GB2542549A - A method of operating a tape drive - Google Patents

Abstract

A tape drive 10 includes first and second spools 16, 18 and a motor control system 42 which includes a first motor 20, a second motor 22, a controller 34 for controlling the operation of at least one of the motors, and a tape monitor device 30, the position of which is adjustable in response to a change in the length of tape extending in a tape path between the first and second spools. The method includes monitoring the position of the tape monitor device, and providing an indication of a required position adjustment of the tape monitor device to adjust a length of the tape path so as to maintain tension in the tape substantially constant. Subsequently controlling at least one of the motors by calculating a corrected rotational velocity of the at least one motor by using the required position adjustment of the tape monitor device; comparing the corrected rotational velocity to a current rotational velocity of the at least one motor and calculating an adjusted rotational velocity. The adjusted rotational velocity is then applied to the at least one motor to achieve the corrected rotational velocity of the at least one motor.

Description

Title: A method of operating a tape drive Description of Invention

The present invention relates to a method of operating a tape drive, particularly, but not exclusively, to a tape drive for use in a printing apparatus, the method including using a tape monitor device to maintain a length of tape extending between two spools of a tape drive and set the tension in the tape.

It has long been known to provide tape drives which include 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 drivable by a respective motor. Such tape drives may be incorporated into a printing apparatus, wherein 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.

In order to avoid wasting ink, whilst maintaining acceptable print quality, it is advantageous to be able accurately to control the movement of the tape, so as to position the next portion of tape to be used directly adjacent a portion of the tape from which the ink has previously been removed.

Since such tapes are very thin, it is important to ensure that the tension in the tape extending between the two spools is maintained between predetermined limits. Too much tension in the tape is likely to lead to the tape being deformed or broken, whilst too little tension will inhibit the correct operation of the device. In the case of a printer, a slack tape is likely to affect print quality. As a tape is wound onto the take-up spool, the diameter (and, of course, the circumference) of the take-up spool increases, and the diameter (and circumference) of the supply spool decreases. This affects the moments of inertia of the two spools, and hence the angular momentum of each of the spools. If both spools were driven at a constant angular velocity, the amount of tape fed into the tape path per degree of rotation of the supply spool would decrease as the circumference of the supply spool decreased, whilst the amount of tape wound on to the take-up spool per degree of rotation would increase. This would eventually lead to the tension of the tape increasing beyond an acceptable limit. Therefore the angular velocity (or step rate) of at least one of the spools is generally variable.

It is known to provide a system which includes one or more guide members which are positioned in a tape path of the tape, between the supply spool and the take up spool (for example as described in US4,909,648). One of the guide members (often known as a “dancing arm”) is typically capable of pivoting back and forth about a pivot point and is used to adjust the path length between the supply spool and the take-up spool. The tape drive typically includes a sensor which detects when the dancing arm is approaching one or the other extreme of its motion. These systems typically have set angular velocities for each of the supply spool and the take-up spool (for example, in the system of US4,909,648, each spool has a slow and fast velocity). The supply spool is operable to supply tape at a set rotational velocity and the take-up spool is operable to take up tape at a set rotational velocity. However, in the event that the take-up spool’s rotational velocity is not sufficient to take in all of the tape supplied by the supply spool, in order to maintain a constant tension, the dancing arm extends the length of the tape path to accommodate all of the tape which extends between the spools and to maintain the tension between predetermined limits. This compensates for the take-up spool not taking in sufficient tape. When the dancing arm reaches its maximum extended position, i.e.it cannot extend the path length any further, the dancing arm can no longer maintain the tension in the tape. The sensor signals that the dancing arm is approaching the limit/extreme of its movement, which indicates that the supply spool needs to slow down and supply tape to the system at a slower rate. Over a period of time, the supply spool may supply less tape to the system than the take-up spool takes, which would tend to cause tension to increase. To maintain the tension between predetermined limits, the dancing arm reverses direction and moves back out of the tape path (i.e. the path length is shortened as the dancing arm moves away from its maximum extreme position). The amount of tape in the tape path decreases, to maintain the tension between predetermined limits. Eventually the sensor may signal that the dancing arm is approaching the opposite (minimum) limit/extreme, and the system must then switch to the first mode of operation again.

This method of operation results in virtually continuous sinusoidal movement of the dancing arm. This results in excess wear on components within the system. Excess wear results in components needing to be replaced regularly. Additionally, because the dancing arm is continuously moving between extreme positions, the tape length is always changing which may put excess stress on the tape.

The dancing arm in this system is rarely in the “ideal” position because it is in continuous substantially sinusoidal motion.

Other known systems include pull-drag system and twin motor systems. Pull-drag systems include a clutch which controls the torque applied to a supply spool, and a stepper motor directly rotating the take-up spool to pull the tape between the supply spool and take-up spool. In a twin motor system, the movement of the motors controlling the spools of tape are coordinated. The supply spool and take-up spool are driven to unwind/wind the same amount of tape during a tape movement. The tension is monitored (directly or indirectly) and the movement of one or both of the motors is adjusted to maintain the tension in the tape between predetermined limits. A problem with both of these methods is that the tape can become deformed during use, and the spools of tape are not always perfectly circular (cylindrical). The control of the or each motor is based upon assumptions about the instantaneous properties of the tape and/or the spools.

The current invention seeks to ameliorate one or more problems with the prior art.

In accordance with a first aspect of the invention, we provide a method of operating a tape drive, of the type operable to transfer a tape between a first spool and a second spool, and which includes two spool supports each of which is suitable for supporting a spool of tape, and a motor control system which includes a first motor and second motor and a controller for controlling the operation of at least one of the motors, the first motor being operable to rotate the first spool and the second motor being operable to rotate the second spool, the motor control system further including a tape monitor device, the position of which is adjustable in response to a change in the length of the tape extending in a tape path between the first spool and a second spool, the method including the steps of: monitoring the position of the tape monitor device, and providing an indication of a required position adjustment of the tape monitor device to adjust a length of the tape path so as to maintain tension in the tape substantially constant; controlling at least one of the motors by: calculating a corrected rotational velocity of the at least one motor by using the required position adjustment of the tape monitor device, comparing the corrected rotational velocity to the current rotational velocity of the at least one motor and calculating an adjusted rotational velocity, and applying the adjusted rotational velocity to the at least one motor, to achieve the corrected rotational velocity of the at least one motor.

According to a second aspect of the invention, we provide a method of operating a tape drive, of the type operable to transfer a tape between a first spool and a second spool, and which includes two spool supports each of which is suitable for supporting a spool of tape, and a motor control system which includes a first motor and second motor and a controller for controlling the operation of at least one of the motors, the first motor being operable to rotate the first spool and the second motor being operable to rotate the second spool, the motor control system further including a tape monitor device, the position of which is adjustable in response to a change in the length of tape extending in a tape path between the first spool and a second spool, the method including the steps of: operating at least one of the motors at a current rotational velocity; monitoring the position of the tape monitor device, and providing an indication of a required position adjustment of the tape monitor device to adjust a length of the tape path so as to maintain tension in the tape substantially constant; controlling at least one of the motors by: calculating a corrected rotational velocity of the at least one motor by using the required position adjustment of the tape monitor device, comparing the corrected rotational velocity to the current rotational velocity of the at least one motor and calculating an adjusted rotational velocity, and applying the adjusted rotational velocity to the at least one motor, to achieve the corrected rotational velocity of the at least one motor.

The method of operating a tape drive may comprise performing a plurality of iterations, each iteration may comprise performing the steps included in the first aspect of the invention, wherein the motor control system may store a first value relating to a first iteration of the method, and may use the first value in conjunction with a second relating to a second iteration of the method, such that a third required position adjustment relating to a third iteration of the method may be minimised whilst maintaining the tape tension between predetermined limits.

The method of operating a tape drive may include the motor control system storing a plurality of values relating to measurements from previous iterations, and the motor control system may use them to minimise a subsequent required position adjustment of the tape monitor device.

The method of operating a tape drive may include the adjusted rotational velocity being applied to the motor controlling the second spool.

The method of operating a tape drive may include the motor control system calibrating the tape drive, the calibration step including determining the diameters of the first and second spools of tape, and providing an indication of the diameters to the motor control system.

The method of operating a tape drive may include the motor control system calibrating the tape drive using a stored value for a length and/or thickness of the tape.

The method of operating a tape drive may include the first spool of tape being a supply spool, which is configured to supply tape into the tape path and the second spool of tape being a take up spool, which is configured to take up tape from the tape path.

The method of operating a tape drive may include the first motor being drivable to supply a known length of tape into the tape path, which may be defined by the relative positions of one or more guide members.

The method of operating a tape drive may include the motor control system including a second controller which uses a measured value of the velocity of a substrate, and may control the movement of the first motor to achieve a corresponding velocity of the tape.

The method of operating a tape drive may include the controller using an acceleration/deceleration of the tape required to begin a printing operation in conjunction with the adjusted rotational velocity to control the second motor.

The method of operating a tape drive may include the first and second motors being controlled, by two separate controllers, independently of one another.

According to a third aspect of the invention, there is provided a printing apparatus which includes a tape drive, of the type operable to transfer a tape between a first spool and a second spool, the tape drive including a tape monitor device, two spool supports each of which is for supporting a spool of tape, and a motor control system which includes a first and second motor and a controller for controlling the operation of at least one of the motors, the first motor being operable to rotate the first spool and the second motor being operable to rotate the second spool, wherein the tape drive is operable in accordance with a method as set out in the first aspect of the invention.

The printing apparatus may be a thermal transfer printer.

The invention will now be described, by way of example only, with reference to the accompanying drawings, of which:

Figure 1 is an illustrative view of part of a thermal printing apparatus including a tape drive according the present invention;

Figure 2 is an illustrative view of an embodiment of a tape monitor device of the apparatus of Figure 1; and

Figure 3 is a flow diagram showing a method of operation of a tape drive in accordance with the present invention.

Referring to figure 1, a part of a printing apparatus 1 is shown. The printing apparatus 1 includes a housing or a back plate (not shown), a tape drive 10, a printhead 28, and a platen/roller 26. The printing apparatus 1 is operable to print an image and/or text onto a substrate (not shown).

The tape drive 10 includes a first spool support 12 and a second spool support 14, upon each of which a spool 16, 18 of tape 24 is mountable. The tape drive also includes one or more guide members (in this example two guide members 30, 31), and a motor control system 42. The first spool support 12 and the second spool support 14 are spaced laterally apart and mounted to the housing or back plate of the printing apparatus 1. The first tape spool 16 is mountable on the first spool support 12, and the second tape spool 18 is mountable on the second spool support 14. The tape 24 is wound onto the first and second tape spools 16, 18 and extends between them in a tape path which is defined by the relative positions of the spool supports and the guide members 30, 31.

The guide members 30, 31 are mounted on the housing or backing plate, and are laterally spaced from one another, and spaced from the first and second spool supports 12, 14. The tape 24 is supplied from the first tape spool 16 (mounted on the first spool support 12), around the guide members 30, 31 and finally onto the second tape spool 18 (mounted on the second spool support 14). A printhead 28 and platen/roller 26 are positioned in the tape path, generally between the guide members 30, 31, on opposing sides of the tape 24.

The first tape spool 16 may also be known as a supply spool. In general, the supply spool is rotatable to supply tape 24 into the tape path. The second tape spool 18 may also be known as a take-up spool. In general, the take-up spool is rotatable to take up tape 24 from the tape path.

In the present example, the tape 24 is inked printer tape. It will be appreciated that the tape drive may operate with other types of tape, e.g. magnetic tape, and other types of apparatus.

The motor control system 42 includes a first motor 20 and a second motor 22. The first motor 20 is operable to rotate the first spool support 12, and the second motor 22 is operable to rotate the second spool support 14. The spool supports 12, 14 are independently driveable and each is rotatable clockwise and anti-clockwise by means of its respective motor 20, 22. In this example, the motors 20, 22 are stepper motors, but it should be appreciated that they could be one of many types of motors which can be operated in a functionally comparable way.

The motor control system 42 also includes a primary controller 34, hereinafter referred to as a print cycle controller 34, which controls the overall operation of the tape drive 10, for example the acceleration, deceleration and direction of movement of the tape 24 between the spools 16,18. The motor control system 42 also includes a first controller 36 and a second controller 38. The first and second controllers 36, 38 control the individual movements of the first and second motors 20, 22, respectively. The controllers 36, 38 are operable to control the angular velocity of each motor 20, 22. The print cycle controller 34 is electrically communicable with the controllers 36, 38. The physical positions of the controllers 34, 36, 38 relative to the remainder of the tape drive 10 are irrelevant for the purposes of the present invention.

The motor control system 42 also includes a substrate sensor which detects movement of the substrate, either directly or by monitoring the movement of the substrate roller 26, for example by means of a rotary encoder. The substrate sensor is operable to provide an electrical signal to at least one of the controllers 34, 36, 38. In the present example, the substrate sensor is configured to communicate with the controller 36 of the first motor 20 and the controller 38 of the second motor 22, at least.

The tape drive 10 includes a tape monitor device (TMD), which provides a signal to the motor control system 42 about a characteristic of the tape 24. The characteristic of the tape about which the signal is provided may be tension or the length of tape 24 in the tape path, for example. In this example, the guide member 30 acts as the TMD. The TMD 30 is capable of generally linear reciprocating movement shown by the double headed arrow A, between a first, minimum extended position and a second, maximum extended position, the latter shown in dotted lines in Figure 2. The TMD 30 includes a position sensor 32, which is operable to monitor the position of at least a part of the TMD 30, and is communicable with the motor control system 42. In the present example, the position sensor 32 is communicable with the second motor controller 38, but it will be appreciated that the position sensor may additionally or alternatively be communicable with the first motor controller 36, or with another part of the motor control system 42. In the present example, the position sensor 32 includes a Hall Effect sensor, and a magnet 33 is positioned adjacent the TMD 30, on the housing or backing plate, such that the Hall Effect Sensor is able to detect relative movement between the TMD 30 and the housing or backing plate. It will be appreciated that the positions of the magnet 33 and the sensor 32 may be reversed. The position 32 sensor is operable to provide an electrical signal to the second motor controller 38 as a result of movement of the TMD 30 relative to the magnet 33, the signal being indicative of the position of the TMD 30 relative to the housing or backing plate. Any suitable type of position sensor may be used in place of a Hall Effect sensor. The sensor 32 need not be carried by the TMD 30.

Embodiments of the TMD 30 may include a biasing member, for example a resilient biasing member, such as a spring, acting against the TMD 30 such that when the length of tape 24 in the tape path changes, at least a part of the TMD 30 moves. It will be appreciated that the tension within the tape may change if the spring obeys Hooke’s Law, or may remain substantially constant if the spring is a constant force device.

The signal to the motor control system 42 allows the motor control system 42 to infer the length of the tape path and, given knowledge of the resilient biasing of the TMD 30, the tension in the tape 24.

Whilst the TMD is described above as being the guide member 30, it will be appreciated that the TMD may be provided as another guide member, or any member which contacts the tape 24 in the tape path.

The TMD 30 may also consist of a moveable guide roller (not shown) which presses against a load cell which gives a signal which is indicative of the tension in the tape 24.

Operation of the printing apparatus 1 will now be described. The tape drive 10 requires calibration before operation can commence. Such calibration is generally required when the printing apparatus 1 is switched on and/or when the first and/or second tape spools 16, 18 are replaced. There are two different situations in which the tape drive 10 needs to calibrate itself.

Firstly, when a new tape 24 is fitted, the first and second tape spools 16, 18 are replaced (i.e. two new tape spools 16, 18 are mounted to the spool supports 12, 14, substantially all of the tape is wound onto the first tape spool tape 16, and very little tape is on the second tape spool 18). The calibration process includes determining an initial estimate of the diameters of each of the tape spools 16, 18 mounted on the spool supports 12, 14. An example of a suitable method of obtaining such an estimate is described in detail in the applicant's published patent application GB 2482167. In addition to this, the controller 34 also uses pre-programmed knowledge of the tape type fitted to determine the total length and thickness of the tape 24.

Secondly, when the printing apparatus 1 is switched on and there is unused tape 24 on the first tape spool 16 (i.e. some of the tape 24 has already been used in a previous operation and a length of the tape 24 has been wound onto the second tape spool 18). The motor control system 42 cannot determine the exact length of unused tape 24 left on the first tape spool 16. The diameters of the first and second tape spools 16, 18 are determined during calibration (as above) and the controller 34, using its pre-programmed knowledge of the type of tape 24 mounted on the tape spools 16, 18, makes an estimate of the length of tape 24 left on the first tape spool 16. A typical printing operation includes a non-printing phase and a printing phase. The non-printing phase may include acceleration or deceleration of the tape 24 and/or rewinding or advancing of the tape 24. Printing operations are generally performed sequentially with no pause in between (i.e. the printing phase of a first printing operation will run into the non-printing phase of the second printing operation). It should be appreciated that there may be pauses between printing operations and depending on the operation of the controller 34 there will often be a negligible pause of time between printing operations.

It is advantageous for any determinations of adjustments which are required to maintain the tension in the tape 24, as described in more detail below, to be made in a non-printing phase, because this is when there is least disturbance in the tape 24. This ensures that the tension in the tape 24 is maintained at a suitable value throughout the next printing phase.

In use, the first and second motors 20, 22 drive the first and second spool supports 12, 14 (and therefore rotate the first and second tape spools 16, 18). The tape 24 advances between the first and second tape spools 16, 18, along the tape path, around the guide members 30, 31 between the spools 16,18. It will be appreciated that the tape drive is bidirectional, i.e. that the tape may travel in either direction between the spools 16, 18. The tape 24 passes between the printhead 28 and the platen/roller 26. A substrate (not shown) passes over the platen/roller 26 (between the platen/roller 26 and the tape 24). During a printing phase of a printing operation, the printhead 28 moves into contact with the tape 24 and transfers ink from the tape 24 onto the substrate.

The first and second motors 20, 22 are operated by the motor control system 42 independently of one another (i.e. by the first and second controller 36, 38, respectively). During a printing operation, the first motor 20 (controlling movement of the supply spool 16) is operated according to the results and certain operating conditions of the printing apparatus 1. The controller 36 is provided with calibration data relating to the diameters of the spools 16, 18, information relating to the movement to be performed by the tape, e.g. advance, reverse, accelerate, decelerate, and/or other information about the print cycle, which is provided by the print cycle controller 34, and also data regarding the movement of the substrate, for example the velocity of the substrate, which is provided by the substrate encoder.

The rotational velocity of the first motor 20 (and therefore the first tape spool 16 mounted on it) may depend on one or more of: the calibration performed at the beginning of operation (i.e. the diameter of the first tape spool 16, total length and thickness of the tape 24), what stage of a printing operation the printing apparatus 1 is in (i.e. whether the first tape spool 16 should be accelerating/decelerating/stopping according whether the tape drive 10 is in a printing phase or non-printing phase, data from the substrate sensor which detects how fast the substrate is travelling and hence how fast the first tape spool 16 needs to supply tape into the tape path, and which type of printing is being carried out (the printing apparatus 1 could be operated in “continuous” print mode or “intermittent” print mode - in intermittent printing the tape 24 and the substrate are held stationary while the printhead 28 is moved across the area to be printed during the printing phase, whereas in continuous printing the substrate is moved continuously and tape 24 is accelerated to match the substrate before the printhead 28 makes contact).

In intermittent printing mode, the first motor 20 is controlled so as to feed out known lengths of tape 24 into the tape path at a known rate during the nonprinting phase to move the used tape 24 through the tape drive 10.

In continuous printing, the first motor 20 is operated during the printing phase so as to feed out known lengths of tape 24 from the first tape spool 16 into the tape path, at a speed that substantially matches the speed of the substrate during the printing phase. During the non-printing phase, the first motor 20 (and first tape spool 16) can be reversed, such that the first tape spool 16 takes up the tape 24. This is often done as preparation to start a new printing phase. The first controller 36 controls the motor 20 so as to rewind known lengths of tape 24 at a predetermined rate, to position a portion of tape 24 in the correct position relative to the printhead 28 to enable minimum wastage of tape 24.

In the course of a tape movement the tape drive 10 performs the following steps. At the beginning of a tape movement the first tape spool 16 begins to supply tape 24 into the tape path of the tape drive 10 (i.e. the first motor 20 drives the first tape spool 16 such that tape 24 is fed into the tape path). The controller 36 uses the information described above to control the angular velocity (i.e. step rate) of the first motor 20. The motor control system 42 aims to match the speed of the tape 24 past the printhead 28 with the speed required by the print mode selected.

The controller 38 which controls the second motor 22 aims to control the angular velocity of the second tape spool 18, so as to take up tape 24 from the tape path at substantially the same rate as tape 24 is fed into the tape path by the first tape spool 16, but the controller 38 is not provided with information about the operation of the first tape spool 16 or the first motor 20. The overall aim of the controller 38 is to maintain substantially constant tension in the tape 24 (or within predetermined acceptable limits). The controller 38 is provided with data relating to the speed of the substrate from the substrate sensor, information from the print cycle controller 34, relating to the stage of a printing cycle that the tape drive 10 is currently in and the signal from the TMD 30. The controller 38 also monitors the angular velocity of the second motor 22. The controller 38 is not (or need not be) provided with information relating to the lengths of tape on the first tape spool 16 or the second tape spool 18, nor the diameters of the spools 16, 18. The controller 38 controls the second motor 22 such that the length of the tape being taken up by the second tape spool 18 during tape transfer is not taken into account. The motor control system 42 does not attempt to directly match the length of tape fed into the tape path with the length of tape taken up from the tape path during a movement of the tape 24. The rate at which the second tape spool 18 takes up tape is based upon knowledge of changes to the path length and signals provided by the substrate sensor.

The second motor 22 may be a stepper motor operated in open loop mode, in which case the controller 38 has direct control over the angular position of the second motor 22. The second motor 22 may be a DC motor in which case the controller 38 monitors the angular position of the second motor 22 using a rotary encoder or equivalent device.

For example, in the event that the second tape spool 18 is rotating too slowly to take up all of the tape 24 which has been fed into the tape path by the first tape spool 16. The TMD 30 moves in such a direction as to extend the length of the tape path (100). Extending the length of the tape path compensates for the “excess” tape 24 fed into the tape path by the first tape spool 16, and maintains the tension in the tape 24 at a substantially constant value (or at least between predetermined acceptable limits). The monitoring of the signal from the TMD 30 takes place continuously. The controller 34 uses its knowledge of the current printing phase to apply weight to the signal. For example, during a printing phase the force of the printhead 28 against the substrate will create disturbances in the tape 24 that need to be ignored.

The position sensor 32 measures/detects the displacement of the TMD 30 and provides a signal to the motor control system 42. The controller 34 monitors the signal and stores the result as a required position adjustment Pr(i). The controller 34 communicates the required position adjustment Pr(i) to the motor control system 42 (102), in the present example to the second controller 38.

The second controller 38 uses the required position adjustment Pr(i) of the TMD 30 to calculate a corrected rotational velocity Vn(i> of the second tape spool 18 (104). The corrected rotational velocity Vnoi) calculated is compared to the current rotational velocity Va (i.e. the actual/measured rotational velocity at the present time) of the second tape spool 18 (106). Based on the difference between the corrected rotational velocity Vn(i) and the current rotational velocity Va, an adjustment is applied to the second tape spool 18 (a “required velocity adjustment” Vr(i)). The corrected rotational velocity Vno) (and hence, the required velocity adjustment Vr(-i)) is calculated to achieve two main goals. It should be appreciated that, in embodiments where the second motor is a stepper motor, the adjustment Vr(-i) will be an adjustment of the step rate of the motor 22.

The first aim is to calculate the rotational velocity required of the second tape spool 18 to return the TMD 30 to a neutral position (i.e. ideally the position of the TMD 30 is maintained in or around a central position, defined between the two extreme positions of the TMD 30) (108). For example, in the event that the TMD 30 moves into the tape path to compensate for sufficient tape not being taken up by the second tape spool 18 to maintain a constant path length (as described above), the revised rotational velocity Vnoi) is calculated taking the required position adjustment Pr(i) into account (i.e. that the TMD 30 has extended the length of the tape path), which is due to excess tape 24 not being wound up by the second tape spool 18. In order to return the TMD 30 to its neutral position, the revised rotational velocity Vn(i> of the second tape spool 18 is faster than the current rotational velocity Va of the second tape spool 18 (i.e. the second tape spool 18 must take up tape 24 at a faster rate).

As the difference between the rate at which the tape 24 is supplied into the tape path by the first tape spool 16, and the rate at which the tape 24 is taken up by the second tape spool 18 decreases, as a result of the adjustment of the velocity of the second spool 18, the length of tape 24 in the tape path decreases. This results in the TMD 30 moving in a direction so as to decrease the length of the tape path (i.e. the TMD 30 moves back towards its neutral position).

The second aim is to calculate the rotational velocity required of the second tape spool 18 to minimise subsequent required position adjustments Pr(n) of the TMD 30 (i.e. to reduce the likelihood of further movements of the TMD 30 being needed). For example, if the motor control system 42 signals to the second motor 22 to speed up (as in the first example above) and the second tape spool 18 takes up more tape 24 than is being supplied by the first tape spool 16, then the length of tape 24 in the tape path will continuously decrease. Initially, this allows the TMD 30 to move back to its neutral condition. However, once the TMD 30 has reached the neutral condition, tape 24 will continue to be taken up by the second tape spool 18. This results in a greater force being exerted on the TMD 30 by the tape 24, and as a result (to keep the force constant on the TMD 30 and therefore the tension in the tape 24 constant) the TMD 30 moves out of the tape path and shortens the length of the tape path. A new required position adjustment Pr(2) is communicated to the controller 38 which will result in the second motor 22 and hence the second tape spool 18 decreasing in rotational velocity (opposite to the example discussed above - i.e. a second revised rotational velocity Vn(2) is lower than the first revised rotational velocity Vn(i))·

The motor control system 42 (in particular the second controller 38) monitors the effect of the changes made to the rotational velocities of the motors 20, 22 on the tape 24. The motor control system 42 adjusts the magnitude of the changes to be applied to the second motor 22 based on past changes and their effects.

The above method may be performed in a variety of ways. For example, machine learning techniques including linear neural networks, non-linear recurrent neural networks or PID algorithms are all suitable.

For example, a linear neural network (i.e. a feedforward network) may provide a plurality of nodes each having an associated activation function. The function maps a weighted sum of input values in, to an output value. The inputs may include the speed of the substrate from the substrate sensor, and the current rotational velocity Va of the second motor 22 (and therefore, the second tape spool 18), for example. Each input in is fed into the network, and associated with a respective weight W·,. A predetermined activation function, which typically equates to a predetermined activation threshold value, maps the weighted inputs to a single output value o. The output value may represent the required velocity adjustment Vrci) for the second motor 22 (and hence, the second tape spool 18). The network uses learning/training techniques, such as back-propagation, for example, to learn and evolve. For example, the weights W, (that are associated with each input in) can be updated using learning rules based on an error term Err,. Where the measured/detected displacement of the TMD 30 is used as the error term, the network may recalculate the weights it associates with each input value (the speed of the substrate from the substrate sensor, and the current rotational velocity Va of the second motor 22), so as to minimise the error term - thus minimising the displacement of the TMD 30.

As an alternative, a non-linear recurrent neural network uses nodes which have binary (or close to binary) activation functions, in combination with providing one or more “hidden nodes” (i.e. without directly observable inputs and outputs), within the network. The activation functions of those nodes map weighted inputs to outputs that feed forward as inputs to other nodes within the network. In this way, the activation functions of the nodes may be determined so as to correspond to system performance, and thus network node values, at earlier times. In a non-linear neural network of this type, data flow is bidirectional through the network, so that values output from later layers of the network are propagated back to earlier layers of the network, so that processing of current inputs is affected by past performance. In this way, the system uses current operational information to influence its choice of future performance.

In both examples, it is possible to tune the system’s learning parameters such that the weights W-, dynamically adjust in response to the movement of the TMD 30 (in other words, in response to the changing length of tape supplied by the supply motor over time. So, in summary, the control of the second tape spool (and in particular a velocity adjustment VR(1) for the second motor 22) is determined based on the speed of the substrate from the substrate sensor, and the current rotational velocity Va of the second motor 22. Using a learning system such as one employing a neural network as described, the displacement of the TMD 30 is used to tune the parameters of the system, to improve future performance. In other words, given a pair of input values, the network outputs a corresponding control parameter based on its current configuration. By measuring or detecting the displacement that occurs as a result of implementing that control parameter (i.e. the degree of displacement of the TMD), the network can be updated to improve future performance, and thus optimise the control of the second motor over time.

Alternatively, a PID loop may use both the required position adjustment from a first cycle Pr(i) (i.e. when the TMD 30 lengthened the tape path) and the required position adjustment from a second cycle Pr<2) (i.e. when the TMD 30 shortened the tape path) and calculate a corrected rotational velocity Vn(23) (and hence required velocity adjustment Vr(23)) for the second motor 22 based on a value which will allow the TMD 30 to move towards the neutral position, but not overshoot it substantially. Over time/subsequent iterations of the method steps, the movement of the TMD 30 is either maintained or reduces (i.e. an Nth required position adjustment Pr(n> is either the same or smaller than a required position adjustment of the cycle before Pr(n--i))·

The second tape spool 18 is rotated at a rotational velocity set by the motor control system 42. This does not take into account any details of the movement of the first tape spool 16 (i.e. it moves independently of the first tape spool 16), and hence it does not take into account how much tape 24 has been supplied into the tape path. The rotational velocity of the second tape spool 18 depends, in part, on the measured required position adjustment Pr(n) of the TMD 30. The rotational velocity of the second tape spool 18 may also take into account one of more of required position adjustments of the TMD 30 in other previous printing operations Pr(n-x), and what stage of a printing operation the printing apparatus 1 is in (i.e. whether the second tape spool 18 should be accelerating/decelerating/stopping according whether the tape drive 10 is in a printing phase or non-printing phase, etc.). An important feature of the motor control system method for the second tape spool 18, is that the control system learns how to adjust the rotational velocity of the second motor 22 to result in fewer and/or smaller required position adjustments Pr{N) to the TMD 30 (i.e. it is an evolving system which improves the longer the printing apparatus 1 is operating).

If the TMD 30 reaches either extreme position of its motion, the motor control system is no longer able to control the tape 24. The motor control system 42 will enter a “fault” condition and stop the tape drive 10 / printing operations. For example, this may happen if the tape 24 becomes damaged during a printing operation.

An advantage of this system is that second controller 38 which controls the second motor 22 responds to the movement of the TMD 30, and hence responds directly to the characteristics of the tape 24 rather than assumptions about the characteristics of the tape 24.

This method of operating the printing apparatus is advantageous because it minimises the movement of the component parts (the TMD 30 is not constantly moving between its extreme positions). This results in less stress on the tape 24 and components needing replacement less often.

The method results in smoother operation of the tape drive 10, because the controller 34 learns the characteristics of the tape 24 and optimises the response of the second motor 22 in relation to the tape changes detected by the TMD 30.

The method monitors the tape 24 continuously enabling the motor control system 42 to respond quickly to changes in the tape tension which are outside of the acceptable limits for the current printing operation.

In the example shown, the first tape spool 16 is the supply spool and the second tape spool 18 is the take-up spool. However, it should be appreciated that the operation of the printing apparatus 1 could be reversed and the first tape spool 16 would become the take-up spool and the second tape spool 18 would become the supply spool. The tape drive 10 is operable bi-directionally.

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 (17)

1. A method of operating a tape drive, of the type operable to transfer a tape between a first spool and a second spool, and which includes two spool supports each of which is suitable for supporting a spool of tape, and a motor control system which includes a first motor and second motor and a controller for controlling the operation of at least one of the motors, the first motor being operable to rotate the first spool and the second motor being operable to rotate the second spool, the motor control system further including a tape monitor device, the position of which is adjustable in response to a change in the length of tape extending in a tape path between the first spool and a second spool, the method including the steps of: monitoring the position of the tape monitor device, and providing an indication of a required position adjustment of the tape monitor device to adjust a length of the tape path so as to maintain tension in the tape substantially constant; controlling at least one of the motors by: calculating a corrected rotational velocity of the at least one motor by using the required position adjustment of the tape monitor device, comparing the corrected rotational velocity to a current rotational velocity of the at least one motor and calculating an adjusted rotational velocity, and applying the adjusted rotational velocity to the at least one motor, to achieve the corrected rotational velocity of the at least one motor.

2. A method of operating a tape drive, of the type operable to transfer a tape between a first spool and a second spool, and which includes two spool supports each of which is suitable for supporting a spool of tape, and a motor control system which includes a first motor and second motor and a controller for controlling the operation of at least one of the motors, the first motor being operable to rotate the first spool and the second motor being operable to rotate the second spool, the motor control system further including a tape monitor device, the position of which is adjustable in response to a change in the length of tape extending in a tape path between the first spool and a second spool, the method including the steps of: operating at least one of the motors at a current rotational velocity; monitoring the position of the tape monitor device, and providing an indication of a required position adjustment of the tape monitor device to adjust a length of the tape path so as to maintain tension in the tape substantially constant; controlling at least one of the motors by: calculating a corrected rotational velocity of the at least one motor by using the required position adjustment of the tape monitor device, comparing the corrected rotational velocity to the current rotational velocity of the at least one motor and calculating an adjusted rotational velocity, and applying the adjusted rotational velocity to the at least one motor, to achieve the corrected rotational velocity of the at least one motor.

3. A method of operating a tape drive according to claim 1 or 2, comprising performing a plurality of iterations, each iteration comprising performing the steps of claim 1 or claim 2, wherein the motor control system stores a first value relating to a first iteration of the method, and uses the first value in conjunction with a second relating to a second iteration of the method, such that a third required position adjustment relating to a third iteration of the method is minimised whilst maintaining the tape tension between predetermined limits.

4. A method of operating a tape drive according to claim 3, wherein the motor control system stores a plurality of values relating to measurements from previous iterations, and uses them to minimise a subsequent required position adjustments of the tape monitor device.

5. A method of operating a tape drive according to any one of the preceding claims, wherein the adjusted rotational velocity is applied to the motor controlling the second spool.

6. A method of operating a tape drive according to any one of the preceding claims, including a calibration step in which includes determining the diameters of the first and second spools of tape, and providing an indication of the diameters to the motor control system.

7. A method of operating a tape drive according to any one of the preceding claims, wherein the motor control system calibrates the tape drive using a stored value for a length and/or thickness of the tape.

8. A method of operating a tape drive according to any one of the preceding claims, wherein the first spool of tape is a supply spool, which is configured supply tape into the tape path and the second spool of tape is a take up spool, which is configured to take up tape from the tape path.

9. A method of operating a tape drive according to any one of the preceding claims, wherein the first motor is drivable to supply a known length of tape into the tape path, which is defined by the relative positions of one or more guide members.

10. A method of operating a tape drive according to any one of the preceding claims, wherein the motor control system includes a second controller which uses a measured value of the velocity of a substrate, and controls the movement of the first motor to achieve a corresponding velocity of the tape.

11. A method of operating a tape drive according to any one of the preceding claims, wherein the controller uses an acceleration/deceleration of the tape required to begin a printing operation in conjunction with the adjusted rotational velocity to control the second motor.

12. A method according to any one of the preceding claims, wherein the first and second motors are controlled, by two separate controllers, independently of one another.

13. A printing apparatus which includes a tape drive, of the type operable to transfer a tape between a first spool and a second spool, the tape drive including a tape monitor device, two spool supports each of which is for supporting a spool of tape, and a motor control system which includes a first and second motor and a controller for controlling the operation of at least one of the motors, the first motor being operable to rotate the first spool and the second motor being operable to rotate the second spool, wherein the tape drive is operable in accordance with the method of any one of the preceding claims.

14. A printing apparatus according to claim 13 being a thermal transfer printer.

15. A method of operating a tape drive substantially as described herein and/or as shown in the accompanying drawings.

16. A printing apparatus substantially as described herein and/or as shown in the accompanying drawings.

17. Any novel feature or novel combination of features substantially as described herein and/or as shown in the accompanying drawings.