Design of Steering Mechanism and Control of Nonholonomic Trailer Systems

-7803-5886-4/00/$10.00© 2000 IEEE 247 one. Being converted to the chained form, a tractor and all trailers can be stabilized to desired positions via. esla.I)lished nonholonomie motion control strategies for the chained form[5, 6, 7]. S0rdalen, Naka~ mura and Chung[8] developed "t, he nonholonomic manipulator," whose kinematic model is similar to those of trailer systems. The real-world tra~ject.ory generated by the nonholonomic motion control tends to contain high frequency oscillations or large overshoot, although the mathematical trajectory in the chained form enjoys a nice convergent profile. Chung and Nakamura[9] then proposed to consider mathematical simplicity in the chained-form transformation and designed "the chained form manipulator." On tile other hand, trailers have been developed and widely used in the industry. The main focus of such design was on reducing passive tracking error fi'om t, ractor's trajectory, and little attention was paid on active motion cent.tel. Automated trailer systems will find an important part in automated factories, ports or airports, if the technology is available. Nonholonomic motion planning/control will be applied when loading and unloadtug freighl.. In this paper, we all.erupt to fidfill the gap between t.he nonlinear control theory for nonholonomic trailer systems and the mechanical design for good passive tracking performance of indust.rial trailer systems. Based on the knowledge of clm.ined form transformation, we design a new passive steering mecha.nism and show that it, provides a trailer with the both properties; namely, the chained-form convertihility and a good passive tracking performance. A proretype is fabricated and used t.o verify the proposed design theory. 2 K i n e m a t i c M o d e l s o f T r a i l e r S y s t e m w i t h S t e e r i n g 2.1 T h e K i n e m a t i c M o d e l We will compare performances of different mechanical design of trailers with and without, steering. The most general design of trailer system is shown in Fig. 1, from which all the comparative designs we discuss are derived by appropriate choice of parameters.