GB2070362A

GB2070362A - Weighing device

Info

Publication number: GB2070362A
Application number: GB8100808A
Authority: GB
Original assignee: Yamato Scale Co Ltd
Current assignee: Yamato Scale Co Ltd
Priority date: 1980-01-14
Filing date: 1981-01-12
Publication date: 1981-09-03
Also published as: FR2473705A1; JPS56100318A; FR2473705B1; GB2070362B; IT8167032A0; JPS6112523B2; IT1172219B; DE3100917C2; DE3100917A1; AU520013B2; AU6592480A

Abstract

A combination weighing machine, which is typically used for packing a plurality of articles in each bag or the like, including a plurality 29 of weighing balances for weighing a plurality of articles each at the same time, and arithmetic means 43 for selecting some of these weighing balances so that the total weight of the articles thereon falls within a predetermined allowable range, the machine also including zero- point correction means 31 arranged such that, by applying a zero-point correction command signal from the outside, the loading operation of the selected balance is inhibited, this balance is left vacant after an unloading operation, and any weight signal output from this empty balance is cancelled or nullified before being fed to the arithmetic means. <IMAGE>

Description

SPECIFICATION Automatic combination weighing machine with improver zero-point correction This invention relates to an automatic combination weighing machine, especially to a zero-point correction system used with the such machine.

The weighing device which is generally referred to as a "combination balance" or "combination weighing device" is used for extracting and collecting a plurality of articles from a group of articles, such as cakes, fishes and vegetables, having relatively large variations in respective weights, so that the extracted group has a weight which is nearly equal to a predetermined intended weight. Atypical example of such a device is disclosed in United States Patent No. 3,939,928, and another example which is improved over that United States Patent in arithmetic arrangement is disclosed in the British Patent Application No. 7942517 filed December 10, 1979.In these devices a plurality of articles or groups of articles are weighed individually by the same number of weighing balances at the same time, all mathematical combinations of the respective weights are summed up respectively and the respective sums are compared with the predetermined intended weight. When the combined weight is within a predetermined allowable range from the predetermined intended weight, the articles on the corresponding balances are collected for packing in the same package.

The electric output of the each weighing balance, representing the measured weight, may vary due to zero-point drift which is mainly caused by change of circumstantial conditions such as temperature and humidity, and contamination of the weighing cradle with flakes of articles. Accordingly, each balance must be corrected in its zero-point frequently in order to maintain its accuracy and reliability. In the prior art devices, however, it has been necessary to shut off the whole device operation during the prosecution of zero-point correction and, in addition, to remove the articles from each balance to make it vacant with a troublesome and time-consuming manual operation.

Accordingly, an object of this invention is to provide a novel and improved zero-point correction system for combination weighing devices, which can execute all operations required for this purpose in fully automatic fashion in co-operation with the mechanism for loading and unloading the each weighing- balance.

According to the present invention there is provided an automatic combination weighing machine, comprising a plurality of weighing units for receiving respective articles and each producing an electric weight signal dependent on the weight of the article(s) received thereon, supply means including a plurality of discharge gates directed towards the respective weighing units and controlled by control signals for supplying a-rticles to the weighing units, a plurality of normally-open switches which can be closed to supply the weight signals from the respective weighing units to a summing device arranged to sum up the weight signals supplied thereto to produce a sum signal, means coupled to said summing device for comparing said sum signal with a predetermined signal range corresponding to a weight range to produce a comparison output signal when the sum signal is within said range, combination control means having a plurality of output terminals coupled to respective control terminals of said normally-open switches for closing the switches according to a predetermined series of successive combinations, and means responsive to the comparison output signal to cause the weighing units producing the weight signals whose sum lies within the predetermined range to discharge the articles received thereon, a plurality of zero-point correction devices connected between the respective weighing units and said summing device and each responsive to an energising signal to cancel the input thereto and produce a zero-level output, means for producing a zero-point correction command signal, and correction control means for each correction device responsive to said zero-point correction command signal to inhibit supply of control signals to the discharge gates of the supply means for interrupting supply of articles to the weighing unit associated with the respective zero-point correction device, the correction control means also sensing a discharge signal causing the said associated weighing unit to discharge the articles received thereon and apply said energising signal to the zero-point correction device in response thereto.

A better understanding of the invention will be had from the following detailed description, given with reference to the accompanying drawings, in which Figure 1 is a schematic block diagram representing a general configuration of the automatic combination weighing machine including the zero-point correction system according to this invention; Figure2 is a block diagram representing a circuit embodiment of the automatic combination weighing machine in which this invention is embodied; Figure 3 is a waveform diagram representing some control signals used for operation of the circuit of Figure 2; Figure 4 is a logic diagram representing an embodiment of the zero-point correction system according to this invention; Figure 5 is a block diagram representing an example of the correction output generator in the system of Figure 4;; Figure 6 is a logic diagram representing a modification of the zero-point correction system of Figure 4; and Figures 7 and 8 are similar diagrams representing other modifications of the systems of Figure 4.

Throughout the drawings, same reference numerals are given to corresponding structural components.

Referring to Figure 1, shown is a general arrangement of various components of a typical automatic combination weighing machine in which the zeropoint correction system in this invention is embodied. This machine is of eight head circular type, which has eight similar weighing units each accompanied with an article loading and unloading system and a zero-point correction system, and a common central control unit 33. In the drawing, only the diametrically opposing first and fifth heads of the eight heads are shown and the reference numerals have suffixes 1 and 5, correspondingly. It is a matter of course that the number of heads is not a matter of confinement but is a matter of selection of the designer.

The article loading and unloading system include a common vibration feeder 11 consisting of a substantially flat circular disc having a peripheral wall. The feeder 11 is provided with a vibrator 13 for applying circumferential vibration to the disc, so that, when the articles are supplied onto the central portion of the disc from a suitable source 15, they are caused to move spirally outwards to the peripheral portion. The peripheral wall of the feeder has eight exit ports having gates 17, respectively, which are normally closed but opened under control of a gate control signal A, respectively.

Under the each gate 17 of the feeder 11, provided is a loading vessel 19 having an outiet at the bottom, which is provided with a gate 21 which is normally closed but is opened under control of a gate control signal B. Under the each gate 21, located is a weighing cradle 23 of the weighing unit. The cradle 23 is provided also with a gate 25 at its bottom opening, which is closed normally but is opened under control of a gate control signal C. The gates 25 of the all weighing units face an underlying collection hopper 27.

Each weighing cradle 23 is provided with a weight sensor 29, such as load cell, for detecting the weight of articles on the cradle 23 to produce an electric signal W indicative of said weight and which is applied through a zero correction device 31 to the central control unit 33. The gate control signals A, B and Care generated in the central control unit 33 and supplied through the each gate control unit 35 to the abovementioned gates 17,21 and 25, respectively.

Aterminal 39 coupled to a suitable potential source (not shown) is connected through a normallyopen push-button switch 37 to the respective zero correction devices for applying a zero-point correction command signal.

An example of electric circuit configuration of the arrangement of Figure 1 is shown in Figure 2. The outputs Wr, ...... W8 of the weight sensors 291, 292, 298 298 of the eight heads of weighing systems are coupled respectively through the zero correction devices 311,312,... 318 and normally-open switches 411, 412,... 418 to a common adder circuit 43. The normally-open switches 41 " 412, .418 have a control terminal each, connected to corresponding one of eight output terminals of a combination generator 45. The combination generator 45 is driven by clock pulses from a clock pulse generator 47 to produce a predetermined set of combinations of output signals from its selected output terminals, in clocked fashion.For example, if the predetermined set of combinations are complete mathematical combinations of the eight outputs, the combination generator may be an eight-bit binary counter having a control input coupled to the clock pulse generator 47 and eight parallel outputs coupled respectively to the corresponding output terminals.

In this case, the logic HIGH level or binary "1" serves as the "output signal" from the each output terminal of the combination generator 45. As widely known by those skilled in the art, the total number of such combinations is 28 - 1 = 512 and the combination generator 45 produces 512 sets of output signals successively in synchronism with the applied clock pulses.

The adder circuit 43 sums up the weight signals W supplied through the switches 41 closed under control of the combination generator 45, to produce a sum output. the sum output is applied to an upper limit comparator 51 and to a lower limit comparator 53. The upper and lower limit comparators 51 and 53 have second inputs coupled respectively to the outputs of upper and lower limit registers 55 and 57, respectively. The upper and lower limit registers 55 and 57, respectively. the upper and lower limit registers 55 and 57, each having an input device such as conventional digital keyboard (not shown), store predetermined upper and lower limits of allowable range of the weight of combined articles, respectively.The comparators 51 and 53 compare the sum output of the adder circuit 43 with the contents of the upper and lower limit registers 55 and 57, respectively, to produce outputs at the same time when the sum is within the allowable range.

These outputs are coupled to an AND gate 59 and the output H of the AND gate 59 is coupled to a set input of a combination memory 49.

The combination memory 49 has eight memory cells coupled respectively to the corresponding outputs of the combination generator 45 for storing the outputs of the combination generator 45 in response to the output H and the AND gate 59, and corresponding output devices for reading out the contents of the memory cells as gate pulses G having a predetermined duration aswhown in Figure 3 in response to HIGH level contents. The gate pulses G are coupled respectively to control inputs of eight gate circuits 61.

The central control unit 33 further includes a timing circuit 63 which produces timing signals A, B, C, D, E and F as shown in Figure 3 under control of the clock pulses supplied from the clock pulse generator 47. The signals A, B and Care coupled through the respective gate circuits 611, 612,... 618 and the corresponding gate control units 351,352,...

358 to the gates- 17, 21, and 25 of the correspondingarticle loading and unloading systems as described above with reference to Figure 1, to open these gates for the durations thereof. The signal D is a reset signal for clearing the contents of the combination generator 45 and the combination memory 49 at the beginning of each cycle of combination. The arrangement as above-described is well known in the art and, therefore, need not be described further.

Now, the description will be made on the zero-point correction system in which the invention is embodied.

A preferred embodiment of circuit configuration of the each zero-point correction device 31 is shown in Figure 4 with the associated gate control unit 35. The gate control unit 35 includes two AND gates 65 and 67 and an amplifier 69 having inputs for receiving the timing signals A, B and C, respectively, supplied from the timing circuit 63, and outputs coupled respectively to the gates 17,21 and 25 of the corresponding loading and unloading system.

The zero-correction device 31 includes an operation amplifier 71 having a non-inversion input coupled to the output of the weight sensor 29 (Figures 1 and 2) and an output coupled through the normallyopen switch 41 to the adder circuit 43 (Figure 2). The output of the amplifier 71 is also fed back through a correction output generatr 73 as described later to its inversion input. The device 31 further includes a flip-flop 75 having a set input S coupled through the switch 37 to the potential source 39 (Figures 1 and 2) and a Q output coupled through an invertor 77 to the second inputs of the AND gates 65 and 67 of the gate control unit 35. The Q output of the flip-flop 75 is also coupled to an AND gate 79 with another input coupled to the output of the amplifier 69 of the gate control unit 35 and an output coupled to a set input S of another flip-flop 81.The output of the flip-flop 75 is further coupled through an invertor 83 to a reset input R of the flip-flop 81. The Q output of the flip-flop 81 is coupled to one inputs of two AND gates 85 and 87 the second inputs of which are coupled to the timing circuit 63 for receiving the start and stop signals E and F as shown in Figure 3. The output of the AND gate 87 is coupled to a reset input R of the flip-flop 75.

A preferred example of the correction output generator circuit 73 is shown in Figure 5. The correction output generator 73 includes a zero comparator 89 having a first input coupled to the output of the operation amplifier 71 and a second or zero level reference input as shown by a ground mark. The comparator 89 serves a function of comparing the output of the operation amplifier 71 with the reference zero level to produce an output representing "plus" when the former is above zero or "minus" when it is below zero. The "plus" and "minus" outputs of the zero comparator is applied to a control terminal of an up/down or reversible counter 91, which counts clock pulses supplies from a clock pulse generator 93 through an AND gate 95, to drive the counter 91 upwards and downwards, respectively.The count output of the counter 91 is converted into an analog quantity or voltage level by a digital-to-analog (D/A) converter 97 and applied to the inversion input of the operation amplifier 71. The second input of the AND gate 95 is coupled to the Q output of a flip-flop 99 having asset input S coupled to the output of the AND gate 85 and a reset input R coupled to the timing circuit 63 for receiving the stop signal F (Figure 3).

Now, the operation of the zero-point correction system as shown in Figures 4 and 5 will be described in detail. It should be noted previously that "zero correction" means an operation for putting the input weight signal of the adder circuit 43 at zero level when the corresponding weighing cradle has been unloaded but not yet loaded again, that is, it is in vacant state.

In case of effecting zero-point correction, one may push the push-button switch 37 (Figures 1 and 2) for a short time comparator 89 produces an output indicative of "minus" to drive the up/down counter 91 downwards or backwards. Then, the counter 91 begins to effect downward or subtractive counting to reduce the output level of the DIA convertor 97, thereby drawing the output level of the amplifier 71 towards the zero level. After some repetition of such correction operations, the output of the operation amplifier 71 is put at the zero level, and the zero-point correction is completed.

Upon completion of the zero correction operation, the stop signal F (Figure 3) is applied from the timing circuit 63 (Figure 2) to the reset input R of the flip-flop 99 to drive it into "reset" state. Then, the Q output of the flip-flop 99 turns to "low" level to disable the AND gate, thereby resetting the counter 91 and disabling the zero correction operation. The stop signal F is also applied through the enabled AND gate 87 to the reset input R of the flip-flop 75 to drive it into "reset" state. Then, the "low" level 0 output is applied through the invertors 77 and 83 to the AND gates 65 and 67 and to the reset input of the flip-flop 81, respectively, to enable the AND gates and return the flip-flop to "reset" state.Under this condition, the loading signals B and A are supplied through the AND gates 67 and 65to the gates 21 and 17, to effect loading of the weighing cradle 23 with new articles.

Thereafter, the normal operation of the combination weighing machine is continued. It is to be noted that the time interval between the start and stop sitnals E and F is previously set up so that a sufficient zero-point correction is obtained within this period.

As the AND gate 85 is disabled by the "reset" state of the flip-flop 81, the subsequent start signals E can not initiate the zero correction operation.

Figure 6 shows a first variation of the zero-point correction device 31 of Figure 4. As readily understood, this circuit is quite similar to that of Figure 4, except that the disabling signal of the AND gates 65 and 67 are to apply a zero-correction command pulse to the set input S of the flip-flop 75 to drive it into "set" state, during the normal operation of the combination weighing machine. Then, the Q output of "high" level is applied through the invertor 77 to the AND gates 65 and 67 to disable them. Thus, the gates 17 and 21 of the loading system are left closed and no article will be loaded thereafter in the weighing cradle 23 (Figure 1) even if the loading signals A and B are fed in the gate control unit 35.

Therefore, after the cradle 23 is unloaded by the unloading signal C supplied through the amplifier 69 to the gate 25, it is left vacant to be ready for zero correction operation.

The unloading signal C is also applied from the amplifier 69 to the AND gate 79 together with the "high" level 0 output of the flip-flop 75, which applies, in turn, its output to the set input of the flip-flop 81 to put it in "set" state. Then, the "high" level Q output of the flip-flop 81 is applied to the AND gates 85 and 87. Under the such ready condition, the start pulse E is applied from the timing circuit 63 through the AND gate 85 to the set input of the flip-flop 99 of the correction output generator 73, to drive it into "set" state. Then, the flip-flop 99 applies a "high" level Q output to the AND gate 95, thereby passing a train of clock pulses from the clock pulse generator 93 to the up/down counter 91 to be counted therein.

Assuming that the output of the operation amplifier 71 has exhibited some positive value regardless of vacancy of the corresponding weighing cradle, the zero comparator 89 produces an output indicative of "plus" to drive the counter 91 upwards or forwards. Then, the counter 91 counts the clock pulses additively and the count is successively converted into corresponding voltage level by the A/D converter 97 and subtracted from the input level atthe non-inversion input of the operation amplifier 71. As a result, if the output of the amplifier 71 has dropped below zero level, the zero supplied from the AND gate 87 but not from the flip-flop 75. Accordingly, the operation of this circuit is also similar to that of Figure 4, except that the AND gates 65 and 67 are disabled after unloading of the weighing cradle 23 is initiated.

As readily understood, the arrangements of Figures 4 and 6 include the AND gates 65 and 67 in the gate control unit 35 for automatically inhibiting to load again the unloaded cradle 23. However, if a suitable device is provided otherwise for sensing the unloading action of the weighing cradle to disable these AND gates, the circuit of Figure 6 can be simplified as shown in Figure 7. While the circuit of Figure 7 includes means for sensing the unloading action to permit reception of the start signal E, it can be further simplified as shown in figure 8 if the such means is provided otherwise for control of application of the signal E. As the operations of these modifications can be easily understood from the above description, no further description will be made thereon.

It should be noted that the above description has been made about a few embodiments for the illustrative purpose only, and that various modifications and changes can be made within the scope of this invention as defined in the appended claim. For example, the zero correction command signal may be applied automatically and periodically by use of a timing device, such as timer.

Claims

1. An automatic combination weighing machine, comprising a plurality of weighing units for receiving respective articles and each producing an electric weight signal dependent on the weight of the article(s) received thereon, supply means including a plurality of discharge gates directed towards the respective weighing units and controlled by control signals for supplying articles to the weighing units, a plurality of normally-open switches which can be closed to supply the weight signals from the respective weighing units to a summing device arranged to sum up the weight signals supplied thereto to produce a sum signal, means coupled to said summing device for comparing said sum signal with a predetermined signal range corresponding to a weight range to produce a comparison output signal when the sum signal is within said range, combination control means having a plurality of output terminals coupled to respective control terminals of said normally-open switches for closing the switches according to a predetermined series of successive combinations, and means responsive to the comparison output signal to cause the weighing units producing the weight signals whose sum lies within the predetermined range to discharge the articles received thereon, a plurality of zero-point correction devices thereon a plurality of zero-point correction devices connected between the respective weighing units and said summing device and each responsive to an energising signal to cancel the input thereto and produce a zero-level output, means for producing a zero-point correction command signal, and correction control means for each correction device responsive to said zero-point correction command signal to inhibit supply of control signals to the discharge gates of the supply means for interrupting supply of articles to the weighing unit associated with the respective zero-point correction device, the correction control means also sensing a discharge signal causing the said associated weighing unit to discharge the articles received thereon and applying said energising signal to the zero-point correction device in response thereto.

2. An automatic combination weighing machine, according to claim 1, wherein each zero-point correction device includes an operation amplifier having a first input coupled to the associated weighing unit, and an output coupled to said summing device and to a second inputthereofthrough a correction output generator, said correction output generator including means responsive to said energising signal to sense the output level of said operation amplifier and produce an output which cancels said output level whereby to provide a zero level output, and said correction control means of each zero-point correction device includes gate means inserted in the signal path of said control signal to the discharge gate of the supply means, said gate means responding to said zero-point correction command signal to interrupt said signal path, and means responsive to said zero-point correction command signal and said discharge signal to apply said energising signal to said correction output generator.

3. An automatic combination weighing machine, according to claim 2, wherein said correction output generator comprises a comparator having a first input coupled to the output of said operation amplifier and a second input coupled to a reference zero level, the comparator producing an output indicating whether the first input level is higher or lower than said reference zero level, a reversible counter having an input coupled to a clock pulse generator through gate means opened in response to said energising signal and a control terminal coupled to the output of said comparator and a digital-to-analog converter for converting the positive or negative count output produced by the counter according to the input at the control terminal, and the output of the converter being supplied to the second input of said operation amplifier.

4. An automatic combination weighing machine, according to claim 2 or 3, wherein said correction control means further include means responsive to a de-energising signal applied after a predetermined time period from the time of applying said energising signal, for re-establishing said signal path for control signals through the gate means to the supply means discharge gates, and at the same time, interrupting application of said energising signal to said correction output generator.

5. An automatic combination weighing machine substantially as herein described with reference to the accompanying drawings.