Background
G&S Seedlings are a major nursery based in the northern suburbs of Perth, supplying vegetable seedlings to the market garden sector in Western Australia. G & S Seedlings Pty Ltd was started in 1990, beginnings with two employees producing 20.000 seedlings a week the business now employs a seasonal workforce of over 30, producing 1,000,000 seedlings a week from its own, purpose built premises on seven hectares (16 acres) in Nowergup.
G&S Seedlings were looking to continue to invest in automation to improve the operation of their Nowergup nursery. The important factors for G&S to consider in the commercial justification of the project were:
- Reduced labour availability makes introducing automation into the nursery vital to allow the future expansion of the business
- The nursery had to be upgraded to allow the potential to produce a higher output in the future
- The nursery had to be adapted to utilise the stackable racks which was the first stage of the nursery automation project
- The automation project must give the benefit of controlling costs.
The success of the project was demonstrated by the reduction in labour required to lay out the racks being reduced from 8 people to 2 people, and from 4 tractors to 2 forklifts.
Glenn McKay, G&S Seedlings
Stage One
Concept & design
G&S Seedlings had already moved to incorporate the Williames Stackable Racks into the nursery as part of a four stage expansion to allow flexibility within the nursery. They decided that an automation system was required to allow the racks to be automatically loaded with trays directly from the Williames Seeding Line and sent to the nursery to be set out. After discussions between the two companies to decide on the concept, G&S Seedlings commissioned Williames Pty Ltd to design, manufacture, supply, install and commission a Rack De-stacking, Tray Loading and Stacking System for the Nowergup Nursery.
Conceptual discussions commenced in March 2010 with the initial Layout Drawings being presented in April 2010. The design of the system was finalised and accepted in August 2010, and an order placed with Williames Pty Ltd. The system was commissioned by Williames Pty Ltd technicians and accepted by G&S Seedlings in February 2011. All through the project Williames worked closely with G&S Seedlings to ensure that the project ran smoothly, and kept G&S informed of the project’s progress at all times.
Williames solution
Originally G&S Seedlings manually handles filled trays from the out-take conveyor from the Williames Seeder onto the metal racks, which were then moved by fork lift to be laid out. This operation required 8 staff and 4 forklifts. The Williames solution was to produce a rack dispenser, tray loader and rack restacking system additional to the existing seeding line. Empty racks would be loaded via fork lift into a dispenser magazine in lots of 10. The racks are held in place on pneumatic pins. A scissor lift is used to support the rack and the pneumatic pins release and the rack is then placed singularly into the tray loading position using the scissor lift mechanism to lower the rack into position.
A new high speed discharge gap-up conveyor was added to the existing Williames seeder to allow the filled trays to back up against a tray arrestor on the conveyor, which removes the gaps between the trays. When a signal from a sensor detects that a full row of 7 trays are present, a pusher arm operated by pneumatic cylinders slides the row across onto the waiting rack.
After 4 rows are loaded the rack is indexed via a chain drive to the stacking magazine, which lifts the rack via a scissor lift vertically into the magazine, where it is held in place by supporting pins. When the magazine is filled with 10 racks, the stack is removed with a forklift and taken for laying out. The operation now requires only 2 people on fork lifts to handle the entire rack handling process.
Conclusion
The success of the project was demonstrated by the reduction in labour required to lay out the racks being reduced from 8 people to 2 people, and from 4 forklifts to 2 forklifts. The benefits can be shown in the following table:
| Original system | Rack Handling system | Savings | |
| Staff required | 8 | 2 | 6 |
| Rate/hour | $20 | $20 | |
| Total cost/day | $1280 | $320 | $960 |
| Total cost/week | $6400 | $1600 | $4800 |
The system proved to have a payback period of less than 12 months. The success of the project has been demonstrated by the subsequent ordering of a second closely related system for de-stacking, washing racks and trays, and re-stacking again for storage.
Stage Two
Concept & Design
G&S Seedlings supply a large number of vegetable growers, varying in size from major players to small family owned farms. Upon the return of the racks and trays from the clients there was a requirement to:
- Wash down the racks to remove any soil
- Thoroughly clean the trays to prevent cross contamination, and
- As an additional function the vegetable seedlings required spraying with Confidor, a insecticide that protects seedlings from sap sucking insects.
Currently this operation is carried out manually, and is very time consuming, with both racks and trays being manually handled and the trays loaded into a washing system. In the new system the rack and tray washing functions had to occur in the same operation, as the returning racks were loaded with empty trays. The Confidor spraying would occur in the periods when washing was not taking place, and would involve spraying racks loaded with germinated seedlings. After discussions with G&S it was decided that these functions could be combined in one system, using the rack washing station as a Confidor spraying system.
Williames solution
The design of the rack dispenser and stacking magazines would be carried over to the new stage at the request of G&S Seedlings, who were comfortable with the design. In between the magazines would be a Tray Removal Station and the combined Rack Washer & Confidor Tunnel. The racks are moved from the Dispenser through the various stages via a chain conveyor.
Tray Removal Station
The racks originally supplied by Williames to suit the requirements of G&S Seedlings to cater for a number of types of trays utilised a 50 x 75mm mesh surface, with a lip around the perimeter to contain the trays during transport. Removing the trays over this lip presented the major challenge of the project. The solution was to lift the trays clear of the rack mesh via a pattern of “fingers” or lifters, which rise up through the mesh, and are mounted on a plate which is lifted pneumatically from beneath the rack. A pair of locating arms swing down to located the rack in the correct position. The trays remain supported by the fingers as they are slid off the rack one row at a time onto a take off conveyor by a pneumatic pusher bar. As the take off conveyor removes each row of trays the pusher moves forward and slides the next row onto the conveyor. When the rack has been unloaded the plate drops down and the rack is moved via a chain conveyor to the Rack washer.
Rack Washer
The purpose of the Rack Washer is to remove any loose soil and rubbish carried back from clients premises. To do this the rack passes through a short tunnel containing two spray bars supplied with mains pressure water to provide a mechanical action to blast off any soil or debris. The water used drains to the sump, and from there to the site water treatment system.
Confidor application
During the Confidor application the Tray Removal Station is inoperative. Full racks are loaded into the dispenser magazine in stacks of ten. The racks are then unloaded from the dispenser and conveyed through the Confidor Tunnel, where a single spray bar applies the Confidor to the plant leaves. The unused Confidor drains into the sump, where it is pumped back to the main Confidor storage tank. The rack then passes on to the Rack stacker.
Tray Washing
After the trays are moved onto the take off conveyor they are moved through a series of right angle conveyors to the Williames Tray Washer, capable of washing over 600 trays per hour and which is manufactured in stainless steel and designed to wash trays using high pressure, low volume water sprays. These sprays are positioned above and below the trays as they are moved through the unit via the conveyor chain. Brushes on the sides and top assist the cleaning process.
Conclusion
The project justification is based on the reduction in time and labour required to carry out the washing process, as well as the ability to relieve pressure on the production staff to clean the trays and racks prior to their next use.