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MECHANISMS (2. Linear motion mechanisms (descarga (6) Levers (A lever is…

- - - - • R is the resistance or load which acts at the other end of the bar.
      - • d is the distance from F to the fulcrum
      - • F is the force or effort appbed at one end of the bar.
      - • r is the distance from R to the fulcrum
    - - Class 2
        
        The resistance is between the fulcrum and and the effort applied
      - Class 3
        
        The effort apphed is between the fulcrum and the rersistance
      - Class I
        
        The fulcrum is between the effort applied and the resistance
- - - - Cogwheels are sets of wheels that have teeth called cogs
        
        Z 1, and Z2, are the numbers of teeth.
        
        N1, and N2, are the velocities of the corresponding wheels
      - N1·Z1=N2·Z1-- Z1:Z2 = N2:N1.
    - - They consist of two pulleys or wheels that are a certain distance apart. Their axles are parallel and they rotate simultaneously due to the effect of the belt.
      - D1=10. D2=30.
    - - This is a screw that moves a helical cogwheel that is set perpendicular to the screw.
        
        Zgrooves is the number of grooves of the screw and Zwheel is the number stress of teeth of the wheel.
        
        Nwheel=Nscrew·Zgrooves:Zwheel.
        
        Nwheel , and Nscrew a re the velocities of the wheel and of the screw.
    - - Fnctton dnves are made up of two or more wheels that are in contact
        The first wheel is called the primary drive wheeL When it moves, it turns or drives the second or output wheel, causing it to move as well.
        
        D, and D, are the corresponding diameters
        They are expressed in units of length: usually millimetres
        
        N1and N2are the velocities of the primary dmve wheel and the
        output wheeL.
      - It is expressed by the followmg equation:
        N1· D1= N2 · D2-- D1 : D2 = N2: N1.
    - - N1 and N2, are the velocities of the corresponding wheels.
      - Z1and Z2, are the number of teeth.
      - N1·Z1=N2·Z2--Z1:Z2=N2:N1.
    - - This is a system of more than two gears, connected together as shown in the diagram.
      - Z1 , Z2, Z3and Z4„are the number of teeth on the wheels.
      - N4:N1=Z1·Z3:Z2·Z4.
      - N1, and N4, are the velocities of the dnve wheel and the dnven wheel.
    - - N1 and N4, are the respective velocities of the drive and driven
        pulleys.
      - D1,D2, D3 and D4, are the diameters of each wheel.
      - N4:N1=D1·D3:D2·D4.
      - Variation in velocity.
        
        Reducing system. N2>N1.
        
        Constant system. N2=N1.
        
        Multiplying system. N2<N1.
- - - - • B and brakes consist of a metal band that puts pressure on a drum attached to the axle of the oblect we want to slow down
      - • Drum brakes include one or two brake shoes that come into
        contact with the drum.
      - • Disc brakes consist of pads and a disc anached to the oblect that we want to slow down
  - - - • By traction. The spnng is stretched, in a bed frame for example.
      - • By torsion. The spnng is twisted, in a clothes peg for example
      - • By compression. The spring is compressed, in a chair for example
  - - - • In bushings the axle or the shaft is inserted in a plain circular piece that is placed inside a housing to provide a bearing surface.
      - • Bearings are made up of two concentric nngs with balls or rollers between them
- - - - This consists of a bolt or threaded bar and a nut that has the same intenor diameter as the diameter of the bolt.
    - - A crank is a bar attached to an axle that is used to turn it A winch and crank handle system consists of a drum that rotates and a crank handle that allows to pull or lift obiects
        A winch is balanced when it satisfies this equation : F·d=R·r -F=R·(( r·R):d)
        
        • F is the force applied and R, the resistance.
        
        • r is the radius of the winch and d, the length of the crank handle.
    - - This uses a pinion that is a small cogwheel, mounted on a rack that is a toothed belt or bar
        The ratio between the number of rotations of the pinion and the veloaty of the movement of the rack is expressed by this equation : L= P·Z·N
        
        • P is the distance between two consecutive teeth in millimetres
        
        • Z is the number of teeth in the pinion.
        
        • L is the veloaty of the rack's movement in millimetres per
        minute
        
        • N is the number of rotations per minute of the pinion
  - - - his is a set of connecting rods attached to a jointed axle. Each of the joints of the axle acts as a crank
    - - This is basically a rotaung object that pushes a follower as it moves
      - We can change the shape and the usable profiles — the outside edge of the piece — that are more or less pointed to produce more complex movements.
    - - This is composed of a crank and a rod called a connecting rod or link.
      - This crank-link-slider system can work in reverse — it can transform
        reciprocating motion or oscillating motion into rotary motion.
      - This device was very important in the development of steam engines.
    - - This consists of a wheel with an off centre rotation axle that doesn't coincide with the centre of its circumference
      - The distance between the centre of the
        circumference and the rotation axle is called eccentricity.