Harmonic Drive SHA CG Series, Руководство пользователя

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2-2 Change in load moment of inertia
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2-2 Change in load moment of inertia
SHA series actuators include Harmonic Drive® gearing that has a high reduction ratio. Because of this, the effects
of changes in the load moment of inertia on the servo performance are minimal. In comparison to direct servo
drive mechanisms, this benefit allows the load to be driven with a better servo response.
For example, assume that the load moment of inertia increases by N-times. The total inertia reflected
to the motor shaft, having an effect on servo response, is as follows:
The symbols in the formulas are:
J
S
: Total inertia moment converted to motor shaft
J
M
: Inertia moment of motor
R: Reduction ratio of SHA series actuator
L: Ratio of load inertia moment to inertia moment of motor
N: Rate of change in load inertia moment

Direct drive
Before: After: Ratio:

Driven by SHA series
Before: After: Ratio:
With the SHA series, the value of R increases from 50 to 161, which means that the value increases
substantially from R
2
= 2,500 to R
2
= 25,921. Then the ratio is Js'/Js
≒
1. This means that SHA drive
systems are hardly affected by the load variation.
Therefore, it is not necessary to take changes of the load moment of inertia into consideration when
selecting a SHA actuator or when setting up the initial driver parameters.
( )
L 1 J J
M
+
＝
Ｓ
( )
NL 1 J ' J
M
+
＝
Ｓ
L 1
NL 1
/Js Js'
+
+
＝








+
2
R
L
1 J J
M
＝
Ｓ








+
2
R
NL
1 J ' J
M
＝
Ｓ
2
2
R / L 1
R / NL 1
/Js Js'
+
+
＝