New Gear Design Solves Automation Snafu

An InTech Corporation customer was experiencing a problem with one of its new paper handling machines. The customer wanted to know how to maintain precise timing between two shafts with corrugating teeth to prevent them from grinding into each other. The issue was causing expensive downtime on the factory floor.

InTech designers decided to create a backlash free, low inertia gear design for this customer. Traditional backlash free gears, similar to the ones in the paper handling equipment, consist of two spur gears, one split in two halves. Once both gears are installed on the shaft, the two halves are rotated manually in opposite directions until both touch the opposite flanks of the wider mating gear. This configuration eliminates backlash. The two narrower gears are fastened together with bolts.

Traditional split design backlash free spur gears

Interestingly, the InTech zero-backlash design rests 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 rather than rotating the narrower gears around their axis, are forced apart in an axial direction. This is accomplished by placing a spring axially between the split gears. Cylindrical guiding pins securely anchored in the metal core of one of the narrower gears 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 and prevent any rotation.

One half of the split gear engages the wide gear on the load carrying flank. The other half is guided by the pins to move axially. It 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 directions, the InTech designers relied on the elasticity of the Power-Core material. When pressed against the helical flank of the wider gear, the tooth of the narrower gear deforms slightly to facilitate engagement along the full length of the flank. Both halves of the split gear and the spring load were calculated to develop sufficient preload to carry the entire torque with enough safety to guarantee a backlash free mesh even during an emergency stop. InTech used proprietary software to calculate expected gear life.

InTech Power-Core helical gear with zero backlash design. Zero backlash design uses split helical gears pushed in opposite directions by a spring and guided axially, to eliminate backlash by preloading the split gear in opposite flanks of the mating gear.

For installation and gear hobbing, the two halves of the split gear were fastened together with the provided bolts, forming a perfect helical gear. This gear was installed on the shaft and meshed with the wider helical gear. The gear half of the split gear with the metal hub was attached to the shaft with a key way and a key. Once the installation of all gears was complete the fastening bolts were removed. With this design, the backlash adjustment became “automatic” as the spring pressure became permanent and there was no need for manual readjustment when tooth wear occurs. By designing all gears in the gear train with Power-Core, the company reduced inertia in the drive by 65%.