If atan2() returns a negative result, add 360 degrees (or the equivalent in
radians) to the result.
Neil
2010/6/11 Viesturs Lācis <viesturs.la...@gmail.com>
> 2010/6/11 Przemek Klosowski <przemek.klosow...@gmail.com>:
> >> 1 #include "rtapi_math.h"
> >> 2 #include "kinematics.h" /* these decls */
> >> 3
> >> 4 const double head_offset = 200;
> >> 5
> >> 6 PmCartesian old;
> >> 7
> >> 8 in t kinematicsForward(const double *joints,
> >> 9 EmcPose * pos,
> >> 10 const KINEMATICS_FORWARD_FLAGS * fflags,
> >> 11 KINEMATICS_INVERSE_FLAGS * iflags)
> >> 12 {
> >> 13 double xy_tan = atan2(pos->tran.y - old.y,pos->tran.x - old.x);
> >> 14 pos->tran.x = joints[0] - head_offset * sin(joints[5]);
> >> 15 pos->tran.y = joints[2] + head_offset * sin(joints[4]);
> >> 16 pos->tran.z = joints[3] + cos(joints[4]) * cos(joints[5]) *
> head_offset;
> >> 17 pos->a = asin(sin(joints[4]) / cos(xy_tan));
> >> 18 if xy_tan = 90 + (180 * i), where i is not 0, but is 1, 2, 3, etc
> >> or -1, -2, -3, -4 etc
> >> 19 then pos->a = asin(sin(joints[5]) / sin(xy_tan));
> >>
> > OK, but what is 'i'? or are you saying that the test is for
> > (xy_tan-90) being an integer multiple of 180? without understanding
> > your geometry, this doesn't make immediate sense to me...
> >
>
> If You recall trignometry from elementary school, tangent values (just
> like for sin and cos functions) repeat every 180 degrees. For example
> tangent of 45 degrees is 1. Just like it is for 225, 405 etc. General
> way to write it is tan(45 + 180*i) = 1, where i is integer - 1, 2, 3,
> 4, 5 etc.
> Actually I seem to have made this bit more complicated as necessary -
> for me xy_tan should be in range from 0 to 359 (including both of
> these numbers), so instead of writing "90 + (180 * i)", I could have
> said "90 or 270".
>
> By the way, how should I limit the xy_tan in the mentioned range from 0 to
> 359?
>
> For example, for deltaX = 1, deltaY = -1 in Excel for atan2 function I
> get value -45 degrees, while I would like it to be 315. This way each
> position for xy_would be described with only one possible value
> instead of several. Like in the given example, it can be -45 or +315
> etc.
>
> >
> > because you whip the value of pos->a betweenthe values based on joints[5]
> and
> > joints[4]--normally I would expect the pos values to be continuous.
> >
>
> Just to make sure that I understand You correctly - do You see the
> probpos->a = asin(sin(joints[5]) / sin(xy_tan));lem in the fact that I
> want to switch from this formula pos->a = asin(sin(joints[4]) /
> cos(xy_tan)); to this formula pos->a = asin(sin(joints[5]) /
> sin(xy_tan));?
>
> If this is the case, then how should I treat the situation that for
> xy_tan values 90 and 270 the cos(xy_tan) = 0 and dividing by zero is
> error. How to solve that? In those situations the nozzle will be
> moving along Y axis and all the tilt should be "in joint[5]", joint[4]
> should be in its zero point. So in this situation joint[4] = 0, but
> pos->a must not be zero. The same situation is for xy_tan values 0 and
> 180 - joint [5] should be in its zero point and all the tilt should be
> "in joint[4].
>
> Are there any suggestions?
>
> Just to remind - I am trying to implement kinematics, where cutting
> head with A and B rotary axis (rotating around X and Y axis
> respectively) are behaving as a cutting head with A and C rotary axis
> (rotating around X and Z axis respectively) where A angle (amount of
> the tilt of the head) is given in g-code, but C is calculated as a
> tangent of the head movement, so that direction of tilt is ALWAYS
> perpendicular to direction of movement.
>
> It seems to me that I have managed implementation of calculating the
> tangent, and that the struggle is with transforming these A-C style
> kinematics into A-B style cutting head.
>
>
> 2010/6/11 yann jautard <brico...@free.fr>:
> >
> >
> > Viesturs Lācis wrote:
> >>
> >> 1) What would correct syntax for line 18 and 19 look like?
> >>
> > could be something like :
> >
> > 18 for (int i=1; i< limit; i++){
> > 19 if (xy_tan == (90+(180*i)) || xy_tan == (90-(180*i)))
> > 19 pos->a = asin(sin(joints[5]) / sin(xy_tan));
> > 20 }
> >
> > where limit is the maximal value I can take.
> > this code is not optimised, because for large "limit" value, il will
> > take a long time to iterate. But should work right for a limit value of
> > 5 or 10.
> >
>
> Thank You for the code!, I will try it.
>
> with best regards,
> Viesturs
>
>
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