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Week11--Lecture - Ideal Worm Gear Design and...

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Unformatted text preview: Ideal Worm Gear Design and Modelling McMaster University Engineering Design & Graphics Engineering 1C03 Dr. T. E. Doyle, P.Eng Dept. of Electrical and Computer Engineering Worm Arrangements •  Worm – Worm Gear Worm Worm Gear (rotaHonal) Worm Arrangements 2 •  Worm – Rack Gear Worm Rack Gear (linear actuator) The Worm Parameter Formula Pitch dia of gear Dgear = (z of gear * p)/PI Pitch dia or worm Dworm = 2 * center distance/ Dgear Lead of worm l = axial pitch / number of threads =px * z of worm Lead angle of worm λ tan (λ) = lead of worm / (pitch dia * PI) Notes:  ­  The axial pitch of the worm px = circular pitch of the worm gear p  ­  Lead angle of worm = helix angle of gear Worm Notes •  Worm has a screw ­like thread •  Meshes with worm gear (rotaHonal) or rack gear (linear) •  We will only consider single “threaded” worm (only 1 tooth that wraps enHre cylinder!) •  ApplicaHon is typically for non ­intersecHng sha\s at 90 degrees •  Worm drives worm ­gear/rack ­gear •  In pracHce, for a 90 degree intersecHon, the lead angle for the worm = helix angle for the gear •  For a worm, we specify the axial pitch vs circular pitch for worm ­gear (same calculaHons as spur gear) Gearing RaHo •  If the worm only has one tooth (1), what is the gear raHo with the worm gear (x)? i = x / 1 •  Speed? Is what you would expect? –  Verify this with MapleSim •  Consider the Rack pair – output speed? –  Verify this with MapleSim Examples What is output velocity of worm gear? Consider – what is rotaHonal speed And direcHon of worm, relaHve to Connected spur? We only need consider worm/worm ­gear Worm Gear Design Accelerator Remember to Generate a Report MapleSim As expected, the output speed is the inverse of the gear raHo. Worm gears are o\en used to greatly reduce angular velocity. ...
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