| 摘要 |
An object of the invention is to effectively prevent surface abrasion in an eccentric part 47 of a crank pin 45 or breakdown of the crank pin 45. A value N obtained by dividing reduction ratio M in an eccentric oscillation type speed reducer 27 by a diameter D passing a center of pin teeth 29 is set to be smaller than 0.20. As the results, temperature of lubricant in the eccentric oscillation type speed reducer 27 can be depressed below 60° C., even though an output rotation speed at a rated torque of the eccentric oscillation type speed reducer 27 has become 28 rpm or more as required from a tact time or so in a factory, whereby a region between the eccentric part 47 of the crank pin 45 and a needle-shaped roller bearing 48 is always lubricated with the lubricant which exerts required lubricating function.
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