Study on the Life Distribution and Reliability of Roller-Based Linear Bearing

Abstract

A study on the life distribution and reliability for a roller guide with cage was carried out with a total number of 90 test samples in two lots (N _s = 38 and 52), and different fatigue life distribution functions, such as the two and three parameter Weibull distributions, and the log-normal distribution were used for analyzing the test data. The basic dynamic load rating formula standardized by ISO in 2004 was also compared with the life test data in relation to the effect of crowning on both ends of the carriage raceway. This study revealed the following: (1) the best fit for the life test data was achieved by the three-parameter Weibull distribution with the third parameter being the minimum life γ, using a Weibull slope of m = 27/20, and a load life exponent of 10/3. The log-normal distribution came second, and the two-parameter Weibull distribution third. (2) The test data did not fit with the two-parameter Weibull distribution using a Weibull slope of 9/8, which had been used in the ISO linear bearing standard. (3) Fatigue failure on the roller guide was initiated near the starting points of the crowning on both ends of the carriage raceway. Almost 70% of the test specimens were found to have uneven and inclined contact situations with the rollers. (4) The basic dynamic load ratings evaluated theoretically fit well to the life test results, while the λ b _m factors were also observed to fall within a suitable value range.

KEY WORDS:

• Basic Dynamic Load Rating
• Linear Bearing
• Log-Normal Distribution
• Rating Life
• Roller Guide
• Rolling Contact Fatigue
• Weibull Distribution
• λ b_m Factor

ACKNOWLEDGMENTS

The authors would like to extend thanks to Mr. T. Shirai of THK Co., Ltd., for the supply of test specimens and Dr. C. S. Sharma of Shinrai Preci-Tech Systems for his fruitful discussion to complete this article. The ministry of Education, Culture, Sports, Science and Technology, Academic Frontier Project of Meiji University, supported this work. The authors extend heartfelt gratitude to all concerned.

Review led by Bob Errichello