COMPLEX MECHANICAL FUNCTIONS CHAPTER 12: PART 4 COMPLEX MECHANICAL FUNCTIONS The role played by a set of components in transferring motion inside a technical object. A system is a set of components that share the same function. MOTION TRANSMISSION SPEED CHANGE MOTION TRANSFORMATION

MOTION TRANSMISSON A system that relays motion from one part to another without changing the nature of the motion. 1 – FRICTION GEAR SYSTEM 2 – SIMPLE GEAR SYSTEM 3 – PULLY AND BELT SYSTEM 4 – CHAIN AND SPROCKET SYSTEM 5 – WORM AND WORM GEAR SYSTEM

1 – FRICTION GEAR SYSTEM FUNCTION: transmits rotational motion between two or more nearby parts. COMPONENTS/OPERATION: has one or more wheels (without teeth) that roll together. ADVANTAGES: economical because its easy to build. not very noisy. DISADVANTAGES: wheels tend to slide one over the other, which is why the system does not always provide smooth continuous motion transmission. EXAMPLES: turntables, audio cassette players, toys

2 – SIMPLE GEAR SYSTEM FUNCTION: transmits rotational motion between two or more nearby parts. COMPONENTS/OPERATION: has two or more gears that come into contact (they mesh). ADVANTAGES: the action of the gears transmits motion constantly since the wheels do not slide. Transmits motion in tiny spaces, such as in a watchcase. Is highly effective since rotational speeds can be very high. DISADVANTAGES: production of these systems requires great precision (for the teeth) which increases costs. A lubricant may be required during use. Is noisy when in operation. EXAMPLES: Watches, manual eggbeaters, salad spinners, hand drills

3 – PULLEY AND BELT SYSTEM FUNCTION: transmits rotational motion between parts that are relatively far apart from each other. COMPONENTS/OPERATION: has belt slides on two or more wheels (referred to as pulleys). Pulleys must have smooth surface for the belt not to break. They might also have raised edges (flanges) to keep the belt in place. ADVANTAGES: does not require lubrication. Makes high-speed motion transmission possible. DISADVANTAGES: the belt can slip, reducing the effectiveness of motion transmission. The belt can break and replacement is sometimes difficult. EXAMPLES: band saw, car alternators, car fans, clothesline

4 – CHAIN AND SPROCKET SYSTEM FUNCTION: transmits rotational motion between parts that are relatively far apart. COMPONENTS/OPERATION: has two or more sprockets that do not touch, plus a chain. ADVANTAGES: the chain meshes with the wheel teeth to prevent slipping. A great force can be applied to the driving wheel to produce motion. DISADVANTAGES: Requires constant lubrication to prolong chain service life. Sprocket speeds are limited, since the chain has a tendency to derail when the mechanism spins too fast or the chain is not taut enough. EXAMPLES: bicycle cranksets, industrial machinery, motor vehicles

5 – WORM AND WORM GEAR SYSTEM FUNCTION: transmits rotational motion to non-parallel parts that are close to one another. COMPONENTS/OPERATION: has a worm and worm gear. The teeth of the worm slide into the groove of the worm gear thread. ADVANTAGES: the system does not loosen when the worm gear is released (can maintain tightness). Can be adjusted precisely. DISADVANTAGES: difficult to build. Wears out quickly. EXAMPLES: car gearboxes, stringed musical instruments, mechanisms to raise and lower basketball nets.

SPEED CHANGE There is a SPEED CHANGE in a motion transmission system when the DRIVER does not turn at the same speed as the driven mechanism. RPMs – REVOLUTIONS PER MINUTE

SPEED CHANGE cont’d FRICTION GEAR AND PULLEY AND BELT SYSTEMS Rotational speed depends on the diameter of the wheels or pulleys. Rotational speed increases when motion is transmitted from a wheel or pulley to a wheel or pulley with a smaller diameter. Rotational speed decreases when a motion is transmitted from a wheel or pulley to a wheel or pulley with a larger diameter. Rotational speed remains unchanged when motion is transmitted between two wheels or pulleys of the same diameter.

SPEED CHANGE cont’d GEAR TRAIN AND CHAIN AND SPROCKET SYSTEMS Rotational speed depends on the diameter of the gear and number of teeth Rotational speed increases when motion is transmitted from one component to another with fewer teeth. Rotational speed decreases when motion is transmitted from one component to another with more teeth. Rotational speed remains unchanged when motion is transmitted between two components with the same number of teeth

SPEED CHANGE cont’d WORM AND WORM GEAR SYSTEMS A worm and worm gear system is used primarily when a large reduction in rotational speed is called for. For every full revolution of a gear the worm gear only moves by one tooth. The greater number of teeth , the greater the decrease in speed will be

MOTION TRANSFORMATION A system that transforms the nature of a motion as it is relayed from one part to another. 1 – SLIDER-CRANK SYSTEM 2 – RACK AND PINION SYSTEM 3 – CAN AND FOLLOWER SYSTEM 4 – SCREW GEAR SYSTEM

1 – SLIDER-CRANK SYSTEM FUNCTION: transforms a rotational motion into a translational motion or vise versa. COMPONENTS/OPERATION: has a connecting rod and crank. A connecting rod is rigid and is connected by rotary links at both ends. A crank is a part of which a rotational motion can be applied. The motion of the crank is transmitted to the connecting rod, which transforms it into a translational motion, before transmitting to another part. ADVANTAGES: can function at great speeds. DISADVANTAGES: has many connecting parts and requires lubrication. EXAMPLES: gas engines, diesel engines, pumps

1 – SLIDER-CRANK SYSTEM

2 – RACK AND PINION SYSTEM FUNCTION: transforms a rotational motion into a translational motion or vise versa (with teeth). COMPONENT/OPERATION: has a straight rod with called a rack, and a gear called a pinion. Sometimes the rack’s surface is not entirely covered with teeth, so the mechanism can be blocked. The motion is transformed by the meshing of teeth. ADVANTAGES: transforms motion without slipping. DISADVANTAGES: because it involves a gear set, it requires a great deal of lubrication. EXAMPLES: steering systems, net tensioners, adjustment mechanisms for some microscopes.

2 – RACK AND PINION SYSTEM

3 - CAM AND FOLLOWER SYSTEM A.K.A. CAM FOLLOWER SYSTEM FUNCTION: transforms rotational motion into translational motion. COMPONENTS/OPERATION: an irregular shaped disk (oval or uncentered pivot) called a cam. When the cam turns, the follower makes a reciprocating translational motion: it goes up, then down. The shape of the cam controls the motion of the follower. A spring usually makes it possible for the follower to return the cam. ADVANTAGES: can configure the cam to modify the follower’s change from translational motion to another type of motion. DISADVANTAGES: has parts that wear out quickly. EXAMPLES: mechanical toys, actuators for the opening/closing of motor valves, sewing machines.

3 - CAM AND FOLLOWER SYSTEM A.K.A. CAM FOLLOWER SYSTEM

4 – SCREW GEAR SYSTEM FUNCTION: transforms rotational motion into translational motion or vise versa. COMPONENTS/OPERATION: atleast one screw and atleast one nut. In some systems, the nut is the driver and the screw transforms its rotational motion into translational motion. And, in some, its the opposite. ADVANTAGES: can expend a great deal of force. DISADVANTAGES: generates a great deal of friction. Is sometimes fragile, which can cause problems with the guide. EXAMPLES: car jacks, cable tensioners

4 – SCREW GEAR SYSTEM