Development of a rotation and swing torque detection system after bearing installation

4.1. Overall structure of detection system

The three-dimensional model of the bearing flexibility detection system structure is shown in Fig. 1. The clamping system is responsible for clamping parts, the swing torque detection system and the rotation torque detection system are responsible for stress torque detection respectively, and the torque calibration system is responsible for verifying the accuracy of the system.

The detection system adopts an integral layout. The inner ring rotation drive system adopts a horizontal structure and is laid flat on the equipment platform table. The inner ring swing drive system adopts a vertical structure and is installed on the equipment platform table. The clamping system is installed on the equipment platform table. superior. The overall structure of the detection system is simple and compact, and it occupies a small area. The rack provides stable support and arrangement space for the components of each system. There is enough space on the main table for installing and replacing parts.

Fig. 1Overall structure of bearing flexibility detection system: 1 – swinging torque detection system; 2 – rotating torque detection system; 3 – clamping system; 4 – rotating torque detection system; 5 –torque calibration system

4.2. Detection system subsystems

(1) Rotating torque detection system. The layout of the rotational torque detection system is shown in the Fig. 2, including the slide rail, support plate, three-claw chuck, expansion rod, turntable, torque sensor, servo drive slide rail, and servo motor, three-claw chuck, expansion rod, turntable, torque sensor The coaxial axis of the sensor and the inner ring of the bearing are in the same straight line. The main function of the rotational torque detection system is to drive the inner ring of the spherical bearing to achieve 360° rotation and detect the torque of the inner ring of the bearing when it rotates in the outer ring. The system provides torque from a servo motor, drives a torque sensor, and the inner ring of the bearing rotates. The torque sensor detects the torque in real time.

Fig. 2Rotating torque detection system: 1 – slide rail; 2 – support board; 3 – three jaw chuck; 4 – up bar; 5 – turntable; 6 – torque sensor; 7 – servo driven slide; 8 – servo motor

(2) Swing torque detection system. The swing torque detection system consists of servo motor, motor fixed plate, fixed column, torque sensor, fixed base plate, sensor fixed plate, shift fork, system fixed base plate, L-shaped fixed plate, servo drive slide rail, U-shaped bracket, fixed base plate, servo The drive slide rail and other components are shown in Fig. 3.

After the parts are clamped, the swing torque detection system provides torque by the servo motor, driving the torque sensor and the shift fork. The shift fork is inserted into the inner ring of the bearing and causes the inner ring of the bearing to swing in the outer ring. The torque sensor detects the torque in real time. Torque measurement formula were normalized according to Eq. (1):

Among them, $T$ is the torque, $F$ is the vector force, $r$ is the radius of torque application.

(3) Calibration system. The calibration system includes a turntable with a protruding rod, a turntable, a tension line, a weight, a calibration bracket, a positioning pin and a slide rail, as shown in Fig. 4. Rotating torque detection system self-test: a tension line is fixed on the ring groove of the turntable, and is connected through the ring groove of the turntable and the weight. The measured data of the torque sensor is compared with the torque converted by the weight. The result approximately indicates that the system is normal.

Fig. 3Swinging torque detection system: 1 – servo motor; 2 – motor fixing plate; 3 – fixed column; 4 – torque sensor; 5 – fixed base plate; 6 – sensor fixing plate; 7 – shift forks; 8 – system fixed base plate; 9 – L-shaped fixed plate; 10 – servo driven slide; 11 – U-shaped bracket; 12 – fixed base plate; 13 – servo driven slide

Fig. 4Calibration system: 1 – turntable with cam; 2 – turntable; 3 – tension line; 4 – weight; 5 – calibration bracket; 6 – position lock; 7 – slide rail

4.3. Torque sensor selection

The torque detection system is one of the core systems of the detector and is the data collection center of the detection system. During the torque detection process, the detection period of the inner and outer rings of the spherical bearing from a static state to a relative rotation state is very short. Using sensors to monitor the operating conditions of the spherical bearing online to accurately determine the starting torque value and swing angle will greatly Make up for the impact of human operation deficiencies on detection accuracy.

According to the design requirements, NS-NJ7-2Nm dynamic torque sensor was selected. It has the characteristics of high detection accuracy, good stability and strong anti-interference. It can measure static torque and dynamic torque, and can continuously measure forward and reverse torque without repeated zero adjustment, is a commonly used measuring device for online measurement of torque values. Its technical parameters are shown in Table 2.

4.4. Error analysis of detection system

As a testing equipment, the joint bearing swing and rotation torque detector inevitably has errors. Combined with the overall design plan of the detector in this article, the possible sources of errors in the detector are analyzed, mainly including the following:

(1) Torque transmission error. Use the servo motor, torque sensor and bearing inner ring drive plate to be directly connected to fix the torque sensor and servo motor to ensure that the servo motor, torque sensor and bearing inner ring drive plate are on the same axis. Bearing support and fixation are not suitable to avoid Torque measurement error caused by bearing sliding friction.

(2) Accuracy error of torque sensor. The accuracy error of the torque sensor is determined by the performance of the torque sensor. For this purpose, a torque sensor with high detection accuracy and good stability can be selected. The accuracy level of the torque sensor selected for this project is ±0.2 % F·S, and the repeatability accuracy is ±0.02 %. F·S.

(3) Static calibration of measurement systems. Determine the relationship between the input and output of the detection to determine the static characteristic indicators of the measurement system. Using the lever method for calibration, apply calibration torque to the torque sensor by multiplying the force by the force arm using the formula. In actual calibration experiments, the room temperature is maintained at 15 ℃-25 ℃, and the standard torque applied for calibration is divided into 10 levels. Apply torque by applying standard weights. To ensure the safety of the equipment, gradually load it to 80 % of the range, and then unload it gradually to no load. The loading and unloading cycles should be repeated three times, and the loading and unloading process should be slow and stable. Unloading should not occur during the loading process, and loading should not occur during the unloading process. The torque application process shows a monotonic increasing or decreasing trend. The calibration experimental data is shown in Table 3.

Based on the least squares method for data curve fitting, after obtaining calibration data in calibration experiments, it is usually necessary to fit the curve between the input and output of the sensor, in order to establish a certain mapping relationship. Ideally, the input and output are expected to have a linear relationship, but in reality, the input-output characteristics of torque sensors are always nonlinear.

Assuming the input of the sensor is: $t_1$, $t_2$, $t_3$...$t_i$...

Output as: $d_1$, $d_2$, $d_3$...$d_i$...

$N$ is mainly determined by the required curve fitting accuracy. When $n=$3, there are:

And substitute the standard torque 𝑇 and the average numerical value $\overline{D}$ in Table 2, the final solution is $c_0$, $c_1$, $c_2$, so the relationship between torque and its numerical value can be obtained: $Ti(\overline{D}$𝑖$)=-1.9625+2.34375\overline{D}i$.