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FAQ  >  ERMs
TiNi Aerospace, Inc.

Shape Memory Alloys



What is the difference between your Pinpullers and ERMs? The ERMs are nearly identical to our Pinpullers in that they share more than 90% of the same parts. However, by adding a ball lock at the coupler interface the load rating is increased by more than one order of magnitude to provide a unique and powerful NEA (Non Explosive Actuator).
How quickly can I reset your ERMs (or Pinpullers)? These can be reset within seconds although it is best to wait at least 3 minutes to ensure that the TiNi element has cooled back to room temperature.
Is the ERM (coupler) designed to react to any side or shear load? No, the ERM is similar to our Frangibolt in that it should be exposed to axial loads (resulting from joint preload) only. Of course the friction in any such bolted joint is capable of reacting to some amount of side load. However, a cup-cone interface between the structure and deployable is recommended if significant side loading is anticipated.
Can I fire the ERM with no external load and does the ejected coupler represent a safety hazard? Yes, you can fire the ERM with nothing attached to the coupler. Generally, you will find that the force is light enough such that the ejected coupler is thrown into the air by only 5 feet or so. Therefore, cupping your hand over it is a common and acceptable method for retaining it. The only safety precaution should be to not put one's head (or eye) directly in the path of the coupler.
Do I need to support the Coupler or ERM body during torque up? No, TiNi's early literature suggested that a "backing wrench" should be used but this is no longer the case. All ERMs are designed to be able to react to the recommended installation torque (i.e. as long as the ERM body is bolted to the structure, the coupler can be torqued into just like any other Nut or Threaded Hole).
What type of locking feature is recommended for use with the ERM hold down bolt? Locking inserts (Heli-coils) installed into the Coupler are the most common approach. Also, other methods such as locking fluid or patches are acceptable. Aeronautical or military applications may benefit from the use of lock down wire as used on any other bolt or fastener.
What is the function of the Kick Off Spring and how much force does it apply to the coupler upon release? Depending on the ERM size, the kick off spring applies a force of 2 to 10 lbf (i.e. very light). Its function is to eject the coupler in the event that no external load or preload is applied.
Can your ERM (and Pinpullers) be sealed for underwater applications? Yes, we have done this for many ERM and Pinpuller embodiments and found it be effective for pressures up to 1000 psi. However, if higher pressures (depths) are expected then the ERM (or Pinpuller) needs to be housed in a pressure compensating enclosure.
Can you change the ERM resistance as in question #2 relating to Pinpuller? Yes, the internals of our ERMs and Pinpullers are nearly identical so many (if not all) Q+A relating to our Pinpullers also applies to our ERMs.
How does your "Load Feedback" ERMs work and can it be applied to both your "top mount" as well as "bottom mount" configuration? Load feedback is offered by installing calibrated strain gages directly in the ERM enclosure. This offers very accurate measurement of preload during torque up. This option is readily introduced into the bottom mount configuration where the Actuator enclosure is in the load path. It has also been incorporated into the Top Mount configuration where the enclosure is not in the load path by use of a "transfer tube".

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