ControlSoft Simplifies Extrusion Barrel Temperature Control
One of the most difficult and commonly seen control problems is the
proper control of slow temperature loops. This is because of the large
mass of material that these loops usually involve. In a heating loop,
for example, both heating power and time are required to heat the system
(long deadtime issues). Then, once the temperature starts to rise, it
will increase slowly but steadily, and will tend to continue to increase
for some time, even after the heating device has been turned off due
to the problem of thermo momentum. Hence, one often ends up with a large
overshoot and oscillatory response (with a very long cycle time).
Such a problem is further aggravated in Extrusion Barrel Temperature
control because there are typically multiple barrel zones in an extruder.
While each zone behaves differently, they also affect each other. The
cooling process further complicates the issues since cooling and heating
behave very differently. Finally, shear energy from the screw also affects
temperature within the system.
MANTRA Software includes a specially designed control strategy incorporated
in the Temperature Control Module (TCM) such that each stage of the control
is treated differently, since different requirements are imposed at different
stages, such as tuning stages, start-up stage, initial control stage,
and run-time production control. With the use of TCM, all these internal
stages are transparent to users. After configuring the TCM block, only
one start button is required for a user to commission TCM control.
ControlSoft's Solution – Mantra Temperature Control Module
TCM is an advanced control solution that takes into account all the
challenges of extruder temperature control, specifically:
- TCM treats different zones differently, since they behave
differently.
- TCM takes into account that neighboring zones
may affect each other, and it coordinates the control among all zones.
- TCM
provides different controller speeds, user selectable.
- TCM uses
model predictive control techniques to better control and predict the
temperature.
- TCM uses different sets of tuning parameters
for startup and steady-state.
- TCM performs auto-tuning during
the start-up time; no additional tuning test is required.
- TCM
provides independent heat/cool control with proper coordination.
- TCM
is applied as supervisory control over the existing control system.
Temperature Control Comparison between TCM and PID
controller on a 4-zone extruder
As the Figure illustrates, even a well-designed PID cannot match the
performance of the MANTRA TCM block.
Key Advantages of the ControlSoft TCM Technology over Traditional PID
Controllers
- Provides a fast startup from cold position with minimum overshoot
to minimize startup time.
- Provides tight temperature control
during production (+/- a few degrees versus significant oscillations
with PID controllers) for more consistent product quality and optimal
utility usage.
- Provides a fast response for product or setpoint
changes to minimize the time to reach stable production temperatures.
- Handles
the dynamics of heating and cooling independently.
- Contains
self-tuning function to minimize implementation time.
ControlSoft's solutions featuring MANTRA TCM technology can increase
the profitability of your process with no replacement of existing hardware
or wiring required.
Select from the following application Notes and Technical Papers:
See other applications.
|
