135
C2+0, Condition (A5) gives a2r3+r2a3=0 or sin(a2+a3)=0. The values a2+a 3=0 or r, and d3=a2=a3=0 mean that joint axes 2 and 4 are aligned so the arm is degenerate.
When 83=7r, then C3=-l and Condition (A4) forces a2=a3 while Condition (A5) now becomes a273-r2c3=0 or sin(a2-a4)=0. The combination of values (a2-a4)=0, a2=a3, and e3=r again force axis 4 to align with axis 2 which puts the arm in a degenerate configuration.
Since the determinants D1 and D2 are simultaneously zero only when the manipulator is degenerate, We can
conclude that a unique value of 82 can always be computed as indicated in Chapter 5 when the arm is non-degenerate.
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