CENTERING DEVICE FOR THE PRODUCTION OF DOUBLE-TOOTHING SPROCKET WHEELS OR PULLEYS AND RELATIVE METHOD OF PRODUCTION

Abstract: Centering device acting upon an already present first ring (14a) of a straight or double helical toothing of gears, sprocket wheels or pulleys to obtain the second ring (14b) of the toothing generated by a pinion shaped cutter (16), a central groove (19) separating said first ring and said second ring. The centering device comprising a retractable pin (20, 120), cooperating during the positioning step of the gear (13), with at least a tooth (15) of the first ring (14a), having a first waiting position (20a, 120a) and a second operating position (20b, 120b) defining the angular position of the gear (13) clamped on the rotary supporting base (18), the angular position being functionally correlated to the plane which contains the axis (25) of the gear (11) and the axis (26) of the cutter (16).

Description: "CENTERING DEVICE FOR THE PRODUCTION OF DOUBLE-TOOTHING SPROCKET WHEELS OR PULLEYS AND RELATIVE METHOD OF PRODUCTION" * * * * * FIELD OF THE INVENTION This invention concerns a centering device to produce sprocket wheels, or pulleys for drive belts, with a straight or bi-helical double-toothing and the relative method of production as set forth in the respective main claims. The sprocket wheels or pulleys to which the invention refers include a central groove which separates the two toothed rings whose teeth are usually inclined from 2° to 60°. The sprocket wheels or pulleys to which the invention refers are advantageously of the type used together with the so-called positive drive belts such as those produced by the Good Year Company and known by the trade name of "Eagle". The invention is used in the field of the production of sprocket wheels generated by generating blades or pinion instruments which move along an axis parallel to the axis of the sprocket wheel and rotate in coordination therewith, both in the forward and in the return movement , the axes being perpendicular to the plane of the piece-bearing table. The invention is used to correctly position the piece to be worked in order to obtain the desired reciprocal positioning of the two mating rings of teeth of the sprocket wheel. The sprocket wheels to which the invention refers may include teeth which coincide with respect to the center line or are offset; the offset distance is advantageously 50% of the pitch. BACKGROUND OF THE INVENTION The state of the art covers sprocket wheels with a straight or bi-helical double-toothing. The latter comprise two coaxial rings of oblique and converging teeth, arranged substantially symmetrically with respect to the intermediate plane of separation, in a substantially herringbone design. The sprocket wheels, according to the shape of the teeth, may be used to transmit movement by means of positive drive belts. Double-toothing wheels are normally worked by positioning and clamping the piece and subsequently activating a cutting instrument acting on the periphery of the piece. On the one hand it is not normally possible to work small double-toothing wheels on a large scale with machines having a single positioning, and on the other hand such a machine involves prohibitive production costs and low productivity. There have also been proposals to work the double-toothing sprocket wheels using machines with a supporting base or piece-bearing table and with a pinion instrument cutting tool which, works by generation with a to-and-fro movement, parallel to the axis of the piece and rotates at the same time in a coordinated manner with the piece to be worked. In this case the unrefined piece is placed with its axis vertical and associated with a shaft, cooperating with the supporting base or piece-bearing table, which determines the starting position with respect to the position of the pinion instrument. In this procedure, two rings of teeth are made in two successive steps; the first step obtains the teeth on a first ring and the second step obtains the teeth on the other ring. However, with this procedure there is the problem of correctly positioning the piece on the machine for the second ring of teeth to be made so as to achieve the precise reciprocal positioning of the first and second ring of teeth. It should be noted that in order to obtain a satisfactory result the axes of the teeth must necessarily meet along the center line of the sprocket wheel within extremely limited tolerances . The play in the connection between the piece to be worked and the shaft which clamps the piece to the supporting base makes it even more difficult to achieve the correct positioning. Therefore it becomes necessary to carry out long and complex operations to adapt the position of the pinion instrument with respect to the piece and vice versa, according to data and measurements monitored by specific equipment . Even with this method then, the cost of production of the sprocket wheels is very high and one of the reasons for this is simply because of the additional operations of removing the shaving. The smaller the sprocket wheel to be made, the greater the problem; even though it is possible to achieve larger sprocket wheels with a sufficient degree of precision, and with overall production times which are reasonable with respect to the total cutting time, until now it has been practically impossible to make small sprocket wheels of this type with any guarantee of reliability and at reasonable cost. The present applicants have designed, tested and embodied this invention to overcome the shortcomings of the state of the art. 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 device which will allow the precise positioning and centering of the pieces required to form double-toothing sprocket wheels to work the second ring of teeth. The invention is applied to obtain double-toothing sprocket wheels generated by cutting blades or pinion instruments. One purpose of the invention is to obtain the precise positioning of the teeth of the second ring with respect to the teeth of the first ring with extremely limited costs and in a short time. Another purpose is to provide a simple, functional device which will allow the piece to form the sprocket wheel to be centered precisely with respect to the pinion instrument, and which will allow the correlated centered position to be maintained throughout the working step. The principal purpose of the invention is to provide a method of production for double-toothing sprocket wheels which will allow a drastic reduction in the times required to center and correctly position the piece to be worked and therefore, more generally, the times and costs of production, while at the same time guaranteeing extreme precision and reliability also for smaller sprocket wheels. The centering device according to the invention is arranged in cooperation with the shaft of the supporting base of the piece to be worked and is placed, for every range of sizes of sprocket wheel, in a pre-set position with respect to the start-of-work position of the pinion instrument. The device cooperates with any tooth, or with any pair of teeth, of the first ring of teeth. The pre-set position is correlated to the extent of the desired staggering, or alignment, of the teeth of the first and second ring of the sprocket wheel. The centering device comprises at least a retractable pin arranged with its axis substantially parallel to the axis of rotation of the sprocket wheel and cooperating with the separating grooves between the teeth of the first ring of the sprocket wheel which is to be made. According to a variant, the centering device has a fork element which cooperates with a tooth of the first ring. According to a variant, the pin or fork element cooperate with the groove, or with the two teeth, substantially along the pitch circle of the tooth. Hereinafter, for simplicity of explanation, we shall describe only the situation with the retractable pin, but the situation with the fork element cooperating with a tooth shall be considered equivalent thereto. According to the invention, the retractable pin can assume at least a first position, or waiting position, wherein it is arranged in a high position above the plane of the supporting base and a second position, or operating position, wherein it cooperates with two teeth of the first ring slightly protruding from the said plane. According to a variant, the retractable pin cooperates with spring means which are suitable, when compressed or released, to define respectively the waiting position or the operating position. The centering device is kinematically connected to the supporting base so that it rotates together with the base, with the sprocket wheel and possibly with the axial positioning and clamping shaft; the sprocket wheel is mounted coaxial to the base and the shaft. According to another variant, the position of the centering device with respect to the axis of rotation of the piece to be worked can be adjusted according to the diameter of the sprocket wheel which is to be made. According to the invention, after the first ring of teeth has been made, the piece is positioned in a work station so that the second ring may be made, the first ring being arranged in cooperation with the supporting base. In this condition, the retractable pin of the centering device is in the waiting position and is then inserted into a groove separating two teeth of the first ring; then the axial positioning and clamping shaft is applied which centers the sprocket wheel with respect to the supporting base and at the same time clamps it with respect thereto. When the sprocket wheel is clamped onto the supporting base, the centering device is in the operating position. The contact between the retractable pin and the walls of the teeth between which it is inserted during the clamping step causes a possible adjustment rotation of the sprocket wheel with respect to the axis of rotation, causing the pair of teeth to be correctly positioned with respect to the pinion instrument . As work progresses to make the second ring, the centering device, since it is solid with the base, moves together with the sprocket wheel, the supporting base and possibly also the axial positioning and clamping shaft, thus maintaining the piece in the correct position for the duration of the whole operation. According to a variant, the retractable pin of the centering device is placed orthogonal to the axis of rotation of the sprocket wheel. According to a further variant, the centering device comprises an auxiliary centering element which is arranged, during the initial equipping and preparation step, above the supporting base and in cooperation with the retractable pin. The auxiliary centering element has the function of centering the cutting tool with respect to the retractable pin before the cycle is started, and therefore it allows to position the cutting tool in the correct angular position with respect to the sprocket wheel to be worked. BRIEF DESCRIPTION OF THE DRAWINGS The attached Figures are given as a non-restrictive example, and show a preferential embodiment of the invention connected with the centering device between two teeth, as follows: Fig. 1 shows a diagram of an assembly to make double- toothing sprocket wheels equipped with the centering device according to the invention; Fig. 2 shows a view from "A" of Fig. 1; Fig. 3 shows a lengthwise section of the centering device according to the invention; Fig. 4 shows a detail of the operating position of the retractable pin with respect to the sprocket wheel; Fig. 5 shows a variant of the invention. Fig. 6 shows a further variant of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the attached figures the reference number 10 denotes generally the centering device according to the invention to produce double-toothing sprocket wheels 11. In the embodiment shown here we shall describe the situation of sprocket wheels 11 with a bi-helical toothing and cooperating with a supporting plane, or piece-bearing table, substantially horizontal and with a clamping shaft which passes through the hollow sprocket wheel. The production of sprocket wheels with a straight double- toothing, or of double-toothing pulleys for drive belts, or piece-bearing tables which are vertical or in any case inclined to the horizontal - all these situations are to be considered equivalent. The bi-helical sprocket wheels 11 comprise two different rings, the first ring 14a and the second ring 14b, of teeth 15 inclined at a desired angle but opposite, with respect to the median plane 29. The rings 14a, 14b are separated from each other by a central groove 19. The centering device 10 is used in association with the assembly to position and center the pieces 13, in order to determine the correct positioning of the pieces 13 to obtain the desired angular positioning between the rings 14a, 14b of the teeth 15. To be more exact, the centering device 10 cooperates with the pinion instrument 16 in order to make the second ring 14b in the desired position with respect to the first ring 14a. The pinion instrument 16, which has teeth which reproduce the teeth 15 to be made on the pieces 13, works by generation and moves to-and-fro (from 16a to 16b and vice versa) along a travel 12, which passes through the central groove 19 parallel to the axis of rotation 25 of the piece 13. The two axes 26-25 (of the pinion instrument 16 and the piece 13) progressively approach one another (each of them moving) until they define the desired depth of the teeth 15. The centering device 10 is placed in a pre-set position with respect to the plane where the axis 25 joins the axis 26 of the pinion instrument 16 in its start-of-work position. In the embodiment shown here, the positioning and centering assembly comprises a supporting base 18 or piece- bearing table; the piece to be worked 13 is arranged on the supporting plane 18b thereof. The supporting base 18 has a coupling cavity 18a into which the shaft 17, which positions and clamps the piece 13 to the base 18, is centered and inserted from above. The base 18 makes the piece 13 rotate, and also possibly the shaft 17. The centering device 10 is radially movable with respect to the base 18 and is mounted, in this case, on a slider which slides on a relative guide 24 which develops radially in and with respect to the base 18. The centering device 10 comprises a main body 21 inside which a retractable pin 20 is elastically constrained; the upper part of the retractable pin 20 is spherical in order to make the reciprocal positioning between the centering device 10 and the piece 13 more precise. The retractable pin 20 may assume at least a first position, or waiting position, 20a wherein it is arranged in a high position above the plane 18b, and a second position, or operating position, 20b wherein it is inserted into the groove 22 between two teeth 15 protruding as much as necessary from the plane 18b. In this case, the retractable pin 20 is associated with spring means 27 of the cup type, housed inside the main body 21. The retractable pin 20 is of the replaceable type and its spherical part mates with the transverse size of the grooves 22 between two of the successive teeth 15. Moreover, the retractable pin 20 is made of a material of great hardness and resistance, at least in its upper part. According to the invention, the upper part of the piece 13 is always worked on by the pinion instrument 16; therefore, after the first ring 14a has been made, the same piece 13 is transferred to another machine arranging the first ring 14a in cooperation with the plane 18b of the supporting base 18. The piece 13 is moreover positioned in such a way as to align one of the grooves 22 with the retractable pin 20. When the axial positioning and clamping shaft 17 is lowered to clamp the piece 13 onto the plane 18b, the pin 20 assumes its operating position 20b, and is inserted inside the groove 22 in a substantially median position. In this case (Fig. 4) , even if it is not necessary, the spherical end of the retractable pin 20 is shaped with respect to the groove 22 in such a way that the points of contact 20c with the walls of the teeth 15 lie on the pitch circle 115. The retractable pin 20 comes into contact with the side walls 15a of the teeth 15 between which it is inserted, and causes a possible adjustment rotation and a consequent centering of the piece 13 with respect to the axis 25, and therefore the correct positioning with respect to the start- of-work position 16a of the pinion instrument 16. The pre-set positioning of the centering device 10, and therefore of the retractable pin 20 according to the desired angular positioning of the first ring 14a and the second ring 14b, guarantee the precise arrangement of the piece 13 with respect to the pinion instrument 16 which thus is found to be, in the start-of-work position 16a, already correctly arranged to begin working on the second ring 14b. When a piece 13 of a greater or lesser diameter is being worked, the centering device 10 is radially displaced from the shaft 17 by moving the slider 23, on which the shaft is mounted, along the relative guide 24. The supporting base 18 includes grooves 28, of any direction or orientation whatsoever, which facilitate the removal of the sprocket wheel 11 once it has been completed, reducing the adherence of the piece to the piece-bearing table caused by the surface tension of the cutting liquid. In the case of Fig. 5, instead of the retractable pin 20 which works in the groove 22 between two teeth 15, there is a fork-type pin 120, elastically contrasted by spring means 127, which cooperates with a main body 121 and includes two spherical elements 30 which cooperate with the sides of a tooth 15 in order to center the sprocket wheel 11 itself. The fork-type pin 120 also has a waiting position 120a and an operating position 120b. In the variant shown in Fig. 6, the centering device 10 comprises an auxiliary centering element 31 which is used in the initial equipping and setting-up step of the tool 16. The auxiliary centering element 31 consists of a plate 32, suitable to rest on the base 18, on which a block 33 is attached; the block 33 contains inside a retractable pin 34 equipped with a protruding head, round in shape, advantageously spherical . The retractable pin 34 is housed inside a containing body 35, attached inside the block 33, inside which it is suitable to slide vertically, for example elastically contrasted, for a short, defined section. With the auxiliary centering element 31 in the working position, the retractable pin 34, is arranged in axial extension of the retractable pin 20 inserted inside the base 18. Under the containing body 35, at a substantially central position of the plate 32, there is a hollow bush 36 with an axial hole 37 which is suitable to cooperate with the head of the retractable pin 20. The height of the base 18 of the plate 32 plus the block 33 corresponds substantially to the height "1" of the tool 16 from the base 18 itself. During the setting-up step, before the piece 13 is arranged on the base 18 and working begins, the auxiliary centering element 31 is rested on and clamped to the base 18 making the head of the retractable pin 20 cooperate with the axial hole 37 of the bush 36 inserted in the plate 32. Then, the tool 16 is displaced radially into proximity with the auxiliary centering element 31 until one of the grooves defined between its teeth comes into contact with the protruding head of the retractable pin 34, with a consequent rotation of the tool 16 to adjust the angle thereof. Then, when its correct angular position has been fixed, the tool 16 is retracted, the auxiliary centering element 31 is discharged from the base 18 and in its place the piece 13 on which the second ring of teeth has to be made is positioned, with a consequent centering of the piece 13 with respect to the retractable pin 20. Due to the axial alignment of the retractable pin 20 and the retractable pin 34, the tool 16 is already in the precise angular position without needing any further adjustments to its position with respect to the piece 13.

Claims: CLAIMS 1 - Centering device to obtain the second ring of wheels or pulleys with double toothing, either straight or bi-helical, generated by cutting blades or pinion instruments (16) , the sprocket wheels being fixed to the supporting base (18) of the tooling machine, the pinion instrument (16) moving with a to-and-fro movement and with an axis (26) parallel to the axis of rotation (25) of the sprocket wheel (11) and rotating in coordination with the sprocket wheel (11) , the sprocket wheels (11) being defined by a first ring (14a) which has already been formed and a second ring (14b) which has yet to be formed, the rings (14a, 14b) being separated by a central groove (19), each ring (14a, 14b) including respective teeth (15) straight or inclined from 2° to 60° with respect to the median plane (29) orthogonal to the axis (25) of the sprocket wheel (11), the centering device cooperating with a supporting base (18) rotating with an axis (25) and defining the plane (18b) on which the piece to be worked, (13) lies and with the pinion instrument (16) acting on the periphery of the piece (13), the plane (18b)- cooperating with a shaft (17) to axially position and clamp the piece (13), the pinion instrument (16) following a travel (12) from a first position outside the ring (14a, 14b) to a second position coordinated with the central groove (19), the device being characterised in that it comprises a retractable pin (20,120) including a first waiting position (20a, 120a) and a second operating position (20b, 120b) , the first waiting position (20a, 120a) cooperating, during the positioning step of the piece (13), with at least a tooth (15) of the first ring (14a) , the second operating position (20b, 120b) of the retractable pin (20, 120) defining the angular position of the piece (13) clamped on the rotary supporting base (18) , the angular position being functionally correlated to the plane which contains the axis (25) of the sprocket wheel (11) and the axis (26) of the pinion instrument (16) . 2 - Device as in Claim 1, characterised in that the retractable pin (20, 120) is rotationally solid with the supporting base (18) . 3 - Device as in any claim hereinbefore, characterised in that the second operating position (20b) of the retractable pin (20) cooperates with a groove (22) between two teeth (15). 4 - Device as in claim 1 or 2 , characterised in that the second operating position (120b) of the retractable pin (120) cooperates with the sides of a tooth (15) . 5 - Device as in claim 3 or 4, characterised in that, in the second operating position (20b, 120b) , the retractable pin (20, 120) has points of contact with the walls of the teeth (15) lying on the pitch circle (115) of the first ring (14a) positioned below. 6 - Device, as in any claim hereinbefore, characterised in that the retractable pin (20, 120) includes a position which can be radially adjusted with respect to the axis of rotation (25) of the supporting base (18) . 7 - Device as in Claim 6, characterised in that the retractable pin (20, 120) is mounted on slider means (23) which are radially movable with respect to the axis of rotation (25) of the supporting base (18) . 8 - Device as in any claim hereinbefore, characterised in that the retractable pin (20, 120) has spherical contact means . 9 - Device as in any claim hereinbefore, characterised in that at least the contact end of the retractable pin (20, 120) is made of material of great hardness and resistance. 10 - Device as in any claim hereinbefore, characterised in that the retractable pin (20, 120) is axially associated with elastic contrasting means (27, 127) . 11 - Device as in any claim hereinbefore, characterised in that the retractable pin (20, 120) has its own axis substantially parallel to the axis of rotation (25) of the supporting base (18) . 12 - Device as in any claim from 1 to 10 inclusive, characterised in that the retractable pin (20,120) has its axis substantially orthogonal to the axis of- rotation (25) of the supporting base (18) . 13 - Device as in Claim 1, characterised in that it comprises an auxiliary centering element (31) suitable to position and angularly center the tool (16) with respect to the piece (13) which is to be worked before the work cycle is started by the tool (16) itself. 14 - Device as in Claim 1, characterised in that the auxiliary centering element (31) comprises a retractable pin (34) assembled on support means (32,33), the support means (32,33) being equipped at the base with a hole (37) suitable to cooperate with the head of the retractable pin (20) so as to clamp in position the auxiliary centering element (31) to the base (18) , the retractable pin (34) being axially aligned with the retractable pin (20) and including at least a position wherein it protrudes above the support means (32,33) and cooperates with one of the teeth of the tool (16) so as to angularly center of the tool (16) with respect to the piece (13) to be worked. 15 - Method to obtain the second ring (14b) in the production of double-toothing sprocket wheels or pulleys (11) generated by pinion instruments (16), the sprocket wheels being fixed to the supporting base (18) of the tooling machine, the pinion instrument (16) moving with a to-and-fro movement and with an axis (26) parallel to the axis of rotation (25) of the sprocket wheel and rotating in coordination with the sprocket wheel, the method adopting the centering device as in the previous claims, the double- toothing sprocket wheels being defined by a first ring (14a) which has already been formed and a second ring (14b) which has yet to be formed, the rings (14a, 14b) being coaxial and separated by a central groove (19) , each ring (14a, 14b) including teeth (15) straight or oblique, the method using a supporting base (18) rotating with an axis of. rotation (25) and defining the plane (18b) on which the piece to be worked (13) lies and a pinion instrument (16) acting on the periphery of the piece (13), the plane (18b) cooperating with a shaft (17) to axially position and clamp the piece (13), the method including first the formation of a first ring (14a) of teeth (15) and then the positioning of the partly worked piece (13) in cooperation with the plane (18b) of a work station, the method being characterised in that the piece (13) is positioned on the plane (18b)- substantially by aligning any one of the teeth (15) or of the grooves (22) of the first ring (14a) with a retractable pin (20, 120) placed in the first waiting position (20a, 120a), then the axial positioning and clamping shaft (17) is activated so as to stably clamp and center the piece (13) with a consequent positioning of the retractable pin (20) in the second operating position (20b, 120b) defining the precise angular position of reference of the piece (13) with respect to the pinion instrument (16) . 16 - Method as in Claim 14, characterised in that the activation of the axial positioning and clamping shaft (17) causes the retractable pin (20, 120) to be inserted in such a way that the retractable pin (20, 120) cooperates with the walls of the teeth (15) defining the groove (22) . 17 - Method as in claim 15 or 16, characterised in that the extraction of the piece (13) is facilitated by the presence of grooves (28) or hollows on the plane (18b) of the supporting base (18) . 18 - Method as in Claim 15, characterised in that it includes a preliminary step of positioning and angularly centering the tool (16) with respect to the piece (13) to be worked before the start of the work cycle of the tool (16), the preliminary step of positioning and angularly centering the tool (16) being performed by an auxiliary centering element (31) which includes a retractable pin (34) which can be axially aligned with the retractable pin (20) and suitable to cooperate with one of the grooves defined between the teeth of the tool (16) .

Inventors: GILL SHERIDAN RALPH, GILL, SHERIDAN, RALPH
Applicants: GILL SHERIDAN RALPH, TECHNOLOGIES RESEARCH HOLDING, GILL, SHERIDAN, RALPH, TECHNOLOGIES RESEARCH HOLDING S.A.
Application year: 1998
Main classification: B23F23
IPC codes: B23F7, B23F23