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Movement Profile
A movement profile defines the desired acceleration rate, run time, speed, and deceleration rate of
the load. For example, suppose with a system at rest (time=0, Figure 2), the programmable motion
controller issues a command to start motion. At this instant, the motor has not yet started to move,
there is no feedback signal, and the error signal is large.
The control wants to reduce the error signal, and the motor begins to accelerate. As the motor
approaches the commanded speed, the error signal is reduced and, in turn, voltage applied to the
motor is reduced. As the system stabilizes at running speed, only nominal power (voltage and
current) are required to overcome friction and windage. At t=x, the load approaches the desired
position and begins to decelerate.
In applications with similar move profiles, most of the input energy is dissipated as heat.
Therefore, in such systems, the motor's power dissipation capacity is the limiting factor.
Acceleration Torque
Determining acceleration rate is the first step. For example, with the movement profile of Figure 2,
the acceleration rate can be determined from the speed and acceleration time. (Dividing the motor
speed rpm by 9.55 converts the speed to radians per second).
S
a
=
m
acc
9.55t
acc
2,000
a
=
= 1,745.2 rad/sec
acc
9.55(0.12)
The torque required to accelerate the load and overcome mechanical friction is:
T
= J
(a
)+T
acc
t
acc
f
= (J
+J
+J
L
LS
m
Example: Our application, Figure 3, requires moving a load through a leadscrew. The parameters
are:
Leadscrew inertia (J
) = 0.00313 lb-in.-s
LS
Motor inertia= 0.0037 lb-in-s
Friction torque (F
) = 0.95 lb-in.
F
Acceleration torque can be determined by equation 3
T
= (0.00052 + 0.00313 +
acc
0.0037) 1745.2 + 0.95
= 13.75 lb-in.
Application Notes
2
) a
+T
acc
F
2
2
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Troubleshooting
