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INTRODUCTION  275














                           (a)




                                                               (b)









                           (c)
                                                                 (d)







                           (e)

            Figure 6.1 Five commonly used 3D robot arm linkages: (a) RRP, “polar coordinates”
            arm, with a spherical workspace; (b) PRP, “cylindrical coordinates” arm, with a cylindrical
            workspace; (c) PPP, Cartesian arm, with a “cubicle” workspace; (d) RRP, SCARA-
            type arm, with a cylindrical workspace; and (e) RRR, “articulate” arm, with a spherical
            workspace.



            is, in our notation, an RRP arm, is especially popular among assembly oriented
            industrial arm manipulators.
              Recall our showing in Chapter 5 that RR, the arm with two revolute joints, is
            the most general among XX arms, X = [P, R]. We will similarly show that the
            arm RRP is the most general case among XXP arms. The algorithm that works
            for the RRP arm will work for other XXP arms.
              While arm configurations shown in Figure 6.1 have nice straight-line links
            that are mutually perpendicular or parallel, our SIM approach does not require
            such properties unless specified explicitly.
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