AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION Standard Patent Applicant (s) Smart Openers Pty Ltd Invention Title: GATE OPERATOR The following statement is a full description of this invention, including the best method for performing it known to me/us: -2 GATE OPERATOR Field of the Invention 5 This invention relates to a gate operator and relates particularly but not exclusively to a swing gate operator. Background Art 10 Hitherto, it has been known to provide gate operators for swing gates and/or sliding gates and/or windows. In one such case for swing gates, an electric motor rotates a threaded shaft either clockwise or anti-clockwise. A nut is is threaded onto the threaded drive shaft so that the nut can travel backwards and forwards along the length of the threaded drive shaft consequent on the direction of rotation of the drive shaft. The threaded drive shaft is mounted either to a mounting adjacent the gate or to a 20 mounting on the gate and the threaded nut is mounted to the opposite of the mounting on the gate or the mounting adjacent the gate. Thus, as the motor is operated, there will be movement to extend or retract the distance between both mountings to open and/or close the gate. A similar 25 arrangement has been provided for sliding gates and windows. It should be appreciated that gates or windows may be single gates or windows, or double gates or windows. In the case of double gates or windows, a respective operator is required for each of the gates or 30 windows. Operators of the above type have proven to be reliable. Despite this reliability, the operators have an inherent problem of not being able to stop the gate or 35 window at an exact or almost exact required end stop position which may represent the fully open or fully closed position of the gate or window. This occurs 2244661_1 (GHMatters) 12/04/10 - 3 because of lost motion in the drive between the threaded drive shaft and the nut when the direction of rotation of the drive shaft changes. In other words, there may be one turn of the drive shaft required before there can be take 5 up of drive in the opposite direction. This lost motion occurs because of the inherent tolerances needed on the mating engaging faces of the threaded drive shaft and the nut. 10 There is need for an improved gate operator. Statements of the Invention In accordance with a first aspect of the present 15 invention there is provided a gate operator comprising an electric motor, a threaded drive shaft coupled to rotate clockwise or anti-clockwise consequent on the direction of rotation of an output shaft of said motor, a traveller coupling screw threadably engaged on said 20 threaded drive shaft to travel backwards and forwards along the length of the threaded drive shaft consequent on the direction of rotation of said threaded drive shaft, said motor being mountable to either a mounting adjacent said gate or to a mounting on said gate, and said 25 traveller coupling being mountable to the opposite of the mounting on said gate or said mounting adjacent said gate, so when the motor is operated there will be movement to extend or retract a distance between both mountings to thereby open and/or close said gate, and 30 wherein said traveller coupling includes a screw thread lost motion minimiser to minimise lost screw thread drive between said threaded drive shaft and said traveller coupling that might occur on change of direction of rotation of said threaded drive shaft. 35 Preferably said lost motion minimiser comprises two thread followers linearly spaced apart along the length of 2244661_1 (GHMatters) 12/04/10 the threaded drive shaft and engaged with the thread on said threaded drive shaft, and biasing means between said thread followers applying a force between the thread followers either 5 urging the thread followers towards each other or away from each other, whereby to maintain a compressive force across screw faces of both thread followers and screw faces of said drive shaft, maintaining those screw faces in tight face 10 to face engagement. Brief Description of Drawings In order that the invention can be more clearly 15 ascertained, an example will now be described with reference to the accompanying drawings wherein: Figure 1 is a schematic plan view of a swing gate with gate operator, 20 Figure 2 is a schematic plan view of a sliding gate with gate operator of the same arrangement shown in Figure 1, 25 Figure 3 represents a motor housing of an example of an embodiment of the invention where Figure 3a shows a top diametrically split portion, and Figure 3b a bottom diametrically split portion, 30 Figure 4 is a close-up detail of a screw threaded drive shaft and traveller coupling in side elevation, Figure 5 is a transverse cross sectional showing the traveller coupling in Figure 4 in large detail, 35 Figure 6 is a front elevational view of a locator pin and biasing means for applying biasing forces to the 2244661_1 (GHMatters) 12/04/10 - 5 traveller coupling shown in Figure 5, Figure 7 is an end view of the traveller coupling part shown on the right hand side of Figure 5, 5 Figure 8 is a view similar to that of Figure 5 without the presence of the locator pins and biasing means, 10 Figure 9 is a transverse cross sectional view of the whole of the gate operator, and Figure 10 is a perspective view of an end of the motor within the gate operator shown in the preceding 15 figures showing a pulse encoder. Detailed Description of Embodiments Referring firstly to Figure 1, there is shown an 20 example of a gate operator 1 operatively connected with a swing gate 3. The swing gate is mounted via a hinge 5 to an upright gate post or wall 7 so that it can swing as shown by the arrows and the dotted lines. The opposite end of the gate 3 to the hinge 5 closes relative to a 25 further post or wall 7 across a gate opening. It can be seen that the gate operator 1 is connected at one end to a mounting 9 at the gate and at the opposite end to a mounting 11 adjacent the gate. The operator 1 has a motor within an outer casing that when operated causes movement 30 to extend or retract the distance between both mountings 9 and 11 to thereby open and/or close the gate. Typically, the mountings 9 and 11 include pivot pin mountings. Figure 2 shows a similar gate operator 1 connected 35 with a sliding gate 13. The gate operator 1 connects with the gate 13 via mounting 9 at one end and with mounting 11 at the opposite end. The gate 13 is typically mounted on 2244661_1 (GHMatters) 12/04/10 - 6 rollers so that when the gate operator is extended or retracted, the gate 13 will be correspondingly closed and/or opened. The operators in each case can be substantially identical. A similar gate operator can be 5 used to open and close a window. Figure 3 shows a motor casing 15 of an example of an embodiment of the invention made from suitable material such as aluminium. The casing 15 is a cylindrical casting 10 and split in two halves as shown by the upper part of casing 15 in Figure 3a and lower part of casing in Figure 3b. Figure 3b shows that the lower half of the casing 15 has a motor chamber 17 and a coupling chamber 19 where there can be drive coupling of the motor spindle output to is a threaded drive shaft 21. The upper half of the casing 15 shown in Figure 3a is generally hollow as shown and the bottom half is generally a mirror image of the upper half. The two casing parts may be assembled one above the other and fastened together by bolts that pass through bolt 20 openings that will be aligned when the two casing parts are assembled. Each of the casing parts 15 has an electrical cable lead passageway 25 therein to allow an electrical lead 27 to operatively connect with an electric motor 29. The right hand end of the casing 15 has an 25 opening 31 through which a pivot mounting may be made mounting the casing 15 to either the gate 3/13 (shown in Figures 1 and 2) at mounting 9, or to the mounting 11 adjacent the gate. 30 Figure 3b shows that the motor 29 has a motor spindle 33 that carries one part of a known coupling 35 at its distant end. In this arrangement, the coupling 35 is within the coupling chamber 19. The motor 29 is within the motor chamber 17 and is held axially centrally therein 35 by means of synthetic rubber isolation '0' rings 37. The motor 29 is therefore suspended within the motor chamber 17 by reason of these 'O' rings 37. The threaded drive 2244661_1 (GHMatters) 12104/10 -7 shaft 21 is connected within a ball race 39 so the ball race 39 is physically located at one end of the threaded drive shaft 21. The drive shaft 21 projects through the ball race 39 and has the other part of the known coupling 5 35 attached to the free end. The ball race 39 is received within a ball race chamber 41 so that the ball race 39 will be physically located and held and positioned longitudinally with the casing 15. When the upper and lower parts are clampingly fitted together, then the outer 10 portion of the ball race 39 is held in a non-rotatable manner within the casing 15 and at an axially fixed position therealong. This mounting with the ball race 39 therefore supports the threaded drive shaft relative to the casing 15. The longitudinal position of the coupling 15 part 35 at the end of the threaded drive shaft 21 can be adjusted by rotation of nut 43 so that the opposed end faces of the couplings 35 can be brought into close relationship with a known synthetic rubber insert therebetween and in drive engagement therewith. In this 20 way, output drive from the motor 29 can be transmitted to the threaded drive shaft 21 so that the threaded drive shaft 21 will be rotated in unison with the spindle 33 of the motor 29. 25 A pulse encoder in the form of a shaft encoder 45 is connected at the end of the motor 29 opposite to the coupling 35 so that during rotation of the motor spindle 33, the pulse encoder will provide output pulse count signals that can be used to determine the angular 30 rotational position of the threaded drive shaft 21. In this case, there will be a direct linkage between the motor spindle 33 and the threaded drive shaft 21. The features of the pulse encoder will be described in due course. 35 Referring now to Figures 4 - 9, there is shown detail of a traveller coupling 47 that is screw threadably 2244661_1 (GHMatters) 12/04/10 - 8 mounted onto the threaded drive shaft 21. The traveller coupling 47 comprises two thread followers 49 and 51 that are mounted onto the threaded drive shaft 21 so they are linearly spaced apart along the length thereof and engaged s with a thread on the drive shaft 21. This is clearly shown in Figure 4. Figure 9 shows how the motor casing 15, threaded drive shaft 21, and the traveller coupling 47 are mounted 10 with respect to each other and within a telescopic outer casing comprising casing parts 53 and 55. The telescopic casing parts 53 and 55 are preferably made from a material such as stainless steel or the like substantially non corrosive material. These casing parts are preferably 15 circular but they may be of other configurations such as rectangular transverse cross section. Figure 9 shows that the casing 15 is mounted relative to the casing part 53 by '0' rings 57. Figure 9 also shows that the traveller coupling 47 is connected with the casing part 55 by a 20 locating screw 59. The extreme left hand end of casing part 55 contains a lug 61 with an opening 63 to permit mounting of the operator 1 to the mounting on the gate, or to the mounting adjacent the gate. The right hand end of Figure 9 shows the opening 31 to permit mounting of the 25 operator to the opposite one of the mountings at the gate or adjacent the gate. It should be appreciated therefore, that as the threaded drive shaft 21 rotates either clockwise or anti-clockwise, the traveller coupling 47 will advance or retreat along the length of the threaded 30 drive shaft 21. This in turn, will cause the casing parts 53 and 55 to telescope with respect to each other but will also extend or retract a distance between the mountings at each end of the operator 1. This, in turn, will permit the gate to be opened and/or closed. Figure 9 shows that 35 the extreme free end of the threaded drive shaft 21 carries a sleeve 65 that slidingly engages with the internal wall surfaces of the casing part 55 and supports 2244661_1 (GHMatters) 12/04/10 -9 that end of the drive shaft. The sleeve 65 is shown also in Figure 4 where it can be seen that a pin 67 extends diametrically through the sleeve 65 and through the threaded drive shaft 21 to locate and hold the sleeve 65 5 thereto. Typically, the sleeve 65 can be made of a self lubricating material such as polyethylene which will exhibit relatively low frictional forces with respect to the internal surfaces of the sleeve part 65. 10 Figure 5 shows how the followers 49 and 51 have a biasing force applied thereto by biasing means 69. In the example shown, the biasing means operates to push apart axially each of the follower parts 49 and 51. In the example shown, the biasing means 69 is the form of coil 15 springs formed as tubes. This is clearly shown in Figure 6. A respective locator pin 71 is received internally of the tubes to support the coil springs. In the example shown, there are two diametrically opposed locator pins 71 and biasing means 69. Each of the pins 71 are received 20 within pin bores 71. The extreme ends of the tubular coil springs are received within bores 75 in the respective opposed end faces of the follower parts 49 and 51. Thus, in the example shown, each of the respective followers 49 and 51 will be linked relative to axial rotation with 25 respect to each other so they will rotate in unison by the pins 71. The biasing means 69 will apply a force outwardly as shown by the arrows in Figure 5. Whilst the biasing means 69 in this example has been 30 shown as providing an outwardly directed bias, other biasing means may be arranged in another example to alternatively provide an inwardly directed bias to draw the followers 49 and 51 towards each other. 35 Because each of the followers 49 and 51 are screw threaded onto the threaded drive shaft 21 in spaced apart locations thereon, the biasing means 69 will apply a 2244661_1 (GHMatters) 12/04110 - 10 compressive force across screw faces of both thread followers 49 and 51, and screw faces of the thread of the drive shaft 21. This, in turn, will maintain all of those screw faces in tight face to face engagement. 5 Accordingly, when the threaded drive shaft 21 is caused to rotate in an opposite direction, the arrangement will provide a screw thread lost motion minimiser coupling to minimise lost screw thread drive between the threaded drive shaft 21 and the traveller coupling 47 that might 10 occur on change of direction of rotation. Without the lost motion minimiser, there may be one turn or more of the threaded drive shaft before the thread faces engage and the traveller coupling 47 commences to advance or retreat in the opposite direction along the drive shaft 15 21. Referring now to Figure 10, there is shown an end perspective view of the motor 29. It can be seen that the motor 29 has a circular outer casing and that a 20 correspondingly sized diameter circular housing 77 is fitted to the rear end of the motor 29. The housing 77 contains the pulse encoder device 79 arranged to rotate in unison with the spindle 33 of the motor 29. The spindle 33 protrudes from the end of the motor housing 29 to allow 25 the pulse encoder device 79 to be coupled therewith. In the example shown, the pulse encoder device is a disk with magnetic markings 81 thereon adjacent the outer circumference. Thus, as the motor spindle 33 rotates, the pulse encoder device 79 allows the magnetic markings 81 to 30 traverse across a magnetic sensor which is configured to provide pulse output signals representing the passing of each one of magnetic markings 81. The sensor has not been shown in order to aid clarity in the drawings. Pulse encoder devices 79 are known generally and there are many 35 different types that can be used. Some have magnetic markings, others are optic sensors to sense markings or openings. Other similar sensors exist and all such 2244661_1 (GHMatters) 12/04/10 - 11 sensors can be used as the pulse encoder device 79. The pulse encoder device provides pulse signals that represent the angular rotation of the spindle 33 of the motor 29. Each pulse therefore represents a particular angular s rotation of the spindle 31. By counting pulses, it is possible to set a gate open position and a gate stop position at particular count values in a known manner in door operator arts, such as in roller shutter door, tilt door or sectional door operators. Accordingly, a user can 10 initially set up the operator 1 by defining a count value for say a gate open position, and a different count value for a gate closed position. The disk that forms part of the shaft and pulse encoder device 79 may rotate multiple times between the gate open and closed positions. 15 However, there will be incremental counting up or down of count values depending on the direction of rotation of the motor 29. Accordingly, when particular count values are reached the motor 29 can be stopped. Whilst a pulse encoder device 79 has been shown, other end limit stop 20 sensing means such as micro switches or the like may be utilised either directly at the gate 3 to sense the physical presence of the gate 7 at open and closed positions, or by mounting a cam driven mechanism in a housing 77 similar to that shown in Figure 10 which causes 25 a micro switch to trip at a required gate open position and a different micro switch to trip at a gate closed position. The housing 77 is closed by an end 83 by screws 85 30 that pass through bores 87 in the housing 77 and screw into the end of the housing of the motor 29. This, in turn, holds the housing 77 captive relative to the housing of the motor 29. 35 Figure 10 shows the electric lead 27 with a multi pin plug 89. The plug is shown with two large diameter high current carrying pins 91 for supplying electric power to 2244661_1 (GHMatters) 12/04/10 - 12 the motor 29, and plurality of smaller diameter lower current carrying pins 93 for obtaining electrical pulse signals from the pulse encoder device 79. Typically, the motor 29 is a 24 volt DC motor which can be reversed in 5 its direction of rotation by reversal of the plurality of the applied DC power. The threaded drive shaft 21 typically comprises a thread of 6 turns per inch. It is conveniently a single 10 start thread but it may be a multiple start thread with a different turns ratio. With a single start thread of six turns per inch, certain problems of known prior art gate operators are minimised. With the known prior art gate operators that have 4 turns per inch, it is possible for a 15 person to push on the gate with considerable force to effect rotation of the drive shaft 21 which, in turn, allows the gate to be fractionally opened with each push. After repeated pushes at the gate, the gate can be opened sufficiently to allow a person to pass. By using a 6 20 turns per inch thread as distinct from a 4 turns per inch thread this problem can be minimised. A combination of the 6 turns per inch single start thread and the traveller coupling 47 together, also further minimises the aforementioned problem. This is because, there is 25 substantially no backlash between the coupling and the threaded drive shaft 21. In the prior art, any corresponding traveller coupling 47 is loosely screw thread fitted relative to the threaded drive shaft 21. This, in turn, allows some inertia to be obtained within 30 the mechanical system itself to effect a small rotation of the threaded drive shaft 21 with each push on the gate. With the traveller coupling 47 shown in the example, there is always a tight engagement of the threads of the traveller coupling 47 and the thread on the threaded drive 35 shaft 21. Thus, the obtaining of inertia to cause a partial rotation of the threaded drive shaft 21 is minimised. In addition, in the prior art, as the thread 2244661_1 (GHMatters) 12/04/10 - 13 faces wear, the traveller coupling 47 has a greater backlash than when initially installed. Thus, as time progresses the above problem is exacerbated. With the biasing provided with the present invention any problems s of wear that existed with the prior art operators is minimised as all the relevant thread faces are always in biased engagement. In addition the motor 29 is arranged to rotate at a 10 speed of around 260 R.P.M. This speed in combination with an approximately 6 threads per inch drive shaft also overcomes a further known problem of prior art gate operators where the operator can exhibit screeching noises. The known operators have 4 threads per inch and 15 use the industry standard speed of rotation of the motor of about 160 R.P.M. This combination unfortunately can result in screeching noise from the operator but with the different speed of motor and different threads per inch this problem is avoided. The lost motion minimiser within 20 the traveller also assists in overcoming the screeching problem as there is now always a tight mating abutment of the faces of the screw threaded drive shaft with the faces of the thread in the traveller. 25 It should be appreciated that the above described operator can be connected with swing gates, sliding gates, windows, and the like. In addition, if there are two such gates or windows that close an opening then a respective operator can be fitted to each respective gate or window. 30 It is to be understood that if any prior art 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 35 or any other country. In the claims which follow and in the preceding 2244661_1 (GHMatters) 12104110 - 14 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 5 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 10 be apparent to persons skilled in the gate operator arts. 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. 15 2244661_1 (GHMatters) 12/04/10