Hardware Recommendations for a XYYZACUW Machine

More
15 Sep 2021 11:33 - 15 Sep 2021 13:54 #220695 by mvp_mk
Hi All,
I am building a gantry XYYZAC Machine with an independent rack style tool changer that I am hoping I’d be able to assign to the U and W which would make it a XYYZACUW then I would control the tool changes with a custom M-code script. 

What protocols are recommended to use and why? Please emphasize the disadvantages.
For Spindle RS-485 Modbus vs PWM control
For Servos STEP/DIR vs CANopen Vs EtherCAT
For Linear Encoders TTL Sine (Analog) or proprietary ones (eg: Heidenhain)

 Do I need a discrete linear encoder for each Y axis? Or does one suffice? How would one sync the two encoders if two encoders are required?

I have a MESA 6I24 do you guys think that would be enough to handle I/O?

Thanks in advance for the advice.
Last edit: 15 Sep 2021 13:54 by mvp_mk.

Please Log in or Create an account to join the conversation.

More
15 Sep 2021 15:09 #220703 by Todd Zuercher
Spindle control: RS-485 (Modbus) offers a lot of options for control and feedback, but is more difficult to configure and isn't real time. Analog or PWM requires more inputs and outputs to achieve the same level of options and feedback as is available from Modbus, so can cost more, but it is or can be all in real-time.

Servo: Step/dir is simple and almost universally supported and can be used both open (without feedback) and closed loop (with encoder feedback) within Linuxcnc. CANopen is generally not close enough to real time for use with Linuxcnc and not really supported. EtherCAT isn't well supported and you may be mostly on your own setting up and configuring it in Linuxcnc.

Linear encoders:  Linuxcnc does not support sine wave analog encoders (that I know of), only quadrature (either TTL or differential pair) or some digital serial options (I don't know the details never used them).  But if you are only interfacing the encoders with your servo drives it doesn't matter use what your drives support.  I think for the linear encoders to be effective you would need to have one per servo motor.  For example if your gantry is long enough and not stiff enough to require two servos then two encoders (one for each side) will be required to keep it square.  That said linear encoders are not always necessary, often only relying on the rotary encoder built into the servo motor provides adequate accuracy.  It will depend on your machine's design (such as drive mechanics and frame stiffness) and your accuracy goals as to whether or not adding linear encoders will even be beneficial. 

A Mesa 6i24 is a good card, but it likely won't be enough by it's self.  Now you need to figure out what daughter cards you will need.  But to figure that out you will have to solidify your list of hardware that you will be interfacing with it.

Please Log in or Create an account to join the conversation.

More
15 Sep 2021 16:13 - 15 Sep 2021 16:17 #220711 by mvp_mk
Thank you Todd for all the advice. It is really appreciated.

So stay clear from EtherCAT and CANopen.

My vision was to let LinuxCNC deal with the Micrometers through the linear encoders and let the Servos and Servo drives deal with the Nanometers using 23-bit integrated rotary encoders.

Is this the best solution? Or is there a better solution? My aim is to reduce any sources of error from mechanical components to close to zero.

Is it necessary to have all the axes that will move simultaneously be on the same MESA card? if so would the SVST8_8IM2 firmware be supported in LinuxCNC?
Last edit: 15 Sep 2021 16:17 by mvp_mk.

Please Log in or Create an account to join the conversation.

More
15 Sep 2021 17:04 - 15 Sep 2021 17:06 #220718 by Todd Zuercher
I don't really have any experience with duel feedback systems, but you might want to check to see if your drives have the capability with doing it all themselves.

You can have multiple Mesa cards, and even use multiple types of command interfaces. Such as one servo using analog commands, another using step/dir and another using something else entirely.

I didn't mean to say that you'd need another Mesa FPGA card. I think your 6i24 ought to be enough. But you may need some of Mesa's daughter cards to connect to it to get all of the io and interfaces you'll need.
Last edit: 15 Sep 2021 17:06 by Todd Zuercher.

Please Log in or Create an account to join the conversation.

Time to create page: 0.081 seconds
Powered by Kunena Forum