Thursday, December 17, 2009

Inventing an Asparagus Harvester – 30 Years of Prototypes

I first decided to invent a selective asparagus harvester in about 1972. I asked my dad one day if he knew of something that needed inventing… I was bored. He was a farmer and an asparagus grower. He told me they needed a mechanical asparagus harvester that would just harvest the ripe spears; a selective asparagus harvester.

Not knowing any better I decided I would build one. At the time I was about 21 years old, fresh out of the army, and pretty good with electronics. I had a ham radio license when I was about 13 years old, built my own transmitters and receivers, and could fix anything from a car radio to a color TV.

I had read about a new kind of imaging device, I think it was one of the first CCD chips. I don’t remember all of the details, but the camera had basically 16 rows and 16 columns of light sensitive elements, and I decided to use that to detect the height and location of the spears on the bed, and I would use blades attached to air cylinders aimed toward the ground at about a 45 degree angle. I used eight cylinders arranged in a row across the bed, and when the camera spotted a spear tall enough to cut, it would activate the valve and fire the air cylinder that was lined up with the same column as the spear.

A friend of mine and I built a little demonstration prototype that had a little gas powered air compressor built out of channel and angle iron and 4 motorcycle tires that we pushed by hand. It had the camera, air compressor, 4 cutting cylinders and a crude pickup device that would grip the spears as they were cut.

That first prototype was enough to interest a local machine shop that decided to take risk of developing a selective asparagus harvester. They hired me for $2000 a month to oversee the development and took a 50 percent share of the rights to the machine. We spent the next ten years working on it, coming up with a new prototype each year.

The camera turned out to be unsuitable for the task, and during those years I tried just about everything you could think of to detect those stubborn spears of asparagus. I tried little wire bales that hung down from above, beam-breaking photo electric sensors, retro-reflective optical sensors, magnetic switches with plastic paddles, and even a Reticon line scan CCD camera, but all had serious drawbacks.

I really wanted to try a laser for illuminating the spears due to the precise position information I could get by using a laser shooting across the bed. It would be able to give me much more accurate information about where the spear was located on the bed and it’s height. But at the time lasers were several thousand dollars, and not nearly rugged enough to mount on an asparagus harvester.

Asparagus spears can be very delicate, and on cold mornings it is very easy to break a spear by just nudging it a bit. So you really don’t want to use something that has to contact the spear to detect it. Using through-beam sensors required mounting the emitter and receiver at the height of the spear you wanted to harvest. If you wanted to cut nine inch spears you mounted the beams nine inches above the bed. Harvestable spears would range from nine inches to about 16 inches on hot days. The longer spears fortunately are harder to break.

We used extremely thin sensors to avoid touching the spears, but you could still see the occasional spear break as it made contact with the sensor itself.
Another problem with sensing the spears was the fact that asparagus spears can lean in any direction, and significantly throw off the targeting of the spear. At the point where the spear reaches the nine inches off of the bed, it can be several inches to one side or to the front or back of where the spear actually emerges from the ground. That makes it a whole lot harder to cut the spear. Especially if the blades are narrow.

In 1984 we gave up the project due to lack of interest on the part of the asparagus growers. The machine was a self-propelled 3 row selective asparagus harvester. It wasn’t perfect yet but it did harvest asparagus.

At that time we used beam-breaking for sensing the spears; I think they were 4-1/2 inch wide channels the spears had to pass through.

The sensing of the spears and locating them were not the only problems we had in developing a selective asparagus harvester.

My next blog entry will discuss the difficulties we had with the air cylinders. And some of the inventive ways we found to address the problems… and why most of them did not work.

The Old Inventor Guy