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Author Topic: Am I loosing Steps, and what should I do  (Read 13995 times)

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Offline g21

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Re: Am I loosing Steps, and what should I do
« Reply #20 on: July 08, 2016, 08:11:50 PM »
This machine has no jibs, is all linear slides. would not hurt to check though but as OP mentioned, it happens on al axis.

Do you have access to a spare USB board in the machine to try? Tried different USB cable (shielded)?

What accel / decal settings do you have set now when this happens?

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #21 on: July 09, 2016, 12:44:28 PM »
Thanks for all the help on this so far guys. much appreciated it

I will do all the tests you recommend next week and feedback. While Im spend the day looking over it, is there anything else you recommend checking/doing/applying etc while Im tinkering

Re: Am I loosing Steps, and what should I do
« Reply #22 on: July 09, 2016, 08:02:26 PM »
Surprisingly nice looking construction. Ferrules on the wires is very good. Drives should have been mounted with heat sinks vertical but my Leadshine drives don't produce much heat. I see a toroidal power supply transformer which is good, but where are the filter caps located? Hard to see how the grounding is done. You should not be concerned about earth grounding. That's a safety issue if not connected but not a control issue. The way the grounding is done inside though is very important. All grounds from every device, circuit boards, drives, motors, etc. must all come back to one ground bus by individual conductors. If any ground wire is connected to multiple devices that is bad. It is hard to tell if any wiring is shielded cable. Cable shields if they exist should only connect at one end, typically at the panel ground bus. However if they are already connected to the case of a device like a motor that is grounded to the frame then they should be insulated from ground at the panel end. If cables for devices like limit switches, signal wires to drives and such are not shielded they should not be bundled with spindle or stepper motor wires but should be separated as far as possible. Last thing. The USB cable may have a shield connected at both ends. The PC has a ground wire to the power source, and the machine has a ground wire to the power source, making a rather non-obvious ground loop that often causes problems.

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #23 on: July 10, 2016, 04:27:53 AM »
Hi Gary,

Thanks for the reply

The pictures I posted are of all the power and control electronics, so I would say there is no input filtering. Ive read that the design of this machine was based around chinese voltage which is around 220v, while the UK is more around 240v / 250v. So as G21 mentioned, the drives dont like over voltage. Could not having a filter circuit inplace therefore be part of this overall design error?
If so, could I get a filter PCB made up, would it just be a capacitor and resistor setup?

I also do not see any specific single gounding junction, so I will need see if I can get my head around that. When you cable shields, do you mean the flexi steel cable cable protection inside cutting area of the cnc or actual EMI sheilding. If the latter....there is no. And the flexi steel cable protection isnt well done (I.E: it dosnt ground at the ends as it still has the PVC wrap on it inside the connection)

I think the USB cable has a clip on ferrite at each end....is this enough

Would it be worth me buying a bunch of ferrites and putting them on then driver wires etc?

I will check on the PC grounding

Offline g21

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Re: Am I loosing Steps, and what should I do
« Reply #24 on: July 10, 2016, 06:55:08 AM »
Hello Rush,

What design error are you talking about? So far we have not yet determined if there is a design error or not.

A filter on the secondary AC power supply (after the transformer) could help reducing spikes and ripple on the AC. You have not answered my earlier question: what is the AC voltage on your drives? You need a multimeter set to AC and measure the power supply lines for your drives with the machine staic and with the machine running.

If you have access to a scope, you could see what how the power supply for the drivers looks like. Also the power supply for the USB card might need to be checked, this appears to have its own power supply on board so a clean AC input is desired although it appears the card has some capacitors on board. Checking this power supply might help also, a scope will tell you if you have a 'dirty' power supply or not.

Ground wiring is quite simple, every component needs to be grounded once and to one common point. Where this common point is or which part of the machine this is (could be the entire frame) is not important but there can only be one connection from the drives to this point. Since the drives do not have a separate ground wire, I assume the frame, or the metal enclosure I see in the picture is the ground and there is one wire from the metal frame to the yellow/green ground wire. All seems to be correct but is worth checking for lose or bad connections.

Shielded wires should have a ground connection only on one side of the wire, quite simple.

I would start with measuring the power supply lines to the drives and the USB card first. See what the AC voltage is and if you have a scope, see if they are clean.

The spindle drive is connected directly to the AC lines at 220V? (measure the voltage to be sure) If so, I would disconnect the spindle drive from the power supply lines and run the test again, this eliminates the spindle driver and spindle motor from the problem.

Let us know what you find.
Re: Am I loosing Steps, and what should I do
« Reply #25 on: July 10, 2016, 09:30:44 AM »
Russ,
I didn't realize your drives were AC powered, I was thinking the trandmsformer was for a DC power supply which would have needed filter caps.
The shielding I was speaking of is cable shields. If your machine has cable carriers to the moving parts and they contain signal wires along with motor cables and neither are shielded that could be a problem.

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #26 on: July 22, 2016, 03:41:31 AM »
Hi All,

Sorry for the delay in getting some data back.

So I have carried out a series of test, mostly concentrating on the Z axis, but the issue is present on the X and Y as well.

Firstly, I measured the voltage at the main input, this was 248 - 249v
Next, the voltage going to each driver was 68v (There seemed to be no drop under load)

So I stripped out the spindle driver and re-ran the position test. Work Piece Zero went from Zero to -0.7969mm (which I think is what you class as gaining steps??)

Next, I stripped out the motor driver that drives the 4th axis (not used it yet!!), as well as disconnecting all leads that go to the front panel.
Re-Ran the test and Work Piece Zero went from Zero to -1.4781mm (which in machine chords was -217.3669 started and finished at -218.8450)

Final Test was pretty much down to bare minimum. I stripped out all the drivers except the Z axis. Removed all power lead not in use. Disconnected X and Y Limit and Home switch (kept Z connected)
Re Ran Test and Work Piece Zero went from Zero to -0.8206mm







Below are just some extra photos I took of the electronics if of any help





Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #27 on: July 22, 2016, 03:44:00 AM »
By the way, I do have a oscilloscope.....but embarrassingly, I don't really know how to use it. Never the less, I gave it a go and connected to the power in of the motor drivers (with the neg lead to the neutral), then twiddled a few knobs and pushed a few buttons, and this is the best I could get??

Re: Am I loosing Steps, and what should I do
« Reply #28 on: July 22, 2016, 10:20:45 AM »
Don't like to keep going on but being a mechanical engineer and I'm sure any problems with the electronics would be a thread going through this design of CNC and highlighted on the web. You never said the make of your machine however I looked on the web and decided it was a Chinese SVM1. looking at the specifications it does not have slide adjustment as you told me earlier in your thread  however the specification does state this.

GAS SPRING COUNTERBALANCE DESIGN
To counter balance the machine head to provide smooth Z axis movement and prevent the head from dropping when the machine is powered down, a heavy duty gas spring is installed. This also reduces the work the Z axis motor has to do when lifting the head.


I still think this is the problem with your machine as I recently repaired a similar Chinese machine with a new gas spring as he kept losing steps due to over run as the gas strut was not assisting the slow down and change of direction of the Z axis. The main problem the user was having was every time he put a new component in the depth was a little deeper than the last one. replacing the gas strut solved the problem.
Jim

 

Offline russh

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Re: Am I loosing Steps, and what should I do
« Reply #29 on: July 22, 2016, 10:40:24 AM »
Hi Jim,

This is the SVM-2 model, but has the same gas strut. Its based on (I believe uses the same castings) the old Mikini, but with updated screws and motors, and a complete electronics system overall as the old mikini had many a problem.

I understand your description of the issue you had, but Im gaining steps, not loosing. So rather than the Z ending up deeper and deeper after every run.....Mine is ending up higher and higher. Maybe the gas strut it pushing the head up to much, although that would be surprising.
The other point is this issue is also on the X and Y axis
« Last Edit: July 22, 2016, 10:46:41 AM by russh »