US20020154948A1

US20020154948A1 - Automatic mode selection in a controller for grading implements

Info

Publication number: US20020154948A1
Application number: US09/761,941
Authority: US
Inventors: Vernon Brabec; Wai Chan; Raymond O'Connor
Original assignee: Topcon Laser Systems Inc
Current assignee: Topcon Laser Systems Inc
Priority date: 2001-01-17
Filing date: 2001-01-17
Publication date: 2002-10-24

Abstract

A method is disclosed for a controller to automatically switch to an alternative control mode to control the height of a grading implement when the output of a positioning sensor is not available. According to the invention, the controller recognizes sensor unavailability and automatically switches to an alternative operating mode to maintain control. In one alternative operating mode, the controller recognizes sensor unavailability and automatically routes the control signal from the unaffected side to the control channel for the affected side. In another alternative operating mode, the controller monitors the current value of an additional sensor for an alternative mode of control until one of the primary sensors becomes unavailable, and then automatically switches to the alternative mode for the affected side, using the last known value for the alternative mode as the set point.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to machine control systems that control the orientation of a grading implement on a construction machine. Specifically, the invention is a method to automate the selection of various alternative operating modes of the controller to eliminate the need for manual operator intervention when a positioning sensor is inoperative.

2. Description of the Relevant Art

Current control systems used for controlling grading implements for earth moving and the like may have several automatic operating modes using different positioning sensors or control methods. In this case, an operator needs to select a single operating mode. This selection is done manually by the operator who determines when and what mode to select for automatic control. If the operator selects a mode that does not have a functioning sensor currently connected to the system or if a selected sensor is currently not providing data for control, the control system will switch from automatic mode to manual mode. When this happens, the operator must either manually switch the system to another automatic mode (which uses an active sensor) or somehow provide inputs to the controller that mimic the inactive sensor.

For example, if the machine is set up to control height relative to a rotating laser reference plane, each end of the grading implement would have a laser receiver extending vertically on a mast. FIG. 1 shows a laser-controlled concrete screed as an example of such a system. The screed 10 is a grading implement that is moved by a boom 12 that extends outwardly from a base 16. Two masts 14 have laser receivers that sense a rotating laser used as a height reference. The laser receivers are connected to a control system that outputs control signals to hydraulic valves at each end of the screed. The receivers sense the vertical position of the laser beam and the control system uses this sensed position to control the elevation of the grading implement with respect to the laser reference plane.

If during movement of the machine a laser receiver moves to a position where the beam from the laser is blocked, the normal response of the control system is to turn off the control outputs for the affected side. The laser receiver on the opposite side may have an unobstructed path to the laser and, if so, continues to operate in a normal manner. This may happen, for example, when the concrete screed is used inside a building and interior posts block the laser beam at certain positions.

The effect of these periods of sensor blackout or unavailability on the final elevation of the grade depends on the movement of the implement during the blackout periods and the desired tolerance of the finished grade. If the uncontrolled movement of the implement during the blackout periods would result in a surface that exceeds the required finish tolerance, the operator must intervene to mitigate the problem. Aside from the present invention, there are two methods of operator intervention in this circumstance—open loop and closed loop.

In an open-loop intervention, the operator must provide control signals to the controller for the affected side by using the manual controls for that side. The operator may accomplish this by manually controlling the elevation of the affected side by visually matching a previous pass. Or, the operator may attempt to manually input the same control signals as the unaffected side. This intervention is practical only if the control signals are simple on/off signals and are represented on a control display by lights or other easily identifiable indicators.

In a closed-loop intervention, the operator must change the current mode of the control system from laser mode to an alternative control mode that uses a different sensor, such as a sonic elevation sensor or a slope sensor. The operator accomplishes this in a typical control system by putting the system in manual, switching the system to the alternative control mode, entering the current elevation or slope to initialize the new mode, and then re-enabling the system for automatic control. The operator must make these multiple inputs quickly or the implement may move outside of the required tolerance during the transition period.

The final grading finish depends on prompt operator action and therefore may degrade if the operator is distracted or otherwise unable to intervene during a blackout period.

SUMMARY OF THE INVENTION

In summary, the present invention is a method for automatically switching to an alternative control mode when the output of a positioning sensor is not available. The present invention replaces manual intervention by the operator with a new automatic method of intervention by the controller. According to the invention, the control system recognizes the periods of sensor blackout or unavailability and automatically switches to an alternative operating mode to maintain control. The control system can make this decision based upon a predetermined priority for the available sensors and control modes and can switch back to the most preferable mode available when the sensors are available and operating.

The present invention has two basic modes of operating, open loop and closed loop. In the open-loop mode, the controller recognizes the sensor blackout or unavailability on the affected side and automatically routes the control signal from the unaffected side to the control channel for the affected side. The controller continues this mode of operation until the affected sensor is available and valid again and then reinstates the original mode of operation. Since the controller is rerouting the control signals, the signals can be more complex than simple on/off signals that manual intervention could handle. The resulting finish will be closer to the desired tolerance and the corrective movement of the implement will be less when the unavailable sensor signal is reacquired.

In the closed-loop mode, the controller of the invention monitors the current value of an additional sensor for an alternative mode of control until one of the primary sensors loses its signal. The controller then automatically switches the mode for the affected side to the alternative mode, using the last known value for the alternative mode as the set point. The controller remains in this alternative mode until recovery from the blackout (sensor unavailability) and then switches back to the original mode.

The features and advantages described in the specification are not all inclusive, and particularly, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification and claims hereof. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and may not have been selected to delineate or circumscribe the inventive subject matter, resort to the claims being necessary to determine such inventive subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a prior Somero S-160 laser screed, which is one possible platform for the present invention. [0015]
FIG. 2 is a diagram of an open-loop mode of operation of the present invention under normal operating conditions. [0016]
FIG. 3 is a diagram of the open-loop mode of operation of the present invention under a sensor-blackout condition. [0017]
FIG. 4 is a diagram of a closed-loop mode of operation of the present invention under normal operating conditions. [0018]
FIG. 5 is a diagram of the closed-loop mode of operation of the present invention under a sensor-blackout condition.[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings depict various preferred embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following discussion that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein. The description omits basic information about grading implement control systems, which a person of ordinary skill is presumed to know. [0020]
The present invention is a method for automatically switching to an alternative control mode when the output of a positioning sensor is not available and switching back to a preferred control mode when the sensor becomes available again. According to the invention, the control system recognizes periods of sensor unavailability, and then automatically switches to an alternative operating mode to maintain automatic control. The control system can make this decision based upon a predetermined priority for the available sensors and can switch back to the most preferable mode available when the associated sensors are available and operating. The present invention reduces the need for intervention by the operator to produce acceptable grading results. [0021]
The present invention has two basic modes of operation, open loop and closed loop, as explained below. [0022]
Open Loop [0023]
In the open-loop mode, the controller of the invention recognizes the sensor blackout or unavailability on the affected side and automatically routes the control signal from the unaffected sensor to the affected side. The controller continues this mode of operation until the affected sensor is available again. When the controller recognizes that both sensors are active, it reinstates the original mode of operation. Since the controller is outputting the control signals, the signals can be more complex than the simple on/off controls required for manual open-loop intervention according to prior practice. For example, the control signals compatible with the invention may be proportional control signals instead of simple on/off signals. The resulting grading finish will be closer to the desired tolerance and the corrective movement of the grading implement will be less when the unavailable sensor signal is reacquired. [0024]
FIGS. 2 and 3 illustrate the open-loop mode of the invention with two [0025] sensors 20 and 22. The sensors 20 and 22 may be laser receivers as described above, although other sensors, such as sonic distance sensors or contacting sensors or other position-sensing devices, could be used. FIG. 2 shows the system in normal operation when both sensors 20 and 22 generate output signals 24 and 26 that are input to a controller 28. The controller 28 outputs left and right control signals 30 and 32 that cause hydraulic cylinders 34 and 36 (or other motive devices) to raise or lower the grading implement.
In normal operating mode, the [0026] controller 28 controls the height of the left side of the implement according to the output of the left sensor 20. The left sensor 20 supplies its output signal 24 to the controller 28, which generates the control signal 30 and supplies it to the left-side hydraulic cylinder 34 to cause the left side of the grading implement to be raised or lowered to reduce any deviation from a desired set point.
Similarly, the [0027] controller 28 controls the height of the right side of the implement according to the output of the right sensor 22 in normal operating mode. The right side sensor 22 supplies its output signal 26 to the controller 28, which generates the control signal 32 and supplies it to the right-side hydraulic cylinder 36 to cause the right side of the grading implement to be raised or lowered to reduce any deviation from the set point.
[0028] Arrows 38 and 40 indicate that this is a closed-loop controller for each side of the grading implement. The hydraulic cylinders 34 and 36 respond to the controller by moving the implement up or down. The up and down movement of the implement is detected by the sensors 20 and 22 and fed back to the controller 28.
FIG. 3 illustrates the method of the present invention when the [0029] right sensor 22 is blocked or otherwise unavailable and does not output a valid signal. The sensors 20 and 22 and the controller 28 are in constant communication because the controller periodically samples the status and output of the sensors. In the preferred embodiment, each sensor has a vertically-disposed linear array of laser detectors, with the center being the set point. The positioning error is determined by which detector in the linear array detects the laser and how far it is from the center of the array. The laser beam that provides the reference plane is a rotating laser that rotates at least five revolutions per second. This means that the sensor expects to detect the laser every 200 milliseconds. If more than 200 milliseconds elapses, then the sensor assumes that the laser light is blocked and signals the controller 28 accordingly. This is accomplished by a 250 millisecond timer, which is reset by each detected laser strike.
If the timer in the [0030] right sensor 22 times out, then the sensor signals the controller 28 that no laser is detected. In that case, the output signal 24 of the left sensor 20 is used by the controller 28 to control both sides of the implement. The controller 28 uses the valid output signal 24 to generate both control signals 30 and 32. The left side feedback path 38 is still intact, but the right side is operating open loop because the right sensor is temporarily inoperative.
When the [0031] right sensor 22 reacquires the laser and outputs a valid signal 26, the controller 28 switches back to the normal mode shown in FIG. 2. The controller 28 continuously monitors the status of the sensors 20 and 22, so when the right sensor 22 signals the controller that it has detected the laser, the controller switches to the normal mode.
If the [0032] left sensor signal 24 is unavailable or invalid but the right sensor signal 26 is available, then the controller 28 uses the right sensor signal to control the elevation of both left and right sides of the grading implement.
Closed Loop [0033]
In the closed loop mode of the present invention, there is an additional sensor and associated control circuitry providing an alternative control mode that is used as a backup when a primary sensor is blocked or otherwise unavailable. The controller of the invention monitors the current value of the alternative control mode until a primary sensor is blocked or otherwise unavailable and loses its signal. The controller then automatically switches to the alternative control mode for the affected side, using the last known output of the alternative sensor as the set point. This maintains the position of the affected side of the grading implement during the period in which the primary sensor is unavailable. The controller remains in this alternative mode until the primary sensor is available again, and then switches back to the original mode. [0034]
The operation of the closed-loop mode of the invention is illustrated in FIGS. 4 and 5. FIG. 4 shows the control system in normal operation, where both [0035] primary sensors 20, 22 generate output signals 24, 26 and the controller 28 and cylinders 34 and 36 control the height of the right side of the implement according to the right sensor and controls the height of the left side of the implement according to the left sensor. The output 44 of an alternate sensor 42 is also monitored and temporarily stored by the controller 28. The primary sensors 20 and 22 may be, for example, two laser receivers and the alternate sensor 42 may be a slope sensor or an ultrasonic distance sensor.
FIG. 5 illustrates what happens in the present invention when the [0036] right sensor 22 is blocked or otherwise unavailable and does not output a valid signal. In that case, the controller 28 uses the output 44 of the alternate sensor 42 to control the right side of the implement. The last signal output by the alternate sensor 42 prior to the right sensor 22 becoming unavailable is used as a set point for the right channel of the controller 28. The controller 28 generates a control signal 32 to raise or lower the right side of the grading implement to minimize the deviation from that set point. In other words, the alternate sensor 42 is used to keep the right side in the same position or attitude as it was in when the primary sensor 22 became blocked. The movement of the implement affects the alternate sensor 42, thus providing a feedback path 46 and closed-loop control of the implement height.
When the [0037] unavailable sensor signal 26 is reacquired, the control system shifts back to its normal mode, as shown in FIG. 4. The description above assumes that the right sensor is unavailable, but the closed-loop mode of the present invention also operates when the left sensor is unavailable.
One preferred embodiment of the present invention includes laser receivers as the [0038] primary sensors 20 and 22, and a slope sensor as the alternate sensor 42. When one of the laser receivers is blocked, then the controller 28 automatically switches to a mode where the slope sensor is used to generate the control output for the affected side. The controller 28 uses the last signal output by the slope sensor prior to the blockage as the set point. The control system controls the height of the affected side to maintain the same slope of the implement as when the blockage occurred. When the blocked laser receiver becomes available again, operation reverts to both laser receivers and the slope sensor reverts to its backup role.
Both the open- and closed-loop modes of the present invention can be available in the [0039] controller 28 at the same time. The controller 28 selects the appropriate mode based upon a predetermined priority set by the operator.
Furthermore, there may be more than one alternate sensor for the closed-loop mode, and a selection priority among the alternative sensors can be set by the operator. If the quality of the signal is available in a form other than on/off, e.g., a proportional control signal, then the [0040] controller 28 can select between the alternate sensors based on a user entered threshold level.
The sensors and associated control systems are not intended to be limited to just the examples presented above, unless so specified in the claims. The primary sensors could be laser receivers as discussed above, but they also could be other sensors such as sonic distance sensors or GPS (global positioning satellite). Furthermore, the alternate sensors used in the closed-loop mode can be sonic distance sensors, slope sensors, accelerometers or inertial platforms, laser receivers, GPS, or a variety of contact sensors. [0041]
From the above description, it will be apparent that the invention disclosed herein provides a novel and advantageous method for grading-implement controllers that automatically switches to an alternative control mode when the output of a positioning sensor is not available. The foregoing discussion discloses and describes merely exemplary methods and embodiments of the present invention. As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims. [0042]

Claims

What is claimed is:

1. A method for operating a controller for controlling the height of a grading implement, comprising the steps of:

providing a left sensor that outputs a left-side output signal indicative of the height of the left side of the grading implement;

providing a right sensor that outputs a right-side output signal indicative of the height of the right side of the grading implement;

providing a controller that is responsive to the left-side output signal for controlling the height of a left side of the grading implement and is responsive to the right-side output signal for controlling the height of a right side of the grading implement;

operating the controller to control the height of the grading implement by responding to the left-side and right-side output signals when both are available; and

if the left-side or right-side output signal is unavailable, then automatically using an alternative sensor to control the height of the grading implement on the side of the unavailable output signal.

2. A method as recited in claim 1 wherein the step of automatically using an alternative sensor includes using the right-side output signal to control both sides of the grading implement if the left-side output signal is unavailable, and using the left-side output signal to control both sides of the grading implement if the right-side output signal is unavailable.

3. A method as recited in claim 1 wherein the step of automatically using an alternative sensor includes using an output signal of a third sensor to control the side of the grading implement having an unavailable output signal.

4. A method as recited in claim 3 further including a step of monitoring the output signal of the third sensor while the left-side and right-side output signals are available, and using the last monitored value of the output signal of the third sensor as a set point when the left-side or right-side output signal becomes unavailable.

5. A method as recited in claim 3 wherein the third sensor is a slope sensor.

6. A method as recited in claim 3 wherein the third sensor is a distance sensor.

7. A method as recited in claim 1 further comprising a step of ceasing to use the alternative sensor when the unavailable output signal becomes available again.

8. A method as recited in claim 1 wherein the left and right sensors are laser receivers.

9. A method as recited in claim 1 wherein the grading implement is a concrete screed.

10. A method for operating a controller for controlling the height of a grading implement, comprising the steps of:

operating the controller to control the height of the grading implement by responding to the left-side and right-side output signals when both are available;

if the left-side output signal is unavailable, then automatically using the right-side output signal to control both sides of the height of the grading implement; and

if the right-side output signal is unavailable, then automatically using the left-side output signal to control both sides of the height of the grading implement.

11. A method for operating a controller for controlling the height of a grading implement, comprising the steps of:

if the left-side or right-side output signal is unavailable, then automatically using an output signal of a third sensor to control the side of the grading implement having an unavailable output signal.