Guidance on Mazak FH4800 ladder edit / Banner light curtain retrofit

We have a Mazak FH4800 that has a load area safety curtain system made by Sunx. We are looking into retrofitting the SunX curtain system with a Banner USCD 1T2 style due to having an abundance of Banners on hand and difficulty with obtaining the Sunx's.

The Sunx reports a safe condition by activating a NC relay, thus opening a 24vdc loop path back to the I/O of the Mazak. The problem I have is that the Banner substitute only has NO relays contacts for this purpose. I thought about adding relays to the circuit to reverse this but there is no way for the USCD to monitor these for a failure condition, which would be required for a legitimate safety installation.

What I'm wondering about doing is reversing the logic in the Mazak ladder so that instead of seeing safe as an open loop, it will see it as closed. The curtain system's relay contacts apparently go right into an I/O extension of the Mazak control and not a safety control as might be expected. I would think it should be as simple as changing a ladder rung XIC to XIO or vice versa. As it is, I don't know enough about the Mazak to find and edit the ladder. Can anyone offer any guidance?

No offense Micah but it sounds like a bad idea. If I understand you correctly the machine will go into alarm when the Sunx system no longer provides 24v to the cnc through the relay. If this is true then changing the system to normally open switch type is dangerous. If the system shorts to ground or if a wire becomes cut or broken then the system will stay in a ready state even when something has passed the light curtain. Emergency stop circuits work in a similar fashion to the Sunx with a normally closed switch. When the switch is pressed it breaks the circuit throwing it into alarm. If a wire is cut or broken then again the system will alarm out because the path has been broken.

The Sunx doesn't provide the voltage, it only passes it back to the machine control. It is opposite from what you're thinking. The Sunx output relay is NC and opens the path when the curtain reports back unbroken. So actually, the current configuration is dangerous according to what you described.

Have you tested the Banner curtain? is it possible the N.O. contacts are beam broken condition?.
IOW a valid beam will close them?
If so you should be able to invert with a relay.
The Mazak ladder is quite proprietary and although probabally a Mitsubishi system, it is not programmable on screen as the Mits is, at least that is what I have found.
Al.

Yes, I tested the Banner. It closes the contacts when the curtain is "clear."

I thought about adding the relay. While it doesn't seem possible that a simple NC relay could weld open, wouldn't that be considered "unsafe" unless it is force-guided and monitored by the curtain control?

BTW, it has a Mazatrol 640M control.

If safety over the simple relay is a concern you could look at integrating a simple safety type?
http://www.phoenixcontact.com/signal...hing/31253.htm
The 640 is a Mitsubishi controller with mazak software.
Al.

After further consideration, I think a simple NC relay in the output path is sufficient because there are other contacts in the new curtain control that can be put in the path of the signal that initiates the dangerous motion (table rotation). If the relay is removed or somehow welds open, these other contacts will break that path. These other contacts are force guided and monitored. If this were to happen, the machine wouldn't know the curtain was broke, but the dangerous motion would be stopped anyway.