GB2586834A

GB2586834A - A mechanism for detecting failed prints

Info

Publication number: GB2586834A
Application number: GB1912758.8A
Authority: GB
Inventors: Cupit James
Original assignee: Dover Europe SARL
Current assignee: Dover Europe SARL
Priority date: 2019-09-05
Filing date: 2019-09-05
Publication date: 2021-03-10
Also published as: GB201912758D0

Abstract

A printer 10 includes a printhead 12 for transferring ink from a tape 22 to a substrate, and a tension control device. A method includes monitoring a characteristic indicative of tension in a tape carried in a tape path and using information about the characteristic of the tension to determine if the printer has failed to carry out a printing operation. The tension control device may include a tension correcting device 30, and the method may include determining that the tension correcting device has failed to move in an expected manner. The failure to move in an expected manner may indicate that the printhead has failed to move in an expected manner and has failed to perform the printing operation. There is also provided a printer including a printhead which is moveable between a non-printing position and a printing position to perform a printing operation and a mechanism for detecting a failed printing operation. The mechanism for detecting a failed printing operation includes a sensor which is operable to monitor a characteristic indicative of tension in a tape. The sensor may be a magnetic sensor. The tension correcting device may be a moveable tape guide member or a dancing arm.

Description

Title: Printing apparatus and method of operation

Description of Invention

The present invention relates to a printing apparatus and a method of operating a printing apparatus, in particular to a printing apparatus which includes a mechanism for detecting a failed printing operation.

It has long been known to provide printing apparatus which include tape drives incorporating two spool supports, one of which supports a supply spool on which unused tape is initially wound, and the other of which supports a take up spool, onto which the tape is wound after it has been used. Tape extends between the spools in a tape path. Each of the spool supports, and hence each of the spools of tape is typically drivable by a respective motor. In such a printing apparatus the tape is an inked ribbon which is moved past a printhead to enable a printing operation to be carried out, to transfer ink from the tape to a substrate (or a part of a substrate) which is positioned adjacent the printhead. The printhead is moveable by a printhead drive mechanism between a non-printing position and a printing position in which it is in contact with the tape, and forces the tape into contact with the substrate to effect the printing operation. The printhead typically repeatedly moves between the non-printing position and the printing position to carry out successive printing operations.

It is advantageous to be able to identify if the printhead drive mechanism has failed, and hence if the printhead has failed to carry out a printing operation.

Known methods of identifying a failure of the printhead drive mechanism include providing an air pressure sensor. A failure in the air supply to a pneumatic printhead drive mechanism is detectable by using a sensor which is fitted in the air supply to the printing apparatus. An output of such a sensor can be mapped to an electrical input to a controller of the printing apparatus, such that when such an electrical input is received, the controller detects that there is a fault. A disadvantage of such a system is that the provision of such a system incurs an additional cost and increased installation time. Furthermore, such a system is unable to detect any other types of failure inside the printing apparatus, for example a leakage or blockage which prevents air flow to the printhead drive mechanism.

So-called 'mark-and-read' systems are also known in the art. Such systems optically scan the substrate after a printing operation should have taken place, and provide a fault indication if the expected marks are not present on the substrate. Again, such systems are seldom installed owing to prohibitive cost and the time taken for installation.

It is also known to use optical sensors to examine used tape to detect whether ink has been removed, and hence whether a printing operation has been carried out. The inclusion of such sensors increases the cost of the printing apparatus.

It is desirable to provide a means of detecting a failure to carry out a printing operation which overcomes some or all of the above disadvantages.

There is provided a method of operating a printing apparatus including a printhead for transferring ink from a tape to a substrate, and a tension control device, the method including monitoring a characteristic indicative of tension in a tape carried in a tape path, and using information about the characteristic of the tension to determine if the printing apparatus has failed to carry out a printing operation.

The tension control device may include a tension correcting device, and the method may include determining that the tension correcting device has failed to move in an expected manner.

Determining that the tension correcting device has failed to move in an expected manner may indicate that the printhead has failed to move in an expected manner, and has failed to carry out the printing operation.

The method may include monitoring at least one of the movement and the position of the tension correcting device.

The characteristic of the tension in the tape may be monitored during an assessment period.

The assessment period may coincide with an initial phase of the printing operation during which the printhead is expected to move between a non-printing position and a printing position.

The tension correcting device may be operable to maintain a substantially constant path length of the tape, and during a printing operation is expected to move to counteract an increase in the path length which is caused by the movement of a printhead of the printing apparatus into a print position, the method including determining that the tension correcting device has failed to move in the expected manner thus indicating that the printhead has failed to move, and therefore that the printing apparatus has failed to carry out the printing operation.

The method may include determining that the printing apparatus has failed to carry out the printing operation when the tension correcting device moves less 30 than a predetermined distance during the assessment period.

The method may include providing a signal when it is determined that the printing apparatus has failed to carry out a printing operation.

There is provided a printing apparatus including a printhead which is moveable between a non-printing position and a printing position to perform a printing operation, a tape drive for moving an inked tape in a tape path past the printhead, and a mechanism for detecting a failed printing operation, wherein the mechanism for detecting a failed printing operation includes a sensor which is operable to monitor a characteristic indicative of tension in a tape in the tape path and a controller which is operable to compare an actual characteristic indicative of tension in the tape in the tape path monitored during an assessment period with an expected characteristic indicative of tension, and in the event that the actual characteristic of tension in the tape differs from the expected characteristic of tension in the tape, the controller is operable to indicate that a printing operation has not been completed as expected.

The mechanism for detecting a failed printing operation may include a tension correcting device which is operable to maintain tension in the tape in an acceptable range and to counteract a change in the length of the tape path caused by the movement of the printhead between the non-printing position and the printing position, by moving in an expected manner each time the printhead moves between the non-printing position and the printing position, wherein the characteristic indicative of tension monitored by the sensor is movement of the tension correcting device.

The sensor may be a magnetic sensor.

The tension correcting device may be a moveable tape guide member.

The tension correction device may be a dancing arm.

The printing apparatus may be a thermal transfer printing apparatus.

Embodiments of the invention will now be described, by way of example only, and with reference to the accompanying drawings, of which: FIGURE 1 is an illustrative view of a part of a printing apparatus, showing a printhead in a non-printing position, a tape and a tape tension control device; FIGURE 2 is an illustrative view depicting two different positions of a part of the tape tension control device of Figure 1; FIGURE 3 is an illustrative side view of a part of a tension control device; FIGURE 4 is an illustrative side view of a part of an alternative arrangement of a tension control device; FIGURE 5 shows a comparison between a trace indicative of a printhead movement command and a trace indicative of a characteristic of a tension control device, when the printing apparatus is functional; and FIGURE 6 shows a comparison between a trace indicative of a printhead movement command and a trace indicative of a characteristic of a tension control device, when the printing apparatus is not functioning as expected.

Referring to Figure 1, there is shown a part of a printing apparatus 10 which includes a printhead 12, a first spool support 14 and a second spool support 16. Each spool support 14, 16 is drivable by a respective motor 19, 21. A spool 18, 20 of tape 22 is mountable on each of the first and second spool supports 14, 16. The tape 22 extends in a tape path between the spool supports 14, 16, and past the printhead 12, the tape path being defined, at least in part, by guide members 30, 31. It will be appreciated that any suitable number of guide members 30, 31 may be provided to maintain the tape 22 in an appropriate tape path. The printing apparatus 10 also includes a substrate roller 32 which supports a substrate adjacent the printhead 12. The substrate roller 32 may alternatively be a platen.

The printhead 12 is moveable between a non-printing position (as shown in Figure 1) and a printing position in which the printhead 12 urges a part of the tape 22 towards the substrate supported by the substrate roller 32. The printing apparatus includes a printhead drive mechanism 13, which effects movement of the printhead 12 between the non-printing position and the printing position. The printhead drive mechanism 13 may be of any suitable type, for example a pneumatic drive mechanism.

The tape 22 is very thin and it is important to ensure that the tension in the tape 22 extending between the two spools 18, 20 is maintained within an acceptable range, for example between approximately 1N and approximately 5N, and preferably approximately 3N. Too much tension in the tape 22 is likely to lead to the tape being deformed or broken, whilst too little tension will inhibit the correct operation of the device. In a printing apparatus, a slack tape can affect print quality.

The printing apparatus 10 includes a tension control device. The tension control device may include a tension monitoring device and/or a tension correcting device. The printing apparatus may include a sensor which monitors a characteristic which is indicative of tension in the tape. In embodiments, such a sensor may be a part of the tension control device.

In embodiments, tension control device may include a moveable guide member 30 which acts as a 'dancing arm' as is known in the art of controlling tension in such printing apparatus. The guide member 30 is moveable back and forth, as illustrated by the double headed arrow A, to adjust, e.g. correct, the length of the tape path between the spools 18, 20, so as to maintain the length of the tape path substantially constant The moveable guide member 30 may be a tension correcting device.

The printing apparatus 10 may include a sensor 34, which is operable to detect one or more characteristics of the tension correcting device. The or each characteristic may be indicative of tension in the tape 22. The sensor 34 is preferably operable to detect one or more of position and movement, for example displacement and/or speed of a part of the tension correcting device. The printing apparatus 10 also includes a controller 36 which may be operable to receive information from the sensor 34 relating to a characteristic of the tension correcting device, for example the position and/or movement of a part of the tension correcting device, for example the moveable guide member 30, and to monitor such information. The sensor 34 may be one of a position, proximity and displacement sensor 34a, and may be a Hall Effect sensor or other type of magnetic sensor, but may be any other suitable type of sensor, for example an optical sensor. It will be appreciated that any appropriate number of sensors may be included in the printing apparatus, each of which may be communicable with the controller 36.

In embodiments of the invention, a part of the tension correcting device, for example the moveable guide member 30, may include a magnet, and the sensor 34 is located in the printing apparatus 10 in a position where it is able to detect the position and/or movement of the magnet, and hence the position and/or movement of the part of the tension correcting device carrying the magnet, for example the moveable guide member 30. The sensor 34 may be operable to provide an analogue signal to the controller 36, however it will be appreciated that the sensor 34 may provide an alternative type of signal to the controller 36, for example a digital signal. It will be appreciated that an appropriate number and arrangement of magnets may be selected. Furthermore, the or each magnet will be of an appropriate type.

An arrangement of a tension control device including the above features is 30 shown in Figure 3.

The moveable guide member 30 is moveable relative to a printer housing or body 50. The moveable guide member 30 may be moveable linearly, substantially in the directions of the double headed arrow A. The moveable guide member 30 may be carried slidably relative to the printer housing 50 and/or a cassette 52 which is removable from the housing 50. The moveable guide member 30 may be moveable along a track member 54.

A part of the moveable guide member 30, for example an end of the moveable guide member 30, is connected to a pivotable arm 42. The pivotable arm 42 is pivotable about a fulcrum 44. A resilient member 46 may also be connected to the pivotable arm 42. The resilient member 46 may be a spring, for example a coil spring. The resilient member 46 may be connected to the pivotable arm 42 on the opposite side of the fulcrum 44 from the connection to the moveable guide member 30. An end of the resilient member 46 which is not connected to the pivotable arm 42 may be anchored, for example to the printer housing 50. The sensor 34 may be positioned near to the pivotable arm 42 to be able to detect movement and/or position of the pivotable arm 42, which is indicative of movement of the moveable guide member 30.

In embodiments, the tension control device may include tension monitoring device. The tension monitoring device may include a sensor 34 which is operable to detect a force applied to a part of the tension control device. For example, the sensor 34 may be a load cell 34b which is operable to detect the force applied to a part of the tension control device, for example a guide member 31. In such an embodiment, the guide member 31 may move in response to a fluctuation in tension, but its purpose is not necessarily to maintain the length of tape in the tape path. The force detected by the sensor 34 may be indicative of tension in the tape 22. An example of such an arrangement is shown in Figure 4. The guide member 31 may be moveable relative to a printer housing or body 50. The guide member 31 may be moveable linearly, substantially in the directions of the double headed arrow A. The guide member 31 may be carried slidably relative to the printer housing 50 and/or a cassette 52 which is removable from the housing 50. The guide member 31 may be moveable along a track member 54. The amount of movement experienced by the guide member 31 in response to a fluctuation in tension may be small, for example less than 1mm. The sensor 34 may be arranged to make a direct measurement of a force or forces experienced by a part of the guide member 31. The sensor 34 may be positioned near to an end of the guide member 31.

It will be understood that the tension monitoring device may be utilised in a printing apparatus which does not include a moveable guide member 30. The tension monitoring device may monitor a characteristic which is indicative of tension which is experienced by a substantially stationary part of the printing apparatus in the tape path.

The printing apparatus 10 includes a mechanism for detecting a failed printing operation 40. The mechanism for detecting a failed printing operation 40 may include the tension control device which may include a tension correcting device and/or a tension monitoring device.

In use, the controller 36 (or another controller, if appropriate) directs the printhead 12 to carry out one or more printing operations, and controls the printhead drive mechanism 13 to move the printhead into the printing position to carry out the or each printing operation and into the non-printing position after the or each printing operation. Moving the printhead 12 into the printing position causes the printhead 12 to move the tape 22 towards the substrate and the roller 32, which increases the length of the tape path. In order to counteract the increase in the path length, the tape tension correcting device, e.g. moveable guide member 30, moves, to correct the length of the tape path.

The tension correcting device 30 moves through a distance which corresponds to the distance moved by the printhead 12 between the non-printing position and the printing position.

The sensor 34 detects the movement of the tension correcting device 30, and provides a signal, for example an analogue signal corresponding to the movement, to the controller 36. The controller expects the printhead 12 to move, in order to carry out the or each printing operation, and therefore expects that the tension control device 30 will carry out an expected, associated movement to counteract the change in the tape path length caused by the movement of the printhead 12.

By monitoring the characteristic indicative of tension, for example the position and/or the movement of the tension correcting device 30, through at least a part of the duration of each printing operation, it is possible to determine whether the printhead 12 has moved and whether or not a printing operation has taken place. In particular, monitoring the characteristic indicative of tension in an initial phase of each printing operation, i.e. during the time when the printhead 12 should move into the printing position, i.e. towards the tape 22, means that if the characteristic indicative of tension, for example the position and/or movement of the tension correcting device is not as expected to counteract the movement of the printhead 12 into the printing position, then it can be determined that the printhead 12 did not carry out its own expected movement, or did not complete its expected movement, and therefore that the printing operation has not been completed. If, for example, it is determined that the tension correcting device 30 has not moved in the expected manner to counteract the planned movement of the printhead 12 which would be necessary for the printhead 12 to come into contact with the tape 22 (i.e. the movement of the printhead 12 from the non-printing position to the printing position), then this could mean that that the printhead 12 has not moved at all, or that the movement was insufficient to reach the printing position. In either situation, this is an indication that the printhead drive mechanism 13 has failed.

It will be appreciated that the sensor 34 may indicate to the controller that a degree of movement of the tension correcting device has taken place, but if the amount of movement is below an expected threshold, then the controller 36 will determine that the printhead 12 has failed to move and that the printing operation has not been carried out. Where the tension control device includes a tension monitoring device, the characteristic indicative of tension may be a measurement of the force exerted on the guide member 30. If the actual value of tension at a given time is not within a predetermined range of an expected value, then the controller 36 will determine that the printhead has failed to move sufficiently and that the printing operation has not been carried out.

The tension correcting device may move to correct changes in path length which accrue owing to the winding and unwinding of the spools 18, 20, however such movements are likely to be small compared to the movement required to counteract the movement of the printhead 12. Also, such changes in tape path length are typically accrued over a relatively long period of time, compared to the rapid change which is caused by the movement of the printhead 12 into the printing position, and can therefore be discounted when determining whether the printhead 12 has carried out its expected movement.

Therefore, a minimum amount of movement can be predetermined, below which it is determined that the printhead 12 has failed to move.

The characteristic indicative of tension is monitored during an assessment period, which corresponds with an initial phase of the or each printing operation, for example during the time period when the printhead 12 should move into the printing position in order to contact the tape 22. During this period, the position and/or movement of the tension correcting device, in an arrangement which includes a tension correcting device, can be assumed to be solely influenced by the need to counteract the movement of the printhead 12, since the system is considered to be stable with respect to previous tension adjustments which have been made. To this end, a short latent period may be imposed between printing operations, to ensure that the tension correcting device is stable.

Following the initial phase, and hence the assessment period, the tension correcting device 30 is expected to carry out additional tension corrections, for example to counteract disruption or disturbances, for example a braking effect caused by the printhead 12 on the substrate roller 32. Such tension correction movements can be disregarded for the purposes of determining whether the printhead 12 has moved into the printing position, as they fall outside the assessment period. The assessment period may in the order of 10-30 milliseconds (ms), and may be approximately 20 milliseconds. The duration of the assessment period may depend upon the operational speed of the printing apparatus, and hence the time taken for the printhead 12 to move into the printing position. The duration of the assessment period can be determined taking into account the other effects on the movement of the tension correcting device 30, which need to be disregarded for the purposes of determining whether the printhead 12 has moved into the printing position. The measurement values of the characteristic indicative of tension may be averaged over the assessment period or over a portion of the assessment period. This assists in neglecting aberrations in the characteristic, for example "spikes" in the measurement of the characteristic having a very short duration relative to the assessment period.

A monitoring period may be an appropriate length to take into account a plurality of planned printing operations, and hence a plurality of assessment periods. If a predetermined number N of successive planned prints is determined not to have taken place, then a fault may be raised. This reduces the risk of false positives, i.e. if a single detected failed print results in a fault being raised, then an anomalous reading could give rise to a fault when, in fact, the print was carried out.

Referring now to Figure 5, this shows a comparison between a head up/down signal provided by the controller 36, as indicated by trace 60 and the signal provided by the sensor 34, as indicated by the trace 62, in a printer apparatus 10 where the printhead 12 is moving in an expected manner, i.e. the printing apparatus is functional. In Figure 5, which shows results from an operational printhead 12, the sensor signal (trace 62) shows a clear correlation between the controller signal which controls movement of the printhead 12 (trace 60) and the characteristic which is indicative of tension, for example movement of the tension control device (trace 62).

Referring to Figure 6, there is shown a comparison between a head up/down signal provided by the controller 36, as indicated by trace 70 and the signal provided by the sensor 34, as indicated by the trace 72, in a printer apparatus 10 where the printhead 12 is not moving in an expected manner, and the printing apparatus 10 may therefore not be fully functional. The correlation between the signal provided by the sensor 34 may not correlate with the expected movement of the printhead 12. For example, trace 72 shows an decrease in tension during the "head down" phase of a planned printing operation (trace 70 high) and an increase during a "recovery" phase of the planned printing operation (trace 70 low). These changes may be caused by the movement of the ribbon 22 around the roller 30 during the print cycle A calibration operation may be carried out to determine an expected variation in the characteristic being measured by the sensor 34 during a successful printing operation. The method may include comparing an actual variation in the characteristic being measured by the sensor 34 with the expected variation.

An advantage of the invention is that it is possible to detect a failure of the printhead drive mechanism 13, for example a failure of the pneumatic system which controls the movement of the printhead 12, without having to use additional components over and above those which are already incorporated into the printer, and there are no additional time or cost implications with this system, as it runs in real time, during each printing process, and no additional components have to be fitted to the printing apparatus 10 either during manufacture or installation or retro-fitted to the printing apparatus 10.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

CLAIMS1. A method of operating a printing apparatus including a printhead for transferring ink from a tape to a substrate, and a tension control device, the method including monitoring a characteristic indicative of tension in a tape carried in a tape path, and using information about the characteristic of the tension to determine if the printing apparatus has failed to carry out a printing operation.
A method according to claim 1 wherein the tension control device includes a tension correcting device, and the method includes determining that the tension correcting device has failed to move in an expected manner.
A method according to claim 2 wherein determining that the tension correcting device has failed to move in an expected manner indicates that the printhead has failed to move in an expected manner, and has failed to carry out the printing operation.
A method according to claim 2 or claim 3 including monitoring at least one of the movement and the position of the tension correcting device.
A method according to any of the preceding claims wherein the characteristic of the tension in the tape is monitored during an assessment period.
A method according to claim 5 wherein the assessment period coincides with an initial phase of the printing operation during which the printhead is expected to move between a non-printing position and a printing position. 2. 3. 4. 5. 6.
7 A method according to any of claims 2 to 6 wherein the tension correcting device is operable to maintain a substantially constant path length of the tape, and during a printing operation is expected to move to counteract an increase in the path length which is caused by the movement of a printhead of the printing apparatus into a print position, the method including determining that the tension correcting device has failed to move in the expected manner thus indicating that the printhead has failed to move, and therefore that the printing apparatus has failed to carry out the printing operation.
A method according to any of claim 5 to 7 where it is determined that the printing apparatus has failed to carry out the printing operation when the tension correcting device moves less than a predetermined distance during the assessment period.
A method according to any of the preceding claims including providing a signal when it is determined that the printing apparatus has failed to carry out a printing operation.
A printing apparatus including a printhead which is moveable between a non-printing position and a printing position to perform a printing operation, a tape drive for moving an inked tape in a tape path past the printhead, and a mechanism for detecting a failed printing operation, wherein the mechanism for detecting a failed printing operation includes a sensor which is operable to monitor a characteristic indicative of tension in a tape in the tape path and a controller which is operable to compare an actual characteristic indicative of tension in the tape in the tape path monitored during an assessment period with an expected characteristic indicative of tension, and in the event that the actual characteristic of tension in the tape differs from the expected 10.characteristic of tension in the tape, the controller is operable to indicate that a printing operation has not been completed as expected.
11. A printing apparatus according to claim 10 wherein the mechanism for detecting a failed printing operation includes a tension correcting device which is operable to maintain tension in the tape in an acceptable range and to counteract a change in the length of the tape path caused by the movement of the printhead between the non-printing position and the printing position, by moving in an expected manner each time the printhead moves between the non-printing position and the printing position, wherein the characteristic indicative of tension monitored by the sensor is movement of the tension correcting device.
12. A printing apparatus according to claim 10 or 11 wherein the sensor is a magnetic sensor.
13. A printing apparatus according to claim 11 or claim 12 wherein the tension correcting device is a moveable tape guide member.
14. A printing apparatus according to any of claims 11 to 13 wherein the tension correction device is a dancing arm.
15. A printing apparatus according to any of claims 10 to 14 wherein the printing apparatus is a thermal transfer printing apparatus.