A MACHINE FOR PREPARING TYRE TREAD DURING RETREADING

Abstract: The grinding machine according to the invention comprises a first support (1) designed to support a tyre (2) in a vertical position and able to rotate about a first horizontal axis (3), a second support (7) positioned vertically on one side of the tyre (2), a third support (8) which can be moved manualy, which is connected to an upper part of the second support (7) by a connector (11) with at least three degrees of freedom, and which, when operating, extends substantially horizontally from the second support (7), passing above the tread of the tyre (2), and a grinder (9) on the third support (8) which is driven by a motor (34) about a second, substantially horizontal axis (33). The grinder (9) is mounted on the third support (8) by means of a fourth support (35) which can rotate about a third, substantially vertical axis (36) which intersects the second axis (33) at the centre of the grinder (9). There being control means (46) for making the fourth support (35) and the grinder (9) rotate about the third axis (36).

Description: Description A machine for preparing tyre tread during retreading Technical Field The present invention relates to a manually controlled grinding machine for grinding the tread of a tyre which is worn or damaged. Background Art To retread a worn or damaged tyre, it is often necessary to perform a given number of preparatory operations on the peripheral surface of the tyre before the actual retreading operation. The first operation normally consists of a so-called "buffing" operation, designed to even out the peripheral surface of the tyre. The second operation is a so-called "scraping" or "rounding" operation (also called "skiving" by experts in the field), which involves making small cavities in the peripheral surface of the tyre, with the aid of a small grinder, to eliminate small imperfections and foreign particles still included in or driven into the rubber, including small stones, nails, etc., to remove air bubbles and/or widen small lesions in the rubber. The cavities formed by scraping or rounding are then filled with raw rubber and the peripheral surface of the tyre is coated with a thin mixture for the underlayer, around 1 mm thick, followed by the application on top of the underlayer mixture of a strip of raw or pre-vulcanised rubber which will form the new tyre tread. The scraping or rounding (skiving) operation must be carried out with extreme care, since if any imperfections remain after this operation, the new tread may come away from the body of the tyre during use of the retreaded tyre. There are machines which allow scraping or rounding to be carried out in a largely automated fashion, significantly simplifying the work of the operator in charge of such operation (see, for example, US patent 5 238 041) . However, these are extremely sophisticated and, therefore, expensive machines. For this reason, scraping or rounding is still done manually, in many cases, with the aid of portable grinding tools or equipment. These portable grinding tools or equipment have a number of disadvantages : a) work is carried out in an environment which is strongly polluted with rubber powder; b) the air in the environment is impregnated with the odours of sulphur and other chemical components of rubber, and sometimes with smoke; c) the use of safety goggles is obligatory not only due to the rubber powder, but also because of the small stones driven into the rubber and fragments of steel shavings from the body of the tyre, since the stones and particles are detached and thrown out at high speed by the grinder; d) the risk of injury is high, since the portable grinding tool or equipment is held in the operator's hands; e) the operator becomes tired, since he or she must support the weight of the grinding equipment, and must perform repetitive and tiring movements; f) the portable grinding equipment produces acute, high intensity noise, which risks deafening the operator, whose head is very close to the working area. Moreover, a grinding machine is known, which allows the reconstruction of tread profiles or the ribs of tyres for tractors or other agricultural machinery or site vehicles and machinery, in order to restore the capacity for adhering to the ground or antiskid properties when the above-mentioned profiles or ribs are worn (see US patent 2 670 526) . However, this known machine is not very suitable for the above-said scraping or rounding, which is not part of its specific purpose. In particular, this known machine does not allow the practical cutting of the cavities which are circular or substantially circular, which are then easily filled with raw rubber. Disclosure of the Invention The aim of the present invention is, therefore, to provide a manually controlled grinding machine which can be manoeuvred easily, practically and without tiring the operator, so as to make circular or substantially circular cavities during the operations for scraping or rounding the peripheral surface of a worn tyre for retreading. Another aim of the invention is to provide a grinding machine which is decidedly less expensive than grinding machines with a high level of automation, and at the same time does not have, or hardly has, any of the above-mentioned disadvantages of portable grinding equipment . Accordingly, the present invention provides a manually controlled grinding machine which comprises: a) a first means of support designed to support the centre of a worn or damaged tyre in the vertical position, and able to turn about a first horizontal axis to turn the tyre about its own central axis of rotation; b) a second means of support positioned vertically on one side of the tyre supported by the first means of support; c) a third means of support, which can be moved manually and which has an elongated shape and comprises a first end connected to an upper part of the second means of support by a connector with at least three degrees of freedom, and a second end which can be grasped by the operator, with the third means of support extending substantially horizontally from the second means of support during operation, and passing above the tread of the tyre supported by the first means of support; and d) a grinder supported by the third means of support between the first and second end of the latter, and which when operating is rotated by a motor about a second substantially horizontal axis in order to grind a desired area of the upper part of the tread of the above-mentioned tyre. The machine disclosed is characterised in that: e) the grinder is mounted on the third means of support by a fourth means of support, which can rotate relative to the third means of support about a third, substantially vertical axis, which intersects the second axis at the centre of the grinder; and f) control means interact between the third and fourth means of support, and can be activated to turn the fourth means of support and the grinder about the third axis . The fourth means of support is preferably set up to turn about the third axis between two end angular positions separated by a preset angle, said preset angle preferably being around 180°. The machine disclosed may also have one or more of the following characteristics: - the third means of support consists of a Y-shaped arm, with a central branch and two side branches, connected by a joint node to a first end of the central branch, with a second end of the central branch being connected to the second means of support, in the form of a column, by the above-mentioned connector with at least three degrees of freedom, where each side branch has a grip at the end opposite the joint node; - the third means of support also comprises a plate fixed to the two side branches close to the joint node, having a circular opening between the two side branches, with the fourth means of support consisting of a circular surface mounted in such a way that it can rotate in the circular opening in the plate thanks to a rotation gear; - the circular surface supports the above-mentioned motor, whose output shaft is parallel with the axis of rotation of the circular surface, with the grinder positioned below the circular surface and supported by a grinder support shaft perpendicular to the axis of rotation of the circular surface and to the motor output shaft, and connected to the above-mentioned output shaft by a pair of bevel gears; - the above-mentioned control means comprise a half-gear fixed concentrically to the circular surface, a cylinder which rotates in both directions of rotation, fixed to the plate, and a pinion fixed to the rotary cylinder output shaft and meshing with the half-gear; - the grip on each of the two side branches of the arm forming the third means of support comprises a first and a second normally open contactor. The first contactor of each grip is positioned in such a way that it closes when the operator grasps the corresponding grip with one hand, and the first contactors of the two grips are connected in series in a first motor control circuit, so that the motor can only operate when the operator grasps the two grips with his or her hands. The second contactor of a first of the two grips may be selectively closed with one of the operator's fingers, and is connected in a second rotary cylinder control circuit, to make the cylinder turn in a first direction when the second contactor of the first grip closes, whilst the second contactor of the second grip can be selectively closed with one of the operator' s fingers and is connected in a third rotary cylinder control circuit, to make the cylinder turn in a second direction, opposite to the first, when the second contactor of the second grip closes; - the grinder is rotated in a direction which allows the rubber particles removed from the tyre by the grinder during treatment to be thrown in a direction which is opposite to the direction of the operator relative to the grinder, and an extractor nozzle is fixed to the circular surface so that its extractor outlet is constantly angled in the direction in which the particles of rubber removed by the grinder are thrown, the extractor nozzle being connected to a dust extractor device by a flexible hose; - the above-mentioned connector with at least three degrees of freedom consists of a ball joint, and the second end of the central branch of the arm forming the third means of support is mounted in such a way that it can slide in a diametric passage made in the ball joint; - in addition to the ball joint, the central branch comprises an extension which supports a counterweight whose position can be adjusted along the extension to allow balancing of the arm which forms the third means of support in a horizontal position; - the two side branches of the arm forming the third means of support have adjustable length. Brief Description of the Drawings Further characteristics and the relative advantages of the present invention are described in detail below with reference to the accompanying drawings, which illustrate a preferred embodiment, without limiting the scope of its application, and in which: Figure 1 is a schematic side elevation of a grinding machine in accordance with the present invention; Figure 2 is a top plan view of the machine illustrated in Figure 1; Figure 3 is a side elevation of one of the two control grips on the machine illustrated in Figures 1 and 2; Figure 4 is a scaled up top plan view of the grinder and other active elements connected to the grinder of the machine illustrated in Figures 1 and 2; Figure 5 is a cross-section along line V-V illustrated in Figure 4 ; Figure 6 is a cross-section along line VI-VI illustrated in Figure 4; Figures 7A and 7B are partial top plan views illustrating how the machine made according to the present invention can make circular cavities in the peripheral surface of a tyre; Figure 8 is a simplified wiring and compressed air diagram for those cases in which compressed air rotary motors are used to drive the active elements of the machine according to the present invention. Detailed Description of the Preferred Embodiments of the Invention With reference to Figures 1 and 2, it may be seen that the grinding machine disclosed comprises a first support 1 designed to support the centre of the vertically positioned worn or damaged tyre 2 to be prepared for retreading. The support 1 can turn about a horizontal axis 3 which coincides with the central axis of rotation of the tyre 2. The rotary support 1 is mounted on a frame 4 which can advantageously comprise control means for making the support 1 turn in step with the tyre 2 about the axis 3, as well as pneumatic, hydraulic, electrical or manually controlled activation means which allow height adjustment of the support 1, and therefore of the tyre 2. The rotary support 1, the frame 4, the control means and activation means can be made in any way known to experts in the field, and therefore are not described in detail, except where necessary to understand the present invention. One side of the frame 4 is fitted with an operating platform 5 for a worker or operator 6, whilst the other side of the frame 4 is fitted with a second support 7. This second support 7 may be, for example, a column which is preferably on a vertical plane perpendicular to the axis 3 and passing through the centre of the tyre 2 on the support 1. The column 7 is preferably height adjustable. For this reason, the column 7 may, for example, consist of two tubes 7a and 7b mounted telescopically one inside the other, and a cylinder or other hydraulic, pneumatic or electrical actuator 10 - which can be controlled by the foot of the operator 6, for example, with the aid of a pedal (not illustrated) fitted on the platform 5 - inside one of the two tubes of the column 7 and connected to the other tube of the column for axially moving the two tubes relative to one another, and so adjusting the column height. The grinding machine disclosed also comprises a third support 8 connected in a jointed fashion to the upper part of the column 7, and when operating extending horizontally from the column to the operator 6, passing over the upper part of the tread on the tyre 2 on the support 1. The third support 8 holds a grinder 9 as described in detail below. The support 8 preferably consists of a Y-shaped arm, with a central branch 8a and two side branches 8b and 8c. The central branch 8a is connected to the column 7 by a connector 11 with at least three degrees of freedom, and preferably four degrees of freedom, that is to say: a) possibility of rotation about a horizontal axis 12 parallel with the axis 3, as indicated by the two arrows FI and F2 in Figure 1; b) possibility of rotation about a vertical axis 13 which coincides with the longitudinal axis of the column 7, as indicated by arrows F3 and F4 in Figure 2; c) possibility of rotation about an axis 14 which coincides with the longitudinal axis of the branch 8a of the support 8, as indicated by the two arrows F5 and F6 in Figure 1; d) possibility of translation along the longitudinal axis of the branch 8a, as indicated by the double arrow F7 in Figure 1. For example, the connector 11 may consist of a ball joint, where the ball joint 15 comprises a diametric passage 16 in which the branch 8a of the support 8 can slide with slight friction. The three branches 8a - 8c of the Y-shaped support 8 may, for example, consist of pieces of pipe with a round or square cross- section, connected to one another at a joint node 17 (Figure 2) . At said node 17, the pipes forming the branches 8a and 8c may be simply welded to one another. Alternatively, the node 17 may consist of an assembly clamp, for example made of moulded plastic or metal, with three seats in which one end of each of the three pieces of pipe forming the branches from 8a to 8c is inserted and fixed by gluing or another appropriate known means . The two branches 8b and 8c are preferably bent so that they have parts 8d and 8e which extend parallel with one another or substantially parallel, as illustrated in Figure 2. The length of each of the two parts 8d and 8e is preferably adjustable. In such cases, each of the two parts 8d and 8e may consist of two pieces of pipe 8d and 8f or 8e and 8g, mounted telescopically one inside the other, which may be reciprocally locked and released using a known type of tightening device 18 or 19. The end of each of the two pipes 8f and 8g furthest from the relative part 8d or 8e, is fitted with a grip 21 or 22 designed to be grasped by the operator 6, as illustrated in Figures 1 and 2. The two grips 21 and 22 are identical, therefore, only one of the two grips is described in detail with reference to Figure 3. Said Figure shows how each grip 21 or 22 is preferably shaped like a pistol grip. Inside the butt 23 of each pistol grip there are two contactors 24 and 25, both normally open and electrically connected, by the wires of a multi-wire cable 26, to grinding machine control circuits, described in detail below with reference to Figure 8. The contactor 24 can be activated, that is to say closed, using a lever 27 which can rotate about an axis 28. Stress is applied to the lever 27 by a spring (not illustrated) so that it projects through an opening in the back 29 of the butt 23. The lever 27 is pressed to oppose the spring return force, closing the contactor 24 when the operator 6 grasps the butt 23 and holds it firmly in his or her hand. The contactor 25 can be activated, that is to say closed, when the operator applies pressure to a trigger 31 at the front 32 of the butt 23 with his or her index finger. The following is a description, with reference to Figures 4, 5 and 6, of the method for mounting the grinder 9 on the support 8. The grinder 9, which during operation rotates about a horizontal axis 33, and is driven by a motor 34 at a relatively high speed, for example at a speed of between 2000 and 5000 rpm, is mounted on the support 8 by means of another support 35. The support 35 can rotate relative to the support 8 about a vertical axis 36 which intersects the axis 33 at the centre 37 of the grinder 9. Specifically, the support 8 also comprises a plate 38 fixed to the parts 8d and 8e of the two side branches 8b and 8c, close to the joint node 17, and comprising a large circular opening between said parts 8d and 8e of the side branches 8b and 8c. The support 35 consists of a circular surface 39 mounted in such a way that it can rotate in the circular opening in the plate 38 thanks to a rotation gear 41, consisting, for example, of a ball gear. The motor 34 which controls the grinder 9 is positioned on and secured to the circular surface 39. The output shaft 42 of the motor 34 is parallel with the axis of rotation 36 of the surface 39, and passes through the latter. The grinder 9 is below the surface 39 and supported by a grinder support shaft 43 perpendicular to the axis of rotation 36 of the surface 39 and to the output shaft 42 of the motor 34. The shafts 42 and 43 are connected to one another by a pair of bevel gears 44 and 45. The machine disclosed also comprises control means 46 which can be activated to make the surface 39 rotate about the axis 36. In the embodiment illustrated in Figures 4 to 6, the control means 46 comprise a half-gear 47 fixed concentrically to the circular surface 39, a rotary cylinder 48 with two directions of rotation, and a pinion 49 fixed to the output shaft 51 of the rotary cylinder and meshing with the half-gear 47. The rotary cylinder 48 is held by a Z-shaped support 52, which is fixed to the plate 38 by screws 53. The grinder 9 is normally a relatively thin disk. As a result, during operation, when the grinder 9 makes contact with the peripheral surface of the tyre 2, it tends to form a relatively narrow notch 54, as illustrated in Figure 5. This kind of notch may be difficult to fill with raw rubber, especially if it is deep. The grinder 9 must, therefore, be able to make a circular or substantially circular cavity in the peripheral surface of the tyre 2. This can be achieved by making the surface 39 rotate at a relatively low speed about the axis 36 by means of the rotary cylinder 48 and pinion 49 meshing with the half-gear 47, while the grinder 9 rotates at a relatively high speed about the axis 33 and makes contact with the peripheral surface of the tyre 2. To make a circular cavity, the surface 39 does not need to be able to perform a complete rotation about the axis 36. In practice, it is sufficient for the surface 39 to rotate about the axis 36 between two end angular positions separated by a preset angle, preferably around 180° . For this reason, in the embodiment illustrated in Figures 4 to 6, a half-gear 47 is used. However, a complete gear may be used. The two end angular positions for the surface 39 may be defined, for example, by two limit switches 55 and 56, normally closed, which are inserted in a control circuit for the rotary cylinder 48 using a method described in detail below, and which can be activated, that is to say opened, by pawls 57 and 58 fixed to the surface 39, after the latter has performed a quarter turn clockwise or a quarter turn anti-clockwise from the position illustrated in Figure 4. In this way, if the surface 39 performs a quarter turn anti-clockwise from the position illustrated in Figure 4, the grinder 9 passes from the position illustrated with the line and dot to the position illustrated with the continuous line in Figure 7A, and forms a cavity 59 which is substantially in the shape of an eight leaning to the right. In contrast, if the surface 39 performs a quarter turn clockwise from the position illustrated in Figure 4, the grinder 9 passes from the position illustrated with the line and dot to the position illustrated with the continuous line in Figure 7B, and forms a cavity 61 which is substantially in the shape of an eight leaning to the left. Superimposing the two Figures 7A and 7B illustrates how, by making the surface 39 first perform a quarter turn in one direction, then a half turn in the opposite direction, a circular cavity is obtained. The motor 34 and rotary cylinder 48 preferably consist of pneumatic motors which can be supplied with compressed air by a compressed air generator 62 consisting, for example, of a compressor 63 driven by an electric motor 64, which is in turn powered by a voltage generator 65 along a line 66 and a main start - stop switch 67, as illustrated in Figure 8. The motor 34 is connected to the compressor 63 output by a pipe 68 fitted with a normally closed solenoid valve 69. The solenoid 71 of the solenoid valve 69 is electrically connected to the line 66 by a line 72. The two contactors 24 in the grips 21 and 22 (Figures 1 to 3) are connected in series in the line 72, as illustrated in Figure 8. In such conditions, when the main start - stop switch 67 is closed, the motor 34 can be supplied with compressed air through the pipe 68 and the solenoid valve 69 only if the two contactors 24 are closed, that is to say, if the two grips 21 and 22 are grasped and held in the hands of the operator 6. As a result, if the operator releases one of the two grips 21 and 22, the current supply to the solenoid 71 of the solenoid valve 69 is interrupted, the solenoid valve closes and the motor 34 stops, thus drastically reducing, or even eliminating the risk of the operator being injured by the grinder 9. The rotary cylinder 48 is connected by two pipes 73 and 74 to a three-position distributor 75, which is itself connected by a pipe 76 to the compressor 63 output. The distributor 75 has a neutral or home position corresponding to a rotary cylinder 48 stop position. In this position, the rotary cylinder 48 is not supplied with compressed air and the pipes 73 and 74 are blocked by the distributor 75, so that the rotary cylinder 48 is practically locked in the position which it occupies at the moment when the distributor 75 is switched to its neutral position. The other two distributor 75 positions correspond to a position in which the rotary cylinder 48 is supplied with compressed air through the pipe 73 and turns anticlockwise (corresponding to a clockwise rotation of the surface 39) , and a position in which the rotary cylinder 48 is supplied with compressed air through the pipe 74 and turns clockwise (corresponding to an anti-clockwise rotation of the surface 39) . These other two distributor 75 positions can be achieved by energising solenoid 77 or solenoid 78 of the distributor 75. Solenoid 77 is electrically connected to the line 66 by the line 79 in which the limit switch 55 and the contactor 25, for example, in the grip 21, are connected in series. Solenoid 78 is electrically connected to the line 66 by a line 81 in which the limit switch 56 and the contactor 25, for example, in the grip 22, are connected in series. In this way, by pulling the trigger 31 of the grip 21 to close the contactor 25, the operator can turn the surface 39 clockwise, and as soon as the operator releases the trigger 31 or the limit switch 55 is opened by the pawl 57, the distributor 75 returns to its neutral position, the rotary cylinder 48 stops turning and the surface 39 stops. Similarly, if the operator pulls the trigger 31 of the grip 22 to close the contactor 25, the surface 39 turns anti-clockwise, and as soon as the operator releases the trigger 31 or the limit switch 56 is opened by the pawl 58, the rotary cylinder 48 stops turning and the surface 39 stops. Given that the motor 34 and the rotary cylinder 48 may require compressed air with different pressure values for operation, there may be pressure limiters (not illustrated) calibrated to the appropriate pressure values in the pipes 68 and 76. Again with reference to Figures 4 to 6, it may be seen how the surface 39 comprises a rectangular opening 82 through which the grinder 9 operating position may be observed. However, the presence of this opening 82 is not essential, since, as shown in Figure 1, the operator 6 has a direct view of the grinder operating zone on the peripheral surface of the tyre 2, with the line of sight passing between the branches 8d and 8e of the support 8 and under the plate 38. As illustrated in Figures 1 to 6, the grinder 9 is rotated in a direction (arrow F) such that the particles of rubber or other particles from the tyre 2 removed by the grinder during treatment are thrown in a direction opposite to that in which the operator 6 is located relative to the grinder. Moreover, an extractor nozzle 83, preferably made of an elastomeric or soft plastic material, is rigidly fixed to the circular surface 39, so that whatever the angular position of the surface 39, the extractor outlet of the nozzle 83 always covers the direction in which the particles of rubber removed by the operating grinder 9 are thrown. A flexible hose 84 connects the extractor nozzle 83 to a dust extractor device 85 (Figures 1 and 2) . In this way, the rubber powders and other particles removed by the operating grinder 9, as well as any smoke produced by the action of the grinder, are effectively extracted and carried outside the operating zone. As illustrated in Figures 1 and 2, the central branch 8a of the Y-shaped support 8 comprises, in addition to the ball joint 15, and extension 8h bearing a counterweight 86. The position of the counterweight 86 may be adjusted along the extension 8h to allow the support 8 to be balanced in a horizontal or substantially horizontal position. In this way, the operator 6 only needs to make a minimal effort to manoeuvre the support 8 with the aid of the two grips 21 and 22 to bring the grinder 9 into contact with the desired zone to be ground on the peripheral surface of the tyre 2 or to move the grinder away from it . Moreover, when the surface 39 is in the position illustrated in Figure 4, the motor 34 and rotary cylinder 48 are at equal distances from the longitudinal midplane of the support 8 in which the central branch 8a of the latter is located. In such conditions, the plate 38, surface 39 and all elements supported by them, are practically balanced relative to the longitudinal axis 14 of the central branch 8a of the support 8, therefore, the operator 6 only needs to make a minimal effort to make the support 8 rotate about the axis 14 if necessary. As indicated in the description above, the grinding machine disclosed has many advantages over the portable grinding tools or equipment previously known and used to carry out scraping or rounding (skiving) operations on a tyre to be retreaded. The above- mentioned advantages include: a) The grinding tool is no longer held in the operator's hands. Instead, the grinding machine is angled and controlled remotely with the aid of two grips 21 and 22. All movements passed from the hands to the portable grinding tool or equipment previously known can be performed with the grinding machine disclosed with the aid of two grips 21 and 22 and the rotary cylinder 48. Both of the operator's hands are occupied and cannot release the grips 21 and 22 without automatically stopping the machine, thus eliminating any risk of injury from the grinder 9. b) Since the head of the operator 6 is further from the operating zone than when using a portable grinding tool or equipment, and since the particles removed by the grinder 9 are thrown in a direction opposite to that in which the operator is located, the risks of eye injury are eliminated. c) The rubber powder produced by the grinder 9 and the other fragments removed by it are thrown directly into the mouth of the extractor nozzle 83, whatever the angular position of the surface 39, so that the rubber powder and other fragments are effectively extracted by the extractor device 85. Similarly, any odours and smoke produced by the action of the grinder are greatly reduced by the extraction at the area in which the grinder 9 operates. d) Thanks to balancing of the support 8 by the counterweight 86, the support 8 and the grinder 9 can be manoeuvred without risks and without tiring the operator 6. e) Given that the head of the operator 6 is relatively far from the grinder operating zone and from the compressed air motor 34, the noise level to which the operator's hearing is subjected is significantly reduced. Obviously, the embodiment of the invention described above is provided by way of example only, without limiting the scope of the invention, and can be subject to modifications and variations which can easily be made by an operator in the field, without thereby departing from the scope of the inventive concept. In particular, the compressed air motor 34 and compressed air rotary cylinder 48 may be substituted with an electric motor and an electric cylinder. In such cases, the motor 34 and rotary cylinder 48 are preferably fitted in a sealed guard, guaranteeing explosion- proof properties. However, this solution is more expensive, therefore, a compressed air motor and rotary cylinder are preferably used. Instead of using a rotary cylinder like the cylinder 48, a linear actuator may be used, such as a pneumatic or hydraulic cylinder whose piston rod activates a rack which meshes with the half-gear 47. Instead of controlling the operation of the cylinder 48 or another actuator using contactors 25 in the grips 21 and 22, the two contactors 25 may be located on the operating platform 5 and activated by the operator's foot, with the aid of a foot pedal for each, or a single rocker pedal. Moreover, instead of positioning the support 7 and the platform 5 in such a way that the support 8 extends at a right angle to the axis of rotation 3 of the support 1, the support 7 and the platform 5 may be positioned so that the support 8 extends parallel with the axis 3.

Claims: Claims 1. A manually controlled grinding machine for grinding the tread of a worn or damaged tyre, comprising: a) a first means of support (1) which supports the centre of a vertically positioned worn or damaged tyre (2) and can rotate about a first horizontal axis (3) , making the tyre rotate about its central axis of rotation; b) a second means of support (7) positioned vertically on one side of the tyre supported by the first means of support (1) ; c) a third means of support (8), which can be moved manually, having an elongated shape and comprising a first end connected to an upper part of the second means of support (7) by a connector (11) with at least three degrees of freedom, and a second end which can be grasped by an operator (6), the third means of support (8) extending, during operation, substantially horizontally from the second means of support (7), passing above the tread of the tyre (2) supported by the first means of support (1) ; and d) a grinder (9) supported by the third means of support (8) between the first and second ends of the latter, which, during operation, is driven by a motor (34) about a second substantially horizontal axis (33) for grinding a desired area of the upper part of the tyre tread; the grinding machine being characterised in that: e) the grinder (9) is mounted on the third means of support (8) by means of a fourth means of support (35) which can rotate relative to the third means of support about a third, substantially vertical axis (36) intersecting with the second axis (33) at the centre (37) of the grinder (9) ; and f) control means (46) interact between the third and fourth means of support (8, 35) and may be activated to rotate the fourth means of support (35) and the grinder (9) about the third axis (36) . 2. The grinding machine according to claim 1, characterised in that the fourth means of support (35) can rotate about the third axis (36) between two end angular positions separated by a preset angle. 3. The grinding machine according to claim 2, characterised in that the preset angle is around 180°. 4. The grinding machine according to any of the claims from 1 to 3, characterised in that the third means of support (8) consists of a substantially Y-shaped arm, having a central branch (8a) and two side branches (8b, 8c) connected by a joint node (17) at a first end of the central branch, with a second end of the central branch being connected to the second means of support (7), in the form of a column, by the connector (11) with at least three degrees of freedom, each side branch (8b, 8c) having a grip (21 or 22) at the end opposite the joint node (17) . 5. The grinding machine according to claim 4, characterised in that the third means of support (8) also comprises a plate (38) which is fixed to the two side branches (8b, 8c) close to the joint node (17), and comprising a circular opening between the two side branches, and characterised in that the fourth means of support (35) consists of a circular surface (39) mounted in such a way that it can rotate in the circular opening in the plate (38) by means of a rotation gear (41). 6. The grinding machine according to claim 5, characterised in that the circular surface (39) supports a motor (34) whose output shaft (42) is parallel with the axis of rotation (36) of the circular surface, and characterised in that the grinder (9) is under the circular surface and supported by a grinder support shaft (43), the latter being perpendicular to the axis of rotation (36) of the circular surface and the output shaft (42) of the motor (34), and connected to the output shaft by a pair of bevel gears (44, 45) . 7. The grinding machine according to claim 6, characterised in that the control means (46) comprise a half-gear (47) concentrically fixed to the circular surface (39) , a rotary cylinder (48) which rotates in two directions and is fixed to the plate (38), and a pinion (49) fixed to the output shaft (51) of the rotary cylinder (48) and meshing with the half-gear (47). 8. The grinding machine according to claim 7, characterised in that the grip (21 or 22) of each of the two side branches (8b and 8c) of the arm forming the third means of support (8) comprises a first contactor and a second normally open contactor (24, 25), the first contactor (24) of each grip being positioned in such a way that it closes when the operator (6) grasps the corresponding grip with one hand, and the first contactors (24) of the two grips (21 and 22) being connected in series in a first control circuit (69 - 72) for the motor (34) in such a way that the motor can only operate when the operator (6) grasps the two grips (21 and 22) with his or her hands, it being possible for the operator to selectively close the second contactor (25) of a first (21) of the two grips (21 and 22) with his or her finger, this contactor being connected in a second control circuit (55, 75, 77, 79) for the rotary cylinder (48), to make the latter rotate in a first direction when the second contactor (25) of the first grip (21) is closed, whilst the operator can selectively close the second contactor (25) of the second grip (22) with one finger on the other hand, this contactor being connected in a third control circuit (56, 75, 78, 81) for the rotary cylinder (48) , to make the latter rotate in a second direction, opposite to the first, when the second contactor (25) of the second grip (22) is closed. 9. The grinding machine according to any of the claims from 5 to 8, characterised in that the grinder (9) is rotated in a direction which means that the particles of rubber from the tyre (2) removed by the grinder during treatment are thrown in a direction substantially opposite that in which the operator (6) is standing relative to the grinder, and characterised in that an extractor nozzle (83) is fixed to the circular surface (39) so that its extractor outlet is constantly angled in the direction in which the particles of rubber removed by the grinder (9) are thrown, the extractor nozzle (83) being connected to a powder extraction device (85) by a flexible hose (84). 10. The grinding machine according to any of the claims from 4 to 9, characterised in that the connector (11) with at least three degrees of freedom consists of a ball joint (15), and the second end of the central branch (8a) of the arm forming the third means of support (8) is mounted in such a way that it can slide in a diametric passage (16) made in the ball joint (15). 11. The grinding machine according to claim 10, characterised in that the central branch (8a) comprises, in addition to the ball joint (15), an extension (8h) bearing a counterweight (86) whose position may be adjusted along the extension, allowing balancing of the arm forming the third means of support (8) in a substantially horizontal position. 12. The grinding machine according to any of the claims from 4 to 11, characterised in that the length of the two side branches (8b, 8c) of the arm forming the third means of support (8) is adjustable.

Inventors: FAROUX FRANCOIS, FAROUX, FRANCOIS
Applicants: FAROUX FRANCOIS, MATTEUZZI SRL, FAROUX, FRANCOIS, MATTEUZZI S.R.L.
Application year: 2001
Main classification: B24B5
IPC codes: B24B5