Linear Motor efficiency

[Syncsync]

My question is: How to select the most efficient linear motor?
I know that the parameter involved is called Km (N/sqrW).
I've also read in an article that the best linear motor design was developed by a French company called ETEL. Is it true? Is the Km parameter a good figure of merit?

 

[SERVOCAM]

How to select the most efficient linear motor?
- Well, it's not just the motor you need to take in consideration. A lot also depends on the efficiency of the amplifier driving the motor, even cables being used.

I know that the parameter involved is called Km (N/sqrW).
- In the past 5 years working with linear motors, I have never heard of this parameter. What exactly does this Constant stand for?


I've also read in an article that the best linear motor design was developed by a French company called ETEL. Is it true? Is the Km parameter a good figure of merit?
- I would say no that it is not a good figure of merit. Was this an article by Etel? Every manufacturer is always saying how they are the best....what every style they make.

The Tubular-Linear Motor Mfgs will say they are the best because they utilize 100% of the magnetic field, the Flat/Platen will say that ours are the cheapest and provide the most power for you dollar, and the u-channel's will say we are the most efficient because or our design.

My question is why are you basing your selection on efficiency? What is your application?



Cameron Anderson - Sales & Applications Engineer
Aerotech, Inc. -

http://www.aerotech.com

"Dedicated to the Science of Motion"

 

[Syncsync]

My application is a fast pick and place machine. Peak force has to be high enough so quick move are possible (33 lbs payload, 10 inches travel in 160 msec), but more important is the continuous force, since the motion has to be repeated on and on after just a 50 msec dwell time.

Quick calculation shows that 820N/700N peak/continuous force is needed (taking into account friction and resistance forces, and 10 lbs for a water cooled linear motor forcer).

The Km is the motor constant. It is given in Newton/sqr(watt). It can be calculated by dividing the force by the square root of the power at a given working point. This is a good figure of merit since it provides information about the motor's efficiency. The higher the Km, the lower the power losses for the same output force.

It is my understanding that the better the efficiency, the higher the continous force for a given motor volume or mass. An inefficient motor (low Km) is gonna be much heavier than an efficient motor (high Km) to provide enough continuous force for the application. Since the inefficient motor is heavier, the total moving mass is larger, thus the continuous force is increased, then an even larger motor is needed and so on, until you find out that it is not possible to find a suitable motor unless its efficency is good enough. This is why the Km factor is crucial in my point of view.

 

[SERVOCAM]

I would like to carry this conversation via email with you. Can you please send me an email? I don't like to really talk product specifics on here (feel like I am trying to advertise for us if I did that and that is not fair, I try to stay non-biased).

cameron.anderson @ aerotech.com

I did find that Km spec in our catalogs, just never heard of it before. Learned something new, thanks! I see what you were getting to regarding efficiency, just never has anyone select a linear motor by efficiency.

I was told this refering to our motors:
"They are quite efficient. If you compare our design to one that's similar size (Anorad,Etel), ours should be more powerful as a result of the different winding technique. Whereas the others place coils side-by-side, which is easier to manufacture, we overlap the coils. As a result, in the same given volume, we can pack more copper."

Our Most powerful is BLMX. We can do water cooling on the U-channel, but only through the base. The BLMFS3-220, flat motor, can have an optional cooling plate. We mainly use forced-air cooling.



Cameron Anderson - Sales & Applications Engineer
Aerotech, Inc. -

http://www.aerotech.com

"Dedicated to the Science of Motion"

 

[jbartos]

Suggestion: Maglev is one area where the linear motors are carefully researched. Visit

http://www.magnemotion.com/technology/Maglev/pdf/M3UrbanSystem.pdf

etc. for more info

 

[avigodner]

Small correction - ETEL is rather Swiss than French company, their products - motors + control electronics - are high performance high cost for space, critical mission and so. Happened to visit them in 1994 in Moteur (near Neuchatel) ...

 

[jbartos]

Suggestion: Visit

http://www.magnemotion.com/technology/LSM_techissues/efficiency/main.shtml

etc. for a linear motor efficiency