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Abu-Hafss
(@abuhafss)
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2020-05-06 9:44 pm  

Hi

I need to use either a stepper or servo motor to pull and position a metallic strip thru a progressive mold. I am just confused which one to choose. I have a fairly good experience of using steppers, and I see that a stepper can do the job easily with precision. But, I have seen mostly servo motors are used for this purpose.

I would appreciate if some guidance is provided for the selection of the motor. It would be worth mentioning that I have no experience of using big servo motors.


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triform
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2020-05-06 10:01 pm  

I would go with a stepper and a chopper drive combo. Is this for a shop-floor type job?


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Abu-Hafss
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2020-05-07 11:19 am  

Yes, it is shop-floor job.

image

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triform
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2020-05-07 1:14 pm  

So you have a big servo on the machine now?  I see.  That one will be connected to a servo amplifier (a big driver)  Is this machine PLC controlled?


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Abu-Hafss
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2020-05-07 7:49 pm  

Yes, that machine is PLC controlled. I want to replicate it using Arduino since the motor controlling steps are not very complex. It does not need position error correction. By the way, the servo motor is not very big. A NEMA23 4.2A stepper would definitely do the job. 


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triform
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2020-05-07 8:49 pm  

I'd say give it a try then!  You will want a motor wire with shielding and a good chopper drive. You can develop with cheaper stuff, but I would get better parts for production.  Noise is an issue with microcontrollers like the Atmega's, so are you planning to run in a shielded type cabinet? You may want to invest in a more rugged Arduino and I think there are a few options from different companies.  Do a google for "industrial" or "rugged" Arduino. EMF on the shop floor would be my biggest concern, but you should be able to overcome all but the worst EMF.

Scott

 


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Abu-Hafss
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2020-05-08 10:54 am  

Thanks for the great tip but I am afraid such rugged products are not available in my area, not even supplied by the local online stores. I have watched this video about one of Arduino based PLC but I don't see anything special for dealing with EMI, expect for the plug-in type connectors.

Could you please share some more information/links for the shielded cabinets? I also somewhere came across the tip to place arduino about 2 meters away from the actual machine.


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frogandtoad
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2020-05-08 1:22 pm  

@abuhafss

As a toolmaker, I have built and designed many press tools and plastic injection moulding tools, and this one looks like a progression form tool to me?

Anyhow, I have also built a few strip feeder systems for many different presses in the past, and the one common thing to be cautious of is reliability, with respect to repeatability!  Meaning, that one slip of the feeder (pitch per stroke), can cause an immense amount of damage, as such a scenario can push the pilots through the material, and break expensive tool steel die's, stripper plates, etc...

I think this is the reason for the server motor over the use of a stepper motor (which can miss steps and not recover them).

Generally, most strip feeder systems I have come across and implemented are all pneumatic in nature, and move to hard stops with the help of micro switches.

If I had the choice over stepper or servo, I would choose the servo, but these days, there are also many closed loop hybrid stepper motors available that can offer the performance of servo's, for a lot cheaper price!

 


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triform
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2020-05-08 2:22 pm  

@frogandtoad

I agree. I had a servo based motion system and had to replicate on a new system.  I was getting the same parts but was asked to "make it cheaper" So I ended going with a Stepper and chopper drive combo with a quad-encoder and running it with a non-PLC system.  Oh, the pain of the stepper losing steps! I did get it to work, but it was a lot of work. For what I was doing (reading moister and size on product lines) the home limits were hit going and coming. This kept it in decent alignment to take the readings. I had a lot of issues with EMF from the stepper to the drive and after moving that to a good cabinet and having nice shielded cable to the motor, most noises were eliminated. I also had a failsafe on it that read and IR prox and if it saw the IR after stopping over the line, then it was off and re-homed. The only time I had issues with it after all the fixes were when IR dryers turned on or increased a lot in power. The control cabinet for those was right next to the motion/collection cabinet.  The older system was controlled by a PLC/Vax combo. The new system was a Z-80 based board I designed. I was able to get the controller board to stepper noise controlled for the most part as well, but again those darn IR dryers were EMF junkies!

If @abuhafss tried a stepper, I would set up a simulation of all stress, mechanical and EMF like you would see on the floor. 


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triform
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2020-05-08 2:29 pm  

@abuhafss

Just a good cabinet with no big EMF sources inside it should work. For the Z-80 based system I mention above, I made a small Faraday cage for the PCB and connections to live in.  It was just a brass mesh screen.  I had to do it because of IR dryers, but you may be fine just in the cabinet.

I would do some heavy stress-testing of the system though 🙂

   


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frogandtoad
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2020-05-08 2:45 pm  
Posted by: @triform

@abuhafss

Just a good cabinet with no big EMF sources inside it should work. For the Z-80 based system I mention above, I made a small Faraday cage for the PCB and connections to live in.  It was just a brass mesh screen.  I had to do it because of IR dryers, but you may be fine just in the cabinet.

I would do some heavy stress-testing of the system though 🙂

   

Agh... I was about to mention some aluminium foil shielding and a faraday cage - Ya beat me to it! 🙂

 


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Abu-Hafss
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2020-05-08 4:11 pm  
Posted by: @frogandtoad

@abuhafss

As a toolmaker, I have built and designed many press tools and plastic injection moulding tools, and this one looks like a progression form tool to me?

Anyhow, I have also built a few strip feeder systems for many different presses in the past, and the one common thing to be cautious of is reliability, with respect to repeatability!  Meaning, that one slip of the feeder (pitch per stroke), can cause an immense amount of damage, as such a scenario can push the pilots through the material, and break expensive tool steel die's, stripper plates, etc...

I think this is the reason for the server motor over the use of a stepper motor (which can miss steps and not recover them).

Generally, most strip feeder systems I have come across and implemented are all pneumatic in nature, and move to hard stops with the help of micro switches.

If I had the choice over stepper or servo, I would choose the servo, but these days, there are also many closed loop hybrid stepper motors available that can offer the performance of servo's, for a lot cheaper price!

 

Yes, you can say it's a strip feeder system installed on a power press. The PLC is controlling the feeder and the stroke of the press. What I concluded from your experience is that servo would be a better choice. 
I have absolutely no experience of PLCs therefore, I should go for Arduino + servo.
I can manage the shielding of Arduino but I might need further help to deal with the servo.

 


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Abu-Hafss
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2020-05-08 8:59 pm  

@frogandtoad Ah yes, a cheaper closed loop hybrid stepper would be a much better choice. 🙂 


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triform
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2020-05-08 10:18 pm  
Posted by: @frogandtoad

Agh... I was about to mention some aluminium foil shielding and a faraday cage - Ya beat me to it! 🙂

 

I have done both.  I got a lot of strange looks from the E&I folks as well as other Engineers.  You will do anything after fighting with a noise issue for 4 days of no sleep because of a deadline 🙂


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Abu-Hafss
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2020-07-10 7:53 pm  

Finally, I decided to go for Servo Motor. But unfortunately, I have absolutely no experience of PLCs and I could not find any tip regarding using AC servo motor with Arduino. I shall appreciate if anyone could share some tips.


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