Dynamic simulation of a planetary gear for robots

University essay from Linnéuniversitetet/Institutionen för maskinteknik (MT)

Abstract: Gear drives are widely applied in mechanical transmission systems and very accurate transmission systems are needed. In the robot industry, the planetary gear train (PGT) is commonly used to promote the torque transmission. One of the advantages of an ideal PGT is that the incoming torque is divided equally among the planet gear wheels. However, different manufacturing and assembling deviations may cause uneven load distributions. This is a serious problem that affects the load capacity and the stability of the torque transmission.SwePart has designed and patented a planetary gear blazing for very high-accuracy robots and zero gaps in the gear maintained during its operating time [25]. The purpose of this project is to determine how deviations such as pitch deviation and stiffness affect the magnitude of the contact forces acting on gear teeth from the ideal geometry.In order to model the ideal geometry, an inspection of the SwePart’s gears was needed. By using SOLIDWORKS, the common normal line which is perpendicular to the teeth profiles can be defined. This means that the base circle which is tangential to that common normal line can also be found.The gear profiles of the PGTs in this study were created using the software MATLAB based on the parametric equation of involute of the base circle. The data generated by MATLAB were then used to create 3D models of the PGTs in SOLIDWORKS. The gears were split into 2N+1 parts if the number of teeth is N, since different magnitude of the pitch deviations needs to be studied. It is more informative to compare the magnitude of contact forces acting on each half tooth.When the gears which are similar to the SwePart’s gears were finished, the x_t document was exported from SOLIDWORKS and imported into MSC_ADAMS to make the simulations. After that the materials were defined in the model and contact forces were added between teeth of the planetary gear and the ring gear. The magnitude of the contact forces acting on the rigid and flexible gear teeth were then compared. So, MSC_ADAMS needs to be used to mesh the rigid bodies to the flexible ones automatically by calling MSC_Nastran.MATLAB was used to compare the results and graphs from different ADAMS models.

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