Influence of geometry on the kinematic performances of a humanoid shoulder-girdle mechanism with clearance in the joints

In mechanisms with joints affected by clearance, the influence of the geometric parameters on the mechanism kinematic performances can be relevant although difficult to predict. The effect of joint clearance is dependent also on the geometry of the pairing elements. This paper focuses on a mechanism of a humanoid shoulder girdle with clearance in the joints and analyzes the influence of geometric parameters on the accuracy of the output link (of the mechanism). The analysis shows that an optimal kinematic design of the mechanism can be achieved with respect to given values of manufacturing tolerances. In addition, the influence of each individual clearance-affected pair on the output link accuracy is evaluated and the optimal clearance allocation can be performed. This enables the fulfilment of the required mechanism performances with a reduction of the mechanism manufacturing costs.