voice coil vs. solenoid cost? 2

[brashear]

Hi,
I am debating using voice coil as a linear actuator for a design, and I am trying to get an idea of their cost. It seems like the are much more costly than solenoids, which have essentially the same components minus the permanent magnet. Any idea for why this is? Thanks

 

[Skogsgurra]

The PM material is expensive and the machining to close tolerances increases cost.

Solenoids are produced in much larger volumes using stampings of cheap raw material like transformer plate and there is no need for tight tolerances.

Solenoid coils are wound on forms while most voice-coils are self-supporting and usually limited by available cooling.

The linear movement used for voice-coils is usually a lot more sophisticated than the plunge-and-spring used in solenoids.

Voice-coils are faster and more linear so I would say there are two distinctly different application areas. Your application must be somewhere in-between if you consider using either technology.



Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[brashear]

So let's say I needed a precise solenoid for a high quality valve, which requires all components to be machined rather than stamped. In this case, the cost differences would be less between the voice coil and solenoid, correct? Using a voice coil in this case would allow precise control of flow rate, not just on-off. Also, what does "wound on forms" mean? Thanks

 

[Skogsgurra]

There are no such things as precise solenoids. Their characteristic is highly non-linear and it is usually not possible to position things with them. That's where voice-coils have their applications.

Wound on form means that there is a coil former and that the winding process is fast and cheap. The voice-coil is self-supporting (no room for a coil former in the air gap) and that is a more costly procedure.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[OperaHouse]

Have you looked into fero fluids? Many years ago a friend of mine took a position at a speaker manufacturer. This was back in the 70's when fero fluids just came out. They used them to manufacture their tweeters. They touted it in advertising as increasing magnetic field and taking away heat. To me it seemed the fluid would dampen high frequencies. He then confessed the only reason they used the fluid was to center the voice coils. He said it speed up the manufacturing so much that it was worth the $1,000 a quart. Later heard that auto manufacturers used the fluid in their speakers because of increased audio efficiencies and extended life. This fluid may be useful in your application in reducing the cost of the magnet.

 

[brashear]

by a "precise solenoid" I don't mean in a positioning sense, but in the that tolerances are tight between the different components. Can the bobbin on a voice coil not act as a coil former to wound the coil on?

The ferofluid to my understanding basically increases the B-field strength in the gap so a smaller magnet can be used. This also increases the drag of the bobbin since ferofluid is more viscous. I will do a performance and cost analysis to see if this is worth it.

 

[OperaHouse]

Recently took apart a disk drive. That had no form it was wound on and was molded in place. Speaker coils are wound on stiff paper or aluminum form. This is probably the reason for the higher cost of voice coils. The coil must be precisely wound and then allowed to set/bake vs a quick almost a scrabble wind on a bobbin. Really expensive magnets can be extremely small. Using that as the motive device may be a better approach with winding the coils externally.

 

[Skogsgurra]

Explanation: In my world, 'form/former' and 'bobin' are the same thing.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...