Estop Implementation.
Posted by
wanliker@a...
on 2003-05-28 00:04:14 UTC
The following message is posted from the Geckdrive group, with the authors
permission. I found it to bee good reading.
bill
List Mom
<<
Message: 7
Date: Mon, 26 May 2003 16:39:28 -0500
From: "Dan-Att" <dsymonds@xxxxxxxxxxxxxxx
Subject: RE: Re:disable input and emergency stops
Gentlemen:
I have followed the Estop thread with some interest. I have been a
machine tool design engineer for 20 + years and have written all the
software for, developed and market my own CNC stepper based control system
based on Gecko drives. I am an electronics and mechanical engineer and as
such have been involved with all phases of the Estop design controversy over
the years. Ultimately all liability issues involving machine tool
electrical design fall under the NFPA 79 industrial machinery design
standard.
Currently my copy of the standard is not available to me but I will
paraphrase the requirements:
That standard DICTATES that all ESTOP circuits remove power from the
driving elements (read drives) and that the circuit be a non processor or
cpu controlled electo/mechanical fail safe circuit. In a nutshell that is a
switch to through a contactor or relay remove the power from the drives.
The circuit must be designed as a "Failsafe" system, such that the relay or
contactor must be "MAINTAINED ON" to allow power to the drive. If the
signal lead to the contactor or relay is cut or open the the drives cannot
be energized or will deenergize due to a fault in the switch circuit.
Granted the prevention of damage to drives due to sudden power removal
should foreseen by the drive manufacturer and taken into account in the
design but the ultimate intent is to prevent injury even if that dictates
electrical or mechanical damage to hardware. That is the extreme end of the
spectrum but still it's the absolute maxim that a machine tool designer must
live by to survive legally.
NFPA 79 by its very nature is a great guideline to building any CNC or
electro/mechanical system whether hobby or commercial. It will prevent a
lot of headaches such as noise problems and such if a bit of attention is
paid to its structure.
Hope this helps.
Dan Symonds
permission. I found it to bee good reading.
bill
List Mom
<<
Message: 7
Date: Mon, 26 May 2003 16:39:28 -0500
From: "Dan-Att" <dsymonds@xxxxxxxxxxxxxxx
Subject: RE: Re:disable input and emergency stops
Gentlemen:
I have followed the Estop thread with some interest. I have been a
machine tool design engineer for 20 + years and have written all the
software for, developed and market my own CNC stepper based control system
based on Gecko drives. I am an electronics and mechanical engineer and as
such have been involved with all phases of the Estop design controversy over
the years. Ultimately all liability issues involving machine tool
electrical design fall under the NFPA 79 industrial machinery design
standard.
Currently my copy of the standard is not available to me but I will
paraphrase the requirements:
That standard DICTATES that all ESTOP circuits remove power from the
driving elements (read drives) and that the circuit be a non processor or
cpu controlled electo/mechanical fail safe circuit. In a nutshell that is a
switch to through a contactor or relay remove the power from the drives.
The circuit must be designed as a "Failsafe" system, such that the relay or
contactor must be "MAINTAINED ON" to allow power to the drive. If the
signal lead to the contactor or relay is cut or open the the drives cannot
be energized or will deenergize due to a fault in the switch circuit.
Granted the prevention of damage to drives due to sudden power removal
should foreseen by the drive manufacturer and taken into account in the
design but the ultimate intent is to prevent injury even if that dictates
electrical or mechanical damage to hardware. That is the extreme end of the
spectrum but still it's the absolute maxim that a machine tool designer must
live by to survive legally.
NFPA 79 by its very nature is a great guideline to building any CNC or
electro/mechanical system whether hobby or commercial. It will prevent a
lot of headaches such as noise problems and such if a bit of attention is
paid to its structure.
Hope this helps.
Dan Symonds
>>[Non-text portions of this message have been removed]