HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Blogs
Guest Blogs

How Does an Engineer Predict Step Motor Pull-Out Torque?

NO RATINGS
View Comments: Newest First|Oldest First|Threaded View
cary2
User Rank
Iron
Empical Caveat
cary2   4/26/2014 2:03:08 PM
NO RATINGS
    You're right of course that performance has to be developed empirically, but the published specs should be carefully considered too. Your performance envelope may exceed the 'intentional published spec.  No matter how well 'checked',  a difference in the two can come back to bite ya. Case in point.

I inherited a (HPLC) syringe pump design, and production had been going along OK for several years. Then one day, assembly/manufacturing observed that it was 'whining' more than usual at final test; it functioned fine, but it was just plain noisy. I went through ALL the checks as to build quality, and etc. and all was fine. A month later complaints came in from an install in Australia: really noisy, particularly against an older system in the same lab; ...should they try to repair it, or what, I was asked. I said no, pull it all. My homework on this issue had already been done, or so I thought. 

I called the U.S. (now defunct) motor maker, and spoke to their manufacturing manager. They had been a large manufacture for years, -and I know our original R&D had worked for 8 months at finding the best price/performance model they could. The OEM said:          "Look, although our name has been out there for decades, we've changed ownership three times since I've been here. Our recent owner had us check our published specs. against the actual performance, and yes, our motors were over-performing. Therefore, they had us 'adjust' our motors to (just) meet specification.' "IF you want the motor that use to have that part number, which over-performed its spec, then you will now have to buy model xxxx-xxxx (and pay more money)."

  Check the empirical torque specs against the published, and see where your performance window lies. With steppers, that's not a trivial task. Also, as your chart would indicate: EMI-EMF is at it's worst when the motors are in a 'hold postion' state.

 [This is also why Europe and Japan do not respect UL versus ISA, JIS blessings IMHO. Medical device and research equipment manufacturers need have contractual QA notification requirements regarding ANY changes that could impact performance, whether the changes remain 'within spec' or not. I've seen UL approval of transformers straining at 80% of its spec-load accompanied by smoke, and loud whistling... and the inspector observ: 'yep, I see no flames, -it's a pass!]'

  

William K.
User Rank
Platinum
The other method of determining pull out torque
William K.   3/28/2014 11:28:16 AM
NO RATINGS
1 saves
Back in the early seventies I did have an occasion to require knowledge of stepper pull out torque, in odrder to avoid damaging parts of a mechanism driven by the stepper motor. Fortunately we had a small dynamometer at that company, and so it was fairly simple to run the speed/ voltage/ pull out torque curves for the speed and running time in our application. The test procedure was fairly sandard.

Given the standard stepper drive systems of the time, the stepper was always run with a much higher voltage and a large series resistor in order to provide a means to overcome the large inductance and allow faster acceleration. What became clear quite quickly was that as th motor warmed up due to the current, the resistance would rise and both the torque and the acceleration would drop. The ultimate solution was to include a stall detection circuit that would see the change in the waveform when the motor stalled and instantly inhibit the drive pulses in that direction. A math model would have been handy, but accounting for thermal effects would have made getting useful results a challenge.

Partner Zone
More Blogs from Guest Blogs
With strong marketplace demand for qualified engineers across the board that currently outstrips the available supply, there may never be a better time for engineers and project managers to advance their careers and salaries. Whether those moves are successful in the short-term and long-term is likely to depend on how the transition from one job to the next is handled.
There are drivers everywhere who turn on their headlights or windshield wipers with no awareness of the development effort behind a switch. Yet from freezing winter to sweltering summer, on dull rainy days and in bright sunshine, switches are expected to function consistently for the lifetime of a car.
Jet engine maker Pratt & Whitney sees additive manufacturing as a production approach that's complementary to -- not a replacement for -- traditional manufacturing processes.
The standards electrical machines and components are required to meet in the food processing industry are far more stringent than those in traditional plant construction. For specialized production environments such as these, components must not only resist thermal and physical stresses, but they must also be resistant to the chemicals used to sterilize equipment.
The word “smart” is becoming the dumbest word around. It has been applied to almost every device and system in our homes. In addition to smartphones and smart meters, we now hear about smart clothing and smart shoes, smart lights, smart homes, smart buildings, and every trendy city today has its smart city project. Just because it has a computer inside and is connected to the Web, does not mean it is smart.
Design News Webinar Series
2/25/2015 11:00 a.m. California / 2:00 p.m. New York
12/11/2014 8:00 a.m. California / 11:00 a.m. New York
12/10/2014 8:00 a.m. California / 11:00 a.m. New York
11/19/2014 11:00 a.m. California / 2:00 p.m. New York
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Mar 9 - 13, Implementing Motor Control Designs with MCUs and FPGAs: An Introduction and Update
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  67


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2015 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service