Yamaha YK120X User Manual

5-8

The YK120X series and YK180X series robots use a harmonic drive as the speed
reduction gear for the X-axis, Y-axis and R-axis. The harmonic drive grease (SK-
2) must be replaced periodically. Determine the harmonic grease replacement
period with the following procedures.
Each axis must be disassembled when replacing the harmonic drive grease, so
contact YAMAHA for servicing.

The harmonic drive replacement period is determined by the total number of
turns of the wave generator used in the harmonic drive. A calculation example is
shown below. It is recommended to replace the harmonic drive when the total
number of turns has reached 1.5

×10

8

 (at ambient operating temperatures of 0

°C

to +40

°C). This means that the replacement period will differ depending on the

following operating conditions. If the robot operation duty ratio is high or the
robot is operated in environments at higher temperatures, the harmonic drive should
be replaced earlier.

Replacement period = 1.5

×10

8

/(n

×60×h×D×N×θ) years

where

n

: Number of axis movements per minute

θ

: Average turn per axis movement

N

: Speed reduction ratio

h

: Operation time per day

D

: Operation days per year

For 

θ, a 90° axis rotation is a one-quarter rotation.

Example) Harmonic drive replacement period when axis rotates an average of

one-quarter with each movement, and moves 10 times in one minute.
(Operation time: 24 hours/day, No. of operation days: 240 days/year)

n

: 10

θ

: 0.25

N

: 50

h

: 24 hours per day

D

: 240 days per year

Replacement period = 1.5

×10

8

/(n

×60×h×D×N×θ)

= 1.5

×10

8

/(10

×60×24×240×50×0.25)

= 3.5 years

50

50

X-axis

Y-axis

30

R-axis