Abstract:The internal screw detection of nuts was taken as the research subject. The disadvantage of the traditional test method was discussed according to the characteristics, which was done by people and wasted time and energy. A fully automatic detector of testing the internal screw was put forward. The detector contains a pneumatic mobile platform and a test system. Considering the influence of such factors as function implementation, economic cost, precision error, the drive mode of air cylinder, servo motor, ball screw and Linear guide rail were adopted to achieve the locating and testing of workpiece exactly. The study for practical situation of the detector of the internal screw was conducted and the control program of the whole system was put forward with PLC and then the program and design of the control system was introduced in detail. The result shows that the design improves the accuracy of the testing of the internal screw, reduces the labor intensity, cut costs and has application value.