MECHANISM: The mechanisms are elements intended to transmit and transform forces and movements from an INPUT element (motor) to an OUTPUT element. Types of movements: Rotary Motion -this is motion in a circle. Linear Motion this is motion in a straight line. Reciprocating Motion this is motion backwards and forwards. Oscillating Motion this is motion in an arc. Types of mechanisms: TRANSMISSION THE TYPE OF INPUT MOVEMENT IS THE SAME AS THE OUTPUT TRANSFORMATION THE MECHANISM TRANSFORMS THE TYPE OF MOVEMENT Circular transmission: the input element and the output element have circular motion. They are primarily designed to vary the speed. Example: gear systems. Linear Transmission: In this case, the input element and the output element present linear motion. They aim to increase the applied force and varying the point of application of force. Example: The lever. Circular-linear transformation mechanisms: in this case the input element has a circular movement, while the output element has linear movement. Example: The rack and pinion mechanism. Circular- alternative transformation mechanisms: In this case, the input element has a circular movement, while the output element reciprocates (backwards and forwards). Example: The slider crank. 1. Transmission mechanisms: 1.1. Linear transmission: a) Lever b) Single pulley c) Movable pulley d) Pulley system 1.2. Circular transmission: a) Friction wheel b) Timing belt pulley c) Gear 2. Transformation mechanisms: 2.1.Circular-linear transformation a) Rack and pinion system b) Screw nut 2.2.Circular-alternative transformation: a) Cam b) Slider-crank c) Crankshaft d) Eccentric
1. TRANSMISSION MECHANISMS: 1.1 Linear transmission: a) Lever: a rigid bar that pivots about one point and that is used to move an object at a second point by a force applied at a third. F d = R r b) Single pulley: A pulley is a wheel on an axle or shaft that is designed to support movement and change of direction of a rope along its circumference. LAW Effort = Load F = R Applications: lifting weights (extracting water from a well, forklift,...).
c) Movable pulley: A movable pulley is a pulley that can freely move. LAW 1 1 Effort = Load F = R 2 2 d) Pulley system When one is fixed and the other mobiles we have a type I system, when half are fixed and the other half movable we have a type II system. The force "F" required to lift a load "R" where "n" is the number of moving pulleys: F = R n 2 Type I F = R 2 n Type II Applications: they are mainly used in situations where you want to move a load by reducing the effort. They are widely used in mountaineering, such as security and rescue systems. 1.2. Circular transmission: a) Friction Wheel: A device in which a wheel is so forcibly pressed against another wheel that the two will revolve together. n = number of revolutions d = diameter n1 d1 = n2 d2 V 1 SHAFTS Applications in the field of electronics and computer science: sound equipment, video, printers, etc. They are also found in dynamos of bicycles, systems of transmission (bicycle), wheels, rockers, turntables... V 2
b) Timing belt pulley: this mechanism transmit the movement of one pulley to another using a belt that connect both. The INPUT pulley is called DRIVER and the OUTPUT pulley DRIVEN. REDUCING SYSTEM: the input velocity is bigger than the output velocity. In this case the input pulley is smaller than the output pulley. n1 d1 = n2 d2 MULTIPLIER SYSTEM: the input velocity is smaller than the output velocity. In this case the input pulley is bigger than the output pulley. This mechanism is essential in automobile engines, the transmission belt. They are also used in washing machine drums, table drill, sewing machine. c) Gear: combination of cogwheels that transmits the circular motion. Rotate in opposite directions. n 1 z 1 = n 2 z 2 n = number of revolutions z = number of teeth Applications: gearbox, motor reducer, watch machine. 2. TRANSFORMATION MECHANISMS: 2.1. Circular-linear transformation a) Rack and pinion system A circular gear (the pinion) engages teeth on a linear gear bar (the rack), this mechanism convert rotational motion into linear motion. Applications: table drill, tripod, sliding door, CD player tray, etc. b) Screw nut: This mechanism consists of a screw and a nut whose purpose is to transform the circular motion into linear. PITCH NUT p = pitch n = number of turns a = p n a = screw advance SCREW
Applications: G-clamp, car Jack, compression washer tap, compas 2.2.Circular-alternative transformation: a) Cam This mechanism transforms a circular movment into an alternative linear movment, which characterictics depend on the cam shape. Applications: explosión motor, music box, loom, water distribution system Loom mechanism b) Slider-crank This mechanism is formed by a crank having a circular movement and a sliding bar which is connected with articulations at one end to the crank and on the other to a guiding system (piston) describing an alternative rectilinear movement that is reversible. Applications: sewing machine, steam machine, explosión motor
c) Crankshaft A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to convert circular motion into reciprocating motion, or vice versa. Applications: Internal combustion engine, bicycle pedal. d) Eccentric In mechanical engineering, an eccentric is a circular disk (eccentric sheave) solidly fixed to a rotating axle with its centre offset from that of the axle. It is used to convert circular motion into reciprocating linear motion, or vice versa. Applications: wiper washer, sewing machine, toys