What is considered Digital or not?

[JerryFlyGuy]

I was recently looking at a pc of Cnc equipment and asked about the control. They told me oh its a proprietary system. I asked is it a basic step/direction control and they said, no its digital via 24bit Resolvers. At this point my eye's glazed over and I was there-after, outta my depth.

Anyone want to clarify this for me? Is not Resolvers kinda an old way of doing things compared to using the new "High count encoders"?

Isn't step/direction a form of digital control?

How does one compare the resolution of 1 resolver to another? How do you compare it to say an 1000line encoder?

I'm getting asked by others if this is a good piece of equipment or not, and I can't really tell them anything as I'm not familiar w/ this type of control system.

Any help appreciated!
Jerry

[Al_The_Man]

It could be network or proprietary bus controlled, the resolvers are not the control per se but the method of motor feedback, generally for sinusoidal AC servo's.
In some cases the resolver is fed back to a semi-intelligent drive and a pseudo encoder signal is derived from this and fed back to a controller and can be scaled according to the resolution you wish.
Resolvers are not of themselves very high resolution devices and usually have to be electronically scaled to be used as an encoder signal.
It may be good equipment. but it depends on if you have to integrate to it or is it self contained?
With networked drives the signal is usually digital format sent over the bus to the drive.
You probabally need more information from the supplier.
Al.

[JerryFlyGuy]

Thanks Al! I was under the impression that a resolver was analog type feedback system. The control is a window's based control on a Abrasive Waterjet. It's claimed to be the first 'Windows based control software used in the market'. It would appear that their system is totally built by them, I'm a bit leary of some of these guy's and their claims. I'd sure hate to be the person to tell the higher up's that I think they have a good product, only to learn its a lemon at a later date.

Al, is there any way to better evaluate these systems? What should a person be asking?

Jerry [LOST.... the next episode ]

[Geof]

For what its worth I would not go for a Windows based system in a production environment because I simply do not think it is stable enough. I know there are versions that are supposed to operate in real time but I take their definition of real time with a grain of salt.

I also would not be willing to put my money out on the 'first' of anything. Let somebody else have the hassle of finding all the bugs and waiting for them to be fixed.

What should you be asking? "Give me a list of satisfied customeres that are willing to answer my questions and allow me to pay a visit." If no list is available then find another make.

[JerryFlyGuy]

I appreciate your cander Geof! I know of one company that uses this same machine. I haven't talked to them about their experiance but I kinda came to the same conclusion as you, until I know a bit more about what they did to make it work on XP, I'm not sure I want to recommend them. There are others who are making the machine control software work on Xp very well [ Mach 3 is a good example, even if it is only considered at a hobby level] so it can be done, but to claim that they invented it and they won't tell you any more than that is a bit scary.. The other issue is that they higher up's are really sold on this unit as its from a know machine supplier [we've bought some other equipment from them and had decent results] however that, to me at least, isn't reason enough just to jump in w/ both feet on the next pc of equipment.

Still lost....

Jerry [ I guess I'll have to stop in on these guy's that have one of these and see what they say..]

[Al_The_Man]

Originally Posted by Geof For what its worth I would not go for a Windows based system in a production environment because I simply do not think it is stable enough. What should you be asking? "Give me a list of satisfied customeres that are willing to answer my questions and allow me to pay a visit."

I wouldn't entirely agree on the first part, I do know of at least three PC based commercial units that are used in an industrial setting that are very stable, one in a Plasma table environment, two are DOS based.
But I would also ask for a some references that I could check with and if possible one in traveling distance that you could may be see in person.
Al.

[ViperTX]

Resolver...they mention 24 bits, which basically means that for each location you get a 24 bit signature...resolvers are also used to give you an absolute position.

Encoders do not give you an absolute position by themselves.

[JerryFlyGuy]

Thanks guy's I'll have to go talk to these fella's who are currently using a machine, it just so happen's that they are only about 60miles away so it is definatly worth the time to check it out!

Viper, So having a 24bit positional feedback is pretty handy, does that mean that on a system like this you don't really need a home switch as it always knows exactly where it is[ instead of just knowing its so many 'counts' from the home position]??

Is this the primary reason to use a resolver instead of an encoder?

Jerry

[Al_The_Man]

Resolvers do not retain machine position at power up, they can indicate absolute angular position. They are non-electronic.
Al.

[NC Cams]

I don't see how any machine can "remember" where it is/was unless it carefully writes something to ROM and then homes itself at start up next time. My Eztrak is supposed to do it and usually it does but it ain't perfect at doing it and it is set to write turn off postion to internal cache file.

As powerful as automotive computers are anymore, you have to tell an automotive computer to start counting over each time the crank rotates - and they are only counting to 3 or 4 depending on the engine. I don't see how a CNC would be any more conducive to "saving" position unless it were programmed to do so - even so, I"d still check cuz I don't trust them.

At start-up, there is so much redundancy that it is damn near impossible for the things to forget where they are or what they're supposed to do next - even if they lose a sensor, they have "limp modes" built in so the thing will at least run.

Haven't seen that level of redundancy support outside of aircraft or aerospace - for sure NOT in some of the "professional" industrial controllers that I've seen.

[Geof]

Originally Posted by NC Cams I don't see how any machine can "remember" where it is/was.......

It is my understanding that this is possible with grey code encoders because they are absolute position encoders but they have the limitation that their resolution is low.

[JerryFlyGuy]

Originally Posted by Geof ...because they are absolute position encoders but they have the limitation that their resolution is low....

So infact they aren't absolute but rather..'Close position encoders'


Jerry