[JeffS]

Hello All,

I am in the process of figuring out how to tune my stepper motors. Holy cow, that is a confusing process (no offense, Tom). My motors are jogging just fine and I am jogging to test my limit sensors, which are inductive. While using KMotionCNC to jog, I will sporadically get the following error:

KMotionDLL: Read Failed - Auto Disconnect.

This forces me to re-enable my drives in KMotion, however I have to go through the Step Response test for each motor before I can actually jog them again in KMotionCNC. This often happens right after a jog command, but sometimes after sitting untouched for a few minutes. I assume that I am doing something incorrectly, or have failed to do something beforehand. I simply don't know what to do at this point. Any help would be appreciated.

Also, if anyone out there would care to walk me through the tuning process I would greatly appreciate that!!!!! A significant request, I realise.

Cheers,
Jeff

[TomKerekes]

Hi Jeff,

Regarding Read Failed: You might have some power supply or grounding issue. Can you describe how you are powering KFLOP? Is the +5V supply isolated from earth GND? How are the drives powered and Grounded? The Spindle? Does it ever occur with the spindle and motor power supplies turned off?

The Step Response Screen is capable of downloading configurations for testing axes. But the main goal is to eventually create a C Program to do all the configuration and enable all the axes and drives. After that KMotion.exe and the Step Response Screen is no longer needed. Everything can then be configured and enabled by simply running the C Program. The C program can be assigned to a button in the application. For Mach3 it can be assigned to the Reset Button. For KMotionCNC it can be assigned to a User Button.

HTH
Regards

[JeffS]

Hi Jeff,

Regarding Read Failed: You might have some power supply or grounding issue. Can you describe how you are powering KFLOP? Is the +5V supply isolated from earth GND? How are the drives powered and Grounded? The Spindle? Does it ever occur with the spindle and motor power supplies turned off?

Thanks for responding, Tom.

The KFLOP is powered by a PC power supply (switching) and should be properly grounded as I have the earth ground (neutral line of 240VAC house supply) bonded to the electrical enclosure that the power supply is in, and the the power supply case is electrically bonded to the enclosure. The drives are powered by a ProtoPlant 3000 which is fed from two 24VDC supplies in series. All are bonded to the enclosure. The spindle is powered by a VFD, all bonded to the enclosure. I use a contactor to control AC to the VFD, and a relay to control power to the PC power supply. In this way, I can power the logic, stepper power and stepper drives, and the spindle all independent of one another. When this problem was occurring, the drives were obviously powered, but not the spindle (contactor open). I will have to test to see if it occurs when the drives are not powered as I cannot recall if it did or not.

I have done my best to separate data lines from power lines, and use shielded cables (bonded to the enclosure) for everything but the ribbon cable from JP7 to the drives. I do not know if standard USB cables are shielded or not. I have thought that perhaps the fluorescent lighting in my shop may be the culprit here as the USB extension cable I am using passes close by, though I have taken care to ensure that it does so at right angles to the tubes so as to minimise any EMI/RFI. Could the USB extension cable be the culprit?

If necessary, I can provide the electrical drawings (wiring diagrams) that I have created for this machine. I am not a pro, but they are quite detailed. If you need to see them, let me know and I will post them.

Cheers,
Jeff

[TomKerekes]

Hi Jeff,

Are you familiar with the concept of a Ground Loop? Its when there are multiple connections between different Grounds. This can result in Gnd currents taking unexpected paths. PC Power Supplies are not really a good idea because they usually have a connection between the DC Gnd and Earth Gnd. You would probably be better with a small +5V@3A isolated (no connection from the DC Gnd and the case or Earth Gnd).

What types of Drives do you have? Are they opto isolated? I'm not sure what you mean by the 24VDC supplies are "bonded to the enclosure". Is the 24VDC Gnd also connected to the case and Earth Gnd. If so that might not be a good idea.

You are using a USB extention cable? How long is it? Check the shield resistance from end to end. It should be less than 2 ohms.

Regards

[JeffS]

Hello Tom,

The bonding refers to the chassis of each power supply being electrically bonded to the main electrical enclosure that houses everything running my CNC machine (minus the PC of course). The main enclosure is then electrically bonded to earth ground (the neutral line of the 240VAC supply to my house). This is for safety. If anything that is supplied with mains current shorts, it will short to its particular enclosure, thus to the main enclosure, thus to earth ground and not through a person.

I did a continuity test and the DC ground from the PC power supply is not electrically connected to its enclosure or the main electrical enclosure so far as I can tell. The output GND of a switching power supply would not normally be connected to earth ground, would it?. I also tested the ground plane of the KFLOP circuit board and it is isolated from earth ground with the PC power supply and the USB connected (but not powered). I hope this means that the DC GND and the earth ground are, in fact, isolated from each other.

The stepper drives that I am using are microstep JK1545's. They are opto-isolated. They are electrically bonded to earth ground by virtue of the fact that they are supplied by a ProtoPlant Power Supply Multiplier that is fed from two Mean Well SE-350-24 power supplies that are in series. The Mean Wells have an earth ground connection (required) and bond their DC output to it. This is passed through the ProtoPlant. These connections are made by the respective manufacturers and I have followed their installation instructions to the letter. The vendor that I purchased the CNC machine (without a controller) from was XZero. When I bought it from him 2 years ago, George (the owner) told me that the KFLOP, JK1545's, and the Mean Well's were commonly installed in his machines and his customers were happy. I added the ProtoPlant because it shunts any back-EMF from slowing steppers to a dummy load (power resistor) so that the reverse polarity doesn't destroy the drives. This is all probably moot as the drives are opto-isolated, but I wanted you to have a fuller picture.

Lastly, the USB extension cable has a DC resistance of 0.7 Ohms. Could its proximity to the fluorescent lights be the issue? The cable is shielded, so it really shouldn't be. I used to install STP data cables next to such lights in data centers all the time and never had an issue.

Is there any other testing that I can do?

Thank you so much for your help! I really appreciate it. I will probably be back here for help with the tuning as well. I haven't done anything like that since college.

Cheers,
Jeff

[JeffS]

On a different subject Tom,

Here is where I really show how much of a CNC Newbie I am:

With regard to tuning the motors, I am following your help files that describe how to configure the KFLOP with the Mach3 Plugin (Mach3 Plugin + KMotion). Step 3 states, "Follow the normal procedures to use the KMotion Executive program to configure and tune all of your motor axes". What exactly are 'all the normal procedures'? Also in step 3 it states, " ... test and tune for correct operation using the Step Response Screen as well as Console commands". I don't know what 'correct operation' should look like with respect to the Step Response Screen and Console commands.

If you, or anyone else, could clarify the tuning process I would be grateful. I am just not sure how to tune the motors, determine if the tuning is optimal, and provide those parameters to Mach3.

Thank you for your patience, and your assistance. Both are greatly appreciated.

Best Regards,
Jeff

[TomKerekes]

Hi Jeff,

Every PC ATX type of PC Power supply I have ever tested has a connection from DC Gnd to Earth Gnd. Most other switching power supplies are usually isolated. So I find it very strange that the PC Power supply is isolated as most all are not.

Something else strange is that you claim KFLOP DC Gnd is completely isolated from Earth GND with the USB Cable connected. We connect the USB Shield to KFLOP DC Gnd on KFLOP. So if the shield is connected to the PC enclosure on the PC end and the PC Enclosure is Earth GNDed then I don't see how it is possible that KFLOP is isolated.

I also don't see how it is possible for two 24V supplies to be connected in series and yet not isolated. One of the supplies would be shorted out.

Regarding the "normal procedures" for configuring your system: you have already completed (or finalizing) that to get your motors to move using the KMotion Screens.

Tuning with steppers basically involves testing higher and higher velocities and accelerations to see what the limits of your system.

Regards

[JeffS]

Hi Tom,

I haven't had the Read Failed error yet today, so I'm going to put a pin in that for a moment, if you don't mind. I would like to ask some questions regarding the Step Response Screen.

I am playing around with the settings, and have a basic understanding of the importance of acceleration, velocity, RPM, torque, etc. Or at least I think I do. What I don't know is what the graph on this screen is telling me. What are the relationships between Command, Position, and Output and what are they telling me about how I should set the tuning of my motors?

Thanks,
Jeff

[JeffS]

Hi Tom,

I have reviewed velocity, acceleration, and jerk so that I have a basic understanding of them, and where they are represented on the curve in the Step Response graph. I've played a bit to make sure that I don't lock up the motors, but that is about as sophisticated as my knowledge will let me be with this step. I am not at all sure how to set the Inv Dist Per Cycle as I am using microstepper drives that are currently set to 256 microsteps per full step. I also don't know if that is the best setting for the drive. I would like to set the soft limits as well, but I imagine that those values would be dependent upon the Inv Dist Per Cycle setting. Unless all of this is rendered unnecessary by virtue of the fact that I am using the Mach3 plug-in? Do I need to take in to account the TPI and number of starts of the ballscrews as well? I am not sure how to proceed. I would appreciate any assistance from you or anyone else who know the answers.

Thanks again,
Jeff

[TomKerekes]

Hi Jeff,

It is up to you to determine the number of stepsper inch your system has. If you can't calculate it theoretically just move a large number of steps and measure how far it moves.

Do not use the invDistPerCycle setting that is for other types of drives. Leave KFLOP operating in steps and set the resolution in the Mach3 Motor Tuning.

Regards
TK

[JeffS]

I just thought I would follow up with regard to the Read Failed error that I was getting when I first started this particular thread. Just in case anyone wants more information.

It turns out that ground loops are not likely the problem. Electro-Static Discharge (ESD) appears to be. Allow me to explain:

My CNC machine sits upon a metal table that has a thick wooden top. The table sits on anti-fatigue mats that cover the floor in my shop. I have not tested them, but I suspect that those mats are insulators. The table is grounded, as it my CNC machine frame and of course the controller. Normally, I wear a pair of Crocs (which are rubber-like and likely insulators as well) when I am in my CNC shop (not my larger shop where protective footwear is a must) as they are comfortable to stand in for long periods of time. Well, it is winter time here just outside of Toronto, Ontario in Canada and that means that the air is pretty dry. Especially when my humidifier is on the blink. Thus, the humidity levels are pretty low in my house. This means that static electricity is a problem. As we are in the middle of the winter here, the temperatures are at their lowest and the air is as dry as it can be. When I wear my Crocs, I get a shock every time I touch a lamp or a light switch to turn it on. Pretty standard. Only recently did I get a shock when I touched my CNC machine.

When I touched the machine and received a small static shock I also heard the Windows machine that runs my control software make the sound that indicates a USB connection has just dropped. The Read Failed error showed up in KMotionCNC and then a moment later Windows made the sound of a USB connection being made. So, with a few more experiences like that I determined that static shocks were knocking down the USB connection between my Windows machine and the KFLOP. I put on a good, thick pair of wool socks that are comfortable enough to wear for a long time and presto! No more static shocks, and I haven't knocked down the USB connection or seen the Read Failed error since. Now I just have to educate myself on how to prevent this a little more permanently. You see, I do understand how to take ESD precautions, However, it is extremely dangerous to be ESD safe around higher voltages such as 240VAC as the ESD precautions make you a PERFECT (absolutely couldn't be better even if you were standing in water!) conductor and increase your risk of a fatal electrocution tremendously. So, I need to do some research. In the meantime, it isn't hard to enter my lab and ground myself to the table before I touch anything else. That seems to be working for now.

I hope that this is of some use to someone. Also, thanks very much to Tom for helping me on this one. I'm still bugging him in another thread, so I thought I should put this one to rest.

Cheers,
Jeff

[Stigoe]

If I remember correctly, ESD wrist band and the like should have a 1Mohm resistor built-in to reduce the current rush when you're touching something with a high electrical potential, so it's not any more dangerous to be around 240V when being ESD safe than when not being ESD safe.

[JeffS]

The ESD precautions that I was referring to include clothing and shoes and proper flooring (which I was always told is much more conductive than that). Not just what you would do when putting a CMOS board into your PC. If I remember correctly, static electricity has a very low current and an extremely short duration which would not hurt you when it goes from your wrist to the ground the strap is connected to. With the full ESD outfit, you are grounded through the contact of your ESD shoes with the flooring. Do that with 240VAC and now you are counting on your circuit breaker to limit the time that you are receiving a shock. This shock will travel through your body from the point of contact to the floor through your feet. It only takes about 10 mA to stop your heart. Besides, who would want to work with their CNC machine while tethered by a wrist strap?

Cheers,
Jeff

[JeffS]

In case anyone is following this thread, or is curious, I would like to add an update.

I took some ferrite cores and wrapped my limit switch cables through them, my USB cable to the KFLOP, and clamped one around the ribbon cable to the KFLOP and reduced my troubles almost to zero. If I remember correctly, these cores inductively 'resist' the voltage spikes and thus dampen them. I can still knock down the USB connection from the KFLOP to the PC if I am not careful, so I use an anti-static wrist strap when I am working with my machine. Now it is seldom that I knock it down. It does still happen and I need to do more research. However, with temperatures outside hovering around -22 degrees Celsius (-7 Fahrenheit) it is pretty dry in the house. I imagine I won't have these ESD issues so badly in a few weeks.

However, if I turn on my vacuum (a universal motor, I believe) it can also drop my USB connection. I solved that problem for the most part by putting it on another circuit that is separate from my machine. It can still do it sometimes, though. I think I need to put an RFI filter on the mains connection to my machine. If anyone out there has any experience in this area, I would appreciate some advice.

Cheers,
Jeff