Light Machine Corp. Benchman XTr (retrofit)

project-pegasus wrote:

So I just need to add a relay between J1-100 and J1-98. What would you recommend to make the ESTOP circuit safer?

Machine safety design has evolved significantly. In the USA, NFPA79 is still relevant, and still more concerned with electrical safety than anything, in Europe, EN 62061 and EN ISO 13849-1 standardize the development of functional safety and control safety respectively. Siemens have a safety doc that gives a good overview.

For example - The estop button circuit on the XT is not redundant, and both wires travel through the same conduit. A short circuit in that conduit could prevent the estop from working. A better safety design would have a dual circuit switch with the wires physically separated. Simlarily the door interlock could also be redundant.

The XT safety design is inherent in the board design and component choice. Such designs are thus expensive to manufacture, expensive to change, expensive to prove and and expensive to certify. Modern machine designs often use modular specific-purpose safety controllers to monitor sensors and effect changes, making that certification easier. Another observation - the estop signal for most of the XT ( ATC excepted ) runs via the motion control card, where presumably the motion control software does some signal handling and powers down the spindle and servos. That pulls a lot of potential failure modes into the situation, not least the fact that the programming of the card can be changed by the PC. What else? Oh, the spindle is powered down by the VFD during estop, but there is no guarantee. A failure in the VFD control logic could leave the spindle spinning. The VFD should be fail-safe, but modern machine designs often include safety contactors to disconnect the motor leads from the VFD too. Disconnecting running motors is undesirable, can damage VFDs, and can result in a slower braking action than a VFD-controlled stop, so many safety controllers include a configurable time-delayed output; the estop first triggers a VFD stop and a couple of seconds later disconnects the motor as a backup.

Once you start looking at it, there's a lot that could be done to make it safer, but you could spend a lot of time and money doing so. It's a bit like trying to bring a classic car up to modern crash test standards - you might be better off just cutting chips.

Thanks for your reply, genixia. Since I don't have a Nextmove card that works I'll be using a stand-alone relay in conjunction with the OEM power distribution board to enable the servos and had planned to incorporate an E-stop into that circuit. I'm still looking at the spindle circuit, but since I don't even have a viable spindle motor at this point (my XT came with the 45K RPM spindle which won't work for my needs) that decision is still quite a ways down the road. BTW, if anyone is still running an XT on the OEM software with a Nextmove card (TGTROPIC??) and would be willing to snap some close-up pictures of their Nextmove move card I would greatly appreciate it. Or if you could post a part number for the card that would be great too. Thanks!

After reading through the Nextmove and Benchman manuals and comparing their sample circuit diagrams with the circuit diagrams TG provided us, I'm now reasonably certain that the Benchman XT and VMC 4000 use Nextmove PC cards with PNP Output configurations and PNP Input configurations giving it the part number NMP001-501. I hope that might be helpful to someone at some point.
What's interesting is that it's fairly easy to change an NPN card to PNP and vice versa.

Mine came with the ISA version of the card with the PC running NT. I'm guessing that was only available in PNP configuration. I briefly looked at getting a PCI version so I could upgrade hardware and OS to extend usability, but for the money I'll just push to linuxcnc instead.

What do you know about your spindle condition? Do you have the ISO10 toolholders still?

I have the machine up and running now, though I'm having some problems getting the ATC to function properly. But the the spindle works fine; I've had it up to 30,000 rpm with no problems. It came with only 5 ISO10 tool holders, but I've seen some Chinese sellers on ebay have some rated to 20,000 rpm. Anyone know the largest diameter tool an ISO10 will fit?

Thanks for that. I just ordered one. I wish I could track down some old Schaublins.

Haha, sounds like you're thinking about keeping that spindle after all. I was hoping to prise those Schaublins away from you. I have a full set of 12, but I too wish I could find more. Look after that spindle - replacing the bearings is an expensive proposition.

Search around - I've seen ER16 collets listed in 13/32", 10.5mm and 11mm. Nothing larger than 11mm though.

FYI, Centerline was not the only high speed spindle we used. There was also a Precise spindle that went to 50K that was much less expensive both to purchase and repair. We were rolling this out when I left in 2006. it was however a 0.75 HP spindle vs Centerlines' 1HP. Mechanically they were interchangable, only required minor reprogramming of the speed control for proper operation. I do not know the Precise part number, but will look into it if anyone is interested.

My XT is from 1999 and has the TDM spindle. I thought they were closer to 2 HP. I also have a VMC 4000 that I was considering selling, but considering the limited tooling sizes I will have with ISO10 I might just hang on to the 4000 because of its larger and more common R8 spindle.