Jeshua Lacock wrote: > Greetings, > > I turned on the power to my system today and my 180 pound gantry shot full > speed crashing hard into the end of my table. > > > > I was a stumped at first as the last time I used it everything was stable. It > turns out that I had a loose connection to the encoder. I am going to soldier > the wires on the pins of the encoder to prevent that from happening again, > but I was wondering if there is anything I can do to disable motor power in > the event a connection to a encoder is lost. > > Yup, this is a problem with servo systems. If the encoder does not provide signals indicating movement, then a runaway is likely. > I understand why it happened - without the encoder live the motor was just > attempting to position itself at 0. > > I am guessing there is not an easy way to detect this condition, but I wanted > to see if anyone else has any thoughts on the subject. > And, yes, you are right, there is no easy way to detect this. The servos on my Bridgeport will fault under a runaway condition, but many will not. The ancient Allen-Bradley control I started with had a circuit that compared absolute velocity from the encoders with absolute velocity from the servo amp's tachometers. If the tach value exceeded the encoder value by 20%, that caused an E-stop. Very good in the days of light bulbs in the encoders. They also compared the A and A/, etc. signals from a differential encoder. If they were both at the same level for more than 1 us, that also caused an E-stop.
The G320X has a scheme that is supposed to detect encoder failure, but I am not sure how well it handles all possible conditions. You can have a break on any signal wire, loss of encoder power, loss of encoder ground. It needs to detect any combination of these. Jon ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
