FIELD

The present invention relates to improvements to a tape drive and methods of controlling a tape drive. In particular, the embodiments of the invention may be suitable for a printing apparatus and, specifically, thermal transfer over-printers (TTO).

BACKGROUND

In a TTO printer, reels of ribbon are supported on spools and in use the ribbon is transferred between a supply spool and a take-up spool. During use of the printer, the rotational drive of the spools is controlled by one or more motors. The take-up and supply spools must be rapidly accelerated and decelerated, ensuring ribbon is in the correct position relative to the print head and substrate so that a printing operation can take place, transferring ink to the substrate. The spools must be coordinated to ensure that ribbon tension is maintained as it passes from the supply to the take-up.

As the ribbons are required to be used efficiently (i.e., to make maximum use of the ribbon), there may be a rewind phase after each printing operation. The ribbon reels need to be accelerated to the required rotational speeds and then these speeds maintained during the printing operation. When the print is finished, the reels are decelerated to stationary before any used ribbon is rewound to be ready for the next print.

Embodiments relating to the present disclosure seek to alleviate one or more of the problems associated with known systems.

BRIEF DESCRIPTION OF THE INVENTION

According to a first aspect of the present invention, we provide a tape drive for use in a printing apparatus including a controller, and a first and a second spool support which are rotatable to move tape around a tape path between the first spool support and the second spool support, wherein the controller is operable to control acceleration and/or deceleration of the tape during an acceleration phase in which the tape is accelerated or decelerated from a starting velocity to a target velocity, and the acceleration phase includes: a plurality of steps, during each of which a respective acceleration / deceleration is applied, and in which an acceleration / deceleration in a first step is higher than a second step, occurring after the first step, when the tape is approaching the target velocity. The acceleration phase may form an S -curve in the velocity of the tape. The acceleration phase may include five or more steps (i.e. steps in which the acceleration or deceleration is different from an adjacent step in the acceleration phase). Optionally, the steps in combination across time may provide an approximate -curve in the velocity of the tape. The acceleration phase may include five steps.

The controller may be operable to determine a target step velocity required for each step. The controller may be operable to set the target step velocity to be substantially the same for every step of the acceleration phase. The controller may be operable to determine a time interval for each step. The time interval may be based on the acceleration / deceleration applied and target step velocity required.

The target velocity (i.e. of the tape) may be determined by a substrate velocity. In other words, the speed of a substrate moving past the tape drive / printing apparatus may be detected and used to set the target for the tape. The controller may be operable to update the target velocity. The controller may be operable to update the acceleration phase while the acceleration phase is occurring.

The controller may be operable to reduce the acceleration in one or more of the steps if the target velocity is decreased. The controller may be operable to increase the acceleration in one or more of the steps if the target velocity is increased. The controller may be operable, in order to update the acceleration phase, to alter a target step velocity required for one or more steps to arrive at the updated target velocity. The controller may be operable to decrease the target step velocity for one or more steps if the target velocity is decreased. The controller may be operable to increase the target step velocity for one or more steps if the target velocity is increased.

The controller may be operable to shorten and / or length one or more of the steps of the acceleration phase.

Within the acceleration phase, the acceleration / deceleration may be highest in a median step. The acceleration phase may represent a bell curve or gaussian curve. The steps either side of the median acceleration step may mirror each other.

According to a second aspect of the invention we provide a printing apparatus including a tape drive according to the first aspect of the invention. The printing apparatus may include a print head, and a sensor or monitor, communicatively coupled with the controller, which is configured to determine a velocity of a substrate moving past the print head.

According to either the first or second aspect, we provide a method of operating a tape drive of a printing apparatus in which the controller performs one of the more of the features outlined in respect of the first or second aspects of the invention.

BRIEF DESCRIPTION OF THE FIGURES

In order that the present disclosure may be more readily understood, preferable embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 illustrates tape velocity (mm/s) against time (ms);

Figure 2 illustrates tape acceleration (m/s ² ) across an acceleration phase;

Figure 3 illustrates velocity (m/s) and distance (m) travelled for a substrate against the velocity (m/s) and distance (m) travelled for a tape where the substrate is decelerating;

Figure 4 illustrates velocity (m/s) and distance (m) travelled for a substrate against the velocity (m/s) and distance (m) travelled for a tape where the substrate is decelerating;

Figure 5 illustrates velocity (m/s) and distance (m) travelled for a substrate against the velocity (m/s) and distance (m) travelled for a tape where the substrate is accelerating;

Figure 6 illustrates velocity (m/s) and distance (m) travelled for a substrate against the velocity (m/s) and distance (m) travelled for a tape where the substrate is accelerating; and

Figure 7 is a schematic view of a tape drive.

DESCRIPTION OF THE INVENTION

A printer includes the reels of ribbon (also known as tape) being transferred between a supply and take-up spool. A print head is used to transfer ink from the ribbon onto a substrate to print a desired image. During printing the ribbon speed needs to be matched to the speed of the substrate which is receiving the printed image. The ribbon is accelerated and decelerated quickly achieve a desired printing rate.

Where mention is made of driving ribbon, it should be understood that the invention described herein may also be applied to general carriage drive.

It has been found that the ribbon / tape does not act as a solid mass, and instead behaves like a distributed system with multiple masses with varying inertia in accordance with the distance from the centre of rotation, and deforms as it is accelerated. This deformation causes the ribbon to store energy in a similar manner to a torsion spring, for example. When this acceleration is removed, the outer part of the ribbon continues to accelerate as the ribbon returns to its unstressed state. This overspeed on the outside of the ribbon then causes torsion in the opposite direction and the ribbon outer edge oscillates in a damped sinewave about the intended speed. This oscillation causes an oscillating torque on the motor shaft(s). Extra current is required in the motor(s) to stop the torque causing the motors to lose control of the ribbon position.

It has been found that the key to reducing the amplitude of the oscillation experienced by the ribbon during rapid acceleration / deceleration, is to minimize rate of change of acceleration in the ribbon (i.e., the DjerkO caused by sudden changes in acceleration).

Using a uniform rate of increase of acceleration or deceleration has been contemplated, but found to be inefficient, as the initial rate of change is still found to be suboptimal, and overall the rate of acceleration is then limited.

Referring to figure 7, a tape drive 1 is described (the tape drive 1 is for use in a printing apparatus and figure 7 illustrates components relating to a printing apparatus alongside the tape drive 1). The tape drive 1 includes a controller 10, a first spool support 12 and a second spool support 14.

The first and second spool support 12, 14 are rotatable to move tape 16 around a tape path between the first spool support 12 and the second spool support 14. As can be seen in figure 7, the tape 16 is mounted / wound on to a spool 20 supported on the first spool support 12, extends around the tape path (in this example, defined by four rollers 18), to a second spool 22 support on the second spool support 14.

The controller 10 is operable to control the rotation of the spool supports 12, 14 (and, thus, controls the transport of the tape 16 around the tape path). In this example, each of the first and second spool supports 12, 14 is rotationally driven by a motor 13, 15. As such, the controller 10 controls signals transmitted to the motors 13, 15 in order to drive the spool supports 12, 14 in the desired manner.

As mentioned above, this tape drive 1 is suitable for use in a printing apparatus. As can be seen, in the example in figure 7, a print head 30 is illustrated. The print head 30 is moved during printing to contact the ribbon / tape 16 (which includes ink on a surface) and push the tape 16 against a substrate 32. Heating elements are provided on the print head 30, which are selectively energised / heated, such that when the print head 10 is in contact with the tape 16, ink is melted and transferred onto the substrate 32 in a desired image. In this example, the substrate 32 is transferred past the print head 30 over a roller or platen 34. In embodiments, the substrate 32 is transported in a similar manner to the tape 16. In other words, a controller (which may be the same controller as the tape drive or a different controller) controls rotation of a first and second substrate spool support, such that the substrate 32 can be transported around a substrate path as desired. It should be appreciated that the substrate transport mechanism does not need to be similar to the tape drive 1 0 the substrate 32 is moved past the print head 30 at a controlled speed.

As mentioned above, the controller 10 controls movement of the spool supports 12, 14 1 this includes both the maintenance of a desired velocity and acceleration and deceleration of the tape 16. In other words, the controller 10 is operable to control acceleration / deceleration of the tape 16 during an acceleration phase. The acceleration phase is where the tape 16 is accelerated / decelerated from a starting velocity to a target velocity.

It should be appreciated that acceleration phase is intended to cover a phase of tape 16 movement in which an acceleration or deceleration is applied to bring the tape 16 to a target velocity. In other words, the target velocity could be faster or slower than the starting velocity. Since the tape drive 1 can move the tape 16 both directions, the acceleration and / or deceleration could be in either direction also. Thus, the target velocity could be negative to switch directions of the tape 16.

The acceleration phase includes a plurality of steps. During each step a respective acceleration / deceleration is applied. Further, an acceleration / deceleration in a first step is higher than a second step, occurring after the first step, when the tape is approaching the target velocity. In other words, the acceleration / deceleration applied to the tape 16 (by the controller 10, through the spool support 12, 14 rotation) is lower in an interval as the tape velocity is approaching the target velocity than the acceleration / deceleration in one of the earlier steps. It should also be appreciated that although some of the examples discussed below mention only OaccelerationO of the tape 16, the same operations can be used for deceleration too.

The velocity of the tape 16 resembles an S-curve in the acceleration phase. In embodiments, the controller 10 implements individual steps, each with a linear acceleration. When viewed across the entire acceleration phase, the steps form an approximate S-curve shape.

This process is illustrated in figures 1 and 2. Figure 1 illustrates velocity against time for a tape drive in which the starting velocity is Omm/s and the target velocity is 10OOmm/s. The controller 10 is operable to split the acceleration phase into five steps. In other words, there are five time intervals in which the acceleration / deceleration applied is selected to ensure the tape 16 arrives at the target velocity at the appropriate time. It has been found that by instead applying a low-jerk approach to the rate of change of acceleration of the motor(s) (e.g. such as an DSD curve D a sigmoid curve), rather than a uniform increase or decrease, the maximum acceleration can be increased, and the motor current reduced, from the levels that would otherwise be required to control a high jerk movement and the resulting oscillations of the ribbon 16.

Figure 2 illustrates the acceleration applied to achieve the velocity curve in figure 1 . As can be seen, the first acceleration applied is relatively low. As explained above, an acceleration applied when the tape 16 is initially not accelerating (i.e. moving at Omm/s or another constant velocity) causes a force in the tape 16. A low acceleration at the start of an acceleration phase reduces the jerk on the tape 16 as it moves from Dno accelerationD to Dsome accelerationD.

Once the tape 16 is accelerating the controller 10 can apply one or more higher rates of acceleration. In this case, the controller 10 implements two further increases in acceleration D essentially, the acceleration progressively increases across three acceleration phase steps.

The same jerk effect is felt by the tape 16 as the acceleration is removed once the tape 16 is at its target velocity. Thus, as the tape 16 approaches its target velocity, the controller 10 reduces the acceleration to a minimum value. Thus, the acceleration phase step immediately before reaching target velocity is lower than the acceleration applied at a peak. In the illustrated example, the controller 10 implements the highest acceleration in the median step of the acceleration phase. After the median step, the acceleration is progressively reduced until the tape 16 reaches the target velocity.

In this example, the controller 10 determines a target step velocity required for each step. In other words, the controller 10 assesses the difference between the starting velocity and the target velocity and divides the velocity difference between the steps of the acceleration phase. In the illustrated example, the controller 10 implements the same target step velocity to each step of the acceleration phase (i.e. the controller is operable to set the target step velocity to be substantially the same for every step of the acceleration phase). In more detail, figure 1 illustrates a velocity difference of 1000mm/s (i.e. the tape 16 needs to increase velocity from Omm/s to 1000mm/s) D in this instance the control 10 divides the velocity difference equally between the five steps of the acceleration phase. Thus, each step has a target velocity increase of 200mm/s.

Once the controller 10 has determined the appropriate velocity change required for each step, the time for each step can be assessed. On some embodiments, the acceleration and the velocity change are known for each step, so the time is calculated accordingly. Inherently, for the steps that have low acceleration (when the tape 16 acceleration is started or ended, as discussed above), the time taken to complete the step and arrive at the target step velocity will be longer than those steps that can accommodate a higher acceleration.

Alternatively it should be appreciated that the controller 10 could determine the acceleration needed in each step of the acceleration phase based on the velocity difference (between the starting velocity and the target velocity) and a time interval in which the tape 16 is required to the be at the target velocity. The controller 10 may assign the require accelerations based on a requirements about the acceleration values permitted. In other words, the controller 10 knows that the first and last accelerations must be lowest and the that the median acceleration should be highest 0 from the requirements the controller 10 can determine what acceleration values should be applied in each step of the acceleration phase so that the tape 16 arrives at the target velocity (in the time required).

It should be appreciated that the controller 10 will have predetermined rules relating to the acceleration that can be applied. Thus, it may know that the first and last steps in the acceleration phase must be the lowest and apply the accelerations accordingly. In other words, the controller 10 has a predetermined shape of what the acceleration curve (i.e. as illustrated in figure 2) should look like and will apply that in all acceleration phases. For example, the shape could be generally or approximate to a gaussian curve.

In some embodiments (i.e. the examples illustrated in figures 1 and 2) the steps of the acceleration phase mirror each other. Thus, the first and fifth steps have the same acceleration, and the second and fourth steps have the same acceleration and the third step has the highest acceleration. The controller 10 in this case only has to determine three different acceleration values. However, this does not have to be the case and is discussed in more detail below.

In some embodiments, the target velocity of the tape 16 is determined / related to a velocity of the substrate 32. In other words, the controller 10 has information relating to the speed of the substrate 32 passing through the apparatus (and past the print head 30) and uses that to determine the target velocity of the tape 16. The substrate 32 movement may be measured by a sensor (not shown) or a monitor, which is communicatively coupled with the controller 10. The sensor or monitor is configured to determine the velocity of the substrate 32 moving past the print head 30. Alternatively, the controller 10 may acquire or have knowledge directly from the substrate 32 movement mechanism 0 i.e. from another controller or system that transports the substrate 32. In any of these scenarios, knowledge of the substrate 32 transport is transmitted to the controller 10 and the controller 10 uses that to determine how to control the movement of the tape 16.

1

A function such as a logistic function /(*) = is an example of a function defining a suitable curve. Other forms of S-shaped curve may also be used. This gradually applies acceleration to the reels and then gradually removes it, minimizing the jerk. In embodiments, this can be implemented by use of a five-step pseudo S Curve acceleration profile to accelerate the motor, for example 0 i.e., a curve approximating an S curve at five values over the range, defining a relatively smoothed profile.

In embodiments, the determination of the acceleration profile is recalculated at intervals during the acceleration process, according to methods described below. In other words, the controller 10 is operable to update the target velocity and update the acceleration phase while the acceleration phase is occurring.

In some embodiments, the target velocity of the ribbon 16 is not known when the ribbon 16 movement is started. This is because the substrate 32 may accelerate or decelerate (or both) during the period in which the ribbon 16 is accelerating.

Thus, in some embodiments, the controller 10 is operable to either increase or decrease the acceleration in one or more steps of the acceleration phase depending on the change in target velocity required. For example, if the target velocity for the tape 16 is decreased, the controller 10 is operable to reduce the acceleration in one or more of the steps. Likewise, if the target velocity for the tape 16 is increased, the controller 10 may be operable to increase the acceleration in one or more of the steps.

In some embodiments, the controller 10 is operable to alter a target step velocity required for one or more steps (which may be instead of or in addition to increasing or decreasing the acceleration) so that the updated target velocity for the tape 16 is reached. For example, if the target velocity if decreased, the controller 10 is operable to decrease the target step velocity for one or more steps. Likewise, if the target velocity is increased, the controller 10 is operable to increase the target step velocity for one or more steps.

Essentially, if the controller 10 assess that the end target velocity has changed from an initial assessment, aspects of the acceleration phase can be altered while the tape 16 is being accelerated. The controller 10 can alter one or both of the acceleration and the target step velocity for one or more steps in the acceleration phase to ensure that at the end of the acceleration phase, the tape 16 has the updated target velocity.

In some embodiments, the steps are calculated (in the DSD curve) as they are required during the acceleration phase. Thus, there is a change the curve characteristics as the substrate 32 speed is changing. The target velocity is the speed of the substrate 32. The target velocity defines the five velocity target points (i.e. each of the steps in the acceleration phase) where the accelerations change. If the velocity target points are recalculated every time the substrate 32 velocity changes, sections of the pseudo S-Curve can be extended or compressed to target the substrate 32 velocity as it changes.

Figure 3 to 6 illustrate examples of substrate 32 and tape 16 movement including an acceleration phase. In each graph, the lines with circles along them correspond to the velocity and the lines with no circles correspond to the distance, the solid lines correspond to the tape 16 and the dashed lines correspond to the substrate 32.

Figures 3 and 4 illustrate an example in which the substrate 32 velocity is slowing down / decreasing over time. Thus, the target velocity for the tape 16 is decreasing over time (and decreases after the controller 10 has initiated the acceleration phase to increase the tape 16 velocity to match the substrate 32).

Figure 3 illustrates an example in which the controller 10 alters the target step velocity of the tape 16 only. In other words, the target velocity at the end of each step of the acceleration phase is decreased as the acceleration phase continues 0 resulting in the tape 16 matching the velocity of the substrate 32 at a time of around 0.03s. However, as can be seen in the graph, the tape 16 velocity as the acceleration phase ends must drop sharply to match the movement of the substrate 32. As outlined above, the sudden change in acceleration rates cause unwanted jerking in the tape 16.

To reduce the jerking effect, both the target step velocity and the acceleration for each step can be altered. This approach is illustrated in figure 4 0 the substrate 32 is slowing down in the same way as in figure 3. However, in this example, the acceleration applied in each step of the acceleration phase is altered alongside reducing the target step velocity. As can be seen, the acceleration in step one of the acceleration phase remains the same as in figure 3 but subsequent acceleration values in the next steps are reduced. The acceleration in the last step is much lower than in figure 3, which results in a smaller change when the acceleration phase ends and the tape 16 matches the velocity of the substrate 32. The trade-off is that the tape 16 joins the substrate at a later time (i.e. the acceleration phase is longer) 0 in this case the acceleration phase ends at about 0.04s rather than 0.03s as discussed above.

Figures 5 and 6 illustrate an example in which the substrate 32 velocity is increasing over time. Thus, the target velocity for the tape 16 is also increasing over time (and increases after the controller 10 has initiated the acceleration phase to move the tape 16 velocity to match the substrate 32). In the same way that figure 3 and 4 illustrate altering just the target step velocity vs. the target step velocity and the step acceleration, figures 5 and 6 illustrate the same. In figure 5, the acceleration phase begins and the controller 10 progressively increases the target velocity reached at the end of each step. This in turn, extends the length of each step to accommodate the longer amount of time it takes for the tape to reach the altered target step velocity. As can be seen, in the last step of the acceleration phase, the tape 16 is still being accelerated toward the substrate 32 value (and extends off the end of the graph).

In figure 6, the controller 10 increases the acceleration in step two onwards (shown by the increased gradient on the tape velocity line in figure 6). This means that the tape 16 reaches the substrate 32 faster. As can also be seen, the difference between the last step of the acceleration phase and when the tape 16 is matched to the substrate 32 is relatively small (which means the tape 16 transitions to a phase where it moves with the substrate 32 more smoothly / less jerk is experienced in the tape 16).

In both examples in figures 4 and 6, the controller 10 is operable to compress or lengthen one or more steps in the acceleration phase. In other words, the length of each step of the acceleration phase can be altered by the controller 10 in order to bring the tape 16 to the new / updated target velocity in an improved way (i.e. with minimised difference between the end of the acceleration phase and the start of the substrate matched phase).

In some embodiments, the acceleration is profile is not allowed to move back from a higher stage to a lower one in the pseudo S-Curve profile. In other words, once the acceleration phase has reached a specific step (e.g. step four in which the acceleration is reduced form step three and as the tape 16 is nearing the end of the acceleration phase), the controller 10 does not reverse the acceleration phase and move the tape 16 backwards to the step three (and the associated increase in acceleration that would bring). This prevents the acceleration from changing rapidly between two values around a velocity target point.

In addition to altering the velocity targets at which the accelerations change, it is possible to alter the acceleration in the sections to reduce the print position error on the ribbon. In the case that the substrate is decelerating, the acceleration values of the pseudo S-Curve are reduced by a function of the amount of reduction in the substrate speed. In the case that the substrate is accelerating, the acceleration values are increased by a function of the amount of increase of the substrate velocity.

Using the approach outlined above, a curve defining the acceleration profile is determined when the motor is to be accelerated, to a target velocity. However, when the acceleration S curve profile is exited at that target velocity, it may be the case that the velocity of the substrate 32 has changed and the target ribbon 16 velocity has therefore also altered during the acceleration process. When this occurs, a mismatch remains between the velocity reached and the target velocity of the ribbon 16, such that the S curve profile ends abruptly, with a correction occurring to reach the revised target velocity. This results in some level of jerk occurring during the highest acceleration phase.

In embodiments, to track the substrate speed, the level of acceleration used in the DSD curve can be updated as the substrate 32 speed changes, and corresponding ribbon target velocity changes. These changes are applied as smoothly as possible to avoid the introduction of additional jerk due to the changes of the rates of acceleration. Importantly, the acceleration needs to be reduced gradually at the end of the acceleration phase as the target velocity is reached.

Note that on the deceleration phase (i.e. after a print is complete) and on all of the rewind phases, the target velocity is known and thus true S curve operation is possible.

It is possible to calculate the steps in the DSD curve as they are required during the acceleration and change the curve characteristics as the substrate 32 speed is changing. Thus, the target ribbon 16 speed changes. The recalculation takes into account the current speed and acceleration of the ribbon 16 and the new target speed and creates an amended acceleration profile for the remainder of the acceleration

In some embodiments, the target velocity of the ribbon may be recalculated at regular intervals, and / or a change in the target velocity may trigger a recalculation of the S curve acceleration profile.

In embodiments, the S curve acceleration profile is defined by a predefined number of acceleration rates occurring at defined time intervals, approximating the shape of the S curve. In some embodiments the curve is defined by five intermediate rates of acceleration over the period of the curve. In other embodiments, more or fewer than five intermediate rates are determined D for example, between 3 and 50, or between 5 and 25, or between 5 and 15, or between 5 and 9, and preferably 5 intermediate rates are determined.

The print cycle may include a tracking phase where the speed of the ribbon 16 tracks the speed of the substrate 32 until the print position on the substrate 32 is reached. By applying an under-speed or over-speed during this tracking phase, it is possible to correct for distance errors in the position of ribbon 16 relative to the substrate 32, without compromising the ribbon 16 use or print boundary on the substrate 32.

Embodiments of the present disclosure improve the handling and transport of the tape 16 in the tape drive 1 . The controller 10 is operable to minimise the jerk in the tape 16. This is achieved by keeping the acceleration low at the start of the acceleration phase D i.e. where the tape 16 starts to accelerate or decelerate is does so without much change from the current / starting velocity. Likewise, as the tape 16 approaches the target velocity, the acceleration I deceleration is low 0 the change between the acceleration phase and the ongoing velocity once the target velocity is met is low.

The rotational speeds are set to deliver the correct linear tape 16 speed past the print head 30. The acceleration and deceleration phases need to be as short as possible to allow the time between prints to be minimised.

Compared to a single acceleration rate applied to the tape throughout the acceleration phase, the discussed operation is advantageous 0 since a low acceleration would reduce the jerk when the tape 16 arrives at its target velocity but would take a longer time to reach the target velocity. Whereas, a high acceleration would result in jerking movement and risks distorting the tape 16. Thus, a linear acceleration is either slow or risks impacting the print quality.

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 invention may also broadly consist in the parts, elements, steps, examples and/or features referred to or indicated in the specification individually or collectively in any and all combinations of two or more said parts, elements, steps, examples and/or features. In particular, one or more features in any of the embodiments described herein may be combined with one or more features from any other embodiment(s) described herein.

Protection may be sought for any features disclosed in any one or more published documents referenced herein in combination with the present disclosure.

Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.