System for determining the development status of a mass such as bread dough in a powered mixer

A system determines the development status of a mass such as bread dough in a powered mixer by applying a set of expert rules to qualitative variables determined from the elapsed mixing time and instantaneous power flow to the mixer over time. The preferred apparatus includes a monitor for tracking the instantaneous power flow coupled with a computer for determining the variables and applying the rules stored in computer memory.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the field of bread dough preparation. The 
preferred embodiment determines the development status of bread dough in a 
powered mixer by applying a set of expert rules to qualitative variables 
determined from the elapsed mixing time and instantaneous power flow to 
the mixer over time. 
2. Description of the Prior Art 
Typical white pan bread is composed of the ingredients of water, flour, 
yeast, sugar, salt and reducing agents. In the commercial preparation of 
white pan bread, the mixing of the bread dough is the most important 
processing step. During the mixing, three important processes occur. The 
first is the blending of the ingredients to achieve a thorough dispersion 
into a homogeneous mixture. The second process is absorption of the water 
into the other ingredients, primarily the flour. The third is development 
of the gluten protein of the flour into a three dimensional matrix so that 
air is retained during fermentation and so that the bread presents the 
desired texture and loaf volume. 
In commercial bakeries, dough mixing is accomplished in a mixing machine 
controlled by an experienced and highly skilled baker. The baker judges 
the characteristics of the dough by smelling, looking and stretching the 
dough, and by listening to the sound of the mixer's motor. Subjective 
judgments based on these characteristics are necessary because the 
attributes of the dough vary from batch to batch. These inconsistencies 
are due primarily to variations in the flour including its water absorbing 
capacity and gluten content. 
In order to eliminate the need for subjective judgment in the mixing 
process, one prior art approach is to control the mixing process on the 
basis of input energy provided to the mixer. For a given mixer and batch 
size, the amount of delivered energy is directly related to the elapsed 
mixing time. In this prior art approach, the time set for the mixing cycle 
is determined by laboratory analysis of the flour protein strength. 
Unfortunately, the protein strength may drift from batch to batch and 
dramatic changes can occur when the flour changes to a different source. 
Another approach is to integrate the instantaneous input power into a 
single line curve that reflects the relative consistency of the dough 
being mixed. This approach, however, only indicates the magnitude of input 
power which does not provide a correct indication of gluten development. 
Other approaches monitor torque on the mixer shaft or rely heavily on 
laboratory testing before each batch. As those skilled in the art 
appreciate, none of the prior art techniques provide a reliable real time 
indication of water absorption and optimal gluten development. 
SUMMARY OF THE INVENTION 
The present invention solves the prior art problems discussed above and 
provides a distinct advance in the state of the art. More particularly, 
the system hereof provides a reliable real time indication of the 
development status of bread dough being prepared in a powered mixer. 
The preferred apparatus includes a powered mixer, a power monitor coupled 
with the mixer for sensing the instantaneous power delivered thereto, and 
a controller coupled with the monitor for determining the elapsed mixing 
time, for deriving a set of qualitative variables, and for determining 
whether these variables satisfy predetermined conditions stored in memory. 
The controller is operable for deriving the statistical mean, standard 
deviation, low frequency energy, and the change of each, for the input 
power over time. From this information, the qualitative variables are 
determined including the water absorption level, and gluten development 
status, with respect to real time. The conditions stored in memory are 
preferably a set of control rules in linguistic form. By applying the 
control rules to the qualitative variables, the development status of the 
dough with respect to real time is determined.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
By way of background, dough mixing can be considered as progressing through 
six stages: blending, pickup, cleanup, development, letdown, and 
breakdown. The blending stage is usually conducted at a low mixing speed 
and is the initial stage for blending the dough ingredients. 
After ingredient blending, the mixer is activated to high speed which marks 
the pickup stage. In this stage, the different flour proteins begin to 
link together to form long chains or strings known as "gluten." 
The cleanup stage is characterized by formation of the dough into a more 
cohesive and hard mass. This is the result of the gluten chains beginning 
to form into a three dimensional matrix. It is this gluten matrix that 
provides the structure to the dough. In this condition, the mixer bars 
throw the dough against the mixer walls and the instantaneous input power 
surges with every pass of the mixer arms through the dough mass. 
In the development stage, the long gluten protein chains become more 
intermixed or tangled and present a stronger three dimensional matrix. As 
a result, the dough presents a drier, more glossy appearance and becomes 
more elastic. As the dough mass winds around the mixer arms and breaks 
against the back wall of the mixer, it exhibits a distinctive audible 
rhythm. 
The end of the letdown stage is the desired end of the mixing process 
because the dough has achieved the ideal development status. The dough 
presents a silky appearance and stretches into smooth, long sheets without 
breaking. In this condition, the dough is ready to be discharged from the 
mixer. 
If dough is mixed too long, it loses its elastic characteristic and becomes 
wet, soft and excessively slack. The over mixing causes the gluten chains 
to separate into a more linear configuration resulting in a drastic 
reduction in the level of polymerization. This is the breakdown stage and 
the dough is of no use for making quality bread. 
Turning now to FIG. 1, apparatus 10 includes powered mixer 12, power 
monitor 14, and controller 16. Mixer 12 is preferably a PEERLESS, 200 
pound, horizontal mixer including mixer body 18 and a three phase, TEFC 
(totally enclosed, fan cooled) induction motor 20 operable at low and high 
speeds. As illustrated, mixer body 18 includes housing 22 and rotatable 
mixing bars 24 coupled with motor 20 by chain driven gear box and shaft 
26. 
FIG. 1A is an electrical schematic diagram of conventional, three phase, 
power monitor 14 using two Hall effect transducers for producing a D.C. 
output proportional to instantaneous A.C. input power. As illustrated, 
monitor 14 is connected using the conventional two-element wattmeter 
method. More particularly, monitor 14 includes current transformers (CT) 
28 and 30 respectively coupled with phases one and three of electrical 
lines 32, 34, and 36 providing power to motor 20. CTs 28 and 30 transform 
the maximum 25 ampere current load to motor 20 to a maximum of 5 amperes. 
Monitor 14 further includes transducer 38 (Ohio Semitronics, Inc., Model 
#P-144E), operational amplifier 40 (type CA3140), resistors R1 (50 Ohms) 
and R2 (9K Ohms), and capacitors Cl (6 uF) and C2 (0.47 uF). One line from 
each CT 28, 30 are connected in common to terminals 4 and 8 of transducer 
38 with the other CT lines connected with terminals 3 and 7 respectively 
as shown. Additionally, voltage inputs are provided to transducer 38 by 
connecting line 32 to terminal 1, line 34 to terminals 2 and 6, and line 
36 to terminal 5. 
Terminals 11 and 12 of transducer 38 produce a D.C. output with terminal 11 
connected by way of resistor R1 to the negative input terminal of 
amplifier 40. Terminal 12 is connected to the positive input terminal of 
amplifier 40 and to one side of capacitor C1; the opposite side of C1 is 
connected to output line 42. Feedback is provided by connecting amplifier 
output line 42 with the negative input terminal by way of resistor R2 and 
capacitor C2 coupled and parallel. Output line 44 is connected to terminal 
12. Output lines 42 and 44 are connected to controller 16 and provide an 
output thereto at a nominal 5 VDC representative of instantaneous power 
flow to motor 20. The instantaneous power readings range between 0 and 15 
kilowatts for the preferred mixer. 
The illustrated controller 16 includes a Hewlett-Packard digital 
oscilloscope (DSO) 46 that receives the power signals delivered on lines 
42 and 44 at a sampling rate of 200 Hz. DSO 46 then digitizes the analog 
input power signal and stores the digitized power flow transient wave form 
at a time base of 5 seconds in real time. This 5 second window of data is 
then stored as a data "frame." Appendix I illustrates the preferred 
software written in HP BASIC for setting up the DSO data acquisition, 
display, analog-to-digital conversion, and data transmission. This 
software records the input power data and also the elapsed mixing time. A 
general purpose interface bus transfers the digitized power signal from 
the output buffer of the DSO to a personal computer 48, preferably 
Hewlett-Packard model HP-216 or other IBM compatible personal computer 
with resident memory. The data acquisition and processing operation occurs 
on an ongoing basis during mixing of a batch of dough. Computer 48 is 
programmed using conventional techniques to perform the functions 
described herein. 
About fifty data frames are required in a typical batch of dough mixing 
with each data frame containing 1,001 data points within the time base of 
5 seconds. From this information concerning the instantaneous power flow 
to mixer 12, computer 48 determines the statistical mean, standard 
deviation, and the Fast Fourier Transform (FFT) low frequency energy using 
MATLAB (off-line), an interactive system and programming language for 
scientific computation and signal processing. In the preferred embodiment, 
the FFT presents a low pass cutoff frequency of 1.4 Hz. 
It has been empirically determined that the mean is related to the 
"stretch" strength of the dough, the standard deviation is related to the 
dough's cohesiveness, and the FFT is related to the viscoelasticity. FIGS. 
2A, 2B and 2C are graphical illustrations of these three parameters over 
time for an actual "good" batch of dough. As illustrated, data smoothing 
is performed by averaging the mean, standard deviation and FFT for every 5 
data frames. 
FIGS. 3A-C and 4 illustrate the next step in the operation in which the 
mean, standard deviation (STD), FFT and high speed elapsed time are 
converted to qualitative variables suitable for use in the preferred 
linguistic rule base illustrated in Appendix II using so-called "fuzzy" 
logic. The Appendix includes the fuzzy logic rules formatted as a look-up 
table, as well as the rules in linguistic format. More particularly, FIGS. 
3A-C illustrate the qualitative variables corresponding to the empirically 
derived labels of very low (VL), low (LO), medium (ME), high (HI) and very 
high (VH) respectively for MN, STD and FFT. FIG. 4 illustrates the labels 
for elapsed time including too short (TS), short (SH), slightly short 
(SS), long (LN) and too long (TL). As will be noted, adjacent labels 
overlap allowing a given input value to fall within one or two labels. The 
membership grade represents the weighting of the belief value within the 
label. 
As an example (see FIG. 3A), a mean value of the referential set of 1.7 
falls within ME at a membership grade of 0.2 and also within HI at a 
membership grade of 0.7. Similarly (see FIG. 3B), a standard deviation 
value of 0.87 falls only within range HI at a membership grade of 0.9. An 
FFT value of the referential set of 155 (see FIG. 3C) falls within range 
ME at a membership grade of 0.1 and within range HI at a membership grade 
of 0.5. An elapsed time value of the referential set of 3:24 (3 minutes, 
24 seconds) falls within range LN with a membership grade of 0.25 (see 
FIG. 4). 
Additionally, qualitative variables concerning the change in the mean, 
standard deviation and FFT are also determined on an ongoing basis as 
illustrated in FIGS. 5A-C corresponding to a negative (NE), zero (ZE), and 
positive (PO) changes. As illustrated, these labels overlap allowing data 
to fall in one or two ranges. 
Next, the qualitative variables are used to determine the gluten 
development of the dough being prepared in mixer 12. The first step is to 
determine gluten development with respect to dough strength or resistance 
as related to the mean (GM), dough cohesiveness as related to the standard 
deviation (GSTD), and viscoelasticity as related to FFT (GFFT). Using the 
example from above, these levels of gluten development can be represented 
.as the union of the discrete sets: 
EQU GM=0/VL+0/L+0.2/ME+0.7/HI+0/VH 
EQU GSTD=0/VL+0/L+0/ME+0.9/HI+0/VH 
EQU GFFT=0/VL+0/L+0.1/ME+0.5/HI+0/VH 
where the coefficients represent the membership grade. The total gluten 
development can be represented as the set union: 
EQU GLUD=GM+GSTD+GFFT 
where "+" denotes set union in which the maximum of each label is taken for 
the total. Thus: 
EQU GLUD=0/VL+0/L+0.2/ME+0.9/HI+0/VH 
Similarly, the "change" variables CGM, CGSTD and CGFFT are determined from 
the conversion discussed in connection with FIGS. 5A-C from which the 
total change in gluten development can be derived as CGLUD. 
The qualitative variables GLUD and CGLUD along with high speed elapsed time 
(HSET) (from FIG. 4) are used as the premises of the linguistic rules set 
forth in Appendix II. These rules are in the form of a conditional 
statement, i.e.: if "X" then "Y" where "X" represents the qualitative 
variables and "Y" represents the development stage of the dough such as 
"pickup" or "cleanup" and also represents a desired action such as 
"increase water." Each rule is continuously applied to each of the three 
qualitative variables which, as described above, are continuously updated 
in a real time manner during the mixing cycle. When the conditions for a 
rule are satisfied, the rule is said to "fire." 
Using the example from above, gluten development GLUD is both medium (ME) 
and high (HI) which is possible because of the overlapping ranges, and 
high speed elapsed time (HSET) is long (LN). Assuming that the change in 
gluten development CGLUD is positive (PO), then rule 18 is the only rule 
in which all of the antecedent conditions are satisfied. This leads to the 
rule outputs that the dough absorption status is "properly absorbed," 
dough mixing status is at the "development" stage, and the recommended 
action concerning the absorption level is to "leave alone." 
As can be observed from inspection of the other rules, the mixing process 
is continuously evaluated in real time as the dough progresses through the 
various development stages and outputs are provided indicating the 
development status of the dough and recommending any corrective action 
that may be needed. For example, if the conditions for rule 2 are 
satisfied, a recommendation is provided to "slightly increase water." In 
contrast, if the conditions for rule 10 are satisfied, the recommendation 
is to "decrease water," which means to add more flour to the dough. 
The following sets forth another example in the operation of the present 
invention: 
EQU GLUD=0/VL+0.3/LO+0.8/ME+0/HI+0/VH 
EQU HSET=0/TS+0.7/SH+0/SS+0/LN+0/TL 
EQU CGLUD=0/NE+0/ZE+1/PO 
Because GLUD is both low and medium, both rules 6 and 7 are firing. This 
results in seemingly contradictory recommendations to both slightly 
decrease water and to slightly increase water. This apparent conflict is 
resolved by taking into account the membership grades in determining a 
specific or "crisp" value for the dough development status and 
recommendation for a percentage change in water content. 
First, the conjunction or minimum of each antecedent membership label for 
each rule is applied using the Compositional Rule of Inference to truncate 
the area under each consequent membership label as illustrated in FIGS. 
6A-C. For the example, this is applied as follows: 
EQU Rule 5=0.3/LO .LAMBDA.0.7/SH .LAMBDA.1.0/PO=0.3 
EQU Rule 7=0.8/ME .LAMBDA.0.7/SH .LAMBDA.1.0/PO=0.7 
These values of 0.3 and 0.7 are used to truncate the areas under the 
corresponding curves in FIGS. 6A-C. More specifically, Rule 5 indicates 
that the development status is at pickup (PU) and the truncated value for 
Curve PU is 0.3. This is indicated by the hash-marked area under the PU 
curve in FIG. 6A. Similarly, for Rule 7 the development status is cleanup 
(CU) with the truncated value being 0.7. This is indicated by the stippled 
area under the CU curve of FIG. 6A. These two areas together form a 
combined area (the overlap is only included once and specifically in the 
largest area). Using the centroid technique, the mathematical moment of 
the combined area is then calculated with reference to the origin. This 
moment represents the center of mass of the combined area and is indicated 
by the arrow in FIG. 6A. From this, it can be seen that the mixing stage 
is weighted toward cleanup (CU). 
The same process is followed for determining a numerical value for the 
dough absorption level. As indicated by the arrow in FIG. 6B, the dough 
absorption level is closer to slightly underabsorbed (SU). In FIG. 6C, 
this process indicates that the output recommendation is to increase the 
water content by 0.8%. Thus, the apparent conflict is resolved and results 
in a specific recommendation. 
The outputs concerning absorption, water and development status can be 
presented on the display monitor of computer 48 to the operator of 
apparatus 10, and can also be connected to the control for mixer 12. For 
example, the water recommendation can activate a water valve for addition 
of the specified water amount or flour valve for addition of the needed 
flour amount, and a development status of "final" or "breakdown" can shut 
off the mixer. 
It will thus be understood that the three outputs of the fuzzy logic 
control system are Mixing Index, Dough Absorption Level and Recommended 
Action (increase/decrease water). The desired output, for a properly mixed 
batch of dough, is a Mixing Index of FN and a Dough Absorption Level of 
PA, i.e., a Recommended Action of LA. The Dough Absorption Level and the 
Recommended Action have a one-to-one relationship with each other. 
Therefore, if one is determined, calculating the other gives redundant 
information. 
The data acquisition and digital signal processor described previously can 
readily be replaced by a more compact, advanced system. For example, use 
can be made of a Motorola integrated circuit (IC) board (MC68HC11). This 
board will have the following IC chips: MC68HC11 microprocessor; 
asynchronous communications interface adapter (ACIA) chip; 
analog-to-digital conversion (ADC) chip; multiplexer chip; electronically 
erasable programmable read only memory (EEPROM) chip; random access memory 
(RAM) chip; and other IC chips as needed. The ADC processing; multiplexing 
commands, calculations for the mean, standard deviation, and FFT; 
communications commands; and storage processes will be programmed in 
assembly language and stored on the HC11 board's EEPROM. This board 
occupies about 16 cubic inches and is powered by about 10 watts from +5 
VDC, +12 VDC, and -12 VDC power supplies. By contrast, the previously 
described apparatus occupies about 10 cubic feet of space and is powered 
by about 400 watts from a 117 VAC source. 
While the fuzzy logic control system described above provides excellent 
real time feed back control in the context of dough development, it will 
be understood that the invention is not so limited. That is, the system 
can provide appropriate feed back control of any process wherein a 
conglomerate mass is mixed, and in which there is a polymerization of the 
mass during the mixing process. It is desirable that the process 
non-intrusively sense the state of the polymerization process by measuring 
the torque required to accomplish the powered mixing, the mixing time, and 
the temperature of the conglomerate mass. Within the context of these 
conditions, many food and chemical mixing and extrusion processes can be 
controlled using the invention. 
As those skilled in the art will appreciate, the present invention 
encompasses many variations in the preferred embodiment described herein. 
Having thus described the preferred embodiment of the present invention, 
the following is desired to be secured by Letters Patent.