Harmonic Drive MMA Series, Manual, Page: 38 / 62

2-3 Examining the operating status
2-5
Se
lec
tion gui
de
lin
es
2
Appe
Acceleration time and deceleration time
Calculate the acceleration and deceleration times for the motor tentatively selected using the following
formula.
Acceleration time:
Deceleration time:
t
a
: Acceleration time [s]
t
d
: Deceleration time [s]
k : Acceleration reduction coefficient 1 to 1.5
The total positioning time may become
shorter if the acceleration is lowered for
the purpose of reducing the settling time
after positioning.
J
M
: Inertia moment of motor [kg
･
m
2
]
J
L
: Inertia moment of load [kg
･
m
2
]
N : Rotational speed of motor [r/min]
T
M
: Maximum momentary torque [N
･
m]
T
F
: Motor friction torque [N
･
m]
T
F
= K
T
× I
R
-T
R
K
T
: Torque constant [N
･
m/A]
T
R
: Rated torque [N
･
m]
I
R
: Rated current [A]
T
L
: Load torque [N
･
m]
The polarity is positive [+] when the torque is applied in the rotation direction, or negative [-] when it is
applied in the opposite direction.

Calculation example 1
Select a motor that best suits the following operating conditions:
･
Rotational speed: 4000 [r/min]
･
Inertia moment of load: 3.0 × 10
-4
[kg
･
m
2
]
･
Since the load mechanism is mainly inertia, the load torque is negligibly small.
(1) According to the conditions above, tentatively select MMAB09 from the table in section 2-1.
(2) From the rating table, the following values are obtained:
J
M
= 1.78 × 10
-4
[kg
･
m
2
], T
M
= 3.0 [N
･
m], T
R
= 0.80 [N
･
m], K
T
= 0.41 [N
･
m/A], I
R
= 2.5 A
(3) Based on the above formula, the motor's friction torque T
F
is calculated as
0.41 × 2.5 - 0.80 = 0.225 [N
･
m].
(4) If k = 1.3, the acceleration time and deceleration time can be obtained as follows from the
above formulas:
t
a
= 1.3 × (1.78 + 3.0) × 10
-4
× 2 ×
π
/ 60 × 4000 / 3.0
≒ 0.
087 [s]
t
d
= 1.3 × (1.78 + 3.0) × 10
-4
× 2 ×
π
/ 60 × 4000 / (3.0 + 2 × 0.225)
≒ 0.
075 [s]
(5) If the calculated acceleration/deceleration times are too long, correct the situation by:
･
Reducing the inertia moment of load
･
Selecting a motor with a larger frame size
ta td
N
Time
Rotational speed
( )
L M
L M a
T T
N
60
π 2
J J k t
−
×
×
× + × =
( )
L F M
L M d
T T 2 T
N
60
π 2
J J k t
+ × +
×
×
× + × =