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5 considerations for safe motion controlled machines

Posted November, 11, 2017

By: Dr. Michael Wrinch 

When developing complex motion controlled machines and safety instrumented systems with budgets that reach well into the millions of dollars, a mismatch or design failure would not only be very hazardous to the end-users, but also extremely costly for both our client and our company.

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Fig 1: Noor Salh - A Hedgehog Controls Programmer Checking Algorithms on a Test Kit

To eliminate these events from occurring we follow functional safety standards and the methodical calculation-review-confirm process with a five step phased approach.  The 5 steps in this phased approach are:

1. Develop a detailed specification

We utilize Theory of Operations and conceptual design methods, then conduct a full review of the specification with an interdisciplinary team

2. Build a test kit
Providing a tool which allows the team to replicate functions, test features and verify specifications based on the conceptual design assumptions as early in the design process as possible is a critical success factor
Fig 1. Is of a photo of one of our controls experts using a test kit that contains a motion control system, encoder, drive and motor that we have used to test a series of safety function responses to a safe torque off command
 
3. Prepare a preliminary design

Developing, and then iterating quickly on early stage designs shortens the feedback loop, and speeds the overall time to delivery of the final product. SISTEMA safety analysis is then used to ensure the correct architectuture and components have been selected. 

4. Finalize the detailed design

Creating, and signing off on the controlled drawings and functions of a detailed final design package ensures accountability, and a clear basis for communication with the teams that are building it

5. Complete Factory Acceptance Testing (FAT)

Testing (with proper documentation) to verify each sub-system meets performance specifications before leaving the factory provides confidence in the quality of the product being shipped, as well as the opportunity to identify and correct any errors at a significantly lower cost compared to product already on a customer site

While any given project, or customer, may require the addition of specific activities to this 5 step process, it is where our planning starts on every project.  We choose to work this way because:

  • It allows us to methodically identify and eliminate challenges as they emerge
  • Interdisciplinary reviews ensure team diversity, and the elimination of Group Think bias
  • Test kits are a fast, efficient way to validate design assumptions and check specialized considerations, such as communication lag or advanced motion precision

While this process has proven itself to us many times, our clients also find it an effective way to manage design risk and effectively communicate concepts. I hope it will help you in your projects.

 

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Dr. Michael Wrinch is a Canadian Functional Safety Professional Engineer and President of Hedgehog Technologies whose expertise is in the design of complex electrical and controls system.

 

 
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