Inverters key to power saving modules

Business Development Manager, Kay Taylor, explains the concept: "On the face of it a moulding machine can consume a lot of power; but most of this is because a standard machine is inefficient when not at full load which applies for a large part of the duty cycle. PowerSaver works by slowing the drive motors during periods when full load is not required. This is managed through our specially developed interface system to ensure a smooth operation to maintain mechanical life by reducing wear as well as reducing consumption."

PowerSaver is a self-contained control unit that can be retrofitted to virtually any moulding machine regardless of make. The heart of the unit is an inverter drive, a Mitsubishi F700, which varies the machine's motor speed (and hence power consumption) as required. The F700 is both powerful and easy to use, with full auto-tuning and a suite of advanced software options including some that optimise the drive for use with injection pumps. Significantly it meets all international regulations, so Sandretto can supply export markets with a single PowerSaver technical specification. 

"If moulding machines typically ran 24x7, pumping out identical products every time, a single profile via our interface driving the F700 is all we would need. We could programme it to churn through the same duty cycle day in day out," Taylor observes. "But the real world is never that simple: moulding machines are constantly being switched between different products coupled with setup procedures and manual operations including start up, each with its own duty cycle." So in the PowerSaver, the F700 is paired with a small but powerful FX3U PLC, also from Mitsubishi. This holds programmes for all of the user company's moulded products, and can switch between them as required. Additionally, it collects and analyses real time information to further optimise energy usage. 

Originally Sandretto's design team thought that an FX3 and an F700 would define the entire concept of the PowerSaver, but when they started introducing it to potential users a refinement suggested itself. "We'd set up a demo, and use a powermeter to proudly show potential users energy savings of 30%," Taylor recalls. "We were pretty impressed with ourselves. But the plant engineers would always come back with a raft of 'What ifs'. The bottom line was that they all wanted two extra capabilities: to see the energy savings in real time, and the ability to manually fine tune settings at any time."

It didn't take the designers long to come up with a solution. They added a Mitsubishi GOT1030, graphic operator terminal or human-machine interface (HMI) to the mix. This little screen shows the operators exactly what is going on inside the moulding machine and allows them to make minor adjustments on the fly to optimise setting in real times. This can be saved in the PowerSaver memory for future use. "The performance of the PowerSaver shot up, because we were suddenly using real time data rather than what is in effect guesswork," says Taylor. "Savings were now hitting over 50%."