Modeling And Performance Assessment For The Grouping Of The Thrust System Of The Shield Machine

The Shield Machine is the modern equipment for tunnel construction, and the thrust system is the key part of the shield machine. The thrust system mainly undertakes the advances of the shield machine. The thrust system should be able to turn around, advance along a designed line, control the pose, correct error, move synchronizedly, and so on. The grouping-oriented control of the thrust system is the core method to advance the shield machine. With the rapid growing of the economy and urbanization, the quantity demand of the shield machine will greatly increase, thus mastering the design theory of the shield machine is exigent. This paper researches the mechanisms of grouping and advancing of the shield machine, the content is listed in the following:1. Equivalent mechanism modeling for the thrust system of the shield machine.The thrust system consists of many hydraulic cylinders distributed in the circular direction. Each cylinder is articulated to the fore part of the shield machine in one end, with another end pressing against the segment by a shoe. The part that the shoe touches the segment is regarded as a spherical pair, and then each cylinder with its two ends is regarded as one SPS leg. So the whole system can be equivalent to a parallel mechanism with many SPS legs. When the thrust hydraulic cylinders are divided into several groups, one group can be simplified to one SPS leg in terms of the composition principle of the forces and the moments. Therefore, the equivalent mechanism of the grouped thrust system can be modeled.2. Proposition of the grouping types for the thrust system.The main load acting on the thrust system is the friction between the shield and the earth. The distribution of the friction is bilateral symmetry. The distribution of the groups of the thrust hydraulic cylinders should comply with the distribution of the load, so that the thrust system will have better compliance. So the groups should also be bilateral symmetry. According to this principle, 8 possible grouping types are proposed for the designer to choose, and the equivalent models of different grouping types are modeled.3. Performance analysis for the thrust system.Based on the equivalent mechanism, position, velocity, statics are analyzed by the inverse method of the parallel mechanism. For sovling the equation of balanced statics when the redundant mechanism is singular, a dividing method is proposed.4. Evaluting indicator for performance analysis of different grouping models.Thrust hydraulic cylinders touches directly to the segments, the reaction force of the thrust force acts on the segments. Since the reaction force is always very large, the uniformity of the reaction force will affect the segments. Bad uniformity of the reaction force will dislocate the segments, even destroy the segments. Based on this, the evaluating indicator of the uniformity of the thrust force is proposed to evaluate different grouping models.