How inverter drives can cut the cost of automation
07 February 2016
Following advice from Eaton, machine builder IMSB has replaced a costly servo-controlled filling system with one based on an inverter drive, making its novel machines much more affordable.
Aetna Group subsidiary IMSB is based in Brazil, where it specialises in the development and manufacture of packaging equipment, including rinsing, filling and capping machines. In addition to standard products, it offers customised machines that meet the specific needs of the food, pharmaceutical, home care and other sectors.
With today’s frequent changes in pack sizes and formats, flexibility is becoming a key requirement for production equipment. In the case of in-line volumetric bottle fillers of the type manufactured by IMSB, this means that end users want to be able to change filling volumes quickly and conveniently to suit different sizes of bottles.
While machines with manual adjustments do allow such changes to be made, setting a new filling volume accurately can take up to an hour, a delay which is difficult to accommodate in modern, fast-paced production environments. Electronic adjustment provides a solution but, until now, it has been necessary to use costly servomotor-based systems to achieve the required accuracy without adversely affecting the machine throughput rate.
IMSB was aware of the market potential for filling machines with electronic volume control if the cost could be brought closer to that of machines with manual control. The challenge was to develop something that would make this possible.
Moving from servos to inverter drives
In IMSB in-line volumetric bottle fillers, the volume of fluid dispensed into each bottle and the rate of flow is controlled by a cam-driven valve system. The cam must rotate to an accurately defined position for each bottle filled, then return to its rest position before the next bottle reaches the filling station. In the past, it had been considered that the only way to position the cam with the accuracy and speed required for this demanding application was to use a servomotor and its associated drive system.
Eaton’s application engineers had a different idea. Instead of a servo system, they proposed that a PowerXL DA1 high-performance inverter drive, in conjunction with an optical encoder, could be used to control the cam and accurately monitor its position. The DA1 features advanced vector control algorithms that provide the rapid response times and high levels of accuracy required by the IMSB bottle fillers.
To complete the system and to make it easier for the end user to operate, an Eaton XV100 unit, combining the functions of a colour touch-screen HMI panel and PLC, was also included. To keep the machine wiring as simple as possible, signals from the encoder and from other machine-mounted sensors are connected to the XV100 using remote input/output units from Eaton’s XI/ON range. The I/O module used with the encoder is a high-speed counter unit with a maximum count rate of 100kHz, easily meeting the requirements of this application.
IMSB developed programs for the XV100 that provide an intuitive recipe-based approach; machine operators simply use the colour touch screen HMI to select the recipe corresponding to the type and size of bottle in use. The XV100 then automatically sets the appropriate mode of operation for the filling valve system as well as the optimum speeds for the in-feed and out-feed conveyors, each of which is controlled by an Eaton PowerXL DC1 inverter drive. The current arrangement offers 15 recipes, but the control system is capable of handling at least 100, should future expansion be required.
During filling operations, the XV100 continuously monitors information it receives from the encoder and uses this - in conjunction with information contained in the chosen recipe - to compute a speed reference signal for the DA1 inverter. To ensure the necessary speed of operation, this signal is sent to the inverter via a CANopen bus connection, along with start and stop signals.
The computation of the reference signal is handled in the XV100 using a special positioning function block written using the CoDeSys software development system. This function block was written by IMSB’s engineers who were already familiar with CoDeSys implementations on other projects.
Precision and repeatability
The accuracy of the new filling system was evaluated by check weighing each bottle and, after an extended period of operation, this revealed that the filling accuracy was achieved in excess of 99.5 percent of cases. In addition, the repeatability and consistency of the filling operation easily exceeded the company’s own strict requirements.
Moreover, these results were achieved at a cost level much lower than that of a servo-based filling system capable of providing similar performance. IMSB customers can now buy a machine with electronic filling volume adjustment for little more than the cost of a machine with manual adjustment, allowing almost instantaneous switching between bottle sizes. IMSB production supervisor, Osmar Vieira, who is responsible for electrical engineering, concludes:
“When we were using servo drives, the cost of automation was simply too high for many potential users of our machines. Eaton, however, offered a complete automation and drives solution that really surprised all of us in terms of performance and value for money. In fact, we are so satisfied that we are standardising on the Eaton solution for all future production of our volumetric filling machines.”
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