August 2003

The XY System, Part II By Mike Porter

My previous article (June 2003 GPN) described a new piece ofautomation recently put into operation: the XY system. The specific growing rangeI described as an example was a new 17-acre facility, and the XY system enablesall movement of material in and out of the greenhouse to be operated by oneperson. I suspect many people were skeptical of the applicability of such asystem to the U.S. market. After all, how many growers are in a position tobuild a new 17-acre range?

The reality is that even though few growers ever entertain aproject of that magnitude, the XY concept is applicable to much smallerprojects. A manager planning for the growth of his 5- to 6-acre operation wouldprobably find the system affordable and justifiable. For growers who wish toautomate existing operations, variations and hybrids of the system are veryfeasible. A system similar to that described in my previous article could beinstalled in a new 6-acre range for less than $3.50 per square foot. And thesystem, which works in conjunction with overhead watering, does not requireconcrete floors, which themselves often cost $3.50 per square foot. We are nottalking about a prohibitively expensive system.

Some More Details

Let’s start by reviewing the XY System in more detail andlook at some optional components.

Placing and removing.The core of the system is a pick and place unit that places and removesmaterial from greenhouse bays (the Y direction). The unit is driven by anoperator and can selectively pick anywhere in each bay. This unit in ourexample was sized to pick 48 carriers or approximately 440 sq.ft. of materialat capacity. Its size coincided with the 30-foot width of the greenhouse bays.It rides into the bays on steel rails, which eliminate the need for a concretefloor. For a 6-acre range, a pick and place unit would cost less than $1 persquare foot, which will vary somewhat with size of operation.

Other options are available to perform the pick and placefunction. Small overhead cranes can and are being used in both new and existingfacilities. These cranes can ride on the same rails as booms, provided therails and greenhouse are designed to handle the load. Two people would normallybe required to move the crane from bay to bay. Most recently constructedgreenhouses have sufficient under-gutter height to accommodate cranes. Both thecost and the capacity of these systems are typically less than the unitdescribed above. Cranes normally select one carrier per cycle, though carrierswill normally be larger than those described above (a bench with a crane, aflat with an XY). Consequently, crane systems will have somewhat lessflexibility than XYs, even though it is still easy to select material fromanywhere in the bay.

Moving. The secondelement in the system is the mechanism to move material to and from theheadhouse and shipping area (the X direction). In new XY systems, this isaccomplished by a transport robot that rides on a concrete transport aisle, iselectrically powered and requires no operator. The cost of one of these shuttlecars is approximately the same as the pick and place unit. The shuttle unit isalso used to move the pick and place unit from bay to bay. More than oneshuttle may be needed to maximize the capacity of the pick and place unit.

Many U.S. growers have justifiable concerns about unmannedrobots in the workplace. The new XYs do require a very wide transport aisle,which can be planned in a new operation but is not viable in an existingoperation. However, other options are available. 1) In the simplest scenarios,movement in the X direction can be accomplished by traditional means such as atrain of carts or trailers; 2) the shuttle car could be operated by a person;3) the size of the shuttle car could be reduced to accommodate narrowertransport aisles, though most newer greenhouse ranges have transport aisleswide enough to accommodate a shuttle car; 4) capacity may be reduced and stillbe more than adequate for a smaller range and 5) if benches are used as acarrier, traditional powered or unpowered transport lines could be used toperform the function of the shuttle car. Again, every decision made with regardto the shuttle device must be integrated with all other elements of the system.

Holding. The thirdelement of any XY system is the carrier or the actual device holding the flats,packs or pots. Carriers, such as the ones in the example we’ve been using, canbe specially designed with a number of features. They can be made to the samesize as cart shelves, designed to work in conjunction with flood floors,designed to stack on a traditional cart base and serve double duty as shippingcarts (which costs less than $1.75 per square per foot), etc. The onlyrequirement is that the carrier must be designed to be easily picked up by thehooks on the pick and place unit. As an example, palletized benches can serveas carriers if the extrusions are designed to allow pickup by an overheadcrane.

Transferring. Thefourth element of any system is the means by which the plant material istransferred from the transport into the headhouse or shipping area. In atotally automated system, this is done robotically. However, it can be doneeasily by more traditional means. This article is intended to concentrate onoperations in the greenhouse itself, so I will not go into detail.

Getting Comfortable

Systems such as the new XYs can seem very complicated. Infact, they are complicated because a greenhouse growing operation itself iscomplicated. The new 17-acre XY we’ve been talking about in the past twocolumns took two years from concept to startup.

It is impossible to overestimate the need for planning whenconsidering automation. Much more time should be spent on planning than onimplementation. As I have discussed in many of these articles, every operationin a greenhouse is related to all other operations. Each individual operation,when looked at in isolation, may not seem complicated, but when viewedtogether, the integration of these operations presents a formidable challenge.This challenge, however, is not insurmountable and can be met by a methodicalplanning process. The result of this planning will be a truly integrated systemthat will provide the grower and the consumer the lowest cost and highestquality plant material.