A control system for labelling apparatus

Abstract

 A control system for a label applicator comprises a label sensor (13) to sense labels (12) on a label carrying web (19) and a product sensor (17) to sense products (16) on a moving conveyor (14). A datum position on each label (12) and each product (16) is identified by the control system and the label sensor (13) and product sensor (17) are linked by a control device (23) which operates to control movement of the label carrying web (19) and the conveyor (14) to ensure that each label (12) is applied to each product (16) with the respective datum positions in a predetermined desired disposition. The control device (23) includes means whereby variations in label or product size or spacing can be compensated for by varying the timing of the acceleration of the label carrying web (19). The control device (23) also includes means to compensate for the inherent response delay present in the label and product sensors (13 and 17) and for variations in the product or label speed.

Description

[0001] This invention relates to a control system for labelling apparatus.

[0002] Conventional labelling machines have sensors which detect and monitor movement of a product to be labelled on a conveyor and accelerate a label carrying web to the same velocity as the conveyor. A further label sensor is used which detects the presence of the label at the ′beak′, where the label is separated from the web and applied to the product, and causes the web to decelerate such that the label is located in a position suitable for application. Variations in conveyor speed, and hence product speed, are detected by way of a shaft encoder mounted on the conveyor.

[0003] With the above known arrangement problems arise in so far as label misplacement can occur to an unacceptable degree. The misplacement of the labels can arise due to variations in the conveyor and hence product velocity, it being necessary to manually adjust the sensor position to compensate for this error. However, this can introduce unnecessary complications to the labelling procedure. A further problem arises with the known arrangement is that detection of the position of each label is usually achieved by sensing the presence of a leading or trailing edge thereof and this can lead to problems with misplacement if the label size varies and/or indeed the product size varies.

[0004] It is an object of the present invention to provide a control system which enables labels to be applied in such a manner that constant placement on the product can be ensured in a particularly simple and efficient manner.

[0005] According to a first aspect of the present invention therefore there is provided a control system for labelling apparatus comprising means to monitor product movement and to cause movement of a label carrying web in accordance therewith, label sensor means to detect labels on said web and to produce an output signal corresponding thereto and means to identify a datum position on each said label and each said product, said product monitoring means and said label sensing means being linked in such a manner as to permit said label to be positioned whereby said datum position on said label is in predetermined disposition relative to said datum position on said product for application thereto, said label datum position being disposed between front and rear edges of said label.

[0006] With this arrangement it is possible to arrange for labels to be presented for application to a product in a simple and efficient manner which facilitates accurate placement on the product.

[0007] A further advantage is gained by the arrangement of the present invention insofar as it is possible to detect the absence of labels or misplaced or differently sized labels on a web, thereby allowing remedial action to be taken prior to application to the product.

[0008] Preferably the label datum position is disposed substantially at the centre of each said label. In this case said product datum position may be disposed substantially at the centre of an outer surface of a peripheral face of said product.

[0009] Said product monitoring means may comprise a sensor to detect movement of a product therepast and in this case the sensor may be an optical sensor. The sensor may be operable to initiate drive means, which drive means accelerates said label carrying web to a speed substantially equal to that of the product. The period of time for which said drive means is initiated by said sensor to accelerate said web may be variable.

[0010] Thus, and in accordance with a second aspect of the present invention, there is provided a control system for a labelling machine comprising means to monitor product movement and to cause movement of a label carrying web in accordance therewith and label sensor means to detect labels on said web and to produce an output signal corresponding thereto, said label sensor means and said product monitoring means being linked in such a manner as to permit said label to be positioned for accurate application to said product, said system further including means adapted to accelerate said label carrying web and means to vary an initiation time for the acceleration of said label carrying web whereby label carrying web and product speed can be arranged to be substantially equal on application irrespective of variation in label or product speed or spacing.

[0011] Preferably said means to vary an initiation time for acceleration is further operable to vary an initiation time for a deceleration of said web.

[0012] Preferably said means to vary the initiation time comprises means for delaying the initiation of the acceleration of the web.

[0013] The second aspect may incorporate some or all of the features of the first aspect.

[0014] Both first and second aspects of the invention may incorporate means to compensate for inherent time delay in detection in said product monitoring means and said label sensor means.

[0015] The invention will now be described further by way of example only and with reference to the accompanying drawings of which:-

Figure 1 shows a schematic representation of one form of apparatus incorporating the system of the invention;

Figure 2 shows a block diagram of one form of control circuitry according to the invention;

Figure 3 shows a representation of the output signal from the label sensor of Figure 2;

Figure 4 shows a schematic representation of different sized labels applied to a product using the apparatus of Figure 1 and conventional apparatus; and

Figure 5 shows a further representation of the apparatus of Figure 1 incorporating example values for label counter value, label spacing, etc.

Referring now to the figures, there is shown in Figure 1 apparatus 10 incorporating the control system of the present invention.

[0016] The apparatus comprises a dispenser 11 which is adapted to support a web carrying labels 12, a label sensor 13 to monitor the labels, a conveyor 14 along which a product 16 may move and a product sensor 17 to sense movement of each product 16.

[0017] The dispenser 11 comprises an elongate member of substantially trapezoidal form, one end 18 of which is tapered inwardly to define a ′sharp′ point or ′beak′. The web 12, in use, moves along an upper surface 19 of the dispenser 11 causing a label to be separated from the web 12 and applied to the product in a manner to be described hereinafter.

[0018] A label sensor 13 is disposed generally above the label carrying web 12 and operates to monitor label position, the absence of presence of a label. The label sensor 13 can take any form as desired or as appropriate, for example the sensor can be an infra red detector.

[0019] A conveyor 14 is provided along which each product 16 is transported into the proximity of the beak 18 of the dispenser 11 in order that one or more labels can be applied thereto.

[0020] The product sensor 17 is mounted above the conveyor 14, or in any other suitable position, and is adapted to sense movement of each product 16 along the conveyor 14. The sensor 17 can take any desired form and is linked to the label sensor 13 in such a manner that the movement of the label carrying web 12 can be matched with the movement of the product 16 on the conveyor such that on application of the or each label to the product 16, the relative disposition of the label to be applied and the product 16 to which the label is to be applied is the same during each application, thereby ensuring accuracy of placement of the label on the product 16. The product sensor 17 and the label sensor 13 are linked by way of control circuitry 20, which is shown more clearly in Figure 2.

[0021] The control circuitry 20 will now be described further in relation to its operation.

[0022] In use, the label carrying web 12 passes over the upper surface 19 of the dispenser 11 at a predetermined rate and movement of the labels thereon is monitored by the label sensor 13. As each label passes under the sensor 13, detection of the leading edge thereof causes the sensor 13 to produce a rising signal, a constant signal over the length of the label and a falling signal upon detection of the trailing edge of the label. Thus it can be seen that the output signal of the label sensor 13 is a square wave signal 21 as is shown in Figure 3, furthermore it will be appreciated that the frequency and duration of the output signal 21 is indicative of the speed of movement of the web 12. The stepper motor 22 which drives the label carrying web 12 is controlled by a motor drive 53 which produces control pulses in accordance with a count in one respective pitch counter 52. The pitch counters 52 form part of the control system 23 which also includes label counters 50 and label gap counters 51. The label counters 50 produce a count indicative of the length of labels which pass the label sensor 13 and the gap counter produces a count indicative of the length of gap between respective labels. Each respective count in the label and gap counters are added together in any suitable manner to produce a count indicative of the pitch of each label and this count is stored in the pitch counters 52. The number of pitch counters 52 included in control system 23 is determined by the label pitch and a value stored in a preset label delay 57 which is used to predetermine a datum position on the label for use in the application procedure.

[0023] On a rising edge 28 of the output signal 21 from the sensor 13, which indicates the presence of a leading edge of a label, the count in the label counter 50 and gap counter 51 respectively are added together as mentioned above and the added count is transferred to a pitch counter 52. It is envisaged that the label counter 50 and gap counters 51 form respective shift registers and, in this case, when the respective counts therein have been added and transferred to a pitch counter 52, the respective stored counts are shifted down one place in each register. Subsequent control pulses from the control 23 increment the label counter 50. On the falling edge 29 of the label sensor output signal 21, which indicates the presence of the trailing edge of the label, incrementing of the label counter 50 is ceased and a counter selector 59 causes actuation of the gap counter 51 so that this counter is now incremented by the control pulses. It will be seen that since the pitch counters 52 are loaded with counts equating to the pitch of each label, variations in label pitch or length are compensated for. It will also be apparent that should a label be missing from the web, the count on the gap counter 51 will be disproportionate to an expected value and thus the control system can act to compensate therefor by feeding a sufficient number of control pulses to bring the next label to the correct position ready for application.

[0024] Application of the label is effected as follows.

[0025] A shaft encoder 61 is linked to a conveyor in such a manner that each pulse from the encoder 61 reflects a proportional movement of the conveyor and hence product 16. The encoder 61 is linked to the control system 23 in such a manner that each pulse can be monitored by the system 23 and any necessary action can be taken to compensate for irregularities in product travel in a manner to be described hereinafter.

[0026] An application sequence will now be described. A product delay 60 stores a predetermined count equivalent to the number of encoder pulses required to move the product 16 the distance between the product sensor 17 and the beak 18. As a product 16 is detected by product sensor 17 the control 23 loads the count stored in product delay 60 into a temporary counter 62. Subsequent encoder pulses decrement the temporary counter 62 until the product sensor 17 detects the trailing edge of the product 16. The count stored in the temporary counter 62 is now divided in a divider 64 by a constant value which is related to the chosen datum on the product 16 and hence the divided count represents the exact number of encoder pulses required to provide the datum position on the product to the beak end 18. This value is then transferred into a respective application counter 65. The exact number of application counters 65 necessary will be dependent upon the product length and pitch and the counts stored therein are shifted down the counters 65 as each label application onto a product is completed. Each application counter 65 is decremented by every pulse from the encoder 61 and thus each product will be controlled by control 23 as it moves from the product sensor 17 to the beak end 18.

[0027] To enable the datum position on the label 12 to be applied in a relative disposition to the datum on the product 16, the respective label counter 50 is divided by at divider 58 a constant value 58 which is related to the chosen datum on the label 12, as mentioned above. The divided count is then converted to be equivalent to the number of encoder pulses 66 and this count is then subtracted from the next to be used application counter 65. Encoder pulses continue to decrement the next to be used application counter 65 until a count of zero is reached. Once a count of zero is reached, the stepper motor 22 will be enabled causing label movement via motor control 53 and therefore in this way, as will be described in more detail below, the respective label 12 will be applied such that the chosen datum position on the label 12 is applied relative to the chosen datum position of the product 16. The stepper motor is driven by motor drive 53 until the relevant pitch counter 52, which is decremented via link 100, reaches zero, at which point the motor 22 is stopped and the label will have been applied.

[0028] Referring now to Fig. 5, there is shown a typical mode of operation of a system of the abovementioned type in which the chosen datum position on the label and product are their respective centres and thus the centre of the label is to be applied at the centre of the product. In this example, labels are 18 control pulses long, gap length is equal to 2 control pulses and the preset label delay 57 is set to 73 control pulses. The next label to be applied to a product will be that indicated as 1, the corresponding pitch counter value is stored as 20 control pulses. The product delay 60 is set to 200 which is effectively twice the actual number of encoder pulses needed for the product to move from product sensor to beak, and product length is equal to 80 encoder pulses.

[0029] When product sensor 17 detects a product, the count stored in the product delay 60 is loaded into temporary counter 62 and subsequent encoder pulses decrement temporary counter 62 until the trailing edge of the product is detected. In this example, at this stage, the count remaining in the temporary counter 62 will be 120. To enable the product centre datum to be determined the constant value in divider 64 will be 2 in this example, hence the value transferred to application counter 65 will be 60. Hence it will be apparent that this count corresponds to the exact distance, represented by a number of encoder pulses, between the centre of the product and the beak 18. As the product 17 approaches the beak 18, each encoder pulse decrements the count in the application counter 65. Once again, in this example a value of 2 will be assigned to the constant in divider 58 and thus the count corresponding to the next to be applied label which is stored in LC4 within the label counters 50 is divided by two. Therefore LC4, which stores a count of 18 will become 9. This divided count is converted into encoder pulses at converter 66 and application counter 65 will be further decremented by a converted label count stored in a counter 66. When the application counter 65 reaches a count of zero, a signal from the control system 23 initiates label application. In this example 20 pulses via the motor drive 53 will be fed to the stepper motor 22 thereby causing the centre of label 1 to be applied to the centre of the product.

[0030] It will be apparent that this system is able to compensate for any variation in either product or label size in such a way as to maintain chosen datum position accuracy.

[0031] To ensure that a label is applied to the product 17 at a speed substantially equal to that of the product 17, the pitch counter count next to used for application is divided into two parts, an acceleration count stored at counter 54 and a deceleration count stored in counter 55. Therefore in this example both accelertion and deceleration counters 54, 55 will store a count of 10 control pulses. As previously described, when a signal via product sensor 17 causes label application to commence, the control system 23 will feed 20 pulses to the stepper motor 22. If the stepper motor 22 has not reached a speed substantially equal to that of the product 16 by the time the number of pulses stored as a count at 54 is reached, then it will be seen that insufficient time to decelerate the stepper motor will remain and an error signal will be raised. If the stepper motor 22 causes the label web to be accelerated to a speed substantially equal to product speed in a count of less than 10 pulses, then the same count is transferred to the deceleration counter 55. In order to compensate for this variation a count equal to twice this is then subtracted from the count stored in the pitch counter 52. The difference between these two counts represents the number of pulses applied via motor drive 53 to the stepper motor 22 before deceleration of the motor will be caused.

[0032] The control system 23 is further capable of compensating for speed variations of the products 16 via a speed compensation device 70. Product speed is measured by the frequency of encoder 61 pulses detected by a speed measurement device 71. The speed detected by the device 71 is then transferred to speed compensation device 70 which is operable to calculate the appropriate compensation value of count to be added or deducted from the next to be used application counter 65 to ensure consistent label 12 placement on product 16 with the chosen datums thereon in the desired predetermined relationship relative to each other.

[0033] It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

[0034] Thus for example the control system 23 can further include devices 72, 73 to allow compensation of inherent response delays associated with the label and product sensors 13 and 17 respectively. Thus a product delay compensate device 72 is operable to introduce a corrective count into the control system 23 to correct response delay in the product sensor 17. The corrective count is converted to encoder control pulses in the convertor 73 and is fed to the application counter 65. The corrective count is subtracted from the count stored in the counter 65. Similarly a label delay compensation device 74 and associated convertor 75 can be provided to compensate for response delay in the label sensor 13.

Claims

1. A control system for labelling apparatus comprising means to monitor product movement and to cause movement of a label carrying web in accordance therewith, label sensor means to detect labels on said web and to produce an output signal corresponding thereto and means to identify a datum position on each said label and each said product, said product monitoring means and said label sensing means being linked in such a manner as to permit said label to be positioned whereby said datum position on said label is in predetermined disposition relative to said datum position on said product for application thereto, said label datum position being disposed between front and rear edges of said label.

2. A control system according to claim 1 wherein said label datum position is disposed substantially at the centre of each label.

3. A control system according to claim 2 wherein said product datum position is disposed substantially at the centre of an outer surface of a peripheral face of said product.

4. A control system according to any one of claims 1 to 3 wherein said product monitoring means comprises a sensor to detect movement of a product therepast.

5. A control system according to claim 4 wherein said sensor comprises an optical sensor.

6. A control system according to any one of claims 1 to 5 wherein said sensor is operable to initiate drive means, which drive means accelerates said label carrying web to a speed substantially equal to that of the product.

7. A control system according to claim 6 wherein the period of time for which said drive means is initiated by said sensor to accelerate said web is variable.

8. A control system for a labelling machine comprising means to monitor product movement and to cause movement of a label carrying web in accordance therewith and label sensor means to detect labels on said web and to produce an output signal corresponding thereto, said label sensor means and said product monitoring means being linked in such a manner as to permit said label to be positioned for accurate application to said product, said system further including means adapted to accelerate said label carrying web and means to vary an initiation time for the acceleration of said label carrying web whereby label carrying web and product speed can be arranged to be substantially equal on application irrespective of variation in label or product speed or spacing.

9. A control system according to claim 8 wherein said means to vary the initiation time for acceleration is further operable to vary an initiation time for a deceleration of the web.

10. A control system according to claim 9 wherein said means for varying the initiation time comprises means for delaying the initiation of the acceleration of the web.

11. A control system according to claim 1 or claim 8 wherein said system includes means to compensate for inherent time delay in detection in said product monitoring means and said label sensor means.

12. Labelling apparatus incorporating a control system according to any preceding claim.

Drawing