E-STOP Circuit - will this cause any problems?

[birchy]

I maintain and repair industrial machines daily (production machines...not CNC) and have never (yet) seen a safety circuit that protects anything other than the end user. Things like E-Stops, gate switches, door interlocks, break-beams, pressure mats, etc are always there to protect the operator and must be activated manually. Things like position sensors, limit switches, etc are always kept separate. I understand the need for limit and homing switches (and not relying on the software), however I disagree that they should be part of the Safety circuit. Run off 24V DC....YES. As part of the machine logic...YES. As part of the Safety circuit...NO.

My reasoning is that if a drive goes to the end of its travel and activates a limit switch, we don't want it to kill everything and have to carry out a manual reset. It's not an emergency or a safety issue. Even if the drive keeps going, the physical stops will prevent it going any further. It might be an inconvenience to the operator but not a safety hazard...unless the machine is badly designed mechanically. So my idea of a limit switch is that it should stop the drive and inform the software but NOT kill the whole machine. Would you not agree?

[JAZZCNC]

My reasoning is that if a drive goes to the end of its travel and activates a limit switch, we don't want it to kill everything and have to carry out a manual reset. It's not an emergency or a safety issue. Even if the drive keeps going, the physical stops will prevent it going any further. It might be an inconvenience to the operator but not a safety hazard...unless the machine is badly designed mechanically. So my idea of a limit switch is that it should stop the drive and inform the software but NOT kill the whole machine. Would you not agree?

No don't agree at all. Course it's a safety issue it's just crashed for some reason how do you know what that reason may be.? To have the system restart with out a manual reset is plan dangerous.!! . . You wouldn't have the machine restart upon releasing E-stop so why would you a Safety limit switch.?

You'll be hard pushed to find any commercial CNC machine that doesn't throw the machine into a reset condition from a limit trip.!

Relaying on Physical stops is bad practice and unhealthy to any machine and relaying on drive over current protection is just plain asking for trouble.!


End of the day it's your machine and components so do it how you feel best.! . . . Me I'll stick with being safe and the slight inconvenience of a reset thank you very much.!