GB2115630A - Weighing apparatus - Google Patents

Abstract

An automatic weight sorter for weighing articles fed successively by a conveyor (2) and then sorting them into predetermined classes based upon their measured weights, includes weighing apparatus with an improved automatic weight correcting device (16) to compensate for the difference between the true static weight of an article and the dynamic weight sensed by the weighing device (12). The correction can be easily preset by applying actual articles to the conveyor for measurement while the apparatus is turned to a set-up mode of operation prior to normal operation being started. During set-up the static and dynamic weights of an article are sensed and stored in memories (26) and (28) respectively for calculating the correction factor to be applied to the dynamic weights sensed subsequently during normal operation. <IMAGE>

Description

SPECIFICATION Weighing apparatus This invention relates to weighing apparatus for an automatic weight sorter.

There are many kinds of devices known in this field, which are used for weighing a series of the same kind of articles successively fed thereto and sorting them into predetermined classes of weight. Some examples of such prior art are disclosed in Japanese Patent Nos. 608507 and 608508 (Publication Nos. 45-36553 and 4536554) cited herein as references. In such devices, articles are fed successively by a weighing conveyor and weighed dynamically, that is, midway during movement. The weight value measured in this manner often differs from the true weight measured statically due to external causes such as shock and vibration.While the measured value is sent to a judging circuit in the succeeding stage in the form of an electric signal, it has been corrected manually in the prior art by adjusting a control element such as a variable resistor inserted in the mid-way of the signal path.

This system is generally satisfactory when the variance in weight of articles is small, the relationship between the statically measured value (hereinunder referred to as "static weight") and the dynamically measured value (hereinunder referred to as "dynamic weight") is fairly constant for each article, and the same kind of articles are handled for long periods of time. However, it suffers substantial drawbacks in such cases as where the abovementioned relationship varies for every article or where the kind of article is changed frequently and the correction applied must be changed correspondingly each time.

According to the present invention there is provided weighing apparatus comprising a conveyor, drive means for driving the conveyor to feed successively articles to be weighed, a weighing device located intermediate the ends of said conveyor for sensing the weights of the articles and producing weight signals corresponding to the sensed weights, and correction means coupled to said weighing device for receiving said weight signals and applying a correction thereto, said correction means including first means selectively operable to produce either a first static measurement command signal, or a second dynamic measurement command signal, second means selectively operable to produce either a third normal operation command signal or a fourth correcting operation command signal, first memory means responsive to said first and fourth command signals to store said weight signal from the weighing device, second memory means responsive to said second and fourth command signals to store said weight signal from the weighing device, means coupled to said first and second memory means for calculating in predetermined manner a value dependent upon the, weight signals stored by the memory means, and means responsive to said second and third command signals to receive the outputs of said calculating means and said weighing device and correcting the weight signals supplied thereto in dependence upon the value calculated by the calculating means, and said conveyor drive means being arranged to stop the conveyor in response to said first command signal and start the conveyor in response to said second command signal.

The invention will now be described in more detail with reference to the accompanying drawings, in which: Figure 1 is a block diagram representing an arrangement of automatic weight sorter embodying this invention; Figure 2 is a graph representing a relationship between dynamic and static weights of an example of article; Figure 3A is a block circuit diagram representing an embodiment of correction circuit according to this invention; Figure 3B is a diagram representing a control switch circuit of the correction circuit of Figure 3A; and Figures 4 and 5 are block circuit diagrams representing other embodiments of the correction circuit of this invention.

Throughout the drawings, same reference numerals identify corresponding components in the different embodiments.

In the automatic weight sorter shown in Figure 1, a belt conveyor 2 is driven between a pair of rollers 4 and 6 by a driving device 8 to transport articles 10 to be sorted successively in arrow direction. Though not shown in the drawing, loading of the articles 10 onto the conveyor 2 may be effected by any known manual or automatic system. Under and between the ends of the conveyor 2, is a weighing device 12 which includes a known spring balance, load cell or the like to sense weights of the articles 10 transported thereto and produce analog dynamic weight signals indicative of the weights sensed.

The analog signals are converted by an analogdigital (A/D) converter 14 into digital weight signals which are supplied to a correction device 1 6. The correction device 1 6 applies predetermined correction to the dynamic weight signal inputs to produce corresponding static weights as described later and supplies static weight signals indicative of the static weights to a judging device 1 8.

The judging device 18 is of a known type and stores in its built-in memories (not shown) predetermined weight values W1,W2...

supplied, for example, from a conventional keyboard input device 20 through switch terminals 21. The judging circuit 18 also includes comparators (not shown) which compare the static weight signal inputs with the contents of the respective memories and supply a distributer 22 with, for example, a sorting signal Sa when the weight signal is greater than W1, a sorting signal W2 when the weight signal is within a range to W1 above W2,. . and a sorting signal Sn+1 when the weight signal is less than Wn, respectively.

The distributer 22 is also of a known type, which includes chutes 24, 242,... 24n+1 corresponding to the respective sorting signals and, for example, electromagnetic mechanical means for supplying the articles 10 corresponding to the weight signals to the corresponding chutes, respectively, in response to the sorting signals. The structures of the respective sections of the above-described automatic weight sorter will not be described further, excepting the correction device, since they have been proposed already in various types and, moreover, have no direct connection to this invention.

According to this invention, the correction device 1 6 includes a pair of memories 26 and 28 which receive the digital weight signals from the A/D converter 14, an arithmetic unit 30 for applying predetermined arithmetic operation to the contents of the memories 26 and 28, and a correction circuit 31 for adding the result of operation to the digital weight signals to effect predetermined correction and producing correction outputs that is, calculated static weight signals. The correction circuit 31 includes a switch board 32 having a pair of change-over switches (not shown), one switch being arranged to produce selectively either a static measurement command signal ST or a dynamic measurement command signal DY and the other switch being arranged to produce selectively either a normal operation command signal NR or a correcting operation command signal CR.The pair of command signals from the each switch may be high and low level signals, or binary "1" and "0" signals, respectively. The static and dynamic measurement command signals ST and DY are supplied to the conveyor driving device 8 which is arranged to stop the conveyor 2 in response to the signal ST and start it in response to the signal DY. The memory 26 receives the static measurement and correcting operation command signals ST and CR and the memory 28 receives the dynamic measurement and correction operating operation command signals DY and CR, from the switch board 33.

These memories 26 and 28 are arranged to store the current output of the D/A converter 14 in response to the presence of the both of such pairs of input command signals, respectively. The correction circuit 31 receives the dynamic measurement and normal operation command signals DY and NR from the switch board 33 and produces a corrected weight output in response to presence of the both of these signals.

Before starting normal operation, the switches on the switch board 33 are turned to produce the static measurement and correcting operation command signals ST and CR. The signal ST actuates the driving device 8 to stop the conveyor 2. On the other hand, the signals ST and CR enable the memory 26 and the memory 26 will store the static weight signal of an article having a reference weight if the article is put on the conveyor 2 just over the weighing device 12 at that time. If one of the switches is then turned to produce the signal DY in place of the signal ST, the driving device 8 will start the conveyor 2 in response to this signal DY. In addition, the memory 28 is enabled by the signals DY and CR.If the same article is put on the conveyor 2 just before the weighing device 12 at that time, a dynamic weight signal is produced when the article passes the weighing device 12, and it is stored in the memory 28. Thus, the memories 26 and 28 are rendered to store static and dynamic weights, respectively. Therefore, they are indicated at static weight memory and dynamic weight memory, respectively, in Figure 1, though they may be quite same in structure. While the both memories conserve their contents thereafter so long as the kind of article is constant and the static and dynamic weights are unchanged, they may be cleared by suitable means (not shown) when a change of the contents is requested.

In the correction system according to this invention, the corrected weight (static weight calculated) is obtained on the basis of mathematical relationship between the static and dynamic weights stored in the memories 26 and 28. The such mathematical relationship is assumed to be predictable empirically or experimentally for each kind of the subject articles and the program for numerical calculation according to this relationship is preset in the arithmetic unit 30 and correction circuit 31. Upon completion of the abovementioned preparation, the other switch is turned to produce the signal NR in place of the signal CR Then, the correction circuit 31 is enabled by the signals DY and NR to apply predetermined correction to the dynamic weight signals supplied from the A/D convertor 14 in co-operation with the arithmetic unit 30.

While, in the drawing, the calculation circuit is divided into two blocks 30 and 31 , the former arithmetic unit 30 being arranged to calculate previously and store the constant portion which has no connection to the successive outputs of the A/D converter 14 and the latter correction circuit 31 being arranged to calculate every time the portion which depends upon these outputs, both blocks 30 and 31 may be constructed as a single unit or may be composed of a commercial microcomputer programmed in accordance with a predetermined schedule of calculation.

The above mathematical relationship varies with changes of shape, size and value and range of weights of the articles. However, it has been found that, in many cases, the difference between the static and dynamic weights, that is, deviation is proportional to the value of dynamic weight, as shown in Figure 2. In the drawing, the abscissa indicates the dynamic weight WD and the ordinate indicates the deviation WC (WD-WS, where WS is the static weight). In this case, in order to obtain deviation WCX corresponding to any dynamic weight WDX, it is necessary to obtain the slope of the straight line as shown. This slope or inclination can be calculated using the foflowing equation by previously storing two pairs of static and dynamic weights WS 1, Wed 1 and WS2, WD2.

WC2-WC 1 WCX=WC1+ (WDXWD 1) (1) WD2-WD 1 Figure 3A shows an example of circuit for adding the deviation obtained from this calculation to the dynamic weight to produce a static weight WSX.

In this circuit, four memories 26" 262,28, and 282 are provided for storing reference static weights WC1 and WC2 and reference dynamic weights WD 1 and WD2, respectively. The output of the A/D converter 14 (Figure 1) is supplied through gates 32 and 34 to the memories 261 and 262 and also through gates 36 and 38 and average circuits 40 and 42 to the memories 28, and 282, to be stored therein, respectively. The average circuits 40 and 42 are same in structure and include an accumulator 44, a counter 48 and a divider 46, each. The accumulator 44 accumulates the input weights and the counter 48 counts the number of these inputs and, when the number reaches a predetermined value N, produces a count output N and then it is cleared together with the accumulator 48.The divider 46 divides the accumulated input by the count output N from the counter 48 to produce an average output. As the value of dynamic weight varies in general every measurement, even if the same article is weighed, the average value obtained from several times of measurement is to be used as the reference value in order to maintain high accuracy.

The gates 32, 34, 36 and 38 are normallyclosed gates (or normally-open switches) controlled by a switching circuit as shown in Figure 3B. This circuit is provided with a switch board 33 (Figure 1) having push-button switches NR, CR, ST and DY for specifying NORMAL OPERATION, CORRECTING OPERATION, STATIC MEASUREMENT and DYNAMIC MEASUREMENT, respectively, and a pair of push-button switches M1 and M2 for specifying a pair of articles having far different weights, respectively. The three pairs of switches NR and CR, ST and DY, and M1 and M2 coupled respectively by dashed lines are interlocked to produce mutuaily complemental binary signals.For example, if the switches NR, ST and M 1 produce "1", " 1 Ml the outputs of the switches CR, DY and M2 are necessarily "0", and vice versa. This switching circuit also includes five AND circuits 82, 84, 86, 88 and 90. The output of the switch NR isconnected to a first input of the AND circuit 82 and the output of the switch CR is connected to first inputs of the AND circuits 84, 86, 88 and 90. The output of the switch ST is connected to second inputs of the AND circuits 84 and 86 and the output of the switch DY is connected to the other input of the AND circuit 82 and second inputs of the AND circuit 88 and 90.

The output of the switch M1 is connected to third inputs of the AND circuits 84 and 88 and the output of the switch M2 is connected to third inputs of the AND circuits 86 and 90. The output of the AND circuit 82 is applied to control inputs of undermentioned normally-closed gates 66, 70, 74 and 78 and the outputs of the AND circuits 84, 86, 88 and 90 are applied respectively to control inputs of the gates 32, 34, 36 and 38. The respective gates are designed to conduct when their control inputs are "1", respectively. Though not shown in Figure 3B, the outputs of the switches ST and DY are coupled to the conveyor driving device 8 as shown in Figure 1, and the driving device 8 is designed to start the conveyor in response to the input "1" and stop it in response to the input "0".

Pushing now the switches CR, ST and Ml, only the AND circuit 84 produces output "1" which opens the gate 32, and the conveyor 2 stops.

Putting a first article on the conveyor 2 just over the weighing device 12 under this condition, the weighing device 12 produces a static weight signal of this article which is supplied through the A/D converter 14 to the correction device 1 6 and then passes the open gate 32 to be stored in the memory 261 as the static weight WS 1. Next, removing the article from the conveyor and pushing the switch M2, the output of the switch M1 becomes "0" and the switch M2 produces output "1". Accordingly, the AND circuit 86, instead of the AND circuit 84, produces an output which opens the gate 34, and the gate 32 is closed.Putting then a second article which is heavier than the first article similarly over the weighing device 1 2 under this condition, the static weight WS2 is stored in the memory 262 in the same manner. Next, removing the article and pushing the switches DY and Ml, only the AND gate 88 produces an output to open the gate 36 and, at the same time, the conveyor 2 is started.

Under this condition, putting the first article on the conveyor and letting it to pass over the weighing device 12, the weighing device 12 produces a dynamic weight signal. Repeating the same procedure N times with the same article, Nnumber of dynamic weights are supplied to the average circuit 40 and the circuit 40 calculate their average value as aforementioned which is in turn stored in the memory 281 as the dynamic weight WD1 of the first article. Similarly, when the switch M2 is pushed and the same procedure is repeated with the second article, its dynamic weight WD2 is stored in the memory 282.

The contentsWSl and WD1 of the memories 261 and 281 are applied to a subtractor 50 which executes subtraction of WC 1 =WD 1 -WS 1, and the result WC1 is stored in a memory 54. On the other hand, the contents of the memories 262 and 282 are supplied to a subtractor 52 which executes subtraction of WC2=WD2-WS2, and the result WC2 is stored in a memory 56. The contents of the memories 54 and 56 are applied in turn to a subtracter 58 which executes subtraction of WC2-WC1 and the result is applied to one input of the divider 62.The contents of the memories 281 and 282 are applied to a subtracter 60 which executes subtraction of WD2-WD1 and the result is applied to the other input of the divider 62. The divider 62 calculates a ratio of K of WC2-WC1 and WD2-WD1, which is stored in a memory 64. The abovementioned elements 50 to 64 may be included in the arithmetic unit 30 of Figure 1. The block corresponding to the correction circuit 31 of Figure 1 includes four normally-closed gates (or normally-open switches) 66, 70, 74 and 78, which are opened by the output of the AND circuit 82 when the switches NR and DY of Figure 3B are pushed to specify normal weighing and sorting operation.Under this condition, the dynamic weight output WDX of the A/D converter 14 is applied through a gate 78 to one input of a subtractor 68 and an adder 80 but can not pass the gates 32, 34, 36 and 38 which are closed due to the output of the switch CR turned to "O". The subtracter 68 receives the content of the memory 28, at the other input and executes subtraction of WDX-WD 1, the result of which is applied to one input of a multiplier 72. The multiplier 72 receives the content K of the memory 64 at the other input and executes multiplication of K(WDX-WD1), the result of which is applied to one input of an adder 76.The adder 76 receives the content WC 1 of the memory 54 at the other input and executes addition of WCX=WC1 +K(WDX-WD1). This result WCX is the deviation as shown by the aforementioned equation (1), which is added to the dynamic weight WDX by the adder 80 to produce a corrected static weight output which is in turn applied to the judging device 18 (Figure 1).

As described above, according to this invention, preparation setup of corrected weighing operation of articles can be effected, without special need of skillful operators, only through turning operation of the switches and accompanying loading of specific articles of the same kind onto the conveyer.

The above embodiment has been described about the case in which the equation (1) and the relationship of Figure 2 are established between the dynamic and static weights. When the variance of weight of articles is substantially small, there are some cases in which the difference between the static and dynamic weights can be deemed constant regardless of the weights of article. Moreover, in some kind of articles, the ratio of the static and dynamic weights may be deemed constant. It is easy for those skilled in the art to design the arithmetic unit 30 and correction circuit 31 suitably in these cases.

Figure 4 shows an example of the arithmetic unit 30 and correction circuit 31 used when the difference between the static and dynamic weights is always constant. In this case, only the memories 261 and 18, are used. The arithmetic unit 30 includes a subtracter 50 for calculating the difference of the contents of the both memories (WC1=WD1-WS1) and a memory 54 for storing the result WC1 of calculation, and the correction circuit 31 includes a subtracter 92 for subtracting the content WC1 of the memory 54 from the dynamic weight signal WDX.

Figure 5 shows another example of the arithmetic unit 30 and correction circuit 31 used when the ratio of the static and dynamic weights is always constant. In this case, the arithmetic unit 30 includes a divider 94 for dividing the content of the memory 26t by the content of the memory 281 and a memory 96 for storing the result of division R=WS11WD1, and the correction circuit 31 includes a multiplier 98 for multiplying the dynamic weight signal WDX with the content of the memory 96.

While the arithmetic unit 30 and the correction circuit 31 may be substituted with those constituted as a unit having a predetermined circuit arrangement as occasion demands as above, it is also possible to utilize a microcomputer arranged to execute the same effect by suitably modifying its operation program.

Claims (2)

Claims

1. Weighing apparatus comprising a conveyor, drive means for driving the conveyor to feed successively articles to be weighed, a weighing device located intermediate the ends of said conveyor for sensing the weights of the articles and producing weight signals corresponding to the sensed weights, and correction means coupled to said weighing device for receiving said weight signals and applying a correction thereto, said correction means including first means selectively operable to produce either a first static measurement command signal or a second dynamic measurement command signal, second means selectively operable to produce either a third normal operation command signal or a fourth correcting operation command signal, first memory means responsive to said first and fourth command signals to store said weight signal from the weighing device, second memory means responsive to said second and fourth command signals to store said weight signal from the weighing device, means coupled to said first and second memory means for calculating in predetermined manner a value dependent upon the weight signals stored by the memory means, and means responsive to said second and third command signals to receive the outputs of said calculating means and said weighing device and correcting the weight signals supplied thereto in dependence upon the value calculated by the calculating means, and said conveyor drive means being arranged to stop the conveyor in response to said first command signal and start the conveyor in response to said second command signal.

2. Weighing apparatus substantially as herein described with reference to the accompanying drawings.