Acorn + Clearpath success stories?

All things related to the Centroid Acorn CNC Controller

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RogDC
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Re: Acorn + Clearpath success stories?

Post by RogDC »

carboncymbal wrote: Thu Feb 11, 2021 6:19 pm
Are you running clearpath power supplies?
Yes, The IPC-5 and the power distribution hub
TaylorPilot
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Re: Acorn + Clearpath success stories?

Post by TaylorPilot »

RogDC wrote: Thu Feb 11, 2021 3:53 pm I built an Avid CNC Pro 6072 with Acorn and Clearpath servos and CNC Depot S30C ATC Spindle following many of the recommendations on the forum.

The system has been performing well, just make sure to install the resistors on the Teknic control cables if required and follow proper grounding and shielding practices and use RF Filters where required.
What servos did you get? I am spec'ing out a 4x8 pro machine and want to do acorn and clear paths. I read on one of the threads in the facebook group that he had to upgrade to the high resolution motors because the 800 steps/rev models didn't allow for proper smoothing with the acorn.
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Re: Acorn + Clearpath success stories?

Post by RogDC »

Taylor,

For X & Y axis I ordered SDSK-3421S-ELN . For X & Y axis you will want the ELN or a gear reduction, the Avid drive is just a little over 1:1 ratio. Due to my space limitations on the sides of the machine for access I went with the ELN motors to save space.

For Z axis I ordered the larger SDSK-3426P-ELN, the 3421's may have been adequate but went with the larger Z motor to have more mass to keep the spindle from falling rather than install a brake system or install a counter balance or gas spring system for the 26# spindle, dust boot, dust hose, mister, and laser. On the Z axis with the 2.54 turns per inch pitch, I am not sure you would need the ELN, but I spent the extra money just in case to make sure the system would perform how I wanted it to.

The Avid Pro Z Axis does have a drag brake on the ball screw to help keep the spindle from falling. I haven't had any issue with the spindle dropping with a drive fault or system powered off. However, the spindle did drop when I removed the motor to check the Oldham coupling. Again, this was more motor than I needed for the Z axis.

The 3411S-ELN would probably be adequate for your X & Y axis, I have way more power than I need with the motors I ordered, very pleased with the performance of the motors with the Acorn.

I only have one power supply and haven't had any issues with lack of power from the power supply for the 4 motors. I'm prepped for a 5th motor for a rotary axis.

My system is overbuilt and I spent more money than required on the Clearpath SDSK motors, but for me it was cheap insurance. I spent about $400 more than going with the smaller motors on X & Y and lower resolution motor for the Z axis. No Regrets.

And select a control cabinet a little larger than what you think you will need.
Gary Campbell
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Re: Acorn + Clearpath success stories?

Post by Gary Campbell »

One more note to DIY builders.......
You will most likely not experience "Step Input Timing" errors if you connect to the DB 25 header (5v line driver signal) rather than the H5/6 Terminals (5/24v open collector signal)

This come from Teknic, but I have yet to determine if they have simply proposed this, or have actually tested it.
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Re: Acorn + Clearpath success stories?

Post by paulwall »

Here's my 4x8' success story. I was a complete novice with no prior CNC building experience with exception of some minor start/stop running operations at a previous job. I built the controller up adapting it to an existing machine platform, and though it was a lot to take on, the information is all out there, and the system worked flawless.

viewtopic.php?f=60&t=4433
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Re: Acorn + Clearpath success stories?

Post by carboncymbal »

paulwall wrote: Fri Feb 12, 2021 9:25 pm Here's my 4x8' success story. I was a complete novice with no prior CNC building experience with exception of some minor start/stop running operations at a previous job. I built the controller up adapting it to an existing machine platform, and though it was a lot to take on, the information is all out there, and the system worked flawless.

viewtopic.php?f=60&t=4433
Thanks so much for sharing. Looks great! I looked through the entire thread and may have missed it, bit would you consider posting a photo of your control panel and/or a summary of your design?

Thanks,
Clay
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Re: Acorn + Clearpath success stories?

Post by teknic_servo »

Step noise was mentioned so I thought the following information could be helpful...

I’m an engineer at Teknic and came across your comment about step input timing errors and noise interference.

The ClearPath motor inputs are optically isolated and current limited. This design provides exceptional noise immunity even in the most difficult EMI environments like plasma CNC machines and applications that use a VFD. The optical isolation hardware of the ClearPath motors provide enough noise immunity that shielded and twisted pair cables between the CNC motion controller and the ClearPath motor are not required.

You might wonder, “if the noise immunity of the ClearPath motors is so good, then why is there a possibility of getting step input timing errors and why are the termination resistors required?” Great question!

The minimum length of time for a step to be “on” is 715ns. In addition, the minimum length of time for the “off” period between steps is also 715ns. The ClearPath “step input timing error” occurs when the “on” time of a step is shorter than 715ns, and/or the “off” time between steps is shorter than 715ns.

Typically this error is elicited when one or more of the following conditions occur:

- The controller has open collector outputs and the resistors specified in the ClearPath manual are not installed correctly, or not at all. Here is a link to the fractional hp ClearPath manual:(https://www.teknic.com/files/downloads/ ... manual.pdf)
An open collector output “drives” the signal to a true logic state but then the return signal “floats” back to its false logic state. This floating nature of the open collector signal means that the signal might not be “off” for at least 715ns required between steps before the next step is sent. This behavior is often exacerbated by capacitance in the control system, whether due to long cable runs or the electrical design.

The Centroid Acorn uses 24VDC open collector outputs, so installing 10k ohm resistors across both the step and direction outputs for each axis of motion is appropriate. This resistor promptly drives the signal to an “off” state between steps. In contrast, a driven TTL signal (this is a different hardware architecture than open collector signals) is less prone to this behavior because the circuitry “drives” the signal to ”on” and then “drives” the signal back to ”off”. This type of signal is referred to as a “driven signal”.

- The controller output voltage is lower than the minimum 4VDC required for the ClearPath motor and is unable to reliably turn on the optical isolated inputs. For example, some controllers only output a 3.3VDC signal.

- The controller's maximum step pulse output frequency is higher than 700kHz, or the step pulse time is less than 715 nS. These settings are typically configurable in the controller.
(https://www.teknic.com/files/downloads/ ... om=100,0,0)

- Shared return paths for outputs. The V+ and GND wires for each controller output should travel the entire distance from the controller to the motor and then back to the controller. Some systems have limited I/O connections so the output signals go individually out to the motor, but then they share a common return path back to the controller. For example, three output signal wires could go out to the motor but then the return wires are tied together and only one return wire comes all the way back to the controller. This can cause problems related to noise immunity.

As a side note, we’ve recently reviewed the Acorn schematics with Centroid and they will be updating their schematics to include this 10k termination resistor. This should address the issue that you mentioned.

I hope this helps you and other users. If you have any other questions regarding the ClearPath motors, please feel free to use Teknic’s "Contact Us' form (https://www.teknic.com/contact) or give us a call at 585-784-7454.

Best regards,
Tom T. - Teknic Servo Systems Engineer
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Re: Acorn + Clearpath success stories?

Post by slodat »

Tom - then why not use the 5v DB25 step/direction outputs on Acorn?
Gary Campbell
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Re: Acorn + Clearpath success stories?

Post by Gary Campbell »

The ClearPath motor inputs are optically isolated and current limited. This design provides exceptional noise immunity even in the most difficult EMI environments like plasma CNC machines and applications that use a VFD.
I have 2 instances in the field where the "Step Input Timing Error" does not occur when the VFD is powered down. (Delta VFD & low rpm motor)
The optical isolation hardware of the ClearPath motors provide enough noise immunity that shielded and twisted pair cables between the CNC motion controller and the ClearPath motor are not required.
Yet the Teknic supplied control wiring is now appears to be twisted pair
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carboncymbal
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Re: Acorn + Clearpath success stories?

Post by carboncymbal »

Gary Campbell wrote: Fri Feb 19, 2021 10:56 am
The ClearPath motor inputs are optically isolated and current limited. This design provides exceptional noise immunity even in the most difficult EMI environments like plasma CNC machines and applications that use a VFD.
I have 2 instances in the field where the "Step Input Timing Error" does not occur when the VFD is powered down. (Delta VFD & low rpm motor)
The optical isolation hardware of the ClearPath motors provide enough noise immunity that shielded and twisted pair cables between the CNC motion controller and the ClearPath motor are not required.
Yet the Teknic supplied control wiring is now appears to be twisted pair
I’m curious about this as well. Do those panels have the recommended pull up resistors installed?

This mirrors some of my experience. I had no issues at all with timing errors (without resistors ) until I ran the VFD at low frequency. High frequency (say, above 120 hz) had no issues and VFD off had no issues. But immediate issues at 30hz. I installed the resistors and had the same issue. Then I added ferrites to the VFD output and the issue was fixed. (These tests were done before I decided to tear the panel down and rebuild)

From this I arrived at my possibly over engineered approach when I rebuilt the panel. Resistors, EMI power filters on all power supplies and VFD, zero phase reactor for the VFD output, and a load reactor on the VFD output output, and Shielded twisted pair wires with proper drain.

So far with limited testing it is working without issue. Time will tell if the issue is resolved.

There was one user of here who converted a boring machine. He said that twisted pair, shielded cable resolved his issue, and didn’t use resistors.

Something doesn’t add up it seems to me. Even with all of the suggested countermeasures suggested above, it seems
Some people still have issues with A VFD causing I put timing errors.

Is it possible that the actual outputs from acorn are being effected due to noise in the cabinet? Possibly in a way that only clearpath servos are sensitive to?
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