4. POWER TRANSMISSIONSYSTEMS

DESIGN AND APPLICATIONS OF INDUSTRIAL ROBOTSSABARIGIRIVASAN.RISBN 978-81-908268-0-8

4. POWER TRANSMISSIONSYSTEMS

DESIGN AND APPLICATIONS OF INDUSTRIAL ROBOTSSABARIGIRIVASAN.RISBN 978-81-908268-0-8

Power Transmission Systems1. Power transmission systems are used to

transmit motion from the prime mover to the end equipment.

2. They are also used for motion conversion like rotary to linear and vice versa.

3. Power transmission systems widely used in robotics are

a) Gearsb) Beltsc) Chainsd) Shafts

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Gears1. Gears are devices that have teeth cut on them

at regular intervals for transmitting motion without slipping.

2. Gears are used for transmitting motion when distance between two shafts are small.

3. Gears have higher transmission efficiency and higher load carrying capacity.

4. Cast iron and high strength alloy steels are used for making gears. Nylon is also used.

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Classification of Gears1. Based on arrangement of teeth for engaging

with another geara) External gearsb) Internal gears

2. Based on teeth designa) Spur gearsb) Helical gearsc) Bevel gearsd) Worm gearse) Racks

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External Gear

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Animation

Internal Gear

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Animation

Spur GearSpur Gear

D E S I G N A N D A P P L I C A T I O N S O F I N D U S T R I A L R O B O T SS A B A R I G I R I V A S A N . R

Straight teeth

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Helical GearHelical Gear

D E S I G N A N D A P P L I C A T I O N S O F I N D U S T R I A L R O B O T SS A B A R I G I R I V A S A N . R

Inclined teeth

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Bevel Gear

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Types of Bevel Gear

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Worm Gear

Animation11

Rack and Pinion

Animation12

Belts1. Belts are used when distance between two

shafts are very large.2. Belts run over friction pulleys mounted on

ends of both the shafts.3. Rubber belts woven with nylon fibres are

most widely used.4. Woven nylon fibres provide adequate

mechanical strength to the belt.

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Types of Belts

Different belt profiles are1. Flat belts2. V – belts3. Cog belts

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Belt Profiles

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Flat Belt Drive

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Flat Belt Drive

Animation17

Cog Belt Drive

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Cog Belt Drive

Animation19

Chains 1. Chains are metal structures made up of

many links joined serially to form a closed loop.

2. They are used for transmitting higher load over long distances without slipping.

3. Sprockets are fitted on both the shafts for engaging the chain.

4. Bush roller chain is widely used.

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Chain and Sprocket

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Structure of Roller Chain

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Shafts 1. Transmission shafts are used to transmit

motion from one end to the other.2. Solid and hollow cylindrical shafts are

widely used.3. Transmission shafts should have high

strength and high wear resistance.4. They should be capable of resisting the twist

to transmit higher torque.5. Couplings and Bearings are used to connect

and support the shafts.23

Couplings1. Couplings are used to connect two different

shafts.2. Couplings are used to connect prime mover

to the actuator and other intermediate transmission systems.

3. A coupling should transmit power without loss.

4. They should be easily assembled and disassembled.

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Types of couplingsCouplings are of two types1. Rigid coupling

a) Flange couplingb) Split muff couplingc) Sleeve coupling

2. Flexible couplinga) Universal joint couplingb) Oldham coupling

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Flange Coupling

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Universal Joint Coupling

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Universal Joint Coupling

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Universal Joint Coupling

Animation29

Universal Joint Coupling

Animation30

Oldham Coupling

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Oldham Coupling

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Oldham Coupling

Animation33

Bearings

1. Bearings are used to provide frictionless free movement to the joints in the robot.

2. Bearings are also used to support the transmission shafts.

3. They helps to reduce wear between moving parts.

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Classification of Bearings1. Based on direction of loading

a) Radial bearingsb) Thrust bearings

2. Based on contact conditiona) Sliding contact bearings

• Journal bearing

b) Rolling contact bearings• Ball bearings• Roller bearings

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Classification of Bearings Based onDirection of Loading

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Ball Bearings1. Ball bearings have hardened steel balls in

between the stationary and moving members.2. Balls are held in place by a ball cage.3. Types of Ball bearings

a) Single row radial ball bearingb) Double row radial ball bearingc) Single direction thrust bearingd) Double direction thrust bearinge) Double direction angular contact thrust bearing

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Ball Bearing

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Types of Ball Bearings

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Roller Bearings1. Roller bearings have hardened steel rollers in

between the stationary and moving members.2. Rollers are held in place by a cage.3. Types of Roller bearings

a) Cylindrical roller bearingb) Needle roller bearingc) Tapered roller bearingd) Spherical roller bearinge) Double row spherical roller bearing

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Types of Roller Bearings

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Motion Conversion1. Motion conversion is the process of

transforming the motion from the primer mover to the required form to actuate the final end equipment.

2. Types of conversiona) Rotary to rotary motion conversionb) Rotary to linear motion conversionc) Linear to rotary motion conversion

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Rotary to Rotary Motion Conversion1. Input rotary motion is converted to output

rotary motion but with different speed and torque levels.

2. Widely used conversion systemsa) Gear trainsb) Harmonic drives

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Gear Trains

1. Gear train is a series of gears connected so that each gear turns proportionally when driven by a prime mover.

2. Output speed and torque can be increased or decreased using gear trains.

3. Step up gear train increases output speed and reduces torque.

4. Reduction gear train reduces output speed and increases torque.

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Types of Gear Trains

Widely used types of gear trains are1. Simple gear train2. Compound gear train3. Planetary gear train

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Simple Gear Train

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Simple Gear Train

Gear Train

Animation49

Simple Gear Train

Gear Train

Animation50

Simple Gear Train

Simple Gear TrainNumber of teeth on gear ܶ�݃� = 21Number of teeth on pinion ܶ� = 11

Gear as Driving Wheel

Gear Ratio = ܶ�݃� / ܶ� = 21 / 11 = 1.909

So, 1 gear revolution = 1.909 pinion revolutions

Pinion as Driving Wheel

Gear Ratio = ܶ� / ܶ�݃� = 11 / 21 = 0.524

So, 1 pinion revolution = 0.524 gear revolution

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Backlash in Gears1. Backlash is the total distance of excessive play

produced at the meshing point between the teeth of two meshing gears.

2. Backlash reduces positioning accuracy.3. Backlash is eliminated by using anti backlash

gears.4. Anti backlash gears has two gears loaded by

a spring in such a way that the teeth and slot alignment of both gears are displaced.

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Harmonic Drives1. Harmonic drives use elastodynamic properties

of metals for its operation.2. It consists of three main parts namely circular

spline, flexspline and wave generator.3. They offer very high reduction ratios and have

good positioning accuracy. 4. They have extremely low backlash as the

flexspline compensates the backlash automatically.

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Harmonic Drive

Animation69

Rotary to Linear Motion Conversion1. Input rotary motion is converted into

output linear motion.2. They are used with rotary prime movers to

operate linear joints.3. Widely used conversion systems

a) Lead screw mechanismb) Rack and pinion mechanismc) Belts and chain mechanismd) Slider crank mechanisme) Cam and follower mechanism

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Lead Screw Mechanism1. It has a long screw supported by bearings on

either ends, engaged with a suitable nut.2. The nut has suitable provisions for mounting

the carriage and it is guided by guide shafts while moving.

3. When the screw is rotated the nut moves back or forth based on the direction of rotation.

4. Acme and square thread types are usually employed in lead screws.

5. Recirculating ball screws offer higher transmission efficiency.

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Lead Screw MechanismLead Screw Mechanism

Driving gear

Guide shaft

End support bearing

MotorNut with mounting flange

Guide shaftLead screw

End support bearing

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Rack and Pinion Mechanism1. The pinion is mated to a suitable rack fixed

to the system.2. The pinion is connected to the motor and

the rack provides the linear motion as output.

3. It is a two way motion conversion system. It can also be used to convert linear to rotary motion.

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Belts and Chain Mechanism1. Belt mechanism has two pulleys over which the

belt rides.2. The two ends of the belt is attached to a

carriage fixed suitably in a guide way.3. When one of the pulley is rotated the carriage

translates back or forth according to the direction of rotation.

4. To transmit higher load chain is used. Instead of pulleys sprockets are used for engaging the chain.

5. The two ends of the chain are connected to the carriage.

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Cam and Follower Mechanism1. Cam is a specialized structure that has a profile

corresponding to the path that the follower should take.

2. When the cam is moved the follower moves according to the cam profile.

3. Types of Cam and follower mechanisma) Radial camb) Linear camc) Closed track radial camd) Closed track linear came) Drum type cam

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Cam and Follower Mechanisms

Animation90

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