Automatic Ploughing

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Overview

0 Objective

0 Introduction

0 Materials and methods0 Experimental results and discussion

0 Conclusion

0 References


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OBJECTIVE

0 To built an apparatus which controls the steering of a

tractor while ploughing and turning at a headland.


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INTRODUCTION

Opto-electronic remote sensing techniques were used

for position finding and a microprocessor based unit

controls the movements of the tractor just before and

during the headland turn.


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Control requirements

0 Two controls are required during automatic

ploughing:

1. Travelling in a straight line, parallel to the first

manually-controlled pass. For this purpose an Opto-

electronic displacement transducer is used.

2. The other control requirement is at the headland. Amicroprocessor based sensor is used to lift the

plough and take U-turn by the tractor.


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The furrow follower


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EXPERIMENTAL TRACTOR


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Schematic diagram of steering servo


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Control of the tractor near to and

during the turn at the headlandControlled by microprocessor based controller which

receives input data from an opto- electronic range and

bearing meter and from a heading indicator.


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The turning technique

0 The technique which has been developed for turning

at the headland is intended for ploughing with a

reversible plough.

0 The tractor is required to reverse its direction and

also to move sideways by a cultivation width, using

the least depth of headland compatible with the man

oeuvre.

0 A modified U-turn has been adopted for the purpose

in preference to a 3-point turn since it involves fewer

gear changes and steering operations.


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The headland

turn


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Cos =W

Where,

W=lateral movement


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Schematic diagram of the controller near to and during the turn


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The components of the

headland turn control system0 The range meter:

The principle of operation of the range meter is the

measurement of the time delay in terms of phasedifference between a projected continuously-modulated

light signal and the reflection received from a reflecting

post.


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Range meter


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The reflecting posts


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Resolution of the range

measurementsThe reflected range represented by a phase delay of onecycle at the lamp modulation frequency of 5 MHz is 30 m andsince the phase relationship of the 5 MHz signals ismaintained after frequency conversion, one whole cycle at

50 kHz also corresponds to 30 m. The range incrementARcorresponding to one 15 MHz clock pulse thus becomes

R=30 mx t/T=0.1m,

Where,

t and T are respectively, the periods of the 15 MHz and the

50 kHz waveforms. At the maximum range of 30 m the totalcount in Cl will be 3000 and to accommodate this number a12-bit binary counter is used. The data in Cl are conveyed tothe controller in 12-bit parallel form.


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calibration of range meter

The calibration shows a good linearity between the measureddistances and the range meter estimates. Over the working range(4-22 m) the error is less than 0.1 m. With a post of 80 mmdiameter and a scanning rate of 1 rev/s the limit of range

estimating ability is about 28 m. At this distance only one sample(i.e. average of 10 phase measurements) is obtained and, also thereturned signal has fallen to a level where the limitations toaccurate phase measurements are starting to be significant. Thelinearity of the calibration is not maintained and at 28 m theestimated range is approximately 0.5 m low. The addition of a self-calibrating facility has ensured that temperature-dependentdisplacement errors are compensated for automatically. Thecalibration constant is not affected by environmental changes.


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Bearing and heading

measurements0 The bearing transducer

The bearing of the boundary post relative to the tractor ismeasured simultaneously with the range measurement by aprecision potentiometer linked to the rotating mirror of the range

meter. A single-turn potentiometer with an electrical angle of 357is used and the zero point is set to be parallel to a line through therear axle of the tractor. This line then becomes the reference for allthe subsequent trigonometric calculations. This datum was chosensince at no time do we use measurements made when the tractor isat or near a right angle to the furrow; a gap of approximately 3inthe angular measurement therefore does not matter. The analoguedata from the bearing transducer is converted into a 12-bit binarynumber before going to the microprocessor where it is processedsimilarly to the range data before it is used in the calculations.


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Calibration of bearing transducer

Calibration of the bearing transducer was effected by

setting a reflecting post at a number of positions

determined geometrically to give a range of bearings from

45 to 135 and from 225 to 325. Normally all the

bearings required for computation will be within these 2

spans. The equipment was operated in its normal scanning

mode and the bearing estimates were shown to be within

0.5 of the calculated bearings over the working ranges.


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The heading transducer


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Implementation of the control

functions


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Microprocessor based controller

0 Hardware description


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Software description

0 Main program


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Final adjustment to the position

of the tractor


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Experimental results and

discussion


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conclusion


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Refrences

Documents

Automatic Ploughing