[b]PLCs can control preforms with integrated internal functions, enabling synchronized operation of the blow molding and conveying devices, linear positioning of the shuttle, and temperature control in 30 zones.[/b] Like most original equipment manufacturers (OEMs) of blow molding equipment, R&B Plastics Machinery Ltd. (R&B), based on multi-functionality, must precisely coordinate the movements of various machines. Their machines previously used closed-loop hydraulic drives paired with dedicated motion control cards. This solution was not only expensive but also difficult to coordinate. Recently, the company successfully implemented motion control functions for blow molding machines using conventional PLCs, which increased output, shortened machine cycle times, and reduced production costs. R&B provides solutions for plastics machinery, casting, processing, and cutting systems. Their products include programmable controllers, touchscreen interfaces, independent preform controllers, tilting or leveling machinery, die surface compensation plates, mechanical cutters, single-screw extruders, and high-precision blow molding equipment. The company can also design and customize equipment to meet various production needs. In addition, they provide machine inspection, installation/removal, repair, and metal cutting services. [align=center]Integrating motion control into the PLC program simplifies programming and improves the performance of R&B Plastics Machinery's series of blow molding machines. Image source: Siemens SEA[/align] Motion Control with PLC A special R&B blow molding machine has nine servo hydraulic drive shafts—three for controlling the parison (the first step in the blow molding process, extruding material into hollow tubes or hemispheres) and six for controlling motion. This machine includes two shuttles, two molds, and two blowpipes. During operation, the clamps repeatedly open and close the molds, the blowpipes repeatedly move up and down, and the conveyor moves the clamps directly below the parison to the blowing position. David Chin, an engineer at NDC Technologies, a strategic partner of Siemens, participated in the R&B control system upgrade project. Chin explained, “R&B uses a standard Siemens Simatic S7 PLC to control these positional movements. We provide a set of functional modules that enable R&B to use the PLC for position control. Other machines might use motion controllers, which are dedicated to servo control and positioning. Our customized functional modules achieve the same functionality and performance as independent controllers.” Chin added, “PLCs typically struggle to achieve high-precision servo control, which is why dedicated motion controllers are widely used. However, in our application, the standard Siemens S-7 PLC handles the motion control function, positioning each component via hydraulic drives.” The PLC also controls the temperature of over 30 areas, including the hopper, extruder, and parison top. Twelve of these areas can both heat and cool, while the other 18 can only heat. The temperature control system must keep the temperature error range of all parts of the machine within 1 degree Celsius. The parison top must be able to heat the cold plastic from the hopper to 415 °F. The standard PLC, with functional modules written in the IEC-61131 standard language, controls all the servo hydraulic drive axes. It does not require a special motion control environment. PLCs with integrated motion control functionality offer superior performance and more efficient processing capabilities compared to dedicated PLCs and standalone motion controllers. R&B initially aimed to achieve preform control via a PLC. Typically, blow molding machines are controlled by mechanical controllers or PC-based automation equipment. The former has a separate preform program unit and dedicated motion control cards; the latter achieves motion control through dedicated code. However, R&B wanted to integrate the preform program into the main machine controller. This could be achieved if the PLC's processing speed was fast enough. Analog data for preform control is input directly from a position detector. All processing is the same as with a regular PLC program. Ultimately, the hydraulic valves driving the preform blow molding are controlled by analog signals output from the PLC. The entire process requires no dedicated equipment. The company subsequently integrated the remaining servo hydraulic axis control programs into the PLC as well. The position detector transmits data to the PLC via an SSI module. If needed, the position data from the SSI module can be synchronized with the PLC program using Siemens' Profibus Isochrone mode. Similarly, the hydraulic valves are all controlled by standard analog output signals. Furthermore, R&B has integrated the program controlling the operation of the blowpipe and conveyor into the PLC. When the conveyor moves the mold to the blowpipe position, the blowpipe moves downwards according to the program. Because the shafts of both (conveyor and blowpipe) are coordinated, this process rarely fails and collisions are not a concern. Before integrating this function into the PLC, R&B could not achieve synchronization between the blowpipe and conveyor because they could not communicate. The PLC's communication protocol enabled synchronization for the first time. Reducing Idle Cycle Time During blow molding, the time it takes for all machines to blow or cool a bottle is roughly the same. However, there are differences between machines in terms of cycle time, especially idle cycle time (the time the machine is not blowing bottles). Cycle time refers to the total time from the start of blowing one bottle to the preparation time for blowing another. The motion control functions in the PLC improve the coordination of idle cycle movements, thereby reducing the interval time between specific actions. They coordinate various actions based on position rather than time. This significantly reduces idle cycle time, giving R&B an advantage in cycle time. The result is a reduction of approximately 20% in idle cycle time. It has been proven that replacing dedicated motion preform controllers with conventional PLC-based automated blow molding solutions offers significant advantages. Since all servo functions are controlled by a single functional module, this translates to better coordination, faster machine cycle times, simpler and more efficient programs, and more streamlined equipment. Furthermore, dedicated hardware, produced on a small scale, inevitably presents challenges in quality control and long-term technical support, requiring design modifications to address emerging issues, all of which increase additional financial investment. PLC-based automation solutions have proven to offer a more attractive overall control system for blow molding compared to PC-based controls. They feature better modules, utilize solid-state memory, do not require third-party operating systems, have a longer lifespan, and offer superior long-term support. One of the key advantages of PLCs compared to PCs is their ability to retain data even in the event of sudden shutdowns (such as power outages). “We now use a single controller to manage both PLC and motion control functions,” says Jake Losee of R&B Plastics. “The communication latency we experienced with separate motion control cards is gone. Furthermore, we can record the rotation of each axis. Previously, with separate software, technicians familiar with the dedicated motion control cards needed to program them. Now, users can do this themselves through a Human-Machine Interface (HMI).” Losee adds, “One of our goals is to streamline our equipment. Additional equipment means higher costs, more cumbersome maintenance, and more supporting software. This requires more training for our maintenance personnel. Integrating motion and preform control with a PLC is indeed a highly optimized control solution.” (Translated by Gao Ming)