Mysteriously Faulting Stepper Motor, Closed-loop

Mysteriously Faulting Stepper Motor, Closed-loop


Hi everyone, welcome back. My name is Kent, and today, we’ll look at
a problem that I had with my CNC mill conversion [Precision Matthews PM25]. Despite their relatively small size, I’m successfully using 280 oz-in NEMA 23 closed-loop three-phase stepper motors. [Leadshine ES-M32320] Being closed-loop, the driver knows if the
motor is out of position and steps are not lost. Also, disturbances introduced by heavy machining can be corrected. Their PID control loop also adjusts current
to the motor, as needed, to minimize error, consumed power, and heating. The performance of the CNC conversion has been great with rapids in excess of 300 ipm. Normally, I limit rapids to 50 or 100 ipm
because the base is tipsy. The closed-loop driver will fault if the motor position error grows beyond a limit. The way I’ve wired the CNC conversion, the
faulting of any axis is treated as an emergency stop and shuts the system down. Occasionally, the x-axis would fault, for
no apparent reason. This was a rare event, and hard to associate with a cause. One day, while touching off a part, the x-axis faulted, causing an emergency stop. Like watching a wreck, without power, the
head came down, and rested on top of the delicate Haimer probe. Perhaps this behaviour should be changed to turn off the spindle and stop motion, but leave the other axes enabled. This would simply require disconnecting
LinuxCNC from control of the driver enable lines. Regardless, the faulting x-axis had to be
solved. Believing the x-axis maybe binding, I loosened the motor mount, but there was no binding. That horrid noise is the motor dithering,
trying all it can to get to the correct position. Turns out, the problem was in the connector. The cable on the x-axis
experiences the most motion The power extension cables have silicone in the connector, but the motor connector lack this strain relief. Without strain releif, one of the pins in
the connector was failing. The closed-loop system, unable to properly
control error was increasing current, and in turn, melting
a pin in the connector. The connector actually melted together. Someone more observant may have
noticed the discoloring of the connector. For the time being, I cut off the
connector and soldered the power wires together. I plan to eventually redo this with an industrial connector. This was a persistent not obvious problem
and I hope this explanation will help others more quickly
solve their problem, if similar. Thank you for watching and subscribing. New videos coming soon.

7 Replies to “Mysteriously Faulting Stepper Motor, Closed-loop”

  1. Check out my most recent video: https://goo.gl/Jj7cU1

    The closed-loop stepper motor was faulting without any apparent reason, I ignored the problem until a Haimer was squished. The graph shown at 0:20 is of the following-error from the stepper motor driver and shows how many steps the motor is currently ahead or behind the commanded position. At 300+ ipm, the following-error range shown in the graph is +/- 40 of 4000 steps/revolution.

  2. Intermittent problems are the hardest to find! I'm glad to see you found it. Your closed loop setup is better than the servo setup on mine. 🙂

  3. Great video Kent. I find these "aviation connectors" on Ebay to be very good. I use them throughout all my machines with alittle silicon grease. Good luck my friend

  4. Yes, those closed loop Nema 23 motors appear have more similarities to 'normal' motors than stepper motors ( UVW connection instead of 'normal' stepper a1, a2 b1and b2) (the Nema 34 differ) Those connectors are prone to be weak. Flimsy at best. Steppers would have probably saved your Haimer from crashing, due to their torque dents. I'm using a gas spring on my BF20 to keeping it up while unpowered . It also helped me increase accelaration for faster peck drilling. What ballscrews are you using? With Nema 34 steppers, i can't go any higher than 400mm/s acceleration on 70V with digital Leadshine steppers. A lower current setting actually helped me to increase the acceleration and speed. I'm using 1604 ballscrews. Thinking about switching them to 1610's to get around the nasty resonation area they are now suffering. The 4.5Nm motors couls easily push the 1610's, and i guess this is part of the failure (too large motors for the relative low load).

  5. Sir in your opinion closed loop stepper motor is best for coin design engraving.my job work size minimum 14mm and maximum size of job work 250 mm so , is it suitable for iron engraving , coin design engraving?

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