Weighing scales – Computer – Electrical
Reexamination Certificate
2003-05-06
2004-12-21
Gibson, Randy W. (Department: 2841)
Weighing scales
Computer
Electrical
Reexamination Certificate
active
06833514
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control system for a high-speed multihead weigher, sometimes called simply a weigher. The multihead weigher is a combinatorial weighing system composed of a series of completely independent weighing modules, called heads, connected to a so called central control unit, composed of a common personal computer (PC) or the like, by means of a low-speed serial network.
2. Description of the Related Art
Generally a combinatorial weighing system is composed of a set of identical modules, each equipped with its own vibrating channel, a loading bucket, a weighing bucket coupled with a load cell or the like and may include a memory bucket. A typical realization of a combination weighing system foresees that these modules are placed according to a circular configuration, even if also other types of configurations are possible, for example a rectilinear one. As will be understood by those skilled in the field of combinatorial weighers, in case of circular configuration the product or articles is delivered radially starting from the machine center, the buckets of each module are filled and the product in the weighing buckets is weighed. The combination of the weights contained in the weighing buckets of the modules that comes closest to the required weight is discharged in a transfer device, for example a cone or a funnel, which conveys the product towards a packaging system.
The electromechanical members with which each module is equipped are the motors for the motion of the buckets, the electromagnets in order to drive the vibrating channels and the load cells to weigh the product inside the weighing buckets. In order to describe the prior art in relation to the control of these electromechanical devices two complementary solutions will be mentioned.
U.S. Pat. No. 4,694,920 to Naito et al. relates to a combinatorial weigher having a control system composed of at least three central processing units which control respectively the acquisition of the electric signals coming out from the load cells (said weight-monitoring section), the devices for the motion of the product to be weighed such as motors and vibrating feeders (said drive-control section) and the digital signals for the selection of the weights combination to be discharged (said main section). As the electromechanical members are distributed on a circular structure whose dimensions are not negligible, there is an evident necessity to reach said devices with some cables starting from a unit which is physically dislocated far from them. The cables are the cause of an increase of the general system costs and are a potential source of malfunction due to possible disconnections. Besides, the presence of cables, whose length is not negligible, for the feeding of motors and electromagnets generates electromagnetic interferences, which can cause malfunctions of the electronic systems incorporated in the machine, as partially pointed out in the U.S. Pat. No. 4,658,919 to Nobutsugu.
U.S. Pat. No. 5,981,881 to Kawanishi et al relates to another architecture, wherein the control system of the machine is composed of a single weighing control unit which is connected through a high-speed local area network (LAN) to the weighing modules. Each module contains some electromechanical members with relative electric drivers and interfaces itself with the LAN through a LAN interface. In this case the previously mentioned problems that accompany use of cables, namely (1) increased cost (2) malfunction due to possible misconnections, and (3) presence of electromagnetic interference, do not exist. However, if a LAN is used, it needs to be a high-speed LAN because the weighing control unit can manage all the weighing modules and can therefore respond quickly to data such as operating conditions or control information between the weighing control unit and the weighing modules. When the number of weighing modules and the machine speed (weights/minute) increase, the quantity of information exchanged between the generic control unit and the peripheral modules increases considerably. In order to allow to the central unit a rapid control of the peripheral members such as motors, vibrating channels, load cells, etc., it is necessary to use a high-speed communication network, such as a LAN. The patent states that the use of a high-speed LAN allows the upgrade of software memorized in the modules control electronics. The prior art mentioned in this patent states clearly that, if the weighing driving sections are connected to the weighing control unit through an ordinary serial telecommunication line, it is impossible for the weighing system to reach high operating speed in terms of weights/minute.
The use of a high speed LAN reveals itself expensive if compared to the simplest serial asynchronous low-speed communication lines used for example in a common PC or similar apparatus. In a typical industrial environment the electromagnetic pollution level is rather high and the presence of electromagnetic interferences can considerably reduce the reliability of a high-speed communication system such as a LAN, causing an increase of the error probability. In general the more such decrease in reliability is marked, the higher the transmission speed of the data. In particularly demanding situations the lack of a reliable link between the central unit and the peripheral modules of the weigher, because of frequent communication errors, can determine an undesired reduction of the weigher working speed. The patent also discusses insertion of electro-optical converters in the communication interfaces, or in the introduction of optical fiber sections inside the network. However, this results in an increase in the hardware complexity and a further increase of costs.
In order to manage a combinatorial weigher there is the necessity of some fundamental functional blocks or electronic subsystems, such as a unit for the calculation of the combinations, a graphic or alphanumerical unit for the input/output of data, a section for the storage of data and programs and a communication interface with the weighing peripheral modules. In some cases these electronic subsystems are placed in different points inside the weigher, while in other cases instead they are dislocated and interconnected with each other in a single housing of the weigher called central control unit. The central control unit is therefore generally composed of a multiplicity of electronic subsystems conceived as intrinsically independent, with definite and separate functions, which together carry out the requested control functions. The disadvantages of such a custom-made architecture appear evident if the possible cost reductions and the decrease of structural complexity are considered. This approach results in high costs due to the design and manufacture of separate subsystems, and loss of reliability due to possible misconnection of the subsystems.
Also the weighing modules are characterized by a set of electronic subsystems such as motor drivers, vibrating feeders electromagnet drivers, calculation digital units and communication interfaces. A critical point as far as the reliability of the weighing modules is concerned consists in a considerable quantity of cables which interconnects the mentioned electronic subsystems. These connections raise the cost of a weighing module and can determine malfunctions due to accidental disconnections.
Often there is the problem of integrating a weighing system in the factory network that controls the industrial plants. Sometimes the possibility to monitor or control a weighing system from a geographically remote place is requested. The above mentioned custom-made control units are generally not set up for this type of application and need hardware expansion modules such as modem or additional LAN interfaces, with consequent increase of the costs and of the system hardware complexity. Also, communication through telephonic public network between the central control unit and a remote controller
Gesuita Enzo
Gusson Francesco
Cooper & Dunham LLP
Gibson Randy W.
Phillips Peter J.
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