Low Inertia, Zero-Backlash Gear Designed for Timing Critical Application
August 5, 2010—
Intech Corporation was approached by a customer with a dilemma involving a new machine for corrugating paper products. The customer was attempting to maintain precise timing between two shafts with corrugating steel teeth to prevent them from smashing into each other. Intech focused on a backlash-free, low inertia gear design as the solution.
The traditional backlash-free gear design consists of two gears, typically spur gears, with one split in two halves. Once both gears are installed on the shaft, the two halves of the split gear are rotated manually in opposite directions until both touch the opposite tooth flanks of the wider mating gear, eliminating any backlash. The two narrower gears are then fastened together, usually by bolts.
The Intech zero-backlash design is based on the same principle of eliminating backlash by engaging the opposing flank of a wider gear with two halves of a split gear. The gears are helical, and instead of rotating the narrower gears around their axis, they are forced apart in an axial direction. This is accomplished by a spring placed axially between the split gears, and cylindrical guiding pins that are securely anchored in the metal core of one of the narrower gears are fit into the counter bores machined into the all-plastic second half of the split gear. The spring force pushes the gears apart, and the pins force the gear to move axially to prevent any rotation.
The principle behind the design is that one-half of the split gear engages the wide gear on the load carrying flank, the front flank and the other half. These are guided by the pins to move axially and will be stopped by the rear flank of the second tooth blocking the axial movement with the helix angle. For the preload of the split gear in opposing direction, Intech relies on the elasticity of the Power-Core polymer material used. By designing all gears in the gear train with Power-Core, inertia was reduced in the drive by 65 percent.
When pressed against the helical flank of the wider gear, the tooth of the narrower gear will deform slightly to allow engagement along the full length of the flank. Both halves of the split gear, as well as the spring load, are calculated to develop enough preload for carrying the entire torque with enough safety to guarantee a backlash-free mesh, even during an emergency stop. Intech uses proprietary software to calculate expected gear life.
For installation and the preceding gear hobbing, the two halves of the split gear are fastened together with the provided bolts to form a helical gear. This gear is then installed on the shaft and meshed with the wider helical gear. The gear half of the split gear with the metal hub is attached to the shaft by a keyway and a key. Once the installation of all gears is complete, the fastening bolts are removed, and the spring does the rest. With this design, the backlash adjustment is automatic, as the spring pressure is permanent, and there is no need for manual readjustment when tooth wear occurs.
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