DC Motor Feedback

[ElecPneuGuy 1]

Ok, so I've got a fully regenerative DC drive controlling a variable speed flywheel application. I'm having issues where I'm not sure I'm going to get my feedback tach or encoder in time before I need to start this machine up. (customer wants a tach, if I can't get tach, they will get an encoder) I'm using an ABB DCS800 drive. Think that I'll have any major speed control issues without using the feedback to the drive? Pros/Cons?

[RussB 22]

.Just a guess here. I would think that you will be able to hold less than 1% variance without the tachometer or encoder. But this depends a lot on the application and load variance, of which you did not share any information. Edited 1 Jan 2010 by RussB

[ElecPneuGuy 1]

It is a stamping press application. The motor is 335HP

[JeffKiper 9]

I think you should be able to use them in open loop with out feedback. The operator is going to adjust it for SPM anyway. I always wanted to use the amp draw to set the counterbalance pressure. It always bothers me that people set the counterbalance so high or so low and can't se how it causes problems with motors.

[Armadillo852 25]

Sparky, 2 things. I come from the stamping press/automotive industry(Worked for Verson Stamping Press and then a Tier 1 auto supplier in Iowa as well. Not to mention GM, Ford, Chrysler as a contractor). We were using a tach on a magnetek drive until we couldn't get it anymore. Then we switched to an encoder. We used a 600HP DC motor. The thing to remember is that once the flywheel starts spinning, it will keep the speed close to where you will need it. We were accurate within 0.4% of commanded motor speed. This is a 2500 ton stamping press with a 20 inch stroke and max speed of 30SPM. We ran 95% of our jobs between 27 and 30 SPM. With inch speed of 10 SPM and micro-inch, and reverse at 8 SPM. The second regarding the counterbalance. If people only knew what damage they are doing by having the counterbalance settings wrong, the stamping world would be a great place. We used automatic counter balance settings based on die weight, and not motor feedback or current draw. I just do not think you can adjust the counterbalance quick enough going off of current draw. It would also be too expensive to do because you would always be exhausting and adding air unless you had a big enough delay, and then that defeats the purpose of having an automatic counterbalance system anyways. If you have any questions or need help with something, let me know. I would love to be back in the stamping/auto world again.

[JeffKiper 9]

We used a 600HP as well with open loop. All the magnetek drive I have ever used also has a tach. We used several GE DV300 with open loop controls flywheels. At 30 SPM 0.4% is what 0.12 SPM. I recall getting that type of accuracy with open loop on some slow presses as well. We used the resolver off the press control as the master for anything so no matter what the speed was everything was synchronize. You couldn't set it on each stroke. You would have to average 10 strokes at first then get a little closer. Then repeat until you are in a dead band. My question on using automatic counterbalance adjustment is what happens when your die shop does a revision and removes a section or adds twice the weight to a die and forgets to re-weight it? I know this doesn't happen in your plant. It happened to our plants all the time. I liked using an AMP probe to set my CB because I could always see the swing in the system. To many times I have seen guys and gals try to read the counterbalance gauge while the press was running. There is NO way to read this swing and make sure the motor loading is consistent. By the way Armadillo852 by name is Jeff not sparky. Welcome to the forum.

[Armadillo852 25]

Jeff, Sorry about the name thing. I replied to the wrong posting. Anyways, of course the tool room never adds or removes anything without re-weighing and marking on the die the new weight. Cough cough choke choke. As Management would say, that is just a lessons learned and a practice that needs to be worked on. I do like the idea of using the current draw to adjust, I just haven't seen it done before by any press manufacturer. Danly, Blow, Verson, Kamatsu, Shuler, Clearing, Niagara. Those are only the presses I have worked on. It makes me wonder if they didn't do it all these years, why? It would eliminate a lot of variables of die weight, and completely take the operator out of the equation. I guess it wouldn't be any different than using an analog feedback(counter balance pressure in tank) to adjust the counterbalance pressure. Just check on the way back to the top and adjust at the top of the stroke. The only issue I can see with it is if you do use motor draw, you will have to make sure your PM's are ALWAYS DONE AND DONE CORRECTLY. You have got my interest peeked now about this Jeff. I am going to ask a few of my engineer buddies that have been in the stamping world for years and see what they think. Now about the feedback device. I do not think you need to be real concerned about what you use. I.E. go cheap. You are just going to command it to a set speed and leave it there anyways. Basically you are using it to make sure the motor is spinning. I assume you are using a pot for speed control anyways. We also have a master and a slave resolver on our press. (Well the one in question) We use the master for adjusting counterbalance pressure off of press angle and for the transfer system. We use the slave just to make sure both entry and exit of the press is moving and we didn't break a shaft. We do not use our press resolvers for speed at all.

[JeffKiper 9]

ElecPneuGuy is the one that originally asked it. I am about like you been in the stamping world for more than a day or two. You are right I haven’t seen it on any press from any manufacture. If you ever see a press with 3 meters next to the CB regulator it was probably one of my old ones. I like to have my current draw swing a little high on the down stroke to keep all the slop out of the connections. I never did care for the manufactures that hid all the regulators behind doors just to keep a clean look. MAKE IT USER FRIENDLY. It kept me in a job for several years until I got tired of the BS. I have only seen 1 or 2 shop do PM's the way things should be DONE AND DONE CORRECTLY. I haven’t got to play with one yetand probably won't being out of the business, but I wonder what happens when you use a servo press as a master and slave everything off of it? Look ay the Accel and Decel you have to have on your loaders and unloaders. Just one of those things that could bite you if you don’t think of it before it hits the door and you try to retrofit an old loader to a new press.