Goodrive350 IP55 High-ingress Protection Series VFD
Basic Operation Instructions
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5.5.20.3 Open-loop torque mode
Open loop means there is no tension feedback signal. In this mode, stable tension can be
achieved by means of motor torque control. The rotation speed automatically changes with the
linear speed of material. The control basis is as follows: For a reel control system, the
relationship between the tension F of the roller with materials, present roll diameter D and
output torque of the shaft is: T = F × D /2. If the output torque can be adjusted according to the
variation of roll diameter, the tension can be controlled. In order to ensure the constant tension
in the process of acceleration and deceleration, the internal friction compensation module and
inertia compensation module have been built in the VFD to calculate the real time rotation
inertia, and compensate the torque according to the actual speed change rate. The control
principle is shown in the following figure.
Calculate the frequency
according to the tension
T=J*d
Ω/dt
+
+
Tension
reference
Rotational inertia of
mechanical system
Rotational inertia
of material
Basic reference
frequency
Inertia torque
compensation
Motor reference
frequency
+
+
Friction torque
compensation
+
+
Relevant modes:
(1) Linear speed input module: It has two functions: calculating the synchronous frequency in
torque control according to the linear speed, and calculating the roll diameter according to the
linear speed.
(2) Tension setting module: Used to set the tension adapting to the control system. It needs to
be adjusted according to the actual situation. After confirmation, the value remains the same.
In some scenarios where the forming effect after winding needs to be improved, the tension
taper function can be used so that the tension decreases as the roll diamter increases.
(3) Real-time roll diameter calculation module: The calculation accuracy of roll diameter
determines the control performance. The roll diameter can be calculated according to the VFD
output frequency and the linear speed. In addition, it can also be calculated through the
thickness or sensor. The linear speed is widely used for the calculation. If the set linear speed
is used for the calculation, you you choose whether to enable the function of roll diameter
change limiting.
(4) Torque compensation module: Torque compensation includes friction torque compensation
and inertia torque compensation. Friction torque compensation is used to eliminate the impact
of friction on tension, and it needs to be adjusted according to actual requirements. rRotation
inertia includes inertial of mechanical systems and that of materials. In order to keep the
tension stable in ACC/DEC, compensation torque is required. In some cases without strict
tension control requirements, disabling rotation inertia torque compensation can also achieve
the control.
(5) Material feeding interrupt detection and processing module: The function is valid when
material feeding interrupt detection has been enabled.
