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An Italian-led project has used fuzzy logic software to produce
a fast response water mixer that can instantly supply bakers with
water at the exact temperature they need to make good dough. Until
now, bakers have had to rely on doser-mixers that can typically take
20 to 40 seconds before the output reaches the desired temperature.
This can affect the quality of the bread and wastes a large quantity
of water that has been expensively heated or cooled.
The project leader has started supplying commercial versions to both
industrial-scale and crafts bakers, and may develop the unit's water
flow meter for other applications.
Bakers find it difficult to produce dough
to consistently high standards throughout the year. In winter, for
example, water at 30°C might be needed to make dough, while in the
summer the water might need to be cooled to 3°C. In the spring,
the water might have to be maintained at 15 to 20°C. These temperatures
vary according to climate and the type of bread being baked.
Bakers understand the importance of controlling water temperature
and many can judge temperature accurately using just a finger. However,
the poor response of the water doser-mixers used in bakeries means
that it might take 30-40 seconds before the water reaches the necessary
temperature, and when it does, it may not remain stable.
This creates serious production problems for bakers because large
quantities of water are wasted before the flow reaches the right
temperature for making dough. During that process, a lot of energy
is wasted in heating or cooling the water that is discarded.
The electronic doser-mixer, developed as a BRITE-EURAM project,
delivers water at the correct temperature within about three seconds
of changing the setting. It combines a fast and accurate temperature
sensor, a motor driven mixing unit and a flow counter. The project
was led by the process control development company, STM Products
of Verona.
Fast temperature sensing
The physics department of the University of Udine in Italy was
contracted to develop a temperature probe able to respond by 63%
to the change in the water temperature being delivered in less than
200 milliseconds (ms). The physics department came up with a K type
thermocouple with an insulated joint and a small mass, with a diameter
of only 1 multimedia, which responds in just 150 ms in water flowing
at 1 m/second. The readings of the temperature probe control a mixer
unit that combines two flows of water to the desired temperature
between cold, refrigerated and warm. If the temperature setting
is changed, the water flow rates are adjusted in opposite directions
using an electronically controlled valve, keeping the total flow
of the water the same. By simultaneously adjusting the two flow
rates, the desired temperature can be reached much faster than if
only one flow were regulated.
If the flow rate is adjusted, the mixer alters the flow of cold
water and at the same time varies the warm or refrigerated flow
to maintain the temperature setting.
Stepping up the accuracy
As well as the simplicity of the design, the doser-mixer is largely
immune to the limestone and chlorine found in water, and is almost
silent.
The mixer unit itself is driven by a stepping linear actuator in
which the rotary motion of an electric stepping motor is translated
into linear movement by a trapezoidal worm screw with a 1.5 mm pitch.
The mixer has about 1,100 resolution positions within a stroke of
the valve of only about 3.5 mm, so the project partners had to develop
a very accurate electronic device to sense when the mixer had reached
the end of its stroke.
They decided to use a Hall effect sensor that produces a changing
signal as it moves in a magnetic field. The system software interprets
the signal to control the stroke with an accuracy of more than 4
micron.
A Hall sensor was also used in the design of the doser-mixer's flow
counter, which had to be as reliable as the expensive units already
on the market, but much cheaper to produce. Inexpensive units, on
the market for primarily domestic use, tend to be unreliable and
unsuitable for bakeries that often operate eight hours a day. STM
fitted a German flow meter body with a turbine carrying a Hall effect
sensor on one vane. The flow of water spins the turbine, with each
rotation corresponding to the passage of a thirtieth of a litre
of water and detected electronically. The electronics components
of the flow meter are encased in resin for protection and the meter
has proved very reliable, as well as being simple to manufacture.
A fuzzy logic approach to control
The doser-mixer's control software was developed by STM and researchers
at the Italian University of Padova. The electrical engineering
department at the university made innovative use of fuzzy logic
to control the mixer shaft. Fuzzy logic software does not make fixed
adjustments to reach a set target, rather it learns from experience
of what is actually happening to change its behaviour in order to
home-in on changing targets. For this reason, fuzzy logic was expected
to cope with the rapid changes in pressure and temperature in the
water delivered to the mixer.
STM says that the fuzzy logic it developed handles fluctuations
in water supply well, including pressure changes in the water pipes
resulting from opening and closing the supply valves. The results
were confirmed when the doser-mixer tested 26 of an initial 30 prototypes
in field trials by the project collaborators Thermogel and Kriotec
of Italy and Danish baker Naturbageri.
The doser-mixer was found to produce water at the correct temperature
in a typical two to four seconds, compared with a typical 20-40
seconds of conventional units. The unit has a temperature accuracy
of plus or minus 0.5°C and a volume accuracy of plus or minus 1%.
The unit's control panel is simple to operate, with an LCD display
and a choice of five languages. Different water batches for different
bread recipes can be pre-programmed.
Proving a success
The first 50 litre/minute production version of the doser-mixer
has been supplied to the bakery equipment installer Kalmijer of
Amsterdam in The Netherlands, and the design is now on the market;
STM hopes to eventually produce 50-80 units each month. The same
software may be used for a larger doser-mixer, able to handle 300
litre/minute.
The company is also considering selling the design for uses such
as sausage making and for controlling water temperatures in normal
plumbing systems. It may also sell the flow meter for other applications,
however, the plastic parts would likely have to be changed for materials
other than water.
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