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Re: Linear actuator braking

Posted: Wed Apr 25, 2018 11:45 am
by Taylor
Here is a fun way to use a vertical linear motor. I believe the machine's intention is to make you sick. It uses an Aerotech BLMX linear motor. ...

Regarding heat...taken from Aerotech's installation manual:
The motor’s temperature rise above ambient establishes a limit on the amount of force producing current allowed through the motor winding. The thermal characteristics of the motor, the effectiveness of the surrounding medium to transfer heat away from the motor, and any supplemental cooling determine the operating conditions. The motor specification tables give the continuous motor current that will result in a predetermined temperature rise of the motor. This temperature rise is based on a single set of operating conditions as noted on the motor specifications. The use of supplemental cooling allows for increases in continuous motor current and therefore increased force. The motor’s thermal limit will not be exceeded so long as the minimum environmental and thermal conditions exist. Poor heat transfer away from the motor, excessive loading, elevated ambient temperatures, etc. are conditions that will cause excessive motor heating and failure. The importance of motor overload and thermal protection devices as described in previous sections becomes apparent.

Talking about electric linear actuators and servos, I think many of the applications have a focus on accuracy. So many times, a brake is used (spring applied or permanent magnet brakes). If zero backlash is required, there are zero-backlash versions of spring applied brakes. Permanent magnet brakes are inherently zero backlash. OK, don't harass me...they are "almost" zero backlash. There is always a little play (but normally not worth measuring).

For linear rail systems, the focus might be on clamping the rail. So, there are many ways. I like the idea of using an electro holding magnet to actuate a clamp. The magnet pulls the clamp together to grip the rail and hold it in place. I don't see the magnet holding the actual rail, the clamp would hold the rail, but it would be actuated by a strong holding magnet. These holding magnets are relatively inexpensive, but the clamping mechanism pretty much needs to be designed by the system designer.

I am thinking about linear motion applications like sliding medical tables. Whether they use a rotary (spring applied or permanent magnet) brake or an electro holding magnet (puck brake) they tend to want to hold that sliding system in place. Otherwise, whoops, grandpa just fell off the table again. Or whoops, the scan is a little fuzzy (accuracy). My gut feel is that many of the brakes are used for safety or accuracy, whether it be on a door guard, and machining operation, a medical table, or something else. Again, a clamp actuated by a holding magnet would work well too.

There are hydraulic and pneumatic rail clamps for very high torque applications. And, like you mentioned, electric brakes for electric motor applications.