You are here: Robotics/Chapter 1/Types of Robots

Let’s walk through a few of the most common types of robots, and then take a look at some robot applications and robotic companies.  While you may immediately think of androids or human-like robots when you think of robots, the reality is that the overwhelming majority of robots are known as manipulators.

Manipulator type robots resemble the function of a human arm. They are a series of links that extends from a fixed-base, attached together by joints, and ending in some type of device – known as the end-effector.  They are an extremely common type of industrial robot.  Which makes sense.  Often tasks have been designed originally to be done by humans – and we do almost all of our physical tasks using our arms and hands.  It is only a natural step to replace this with a robotic arm, which can do jobs that are dangerous, dirty and dull.  And they can also be most cost effective, and offer a higher level of consistency and quality. Often the end effector does not resemble a human hand.   While it may have hand-like function to grip things and transport objects and materials, often the end-effector is equipped with specialized equipment in order to perform a task.  The robot could be equipped with a device to weld car parts together, or paint, or maybe it is equipped with a cutting or grinding tool.  Regardless of the end-effector type, all robots with a fixed based, joints and sequential links are known as manipulators.  Many would be customizable for whatever the task is.  As long as a manipulator is suitable for the task, the end-effector can be pretty much whatever the application calls for, as long as it is technically feasible.  In anther section, we will get into the details of manipulator type robots.  But for now, let’s briefly discuss the history of manipulator type robots and some of the many applications and types.

George Devol, in 1954, created the first programmable robot called the Unimate.  The Unimate laid the groundwork for future robots and gave birth to the modern robotics industry.  It wasn’t until 1961 that this robot was employed by General Motors to work with die-casting machines.  Basically, it was able to lift and stack very hot metal parts that had been die-cast.  Additionally, it was equipped to weld parts on auto bodies.  It weighed roughly 4000 pounds.  Eventually, 450 Unimate robots were used in the die casting process. By 1969, GM rebuilt its plant in Lordstown, Ohio.  The level of automation by use of industrial robots was unprecedented, and the plant was able to pump out 100 cars every hour, which was nearly double that of any other plant.  The rest of the automotive companies were slow on the uptake but eventually caught on, and before too long Unimates were being shipped to Fiat, Mercedes-Benz, BMW, and Volvo, to name a few.  Later, Devol created the first robot company in 1962, which he called Unimation.  in 1978, Unimation went on to build the Puma robot.  Puma stood for Programmable Universal Machine for Assembly.  It was initially developed for General Motors.

Within the category of manipulator robots, there are two main types of robots: articulated and linear.  An articulated robot is connected by joints which allow rotational movement.  This is basically a human arm.  Your shoulder, elbow and wrist joints all allow for rotational movement.  Articulated robots are fixed at one end (the base) and a series of links connected by joints make up the arm.  Linear robots do not offer rotational movement – all movements are linear (straight).  This setup also allows the robot ‘links’ to be supported at both ends, as oppose to a articulated manipulator which is only supported at the base.  These two types of robots offer various advantageous and disadvantages.

Typically, articulated manipulators are able to handle less payloads since there is significant unsupported mass, and the robot has to hold up the weight of it’s own arm in addition to whatever payload it is handling.  If the payload is held in a fully extended position, the forces on the robot’s links can be high.  Imagine holding out a 10 pound weight with your arm fully outstretched.  It is significantly more difficult than holding in close to your body.  This is due to the torque that is generated by holding the weight out from your body, which your shoulder joint must resist.  Well, it is the same way with an articulated robot.  Since cartesian robots are supported at both ends, they can handle significantly higher payloads.  But manipulator types are becoming more popular in industry, often due to their flexibility and dexterity.  They can typically reach into tight spaces and angle their end-effectors in various orientations.  This means that while cartesian robots are typically best suited for pick-and-place operations, manipulators can do a variety of tasks – such as picking up a component and reorienting it, or perform welding on components at various orientations.  In the past, manipulator robots have typically been slower than cartesian robots, but that is less the case these days.  As motors become smaller yet more powerful and processing speeds have increased, the typical drawbacks to manipulator type robots are dwindling.

Within articulated type manipulator robots, there are many different configurations.  In the past, SCARA type robots have been widely used.  This robot (discussed below) has four axis of motion – the X, Y, Z directions, and the wrist joint has the ability to rotate (roll).  More and more manufacturers are looking to 5-axis or 6-axis type manipulators for more complex work.  These robots can move in almost any direction, giving the robot the ability to manipulate the payload in any way – more true to how a human arm works.  These articulated robots have improved dramatically in recent years, offering the speed and precision of SCARA and cartesian type robots, but with a higher degree of flexibility.

SCARA is a well known type of robot manipulator.  It stands for Selective Compliance Assembly Robot Arm.  The last three words make sense – but what is the ‘Selective Compliance’ part about?  Basically, compliance means that the robot can flex a little bit.  Just as a human arm can as well – it isn’t perfectly rigid.  Compliance can be good for certain assembly tasks.  For instance, imagine you are trying to put a round peg into a round hole.  If the robot is perfectly rigid and the peg and the hole aren’t quite lined up, then the robot will try to force the peg into the hole, possibly damaging the components or the robot itself if it does not fit properly.  However, if the robot is able to flex a little bit when inserting the peg, then it can correct for that slight misalignment and avoid damage.  It is not necessarily an intuitive concept, to have a robot flex, and it doesn’t flex a lot – just enough to overcome small misalignments during assembly operations. This compliance is due to the way the robot’s joints are laid out.  It has a parallel axis joint layout, meaning that it is rigid in the Z direction (up and down), but can flex in the X-Y plane (horizontally). This compliance is one of the main attributes of the SCARA robot; it is in the name after all.

A second important attribute is the way that the robot’s joints are laid out similar to a human arm.  They have a shoulder, elbow and wrist joint.  The shoulder and elbow joints allow for rotation about the vertical axis, meaning they move around in circles.  The wrist joint allows for vertical up and down motion.  The fact that the elbow and shoulder joint rotate around the vertical axis means that the robot can rotate easily.  However, SCARA robots usually are not able to lift heavy payloads as easy as say a cartesian robot.  This is because the joints are all located at the end of each arm, and the robot is only fixed at the base, meaning that there is significant unsupported mass.  Think of the human arm – arms are relatively long and only supported at the base – the shoulder joint, where it connects to the rest of the body.  If you arm was extremely long, it would be difficult to control and difficult to pick up lark objects.  SCARA type robots are best suited to smaller payloads.  Regardless, they are often the first choice for many applications due to their speed and reputation for ruggedness (of course this depends on the manufacturer of the robot as well).

It’s configuration means that it can easily fold up out of the way, or extend into small areas and still perform the necessary operations.  This is ideal for working in tight environments, such as a factory setting, where the use of space should be optimized.  Compared to other robot manipulators (such as the Cartesian robot system discussed below), the SCARA is faster and can perform in smaller spaces.  But, it is also typically more expensive.  This robot was developed in 1981 by Sankyo Seiki, Pental and NEC.  SCARA type robots are not built by a single company.  Rather, it is a type of robot, and many companies build many variations of SCARA (all with the same common joint architecture) to perform a variety of tasks.  For example, Epson builds a variety of SCARA type robots – small ones for extreme precision (down to 0.005mm repeatability), to bigger, heavy duty SCARAs able to handle payloads of almost 40 pounds.

Although SCARA type robots offer greater flexibility than cartesian robots, they still lack some flexibility when compared to articulated type manipulators.  SCARA has 4-axis of movement – X, Y, Z directions, and the ability for the wrist to rotate (roll).  Other articulated manipulators offer high degrees of motion – 5 or 6-axis.  Typically, SCARAs have been faster and more precise than the 5 or 6-axis robots, but this is changing and more and more manufacturers are looking to a type of robot that can offer greater flexibility and freedom of motion.

Cartesian robots are a very simple type of robot.  All of the joints are linear, which means that there is no rotation.  All three axes move in straight lines, moving back and forth.  This allows the end-effector to move anywhere in the robot’s workspace by controlling all three directions of movement.  The lack of rotational joints puts it at a severe disadvantage compared to articulated manipulators.  But since the links can be supported by two points, a cartesian robot has the capability to carry much heavier payloads.  Cartesian robots supported at both ends are usually called Gantry robots and are ideal for pick-and-place operations where heavy payloads require moving.  The other big advantage of cartesian robots is that the controls are quite easy to program.  With an articulated robot, the robot must constantly calculate how much torque to provide to each motor located in each joint, to support the end-effector and whatever payload is being held.  This will change as the robot moves, swings, extends and retracts.  The math is quite involved in the operation of a articulated manipulator.  But with a cartesian robot, it is simply a matter of telling each individual actuator how far to move back and forth, which involves fairly basic mathematics and control. But the buyer of the robot probably does not care about the math involved, as long as the articulated robot works and is relatively easy to program and operate.  So from the customer’s perspective, the complicated kinematic and dynamic calculations necessary to operate the articulated robot are the engineer’s concern.  Of course, some of the savings of building a less complicated cartesian robot are passed onto the customer – cartesian robots are often less expensive that articulated types.  A popular use currently for cartesian type robots is 3D printer.  The disadvantage of cartesian robots is they are not flexible in how they move.  They are unable to move around obstacles or reach into tight spaces.

Yamaha Robotics has a decent page where it discusses the applications (although the applications tend to be a bit boring) of some cartesian robots.  Cartesian robots can be used for applications of adhesive to parks, transferring integrated chips from a pallet to a different area, for processing sheet metal, for moving and stacking heavy objects, or for precision spot welding.  Other applications include fitting the robot with a cutting tool, or a camera to perform surface checks on parts.  You can see that the majority of these are only supported at a single base, and so are not necessarily intended to lift heavy payloads (however, they do list a single supported cartesian robot with the ability to lift heavy workpieces due to something they call ‘air balancing’).  Some of these robots only move in two axes – such as X and Z (able to move side to side along a line and then up and down).  Sometimes, speed and precision is listed.  One robot is quoted as being able to move nearly 1900mm per second – about 6 feet every second – in the X and Y directions.  Another robot is shown to have accuracy of +/- 0.05mm, which means that if you need to move it to a very precise location it would only be off by 5% of a millimetre – or 50 micrometers – less than the thickness of a sheet of paper.

We’ve already talked about some of the advantages of cartesian robots – they are simple to build, operate, relatively inexpensive and can handle large payloads.  Particularly with Gantry robots, they can be made to have high accuracy and repeatability due to the support from both ends, and their rigidity.  This makes them ideal for tasks where precision and accuracy is important.  Although, as articulated manipulators becoming more advanced, this particular advantage is being erased.

Let’s talk a bit more about Gantry Robots, which are cartesian type robots supported at both sides.  These robots can be built very large, with the ability to handle payloads of thousands of pounds.  They are also relatively inexpensive.  A disadvantage of Gantry robots when compared to articulated manipulators or cartesian robots only support at a single base is that they take up a fair amount of room, since a support frame is required.  They are not free standing.  Because of the support frame, they typically can cover much larger workspaces than articulated and single supported cartesian robots.  It is interesting to note that about 20 years ago, in the 1990s, Gantry robots were considered to be slow, inefficient and inflexible.  But with advances in motors, actuators, and other aspects of robotics, Gantry robots are looked for favourably upon.  Some of them can move extremely quickly, on par with the speed of articulated robots.  Of course, the basic design has not changed, and so they remain at a disadvantage in terms of movement and flexibility compared to articulated.  But they are ideal for pick-and-place.  And with advances in materials, like switching out steel parts for high-strength aluminum or even composite materials, Gantry robots can be made larger and faster than ever before.

The PUMA robot is another popular type of industrial robot that you should be aware of, since it holds an important place in robotics history.  It is one of the most widely used and widely imitated designs in the history of industrial robotics.  It stands for Programmable Universal Machine for Assembly, or Programmable Universal Manipulation Arm.  Originally, this articulated manipulator was developed at Unimation, for General Motors.  Stanford University sometimes receives credit for the development of this robot, since the designer, Victor Scheinman, worked on early designs while at the university.  Unimation produced a significant number of robots until the company was eventually purchased by Westinghouse in 1980, and then later again by other companies, including Nokia Robotics.  The robots came in a few different sizes – models were available as 200, 500 and 700 series, going from small desktop sized robots to significantly larger PUMAs designed for assembly line work, as well as welding and paint.

Canadarm is a robot manipulator that is a bit unusual, as it was installed on the Space Shuttle orbiters instead of a factory somewhere on Earth.  As you can imagine, there were unique challenges to building a robot for use in space – but there were also some advantages as well.  It was officially know as SRMS – Shuttle Remote Manipulator System.  It was able to perform a number of tasks, such as deploying and capturing payloads being delivered between the space shuttle and the space station.  It was also capable of deploying satellites.  It was also used for inspecting the exterior of the shuttle for any damage, particularly for inspecting potential damage to the thermal protection system, after the Columbia disaster.  What is particularly fascinating about the Canadarm is that on Earth it is unable to even lift it’s own weight.  But in Space, it is able to lift and move about 7000 pounds – nearly two Ford F150 pickup trucks (although the original arm was only able to deliver a payload of about 700 pounds – the capacity was increased in the 1990s).  The original arm first went into service in 1981.  Since then, there were several more built until it’s final mission in July 2011.  The robot manipulator was nearly 50 feet long and only just over a foot in diameter, weighing in at roughly 1000 pounds.  The arm was designed with six joints – two at the shoulder allowing for yaw and pitch movements, one elbow pitch joint and a total of three joints at the wrist allowing for yaw, pitch and roll movements.  This design roughly mimics a human arm.  Since the arm extended out of the Space Shuttle’s payload bay, engineers equipped it with an explosive device allowing the arm to be jettisoned into space in the event that the arm was unable to return from it’s extended position – either due to the arm failure or some external damage during service.  This way, the bay doors could be closed so that the shuttle could return to earth.  Not your typical robot manipulator feature!

There are also some robotic companies that you should be aware of, some of which will be briefly discussed here.  FANUC Corporation is a Japanese electromechanical manufacturer specializing in robotics.  They are one of the biggest sellers (if not the biggest) of industrial robots in the world.  Take a tour of any manufacturing plant, and there is a good chance that you will see a FANUC robot performing some task.  They make a wide variety of robots, specializing in articulated manipulators, with payloads varying from 0.5 kg to over 1300 kg.  They offer robots with 2-axis to 6-axis.  The M-2000iA 6-axis robot that they make can handle payloads of 1350 kg with a maximum reach of over 3.7m and weights 8600 kg!  It’s recommended uses include assembly, material removal and part transfer.  If you go to the FANUC website, you can view robots by application.  A few of those listed: arc welding, assembly, material removal, painting, palletizing, part-transfer, picking/packaging, and spot welding.  Click on any application, and you will be able to see a list of videos, showing the various types of robots in action.

So far we’ve only discussed robot manipulators.  They might not be glamorous, but they are easily the majority of robots in use all around the world, performing mostly various manufacturing and process jobs.  These robots all have a fixed base; they are fixed on the ground unable to move.  Let’s move onto the category of mobile robots.  Now, there are a few different ways of making a robot move.  It could mimic an animal by having legs, or instead use wheels to move around – such as NASA’s Mars Exploration Rover.  Mobile robots are less widely used, but the number of applications for robots that can move is widespread.  There is also the option of the mobile robot being autonomous (unmanned), able to navigate through a strange environment using sensors and feedback alone.  Other types of mobile robots need some sort of guidance to follow a predetermined path, in a relatively controlled space.

What is particularly interesting about mobile robots is the extremely wide range of applications.  The majority of manipulator type robots (fixed) will be found in an industrial setting.  Mobile robots are used everywhere from Hospitals to Battlefields.  A big industry use for mobile robots is to transfer materials and products in warehouses.  Think of the size of Amazon’s warehouses, for instance.  Mobile robots able to retrieve packages and deliver them to the correct location without the need for an employee to walk miles over the course of day can be hugely beneficial.  There are also many examples of household robots, such as the Roomba which is a robot vacuum capable of navigating a persons home, cleaning, without any human intervention.

Let’s talk for a bit about specific robot applications – not in terms of articulated manipulator versus mobile robots, but instead by industry.  First, the healthcare industry.

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