Abstract:
A sprocket wheel or double helical gear loader for a machine which generates gears by pinion shaped cutters. The machine includes a gear bearing table having a centering device and a rotatable supporting base. The loader includes a turntable which advances step-by-step about an axis of rotation of the base. The turntable includes on its periphery a plurality of gear holders, which can be intermittently positioned at cutting stations and a discharge station of completed gears. A gear is secured to the turntable through gripping arms, which surround the gear about a whole of the gear perimeter except for an aperture. A cutter passes through the aperture. The gripping arms are movable to accommodate gears of different sizes.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This Application is a continuation of International Application PCT/GB98/03300, filed Nov. 4, 1998, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention concerns a loader for sprocket wheels, and also the method to automatically position double-toothing sprocket wheels which use the loader, as set forth in the respective main claims. 
     The invention is used in machines to produce single-toothing or double-toothing sprocket wheels generated by cutting blades or pinion instruments. 
     The invention may cooperate with centering devices employed in the case of sprocket wheels with double, straight or bi-helical toothing, wherein the second ring is produced in a subsequent step to the production of the first ring. 
     The invention is used to carry the pieces to be worked, automatically and in sequence, into correspondence with the operating station of the pinion instrument and subsequently to discharge the completed sprocket wheels from this station, at the same time positioning a new piece to be worked. 
     The state of the art covers positioning and centering assemblies employed in the production of sprocket wheels; such assemblies substantially comprise a supporting base cooperating with a shaft for the axial positioning and clamping of the piece, and are associated with a pinion instrument acting peripherally to the piece to form teeth thereon. 
     The unrefined piece is arranged on the supporting base on which it is then made to rotate, while the shaft clamps it in position. 
     While the piece is rotating the pinion instrument works the piece, rotating and moving alternately and in coordination with the rotation of the supporting base. 
     In order to work the pieces the worker must load the piece each time onto the supporting base at the beginning of the operation and must remove the piece when the work has been concluded. 
     These loading and unloading operations considerably slow down the production cycle; it must also be considered that a single worker has to look after two or more machines, and therefore the efficiency of these machines is considerably reduced. 
     In the production of double-toothing sprocket wheels, or sprocket wheels comprising two rings of teeth which are symmetrical to the median transverse plane of the piece, the worker is obliged to further position the piece in the course of his work since the two rings are made in two different steps and normally on two different machines. 
     When the second ring has to be made, the piece has to be angularly positioned with extreme precision with respect to the pinion instrument in order to obtain the desired, accurate reciprocal positioning between the teeth of the two rings. 
     This involves a further lengthening of the working times, with a consequent slow down of the production cycle, a reduction in the efficiency of the machines and an increase in production costs. 
     WO 88/05364 describes a rotary loader for pieces to be machine-worked, which comprises seatings, open towards the outside, wherein the piece is inserted. 
     These seatings are delimited by clamping elements, for example wedge-shaped, screwed to the body of the loader and which act under pressure on the side of the piece to be worked. 
     This kind of loader entails long, complex operations to insert the piece and adapt the size of the seating, which require the wedge-shaped elements to be disassembled. 
     Moreover, the range of sizes and shapes of the pieces which can be worked is very limited, inasmuch as it is not possible to vary by much the size and the shape of the seating, except by using differentiated clamping elements for every size of piece. 
     Furthermore, in the housing seatings the pieces to be worked are, for a substantial portion, arranged outside the seating, which can cause knocks or damage during the complete rotation of the loader. 
     The present applicants have designed, tested and embodied this invention to overcome the shortcomings of the state of the art and to achieve further advantages. 
     SUMMARY OF THE INVENTION 
     The invention is set forth and characterised in the respective main claims, while the dependent claims describe other characteristics of the idea of the main embodiment. 
     The purpose of the invention is to achieve a loader for sprocket wheels which will allow the pieces which have been worked or still have to be worked to be positioned in/removed from the operating zone quickly and automatically. 
     Another purpose of the invention is to limit the inactivity of the pinion instrument between two successive operations, limiting manual intervention to a minimum, reducing dead times of the working cycle, increasing the efficiency of the machines and reducing production costs. 
     A further purpose is to obtain an automatic positioning method, when working with double-toothing sprocket wheels and cooperating with a centering device, which will ensure the precise angular positioning of the piece in order to begin making the second ring. 
     The loader according to the invention may be associated with an assembly to position and center the pieces which form the sprocket wheels, and cooperates with the supporting base. 
     The loader comprises a turntable element which has on its periphery a plurality of housing seatings suitable to contain the pieces which are to be worked in order to form the sprocket wheels. 
     According to a variant, the turntable is defined by a rotary ring or by a conveyor belt including the plurality of seatings on its periphery. 
     Each housing seating has at least a front-aperture of a size mating with the size of the pinion instrument, so that the pinion instrument can work without coming into contact with the loader. 
     According to a variant, the housing seatings are slightly wider than the diameter of the piece to be worked so as to determine a desired play between the housing seating and the relative piece. 
     According to another variant, the housing seatings have a width which is variable and/or can be adjusted to allow pieces of a different diameter to be housed therein. 
     According to another variant, the turntable element cooperates with an underlying sliding support and the pieces to be worked, arranged inside the housing seatings, lie thereon. 
     At the beginning of the cycle, the pieces to be worked are arranged in the housing seatings of the turntable element; the latter is then made to rotate until it places a first piece in correspondence with the operating station of the pinion instrument; once the piece is centered and clamped onto the supporting base, work thereon begins according to conventional methods, with a rotation of the piece-bearing table and the sequential formation of the teeth. 
     It is possible to perform this work thanks to the presence of the front aperture of the housing seating, which allows the pinion instrument to be inserted onto the piece which is to be worked. 
     When this operation is complete, the piece is freed from the grip of the machine and the turntable element is rotated once more, the sprocket wheel which has just been formed is discharged from the operating station and at the same time a new piece is brought into correspondence with the operating station. 
     While the other piece is being worked, the first sprocket wheel can be removed from the relative housing seating and replaced by a new piece which is to be worked. 
     According to the invention, in the case of a double-toothing wheel, the loader cooperates with centering means, rotationally solid with the piece-bearing table, suitable to automatically position in a correct manner the piece being worked with respect to the pinion instrument in order to make the second ring of teeth according to the desired reciprocal angular positioning of the teeth of the two rings. 
     According to this embodiment, the centering means, which can be in any circumferential point whatsoever with respect to the piece which has just been worked, are rotated through a desired arc, after the completed piece has been discharged, by means of rotating the piece-bearing table. 
     This rotation is used to carry the centering means into alignment with the straight line orthogonal to the inner and outer lines tangent to the ideal position of the piece to be worked on the piece-bearing table. 
     In the case of a circular loader, with an axis of rotation parallel to the axis of rotation of the piece-bearing table, the straight line is the conjunction of the two centres of rotation, respectively of the loader and of the piece-bearing table. 
     Subsequently, the loader advances and positions the new piece, on which the second ring has to be made, in correspondence with the axis of rotation of the piece-bearing table. 
     As the loader advances, the centering means comes into contact with a groove or tooth of the first ring which is already complete and defines the precise angular reference position of the piece from which to start working; it is in this position that the loader stops and that working starts. 
     This definition of the reference position involves a rotation of the piece which is caused by the contact of the centering means and at least one tooth of the first ring. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The attached Figures are given as a non-restrictive example and show a preferred embodiment of the invention as follows: 
     FIG. 1 is a part view from above of a loader for sprocket wheels according to the invention; 
     FIG. 2 is a part view from “A” of the loader shown in FIG. 1; 
     FIG. 3 shows a variant of FIG. 2 when double-toothing sprocket wheels are in production; 
     FIGS. 4 a ,  4   b  and  4   c  show diagrammatically the steps the loader takes to position a double-toothing sprocket wheel whose second ring has yet to be made. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the attached Figures, the reference number  10  denotes generally the loader for sprocket wheels  11  according to the invention, which comprises a turntable element  12  cooperating with a positioning/centering assembly  13 . 
     In this description we shall refer to a positioning/centering assembly  13  comprising a piece-bearing table with a substantially horizontal supporting base  15 , a clamping shaft  17  which is axially inserted inside the central hole of the piece and an underlying cavity made on the supporting base  15 . 
     This embodiment however does not limit the field of the invention to variants wherein the supporting base is vertical or in any case oblique, or wherein the piece has no hole and the shaft clamps it on the supporting base by means of tailstocks. 
     Moreover, we shall refer to a loader of the circular type rotating around an axis of rotation  31  substantially parallel to the axis of rotation  33  of the piece-bearing table even if, in variants which are not shown here, the loader  10  can have substantially any configuration whatsoever, not only circular. 
     In this case, the turntable element  12  is arranged above the supporting base  15  and in a position of non-contact with the pinion instrument  14  and is made to advance by the desired value by command means  30  of the type known to the state of the art. 
     The turntable element  12  includes on its periphery a plurality of housing seatings  18  for the pieces  19  to be worked to obtain the sprocket wheels  11 . 
     The housing seatings  18  have a frontal aperture  18   a  through which the pinion instrument  14  passes. 
     In this case, the turntable element  12  consists of two disks, the first upper disk  16   a  and the second lower disk  16   b , keyed onto the axis of rotation  31  of the loader  10 . 
     Advantageously, in the operating position the axis  31  is substantially on the plane which contains the axis of the pinion instrument  14  and the axis of the piece  19  which is to be worked. 
     Each of the two disks  16   a ,  16   b  has on its periphery retaining and containing means consisting of mating gripping arms, respectively  20   a  and  20   b , which are arc-shaped and together define the housing seatings  18  for the pieces  19 . 
     The gripping arms  20   a ,  20   b  surround the piece  19  substantially for the whole of its perimeter, except for the front aperture  18   a.    
     The two disks  16   a ,  16   b  can be rotated in both directions in a reciprocally independent manner and with respect to the axis of rotation  31 ; it is thus possible to vary the width of the housing seatings  18  according to the diameter of the pieces  19  to be worked. 
     The housing seatings  18  also have an automatic self-centering and positioning function so that the axis of the piece  19  lies substantially always around the same circumference and the piece  19  arrives at the work station already in the correct position. 
     In this case, in a position underneath the turntable element  12 , the loader  10  has a sliding support  21 , complanar with respect to the plane  15   a  of the supporting base  15 , and developing in correspondence with the housing seatings  18 . In this case, the sliding support  21  consists of an annular guide  22 . 
     At the beginning of the production cycle, the disks  16   a ,  16   b  are rotated in the appropriate manner one with respect to the other in order to correctly define the width of the housing seatings  18 , according to the diameter of the pieces  19  to be inserted; as this adjustment is made, a desired play is allowed in the connection between the housing seatings  18  and the pieces  19  so that the latter can rotate around their axis even though they are contained in the housing seatings  18 . 
     Inside each housing seating  18  a piece  19  is therefore arranged resting on the sliding support  21 , and the turntable element  12  is made to rotate by a desired value α corresponding to the angular distance between two of the housing seatings  18  so as to bring a first piece  19  in correspondence with the operating station  23 . 
     As the turntable element  12  rotates, the pieces  19  resting on the sliding support  21  are drawn by the disks  16   a ,  16   b.    
     The shaft  17 , suitable to axially clamp the piece  19  to the supporting base  15  while it is being worked, is then lowered and inserted into the relative coupling cavity  15   b  on the supporting base  15  (FIG.  2 ). 
     The supporting base  15  then begins to rotate in coordination with the pinion instrument  14  so as to work the piece  19 ; the pinion instrument  14  gains access to the piece  19  through the front aperture  18 a of the housing seatings  18 . 
     When a first sprocket wheel  11  has been completed, the turntable element  12  rotates, carrying a new piece  19  into correspondence with the operating station  23  so that work can be started on it, while at the same time the completed sprocket wheel  11  is taken into correspondence with a discharge/replacement station  24  (FIG.  1 ). 
     In the discharge/replacement station  24  the sprocket wheel  11  is removed from the relative housing seating  18  and replaced by a new piece  19  to be worked. 
     In this way, the invention provides a substantially continuous production cycle which limits to a minimum any inactive times of the pinion instrument  14 , greatly reduces the need for manual intervention and gives the machine considerable autonomy according to the number of pieces  19  which have to be worked and which are contained in the loader  10 . 
     In the production of double-toothing sprocket wheels  11 , the loader  10  cooperates with a centering device  25 , which is the subject of a separate patent title, and is shown only partly in FIG.  3 . 
     The case shown here refers to a double-toothing sprocket wheel  11  with sloping teeth, of the bi-helical type, but the invention may be applied in the same way to sprocket wheels  11  with straight double-toothing. 
     In the case of double-toothing sprocket wheels  11 , the production cycle has the rings  27   a ,  27   b  of teeth  28  achieved in two successive steps. 
     The loader  10  is therefore loaded with pieces which have the first ring  27   a  already formed and the partly worked piece has to be positioned with respect to the piece-bearing table so that the second ring  27   b  can be made. 
     The desired precise reciprocal angular positioning between the teeth  28  of the first ring  27   a  and of the second ring  27   b  is obtained by means of the centering device  25 . 
     In this case, the centering device  25  comprises a retractable pin  26  protruding from the supporting base  15  and solidly rotating with the supporting base  15  of the piece-bearing table. 
     The positioning procedure is shown in FIGS. 4 a ,  4   b ,  4   c.    
     When work on the piece has been completed, the retractable pin  26  may be in any circumferential position of the supporting base  15 , for example in the position referenced by  26   a  in FIG. 4 a.    
     After the pinion instrument  14  has been placed in a position of non-contact, the supporting base  15  is rotated from this position in either one direction ( 32   a ) or another ( 32   b ) so as to carry the retractable pin  26  into a position of alignment along the straight line orthogonal to the inner and outer lines tangent to the ideal position of the piece  19  with respect to the piece-bearing table; this straight line coincides, in this case, with the conjunction of the centres of rotation of the loader  10  and the supporting base  15 . 
     When the supporting base  15  has reached this position, it is stopped, to define the reference position of the piece  19  to be worked with respect to the start-of-work position of the pinion instrument  14 . 
     It should be noted that the rotation of the piece-bearing table is always connected by means of a kinematic chain (either mechanical or electric) to the rotation of the pinion instrument  14 . 
     This condition of alignment corresponds with the position of outer tangency  26   b  (continuous line in FIG. 4 b ) or of inner tangency  26   c  (shown by a line of dashes in FIG. 4 b ) to the piece  19  to be worked when, in the following step, the said piece  19  is carried to the working position so that the second ring  27   b  of teeth can be made. To be more exact, when the loader  10  is rotated to carry the piece  19  into correspondence with the operating station defined by the supporting base  15 , the retractable pin  26  is inserted between two teeth  28  of the first ring  27   a , coming into contact therewith and clamping the piece  19  in the correct reference position. 
     This clamping action causes a rotation movement to adjust the piece  19  in the opposite direction to the direction of advance given by the rotation of the turntable element  12 . 
     In one embodiment, the upper shape of the retractable pin  26  can be such that, when it is inserted inside the groove  29  between two teeth  28 , it causes contact points with the walls of the teeth  28  lying on the pitch circle of the said teeth  28 . When the positioning procedure is complete, the pinion instrument  14  is taken back to its working position so as to make the second ring  27   b  of teeth on the piece  19 . 
     It is understood that the teachings of the invention which are valid for circular loaders  10  can be directly transferred to round loaders either including a conveyor belt or any other type.