Heidenhain and their "reference mark" scales vs DRO's that keep numbers in memory...

Heidenhain and their "reference mark" scales vs DRO's that keep numbers in memory...

In other words, best I can tell there is no way for a current generation (and maybe past generations as well) Heidenhain to keep the last axis numbers in memory after you shut down the power. You have to either enter new numbers or move to the reference mark on the scale.

In contrast I have noticed that both Accurate and Newall DRO's will keep the last numbers in memory even after DRO is off (in the case of Newall even if power is disconnected !) Why is Heidenhain not like that ?

Not sure what you mean exactly..
My HH DRO's keep track of any datum set points in all axis when powered off if you set them.....But you must pass a reference mark on the scale (move the axis) to
re-sync the scale to the box for each axis.......Not sure what else you need...

Don't see how you can keep track of position when powered off without some sort of reference on the scale unless the DRO has powered "absolute" scales.
Or am i missing something...Cheers Ross

I think this is what is available:

- the DRO just counts the pulses, and loses all data when switched off. The older ones.
- the DRO counts, but keeps data in memory when switched off. How most cheap DRO works. I think when the axis are moved while the DRO is off, you get wrong data when switched on.
- the DRO counts, but has refence points. Heidenhain, and most CNC machines. Prevents wrong data when switched on again. However miscalculation is still possible but almost never happens.
- the DRO uses absolute scales. As fas as I know the only absolute scales are the Mitutoyo AT715 scale. Gives right away the correct data when switched on, no refence needed. (also how Okuma CNC machines works) I think this is the best system however scales are limited in lenght because every position on the scale has it's unique code.

Kees said:

- the DRO uses absolute scales. As fas as I know the only absolute scales are the Mitutoyo AT715 scale. Gives right away the correct data when switched on, no refence needed. (also how Okuma CNC machines works) I think this is the best system however scales are limited in lenght because every position on the scale has it's unique code.

Click to expand...

There are many different ways to achieve absolute scales. And many suppliers of such.

The 3 basic styles are:
- power the readhead while the unit is switched off. Fanuc does this.
- Grey encoders. Most common for rotary measurement.
- Paired relatively prime scales.

Paired relatively prime scales are the most common solution for linear measurement systems. They work by having two scales in close disagreement, and correlating the actual position to the degree of disagreement between the scales.

The downside to paired relatively prime scales is that it takes a certain amount of motion to correlate the disagreement. The amount of motion required to 'lock-up' is position dependant upon the layout of the scales.

HH reference marks sort of work like paired relatively primes scales. The distance between any two reference marks is unique, so upon passing the 2nd reference mark the DRO can calculate the absolute position.

HH has a line of absolute scales for DRO applications.I believe it is the LC115/415 line.They cost a lot more than the already expensive LS line and can communicate only with HH's flagship DRO, pt880...