Prototyping an asparagus harvester.

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The Asparagus Harvester - an agricultural invention prototype

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Developing the prototype - a 10 year project.

Ok, it wasn't quite as easy as I thought it would be.  

In developing the prototype asparagus harvester we had a number of hurdles to overcome.  There were both technical challenges and human ones.

For example, it's not easy to simulate an asparagus field, so it was very important to test the harvester on real asparagus beds in the spring.  However, most of the time it was very difficult.

We always had an agreement with a local farmer to experiment with our machine on an acre or so well ahead of time each spring.  It rarely worked out.  Typically after a week or so the farmer would tell us his picking crew was upset so we would have to leave, or  some other excuse. Often we ended up with just one or two rows. It was very discouraging.  

Over the years we tried a great variety of ways to simulate asparagus beds. We tried everything from blocks of clay with plastic tubing stuck in them laid out in the parking lot, to conveyors running under a stationary harvester.  

In the end, there is no ideal substitute for a real asparagus bed.  One of the reasons it took so long to develop the harvester was that by the time we figured out what the problems with our prototypes were, the season was over and we had to wait another year to test our improvements.

My optical spear sensing system proved to be too crude to be effective.  The original pick up system was scrapped, it was better at throwing harvested spears at the tractor driver than putting them on a conveyor belt.

When I tried to find very high speed air cylinders for the cutters there weren't any fast enough.  When I tried to get the air cylinder manufacturers to modify their cylinders to increase the speed they told me it couldn't be done.  They usually said air cylinders can't go that fast.  So we built our own, and they worked.

The air cylinders on my current prototype have a diameter of 1-1/2 inches with a 16 inch stroke.  They will do a complete full stroke cycle in less than 200 milliseconds.  That's over 5 strokes per second. 

However, the harvester needs to travel at over 2 mph if it is to cover enough ground to be economically viable.  2 mph is a shade over 35 inches per second. 3 mph is almost 53 inches per second.  So while the air cylinder is on it's way down to cut the spear, the machine moves forward about 3-1/2 inches at 2mph and over 5 inches at 3mph.  

Since it is impractical to try to keep the machine moving at the exact same speed all of the time with many different field conditions, I had to provide a timing circuit that would measure the ground speed of the machine, and set the time delay between sensing the spear and activating the air cylinders to cut the spear.

For the first few prototypes I used Intel single board computers.  I wrote the programs in machine language, storing them on paper tape. I had a teletype machine with a paper tape punch and reader.  Once I had the program worked out I would rent a prom programmer and program a prom chip for the single board computer.  Eventually I ended up designing custom digital control circuit boards to do the job.  I became proficient at  wire-wrapping circuit boards.

We started out with small one-row harvesters pulled by an old Farm all Type M tractor.  Often my wife would drive the tractor while I walked alongside the harvester trying to figure out why it was or was not doing whatever it was supposed to. 

A couple of years I worked without pay just to keep the project alive.

I remember taking the machine down to El Centro in Southern California to demonstrate it to an interested asparagus grower.  It was one of the early designs, a single row tractor pull model.  When we fired up the tractor, the ignition noise from the tractor fried my computer.

Another time I had hauled the harvester up to Pasco Washington for a demonstration, and due to a malfunction in the controller, all eight air cylinders stuck at the end of their strokes and after being dragged through the dirt for a few feet, bent into U shapes.

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