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Course Project Topic

VSS Case Study – Part1

c©Simon Bennett, Steve McRobb, Ray Farmer 2002, 2010

1 High Bay Storage Control System

Vertical Storage Solutions (VSS) is a supplier of high bay pallet storage systems for warehouses. A high bay

system is essentially a large shelving unit for storing pallets in a warehouse (Figure 1). Each set of shelves is

separated from the next by a narrow aisle. Electrically operated cranes move along the aisles horizontally and up

and down vertically in order to move pallets to shelf locations in the high bay system. Each crane can also move

along the end of the shelving system so that it can move from aisle to aisle and to a loading area where pallets can

be loaded onto and off the cranes. High bay systems are much higher than conventional pallet racking, which is

designed to be accessible to fork-lift trucks. High bay systems often are built two or three storeys below ground

level and may be several storeys high. The typical height of a high bay system may be 25 metres (80 feet).

Figure 1: High bay shelving

VSS has an existing software package that controls its high bay systems and wants to rewrite it. The existing

system is written in C and uses C-ISAM files to store data. The supplier of the C-ISAM libraries is discontinuing

support, and VSS wants to move its system to a newer platform. The existing storage control system (SCS)

interfaces to other warehouse management systems (WMS) through a series of text files that are transferred into

a specific directory on the machine that runs the SCS. VSS want to change this interface so that other WMS can

send messages to the SCS using SOAP-based web services.

2 Requirements

The requirements for the new SCS were described in an interview with George Carpenter the technical director

carried out by Serge Dassault a business analyst from VSSs IT supplier. At this point, Serge has already introduced

himself and set the scene for the interview.

SD: Mr Carpenter, Id like to try to get a summary view of what the storage control system needs to be able to

do. Can you start by giving me an idea of what the overall requirements are?

GC: Sure. I think its important to start by stressing what it is were trying to achieve with the new version of the

SCS.

SD: Fine. Do you want to start with the changes then?

GC: Yes. Firstly, we want to achieve more automation of the storage process. Currently, each crane has a driver

who gets instructions about what job to do next. They then issue some instructions to the crane about where

to move to, and the crane follows their instructions. More and more of our customers want to reduce staffing

costs. And for a lot of customers, all the movements are of whole pallets, so they dont need a driver on the

crane.

SD: Sorry, what do you mean by whole pallets? Is there another way of storing things?

GC: Yes, some customers dont work at the pallet level, they store things in cartons, you know, cardboard boxes.

So although they keep pallets in the high bay each pallet may have several cartons of different products on

it. Sometimes, the driver has to fetch cartons off the pallet onto the crane. Its relatively easy to automate

moving whole pallets onto and off a shelf, but we cant automate moving individual boxes yet.

SD: What else?

GC: The web service interface is vital. More and more of the companies we deal with who produce the warehouse

management systems want to treat the high bay as a service with a standard set of operations that they can

invoke.

SD: Are there any more key changes?

GC: Yes, the last one is that we want to improve the job scheduling. The old way of working is for jobs to be

received by the SCS and for it to execute them in sequence, so if the SCS gets a request to put a pallet in

slot A-3-15, then a request to put a pallet in B-4-1, then a request to fetch a pallet from A-3-16. It will do

the jobs in that order, but A-3-16 is right next to A-3-15, so it would be more efficient to fetch that pallet

straight after it drops the one off in the slot next to it. We want it to be more intelligent about what it does.

That saves time for the customer, and also energy. Were trying to make our systems more energy-efficient

both from an environmental perspective and because electricity costs money, so we can reduce the running

costs for our customers.

SD: Okay, got that. Any other key requirements?

GC: No, thats it. The rest is just routine stuff.

SD: Okay, lets talk about the routine stuff. Lets start with the interface with the warehouse management system.

It seems to me that the operations that the WMS can request should give us a good picture of what the

requirements are.

GC: Sure. There are basically two tasks with variations.

SD: They are?

GC: Store something in a slot and retrieve something from a slot.

SD: So, lets talk about the web service operations. What data do they need as input and what kind of response

do they give?

GC: Youll need to look at the WAF spec. for the detail, but essentially, the first operation is something like

storeLoad. And it expects to be given the load type, which is pallet or non-pallet. If its non-pallet then it

needs to know the number of cartons. Then the weight of the load we try to store heavier loads lower down

and lighter ones higher up to minimise the stress on the shelving. The product code, though thats optional,

then the licence plate number.

SD: Hang on. Two points there. Firstly you say that the product code is optional, and then this licence plate.

GC: Okay. The product code is optional because we can store things in two modes product aware and product

unaware. If the high bay system knows what the product code is then it can do things like storing fast-

moving products closer to the loading bay, it can also handle requests to fetch a product rather than a pallet

or a carton. If the high bay system doesnt know what the product code is, then the pallet is just a black box

as far as its concerned. It can store the pallet and it can retrieve it, but it doesnt know whats on it, the WMS

has to keep track of whats on each pallet and request the right pallet back from the high bay when it needs

it.

SD: Okay, and the licence plate?

GC: Each pallet or carton has a large printed barcode label on it. When the crane loads the pallet in the loading

bay it scans the licence plate to check that its got the right pallet. If its a carton then the driver scans it with a

hand-held scanner. When the crane collects a pallet from a slot, it scans the licence plate again to make sure

its retrieving the right pallet, and similarly, if its just some cartons that are being retrieved, then the driver

scans their barcodes.

SD: So what happens if a job has been loaded onto the crane and it gets a cancelJob request?

GC: The crane will stop and return the load to the loading bay and the status of the job gets changed to Available.

SD: So presumably Available is the state that a job is in if a load has been retrieved normally.

GC: Yes. Do you want to talk about retrieveLoad now?

SD: Yes, please.

GC: Okay, so retrieveLoad needs to know the licence plate number if its retrieving a pallet or some cartons. Or

if its in product aware mode, then it needs to know the product code and the quantity.

SD: Anything else?

GC: No, either it fetches products based on the licence plate on the pallet or carton or by product code.

SD: What about batch numbers? Can it request a particular batch?

GC: Youre right. Yes it can, though usually we let the high bay SCS provide the batch with the earliest batch

date. But sometimes there are situations where you need to retrieve a particular batch, for example if the

batch has been recalled by the manufacturer because of a fault.

SD: Okay, so weve got three operations that can be requested of the high bay service: storeLoad, retrieveLoad

and cancelJob. Any others?

GC: No, thats it.

SD: What about the job statuses for retrieval jobs? Are they the same? Waiting, Loaded and Stored?

GC: No, Waiting, Loaded and Available.

SD: Right what about other aspects of the system? How about safety? Can two cranes be in the same aisle at the

same time?

GC: Yes, but they cant pass one another. So one crane can enter an aisle from one end, and another from the

other end, but they cant get past one another. They are lifted from above by an overhead gantry system.

SD: How many cranes would you have in a typical installation?

GC: It varies, and depends on the level of activity as well as the size of the high bay, but typically one crane per

six aisles.

SD: What about user interfaces?

GC: Yes, there is one.

SD: And?

GC: One for the driver. There is a display and a keypad on the crane for the driver. It tells him or her what job

is being carried out, what is to be stored or retrieved and which location in the shelving its going to. When

its not working in automated mode, it can also be used to display a list of jobs to the driver, so he or she

can select which job to do next. The other thing is that when the driver scans a licence plate it displays

information about the pallet or carton thats just been scanned.

SD: So whats the typical sequence of events for the driver using the interface?

GC: Typically a driver would start work on a crane, get up the list of jobs allocated to that crane, select one,

usually the first on the list. If its a storage job, the crane will move to the loading bay and display information

about what has to be picked up. If its a pallet, the driver will let the crane scan it and collect it. If its

cartons, then the display will show how many cartons to collect and some information about the licence

plate numbers. The driver scans the licence plates, and the interface confirms that theyre the right ones

or flashes up an error message if theyre wrong. The driver loads the cartons. Then presses a button or

something to say the crane is ready to move to the storage slot. The crane moves to the slot. Again if its a

pallet it automatically puts the pallet onto the shelf. If its cartons, the driver scans them and loads them onto

the shelf manually. Finally, the driver presses a button again to say the job is done, and the list of jobs gets

displayed again to select the next one. If the job is a retrieval one, then the crane moves to the storage slot,

if its a pallet job it scans the pallet and pulls it off the shelf. Otherwise the driver reads how many cartons to

pull off, scans them and loads them onto the crane. Really, its just the same as the storage job except in the

opposite order.

SD: Thanks very much for your time today. Ill be writing up my notes and Ill send a copy to you to check.

GC: Thanks. Id appreciate that.

High Bay Storage Control System
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IND 708 – Information Systems