Automating Sticking

February 27, 2003 - 13:59

Integrating labor and automation.

There are some operations that cannot be totally automated -- at least not yet. The human mind and hand are a remarkable combination, and together, they make some tasks that have stumped mechanical equipment seem relatively simple. The process of sticking cuttings is one area where total automation is difficult.

As I have stated in previous articles, some operations should not be automated even if the technology to automate exists. The payback must be sufficient to justify the investment. There are also some operations that cannot be totally automated -- at least not yet. The human mind and hand are a remarkable combination, and together, they make some tasks that have stumped mechanical equipment seem relatively simple. The process of sticking cuttings is one area where total automation is difficult.

Today, most cuttings are delivered to growers in bunches. A human can separate these bunches without much difficulty, but this operation is virtually impossible for a machine. Additionally, many cuttings are very delicate, and handling them with mechanical fingers is difficult. Again, the human hand can do this handling with relative ease. However, any grower sticking a significant number of cuttings needs an awful lot of those hands.

Automating Economically

Because of the significant labor required and the growing market -- the market for plants derived from cuttings seems to be growing faster than the overall market -- automation would be a great help to growers. When we look beyond the actual sticking itself, many things can be economically automated in a typical sticking line such as the following:

* Position 1 consists of a tray destacker and a tray filler to provide filled trays to the sticking line.

* Position 2 is a watering tunnel to wet the filled trays. Proper moisture content is obviously critical to successful sticking.

* Position 3 is a dibbling unit to finish the preparation of the trays for planting.

* Position 4 is an output conveyor that can be used as a buffer belt to allow optimum efficiency on the line.

These four stations are integrated electronically, and each station is flexible to accommodate different tray sizes, watering requirements and hole sizes.

The four stations should be used even if the rest of the sticking line is not purchased. The cost for the four stations would be approximately $35,000, depending on the degree of flexibility required, and can be operated by one person.

Position 5 represents the heart of the sticking line. In the diagram below, there are 24 workstations where people do the actual sticking. Growers are using lines with as few as 6-8 workstations, depending upon their capacity requirements. Each workstation consists of an adjustable-height, stainless-steel table. This table is sized to allow a space for trays, cuttings and rooting hormone. Down the center of the line are two conveyors, mounted one on top of the other. The top conveyor supplies filled flats to each workstation. Each workstation has a stop position to ensure a filled flat is always ready for pulling at each station. The line is electronically controlled to ensure a constant flow of flats. The operator simply pulls a flat off the upper conveyor and proceeds with sticking. An electronic counter records the flat count at each workstation. When the flat is filled with cuttings, the operator places the flat on the lower conveyor for transport to succeeding stations. At the end of the line, each flat is counted again to continuously measure output. The speed of the line is adjustable, and the line is electronically integrated with the preceding and succeeding stations.

Position 6 is another watering tunnel to ?water-in? the newly stuck cuttings.

Position 7 is an output conveyor.

Line Basics

One of the problems of most sticking operations is that they are set up in the propagation house itself, leading to less-than-ideal working conditions. As with most automation, a sticking line should be located in a headhouse. It should be close to the propagation range, but not in it. This requires planning, as with any other kind of successful automation.

The total cost of positions 5-7 typically ranges from $3,500-4,000 per workstation. Is this investment justified? Sticking rates vary from operation to operation, depending on the skill and experience of the people, as well as the type of plant being planted. A typical rate is 800 cuttings per hour per person, but rates of 600-1,000 per person per hour are not atypical. After installation of a line, you can expect an increase in output of as much as 50 percent. Thus, a manual operation with an output of 800 cuttings per hour per person could expect an output of 1,200 cuttings per hour per person. The 24-station line illustrated on the previous page would do the work of 36 people on a manual line. If the line is run for eight weeks, or 320 hours, the labor cost (at $10 per hour) would be $76,800 to stick nine million cuttings. The same production on a manual line at 800 cuttings per person per hour would require 36 people at a cost of $115,200. The savings of $38,400, compared with a cost for positions 5-7 of $80,000-90,000, would represent a payback in slightly more than two years. The ability to lease this type of equipment means that the savings each year would exceed the annual lease payments, resulting in positive cash flow each year.

Another factor to be considered is the difficulty of finding good people. As good people become more scarce, finding those extra 12 people to run a manual line will be more difficult. Also, as with any automation, the ability to run the equipment for two shifts effectively reduces the per-station cost by half. In the above example, only 12 stations would be required to achieve the same output, and the payback period would be reduced to slightly more than one year.

As I stated at the beginning of the article, the sticking process cannot be totally automated, but what about the future? The future has arrived at one Dutch grower. His crop, chrysanthemums, lends itself to mechanical sticking more than some more-delicate crops. To solve the other automation problem, separating the cuttings, he has set up an operation at his African source, where labor is cheap, to separate and place the cuttings in special strips designed to be fed into an automated sticking machine. The result is a line as fully automated as current plug transplanting lines. The key to this automation was looking at the entire process and not just trying to mechanize the currently used process. Providing the cuttings in strips rather than bunches was the key. Your automation supplier can help you find the key to your future.

About The Author

Mike Porter is president of Nexus Corporation, Northglenn, Colo. For advice about automation implementation, he can be reached at (303) 457-9199 or automation@nexuscorp.com.

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