Synthesis of variation structure in case of indirect torque measurement
When measuring the torque dynamic constituents by a variation structure there revealed two shortcomings, greatly limiting its application: firstly, uncertainty of the measurement result under the set permanent values of a motor drive power and, secondly, cut-off of low-frequency range of the input signals as a result of the differentiating characteristics of measuring channels. The authors propose a synthesized torque meter free of the above-mentioned drawbacks. The essence of the proposal is the synthesis of the variation structure of the torque measurement in case of the indirect method of measurement on the example of a measuring instrument to drive the drill rig with a DC electric motor. Adjusted variation structure allows eliminating differentiation property, which leads to an increase of the frequency range of the input signals up to the values of f = 0 and automatic elimination of the appearance of the uncertainty occurrence of the measurement result. The estimation of the meter dynamic properties, which are completely determined by the time constants of low-pass filters in the measurement channels of a drive motor current and the channel angular velocity measurement. The effect of the difference ratios of the measuring channels’ inertial properties on the variance of the measurement result estimation and, consequently, on the random error value, is determined. Some mathematical simulation modeling of the meter and the drive on the basis of Monte Carlo method, which allowed carrying out the calculation of random errors and identifying their dependence on the ratios of the measurement channels’ inertial characteristics are performed. Based on studies conducted, there determined the maximum value of torque measurement error, that allowed making a conclusion about the metrological involvement of the synthesized meter. It is shown that the proposed torque meter is suitable for all kinds of motor drives with meters-converters into electrical value.