The torque change of mechanical power equipment is an important information of its operation status. Torque testing is an indispensable content for the development, quality inspection, optimization control, working condition monitoring and fault diagnosis of various mechanical products. Torque sensors have been widely used in the optimization design and intelligent control of power drive systems of various mechanical equipment. At present, there are many types of torque sensors developed and researched at home and abroad. In principle, they are mainly divided into four types: strain type, magnetoelastic type, angle type and other types. Strain type sensor This type of sensor is currently the most widely used sensor at home and abroad. It adopts the traditional method of attaching strain gauges on the surface of the rotating shaft, using appropriate circuits to obtain signals, and then analyzing and processing. Figure 1 shows a schematic diagram of the patch of this sensor. According to the theory of material mechanics, for a shaft subjected to pure torque, the direction of the principal stress on its surface is at an angle of 45° and 135° to the axis, and the absolute value of the principal stress is equal to the maximum shear stress. Therefore, two strain gauges are attached to the torsion shaft of the sensor in two directions, 45° and 135° to the axis, and they are connected into a differential full bridge. The output voltage is proportional to the torque on the torsion shaft. This type of sensor is still widely used in the torque measurement of static and low-speed rotating systems due to its low cost and simple operation. In the past, the method of transmitting torque information using a collector ring was more commonly used. Due to the wear of its contacts and the change of contact resistance, the measurement accuracy and service life of the sensor are affected, and there is a lot of noise. With the development of large-scale integrated circuits, solid-state module devices and microcircuits, since the 1980s, domestic and foreign countries have successively introduced the application of radio telemetry technology in rotating shaft torque measurement. In terms of domestic conditions alone, there are three representative ones. (1) The online dynamic torque tester developed by Luoyang Institute of Technology and other units concentrates the detection and transmission circuits on a 20 mm × 35 mm printed circuit board, which is fixed to the sensor and rotates with the sensor. It converts the torque signal into an electrical signal through the sensor, and the transmitter sends a frequency signal proportional to the torque. After the receiver and processing circuit, it is converted into voltage, and the instantaneous torque is digitally displayed. When the torque exceeds the set value, the instrument alarms to protect the equipment. In order to improve the ability to resist natural interference, a series of measures are taken during the circuit design process, such as shielding of the bridge, transmitter, and battery, reasonable wiring, and correct grounding, so as to reduce the impact of electromagnetic interference sources on the instrument.
(2) The infrared torque tester developed by Yanshan University uses infrared rays to remotely measure the torque of rotating components. This test system consists of two parts: an infrared data receiving device (host) fixed to the ground and a measuring and infrared data transmitting device (measuring device) installed on the rotating shaft. The working principle is: when the host starts the optical signal of the measuring device, the receiving diode on the rotating shaft disc converts the optical signal into an electrical signal, which is transmitted to the P1.0 port of the single-chip microcomputer through the amplifier, and the single-chip microcomputer is started for data acquisition. The bridge composed of the resistance strain gauge converts the resistance change caused by the torque into an electrical signal, which is amplified by the amplifier and received by the sample/hold device and input to the A/D port of the single-chip microcomputer for analog-to-digital conversion. The converted data is stored in the data memory RAM. After completing the acquisition of a data block, the single-chip microcomputer starts to measure the time required for 1 rotation. According to the rotation cycle, the transmitted data is encoded and the data is transmitted through 3 infrared transmitting tubes in time-sharing infrared rays. After receiving, the host analyzes and processes it, and displays the maximum value, minimum value and peak-to-peak period of the torque on the LCD screen of the receiving device. Using infrared rays to collect and transmit data on rotating machinery has extremely strong anti-interference ability and data reliability. According to the research at home and abroad in recent years, torque measurement is showing the following development trends:
(1) From static testing to dynamic online testing;
(2) From measuring strain first and then indirectly converting it into stress or torque to directly measuring stress or torque, and improving the detection accuracy;
(3) The test system is developing towards miniaturization, digitization, intelligence, virtualization and networking;
(4) From single function to multi-function, including self-compensation, self-correction, self-adaptation, self-diagnosis, remote setting, state combination, information storage and memory;
(5) Torque detection is combined with the control system of the power device to achieve the optimal configuration between speed, torque and output power, ensuring that the mechanical equipment operates in the best state.