Shaft systems of large marine vessels transfer the kinetic energy produced by the engine to the propeller. The explosive force that gets produced in the cylinder's combustion chamber acts on the top of the piston and gets transferred to the connecting rod which connects to the crankthrow. The crankshaft, composed of the thrust shaft, journal shaft, and flange shaft, connects to the crankthrow, whose role is to convert the piston's linear reciprocal movement into a rotational movement, and to the intermediate shaft, which delivers that rotational movement to the propeller.
Existing assembly methods give foremost consideration to the avoidance of product damage of two-part crankshafts by affording a tolerance of approximately 50mm during primary mobile installation and afterwards applying a manual fine-moving method. While this guarantees safety, it has the disadvantage of prolonging operation duration and demanding more work, so improvement research is imperative. To solve problems that can arise in the assemblage of two-part crankshafts adopted by large-scale engines, proposals to improve the process have been made and experimentally reviewed, including the measurement of mobile displacement using image processing techniques, and the application of techniques that craft the input signals that control the cranes.
In this research, a method was proposed that designed an input-shaping machine that was capable of positioning the crane in a particular desired location. In the study, simulations were conducted that utilized this input-shaping machine to first confirm the elimination of vibrations then to confirm the final positioning of the crane. A natural frequency of 1Hz and acceleration period of 0.05s were afforded. A duration two or more times the acceleration period was established and checked to make sure it did not affect the input-shaping operation. Another item that was checked was the absence of residual vibrations in the object being moved after the input-shaping. The following conclusions were obtained after the results.
In applying the input-shaping technique proposed in this research to the mock assembly process of the two-part crankshaft, the process of proximity feeding of the moving shaft via the crane was improved, which resulted in the possibility of proximity feeding down to an interval of approximately 1.5mm as well as a great reduction of man-hours.
Using the image processing techniques, in order to move a 250-ton crankshaft situated above the rail, in the case of the existing process which strikes the lower jig, the instrumentation yielded displacement per strike of approximately 1/1,000mm and was the primary reason for process delay. In the case of ceiling cranes, there exists a critical point in the large variation of the object's residual vibration tendency, depending on the weight of the moving object. The test subject cranes had these critical points appearing for objects above 140 tons. Automatization of the proximity moving of two-part assemblage for large vessel would require optimization of the crane's critical point.