Mark Cason wrote: > I am new to this list, so this just may be a rant, but the purpose of >a E-Stop system, (and I do mean system, as this is how it should be >looked at) is NOT to remove power from a machine, but to FREEZE the >machine in place, at the expense of damaging the machine. (and possibly >saving somebody's life) > > It depends on the machine and the industry regulations that you need to comply with. In the semiconductor industry, for example, the Semi-S2 specs require that an E-Stop remove "all hazardous energies" from the system as quickly as possible. Other parts of the spec talk about how fast the atmosphere in the machine must be evacuated (they use caustic and poisonous gases).
Of course, many people on this list are using EMC in a home shop environment, where there are no hard and fast rules, only rules of thumb. I agree that E-Stop is a system, and that many people don't fully grasp what it means (most notably anyone who thinks that a button on a GUI or a hotkey in the software constitutes E-Stop). > I have been seeing info being given out on this list, where people are >giving out advice to just hook up a E-Stop button to the power supply to >stop a machine. This info MAY work, but it is not the recommended way >to do things. I look at that big red button on most machines as nothing >more as a power off button. > > For a small machine, particularly a stepper-based one, disconnecting power is a viable means of stopping the machine. It's not the fastest, but it probably is the most reliable. Decelerating the motor at the fastest rate possible would be better, but you still run the risk of decelerating too quickly, which will cause a loss of sync, which might as well be a power-off in some situations. >Here is an example that I can give you: > Say somebody builds a hydraulic, or worse, pneumatic Z-Axis. If >someone gets there hand stuck in a part directly under the Z-Axis, and >they hit a E-Stop that removes power from the machine, then that >person's hand will will sustain serious injury. the spindle will still >be turning for a couple seconds after power is lost, and the Z-Axis, >with no power holding it up, will start to fall. A small diameter end >mill can cut a nice round hole quickly through flesh. > > A Z axis of these types should have a brake. Brakes usually engage when power is removed, specifically for the purposes of E-Stop. Of course, we still have the question of whether the motors would stop faster if power is removed or if the drive uses all possible effort to stop the motors, but that's for the individual machine integrator to decide based on their situation. You do want to turn the motor power off at some point, but deciding when is difficult. Consider a person whose hand is caight between a tool (not spinning - no need to be gross here) and a vise. What you want is for the pressure on the hand to go away - ie, stop powering the motor into the hand. But, you want to be able to drive the axis back a little manually, which can't be done if the drive is still commanding a stop (or hold). > I am not saying that a hydraulic/pneumatic system is PRACTICAL, but I >am saying that people will do anything, and there are other systems that >can fail in a similar fashion. A punch press is one of them. > > Nobody knows what somebody will be using this software for, and just >using a blanket statement to remove power from a machine, WILL hurt >somebody eventually. > > Any blanket statement could cause someone to do something that will get someone hurt eventually, including one that says that removing power is never the answer. I think you're bringing up a very good point though - *THINK* about what you need to do to make *YOUR* machine safe, and then do it. Thanks for listening - Steve ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
