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How do glass scales work on other machines?

We have a Hass VF3SS with glass scales factory installed. We are having a major issue with how they are behaving. Here's what's happening. I position to Y0 in rapid or a 400 ipm, doesn't matter, with an indicator in the spindle. The machine comes up about .001 short and then slowly floats to zero after about 5 seconds. After many, many, many hours of on the phone support, playing with settings, parameters, HAAS confesses that their spec. is the glass scales are allowed 3 seconds to settle into position. You've got to be kidding??? So the only time glass scales are really used is when the axis is stationary for 3-5 seconds and the axis can settle into position, i.e. boring a hole, but never during continuous 3-d cutting.

So where is the .001 float coming from? The difference between the motor encoder, with Electronic Thermal Comp, lead screw comp, and any other comps applied to the motor encoder and the positioning of the glass scale. So in order to eliminate the float the motor encoded with comps applied to match the location of the glass scales and any temperature.

The other problem is when we turn off the glass scales in the parameters and only run with the motor encoder the Electronic Thermal Comp doesn't seem to be working correctly. It's not holding our G54 x0 y0 location because of ball screw growth, or ETC comping incorrectly.

Any comments would be appreciated.

Roland

Reply to
Roland
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Not sure what brand Haas uses, but they all are similar. On a Heidenhain sealed linear scale the actual readhead rides on a little carriage that is coupled to the stage through wire flexures. This when added to the rubber lip seals around the coupling to the stages causes the scale some small level of stick/slip, and hysteresis. We use to rip the lips out of them to eliminate the error, but this will allow them to become contaminated quicker.

Reply to
jeff

I don't think the settling is related to the reader head carriage. I think it is the motor encoder says to go 10" on it's scales, the machine stops, and then the glass scales takes over and says this is actually 10" and moves the table, but it takes 5 seconds for the scales to catch up and correct.

Roland

Reply to
Roland

"Roland" wrote in news: snipped-for-privacy@corp.supernews.com:

Sounds to me like they are handing off control from one component to the other (takes some time), then they are going through a completely different set of gain controls for the drive and really creeping up on target position.

Reply to
Anthony

3-5 seconds is still a pretty long time--maybe tight gibs and/or too little gain here is what I'm thinking..
Reply to
PrecisionMechanicaL

you are not the first one to have this problem. the easiest is to disable it.

good luck

tools

Reply to
toolsntoys4u

No matter how popular the machine, or how attractive the price, or how slick the sales presentation, there are still, always, real and important differences between good controls and the ones built by Toys-R-Us engineers using Radio Shack components. Welcome to the real world.

KG

Reply to
Kirk Gordon

Tools,

Do you have any more insight on this issue? Sounds like you know somebody that has had issues with Haas glass scales.

Roland

Reply to
Roland

Does the .001 float on all axis or just one of them? My controller did something similar and I had to zero the controller and servo drive to correct the problem. Many motion controls use + and - 10 volts to the servo amplifier to control the speed and direction of a servo. Zero volts is for zero speed, -10V for full speed reverse, +10V for full speed forward. With a zero speed command, such as when you are "in position", the controller should be giving a 0V command to the servo amp. With a 0V command, the servo amp should not be trying to move the servo motor. If the controller is out of adjustment, or the amp is out of adjustment, it can command a move when it's not supposed to. This could cause all your moves to either overshoot or undershoot the commanded position. The integrator in the control system will slowly build up over time and correct for this offset, giving you a couple of seconds delay and then moving the axis to the correct position.

If all your commanded moves overshoot in the same direction (i.e.. 0.001,

10.001) or undershoot (i.e.. -0.001, 9.999) you can probably correct it by adjusting an offset or zero pot on the amplifier (and/or controller). If all of your motions are coming up too short or too long, you may need to adjust your PID gains. I'm not sure if this is what it going on with your system, but it sounds like it could be. Hope this helps

Reply to
RogerN

Thanks for informative response. I'll look into this.

Roland

Reply to
Roland

Late answer and a wild guess: If the scale is "intelligent" it does its own averaging to avoid jitter. Their algorithm needs 3 seconds to settle.

Nick

Reply to
Nick Müller

Reply to
Jon Grimm

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