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# MOTION TRANSMISSION

If an electric motor switched ON, its shaft will start rotating which is a type of motion. Two types of systems can be employed to transmit this motion, either “Mechanical systems” or “Hydraulic systems

Mechanical transmission systems:
Several mechanical systems can be used to transmit motion according to type & shape of motion; the following are some mechanical transmission systems:

Hinged bars:

Hinged bars can be used to transmit or convert several shapes of motion, as an example, Fig.1.19 shows simple hinged bar mechanism which can be used to convert rotary motion (e.g. from an electric motor) to a linear motion (reciprocating). This mechanism is used in reciprocating compressor & pumps, internal combustion engines, etc.
Fig.1.19 Converting rotary to reciprocating motion

Gears:

Gears have several shapes with each shapes is used for certain type of motion transmission
Fig.1.20 shows a Spur gear, which is used to transmit rotary motion with the same, lower or higher rotating speed.
Fig.1.20 Spur gear

Fig.1.21 shows pair of spur gears, used to increase speed; drive gear (green) has diameter D1 & rotating speed N1, while driven gear (yellow) has diameter D2 & rotating speed N2. Gear pair speeds and diameters are proportional,

D1/D2 = N2/N1 or,
N2 = N1 x D1/D2
i.e. N2 > N1
Fig.1.21 Spur gear pair to increase speed

Fig.1.22 shows another pair of spur gears, used to reduce speed; drive gear (red) has diameter D1 & rotating speed N1, while driven gear (blue) has diameter D2 & rotating speed N2. In a similar way to previous pair,

N2 = N1 x D1/D2
i.e. N2 < N1
Fig.1.22 Spur gear pair to reduce speed

Also, spur gears can be used to transmit motion with the same speed; in this case both gears should have the same diameter.

Note that direction of rotation is changed in above mentioned spur gear pairs, i.e. if drive gear rotates clockwise, then driven gear will rotate anti-clockwise. If original direction is required, then a third gear can be added as shown in Fig.1.23, the yellow gear has similar diameter to blue gear, so the speed will remain the same (N2) but with different direction similar to red gear. This is known as simple gear train.
Fig.1.23 Simple gear train

Fig.1.23 shows “Rack” or Rack gear” which is used together with spur gear to convert rotary motion to a linear motion.

Fig.1.23 Rack gear

In addition there are different types of gears as shown below; Fig.1.24 & 1.25 shows bevel gears which are employed to transmit rotary motion perpendicularly with or without speed change. Fig.1.24 shows “straight bevel gear”, while Fig.1.25 shows “Spiral bevel gear

Fig.1.24 Straight bevel gear
CHAIRAVALLI – ITALY
Fig.1.25 Spiral bevel gear – CHAIRAVALLI – ITALY

Fig.1.26 shows “worm gear” and Fig.1.27 shows worm gear meshed with spur gear. This mesh is used to transmit rotary motion perpendicularly

Fig.1.26 Worm gear
Fig.1.27 Worm/spur gear mesh

Pulleys & belts:

This is another method of transmitting rotary motion, as shown in Fig.1.28; pulley is a grooved disc that can be connected to a shaft. As shown in Fig.1.29, drive pulley (red) is connected to a motor shaft & driven pulley (blue) is connected to a machine shaft, both pulleys are connected together by a belt.
Fig.1.28 Pulley
Fig.1.29 Two pulleys & belt

Similar to gears, pulleys can transmit motion with same, lower or higher speed.
If drive pulley has a diameter D1 & speed N1,
Driven pulley has a diameter D2 & speed N2, then
D1/D2 = N2/N1, or
N2 = N1 x D1/D2
If D1 > D2, then N2 > N1 & if D1 < D2, then N2 < N1

Cams:

Cam is a special shape disc employed to convert rotary motion to a linear motion but with special shape. Cams have endless number of shapes (profiles) that can be manufactured according to required linear motion harmony of cam touched follower. Fig.1.30 shows a type of cams called “Eccentric cam”, this cam is a cylindrical disc with center line of rotation is shifted from its geometrical center line.

Fig.1.30 Eccentric cam

Fig.1.31 explains in steps the follower positions as cam is rotating;

Position 1; starting position, cam is rotating & follower is going down
Position 2; cam turned 90 °, follower lowered down, cam continues rotating,
follower is still going down.
Position 3; cam turned another 90 °, follower again lowered down to its lowest
position, cam continues rotating, follower is start going up.
Position 4; cam turned another 90 °, follower shifted up, cam continues
Rotating, follower is still going up.
Position 5; cam returned to original position, follower reached its higher
position, cycle will be repeated.
Fig.1.31 Eccentric cam positions
Fig.1.32 Miscellaneous cams

Fig.1.32 shows some examples of different profile cams.

Hydraulic transmission systems:

Hydraulic transmission systems use liquids (e.g. oil) to transmit motion. Hydraulic motion transmission has several systems; Fig.1.33 shows one of these systems, composed of an oil pump which pumps oil through piping to a piston in cylinder, to move it linearly under oil pressure. Piston linear motion can be converted to rotary motion (if required) through hinged bar mechanism shown in Fig.1.19.
Hydraulic systems have several advantages such as; possibility of transmission even for long distances through piping, easy control through controlling of oil flow rate, pressure or direction, less noise with remote pumps, etc.
Fig.1.33 Hydraulic motion transmission