DC motor speed control of annual-ring measuring instrument based on variable universe fuzzy control algorithm

A annual-ring measuring instrument drives a drill needle into a tree by a DC motor and determines the age of the tree according to the change of the resistance of the drill needle. Because the density of trees varies greatly among different tree species, even in the same tree, the density of early wood and late wood also varies greatly, the resistance of the drill needle varies greatly and the load of the DC motor varies greatly. If the DC motor is not controlled by a suitable speed control algorithm, the speed error of the DC motor will be very large. The measuring accuracy of the annual-ring measuring instrument decreases with the increase of the DC motor speed error. How to improve the accuracy of motor speed is one of the key technologies in the annual-ring measuring instrument. The principle of PID control algorithm and variable universe fuzzy control algorithm were analyzed. The two control algorithms were used to control DC motor of annual ring measuring instrument, respectively. The discs of 7 tree species, including Larix, Pinustabulaeformis, Spruce, Poplar, Betula platyphylla, Betula koraiensis and Quercus liaotungensis were drilled by the annual-ring measuring instrument that was controlled by PID control algorithm and variable universe fuzzy control algorithm, respectively. The experimental tree species included conifers, hard broadleaf trees and soft broadleaf trees. The wood density distribution of experimental trees basically covered the density distribution range of common trees in temperate zone. Five discs were selected for each experimental tree species, and each disc was tested twice with the two control algorithms, respectively. The starting measurement points of the two control algorithms were as close as possible and the measurement directions of the two control algorithms were the same in every group test to ensure that the drilling paths of two control algorithms in the disc was close, and the difference of wood properties of the two drilling paths was little. The starting characteristics of DC motor, the standard deviation of DC motor speed error was analyzed. If the motor was controlled by the variable universe fuzzy control algorithm, it took about 90 ms to reach a stable state after the motor was started, while if the motor was controlled by the PID control algorithm, it took about 160 ms. In 70 tests, the average error standard deviation of the variable universe fuzzy control algorithm was 33.8 r/min, and that of the PID control algorithm was 40.3 r/min. The control precision of the variable universe fuzzy control algorithm was 0.21% higher than that of the PID control algorithm. Among the 7 tested tree species, the variation range of error standard deviation of variable universe fuzzy control algorithm of 6 tree species was less than that of PID algorithm, and that of variable universe fuzzy control algorithm of only one tree species was slightly larger than that of PID algorithm. The experimental results show that the variable universe fuzzy control algorithm has the advantages of faster response, better robustness and smaller steady-state error compared with PID control algorithm. Therefore, the variable universe fuzzy control algorithm was selected to control the DC motor of the annual- ring measuring instrument.