How to select right Turbocharger Size for your car

Turbocharger Size

Turbo selection isn’t what it used to be. Once upon a time, self-proclaimed engineers were content to build an engine that produced massive power at high rpm, but drove like a dog at anything but. However, once hot-rodders figured out that anybody could bolt a junk turbo to any engine and make power, focus shifted from top-end force to overall driveability. With a little bit of extra work, anyone with a seventh-grade education can one-up the experts of yore and pick the perfect turbo for any application.



  1. Assess your budget. Building a turbocharged engine isn’t about just bolting a giant huffer to the exhaust manifolds and calling it a day. The turbo might only cost you $500, but a good install doesn’t stop there. Turbochargers make power as a function of the engine’s original horsepower and torque, so building an engine to make more power before bolting the turbo onto it will likely yield benefits that compensating with huge boost won’t.


  1. Determine the required airflow in cubic feet of air per minute. Boost doesn’t make power, it just shoves more air through your engine. Because engines typically operate an air/fuel ratio of about 14 parts air to 1 part fuel, and because gasoline contains a certain amount of energy (about 114,000 British Thermal Units per gallon), you can make a direct correlation between airflow in cfm and horsepower. That ratio is about 150 cfm to 100 horsepower. As an example, let’s put together a 900 horsepower Chevrolet 350: For this application, you’ll need about 1,350 cfm of air.


  1. Calculate your engine’s non-turbo airflow in cfm. There are three ways to do this: You can either use an online cfm-to-horsepower calculator that takes engine displacement, efficiency and rpm into account, and you can extrapolate from the engine’s stock horsepower; or you can take the engine to a dyno room and check it. For our example engine, we’ll say that (in non-turbo form) it produces 300 horsepower at 5,500 rpm, at an 80 percent volumetric efficiency. The online calculator gives us 446 cfm airflow, and using the 150-cfm/100-horsepower ratio gives us 450 cfm.


  1. Divide your required airflow by your engine’s stock airflow to determine the required boost pressure ratio (the ratio of boost pressure to atmospheric pressure, which is about 14.7 psi). For the example engine, you arrive at a pressure ratio of exactly 3.00. Here’s a bit of trickery, though: Dividing desired horsepower by non-turbo horsepower will give you the same pressure ratio figure as going through this long-form cfm-to-horsepower-to-pressure ratio calculation. You only went this far to understand the factors that you’ll be dealing with in turbo selection from here on.


  1. Look through a manufacturer’s selection of “turbo maps.” A turbo map is a graph that indexes airflow to pressure ratio, and gives a visual representation of turbo efficiency at a given pressure ratio and cfm. You’ll see pressure ratio on the vertical axis and the airflow on the horizontal axis. A compressor map looks something like an elongated bulls-eye: the center of that bull’s eye is the compressor’s maximum efficiency range, which is where it makes boost without producing excess heat.


  1. Compare your engine’s required pressure ratio and airflow in cfm to various compressor maps and find one that puts your target airflow/pressure point in the center-to-upper-right-hand corner of the compressor’s maximum efficiency range (the center of the bulls-eye). Many times you’ll find airflow expressed in the metric “m3/s,” or meters cubed per second. To convert cfm to m3/s, multiply cfm by 0.00047. For our example engine, we’ll need to find a turbo that supplies full efficiency at a 3.00 pressure ratio at 0.6345 m3/s flow. Again, find a compressor where that point falls in the center-to-upper-right-hand corner of the turbo’s maximum efficiency range.


  1. Repeat Steps 2 through 7, using the engine’s peak torque rpm. The Chevy 350 in our example makes its peak torque at 2,000 rpm, where (according to the stock dyno graph) it makes 140 horsepower. Apply the 150-cfm/100-horsepower rule and you’ll find that this engine uses 210 cfm at that rpm. Multiply that airflow by the required pressure ratio (3.00) and you have your low-end boost response requirement. In addition to producing a 3.00 pressure ratio at 1,350 cfm (0.6345 m3/s), it should produce that same 3.00 PR at 630 cfm (0.2961).


  1. Search and search some more until you find a turbo that’s completely spooled up (producing a 3.00 PR, in this case) at your torque-peak airflow and maintains that PR through the engine’s horsepower-peak airflow. You’ll often find that, for larger engines like our 350, such turbos do not exist. No turbo out there will provide those PR and flow numbers over such a wide spectrum of airflow.


  1. Re-calculate for a multiple-turbo setup. If you can’t find a turbo to fit, divide your airflow figures by the number of turbos you want to use. Two turbos flow twice as much air as one, and smaller turbos have a wider efficiency range relative to absolute airflow than smaller ones. So, for our example 350, divide 1,350 cfm (0.6345 m3/s) and 630 cfm (0.2961) by two; now you need a pair of turbos that will provide a 3.00 PR at 675 cfm (0.3172 m3/s) to 315 cfm (0.1480 m3/s). That’s a spread of only 360 cfm for the little twin-turbo setup, versus 720 cfm for the single, big turbo setup — a much more achievable goal for any compressor.


  • If you got all disappointed when you got to Step 7 and found out that you’d have to do everything over again, then find a turbo that fit both requirements, then don’t feel bad. Some of the biggest names in the business don’t bother calculating the airflow spread from peak torque to peak horsepower. However, this little oversight just isn’t cool for modern turbo-engine builders. The modern turbo engineer understands that quality turbo selection is about performance throughout the engine’s entire operating range, not just at peak horsepower. Turbo lag is so 1980s.


  • When you do turbocharge your vehicle, make sure to support it with other modifications, as the turbo will probably make other parts of your car break.
  • It would be a good idea to install forged pistons, increase injector capacity, a higher flowing fuel pump, a new exhaust system, head studs, and forged connecting rods.
  • Installing a turbocharger yourself, and making it live, is a very difficult and in depth project. If you’re a beginning mechanic, it is not recommended that you try this unless you have someone experienced helping you.
  • The increased power of your vehicle can also make other parts of your car break. It could snap your axles, bend your drive shaft, break the rear end in a RWD car, and even bend your car from the increased torque. Be sure to upgrade the other parts of your car at the same time as you install the turbocharger, or else you could end up with a powerful car sitting in the driveway because there’s no way to put the power down.


Differences Between Rotary & Reciprocating Compressors

Rotary and reciprocating compressors are both components of gas transfer systems. They both have the same purpose–to bring a gas into the system, inhale exhaust, then repeat the process. They both do this by changing the pressure at certain points in order to force gas in and exhaust out.


One key difference is that reciprocating compressors use pistons while rotary compressors do not. A reciprocating compressor has a piston move downwards, reducing pressure in its cylinder by creating a vacuum. This difference in pressure forces the cylinder door to open and bring gas in. When the cylinder goes back up, it increases pressure, thus forcing the gas back out. The up-and-down motion is called a reciprocating motion, hence the name.


Rotary compressors, on the other hand, use rollers. They sit slightly off-center in a shaft, with one side always touching the wall. As they move at high speeds, they accomplish the same goal as the reciprocating compressors–one part of the shaft is always at a different pressure than the other, so gas can come in at the low pressure point and exit at the high pressure point.

Advantages and Disadvantages

Reciprocating compressors are marginally more efficient than rotary compressors, generally being able to compress the same amount of gas with between 5 and 10 percent less energy input. However, since this difference is so marginal, most small-to-medium level users are best off using a rotary compressor. Reciprocating compressors are more expensive and require more maintenance, so it is often not worth the extra cost and headache for such a small difference in efficiency.

Large users, however, are generally best-served by reciprocating compressors. These are users for whom 5 percent represents a substantial figure, often substantial enough to justify the added expense.

Comparison Between Reciprocating and Rotary Compressors

Comparison between Reciprocating and Rotary Compressors can be done in aspects like pressure ratio, handled volume, speed of compressor, vibrational problem, size, air supply, purity of compressed air, compression efficiency, maintenance, mechanical efficiency, lubrication, initial cost, flexibility and suitability.
Reciprocating Compressors
Rotary Compressors
1 Pressure Ratio Discharge Pressure of air is high. The pressure ratio per stage will be in the order of 4 to 7. Discharge pressure of air is low. The pressure ratio per stage will be in the order of 3 to 5.
2 Handled Volume Quantity of air handled is low and is limited to 50m3/s. Large measure of air handled can be handled and it is about 500 m3/s.
3 Speed of Compressor Low speed of compressor. High speed of compressor.
4 Vibrational Problem Due to reciprocating section, greater vibrational problem, the parts of machine are poorly balanced. Rotary parts of machine, thus it has less vibrational problems. The machine parts are fairly balanced.
5 Size of compressor Size of Compressor is bulky for given discharge volume. Compressor size is small for given discharge volume.
6 Air supply Air supply is intermittent. Air supply is steady and continuous..
7 Purity of compressed air Air delivered from the compressor is dirty, since it comes in contact with lubricating oil and cylinder surface. Air delivered from the compressor is clean and free from dirt.
8 Compressed efficiency Higher with pressure ratio more than 2. Higher with compression ratio less than 2.
9 Maintanence Higher due to reciprocating engine. Lower due to less sliding parts..
10 Mechanical Efficiency Lower due to several sliding parts.. Higher due to less sliding parts.
11 Lubrication Complicated lubrication system. Simple lubrication system.
12 Initial cost Higher. Lower.
13 Flexibility Greater flexibility in capacity and pressure range. No flexibility in capacity and pressure range.
14 Suitability For medium and high pressure ratio.
For low and medium gas volume.
For low and medium pressures.
For large volumes.

Some Everyday Examples of the First & Second Laws of Thermodynamics

The laws of thermodynamics dictate energy behavior, for example, how and why heat, which is a form of energy, transfers between different objects. The first law of thermodynamics is the law of conservation of energy and matter. In essence, energy can neither be created nor destroyed; it can however be transformed from one form to another. The second law states that isolated systems gravitate towards thermodynamic equilibrium, also known as a state of maximum entropy, or disorder; it also states that heat energy will flow from an area of low temperature to an area of high temperature. These laws are observed regularly every day.


Melting Ice Cube

Every day, ice needs to be maintained at a temperature below the freezing point of water to remain solid. On hot summer days, however, people often take out a tray of ice to cool beverages. In the process, they witness the first and second laws of thermodynamics. For example, someone might put an ice cube into a glass of warm lemonade and then forget to drink the beverage. An hour or two later, they will notice that the ice has melted but the temperature of the lemonade has cooled. This is because the total amount of heat in the system has remained the same, but has just gravitated towards equilibrium, where both the former ice cube (now water) and the lemonade are the same temperature. This is, of course, not a completely closed system. The lemonade will eventually become warm again, as heat from the environment is transferred to the glass and its contents.


Sweating in a Crowded Room

The human body obeys the laws of thermodynamics. Consider the experience of being in a small crowded room with lots of other people. In all likelihood, you’ll start to feel very warm and will start sweating. This is the process your body uses to cool itself off. Heat from your body is transferred to the sweat. As the sweat absorbs more and more heat, it evaporates from your body, becoming more disordered and transferring heat to the air, which heats up the air temperature of the room. Many sweating people in a crowded room, “closed system,” will quickly heat things up. This is both the first and second laws of thermodynamics in action: No heat is lost; it is merely transferred, and approaches equilibrium with maximum entropy.


Taking a Bath

Consider a situation where a person takes a very long bath. Immediately during and after filling up the bathtub, the water is very hot — as high as 120 degrees Fahrenheit. The person will then turn off the water and submerge his body into it. Initially, the water feels comfortably warm, because the water’s temperature is higher than the person’s body temperature. After some time, however, some heat from the water will have transferred to the individual, and the two temperatures will meet. After a bit more time has passed, because this is not a closed system, the bath water will cool as heat is lost to the atmosphere. The person will cool as well, but not as much, since his internal homeostatic mechanisms help keep his temperature adequately elevated.


Flipping a Light Switch

We rely on electricity to turn on our lights. Electricity is a form of energy; it is, however, a secondary source. A primary source of energy must be converted into electricity before we can flip on the lights. For example, water energy can be harnessed by building a dam to hold back the water of a large lake. If we slowly release water through a small opening in the dam, we can use the driving pressure of the water to turn a turbine. The work of the turbine can be used to generate electricity with the help of a generator. The electricity is sent to our homes via power lines. The electricity was not created out of nothing; it is the result of transforming water energy from the lake into another energy form.

Basic terms for Mechanical Engineering

Basic terms for Mechanical Engineering

List of basic terms for Mechanical Engineering

1. Torque or Turning Force
2. Couple
3. Moment
4. Stress
5. Strain
6. Spring
7. Specific Weight
8. Specific Volume
9. Specific Gravity
10. Specific Heat
11. Viscosity
12. Buoyancy
13. Discharge of Fluid
14. Bernoulli’s Equation
15. Device for Fluid
16. Mach Number
17. Hydraulic Machine
18. Draft Tube
19. Thermodynamics Laws

  •  zeroth law
  • First law
  • second law

20. Entropy
21. calorific value of fuel
22. Boiler/Steam Generator
23. Superheater
24. Air Preheater
25. Boiler Draught
26. Nozzle
27. Scavenging
28. Supercharging
29. Turbocharging
30. Governor
31. Flywheel
32. Rating of fuel-
S.I. engine
C.I. engine
33. Stoichiometric Mixture/ Stoichiometric Ratio
34. Heat Transfer
35. Thermal Conductivity
36. Heat Exchanger
37. Refrigeration
38. 1 tonne Refrigeration
39. Humidification
40. Dehumidification
41. Gear Train
42. Gyroscopic Couple
43. Heat Treatment
44. Ferrous-Metal
45. Non-ferrous metal
46. Allowance
47. Tolerance
48. Clearance
49. Stiffness
50. Toughness
51. Fatigue
52. Nuclear Fission
53. Nuclear Fussion
54. Welding
55. Machine Tool
56. Cutting Tool
57. Indexing
58. Jig
59. Fixture


Torque or Turning Force:
It is the total amount of force which is required to create acceleration on moving substance.

Two forces those acts on equally,parallely & oppositely on two separate points of same material.

It is the amount of moving effect which is gained for action of turning force.

It is the force that can prevent equal & opposite force. That means, it is the preventing force. If one force acts on outside of a material, then a reactive force automatically acts to protest that force. The amount of reactive force per unit area is called stress. e.g. Tensile Stress, Compressive Stress, Thermal Stress.

If a force acts on a substance, then in that case if the substance would deform. Then the amount of deformation per unit length of that substance is called strain.

It is one type of device which is being distorted under certain amount of load & also can also go to its original face after the removal of that load.

Its function:

  • To store energy.
  • To absorb energy.
  • To control motion of two elements.

Load per unit deflection. The amount of load required to resist the deflection.

Specific Weight:
Weight per unit volume of the fluid.

Specific Volume:
Volume per unit mass of the fluid.

Specific Gravity:
It is the ratio of specific weight of required substance to specific weight of pure water at 4 degree centigrade temperature.

Specific heat:
The amount of heat required to increase 1 unit temperature of 1 unit mass.

Dynamic Viscosity:
The amount of resistance of one layer of fluid over other layer of fluid.

Kinematic Viscosity:
It is the ratio of dynamic viscosity to density.

When a body is immersed in a liquid, it is lifted up by a force equal to weight of liquid displaced by the body. The tendency of liquid to lift up an immersed body is buoyancy. The upward thrust of liquid to lift up the body is called buoyancy force.

Bernoulli’s Equation:
P/γ +V²/2g +Z = Constant

Where, P = pressure,V = velocity,Z = Datumn Head

Devices for fluid:

It measures discharge of fluid.
Notches :
It measures discharge of fluid.
Orifice meter:
It measures discharge of fluid.
Pitot tube :
It measures velocity of fluid.

Mach Number:
It is the ratio of the velocity of fluid to the velocity of sound.
M=1 —————– Sonic flow
M> (1-6) ———– Super-Sonic flow
M>6 —————- Hyper-Sonic flow

Fluid discharge/Fluid flow:
Quantity of fluid flowing per second.

(through a section of pipe/ through a section of channel)


where, V= velocity of fluid,A= cross-sectional area of pipe/channel
Note: 1m³ = 1000 L1 cusec = 1 ft³/sec1 ft = 0.3048 m

Hydraulic Machine:
Turbine,Pump,Compressor etc.

Draft tube:
It attaches with reaction turbine . Its function is to reduce energy loss from reaction turbine & it also reduce pressure at outlet which is must blow the atmospheric pressure.

Thermodynamics Laws:
Zeroth Law:
If two body are in thermal equilibrium with a third body then these two body are also in thermal equilibrium with each other.

First Law of Thermodynamics:
In a closed system, work deliver to the surrounding is directly proportonal to the heat taken from the surrounding.And also, In a closed system, work done on a system is directly proportonal to the heat deliver to the surrounding.

Second Law of Thermodynamics:
It is impossible to make a system or an engine which can change 100 percent input energy to 100 percent output.

It is a thermodynamic property.

ds = dq/T

where, ds = change of entropy, dq = change of heat, T = Temperature.

In adiabatic process, entropy can not change. Actually,lacking or mal-adroitness of tranfering energy of a system is entropy.

Calorific Value of fuel:
It us the total amount of heat obtained from burning 1 kg solid or liquid fuel.

Boiler/Steam Generator:
It is a clossed vessel which is made of steel. Its function is to transfer heat to water to generate steam.

It is a part of boiler. Its function is to heat feed water which is supplied to boiler.

It is a part of boiler. Its function is to increase temperature of steam into boiler.

It is a part of boiler. Its funtion is to preheats the air to be supplied to furnace and it recover heat from exhaust gas.

Boiler Draught:
It is an important term for boiler. It is the difference of pressure above and below the fire grate. This pressure difference have to maintain very carefully inside the boiler. It actually maintains the rate of steam generation. This depends on rate of fuel burning. Inside the boiler rate of fuel burning is maintained with rate of entry fresh air. If proper amount of fresh air never entered into the boiler, then proper amount of fuel inside the boiler never be burnt. So, proper fresh air enters into the boiler only by maintaining boiler draught.

Nozzle is a duct of varying cros-sectional area. Actually, it is a passage of varying cross-sectional area. It converts steam’s heat energy into mechanical energy. It is one type of pipe or tube that carrying liquid or gas.

It is the process of removing burnt gas from combustion chamber of engine cylinder.

Actually, power output of engine depends on what amount of air enter into the engine through intake manifold. Amount of entry air if increased, then must be engine speed will increased. Amount of air will be increased by increasing inlet air density. The process of increasing inlet air density is supercharging. The device which is used for supercharging is called supercharger. Supercharger is driven by a belt from engine crankshaft. It is installed in intake system.

Turbocharging is similar to the supercharging. But in that case turbocharger is installed in exhaust system whereas supercharger is installed in intake system. Turbocharger is driven by force of exhaust gas. Generally, turbocharger is used for 2-stroke engine by utilizing exhaust energy of the engine, it recovers energy otherwise which would go waste.

Its function id to regulate mean speed of engine when there are variation in the load. If load incrases on the engine, then engine’s speed must decrease. In that case supply of working fluid have to increase. In the otherway, if load decrease on the engine, then engine’ speed must increase. In that case supply of working fluid have to decrease.Governor automatcally, controls the supply of working fluid to the engine with varying load condition.

It is the one of the main parts of the I.C. engine. Its main function id to store energy in the time of working stroke or expansion stroke. And, it releasesenergy to the crankshaft in the time of suction stroke, compression stroke & exhaust stroke. Because, engine has only one power producing stroke.

Rating of fuel:
S.I. Engine:
Octane number. Octane number indicates ability of fuel to resist knock.

C.I. Engine:
Cetane Number. Cetane number indicates ability of ignition of diesel fuel. That means, how much fast ignites diesel fuel.

Stoichiometric ratio:
It is the chemically correct air-fuel ratio by volume. By which theoretically sufficient oxygen will be gotten to burn all combustible elements in fuel completely.

Heat Transfer:
It is a science which deals with energy transfer between material bodies as a result of temperature difference.There are three way to heat transfer such as-ConductionConvectionRadiation

Thermal Conductivity:
It is the quantity of heat flows between two parts of solid material by conduction. In this case following consideration will be important fact-

  • Time—— 1 sec
  • Area of that solid material——– 1 m²
  • Thickness of that solid material—— 1m
  • Temperature difference between two parts of that material—— 1k

Heat Exchanger:
It is one type of device which can transfer heat from one fluid to another fluid. Example- Radiator, inter-cooler, preheater, condenser, boiler etc.

It is the process of removing heat from a substance. Actually, extraction of heat from a body whose temperature is already below the temperature of its surroundings.

1 tonne of refrigeration:
It is amount of refrigeration effect or cooling effect which is produced by uniform melting of 1 tonne ice in 24 hours from or at 0 degree centigrade or freezing 1 tonne water in 24 hours from or at 0 degree centigrade.

It is the addition of moisture to the air without change dry bulb temperatur.

It is the removal of moisture from the air without change dry bulb temperature.

Gear Train:
Meshing of two or more gear. It can transmit power from one shaft to another shaft.

Heat Treatment:
Operation involving heating and cooling of a metal in solid state for obtaining desirable condition without being changed chemical composition.Its object-increase hardness of metal.increase quality of metal ( heat, corrosion,wear resistance quality )improve machinability.

Ferrous Metal:
1. Cast Iron – (2-6.67)%C, Si, Mn, P, S

2. Steel – (0-2)%C

3. Wrought Iron – 99.5% Fe

Non-Ferrous Metal:
1. Brass – (Cu+Zn)

2. Bronze –

(Sn+Cu) —— Tin Bronze

(Si+Cu) ——- Silicon Bronze

(Al+Cu) ——- Aluminium Bronze

It is the difference between basic dimension of mating parts. That means, minimum clearance between mating parts that can be allowed.

It is the difference between upper limit of dimension. It is also the permissible variation above and below the basic size. That means maximum permissible variation in dimensions.

It is the difference in size between mating parts. That means, in that case the outside dimension of the shaft is less than internal dimension of the hole.

It is the ability to resist deformation.

It is the property to resist fracture.

When a material is subjected to repeated stress below yield point stress, such type of failure is fatigue failure.

Nuclear Fission:
It is a nuclear reaction by which one big nucleous divided into two or more nucleous.

Nuclear Fusion:
It is also a nuclear reaction by which one big nucleus will produced by adding two small nucleus.

It is the process of joining two similar or dissimilar metal by fusion.

Arc Welding –

* need D.C current

* produced (6000-7000) Degree Centegrade Temperature

Gas Welding –

* Oxy – acetylene flame join metals

* Oxygen & acetylene gas works

* produced 3200 Degree Centegrade Temperature

Machine Tool:
It is the power driven tool. It cut & form all kinds of metal parts.

Example – 1. Lathe  2. Drill Press 3. Shaper 4. Planer 5. Grinding  6. Miling  7. Broaching 8. Boring

Cutting Tool:

Tool Materials for Cutting Tool:
1. High Carbon Steel

2. High Speed Steel (W+Cr+V)

3. Carbide (W Carbide+Ti Carbide+Co Carbide)


It is the method of dividing periphery of job into equal number of division. Actually, it is the process of dividing circular or other shape of workpiece into equal space, division or angle.

It is one type of device which hold & locate workpiece and also guide & control cutting tool. It uses in drilling, reaming and tapping.

It is one type of device which hold and locate workpiece. It uses in miling, grinding, planning & turning.

Introduction to Robotics

Introduction to Robotics

Robotics is a relatively young field of modern technology that crosses traditional engineering boundaries. Understanding the complexity of robots and their applications requires knowledge of electrical engineering, mechanical engineering, systems and industrial engineering, computer science, economics, and mathematics. New disciplines of engineering, such as manufacturing engineering, applications engineering, and knowledge engineering have emerged to deal with the complexity of the field of robotics and factory automation.

 The term robot was first introduced into our vocabulary by the Czech playwright Karel Capek in his 1920 play Rossum’s Universal Robots, the word robota being the Czech word for work. Since then the term has been applied to a great variety of mechanical devices, such as teleoperators, underwater vehicles, autonomous land rovers, etc. Virtually anything that operates with some degree of autonomy, usually under computer control, has at some point been called a robot. In this text the term robot will mean a computer controlled industrial manipulator of the type shown in Figure 1.1.


This type of robot is essentially a mechanical arm operating under computer control. Such devices, though far from the robots of science fiction, are nevertheless extremely complex electro-mechanical systems whose analytical description requires advanced methods, presenting many challenging and interesting research problems.

An official definition of such a robot comes from the Robot Institute of America (RIA): A robot is a reprogrammable multifunctional manipulator designed to move material, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks.

The key element in the above definition is the reprogrammability of robots. It is the computer brain that gives the robot its utility and adaptability. The so-called robotics revolution is, in fact, part of the larger computer revolution.

Even this restricted version of a robot has several features that make it attractive in an industrial environment. Among the advantages often cited in favor of the introduction of robots are decreased labor costs, increased precision and productivity, increased flexibility compared with specialized machines, and more humane working conditions as dull, repetitive, or hazardous jobs are performed by robots.

The robot, as we have defined it, was born out of the marriage of two earlier technologies: teleoperators and numerically controlled milling machines. Teleoperators, or master-slave devices, were developed during the second world war to handle radioactive materials. Computer numerical control (CNC) was developed because of the high precision required in the machining of certain items, such as components of high performance aircraft. The first robots essentially combined the mechanical linkages of the teleoperator with the autonomy and programmability of CNC machines.

The first successful applications of robot manipulators generally involved some sort of material transfer, such as injection molding or stamping, where the robot merely attends a press to unload and either transfer or stack the finished parts. These first robots could be programmed to execute a sequence of movements, such as moving to a location A, closing a gripper, moving to a location B, etc., but had no external sensor capability. More complex applications, such as welding, grinding, deburring, and assembly require not only more complex motion but also some form of external sensing such as vision, tactile, or force-sensing, due to the increased interaction of the robot with its environment.

It should be pointed out that the important applications of robots are by no means limited to those industrial jobs where the robot is directly replacing a human worker. There are many other applications of robotics in areas where the use of humans is impractical or undesirable. Among these are undersea and planetary exploration, satellite retrieval and repair, the defusing of explosive devices, and work in radioactive environments. Finally, prostheses, such as artificial limbs, are themselves robotic devices requiring methods of analysis and design similar to those of industrial manipulators.

Classification of Robotic Manipulators

Robot manipulators can be classified by several criteria, such as their power source, or way in which the joints are actuated, their geometry, or kinematic structure, their intended application area, or their method of control. Such classification is useful primarily in order to determine which robot is right for a given task. For example, a hydraulic robot would not be suitable for food handling or clean room applications. We explain this in more detail below.

Power Source. Typically, robots are either electrically, hydraulically, or pneumatically powered. Hydraulic actuators are unrivaled in their speed of response and torque producing capability. Therefore, hydraulic robots are used primarily for lifting heavy loads. The drawbacks of hydraulic robots are that they tend to leak hydraulic fluid, require much more peripheral equipment (such as pumps, which require more maintenance), and they are noisy. Robots driven by DC- or AC-servo motors are increasingly popular since they are cheaper, cleaner and quieter. Pneumatic robots are inexpensive and simple but cannot be controlled precisely. As a result, pneumatic robots are limited in their range of applications and popularity.

Application Area. Robots are often classified by application into assembly and non-assembly robots. Assembly robots tend to be small, electrically driven and either revolute or SCARA (described below) in design. The main non-assembly application areas to date have been in welding, spray painting, material handling, and machine loading and unloading.

Method of Control. Robots are classified by control method into servo and non-servo robots. The earliest robots were non-servo robots. These robots are essentially open-loop devices whose movement is limited to predetermined mechanical stops, and they are useful primarily for materials transfer. In fact, according to the definition given previously, fixed stop robots hardly qualify as robots. Servo robots use closed-loop computer control to determine their motion and are thus capable of being truly multifunctional, reprogrammable devices.

Servo controlled robots are further classified according to the method that the controller uses to guide the end-effector. The simplest type of robot in this class is the point-to-point robot. A point-to-point robot can be taught a discrete set of points but there is no control on the path of the end-effector in between taught points. Such robots are usually taught a series of points with a teach pendant. The points are then stored and played back. Point-to-point robots are severely limited in their range of applications. In continuous path robots, on the other hand, the entire path of the end-effector can be controlled. For example, the robot end-effector can be taught to follow a straight line between two points or even to follow a contour such as a welding seam. In addition, the velocity and/or acceleration of the end-effector can often be controlled. These are the most advanced robots and require the most sophisticated computer controllers and software development.

Geometry. Most industrial manipulators at the present time have six or fewer degrees-of-freedom. These manipulators are usually classified kinematically on the basis of the first three joints of the arm, with the wrist being described separately. The majority of these manipulators fall into one of five geometric types: articulated (RRR), spherical (RRP), SCARA (RRP), cylindrical (RPP), or Cartesian (PPP)

Each of these five manipulator arms are serial link robots. A sixth distinct class of manipulators consists of the so-called parallel robot. In a parallel manipulator the links are arranged in a closed rather than open kinematic chain. 

Robotic Systems

A robot manipulator should be viewed as more than just a series of mechanical linkages. The mechanical arm is just one component in an overall Robotic System, illustrated in Figure 1.3, which consists of the arm, external power source, end-of-arm tooling, external and internal sensors, computer interface, and control computer.


 Even the programmed software should be considered as an integral part of the overall system, since the manner in which the robot is programmed and controlled can have a major impact on its performance and subsequent range of applications.

Accuracy and Repeatability

The accuracy of a manipulator is a measure of how close the manipulator can come to a given point within its workspace. Repeatability is a measure of how close a manipulator can return to a previously taught point. The primary method of sensing positioning errors in most cases is with position encoders located at the joints, either on the shaft of the motor that actuates the joint or on the joint itself. There is typically no direct measurement of the end-effector position and orientation. One must rely on the assumed geometry of the manipulator and its rigidity to infer (i.e., to calculate) the end-effector position from the measured joint positions. Accuracy is affected therefore by computational errors, machining accuracy in the construction of the manipulator, flexibility effects such as the bending of the links under gravitational and other loads, ear backlash, and a host of other static and dynamic effects. It is primarily for this reason that robots are designed with extremely high rigidity. Without high rigidity, accuracy can only be improved by some sort of direct sensing of the end-effector position, such as with vision.

Once a point is taught to the manipulator, however, say with a teach pendant, the above effects are taken into account and the proper encoder values necessary to return to the given point are stored by the controlling computer. Repeatability therefore is affected primarily by the controller resolution. Controller resolution means the smallest increment of motion that the controller can sense. The resolution is computed as the total distance traveled by the tip divided by 2n, where n is the number of bits of encoder accuracy. In this context, linear axes, that is, prismatic joints, typically have higher resolution than revolute joints, since the straight-line distance traversed by the tip of a linear axis between two points is less than the corresponding arc length traced by the tip of a rotational link.

In addition, rotational axes usually result in a large amount of kinematic and dynamic coupling among the links with a resultant accumulation of errors and a more difficult control problem. One may wonder then what the advantages of revolute joints are in manipulator design.

The answer lies primarily in the increased dexterity and compactness of revolute joint designs. For example, Figure 1.4 shows that for the same range of motion, a rotational link can be made much smaller than a link with linear motion. Thus, manipulators made from revolute joints occupy a smaller working volume than manipulators with linear axes. This increases the ability of the manipulator to work in the same space with other robots, machines, and people. At the same time revolute joint manipulators are better able to maneuver around obstacles and have a wider range of possible applications.


Wrists and End-Effectors

The joints in the kinematic chain between the arm and end effector are referred to as the wrist. The wrist joints are nearly always all revolute. It is increasingly common to design manipulators with spherical wrists, by which we mean wrists whose three joint axes intersect at a common point. The spherical wrist is represented symbolically in Figure 1.5.


The spherical wrist greatly simplifies the kinematic analysis, effectively allowing one to decouple the positioning and orientation of the end effector. Typically, therefore, the manipulator will possess three degrees-of-freedom for position, which are produced by three or more joints in the arm. The number of degrees-of-freedom for orientation will then depend on the degrees-of-freedom of the wrist. It is common to find wrists having one, two, or three degrees-of-freedom depending of the application. For example, the SCARA robot shown in Figure 1.14 has four degrees-of-freedom: three for the arm, and one for the wrist, which has only a rotation about the final z-axis.


It has been said that a robot is only as good as its hand or end-effector. The arm and wrist assemblies of a robot are used primarily for positioning the end-effector and any tool it may carry. It is the end-effector or tool that actually performs the work. The simplest type of end-effectors are grippers, which usually are capable of only two actions, opening and closing. While this is adequate for materials transfer, some parts handling, or gripping simple tools, it is not adequate for other tasks such as welding, assembly, grinding, etc. A great deal of research is therefore devoted to the design of special purpose end-effectors as well as to tools that can be rapidly changed as the task dictates. There is also much research on the development of anthropomorphic hands. Such hands have been developed both for prosthetic use and for use in manufacturing. 


Subscribe and receive the following...

  • Blog and News updates
  • Forum Discussions
  • Tutorial alerts