Influence of the way of applying load on the accuracy of determining low-power drive unit properties

W artykule podjęto zagadnienie odwzorowania przebiegu obciążenia wnoszonego przez mechanizmy urządzeń mechatronicznych małej mocy. Wskazano na wpływ zachowań hamulców elektromaszynowych i elektromagnetycznych ciernych, stosowanych do tych zadań, na dokładność odwzorowania oczekiwanego przebiegu zmian wartości momentu obrotowego w trakcie badań doświadczalnych. Przedstawiono charakterystyczne ich zachowania. Sformułowano zakres czynności, które powinien podjąć eksperymentator dokonując wyboru zespołu obciążającego do stanowiska badawczego układów napędowych małej mocy pracujących w stanach nieustalonych.The paper considers a problem of representing the course of load introduced by mechanisms of low-power mechatronic devices. There is shown the influence of the behaviour of electro-machine and electromagnetic friction brakes used for these purposes on the accuracy of representing the course of torque fluctuations expected during experimental studies. Specific features and behaviour of these brakes are presented. In the case of electromagnetic friction brakes, the course of fluctuations of the developed friction torque is influenced, besides variations of the value of the excitation current, by processes taking place within the magnetic circuit, especially within the powder film (wear products) located in its gap. Representation of load value quick variations enables usage of plate brakes. Correct selection of the friction unit material limits the wear of friction surfaces in this kind of brakes. In the case of applying electromagnetic units as a load, an influence of the rotational speed on the value of the developed torque has to be taken into consideration: for DC motors it is a linear dependency, and for eddy current and hysteresis brakes - a nonlinear dependency. Use of DC motors is connected with the developed torque minimal value, below which they cannot be used in experimental stations. On the other hand, in the case of using eddy current and hysteresis brakes, a significant value of the moment of inertia is introduced, putting an additional load on the tested drive unit. Furthermore, there is defined the scope of activities that should be undertaken while choosing a loading unit to be used in an experimental station for low-power drive systems operating in transient states