6/28/2016 2:41 PM  
Joined: 6/29/2012 Last visit: 4/3/2020 Posts: 730 Rating: (4) 
I have to revamp a machine from Masterdrive to Simotion. In Masterdrive the master axis has a cycle length of 1000 000 LU (that stands in fact for a circumference of 1000mm). I should want to make it comparable in the Simotion, so I think about using lineair axis with a modulo of 1000 mm. This should be no problem, but was told if you have a lineair axis with modulo that keeps on turing in the same direction, that after many many rotations the position will not be correct anymore because of pi (3.14....) has a finite precision in the controller, and so you will accumulate a fault. For a rotary axis you would not have this problem, is this really so? Am I in this obliged to use a rotary axis for endless rotary movement (if I want precision even after multiple turns in same direction)? 
6/28/2016 6:50 PM  
Joined: 6/9/2014 Last visit: 8/18/2019 Posts: 122 Rating: (10) 
Absolutely yes, save yourself the trouble you mentioned and use rotary axis if the absolute angle of the axis is critical. Also, as you may already know, additionally you need to enter the exact numerator/denominator gear ratio from the motor shaft to the load. So mechanically only timing belts, chains, or gearbox gearing can be used (no vbelts or anything else that can slip). 
6/29/2016 7:51 AM  
Joined: 6/29/2012 Last visit: 4/3/2020 Posts: 730 Rating: (4) 
For the moment I am not sure yet if a lineair axis with modulo gives indeed problems position repeatability if it rotates continuously in the same direction. 
6/29/2016 8:25 AM  
Joined: 9/23/2005 Last visit: 4/8/2020 Posts: 2557 Rating: (387) 
There's nothing like a problem with the PI in this case. I you parametrize gear ratio correctly and say that the axis is linear with modulo and one turn of the load is 1000 mm, it's completely no different to saying that it is rotating and has modulo. 
Regards, 

6/29/2016 8:43 AM  
Joined: 6/29/2012 Last visit: 4/3/2020 Posts: 730 Rating: (4) 
If in my case I mark the position when the load is at 0 mm, I let it turn continuously in positive direction for 10 000 000 modulo cycles and then let it position to 0 mm, will it stop at the mark I set at the beginning? 
6/29/2016 7:24 PM  
Joined: 9/23/2005 Last visit: 4/8/2020 Posts: 2557 Rating: (387) 
If I understood you well, then it's true. As I wrote, there can be problem with load gearing ratio. But then you will get warning from Simotion that long term axis stability can't be assured. 
Regards, 

6/29/2016 7:38 PM  
Joined: 6/9/2014 Last visit: 8/18/2019 Posts: 122 Rating: (10) 
DavidBrown, If you want to do it the old way, and just say there is 1:1 gear ratio and 1000 mm modulo on a linear axis, you are going to run into issues. 
6/29/2016 9:05 PM  
Joined: 6/29/2012 Last visit: 4/3/2020 Posts: 730 Rating: (4) 
If I understand well, one post above says it will be ok, the other it will not be ok. 
6/30/2016 8:22 AM  
Joined: 9/23/2005 Last visit: 4/8/2020 Posts: 2557 Rating: (387) 
Please show the sketch of your axis  gearings and how your load looks like. 
Regards, 

6/30/2016 11:32 AM  
Joined: 6/29/2012 Last visit: 4/3/2020 Posts: 730 Rating: (4) 
It concerns conversion of Masterdrive MC to Simotion. Parameter of Masterdrive MC : p171 Pos Resolution 15 p180.1 AVWF numerator 3125 U601 MasterAxisCycle 1000000 U604.1 Gearbox numerator 10000 
Follow us on