The invention relates to a transmission apparatus in connection with a pulling equipment intended for moving especially a cable or a corresponding product, the transmission apparatus comprising a shaft that is operated by a motor and that is connected to an output shaft of the transmission apparatus by means of cog wheels, said output shaft being connected to means that are in contact with the cable or a corresponding product and that move the cable, the motor being arranged to rotate the output shaft via the driven shaft and the cog wheels in the direction of motion of the cable or the like and, if necessary, to decelerate the rotation of the output shaft in the direction of motion of the cable or the like, the cog wheels being arranged to form a circle extending from the motor-driven shaft to the output shaft and correspondingly from the output shaft to the motor-driven shaft.
In addition to cables, the phrase xe2x80x9ca cable or a corresponding productxe2x80x9d refers in the present application to ropes, conductors and other products formed from strands, and to semi-finished articles of the products at different stages of production.
When sheathed cables are produced, the sheath must be vulcanized and cooled after the forming stage. For this purpose, the processing line is provided with a vulcanizing tube that is followed by a cooling pipe in the direction of travel of the cable. A metal conductor to be coated is passed through the vulcanizing tube and the cooling pipe by means of a first pulling equipment placed before the extruder and a second pulling equipment located after the cooling pipe. During the vulcanization, the cable is supported in the horizontal extruder process entirely by the aforementioned pulling equipments or by the first pulling equipment, the cooling pipe and the second pulling equipment. The cable travels along a catenary trajectory at least in the vulcanizing tube, which means that at least the vulcanizing tube must be catenary in shape.
During the vulcanization process, the cable must not get into contact with the hot vulcanizing tube, and therefore it is necessary that the cable is kept straight so that it does not touch the inner surface of the vulcanizing tube. If the cable touches the surface of the vulcanizing tube, the cable sheath will be damaged and the cable cannot be used for the intended purpose. The aforementioned matters set great requirements for the operation of the pulling equipments. A pulling equipment, for example a drive wheel, must grip the metal conductor without any slipping between the conductor and the drive wheel, the frame of the pulling equipment must be very sturdy and firmly attached to the bearing surface, the drive wheel must be firmly mounted in bearings to the frame in order to minimize the risk of vibration and oscillation, and for the same reason the transmission of the pulling equipment must operate as smoothly as possible without clearances. The clearance-free operation of the transmission of the pulling equipment is highly significant especially when loading takes place mainly in the direction of motion, as for example in the cable vulcanization process, where the motor may get into decelerating action in connection with certain cable sizes due to the tensile force of the cable. In other words, the motor may change its pole, whereupon the clearance of the gear transmission produces a tug, which easily results in harmful oscillation of the cable.
In prior art pulling equipments, rotation of the drive wheel is based on a transmission apparatus that is formed of a gear rim and a cog wheel and that is placed between an actuator and the drive wheel. In such arrangements, the drive wheel is provided with a gear rim that is coaxial with the axis of rotation of the drive wheel and that comprises either inside or outside gearing, and the pulling equipment is provided with a motor-driven cog wheel. The speed of the motor is controlled by means of a sensor placed in the vulcanizing tube and used to measure the location of the sheathed cable in the tube. The pulling equipment provided at the output end of the cooling pipe is usually run at a constant speed, and the location of the cable in the vulcanizing tube is adjusted by means of control of the rotational speed of the pulling equipment located before the extruder.
In practice, it has been noted, however, that despite very accurate machining of the gear teeth, vibrations occur in the pulling equipment in connection with the gear transmission described above, and the vibrations result in harmful oscillation of the cable in the vulcanizing tube. This is obviously a result of too big clearances between the teeth, the clearances becoming more evident with heavy loads. It should be noted that in the present cable vulcanization lines the distance between the pulling equipments may be as much as 200 meters, which means that a hanging cable causes considerable loading in the drive wheel and the teeth. A possible elliptical shape of the gear rim also causes variation in the clearances of the teeth and therefore in the steadiness of the pulling.
In another prior art arrangement, the drive wheel is replaced with several closely positioned rollers that are mounted in bearings in a substantially semicircular formation, and an inner endless rubber belt travels over the rollers. Outside the curved roller conveyor there is an outer endless rubber belt that passes over a sheave and presses against the roller conveyor in a semicircular form. The metal conductor to be coated travels between the inner and the outer belt to extruders. The speed of the metal conductor in the extruder is adjusted by decelerating the speed of the sheaves around which the inner belt travels. With this arrangement it is possible to avoid the drawbacks resulting from the clearances of the gear transmission, but on the other hand, the decelerating effect provided by means of the drive wheel is simultaneously lost.
Another essential drawback is that the inner rubber belt is subjected to a great pressure that is produced by the rollers and the outer rubber belt and that tends to lead to a breakdown of the inner rubber belt. Another drawback is that the outer rubber belt tends to slide away from the drive groove and therefore breaks.
Another example of prior art arrangements is a caterpillar-type pulling mechanism, which is arranged in connection with a drive wheel that is firmly mounted in bearings in the frame structure, the pulling mechanism being used to forward the metal conductor. On the one hand, such an arrangement improves for example the decelerating effect, but on the other hand, this kind of separate caterpillar equipment comprises clearances, which cause problems with vibration as described above.
An example of prior art arrangements is a pulling equipment where the force is conducted to the central shaft of the drive wheel by means of a worm gear. Such a gear is loaded with a high torque and therefore the equipment must be provided with a rather heavy construction, which also means that it has often rather great clearances that also cause the aforementioned problems with vibration.
The purpose of the present invention is to provide a transmission apparatus with which the prior art drawbacks, such as the vibration problems caused by the clearances of the transmission, can be eliminated. This is achieved with a transmission apparatus according to the invention, which is characterized in that the cog wheels are helical gearwheels and that one cog wheel shaft is arranged to be moved in its longitudinal direction when the rotation of the output shaft is being decelerated, whereupon during the movement of the cog wheel shaft, the cog wheels situated on the shaft are arranged to rotate, due to opposite helicity of the teeth of the cog wheels, the adjacent cog wheels that are in mesh with the first cog wheels, thus eliminating the free play occurring between the cog wheels during the deceleration.
The primary advantage of the invention is that the invention provides even transmission that does not cause harmful vibrations in the cable or a corresponding product. Another advantage of the invention is its simplicity, wherefore the start-up and use of the invention will be advantageous.