Machine Control System Design - The Basics

Written by Nigel Adams - Engineering Director - Prolec LTD - Poole, UK

Created on Saturday, 05 September 2009 12:18

I have recently been updating my knowledge of the various excavator machine guidance solutions available. This has involved reviewing all currently commercially available products within this genre and it has been of great personal benefit in doing so – something I strongly recommend anyone involved in this industry – whether your background be technical, commercial or user. To quote one of the many sayings drummed into me from an early point in my engineering career “time spent on reconnaissance is rarely wasted”. I have been surprised at the wide range of technology (hi and lo) and the design philosophy employed by the respective manufacturers to produce their end product and the results that can be achieved with it. I intend to bring some of the more interesting products to your attention at later date, but at the moment it is suffice to say that almost any application and budget can be met. In the meantime I thought it useful to introduce you to the concepts and methodology used when designing complex products such as these so that you may understand the thought process involved in producing the systems that you use /are intending to use.

The need for any of these products will have been borne from credible market research. Some products may look like the next iteration of an existing family line, but they will still have had to undergo the same market justification. As well as producing the necessary documentation to get the go ahead from the required financial authorities (never easy!), this phase will also bring the necessary operational requirements to the attention of the design department.

The need for system upgrades will also be considered – is this going to be the start of a new product line with an upgrade strategy e.g. 1D, 2D, 3D ? or is it a standalone product not offering scalability? It is the responsibility of the market research and subsequent requirements specifications to ensure that all major categories are covered.

This isn’t the same as the production of the design specification; this is merely the needs and wants of the system, plus the forecast for potential sales and revenue.

The engineering specification will be generated from this requirement, and a whole department of product specialists or the design engineer may do depending upon the size of the organisation this. Other documents will also be required to determine the operation, testing, verification, validation etc. but in essence this is the point at which the products technical capabilities are defined.

So what would you find in the engineering specification? Well many of the features that I covered in my earlier articles on will be defined here:

Operating requirements
Functions
User Interface
Accuracy
Environmental specification
Electrical specification
National Standards
Mechanical design constraints

With these features clearly defined a range of engineering departments – electrical / electronic design, software, mechanical design can go about their respective tasks in creating the product. But what is required to do this ?

Well, regardless of company size there will always be the need to employ creative individuals (they may be part of the engineering staff, specialist design department or hired for this particular task) to come up with many of the product features that are not always clearly defined in the specification. This will range from the way in which data is presented to the user and the way in which he interacts (more of that in a minute) down to the appearance and ergonomics of the product. I know that critics will say that everything must be in the specification, but you can clearly see and experience the difference between a product spawned from a specification only and that which has had barely restrained creative juices added.

So we have the specifications and the right people employed, just what will they consider when designing the hardware. We will take the in-cab display for instance; here are a few posers –

What size should it be?
Colour or monochrome?
Graphic or text only?
Touchscreen?
Interfaces e.g. USB or other storage device?
Where and how will it mount in the cab?
Permanent or temporary fixture?
How to connect it to other components and power?
Is it safe to use e.g. no sharp edges / corners?
What colour should it be?
Can it be used within other product ranges?

And we still have to include the considerations in the engineering specification.

All these same considerations are applied to all system components, however we aren’t only just concerned with the individual components we also need to be aware of the non-operational aspects:

How to install the system?
What cables and where do they go?
Any specialist installation tools required?
Ease of maintenance and repair?

So as another example, an angle sensor –

Well yes it must be accurate and meet the environmental and electrical needs, but what of the installation and calibration? Regardless of how good the product is, installation and calibration can be a huge cost to the customer so this needs to be kept to a minimum time. The installation must not damage the machine (obvious I know, but you’d be surprised) and must be able to be easily maintained – the best sensor is the one that can be replaced without having to go through a lengthy recalibration process. The installation has to offer adequate protection of the device for its normal working life (at Prolec we mount our sensors in a protective “shoe” which offers protection to the sensor and cable connectors and allows easy sensor replacement).

So as you can see, the design engineer’s life is not an easy one and the product design process can go through many prototype design phases.

Let’s assume we have designed our hardware and have a complete suite of working sensors and interfaces, now what?

Well this is the most important part – what the user sees and does.

How is the data to be displayed?

Is the displayed data at a fast enough rate for real time use ? (If not, then make it so – there is nothing worse than moving the excavator and watching the display play catch up)

How do you access the different functions?

Do you provide operating menus?

How do you cope with multiple languages (icon driven menus are a great substitute for text heavy systems and if designed intuitively enough are easy to become familiar)?

Do you need to interface with other software and data packages?

How do you cater for software upgrades?

In a nutshell – it has to be user friendly. It is very easy to create a product that is engineered very well but is bloody useless, and it is always worth taking a step back and checking with non-engineering sources if the product is on the right track.

And when all this is done it has to be tested. This includes bench testing, environmental testing, electrical testing, field trials, end-user trials and each time the system is reworked or changed it has to go through the tests again!

I have only scratched the surface of the process behind the product design, but it should have given you an understanding of what has been done to create these products and hopefully appreciate the many hours of effort that have gone into bringing into life what is in reality the needs of the market which after all are the valued opinions of the end users such as you.

{mosaddphp:mega.php}