Reduce Worm Gear friction in reverse direction

[fish1117]

Hi,

I'm designing a worm Gear, module=1 and ratio 30. The lead is driven by a DC motor, and the worm wheel is connected to the load.

Although the motor power is controlled to protect the gear, when the load hit on the hard limit, the worm gear are stuck, and the motor can not turn it back in the reverse direction.

In order to turn it back after hitting the hard limit, I increase the voltage of reverse direction(3 times higher than the voltage of hit-direction). By this, the problem is almost solved, 95% of the trials are succeed then.

To make the design more reliable, my question is:

Is there anything I can do about the worm gear to reduce the reverse friction of the worm gear when it hit (module, pitch, worm wheel, mesh, ...), so that it can be easier to turn back after it hit a hard limit ?

Thank you.

 

[MikeHalloran]

Don't let it hit a hard limit, ever.
I.e., add limit switches somewhere that will slow the motor as it approaches the hard limit, and stop it before it ever reaches the hard limit.


Mike Halloran
Pembroke Pines, FL, USA

 

[btrueblood]

What Mike said, in spades.

 

[mraabe]

You would have to increase the lead angle, but is is better to avoid the hard limit.

 

[MikeHalloran]

Another alternative is to put a mechanical rotation limiter on the input shaft. You still have to phase it so it's centered between the hard stops on the output shaft.

... which will _always_ jam a 30:1 worm set.

... unless you _seriously_ reduce the drive torque before reaching the stops.

--- which requires limit switches or position feedback, so you might as well stop the drive before reaching the hard stops.





Mike Halloran
Pembroke Pines, FL, USA

 

[plasgears]

A thermistor in the circuit would cut the current and limit the bottoming torque. We used it in automotive car seats and other DC driven devices. At stall, the current spikes and the thermistor responds by increasing resistance. It works rather quickly.