosure is directed to a system for determining a position of a hydraulic cylinder component and, more particularly, to an adaptive system that uses feedback information to increase system accuracy in determining the position of a hydraulic cylinder component.

BACKGROUND

Various types of work machines may include one or more hydraulic cylinders for aiding in accomplishing a work function. These hydraulic cylinders are configured such that controlled flow of hydraulic fluid into one or more fluid reservoirs in the cylinder has the effect of retracting or extending a piston into or out of the cylinder. The movement of the piston may be used to move various work implements on the work machine. Hydraulic cylinders may be included on nearly any type of work machine such as, for example, track type tractors, wheeled tractors, shovel/excavators, dump trucks, garbage collection trucks, skid steers, etc.

For several reasons, it may be desirable to determine the position of the piston during operation of a hydraulic cylinder. For example, because the piston position may be operatively connected to a work implement, knowledge of the piston position may translate into knowledge of the position, orientation, or state of the work implement. This information may be used for setting motion limits on the work implement or for automating one or more functions of the work implement. Further, knowing the position of the piston in the cylinder may aid in controlling the operating conditions of the cylinder. For example, the operation of the cylinder may be smoothed by slowing the movement of the piston near its fully retracted or fully extended positions.

Several systems have been proposed for determining the position of a piston in a hydraulic cylinder. Many of these systems rely on information provided by one or more sensors associated with a hydraulic cylinder. For example, certain systems may include a position sensor to directly measure the position of the piston. Other systems predict the position of the piston based on information provided by pressure sensors that measure the pressure of the actuating hydraulic fluid in the cylinder. While these systems may be adequate for determining piston position, the addition of sensors can add significant cost and design complexity to the work machine.

Other systems have been contemplated that do not rely on the use of position and/or pressure sensors to determine the position of a piston in a hydraulic cylinder. For example, U.S. Pat. No. 5,004,264 to Kazaki et al. (“the '264 patent”), which issued on Apr. 2, 1991, describes a hydraulic system, used in an automotive suspension system, that includes a position control device to control the position of a piston in a hydraulic cylinder. The position control device functions by monitoring the magnitude of a control signal provided to a solenoid-operated fluid flow control valve. Using a predetermined relationship between the current of the control signal and flow rate in the hydraulic cylinder, the position control device calculates the position of the piston based on the magnitude of the current of the control signal and the period of time during which the current is supplied to the solenoid-operated valve.

While the system of the '264 patent may be able to determine the position of a piston in a hydraulic cylinder without the use of position and/or pressure sensors, the system of the '264 patent includes several shortcomings. For example, while the system of the '264 patent accounts for position prediction errors that can accumulate during operation of the hydraulic cylinder, the system uses this error information only to adjust the final position of the piston. The system of the '264 patent does not make use of this error information to adaptively adjust a position prediction algorithm. Thus, the system of the '264 patent is unable to dynamically model the performance of the positioning system to reduce or eliminate errors from the position calculation.

The present disclosure is directed to overcoming one or more of the problems of the prior art position control system.

SUMMARY OF THE INVENTION

One aspect of the present disclosure includes a position determining system. This system may include a hydraulic cylinder and a flow control device operatively connected to the hydraulic cylinder. A controller may be configured to supply an actuating signal to the flow control device. The controller may be configured to monitor a characteristic associated with the actuating signal, determine a hydraulic fluid flow rate in the hydraulic cylinder based on stored information relating the hydraulic fluid flow rate to the characteristic associated with the actuating signal, calculate a position of a component associated with the hydraulic cylinder based on the hydraulic fluid flow rate, and update the stored information when the determined position deviates from an actual position of the component.

Another aspect of the present disclosure includes a method of determining the position of a component associated with a hydraulic cylinder. The method may include monitoring a characteristic associated with a control signal supplied to a flow control device operatively connected to the hydraulic cylinder and determining a fluid flow rate in the hydraulic cylinder based on stored information relating the fluid flow rate to the characteristic associated with the control signal. A position of the component may be calculated based on the determined fluid flow rate. An error value corresponding to a difference between the calculated position and an actual position of the component may be determined, and this error value may be used to update the stored information.

Another aspect of the disclosure includes a work machine. The work machine may include a power source, a frame, and a work implement operatively connected to the frame. At least one hydraulic cylinder may be operatively connected to the frame and configured to assist in moving the work implement. A flow control device may be operatively connected to the hydraulic cylinder, and a controller may be configured to supply an actuating signal to the flow control device. The controller may be further configured to monitor a characteristic associated with the actuating signal, determine a hydraulic fluid flow rate in the hydraulic cylinder based on stored information relating the hydraulic fluid flow rate to the characteristic associated with the actuating signal, calculate a position of a component associated with the hydraulic cylinder based on the hydraulic fluid flow rate, and update the stored information when the determined position deviates from an actual position of the component.

DETAILED DESCRIPTION

FIG. 1provides a pictorial illustration of a work machine10. While work machine10is shown as a track type tractor, work machine10may include various other types of machines. For example, work machine10may be a wheeled tractor, shovel/excavator, dump truck, garbage collection truck, skid steer, or any other type of machine or device that includes one or more hydraulic cylinders.

Work machine10may include a power source12, a frame14, and a work implement16operatively connected to frame14. Work machine10may also include at least one hydraulic cylinder18operatively connected to frame14and configured to assist in moving or controlling work implement16. A controller20may be included for electronically controlling the operation of hydraulic cylinder18.

Work implement16, while illustrated inFIG. 1as a blade for a track type tractor, may constitute any type of device that can be controlled and/or moved using a hydraulic system. For example, work implement16may include a scraper, shovel, ripper, loading arm, bucket, pile driver, mower, and grappling device, or any other hydraulically controlled device.

FIG. 2provides a block diagram representation of a position determining system30according to an exemplary disclosed embodiment. Position determining system30may include controller20to control the operation of a fluid actuator system32using control signals passed over communication line34.

Controller20may include any devices suitable for running a software application. For example, controller20may include a CPU, RAM, one or more memory storage devices, I/O modules, etc. In one embodiment, controller20may constitute a unit dedicated for control and operation of the hydraulic systems of work machine10. Alternately, however, controller20may be integrated with and/or correspond to an electronic control unit (ECU) of work machine10.

Fluid actuator system32may include any components capable of controlling the flow of hydraulic fluid into and/or out of hydraulic cylinder18. For example, fluid actuator system32may include various valves, pumps, conduits, and pilot pressure devices (not shown). In one embodiment, fluid actuator system32includes a flow control valve36.

In response to a current signal supplied to fluid actuator system32by controller20, flow control valve36may control the flow of hydraulic fluid between a hydraulic cylinder18and a fluid supply38via conduits40. The current signal from controller20may be applied directly to flow control valve36to actuate a solenoid, for example, associated with flow control valve36. Alternatively, the current signal supplied by controller20may be applied to one or more other devices or systems in fluid actuator system32and external to flow control valve36configured to control the operation of flow control valve36.

Ultimately, the rate of fluid flow allowed by flow control valve36may be related to the magnitude of the current signal supplied by controller20. This relationship may be calculated or empirically determined and stored in a memory42, for example, as a current versus fluid flow rate map. During operation of system30, controller20may access this stored information to determine the fluid flow rate into or out of hydraulic cylinder18that results from a control signal having a certain current magnitude.

The hydraulic fluid supplied to hydraulic cylinder18has the effect of moving a piston44. Specifically, depending on the configuration of hydraulic cylinder18, the flow of hydraulic fluid into hydraulic cylinder18may be used to extend piston44out of cylinder18and retract piston44into cylinder18. Through a linkage46, the motion of piston44can be translated to or used to control work implement16, for example.

Position determining system30may be configured to determine the position of any moving component of hydraulic cylinder18. In one embodiment, for example, position determining system30may be configured to determine the position of piston44with respect to hydraulic cylinder18. Using the determined position of piston44, especially in situations where there is a known relationship between the position of piston44and the position of work implement16, controller20may be configured to determine a position of work implement16by translating from the determined position of piston44.

Controller20can determine the position of a component of hydraulic cylinder18(e.g., piston44) using the current to flow rate map stored, for example, in memory42. Because controller20can generate the current signal supplied to fluid actuator system32, controller20may be aware of the magnitude of the current signal and can be configured to monitor the magnitude of the current signal over time. In other systems where a component other than controller20generates the control signal, controller20may be configured to monitor the magnitude of the current signal generated by the other component. Controller20may access the current-flow rate lookup table in memory42to determine the hydraulic fluid flow rate that corresponds to the magnitude of the current signal. Based on known characteristics of hydraulic cylinder18, including, for example, the surface area of piston44exposed to the hydraulic fluid, a velocity of piston44can be determined based on the fluid flow rate. To calculate a displacement of piston44, this velocity can be integrated over a period of time during which the current signal is applied to fluid actuator system32.

Position determining system30may also determine the presence of any errors in the calculated position of piston44. For example, a switch48may be used to determine when hydraulic cylinder18has reached a fully retracted position (i.e., when piston44reaches its minimum displacement). Another optional switch (not shown) may be used to determine when hydraulic cylinder18has reached a fully extended position (i.e., when piston44reaches its maximum displacement). Switch48may communicate with controller20over communication line50, for example. It should be noted that various other methods for determining when hydraulic cylinder18has reached a fully extended or fully retracted position may be used in alternative embodiments.

By determining when hydraulic cylinder18has reached a fully extended or a fully retracted position, there may be at least one point during the operation of hydraulic cylinder18where the actual position of piston44is known. Controller20may be configured to compare this actual, known position of piston44to the position calculated by integrating the velocity of piston44. Controller20may be further configured to determine an error value corresponding to a difference between the actual, known position of piston44and the calculated position of piston44.

Several factors may contribute to a non-zero error value. For example, changes in temperature may affect the viscosity of the hydraulic fluid. Such a change in viscosity may lead to lower than expected fluid flow rates for a particular current magnitude. Wear in the components of hydraulic cylinder18may also cause deviations from the stored current versus fluid flow rate map. Further, the initially stored map may, itself, contain inaccuracies that translate into errors in the calculated position of piston44. If left unaccounted for, these errors could accumulate during each motion cycle of hydraulic cylinder18and render the calculated position of piston44unsuitable for certain applications.

Rather than simply adjusting the actual position of piston44or restarting the procedure of calculating the position of piston44, neither of which would eliminate further errors in the calculated position of piston44, the disclosed system includes an adaptive characteristic that can enable it to account for error causing factors and reduce or eliminate future errors from the calculation of the position of piston44. For example, in response to a non-zero error value obtained by comparing the calculated position of piston44to the actual position (e.g., a fully extended or fully retracted stage of motion of hydraulic cylinder18), controller20may generate an updated control current versus fluid flow rate map, including one or more modified values, that may aid in reducing or eliminating the error value. This updated map may be stored in memory42such that subsequent calculations to determine the position of piston44, based on the updated map, may include less or even no error.

Controller20may be configured to calculate a position of piston44, determine the presence of an error, and generate an updated map after any number of motion cycles of hydraulic cylinder18. For example, an error value may be determined and an appropriate map may be generated after two, three, or more motion cycles. Alternately, controller20may be configured to determine an error value and generate an updated map for each motion cycle of hydraulic cylinder18. In the case where two or more devices, such as switch48, are present, an error value may be determined and an updated map may be generated multiple times for each motion cycle of hydraulic cylinder18.

Controller20may also be configured to account for time delays that may occur during operation of hydraulic cylinder18. For example, each time a new control signal is supplied to fluid actuator system32, there may be a delay between the moment the control signal is issued and the time that piston44begins to move or changes its current motion state. If not accounted for, these time delays may accumulate and contribute to non-zero error values between the calculated position and actual position of piston44. While it may be possible to at least partially account for the time delays in the updated maps generated by controller20, these time delays may also be accounted for in the actual piston position calculation. For example, by monitoring the number of time delay-causing events, controller20may adjust the calculated piston position by an appropriate amount to compensate for the total number of time delayed events.

FIG. 3provides a flow chart illustrating the steps of an exemplary disclosed position determining method. At step100, controller20monitors a characteristic (e.g., current magnitude) associated with the control signal supplied to fluid actuator system32. At step110, controller20may determine a fluid flow rate in the hydraulic cylinder based on information, such as a current magnitude versus fluid flow rate map, stored in memory42. At step120, controller20may calculate a position of a component of hydraulic cylinder18(e.g., piston44) based on the determined fluid flow rate. At step130, controller20may determine an error value corresponding to a difference between the calculated position of the component and an actual position of the component. At step140, controller20may update the fluid flow rate versus current magnitude map stored in memory42based on the error value.

INDUSTRIAL APPLICABILITY

The disclosed adaptive position determining system may be adapted for use with any hydraulic system. By not requiring dedicated position and/or pressure sensors to operate, the disclosed position determining system may offer a lower cost and more simply configured system compared to the position determining systems of the prior art. Further, the error correction capability of the present system can minimize or eliminate the effects of accumulating errors during the operation of a hydraulic cylinder. By observing these errors in a feedback type operation, the present system also has the ability to adapt to new operating environments or conditions by updating its own information maps to minimize or eliminate the reoccurrence of those errors.

The disclosed system may be included on various work machines for determining the position of work implements operatively connected to one or more hydraulic cylinders. For example, in one embodiment, the position determining system may be included on a track type tractor for determining the position of a hydraulically operated blade. The system may also be used for determining the position of various hydraulically operated components of a garbage collection vehicle. In one embodiment, the position determining system may be used to determine the position of a loading arm of a side-load garbage collection truck.

The disclosed position determining system may provide several functional benefits. In one embodiment, the system may be used to monitor the stage of extension of a hydraulic cylinder and to adjust the speed of extension or retraction during certain stages of operation. For example, the operation of a hydraulic cylinder may be slowed near the fully retracted and fully extended positions of the hydraulic cylinder to minimize wear and/or damage to the cylinder that may be caused when a piston of the cylinder slams against mechanical stops at the fully extended or retracted positions.

The disclosed system may also be used in a motion limiting operation for a work implement. Particularly, by determining the position of a component of a hydraulic cylinder and translating that position to a position of a work implement, a controller can determine whether a possible violation of a motion limit exists. In such a condition, the controller can electronically control the movement of the hydraulic cylinder, and therefore, the work implement, to operate only within predetermined motion limits.

In another embodiment, the position determining system may be used to enable an automatic positioning feature of a work implement. For instance, a controller may be configured to move the work implement to one or more predetermined locations and to use the disclosed position determining system to determine when the work implement reaches the desired predetermined location. In the case of a garbage collection vehicle, a controller may be configured to automatically return a trash bin to its original position and orientation after collecting the contents of the bin.

It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed position determining system without departing from the scope of the disclosure. Additionally, other embodiments of the disclosed system will be apparent to those skilled in the art from consideration of the specification. 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.