Application Examples; Conveyor Belt - Danfoss VLT Brake Resistor MCE 101 Design Manual

Application Examples

6 Application Examples

6.1 Conveyor Belt

Illustration 6.1 shows the relation between the braking
power and the acceleration/braking of a conveyor belt.
Note:
•
The motor power during braking is negative,
since the torque on the motor shaft is negative.
•
The motor power is time-dependent.
The braking power (the power to be dissipated to the
brake resistor) corresponds almost exactly to the negative
motor power plus losses in the motor and the frequency
converter.
Kinetic energy (E) in conveyor belt + motor:
2
E = 0.5 × m × v j × ω
+ 0.5 ×
where
m = mass with linear movement [kg]
v = speed of mass with linear movement [m/s]
j = inertia of motor and gear box [kgm
ω = motor speed [rad/s]
n × 2π
ω = motor speed = rad /
60
This formula is also expressed as follows:
2
E = 0.50 × m × v + 0.0055 ×
However, not all of the energy is dissipated in the brake
resistor. The friction of the conveyor belt and the power
loss of the motor also contribute to the braking function.
So, the formula for energy dissipation (E
resistor is as follows:
2 2
E b m v jω
0.5 × + 0.5 0.5 ×
= −
where
M = Friction torque [Nm]
f
ŋ
= Motor efficiency
M
MG90O202
Design Guide
2
Ws
2
]
s
2
j × n Ws
) to the brake
b
M f ω η
Ws
×
M
Danfoss A/S © Rev. 05/2014 All rights reserved.
Insert:
n × 2π
ω =
60
The result is:
2
E b m v j × n
0.5 × + 0.0055 ×
=
2
n × M f × η
0.052 × Ws
−
M
27
6 6