(A) study on the vibratory assembly method for robotic assembly

Abstract

Flexible assembly system utilizing an industrial robot, which is widely studied nowadays, have to mate various parts contrary to the fixed assembly system. Since the constituents of such system may have positioning uncertainties, such FMS requires programmability and adaptability to cope with various assembly environments. However, it is very difficult to obtain a complete a priori knowledge of their characteristics. In precision assembly, even small misalignment between two mating part can cause large mating force and make the assembly be impossible as a result. Although many assembly methods were investigated to overcome those problems up to now, they have still some problems: limited applications, no programmability or using high cost sensing devices. As one of the assembly method, a vibratory assembly method is considered in this thesis. A PWM controller-based pneumatic vibratory wrist is developed, which has programmability and controllability. Although the method yields improved performances, they are critically dependent upon various system parameters. This necessitates an accurate evaluation of the vibratory assembly method. The thesis is composed of three main parts. firstly, the characteristics of the vibratory wrist are investigated through a series of simulations and experiments. The vibration characteristics such as the magnitude and the trajectory can be exactly controlled by the carrier frequencies. In addition, the center position of the vibration is regulated at the desired positions due to PI controllers. Secondly, the assembly performances are investigated through a series of insertion experiments. The assembly performance is verified through chamferless peg-in-hole task. The results show that searching a hole was performed very fast without any search algorithm at almost all carrier frequency ratio. The positioning error range in which the peg can be inserted is much dependent upon the vibration magnitude. However, there is impactforces in s...