Category: Precise Farming

Headland Alert: OK so we can do parallel lines; and this would go a long way in reducing the overlap; but what is next?  What about the turns, or at least a warning of the turns?  We learned early on, when we introduced auto-steering, that the driver’s attention waned, with little to do as the tractor drove itself across the field.  One was now free to make a call on a cell phone, or have lunch, or maybe even have a nap.  We heard of all kinds of horror stories of farmer’s falling asleep and the tractor faithfully following its line right into the neighbors field, or onto a highway, or into a slough.  Consequently, we introduced a headland alert, which was nothing more than a beeper that went off just before the headland.  However, it was still incumbent upon the operator to recognize the warning and to make the turn in the headland.   The next evolutionary improvement would be to make the turn in the headland.  A perfect U turn.

                           

Auto Steer: There is more to driving a nice straight line down the field than one first thinks.  Yes, one needs to judge the distance to the last pass, but just as important is the angle of approach and the rate of convergence/divergence to the last pass. When we drive manually, we combine all these visual cues and make a quick calculation as to how much we should move the steering wheel.  We do it without even thinking – it becomes so automatic.  It’s not perfect, but one can get pretty good at judging the distance and the angle to the last pass. Can we mechanize the control of driving a farm tractor?  The distance to the last pass can be done with a positioning system like GPS, but how do we measure the angle?  And we don’t have all day to do this, it must be done quickly, it must be done now – without delay.  A delay in a control system becomes the juggernaut   Eventually, we used GPS for the position, even though it’s accuracy and delay were questionable. Later we will see how the plant row can be used to improve the accuracy.  An electronic gyro would be used to acquire the angle, but it was not without challenge.  Electronic gyros put out a voltage that is proportional to the turning rate.  One must integrate this to get an angle.   And there is drift in the output with age and temperature. Corrections and compensations must be done in real time. Also, the vibration of the tractor, if close to the sample rate of the gyro, could result in egregious angle errors.

In Engineering we are taught that a control system with the least error in tracking is one with critical damping.  So, if we are driving and we are off the desired line, we want to get back to where we belong as quickly as possible and this will result in some over-shoot. There will be a little loop in the corrective action taken.  When doing the auto-steering trials; I soon learned that farmers wanted to forego this optimum response.  They did not want to see any little loops or squiggles – they wanted a perfectly straight line no matter how long it took or the resulting accumulated overlap error.  They wanted a controlled correction that was over-damped.

   There were three things used in determining the steering correction: the offset, the angle and the tractor’s rate of turn.  Let’s look at each of these more carefully.

The Offset:  This is the perpendicular distance of the center of the tractor, to the desired track line.  It is shown in Fig 1 as the offset.  The desired track line is set by the driver doing a strike line across the field.  From this strike line a set of parallel lines is calculated one implement width apart.  The desired track line is the parallel line closest to the tractor’s position. When the positioning systems coordinate (GPS) is received on the tractor a calculation is made using a point to line formula, yielding the offset. GPS is accurate to ten feet, but it can be improved by using differential GPS, DGPS to get to within about a foot.  This can be made even better with Real Time Correction, RTK GPS, to get to inches, especially if we are using relative measurements within minutes of each other.  However, all positioning systems do not report the current position of the tractor, they report where the tractor was a moment ago, a fraction of a second ago. This just adds to the difficulty of steering.

The Angle: The tractor is shown on its course line to the * on the desired track line as shown in Fig 1.  The angle j is the angle between the actual course line and the desired course line.  Some call it the angle of attack.   When we have a large offset, we need a large angle of attach, but as we get closer to the desired line, we want to make the angle smaller and smaller so that we don’t overshoot the line.  One could think that driving is actually just aiming a few hundred yards down onto the desired line.        

Rate of Turn: The tractor could be turning, so the turning will determine what the angle will be in the future.  So it is another factor in determining the steering correction.  An electronic gyro is used to determine the rate of turn, such as degrees per second. The gyro we used put out a voltage from zero to five volts, with the mid voltage of about 2.5 volts being no turn.  A voltage higher than this was a left turn, and one lower than this was a right turn. We called this no turn voltage zero_w.  It was not exactly 2.5 volts.  It was initially calculated by averaging 32 readings when the tractor was standing still.  When the tractor was moving, a reading from the gyro minus zero_w gave the turn-rate.  Digital integration of the turn-rate gave the angle j. Angle j is acquired and adjusted by taking the inverse tangent of the difference of past offsets over the distance traveled. The correction to the steering = offset  –  angle  – turn-rate..  This correction was a pulse applied to a hydraulic valve that put a squirt of oil into the steering ram.

                             

1. Overlap: How bad is it?   I have heard of stories of how some farmers could drive, straight as an arrow and with no overlap, hour after hour, day after day; but, I knew that I overlapped when I drove, and I had seen many fields in which overlap was evident.  But, just how much was this overlap? Could it be measured?   Was I trying to solve the problem of eliminating the overlap, if it really wasn’t a significant problem?  After some investigation, it became apparent to me that no one had actually measured the overlap of manual driving.  We needed a way to measure this and we had to do this without the operator being aware of the measurement being taken.   I was well aware of an operator being able to drive more accurately when he or she was aware that someone was watching. I knew first-hand that I always was much sharper, and drove more accurately when someone was watching or where it would be noticed from the road. The overlap measurement must be done without the driver being aware of our intent.

  We devised three non-intrusive ways to measure overlap:. 

  a) Stop and spot and measure the actual overlap with a measuring tape.

  b) Measure the width of the field, and the width of the implement. By counting the number of passes made to complete the field, one could calculate the overlap.  The number of passes multiplied by the width of the implement would equal the field width.  Any excess passes to this would be overlap.

 c)  I rented a plane and had my passenger take a number of pictures of a farmer driving as I buzzed the operation from behind, without the farmer being aware of our presence.  After analyzing the photos for relative widths; it was determined that the overlap increased and was proportional to the implement’s width.

   The overall average overlap was 10% of the implement’s width.  A ten-foot implement would typically result in one foot of overlap, whereas a 50 foot implement would result in five feet of overlap.  Now we knew, and yes it would be a worthwhile project to reduce or even eliminate the overlap.

  There have been many improvements to crop production over the years. Most of these improvements have originated from the farmers themselves. I grew up on a farm observing many of the changes.  When I was ten years old, just a kid, I was driving tractor, a John Deere 830  pulling a 14 foot cultivator.  My Dad would do the perimeter of field for headlands and around the sloughs; and after doing the strike line, I was put on the open-air tractor to slowly go back and forth until the field was done. I couldn’t get into too much trouble – nothing to hit. Just wide open, back and forth.   Oh, it was so boring.  And I had plenty of time to think about how this could be done better.  I wasn’t the best driver, getting the line crooked, and the overlap was terrible; but I learned quickly that overlapping was much preferred over the deadly sin of missing.  I just kept thinking: There must be a better way; I didn’t know what that better way was, but surely there must be.

    I didn’t do much until I graduated as an Engineer and worked in Ottawa on new computerized telephone switches.  I learned about computers from the ground up and soon learned what computes could and couldn’t do.  I was intrigued by how a computer could control equipment.  I also became a pilot and learned about auto-pilots.  If a plane could be set up to drive automatically from point A to point B; then why couldn’t a tractor be programmed to drive from point A, at one end of the field, to point B, at the other end of the field.  I got my chance to tackle this question.

   In 1982, I was hired into the Engineering Faculty at the University of Regina.  This was my opportunity to work on the problem of driving farm tractors better – without overlap or missing. A tractor with auto-pilot or auto-steering. To do this, we needed to know where the tractor was at all times; we needed a positioning system.  There was no GPS, so a positioning system needed to be developed.  With the help of a few students, we developed our own positioning system. In 1985 a John Deere 4020 was outfitted with some crude steering wheel controls to drive and work a small field, including turns. We used an Osbourn portable computer to do the calculations of triangulating to our VHF beacons to determine the position of the tractor. CBC recorded the demonstration and it was broadcast in Canada on Country Canada in 1985. This was the debut for auto-steering; we showed that it could be done; but, did farmer’s really want or need it?

    Now that I am retired, I decided to put my thoughts and experience down on paper. Taking what I learned as a boy on the farm, hoeing in the garden and driving tractor as a kid; and my experience with being a pilot and as a professor in electronic engineering, I am in a unique position to bring all this together in what I think are some pretty exciting changes that can be achieved in farming, using existing technology. These are my ideas that I have developed throughout the years and as such I am writing this in the first person.  This is the first chapter of my story; there are many to follow.