GB2237897A

GB2237897A - Method of controlling the operating speed of a processing machine

Info

Publication number: GB2237897A
Application number: GB9021724A
Authority: GB
Inventors: Guenter Bleisch; Matthias Weiss; Thorsten Mueller; Michael Aurin
Original assignee: DEUTSCHE VERPACKUNGSMASCH
Current assignee: DEUTSCHE VERPACKUNGSMASCH
Priority date: 1989-10-12
Filing date: 1990-10-05
Publication date: 1991-05-15
Also published as: IT9048347A1; DE4027007A1; DD285649A5; IT9048347A0; GB9021724D0

Abstract

The operating speed of a processing machine is reduced when temporarily reduced quality of the stock being processed occurs: for example when changing from one roll of wrapping material to another in a packaging machine. For this purpose the start of a processing phase (t1 to t5) of reduced reliability is determined, the operating speed is reduced from this instant to a value (nB*) which, during the processing phase of reduced reliability, at least guarantees the fulfilment of functions under the given processing conditions, and the operating speed is subsequently restored to the preset overall value (nB). Articles which may be double wrapped or incorrectly wrapped can be extracted from the processing line during the changeover. Fewer incorrectly wrapped articles need be diverted due to the reduced operating speed and the normal speed (nB) can be higher thereby optimising the overall output of the machine. <IMAGE>

Description

2 2 _ 17 j 53 17 METHOD OF CONTROLLING THE OPERATING SPEED OF A PROCESSING

MACHINE The present invention relates to a method of controlling the operating speed of a processing machine.

In processing machines for piece goods, it is known to regulate the machine operating speed according to the quantity of the stock to be processed. Thus, according to DE-OS 3120603 the operating speed of a processing machine is constantly determined by computation based on the entered number of vessels, the treatment time, the possible product ivity and the actual degree of filling of the vessels, and is utilised for regulation of the operating speed of the machine itself 1 and/or associated machines. The determination takes place according to a computation algorithm by means of computer on the basis of sensor pulses from the machine. The regulation magnitude is automatically varied adaptively by the sensor pulses. According to DE-OS 2740175, the operating speed of a processing machine is regulated according to the quantity of stock to be processed, which is determined by sensor pulses from a store.

It is disadvantageous in both arrangements that regulation of the operating speed takes place only according to a defined number of items of stock to be processed, and that factors, which reduce relia bility and productivity, from the treatment process are not taken into consideration.

This disadvantage is eliminated by processing machines, which, for conditions of reduced processed stock quality or other conditions relating to processing, permitmanual switching over to an operating speed which is lower than the set one. This is applicable to, for example, pole-changing alternating current motors for stepwise - - 2 -reduction in the operating speed of the machine, and wide V-belt gears or thyristor-controlled direct current motors with resistance connected in front thereof for the stepless reduction in the operating speed of the machine.

It is disadvantageous in all these machines that a reaction to reduced reliability of the treatment process cannot take place at the right time, because of the necessity of manual resetting of the operating speed.

In an -arrangement according to DD-WP 246641, the processing conditions and available quantity of stock to be processed are taken into consideration through the regulation of the operating speed, the values of which are determined according to efficiency-oriented characteristic magnitudes, and a time-related stability of the treatment process isachieved through uniform operation of the machine.

However, it is still disadvantageous that, with a preset overall operating speed, temporarily reduced quality of processed stock leads to increased production waste until recognised by the operator. If, on the other hand, processing phases causing reduced stock quality should be taken into consideration by presetting of a lower overall operating speed, there would be losses in productivity.

For example, the packaging material in a packaging machine, such as a wrapping machine for sweets, is supplied from rolls in a store. A requirement for high operating speeds has led to an arrange ment for automatic ch-ahge of the packaging material feed from parallelly arranged stores. This change of the packaging material feed constitutes a processing phase during which a temporarily reduced quality of processed stock and/or other processing conditions influence the preset -- 3 overall level of the operating speed.

It would thus be desirable to improve the output of processing machines, especially by way of a method for correction of the set operating speed of a processing machine in the case of temporarily reduced reliability.

According to the present invention there is provided a method ofcontrolling the operating speed of a processing machine, the method comprising the steps of controlling the machine operating speed in dependence on coefficients related to efficiency so as to be at a value predetermined to be optimum for an entire processing operation to be performed by the machine or for a stage of such operation in which constant conditions prevail, identifying the starting instant of any phase of the processing operation predetermined to be of reduced reliability when performed by the machine operating at said optimum value speed, reducing the machine operating speed from that instant to avalue at which the processing operation can still be performed with a predetermined acceptable level of reliability, and subsequently restoring the machine operating speed to said optimum value.

In a preferred example of the method, the control of the machine is on the basis of its failure behaviour, wherein the control takes place according to coefficients related to effectiveness and the machine is operated at an overall operating speed, recognised as optimum, for the entire operating time or a portion thereof characterised by constant operating conditions. The instant of impending and/or necessary processing phases of reduced reliability is determined, the operating speed is reduced from this instant to avalue which, during that phase, ensures at least the fulfilment of functions under the given processing conditions, and the operating speed is subsequently increased back to the overall value.

An advantage of such a method is that a reduction in the operating effort may be achieved through cessation of the need to eliminate faults, for example during a changeover of packaging material. Actual productivity may be increased and processing costs reduced due to a lower number of failure portions as well as a possibly higher operating speed for the machine.

An example of the present invention will now be more particularly described with reference to the accompanying drawing, the single figure of which is a diagram illustrating steps in the control of the operating speed of a processing machine.

Referring now to the drawing, in many types of packaging machine, for example wrapping machines for sweets, the packaging material is fed from rolls in a store. High operating speeds have led to the need for automatic change of the packaging material feed from parallely arranged stores. The automatic change 6f packaging material feed represents a processing phase in which significant productivity losses arise. The reason for this is both the standstill of the machine on failure of the changing equipment and the waste which is caused by the change in packaging material feed. Such waste may be, for example, doubly wrapped products or products not wrapped due to faults, all of which must be rejected.

The probability of failure of the changing equipment as well as the number of waste products rejected and the losses in productivity resulting therefrom follow a proven relationship to the set operating speed of the processing machine. The same relationship is valid in - respect of the control of a product shunt for the separating-out of reject products for the ratio of the number of products, which are of correct quality and thereby sorted out unnecessarily, to the number of the products which must be sorted out because of double wrapping or other reasons causing waste. These losses in productivity can thus be considered to be a magnitude dependent on operating speed. This is true for the computation of overall optimum values as well as also for the selection of an operating speed n. of the packaging machine to be preset on the basis of empirical values. In this manner, in view of their dependence on the respective processing conditions, they influence the computed actual productivity for the entire running time of the packaging machine.

The opening duration of the shunt, provided in the packaging machine, for the sorting-out of the products manufactured during the change in the packaging material feed is determined by the maximum duration within which doubly wrapped products can arise and which is needed for the travel from the station of the last fold-Ing operation to the shunt. In the past, a constant opening time has been preset, so that a greater quantity of products manufactured to correct quality are sorted out unnecessarily in normal operation, where this time duration is smaller in dependence on rotational speed than the maximum time duration.

In the method exemplifying the present invention, the instant for the beginning of the changeover in the packaging material feed is identified by an appropriate sensor. As a rule, this takes place through ascertaining the instant t1, which is a limit value of the degree of filling of the packaging material store PM1 in use, or of 4 the instant t 2' which is, the instant of attainment of the unfilled state in the case of the store PM1. Thereby, the beginning of a processing phase is defined, for which a changed operating speed n B is to be set relative to the preset overall or normal value n Since B the functional reliability of the processing machine falls with increasing rotational speed or operating speed, this is speed reduced to the value n B which still guarantees fulfilment of the functions under the prevailing processing conditions. In that case, "fulfilment of functionC signifies a fulfilment probability which is economically acceptable under use conditions, n B thus being less than n B After the feed of the packaging material has been changed at instant t 2 from the run-down store PM1 to a new, filled store PM2, and the product shunt for the sorting-out of doubly wrapped stock (for example sweets) has been opened at instant t 31 the final portion of packaging material is withdrawn from the store PM1 at instant t 4 and applied to the articles to be wrapped and the product shunt is closed again at instant t 5 The operating speed is then increased from n B back to the overall value n B It is thereby achieved that the probability of the fulfilment of functions of the equipment for the changeover of packaging material feed is able to be calculated and reaches a value which is greater than the previously set value. The automatic packaging material change can take place without, or with a substantially smaller number of, faults. Consequently, higher values for the operating speed can be preset outside the phase of packaging material change. This means that the preset overall operating speed can be brought from n 0 to n B Since this is applicable to the predominant part of the processing time, it 1 is thus possible to achieve a higher level of productivity of the packaging machine.

In addition, the necessary opening duration of the shunt for the sortingout of waste products can be preset exactly so that for example, only doubly wrapped products are separated out.

Claims

-8 CLAIMS 1. A method of controlling the operating speed of a processing machine, the method comprising the steps of controlling the machine operating speed in dependence on coefficients-related to efficiency so as to be at a value predetermined to be optimum for an entire processing operation to be performed by the machine or for a stage of such operation in which constant conditions prevail, identifying the starting instant of any phase of the processing operation predetermined to be of reduced reliability when performed by the machine operating at said optimum value speed, reducing the machine operating speed from that instant to a value at which the processing operation can still be performed with a predetermined acceptable level of reliability, and subsequently restoring the machine operating speed to said optimum value.

1

2. A method as claimed in claim 1, wherein the step of identifying the starting instant comprises monitoring a parameter of the machine operation by means of a sensor.

3. A method as claimed in either claim 1 or claim 2, wherein the step of identifying the starting instant comprises designating as said instant a point in time which is immediately prior to the onset of said phase.

4. A method as claimed in either claim 1 or claim 2, wherein the step of identifying the starting instant comprises designating as said instant a point in time which precedes the onset of said phase i:

ii 9 - by a given amount.

5. A method as claimed in any one of the precedi.ng claims, wherein said phase comprises a changeover from an old to a new store of material processed by the machine.

6. A method as claimed in any one of the preceding claims; wherein the step of reducing the machine operating speed is carried out for a plurality of such phases and the speed is reduced by a constant amount.

1

7. A method as claimed in any one of claims 1 to 5, wherein the step of reducing the machine operating speed is carried out for a plurality of such phases and the speed is reduced by a variable amount dependent on processing parameters of the respective phase.

8. A method as claimed in dlaim 1 and substantially as hereinbefore described with reference to the accompanying drawing.

Published 1991 atThe Patent Office. State House. 66/71 High Holborn. London WC I R4TP. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point. Cwmfelinfach. Cross Keys, Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Marv Cray, Kent.