Very slow rotation speeds
Very slow rotation speeds
(OP)
We have an old (35+ yr) system that spins a cone gear at very slow speeds: input rotation needs to be as slow as about 2.5e-4 rpm, i.e. 4000 minutes per rev. The old system we had involved an AC synchronous motor running at 15 rpm, a 4:1 reducer, a multigear reducer (ranging from 2:1 to 1000:1, and a 16:1 reducer to the cone gear. The input torque on the cone gear needs to be about 100 in-lb. The manufacturer hasn't made the multigear reducer in over 20 years (pull and turn shifter). The multigear is malfunctioning (I think it is slipping, but we don't have the time or expertise to take apart and diagnose).
I have two questions: 1. Do these multigear reducers still exist, and if so, can anyone suggest manufacturers?
2. An alternate solution (need slow, constant rotation, and need to be able to repeat a speed (similar to the way I used to be able to when I set the dial to a particular gear ratio)) that I was thinking of was using a stepping motor, with the appropriate reducers to get to an acceptable torque. Would using microstepping to rotate the motor very slowly be a reasonable use of a stepping motor?
Any help would be appreciated. I am completely out of my element on this one.
I have two questions: 1. Do these multigear reducers still exist, and if so, can anyone suggest manufacturers?
2. An alternate solution (need slow, constant rotation, and need to be able to repeat a speed (similar to the way I used to be able to when I set the dial to a particular gear ratio)) that I was thinking of was using a stepping motor, with the appropriate reducers to get to an acceptable torque. Would using microstepping to rotate the motor very slowly be a reasonable use of a stepping motor?
Any help would be appreciated. I am completely out of my element on this one.





RE: Very slow rotation speeds
RE: Very slow rotation speeds
They change mechanical state within a few ms of the electrical state changing, no matter how infrequently a step is executed. The resulting micro- hammer- blows can do an amazing amount of damage to a geartrain.
Mike Halloran
Pembroke Pines, FL, USA
RE: Very slow rotation speeds
There is also another problem related to frequency converters at low frequencies. That is the thermal behaviour of power transistors. Now you have almost DC current, which means that on- and off- periods for power transistors become very long, and this means that the temperatures of transistors go up and down (at normal frequencies they are quite constant), which can break the transistors mechanically quite fast (thermal expansion). This is quite well-known problem related to converters at very low frequencies.
RE: Very slow rotation speeds
Is the speed on a stepper that hard to control? My understanding was that as long as the pulses from the driver are constant, the motion will be predictable. I can understand how things may fall apart once the speed approaches zero, but what about at somewhat higher speeds (lets say around 4 to 10 rpm?
RE: Very slow rotation speeds
On a micro scale, the step motor is stationary most of the time, and rings at every step. It's not clear from your specification so far if that's a problem or not.
Mike Halloran
Pembroke Pines, FL, USA
RE: Very slow rotation speeds
The gearbox you have sounds similar to what is on a typical milling machine or lathe.
RE: Very slow rotation speeds
Lionel, you're right the gearbox reduced from 2:1 down to 1000:1, a 500-fold range. The biggest gearmotor range I've been able to find is about 150-fold. Has anyone seen different?
RE: Very slow rotation speeds
A similar solution with a PM servo will probably work even better. Lots of suppliers in Germany (handle "Bergbau" says you may be from that part of the World).
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...