Rotation mechanism

A rotation mechanism includes a mandrel, a rotation axle, a needle roller bearing and an angular bearing. The mandrel includes a shaft portion, a first annular contact portion and a second annular contact portion. The shaft portion has an outer surface, and the first annular contact portion and the second annular contact portion are located on the outer surface and respectively surround the axis of the mandrel. The rotation axle includes an annular portion, a third annular contact portion and a fourth annular contact portion. The annular portion has a shaft hole and an inner surface forming the shaft hole. The third annular contact portion and the fourth annular contact portion are located on the inner surface, and the mandrel passes through the shaft hole. The needle roller bearing is in contact with the first annular contact portion and the third annular contact portion, and is located between them.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 102142276 filed in Taiwan, R.O.C. on Nov. 20, 2013, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The disclosure relates to a rotation mechanism.

BACKGROUND

Both the three-axis machine and the five-axis machine need to be equipped with an automatic pallet changer (APC) in order to improve the processing efficiency. The APC comprises a rotary stage capable of quickly replacing the workpiece by its rotation mechanism. The rotary stage usually comprises a fixed axle and a rotation axle. A bearing is disposed between the fixed axle and the rotation axle in order to reduce the friction between them, thereby improving the stability of the rotary stage and reducing its abrasion. Nonetheless, when the workpiece is not evenly distributed on the rotary stage, the rotary stage in rotation shakes because the bearing of the rotary stage is uneven.

Therefore, it is important to solve the problem caused by uneven weight distribution of the work piece on the rotary stage because this may improve the stability and the durability of the rotary stage.

SUMMARY

A rotation mechanism comprises a mandrel, a rotation axle, a needle roller bearing and an angular bearing. The mandrel comprises a shaft portion, a first annular contact portion and a second annular contact portion. The shaft portion has an outer surface, and the first annular contact portion and the second annular contact portion are located on the outer surface and respectively surround the axis of the mandrel. The rotation axle comprises an annular portion, a third annular contact portion and a fourth annular contact portion. The annular portion has a shaft hole and an inner surface forming the shaft hole. The third annular contact portion and the fourth annular contact portion are located on the inner surface, and the mandrel passes through the shaft hole. The needle roller bearing is in contact with the first annular contact portion and the third annular contact portion, and is located between them. The angular bearing is in contact with the second annular contact portion and the fourth annular contact portion, and is located between the outer surface and the inner surface.

DETAILED DESCRIPTION

FIG. 1is a sectional view of a rotation mechanism according to an embodiment of the disclosure;FIG. 2is a partially enlarged view ofFIG. 1. As seen inFIG. 1andFIG. 2, the rotation mechanism10is an automatic pallet changer (APC), but it is not limited thereto. The rotation mechanism10comprises a mandrel100, a rotation axle200, a needle roller bearing300, an angular bearing400and a tray500.

The mandrel100comprises a shaft portion110, a first annular contact portion120and a second annular contact portion130. The shaft portion110has an outer surface111, the first annular contact portion120and the second annular contact portion130are located on the outer surface111of the shaft portion110. The first annular contact portion120and the second annular contact portion130may be blocks or grooves. In this embodiment, the first annular contact portion120and the second annular contact portion130are blocks and they are formed as a single unit. The first annular contact portion120has a first contact surface121and the second annular contact portion130has a second contact surface131. The first contact surface121and the second contact surface131respectively surround the axis A of the mandrel100, and both the normal vector of the first contact surface121and the normal vector of the second contact surface131are parallel to the axis A of the mandrel100.

The rotation axle200comprises an annular portion210, a third annular contact portion220and a fourth annular contact portion230. The annular portion210has an inner shell211and an outer shell212. The inner shell211has a shaft hole211aand an inner surface211bforming the shaft hole211a. The outer shell212surrounds the inner shell211and is fixed to the inner shell211by screws. The third annular contact portion220and the fourth annular contact portion230are located on the inner surface211bon the annular portion210. The third annular contact portion220has a third contact surface221while the fourth annular contact portion230has a fourth contact surface231. The third contact surface221and the fourth contact surface231respectively surround the axis A of the mandrel100, and both the normal vector of the third contact surface221and the normal vector of the fourth contact surface231are parallel to the axis A of the mandrel100. In this embodiment, the third annular contact portion220and the fourth annular contact portion230are detachably installed on the opposite sides of the inner shell211respectively, thereby facilitating the assembly of the rotation mechanism10. The mandrel100penetrates the shaft hole211a. The first contact surface121faces the third contact surface221while the second contact surface131faces the fourth contact surface231.

The needle roller bearing300comprises a frame body310and a plurality of needle rollers320. The needle rollers320are rotatably disposed on the frame body310and the axes of the needle roller320intersect and are perpendicular to the axis A of the mandrel100. The needle rollers320are in contact with and are located between the first contact surface121and the third contact surface221. Since the contact area of the needle roller320with the first contact surface121and the inner shell211is larger than that of the balls420with the first contact surface121and the third contact surface221, the needle roller bearing300is able to resist the large external force along the axial direction and the bending force caused by uneven weight distribution of a work piece (not shown).

Moreover, the vertical thickness of the needle roller bearing300is small, so that the room for objects on the mandrel100and the rotation axle200is enlarged.

The angular bearing400is an angular contact ball bearing or an angular roller bearing. In this embodiment, the angular bearing400is the angular contact ball bearing, but it is not limited thereto. In other embodiments, the angular bearing400can be the angular roller bearing, though the angular contact ball bearing is easier to be assembled than the angular roller bearing. The angular bearing400comprises a first annular fixed frame410, a second annular fixed frame430and a plurality of balls420. The second annular fixed frame430surrounds the first annular fixed frame410and the balls420are rotatably disposed between the first annular fixed frame410and the second annular fixed frame430, so that the second annular fixed frame430can rotate relative to the first annular fixed frame410. The angular bearing400is in contact with the second annular contact portion130and the fourth annular contact portion230, and is located between them. Additionally, the angular bearing400is also located between the outer surface111and the inner surface211b. Specifically, the second contact surface131and the outer surface111are respectively in contact with the opposite sides of the first annular fixed frame410, while the fourth contact surface231and the inner surface211bare respectively in contact with the opposite sides of the second annular fixed frame430. Thereby, the angular bearing400can resist axial force and radial force between the mandrel100and the rotation axle200.

The rotation axle200passes through the tray500which is fixed to the outer shell212. The tray500has a carrying surface510and the bottom surface520that are opposite to each other. The carrying surface510is used for carrying objects. The center of the balls420is located between the extending surface of the carrying surface510and the extending surface of the bottom surface520. To have a better resistance to the radial force, in this embodiment, the position of the center of the balls420is closer to the carrying surface510. That is, the distance between the center of the balls420and the carrying surface510is less than the distance between the center of the balls420and the bottom surface520.

In this and some other embodiments, the rotation mechanism10further comprises a base600and a piston700. The bottom surface520of the tray500faces the base600. The piston700has a main body710and a rod720. One end of the rod720is connected to the base600, while the other end of the rod720is connected to the main body710. The mandrel100is fixed to the base600. The mandrel100has a first oil chamber140, a second oil chamber141and an annular flange142. The second oil chamber141is located below the first oil chamber140. The annular flange142is between the first oil chamber140and the second oil chamber141, and has a through hole143. The rod720penetrates the through hole143. The main body710is in the first oil chamber140and is configured for sliding relative to the mandrel100, so that the mandrel100can move close to or away from the base600by sliding relative to the piston700. As a result, via hydraulic control, the rotation mechanism10can lift the mandrel100and this drives the tray500to go up and down.

FIG. 3is sectional view of the rotation mechanism ofFIG. 1carrying a work piece with uneven weight distribution. As seen inFIG. 3, the tray500of the rotation mechanism10carries a first workpiece20and a second workpiece22. The weight of the first workpiece20is less than the weight of the second workpiece22. Assuming the distance between the center of gravity of the first workpiece20to the axis A of the mandrel100is equal to that between the center of gravity of the second workpiece22to the axis A of the mandrel100, the force F1applied by the first workpiece20on the tray500is less than the force F2applied by the second workpiece22on the tray500. This leads to uneven distribution of weight. These two forces result in the skew of the rotation axle200and therefore generate axial force and radial force between the rotation axle200and the mandrel100. Moreover, when the rotation axle200rotates along the axis A of the mandrel100(along the direction of arrow a), the tray500generates radial force between the rotation axle200and the mandrel100. It should be noted that the axial force herein refers to the force parallel the axis A of the mandrel100, while the radial force herein refers to the force parallel to the radial direction of the mandrel100.

The needle roller bearing300has great resistance of axial force, while the angular bearing400has great resistance of axial force and radial force. Hence, the needle roller bearing300is disposed on the position where a large portion of axial force exists, while the tray500is disposed on the position where both the axial force and the radial force exist. Thereby, this arrangement mitigates the skew of the rotation axle200and the abrasion between the mandrel100and the rotation axle200, which improves the stability and the durability of the rotation mechanism10.

Moreover, in this embodiment, only the needle roller bearing300and the angular bearing400are used (namely, fewer bearings are used than the conventional art), so the cost of the rotation mechanism10is reduced. Additionally, the needle roller bearing300and the angular contact ball bearing400are easy to install and this is likely to avoid deformation of the mandrel100and the rotation axle200. Thereby, the rotation mechanism10can have better concentricity.

FIG. 4is a sectional view of the rising rotation mechanism ofFIG. 1. As seen inFIG. 4, oil flows into the second oil chamber141by the hydraulic control, in order to make the mandrel100rise (along the direction of arrow b). The axial force is generated as the main body710of the piston700strikes the annular flange142, and the needle roller bearing300can resist this axial force, thereby reducing the impact of the rising of the rotation mechanism10.

To sum up, in the rotation mechanism of the disclosure, the axial force between the mandrel and the rotation axle is resisted by the needle roller bearing, and the axial force and the radial force between the mandrel and the rotation axle are resisted the angular bearing. This mitigates the skew of the rotation axle and the abrasion between the mandrel and the rotation axle, thereby improving the stability and the durability of the rotation mechanism.

Furthermore, since the vertical thickness of the needle roller bearing is small, the room for placing the objects on the mandrel and the rotation axle is enlarged.