4. Ball bearing slip test The dynamic simulation of rolling bearing can predict the contact angle, load and angular velocity component of the ball under various working conditions. Since the three-dimensional characteristics of ball motion in rolling bearings are not easy to observe, there are fewer experimental studies on ball bearing slip compared to roller bearings. Foreign scholars mainly measure the rotational speed of the cage by means of magnetized rolling elements and optics, and monitor the slip rate of the rolling elements or cages. Literature [7] was the first to study the motion of the angular contact ball bearing under the thrust load by measuring the magnetic flux change caused by the magnetized ball, and obtained that the angular velocity of the ball is closely related to ZFc/Fa, when Fc/Fa>When it is 0.1, the deviation of the angular velocity of the ball from the predicted value of Jones ferrule control theory is very obvious, and the rolling axis of the ball is skewed, indicating that the inertial effect (gyro moment and centrifugal force) causes the change of the angular velocity component of the ball's rotation, which leads to a decrease in the ball's revolution speed. . Reference [12] widened the cage and arranged displacement sensors in the axial and radial planes near the end of the cage to measure the three-dimensional motion and rotational speed of the cage. Reference [28] developed a technique to measure the direction of the ball rolling axis using an optical device, which can evaluate the ball bearing kinematics. Reference [29] installs a metal sheet on the cage, uses a magnetic sensor to measure the rotational speed of the cage, and uses this test device to measure the effect of lubricant reduction (depleted oil) on the minimum preload threshold of the overall cage slip. Reference [30] introduced the use of radioisotopes to detect the slippage of bearings, fixed cobalt or iridium (Co-60, Ir-192) wire radioactive sources on the cage, and used the inverse square law (that is, the radioactive intensity transmitted to a certain point is inversely proportional to the According to the principle of the square of the distance from the radiation source to this point, the rotational speed of the cage is measured and the slip rate is calculated. The equipment that uses radioactive elements to measure the cage rotation speed is complex, expensive, and the radioactive material is harmful; while the magnetoelectric induction method is only suitable for the measurement of the cage rotation speed of medium and low speed bearings, and the scope of use is limited. Domestic scholars mainly calculate the slip rate by measuring the rotational speed of the cage to reflect the overall slip of the bearing. The measurement of cage rotation speed is mostly through eddy current sensors, force sensitive sensors and magnetoelectric, photoelectric and optical fiber photoelectric coupling digital test devices. Reference [31] uses an eddy current displacement sensor to measure the rotational speed of the bearing inner ring and cage, which can be used in high-speed and light-load conditions. Reference [32] attaches a miniature stress sensor to the raceway of the outer ring of the bearing, and measures the rotational speed of the aero-engine bearing cage by detecting the centrifugal force of the rolling elements revolving with the cage and the compressive stress pulse on the outer ring. Instantaneous slip rate. Reference [33] uses an optical fiber sensor to measure the passing frequency of the rolling elements, and calculates the rotational speed of the cage according to the average value of the revolution speed of all rolling elements. The optical fiber sensor has the advantages of insensitivity to electromagnetic interference, high sensitivity, and wide measurement frequency. Reference [34] uses the principle of ultrasonic reflection to measure the passing frequency of rolling elements and the rotational speed of the cage. Compared with the traditional optical speed measurement method, the ultrasonic speed measurement method does not require special treatment of the cage and is not sensitive to the oil mist environment. References [35-38] use a high-speed camera to continuously take pictures of the end of the running cage. According to the position of the marking point on the cage, the rotation speed of the cage is obtained through an image processing algorithm. It does not need to make any changes to the cage and is not sensitive to the environment. , which can easily measure the movement and speed of the cage in the radial plane, but it is not suitable for high-speed conditions due to the limitation of the camera shooting frequency. At present, although domestic and foreign scholars can use different methods to monitor the instantaneous or average slip rate of rolling elements and cages, but for special working conditions (such as high speed, variable load, variable rotation speed, etc.) Further research is required. 5. Determination of the preload force to prevent slippage The purpose of studying ball bearing slippage is to reduce or avoid slippage, thereby prolonging bearing service life and improving reliability. According to the above review of ball bearing slippage theory and experimental research, the factors affecting ball bearing slippage include: structure (ball diameter, number of balls, contact angle, groove curvature, cage clearance), working conditions (load, speed, temperature, time) denaturation), lubrication (lubrication method, lubricant characteristics, drag curve), etc. The influence mechanism of these factors on bearing slip is complex, and there are couplings between different factors, so it is difficult to reduce bearing slip by changing a single factor. The most common way to prevent bearing slippage in engineering practice is to apply preload. Appropriate pre-tightening force is applied to the bearing, on the one hand, it can prevent the bearing from slipping, reduce friction, heat generation and wear, and improve the service life of the bearing;