In the European market, palletising robots represent a large share of the use compared to other robots. The main advantage of palletising robots is that, high speeds can be achieved for different payload sizes, by virtue of the parallelogram mechanism, which allows the robot to use only 4 axes. The parallelogram mechanism ensures that the clamping flange is always parallel to the robot base. As long as the parallelogram mechanism has a perfect geometry, the clamping flange maintains the perfect parallelism with the robot base. The problem in demanding applications of the clamping flange angle arises due to the errors and deviations of the parallelogram mechanism projection from its ideal geometry. All the possible causes of the problem are summarised as follows: incorrect lengths of the links of the parallelogram mechanism, deformation of these links and bending in the joints of the parallelogram mechanism. On the basis of the measurements of the clamping flange inclination, the length of the parallelogram geometry and the static and kinematic analyses, it was established that the links’ lengths within the tolerance range have a negligible impact on the inclination. In the most critical case, the deformation of the links themselves has a small impact, and the bending deformation in the joints has a substantial effect, which significantly changes the links lengths in the parallelogram mechanism projection. The critical joints were identified and a solution was reached that increases the stiffness in one bearing joint by using a different bearing design.
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