When Nidec SR Drives (NSRD) was commissioned to develop and manufacture a high-powered interior permanent magnet (IPM) motor for a customer which manufactures hybrid power systems for commercial vehicles, the company experienced problems when attempting to balance a rotor. The rotor contained powerful rare earth magnets and the magnetic fields were interfering with the pickup signals.
Furthermore, they were not balancing on the rotors’ bearing journals as these were set in from the outside of the part. Because of these two significant issues, NSRD’s engineers could not be confident in the balance results or that the part had been balanced with any degree of accuracy.
As a solution, Universal Balancing supplied the company with a tailored system.
“The pickups on our previous machine were moving coil sensors which were affected by the magnetic field of the IPM rotor and this was showing the rotor to be in balance when it was not,” explains Simon Gibson, electromechanical design technician at NSRD. “It was really important to solve the problem because the motors were going in to our customer’s vehicles and we needed to be certain that they were balanced correctly.”
Universal Balancing’s business manager, Paul Fowler, said: “We proposed a specialist set of roller bearings to protrude in the available space in order to balance the part on actual bearing journals as it is normally best practice to replicate production conditions.
“In addition, we were able to offer our own specialist correction software. In each correction plane there are eight recesses where putty can be added to counter the dynamic unbalance. Our Winbal software enables NSRD to specify these locations in addition to the maximum amount of weight (putty) that can be applied in each one to ensure it does not protrude beyond the brass face. The exact amount of putty which has to be added in each location is then displayed so the customer can weigh it beforehand – and bring the part within tolerance at the first attempt.”
A further challenge presented itself when it became apparent that the machine was to be installed on the first floor of the 20,000 sq ft facility, on a surface that was not originally designed to be used for industrial purposes.
Gibson said: “When we came to install the machine we found that the floor was built with Bison beams which are not solid but have a hollow centre. However, the flooring did not compromise the operational efficiency of the balancing machine in any way, underlining its measurement accuracy.”