用凌阳SPMC75F2413A单片机配合编码器对直流电机进行闭环反馈控制，使直流电机带动的钩状扫描针停在规定的位置上.使用PID反馈控制算法进行反馈控制，使用编码器将钩状扫描针的位移转换为电脉冲，通过单片机对采回的电脉冲进行分析处理，与规定值比较，利用差值算出PWM输出信号，控制直流电机正转或反转，即钩状扫描针若高于规定位置直流电机随即反转，若低于规定位置直流电机正转.

Closed feedback control to DC motor was made by PID based on SPMC75F2413A SMC and coder in order to make the hookliked scanning probe driven by the DC motor to rest on the specified position. The PID feedback control algorithm can be used to realize displacement control. The coder changes the displacement of the hookliked scanning probe to electric pulse. Through SPMC75F2413A SMC, these electric pulses were analyzed and compared to the specified value. The output signals were calculated by the differences to control the right and reverse round of the motor, i.e. when the hooklike probe is higher than the position, the DC motor rotates reversely immediately, if lower, the motor rounds rightly.