Coupling-Fundamentals of Design-Handout, Exercises of Fundamentals of Design

Download Coupling-Fundamentals of Design-Handout and more Exercises Fundamentals of Design in PDF only on Docsity! Couplings: Cheap & Easy Example * What about in a robot design contest where two shafts may be linearly misaligned axially, vertically and horizontally, and angularly misaligned? Sn Se a ee — How can you design a simple one-piece coupling to enable one shaft to transmit torque to the other shaft? * Can the coupling be made from plastic tube to reduce shock loads? * Would O-rings be useful to nominally center it? — Critical: Note the clearance between HA the coupling bore and both shafts! mat wt docsity.com Images removed due to copyright restrictions. Please see: http://www.jelesion.com/html/power/couplings.html http://www.jelesion.com/html/power/universal.html docsity.com ¢ Binary Link: Two nodes: * Temary Link: Three nodes: * Quatemary Link: Four nodes: ¢ Pentanary Link: Five nodes! (Can you find it?!) docsity.com 5-Bar Linkages * Compare a simple 4-bar linkage for pliers or small bolt cutters to a 5-bar linkage (5 bars, 5 joints, 2 DOF) for bolt cutters ¢ Where are the 2 degrees of freedom? bs 5 — The FRs of the pliers are for wide range of motion and modest clamping force What effect does the screw have on the pivot? — The FRs of the bolt cutters are for modest motion with extreme force ¢ A 5-bar linkage can also act like a toggle mechanism Cutting blade links Connection link ® docsity.com Gears! Gears are most often used in transmissions to convert an electric motor’s high speed and low torque to a shaft’s requirements for low speed high torque: — Speed is easy to generate, because voltage is easy to generate — Torque is difficult to generate because it requires large amounts of current Gears essentially allow positive engagement between teeth so high forces can be transmitted while still undergoing essentially rolling contact — Gears do not depend on friction and do best when friction is minimized Basic Law of Gearing: — Acommon normal (the line of action) to the tooth profiles at their point of contact must, in all positions the contacting teeth, pass through a fixed point on the line-of-centers called the pitch point — Any two curves or profiles engaging each other and satisfying the law of gearing are conjugate curves, ¢ the relative rotation speed of the gears will be constant docsity.com Gears are generally used for one of four different reasons: •To reverse the direction of rotation •To increase or decrease the speed of rotation •To move rotational motion to a different axis •To keep the rotation of two axes synchronized Most gears that you see in real life have teeth. The teeth have three advantages: 1. They prevent slippage between the gears. Therefore, axles connected by gears are always synchronized exactly with one another. 2. They make it possible to determine exact gear ratios. You just count the number of teeth in the two gears and divide. So if one gear has 60 teeth and another has 20, the gear ratio when these two gears are connected together is 3:1. 3. They make it so that slight imperfections in the actual diameter and circumference of two gears don't matter. The gear ratio is controlled by the number of teeth even if the diameters are a bit off.s are a bit off. Image removed due to copyright restrictions. Please see http://static.howstuffworks.com/gif/gearside1.gif docsity.com Images removed due to copyright restrictions. Please see: http://www.fi.edu/time/Journey/Time/Escapements/gearbevel.gif http://www.fi.edu/time/Journey/Time/Escapements/rackpinion.gif Bevel Gears Bevel gears have teeth cut on a cone instead of a cylinder blank. They are used in pairs to transmit rotary motion and torque where the bevel gear shafts are at right angles (90 degrees) to each other. Rack and Pinion A rack and pinion mechanism is used to transform rotary motion into linear motion and vice versa. A round spur gear, the pinion, meshes with a spur gear which has teeth set in a straight line, the rack. docsity.com Image removed due to copyright restrictions. Please see http://www.fi.edu/time/Journey/Time/Escapements/wormgear.gif�� Worm and Wormwheel A gear which has one tooth is called a worm. The tooth is in the form of a screw thread. A wormwheel meshes with the worm. The wormwheel is a helical gear with teeth inclined so that they can engage with the thread- like worm. The wormwheel transmits torque and rotary motion through a right angle. The worm always drives the wormwheel and never the other way round. Worm mechanisms are very quiet running. Image from Wikimedia Commons, http://commons.wikimedia.org docsity.com docsity.com ¢ Given the top output shaft speed, what is the motor shaft speed (in rom)? docsity.com http://auto.howstuffworks.com/wiper1.htm docsity.com