5101
General Mach Discussion / Re: My retrofit nightmare
« on: May 11, 2013, 08:15:37 AM »
The purpose of the E-Stop is to stop your machine as quick as possible in as safe condition.
This can mean many things and involve many different methods depending on the machine itself.
For example removing the enables from a drive on a machine with friction on the axis will stop it very quickly, doing the same on a machine that has little friction (profile rails etc) can make it travel for quite a distance after the enable has been removed. Then of course there are axes that have gravity affecting them, that requires a brake on the axis so that when holding of the motor is removed it does not fall uncontrollably.
Also and E-Stop should ideally be multi layered, at its simplest is removing the power from the drives (by whatever means) and also informing the control (Mach) of an E-Stop situation so that Mach will halt the motion. A lot of people rely solely on the control issuing the E-Stop, this is not a god idea as if something goes wrong with the software then it will not stop, that is why a multi layered approach is best.
Also you do not really want to remove power (in most situations) from the control in an E-Stop, ie you want to keep Mach (and the ESS) ALIVE.
With your setup a simple approach could be to have a dual pole E-Stop, one NC one NO. The NC contacts would go to Mach via the E-Stop input and the NO contacts would connect to your drives enable signals. So what would happen in an E-Stop is the drives would get a signal on their Enable inputs which would disable them and at the same time Mach would get a signal on its E-Stop input and would halt motion. That is the minimum seup I would go for in your situation with your hardware.
Hood
This can mean many things and involve many different methods depending on the machine itself.
For example removing the enables from a drive on a machine with friction on the axis will stop it very quickly, doing the same on a machine that has little friction (profile rails etc) can make it travel for quite a distance after the enable has been removed. Then of course there are axes that have gravity affecting them, that requires a brake on the axis so that when holding of the motor is removed it does not fall uncontrollably.
Also and E-Stop should ideally be multi layered, at its simplest is removing the power from the drives (by whatever means) and also informing the control (Mach) of an E-Stop situation so that Mach will halt the motion. A lot of people rely solely on the control issuing the E-Stop, this is not a god idea as if something goes wrong with the software then it will not stop, that is why a multi layered approach is best.
Also you do not really want to remove power (in most situations) from the control in an E-Stop, ie you want to keep Mach (and the ESS) ALIVE.
With your setup a simple approach could be to have a dual pole E-Stop, one NC one NO. The NC contacts would go to Mach via the E-Stop input and the NO contacts would connect to your drives enable signals. So what would happen in an E-Stop is the drives would get a signal on their Enable inputs which would disable them and at the same time Mach would get a signal on its E-Stop input and would halt motion. That is the minimum seup I would go for in your situation with your hardware.
Hood