Research And Implementation Of Ultrasonic On-Machine Thickness Measurement Device With Tool Holder

Thin-walled parts are widely used in aerospace and other fields because of its lighter weight,higher bearing capacity and higher strength.At the same time,this type of parts has higher requirements for machining accuracy.The thickness of such parts is a critical parameter.To ensure this index,thickness inspection is required during machining process.At present,although manual measurement of workpiece on machine can solve this problem,it introduces labor cost and reduces the machining efficiency.Therefore,it is imperative to develop an automatic thickness measurement system on machine for thinwalled parts with high efficiency and universality.There are many methods to measure thickness,among which ultrasonic thickness measurement is more suitable for onmachine measurement of thin-walled parts because of its non-destructive property,high penetrability,applicability of non-metallic material and low cost.Accordingly,an ultrasonic on-machine thickness measurement system with tool holder is proposed in this paper to solve the above problems.The main research contents are as follows:(1)The factors affecting ultrasonic thickness measurement during machine tool processing are investigated,and an ultrasonic on-machine thickness measurement method suitable for this working condition is proposed.It mainly includes the following three parts.(a)Independent ultrasonic on-machine thickness measurement device which avoids wired connection and can be quickly replaced.(b)The cutting fluid is used as ultrasonic coupling agent to avoid many problems caused by the introduction of additional coupling agent.(c)The ultrasonic transducer with reasonable parameters is selected to make the whole machine have better ultrasonic performance.(2)The denoising method and thickness feature extraction method for ultrasonic echo signal are choosed.By analyzing and comparing various algorithms,the proposed algorithm can improve the computational efficiency and reduce the use of logic units in the FPGA as much as possible under the premise of guaranteeing the accuracy of calculation.(3)The hardware circuit and mechanical structure of the whole machine are designed and implemented.The main design criteria for the circuit part is to get better echo signal and lower power consumption as far as possible under the condition that the overall function can be completed.It mainly includes ultrasonic excitation circuit,signal processing circuit,auxiliary circuit,main control circuit and so on.Mechanical structure needs to be waterproof,oil-proof,anti-electromagnetic interference and quickly replaceable.It is also required to have flexible contact between the ultrasonic probe and the workpiece during measurement.It mainly includes BT-40 tool holder,cavity for mounting circuit,clamping mechanism for probe with flexible contact function and so on.(4)The implementation of embedded software based on Verilog for ultrasonic onmachine thickness measurement device is shown.Firstly,the implementation and optimization of software based on the theoretical algorithm studied in the second part are completed.Then the functions of time sequence control,thickness measurement,wireless communication,electric quantity detection,automatic startup and shutdown are realized.Finally,the debugging of the prototype was realized.The accuracy of measurement and the functions of the prototype are verified by experiments in a simulated real working environment.