With the Chinese tire industry undergoing a period of massive growth—the total volume of tires produced in China increased from 112.4 million in 2000 to 630 million in 2014, accounting for more than one-third of the total global output—the rapid deployment of modern automation technologies has played a critical role in enabling this growth and positioning the industry to meet future market demands. Of all the equipment involved in the tire manufacturing process, composite extruders and four-roll calenders (a series of hard pressure rollers used to form or smooth a sheet of material) and their associated lines are the areas where networking communication lengths are the longest and where the greatest volume of communications data and number of stations reside.
The precision with which an extruded, semi-finished tire is produced plays a decisive role in the ultimate quality of the finished tire. Consequently, a great deal of attention to the control and drives systems of extruding equipment is required. This is why the application of a CC-Link IE network on a project at a leading Chinese tire manufacturer not only helped this manufacturer improve its production operations, it laid the foundation for the company’s ability to meet its planned annual production of 20 million semi-steel radial tires.
The automation project at this tire manufacturing facility combined the Mitsubishi Electric A800 variable-frequency drive’s speed and tension control system (floating roller function) with the CC-Link IE network. Another key technology coupling used in this project was the Mitsubishi Electric QJ71MES96 module (an energy source monitoring module) along with the CC-Link IE Energy option. The CC-Link IE Energy Management Communication feature optimizes detailed energy consumption monitoring. This function facilitates the collection and monitoring of energy data at the device/equipment level to realize significant energy savings throughout the facility.
Extruding and calendering
On an extrusion line, the stability of feeding materials is the most important influencing factor. Therefore, the feeding process is controlled by a pressure sensor in the extruder’s nose. Every time a change in pressure is detected in the channel of an extruder nose, it can be proportionally fed back to the extruder and compensated for by adjusting the screw speed. Since every extruder is controlled independently, if the pressure inside the extruder nose is kept stable, the stability of the distribution of the rubber output and the semi-finished extrusion product can be guaranteed. Moreover, by using a continuous weighing system to monitor and check deviation in the quality of the semi-finished product, if any deviation from the tolerance set for the continuous quality of the semi-finished product is detected, the change is fed back to the production line drive and the speed is adjusted accordingly.
The main requirements of calendering are that distribution of tension should be stable and in accordance with process requirements. Calendering tension is mainly determined by the difference in the transmission speeds of the two machines. Therefore, the electrical system plays a determining role in tension adjustment and requires that the speed of each electric engine be automatically aligned on the basis of conveyor speed, with fine-tuning automatically performed on the basis of actual tension. In addition, during the continuous production process, roller spacing is automatically calculated, maintaining conformity with the designated width. This means that the power and drive systems must have high-performance calculation and response speeds as well as high-speed, stable network communications.
Network technology assessment
Other automation suppliers looking to win this project also provided the tire manufacturer with solutions based on Ethernet network protocols. But when the performance and features were compared, CC-Link IE was shown to be superior to others in meeting the customer’s requirements. The biggest differentiators were network structure, speed and bandwidth capabilities.
One of the other proposed network protocol models used TCP/IP communication with a star topology structure, supporting a maximum communication speed of 100 Mbps. A maximum of 64 TCP/IP connections and 128 controllers were permitted for each module on this network. The distance between stations on this network was not specified, although expansion could be achieved with fiber-optic repeaters. The other proposed network for this project used Cat5 cable, with a maximum distance of 100 m and speed of 100 Mbps using TCP/IP communications. Topology structures for this network included star, tree, linear and ring. The input/output data volume for one series of interface modules in this architecture was 256/256, and it was expandable to 63 stations. A maximum of 256 stations could be connected with a second series of modules.
CC-Link IE’s communication speed is 1 Gbps, with a token-based communication technique providing for inherent deterministic communications. The maximum number of stations connected on a single network is 120 and the maximum number of networks is 239. Using multimode optical fiber, the maximum distance between stations is 550 m. When dual-loop topologies are used, the maximum transmission capacity is 1,920 bytes.
CC-Link IE uses tokens to control data transmissions and network shared memory for real-time data communications. Real-time requirements are high for composite extruders and four-roll calenders and their lines. Therefore, carrier sense with collision detection commonly used in general-purpose Ethernet cannot meet these requirements very well. The use of Ethernet tokens in CC-link IE to control the access time for each station to network shared memory means that only stations with tokens can read and write network shared memory, providing a level of security as well as determinism.
As a token is transferred to each station in a network, the station can separately complete its reading and writing of network shared memory. In this way, there can be no collisions when data is transmitted in the network. Since CC-Link IE uses Gigabit Ethernet technology, the transmission speed of tokens in the network is very fast, making connection scan time short. Plus, the CC-Link IE network can not only operate the current network configuration in a loop, thereby minimizing the probability and impact of communications faults, it can also support star and linear network topologies, as well as topologies combining them. This Gigabit Ethernet technology also provides the bandwidth to expand the communications and network data transfers without affecting the control of the network.
Matching drives with network capabilities
With the decision to use the CC-Link IE network made, this Chinese tire manufacturer then chose the Mitsubishi Electric A800 series variable-frequency drive (A800-R2R) due to its proven ability to control floating rollers and tension in composite extruders and calenders and their lines.
The cooling and winding equipment located at the end and back end of the composite extrusion production line is a crucial link in the entire production line. The quality of its operation does not only have an impact on the condition of every operational segment of the line, but also impacts the finished products. Speed matching on these lines requires high-precision speed control. Winding control, in particular, requires good stability, high precision and constant tension control. In essence, line speed matching and winding control must ensure that the products are not stretched, no matter what changes might occur to the line speed or how the reel diameter of spools might change.
Mitsubishi Electric’s A800 variable-speed drive combines the required level of speed matching and reeling functions via speed tension control (floating roller control), torque tension control (with tension testing), constant tension control (without tension testing), roll diameter calculation compensation/preliminary roll diameter calculation/roll diameter memory, taper control, automatic adjustment of speed gain, short line detection, inertia compensation and materials length recording function. Since the external analog signals and operational controls are all completed within the variable-frequency drive, the application of the A800 variable-frequency drive in composite extruders and four-roll calenders and their lines mitigates the load of PLC operations and network communications while also avoiding human uncertainty.
When winding begins, the automatic arbitrary roll diameter calculation function can calculate the current roll diameter when starting, as the floating roller moves from its lower position to its target position. This facilitates winding with an arbitrary roll diameter. When winding is interrupted, the A800 can automatically adjust speed gain as the diameter continuously changes, thereby providing high system performance and safety. In addition, the inertia compensation function can reduce the phenomenon of tension lag resulting from increased deceleration. When winding operations have finished, the broken line testing function automatically detects the product tail to prevent excess speed.
The superiority of a CC-Link IE network has given the tire manufacturer a comprehensive solution featuring automation, energy management and information meeting the requirements of Industry 4.0. With the aim of ever-increasing partner satisfaction, the CC-Link Partner Association (CLPA) provides an industrial Ethernet network with an appropriate integral solution while providing Industry 4.0 customer needs.