Servomotor - Speedreducer - Needlepositioning/EPS

[Pterytus]

When I updated my aerostar JM-822  servomotor driven machine with a speedreducer (see:

this modification resulted in the EPS/needlepositioning not working any more, the controller froze with an error message. This seems to be a common problem once the overall transmission ratio exceeds a certain limit (usually by adding a speedreducer).

User Captayne already posted his solution, which resulted in alternating TDC/BDC-needle behaviour when stopping the machine.
https://leatherworker.net/forum/topic/6 ... ent=467360

So I took a look inside my sensor module (Zhejiang Aerostar JM-822 750W) and found two sensor-chips (one each for up and down) and one magnet mounted on the rotor-PCB, which features two mounting-holes 180° opposite to each other, so one is left blank.

 

I glued a second magnet on top of the PCB in position of the second blank hole (180° offset) in the same N/S orientation as the original one, put it back together and replaced it on the machine.

In the controller setup there is a menu item N.B: "synchronizer type", which can either be set to "1" or "2".

After setting it to "2" the EPS system works perfectly again. Releasing the pedal will move the needle to BDC (down), pressing the pedal backwards will move the needle to TDC (up) just as desired.

 

So if you have the same (or a similar) setup and the EPS does not work properly it might be worth taking a peek inside the sensormodule as well...

 

 

Edited October 5, 2019 by Pterytus
typo

[dikman]

Very interesting. Mine is one which doesn't work with a reducer and although I don't need one you've got me curious.

[Constabulary]

[mikesc]

For those who use an NPS.... cool :)

[Matt S]

From someone who does use a NPS... thank you!

[dikman]

I opened mine up and it looks the same (other than having a metal housing). I'll glue a suitable magnet on later and see what happens.

[dikman]

Well, the mod had an effect but still doesn't quite work right. Unfortunately I don't have the option of changing the sensor parameter from 1 to 2, it's there but not accessible so this may be the problem.

I opened up the hole in the disc and glued a magnet in, which works fine. My Seiko has a large 8" pulley on the head which gives me about a 3:1 ratio. When I first fitted the NPS the motor simply wouldn't run properly, due to the ratio, and kept throwing up an error code. Fitted the modded NPS and now it will run fine but I can't set it to stop either needle up or down. What happens is if the needle is moving down when I take my foot off the pedal then it stops needle down, if it is moving up when I take my foot off then it stops needle up. Sometimes heel down sends the needle up, sometimes it has no effect.

An interesting experiment nevertheless - so near and yet so far.

 

Edit:I just re-read Captayne's post, referred to above, and I'm getting the same results that he did. While he thought that being able to "choose" whether you wanted the needle to stop up or down was great that will only work if you are sewing very slow, in order to "control" which direction you want it to stop. If you're sewing that slow then there's no need for the NPS anyway.

Edited October 6, 2019 by dikman

[Constabulary]

1 hour ago, dikman said:

 If you're sewing that slow then there's no need for the NPS anyway.

Thats why I never tried it again. I just removed the NPS - done.

I think the 2nd magnet does not work for "2-Button" JACK servos because you cannot change the magnet settings (at least I wasn´t able to figure out how). Anyway, I think I will try this one day when I set up something new - maybe I will choose a different motor then.

[Pterytus]

In case your needle stops in down position (BDC) unwanted, just give your pedal on (really) short tip with your toes and it should move up (TDC) because the controller "thinks" you want another full revolution, which - in case of two magnets - means half a revolution of your machine in reality. Fortunately it would never rotate MORE than wanted, only sometimes half a revolution less than wanted, which can be "corrected" by another half revolution.

Heel down should only reverse what happend previously. If it stopped in BDC, heel down should move it up - if it stopped in TDC, heel down should move it down. As in: Rotating forwards till the next detection of a magnet signal at the BDC-sensor-chip.

Not perfect, I admit, but maybe it helps you to "deal" with it.

[Gymnast]

On ‎10‎/‎5‎/‎2019 at 10:06 AM, Pterytus said:

User Captayne already posted his solution, which resulted in alternating TDC/BDC-needle behaviour when stopping the machine.
https://leatherworker.net/forum/topic/6 ... ent=467360

Thank you Pterytus for exploring the NPS of the Zhejiang sensor module and the reference above. I was not aware, that NPS was made that simple. If you have got a high speed machine, then I suppose that the machine will be unable to stop from high speed within a few degrees of the main shaft, because you got too much moment of inertia. So first the electronics need to slow down the motor to a low speed, and then it need to stop when the next signal from the NPS hall element arrive.

I am a little suppriced by the fact, that the upper stop and lower stop of the needle are made with a distance of 180 degrees. I think I read somewhere, that you like to have the lower stop just a bit later than the hook have catched the upper thread, so the needle eye levels with the needle plate surface in upwards direction. I supposed that the upper stop was at max height of needle, but it may be that it is at max height of the take-up lever and then it may be close to 180 degrees.

Anyway, I wish that you one day will get a speed control like me with a pedal force sensor. My show off is here: https://leatherworker.net/forum/topic/86489-do-you-like-this-speed-control/

[Pterytus]

You are right, this time-needed-to-slow-down issue came to my mind as well. Maybe the controller DOES learn the exact degrees of the machine and determines when to begin slowing down in order to stop at the desired position - which would make sense, although a little more sophisticated software-wise than just stopping at the signal. With my deliberately slow machine it would not make that much of a difference, I think.

Well, the sensor-chips inside the sensor-module Are 180° offset (see picture above). However, if the controller DOES learn the number of motor-revs needed to make one revolution at the machine, it actually COULD stop earlier or later. And you would want it the way you described and not exactly half a revolution offset.

The German manual to my JM-822 is not very helpful (baaaad translation and just a few words as description) but I think there is a menu item to adjust the TDC and BDC needle position. Up to now I did not dare to change these settings ;-)

But now that the NPS seems to work it might be worth a try.

By the way: Does any of you guys happen to have an ENGLISH manual for the Aerostar JM-822?

I think that might clarify some of the menu items - the combination of two bad translations should be better than just one, right? :-D

[dikman]

Pterytus, as I mentioned the "heel down" operation on mine is intermittent so not a lot of use. An NPS is doubtless great if you're doing high speed sewing but as Constabulary has re-iterated if you're slowing slowly then there is little to no benefit, and I think it's a safe bet that many on here sew their leather fairly slow. The whole idea behind fitting speed reducers is, after all, to try and tame the beast, so to speak.

As I said before it's been an interesting experiment so thanks for posting, it obviously works for some servos, just not mine.