A self-aligning ball bearing is a bearing equipped with spherical rolling elements between the inner race of two raceways and the outer race of a spherical raceway. It can withstand large radial loads and also withstand certain axial loads, as shown in Figure 1. The outer raceway of this type of bearing is spherical, therefore it has self-aligning performance. The main characteristics of a self-aligning ball bearing are: (1) The outer raceway of the self-aligning ball bearing is a part of a spherical surface, with the center of curvature on the bearing axis. Therefore, the bearing has a self-aligning function and can automatically adjust when the shaft or housing bends without increasing the bearing burden. (2) Can withstand radial loads and moderate axial loads in both directions. But it cannot withstand torque loads. This type of bearing has a small contact angle, and the contact angle remains almost unchanged under axial load. It has a small axial load capacity and a large radial load capacity, making it suitable for situations with heavy loads and impact loads. (3) Double row self-aligning ball bearings with tightening sleeves and locking nuts can be installed at any position on the optical axis without the need for shaft shoulder positioning. As shown in Figure 2 Spherical roller bearings are bearings assembled with drum shaped rollers between an inner ring with two raceways and an outer ring with a spherical raceway, as shown in Figure 3. Spherical roller bearings have two rows of rollers, which mainly bear radial loads and can also withstand moderate axial loads in either direction; Has high radial load capacity, especially suitable for working under radial heavy loads or vibration loads, but cannot withstand pure axial loads. The main characteristics of self-aligning roller bearings are: (1) Similar to self-aligning ball bearings, the outer raceway of self-aligning roller bearings is a part of a spherical surface, with its curvature center on the bearing axis. The outer raceway of this type of bearing is spherical, so its self-aligning performance is good, and it can compensate for coaxiality errors, thus achieving automatic self-aligning. (2) In the section perpendicular to the rolling direction, the roller generatrix is curved and can fit well with the inner and outer raceways. The rollers are in linear contact with the raceways and can withstand radial and axial loads, with good impact resistance. (3) The alignment between the rollers and the raceway of self-aligning roller bearings is high, and both are curved busbars, resulting in severe relative sliding and greater friction than cylindrical roller bearings. Therefore, self-aligning roller bearings allow for lower operating speeds. (4) Ordinary tapered roller bearings have asymmetric rollers that generate an axial force during operation. The rollers are subjected to this force and come into contact with the central fixed edge. Symmetrical tapered roller bearings use a movable intermediate retaining ring that can move along the axial direction. In this way, the rollers are no longer constrained by the central edge and the inner race groove is eliminated. Longer rollers can be used to improve the bearing capacity. (5) The contact angle of a single row self-aligning roller bearing is 0. Under axial load, there is no significant change in contact angle, and a small axial load can generate a large contact force between the roller and the raceway. Therefore, when the axial load is relatively greater than the radial load, a single row self-aligning roller bearing cannot withstand the combined radial and axial loads.