This invention relates to a combinatorial weighing system. More particularly, the invention relates to a novel combinatorial weighing method capable of raising weighing speed, and to a combinatorial weighing apparatus for practicing such method.
A combinatorial weighing apparatus operates by supplying a plurality of weighing machines with articles to be weighed, computing combinations based on weight values obtained from the weighing machines, selecting a combination giving a total combined weight value equal or closest to a target weight, and discharging the articles solely from those weighing machines corresponding to the selected combination, thereby providing a batch of weighed articles of a weight equal or closest to the target weight.
The control system of such a combinatorial weighing apparatus will now be described in brief with reference to FIG. 1. The apparatus includes n-number of weighing machines M.sub.1 through M.sub.n respectively comprising weight sensors C.sub.1 through C.sub.n, each of which is constituted by, e.g., a load cell, and weighing hoppers, not shown, attached to the weight sensors. The weighing hoppers of the weighing machines M.sub.1 through M.sub.n are so adapted as to be opened and closed by respective drive units A.sub.1 through A.sub.n controlled by a computation controller 50, described below. The weight sensors C.sub.1 through C.sub.n sense the weight of articles introduced into the respective weighing hoppers, each weight sensor producing a weight signal, namely an analog value corresponding to the weight sensed thereby. The weight signals from these weight sensors C.sub.1 through C.sub.n are applied as multiple input signals D.sub.1 through D.sub.n to a multiplexer 1 via amplifier circuits E.sub.1 through E.sub.n and filters F.sub.1 through F.sub.n, respectively. The multiplexer 1, which is composed of analog switches or the like, responds to a selection command S.sub.o from the computation controller 50 by selectively applying the weight signals D.sub.1 through D.sub.n as weight data to a buffer circuit 11 in sequential fashion. The buffer circuit 11 delivers the weight data signals D.sub.1 through D.sub.n received from the multiplexer 1 to a sample/hold circuit 12 upon subjecting the signal to an impedance conversion. The sample/hold circuit 12 repeatedly samples and holds the weight data signals D.sub.1 through D.sub.n subjected to the impedance conversion by the buffer circuit 11, and delivers the weight data signals to a buffer circuit 13. The latter subjects the signals to an impedance conversion, producing analog weight data signals delivered to an analog-digital converter (A/D converter) 2. The latter converts the analog weight data signals from the buffer circuit 13 into digital signals applied to the computation controller 50. The latter is composed of a microcomputer and includes a processor 501 for performing combinatorial calculations, a read-only memory (ROM) 502 storing a control program for combinatorial processing, and a random-access memory (RAM) 503 for storing the weight data as well as the results of processing performed by the processor 501. The computation controller 50 computes combinations on the basis of the weight data, selects a combination, referred to as the "optimum combination", giving a total combined weight value equal or closest to a target weight, and delivers discharge commands S.sub.1 through S.sub.n to the drive units A.sub.1 through A.sub.n of respective weighing hoppers belonging to those weighing machines M.sub.1 through M.sub.n which correspond to the selected combination.
Since a combinatorial weighing apparatus of the foregoing type is based on static weighing, the weighing machines M.sub.1 through M.sub.n must attain a quiescent, stabilized state by the time the computation controller 50 reads the weight data D.sub.1 through D.sub.n delivered by these weighing machines. Accordingly, in the conventional combinatorial weighing apparatus, a timer is set to a time period within which the weighing machines are expected to stabilize, and the timer is started at the exact instant the loading of the articles into the weighing hoppers of the weighing machines is completed. When the set time period has expired, the timer issues a signal in response to which the computation controller 50 sends the selection command S.sub.o to the multiplexer 1 and reads in the weight data D.sub.1 -D.sub.n from the weighing machines M.sub.1 -M.sub.n.
To maintain good weighing accuracy, the aforementioned time period must be set with some margin for safety. Even though weighing machines may actually stabilize early, therefore, the weight data cannot be read until the set time period has fully expired. Accordingly, weighing speed with the conventional arrangement is limited by the time period to which the timer has been set and is difficult to raise without diminishing weighing accuracy. Furthermore, with the conventional weighing system, there is no confirmation that the weighing machines have actually stabilized when the weight data are read. For this reason, reading of the weight data cannot be inhibited in the event that the quiescent state of the weighing machines is upset by an external disturbance, such as floor vibration, which occurs during the reading operation.