When gear teeth mesh together conventionally, each can be subject to a high level of stress due to the contact pressure: especially in high-torque applications. This obviously leads to shortened working life.
So now imagine pressing the gears together so that, instead of making contact via a single pair of teeth, there is a flattened region, consisting of many teeth, where the gears mesh.
Each of these ‘wheels’ would need to be constructed in the form of a caterpillar track. Instead of a rack and pinion arrangement, this effectively becomes two racks of different lengths.
There would be a degree of indeterminacy as to how much stress each pad carries at any moment but this approach would reduce the stress on each track pad and also potentially allow variable contact geometry for different types of duty.