2011/4/19 andy pugh <[email protected]>: > On 19 April 2011 08:12, Viesturs Lācis <[email protected]> wrote: > > >From my readings about DH parameters, I understand that in prismatic >> joints the D is the joint variable. D is measured along Z axis of >> joint's coordinate system. So for joint 0 to be prismatic in X, I just >> need to rotate it's coordinate frame so that joint's Z matches base's >> X. It is done with Theta and Alpha parameters: >> 1) Theta rotates around "old Z" - that is base's Z. So I should rotate >> it by 90 degrees so that "new X" point along "old Y"; > > Rotating a vector parallel to Z around Z leaves it parallel to Z. > >> 2) Alpha rotates along "new X" - so I should rotate by the same 90 >> degrees in the same direction so that "new Z" matches "old X" > > And a rotation about X leaves it perpendicular to X. > > (Alpha then theta would work, theta then alpha can't).
I feel that we have misunderstanding here... Alpha rotates around X (X stays, Z (and Y) are moved), theta - around Z (Z stays, X (and Y) are moved). And theta goes first, alpha is second. So theta should move X to where Y was and then with alpha (by turning around the "new" - already displace - X axis) Z would be placed, where was X. Please, take a look - I drew small sketch, how it is done in 2 steps: http://www.cutting.lv/fileadmin/user_upload/DH.JPG > Is it possible to call your linear axis "Y" and just live with it? > > Otherwise you could create a 7-joint kins with Alpha-0 = 90 and THETA-1 = 90. Well, actually I already had a thought that I could do that for one particular machine, but I would like genserkins to work correctly. >>> There is a spurious conversion from linear mm to radians. You need to >>> move the joint 360mm to move Y or Z by pi mm. >>> line 444 in genserkins looks like one likely culprit. >> >> Line 521 converts them back to degrees. > > But the linear axes should never be converted, nor be converted back. Yes, I agree, it should not do that. Please, I would really really appreciate more opinions on this matter! Viesturs ------------------------------------------------------------------------------ Benefiting from Server Virtualization: Beyond Initial Workload Consolidation -- Increasing the use of server virtualization is a top priority.Virtualization can reduce costs, simplify management, and improve application availability and disaster protection. Learn more about boosting the value of server virtualization. http://p.sf.net/sfu/vmware-sfdev2dev _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
