Automatic mode selection in a controller for grading implements

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.

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: 
 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;    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: 
 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 output signal of a third sensor to control the side of the grading implement having an unavailable output signal.