Method of evaluating the efficiency of an automatic machine

A method of evaluating the efficiency of an automatic machine, whereby, upon completion of a given production lot, a current performance index achieved by the automatic machine during manufacture of the production lot is calculated; and the current performance index is memorized in a nonvolatile memory, together with various characteristic parameters relating to the processing performed. To evaluate the efficiency of the automatic machine, the current performance index is compared with historic performance indexes memorized previously during operation of the automatic machine and having characteristic parameters substantially similar to the characteristic parameters of the current performance index.

FIELD OF THE INVENTION

The present invention relates to a method of evaluating the efficiency of an automatic machine.

The present invention may be used to advantage on an automatic cigarette packing machine, to which the following description refers purely by way of example.

BACKGROUND OF THE INVENTION

Automatic cigarette packing machines are normally supplied together with a maker's table listing various machine performance indexes (e.g. output per hour, faults per hour, average downtime, etc.) and respective acceptance ranges. And to evaluate the efficiency of a machine, the user determines the actual value of one or more performance indexes, compares the actual value with the respective acceptance range indicated by the maker, and, in the event one or more performance indexes are outside the respective acceptance ranges, proceeds to program maintenance and/or inspection of the machine accordingly.

Though widely used by cigarette manufacturers, the above method of evaluating the efficiency of an automatic cigarette packing machine has been found to result, in some situations, in the programming and performance of substantially pointless maintenance and/or inspection work, and, in other situations, in the performance of maintenance and/or inspection work with a certain delay with respect to occurrence of the problem.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of evaluating the efficiency of an automatic machine, designed to eliminate the aforementioned drawbacks, and which at the same time is cheap and easy to implement.

According to the present invention, there is provided a method of evaluating the efficiency of an automatic machine for processing articles grouped into a succession of production lots; the method comprising calculating, upon completion of a production lot, a current performance index of the automatic machine achieved during production of said production lot; and the method being characterized by memorizing the current performance index in a nonvolatile memory, together with various characteristic parameters relating to the processing of said production lot; and evaluating the efficiency of the automatic machine by comparing the current performance index with at least one historic performance index memorized beforehand during operation of the automatic machine and having characteristic parameters substantially similar to the characteristic parameters of the current performance index.

DETAILED DESCRIPTION OF THE INVENTION

Number1in the accompanying drawing indicates as a whole an automatic packing machine for producing packets2of cigarettes, and which is of substantially known type, e.g. of the type manufactured by G.D. S.p.A. and marketed under the name “X500”.

Packing machine1comprises a control unit3housed in a cabinet4located close to packing machine1and connected to packing machine1by electric cables (not shown).

Control unit3also performs the functions of a user-interface or so-called “HMI” device, and therefore incorporates a known industrial computer comprising a data display screen5, and a keying device6normally defined by a keyboard and/or pointing device. Alternatively, keying device6may be integrated in screen5by means of a so-called “touch-screen” function.

In a further embodiment, control unit3comprises a network connection—typically operating according to the Ethernet standard—by which a known remote user-interface device (not shown) can interact with control unit3.

Packing machine1comprises a number of known operating devices7(not shown singly), each for performing a given function, and which may comprise, for example, transfer conveyors (typically wheels), gumming devices, movable folding devices, embossing devices, control sensors, etc.

In actual use, packing machine1receives, at the input, a number of materials8—in particular, a stream of cigarettes9, and sheets of wrapping material unwound off reels10—which are processed by operating devices7to obtain packets2of cigarettes at the output of packing machine1.

Production of packets2of cigarettes is normally divided into production lots, each comprising a given number of packets2of cigarettes of a given homogeneous type, so that two successive lots may differ as to the type of packets2of cigarettes. Packets2of cigarettes may be of numerous types, and may differ, for example, as to the type of wrapping material employed (in particular, the graphics imprinted on the wrapping material); the size of packets2of cigarettes; the arrangement of cigarettes9inside each packet2of cigarettes; and the size of cigarettes9.

To produce each type of packet2of cigarettes, packing machine1must be set to a respective operating configuration corresponding to a given configuration of operating devices7; and, when the type of packet2of cigarettes changes from one production lot to the next, the operating configuration of packing machine1must also be changed, as is known, by making given technical adjustments or changes to at least some of operating devices7of packing machine1.

For each production lot, or each fraction of the same production lot, control unit3determines a performance index I of packing machine1representing a synthetic estimate of the overall performance of packing machine1during manufacture of the lot considered.

Performance index I is defined by a vector of four numeric variables V1, V2, V3, V4, wherein variable V1is an indicator of the quality of packets2of cigarettes produced by packing machine1; variable V2an indicator of the productivity of packing machine1; variable V3an indicator of the downtime of packing machine1; and variable V4an indicator of the state of operating devices7of packing machine1.

In another embodiment, performance index I is defined by a single numeric variable V normally obtained by mathematically combining the above four numeric variables V1, V2, V3, V4. In an alternative embodiment, performance index I is obtained by calculating a weighted average of variable V1(quality of packets2of cigarettes), variable V2(productivity), and variable V4(state of operating devices7).

Each packet2of cigarettes produced on packing machine1undergoes various optical quality control checks at a known control station (not shown) located along a known output conveyor (not shown) of packing machine1. Each quality control check of a packet2of cigarettes provides for measuring the value of a respective characteristic quantity of the packet2of cigarettes; comparing the measured value with a corresponding reference value; and rejecting the packet2of cigarettes if the deviation between the measured value and reference value is outside a given acceptance range. The value of variable V1of each packet2of cigarettes is determined by calculating a weighted average of the percentage deviations between the measured values and respective reference values; and the value of the overall variable V1of an entire production lot is obviously determined by calculating the average of the variable V1values of each packet2of cigarettes forming part of the production lot.

The value of variable V2of a production lot is determined by subtracting from the number of packets2of cigarettes produced per unit of time the number of packets2of cigarettes rejected per unit of time, both of which numbers are normally recorded on known cigarette packing machines. A respective correction coefficient, depending on the quality of materials8supplied to packing machine1, may be applied to the final value of variable V2, and is preferably a multiplication coefficient of 0 to 1, which assumes a value 1 when the quality of materials8is excellent, and a value of less than 1 (normally not less than 0,9) when the quality of materials8is less than optimum.

The value of variable V3of a production lot is determined by dividing total downtime of the machine by total operating time, both of which times are normally recorded on known cigarette packing machines.

The value of variable V4is determined by calculating a weighted average of the state indicators of each operating device7; and the state of each operating device7is in turn determined as a function of the actual lifetime of operating device7, or by calculating a weighted average of a first contribution depending on the lifetime of operating device7, and a second contribution depending on the estimated condition of operating device7.

The first contribution is determined by dividing the actual lifetime of operating device7by the estimated lifetime of operating device7. The estimated lifetime is provided by the maker of operating device7, and may be corrected as a function of the average lifetime achieved by the same type of operating device7on packing machine1.

The second contribution is determined as a function of control signals acquired by direct or indirect measurements on packing machine1. More specifically, the second contribution is determined according to the formula:
SC=|Cc3−Ccci|/Vrm
where:SC is the second contribution;Cc3is the current condition of operating device7estimated from the currently acquired control signals of operating device7;Ccci is the initial condition of operating device7deduced from the control signals of operating device7acquired after installation and set-up;Vrm is the maximum |Cc3−Ccci| difference value recorded in previous cases of replacement and/or failure of operating device7.

In actual use, at the end of a production lot or a fraction of it, control unit3automatically and independently calculates the current performance index I achieved by packing machine1during manufacture of the production lot; memorizes the current performance index I in a known nonvolatile memory (not shown) together with various characteristic parameters relating to processing of the production lot; and searches its memory for historic performance indexes I memorized previously during normal operation of packing machine1, and having characteristic parameters substantially similar to those of the current performance index I. To evaluate the efficiency of packing machine1in the manufacture of the production lot in question, the current performance index I is compared with the historic performance indexes I having characteristic parameters substantially similar to those of the current performance index I.

On detecting a significant difference between the current performance index I and historic performance indexes I, control unit3generates an operator control request signal.

In a preferred embodiment, characteristic production lot parameters comprise the type of packets2of cigarettes forming part of the production lot; the quality of materials8supplied to packing machine1to process the production lot; and mean ambient conditions (typically temperature and humidity) during processing of the production lot.

To enable as consistent a comparison as possible between current and historic performance indexes I, the historic performance index I may be corrected by applying a respective correction coefficient depending on the difference between the characteristic parameters of the current performance index I and those of the historic performance index I.

Though cheap and easy to implement, the above method of evaluating the efficiency of packing machine1in the manufacture of a given production lot is highly effective, by taking into account not only factors extraneous to packing machine1—such as the type of packets2of cigarettes, the quality of input materials8, and ambient conditions—but also features peculiar to packing machine1itself, which as a whole inevitably differs from any other machine of the same model. Such difference are caused by construction tolerances and by the life of packing machine1(use, maintenance, changes in set-up, repairs), and may eventually become highly significant.