POWER TRANSMISSION SYSTEMS

2 Power Transmission Systems 1.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)Gears b)Belts c)Chains d)Shafts

3 GearsGears 1.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.

4 Classification of Gears 1.Based on arrangement of teeth for engaging with another gear a)External gears b)Internal gears 2.Based on teeth design a)Spur gears b)Helical gears c)Bevel gears d)Worm gears e)Racks

External Gear Animation 5

Internal Gear Animation 6

7 SPUR GEAR  Straight teeth mounted on parallel shafts  Many used at once to create very large gear reductions  tooth profile is parallel to the axis of rotation, transmits motion between parallel shafts.

8 Helical Gear  teeth are inclined to the axis of rotation, the angle provides more gradual engagement of the teeth during meshing, transmits motion between parallel shafts.

9 Bevel Gear Gears that mesh at an angle, usually 90° Changes the direction of rotation.

10 Worm Gear Changes the direction of turning motion by 90° Decreases the speed of turning from screw to gear and increases the force

11 Rack and Pinion Converts rotary motion to back and forth motion

12 BeltsBelts 1.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.

13 Types of Belts Different belt profiles are 1.Flat belts 2.V – belts 3.Cog belts

14 ChainsChains 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.

15 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.

16 Couplings 1.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.

17 Types of couplings Couplings are of two types 1.Rigid coupling a)Flange coupling b)Split muff coupling c)Sleeve coupling 2.Flexible coupling a)Universal joint coupling b)Oldham coupling

18 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.

19 Classification of Bearings 1.Based on direction of loading a)Radial bearings b)Thrust bearings 2.Based on contact condition a)Sliding contact bearings Journal bearing a)Rolling contact bearings Ball bearings Roller bearings

20 Ball Bearings 1.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 bearing b)Double row radial ball bearing c)Single direction thrust bearing d)Double direction thrust bearing e)Double direction angular contact thrust bearing

21 Roller Bearings 1.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 bearing b)Needle roller bearing c)Tapered roller bearing d)Spherical roller bearing e)Double row spherical roller bearing

22 Motion Conversion 1.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 conversion a)Rotary to rotary motion conversion b)Rotary to linear motion conversion c)Linear to rotary motion conversion

23 Rotary to Rotary Motion Conversion 1.Input rotary motion is converted to output rotary motion but with different speed and torque levels. 2.Widely used conversion systems a)Gear trains b)Harmonic drives

24 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.

25 Types of Gear Trains Widely used types of gear trains are 1.Simple gear train 2.Compound gear train 3.Planetary gear train

26 Backlash in Gears 1.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.

27 Harmonic Drives 1.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.

28 Rotary to Linear Motion Conversion 1.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 mechanism b)Rack and pinion mechanism c)Belts and chain mechanism d)Slider crank mechanism e)Cam and follower mechanism

Lead Screw Mechanism 1.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. 71

30 Rack and Pinion Mechanism 1.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.

31 Belts and Chain Mechanism 1.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.