Self-Lube Gears Increase Reliability and Efficiency

Dexter Magnetic Technologies of Elk Grove Village, Ill., recently devised a dual-axis robotic manipulator that controls sputtering in the manufacture of computer hard drives. Unfortunately, the device relied on a sophisticated drive and pulley system that quickly developed troublesome, excessive wear.

The drive has two single-sided timing pulleys configured in two independent sections, each of which uses two single-sided timing belts, explains Chris Ras, product development manager at Dexter. The faster of the two drives needed frequent and precise tensioning to eliminate belt stretching and compensate for excessive wear.

Ras explored gears as an alternative to the belt drive with the help of Intech Corp., Closter, N.J. There were problems with this approach, though, because of the cramped quarters involved, and because the application featured both high torque and reversing torque. Moreover, the gears would need to be retrofitted into equipment on location at the customer’s facility.

Intech’s engineers used proprietary gear-calculation software to review load data and size the company’s self-lubricating plastic gears for the job. They also increased the load-carrying capacity of the Power-Core gears by applying an innovative plus/plus gear mesh modification to the gear train. The final design included two stainless-steel drive gears and a backlash-free plastic idler gear with a stainless-steel core. In addition, a special idler-gear shaft made for a field-ready retrofit.

The redesign resulted in smooth manipulator motion and greatly improved reliability. Tests determined that drive efficiency rose 15%. Ras reasoned that this was in part from eliminating radial stresses that belt tensioning transferred to the bearing. Gears, on the other hand, place minimal stress on the bearings, transmitting virtually all the drive force onto the mating gear teeth.