A thorough understanding of the mechanical load is crucial to successful motion applications. Gear designers are experts in understanding the mechanical load. Not just the RMS power requirement, but other issues such as impulse loads, the impact of heat on part geometry and life expectancy.
Gear design, like electric motor design, has continued to evolve as clever designs have been developed in an effort to meet unique requirements and competitive situations. The parallel spur gear reducer and worm and spur gear have been the two most common solutions in industrial gear reducers for many years. While these systems have been used for many power train applications, they have performance limitations that makes them impractical for use in motion applications. Relatively high backlash creates problems in many situations where the control system can become unstable hunting for the error in the gear mesh. Low efficiency in the gear reducer is no longer acceptable in today’s energy conscious economy .
More exotic geometries like planetary, cycloidal, and harmonic have emerged over the years and have becomes established solutions, available off-the-shelf products ready to use. Each of these technologies has it’s own unique attributes that must be considered in motion applications. All are capable of high accuracy and low backlash. Claims of zero backlash by some vendors need to be tempered by the fact that backlash may be hard to measure, but in the case of rolling or flexing geometries, cycloidal and harmonic reducers, there is torsional flexure taking place.
One of the less well know solutions is the double enveloping worm and spur. The double enveloping geometry is similar to a lead screw with 2 threads in it. The difference is that the two threads are very close together and machined on opposing sides in order to have a thread in mesh with the surface of the spur gear tooth and the back of the opposing tooth. In this way the backlash that would normally exist is taken up and accuracy in the low arc-minutes is achievable. In addition, the pitch of the thread requires the spur gear to be cut as a helical tooth,, Combined with multiple teeth in mesh, the resulting gear set is very energy dense and efficient. An incredible accomplishment when compared with the worm & spur designs of the past.
As with the motor industry, gear designers are constantly pushing the envelope, coming up with new solutions, breaking some of the old rules and creating new rules.
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