A method and apparatus for an in-motion weighing system which includes a package conveyor, a weigh pan, a package detector positioned adjacent to the conveyor and upstream from the weigh pan, a timer for determining the time required for a package to pass by the package detector, means for storing the time required for a point on the conveyor to transition the weigh pan, means for subtracting the package passing time from the weigh pan transition time for establishing a read scale window, and a means for measuring the average weight of a package on the weigh pan during the read scale window.

FIELD OF THE INVENTION 
The present invention is related to in-motion weighing, commonly referred 
to as checkweighing, and a method for automatically establishing weighing 
parameters which includes an adaptive timing algorithm for establishing 
read scale time as a function of package length. 
BACKGROUND OF THE INVENTION 
Present day society relies on extensive use of automation for packaging 
products for sale. This usually entails a means for determining the 
quantity of material placed within a retail package. Weighing is the most 
practical and acceptable form for controlling the material placed in a 
package and this is accomplished largely by scales known as in-motion 
weighing devices or checkweighers. Because of the speeds involved, this 
requires very precise real time measurement of containers prior to 
entering the weighing/filling station and during the filling operation so 
that filling may be terminated at a precise point. Setting up such a 
system is critical, the slightest miscalculation will result in enormous 
losses by over filling packages or excessive customer complaints and 
lawsuits due to under-filled packages. 
In the past, the very critical operation of setting up an in-motion weigher 
was usually accomplished manually with the aid of an assortment of 
calculating devices and test equipment. The steps included a first 
operation where the load of the platform sitting on top of the transducer 
device was calculated. This is commonly referred to as the dead load. 
Once the dead load was established, a ranging function was set. This was 
accomplished via a potentiometer using the highest weight package to set 
up the system. Alternately, the gain or range potentiometer was adjusted 
each time a different weight range was used. 
Typical transducers used in such systems are a strain gauge load cell or a 
flexure type scale system using either a LVDT (Linear Variable 
Differential Transformer), a DCDT (Direct Current Differential 
Transducer), or force restoration (a magnetic means of counteracting 
forces in the scale by pumping current in the opposite direction to bring 
the scale back to an equilibrium point which must be offset). 
Because the systems are electronic, they have some inherent noise imposed 
on control signals; typically, in-motion or checkweighing scales have 
noise in the range of 20 Hz or lower. This and higher values of noise have 
been filtered out by a low pass filter. However, the method by which this 
was done in the past used typical active analog filters and required quite 
a bit of human intervention to monitor the actual scale output and 
determine the appropriate resistor network or resistor values to tune the 
filter to provide a reasonable weight signal and eliminate higher 
frequency noises. 
A recorder or oscilloscope was required to determine the point at which 
sampling of the net weight signal was taken. The window over which the 
weight signal was read was a potentiometer type adjustment requiring human 
intervention. Furthermore, the filter value was dependent on the package 
speed and weight and, therefore, any time a speed or weight change was 
required, manual intervention and resetup were required. Analog filter 
values also limited the rate at which packages could be weighed due to 
charge and discharge time of the filters being used. 
The development of microprocessor controlled checkweighing has eliminated 
many of the difficulties inherent in the prior art systems discussed above 
but checkweighers are still designed to weigh every package for a fixed 
amount of time called the "read scale time". As the item to be weighed 
moves across the weigh pan, the weight curve rises, bounces, stabilizes 
for a period of time, and then falls as the package exits the weigh pan. 
During a portion of the period of time for which the package has settled, 
the checkweigher samples the weight curve and determines the weight of the 
package. 
The period of time during which the package is stable and therefore 
"weighable" depends upon the length of the package, the speed of the 
conveyor belt, and the length of the weigh pan. Normally the speed of the 
belt is fixed and the length of the weighpan is always fixed. Therefore 
the length of the period of weighability is chiefly a function of package 
length. The shorter the package, the longer the period of "weighability". 
The longer the period of weighability, the longer the read scale time can 
be. Within the range of read scale times typically available to in-motion 
checkweighers, it has been established that the longer the read scale 
time, the better the accuracy. This is because a longer read scale time 
enables the system to filter out more of the low frequency noise which 
compromises checkweigher accuracy. Thus it is desirable to have as long a 
read scale time as possible. 
Checkweighers use one of two strategies to overcome problems created by 
fixed read scale times. In one approach, the read scale time is fixed for 
all packages to the value permitted by the longest package to be weighed, 
i.e. a short read scale time. In such systems, the shorter package will 
not be weighed as accurately as they can be, or in some situations- as 
accurately as they need to be. 
In the second approach, the different size packages are presented to the 
checkweigher in a slow and predictable manner, so that it can choose from 
a variety of different read scale times stored in its memory. This is too 
expensive. Packages have to be separated and sorted by length plus it is 
too expensive to slow down production for benefit of the checkweighing 
operation. Furthermore, it is complicated to arrive at a set of different 
read scale times from a series of different calibrations. 
The potential errors and operator skill requirements of prior art systems 
are obvious and this has led to constantly increasing packaging costs and 
thus increase consumer costs. 
OBJECTIVES OF THE INVENTION 
In view of the problems inherent in the prior art in-motion weighing 
systems, it is a primary objective of the present invention to provide an 
automated in-motion checkweighing system which accomplishes all major 
control functions via a microprocessor manipulated algorithm which 
dynamically responds to the randomly varying lengths of rapidly moving 
packages and optimizes its read scale time to exploit the maximum 
available period of "weighability" for each and every package. 
Another objective of the present invention is to provide a continuous or 
in-motion weighing system incorporating methods of control/machine setup 
that reduce the number of operator inputs which guide the setup and use 
more intuitively understandable operator inputs. 
A still further objective of the present invention is to improve the 
accuracy of state-of-the-art in-motion weighing devices. 
Another objective of the present invention is to provide an automatic setup 
for weighing machines where the weighing process is optimized by unique 
algorithms. 
Another objective of the invention is to provide a weighing device wherein 
weight sampling is optimized automatically; i.e., the window over which 
weights are taken are automatically determined. 
Another objective of the invention is to eliminate spurious readings by 
using algorithms which control sampling times, the time between samples, 
and sampling rates and impose digital limits on data taken. 
Another objective of the invention is to provide a system where the 
sampling rate for reading weights is increased or decreased to fit the 
available weight information window based on a determination of package 
length, therefore allowing lower filter values if higher time exists and 
achieving better accuracy. 
These and other objects, features and advantages of the present invention 
will become more clearly apparent from the following detailed description 
of various embodiments of the invention, which refers to the appended 
drawings and is given by way of illustration, but not by limitation. 
SUMMARY OF THE INVENTION 
The in-motion weighing system presented in this patent is designed to allow 
an untrained operator to set up and weigh a package or a plurality of 
packages advancing down a packaging conveyor. The system incorporates 
circuitry including a microprocessor controlled programmable gain 
amplifier in a fashion which eliminates potentiometers, jumpers, 
resisters, and other components needed by the prior art systems to 
manually adapt or change the weighing functions of the automated packaging 
systems. The microprocessor accomplishes these goals through the 
manipulations of algorithms which cause the automatic setting of system 
parameters based on system constants and desired operations. The 
algorithms include setting up or establishing scale offsets, gain, weight 
timers based on package length and responsive digital filters for 
eliminating system noises.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates the display and control panel of an in-motion weigher or 
checkweigher designed according to the present invention. It includes a 
multifunction display 10 comprised of the following indicators. 
A Zone Indicator Display, 11, including Zone 1 (Red)--gross underweights; 
Zone 2 (Yellow)--just under; Zone 3 White)--accept; Zone 4 (Blue)--just 
over; and zone 5 (Green)--gross overweight. 
A Weight Mode Indicator "DEVIATION FROM TARGET/ACTUAL", 12, which indicates 
the deviation from target or actual weight readout modes. 
An LCID Weight Display, 13, which displays the actual net weight of the 
product or variation as a plus or minus from targets. 
A Weight Unit Indicator, 14, which displays weight units in grams, 
kilograms, ounces, or pounds. (Operator selected). 
System Status Indicators, 15, provide: 
"SAMPLE KAGE" (orange indicator 16) which indicates that the system has 
automatically ejected package(s) from the line and displays the weight for 
operator verification. This allows a product weight check on accuracy 
without stopping or interfering with line operation. 
A "NO TOTAL" (Orange indicator 17) which indicates that the counters are 
"off" during set-up and calibration. 
A "GOOD REZERO"(Green indicator 18) which indicates that the scale is 
automatically rezeroed every time there is a gap of one or more packages 
in the production flow. 
A "NEEDS REZERO" (Red indicator 19) immediately alerts the operator to 
excessive product build up on the scale or that automatic rezero is 
overdue. 
A "KAGE SING" (Red indicator 20) alerts the operator that packages 
are too close together for accurate weighing. 
A "SCALE NOISE" (Red indicator 21) alerts the operator of excessive 
internal and/or external interference i.e., vibration, air currents, and 
unstable product transfer. 
An alphanumeric display, 30, prompts the operator in all checkweigher 
functions it uses full English language to verify inputs, calibrations, 
set-up diagnostics, etc. 
A direct key pad access input device, 40, includes 28 discrete, tactile 
keys. The keys on the left side of this sub-panel are set function keys 
which provide single stroke, direct access to the most commonly used 
operator functions. For instance, the "NO TOTAL" key, 41, turns off the 
product counters so trial and test packages can be run without affecting 
product count information already stored in memory. 
The "SAMPLE KAGE" key, 42, automatically ejects package(s) from the line 
and cause up to the last 10 weights to be displayed for operator 
verification. Thus the operator can take an actual product weight and 
check accuracy without stopping or interfering with production. 
The "TARGET/TARE" key, 43, enters target weight and associated tare for up 
to 25 products. 
The "ZONES" key, 44, enables the operator to view and/or change current 
product set point limits. 
The "KEY CODE" key, 45, provides three levels of security: KEY LOCK=on - 
off - run. 
KEY CODE=KEY LOCK bypassed by numerical password. 
SUPER KEY CODE=allows supervisor to select level of operator access. 
The "CLEAR TOTALS" key, 46, zeros the production counters for selected 
product zones. 
The "VIEW TOTALS" key, 48, calls up the counters for package count and 
percentages by zones for "Accepts", "Overweights", "Underweights" and 
"Total". 
The "PROD" key, 49, instantly recalls all of the product parameters and 
totals for any of the 25 individual pre-entered products. 
The ". - ON/OFF" key, 50, enters the decimal point position for numeric 
entries and accepts or rejects status by individual zones. 
The keys on the right hand side of the sub-panel are a distinguishable 
color from those keys on the left hand side of the panel and they provide 
menu selection and control functions. 
The "HELP/SETUP" key, 51, provides a step-by-step narrative for control 
calibration 
The "NORMAL/DISP" key, 52, returns the system to the original operating 
mode and displays current set-up limits. 
The "MENU" key, 53, provides access to all operator functions, i.e.; 
choose, view, and change the desired operating mode. 
The "CANCEL" key, 54, deletes the last entry. 
The "ENTER" key, 56, enters data into memory. 
The cursor or arrow keys, 55, allow the operator to scroll through the 
entire menu. 
The ten numeric keys in the center of the sub-panel are used to enter 
values as required. 
The circuitry controlling and controlled by control panel 10 is illustrated 
in FIGS. 2 and 3 wherein the embedded controller and control panel are 
designated 208 and interconnected to the system by microprocessor 
interfaces 206, 210, and 213. The embedded controller is a standard state 
of the art integrated circuit system including a microprocessor, static 
RAM memory with battery back-up, an EPROM program memory, an EEPROM for 
nonvolatile storage of product related data, timers, an interrupt 
controller, an input/output interface, a keyboard interface, and a display 
interface. FIG. 2 illustrates the system adapted to use an analog load 
cell such as the resistive bridge load cell 201 (the resistive bridge 
illustrated is for simplification of the presentation only). The analog 
voltage level produced by the load cell, regardless of type, is applied to 
preamplifier 202 and then via a low pass filter 203 to a programmable gain 
amplifier 204. The programmable gain amplifier 204 includes an 
instrumentation amplifier 205 which receives a scale offset input and the 
scale weight signal. The programmable gain amplifier also includes an 
analog switch array 209 which allows the resistive elements controlling 
gain to be switched by the microprocessor via the microprocessor interface 
210 and thus control the amplifier gain. 
The scale offset 214 input is adjusted by a microprocessor interface 206 
through a digital-to-analog converter 207. This adjustment entails setting 
the offset level of the instrumentation amplifier 205 of the programmable 
gain amplifier 204. 
The output of the programmable gain amplifier is applied to a low pass 
filter buffer 211 and then to the microprocessor via an analog-to-digital 
converter 212 and interface 213. The microprocessor preforms sampling 
routines on the incoming signal and smooths the data by functioning as a 
digital filter. 
FIG. 3 is an adaptation of FIG. 2 designed for use with a digital load cell 
215 such as a quarts crystal transducer, etc. 
Irrespective of the type of load cell, the system uses digital signal 
processing which provides better accuracies compared to existing equipment 
and superior noise free operation. This is exemplified by the summaries of 
test data presented in FIGS. 4, 5, and 6. FIG. 4 depicts the weight vs. 
time curve relative to the target weight in a no-filter system. Note that 
the no-filter system has a 2.5 gram tolerance which in the example equates 
to an error potential of 2.5%. FIG. 5 depicts the weight vs. time curve 
relative to the target weight in an analog-filter system. Note that the 
analog-filter system has a 0.25 gram tolerance which in the example 
equates to an error potential of 0.25%. FIG. 6 depicts the weight vs. time 
curve relative to the target weight in a digital-filter system which has a 
0.05 gram tolerance that in the example equates to an error potential of 
only 0.05%. 
Digital filtering is a form of signal processing that is done in the 
digital domain as opposed to the continuous or analog domain. The digital 
domain is also known as the discrete time domain and is represented by 
`z`, the discrete time complex variable. The z domain corresponds to the 
imaginary parts and are frequently shown graphically. The graphical 
representation is known as the `s` plane in analog and the `z` plane in 
digital. System response can be determined from these graphs by plotting 
the poles and zeros of the system's transfer function. 
The transfer function of an analog filter is given as: 
##EQU1## 
where: s is the complex variable equal to I+jw n is the filter order 
a and b are the coefficients that determine the response of the filter 
(i.e. low pass, high pass, Butterworth, etc.); and A is the amplification 
constant. 
The transfer function is used to determine the values of the components 
used to make the filter (values of resistors and capacitors). 
The transfer function of a digital filter is given as: 
##EQU2## 
where: z is the digital complex variable a.sub.n are the numerator 
coefficients (zeros) 
b.sub.n are the denominator coefficients (poles) that also determine the 
filter response 
The transfer function can be expressed as a difference equation: 
EQU Y(n)=A(a.sub.o X(n)a.sub.1 X(n-1)+. . . +a.sub.k X(n-k)-b,Y(n-1) . . . 
b.sub.k Y(n-k)) 
where: Y(n) is the present output samples 
Y(n-1) the previous out sample, etc. 
X(n) the present input sample 
X(n-1) the previous input sample etc. 
There are two types of digital filters; recursive and non-recursive. 
Recursive filters are also known as infinite impulse response or IIR 
filters and can be made to emulate an analog filter. They are known as 
recursive because they use previous output samples (feedback). The 
feedback terms are also called the poles of the system and are represented 
by the denominator terms of the previous equation. Non-recursive filters 
don't have feedback terms and don't have a "Z" counterpart in the analog 
world. They are also known as finite impulse response filters or FIR 
filters. They only have zeros (numerator) terms and are represented by the 
previous equation without the denominator. 
A second order recursive digital filter is given by: 
##EQU3## 
The transfer function can also be converted to a difference equation: 
EQU Y(n)-A(a.sub.o X(n)+a.sub.1 X(n-1)+a.sub.2 X(n-s)-b.sub.1 Y(n-1)-b.sub.2 
Y(n-2)) 
where: Y(n) is the present output sample 
Y(n-1) is the previous output sample 
Y(n-2) is the second previous output sample 
X(n) is the present input sample 
X(n-1) is the previous input sample 
X(n-2) is the second previous input sample 
This equation is represented in graphical form in FIG. 7. This form is 
known as the Direct form. It has four delay elements (Z.sub.-1), 5 
multiplies, and 6 adds. 
Another very popular form is the Canonical form illustrated in FIG. 8. The 
Canonical form has the advantage of only two delay elements per second 
order cell compared to four delay elements per cell for the Direct form. 
The Direct form, however, can have its delay elements precharged to some 
output value. 
Filters of higher order can be made by adding additional cells as 
illustrated in FIG. 9. 
The response of the digital filter is determined by the coefficients a and 
b. There are computer programs available that will compute the 
coefficients given the sampling rate, type of filter, and order. 
The canonical form digital filter is presently used in the Front-end 
software. The coefficients were provided by Augusto Mayer of Toledo 
Research Center (TRC). The response of the filter is Gaussian, 4 pole, low 
pass where the cutoff is 2% of the sampling rate. The filter needs 80 
samples "run through" to come to the full value given a step input as 
illustrated in FIG. 10. 
The Front-end digital filter is used in a "gated" mode. The filter is 
"turned on" only after the delay to weigh timer has timed out. This makes 
it possible to use a lower cutoff than would be possible in a continuous 
mode. The filter takes 40 samples during the read scale time and processes 
those samples during the time between packages, see FIG. 11. The 40 
samples are "run through" twice to satisfy the needed 80 samples. The time 
between samples is the sampling period and is determined by the filter 
cutoff point; the lower the cutoff the longer the sample period. 
The system is designed to allow an untrained operator to set up and weight 
a package "from scratch". The system's circuitry is microprocessor 
controlled. This eliminates the potentiometers, jumpers, and resistors 
that needed manual changing on our previous controls. The digital signal 
processing enabled by the circuitry of FIGS. 2 or 3 allows automatic 
setting of controls through the use of equations or algorithms. The 
circuitry controlled in setting up a scale is the offset, the gain, weigh 
timers, and the digital filter. The setting of these values adapts the 
system to any scale, weight range, and package speed. 
The Range Routine is used to set the gain and offset to the optimal values 
for a given load cell, dead load, and weight range. The circuits adjusted 
are the 8-bit (values from 0-255) digital-to-analog converter, 207 of FIG. 
2, and the programmable gain amplifier, 204. The procedure for setting the 
gain and offset involves adjusting the digital-to-analog converter (DAC) 
and programmable gain amplifier (PGA) and instructing the operator to 
place a package on and off the scale until optimum values for the DAC and 
PGA are found according to the logical operations of ranging and set 
offset algorithms as illustrated in FIGS. 12 and 13. 
The system automatically calculates values for the delay-to-weigh, read 
scale, delay to rezero and digital filter cutoff for each package 
individually during production by exercising the logic of FIG. 14. 
("During production" means while the system is being used in a packaging 
plant which is producing packages for weighment and sending them across 
the checkweigher.) This is accomplished by using two measurements and two 
adjustment factors. These four pieces of information are set to default 
values, but can be changed by the operator in order to optimize the timing 
calculations. The two measurements are the speed of the conveyor belt over 
the scale in feet per minute and the length of the weigh pan in inches. 
The two adjustments are a "delay to weigh" adjustment and a "read scale 
time" adjustment, both entered in milliseconds. The checkweigher uses the 
two measurements to arrive at a "raw read scale time" according to the 
following formula: 
##EQU4## 
The raw read scale time is the time it takes the leading edge of a package 
to traverse the full length of the weight pan. This value is stored in the 
checkweigher memory. 
The delay to weigh, delay to rezero, specific read scale time, and digital 
filter cutoff value for each individual package is calculated during 
production as each package traverses the weigh pan by exercising the logic 
of FIG. 14, described as follows. This is the weighing process, as well. 
In the adaptive timing system, the calculation of timers is an inherent 
part of the weighing process: 
1) The leading edge of package reaches the upstream end of the weigh pan, 
triggering the package detector device which is used to measure the length 
of the package. 
2) The calculation of the specific read scale time for this package is 
begun by initially setting it equal to the raw read scale time (the 
calculation of which is explained above). It is stored in the checkweigher 
memory where it remains during the adjustments it undergoes according to 
the following steps 3 and 5. 
3) Every N milliseconds, (where N is typically, though not exclusively, 
defined to equal either 10 or 2), the package detector is interrogated. 
IF the package has not yet fully loaded on to the weigh pan, the detector 
will so indicate and the software will deduct N milliseconds from the 
specific read scale time for this package. It will wait N milliseconds and 
repeat step 3. 
IF the package has fully loaded on to the weigh pan, the detector will so 
indicate and the software will deduct N milliseconds from the specific 
read scale time and go on to step 4. 
4) The delay to weigh timer will be set equal to the delay to weigh 
adjustment and it will be started. 
5) The specific read scale time for this package will be reduced by an 
amount equal to the delay to weigh adjustment and then reduced again by an 
amount equal to the read scale time adjustment. [the distinction between 
raw read scale time and specific read scale time is this: the raw read 
scale time is the amount of time it takes a package to traverse the entire 
weight pan and the specific read scale time is that portion of the raw 
read scale time during which the entire package is on the weigh pan and 
sufficiently stable to perform the weighing process. Any reference to "raw 
read scale time" in this document refers exclusively to the "raw read 
scale time". Any reference to "specific read scale time" or "read scale 
time" are both to be construed as referring only to the "specific read 
scale time." ] The weighing clock will be started using the specific read 
scale time for this package. The digital filter cutoff value is calculated 
from the specific read scale time. The digital filter uses a sample rate 
clock that takes an ADC reading on every clock tick. A total of 40 samples 
are taken during the specific read scale time. The sample rate is given 
by: 40 samples divided by the read scale time. The longer the read scale 
time, the lower the sample rate frequency. The lower the sample rate 
frequency, the lower the filter cutoff. The two unique features of the 
digital filter are: it only filters the "top" of the weight curve, and the 
weight samples are "run through" the filter twice, which produces a more 
effective filtering action. The unique feature of the adaptive timing 
system is that the read scale time is maximized for each package, keeping 
the filter cutoff as low as possible; thereby maximizing noise 
reduction--and therefore weighing accuracy--for each package individually. 
6) At the time the specific read scale time is calculated, the delay to 
rezero is also calculated and set equal to the sum of the raw read scale 
time plus the delay to weigh adjustment. The delay to rezero timer is 
started. 
EQU delay to rezero=raw read scale time+delay to weigh adjustment 
7) The delay to weigh timer begun in step 4 times out and the package is 
weighted using the read scale time and filter cutoff calculated in step 5. 
8) The delay to rezero timer begun in step 6 times out and the system 
attempts a rezero operation. 
FIGS. 15a and 15b illustrate the process described above. FIG. 15a 
illustrates the timing which results with a long package. FIG. 15b 
illustrates the timing which results with a short package. Each package is 
depicted in four successive points in time as it moves onto, across, and 
off of the weigh pan (the weigh pan is the scale). The detector for 
measuring package length is located at the infeed end of the weigh pan. 
The timing which results from the analysis of the package length is shown 
in the bracketed timing spans o the diagram. The key difference is in the 
specific read scale time, which is designated as C in these diagrams. it 
is wider for the short package than for the long package and, in both 
cases it is as wide as it can be. These diagrams superimpose the "weight 
curve" on the timing spans in order to illustrate the relationship between 
the stable portion of the weight curve and the timers. The "weight curve" 
is like a graph depicting weight and time. Time is the horizontal axis. 
Weight is the vertical axis. The weight rises as the package makes its way 
on to the weigh pan, bounces a little as the package settles down, 
flattens during its passage across the weigh pan and then falls off as the 
package exits the weigh pan. A little more bouncing after the falloff is 
followed by a stable, scale empty period indicating a propitious time for 
a rezero operation. 
It is the ability to change the read scale time from package to package 
which is the real value of the invention, enabled by the inclusion of a 
package detector capable of measuring the length of a package. Shorter 
packages will have longer read scale times, therefore a lower digital 
filter cutoff, therefore better noise elimination, therefore more accurate 
weighing. Every package will have as long as read scale time as possible, 
therefore every package will be weighed as accurately as possible for the 
given belt speed. Under the prior art, no means of measuring differences 
in package length was employed and the read scale time for ALL packages 
was fixed to the same value, specifically a value appropriate for the 
longest package, i.e. a short read scale time. The potential use of a 
longer read scale time with shorter packages was unexploited. With 
adaptive timing, the checkweigher takes maximum advantage of the time each 
individual package is on the scale. 
The system determines a weight by measuring the difference between a 
package passing over the scale and the "rezero value" or weight of an 
empty scale. The system continuously reads the scale or does rezero 
attempts whether or not product is being run. Rezeros are needed to 
counteract the effects of drift, product buildup, and other temperature, 
electronic, and mechanical effects. The system employs a complicated 
rezero algorithm that is implemented by the logic of FIG. 16. It is user 
adjustable. FIGS. 17 and 18 show the rezero algorithm graphically. 
A rezero attempt is evaluated and compared to the rezero range as one of 
the criteria for updating the rezero value. The rezero range is given as a 
percent of scale range. This percent of scale range is ultimately 
converted into counts around the current rezero value, which is also in 
counts, see FIG. 17. If a new rezero value passes the other criteria for a 
successful rezero attempt (rezero prevent and slope tolerance) then the 
new rezero value is compared to the current rezero values, range. If the 
new attempt is within the current range then the new rezero value is 
calculated as a proportional incremental value between the current rezero 
value and the new rezero attempt. 
For example, if the current rezero value is equal to 500 counts and the 
range is 100 counts, the current rezero range extends from 600 counts to 
400 counts. If the new rezero attempt is equal to 550 counts and the 
increment is equal to 50% (user enter) then the new rezero value will be: 
500 counts +((550-500).times.50%) or 525 counts. If the new attempt value 
is greater than the current range, say 650 counts, then the rezero value 
is not updated but the new attempt value is "remembered" (the value of 650 
counts is stored in memory). 
If on the next rezero attempt the value is outside the current rezero range 
(400 to 600 counts in our example) but within range of the last attempt, 
then the rezero value is updated to the new value without an incremental 
percent. 
In the foregoing example, if the new attempt is equal to 700 counts, 
(outside the current range of 400 to 600 counts, the last attempt was 650 
counts). The range is adjusted around the last attempt. The range is set 
to 650.+-.100 counts or 550 counts to 750 counts. Since the new attempt 
lies within this range and the new attempt also passes the other criteria 
for a successful rezero (rezero prevent and store tolerance) and it is the 
next consecutive attempt, then the rezero value is updated to this new 
value or 700 counts. 
This unique feature of the rezero algorithm compensates for product 
spillage or other effects that can produce a large jump in the rezero 
value. The incremental percent helps filter small jumps in the rezero 
value (those within the rezero range) and still provides for rezero 
changes due to drift or small amounts of product buildup. The slope 
tolerance feature rejects rezero attempts that have too large a noise 
content or reflect a package coming or leaving the scale. The rezero 
prevent allows weighing the package statically (package on scale without 
running) without the package being rezeroed out. All the rezero 
parameters, i.e. prevent slope tolerance, range, and increment can be user 
altered to achieve the best possible accuracy. These parameters are also 
stored on a product by product basis with up to 25 sets of parameters 
available in a single system. A larger memory can be used to store an ever 
greater number of product parameters. 
A rezero attempt occurs after the delay-to-rezero timer times out. Samples 
are taken and filtered similar to weighing. A rezer attempt is discarded 
if the following occur: 
1) The range of unfiltered samples exceed, in value, a range called slope 
tolerance. 
2) The rezero attempt exceeds a maximum ceiling called the rezero prevent. 
3) A weigh cycle has been initiated. 
If the rezero attempt passes the above (3) criteria, its value is checked 
to see if it is in range with respect to the previous rezero attempt. If 
the attempt is within the rezero range, then a new rezero value is 
calculated by applying an incremental percent. The equation is given by: 
##EQU5## 
The rezero parameters--range, slope tolerance, prevent, increment--are all 
entered as percents of product range. 
If the rezero attempt is out of range of the rezero value, its value is 
remembered until the next rezero attempt. If that attempt is also out of 
range of the rezero value (two consecutive out of range attempts) and the 
two attempts are also within range of themselves, then the rezero value is 
updated to the last attempt. This feature allows both an incremental 
rezero, which helps in a noisy scale environment, and a rezero procedure 
that handles scale levels that jump to different levels because of product 
spillage. 
The system weighs a package according to the weighing/timing process 
described above and illustrated in FIG. 14. 
The weigh routine also checks if there was excessive noise during scale 
interrogation. This is done by comparing the highest and lowest 
prefiltered scale readings with a preset range called the scale noise 
range. If the sample range is greater than the scale noise range, then an 
alarm is activated (scale noise indicator). Scale noise range is input the 
same as rezero slop tolerance; as a percent of product range. 
Weight calibration is part of the automatic setup procedure. It is the last 
step in the process and can be entered separately, if desired. The 
calibrate procedure is multiple pass with provision for cancelling the 
last pass if there was a problem with it. To assist the operator, the 
"scale counts" are displayed on the weight display. The calibrate 
procedure also does an "initial rezero". The initial rezero measures the 
empty scale using a special routine that provides the utmost filtering 
possible. A special low frequency cutoff digital filter is used for the 
initial rezero. This provides a very accurate rezero result. A standard 
rezero, using the automatically determined digital filter, is used between 
passes of the multiple pass calibrate. The average of all the calibrate 
passes is used to determine the weight calibration factor. 
The preceding routines illustrated by FIGS. 12 through 16 are executed by 
the microprocessor as an interacting group of algorithms which preform the 
following steps. 
The ranging function is the process of setting both the gain and the 
offset. Gain and offset affect each other. By changing the gain the offset 
is effected. The gain is adjusted when there is a package on the scale and 
the offset is adjusted when the scale is empty. The procedure for setting 
the range consists of the interaction of Steps 1 and 2 which follow. 
Step 1--execute a ranging routine to establish the gain for the 
programmable gain amplifier with a sample item on the load sensing stage 
by: 
(a) setting the gain of the programmable gain amplifier to maximum. 
(b) setting the programmable gain amplifier offset to minimum. 
(c) execute Step 2 (a) through (h) 
(d) placing a package on the scale platform. 
(e) lowering the gain of the programmable gain amplifier in incremental 
steps. 
(f) reading the count of the analog-to-digital converter after each of said 
incremental steps. 
(g) stopping lowering the gain when the count of the analog-to-digital 
converter equals less than 80% of a predetermined percentage of the range 
or the gain of the programmable gain amplifier is less than zero. 
(h) determine if the gain of the programmable gain amplifier is less than 
maximum, if it is, increment the gain by one increment, if it is not, 
proceed with Step 3. 
(i) execute the Step 2 sequence, set offset routine, Steps (a) through (h) 
to reject the gain setting. 
(j) determine if the count of the analog-to-digital converter is less than 
80% or a predetermined percentage of the range, if it is, proceed to Step 
3 and if it is not, decrement the gain by one increment and execute the 
Step 2 sequence, set offset routine, Steps 2 (a) through (h). 
Step 2--executing a set offset routine for establishing a programmable gain 
amplifier offset when the load sensing stage is empty by: 
(a) clear the scale platform 
(b) raising the offset for the programmable gain amplifier in incremental 
steps. 
(c) reading the count of the analog-to-digital converter after each 
incremental step. 
(d) stop raising the offset when the count of the analog-to-digital 
converter equals less than 10% or a predetermined percentage of the range 
or said offset is at maximum. 
(e) determine if the offset is less than maximum. 
(f) if the offset is less than maximum, determine if the offset is greater 
than zero. 
(g) if the offset is greater than zero, decrement the offset by one 
increment. 
(h) return to Step 1. 
The purpose of the cycling between Steps 1 and 2 in the RANGE routine 
(resetting the gain and offset) is to provide the optimal values for gain 
and offset. These values of gain and offset are stored on a product by 
product basis. This allows the system to store up to 25 different ranges 
for up to different products. 
Step 3--The system weighs a package according to the weighing/timing 
process described above and illustrated in FIG. 14. 
Step 4--execute a rezero routine for resetting the system for the next 
weighing operation by: 
(a) running the digital filter routine on 40 or a predetermined number of 
samples. 
(b) determine if the filter output is less than the maximum rezero value. 
(c) determining if the slope tolerance of the unfiltered samples is within 
limits. 
(d) determining if the filter output is outside of the rezero range limits 
if the slope is within limits, 
(e) if the filter output is inside of the rezero range limits, update the 
rezero value by an incremental percent. 
(f) if the filter output is outside of the limits, determine if there has 
been two consecutive out-of-range rezero attempts where the attempts were 
within range of each other, if true, update the rezero value. 
The preceding steps automatically set up the system's electronic functions 
through the use of algorithms which automatically optimize weight sampling 
by automatically establishing the duration of the sample window as a 
function of product line speed. Spurious readings are eliminated by the 
algorithms which control sampling times, the time between samples, and 
sampling rates and impose digital limits on data taken. 
In addition, the preceding steps result in the execution of the following 
steps by manipulation of data through algorithm execution by the program: 
Available counts per unit weight are optimized by weight range and package 
characteristics and speeds, therefore allowing better accuracy than 
achievable in the past where trade-offs were made to achieve setup of the 
machine by maximum weight, maximum speed, optimization during the setup 
procedure and, therefore, throwing away--for example--counts per gram or 
filter capability at slower speeds. 
The sampling rate for reading weights is increased or decreased to fit the 
available weight information window, therefore allowing lower filter 
values if higher time exists and achieving better accuracy. 
Product effect and electrical or mechanical drift effect are compensated 
for by unique incremental and proportional rezero algorithms. 
Required sampling times are reduced by reiterations of samples to increase 
overall number of samples without excessive sampling window, therefore 
allowing higher rates of speed than normally possible. 
Unique sampling rates and filter settings are established for rezero and 
weighing algorithms. 
The effect of low frequency background noise is eliminated by using 
different filter values for the rezero as compared to the weighing 
function. 
The memory effect encountered when weighing at high rates of speed due to 
charging and discharging of analog filters is eliminated. 
The individual electronic component parts used to assemble this invention 
have not been specifically identified in the Description Of The Invention 
to avoid confusion generated by the rapidly advancing electronic 
technology and because it is the inventors intention that this invention 
should follow technological advancements. It should be reduced to practice 
using the latest hardware which can be assembled by one reasonably skilled 
in the art in accordance with the specification and drawings presented 
here with. The following is a list of the main components used by the 
inventor to create his most recent version of the invention. Their 
function and application is defined by manufacturers' specifications which 
are incorporated here in by reference. 
______________________________________ 
Microprocessor 
Intel N80C188-10 
Programmable Gain Amplifier 
Analog Switch Array 
Harris HI-507-5 
Instrumentation Amp 
Analog Devices AD625C 
Low Pass Filters 
First Stage Linear Technology 
LT1007 
Second Stage Harris HA3-2605-5 
Analog-To-Digital 
Crystal CS5014-KP28 
Converter Semiconductor 
Digital-To-Analog 
PMI PM7524HP 
Converter 
Pre-Amp (Op-Amps) 
Linear Technology 
LT1028ACN8 
______________________________________ 
The adaptive timing strategy employed in the invention requires the 
operator to enter the conveyor belt speed in feet per minute and the weigh 
pan length in inches. The invention uses these entries to calculate a raw 
read scale time. It also requires that a photoelectric eye or other 
package detector be placed at the upstream end of the weigh pan. 
Alternately, the strategy may be employed by 
(a) position a detector at both ends of the weigh pan and measuring the raw 
read scale time by measuring the time it takes a package to traverse the 
distance between the sensors. This eliminates the need for the operator to 
enter any numbers. Or 
(b) requiring the operator to enter the raw read scale time along with the 
delay to weigh adjustment and read scale time adjustment already being 
entered. To do this the operator, rather than the checkweigher, would 
calculate the raw read scale time. 
Adjusting the specific read scale time to the length of the package allows 
checkweighers confronted with packages of random length to weigh each 
individual package more accurately. The read scale time is not dictated by 
the longest package and imposed upon shorter packages. The shorter 
packages can now be weighed to better accuracy because they will be 
weighed for a longer period of time. 
The adaptive timing algorithm of the invention is also useful in 
applications where packages are of fixed length but tend to skew as they 
move on to the weigh pan. Different amounts of skew present different 
package profiles to the detector, effectively creating different length 
packages. Presently it is common for badly skewed packages to be 
misweighed because they partially exit the weigh pan during the read scale 
time. The only way to prevent this skewing inaccuracy under current 
technology is to shorten the read scale time, which compromises the 
accuracy of the non-skewed majority of the packages. The adaptive timing 
algorithm of this invention will adjust the read scale time automatically 
and dynamically to compensate for skewing and thereby obtain a better 
weighment for every package, skewed or not. 
It will now be understood in view of the applicants, teaching herein, that 
variation in operational steps, algorithm, algorithm execution, material, 
dimensions and geometry are contemplated as being within the scope of the 
present invention, which is limited only by the appended claims.