2013/12/26 Robert Ellenberg <[email protected]> > > > > The limits should definitely be pluggable to account at least for angular > > limits of ball joints etc. > > BTW some standard cone workspace for AB axes would be OK for many > parallel > > robots. > > > > But usual kinematics module seems enough for velocities and accelerations > > check if the planner could perform it. > > > My 2 cents: > > I like the idea of a reachability check, but I'm not sure the limit check > is the right place for it. A common way to measure reachability for a robot > like a 6DOF arm is with a pre-computed reachability space. First, you > sample a bunch of robot poses, rejecting any poses that are in collision. > The ones that are left (and the corresponding workspace positions) are your > reachable space. > > When you run the reachability check, if your pose is near enough to one of > these points, then it's a reachable pose. There are simplifications you can > make for cases like the linear delta robot, but fundamentally this is a > search problem, which means many (possibly slow) steps. > > In my opinion, the limit check is really just there to keep the axes from > going past their physical limits. Even on a trivial case like a CNC mill, > there are "dead" spots that you can't easily check for (such as a big vise > in the middle of the table!). Your part program is designed to avoid the > fixture, but ultimately it's an act of faith to hit play. > > For many parallel robots some combinations of cones and cylinders can describe their actual workspace pretty well. For a serial robot arm it's can be more complicated but those cones and cylinders (along with joints limits) are much better than a trivial XYZ box. For CNC mill from your example it could be useful to exclude some smaller boxes or cylinders out of the rectangular workspace. Of course, a prepared and checked G-code is (more or less) safe but using actual machine workspace limits makes it double safe.
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