Labelling Machine With Pneumatic Monitor

Abstract

A high speed labelling machine which picks up and lays down labels by means of an "apertured" pressure-and-vacuum head includes a monitoring system for assuring against faulty labelling. The monitoring system employs a pressure switch -- rather than a vacuum switch -- to check for vacuum during the monitoring operation. Use of a pressure switch as a vacuum detector is made possible by means of a chamber connected to the head, and to which an auxiliary internal pressure is applied ... the pressure switch being also connected to the chamber.

Description

BACKGROUND OF THE INVENTION

Machines which are used to apply labels or the like to packages or cartons are often used in high speed operations having a high volume of production. These machines often have a movable applicator head which picks up, prepares, then applies a label to a carton or package. One way to pick up a label and hold it is by means of a hollow "apertured" applicator head to which a vacuum is applied. As a label is moved beneath the head, suction from the vacuum causes the label to be drawn up against the head, covering the apertures. This blocking of incoming air allows a partial vacuum to be achieved in the applicator head. The label may then be moistened or heated while the head is moved into a position for application of the captive label to a package. When the head and label are in contact with the package, the vacuum is turned off and, simultaneously, a high pressure is introduced into the head, and the label is blown firmly against the package.

In order to maintain realistic quality control levels and to prevent a large number of rejects, the performance of the aforesaid machine must be continuously monitored. Because machines of this type operate at high speeds and have a large volume of production, monitoring of the label application operation must occur almost at the instant a label is applied to a package. If the monitoring apparatus were employed later, by the time a malfunction was detected and an alarm activated, too great a number of defectively labelled packages would have been produced.

A method of detecting the presence of a label in position on the applicator head is by sensing whether a vacuum has been achieved inside the head. This is most easily done by connecting a vacuum sensing switch to either the head or to the conduit connecting the head and the pressure sources.

Vacuum sensing switches are theoretically ideal for this application, but in practice their use has often presented problems. One such problem is the high degree of sensitivity that is necessary to detect a slight drop in pressure. A label in the correct position on the head will cause only a slight drop from the low pressure created by the suction when no label is on the head. Such sensitivity problems are further compounded when a label being held by a head is slightly askew, so that not all the suction holes are covered, thus causing an even smaller decrease in pressure to be detected. Vacuum sensors which can detect small changes in pressure are notoriously difficult to calibrate and adjust, and tend to be rather costly.

The type of machine on which such vacuum sensors are desired to be used also presents a problem: in the normal course of production, these machines may be required to use labels having different sizes and shapes without changing the applicator head; such different labels will present not only different, but also smaller, pressure increments that must be detected. Detection of such small and varied increments requires either substitution of a different vacuum sensor or the recalibration of the existing one. Both of the above solutions require the machine to be shut down for a period, causing a loss of production which is highly undesirable.

Another problem stemming from the use of vacuum sensing switches is their relatively slow response time; that is, the total time it takes to sense a variation in pressure plus the time it takes for the switch to change states.

As already mentioned, machinery of this type operates at high speeds and can be made to operate so fast that the slow response time of the vacuum switch is the limiting factor which prevents further increases in operating speed.

These problems associated with vacuum switches have been tolerated in the past as inherent system limitations. However, the search for a more reliable, faster operating vacuum switch has been an ongoing project.

SUMMARY OF THE INVENTION

To eliminate the aforesaid problems that have become associated with vacuum sensing switches, the invention proposes the use of a common pressure-sensing switch in combination with an external air pressure supply and a specially designed pressure chamber, thereby to remove the troublesome vacuum switch from the system.

Were a pressure-sensing switch to be used as a direct substitution for a vacuum switch, it would serve only to indicate an increase in air pressure. However, in a labelling machine of the indicated type, the absence of high pressure does not indicate the presence of a vacuum (i.e., a label in position) ... hence, such direct substitution will not supply all the desired information in regard to system performance.

The use of pressure sensing switches immediately overcomes one of the drawbacks associated with vacuum switches: i.e., response time. Pressure switches normally have a much faster response time than vacuum switches. One reason for this is that a measureable change in a relatively high pressure represents, for example, at least one pound per square inch, while a measureable change in a relatively low pressure (vacuum) represents a change of less than one-half pound per square inch. More force on the diaphragm of a pressure sensing device will allow the diaphragm to have greater travel and will permit faster switch actuation.

Use of the invention also eliminates difficulties caused by different size labels. The external air supply to the pressure chamber is adjustable, and since such air supply controls the level at which the pressure switch changes state, i.e., goes from on to off, the system of the invention can easily be made to recognize pressure changes caused by any size label. Such adjustments may be made almost instantly by setting the external pressure to a predetermined level, thereby obviating the necessity for any machine shutdown.

The specially shaped chamber is provided with a small orifice at the connection with the conduit leading to the applicator head, thus effectively isolating the sensing apparatus from the main system and preventing such apparatus from loading the system.

By allowing the external air pressure to remain on always to pressure the chamber, the pressure switch tends to be actuated at all times, air passing out of the chamber being expelled from the applicator head apertures. Because of the small orifice at the point where the chamber joins the indicated conduit, when the high pressure air is applied to the head, most of it will not enter the chamber but will be expelled from the applicator head. When the vacuum is applied, air is both drawn in through the holes in the applicator head and removed from the chamber through the small-sized orifice. By providing the correct size for such orifice, and by adjusting the external air pressure being fed into the chamber, the pressure switch can be made to change states only when the vacuum is on and a label is affixed over the apertures in the applicator head. Another orifice is also provided in the chamber to act as a pressure relief, since the chamber is alternately pressurized and evacuated. Means are also providing for producing an alarm signal and/or stopping the machine when a nonconformance condition is detected, e.g., when a label is stuck to the head when it should have been applied to a package.

To illustrate the advantages of the invention, it is shown and discussed as means for improving an existing machine, but it should be understood that the invention is not limited to this type of application. The invention provides apparatus whereby a sensitive pressure switch is adapted to perform, with greater sensitivity than the function of a vacuum switch.

The invention will be described with reference to the figures, wherein:

FIG. 1 is a schematic block diagram illustrating apparatus embodying the invention, and

FIG. 2 illustrates waveforms useful in describing the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a web of material 21 having labels printed thereon is caused to move by means of a drive roller 22; as the web moves, a photoelectric cell 23 senses the discrete labels of the web. The output signal from the photoelectric cell is used to synchronize the cutting of the web 21 into detached labels, such cutting being accomplished by a chopper 25. After being separated from the web 21, an individual label 24 may be moved to the position of an applicator head 26 by any suitable means such as rollers or the like.

It should be noted that means for providing the correct sequence of machine operations is shown as a controller 27; and such controller may be in the form of a common timing sequencer consisting of rotating cams and switches, or it might be an electronic timer with no moving parts.

Since an objective of the invention is to detect the presence of a label on the applicator head 26 at the earliest possible time, when the machine is first started, an adjustable air pressure supply 30 connected to a chamber 31 is turned ON. The chamber 31 is connected to a standard pressure sensitive switch assembly 32 having a displaceable diaphragm 33 which operates a switch 34. Such switch 34 is electrically connected to logic 35 for indicating the state of the switch assembly 32 The logic 35, depending on the operation of the switch 34, operates an alarm 36 and a "machine stop" command signal line 37. The chamber 31 is connected via a suitably small orifice 42 to a main conduit 38 which runs to the applicator head 26. The adjustable air pressure 30, when ON, causes the pressure inside the chamber 31 to be sufficiently high to cause the diaphragm 33 to displace and place the arm of the switch 34 in contact with a contact 1. This may or may not indicate a malfunction, depending on the state of the alarm logic 35 and the controller 27.

As the cut label 24 moves into position with respect to the applicator head 26, a suction is applied to the head through the main conduit 38 by actuation of a solenoid valve 28 which is connected between the main conduit 38 and a vacuum source 40. Upon applying the vacuum, air is sucked in through holes 41 in the applicator head 26; and the pressure inside the main conduit 38 is lowered. The chamber 31 also tends to be evacuated, causing its pressure to be lowered accordingly. Because of the size of the orifice 42 and the amount of air being supplied by the adjustable pressure supply 30, the low pressure caused by the vacuum source 40 is not sufficient to overcome the higher pressure being supplied to the chamber. This is a key feature of the invention. After the label 24 has moved into position, the holes 41 in the applicator head will be covered and the pressure inside the head 26 and the main conduit 38 will drop even lower; and as this pressure drops, it tends to overcome the high pressure in the chamber 31, creating a partial vacuum and causing the diaphragm 33 to relax, thereby placing the arm of the switch 34 in contact with a contact 2. This indicates the presence of a relative vacuum at the head 26 and hence the presence of a label. If a sequencing controller 27 has signalled the alarm logic 35 that a label is required to be on the head at this time (Test 1), then the switch 34 is in its correct state and no malfunction condition will be indicated. If a label is not in the required position, the suction created by vacuum source 40 will not be sufficient to overcome the pressure in the chamber 31; the diaphragm 33 will not relax; and the switch 34 will not be in the correct state, when compared with the signal from the alarm logic 35. This will indicate a malfunction and the machine will be commanded to stop.

The operation thus having passed its first test successfully, i.e., a label 24 is present at the correct point in the cycle, the label 24 is heated to allow it to adhere to a carton or package 45 which is being positioned for labelling by a conveyor belt 50. Label heating is accomplished by heater wires 44 located inside the applicator head 26, the temperature being controlled by a suitable heater control 43. As the label is being heated, the applicator head 26 is lowered towards the package 45 by suitable means 52. At the instant that the applicator head 26 contacts the package, the vacuum holding the label to the head is removed by closing the solenoid valve 28 and, at substantially the same time, applying a high pressure to the applicator head by turning (opening) a solenoid valve 29. The solenoid valve 29 is connected by a suitable conduit between a high pressure air supply 60 and the main conduit 38.

When high pressure air is applied to the head 26, the label 24 is forced away from the head and into contact with the package 45, to which it becomes firmly affixed, by the high pressure air being expelled from the holes 41 in the applicator head. The high pressure is then removed from the head 26 by closing the solenoid valve 29, and suction is then applied again to the applicator head by opening the solenoid valve 28. A signal from the sequence controller 27 to the applicator head actuator 52 causes it to begin to reposition the head 26 to receive the next label from the chopper 25.

Since an objective of the invention is to prevent the production of packages without labels, the applicator is checked (Test 2) to determine that the label 24 is, in fact, gone, i.e., applied to a package 45: Suction having been applied to the head 26, air enters the holes 41 and causes the pressure in the main conduit 38 to drop, but not sufficiently to overcome the relatively high pressure in the chamber 31 caused by the pressure supply 30. The pressure in the chamber 31 causes the diaphragm 33 to be displaced, and causes the arm of the switch 34 to come into contact with the contact 1, thereby indicating at this time, per the alarm logic 35, the correct state for the head 26, i.e., no label present. Were a label to be stuck on the applicator head 26, however, a vacuum would exist sufficient to cause the pressure in the chamber 31 to be overcome and to cause the arm of the switch 34 to be in contact with contact 2, whereby the alarm logic 35 would cause a malfunction to be indicated and the machine stopped.

In regard to FIG. 2, the relative states of the two solenoids 28 and 29 are shown in chart A as they are energized and de-energized through one cycle of the labelling machine. At the point indicated where neither solenoid is energized, a label is being positioned beneath the holes in the applicator head 26. The vacuum is then turned ON and the label is captured by the head. When the label is seized by the applicator head, the head is caused to move downward toward the package to be labelled, as indicated by waveform B, FIG. 2. At this time it is desired to test for the presence of a label (Test 1).

Test 1 having been successfully passed, the label is applied to the package by turning OFF the vacuum and turning ON the pressure as shown by waveform A of FIG. 2. After the label is applied to the package, the head is returned upward to its up position. At this time, the head is checked (Test 2) to determine if the label has indeed been applied.

If the label has been applied, the vacuum (applied during Test 2) in the line 38 is insufficient to overcome the pressure of the supply 30, causing operation of the alarm 36 as described above. But assuming that Test 2 is completed without alarm, the vacuum is turned OFF, and the next label moved into position beneath the applicator head; the vacuum being thereafter again applied, causing the pressure-vacuum cycle to begin anew.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

We claim:

1. An apparatus for handling label-like elements, comprising:

a hollow applicator head having at least one external aperture into the hollow thereof,

means for selectively applying vacuum and pressure to said head,

means for positioning an element to be handled so that it covers said aperture, whereby the element may be picked up and laid down by said head,

a pressurized chamber pneumatically connected continuously to said head through an orifice of selected size, and

a pressure switch pneumatically connected to said chamber for indicating pressure changes in said chamber resulting from applying said vacuum to said head.

2. The apparatus of claim 1 further comprising means responsive to a position of said pressure switch for generating a signal indicating a malfunction of said apparatus.

3. The apparatus of claim 2 further comprising means responsive to said signal for interrupting the operation of said apparatus.

4. The apparatus of claim 1 further comprising means for maintaining the pressure of said chamber within selected limits,

wherein the size of said orifice is such that said pressure in said chamber decreases to a level sufficient to operate said pressure switch only when the said element completely covers said aperture or apertures in said applicator head.