Abstract:
A conveyor system having an expansion conveyor interposed between some of a plurality of conveyors of a conveying unit to extend the conveying line when trouble is detected at a receiving unit. Upon detection of trouble the extruder revolution speed and the conveyor speed are changed to reduce the conveying speed not to carry molded products to the receiving unit.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method of conveying extrusion molded products which are continuously extruded, such as tire treads, and to a device for use in the method. 
   2. Description of the Prior Art 
   In an extruding/conveying line of the prior art, the above treads are delivered from an extruder at an extrusion speed which is determined according to the size of the extruded treads and carried to a receiving unit at the same speed as the above delivery speed by a plurality of conveyors. 
   However, since the conveying speed is fixed in the above prior art method, when a trouble occurs in the receiving unit, for example, the extruding/conveying line must be suspended and also work for processing after suspension before the resumption of extrusion takes a long time. Further, a trouble occurs in the end portion of an extrusion molded product during the time from the resumption of extrusion to the production of a quality product. 
   When a tread is removed before the receiving unit or when a tread is carried to a place other than the receiving unit, a quality product cannot be received by a predetermined method, whereby it is regarded as an inferior product. 
   It is an object of the present invention which has been made in view of the above problem to provide a method of conveying extrusion molded products, which prevents extrusion molded products from being carried to a receiving unit without suspending a conveying line for a predetermined time even when a trouble occurs in the receiving unit as well as a device for use in the method. 
   SUMMARY OF THE INVENTION 
   According to a first aspect of the present invention, there is provided a method of conveying extrusion molded products from a material feed unit to a receiving unit by a plurality of conveyors, comprising interposing at least one expansion conveyor between conveyors out of the conveyors to expand or contract the expansion conveyor in order to adjust the conveying speed of the extrusion molded products. Thereby, even when a trouble occurs in the receiving unit, the above expansion conveyor is expanded to extend the conveying line so as to buffer the above extrusion molded products while they are carried. Therefore, the extrusion molded products are not carried to the receiving unit without suspending the conveying line for a predetermined time. After the trouble is solved, the above expansion conveyor is contracted to shorten the conveying line and the extrusion molded products in stock can be carried to the receiving unit swiftly. Therefore, productivity can be improved. 
   According to a second aspect of the present invention, there is provided a method of conveying extrusion molded products, wherein the conveyor speed of the conveyors can be changed to several levels. Thereby, when the above trouble occurs, the conveying speed is reduced to extend the time elapsed before the buffer becomes full and after the trouble is solved, the conveying speed is increased to return the conveying line to normal operation swiftly. 
   According to a third aspect of the present invention, there is provided a method of conveying extrusion molded products, wherein the delivery speed of the material feed unit is controlled according to a change in the conveyor speed of the conveyors. Thereby, the extrusion molded products can be carried smoothly. 
   According to a fourth aspect of the present invention, there is provided a method of conveying extrusion molded products, wherein when the material feed unit has a plurality of extruders, the speed of each extruder is controlled according to a change in the conveyor speed of the conveyors. 
   According to a fifth aspect of the present invention, there is provided a method of conveying extrusion molded products, wherein a response delay of the delivery speed of the material feed unit to the conveyor speed of the conveyors and the attenuation time are obtained in advance and when the conveyor speed of the conveyors is changed, the target value of the delivery speed is set based on the response delay and the attenuation time. 
   According to a sixth aspect of the present invention, there is provided a method of conveying extrusion molded products, wherein the target value of conveying speed is set according to the throughput of the receiving unit. 
   According to a seventh aspect of the present invention, there is provided a device for conveying extrusion molded products, having a plurality of conveyors to carry extrusion molded products from a material feed unit to a receiving unit, wherein at least one expansion conveyor is interposed between conveyors out of the plurality of conveyors. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram showing the constitution of a device for carrying extrusion molded products according to a preferred embodiment of the present invention; 
       FIG. 2  is a flow chart showing a method of carrying extrusion molded products according to the preferred embodiment of the present invention; 
       FIG. 3  is a diagram showing a speed table for conveyors and extruders; 
       FIG. 4  is a diagram showing a response delay of the delivery speed of a tread extruder to the conveying speed of the conveyors and attenuation time; and 
       FIG. 5  is a diagram showing a control example of the delivery speed of the extruder. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A preferred embodiment of the present invention will be described hereinbelow with reference to the drawings. 
     FIG. 1  is a schematic diagram showing the constitution of a device for conveying extrusion molded products according to the present invention. In  FIG. 1 , reference numeral  10  denotes a tread extruder (to be referred to as “extruder” hereinafter) which is a material feed unit for delivering extrusion molded products at a predetermined delivery speed,  20  a conveying unit for carrying belt-like extruded treads  1  delivered from the extruder  10 , which comprises a plurality of conveyors  21  to  27  and buffer means  20 Z interposed between an inverted conveyor  24  and an inclined conveyor  25  and consisting of an expansion conveyor  20   a , inverted conveyor  20   b  and expansion conveyor  20   c , and  30  a receiving unit for receiving the carried extruded treads  1 , which is located on a downstream side of the last conveyor  27  of the above conveying unit  20 . 
   Reference numeral  41  denotes a speed control CPU for controlling an extruder revolution R corresponding to the delivery speed of the extruder  10  and the conveyor speed V of the conveyors  21  to  27 ,  20   a ,  20   b  and  20   c ,  42  an expansion control CPU for expanding and contracting the expansion conveyors  20   a  and  20   c  of the buffer means  20 Z and moving the position of the inverted conveyor  20   b  according to the expansion or contraction of the above expansion conveyors  20   a  and  20   c , and  43  a reception control CPU for monitoring and controlling the tread receiving and processing states of the receiving unit  30 . 
   A description is subsequently given of the operation of the device for conveying extrusion molded products of the present invention with reference to the flow chart of  FIG. 2 . 
   In step S 10 , the belt-like extruded treads  1  are delivered from the extruder  10  to the conveying unit  20  at a predetermined extruder speed (extruder revolution) R 0  and carried to the receiving unit  30  at a conveyor speed V 0  corresponding to the above extruder revolution R 0 . The control of the above extruder revolution R 0  and the conveyor speed V 0  is carried out by the speed control CPU  41 . 
   The reception control CPU  43  monitors whether there is a trouble in the tread receiving and processing states of the receiving unit  30  (step S 11 ). When there is no trouble, the above normal operation is continued. When a trouble occurs in the receiving unit  30 , the above trouble information is sent to the expansion control CPU  42  and the speed control CPU  41  from the above reception control CPU  43  to enable the expansion control CPU  42  to expand the expansion conveyors  20   a  and  20   c  of the buffer means  20 Z and move the inverted conveyor  20   b  in accordance with the expansion of the above expansion conveyors  20   a  and  20   b  so as to extend the conveying line and to enable the speed control CPU  41  to change the extruder revolution R and the speed V of the conveyors  21 – 27 ,  20   a ,  20   b  and  20   c  of the conveying unit  20  to R L  (&lt;R 0 ) and V L  (&lt;V 0 ), respectively, so as to reduce the conveying speed, thereby buffering the extruded treads  1  not to carry them to the receiving unit  30  (step S 12 ). 
     FIG. 3  is a speed table showing the extruder speed (extruder revolution) R and the conveyor speed V controlled by the speed control CPU  41 . In this embodiment, the conveyor speed V is set to several levels (the conveyor speed V is set to a range of 0.5 to 20 m/min in increments of 0.1 m/min) and the delivery speed of the extruder  10  is controlled according to a change in the conveyor speed V of the above conveyors. When there are a plurality of extruders  10  (extruder # 1  and extruder # 2  in this embodiment), the revolution R of each extruder is changed according to the above conveyor speed V. 
   When the speed of the extruder  10  (extruder revolution R) is changed according to the above conveyor speed, the amount of extrusion becomes insufficient. Therefore, as shown in  FIG. 4 , a response delay of the delivery speed of the extruder  10  to the conveyor speed of the conveyors and the attenuation time are obtained in advance and the target value of the above delivery speed is set based on the above response delay and the attenuation time when the conveyor speed of the conveyors is changed. Stated more specifically, as shown in  FIG. 5 , the target value of delivery speed of the extruder  10  is set to a value obtained by adding the response delay “r” to the above conveyor speed. How fast (in seconds) the delivery speed of the extruder  10  is reduced to a target value is determined by the attenuation time “T” as a parameter for each extruder  10 . Thereby, even when the speed is variable, predetermined quality products can be obtained. 
   The conveyor speed V L  and the extruder revolution R L  which are changed to reduce the delivery speed may be determined according to the trouble information sent from the reception control CPU  43  to the speed control CPU  41  or may be reduced stepwise every a predetermined time. 
   Thereby, when a trouble occurs in the receiving unit  30 , it can be solved without carrying the extruded treads  1  to the receiving unit  30  until the above buffer means  20  becomes full, thereby making it possible to avoid the manufacture of inferior products. 
   During the above low-speed operation, the reception control CPU  43  monitors whether the trouble in the receiving unit  30  is solved or not (steps S 13  and S 14 ). When the trouble is not solved, low-speed operation is continued. If the trouble is not solved within a predetermined time during which buffering is possible, the delivery of the extruded treads  1  is suspended (step S 15 ). 
   When the trouble is solved, the routine proceeds to step S 16  where information on the solution of the trouble is sent to the expansion control CPU  42  and the speed control CPU  41  from the reception control CPU  43  so that the expansion control CPU  43  can contract the expansion conveyors  20   a  and  20   c  of the buffer means  20 Z to the full, thereby minimizing the length of the conveying line and that the speed control CPU  41  changes the extruder revolution R and the conveyor speed V of the conveyors  21 – 27 ,  20   a ,  20   b  and  20   c  of the conveying unit  20  to R H  (&gt;R 0 ) and V H  (&gt;V 0 ), respectively, to increase the conveying speed and carry the buffered extruded treads  1  to the receiving unit  30 . 
   To shift to the high-speed operation, like the above low-speed operation, a response delay of the delivery speed of the extruder  10  to the conveyor speed of the conveyor belts and the attenuation time are obtained in advance, and the target value of delivery speed of the extruder  10  is set based on the response delay of the extruder  10  and the attenuation time. 
   The above high-speed operation is continued until the conveyance of the extruded treads  1  in stock ends (step S 17 ) and then changed to normal operation, and the operation of the device is suspended when the conveyance of the extruded treads  1  ends (step S 18 ). 
   Thereby, after return from a trouble, products in stock can be carried swiftly and the conveying line can be returned to normal operation swiftly. 
   According to this embodiment, since the buffer means  20 Z consisting of the expansion conveyor  20   a , inverted conveyor  20   b  and expansion conveyor  20   c  is interposed between the conveyors  24  and  25  of the conveying unit  20 , when a trouble occurs in the receiving unit  30 , the expansion conveyors  20   a  and  20   c  of the buffer means  20 Z are expanded by the expansion control CPU  42  to extend the conveying line, and the extruder revolution R and the conveyor speed V are changed by the speed control CPU  41  to reduce the conveying speed in order to buffer the extruded treads  1  not to carry them to the receiving unit  30 . Therefore, the trouble can be solved without carrying the extruded treads  1  to the receiving unit  30  until the above buffer means  20 Z becomes full, and the manufacture of inferior products can be avoided, thereby making it possible to improve production efficiency. 
   When the above trouble is solved, the conveying line of the buffer means  20 Z is made the shortest and the extruder revolution R and the conveyor speed V are changed to increase the conveying speed and the buffered extruded treads  1  are carried to the receiving unit  30 , thereby making it possible to carry the extruded treads  1  in stock swiftly. Therefore, the conveying line can be returned to normal operation swiftly. 
   In the above embodiment, the method of conveying the extruded treads  1  has been described. The present invention is not limited to the above method and may be applied to a method of conveying general extrusion molded products which are continuously delivered from the material feed unit. 
   The position of the buffer means  20 Z is not limited to the position shown in  FIG. 1  and may be between any conveyors out of the conveyors  21  to  27 , and the buffer means  20 Z may have at least one expansion conveyor. 
   The speed table showing the extruder revolution R and the conveyor speed V of  FIG. 3  may be suitably set according to the actual situation of the conveying line. 
   INDUSTRIAL FEASIBILITY 
   As described above, according to the present invention, at least one expansion conveyor is interposed between conveyors in the conveying line of extrusion molded products to be expanded or contracted in order to adjust the conveying speed of the extrusion molded products. Therefore, even when a trouble occurs in the receiving unit, the conveying line is extended by expanding the above expansion conveyor to buffer the above extrusion molded products while they are carried. Therefore, it is possible not to carry the extruded products to the receiving unit without suspending the conveying line for a predetermined time. After the trouble is solved, the conveying line is shortened by contracting the above expansion conveyor to carry the extrusion molded products in stock to the receiving unit, thereby making it possible to avoid the manufacture of inferior products and to resume carrying the molded products to the receiving unit swiftly. Consequently, productivity can be greatly improved. 
   Since the conveyor speed of the above conveyors can be changed to several levels, the conveying speed can be reduced when the trouble occurs, thereby making it possible to extend the time elapsed before the buffer becomes full, and the conveying speed can be increased when the trouble is solved, thereby making it possible to return the conveying line to a normal state swiftly.