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Path Mate - 'The mate cannot be solved with the value specified'

Question asked by John Wayman on Jul 4, 2018

I have homed in on my problem.

I am trying to make a posable model of an industrial robot. It is the identical problem posed in the 11th Power User Challenge, last year. There were some excellent suggestions coming from that challenge, with the one that seemed to suit us best coming from John Stoltzfus, namely the use of a helix to mate the moving part to. This yields the ability to move a robot joint more than 360 degrees.

However, we need to pose this robot model, and Solidworks has given us the Mate Controller for just that task. Sadly, in order to use the Mate Controller, I need to use a Path Mate, with the constraints set to % along path. The coincident mate between spline and sketch point suggested by John is not valid for a mate controller.


Now, here is the problem:


The Path Mate reports the error shown in the title:




using the attached assembly model (or, indeed, the proper robot model) when the mate controller sets the value of the mate to anything between 95.6 and 97.8%, or to exactly 100%. It is happy between 0 and 95.5% and between 97.9 and 99.9%.


Why would that be?



I have tried every variation of path mate settings I can think of, with roll control and without, with pitch/yaw control and without. I have tried mating the axes coincident, mating an axis concentric with a sketch circle, mating a sketch point coincident with an axis, they all yield the same issue.

If I remove every other mate and leave only the path mate, I can drive it from end to end (but the moving part goes all over the place, rather than rotating around the axis at the centre of the helix).

If I make the path mate driven in the mate controller, I can drag the moving part from end to end of the spline.

If I make the path mate free, instead of % along path, I can drag it from end to end, but it is no longer valid for the mate controller.



A bit more information:

If I change the pitch between 0.01mm and 10mm, it seems to make no discernible difference to the behaviour. If, however, I change the diameter of the helix cross section from 175mm to 2mm, I seem to be able to drive the mate controller from 0 to 99.9% without issue. If I go to 100%, it still flips back to the 95% ish position.



What is my error with the attached model?



SW 2018, SP3