Study And Manufacture Of Digital Display Low Torque Wrench

As a bolt or nut tightening tool, the digital display torque wrench based on MCU is akind of intelligent instruments. It plays an important role in the fastening occasions,particularly, in the equipments demanding higher torque. It can accurately measure anddisplay the output torque, and will have a broad application prospect in the market.In the paper, a resistance strain gauge torque sensor is used, the weak signal when thetorque changes is collected. After amplifying, filtering and removing of interference withsignal conditioning circuitry, the torque signal is sent to the MCU P89LPC932byhigh-precision analog-to-digital converter handled, and then it call the A/D conversionsubroutine to calculate the torque value. At last the torque value is sent to the LCD displayand precisely displayed. If the measured torque values meet or exceed the specified torquevalue, the wrench will send out audible and visual alarm.In the wrench hardware circuit, a large-capacity li-ion battery is used as the power thatcould be directly charged with the USB interface. During the charging process it can displaythe charging capacity, and a charging protecting circuit is designed for it. The circuit adoptsuniform stabilized voltage power in strain gauge bridge, a signal amplifying circuit, A/Dconverter and MCU and so on, which reduces the impact of the changing in voltage to acertain extent. In order to make the hardware circuit smaller, extend the using time andimprove the measuring precision, the components with small size, low power consumptionand high precision are selected. In addition, the wrench also has low power prompt, a soundand light alarm device and can shut down automatically.The digital wrench has two working modes: tracking and the peak hold. With three kindsof common engineering units: N.m, lb.ft and lb.in, it can be set by keyboard according to therequirements. Four thousand of torque value can be stored in the wrench’s memory, thedigital torque wrench data management system was designed in order to record and view theparameters for the torque values conveniently which can improve production efficiency.Finally, through doing measuring experiments on the digital wrenches, the results show thatall properties have reached the design requirements.