APPARATUS FOR CONTROLLING ROLLER OF AC¬

CUMULATOR CONVEYOR Technical Field [1] The present invention relates to an accumulator conveyor that is capable of suspending transportation of an object for a predetermined time, and more particularly, to an apparatus for controlling a roller of an accumulator conveyor, in which when a conveying object is temporarily suspended by a stopper, though the operation of power transmission parts, such as a sprocket, are not suspended the rotation of rollers under the object are suspended to prevent damage on the object and overload on the power transmission parts. [2] Background Art [3] A roller accumulator conveyor is used to transport an object (part) in a production line of a factory. The roller accumulator conveyor transports the object from one processing place to the next processing place for machining or assembling. A stopper is installed on the roller accumulator conveyor to temporarily suspend the conveying object or move the object to a storing place. [4] Generally, when the object is suspended by the stopper the rollers of the roller ac¬ cumulator conveyor do not stop their rotation, causing friction between the object and the rollers. Since the friction continues until the object is re-conveyed to another place, the friction causes damage on the object. Also, since power transmission parts such as a sprocket of the accumulator conveyor are not stopped when the object is suspended, the power transmission parts are overloaded due to the friction between the object and rollers. This overload may shorten the life of the power transmission parts. [5] To obviate this problem, the roller accumulator conveyor is designed to stop the rotation of the rollers when the stopper suspends the object. [6] FlG. 1 is a sectional view of a roller accumulator conveyor according to the related art. Referring to Fig. 1, a roller accumulator conveyor includes a driving axle 10 rotating in association with power transmission parts such as a sprocket, a driving friction disc 11 fixed around the driving axle 10, a driven friction disc 12 abutted on the driving friction disc 11, and a roller 13 rotating in association with the driven friction disc 12. Also, an adjusting part 15 is installed around the driving axle 10 and a spring 14 is disposed between the adjusting part 15 and the driving friction disc 11. [7] The spring constant of the spring 14 is adjusted depending on the friction co¬ efficient between the driving friction disc 11 and the driven friction disc 12, such that the abutment between the driving friction disc 11 and the driven friction disc 12 is maintained without slipping during the transportation of the object, and the abutment is maintained to allow slipping when the object is suspended by a stopper. That is, the rotation of the driving friction disc 11 is transmitted to the driven friction disc 12 to rotate the roller 13 during the transportation of the object, and the rotation of the driving friction disc 11 is not transmitted to the driven friction disc 12 due to the factional force between the object and the roller 13 when the object is suspended by a stopper. [8] However, it is difficult to adjust the spring constant and friction coefficient because of abrasion of the friction discs 11 and 12, penetration of foreign substances, and change of the friction coefficient due to long use. [9] Therefore, the operational relationship between the driving friction disc 11 and driven friction disc 12 is not properly maintained with the spring 14. That is, the roller 13 may not be stopped when the object is suspended, causing damage on the object and overload on the power transmission parts. [10] To obviate this disadvantage, an alternative accumulator conveyor is disclosed in Korean Patent No. 0399455, in which plural grooves are formed at opposite surfaces of a driving-motor panel and a driven-motor panel and plural steel balls are installed in the grooves. However, this alternative accumulator conveyor produces loud noise and pulsating torque. [H] Disclosure of Invention Technical Problem [12] An object of the present invention is to provide an apparatus for controlling a roller of an accumulator conveyor, in which a plurality of needle rollers are radially disposed between a driving friction disc and a driven friction disc to make line contact and rolling contact between the needle rollers and the friction discs instead of making direct face contact between the friction discs, thereby preventing variation in torque due to penetration of foreign substances and possibility of failure. [13] Another object of the present invention is to provide an apparatus for controlling a roller of an accumulator conveyor, a plurality of needle rollers are disposed between a driving friction disc and a driven friction disc at different angles to the radius of the friction discs to make line contact and rolling contact between the needle rollers and the friction discs instead of making direct face contact between the friction discs, thereby obtaining various driving torque ranges for carrying an object. [14] Technical Solution [15] According to an aspect of the present invention, there is provided an apparatus for controlling a roller of an accumulator conveyor that is provided with a driving axle, axle supporting bearings installed on a table to support both ends of the driving axle, a sprocket coupled to one end of the driving axle to transmit power from a driving motor to the driving axle, a roller in which the driving axle is inserted, at least one roller supporting bearing interposed between the driving axle and the roller to support the roller, and a stopper for suspending an object conveying on the roller for a pre¬ determined time, the apparatus including: a driven friction disc fixed to an end of the roller from the one end of the driving axle where the sprocket is coupled, rotation of the driven friction disc being not associated with the driving axle; a driving friction disc fixed around the driving axle beside the driven friction disc; a retainer disposed between the driven friction disc and the driving friction disc, the retainer including a plurality of needle rollers that make line contact or rolling contact with the driven friction disc and the driving friction disc; a spring having an end abutted on the driving friction disc to press the driving disc toward the driven friction disc; and an adjusting part abutted on the other end of the spring to adjust the pressing force of the spring by varying the length of the spring. Advantageous Effects [16] According to the present invention, an apparatus for controlling a roller of an ac¬ cumulator conveyor is designed such that an object can be suspended for a pre¬ determined time during transportation without damage on the object and overload on power transmission parts, thereby reducing possibility of failure and maintenance cost and increasing product reliability. [17] Brief Description of the Drawings [18] FlG. 1 is a sectional view of a roller accumulator conveyor according to the related art. [19] FlG. 2 is a front view of an accumulator conveyor according to the present invention. [20] FlG. 3 is a sectional view of a roller portion of an accumulator conveyor according to the present invention. [21] FlG. 4 is an enlarged view of a driving control portion that is indicated with a dashed line in FlG. 3. [22] FlG. 5 shows one embodiment of a retainer. [23] FlG. 6 shows another embodiment of a retainer. [24] Best Mode for Carrying Out the Invention [25] Now, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. [26] FlG. 2 is a front view of an accumulator conveyor according to the present invention. [27] Referring to FlG. 2, an apparatus for controlling a roller of an accumulator conveyor includes driving axles 1, rollers 3, stoppers 300, and a driving motor 2. An object 5 (two are shown) is conveyed on the rollers 3. [28] FlG. 3 is a sectional view of a roller portion of an accumulator conveyor according to the present invention, and FlG. 4 is an enlarged view of a driving control portion that is indicated with a dashed line in FlG. 3. [29] Referring FlGs. 3 and 4, the controlling apparatus includes a sprocket 200 installed at one end of the driving axle 1 and an axle supporting bearings 210 installed on a conveyor table to support both ends of the driving axle 1. The driving axle 1 is inserted in the roller 3, and roller supporting bearings 4 are interposed between the driving axle 1 and the roller 3 to support the roller 3 to support the roller 3. [30] Near the sprocket 200, the controlling apparatus includes a driven friction disc 120 coupled to the roller 3, a driving friction disc 110 coupled to the driving axle 1, a spring 140 of which one end is abutted against the driving friction disc 110, and an adjusting part 150 abutted against the other end of the spring 140 to adjust the length of the spring 140. [31] The object 5 is conveyed on the roller 3 installed around the driving axle 1. The driven friction disc 120 includes a stepped portion tightly fitted into the roller 3 and an opposite flat portion. A plurality of needle rollers 131 make line and rolling contact with the flat portion of the driven friction disc 120. [32] The needle rollers 131 are mounted in a retainer 130 that is interposed between the driven friction disc 120 and the driving friction disc 110. [33] FlG. 5 shows one embodiment of a retainer. Referring to FlG. 5, a retainer 130 is ring-shaped with a predetermined thickness. The retainer 130 includes a plurality of needle rollers 131 and a plurality of rectangular through holes 132 in which the needle rollers are mounted. The through holes 132 are arranged at an angle (a) to the radius of the retainer 130. [34] FlG. 6 shows another embodiment of a retainer. Referring to FlG. 6, a retainer 130 includes a plurality of needle rollers 131 and a plurality of rectangular through holes 132 in which the needle rollers are mounted. Some of the through holes 132 are arranged at an angle (a) to the radius of the retainer 130, and the others are arranged at an angle (b) to the radius of the retainer 130. Alternatively, the through holes 132 may be arranged at different angles to the radius of the retainer 130. [35] Since the needle rollers 131 inserted in the through holes 132 of the retainer 130 are arranged at the same angle or different angles to the radius of the driving friction disc 110 and the driven friction disc 120, there coexist slipping and rolling contacts between the needle rollers 131 and the friction discs 110 and 120. [36] Frictional force resulted from the slipping contact enables power transmission from the driving friction disc 110 to the driven friction disc 120. Therefore, the power transmission can be controlled by adjusting the arranged angles of through holes 132 with respect to the radius of friction discs 110 and 120. [37] Since the needle rollers 131 are securely mounted in the retainer 130 and are in line contact and rolling contact with the driving friction disc 110 and the driven friction disc 120, torque variation due to foreign substances can be minimized. [38] Referring again to FlGs. 3 and 4, the driving friction disc 110 has a shape similar to the driven friction disc 120. The driving friction disc 110 has a stepped portion at one side and a flat portion at the other side. The driving friction disc 110 is installed around the driving axle 1 with the stepped portion pointing toward the sprocket 200 and the flat portion making line and rolling contact with the needle rollers 131. The one end of spring 140 is disposed around the stepped portion of the driving friction disc 110. [39] The adjusting part 150 is disposed around the axle 1 to adjust the tension of the spring 140 by varying the length of the spring 140. The adjusting part 150 includes a stepped portion around which the other end of the spring 140 is disposed and a female thread at its inner circumference to mate with a male thread formed around the driving axle 1. The female thread of the adjusting part 150 and the male thread of the driving axle 1 allow forward and backward movement of the adjusting part 150 on the driving axle 1, such that the tension can be adjusted by moving the adjusting part 150. [40] The sprocket 200 coupled to one end of the driving axle 1 receives driving torque from the driving motor 2 disposed under the conveyor table via a chain or the like to rotate the driving axle 1. The axle supporting bearings 210 supporting the both ends of the driving axle 1 allow smooth rotation of the driving axle 1, such that the object 5 on the roller 3 can be stably transported. [41] The stopper 300 (two are shown) temporarily suspends the object 5. For example, the stopper 300 suspends the movement of the object 5 until the previously transported object is transported to the next processing place. [42] When the object 5 is suspended by the stopper 300, stopping force resulted from the friction between the object 5 and the rollers 3 becomes larger than the frictional force resulted from the slipping contact between the needle rollers 131 and the friction discs 110 and 120, such that the driven friction disc 120 does not rotates though the driving friction disc 110 still rotates. Therefore, the rotation of the rollers 3 can be suspended when the object 5 is suspended by the stopper 300. [43] An exemplary assembling process of the controlling apparatus of the present invention will be described. The roller supporting bearing 4 and roller 3 are disposed around the driving axle 1. Then, the driven friction disc 120, the retainer 130 with the needle rollers 131, the driving friction disc 110, the spring 140, and the adjusting part 150 are sequentially disposed on the axle 1 besides the roller 3. Also, the sprocket 200 is coupled to one end of the driving axle 1 next to the adjusting part 150, and the axle supporting bearings 210 are disposed around both ends of the axle 1. [44] While the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims. [45] Industrial Applicability [46] According to the present invention, an apparatus for controlling a roller of an ac¬ cumulator conveyor is designed such that an object can be suspended for a pre¬ determined time during transportation without damage on the object and overload on power transmission parts, thereby reducing possibility of failure and maintenance cost and increasing product reliability. Therefore, the apparatus can be applied to various industrial fields requiring conveyor system for machining and assembling processes. [47]