Using DMM 750W servo as spindle motor

[Richards]

Marty, those are excellent questions. I can't speak yet for operational use on my Taig Mill because I'm still bench testing the DMM DYN4 750W driver/servo on the test bench. But I can answer these questions:

Configuration: The wiring diagram from DMM is easy to follow. When followed exactly, the servo is under user control.

Creeping: That was harder to solve. Some of my entries on this thread addressed that problem. My last post details my solution. Basically, I only enable the servo when the Acorn asserts either a Spin Forward or a Spin Reverse command. The default configuration of the DMM DYN4 servo is to spin forward when the Enable line is NOT grounded. Even at 0V, the motor would creep. The motor reverses when the Direction signal is grounded. I wanted to use Acorn's Spin Forward and Spin Reverse Signals. I tried using the Spindle Brake signal as an enable signal, but there was a short delay when the servo would creep. It was easy enough to use an Acorn Output to control servo enable, but that would require insert code into any program to use my M-codes. I didn't want to do that. Using the CLICK PLC solved my problem. Using three relays would also work. One relay for Spin Forward. One relay for Spin Reverse and the coil of the 3rd relay turned whenever either of the other two relays activates. That's the logic in the CLICK screen shot that I posted.

Encoder: The DMM wiring diagram includes a schematic for wiring the DYN4 encoder directly to the Acorn. It works; however, unless the servo drives the spindle at 1:1 ratio, or an exact multiple 2:1, 3:1, etc., the user would probably need to add an external encoder.

Displaying RPM correctly: Yes. I used a digital tachometer to cross check the RPM display by Acorn and actual. They match.

Low End Torque: Unknown. I'm still bench testing.

[martyscncgarage]

Marty, those are excellent questions. I can't speak yet for operational use on my Taig Mill because I'm still bench testing the DMM DYN4 750W driver/servo on the test bench. But I can answer these questions:

Configuration: The wiring diagram from DMM is easy to follow. When followed exactly, the servo is under user control.

Creeping: That was harder to solve. Some of my entries on this thread addressed that problem. My last post details my solution. Basically, I only enable the servo when the Acorn asserts either a Spin Forward or a Spin Reverse command. The default configuration of the DMM DYN4 servo is to spin forward when the Enable line is NOT grounded. Even at 0V, the motor would creep. The motor reverses when the Direction signal is grounded. I wanted to use Acorn's Spin Forward and Spin Reverse Signals. I tried using the Spindle Brake signal as an enable signal, but there was a short delay when the servo would creep. It was easy enough to use an Acorn Output to control servo enable, but that would require insert code into any program to use my M-codes. I didn't want to do that. Using the CLICK PLC solved my problem. Using three relays would also work. One relay for Spin Forward. One relay for Spin Reverse and the coil of the 3rd relay turned whenever either of the other two relays activates. That's the logic in the CLICK screen shot that I posted.

Encoder: The DMM wiring diagram includes a schematic for wiring the DYN4 encoder directly to the Acorn. It works; however, unless the servo drives the spindle at 1:1 ratio, or an exact multiple 2:1, 3:1, etc., the user would probably need to add an external encoder.

Displaying RPM correctly: Yes. I used a digital tachometer to cross check the RPM display by Acorn and actual. They match.

Low End Torque: Unknown. I'm still bench testing.

Did you order the DYN4/AC Servo from DMM specifically for both spindle and positioning use? I ask that because that drive has special firmware.
The creep can be eliminated by using the enable input. See the attached diagram from DMM for combo spindle/position use.

Given the small nature of your machine, you will probably be running the AC servo at higher speeds on small parts. I don't think you'll have a torque problem.

You are correct about the encoder. Most users are trying to run the spindle at 1:1 so they have the benefit of using the encoder output for rigid tapping, CSS, threading etc.

I know you are versed in PLC use. Most typical DIYers are not. DMM's combo spindle/position solution seemed like a good idea. I'm just wondering how many successfully implemented it with satisfaction.
Marty

[Richards]

Marty,
I'm using a DMM DYN4 750W driver/servo that was purchased to drive an axis (X, Y, or Z). I was thinking of purchasing another DMM DYN4 750W or 1000W driver/servo as a spindle motor, but DMM responded with a schematic that showed how to connect the driver/servo that I already had as a spindle motor. Except for the "creeping", it works as expected per the DMM schematic. After I mount the motor to my Taig, I hope to do tapping. Having the motor's shaft creeping outside direct control from the Acorn in a tapping operation seems to be a red flag item.

After thinking about using relays instead of a PLC, I came up with this simple two relay solution. Any small DPDT 24VDC coil relay should work. I like the 10A type that plugs into a DIN rail socket for easy maintenance. (About $15 to $20 each with socket.) I've included suppression diodes that will protect the Acorn against surges when the relays are turned off.

[cncsnw]

There are already relays connected to the Acorn PLC outputs. It should only take a couple lines of logic in the Acorn PLC program to implement what you need here.

Unfortunately, the Acorn PLC program tries to include far too many features at once, and as a result can be needlessly difficult to untangle when you want to make simple changes.

[Richards]

CNCSNW,
The problem is that the enable line needs to be cut (floating) and the dir line needs to be grounded, i.e., DTDP instead of STDP. When either Spin_forward or Spin_reverse activates, those signals pull the DYN4 signal low (on Dir, Spin_forward is NOT connected to the DYN4 drive). To stop the creeping, the DYN4 Enable signal must be pulled low when the motor is stopped and left floating when the motor is running. The DPDT relays do that. I don't see how a single STDP relay used on the Acorn could perform both functions at the same time.

[cncsnw]

If I were doing it, I would gut most of the existing spindle brake, SpinFwd, SpinRev, G540Spindle vs. StandardSpindle, etc. code and start with something clean.

But, supposing you want to start with what Centroid gave you; supposing you previously defined Acorn PLC outputs to be "SpinFWD" and "SpinRev"; and supposing you want to have new outputs that are "SpindleDisableOut" and "SpindleReverseOut".

1) Redefine "SpinFWD" and "SpinREV" to be memory bits.
2) Name the outputs SpindleDisableOut and SpindleReverseOut.
3) Add the following lines at the bottom of StandardSpindleStage:

Code: Select all

IF !(SpinFWD || SpinREV) THEN (SpindleDisableOut)
IF SpinREV THEN (SpindleReverseOut)

On reflection, our new "SpindleReverseOut" is identical to the previous "SpinREV", so that could just be left as it was.

[Richards]

cncsnw,
Thanks for the suggestion. It shows what can be done if we look under the hood. The problem is that once we modify system code, someone has to maintain those changes every time Centroid changes hardware or software. That's not a problem for programers, but it can be a really big problem for end users who's know G-code and only G-code and want to plug and play new hardware and new software. That's why I've been looking for a way to use the DMM DYN4 drive/servo using only factory settings on the Acorn side. Using two relays costs about $30 but it only requires point to point wiring. Once the wiring has been done, that's it - job finished. If a relay burns out, it's a $10 repair. A CLICK PLC is similar. The PLC is preprogrammed and shipped to the customer with wiring instructions, i.e., connect Acorn Out3 N/O to CLICK terminal #1 using wire #101. The user doesn't need to know anything about programming a PLC, just as an Acorn user doesn't need to know how to do anything more than follow Centroid supplied schematics.

[rangerboy347]

cncsw
i have the same setup and i'm using the brake output so the spindle doesn't turn but when i command m3 the spindle goes backwards first then forward. but if i click the button for forward (m3) it goes forward without going backwards first. and same for button reverse (m4) any ideas on what if causing this? its not a problem until i want to rigid tap.

[cncsnw]

I am not familiar with any "button for forward (m3)" or "button reverse (m4)", so it is hard to guess what your issue might be.

If you are looking for free advice, you should start a fresh thread on this forum, and include a report from your system.

If you would like to hire my help, e-mail me a report from your system and the most coherent explanation of the sequence you can manage (using terms like "MDI" or "running a CNC program" or "pressing the green spin start key on the VCP while in Manual spindle mode with the CW direction selected", etc.).

[martyscncgarage]

cncsw
i have the same setup and i'm using the brake output so the spindle doesn't turn but when i command m3 the spindle goes backwards first then forward. but if i click the button for forward (m3) it goes forward without going backwards first. and same for button reverse (m4) any ideas on what if causing this? its not a problem until i want to rigid tap.

As Marc mentioned, please start a new post and follow this post. We can't "See" what you "See"
Let us know if you are trying to use a DMM AC servo for a spindle motor.
With more information we can try and help.

Marty