Hydraulic + Linear Scale Surface Grinding Machine Retrofit

Hello.
I have purchased a 50 year old machine (here we go again....) with the intent of retrofitting it.

The machine is a horizontal surface grinding machine with hydraulic axis, driven by directional valves.
The Z axis lowers up/down hydraulically, and it is manually adjusted to the desired height with high precision.
The X axis moves back and forth in order to grind the part, and the Y axis can also move back and forth.

My intent is to install linear scale encoders on them, feed them to a mesa board, and drive the hydraulic valves with directional control only. I would then insert g-code and the machine would work by itself.

The linear scale encoders are simple, and connecting them to linuxcnc is too. I will be buying a 7i95 or 7i96s with an additional encoder board. 
The main issue i see, right before starting this project, is the need to send the directional signal to the valves, in order to tell the system to move.

- I use the stepgen direction pin to drive the valves, as it assumes negative voltage for negative direction and positive voltage for positive direction. I would then completely ignore the pulse step generator. Or is there a better way to do this, with chargepump or some other function?

- I need to allow a bigger following error, as there is no problem to this: i dont have any issue in moving a bit more than needed in X/Y, as this machine is only a surface grinder, and all the parts in the worktable will be surfaced at the same height.

I will be posting pictures as i progress with this retrofit, painting the machine, making the HMI, etc.
I like the way it works hydraulically, as the axis move quite fast and smoothly, without a sound, even though the machine is really old, so i wouldn't want to install servos/ballscrews.

Any suggestions will be highly appreciated.
Thank you guys!

 

I assume it all depends on the hydraulic arrangement and what it is capable of as is. Respective what you want to get out of the machine that cannot be done and what you are willing to change (aka spend extra) on the hydraulics.

I am by no means a hydraulic experienced person other than having pushed buttons on them.

I doubt you can drive an on/off hydraulic valve with pwm in order to regulate the liquid flow.

As I understood it, some of the grinders use a simple mechanical bi-directional valve ( without electrical components) it sits in the table middle, then some sort of a bypass to slow down and speed up. More or less fully mechanical and simple.
For the x-Axis on those grinders a linear scale would be "wasted", they just move back and forth anyway. Adjustable with mechanical stops.

You can buy a lot of things e.g. Ethercat servo valves, +-10V proportional valves, On/off valves combined with flow restriction to ramp the system down or adjust pressure. (simple I/O) logic.
Mesa 7i65 has Analog servo outputs to generate +-10V. (probably cheaper than a valve for a fighter jet )
I make a bet you can also get some Ethercat adapter that can ouput +-10 V.

You will want to evaluate if kicking out certain hydraulic actuators and replace them with a motor and ball screw is the better approach.

I guess you will have to dive into the hydraulic system first, in order to see how the thing works now. Then see what is required. Very interesting topic. I will follow along.
 

Hey thank you for your reply
Here are some pictures of the machine, apparently, and as it should, the Z and Y are ballscrews. 

will be posting more info

I would be looking for a linear motor for X. No moving parts and good speed.

If you use a 7I95, a 7I83 will give you the analog +-10V outputs required
 

Hi,

does not look like a ball screw to me. More like a regular "ACME" srew?

@scotth A linear motor? How much does it cost for a grinder that size and how to put it into the machine?

Curious.... yes get a linear motor.

If you buy a new Studer it will be linear.
As to the cost, good luck on that. Ebay?

Haha, I would rather go to the local HIwin shop or contact Chieftek

I think to stick with the hydraulic x-axis will be less complicated an maybe even a little cheaper. haha!

@santi : get the linear motor!

Suspicion rises when the local sales wants to visit in person to ask for your requirements and the internet only says. Contact local sales for price information.

I wouldn't worry about table feed on a surface grinder, cross feed and down feed are easy and give you the best bang for the buck.
The directional valve on the table is pretty much hopeless for positioning.