Scott Reynolds has 31 years of experience commercializing new technology products in microelectronics, medical device and industrial motor markets. Co-inventor on several patents in the fields of electronics and motors, Reynolds is a graduate of the University of Arizona, BSME. As ETM’s director of engineering since 2008, Reynolds serves ETM’s technical, operations and business teams. For more information, email firstname.lastname@example.org or visit www.etmpower.com.
Cost and operational advantages of new direct-drive motor technology have been validated for driving peristaltic pumps. Based on transverse flux innovations, these motors have been used in a variety of high-torque, low-speed applications from conveyors to industrial fans, and recently extended their breadth of operation to include positive displacement pumps.
Peristaltic pumps require relatively high torque at low rotational speeds, typically in the range of 5 to 500 rpm, well below the direct-drive capability for incumbent, conventional alternating current (AC) or direct current (DC) motors.
As a result, incumbent motors are operated at a higher speed (more than 1,000 rpm), and a speed reduction gearbox is necessary to achieve the required torque and rotational speed. These geared drive systems can be large, heavy and inefficient.
The new direct drive motors based on transverse flux technology deliver high continuous torque at low rotational speeds, which eliminates the need for a speed reduction gearbox. This reduces the drive system weight, size, temperature and power consumption of the pump system while offering a wider operating speed range.
These motors cover a range of both peristaltic and hose pumps.
This transverse flux technology employs increased pole count and low resistance coils, delivering five to 10 times more continuous torque by mass compared to conventional AC or DC motors.
In addition, the higher losses in geared drive systems mean the conventional motors need to be oversized to meet the output power requirements. As a result, these drive systems can be priced as much as 50 percent less than geared drive systems.
Motor Regulation Impact
Efficiency legislation is creating an ever-growing focus on motor and pump system efficiency. Some AC induction motors can suffer from losses in variable speed or variable load applications. As speed moves away from nominal rpm in conventional motors, efficiency can fall to less than 50 percent.
Gear losses caused by sliding friction and movement of viscous oil can further compound overall drive system power loss. The direct drive motors based on transverse flux technology have low coil resistance and high pole count, an ideal combination for efficient torque production at low speeds. Power consumption versus pump speed can be reduced 30 to 60 percent.
Most AC geared peristaltic pump drive systems offer a maximum turndown ratio of 10:1 (i.e. max pump speed is 10 times greater than the minimum speed). This ratio is often limited by variable frequency drives (VFD) used to operate AC induction motors.
The transverse flux-based direct drive systems operate from five to 500 rpm, a turndown ratio of 100:1. Testing has also shown that the systems are capable of operating at higher continuous loads. This also enables OEMs to replace many motor and gearboxes with far fewer direct drive systems and results in simpler inventory management, improved working capital turns, easier replacement parts service and lower inventory costs.
Over time, gearbox seals can leak, gears can wear out and the systems can require increased maintenance. The advanced direct drive systems have a single moving part, the motor rotor, which enables greater reliability, reduced maintenance and reduced noise. Installation of AC gear motor systems often requires an electrician to connect the controller to building mains while the new direct drive systems are pre-wired with a 110V cable and plug.
End users choose these smaller motor systems due to their ultra-high continuous torque density, which eliminates the need for extra parts (e.g. gearbox), thereby decreasing costs and system losses amongst various additional benefits.