SteadyWeb5™ Tension Controller
vs EasyWeb™ Torque Controller
They look similar and come in the same size box. So, what are the functional differences between DFE's SteadyWeb5™ Tension Controller and the new EasyWeb™ Torque Controller?
The SteadyWeb5 Tension Controller is a closed loop automatic tension
controller with multiple capabilities to accurately control the tension of any
material in any web fed process. To function the SteadyWeb5 Controller requires a
feedback signal from tension transducers mounted in the web path.
The EasyWeb Torque Controller is an open loop controller
used to adjust the torque applied to a roll of material as it is
wound/unwound at the beginning or end
of a process. While the tension of the material is affected by the torque
adjustment, the EasyWeb is not a tension controller. To be a tension controller the EasyWeb would need some means
of measuring tension. It's missing the direct tension measurement as feedback.
How they work
The SteadyWeb5 Tension Controller has multiple capabilities for
control. It can be used as an unwind
controller, a rewind controller, or as an intermediate controller. The basic
unwind/rewind control format would be to use the feedback from the tension
transducers mounted in the web path to monitor the tension applied to the web
material and automatically adjust the output to the brake or drive to maintain the
material tension at the operator-selected set point. This is the same control
scheme used by the cruise control of your automobile, you set the desired speed and the control system adjusts the output to maintain the speed at the
desired point. The automatic control function of
the SteadyWeb5 is based on motor speed or brake/clutch torque to maintain the material
In addition to the basic closed loop transducer feedback
system mode the SteadyWeb5 can be set to operate in a speed follow tension trim mode.
In this mode the controller receives a line speed signal from the process and
the motor follows this speed. The tension transducers provide a feedback signal
to the controller and it adjusts (trims) the speed signal based on the tension
feedback so that tension always remains at the operator selected set point.
This mode of operation is used in an intermediate nip application or in a
surface rewind application.
A variation of this is the speed follow diameter compensated
tension trim mode. In this instance the controller is used in a center driven
unwind or rewind application. The controller is provided with a line speed
signal that is trimmed by the roll diameter (can be a measured or calculated
diameter) that modifies the speed of the roll as the roll changes in diameter,
and the transducer feedback is used to trim this modified speed signal to
maintain precise tension in the material. In addition to these control
modalities the controller can also provide a tapered tension function for
rewinding materials. In a driven application for unwind, rewind, or
intermediate use the controller functions by adjusting the speed of the motor
to maintain the desired tension in the web.
The EasyWeb Torque Controller functions based on the speed
of the material passing through the process and the diameter of the roll being
controlled. The line speed is used as a basis for the controller to provide the
torque desired to operate the brake, clutch, or drive being used. The controller takes the line speed signal
(DC Volts or encoder pulses) and a roll signal (can be a roll speed signal or a
measured roll diameter) and calculates an output to set the torque of the
controlled device. In the case of a
calculated diameter the controller calculates the diameter of the roll based on
the line and roll speed signals received. If a direct measurement, the
controller adjusts the torque based on this diameter. The controller provides a decreasing torque signal for an unwind
and an increasing torque signal for a rewind.
While these torque outputs do
create tension in the material the control is not and can not be based on
material tension as there is no feedback (tension transducers) to create a
closed loop control system. The Easy Web can provide a tapered output for
rewind applications similar to the SteadyWeb5 but again it is a calculated taper and
torque with no means of registering web tension.
The tension meter graphic in the above illustration is a calculated estimation only. This is taken from a screenshot of a simulation we run to demonstrate the principle of the EasyWeb Torque controller. See a video of the EasyWeb's simulation demo here .
The choice as to which controller to use in a given
application is dependent on individual desires, criticality of control, and in
some cases simply cost. It is safe to say that the SteadyWeb5 is the best choice in
almost all applications due to the simple fact that it is a closed-loop controller
thus providing precise control and displayed results. However in the case where
there is no space for tension transducers the Easy Web is the best alternative.
For the price-sensitive customer, the EasyWeb will be somewhat less expensive
to add due to the simple elimination of tension transducers and cables.
Overall, if accuracy is desired it is always best to select the closed-loop
option. However, if space for transducers is not available then the Easy Web open
loop controller is an option that will provide dependable torque based web
Don't hesitate to contact me with questions or for a free analysis of your application.
For further discussion on the subject of open loop torque control, see this article from web handling expert, Tim Walker, of TJ Walker and Associates. The article was published in Tim's recent Web Lines column on PFFC-online.com.