This model can be found in the 20-sim demo directory.
You can open this model and simulate it yourself using the free 20-sim demo/viewer!

Using Wormgears

Description

The extended wormgear model in 20-sim shows two drawbacks of wormgears: friction that can lead to self-locking and backlash caused by play between the gear teeth. Self locking is demonstrated in the other wormgear model. Backlash is demonstrated here. 

The backlash that is used in the wormgear model is equivalent to the translational backlash and uses the same parameters. Translational backlash is extensively explained in the model UsingBacklash.em. So the reader is advised to study this model first. 

The wormgear model consist of an ideal motor that yields a prescribed rotary motion. The rotary motion is converted to a rotation of a lever. Each time the lever passes the right-up position (either hanging or standing) it is forcing the backlash to traverse the play zone. The backlash represents here the freedom of movement that the gearwheel teeth experience between the spindle teeth. Although the chosen backlash is very small (100 um), due to small radius of the wormwheel (20 mm) the freedom of movement of the lever is noticeable (0.3 degree). 

The following plot shows a simulation run of the worm-gear model.

The position error of the input shaft (spindle) and lever (wheel). 

As you can seen the lever error shows a clear switching of the wormgear backlash.