Marcus and Eva wrote: >Hi All: > I have an application for a stepper that needs to be able to lift and >lower a load repeatedly at frequent intervals for long durations using a >ballscrew. >Here's the stats: >Weight to lift...100 lb max >Pitch of screw...0.200" >Speed of lift or lower... 20" per min max >Belt reduction...1:2. >Typical motion stroke... 0.020" >Typical duration of action ...8 hours > >My question is: how do I set up the calculation to determine the size of >stepper I need assuming negligible friction in the guide rails (linear ways) >and screw (ballscrew) and allowing a decent margin of safety. >The application demands good response time and I don't want to let the >system get hot, so I'm thinking to overbuild rather than go too skimpy. > > First, you need to figure out the acceleration required. Will this be run by a motion control program, or a 555 timer or somthing? A motion control program that can ramp up the step rate at the beginning and down at the end of the move will perform much better than something that just suddenly turns on at a constant step rate.
If you assume the screw is really just a drum with a string wrapped around it, with a circumference equal to .2", you'll have the same torque as the screw. Since you spec a 2:1 belt reduction, you can assume the torque needed by the motor is half that at the screw. That diameter would be .064", for a radius of .032" and the steady state torque would be 100 Lbs * .032" = 3.2 Lb-In, or 51.2 Oz-In. With the reduction, 25.1 Oz-In would be needed. Assuming no great acceleration is required, and you won't be starting abruptly at constant velocity, something around 250 Oz-In should do fine. The stroke is .020" ? That's only 1/10th of a turn of the ballscrew! 1/5th of a turn of the motor = 40 full steps. Hmmm, not a lot of time for acceleration- constant vel-deceleration ramps. Worst case is 20 steps accelerating, 20 steps decel. So, you have to go from zero speed to 20 IPM in 20 steps, or from zero to 667 steps/second in 3 milliseconds. I'm not sure this is a good application for a stepper motor! I think maybe you should start looking at servo systems. Jon Addresses: FAQ: http://www.ktmarketing.com/faq.html FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/ Post Messages: [EMAIL PROTECTED] Subscribe: [EMAIL PROTECTED] Unsubscribe: [EMAIL PROTECTED] List owner: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Moderator: [EMAIL PROTECTED] [EMAIL PROTECTED] [EMAIL PROTECTED] [Moderators] URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO OFF Topic POSTS: General Machining If you wish to post on unlimited OT subjects goto: aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if you have trouble. http://www.metalworking.com/news_servers.html http://groups.yahoo.com/group/jobshophomeshop I consider this to be a sister site to the CCED group, as many of the same members are there, for OT subjects, that are not allowed on the CCED list. NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM. DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........ bill List Mom List Owner Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
