Automated Container-Handling System for Container Production Nurseries

Hagen Schempf Todd Graham Robert Fuchs Chris Gasiorhagen+@cmu.edu tgraham@rec.ri.cmu.edu rfuchs@rec.ri.cmu.edu cgasior@rec.ri.cmu.edu

Carnegie Mellon UniversityRobotics Institute5000 Forbes Ave.

Pittsburgh, PA 15213

I. ABSTRACTProduction of nursery crops in the US is accomplished incontainer- and field-growing conditions, with propagationand seedling-rearing carried out in greenhouses.Container-grown crops represent 60% of the US marketand represent a highly labor-intensive and thus costlysegment of ornamental crop production. The USDA,NASA and the ANLA have collaborated to develop anautomated in-field container-handling system for reducingdependence on foreign labor while also increasingproductivity. A first-generation system was developed atCMU, capable of automatically lifting and conveyingplants from the ground (in a variety of regular patterns)onto trailers, and vice-versa. The system is capable ofhandling a vast array of container-designs from differentmanufacturers, and spans the size-range from #1 to #5(approximate equivalence to gallons). The system isdesigned to handle 45,000 containers per 8-hour day withone to two operators. Testing currently underway indicatesthat the system approach is valid, with the next incarnationrequiring reduction in size and weight, as well as reductionin manufacturing costs; a new design is currentlyunderway, with as-built designs and experimental resultsfor the first prototype’s performance presented herein.

II. INDUSTRY OVERVIEWUS ornamental horticulture is a rapidly growing, $11billion dollar a year industry (about 10% of the grossagricultural output of the US alone), tied to a dwindlingmigrant work force, working in outdoor conditions in verylarge acreage areas (see Figure 1).

Figure 1 : Typical container nursery view & labor task

Unskilled labor is becoming more costly and harder tofind, while it is still needed to move potted plants - thisrepresents a manual handling task of at least 450 millionunits per year, each handled 3 to 4 times a year. Thenursery industry must address this problem if it is tosurvive and continue to flourish in the next millennium.

Nursery production automation is a growing fieldworldwide. At the highest level there are three main areas,namely greenhouse operations, container yards and fieldnurseries. Within these groupings, there are several areasthat lend themselves to automation (see Table 1):

Table 1 : Automation Areas for Nursery Industry

In these areas it was judged [2] that automation hasachieved different levels of automation-penetrationworldwide - the levels are expressed in the histogramshown in Figure 2:

Figure 2 : Automation Levels in Nursery Industry

AREA AUTOMATION-FRIENDLY

Greenhouse Seed/Propagate, Pick/Ship, Gather, Transplant/Set

Container Yard Field Movement. Upshifting, Order-Picking, Shipping

Field Nursery Dig, Plant, Stake, Harvest, Container Handling

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

Series1 90% 30% 45% 75%

GREENHOUSE PROPAGATION CONTAINERS FIELD

GR

EE

NH

OU

SE

PR

OPA

GA

TIO

N

CO

NT

AIN

ER

FIE

LD

NU

RSE

RY

Current automation in the nursery production fieldworldwide are very wide-scattered, depending on thespecialty-area. Holland [1], Germany, Italy and Englandare world leaders in the automation of greenhouseproduction, whether that be for woody ornamentals,flowers or even vegetables. Equipment from suppliers inthese countries, and the associated infrastructure, are inuse worldwide. Equipment ranges in variety from plug-planting machines, potting machines and flower imagingand quality segregation to automated soil-mixers, -fertilizers and washing machines (excerpt in Figure 3).

Figure 3 : Greenhouse automation equipment

Field-nursery production automation is primarily limitedto the development of assistive tools, which assist in theexcavation of field-grown trees and inventorying systemsfor such trees (see Figure 4).

Figure 4 : Field Nursery automation equipment

Container-handling devices for field-use, which is where

most of the labor-costs are expended, have not seen anyintensive development in the US nor abroad - for goodreasons; systems that are available are shown in Figure 5.

Figure 5 : Container Nursery automation equipment

The variety in container-types and surface-conditions andnursery layouts is vast - they way greenhouse automationwas made successful is through standardization of theinfrastructure (containers, conveyors, irrigation, etc.),which is still sorely lacking in the US. Talks aboutstandardized containers has been ongoing for many years,but due to the nature of the business, has not taken afoothold in the US. Differentiation amongst growers,climatic conditions and simple opinion-variabilityamongst growers results in methods and principles thatmake it hard to apply automation broadly in this vastmarket, without requiring dozens of various dedicatedmachines for different growers/growing-regions (therebyreducing the attractiveness to equipment developers).

III. PERFORMANCE REQUIRE-MENTS

The motivation to automate being obvious, it becomesimportant to realize that the US market has a high affinityto price and performance. The performance requirementsthat were derived for the proposed container-handling

Table 2: Performance Metrics

DESCRIPTOR TARGET VALUE

Containers moved in the field per hour Meet/Exceed 4-person daily rate 25,000/daya

a. Refers to #1 containers in an 8-hour workday with a single operator, or about 2,500 containers/hour!

System Design Stand-alone System N/A

Trailer Compatibility Compatible with typical trailer 4’ x 10’

Operator Reduction Single-operator for system 1 Operator

Quality and Control Assurance No extra plant/container damage N/A

Multi-container usability Adaptableb to #1, 2, 3 & #5s

b. manually adjustable over a range or usage of a different tool-head

Yes

Container Configurations Can-to-Can, Can-tight, Spacedc

c. in a follow on system adapted based on the baseline system

Yesc

Multi-surface operability Gravel, Geotextile - NO Poly! Yes

Cold-Frame Compatibility Access into/sideways frames Yesd

d. possibly with minor modifications in the door and/or hoop-structure and irrigation-location

Cost-Effectiveness Typical stand-alone system $50K to $75K

system, focussed around several key areas, namely (i)throughput (containers/day), (ii) applicability to existinginfrastructure (containers, groundcover), (iii)compatibility with existing equipment (trailers, cold-frames), (iv) manpower reduction, (v) job-quality(compared to manual), and (vi) cost-effectiveness (ROI-based). The system has to be able to pick-up and drop-offin can-to-can and can-tight, as well as diamond-spacedconfigurations, and do so at a rate to pay back for thesystem in terms of labor-savings within as few seasons aspossible. Performance variables and the expected value foreach are shown in Table 2.

IV. SYSTEM DESCRIPTIONThe design developed for the automated field-containerhandling system represents a self-mobile outdoor platformpowered by an IC engine, perceiving containers through aset of ranging IR-sensors, controlled through on-boardPLC-based ladder-logic computers, and actuated through aset of electro-hydraulic actuation systems. A CAD-rendering of the developed system is shown below inFigure 6:

Figure 6 : CAD image of the container handling system

The above design relies on a self-powered skid-steeredplatform with rear floating rocker-arm caster-axle. Thecontainers are now grabbed using a squeeze-pinch andmoved in a circular arc fashion to a conveyor that speedsthem off to the side (onto a waiting trailer); the operationis run in reverse for setting down and spacing outcontainers. Two grabbers ensure that a full 6-foot widerow of containers is moved every 8 seconds. Sensor-guided driving aligns the frame to pick up or drop off inany desirable configuration.

The overall system can thus be seen to consist of severalmajor elements, including (i) frame, (ii) drive & steer, (iii)container grabber & handler, (iv), and power & controlsystems. The roles and interconnections of each of theabove modules can be generically described as detailedbelow:

FRAME: The frame consist of an open U-shapedweldment, upon which rest the IC power-plant, hydraulicdrive system, power and control electronics, locomotionand steering system, as well as the container grabbing andhandling head and its associated conveyors. The system

Side Conveyance

Grabber-Bar(1 of 2)

Combine Head

Power Source(IC Engine)

Eject/FeedConveyor

Drive & SteerWheels

Control Box(1 of 2)

Frame

Batteries&

Hydraulics

Fuel-Tank

Side Conveyance

Grabber-Bar(1 of 2)

Combine Head

Power Source(IC Engine)

Eject/FeedConveyor

Drive & SteerWheels

Control Box(1 of 2)

Frame

Batteries&

Hydraulics

Fuel-Tank

was oversized so as to allow for laboratory testing of allpossibly useful features, which are then to be evaluatedfor inclusion in the commercial prototype (see Figure 7):

Figure 7 : Frame undergoing assembly

POWER & CONTROL: The main power source for thesystem consists of an internal combustion-enginemounted on the frame, providing both electrical power viaa generator, and hydraulic power through a direct-coupledpump. The power is regulated through a dedicatedcabinet, while the electronics and controls for the PLC andthe relays and valves are housed in a separatecompartment. Fuel-tanks and cooling radiators aremounted on the frame as well. A picture of the subsystemsis shown in Figure 8:

Figure 8 : Power & Control Subsystems

HYDRAULIC DRIVE & STEERING: The hydraulicsystem is used to provide driving/steering power to thewheels, as well as articulating the grabber arms andpinching endeffectors. The drive and steering for thehandling system is achieved by driving the two frontwheels in a differential manner, while letting the systemfollow based on a simple rear-mounted rocker-arm caster-axle. The individual systems are shown in Figure 9 indifferent stages of assembly.

CONTAINER GRABBER: The method used to grabcontainers reliably, without requiring any dedicatedcontainer design, is based on a simple double half-moonfriction-clamp design. By ganging these pinch-grabbersalong an actuated rail, a whole row of containers can begrabbed at once and moved around. The bar-mountedpinch-grabber arms are mounted on a set of two rotatingside-arms, allowing a combine-like full rotation of eachrow that has been grabbed; and internal gearing-passensures that the containers remain level during any part of

COMPUTER INTERFACE POWERCOMPUTER INTERFACE POWER

ENGINE

the rotation. The sensory system used to control themachine-heading, combine-head rotational position, arm-extension and pincher open-close states, is based on theprocessing of infrared range-measurements fromembedded sensors [3].

Figure 9 : Locomotion and Steering Subsystems

Preliminary testing on a single pincher and a full pinch-grabber bar basis have determined that this approach isreliable and robust to container types and outdoorconditions. Images depicting the pincher system duringindoor testing, are shown in Figure 10.

Figure 10 : Container Grabber Subsystems

PINCH-GRABBER ARM ARRANGEMENT IN LABORATORY TESTING

CUSTOM CYLINDER

PINCH-GRABBER TESTING

ELECTRONICS: The electronics and control system isbased on commercial-off-the-shelf industrial automationhardware. The hardware architecture is shown in Figure11. The control system hardware consists of an Allen-Bradley SLC-500 PLC, two Delta Computer Systemsmotion controllers and a variety of other components (e.g.sensors, relays, and contactors, etc.). As noted in Figure11, the PLC communicates with the motion controllers viaEthernet. The PLC performs all supervisory and discretedevice control. The PLC chassis houses the CPU andseveral I/O modules for: a) discrete and analog sensorsinputs (e.g. proximity switches, IR sensors for containerlocalization, etc.), and b) discrete outputs (e.g. solenoidvalves, indicator lights, etc.). The motion controllerscoordinate and control all 10 axes. The ten axes include:(i) two (2) drive wheels for locomotion, (ii) combine headrotation, (iii) four (4) hydraulic cylinders for thetelescoping tubes, and (iv) the three conveyors. Thesystem operator will interact and control the system viabuttons, switches, and a joystick (see Figure 8).

Figure 11 :High-Level Electronics Architecture

CONTAINER SENSING: In order to perform up-closepositioning of the grabber-head so as to achieve ‘proper’alignment with the containers for a full-row pick-up,despite the potential misalignment of the tool systemitself, the misplacement of containers, etc., requires theuse of an integrated sensing system. The most suitablecandidate for simplicity, ruggedness and reliability turnedout to be a non-contact infrared ranging system (seeFigure 12). To build the range-imager, we integratedseveral of these relatively short-range (4 inches to 2 feetdepending on IR diode-power) sensors onto the side of theframe along the pickup-line. This allows us to not onlyachieve a good ‘average’ sensory-alignment reading, butto also have a much better idea of the alignment of thecontainer-row in the field, which will be useful if we areto properly space containers in the field. The test-setup weused (see Figure 12), includes a suite of several IRsensors, which are multiplexed through a computers’ I/Oport (parallel in the experimental setup’s case) to obtainrange-readings from each sensor at a rate of 10 persecond. These readings are then processed based on the

Ethernet

Motion Controller # 2

Motion Controller # 1

PLC CPU, I/O Cards

Field Devices

6 Axis, Quadrature 4 Axes, LDT

calibration-curve for each sensor, and then a range-map isbuilt.

Figure 12 : IR Sensing System & Setup

If the sensor-array is moved laterally and in front of a rowof pots, an image can be generated which a computerinterprets so as to determine the inter-container spacing,which in turn can be used to determine the proper locationof the gaps between the containers. This process makes theaccurate placement of he grabber-head possible so as toprovide final alignment through heading control andgrabber-arm extensions. The block-diagram of thesoftware that was developed in order to perform theranging, computation and grabber-head alignment(including gross alignment by way of heading anddisplacement of the entire system), can be depicted asshown in Figure 13:

Figure 13 : Software Sensor-Control Diagram

SOFTWARE: The control system logic is implementedvia Allen-Bradley’s ladder-logic programming language.The RSlogix development environment was the primarytool for development of the ladder-logic control program.Unlike most industrial ladder logic programs, thesoftware/control program was written using a modular,systematic approach. This systematic approach makes the

TEST JIG

SHARP GP2D02

EXPERIMENTAL DATA

0

100

200

300

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61

Measurement Number (measurement taken every half-inch)

Sen

sor

Rea

ding

(0-

255)

Top view

Computer I/O Port

RangeCalibration

RangeComputation

RangeImaging

Done

Y

N

Index-MoveGrabber-Head

and Storage

ModelFitting

Offset andMisalignmentComputation

Index-Move Grabber-Head andGross Alignment

ϕ R1R1

O1

code more reliable and easier to debug and maintain. Thesoftware architecture is shown in Figure 14. The programconsists of a main program, device control, inputreferences, output references and several processes. Themain program provides overall control. The device controlis the only place where devices are controlled. The inputand output references map all internal software variablesto the I/O hardware. The processes are where the majorityof the control logic is implemented. These processesrepresent basic functionality of the system’s various subsystems and are where the machine operation issequenced. For example, one of the processes is forloading/queuing of the transfer conveyor so a grabber armcan pick up the containerized plants and set them on theground. Another process, for example, is for unloading theconveyors after a grabber arm has placed containerizedplants on the conveyor.

Figure 14 : Software Architecture Layout

SYSTEM: A fully assembled locomotion platform of thecontainer handling system is shown in Figure 15 duringlocomotion trials on the experimental nursery at CMU’sNational Robotics Engineering Consortium experimentalnursery:

Figure 15 : Fully integrated container handling system

V. FIELD TESTINGThe handling system shown in Figure 15, was tested atREC’s experimental nursery. The system performancewas measured over a 6-foot wide and 50 foot long bed

Main

Input References

Device Control

Output References

Process N

Process 2

Process 1

MAIN

INPUT REFERENCES

DEVICE CONTROL

OUTPUT REFERENCES

PTROCESS 1

PTROCESS 2

PTROCESS N

using a variety of #1 containers and different plant-typesand weights (see Figure 16).

Figure 16 : Test-nursery field-trial setting

Initial testing indicates that the sensing scheme was able toposition the system accurately enough (to within 0.15m),yet the closed-loop speed needs to be increased to achievea productivity increase of about 30% (currently at ~20,000 containers per 8-hour day). The time spent betweengrabbing containers off the ground and hand-off onto theconveyor needs to be sped up to increase cycle-time aswell. Large steering corrections did not result in expectedbehavior, due to the variability in traction we re seeing dueto different groundcover and the fact that the weightdistribution between the front driving wheels and the rearcaster-axle is 30/70. The operator interface was found tobe simple enough to use, even when manual reset andresumption of automated handling was required. Minorimprovements in mounting and cooling for certainsubsystems are being undertaken to complete the testingprogram before the onset of winter.

VI. SUMMARY & CONCLUSIONSThe container handling system presented herein representsa major step towards automation of labor-intensivecontainer-handling tasks in medium to large-sizedcontainer nurseries in the US. The system represents a newclass of smart outdoor automation systems utilizingexisting hard-automation components, aided by smartsensors, intelligent software and innovative mechanismdesign. Testing of the system has shown its potential toachieve the desirable productivity of 25,000 to 45,000 #1containers per day with one to two operators, withoutregard to the type of hauling-trailer. The system is capableof handling a large variety of containers available throughUS manufacturers. Groundcovers suitable for the machineand tested to date, include gravel and stone/asphalt/concrete. The current system needs to be reduced inweight and size (mostly width), as well as re-engineeredfor lower manufacturing costs. System maintenancerequirements are expected to be reduced by switching toexclusively electrical power on board.

VII. FUTURE WORKThe system presented herein represents the firstgeneration of field-container handling systems. We arecurrently simplifying and shrinking the system design,and expect to prototype an improved commercialprototype by the end of 2001. In addition, CMU isdeveloping other more simple manual tools for assistinggrowers that have switched to growing trees in the groundin large containers (pot-in-pot) and those retailersinvolved in the landscape and garden-center sectors in thisindustry.

VIII. ACKNOWLEDGEMENTSThe container handling system was jointly funded atCarnegie Mellon University (CMU), by NASA underresearch-grant #NCC5-223, the US Dept. of Agricultures’(USDA) Agricultural Research Office (ARS) under aSCA (#58-1230-8-101/58-3607-0-130), and a grant fromthe Horticultural Research Institute (#1999-128/2000-163), the research-arm of the American Nursery andLandscape Association (ANLA). We wish to furtheracknowledge the help from many growers and nursery/agricultural equipment/supply providers (MidWestGroundcover, John Deere, Toro, Lerio, Nursery Supplies,etc.) in the industry, that have gone out of their way toassist in the development through advice and equipmentand supplies donations.

The above-described system and process has beendescribed to the USPTO as part of a patent-filing - it has apatent-pending status.

IX. REFERENCES[1] “VISSER - Product Descriptions.”, Company Cata-

log and CD, November 1999[2] Schempf, H., “Automation and Mechanization: The

Future of the Nursery Industry in the US”,NEGrows Conference, Boston, MA, January 21-27,2000

[3] Dias, B., Stentz, A., Schempf, H., ‘Sensory-basednursery container detection’, RI Tech Report Draft,Carnegie Mellon Univ., Pittsburgh, September 2000

[4] Product Literature for various companies: Bouldin-Lawson, Javo, Baertschi-FOBRO, Goetsch, Urdi-nati, etc.

[5] ‘Systems for Success’, by D. Hughes, Jr., CedarRapids, IA, ISBN 0-9655037-0-4

[6] “New Ideas”, Bi-monthly Newsletter, WholesaleNursery Growers of America, 1991 - 1999.

[7] Jagers, F. et al, “Hi-Tech take-over of pot-plantgrading”, FlowerTECH 1998, Vol.1/No.1

[8] Adrain, J.L., et al, “Cost Comparisons for Infield,Above Ground Container and Pot-in-Pot Produc-tion Systems”, Journal of Environmental Horticul-ture, Vol.16, No.2, June 1998, p.65

[9] ‘American Standard for Nursery Stock’, AmericanAssociation of Nurserymen, ANSI Z60.1-1996,Nov. 6, 1996