Drive units for driving shutter doors

Abstract

A drive unit for driving a shutter door. The drive unit comprises a control unit, and a motor controlled by the control unit, the motor comprising an axle. The drive unit also comprises a roller barrel driven by the axle of the motor, arranged to have a shutter door mounted upon it so that the motor can extend and retract the shutter door by rotating the roller barrel. The drive unit also comprises a switch arranged to be activated when, while the roller barrel is driven by the motor to extend the shutter door, the roller barrel is prevented from rotating. The control unit is arranged to stop extending the roller door when the switch is activated.

Description

[0001] Drive units for driving shutter doors

[0002] Field of the Invention

[0003] The present invention concerns drive units for driving shutter doors. More particularly, but not exclusively, the invention concerns drive units for driving shutter doors that are arranged to detect obstacles in the path of a shutter door during extension of the shutter door. The invention also concerns shutter door assemblies and methods of installing a drive unit in a shutter door assembly.

[0004] Background of the Invention

[0005] Shutter door assemblies are commonly used in shops, warehouses, garages and factories and the like, to close entry and exit openings, loading bays and the like. As people, vehicles and other obstacles may be present underneath a shutter door when it is being extended, it is common for shutter door assemblies to be able to detect obstacles that are in the way of a shutter door during extension, and stop or retract the shutter door to prevent damage to the internal components of the shutter door assembly, and to prevent injury to people and damage to obstacles that are underneath the shutter door.

[0006] A known shutter door assembly that can detect when there is an obstacle is shown in Figure 1, which is an exploded view of the shutter door assembly 1. The shutter door assembly 1 comprises a drive unit 3 that can extend and retract a shutter door 9. The ends of the drive unit 3 are fixed to the top of the opening covered by the shutter door 9 by brackets 15, so that the drive unit 3 extends horizontally across the top of the opening. The drive unit 3 and the top of the shutter door 9 are enclosed withing a casing 19, and the sides of the shutter door 9 extend into guide rails 17 which are mounted on either side of the opening below the brackets 15, and act to keep the shutter door 9 in the correct position.

[0007] The drive unit 3 comprises a motor (not shown) and a rotatable roller barrel 7. The shutter door 9 is mounted on the roller barrel 7 by three locking devices 11, which act to prevent the shutter door 9 being retracted by being pushed upwards when the shutter door 9 is at its maximum extension. The drive unit 3 can extend or retract the shutter door 9 by rotating the roller barrel 7 in the desired direction.

[0008] A flexible tube 13 is mounted on the bottom of the shutter door 9. At one end of the flexible tube 13 is a light-emitting diode (not shown), and at the other end of the flexible tube 13 is a light sensor (again not shown), so that in normal use the light sensor receives light from the light-emitting diode. However, if, during extension of the shutter door 9 by the drive unit 3, the bottom of the shutter door 9 meets an obstacle, the flexible tube 13 will be compressed, preventing the light from the lightemitting diode being received by the light sensor. This allows the presence of an obstacle to be detected, and the drive unit can accordingly stop extending the shutter door 9, or retract it, to prevent damage to the shutter door assembly 1 and / or the obstacle.

[0009] Other obstacle detection systems are known, for example systems that use a laser and sensor mounted at opposite sides of the bottom of the opening covered by the shutter door, so that any obstacle will break the beam of the laser and so be detected.

[0010] However, a disadvantage with known shutter door assemblies that are able to detect obstacles is that the detection apparatus needs to be positioned at the bottom of the shutter door, or at the bottom the opening the shutter door covers, so separately to the drive unit. This complicates installation and maintenance of the shutter door assembly.

[0011] The present invention seeks to solve or mitigate some or all of the above- mentioned problems. Alternatively or additionally, the present invention seeks to provide improved drive units for driving shutter doors, improved shutter door assemblies and improved methods of installing a drive unit in a shutter door assembly.

[0012] Summary of the Invention

[0013] In accordance with a first aspect of the invention there is provided a drive unit for driving a shutter door, wherein the drive unit comprises: a control unit; a motor controlled by the control unit, the motor comprising an axle; a roller barrel driven by the axle of the motor, wherein the roller barrel is arranged to have a shutter door mounted upon it so that the motor can extend and retract the shutter door by rotating the roller barrel; a switch arranged to be activated when, while the roller barrel is driven by the motor to extend the shutter door, the roller barrel is prevented from rotating; and wherein the control unit is arranged to stop extending the roller door when the switch is activated.

[0014] The roller barrel will be prevented from rotating while the roller barrel is driven by the motor to extend the shutter door when the shutter door is prevented from extending, i.e. when there is an obstacle. By having the switch activated when the roller barrel is driven by the motor to extend the shutter door but the roller barrel is prevented from rotating, the presence of an obstacle can be determined using only components of the drive unit itself, and so no components separate from the drive unit, for example at the bottom of the shutter door or the bottom of the opening covered by the shutter door are required.

[0015] The motor may be arranged such that, while the roller barrel is driven by the motor to extend the shutter door, when the roller barrel is prevented from rotating the axle of motor can continue to rotate by an amount; and the switch may be arranged to be activated when the axle of the motor rotates relative to the roller barrel. In this case, the drive unit may further comprise: a drive plate driven by the axle of the motor; and a receiving plate mounted on the roller barrel; wherein the drive plate is arranged to rotate the receiving plate, wherein drive plate is arranged to rotate by an amount relative to the receiving plate when the receiving plate is prevented from rotating, and wherein the switch is arranged to be activated when the drive plate rotates relative to the receiving plate. One of the drive plate and the receiving plate may comprise a plurality of protrusions that extend into recesses in the other of the drive plate and the receiving plate, and the drive plate may be arranged to rotate the receiving plate using the protrusions and the recesses. The recesses may be depressions in the drive plate or receiving plate, or may be holes through the drive plate or receiving plate.

[0016] Alternatively, the switch may be arranged to be activated when the roller barrel is forced upwards within the drive unit by the shutter door. The control unit may be configured to determine the distance of the bottom of the shutter door from its maximum extension. This allows the control unit to control the shutter door appropriately dependent upon its distance from the ground. For example, the control unit may stop extending the motor when the bottom of the shutter door is at its maximum extension or when the bottom of the shutter door is at its fully retracted position, to prevents unnecessary strain on the motor and the roller barrel when the roller barrel is unable to rotate any further.

[0017] The control unit may be configured, when the distance of the bottom of the shutter door from its maximum extension is less than a predetermined distance, to allow the shutter door to continue to be extended when the switch is activated. This means the control unit can continue to extend the shutter door when it approaching being fully closed, allowing the shutter door to be closed properly, even though the bottom of the shutter door pushing against the ground my cause the switch to be activated. The predetermined distance may be at least 50mm, or any other desired distance.

[0018] The control unit may comprise non-volatile memory configured to store data indicative of the distance of the bottom of the shutter door from its maximum extension. This allows the drive unit to retain the distance of the bottom of the shutter door from its maximum extension even if it is switched off temporarily.

[0019] The control unit may comprise a machine learning module arranged to receive data indicative of the operation of the motor by the control unit and configured to determine the distance of the bottom of the shutter door from its maximum extension. The data indicative of the operation of the motor by the control unit may include the period of time that the motor is driven to extend or retract the shutter door. It has been found that a suitably trained machine learning module is able to determine the distance of the bottom of the shutter door from its maximum extension using such information, despite the relationship between the distance the shutter door travels and the period of time that the motor is driven not being linear, due to the effect of the temperature of the motor while it is driven on the performance of the motor.

[0020] The control unit may comprise a temperature sensor arranged to sense the temperature of the motor, and the machine learning module may be configured to use the temperature sensed by the temperature sensor to determine the distance of the bottom of the shutter door from its maximum extension. The control unit may be configured to control the motor to drive the roller barrel to retract the shutter door by a predetermined distance when the switch is activated. This means that during extension of the shutter door, if an obstacle is detected, the shutter door will be raised by the predetermined distance so that it is no longer in contact with the obstacle. The shutter door may be retracted by a small amount, for example 10mm or 50mm, or may retract the shutter door to its fully retracted position.

[0021] In accordance with a second aspect of the invention there is provided a shutter door assembly comprising: a shutter door; and a drive unit mounted to the shutter door, wherein the drive unit is as described above.

[0022] The shutter door may be arranged to be locked when the bottom of the shutter door is at its maximum extension. The shutter door assembly may comprise one or more locking devices on the roller barrel of the drive unit, wherein the one or more locking devices are arranged to prevent retraction of the shutter door.

[0023] In accordance with a third aspect of the invention there is provided a method of installing a drive unit in a shutter door assembly comprising a shutter door as described above, wherein the drive unit is as described above, comprising the steps of mounting the drive unit in the shutter door assembly; mounting the shutter door to the roller barrel of the drive unit; calibrating the drive unit by: causing the control unit to extend the shutter door so that the bottom of the shutter door is at its maximum extension; causing the control unit to retract the shutter door so that the bottom of the shutter door is fully retracted.

[0024] In accordance with a fourth aspect of the invention there is provided a drive unit for driving a shutter door, wherein the drive unit comprises: a control unit; a motor controlled by the control unit; a roller barrel driven by the motor, wherein the roller barrel is arranged to have a shutter door mounted upon it so that the motor can extend and retract the shutter door by rotating the roller barrel; detecting apparatus arranged to detect an obstacle preventing the extension of the shutter door; wherein the control unit comprises: a machine learning module arranged to receive data indicative of the operation of the motor by the control unit, and configured to determine the distance of the bottom of the shutter door from its maximum extension; wherein the control unit is configured to stop extension of the shutter door when the detecting apparatus detects an obstacle is preventing the extension of the shutter door; and wherein the control unit is further configured, when the machine learning module determines that the distance of the bottom of the shutter door from its maximum extension is less than a predetermined distance, to allow the shutter door to continue to be extended when the detecting means detects an obstacle preventing the extension of the shutter door.

[0025] It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

[0026] Description of the Drawings

[0027] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0028] Figure 1 shows an exploded view of a known shutter door assembly;

[0029] Figure 2 shows a side view of a drive unit according to a first embodiment of the invention;

[0030] Figure 3 shows a front view of a drive plate of the drive unit of the first embodiment; Figure 4a shows a front view of a receiving plate of the drive unit of the first embodiment in a first configuration;

[0031] Figure 4b shows a front view of a receiving plate of the drive unit of the first embodiment in a second configuration;

[0032] Figure 5 is a schematic representation of the functionality of the drive unit of the first embodiment; and

[0033] Figure 6 is a flow-chart of a method of installing the drive unit of the first embodiment in a shutter door assembly.

[0034] Detailed Description

[0035] A drive unit for driving a shutter door in accordance with a first embodiment of the invention is now described with reference to Figures 2 to 4.

[0036] Figure 2 shows a drive unit 20, which comprises a mounting plate 35 at one end, a body portion 24 fixed to the mounting plate 35, a roller barrel 25 fixed to the body portion 24, and a mounting rod 31 extending from the roller barrel 25 at the other end of the drive unit 20. (The roller barrel 25 is in practice longer than shown in Figure 2 so as to span the width of the opening covered by the shutter door, as indicated by the jagged lines across its middle.)

[0037] The body portion 24 is fixed to the mounting plate 35 so that they cannot rotate with respect to each other. The body portion comprises a control unit 21, as described in more detail below, and a motor 23 controlled by the control unit 21. The motor 23 is mounted within the body portion 24 such that its housing cannot rotate with respect to the body portion 24. The axle 27 of the motor 23 extends from the end of the body portion 24 opposite the mounting plate 35.

[0038] The roller barrel 25 is then mounted on the axle 27 of the motor 23. In particular, the axle 27 is fixed to a drive plate 26 positioned within the roller barrel 25, which is fixed in place along the length of the roller barrel 25 but can rotate with respect to the roller barrel 25. The drive plate 26 is connected to a receiving plate 28, through which the axle 27 passes. The receiving plate 28 is fixed to the roller barrel so that it cannot rotate with respect to the roller barrel 25. On the receiving plate 28, positioned above the axle 27, is a switch 29, which is connected to the control unit 21. The operation of the axle 27, drive plate 26, receiving plate 28 and switch 29 is described in more detail below.

[0039] Locking devices 33 are positioned on the surface of the roller barrel 25, of which portions of three can be seen in Figure 2, and on which a shutter door can be mounted, similarly to the mounting of the shutter door 9 on the roller barrel 7 in Figure 1.

[0040] The drive plate 26 is shown in more detail in Figure 3. As discussed above, the drive plate 26 is fixed to the axle 27, so that the axle extends through the centre of the drive plate 26. The drive plate 26 has two protrusions 36 on either side of its surface facing the receiving plate 28. As can also be seen in this figure, the end of the axle 27 extending from the drive plate 28 is partially cut away, so that a shelf 27a is formed from a segment of the axle 27 that extends from the drive plate 28 on the side facing the receiving plate 28.

[0041] The receiving plate 28 and the switch 29 are shown in more detail in a first configuration in Figure 4a. The receiving plate 28 has holes 38 on either side, through which the protrusions 36 of the drive plate 26 extend. As can be seen, the holes 38 are curved and are roughly twice the length of the protrusions 36, allowing the receiving plate 28 to rotate a small amount with respect to the drive plate 26, until at either extreme when the protrusions 36 touch the extreme edges of the holes 38.

[0042] The receiving plate 28 has a circular hole 41 through its centre, through which the axle 27 extends. The circular hole 41 is larger than the axle 27, so that the axle 27 does not touch the receiving plate 28. Mounted on the receiving plate 28, above the axle 27, is the switch 29. As can be seen, the switch 29 is a microswitch, with a lever 29a extending across the circular hole 41 so that it touches the shelf 27a of the axle 27 towards one end. In the configuration shown in Figure 4, the drive plate 26 is at its most clockwise position with respect to the receiving plate 28, so that the protrusions 36 are at the clockwise extremes of the holes 38, and the switch 29 is not activated.

[0043] The receiving plate 28 and the switch 29 are shown in a second configuration in Figure 4b. In this configuration, the drive plate 26 is at its most anticlockwise position with respect to the receiving plate 28, so that the protrusions 36 are at the anticlockwise extremes of the holes 38. As can be seen, in this configuration the axle 27 is rotated with respect to the receiving plate 28, which results in the shelf 27a of the switch 27 pushing the lever 29a toward the body of the switch 29, so that the switch 29 is activated.

[0044] The significance of the configurations of Figures 4a and 4b during operation of the drive unit 20 is described in more detail below.

[0045] Figure 5 is a schematic diagram showing the functionality of the components of the drive unit 20. The control unit 21 receives an external power supply 75, which is uses for its own power supply, and also to provide power to drive the motor 23. The control unit 21 is also connected to the switch 29, so that it can identify if the switch 29 is activated. The control unit 21 is in radio communication with an external remote control 70, which can be used by an operator to instruct the drive unit 20 to extend and retract the shutter door.

[0046] In addition, the control unit 21 comprises a machine learning module 21a, and is in communication with non-volatile memory 77, i.e. memory that retains data in the absence of a supply of power, using which it can store data from the machine learning module 21a, as described in more detail below.

[0047] The operation of the drive unit 20 when extending and retracting a shutter door, and when an obstacle is present, is now described. When the drive unit 20 is mounted in a shutter door assembly covering an opening, the mounting plate 35 will be fixed to a bracket such as the bracket 15 of Figure 1 on one side of the opening, so that the mounting plate 35 cannot rotate with respect to the opening. The mounting rod 31 at the other end of the drive unit 20 will be positioned in a bracket which holds it in place horizontally and vertically, but allows it to rotate.

[0048] When a shutter door is mounted on the roller barrel 25, it will hang down from the left-hand side of the receiving plate 28 as shown in Figures 4a and 4b. Consequently, when the shutter door is open or partially open, gravity acting on the shutter door will act to rotate the roller barrel 25, and so the receiving plate 28, anticlockwise with respect to the drive plate 26. Thus, the receiving plate 28 and the drive plate 26 will be in the configuration shown in Figure 4a, with the protrusions 36 of the drive plate 26 at the clockwise extreme of the holes 38, and the switch 29 not activated. If the motor 23 is not being driven by the control unit 21 to extend or retract the shutter door, the axle 27 of the motor 23 will not rotate, so the drive plate 26 will not rotate, and the receiving plate 28 will be held in position with respect to the drive plate 26 by the protrusions 36, thus holding the roller barrel 25 and the shutter door in position.

[0049] If the remote control 70 is used by an operator to instruct the control unit 21 to retract the shutter door, the axle 27 of the motor 23 will be rotated clockwise. This rotates the drive plate 26 clockwise, causing the protrusions 36 push against the clockwise extreme edges of the holes 38. This causes the receiving plate 28 and the roller barrel 25 to retract clockwise, retracting the shutter door.

[0050] If, on the other hand, the remote control 70 is used by an operator to instruct the control unit 21 to extend the shutter door, the axle 27 of the motor 23 will be rotated anticlockwise. This rotates the drive plate 26 anticlockwise, and the protrusion 36 of the drive plate 26 will no longer prevent the receiving plate 28 and roller barrel 25 from rotating anticlockwise due to gravity acting on the shutter door, so allowing the shutter door to extend. However, importantly, the motor 23 does not force the shutter door to extend, due to the drive plate 26 forcing the receiving plate to rotate anticlockwise. Rather, the drive plate 26 allows the receiving plate 28 to be rotated clockwise due to the shutter door being pulled downwards by gravity. As a consequence, the drive plate 26 and the receiving plate 28 will remain in the configuration shown in Figure 4a, with the protrusions 36 of the drive plate 26 at the clockwise extreme of the holes 38.

[0051] However, should the shutter door encounter an obstacle during extension, it will remain in position instead of being pulled downwards by gravity. In this situation, the drive plate 26 will continue to rotate anticlockwise, but the receiving plate 26 will remain in position. The receiving plate 28 and the drive plate 26 will therefore move to the configuration shown in Figure 4b, with the protrusions 36 of the drive plate 26 at the anticlockwise extreme of the holes 38. As this happens, due to the rotation of the axle 27 with respect to the receiving plate 28 the switch 29 will be activated by the shelf 27a of the axle 27 acting upon the lever 29a of the switch. This indicates to the control unit 21 that an obstacle is present, and the control unit 21 will then stop extending the shutter door, to avoid any damage to the shutter door assembly or the obstacle.

[0052] In other embodiments, the control unit 21 may be configured to retract the shutter door a desired amount when it is determined that an obstacle is present. It will be appreciated that the switch 29 will also be activated when the shutter door reaches its maximum extension and comes into contact with the ground, even when no obstacle is present. In such a situation, if the control unit 21 were to determine that an obstacle was present, the shutter door could be prevented from closing completely, or retracted by the control unit 21, preventing the shutter door from locking in a closed position.

[0053] To avoid this, in certain embodiments of the invention including the present embodiment, the control unit 21 is configured to determine the distance of the bottom of the shutter door from the ground using the machine learning module 21a, which is described in more detail below. The control unit 21 is configured so that, when the shutter door is within 50mm of the ground, the door is not stopped or retracted if the switch 29 is activated, so that the shutter door is not prevented from closing completely.

[0054] The machine learning module 21a is now described. The machine learning module 21a has been trained so that, when calibrated for use with a particular shutter door, it is able to determine the distance of the bottom of the shutter door from the ground.

[0055] The machine learning module 21a determines the distance of the bottom of the shutter door from the ground using only the time period over which the motor of the drive unit 20 retracts or extends the shutter door, from which it is able to determine the distance the shutter door has moved. The relationship between the time the motor 23 is activated and the distance the shutter door travels will not be linear, due changes in the temperature of the motor while it is activated affecting its performance, amongst other things. However, it has been found that by training the machine learning module 21a on different shutter door assemblies, reliable determination of the distance of the bottom of the shutter door from the ground can be achieved. In other embodiments of the invention, a temperature sensor that senses the temperature of the motor may also be used by the machine learning module 21a, to give a further input to use to determine the position of the shutter door.

[0056] The machine learning module 21a is calibrated during installation of the drive unit 20 in a shutter door assembly, as now described with reference to the flow chart of Figure 6. First, the drive unit 21 is mounted in the shutter door assembly (step 101), and the shutter door is mounted to the roller barrel 25 of the drive unit 21 (step 103). The shutter door is then extended to its maximum extension (step 105), i.e. to the point at which it touches the ground. The shutter door is then retracted to its fully retracted position (step 107).

[0057] By performing these steps using the control unit 21, the machine learning module 21a is provided as input the time the motor 23 takes to fully retract the shutter door from the fully extended position. In addition, the machine learning module 21a knows that the shutter door is initially in the fully retracted position. Using this information, it is able to keep track of the distance of the bottom of the shutter door from the ground as the shutter door is extended and retracted, even if the shutter door is not fully extended or retracted. Further, the control unit 21 can store in the nonvolatile memory 77 the position of the shutter door, so that the machine learning module 21 is able to continue to determine the position of the shutter door even if the drive unit 20 is switched off temporarily. Finally, if the shutter door is fully extended or fully retracted, the machine learning module 21a can use that to determine the distance of the bottom of the shutter door from the ground (i.e. zero, or the maximum possible), so eliminating any “drift” there may be in the determined distance.

[0058] While the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0059] The skilled person will appreciate that in other embodiments of the invention, an obstacle may be detected by a switch that is activated when the roller barrel is forced upwards within the drive unit, as will occur if the shutter door is not able to extend, but the motor is trying to rotate the roller barrel so as to force it downwards. In this case, switch may be positioned above the roller barrel so that it is pushed when the roller barrel moves upwards.

[0060] The skilled person will also appreciate that in embodiments of the invention, the machine learning module such as the machine learning module 21a may be used with a shutter door assembly that uses another method to detect an obstacle, such as the flexible tube, laser or any other suitable method, with the machine learning module determining the distance of the bottom of the shutter door from the ground to prevent the ground being detected as an obstacle and so prevent the shutter door being fully closed.

[0061] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

Claims1. A drive unit for driving a shutter door, wherein the drive unit comprises: a control unit; a motor controlled by the control unit, the motor comprising an axle; a roller barrel driven by the axle of the motor, wherein the roller barrel is arranged to have a shutter door mounted upon it so that the motor can extend and retract the shutter door by rotating the roller barrel; a switch arranged to be activated when, while the roller barrel is driven by the motor to extend the shutter door, the roller barrel is prevented from rotating; and wherein the control unit is arranged to stop extending the roller door when the switch is activated.

2. A drive unit according to claim 1, wherein: the motor is arranged such that, while the roller barrel is driven by the motor to extend the shutter door, when the roller barrel is prevented from rotating the axle of motor can continue to rotate by an amount; and the switch is arranged to be activated when the axle of the motor rotates relative to the roller barrel.

3. A drive unit according to claim 2, wherein the drive unit further comprises: a drive plate driven by the axle of the motor; and a receiving plate mounted on the roller barrel; wherein the drive plate is arranged to rotate the receiving plate, wherein drive plate is arranged to rotate by an amount relative to the receiving plate when the receiving plate is prevented from rotating, and wherein the switch is arranged to be activated when the drive plate rotates relative to the receiving plate.

4. A drive unit according to claim 3, wherein one of the drive plate and the receiving plate comprises a plurality of protrusions that extend into recesses in the other of the drive plate and the receiving plate, and wherein the drive plate is arranged to rotate the receiving plate using the protrusions and the recesses.

5. A drive unit according to claim 1, wherein the switch is arranged to be activated when the roller barrel is forced upwards within the drive unit by the shutter door.

6. A drive unit according to any preceding claim, wherein the control unit is configured to determine the distance of the bottom of the shutter door from its maximum extension.

7. A drive unit according to claim 6, wherein the control unit is configured, when the distance of the bottom of the shutter door from its maximum extension is less than a predetermined distance, to allow the shutter door to continue to be extended when the switch is activated.

8. A drive unit according to claim 7, wherein the predetermined distance is 50mm.

9. A drive unit according to any of claims 6 to 8, wherein the control unit comprises non-volatile memory configured to store data indicative of the distance of the bottom of the shutter door from its maximum extension.

10. A drive unit according to any of claims 6 to 9, wherein the control unit comprises a machine learning module arranged to receive data indicative of the operation of the motor by the control unit and configured to determine the distance of the bottom of the shutter door from its maximum extension.

11. A drive unit according to claim 10, wherein the data indicative of the operation of the motor by the control unit includes the period of time that the motor is driven to extend or retract the shutter door.

12. A drive unit according to claim 10 or 11, wherein the control unit comprises a temperature sensor arranged to sense the temperature of the motor, and wherein the machine learning module is configured to use the temperature sensed by the temperature sensor to determine the distance of the bottom of the shutter door from its maximum extension.

13. A drive unit according to any preceding claim, wherein the control unit is configured to control the motor to drive the roller barrel to retract the shutter door by a predetermined distance when the switch is activated.

14. A shutter door assembly comprising: a shutter door; and a drive unit mounted to the shutter door, wherein the drive unit is as claimed in any preceding claim.

15. A shutter door assembly according to claim 14, wherein the shutter door is arranged to be locked when the bottom of the shutter door is at its maximum extension.

16. A shutter door assembly according to claim 15, further comprising one or more locking devices on the roller barrel of the drive unit, wherein the one or more locking devices are arranged to prevent retraction of the shutter door.

17. A method of installing a drive unit in a shutter door assembly comprising a shutter door, wherein the drive unit is as claimed in any of claims 1 to 13, comprising the steps of mounting the drive unit in the shutter door assembly; mounting the shutter door to the roller barrel of the drive unit; calibrating the drive unit by: causing the control unit to extend the shutter door so that the bottom of the shutter door is at its maximum extension; causing the control unit to retract the shutter door so that the bottom of the shutter door is fully retracted.

18. A drive unit for driving a shutter door, wherein the drive unit comprises: a control unit; a motor controlled by the control unit; a roller barrel driven by the motor, wherein the roller barrel is arranged to have a shutter door mounted upon it so that the motor can extend and retract the shutter door by rotating the roller barrel;detecting apparatus arranged to detect an obstacle preventing the extension of the shutter door; wherein the control unit comprises: a machine learning module arranged to receive data indicative of the operation of the motor by the control unit, and configured to determine the distance of the bottom of the shutter door from its maximum extension; wherein the control unit is configured to stop extension of the roller door when the detecting apparatus detects an obstacle is preventing the extension of the shutter door; and wherein the control unit is further configured, when the machine learning module determines that the distance of the bottom of the shutter door from its maximum extension is less than a predetermined distance, to allow the shutter door to continue to be extended when the detecting means detects an obstacle preventing the extension of the shutter door.

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