Denso SMT7 - Knowledge Required for Servomotor Selection

Chapter 2 Engineering Design of Servo Mechanism
22
2.2 Knowledge Required for Selection of Servomotors
This section describes basic knowledge required for selecting an optimal servomotor
output and reduction gear ratio in designing of servo mechanism drive including
robots.
Calculation of load drive torque (T) (conversion into the motor shaft's)
Drive torque = Inertia + Friction + Particular
T (Nm) = (I
٠


) + (N٠Ki + T
FM
+ T
FD
) + (Tg + Ts) ٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠٠ (1)
Where I = Total inertia moment in conversion into the motor shaft's (Nms
2
)


= Motor shaft angle acceleration (rad/s
2
)
N = Motor usage rpm (rpm)
Ki = Braking constant (see motor catalog) (Nm/rpm)
T
FM
= Motor static friction torque (see motor catalog) (Nm)
T
FD
= Friction torque of transmission system, etc.
(conversion into the motor shaft's) (Nm)
Tg = Gravity holding torque (conversion into the motor shaft's)(Nm)
Ts = Interference torque, centrifugal force, coriolis force, etc.
(conversion into the motor shaft's) (Nm)
Calculation of motor max. occurrence torque (T
M
) (conversion into the motor shaft's)
T
M
(kgcm) = I
R
٠Kt
Where I
R
= Max. current value which can be applied to motor (Ao٠p)
Kt = Torque constant (See motor catalog) (Nm/Ao٠p)
Or this is shown by the "Instantaneous max. torque" in the motor catalog.
[Note]
T
M
> T shall be formed.
However, drive torque T shall be designed within 2.5 times of motor rated torque as SMT7.
٠٠٠٠٠(2)