Method for automatic depth control for earth moving and grading

• US 5,235,511 A
• Filed: 03/23/1990
• Issued: 08/10/1993
• Est. Priority Date: 06/09/1988
• Status: Expired due to Term

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Spectra-Physics Incorporated (MKS Instruments Incorporated)
• Inventors: Middleton, Christopher O., Robson, Colin L.
• Primary Examiner(s): Chin, Gary
• Application Number:
  US07/497,982
• Time in Patent Office: 1,236 Days
• Field of Search: 364/424.07, 364/571.03, 364/571.04, 364/571.07, 364/474.35, 364/561, 364/562, 56/10.2, 56/DIG. 15, 172/4, 172/4.5, 73/624, 73/629
• US Class Current: 701/50
• CPC Class Codes: E02F 3/847 using electromagnetic, optical or acoustic beams to determine the blade position, e.g. laser beams
• CPC Class Codes: E02F 5/14 Component parts for trench excavators, e.g. indicating devices travelling gear chassis, supports, skids
• CPC Class Codes: E02F 9/2045 Guiding machines along a predetermined path for graders E02F3/841; machines for construction of roads E01C19/004
• CPC Class Codes: G01S 15/88 Sonar systems specially adapted for specific applications seismic or acoustic prospecting or detecting G01V1/00
• CPC Class Codes: G01S 2007/52012 involving a reference ground return
• CPC Class Codes: G01S 7/52006 with provision for compensating the effects of temperature

Abstract

A method and apparatus for automatically controlling the depth of earth grading for utilization with a grader or paver is disclosed. The method includes determination of time taken for an acoustic pulse to travel from a transducer to a reference surface and back, with this value being used to calibrate a microprocessor-controlled distance-measuring device. As the grader moves over a surface to be graded, the distance to the reference surface is constantly detected by a repeated emission and detection of such acoustic pulses. The timing of the echoed pulses is converted to addresses in a look-up table which contains control words symbolizing commands to be given to hydraulic rams carried by the grader. By implementing these commands, the depth of the blade relative to the reference surface is constantly updated, compensating for variations with the height of the reference surface. A thermistor is provided to automatically compensate for temperature variations as the grading takes place. Displays are provided for the operator of the vehicle to show what type of adjustments are being made to the blade, and whether the height of the reference surface is outside the range of sensitivity of the follower. The follower is automatically calibrated for a given blade depth by repeated incrementation of a delay time variable until a zero adjustment command is generated for the blade control.

Claims

1. A method of controlling a hydraulic system for grading a first surface at a chosen depth relative to a reference surface with an earth grader carrying a vertically adjustable blade at the chosen depth relative to the reference surface by action of the hydraulic system on the blade, including the steps of:

implementing a calibration procedure, including automatically determining a delay tie referenced to a travel time of an acoustic pulse from a transducer to the reference surface and back to the transducer, so that the delay time corresponds to the chosen depth of the blade as determined by an operator of the earth grader;

emitting a ranging pulse from the transducer toward the reference surface a first time, the transducer being mounted in a fixed position relative to the blade, such that the ranging pulse reflects from the reference surface back toward the transducer;

starting a counter at a second time which is the length of the delay time after the first time;

stopping the counter when the reflected ranging pulse reaches the transducer, thereby generating a count corresponding to the length of time taken by the ranging pulse to reflect from the reference surface back to the transducer and further corresponding to an actual blade depth;

vertically adjusting the blade by a distance relating to the count such that the actual blade depth corresponds to the chosen blade depth;

repeating the steps of emitting the ranging pulse, starting and stopping the counter, and vertically adjusting the blade, whereby variations in the height of the reference surface are automatically compensated by the adjustments of the blade as the grader moves along the reference surface;

wherein the step of automatically determining the delay time includes the steps of;

setting the delay time to a predetermined minimum;

emitting a test pulse from the transducer toward the reference surface at a third time for reflection back toward the transducer while the blade is at the chosen depth;

starting the counter at a fourth time which is the delay time after the third time;

stopping the counter upon reflection of the test pulse back to the transducer;

determining a test count corresponding to the time of stopping the counter and further corresponding to the time taken by the test pulse to reflect from the reference surface back to the transducer; and

repeatedly adjusting the counter time upwards and repeating the steps of emitting the test pulse, starting and stopping the counter, and determining the test count, until the test count corresponds to a zero adjustment to the blade, thereby calibrating the delay time for ensuring that the blade will remain at the chosen depth.