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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to window closers, window stays and door closers. The invention also relates more generally to mechanisms such as, though not limited to, window closers, window stays and door closers which operate on a wedge principle. For example, the invention may be applicable to scissor-action mechanisms which incorporate a wedge principle of operation. 
     2. Description of Related Art 
     Present window closers include latches, chain winders and wire winders. Window latches cannot be used as stays and only latch in the final, lock-up position. Therefore, friction, a notch or some other type of stay is required to maintain a window or door ajar. Chain and wire winders do not require additional stays, however both are vulnerable in the open position to outside factors. Both, the chain and the wire tend to deflect and allow the window to partially close. A latch is usually required to secure the window in the closed position. 
     Present door closers include spring loaded member mechanisms with hydraulic or pneumatic braking arrangements to prevent slamming of the door. Some less expensive door closers do not incorporate the braking arrangement. 
     BRIEF SUMMARY OF THE INVENTION 
     It is the object of the invention to overcome or substantially ameliorate at least one of the above disadvantages and/or more generally to provide improved window and door closing mechanisms. 
     There is disclosed herein an opening/closing mechanism for a window or door, the mechanism including: 
     a primary track secured to or formed integrally with a window or door jamb, 
     a secondary track secured to or formed integrally with a window or door frame, 
     an operating member pivotally secured at one end thereof to the primary track and/or window/door jamb, and mounted at its other end so as to be linearly moveable along the secondary track, the operating member including a guide surface which extends along the member, the association of the operating member with the primary track being such that a line parallel to the guide surface crosses a longitudinal centre line of the primary track at a substantially constant, shallow, acute angle throughout a substantial range of operation of the mechanism, and wherein the guide surface includes a curved profile along at least a part of its length, and 
     a guide including means engageable with said guide surface, the guide being retrainedly moveable along said primary track whereupon interaction of the guide with the guide surface causes pivotal movement of said operating member about said one end thereof. 
     Preferably the guide surface is an edge of a slot formed in the operating member, the line parallel to the guide surface being a centre line of the slot. 
     Preferably the guide includes a roller car which can roll along the primary track and includes a guide roller which rides along the slot. 
     Preferably the point of pivotal attachment of the operating member to the primary track is linearly moveable along the primary track, the guide being fixed to the primary track. 
     There is further disclosed herein an opening/closing mechanism for a parallel opening window, the mechanism including: 
     a primary track secured to or formed integrally with a window jamb, 
     a secondary track secured to or formed integrally with a window frame, 
     a pair of operating members each pivotally secured at one end thereof to the primary track and/or window jamb, and each being pivotally mounted to, and so as to be linearly moveable along, the secondary track, the operating members each including a guide surface which extends along the member, the association of the operating member with the primary track being such that a line parallel to the guide surface crosses a longitudinal centre line of the primary track at a substantially constant, shallow, acute angle throughout a substantial range of operation of the mechanism, and wherein said guide surface includes a curved profile along at least a part of its length, and 
     a pair of guides, each including means engageable with said guide surface of a respective one of said operating members, the respective guide being restrainedly moveable along said primary track whereupon interaction of the guide with the respective guide surface causes pivotal movement of said respective operating member about said one end thereof. 
     Preferably each guide surface is an edge of a slot formed in the respective operating member, said line parallel to the guide surface being a centre line of the slot. 
     Preferably the guide includes a roller car which can roll along the primary track and includes a guide roller which rides along the slot. 
     Preferably the roller cars are attached to a wire rope or other flexible tension member, which wire rope passes around a sheave to a drum, rotatable by means of a handle, rotation of the handle thus causing movement of the respective roller car to effect movement of the window. 
     Preferably there is associated with each operating member a scissor member, each respective scissor member being pivotally interconnected to both the primary and secondary tracks. 
     There is further disclosed herein an opening/closing mechanism for an awning type window, the mechanism including: 
     a slide rod secured to or formed integrally with a window jamb, 
     a track secured to or formed integrally with a window frame, 
     an operating member pivotally, slidably attached at one end thereof to the track and slidably attached at the other end thereof to the slide rod so as to pivot about the longitudinal axis of the slide rod and an axis normal thereto, the operating member including a guide surface which extends along the member, wherein a line parallel to the guide surface and the longitudinal axis of the rod cross each other at a substantially constant, shallow, acute angle throughout a substantial range of operation of the mechanism, and 
     rotational means associated with the window jamb and engageable with the operating member so as to slide said one end thereof along said rod and pivot same about both said axes. 
     Preferably the mechanism includes a base frame that includes a pair of bearing blocks, a guide block and a swing block, the bearing blocks supporting said slide rod. 
     Preferably a slide block is slidably attached to the slide rod and the operating member is pivotally affixed to the slide block. 
     Preferably one elongated edge of the operating member is smooth, whereas the opposed edge is provided with a curved rack of gear teeth. 
     Preferably there are two bearing blocks supporting the slide rod and between which the slide block slides and wherein there is provided a connecting rod between the guide block and the swing block along which the slide block also slides, the connecting rod being parallel to the slide rod and maintaining the guide block and slide block in aligned association when pivoting about the longitudinal axis of the slide rod. 
     Preferably the rotational means includes a gear mounted upon the guide block, the gear being inter-engaged with the rack of teeth. 
     Preferably the gear is driven by a drive gear which is rotated by means of a handle. 
     There is further disclosed herein an opening/closing mechanism for a door, the mechanism including: 
     a pair of guide rods secured to the door jamb, 
     a track secured to the door, 
     an operating member pivotally secured at one end thereof to said guide rods and pivotally mounted to the track so as to be linearly moveable therealong, the operating member including a guide surface which extends along the member. 
     a guide including means engageable with said guide surface, 
     the association of the operating member with the track being such that a line parallel to the guide surface crosses a straight line passing through the centre in between the guide rods and the point of pivotal attachment of the operating member to the door jamb at a substantially constant, shallow, acute angle throughout a substantial range of operation of the mechanism. 
     Preferably the guide surface includes a curved profile along at least a part of its length. 
     Preferably the guide surface is an edge of a slot. 
     Preferably the guide includes a guide roller received within the slot. 
     Preferably the line parallel to the guide surface is the centre line of the slot, operation of the mechanism. 
     Preferably the angle varies by providing a fluctuation or fluctuations in the curve of the guide surface. 
     Preferably, in all of the above embodiments, the angle of crossing is substantially constant. In the door opening/closing mechanism, this angle may be varied by providing a fluctuation or fluctuations in the curve of the guide surface to decelerate the door during its closing movement. 
     Typically, the primary slide track is affixed to the head of the door jamb through the end blocks and the secondary slide track is affixed to the top of the door. When the door is opened, one end of the operating member moves with it through the pivotally attached slide engaged in the secondary slide track. The other end of the operating member pivots on a pivot pin affixed to the near end block, one side of the slot in the operating member exerting force upon the roller affixed to the sliding block and forcing the sliding block to slide towards the near end block, thereby tensioning the spring. When the door is released, the spring recoils and forces the sliding block towards the outer end block, exerting force through the said roller upon one side of the slot in the operating member, causing the operating member to pull the door shut through the pivotally affixed slide engaged within the secondary slide track affixed to the door. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings. 
     FIG. 1 is a schematic plan view of a closer; 
     FIG. 2 is a schematic perspective view of a closer having a scissor mechanism; 
     FIG. 3 a  is a side view of a directly operated roller car; 
     FIG. 3 b  is an end view of a directly operated roller car; 
     FIG. 3 c  is a top view of a directly operated roller car; 
     FIG. 4 a  is a side view of a remotely operated roller car; 
     FIG. 4 b  is an end view of a remotely operated roller car; 
     FIG. 4 c  is a top view of a remotely operated roller car; 
     FIG. 5 is a schematic plan view of a gear driven closer; 
     FIG. 6 is an enlarged, partial slide elevation of a gear driven closer; 
     FIG. 7 is a schematic plan view of a door closer; 
     FIG. 8 is a schematic illustration depicting a method adopted in determining the curvature of the guide surface, and 
     FIG. 9 is a schematic illustration depicting a refined means of determining the curvature of the guide surface so as to maintain a constant crossing angle. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIGS. 1 and 3 of the accompanying drawings, there is schematically depicted a mechanism for opening and closing windows. The mechanism includes an operating member  1  typically interconnected between a primary slide track  4  and a secondary slide track  6 . The primary slide track  4  is intended to be secured to a window jamb whereas the secondary slide track  6  is intended to be affixed or formed integrally with a window frame. The near end of the operating member  1  is anchored on the centre line  3  to the primary slide track  4  by a pivot pin  2 . The outer end of the operating member  1  is fitted with a pivoted slide  5  which is engaged into the secondary slide track  6 . A roller car  9  incorporates guide wheels  14  which keep it constantly aligned with the centre line  3  of the primary slide track  4 . 
     A guide roller  7  is affixed to the body of the roller car  9  and is engaged in the slot  8  of the operating member  1 . 
     The centre line  10  of the slot  8  in the operating member  1  crosses the centre line  3  of the primary slide track  4  at an acute angle  13  which remains substantially constant through all stages of operation of the operating member  1 , thereby providing ease of operation and self locking capability. 
     When the roller car  9  operates in direction  11 , the guide roller  7  exerts force upon the upper side of the slot  8 , causing the operating member  1  to travel in direction  12 , moving the pivoted slide  5  and the secondary slide track  6  to a desired position. The purpose of the curved portion of the slot  8  is to ensure that a substantially even force is exerted between the operating member  1  and the guide roller  7  throughout the operation of the device. 
     The roles of the pivot pin  2  and the guide roller  7  may be reversed, whereby the pivot pin  2  would be mounted on a car not unlike the roller car  9  which can travel along the centre line  3  of the primary slide track  4 . The guide roller  7  would be affixed to the primary slide track  4 . 
     In FIGS. 2 and 4 of the accompanying drawings, there is schematically depicted a remotely controlled opening and closing mechanism for parallel opening windows. In this embodiment, the near ends of the operating members  1  are anchored by pivot pins  2  to the outer ends of the primary slide tracks  4 . The outer ends of the operating member  1  incorporate pins  15  which serve as axles for guide wheels which travel within the secondary slide track  6 . At centres  16 , directly in the middle between the anchor pivot pins  2  and the axle pins  15 , there are pivotally attached sets of scissor members  17 , the pivotal centres  16  being directly in the middle between the scissor members&#39; pivotal anchors  18  and pins  19  which serve as axles for guide wheels which travel within the primary slide tracks  4 . 
     The roller car  20  in FIG. 4 is fitted with guide wheels  14  which travel within the primary slide track  4 . A guide roller  7  and a wire rope anchor block  21  are affixed to the body of the roller car  20 . The roller car  22  is a mirror image of the roller car  20 . 
     The body of the roller car  23  is extended in relation to the roller cars  20  and  22  and the roller  7  is here fitted at position  24 . The roller car  25  is a mirror image of the car  23 . 
     A flexible wire rope  26  is anchored at point  27  to the reel  28 , runs a number of turns around the reel  28 , passes around the sheave  29 , through the anchor block  21  of the roller car  25  where it is anchored, continues to and around sheave  30 , through the anchor block  21  of the roller car  22  where it is anchored, continues to and around sheave  31 , passes under the reel  28  to and around sheave  32  and through the anchor block  21  of the roller car  23  where it is anchored onto and around sheave  33 , through the anchor block  21  of the roller car  20  where it is anchored, continues to and around sheave  34 , continues to and around the reel  28  to the anchor point  35  where it is anchored and terminated after forming a continuous loop. When the crack member  36  is operated in an anti-clockwise direction, the shaft  37  operates the reel  28 , the flexible wire rope  26  coming from the sheave  32  is wound onto the reel  28  and the flexible wire rope  26  leading to the shave  29  is unwound from the said reel  28 . The arrows show directions of travel of roller cars  20 ,  22 ,  23  and  25 . 
     The roller cars move in unison. The guide rollers  7  affixed to the roller cars exert force upon the sides of the slots  8  in the operating members  1 , causing motion to the operating members  1  and through pivots  16 , to the scissor members  17 , providing parallel motion of the secondary slide tracks  6  towards and in respect to the primary slide tracks  4 . 
     The scissor mechanism in this embodiment may be modified by shortening the operating members  1  to where they engage the pivoting centres  17  and by modifying the slots  8  as required to provide full closure of the mechanism. In this variation, the secondary slides are no longer required and pivots  18  may be directly affixed to the window. 
     In FIGS. 5 and 6, there is schematically depicted a closer for awning type windows. In this embodiment, the base frame  38  incorporates a bearing block  39  which also serves as a frame side block. The base frame also includes a bearing block  40  and a side block  41 . The bearing blocks  39  and  40  support a main slide rod  42  which in turn supports a swing block  43 , a pivot slide block  44  and a guide block  45 . A connecting rod  46  which is parallel to the main slide rod  42  is firmly affixed to the swing block  43  and the guide block  45 , thereby forming an assembly which allows the pivot slide block  44  to slide freely between the swing block  43  and the guide block  45  and, in addition, allows the three blocks  43 ,  44  and  45  to swing in unison, providing a variable operating angle  62  for the operating member  47  which is pivotally affixed to the pivot slide block  44 . The operating member  47  incorporates gear teeth  48  at the outer side of the curved section  49 . The inner side  50  of this curved section  49  is smooth to provide a smooth running surface for the guide roller  51  which is affixed to the guide block  45 . The inner side  50  of the operating member  47  and the datum line of the gear teeth  48  are parallel in relation to each other. The centre line of the curved section  49  of the operating member  47  and the centre line of the main slide rod  42  cross each other at a constant, shallow angle  52 . A slide  53  is pivotally affixed to the far end of the operating member  47  and travels freely within a slide track  54 . The slide track is to be affixed to an awning type window. 
     A gear  55  is mounted upon the guide block  45 , directly opposite the guide roller  51 . The teeth of the gear  55  mesh with the teeth  48  of the operating member  47 . 
     The gear  55  of the guide roller  51  provide a firm guide, locating the operating member  47  therebetween, in a similar manner as rollers  7  guide the operating members  1  in the embodiment of FIGS. 1 and 2. 
     A gear  56  which has a greater number of teeth than the gear  55  is affixed to the gear  55  and they rotate in unison on a common axle  57  which is affixed to the guide block  45 . Gear  58 , with a lesser number of teeth than gear  56  is affixed to a shaft  59 . Also affixed to the shaft  59  is a crank handle  60 . A spring loaded catch  61  locks the gear  56  and prevents movement of the operating member  47 . When the crack handle  60  is rotated in an anti-clock-wise direction, the shaft  59  transmits this motion to gear  58  which lifts the catch  61 , allowing gear  56  to rotate and turn the gear  55  which drives, through teeth  48 , the operating member  47 , pulling with it the pivot slide block  44  and with the aid of the guide roller  51 , forcing the slide  53  and the slide track  54  away from the base frame  38  of the closer. 
     As an alternative to a gear operable mechanism, the rod  42 , instead of being a fixed, smooth surfaced rod might be an externally threaded component adapted to rotate about its longitudinal axis. The slide block  44  might than be internally threaded so as to cooperate with the external thread of rod  42 . The rod  42  could be driven to rotate by means of a “constant velocity” type sequence of universal joints between the end of the rod and a manually rotatable handle. 
     In FIG. 7, there is schematically depicted an automatic door closer. In this embodiment, the primary slide track  63  is affixed to the head of the doorjamb  64  and the secondary slide track  65  is affixed to the top part of the door  66 . The primary slide track  63  incorporates two slide rods  67  anchored within a near side block  68  and the far side block  60  to form parallel slide tracks, along which a sliding block  70  slides freely. A guide roller  71  is affixed to the sliding block  70  and is engaged in the slot of the operating member  73  which is pivotally attached to the near side block  69  by a pivot pin  62 . To the far end of the operating member  73 , there is pivotally attached a slide  74  which slides freely within the secondary slide track  65 . A spring  75  is attached to the far side block  69  and the sliding block  70 . The centre line  76  of the slot in the operating member  73  and the centre line which passes directly through the centres of the guide roller  71  and the pivot pin  62  cross each other and form an acute angle  80  which is substantially constant but may be varied to facilitate increases or decreases in the speeds of operation. 
     It is to be noted that the slot in the operating member  73  is not essential to the operation of the closer, only the outer part  77  of the operating member  73  is necessary. However, the inner part  78  does provide additional strength and ease of handling. 
     When the door  66  is pushed open, the slide  74 , pivotally affixed to the operating member  73  and engaged within the secondary slide track  65  which is affixed to the said door  66 , pulls the free end of the pivoted operating member  73  with it, causing the outer surface  79  of the operating member  73  to exert force upon the guide roller  71  affixed to the sliding block  70 , causing the sliding block  70  to slide along the two slide rods  67  towards the near side block  68 , and tensioning the spring  75  in the process. 
     When the door  66  is released, the spring  75  recoils and forces the sliding block  70  towards the far side end block  69 , exerting force through the guide roller  71  upon the outer surface  79  of the slot in the operating member  73 , causing the operating member  73  to pull the door  66  shut through the pivotally affixed slide  74  engaged within the secondary slide track  65 , affixed to the door  66 . 
     In FIG. 8 there is schematically depicted a diagram which illustrates certain principles of the present invention. Two lines  81  and  82  radiate from a pivot pin  83 . A wedge shape  84  is depicted in three positions to illustrate the relationship between the wedge  84  and the lines  81  and  82 . The lines  81  and  82  represent the lines to two members of a mechanism pivotally interconnected at  83 . The line  81  is stationary, whereas the line  82  moves about the pivot point  83 . 
     When the wedge  84  is pushed from its original position  86  towards the pivot point  83 , it causes the line  82  to swing in an arc away from line  81 . As can be seen, the angle between the line  82  and the wedge plane  87  changes through this operation, degrading the wedge effect, increasing friction at a contact point between the upper left corner of the wedge and the line and reducing leverage. 
     If the wedge  84  is replaced by a round shape  88 , representing a roller for example, friction is reduced, the wedge effect is retained, however the leverage is reduced. To circumvent this disadvantage, the line  82  is modified to become the modified line  85 , incorporating a lever  89  and angled segments  90  which cooperate, if crudely, with the wedge plane  87 , thereby forming a substantially constant angle throughout the operation. 
     The above described principle may be applied in many ways. For example, the lines  81  and  82  can be straight and the form of wedge  84  can be unequal. Alternatively, the wedge  84  can be equal in shape. Either one of the lines  81  and  82  can be stationary or pivotable. The pivot point  83  can be stationary and the wedge  84  or roller  88  can be mobile. Alternatively, the pivot point  83  can be mobile and the wedge  84  or roller  88  can be made stationary. Either line may have a lever section, such as section  89  added to increase leverage. Wedge  84  may be substituted with roller  88 . 
     Member  81  can be straight and member  82  can be substituted with a modified member  85 . The wedge effect is provided by the wedge  84 , an equal wedge or a roller  88 . Either one of the lines  81  and  85  can be stationary or pivotable. The pivot point  83  can be stationary and the wedge  84  or roller  88  can be mobile. Alternatively, the pivot point  83  can be mobile and the wedge  84  or roller  88  can be stationary. 
     In FIG. 9 of the accompanying drawings, the flat segments  90  of FIG. 8 are refined, the intention being to approximate a smooth curve. This may be attained in the following manner: a number of radial lines are drawn from the pivot point  83 . These radial lines may be drawn at 5° increments. A line is drawn at, say 38° across a first of the radial lines. The point at which this line intersects the next radial line then has another line drawn at 38° therefrom to the next radial line and so on. The angle of 38° is arbitrary as is the choice of 5° for the radial line increments. An angle acuter than 38° would provide a greater wedge effect and increments of less than 5° would provide a smoother curve. 
     With reference to FIGS. 1,  2 ,  5  and  7  of the accompanying drawings, line  81  represents the primary track and the line  85  represents the centre line of the slot in the operating member within which the wedge roller  88  is engaged, or the centre line of the body of the operating member. This requires two rollers  91  to provide the desired wedge effect in both directions. 
     When the wedge roller  88  or rollers  91  are moved towards the pivot point  83  or the pivot point  83  is moved towards the roller  88  or rollers  91  along the primary track  81 , the wedge effect causes the outer end of the operating member  85  to swing in direction  92 . 
     The reason for so forming the curve in slot  79  is to ensure that a substantially even force occurs between the slot and the guide roller  71  throughout the operational movement of the apparatus. This principle applies to the operating members of all of the above disclosed embodiments.

Summary:
A opening and closing mechanism for a door or a window including a stationary primary track, a movable secondary track, an operating member with one end pivotally fixed in the primary track and an opposite end movable along the secondary track, and a guide engageable with a guide surface of the operating member. The guide surface is curved along at least a portion of a length thereof such that a tangent to the guide surface at a point where the guide surface crosses a longitudinal center line of the primary track forms an acute angle with the center line. The acute angle is substantially constant throughout the range of pivotal movement of the operating member.