I am designing a lifting device for practical use which is powered by a dc motor with worm gear. The lifting device should be able to hold the load in place at a certain height.however, i read that wormgears are self locking only in situations where shock and vibration are not present, in other words, if the lifting device is not perturbed in any way, the self-locking feature will probably perform as intended. This could present a problem for security reasons and functionality if the lifting device is intended for use in varied conditions. My question is, should I consider others options, like different types of gears or persist with the worm gear
I've seen from simple observation that many lifting devices using winch mechanisms use worm gears. One advantage of using this mechanism is the high gear ratio (reduction) created with few components.
In my search to validate this reference, I found the answer to a post in the Engineering Stack Exchange in which the replying party suggests that a worm gear design will be self-locking even if such a feature is not desired.
The answer also suggests that the angle on the worm gear (lead angle) will reduce or increase the self-locking capacity. This makes sense in that a nearly perpendicular gear engagement will have substantial friction resisting back-drive, while a more oblique angle will allow the teeth to slide more easily.
Even with some vibration and shock, a perpendicular lead angle may not have movement beyond a degree or so of rotation. If more mechanically complex construction is not a problem, one worm gear driving another, driving the winch would increase the self-locking capacity. I attempted to find an image of this type of assembly and failed. It may be excessive and impractical.
In the process, I discovered a worm gear being driven by a conventional reduction gear set, which increases the self-locking by requiring that the worm gear and the gear set be back-driven. Using a multi-level planetary gear set as a reduction gear set would fall into the overkill category, I believe, as planetary gear sets of multiple rings have substantial resistance to being back-driven.