On 12/26/2013 2:00 PM, Andrew wrote: > >> Details: >> Given a maximum X, Y, and Z velocity of 1.0, the maximum speed of an XY >> move is 1.414 (or SQRT(2)), and the maximum speed of an XYZ move is 1.73 >> (or SQRT(3)), so I have to set my limits to 1/1.73 (0.577) of the actual >> limits or the machine will exceed them in the "corner" case. >> (pun intended) >> >> > There's another problem: dJ1/dX can significantly exceed 1, the same for > dJ1/dY and dJ1/dZ (say J1 is the first joint). > And during XYZ move dJ1 = dJ1/dX + dJ1/dY + dJ1/dZ can be very large in the > worst case. > > I have exactly the same with my parallel robot, even worse for 6axis. > > The solution I can think of: calculating each joint velocity and > acceleration before each move (at several points at least for a long moves) > and then decreasing XYZ velocities to fit joint velocities to their limits.
Yes, the problem can get arbitrarily hard, depending on exactly what you want to check and if you're doing things like mapping the move into joint space in order to run the check. That's a big reason I think the limit check(s) should be plug-able. For now, I'd be happy with something that simply limited the combined XYZ velocity and acceleration limits to a particular value. But if the CPU cycles are available, there's no reason code couldn't be written that worked with the real joint limits and worked backwards through the kinematics. But before anything fancy can happen, there needs to be a way to implement a more sophisticated check for the various limits. -- Charles Steinkuehler [email protected]
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