Machine safety: What does ‘reset’ mean?
Who hasn’t heard the term “reset” around machine control? And, how many understandings are there from machine builders to machine users? Oh, and what about the standards writers?
My first thought on this subject was to look in several current standards to see how the term “reset” was defined. Much to my surprise “reset” was not listed with a definition. However, many standards describe within their document how to perform a “reset” – but of what?
Secondly, in my opinion, I thought of what folks have described over the past 20 years or so:
Manufacturers (users) – they have described “reset” as having to do with resetting the control system to a run mode typically after an emergency stop condition.
Machine Builders – they often talk about resetting the stop function to allow another mode like run, micro-inch, set-up, etc.
Component Suppliers – sometimes they talk the required push and twist action of resetting their e-stopping device.
Control System Suppliers – they, however, often talk about resetting the control system to production mode whether the “reset” of a stop/e-stop was caused by a device or the machine control logic.
Standards (and writers) – these documents often describe the required steps involved in re-energizing the control system/motion to run production following various types of stopping conditions including some typical precautions and informational references.
In my opinion, ANSI B11.19-2010, Performance Criteria for Safeguarding, represents a very up to date and comprehensive approach to the requirements surrounding “reset”. Clause 6 in particular has an excellent Table that offers explanatory comparisons of three primary functions; Stop, E-Stop and Protective (Safety) Stop. This standard also does a great job of referencing other Standards like NFPA 79 – 2012, Electrical Standard for Industrial Machinery, as well as other ANSI Standards and reference materials.
It’s probably fair to say that the best understanding of “reset” comes from several of the latest machine guarding standards and several years of practical experience in combination with your specific type(s) of machinery and control systems.
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