APPARATUS FOR GROOVING TYRES

Abstract: An apparatus for grooving a tyre comprises a tyre support shaft (21) for rotatable supporting the tyre and a support frame (31) having a cutter device (5) mounted thereon. The cutter device (5) and the tyre support shaft (21) are movable relative to each other in a transverse direction parallel with the tyre support shaft (21) and perpendicular to the tyre support shaft (21). The cutter (5) is supportable at a desired angle with the tread surface and the cutter blade (5) is rotatable in the direction of the groove to be formed. The cutting position of the cutter (5) is on the axis (39) of an arm support shaft (38) and is controllable by the combination of orthogonal coordinates to simplify the control program for the apparatus. When required, the cutter (5) is swingably attached to a cutter holder (41) to enable the cutter (5) to cut the tyre rubber and to be released therefrom with ease without the need to heat the cutter (5). When the cutter (5) is provided with a heater, the cutter heating temperature and operation speed are so controlled that the temperature of rubber around the cutter (5) is maintained at a predeter­ mined constant level.

Description: The present invention relates to a grooving apparatus for cutting a tread pattern in tyres. Conventionally, a hand cutter is generally used for manually grooving tyres which were produced for testing purposes or on a small production basis i.e. for forming a tread groove pattern in vulcanised plain tyres having no tread pattern. This manual procedure requires skill and is time-consuming. For large sized tyres having relatively a simple groove pattern, unexamined Japanese Patent Publication SHO 56-162633 and the corresponding European Patent Application published as EP-A-0038278, for example, discloses an apparatus which comprises a shaft for supporting a tyre, a support frame movable axially of the shaft and perpendicular to the shaft, and a cutter mounted on the support frame, directed toward the surface of the tyre to be worked on and rotatable according to the angle of the groove to be formed, such that a cutter is heated and caused to cut into a shoulder face of the tyre. For heating and movement alone the contemplated pattern, the cutter is controlled by a computer according to a program. Although large sized tyres generally have simple tread patterns which can be formed by a relatively simple movement of the heated cutter, small sized tyres such as passenger car tyres have grooves of complex shape which require the complex movement of the cutter. The prior art is not always capable of meeting this requirement. Further because the pattern grooves are cut by the heated cutter and the rubber portion around the cutter is heated, for example, to a temperature of about 200°C or higher. It his very likely that the physical properties of the vulcanised rubber changes and the elasticity of the rubber is impaired and the quality of the tyre is ill affected. The heating is also likely to scorch or melt the neighbouring rubber portion, failing to form grooves of clear-cut shape or to assure the required running characteristics fully. When forming grooves of double stepped shape, the cutter will burn out to become inoperative. Another problem,encountered is that the heating reduces the durability of the cutter. Although it appears possible to use a multi-articulated robot for supporting the cutter for grooving, the cutter shaft must then be given greater freedom, which renders the control program complex, making the tyre grooving apparatus expensive. Accordingly, the present invention provides an apparatus for grooving a tyre including a tyre support shaft for supporting the tyre rotatably and a support frame having a cutter device mounted thereon, the cutter device and the tyre support shaft being movable relative to each other in a transverse direction direction perpendicular to the support shaft a pivotal arm pivotally mounted on an arm support shaft having an axis a cutter holder rotatable about an axis perpendicular to the axis of the arm support shaft, and a cutter attached to the cutter holder, the apparatus being characterised in that the cutter is located so that the cutting position P is located on the axis of the arm support shaft. The above structure is additionally provided with means for swinging the cutter in the cutting direction at the start and end of cutting and/or means for heating the cutter. The structure is further provided with means for controlling the temperature and/or the velocity of movement of the cutter. With the primary structure, the cutting position of the cutter is retained on the axis of the arm support shaft at all times, and the axis come into line with the cutting position, so that the amount of movement of the support frame as well as the pivotal arm can be calculated with ease. This makes programming of the computer easy for the present apparatus. Further in the case where the cutter only is adapted to swing in the cutting direction for a shovelling action, grooves can be cut with the cutter without heating the cutter. When the cutter is caused to swing in the cutting direction while being heated, the intial cut can be formed quickly, with the cutter prevented from burning. Further if the means is provided for controlling the temperature and/or velocity of the cutter, the control means assures sharp cutting, reduced damage to the rubber, prolonged cutter life and increased cutting speed. Fig 1 is a side elevation showing a first embodiment of the invention; Fig 2 is a front view of the same; Figs 3, 4 and 5 are diagrams showing the position of a cutter during cutter operation; Fig 6 is a block diagram showing a control system; Fig 7 is a flow chart for the operation of the above embodiment; Fig 8 is a diagram showing the electric circuit of cutter heating means according to a second embodiment of the invention Figs 9 (a) and (b) are a front view and a side elevation, respectively, showing means for detecting stress acting on a cutter according to a third embodiment of the invention; Fig 10 is a flow chart for the operation of the third embodiment; Fig 11 (a) is a characteristics diagram showing the relation between the stress and the rubber temperature around the cutter operation speeds to illustrate control based on stress detection for the third embodiment; Fig 11 (b) is a characteristics diagram showing the relation between the stress and the cutter heating temperature at varying cutter operation speeds; Fig 12 (a) to (c) are diagrams for illustrating three methods of control based on stress detection; Figs 13 (a) and (b) are diagrams for illustrating the operation of the first embodiment; and Fig 13 (c) is a diagram for illustrating the operation of the related-art apparatus. A first embodiment of the invention will be described below with reference to Figs 1 and 2. Indicated at 1 is a base, at 2 a tyre support, at 3 a carriage, at 4 a pivotal arm, at 5 a cutter and at 6 a tyre. The tyre support 2 is fixedly mounted on the base 1. The tyre 6 is mounted on a tyre support shaft 21 on the support 2 and is rotated by a motor 22 through an unillustrated reduction gear. Indicated at 23 is a tyre fastening handle. The carriage 3 is movable in a transverse direction (Y-axis direction) parallel with the tyre support shaft 21 on rails 31 parallel with the shaft 21 by unillustrated motor and screw rod. A support frame 32 supported by the carriage 3 is movable upward or downward (Z-axis direction) along a guide rod 33. The frame 32 is movable through a ball screw by rotating a screw rod 35 by a motor 34. The carriage 3 may be made movable on rails 36 on the base 1 along a guide bar 37 by unillustrated motor and screw rod, in a direction perpendicular to the axis of the tyre support shaft 21, i.e. toward or away from the tyre 6 (X-axis direction). This movement gives the movement of the cutter increased freedom for cutting large sized tyre. An arm support shaft 38 projecting from one side of the support frame 32 has an axis 39 extending in the X-axis direction perpendicular to the tyre support shaft 21, and being in line with the cutting position P for the cutter as shown in Fig 5 (see dotted line). The shaft 38 is rotatable about the axis 39 in the direction of arrow A shown in Fig 2 by a motor within the frame 32 through an unillustrated reduction gear, whereby the cutter 5 is maintained at a desired angle with respect to the curved surface of the tyre tread. It is especially desirable that the axis 39 be in agreement with a tangent to the cutting position P. When the cutting position P is on the axis 39 of the arm support shaft 38, the cutting point and the centre of movement are at the same point, so that the amount of movement of the cutting position can be calculated in terms of the amount of movement of the axis 39 only. This facilitates programmed control by a computer. With reference to Fig 13 (a) the directions of movement of the cutter with respect to the axis are represented by A, Y and Z. As seen in Fig 13 (b), cutting points (1) (before movement) and (2) (after movement) are in coincidence with centres of movement (1) and (2), respectively, according to the invention. Accordingly, the amount of movement of A axis (axis 39) is calculated as follows. Y2 = Y1 + a Z2 = Z1 + b A2 = A1 + c With the above-mentioned apparatus of the related art, cutting points (1), (2) differ from centres of movement (1)', (2)' as seen in Fig 13 (c), so that the amount of movement of A axis is calculated as follows. Y2 = Y1 + a + d.sin c Z2 = Z1 + b + d (1 - cos c) A2 = A1 + c wherein d is the distance between the cutting point (1) or (2) and the centre of movement (1)' or (2)'. With the related art apparatus, the amounts of movement along Y axis and Z axis need to be calculated in addition to that along A axis for the correction of the cutting point relative to the centre of movement. The pivotal arm 4, which is fixedly mounted on the arm support shaft 38, is provided with a cutter holder 41 at its forward end. The holder 41 is positioned perpendicular to the axis 39 and rotatable in the direction of arrow B about a cutter holder shaft 46 by a motor 42 through an illustrated reduction gear. By this rotation, the direction F of cutting by the cutter 5 (Fig 4) is made to agree with the direction of a groove 63 to be formed. Further as seen in Fig 5, the cutter 5 is mounted on a swing shaft 43 mounted on the holder 41 and extending transversely thereof so that the cutting position P will be on the axis 39. Further when an actuator 44 is provided as seen in Figs 1, 3 and 5 for rotating the swing shaft 43 at the start and end of cutting to swing the cutter 5 in the cutting direction (arrow C in Fig 1), the swing of the cutter by the actuator 44 reduces cutting stress for the cutter, whereby the load on the cutter balde can be diminished. Consequently tread grooves can be cut easily without the necessity of heating the cutter 5. Servo motors of the electric or hydraulic type are used as the motors. As shown in Fig 3, the cutter 5, when seen from the front, is U-shaped, V-shaped or otherwise shaped in conformity with the shape of the groove to be formed. The cutter is fixedly held by clamp means 52, and the position thereof is adjustable depthwise so that the cutting position P will be in coincidence with the axis 39. The cutter has a cutting edge 51 at one or each side as seen in Fig 5. The motors and the actuator are controlled by a computer under programmed command according to the diameter and tread pattern of tyres. Fig 6 shows the overall computer control system. Indicated at 100 is the computer, at 101 the grooving apparatus of the invention, at 102 a control panel and at 104 a power control box. Fig 7 is an operation flow chart. The operation of the first embodiment (wherein the cutter is not heated) will be described. With reference to the flow chart of Fig 7, the axes are set to a predetermined origin, a tyre 6 is fixedly mounted on the tyre support shaft 21, and the motor 22 is turned on to rotate the tyre. The carriage 3 is moved along the rails 31 in the Y-axis direction, and the support frame 32 is lowered in the Z-axis direction by the motor 34 and the screw rod 35 to adjust the cutter 5 so that grooves are cut at the top of the tyre 6. When the rails 36 are provided, the carriage 3 is moved in the X-axis direction (toward or away from the tyre) to adjust the cutting position of the cutter. The angle of the pivotal arm 4 is adjusted by rotating the arm support shaft 38 so that the axis 45 of the cutter 5 will be at a desired angle with the tyre tread as shown in Fig 3. For example, for a vertical groove 61 as shown in Fig 3, the arm 4 is positioned vertically, while for an inclined groove 62, the arm 4 is turned in the A direction (Fig 2) in accordance with the inclination to incline the cutter axis 45. At this time, the carriage 3 is moved in the Y-axis direction, and the support frame 32 is adjusted in the Z-axis direction in accordance with the position of the groove to be cut. With the present apparatus, the cutting point is in coincidence with the centre of movement. This facilitates calculation of the amount of movement and control by the computer. Further for a tread pattern groove 63 which is inclined with respect to the centre line 60 of the tyre as seen in Fig 4, the cutter holder 41 is rotated by the motor 42 in the direction of arrow B (Fig 1) about the cutter holder shaft 46 to cause the cutting direction F of the cutter 5 (shown in section in Fig 4) to agree with the direction of the inclined groove 63. When the cutter 5 is to bite into the tyre 6 at a groove start position d with the start of grooving operation, the swing shaft 43 is rotated in the direction of arrow C (cutting direction) shown in Fig 5 by the actuator 44 (Fig 1) to swing the cutter 5 only and force the cutter into the tyre surface in the cutting direction. This movement reduces cutting stress and diminishes the load on the cutter 5, consequently decreasing the likelihood of the cutter 5 breaking and permitting the cutting edge 51 to cut the vulcanised hard tread rubber. Thus, the tyre can be cut easily without the need to heat the cutter. Further when the cutter 5 is to be removed from the tyre at the groove end portion (not shown), the actuator 44 similarly swings the cutter in the removing direction. During the cutting operation, the carriage, pivotal arm, cutter holder and cutter are moved under the control of the computer 100 shown in Fig 6. Useful for this control are position sensors, such as encoders, for detecting the movement of parts of the apparatus 101 by the motors and a stress sensor for detecting the stress acting on the cutter (embodiment equipped with such a stress sensor will be described later). The detection signals as control factors are fed to a data control unit, whereby optimum cutting conditions (e.g. cutter speed in the present embodiment) are determined for continuation of smooth cutting operation. The present embodiment can be so modified that the arm support shaft 38 for the pivotal arm 4 is mounted on the support frame 32 vertically to position the cutter 5 immediately beside the tyre 6. While the foregoing first embodiment refers to tyre grooving without heating the cutter, a second embodiment of the present invention includes suitable means for heating the cutter 5. This embodiment has the advantage that the cutter cuts at a higher speed with greater sharpness than when the cutter is not heated. When heated, the cutter easily cuts grooves without swinging, but if caused to swing, the cutter starts to cut at a further increased speed, and this has the advantage of preventing the drawback of decrease of the cutter life due to the burning of the cutter before cutting. Fig 8 shows the electric circuit of the heating means, in which the primary winding of a transformer T is connected to an a.c. power supply e via relay contacts R1 to R5. The cutter 5 is connected to the secondary winding of the transformer via a current transducer CT for checking discontinuity for checking the breakdown of the cutter. When the cutter 5 is to be heated, the relay contact R1 is closed, and one of the relay contacts R2 to R5 is closed. The current through the cutter 5 increases to give a large amount of heat to the cutter as the closed relay contact shifts from contact R5 toward contact R2. The relay contacts are closed immediately before cutting to heat the cutter 5 and cut the tyre. On completion of cutting operation i.e. immediately before the cutter 5 is removed from the tyre into air, the relay contacts are opened, whereby burning of the cutter can be prevented. The amount of current through the cutter 5 is checked by the current transducer CT, and when the current is interrupted, an alarm is given to indicate a breakdown of the cutter 5. Tyres can be grooved by the cutter with heating and with a swing motion similarly by controlling blade temperature control means (Fig 6) having the current value varying circuit and included in the grooving apparatus 101, by the computer 100 (Fig 6) under a program. According to a third embodiment of the invention, the second embodiment is further provided with means for detecting stress on the cutter for optimally controlling the temperature and/or operation speed of the cutter based on the detection signal from the stress detecting means. This embodiment will be described with reference to Figs 9 to 11. Figs 9 (a) and (b) show a blade stress sensor 53, for example, of the strain gauge type in contact with the holding portion of the cutter 5. Via lead wires 54, the detection signal from the sensor is fed from the grooving apparatus 101 (Fig 6) to a universal input-output unit (Fig 6) in the computer 100. Fig 10 shows a flow chart for controlling the blade temperature and/or operation speed in grooving by performing the predetermined calculations to be stated below based on the detection signal from the stress sensor and executing an interrupt process at a given interval. This control based on stress detection basically resides in controlling the cutter heating temperature and operation speed so that the temperature of rubber around the blade is maintained at a level below 200°C (i.e. at a temperature which does not cause damage to the rubber and which assures sharp cutting). First, the values to be set for the control are determined by the following procedures. 1) For each of the tyres of various tread rubber compounds, a grooving experiment is conducted using a sensor for measuring the ruber temperature around the blade, a blade stress sensor, a cutter operation speed measuring instrument and blade heating temperature measuring instrument to measure these temperatures, cutter operation speeds (V A , V B , V C , ...) and blade stress values and to establish the relation between the rubber temperature around the blade, the blade stress value and the cutter operation speed as seen in Fig 11 (a), and the relation between the blade heating temperature (t A , t B , t C ...) the blade stress value and the cutter operation speed as seen in Fig 11 (b), and the said relations as shown in Fig 11 (2) (b) are based on an inverse proportion or an exponential function. 2) An optimum rubber temperature (below 200°C) t1 around the blade is optionally determined for each shape of groove to be cut (or for each cutting unit (in the same direction)). The temperature t1 is dependent on the rubber compound, cutter break down ratio, cutting conditions (quick or slow cutting), etc. The cutter heating temperature and operation speed are to be so controlled that the rubber temperature around the blade will be at the constant value t1. 3) With reference to Fig 11 (a), the optimum rubber temperature t1 around the blade is set in terms of an optimum blade stress value τ1 (in the case of initial operation speed V B ). The initial operation speed is determined by the shape of groove (depth, width straight or curved). 4) With reference to Fig 11 (b), an optimum blade heating temperature tB giving the optimum blade stress value τ1 is determined (at the initial operation speed V B ). The temperature tB is a condition to be set for computer control. The control based on the set values can be effected by three methods, i.e. a first method 105 in which the blade heating temperature is varied with the cutter operation speed maintained at a constant value, a second method 106 wherein the cutter operation speed is varied with the cutter heating temperature kept constant (inclusive of a case where the cutter is not heated), and a third method 107 wherein the cutter heating temperature and the operation speed are varied as seen in Fig 10. By these methods of control, the rubber temperature around the blade, in other words, the stress value can be maintained at a constant (predetermined) value. The temperature of the cutter is controlled by the blade temperature control means having the current value varying circuit already described with reference to the second embodiment. The operation speed is controllable by a position control unit and servo control unit (Fig 6) of the microcomputer 100. The control is effected not only during grooving but also during the swing motion (at the start and end of cutting). The temperature of the cutter blade, i.e. the value of current to be passed through the blade and the operation speed of the blade for starting a cutting operation are values predetermined according to the rubber temperature, the composition of the rubber compound, the shape of groove to be formed, etc. These values are thereafter calculated as specified at a given time interval based on the stress detected. The three methods 105, 106 and 107 will be described individually with reference to Figs 12 (a), (b) and (c). 1) First method wherein the heating temperature is varied with the blade operation speed kept constant. With reference to Fig 12 (a) (similar to Fig 11 (a)), suppose the set stress value is τ1, and the detected stress value is τ2 (same as hereinafter). If τ2 > τ1, the blade heating temperature is increased by the small temperature difference Δt between the current level and the optimum heating temperature (set value). The blade heating temperature therefore reaches the set value and the stress is corrected to the set value also, so that the rubber temperature is maintained at a predetermined constant level. This method controls the cutter temperature singly, hence assuring a simple grooving control. 2) Second method wherein the operation speed is varied with the heating temperature kept constant. As seen in Fig 12 (b) (determined from Fig 11 (b)), if τ2 > τ1, the operation speed is reduced by the small speed difference ΔV between the current speed and the optimum operation speed (set value). This permits the operation speed to reach the set value and the stress value to be corrected to the set value, so that the rubber temperature is maintained at the predetermined constant value. This method is suited to rubber compounds which are prone to damage due to heating. 3) Third method wherein both the heating temperature and the operation speed are varied. When τ2 > τ1 as seen in Fig 12 (c), the heating temperature is increased by Δt, and the operation speed is decreased by ΔV. This method assures control with higher precision than the methods 1) and 2). The three control methods 105, 106 and 107 involving the foregoing calculations enable the cutter to cut the tyre rubber with improved sharpness with reduced damage to the rubber and gives a prolonged life to the cutter. The second and third methods 106 and 107 control the cutting operation with higher precision. Besides these control methods, PID (proportion, integration, differentiation) control can be resorted to based on the detected stress value to achieve improved precision control. Thus, the present invention of an apparatus for grooving a tyre provides a primary structure comprising a cutter device mounted on a support frame and a tyre support shaft for rotatably supporting the tyre which are movable relative to each other in a transverse direction parallel with the shaft and in a direction perpendicular to the shaft, an arm support shaft projecting from the support frame, a pivotal arm fixedly mounted on the arm support shaft, a cutter holder mounted on the pivotal arm and positioned at right angles with the axis of the arm support shaft, and a cutter attached to the cutter holder, the cutting position of the cutter being located on the axis. The apparatus is therefore adapted to form versatile groove patterns according to a simplified control program and is inexpensive in its entirety. When the cutter is made swingable in the cutting direction without heating, troubles such as scorching of tyre, collapse of grooved portions, damage to the cutter can be eliminated. When the cutter is made to swing as heated, the cutter starts cutting at a higher speed with reduced likelihood of blade burning. The blade temperature and/or speed may be controlled based on the detected stress value so that the rubber temperature around the blade is maintained at an optimum value. This enables the cutter to cut the tyre rubber with increased sharpness and reduced damage to the rubber, further giving a prolonged life to the cutter.

Claims: An apparatus for grooving a tyre including a tyre support shaft (21) for supporting the tyre (6) rotatably and a support frame (32) having a cutter device (5) mounted thereon, the cutter device (5) and the tyre support shaft (21) being movable relative to each other in a transverse direction parallel with the support shaft (21) and in a direction perpendicular to the support shaft (21), a pivotal arm (4) pivotally mounted on an arm support shaft (38) having an axis (39), a cutter holder (41) rotatable about an axis perpendicular to the axis (39) of the arm support shaft (38), and a cutter (5) attached to the cutter holder (41) the apparatus being characterised in that the cutter (5) is located so that the cutting position P is located on the axis (39) of the arm support shaft (38). An apparatus according to claim 1 characterised in that the cutter holder (41) is pivotally movable to render the cutter (4) swingable in the direction of cutting. An apparatus according to claim 2 characterised in that the arm support shaft (38) is so projected that the axis (39) thereof coincides with a tangent to the cutting position of the cutter (4). An apparatus according to claim 2 characterised in that the tyre support shaft (21), the support frame (32), the pivotal arm (4), the cutter holder (41) and the cutter (5) are movable under the control of a computer. An apparatus according to claims 1, 2 or 3 characterised by means for heating the cutter (5). An apparatus as defined in claim 5 characterised in that the cutter heating means comprises a circuit for controlling electric current, and the circuit includes discontinuity checking means. An apparatus according to claims 5 or 6 characterised by means for detecting the stress acting on the cutter (5) during cutting and means for controlling the temperature of the cutter based on the stress value obtained by the detecting means. An apparatus according to any of claims 3-7 comprising means for detecting the stress acting on the cutter during cutting and means for controlling the operation speed of the cutter based on the stress value obtained by the detecting means.

Inventors: ARITA MASAKAZU, NAGAHATA, TORO, SHIBATA, EIGI, TAKAMI, MASAO, TAMURA, TADAHIKO
Applicants: SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1986
Main classification: B29D30
IPC codes: B24B5, B23B5, B29D30, B26D3