fanuc 6 and ttl linear scales

[skippysmt]

high all got a good one i need to know is it possible to fit a ttl linear scale on to a fanuc 6mb as you can no longer get inductosin scales .has any one done it and what scales did you use one single marker pulse type or ones with a marker ever 20 mm or so i await a reply.
plus i want a fanuc 6mb contection manual any one got one for sale got a maintance one but need to know a few more details.
as what i whant to do is retrofit my matsura 1000 with a fanuc 6 as i have loads of spares but i want scale feed back to make it accurate please help

[Al_The_Man]

Most of the scales available are TTL, with the exception of some Heidenhain, which can be either TTL or low signal sine wave.
You should only require a marker at one end for zero index.
You may have a problem with 'hunting' if you have any degree of backlash between motor and scale, unless you go with dual feedback, motor encoder AND scale, but I don't recall if the 6 will support D.F.B.
Also I seem to recall the scaling is limited on the 6, so you may need to get compatible resolution scales.
Al.

[Dan Fritz]

The 6 control accepts a dual differential TTL level signal from the pulse coders, so if you have a linear scale that sends the same type of signals, the control should be OK with it. The inputs to the CNC are for an "A" pulse, a NOT A pulse, a B pulse, and a NOT B pulse. The A and NOT A signals must always be opposite (A pulse goes high, NOT A pulse goes low). The A pulse and the B pulse should be 90 degrees out of phase. The control will alarm out if the A and NOT A pulses are not always opposite (or the B and NOT B pulses for that matter). For zero-return, the control needs a ZERO pulse and a NOT ZERO pulse, which can be periodic or can be just a single pulse at the zero return point.

Al_The_Man is right that linear scales can create lots of other problems. You must certainly have a very tight connection between motor rotation and linear motion or you will get of "dithering" and unstable oscillations when the servo is stationary.

The Fanuc 6 has parameters for DMR (detect multiplying ratio) and CMR (command multiplying ratio) for each axis. By setting these parameters, you can use almost any resolutution scale. As a general rule, here how it's done:

The DMR parameter for each axis can be set to 1, 2, 3, and 4. This ratio determines how the CNC sees the pulse coder signals. If set to "1", the control sees every rising edge of the A pulse as a valid detect unit. If set to "2", the control sees the rising edge AND the falling edge of the A pulse as a detect unit. A DMR of 3 reads the rising and falling edges of the A pulse and also the rising edge of the B pulse, and a DMR of 4 reads the rising and falling edges of both the A and B pulses. To make a long story short, you use the DMR to set how fine an increment the CNC can use for positioning. Generally, the finer the better.

With Fanuc rotary encoders, you will always see a 2000 ppr encoder used with 2mm, 4mm, 6mm, 8mm or .200 inch, .400 inch ballscrews. You will also see a 2500 ppr encoder used with 2.5mm 5mm, and 10mm screws and also with .250 inch or .500 inch ballscrews. This is so the DMR/CMR settings can make things agree between the axis linear motion and the detect unit. You shouldn't have to worry about this with linear scales.

If your detect unit is .0001 inch or .001 mm, then you can use a CMR of "1". if the detect unit is .00005 inch or .0005 mm, then you use a CMR of "2" because the CNC must move two detect units for every COMMAND unit of .0001 inch or .001mm

The bottom line is that if the DMR or CMR are not set right, your actual slide motion will not be the same as the motion indicated on the position display. Lathes use these settings to get the X axis to move half of the displayed motion so your display reads in DIAMETER instead of RADIUS. You don't have this problem on a mill.

Just don't buy a scale with an oddball number of pulses per inch (or per mm). If you get something like 1024 pulses per inch, there is no way to set the CMR and DMR to make things work out. If you use an inch increment scale, then you're machine will use a "Machine increment system" in inches, and you'll need to use inch/metric conversion to move in millimeters. If your scales are in metric, then your machine increment system will be in metric and you'll have to use inch/metric conversion to move in inches. With rotary encoders, the machine increment system must always match the pitch of the ballscrews (inches or mm) , but with linear encoders you don't have to worry about this either.

One hard & fast rule with the Fanuc 6: You can't "mix & match" inch and metric. If one axis has a metric scale, then ALL axes must have a metric scale (you can't use an inch scale on X and a metric scale on Y, for example).

Good luck.