The relationship between industrial robot accuracy and bearing design
- 2019/11/28 17:42:34
Industrial robots are a new type of high-tech intelligent machine that can replace some of the manual industrial production. As an industrially produced robot, it is possible to describe its requirements in three words: fast, accurate and stable.
For the current robot production technology, it is easier to get faster and faster, and if it is fast and stable, it must be relatively difficult.
Here is a word defined: the repeatability of industrial robots - the industrial robot repeats an action (usually 10-20 times), and the mean deviation of each time from the planned position is its repeat positioning accuracy. Measured with a laser interferometer.
For industrial robots, accuracy is a very important factor that directly affects product quality and productivity. The main factor affecting the accuracy of industrial robots is the bearings, so what kind of bearings can make industrial robots have higher precision?
1. Design of key structural parameters
Industrial robot bearings have long life, high rigidity and low friction. Therefore, when designing industrial robots, not only the maximum dynamic load rating should be considered, but also the optimal value of each structural parameter should be carefully selected to improve The contact stress distribution of the bearing parts reaches the optimum contact state for the formation of the lubricating oil film and improves the service life of the bearing.
2, the ferrule channel position
The inner and outer rings of the contact ball bearing of the industrial robot adopt the integral structure, and the general sectional area is only 20% of the same inner diameter standard bearing, so the radial wall thickness of the cage is very limited. If the channel position is designed in the bearing The center of the width, so that the bearing becomes a symmetrical structure, while the strength of the bottom of the cage pocket and the mounting position of the sealing ring will be limited. Therefore, in order to ensure that the bearing cage has sufficient strength and the sealing ring has sufficient installation space, the groove position adopts an asymmetrical design on both end faces.
3, the determination of the height of the rib
When the contact ball bearing of an industrial robot is in working condition, it must bear a certain axial load while receiving a certain radial load. If the axial load is too large, it may cause the steel ball to contact the edge of the inner and outer rings or the contact ellipse between the rib and the raceway to be cut off. At this time, stress concentration will occur and the bearing ring will be affected. Wear and thus affect accuracy.
Therefore, when the rib height is designed, the minimum rib height J of the bearing ring is calculated according to the Hertz contact stress theory according to the axial load of the bearing, and the diameter of the ferrule rib is calculated. In the design, the contact ball bearing cross-sectional area is considered to be small, and the rib height coefficient can be smaller than the deep groove ball bearing under the premise of meeting the use requirements.
4, sealing structure design
The early damage of the bearing of an industrial robot is generally because the sealing property is not good, because the sealing property is not good, and impurities or other contaminants in the air easily enter the bearing, thereby gradually failing the grease, resulting in bearing damage. Therefore, the sealing of the bearing is critical. Therefore, when designing a sealed bearing, it is necessary to consider the sealing, and at the same time take into account the specific working requirements of the bearing and the specific structural form of the bearing.
Industrial robots are moving toward miniaturization, light weight, and precision. Therefore, the lubrication of bearings for industrial robots is preferably greased by means of a lubrication method with a sealing structure.
5, for the characteristics of industrial robot bearing wall thin
There are two ways to match the bearing inner ring and the sealing lip:
Contact seal with inner ring seal lip in contact with inner ring rib
Non-contact seal with inner ring seal lip in contact with inner ring rib
The contact seal is better than the non-contact seal for dust and grease leakage, but its friction torque is large and the temperature rise is high. Considering the large friction torque, it has an adverse effect on the robot mainframe. The design is generally a non-contact seal. structure.
In addition, since the bearing ring wall is very thin, the inner and outer rings of the bearing are easily deformed, so the inner ring rib can adopt a grooveless structure, but the sealing gap should be strictly controlled.