Step-Direction vs Analog Command vs CW/CCW Signals

Hi Guys,

I am about start to finish the retrofit of one of my old welding robots,


The motors on the robot are Yaskawa AC servos from the early 90's. Interfacing them to Linuxcnc would be a major job because of the proprietary encoders on these drives.

Ideally I would like to replace the whole motor with ethercat AC servos but six motors and drives add up to the tune of $4000 USD.
So my next solution is to replace the encoders and use new drives to control them.

My question is about control signals, Is there any performance difference between the different control methods. The DMM drives I am using, www.dmm-tech.com/Dyn4_main.html, support many different control types, Step/Direction, Analog command and CW/CCW.

Is there a reason I should chose one method over the other?

thefabricator03 wrote:

Hi Guys,

I am about start to finish the retrofit of one of my old welding robots,

The motors on the robot are Yaskawa AC servos from the early 90's. Interfacing them to Linuxcnc would be a major job because of the proprietary encoders on these drives.

Whats the drive model. Yaskawa? Usually they have the encoders going to the drive from the motor but also output quad that should work as axis encoder inputs.

This is one of two servo control boards,



As I said early 90's vintage, I dont want to be dealing with electrical gremlins from electronics that are as old as I am.

Mounting new encoders and using the existing motors is surprisingly easy, The new drives have software that I can set the parameters of the motor.

From my research the absolute encoders on these motors output a very specific pulse that only the Yaskawa drives can decode.

I have been using CACR yaskawa drives in two of my machines and they have never failed once. Just saying, they are built pretty robust. Every CACR drive I have seen has quad encoder output. doesnt hurt to try.

I wouldn't even know where to start interfacing the old drives with linuxcnc, would you happen to have a manual for them?

the yaskawa cacb 3axis AC servo controls are standard
there are all documentation on yaskawa homepage downloadcenter

I cannot find any manuals or anything regarding that specific drive on the yaskawa site or even google.

I think I am better off replacing the drives and encoders. At least I will have manuals for my new drives and Ill be able to tune the servos properly with the drive software.

If I use analog commands, What Mesa card would I need for up to 8 axies?

Also with the Mesa card, will it be able to take the encoder feedback and close the loop in LinuxCNC?

Would a 7I92H and two 7I77 analog servo card be what I would need or can I get 8 axises with other cards? The combo above would give me up to 12 axies.