AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Innovation Patent Applicant: Smart Openers Pty Ltd Invention Title: A SENSOR ASSEMBLY The following statement is a full description of this invention, including the best method for performing it known to me/us: -2 A SENSOR ASSEMBLY This application is a divisional application of Australian patent application no. 2008264221, the 5 disclosure of which is incorporated herein by reference. Field of the Invention This invention relates to a sensor assembly for a 10 door operator. Background Hitherto, door or gate openers have been utilised for 15 the opening of doors or gates such as roller doors or swing gates or sliding gates. As the weight of the doors or gates increases due to the size of the doors or gates, then increased power motors and increased strength structural drive trains are required to impart the 20 necessary driving forces to open and close the doors or gates. The difference is contrasted quite markedly with doors or gates for domestic use and doors or gates for industrial use. A manufacturer and/or supplier of the components for door or gate openers is required to stock a 25 large inventory of components to accommodate for domestic doors and gates, and industrial doors and gates. In addition, for industrial doors or gates, the components, being extra power motors and extra strength drive trains can become quite expensive which, in turn, makes 30 installation of industrial door or gate openers unnecessarily expensive. Typically, in order to provide the necessary driving torque for industrial doors or gates DC motors used in domestic doors or gates have been abandoned and more expensive larger torque capacity AC 35 motors have been used. 843991_1 (GHMatters) P76363.AU.1 15107/11 -3 Summary of the Invention According to a first broad aspect of the present 5 invention there is provided a sensor assembly for a door operator, said door operator being of the type having a motor for providing drive power, a drive train adapted to couple drive power from the motor to a door to cause opening and closing of the door and a controller adapted 10 to control the motor, the sensor assembly co-operating with the controller to stop the door at a set open position and a set closed position; the sensor assembly comprising: an input shaft for connecting the sensor assembly is with the drive train so the input shaft will be rotated as the door is opened and closed during both motor driven and manual operation, wherein said input shaft is removably connectable with the drive train via a removable drive coupling to enable the sensor assembly to be subsequently 20 removed, the removable drive coupling comprising a male component and a female component, and a door position limit sensing means that operates to sense when the door has reached a set open or a set closed position, the door position limit sensing means coupled 25 via the input shaft to the drive train such that the door position limit sensing means maintains a direct connection with the drive train when the door to which the door operator is connected is operated manually. 30 In an embodiment, said input shaft carries a worm gear directly engaged with a gear carried by an axle and wherein said sensing means senses movement of the door based on rotation of said axle. 35 In an embodiment, the male component of the drive coupling comprises the input shaft and the input shaft extends into a female component in the form of a hollow 843991_1 (GHMatters) P76363.AU. 1 15/07/11 - 4 interior of a driven shaft in the drive train. In an embodiment, the input shaft carries a coupling means for coupling the input shaft to the hollow interior, 5 and wherein said coupling means permits the coupling to be removed by retraction of said input shaft from said hollow interior. The invention also provided door operator having a 10 motor for providing drive power, a drive train adapted to couple drive power from the motor to a door to cause opening and closing of the door, a controller adapted to control the motor, and a door position sensor assembly as described above removably connected to the drive train. 15 Brief Description of the Drawings In order that the invention can be more clearly ascertained, reference will now be made to the 20 accompanying drawings showing examples of embodiments wherein: Figure 1 is a perspective view showing a roller door operator including a modular gear box in the form of a 25 motor drive module, Figure 2 is a view similar to Figure 1 showing the use of a motor drive module and an output drive module piggy-backed together, 30 Figure 3 is a view similar to that shown in Figure 2 but showing the input drive module piggy-back connected with an intermediate module which, in turn, is piggy-back connected with an output drive module, 35 Figure 4 is a front perspective view of the motor drive module, 843991_1 (GHMatters) P76363.AU.1 15/07/11 - 5 Figure 5 is a perspective view of the internal drive train of the motor drive module shown in Figure 4, 5 Figure 6 is a perspective view of the motor drive train shown in Figure 5 taken in another direction, Figure 7 is an exploded perspective view of the motor drive module casing and its internal drive train 10 components, Figure 8 is a perspective view of at least one gear carried internally of the casing, is Figure 9 is a perspective view of a ball race assembly, Figure 10 is a perspective view of a clutch mechanism, 20 Figure 11 is a side elevational view showing the at least one gear on an output shaft and showing the clutch mechanism, 25 Figure 12 is a perspective view of the axle/drive shaft of the output drive, Figure 13 is an exploded perspective view showing the arrangement of the piggy-back mounting of a drive module 30 with an output module, Figure 14 is a transverse cross-sectional view of an output module showing an internal drive train therein, 35 Figure 15 is a perspective view showing the drive train components of the motor drive module drive connected with the drive train components of an output module, 843991_1 (GHMatters) P76363.AU.1 15/07/11 -6 Figure 16 is an exploded perspective view showing the piggy-back arrangement for mounting of a drive module with an intermediate module and an output module, 5 Figure 17 is a perspective view showing the drive train components in the piggy-back arrangement shown in Figure 16, 10 Figure 18 is an exploded perspective view of a motor drive module and an output drive module showing a door curtain position limit sensing mechanism with a case therefor, 15 Figure 19 is a view similar to Figure 18 but with all the components in assembled relationship, Figure 20 is an end perspective view of the curtain position limit sensing mechanism with case removed, 20 Figure 21 is an exploded side perspective of the components of the curtain position limit sensing means, and 25 Figure 22 is an electric circuit block schematic diagram of a mains power supply, operator control electrics and a back-up battery. Detailed Description of Embodiments 30 Referring firstly to Figure 1 there is shown a perspective view of a roller door operator including a motor drive module. Whilst the motor drive module can be connected with any type of door system, this example is 35 for use with a roller door installation. Similarly, the motor drive module can be connected with any gate opener system. The invention is not to be limited to use with 843991_1 (GHMalters) P76363.AU.1 15/07/11 - 7 roller door installations. The door operator shown in Figure 1 is typically for use with a domestic roller garage door. Here, there is provided a mounting chassis 1 which can be mounted in a suitable operable position 5 adjacent the side edge of a roller door curtain. Typically, the chassis 1 is mounted to a facia wall of a garage door opening by brackets (not shown). The chassis 1 may be a sheet of metal or other suitable material. In this example, the chassis 1 is a sheet of aluminium. 10 A modular gear box 3, in the form of a motor drive module 5 is mounted to the chassis 1 to drive a sprocket gear 7 that is on the opposite side of the chassis 1 to the motor drive module 5. A chain drive 9 passes over the is sprocket gear 7 and over a larger tooth wheel 11 so that drive from a D.C. electric motor 13 can pass through the modular gear box 3 to the sprocket gear 7, through the chain drive 9 to the tooth wheel 11 to, in turn, rotate the tooth wheel 11. There will be a gear ratio reduction 20 from the output of the electric motor 13 to an output drive of the modular gear box 3 which, in turn, drives the sprocket gear 7. There will be further gear ratio reduction between the sprocket gear 7 and the tooth wheel 11. That provides an overall drive ratio reduction 25 between the motor 13 and the tooth wheel 11. The tooth wheel 11 is suitably journalled for rotation about its central axis 15 relative to the chassis 1. The tooth wheel 11 has two extending fingers 17 that are used when the door operator is mounted at the side edge of a roller 30 door curtain to engage on each side of a spoke arm of a door curtain drum wheel (not shown) to impart drive to roll up or roll down the door curtain. The arrangement for connecting with the door operator and the roller door drum wheel are known in the art per se and have therefore 35 not been shown. Figure 1 shows that the modular gear box has a 843991_1 (GHMatters) P76363 AU. 115107/11 -8 support structure which, in this example, is. a generally rectangular shaped casing 19. This casing can be made of a suitable material such as metal or industrial quality plastics. In this example, the casing 19 is preferably s made from a die cast aluminium. Figure 2 shows a perspective view similar to that shown in Figure 1 with two interconnected modular gear boxes 3, where one is the motor drive module previously 1o described in Figure 1, and the other is an output drive module 21. Here, it can be seen that the motor drive module 5 is piggy-backed to the output drive module 21 and that the support structures of each, being the casings 19 of the modular gear boxes 3, are of the same physical size is to permit mating piggy-back interconnection. Figure 3 is a view similar to that shown in Figure 2 showing three interconnected modular gear boxes 3 being the motor drive module 5, the output drive module 21, and 20 an intermediate drive module 23. Here all three modules 3 are piggy back connected with each other so there will be a drive train established between all three modules. Thus, drive from the electric motor 3 will pass successively through the three modules to drive the 25 sprocket gear 7 and the tooth wheel 11. The examples shown in Figure 2 and 3 enable the same size motor drive module 5 to be utilised for different size and weight door or gate installations Thus, where 30 the door operator shown in Figure 1 is particularly suitable for use with a domestic door, the examples shown in Figure 2 and 3 are more suited to heavier and larger type doors such as those in semi industrial or industrial applications. In this case, the same D.C. electric motor 35 13 can be used in the motor drive module 5 for all of these different types of installations without the need for additional components and sizes of motors and 843991_1 (GHMatters) P76363.AU.1 15/07/11 -9 structural strength components. The casings 19 of all the modules are provided with mounting means (to be described hereinafter) for permitting piggy-back mounting to'each other and to provide for correct alignment of the output 5 drive of one module with an input drive of a similar module whilst maintaining drive train engagement therebetween. In other words, the output drive from one module will connect with or form part of the input drive of an adjacent piggy-back module. 10 Referring now to Figures 4 - 12 it can be seen that the motor drive module 5 has a generally rectangular shaped casing 19 formed of two parts. The casing is hollow as shown specifically in Figure 7. The casing 19 15 has a mount 25 to permit mounting of an external power drive such as from an electric motor 13. The casing also has an external projecting boss 27 through which an output drive shaft 29 passes. The output drive shaft 29 preferably contains an output gear 31 on the free end 20 thereof, although the output drive shaft 29 may be a shaft to which a sprocket gear 7 is directly attached (as shown in Figure 1). When multiple modules are to be piggy backed together, then the output drive shaft 29 has an output gear 31 fitted thereto as shown. The casing 19 25 also has a protruding clutch operating lever 33 which will permit drive engagement and drive disengagement of an internal clutch to be referred to shortly. The casing 19 also includes mounting means 35 which permits piggy-back mounting of one module to another module and aligned 30 mounting of the respective modules. In the examples shown, the mounting means 35 comprise bolt openings 35 which are aligned between modules. These mounting means 35 will be described more fully hereinafter. 35 Each of the casing 19 parts are held together by bolts 37 (see Figure 7) that pass through aligned openings 39 in each of the respective parts of the casings 19. 843991_1 (GHMalters) P76383.AU.1 15/07/11 - 10 The drive train within the casing 19 includes at least one gear 41. The at least one gear 41 is connected to said output drive shaft 29 to independently rotate 5 about a central longitudinal axis of the output drive shaft 29 on a bearing sleeve 43. Figure 9 shows an enlarged version of the bearing sleeve 43 comprising an outer metallic casing 45 with an internal ball race 47. The internal diameter of the ball race 47 equals the io external diameter of the output drive shaft 29 at the position where it is to be fitted along the length of the output drive shaft 29. The external diameter of the ball race 47 corresponds to the internal diameter of the central opening 49 of the at least one gear 41. 15 Typically, press fitting arrangements are provided between the central opening 49 and the external diameter of the ball race 47, and the internal diameter of the ball race 47 with the external diameter of the output drive shaft 29. The balls in the ball race therefore provide free and 20 independent rotation of the at least one gear 41 relative to the output drive shaft 29. An input drive is provided to the gear box through a worm gear 51 which drive engages with the at least one gear 41. The worm gear 51 has a "D" shaped axle 53 which is locatable within a female 25 corresponding 'D" shaped socket in the motor 13 drive. Thus, when the motor 13 is fixed to the casing 19 of the gear box 13, drive from the motor 13 can be imparted to the input drive worm gear 51. The worm gear 51, in turn drives the at least one gear 41 about the central axis of 30 the drive shaft 29. A clutch mechanism shown generally as 55 is used to impart drive from the at least one gear 41 to the output drive shaft 29. In this example, the clutch mechanism 55 35 is a dog-clutch. The clutch mechanism 55 comprises a metal clutch disk having protruding dog fingers 57. The dog fingers 57 are located within dog finger recesses 59 843991_1 (GHMatters) P76363.AU.1 15/07/11 - 11 on an end face of the at least one gear 41. The clutch mechanism 55 is carried on the output drive shaft 29 so that it can move longitudinally along the longitudinal axis of the output drive shaft 29 so that in one s longitudinal position it will be in drive engagement with the dog fingers 57 engaged within the dog finger.recesses 59, and so that in a different longitudinal position there will be drive disengagement between the dog fingers 57 and the dog finger recesses 59. The clutch mechanism 55 10 carries internal key slots 61 which mate with upstanding keys 63 carried on the output drive shaft 29 which allow the clutch 55 to move longitudinally along the longitudinal length of the output drive shaft 29 whilst still maintaining a key driving arrangement between the 15 keys 63 and the key slots 61. The clutch 55 has a central internal opening 65 (see Figure 10) which is received directly over sleeve parts 67. The materials of the sleeve parts 67 may be chosen to facilitate easy sliding movement of the clutch mechanism 55 thereover. Figure 12 20 shows that the sleeve part 67 contain detente 69 which are spring loaded in a direction outwardly. The detents in turn, locate in detent grooves 71 in the opening 65 of the clutch mechanism 55. The detents 69 are diametrically opposed across the output drive shaft 29 and snap lock 25 hold the clutch mechanism 55 in an axially extended or retracted position where the dog fingers 57 are either displaced from the dog finger recesses 59 or engaged therein. 30 The clutch mechanism 55 is caused to be displaced along the longitudinal length of the output drive shaft 29 by a clutch operating lever 33 which swings a yoke shaped actuator 73 via axle 75. The yoke shaped actuator contains fingers 77 that locate in an actuator groove 79 35 in the clutch mechanism 55. Thus, the clutch operating lever 33 can be swung to, in turn, displace the clutch mechanism 55 longitudinally along the axial length of the 843991_1 (GHMatters) P76363AU.1 15107111 - 12 output drive shaft 29 to engage and disengage the clutch mechanism 55 to allow or disallow drive from the input drive to the output drive of the modular gear box. The output drive shaft 29 is supported within the parts of the 5 casing 19 by ball race rollers 81 which nest in corresponding recesses within the casing parts. The worm gear 51 is supported in the casing by ball race rollers 83 which also nest into corresponding recesses in the casing parts. 10 The bolts 37 hold the two casing parts together with all the components in an assembled relationship. Referring now to Figure 13 there is shown an exploded 15 view of a motor drive module 5 to be connected with an output drive module 85. Here each of the casings 19 are ready to be assembled in a piggy-back mounting arrangement to each other. Here, the mounting means 35 are shown so they can be aligned with each other so suitable bolts can 20 pass through the openings to hold the respective modular gear boxes 3/5 in an assembled aligned relationship. In this arrangement, the output drive module 85 has a similar casing 19 to the modular gear box casing 19 and 25 has stand offs 87 at each of the mounting means 35 which correspond in depth to the depth of boss 27. Thus, when the modules 3 and 85 are connected together in a piggy back arrangement, the stand offs 87 space the opposed faces of the casing 19 from each other and correctly align 30 the output gear 31 of the motor drive module 5 with the at least one gear 41 within the output drive module 85. Figure 14 shows the at least one gear 41 directly drive connected with an output drive shaft 89. The at 35 least one gear 41 is physically drive connected with the output drive shaft 89 by a key so that the output drive shaft 89 will be rotated as the at least one gear 41 is 843991_1 (GHMatlers) P7363.AU.1 15/07/11 - 13 rotated. Figure 14 shows a bearing 91 for supporting the free end of the output drive shaft 29 of the motor drive module 5 so that the output gear 31 will mate with the at least one gear 41. 5 The output drive shaft 89 is arranged to pass through the chassis 1 and receive the sprocket gear 7 fixed thereto. A keyway 93 is provided to effect keying of the sprocket gear 7 thereto. 10 Figure 15 shows the internal drive train components for the arrangement shown in Figures 13 and 14. Figure 15 also shows two ball races 95 which support the output drive shaft 89 in the casing 19. 15 Referring now to Figure 16, there is shown an arrangement of three modular gear boxes 3 , being a motor drive module 5, the output drive module 85, and an intermediate drive module 97. Here, the casing 19 of 20 intermediate drive module 97 is made from similar material as the casing 19 of the motor drive module 3 and the output drive module 85. The mounting means 35 are positioned so that they will be aligned in corresponding mating arrangement with each of the casings 19 between the 25 respective modules 3. The intermediate module 97 has stand offs 87 for similar purposes as the stand offs of module 85. The intermediate module 97 hez an output drive shaft 99 that is provided with an output gear 101. The output gear 101 is for engaging with the at least one gear 30 41 within the output drive module 85 in a similar fashion to that described previously for the output gear ?1 in the drive module 5. When the three drive modules are interconnected, then the output gear 31 of the drive module 5 connects with the at least one gear 41 in the 35 intermediate module 97, and the output gear 101 connects with the at least gear 41 in the output module 85. The arrangement of the gear drive train is shown in Figure 17. 843991.1 (GHMatters) P76363.AU.1 15/07/11 - 14 Figure 17 also shows ball races 103 for supporting the output drive shaft 99 of the intermediate drive module in the casing 19. Figure 17 also shows a further ball race 105 which nests in a suitable recess in the casing 19 of 5 the intermediate drive module 97. This ball race 105 supports the output drive shaft 29 of the motor drive module 5 so that the output gear 31 thereof drive engages with at least one gear 41. 10 Whilst the embodiments herein describe a male fitting arrangement of an output drive shaft into an adjacent module to drive the at least one gear therein, the arrangement may be reversed so there is a female arrangement in one of the drive modules such as the motor 15 drive module 5 from which an output can be taken to the next adjacent module. It should be appreciated that the above embodiments minimise the inventory required for providing door and 20 gate openers across a range of applications such as domestic installations through to heavy industrial installations. In each case, the same electric motor 13 may be provided for all embodiments. The gear reduction ratio through each one of the drive modules can be 25 arranged to be approximately 50:1. Thus, with three modules interconnected in piggy-back arrangement, there is a 150:1 reduction ratio which has been found satisfactory for even the heaviest of industrial doors and/or gates. 30 It should also be appreciated that the mounting means 35 may include other arrangements for ensuring aligned relationships between adjacent piggy-back modules, and these may be additional to or alternatives to the openings described. For example, there may be protruding figures 35 or similar on the casing of one of the modules to be received in corresponding apertures in the casing of an adjacent module. Alternatively the casing on one module 843991_1 (GHMatters) P76363.AU.1 15/07/11 - 15 may have a female cavity defined by a peripheral lip around the casing and the adjacent module may have one or more corresponding projections to align and locate with the cavity. 5 Figures 18 and 19 show perspective views of an output drive module 21, a motor drive module 5, and a door position limit sensing means 107 having a casing 109 therefor. The door position limit sensing means 107 is 1o used to sense when the door has reached a fully open or a fully closed position as required for each particular installation. When the door reaches these extreme positions of travel, then the door position limit sensing means 107 acts to operate with an operator control 15 electrics module (to be referred to hereinafter) to stop the motor and to ensure that when the motor is next activated it will operate in the opposite direction of travel so that the door gate can be moved towards the other extreme end position. Many different types of door 20 position limit sensing means are known per se. Some operate by causing cams to rotate which, in turn, trigger operation of micro switches. Other door position limit sensing means include shaft encoders that determine the position of the door by extracting pulses from a shaft 25 encoder which generates signals for increments of travel of the door or gate opener. In the example shown in Figures 18 and 19, the door position limit sensing means 107 comprises a micro switch door position limit sensing means that operates with rotating cams 111. 30 The door position limit sensing means 107 is mountable relative to the motor drive module 5 by fitting to an outwardly extending boss 115 that forms part of the casing 19 of the motor drive module 5. The boss 115 is 35 not clearly shown in any of the other drawings. Figure 7 shows an internal part of the boss 115. The door position limit sensing means 107 has a central body 117 that is 843991_1 (GHMatters) P76363.AU.1 15/07/11 - 16 made from metal or a suitable industrial grade plastics. The body 117 is generally circular to match the circular perimeter of the boss 115 so that it can mate therewith. The body 117 has a central platform part 119 which is 5 better shown in Figures 20 and 21. The limit sensing means 107 includes a central axle 121 that passes through the platform part 119 so that it is axially aligned with the output drive shaft 29. The output drive shaft 29 includes a central bore (not shown) into which the axle 10 121 is received. The axle 121 carries two "0" rings 123 that frictionally engage with the internal circumferential surfaces of the bore in the output drive shaft 29 and pick-up rotational drive from the output drive shaft 29. The axle 121 carries a worm gear 125 (see Figure 21) which 15 drives a pinion wheel 127 that has an integral axle 129 that extends mutually perpendicular to axle 121. The axle 129 is carried in "U" shaped cut-out bearing surfaces 131 provided in the platform part 119. The axle 121 and the axle 129 are held captive relative to the body 117 by a 20 cover 133. The cover 133 has an axle 121 receiving opening 135 and a pair of downwardly extending axle 129 support arms 137. When the output drive shaft 29 is rotated, then drive is imparted to the axle 121 which, in turn, rotates the worm gear 125 which rotates the pinion 25 wheel 127 and drive rotates the axle 129. The axle 129 extends outwardly past the side faces of the platform part 119 and carries respectively at the left and right hand sides thereof two "0" rings 139. The axles 129 and the "0" rings 139 are arranged to fit within hollow bores 141 30 of two cams 111. Thus, the cams 111 are caused to be carried by the axles 129 and to pick-up frictional drive therefrom. The "0" rings 139 permit the cams 111 to be independently rotated relative to the angular position of the axle 129 for setting respectively an open position and 35 a closed position. The cams 111 can be independer.tly adjusted with a screwdriver engaging screwdriver -slots 143. Each cam 111 includes a notch 145 which sets the 843991_1 (GHMatters) P76363.AU.1 15/07/11 - 17 respective open and closed positions. Thus, by rotating the individual cams 111 with respect to the axle 129, the angular position of the respective notches 145 can be appropriately set. 5 The door position sensing means 107 carries two micro switches 147 that are mounted to backing plates 151 by bolts 153. The backing plates 151 are, in turn, mounted to the platform part 119 by bolts 155. The micro switches 10 147 have operating arms 157 with distal end rollers 159. The rollers 159 engage with the outer circumferential cam surfaces of the cams 111 and when the rollers 159 engage within the notches 145, the micro switches 147 provide signals representative of the set end positions of travel 15 for the open and closed positions respectively. A cover 161 is provided over the body 117. The cover 161 contains screwdriver access openings 163 to permit engagement with the screwdriver slots 143 in the cams 111. Only one of the openings 163 is shown in Figure 18. 20 It should be appreciated that the "0" rings 139 provide frictional slip drive connection of the cams 111 with the axle 129 and enable adjustment of the angular positions of the notches 145 whilst still maintaining a 25 frictional drive coupling therebetween. It should also be appreciated that the door position limit sensing means 107 is a module in its own right and can be removed and replaced with a different door position 30 sensing means 107 such as a shaft encoder door position limit sensing means 107. This may be necessary in some installations when the electric circuit module (to be described hereinafter) is updated or modified. The ability to have different types of limit sensing means 107 35 provides flexibility of the gear box modules for use with different types of electrics control modules, and therefore further assists in minimising the number of 843991_1 (GHMatters) P76363.AU.1 15/07/11 - 18 stock components required to be held for different. types of door and/or gate installations. The gear ratios are chosen so that for a full 5 distance of travel of the door which may be greater than the distance between the required opened and closed stop positions of the door, the axle 129 will rotate not greater than 3600. Accordingly, if it is necessary to release the clutch in the event of a power failure (even 10 from a back-up battery), so the door can be manually opened and closed, the axle 129 will always be maintained in drive connected relationship with the door. Thus, when power is restored and the clutch re-engaged, the sensor will still have the original opened and closed stop 15 positions maintained such that re-setting will not be required. Referring now to Figure 20, there is shown a schematic circuit diagram for the door or gate opener. 20 Here, the door or gate opener is controlled by an operator control electrics module 127. The electric motor 13 is a 24 volt D.C. motor of 150 watt or greater capacity. Mains power is supplied to rectifier power supply module 129 which, in turn, supplies D.C. power from the mains to the 25 operator control electrics 127, and to a back-up battery 131. The operator control electrics module 127 provides all the necessary electrical interface with the electric 30 motor 13 and with the limit sensing means 107. In order to reverse the direction of rotation of the electric motor 13, the operator control electrics 127 reverses the polarity of the power supplied to the electric D.C. motor 113. This occurs when the door or gate is driven to a 35 fully open or fully closed position or if door or gate is stopped during its movement. In addition, the operator control electrics module 127 may contain user operable 843991_1 (GHMatters) P76363.AU.1 15/07/11 -19 controls for operating electric motor 13 and/or it may include remote radio control means that enables a user to operate a transmitter to, in turn, open and close a door or gate. Under normal operating conditions, the mains 5 A.C. power provides power via the rectifier power supply 129 to operate the electric motor 113 and to charge the back-up battery 131. In the event of a mains power failure or interruption, the back-up battery 131 provides power to operate the operator control electrics module 127 10 and also the electric motor 113. Thus, in the case of domestic, semi industrial or industrial door or gate openers comprising one or more of the modules 3, 5, 7 referred to herein, then the door or gate can be opened. This contrasts with known door or gate openers for semi 15 industrial and industrial doors or gates where hitherto, it was standard to provide an A.C. motor to provide the necessary driving torque. In such cases, a battery -backup will not be economically feasible as it requires conversion of the battery D.C. power to A.C. which is 20 expensive. In addition a manual chain drive wheel is required to be used to enable the door to be manually opened. Such chain driven wheel has to be drive de coupled when the motor is operating, and all of this results in an expensive opener mechanism. In the present 25 case, because the electric motor 13 is a DC motor then adequate power can be supplied from the back-up battery 131 to open even the largest of industrial doors (provided the necessary modules 3, 5, and 7 are interconnected). Accordingly, use of the examples of the invention 30 described above provide an advantage over known installations particularly for semi industrial and industrial door or gates where an emergency powered back up has not been economically possible. 35 The nature of the fitting of the limit sensing means 107 to the gear box enables an interchange of different types of limit sensing means 107. Thus, for example, if 843991_1 (GHMatters) P76363.AU 1 15/07/11 -20 limit switch sensing means in the form of micro switch limit sensing means are utilised in one example, then the limit switch sensing means 107 may be removed and replaced with an alternate limit sensing means 107 such as a shaft 5 encoder limit sensing means such as magnetic or an optical shaft encoder. Accordingly, as operator control electrics 127 change due to improvements, it may be necessary to change from one limit switch sensing means 107 to an alternate limit sensing means 107. The arrangement 10 disclosed above permits this to be achieved without replacing the whole of the gear box unit. It should also be appreciated that the connection of the limit sensing means 107 is to a part of the drive with is the door that is always maintained regardless of the operation of the clutch mechanism 55. Thus, when the clutch mechanism 55 is released and the door raised manually, the door position sensing means 107 will maintain a direct drive with the movement of the door and 20 will not need to be recalibrated when the clutch mechanism 55 is re-engaged. It should be noted that the at least one gear 41 in each module is carried by the support structure, via ball 25 race bearings. Axles within each module are also supported by ball race bearings. In known door and gate openers, ball race bearings have not been utilised because the thinking has been to provide low cost openers and. it was perceived that ball race bearings would add 30 unnecessary cost with no advantage. Accordingly sleeve bearings have been accepted as satisfactory. Ball race bearings inherently have lower frictional components than sleeve bearings. Thus, by using ball race bearings, low powered D.C. motors of about 150 watts capacity and 35 greater can now be used to drive not only domestic doors and gates but also semi industrial and industrial doors and gates. Whilst the cost of ball races is slightly 843991_1 (GHMatters) P76363AU.1 15/07/11 - 21 greater than that of. .sleeve bearings, the cost is not so great as to render modular gear boxes and/or door and gate openers containing such modules prohibitively expensive. The advantage to be gained by using modular gear boxes 5 with DC electric motors, rather than conventional A.C. motors for semi industrial and industrial applications overall is that overall lower cost units can be provided. It is to be understood that, if any prior art 10 publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. 15 In the claims which follow and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such-as "comprises" or "comprising" is used in an inclusive sense, i.e. to 20 specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. Modifications may be made to the invention as would 25 be apparent to persons skilled in the art of making door or gate opener devices. These and other modifications may be made without departing from the ambit of the invention the nature of which is to be determined from the foregoing description. 30 843991_1 (GHMatters) P76363.AU.1 15/07111