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motor type selection - laboratory instrument 3

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tgwms

tgwms

Mechanical
Jul 19, 2007
6
We are planning a benchtop laboratory product which turns a special processing device for grinding and homogenizing various tissues and plant matter. I am doing research to find the best type of motor to do the job. My experience is with direct-drive brushless motors and gearhead DC motors, but before I use one of those simply because I don't have experience elsewhere I wanted to have a discussion about (blank slate, fresh start, clean paper) how do I choose the best motor type for this application in regards to power, speeds, control complexity, and cost.

Here are the speed ranges, accuracies, and maximum torques I am working with:
200 to 500rpm +/- 10% 180mNm
500 to 1500rpm +/- 10% 250mNm
1500 to 4000rpm +/- 10% 200mNm
-1000rpm(clean cycle) +/- 10% 150mNm

Positioning is not important, all we need are the speeds to those accuracies and torques. The last speed is a reversing cycle. Cost needs to be kept to a minimum. The unit must work in 115 and 220V regions, so using a desktop universal power supply and working with DC is optimal.

so... gearhead DC? direct-drive brushless? AC syncronous? servo motors? stepper? some other motor type I'm not aware of?

I searched my heart out for this topic, and was surprised to not have found the information already. I hope this thread becomes useful for other engineers.

This is a great forum... an incredible resource to the community. Thanks to the Tecumseh Group and all participating industry professionals!


"Imagination is more important than knowledge" -Albert Einstein
 
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Since you need variable speed, 3 phase gearhead induction motors driven by VFD's are hard to beat. I'd look at Oriental Motors for the gearhead motors. Perhaps Delta Electronics or Panasonic for the VFDs.

 
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TGWMS,
In addition to the requirements stated (speeds, torques, low cost,and supply voltage), you will have to consider things such as; noise, life, size, efficiency, annual volumes, maintenance (or discard), etc.
Does one motor have to satisfy the entire range of speeds/torques?
Enquiring minds want to know...

[ponder]
 
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Good points... sorry, some things I take for granted as I am around these projects everyday. The device could most easily be compared to a kitchen blender in size and useage, however unlike the blender, noise must be kept to a minimum. Efficiency is not a concern. Annual volumes are below 100. Average duty cycle could be represented as a cycle consisting of 10 seconds at +2000rpm then 2 seconds at -1000rpm... this would be repeated for 3 minutes... and that needs to happen everyday for 5 years.

Thank you sreid... I am on oriental motors' site now.

"Imagination is more important than knowledge" -Albert Einstein
 
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Sorry. But it looks like your old friend, the DC motor, is just right for this job also.

The problem with DC motors is normally that you need to change brushes now and then. But, with that duty cycle of yours (is it really not more than 3 minutes every day?) you can run a standard automotive DC motor for many years without any brush problems. It has many advantages. Low voltage, simple drive elecgtronics (an H bridge controlled by a onechipper), mass produced, low price. In fact only advantages - no drawbacks as far as I can see. Spares are also available globally.

Go to: and look at DPD 24 V 100 W. Speed range is +/-4000 RPM.

And, you do not need a gearhead for this application. But that is something you already knew.

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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wow skogsgurra... i wasnt expecting someone to go so far as even recommend a part number- thanks! and yes, that indeed looks well suited. now if the bosch website would just cooperate and give me a US distributor! ha

can your H-brige control solution meet the 10% speed accuracy needed?

thanks clyde as well... i have app engineers for each of those manufacturers going through their catalogs.

/////////////////////////////
"Imagination is more important than knowledge" -Albert Einstein
contract engineering and brainstorming
 
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aaahh... yes i should look up these electrical terms before i ask dumb questions. thanks keith and wikipedia.

so off 'topic', but to control a DC motor closed loop to 10% accuracy do i need an encoder or can it be done with back EMF?

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"Imagination is more important than knowledge" -Albert Einstein
contract engineering and brainstorming
 
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No encoder, just a switch. You watch how fast the switch is doing its thing. It can even be a white mark on a black shaft looked at with a non-contact optical sensor.

Keith Cress
Flamin Systems, Inc.-
 
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I presume you are designing this 'blender' from the ground up for production. You would want a microcontroller to handle the HMI, to providing the user functions desired, and to control the motor. May I suggest you look up Microchip's DC motor control development board.


You can take a Microchip course for a few dollars that puts one of these in your hands and gives you a day with motor experts and lunch. I took it and was very pleased with it.

This could blast you up the learning curve!

Keith Cress
Flamin Systems, Inc.-
 
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Or, you can use back-EMF. If you compensate for load - which is proportional to armature current - you can easily get within 0/-10 percent. Around +/-1 % (we are talking FS) is doable with larger motors, so there is some leeway. There are probably standard controllers available from tens of suppliers. I'll look around to see what comes up.

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

But does he really mean just once a day?
 
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We are all eagerly waiting for that answer. Suspense is killing me :)

Gunnar Englund
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
 
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yup... once a day. an average user would only use this device for 3 mins (average) per day each day for the 5 year life of product.

thanks for the electrical hints towards control schemes... i wont be doing the design myself; we will contract that. i simply wanted to research relative complexities (costs) for the different motor control types so i can plan the optimal system.

thanks again guys!

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"Imagination is more important than knowledge" -Albert Einstein
contract engineering and brainstorming
 
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