Abstract
In this paper, a precise nonlinear dynamic analysis of an automatic pipe-cutting machine and design process for the speed controller using the nonlinear model are presented. This machine uses magnet to attach itself to the pipe against gravity. The machine has well aligned four wheels that are driven by DC motor and its speed is measured with hall sensors in the motor. During pipe cutting process, the tangential force due to the gravity acting on the pipe-cutting machine widely varies. That is, without any control, the cutting machine gets fast when moving from the top to the bottom of the pipe and slow when moving from the bottom to the top. Actually the system is kind of a nonlinear system where the tangential component of the gravity is function of climbing angle of the cutting machine along the pipe. The cutting quality is deteriorated with irregular cutting speed. Especially jerking motion is critical. It is necessary to maintain constant cutting speed to obtain good cutting quality. To design a precise controller for this system, it is necessary to obtain a dynamic model of the system as exact as possible. The machine is modeled as a nonlinear multibody dynamic system and the multibody model is verified with experimentally measured results. For the design of control system, the interactive off-line computer simulation with developed dynamic model is performed with experimentally obtained parameters. Co-simulation processing method is proposed to estimate angular position along the pipe from the feedback signal of motor. and compensate gravity effect to obtain constant driving speed.
