Allen-Bradley 20G - Page 12

12 Rockwell Automation Publication PFLEX-AT001L-EN-P - September 2017
Chapter 2 Determining Dynamic Brake Requirements
• Speed rating from motor nameplate in rpm or rps (radians per second)
• Required decel time (per
Figure 2, t
3
– t
2
). This time is a process
requirement and must be within the capabilities of the drive programming.
• Motor inertia and load inertia in kg•m
2
or WK
2
in lb•ft
2
• Gear ratio (GR) if a gear is present between the motor and load
• Motor shaft speed, torque, and power profile of the drive application
Figure 2 shows typical application profiles for speed, torque and power. The
examples are for cyclical application that is periodic over
t
4
seconds. The
following variables are defined for
Figure 2:
(t) = Motor shaft speed in radians per second (rps)
N = Motor shaft speed in Revolutions Per Minute (rpm)
T(t) = Motor shaft torque in Newton-meters
1.0 lb•ft = 1.355818 N•m
P(t) = Motor shaft power in watts
1.0 Hp = 746 watts

b
= Rated angular rotational speed

o
= Angular rotational speed less than 
b
(can equal 0)
-P
b
= Motor shaft peak regenerative power in watts

2N
60
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=
Rad
s
----------
Rad
s
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