The excavator characteristic of the electric drives of the digging mechanisms is a necessary but insufficient condition for limiting the moment. With unfavorable dynamic properties of the electric drive system in the modes of abrupt stopping, torque peaks may occur that significantly exceed the stopping value corresponding to the static excavator characteristic.
Therefore, in the further presentation, special attention will be paid to the analysis of the dynamic properties of the electric drive system. The likelihood of mechanical overloads is characteristic of other basic mechanisms that are not directly involved in the digging process. As mentioned above, the electric drive for lifting on the dragline during the digging process plays an auxiliary role and has an insignificant load in this mode..
However, dangerous mechanical overloads can occur when a bucket breaks off after digging, when a loaded bucket is lifted under conditions of large stretching, etc. Although to a lesser extent, such mechanical overloads are also likely on the swing mechanism, for example, when cleaning a face. Therefore, the requirement to limit the moment during mechanical overloads is imposed on all main electric drives of excavators, and the main means of limiting the moment is the use of an electric drive with an excavator characteristic.
However, the requirements for the shape of the excavator characteristics for mechanisms that are not involved in digging are significantly different. Transient processes of the electric swing drive significantly affect the performance of the mechanism, since the time spent on rotation reaches 70-80% of the excavation cycle time.
The minimum transient time and, therefore, the maximum performance can be obtained if the specified allowable acceleration is fully used in all modes. In other words, the optimal from the point of view of performance should be considered the uniformly accelerated course of transient processes at a constant acceleration equal to the given one. In this case, the permissible starting torque of the swing drive must be equal to