We need insight when defining requirements
We all probably know Fred’s fight against the use of “MTBF” as a default measure of reliability.
And I concur. “MTBF” offers the least insight to product reliability. It offers little to the user in terms of realizing the benefits of reliability.
However, we all would like to see products that deliver more appealing benefits; and reliability is a key factor. But reliability is only part of the equation.
Technical performance is important.
So is price. So is appearance. So is delivery. So is the customer: different customers may see the world differently. And so may your competitors.
So, we can’t all adopt the same measurement for reliability.
Where do we start? …With the customer (or end user)! How will they use the product?
Where will they gain benefit from it? Is this $? Is this mission success? What are the pains of product failures? Do logistics and maintenance support the product?
How long will they use it before replacement? What motivates the replacement?
Each product and its scenario are different. We can’t make assumptions, or otherwise, we may miss the point (and our competitors won’t).
I will illustrate with 3 case studies.
Case Study 1: Advertising displays
You will be familiar with the increasing use of electronic billboards.
Revenue from these comes from paid advertising, and downtime is lost revenue. Therefore, downtime needs to be minimized: good system reliability and quick-response repair go to achieving this.
However, quick-response repair costs big-$. This is seen as the big-PAIN of poor reliability.
MTBF gives no ability to plan maintenance and does not forecast failure. Other failure distributions can give some forecast, but it is unreasonable that all components (sources of failure) will follow the same distribution.
In any case, no customer is able to express his requirement in terms of mathematical distributions. So why write a requirement that forces or implies this?
The customer is focused on minimizing unplanned maintenance. So, we should define his requirement in the same manner.
No more than X unplanned maintenance events per year per billboard
The supplier and customer agreed that this should be delivered by at least 90% of billboards, thus setting a confidence bound for assurance measurement.
Equally, they could have agreed on warranty terms to cover individual instances where there was more than one event.
Internal specifications covering sub-system reliability, redundancy, planned repair of redundant failures, and other modeling, were then used to optimize the delivery of this requirement.
Product life was also included in the customer requirement. This had a major impact on return on investment. The “No more than…” applied to the whole life.
Besides more-involved and happy customers, this approach to requirements also had benefits within the company.
Design & development teams began to explore and learn how design features and failure risks integrated with maintenance management. They became pro-active leaders in exploring how best to deliver reliability.
Reliability is no longer a “numbers game” but rather an “engineering game”.
Case Study 2: Household gadgets
Household gadgets costing sub-$20 are not known for their reliability.
However, these gadgets can support high profits through the use of consumables. Therefore, it is important that the customer not only purchases the gadget but also continues to use it actively for an extended period.
Reliability of relatively simple devices is often a case of avoidance of “own goals”, namely poor execution.
Poor design. Poor manufacture. Poor understanding of how the customer will use the device.
Adopt and use best practice. Use good suppliers, those with expertise in their field.
Keep it simple. Emphasize quality assurance. (Six Sigma is a good place to start.)
Measured reliability assurance is unlikely to be cost-effective. Remember that the greater the reliability to be demonstrated, the more costly will be that demonstration.
Concentrate on identifying risks within the device design and manufacture, and implementing cost-effective and targeted plans to minimize.
Chemical attack on seals? Wear of polymer parts? Manufacturing variability? Each project is different. Start with an effective FMEA!
A simple spreadsheet will identify how much should be spent on reliability risk activities, based on the payback through consumable sales.
Reliability = $$$.
Case Study 3: Game-changing start-up
A new technology offered a game-changing product, offering equal performance at 1/10 the price of existing products.
Existing products were limited to the professional market. The new product opened the consumer market.
The mostly-electronic product did not pose a significant reliability risk in terms of day-to-day failures. Good design practice to control electronic temperatures/loads and good manufacturing quality would cover those.
However, hardware and software robustness was identified as a much greater risk. Consumers are known to be quite abusive of handheld electronics.
Cellphone manufacturers know all about drop impact, moisture ingress, contamination, connector damage, and other “failures” outside any “controlled environment” reliability specification.
User interfaces need to be fast and responsive across a wide range of scenarios, often with high levels of “noise”.
Therefore, robust functionality across a wide range of “abuse” and “noise” was set as the reliability requirement, backed up by good design and manufacturing practice.
This product met with great success in both the consumer and professional markets. Success also resulted in first-responder and military customers, and further development.
A game-changing SUCCESS!
Product reliability is not an end in itself.
It is a performance feature that helps deliver the right product to a customer or user. We need to understand how to leverage additional benefits, and that requires a clear understanding of your customers.
Ask yourself “do I really understand how product reliability helps our customers?” or “how does our expression of reliability requirements leverage customer benefits?”
If you don’t know, or would like to discuss this further, contact Les@lwcreliability.comAsk a question or send along a comment. Please login to view and use the contact form.