Electronic Lead Screw Project

[ZanParticipant @zan]

In addition any lost motion will present itself as a tiny tiny extra cut on the trailing flank It is also reminiscent of the clough42. Calculations for floating point calculations within the code

[Robert Atkinson 2Participant @robertatkinson2]

Posted by Phil Grant on 07/12/2019 10:03:14:

I have a question about the type of stepper motor to use for this application, why is the servo option considered to be better?

My understanding is that a servo with feedback is Ideal where positional accuracy is required, say a cnc axis control.

This application requires synchronisation between the spindle and the leadscrew if steps are missed due to external factors then the synchronisation is lost and adding steps on will not recover that synchronisation between the spindle and leadscrew.

I would think spending extra on a more powerful stepper motor would make more sense leading to no missed steps in the first place.

Or have I missed something?

You are correct that if the motor is large enough and properly set-up then closed loop should not be required. The advantage of closed loop is that it corrects for any lost steps. This keeps the positions correct to the end but would not correct any surface finish issues caused by the missed steps. A correctly sized and set-up open loop motor that does not miss steps is better than a closed loop one that does but corrects. These units are not strictly servo systems, they are steppers with monitoring and automatic correction.

Edited By Robert Atkinson 2 on 07/12/2019 11:08:04

[LimpetParticipant @limpet]

From what I understand ( I could quite easily be wrong) as Robert says if the stepper is large and accurate enough a closed loop is not required however bearing in mind that most? of us are not prepared to buy industrial quality motors and are probably not of that standard. As the spindle encoder is calculating position ever milli second or so (if I remember right from the video) the servo motor is checking position at each calculation and adjusting if required whereas a stepper motor could (like a servo) miss a step or two – through additional torque required through cutting forces on a tougher spot in the material – the servo will correct the small amount on the fly while the stepper will compound the error to the end of operation.

Lionel

[blowlampParticipant @blowlamp]

Having converted my Denford Starturn 8 CNC lathe from NEMA 34 to a 24 sized closed loop stepper system, there is no way that I would go back to a conventional stepper setup.

I find many improvements, such as faster top speed, the system is far smoother with virtually no mid-band vibration and has better acceleration & deceleration, which is vital if your lathe varies its speed when a heavy cut is applied or removed. Also, if steps are missed such that the closed loop can not recover the situation, then a fault condition will cause the driver to halt and send a fault signal back to the ELS (if it has such a facility to acknowledge) or the CNC controller.

I couldn't personally live with the idea of lost steps being acceptable, even if only a few, because that would certainly not work when we're talking about repeatable work, particularly on diameter with a CNC lathe.

It's good to know your machine is maintaining correct position and will do so all day. It gives peace of mind compared to my previous experience whereby there was an uncertainty about parts reliably coming out to size.

Martin.

[Roy VaughnParticipant @royvaughn26060]

Thanks for that insight Martin, not worth potentially spoiling the ship for a h'p'orth of tar.

Re the motor controller, is it always necessary to set it up from a PC or are they normally supplied pre-configured? I'm thinking particularly of the hybrid stepper kits from Stepperonline?

Roy

[blowlampParticipant @blowlamp]

Posted by Roy Vaughn on 07/12/2019 12:37:19:

Thanks for that insight Martin, not worth potentially spoiling the ship for a h'p'orth of tar.

Re the motor controller, is it always necessary to set it up from a PC or are they normally supplied pre-configured? I'm thinking particularly of the hybrid stepper kits from Stepperonline?

Roy

For almost all applications (99% I would think) they are ready to go. My understanding is that the driver constantly monitors & updates its output 'on the fly' to best suit the current operating conditions – I believe that is why they are based around a very powerful processing chip.

Martin.

[Robert Atkinson 2Participant @robertatkinson2]

I did say "and correctly set-up" open loop system. Stepper systems appear very simple but actually require quite a lot of care to get optimum performance. A closed loop system may well hide much much of this from the user. A closed loop sytem that is missing steps will be out of phase because it can't correct until a step is missed so best case will be at least one step "behind". More sophisticated closed loop controllers can auto-tune the system settings but it's not clear to me if the cheap systems can do this. Correction for lost steps does not have to be done by the stepper driver. If an encoder is fitted to the leadscrew the ELS controller can monitor for lost steps and correct accordingly. One thing that can make a big difference to stepper motor performance in this type of application where resonances are not constant is an inertial damper. Basically a flexibly mounted mass on the motor shaft. https://www.phytron.eu/products/mechanics-equipment/dmp-20-29-37-inertial-damper-for-stepper-motors/

Robert G8RPI.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by blowlamp on 07/12/2019 12:18:17:

[…]

I find many improvements, such as faster top speed, the system is far smoother with virtually no mid-band vibration and has better acceleration & deceleration, which is vital if your lathe varies its speed when a heavy cut is applied or removed. Also, if steps are missed such that the closed loop can not recover the situation, then a fault condition will cause the driver to halt and send a fault signal back to the ELS (if it has such a facility to acknowledge) or the CNC controller.

[…]

.

Grateful if you could clarify something for me, Martin

Does the closed-loop control things at the micro-step level, or only full steps ?

MichaelG.

[blowlampParticipant @blowlamp]

Posted by Michael Gilligan on 07/12/2019 14:24:20:

Posted by blowlamp on 07/12/2019 12:18:17:

[…]

I find many improvements, such as faster top speed, the system is far smoother with virtually no mid-band vibration and has better acceleration & deceleration, which is vital if your lathe varies its speed when a heavy cut is applied or removed. Also, if steps are missed such that the closed loop can not recover the situation, then a fault condition will cause the driver to halt and send a fault signal back to the ELS (if it has such a facility to acknowledge) or the CNC controller.

[…]

.

Grateful if you could clarify something for me, Martin

Does the closed-loop control things at the micro-step level, or only full steps ?

MichaelG.

 

 

 

 

Michael, the motors have a 1000 line encoder fitted at the rear of the motor and are connected back to the driver in a quadrature configuration, thus giving 4000 pulses per turn of the motor. The closed loop circuit can electronically work up to and maintain position of that 4000 figure.

Many of these drives allow micro-steps into the 40000+ steps per rev region, but I would imagine this more of a marketing feature than of any real world value.

 

Martin.

 

Skip to the 7 minute mark to see the 'wrench test'.

 

Edited By blowlamp on 07/12/2019 15:02:39

[Michael GilliganParticipant @michaelgilligan61133]

Posted by blowlamp on 07/12/2019 14:58:49:
.

Michael, the motors have a 1000 line encoder fitted at the rear of the motor and are connected back to the driver in a quadrature configuration, thus giving 4000 pulses per turn of the motor. The closed loop circuit can electronically work up to and maintain position of that 4000 figure.

[…]

.

That’s the important bit … Thanks

MichaelG.

[JimmehParticipant @jimmeh]

Posted by Phil Grant on 07/12/2019 08:02:16:

I bought my kit (just a stepper motor and driver) from Stepperonline, they were quite cheap and deliver from different countries and they have some offer codes at the moment (I have no affiliation with them)

LINK

Thanks for the link Phil. The website offers some good advice for complete noobs like myself for choosing a suitable power supply. I also like the fact that all of the data sheets and tech specs are available. 

I'm hoping the 4.5Nm nema 24 I've just ordered can be squirrelled away in a hollow under the headstock of my WM250vf.

Edited By Jimmeh on 07/12/2019 20:36:56

[ZanParticipant @zan]

Here is the information from Tony Jeffree regarding stepper motors referred to in his cnc conversion. I have photographed and erased unrelated parts and numbers the images. It is part of a series he produced about converting a Taig mill to cnc in MEW Dec. 2006 I have discussed with Neil about presenting this info.

He deals with basic info and information simple methods how to assess the torque amp drive select stepper motors

I’m not posting the info here, but you can view it in my album called ….. Leadscrew…….

Servo or stepper?

Regarding blowlamp and his valuable info regarding servo motors, he I think is spot on with regard to full cnc esp on the cross slide fir maintaining accurate diameters. I do not think this is so important for the leadscrew alone. Time will tell. I have spare steppers, and driver systems and I will test them out first and replace with a servo if there seems to be a problem

[Michael GilliganParticipant @michaelgilligan61133]

My encoder arrived safely today

I checked the tracking … Despatched by the seller on 05-Dec, it arrived at Heathrow and was passed to Royal Mail on 13-Dec

MichaelG.

[ZanParticipant @zan]

Mine arrived a week ago, dispatched on dec3. That was quicker than expected!

[Michael GilliganParticipant @michaelgilligan61133]

You must have just beaten the [U.K.] Christmas postal chaos

MichaelG.

[LimpetParticipant @limpet]

Still waiting for mine I'm expecting it mid Jan

Lionel

[Roy VaughnParticipant @royvaughn26060]

Ordered all the bits end-November and nothing took more than 10 days or so to get here.

Roy

[Dennis RParticipant @dennisr]

Mine was due anywhere between Jan 2 and Feb 12, but arrived early on Dec 18, very fast service.

Dennis

[dcostaParticipant @dcosta]

Hi Phil,

just finished assembling the components on the board and I don't think I made any mistakes.
However, if possible, I would like to test the assembly before moving on. Can you, please, tell me if there are any tests I can do to make sure I haven't screwed up?

Thanks in advance
Dias Costa

Edited By dcosta on 28/12/2019 19:10:00

[Phil GrantParticipant @philgrant54580]

The first test I did was to test the voltages on the pins that supply the TI board are correct.

To do this plug in the 5V supply to the power connector without plugging the PCB onto the TI board and test the voltages on the 5V and 3.3V pins.

Once this is done and the voltages are correct you should then be OK to plug it into the TI board.

If you have flashed the TI board and have a display connected then the display should work when you apply power, if not then a multimeter or oscilloscope may be needed, Clough42 has a YouTube video on what should be seen with an oscilloscope.

Good luck,

Phil

[ZanParticipant @zan]

Got mine assembled n tested yesterday, did the ti board today.

Removing the switch covers was a nightmare!

All works with encoder in the drill giving correct rpm , but as yet I can’t get the stepper turning. No scope to see what’s happening at the outputs. I’ll have to check n recheck as well as checking stepper system with the arduino

so when it’s turning slowly I can then try voltages on the output pins with an analog meter , my digital is too slow and prob remove the micro steps in the ti settings fir a slower step n longer pulse. Then I’d be stumped

[Phil GrantParticipant @philgrant54580]

Zan,

Have you got the logic level the right way for the stepper driver module, I can't remember which way they should be off the top of my head.

Have you connected with a common ground or a common 5V?

Phil

[ZanParticipant @zan]

Thanks Phi I think there’s a mention about this in the software loading video, l I’ll check that later but I used all the same connections as I did from the arduino which worked a while back , I think I’m common 5 v so by rechecking with the arduino I’ll be able to measure the voltages

by the way, the display connector pins projection under the board fouls and shorts onto one of the small jumpers on the ti board if it’s pushed fully home So don’t push it in. I’ll add some insulation here. This stopped the display working , interestingly, clough42’s board is inverted compared to ours with the power socket where our display connector is.

[Phil GrantParticipant @philgrant54580]

Yes I noticed that I had the connectors the opposite way around on my design, that's one reason why I used an surface mount power connector to stop it fouling the pins underneath.

If you trim the protruding pins that stick out of the bottom on the display connector it shouldn't foul anything, maybe I should update the info document.

To check the wiring of the stepper driver check out Cloough42 videos, they can be wired either way and you arduino setup may have been wired tho other way and worked fine but the ELS may need to be wired the other way, i will check my wiring later.

Phil

[Phil GrantParticipant @philgrant54580]

Yes it looks like it a common 5V with switched grounds

Link to wiring plan

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