Harmonic Drive FHA Mini Series, Manual

Page: 31 / 50

Chapter 2 Guidelines for sizing
FHA-mini
31
2-4-5 Calculating equivalent duty
The load conditions, which is torque, speed, moment of
inertia, acceleration/deceleration time, loading time, are
limited by the actuator to drive the load. To select the
proper actuator, the equivalent duty of the load should be
calculated.
The %ED (percent equivalent duty) is:
where, ta: acceleration time in second
td: deceleration time in second
tr: driving time in second
t: single cycle time in second
K
La
: duty factor for acceleration time
K
Lr
: duty factor for driving time
K
Ld
: duty factor for deceleration time
• Example 2: getting duty factors of K
La
, K
Lr
and K
Ld
With an example of the duty factor graph for FHA-11C-50 actuator, the way of getting the duty factors of
K
La
, K
Lr
and K
Ld
is descrived as follow:
The load conditons are same as the example described in the example1: the inertia load is accelerated
by the maximum torque, and is driven with a constant speed, and is decelerated by the maximum
torque. The displacement angle is 120 degrees and the cycle time is 0.8 s.
(1) K
La
, and K
Ld:
: the speed is desided at 50 rpm as the average of 0 and 100 rpm.
Then, K
La
K
Ld
1.7 from the graph.
(2) K
Lr
: as the inertia load, Tr 0. Then K
Lr
0.9 from the graph.
(3) The driving time is calculated as the area of the trapezoid of speed-time graph. Then the
displacement angle is:

= (N / 60) x {tr + (ta + td) / 2} x 360
Then, tr =

/ (6 x N) – (ta + td) / 2
Substituting 120 deg. for

,0.072(s) for ta, 0.046(s) for td, 100rpm for N, the driving time is:
tr = 120 / (6 x 100) – (0.072 + 0.048) /2 = 0.14(s)
(4) Because the cycle time is 0.8(s), the %ED is obtained as follows:
%ED = (1.7 x 0.072 + 0.9 x 0.14 + 1.7 x 0.048) / 0.8 x 100 = 41.2%
It is possible to drive the actuator with the load
specifications continuously, because the
%ED is less than 100%.
If the %ED is excessed 100%, correct the
situation by:
•Changing the speed-time profile
•Reducing load moment of inertia
•Selecting an actuator with a larger frame size
(1) K La , K Ld
(2) KLr
Speed [rpm]
To
rq
ue
[
N
m]
Plate:150x150x6(mm)
•
FHA-11C-50
KL=0.33
0.67
1
9
7
6
5
4
3
2
0
1
10
1.5
2
2.5
8
150 100 50 0
Allowed range
100V
200V
Ta, Tr, Td: output torque
ta
td
N
tr
Time
Speed
t: duty cycle
ts
Ta
Time
Torque
Td
Tr