Joint analysis in rapid fabrication of non-assembly mechanisms

Purpose - The main purpose of this study is to develop a systematic method that can minimize joint clearance for non-assembly mechanism fabrication using a layer-based fabrication technology. Design/methodology/approach - Joint clearance is one of the key factors affecting a mechanism's performance. Hertz theory is adopted to analyze the joint clearance-penetration displacement relationship and the impact force-displacement relationship. This analysis has indicated the importance of reducing joint clearance. To reduce joint clearance in layer-based fabrication, a drum-shaped roller is proposed for pin joint design in non-assembly mechanism fabrication. Compared to cylindrical pin joint design, a drum-shaped roller joint results in less impact force in mechanism operation. Furthermore, the joint clearance can also be drastically reduced. Findings - Large joint clearance could introduce instability into the dynamic behaviour of a mechanism. By applying a drum-shaped roller, the instability could apparently be alleviated. This has been demonstrated by both simulation and fabrication of a number of mechanisms with and without drum-shaped pin joints. Practical implications - Since the proposed joint design can reduce the joint clearance in rapid fabrication of non-assembly mechanisms, it is possible to expand layer-based rapid fabrication techniques for more mechanism design applications. Originality/value - Layer-based fabrication technologies have two distinct advantages: building parts without geometry restriction; and building subsystems (static or mobile) without the need for assembly. Only very few previous studies have investigated the applications that can benefit from the second advantage due to the limited accuracy of layer-based technologies in making joints of a mechanism. Through the proposed drum-shaped roller pin joint design together with the proposed joint design guidelines, joint clearance can be reduced significantly. Thus, sub-systems or mechanisms built using layer-based technologies could have accuracy close to the design specification. This will expand the application of layer-based technologies to more mechanism or mobile mechanical system studies.