Datasheet

QBL4208-1024-AT Hardware Manual • Hardware Version V1.00 | Document Revision V1.00 • 22.02.2019
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6 Motor Sizing
For the optimum solution it is important to fit the motor to the application. The three key parameters are
peak torque requirement, RMS torque requirement and motor velocity.
6.1 Peak Torque Requirement
Peak torque TP is the sum of the torque due to acceleration of inertia (T
I
), load (T
L
) and friction (T
F
):
T
P
= T
J
+ T
L
+ T
F
The torque due to inertia is the product of the load (including motor rotor) inertia and the load acceleration:
T
J
= T + a
The torque due to the load is defined by the configuration of the mechanical system coupled to the motor.
The system also determines the amount of torque required to overcome the friction.
6.2 RMS Torque Requirement
Root-Mean-Square or RMS torque is a value used to approximate the average continuous torque require-
ment. Its statistical approximation is with
• t
1
: acceleration time
• t
2
: run time
• t
3
: deceleration time
• t
4
: time in a move
T
RMS
=
q
T
2
P
+(T
L
+T
F
)
2
∗t
2
+(T
J
−T
L
−T
F
)
2
∗t
3
t
1
+t
2
+t
3
+t
4
6.3 Motor Velocity
The motor velocity is also dictated by the configuration of the mechanical system that is coupled to the
motor shaft, and by the type of move that is to be affected. For example, a single velocity application
would require a motor with rated velocity equal to the average move velocity. A point to point positioning
would require a motor with a rated velocity higher than the average move velocity. (The higher velocity
would account for acceleration, deceleration and run times of the motion profile).Figure 6.1: Trapezoidal
move and triangular move relates rated motor velocity to average move velocity for two point to point
positioning move profiles.
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