- #1
evi7538
- 36
- 13
Hello colleagues,
I'm designing a simple precision rotational mechanism for angular positioning of an optical element. I need a total rotation travel angle of about 50 deg at a low speed (a few seconds for the full travel) with about 4000 discrete positions over the travel angle. Any systematic positioning errors can be calibrated so I don't necessarily need an ultra-high positioning absolute accuracy. The most important parameter is high positioning repeatability, or low positioning noise. I need the repeatability below a few arc sec but the system has to be of small size and low cost so I can not use precision positioning stages. I tried a stepper with precision planetary gear and the positioning noise was terrible. I'm now thinking of using a stepper motor with small step angle (0.8 deg) in a microstepping mode (around 100 microsteps per step) and replacing the bearings with some high grade low friction ball bearings. Finding a stepper is not a problem, there is plenty of them available (e.g. NEMA 14 0.8deg steppers) but I need an advice on the bearings. I guess I need a bearing with the lowest friction and the highest friction evenness and repeatability. Basically, the positioning noise of the mechanism is proportional to (motor torque) / (friction noise). There are so many bearing options: ABEC classes from 1 to 9, types of steel, ceramic or steel balls, types of oil, cage types and cage materials (metal, nylon, Teflon). I guess the higher the ABEC class the lower the friction and positioning noise but what are the other right options to get the lowest friction and friction noise?
Are there any other types of bearings with even lower friction than ball bearings? Any magnetic or other types of bearings? I know about the air bearings (those are used in Michelson interferometers) but they need a pump and make the system expensive and bulky so it's not an option for me.
Thanks!
I'm designing a simple precision rotational mechanism for angular positioning of an optical element. I need a total rotation travel angle of about 50 deg at a low speed (a few seconds for the full travel) with about 4000 discrete positions over the travel angle. Any systematic positioning errors can be calibrated so I don't necessarily need an ultra-high positioning absolute accuracy. The most important parameter is high positioning repeatability, or low positioning noise. I need the repeatability below a few arc sec but the system has to be of small size and low cost so I can not use precision positioning stages. I tried a stepper with precision planetary gear and the positioning noise was terrible. I'm now thinking of using a stepper motor with small step angle (0.8 deg) in a microstepping mode (around 100 microsteps per step) and replacing the bearings with some high grade low friction ball bearings. Finding a stepper is not a problem, there is plenty of them available (e.g. NEMA 14 0.8deg steppers) but I need an advice on the bearings. I guess I need a bearing with the lowest friction and the highest friction evenness and repeatability. Basically, the positioning noise of the mechanism is proportional to (motor torque) / (friction noise). There are so many bearing options: ABEC classes from 1 to 9, types of steel, ceramic or steel balls, types of oil, cage types and cage materials (metal, nylon, Teflon). I guess the higher the ABEC class the lower the friction and positioning noise but what are the other right options to get the lowest friction and friction noise?
Are there any other types of bearings with even lower friction than ball bearings? Any magnetic or other types of bearings? I know about the air bearings (those are used in Michelson interferometers) but they need a pump and make the system expensive and bulky so it's not an option for me.
Thanks!
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