MATERIALS HANDLING
surface roughness <0.5 µm. T is facilitates cleaning of the surfaces in contact with the product. T e motor technologies used to
date have had to make sacrifi ces: “For classic asynchronous motors whose rotor is a squirrel-cage rotor, the control range remains limited to 1:10 (1:50 is possible in individual cases). With encoder feedback, signifi cant expansion is possible,” said Maurice Wirkner, an application manager at Lewa. “In addition, the drive is relatively ineffi cient outside the rated speed range – especially at low speeds. T is requires the drive to be oversized, which increases operating costs.” Servomotors are optimised for highly dynamic requirements and also cover the complete control range (1-210 pump strokes), however, they are more expensive to purchase and in addition, require a servo inverter for control.
WIDE-RANGE SPEED CONTROL Lewa has now expanded its own portfolio with a drive technology that does not have these weaknesses. “Unlike the asynchronous motor, the rotor of this drive consists of permanent magnets and rotates synchronously, i.e. without load-dependent slip,” Wirkner explained. “Among other things, it features an extreme control range, which often makes the use of multiple pumps for diff erent fl ow rates unnecessary.” Particularly in the case of multiple pumps, an additional manual stroke adjustment or electric stroke adjustment can be dispensed with and the required fl ow rate can be realised by speed control only. T e PMSM also has a constant torque. T e complete torque can be applied from engine speed 0rpm (standstill) up to the rated speed of the motor. T is ensures particularly smooth and gentle system start-up, since each process can be started with a pump capacity of 1% instead of the usual 10%. It also features a high short-term
overload capacity, which enables a drive design without oversizing for the starting torque. As a result, smaller, more cost- effi cient sizes can be realised than with classic drives. “Like the asynchronous motor, the PMSM can be controlled via a standard frequency converter, so users can rely on common parts,” Wirkner explained. “With the servomotor on the contrary, it would be necessary to purchase expensive servo controllers.”
Functional testing with the MSM prototype and an ecodos pump
T e compact drive can be easily cleaned due to its fanless design and off ers high IP protection. If required an additional conversion process – called nsd tupH – can be applied to the aluminium body for FDA requirements. T is makes the surface extremely resistant and even easier to clean – ideal for applications with stringent hygienic requirements, such as aroma metering in the food industry or additive dosing in the pharmaceutical industry.
The PMSMs added to the portfolio feature a control range of 1:200, enabling a wider range of applications to be covered by the same drive or pump
ENABLING COST REDUCTION T e sole limitation of the currently used PMSM is that it is only available for safe areas. “T anks to wide-range speed control with IE5+ PMSM, we can meet the increasing customer demands for a wider adjustment range and lower energy consumption, as well as overall costs,” said Wirkner to sum up the situation. “T e topic of energy effi ciency in particular is becoming increasingly important for our customers. A decentralised solution in which the frequency converter is installed directly on the PMSM, can now be implemented with Getriebebau Nord, our motor partner for PMSM, too.”
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