The excavator characteristic of electric drives of 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 sharp stalling, torque peaks may occur that significantly exceed the stall 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 probability of mechanical overloads is also characteristic of other main mechanisms that do not directly participate in the process of digging. As mentioned above, the dragline lifting electric drive plays an auxiliary role in the digging process and has an insignificant load in this mode.
However, dangerous mechanical overloads can occur when the bucket breaks off after digging, when lifting a laden bucket under conditions of large stretch, etc. P. Although to a lesser extent, such mechanical overloads are also likely on the turning mechanism, for example, when cleaning the face. Therefore, the requirement to limit the torque during mechanical overloads is imposed on all the main electric drives of excavators, and the main means of limiting the torque 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. The transitional processes of electric drive significantly affect the performance of the mechanism, since the time spent on rotation reaches 70-80% of the time of the working cycle of excavation.
The minimum time of transitional processes and, therefore, maximum performance can be obtained if the specified permissible acceleration is fully used in all modes. In other words, the optimal in terms of performance should be considered uniformly accelerated course of transitional processes with constant acceleration equal to a given. In this case, the permissible starting moment of the electric drive should be equal