DRO warning

Warrensmith · Jan 7, 2019

Anyone contemplating the purchase of a new DRO try before you buy, unfortunately some of the newer units around do not perform well.

We recently purchased a new Fagor 40i-TS because of its RPM and surface speed displays and that function works well however the positional display is noticeably laggy ie. when you move the hand controls it takes time for the display to respond and after you have stopped the position keeps updating for a period of time. Unless you are stationary the display is about 2 update cycles (1/2 sec.) behind the machine which makes it very hard to use.

The new fancy LCD displays might look good but they come with a processing time penalty and Fagor have not prioritised the functionality so position is updated in real time.

We have tried working through this with their engineers however they are blaming everything but their poor programming. Unfortunately our experience over the last 10 years has not been good when purchasing new equipment it seems the new norm is do no testing just push it out the door quickly.

W

IrishMiller · Feb 19, 2019

Did you ever get a solution to the problem with the Fagor 40i-TS DRO? I am looking at the same DRO for the CSS function but if there is a time lag on the updating of the display, then it is of no use to me and I need to search elsewhere.

DMF_TomB · Feb 20, 2019

Warrensmith said:
Anyone contemplating the purchase of a new DRO try before you buy, unfortunately some of the newer units around do not perform well.

We recently purchased a new Fagor 40i-TS because of its RPM and surface speed displays and that function works well however the positional display is noticeably laggy ie. when you move the hand controls it takes time for the display to respond and after you have stopped the position keeps updating for a period of time. Unless you are stationary the display is about 2 update cycles (1/2 sec.) behind the machine which makes it very hard to use.

The new fancy LCD displays might look good but they come with a processing time penalty and Fagor have not prioritised the functionality so position is updated in real time.

We have tried working through this with their engineers however they are blaming everything but their poor programming. Unfortunately our experience over the last 10 years has not been good when purchasing new equipment it seems the new norm is do no testing just push it out the door quickly.

W

.
hand controls ? you talking cnc handle mode ??
.
obviously many cnc have servo oscillation problem where when moved by handle, rapid or memory mode they often oscillation back and forth from a second to 10 or more seconds. easily seen with .0001" indiator and move in handle.
.
just sayings its possible DRO is showing you what is happening

trevj · Feb 20, 2019

The shop I last worked in had a Newall C80 with Constant Surface Speed, on a new Colchester/Dai Lan(I think) VFD equipped lathe.

It pretty much behaved the same way, always a lag time between movement and registering on the read out. It flickered rather than settling in to it's readings too, a right pain in the bum to use. Both axiis, same behavior.

In addition to all that, the CSS function was disabled due to a safety recall. Not that it ever worked as advertised either.

Sat down and played with every option and setting in the manual, and pretty much just stopped using the DRO for anything that required any real delicacy.

EPAIII · Feb 20, 2019

I find that pretty shocking. Heck, even a $10 Chinese digital caliper gives you a essentially instant readout.

trevj said:
The shop I last worked in had a Newall C80 with Constant Surface Speed, on a new Colchester/Dai Lan(I think) VFD equipped lathe.

It pretty much behaved the same way, always a lag time between movement and registering on the read out. It flickered rather than settling in to it's readings too, a right pain in the bum to use. Both axiis, same behavior.

In addition to all that, the CSS function was disabled due to a safety recall. Not that it ever worked as advertised either.

Sat down and played with every option and setting in the manual, and pretty much just stopped using the DRO for anything that required any real delicacy.

CarbideBob · Feb 20, 2019

No experience with this one but I find the statement ".. but they come with a processing time penalty and Fagor have not prioritised the functionality so position is updated in real time." strange indeed.
Makes no sense if you have ever designed and built a DRO. A 1/2 second is literally miles in this signal processing world.
Calculating speed or velocity is different as you need to average many samples.

I do find Tom's comment of "just sayings its possible DRO is showing you what is happening" more likely.
Seen servo loops that can take up to 10 seconds to get where they should be. Some never close the last few counts.
This can be verified or discarded as a problem with LVDTs or good DTIs.
1/2 second is a 120hz total system bandwidth which is certainly not unheard of for a machine slide.

Why your engineers don't know about such things or how to check/verify what is going on I can't answer.
Bob

trevj · Feb 20, 2019

EPAIII said:
I find that pretty shocking. Heck, even a $10 Chinese digital caliper gives you a essentially instant readout.

I just found it really frustrating.
The rest of the DRO equipped machines in the shop wore Acu-Rite, and those worked very well.

Never did get that DRO working like we thought it should. Pretty sure they surplussed that lathe off not long after I left there. The price of having managers who knew nothing of what we actually needed to do what WE did, wandering through with their entourage, asking the eternal questions "What's that?" "Do we need it?".

DMF_TomB · Feb 21, 2019

if servo oscillation bad i have seen continuous never stopping oscillation back and forth often over .0010"
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some cnc read .00001" and they obviously tend to bounce back and forth alot. sometimes display is slowed to update reading once per second rather than 10 times a second. some cnc have a servo diagnostic screen showing the quick back and forth changing readings. its used for servo tuning.
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many reasons for servo oscillation usually number one is the scale is dirty needing cleaning. number 2 is a worn loose ball screw nut or worn ball screw thats extra worn in certain spots

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