CA1220498A - Combination weighing system - Google Patents

Abstract

ABSTRACT

A weighing system having a processed readout comprising: a scale for receiving a quantity of product to be weighed and including a weight sensor producing an output signal corresponding to the weight of the product received; and signal averaging means connected with the scale to receive the output signal and having means for sampling the signal multiple times during a sampling period, adding means for summing the signal samples and obtaining a sample sum, and means for dividing the sample sum to obtain the average signal.

Description

A COMBI~ATION WEIGHING SYST2M
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BACRGROUND OF THE INVENTION
The present invention xelates to weighing systems and is concerned in partieular with weighing systems util-izing a plurality of scales to achie~e a minimum q~alified weight from a selected combination of the scale~.
Many products such as fruits, vegetab~es, candies and other small items are produced ox manufactured with varying sizes and weights, and are handled in bulk quanti-ties prior to b~ing separated in groups and packaged;, Combination weighing systems have been developed for se-lecting from a plurality of individual scales containing the product a particular combination of scales which cum-ulatively provides a total weight closely approximating or eq~aling the target or stated contents weight. Such weighing systems are described, for example, in U.S. Pat-ent Nos. 3,939,928 and 4,267,B94.
Combination weighin~ systems have bec:ome more common through the advent of th~ microprocessor which is capable of sampling multiple combinations of scales in a very short period of time and determining which combina-tion most satisfactorily pro~ides a targe~ weight. When the combination has ~een identified, those sca~e belong-ing to the combination are dumped into a common chute which discharges the collected product into a film wrapper or other containsr in a packaging machine~ ~he proc~ss may be carried out repeatedly by a microprocessor with the scales rPloaded or with the dumped ~cales eliminated from the search processe~ until they are reloaded~
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The flexibility of microprocessors allows a mult-itude of scales to be examined during the search process and permits weight parameters to be readily adjusted in accordance with varying prod~ct and production demands.
However, it is important that the weight information from each scale be accurate throughout extended periods of use and not be affected by drift in the components which pro-cess the weight information~ For this rea'son, calibration systems are generally employed in the scale, and the sys-tems are periodically activated to update ~he weigh;ng parameters used by the processor.
Samplin~ of a weight in a given scale is fre-quently complica~ed by the environment in Which the scales operate. Scales are commonly loaded from a vibrating feederr and in order to isolate the scales and the weight measurement from the effects of the vibrator, resilient mounts support the critical measuring sensors and the scales. Never~heless, spuriou~ errors are introduced into the weight siqnals and produce inaccurate results in the final weight.
In spite of the speed wi~h which mi~roprocessors opexate in comparison to the mechanical weighing devices, cycle times for performing the microprocessor functions are important because they are added to the samplinq and reading times~ and one microprocessvr may service a number of scales which are loaded in staggered sets.
It is ~ccordingly an obi~ct of the present inven-tion to provide solutions to the problems mentioned above.

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SUMMARY OF THE INVENTION
The present invention resides in a combination weighing system that i~ designed to search for and obtain a minimum qualified weight of product from among multiple quan~ities of the produc~. The system includes a plural-ity of scales, each of which receive5; and weighs a quan~ity of the product and provides a weii~ht signal rep-resentative of the weight in the scale.
In one aspect of the invention, ~he scale has a weighing tray for holding the pr~duct and a member such as a st~ain gauge that is s~rained by the weight of product during a weighing operation. Cali~ration means are pro-vided in the scale to de~ermine the parameters of ~are and slope in a weighing calculation, and in~luded in the cali-bration means is a weight of known amount that is lowered and raised from the scale in a calibration processO The weight is joined with an actuator means, such as an air cylinder~ by a coupling having first and second inter-locking members that disengage automatically when the weight is resting on the scale.
In another aspe~t of the invention, the output signals from the scale are sampled and processed to im-prove accuracy and elimînate spurious errors caused by vibrations and other disturbances. Signal averaging means are connected with the scale to receive the output signal and include sampling means for sampling the signal multi~
ple times to establish the average value of the signal from the various samples.
In still a further aspect o the invention, the combination of scales which provides the minimum qualified . -3-~21;~
weight is identified through a search operation based upon an ordered search sequence of all combinations of the scales~ The search is conducted by a search control means ~hich has means for omitting from the searchr combinations of scales having subcombinations previously searched and found to be q~alified at or above a target weight. Elim-inati~n of certain combinations from the search sequence reduces cycle time~ The search sequence is also esta-blished by adding one new or different scale to the com-binations or subcombinations previously searched. In ~his manner, the volume of data manipulated during each step of a search sequence is minimized with corresponding improve~
ments in cycle time.

B~IEF DESCRIPTION OF THE DRAWINGS
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Fig. 1 is a blo~k diaqram schematically illus-trating a combination weighing system embodyiny the pre- -sent invention.
Fig. 2 is 3 horizontal elevation view partially in section of a weighing scale including ~alibrating and weight-sensing mechanisms.
Fig. 3 is a fragmentary view of th~ calibrating mechanism in Fig. 2 and shows the coupling engaged, Fig. 4 is a fraqmentary view of the calibrating mechanism and shows the couplinq disengaged.
Fig. 5 is an alternative embodiment of the coup-ling in Fiqs. 3 and 4.
Fig. 6 is an electrioal diagram of the weight signal acquisition component~ of the combination weighing system.

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Fig. 7 is a diagram of the signal averaging and calibration elements in a microprocessor ~f the com~ina-tion weighing system.
Fig. 8 is a char~ showing all of the combinations of scales in the search sequence of a four-scale system.
Fig. 9 is a d.iagram showing ~he details of the combination searching elements of the microprocessor in the combination weighing system.
Figs. 10A & B are a ~low chart of the combination search routine.
Fig. 11 is a schematic diagram of the sequencer utili~ed in the search rou~ine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 illustrates the principal components of a combination weighing system which searches for and obtains the best combination of scales which collectively provide a measured weight of product not less than a predefined target weight. The products may be fruit, nuts or other items which have random weights and which are loaded in groups into the plurality of scales from whi~h the combin-ation is selected. When a "best" combination has been established, the corresponding scales are dumped intv a collector device or funnel for wrapping or deposit in a single package at the measured weight. The system may have any number "n" of scales 10, which are respectively de~ignated 10-1, 10-2 . . . 10-N.
Each of the scales 10 has the ~ame ba~ic con-struction, which is described in greater detail below in connection with Figs. 2-5, and produces an electrical _5_ 9~
output signal indicative of the weigh~ of product loaded in the scale for sampl;ng and calibration circuits 12.
After suitable sampling and other pxocessing, the weight data acquired from the electrical signa1s i~ loaded into a weight memory table 14 to more easily facilitate the loca-tion of weight data during a search for the best combina-~ion. In a preferred embodiment of the invention, the memory table and all of the components in Fig. l apart from the scales and the dump controls 18 are comprised by a microproces~or having the capability of form~lating the illustrated elements when program~ed~ One commercially available microprocessor suitab1e for this function is a model 6809E manufactured by Motorola, Inc. of Austin, Texas.
Within the microprocessor, the weight memory table 14 is formed from part of a random access memory that is shared with a sequence memory table 20. The sequence memory table is operated in conjunction with an index register 22 and a search controller 24 through a data ~us 26 to maintain a current record of the unex-hausted sub-combinations and corresponding weights durins a search operation. A more detailed description of the function and operation of the tables 14 and 20 is provided below in connection with FigO 9.
an arithmetic unit 30 receives the weight data for the scales of each combination and adds the weights together to obtain a subtotal for the combination. The target weight comparator 32 compares the s~btotal with a predefined target weight that represents, for example~ the desired weight in each package produced by the ~ystem. If .

a subtotal is equal to or exceeds the ~arget weiyht, then that combination of scal~s will provide a qualified weight for packaging. In comparator 34 all qualified weights are compared wi~h the best qualified weight previously located during the ~earch operation. If the previously located weight is larger, then the c~rren~ly searched combinatio~
and weight replace the previous best weight and combina-tion s~ored in the search memory 36. ~s the search pro-cess continues, the best weight stored in the ~earch memory may be periodically replaced by lower qualified weights, and when the search process has been completed, the minimum qualified weight and corresponding combination may be read from the memory through a decoder 38. The decoder supplies dump information to the dump controls 18, and those scales comprising the best combination are dumped and then refilled for another search. The process continues in cyclic fashion as long as there is product and packages to be filled.
The combination weighing system in a preferred embodiment employs a programmed microprocessor to conduct the search and comparison operations because microproces-sors provide the speed and accuracy for performing the arithmetic and comparison operations in cyclic fashion.
The processors also permit system parameters, such as the number of scales and the magnitude of ~he ~arget weight~
to be varied by simple changes in programmed data.
Fig. 2 illustrates the structure of one scale 10 with provi~ions for calibrating the output signal automat-ically between weighing operations. The scale includes a tray structure comprised by a weighing tray 40 suspended ~22~
from a balance beam 42 within the scale housing 44. The tray 40 is suspended by chains 41 from the balance beam and may be dumped by the controls 18 in Fig. 1. The balance beam is suppor~ed by flex hinges 46, 4B from the housing and ~y a range spring 50 ~hich i~ placed in ten-sion by the tray 40 and weight thereon. 'rhe rang~ spring is secured at its lower end to the balance beam and at its upper end to a cantilevered arm 52 of the housing by an adjusting screw 54. The ~crew can be adjusted in the tare condi~ion to approximately center the balance beam 42 within the housing. A dash pot S~ extends between the balance beam and the cantilevered arm 5~ to damp oscilla-tions of the balance beam brought about by the mass and spring components of the system.
A load sensor which in the preferred embodiment is a strain gauge 60, is mounted at the projecting end of a support block 62 secured in the housing. A straining mem~er or wire 64 is connected between the gauge and the balance b~am 42.
When product is loaded into the weighin~ tray 40, both the range spring 50 and the strain gauge 60 are strained; however, due to its greater stiffness, the gauge absorbs the principal portion of the load and produces an output signal which is representative of the weight of the product loaded plus any tare weight, that is the weight of the balance beam 42 and tray ~0 which is not supported by the range ~pring 50 in the unloaded condition. Produ~t which adheres to the weighing tray 42 after a dump opera-tion also becomes a part of the tare weight.
In order to calibrate the scale 10 and eliminate tare weight from the weighin~ 2O~r~ ns, a calibration weight 70 is suspended from the housing 44 by 3 pneumatic-ally operated spring and cylinder assembly 72~ Normally the cylinder assembly is deactiYated and the spring 74 surrounded ~he piston rod 76 at the upper end ~f the assembly lifts the calibration weight clear of the balance beam 72 and other tray structure. However, during a cali-bration operation, the assembly 72 is actuated and the piston lowers the calibration weight 70 onto the balance beam as shown. Through a unique coupling 78 the cylinder assembly 72 is totally disengaged from the calibration wei~ht, and thus only ~he addition of the calibration weight 70, which is of known amount, is felt by the strain gauge 60~
Figs~ 3 and 4 illustrate the unique coupling 78 and its method of operation in grea~er detail. In Fig. 3, the coupling is comprised by a first link 80 depending from the piston rod 76 and a second link 82 projecting rigidly upward from the body of the calibration weight 70.
When the weight is supported free and clear of the balance beam 42 as shown, the links 80, 82 are contacting and in load transmitting relationship due to gravitational Porces on the weight. However, when the calibration weight 70 is lowered onto the beam 42 as shown in Fig. 4, the links 80, 82 become automatically disengaged altho~gh they are still interlocked, and the full mass of the calibration weight including the link 82 i~ supported on the beam. The coup-ling 78 formed by the links is ~imple in structure and pr~cise in operatiun. The coupling totally uncouples the air cylinder 72 which lifts the calibration weight from ~2Q~
the beam and insures that it is only the weight and not the cylinder or any portion thereof which infl~ences the meas~rements taken while calibrating.
It is important to have an accurate weight signal from the scale especially when the contents of several scales are being measured to obtain a desired target weight. If each scale is inaccurate, the inaccuracies are carried forward cumulatively into the combination wei~ht.
Additionally, drift in the electrical or measuring por-tions of the system may cause further error~ All of these errors can be circumvented by periodically calibrating the output of the scale.
A calibration operation is performed by first readin~ the output of the strain gauge 60 while the scale is empty and by then lowering the calibration weight onto the tray structure and taking a second reading. The first reading constitute~ the tare weight and the second reading represents the magnitude of the tare and calibration wei~ht which is known. By subtracting the two readings, a scale factor or slope of the output signal is obtained for use in accurately measuring subsequent loads above and below the calibration weight Fig. 5 shows an alternate embodiment of the coup-ling between the cylinder 72 and the ~alibration weight 70. In this embodiment, a cup 86 secured to the weight 70 loosely envelopes a ball 88 suspended from the piston rod 76 by a cord 90. The cup is swaged or otherwise closed to form at its upper end an aperture 92 smaller than the dia-meter of the ball 88. The weight 70 may be raised by the piston xod 76 and be lowered and disengaged from the rod 4~i 3 when the ball reposes at a central position within the cavity of the cup. The cup B6 and the b~ll 88 are func-tionally equivalent to the links 80, 82.
~ ig. 6 illustrates the electrical circuitry which acquires weight data from the strain ga~ges 60 in the scales of the combination weighing system of Fig. 1. The strain gauge is typically a bridge structure, and the out-put of the bridge is fed to a high-gain instrumentation amplifier lOOo In one embodiment of the! invention, the amplifier converts the differential signal of the strain ga~ge to a single ended signal and amplifies it by a fac-tor of 600.
The output o the instrumentation amplifier is applied to a low-pass RC filter circuit ~02 which has~ for example, a 30 millisecond time constant to suppress high order signal oscillations due to vibrations of feeders and other environmental factors surrounding ~he scales. The filtering circuit operates in combination with mechanical isolato~s in which the scales are generally mounted.
The sampling and calibra~ion circuits 12 of Fig, 1 include a scale selecting and sampling circuitry 106 in Fig. 6. This circuitry receives the strain gauge signals from ~ach scale in a multiplexer 108 controlled by a chan-nel decoder 110. The decoder causes the ~ultiplexer to sample ~he output signals from each scale in order, and the sampled values are sequentially loaded into a sample and hold circuit 112. Timin~ and control of the decoder 110 and sample circuit 112 is controlled by the circuitry 114, and the sampled signals are transferred serially from th~ circuit 112 to an analog-to-digital converter 116 ~L2~
In order to improve the reliability of the weig~t signals from the scales, the signals are sampled several times and then averaged~ For example, in one embodiment of the invention having ten scales, the conversion-to-digital for~at is postponed until approxima~ely 130 to 140 milliseconds prior to dumping of ~he scalles. Each output signal is then converted to a digital value once every five milliseconds, and the digital signals are relayed to a data bus 122 through a buffer amplifier 118 and data bus driver 120.
The sampled signals are averaged in the elements of the data processor shown in FigO 7. The consecutively sampled values from a given scale are combined in the adder 12~. The added si~nals are stored during the samp-ling period in an accumulating register 126-1, 126-2, 126-3 0 . . or 126-N corresponding to the particular scale from which the signal originated. For example, the digi-tal value of the signal from scale ~o. 1 is sampled six-teen times at 5 millisecond intervals for a total sampling period of 80 millisecondsO The sixteen samples are se-quentially added and stored in the accumulating register 126-lo After the sampling period, the 3ccumulated sum is divided by 16 in divider 128 before the signal is used in calibration and tare circuitry 130. The process of aver-aging the sampled signals multiple times prior to utiliza-tion provides a more reliable signal less ~ffected by disturhances in and around the scale. In one embodiment of the invention, it has been found th~t the averagin~
technique improves tha accuracy of the sy~tem by a factor of 2 to 4 times in comparison to a single-sample sy~tem.

The calibration and ~a~r~ itry 130 ob~ains the tare weight and slope during calibration to provide during weighing a sign~l represen~a~ive of the ne~ weight of product in the scale~ ~he net weight signal i5 then transmitted to the scale memory table 14 for storage and use during a search operation.

COMB~NATION SEARCH
In other combina~ion weighing systems, the tech-nique of locati~g the best combination of scales is com-prised of examining every combination possible and comparin~ the various combinations with one another until the minimum combination providing a weight equal to or greater than a given ~arget weight is foundO This tech-nique requires that the microprocessor examine 2n _ 1 combinations where "n" i5 the number of operative scales being examined~ ffowever, by establishing a special seareh sequence having consecutive steps in which the preYiously examined combinations are added to one nessw scale not exam-îned in the previous step, it is poss7ble to omi~ or skip certain st~ps of the sequence and thereby reduce the cycle time for each search operation~ For example, if a partic-ular combination of scales has been previously searched and that combination yields a total weight equ~l to or in excess of the target weight, there is no further need to e~amine other combinations in which the previously searched and qualified combination i8 included~ In other wo~ds, another combinas~ion of lesser weight cannot be found by adding other ~cales to the previously searched and qualified combination.

s~ -13-This concept is more clearly understood by exam-ining a search sequence established in accordance with the present invention and by discussing an example which il-lustrates the point. Fig. 8 ~hows a chart listing all 15 pQssible combinations in columns a-o that can be generated with four different scales. Furthermore, the combin~tions have been arranged in accordance with the sequence of the present invention which establishes ~ priority order among the scales. ~or purposes o illustration, it will be assumed that the priority corresponds to the numerical designation on the scale, the No. 1 scale having highest priority. The sequence thus established adds one new scale in each step of the sequence as illustrated in combinations a-d and then replaces the lowest priority scale in the exhausted combinations in order o~ priority.
In other words, when combination e has been reached, all possible combinations, including the subcombination of scales 1, 2 and 3 have been examined and ~hus the com-bination of scales 1, 2 and 3 has been exhausted. The lowest priority scale~ scale ~o. 3~ is replaced by the next scale, scale No. ~ t in the series. The same comments apply to combination f since the subcombination of scales 1 and 2 is exhausted and when combination h has been searched, the combination consisting of scale 1 itself has been exhausted. Thus in combination i, scale No. 1 has been replaced by the next scale, scale No. 2, in priority order.
The search sequence begins with combination a consisting only of scale No. 1. Assuming that scale No. 1 does not reach the mlnimum combination or target wei~htr ~14-~2~0~L98 the next combination b is examined. Assume also that com-bination ~ does not reach the target weight and therefore combination c is examined. I combination c exceeds the target weight and is th~s a qualified combinationr ~here is no purpose in examining combination cl because it is impossible or that combination to yield a lesser quali-fied weight than its subcombination consi9ting of combin-ation c. Accordingly, combination d is omitted or skipped in the search sequence.
In order to establish the number of steps that can be skipped in the sequence, an ADDEND equal to the number of steps to advance is assigned to each combina-tion. The addends are illus~rated in Fig. 8 with their associated combinations, and a brief analysis of the addends indicates that they are equal to 2n N, where "n"
is the number of scales being searched and "N" is the num-ber of the lowest priority scale in the combination.
Applying any one of the addends to the combinations shown in the chart illustrates ~heir utility. For example, if the combination c produces a qualified weight, then there is no need to examine combination d and thus the search ~equence should gkip from combination c to e. The addend value of 2 indicates that the search sequence should ~d-vance or be increased by two steps rather than one ~hich omits combination d fro~ the search sequence. The ability to define the addends by the expression 2n N is directly relat~d to the manner or formula by which the search se-quence is established as described above. Furthermorer the expression for the addend is valid regardless of the number of scales being searched as long a~ the search .

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sequence is established as described.
Fig. 9 illustrates in detail the weight memory table 14, the sequence memory table 20r the index register 22, the search controller 24 and the æeareh memory 36.
These element~ of the microprocessor are the primary com-ponents involved in the search operation apart from the arithmetic operation~ performed by the arithmetic unit 30 and comparators 32, 34.
The weight memory ~able 14 includes a number of memory locations or addresses which as ill~strated store the weight information and associated addend for each scale. For example, the weight measured in scale 1 and the associated addend are stored at address Ql. Aceess ~o either the addend or the weight data is accomplished by the index register ~2 which has a duzl pointer 136 that moves between the various addre~ses to read the data~ The addresses of the ~emory table are read in a predetermined order to formulate the variouæ combinations in the search sequence. Specifically, the index register 22 s~arts with the data in the addres~ Ql and builds the combinations downwardly from that pointO Therefore~ the order in which the addresses are scanned establishes the priority order of the scales in the search sequence as described in con-nection with Fig. 8, and by loading the weight data of a particular scale at a given address, a given priority is assigned to that scale. It will be understood that be-cause a given address represent~ a given priority, the addend data at a given address only ~hanges with the total number of sc~les being ~earched.
~ he ability to establish priority among the plurality of scales may be used advantaqeously to ensure that all scales in the syste~ receive approximately the same activity over a number of loading and dumping cycles.
For example, if one scale i5 not dumped over a period of cycles, ~he prod~ct may gather moisture or otherwise deteriorate, or may not flow satisfactorily through the packaging machine in the same manner as the fresher pro~
duct from other scales. This situation is remedied by ensuring that the oldest scales, that is the scales that were not included in the best combination dumped in the previous cycle, are given priority in subse~uent search.
~ he assignment of priority is readily accom-plished in the ~eight memory table 14 by pushing the weight data from the lower priority addresses toward the top of the table after dumping and clearing the weiyht data of the dumped scales from the ta~le. Pushing or moving data upwardly from the bottom toward the top of a memory s~ack is an elementaxy data proces~ing function.
The memory table 1~, in addition to having one address for each scale, has one additional address Q(n ~ 11 in which a large negative weight is stored with a zero addend. This data is used in the search routine as described in further detail below to indicate ~hat the last scale in the priority order has been examined and that either the search is done or other subcombinations sh~uld be examined~
Addîtionally, the memory table 14 may have fur-ther addresses Q(5 ~ 1~ to handle spare scales that are used to achieve best combinations from a greater plurality of ~cales.

The search of various combinations of scales in a search sequence is regulated primarily by the search con-troller 24, and the con~roller causes the poin~er 136 of the index register 22 to move back and forth between the various addresses of the weight memory table 14 to obtain the weight data for proeessing through the arithmetic unit 30 and the comparators 32, 34.
The search memory 36 main~ains a current record of important parameters during a search operation. At address 140, ~he memory stores the current subtotal for the particular combination of scales being examined at a given step in the search sequence. The step of the se-quence corresponding to that combina~ion is stored in coded form at address 142. The bes~ weight revealed in previous steps of the search sequence and the correspond-;ng be~t combination identified by the sequence number which produced that weight are stored in memory addres~es 144 and 146, respectively. The best weight data is, of course, utilized by the comparator 3g in each comparison step. The combination of scales which produces that weight is uniquely associated with the seq~ence number at address 1~6 and the actual combination can be derived from the sequence number throuqh ~he decoder 38. The target weight i8 a fixed parameter and is stored at the beginnin~
of the search operation at address 148. The last addend at address lS0 is stored at the end of a ~earch operation and is utilized to decode the best combination sequence number and determine the combination, S-flag information at address 152 i~ utilized as an instructional command to permit the search sequence to start.

The structure of the sequence memory table 20 is essentially similar to the structure of the memory table 14, and data is en~eredr read and expunged from the table 20 at ~ddresses identified by the index register through the dual pointer 156. It must be understood that the index register 22 is a ~ingle register with ~he psintPrs 136 and 156 ganged and operated jointly.
The function of the sequence ta~le 20 during a search is to maintain a record of the exhausted and unex-ha~sted combinations together with the associated suhto-tals of the weights in those combinations. Additionally, the table 20 utili2es the sequence number or alternatively a negative punctuation mark or number to assist the index register in advancing through the search sequence wi~h steps omitted as defined above. Specific operations of the sequence table 20 are discussed in greater detail below in conjunction with Figs. lOA and lOB.
Figs. lOA and lOB comprise the flow chart defin-ing the programmed search routine performed by ~he search controller 24. The search routine is entered at 160 and initially examines the S flag at branch 162 to determine if a search routine should be carried out. The S flag is stored in memory 36 after each of the scales has been loaded and a wei~ht on the scale is confirmed. If loading is not complete, no S flag signal is given and the ~earch routine i5 exited at 163. The search controller may then wait and reenter the search routine or take other remedial steps until the S flag indicates that a search may proceed with selected scales identified in the weight memory 14.
At the ~irst instruction 164 of the search operation, initial values of the ~earch sequence number and weight subtotals are set in the sequence table 20.
The initial value set in the table at address S0 in Fig. 9 represents step 0 of ~he sequence and the corresponding weight is also 0; however, in a microprocessor, the digi-tal codes enter~d for these numbers may not be numerically equivalent~
As indicated at instruction 166, the current se-quence number and subtotal are s~ored in the sequence table and the memory 36 without conse~uence at thi~ step of the ~equence, and the pointers of the index register are stepped downwardly to addresses Sl and Qla At in-struction 168, the weight of scale 1 is added to the current subtot31, then being 0, at address 140 in the search memory 36. The new subtotal is then examine~ at branch 170 to determine if the last and lowest prisrity scale in the table 1~ had been examined, and thus a sub-combination was exhausted. A large negative value is always obtained under these circ~mstances by storing at addre~s Q(n + 1) of the memory table 14 a negative weight value well in excess of any expected weight produced by the combinations of the scales. If the negative value is obtained, then the program branches to a subroutine Pl at 172 as described further below.
If the subtotal is positive at branch 170, a ~econd test is ordered at branch 174 to determine if the subtotal is le~s than the target weight stored in the search memory 36. Thi~ test is performed by the compara-tor 32. If the subtotal i~ less than the target weight, the corresponding combination i~ not qualified to form a

2~-package since it is a yeneral ~ o~ ~ ~e search processthat any gualified combination ~ust equal or exceed the target weight. Unqualified weights follow the proyram branch P0 from the branch 17~ to instruction 176 which causes the current sequence number, being 0, in memory 36 ~o be increased by 1.
The instruction 176 is pursued with the a~d of a digital sequencer within the search cont:roller 24, and Fig. 11 illustrates one embodiment of the sequencer in greater detail. The sequencer includes a CURRENT SEQUENCE
register 180 which is loaded throu~h a clocked control gate 182 from one of several sources. A preset sequence number is loaded into the register 180 from preset data 184 during the initializa~ion operation detailed at in-struction 164 in Fig. lOA. During the course of a search operation, the instruetion 176 of Fig. lOA enables the ~1 adder 186 so that the curxent sequence number is incYeased by one and the increased value is then loaded into the register through the gate 182. The output of the register is also stored in the search ~emory 36. An ADDEND adder 188, which may be enabled at a later phase of the search operation, adds to the current sequence n~mber the addend associated with ~he new scale in a searched combination and loads the sum in the register 180 through the gate 182. Thus, the se~uencer of Fig. 11 can be advanced in ~ingl~ or ~ultiple steps depending upon the ena~led adder and the value of the addend.
In accordan~e with instruction 166 in Fig. lOA, the new, cu.~rent sequence number, now step 1, together with the associated subtota~, which is the weight of the first combination, that is, scale 1, are now stored at address Sl in ~he sequence register 20 and in the search memory 36. Since the subtotal has not qualified at or above the target weight, the subtotal is needed to esta-bli5h the weight of other combinations in subsequent steps of the search sequenceO Storage of thP subtotal in ~his manner minimizes the number of arithmetic operati~ns that must be made to determine subtotals developed from a plux-ality of scales.
Instruction 166 also indexes both pointers 155 and 136 of the index regis~er downwardly to the next address spaces in the tables 1~ and 20, and the cycle through the branch P0 is repeated wi~h addi~ional weights from lower priority scales being added until eventually the test 174 identifies a weight in e~cess of the target weight. The associated comhination is now qualified and the search process advances to subroutine P2 at 1~0~
Subroutine P2 is illustrated in greater d~tail in Fig. lOB. At t~st 192 conducted by the best-weight com-parator 34, the subtotal for a qualified combination is compared with the best previous weight to determine if a lesser qualified weight is provided by the subtotal. If the subtotal is less, then instruction 194 causes the new best subtotal to be stored in the search memory 36 togeth-er with ~he sequence number. If the subtotal is equal to or greater than the previous best sum, no change in the search mernory occurs. Rejection of combinations equal to the previous best weight combinations gives priority to the older scales at this point.

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Regardless of the results of test 192, instruc-tion 196 ca~se~ the addend circuitry 188 in Pig. 11 to add to the current sequence the addend as~ociated with the lowest priority scale in the qualified combination. It i~
this fea~ure of the search operation which allows one or more Rtep~ of the search sequence to be omitted as ex-plained above in connection with Piy. B. The omi~sion of unnecessary steps in the search sequence which i~ an iterative process reduces the search time and all~ws the ~ystem to be shared among several groups of ~cal~s or to handle larger numbers of scales more efficiently. From instruction 196, the search operation proceeds to subrvu tine Rl at 198.
The Rl ~ubroutine is illustrated in Pig. lOA and includes instruction 200 that ~auses the previous subto-tal, that i~ the ~ubtotal stored in the previou~ address of the the sequence table, to be entered in the next address of the ~equence table. This step of the oæeration enable~ une~hausted ~ubcom~ination~ of the qualified com-binations tv be further considered in the search process.
For ~xample, if the combination c in Fig. 8 proved to be a qualified combination, then the ~ubtotal of combination b would be stored at the next address in the sequence table for use in determinin~ th~ weight of eombination e.
In instruction 202, the address bearing the pre-vious ~ub~otal i~ flagged by enterin~ a negative punctua-tion mark or number with the pxeviou~ subtotal to identify that subtotal as being exhau~ted the next time that that addre~s of the tabïe i~ examined through the pointer~ 156 of the inde~ register a~ expla~ned below in connec~tion ~2~
wlth ~broutine Pl. Such a punctuation mark enables the microprocessor to readily identify and expunge from the table ~equences and subto~als which have no further uti 1-ity in a given search operation. The ins~ruction 202 also causes the previous subtotal ~o be ~tored in the s~arch mQmory 36 and indexes the pointer 136 downwardly to the n~xt scale in the weight 14.
The search continues by adding the weight of the next scale as indicated at instruction 168 and repeating subroutines P0, P1 or P~ a~ described above~
After the lowest priority ~cale has been tested in a combination, the next movement of the psinter 136 causes the test 170 ~o divert ~he proyram to ~ubroutine Pl shown in Pig. lOB. Under these conditions, the search is either finished because all combinations have been tried or the 8earch has reached an intermediate stage in the sequence where a subcombination has been exhausted. Sub-routine Pl c~uses the pointer 156 t~ index upwardly through th~ sequen~e memory table 20 to either the initial S0 wheD the seareh is finished or to some intermediate addxess in the table whers the ~equenc~ entry identifis~ a new unexhausted subeombination.
Accordingly, havinq determined that th~ lowest priority scale has been examined, the first instruction 210 of the subroutin~ Pl clears the sequenee entry at the current address of the ~equenc~ table and lndexes the pointer 156 upwardly ts the preceding addre~ a~ indicated at instruction 212. The ~equence entry is t~ted accord-ing to th~ instruction 214, and the te t is carried out at 216 to determine if the seque~nce e4t~ ~ is either a posi-tive 3equence number, a negative punctuation mark or zero.
The negatiYe number indicates that the combination associ-ated with that previous entYy wa~ exhaus~ed, and in ~hat event, the entry 5 cleared and the pointer 156 is stepped further upward ~hrouyh the 3equence table by again follow-ing the instructions 210-21~. If the equence entry is po~itive at test 216t then the 3ubcombinc~tion ls not ex-hausted and the program proceeds to in~truction 218.
Also, if the entry i~ zero, indicating that the address S0 ha been reaehed in the table~ the same ins~ruction 218 is pursued. Instruction 218 move~ the pointer 156 one step further upward in the table 20 to reach the unexhausted combination if a search is not over. ~o determine whether the search i~ over or not, the results from the test 216 are re-examined at the test 220. Ass~ming that the search is not overp ~he sequence entry will be positive and the search is thus continued to examine other combinations~
including the unexhausted combination ~hrough subroutine Rl as indicated at l9S.
EYentually, all of the ~ubcombinations are ex-hausted and the results of the tes~ 220 indicate that the pointer 156 has reached address S0. The zero entry in the sequence number location is identiied and in that event, instruction 222 cause~ the large~t addend to be entered in the ~LAST ADDEND~ location of the ~earch memory 36, and the ~ubroutine is exited at 1630 The microproce~or util-izes the last addend figure in decQding the best sum com-bination from the sequenc~ number. The large~t addend is indicative of how many ~cale~ were utilized in the sear~h -25~

and is a key element ;n decoding ~e s4e9~ence number.
In summary, a combination weighing system has been described in which a novel scale calibration system is used to e.~tablish calibrated measurements fxom the scale between weighing operations. The 3ignal produced by the scale is used in a combination weighing system having a plurality of similar scales, and in orde!x to improv~ t~e reliability and accuracy of the measurem~ents, the weight signals are averaged after multiple samples are taken. To determine the best combination of the scales approaching a target weight, combination~ of the weights from the scales are examined on the basis of a predetermined search se-quence, and certain steps of the sequence are omitted to shorten the search operation.
While the present invention has been described in a preferred embodiment, it should be understood that nume-rous modification~ and substitutions can be made without departing from the spirit of the invention. For example, it is not essential to utili~e the precise scale Rtructure shown in Figs. 2-5 in the combination system shown in Pig.
1. Other scales providing weight signals may also be used. The averaging technique improves reliability of the weight signals, but it not essential to the described searchi~y operation. The searching process may be carried out with the same number of ~cales in each cycl~ of oper-ation, or the micropro~e~sor may omit from ~ucces~ive cycles tbose scale~ that have not been reloaded. Accord-ingly, the present inYention has been described in a pre-ferred embodiment by way of illu~tration rather than limitation.

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A weighing system having a processed readout comprising: a scale for receiving a quantity of product to be weighed and including a weight sensor producing an output signal corresponding to the weight of the product received; and signal averaging means connected with the scale to receive the output signal and having means for sampling the signal multiple times during a sampling period, adding means for summing the signal samples and obtaining a sample sum, and means for dividing the sample sum to obtain the average signal.

2. A weighing system having an averaged readout as defined in claim 1 further including a low pass filter between the weight sensor and the signal averaging means to minimize the effects of high frequency vibrations on the sampled signal.

3. A weighing system having a processed readout as defined in claim 1 wherein the weight sensor provides an analog output signal, the adding and dividing means are digital circuits, and an analog-to-digital coverter is connected between the sensor and the digital circuits.

4. A weighing system as defined in claim 1 further including calibration means connected with the scale for calibrating the output signal from the sensor.

5. A weighing system as defined in claim 4 wherein the calibration means includes a calibration weight and means for placing and removing from the scale.