Mechanical Industrial Robotics Computer Science Essay

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In this report, we will research and document the different types of industrial robots commonly used in manufacturing industry. From this report we will investigate into the key elements of industrial robots, which will cover robotics types and there applications, principles of operation (working envelops and basic mechanical principles), end effectors and manipulators, surrounding environment and safety requirements.

From this report we will also investigate into different power units that are normally used in modern robotic applications. This would investigate into air, electric and hydraulic power sources. From an engineer's point of view, we would also investigate into the maintenance requirements for the three power sources mentioned and the suitability for specific tasks of robotics with the different power sources.

This report will also cover the methods used to gain accuracy and speed control, from this we will investigate the different forms of feed back loops, drive ratios, types of sensors and feedback facilities.

Industrial robots

Types and there applications

There are six main types of robots that are commonly used by industry such as:

Cartesian robot

Cylindrical robot

Polar robot

SCARA robot

Articulated robot

Parallel robot

These robots above are commonly used in industry today, but this is excluding end effectors and other robots custom made for a customer.

The Cartesian robot is commonly used for pick and place type of work, where a product is picked from a machine and place on a type of conveyor belt. These could be used if the operation is dangerous for an operator or the operation requires replicating over a long period of time.

Principles of operations

Cartesian robot

A Cartesian robot which is similar to a gantry robot are commonly used for pick and place applications, assembly operations, tooling handling and some forms of basic welding. As you can see in Fig 1.0 the Cartesian robot works off a 3 axis x, y and z, as you can also see its working envelope can be relatively large but this type of robot as many advantages and limitation such as:

Fig 1.0

Advantages

Large working envelope

Minimal floor space required

Ideal for repetitive pick and place tasks

Gantry robots are used for larger working envelopes

Easy to program with only 3 axis

Limitation/disadvantages

Cant reach around corners

Limitation in the working envelope

Cant perform complicated tasks

Fig 1.1Cylindrical robot

Cylindrical robots and commonly used for assembly operations, handling operations and spot welding. As you can see from Fig 1.1 the axis are x, y and z but in different directions compared to the Cartesian robot. This robot also works off a centre cylinder allowing the arm to rotate approximately 260°. Same as any other robots, this robot has advantages and limitations:

Advantages

Large rotational working envelope

Y axis, allowing the arm to reach into machinery

Ideal for pick and place applications

Easy to program with only 3 axis

Limitation/disadvantages

Limited working envelope due to rotational cylinder

Can't reach around obstacles

Can't perform complicated tasks

Spherical/Polar robot

Fig 1.3

The polar robot is very similar to the cylindrical robot above but has the ability to angle the y axis up and down. Also similar to the cylindrical robot above this also has the ability to rotate approximately 260 °.

This type of robot is used for spot welding, die-casting, gas welding and arc welding. Some advantages and limitations of this type of robot are:

Advantages

Large rotational working envelope

Y axis, allowing the arm to reach into machinery

Easy to program with only 3 axis

Y axis has the ability to pivot

Limitation/disadvantages

Limited working envelope due to rotational cylinder

Can't reach around obstacles

Can't perform complicated tasks

SCARA robot

Fig 1.3

SCARA robot stands for selective compliant assembly robot arm. This robot is commonly used for pick and place, applications of sealant, assembly operations and handling machine tools. The SCARA robot also has two rotary joints to provide compliance in a plane.

Advantages

Ideal for pick and place applications

Easy to program with only 3 axis

Limitation/disadvantages

Limited working envelope due to rotational cylinder

Small rotational working envelope

Can't reach around obstacles

Can't perform complicated tasks

Articulated Robot

Fig 1.4Articulated are also commonly used for assemble operations, diecasting, fettling machines, gas welding, arc welding and spray painting. This robot has a minimum of 3 rotary axis. These robots can be commonly found in car manufacturing industry to perform complicated or easy but repetitive operations.

Advantages

Ideal repetitive tasks such as spray painting

Easy to program with teach method

Can reach around small obstacles

Limitation/disadvantages

Have large working envelop, which require large amount of working space and guarding

Parallel Robots

Fig 1.5Parallel robots are commonly found in flight, roller coaster and other simulator at fair grounds. This type of robot is also known as Tricept, Hexapod, or Delta robot dependent on the number of working arms. Fig 1.5 shows a typical Parallel or Tricept robot found in industry.

Advantages

Ideal repetitive tasks such as pick and place

Easy to program with teach method

Limitation/disadvantages

Can't reach around obstacles

Requires to be mounted above the conveyor or assembly area.

End effectors and manipulators

Actuators

There are many different types of pneumatic actuators for robots that are used for different applications and processes. These can be divided into two different sections such as:

Factory standard (from supply)

Custom made

Factory standard actuators are normally pre-made general actuators that are used in general industry. These actuators can be purchased directly from the manufacture and delivered within a short amount of time (few days), These actuators come in many different shapes and sizes such as:

Parallel grippers

Angular grippers

Linear grippers

Sheet metal grippers

Rotary actuator

General small cylinders

Custom made actuators, are actuators that require an accurate size, movement or a special material for its working environment. The actuators may need to be custom made by the supply to fit the requirements of the robot tasks.

Control valve

Control valves come in many different shapes and sizes, they generally have two basic operations either on or off. There are many control vales the two main valves that are normally used are:

Solenoid valves

Vacuum vales

Solenoid vales come in a few different styles, such as

Single acting solenoid valves

Double acting solenoid valves

D.C. solenoid valves

A.C. solenoid valves

Verity of different ways and positions

Also vacuum vales are commonly used in pick and place robots, to pick up small electronic components to larger but light weight products.

Surrounding environment and safety requirements

The surrounding environment and safety requirements can have a large cost effect on installing a robot in a industrial environment. The surrounding environment may effect the robot purchase and the ability to complete the tasks required. There may be a lack of space to install a robot or the environment may be dirty, toxic or corrosive. These factors have a big effect on the robots where a clean room may be needed, higher and more frequent maintenance costs and impact sensors may be required for some environments (such as nuclear).

When considering the environment the robot will be installed there are also some safety requirements to be considered such as light curtains, guarding, emergency stops and isolators. A light curtain may be used to allow products to run down a conveyor but will prevent an operator or technician from entering the working envelope. An isolator would be used for more maintenance purposes to isolate the robot when maintenance is being carried out to prevent unwanted movement or operations (the isolator would have to be locked off).

Robotic power units

Power sources

There are three main types of power sources such as:

Pneumatic

Hydraulic

Electric

Pneumatic

There are many manufactures of specialized pneumatic equipment for robots but the main manufacturers are:

Bosch-rexroth

SMC

Festo

Smartech

These manufactures can be also assist you on site with some of the robotics complicated programming or even aid in with problem solving (which robotic system to use). They supply specializes pneumatic equipment (custom made) in factory to the customer.

This type of robot would be used in a basic 1 position pick and place applications or basic transfer applications. Directional control valves, spring return valves and vacuum valves commonly control pneumatics equipment. These control methods would control rod-less cylinders, linear cylinders, grippers, vacuum cups and other similar equipment.

Pneumatic robots would commonly use micro-switches and sensors to control its position and act as a form of feedback back to the PLC.

Advantages

Basic type of robot

Can be designed and built on site

Ideal for basic applications

Ideal for light weight products

Disadvantages

Cannot perform complicated tasks

May be high maintenance dependent on equipment

Requires guarding

Hydraulic

A hydraulic robot that is powered by hydraulic actuators and is controlled by servo valves, directional control valves and spring return valves. There are different control methods to achieve different results such as position control, speed control or using hydraulics to lift a high payload.

You can use a servo valve to achieve speed and position control with the robot

Advantages

Heavy payloads

Easier than other robots to program

Basic movements

Disadvantages

High maintenance

Slow speeds

Can't reach around obstacles

Electrical

An electrical robot would be commonly used on pick and place tasks where more than 1 position is required i.e. putting products on more than 1 conveyor. The drivers and the PLC would control the electric axis where the position would be measured. You would require a good knowledge to program these types of robots accurately and quickly. A electric robot would use a combination of micro-switches, reed switches, sensors and position transducers. All this information would then be feed back to the PLC and used to gain control and accuracy.

Advantages

Reliable robot

Can perform complicated tasks

Low maintenance

Disadvantages

Can be difficult to program

Requires guarding

Maintenance requirements for electric robots

Electric robots require low maintenance in a normal working environment as they last the life of the bearings. The only maintenance they generally require is a regular clean down to prevent a build up of dirt, safety check (i.e. emergency stops, light curtains and door mechanisms). The only other maintenance would be a visual check on the control gear (contractors, safety relays and switches)

Intelligence of an industrial robot

Robots our days are seen as intelligent but are quite simple, as they cannot think for them self. They require our knowledge and programming skills to carry out tasks that appear intelligent, with the combination of programming and software robots are able to store data such as images, number, letters and voice to perform tasks in and out of industry. Also according to (information from http://www.eetimes.com/design/industrial-control/4013678/Advances-in-industrial-robot-intelligence)

"Advances in industrial robot intelligence

Mark Handelsman, FANUC Robotics America Inc.

Perhaps the most important long-term trend has been the increased advances in robot intelligence. Since their initial inception, robots have had some level of intelligence in making decisions about part availability, checking if a feature is present, detecting error conditions, or related issues. In most cases, this intelligence was based on a specific sensor detecting a specific condition.

For example, a photo eye is used to detect that a part is present, and in the correct orientation through the presence or absence of a pin, detent or other feature. This photo eye is then wired to a PLC or directly to the robot controller. At the appropriate time in the robot program the robot checks this photo eye to confirm that the part is in position and in the correct orientation before picking it up or performing some other operation.

Using a photo eye or similar sensor for this example is a simple and reliable approach, and is probably the right choice in this instance. However, opportunities for automation are not always this simple. Multiple part styles may need to be handled. The means of differentiating parts may be more complex.

Parts or the manufacturing process may not lend itself to simple conveyors. For example, parts located in bins, with layers separated by a slip sheet are commonly used for metal parts. Parts may have complex geometries, making them more difficult to locate without the additional cost for fixtures to locate the parts."

This explains the advances today in robots with the use of data and software.

Common methods of programming robotics

From my research I found "There are three basic methods for programming Industrial robots but currently over 90% are programmed using the teach method." (taken from http://www.autokinematics.com/ Programming-Methods.html)

The three main types of programming are:

Teach method

Lead through method

Off-line programming method

Teach method

The teach method can be commonly used where a change in program is required on a regular basis but does not require some one with a great deal of knowledge. This method does not change the program but alters the limits of the robot i.e. you teach it the positions by manually driving the robot with the use of a joystick or keypad entry. According to http://www.autokinematics.com/ Programming-Methods.html,

"The co-ordinate systems available on a standard jointed arm robot are:

Joint Co-ordinates

The robot joints are driven independently in either direction.

Global Co-ordinates

The tool centre point of the robot can be driven along the X, Y or Z axes of the Robots global axis system. Rotations of the tool around these axes can also be performed

Tool Co-ordinates

Similar to the global co-ordinate system but the axes of this one are attached to the tool centre point of the robot and therefore move with it. This system is especially useful when the tool is near to the workpiece.

Workpiece Co-ordinates

With many robots it is possible to set up a co-ordinate system at any point within the working area. These can be especially useful where small adjustments to the program are required as it is easier to make them along a major axis of the co-ordinate system than along a general line. The effect of this is similar to moving the position and orientation of the global co-ordinate system."

My understanding of this method of programming is very simple you will move each axis as required and record each position. This method would be a easy programming method but without the required downtime to program the robot for different tasks.

Lead through

A lead through method of programming is a simple method of programming just but physically moving the robotic arm to follow the required path. This type of programming method is ideal for tasks such as spray painting but any errors while programming cannot easly be removed without re-programming.

Off-line programming

This method of programming, is programmed off-line and then uploaded to the robot but with advances in technology you are able to program a robot by using CAD data (according to http://www.autokinematics.com/ Programming-Methods.html) By doing this will decrease down time of the robot,

References

Mark Richards - Electrical engineer

Tony Butler - Electrical engineer

Jonathan Bedgood - Production Engineer

Pictures

Fig 1.0 - http://prime.jsc.nasa.gov/ROV/images/cartesian.GIF

Fig 1.1 - http://media.photobucket.com/image/Cylindrical%

20robot/qtulsan/QP070826_c_cylindrical2

Fig 1.2 - http://prime.jsc.nasa.gov/ROV/types.html

Fig 1.3 - http://img.directindustry.com/images_di/photo-

g/scara-robots-241150.jpg

Fig 1.4 - http://img.directindustry.com/images_di/photo-

g/articulated-robots-162230.jpg

Fig 1.5 - http://www.robotmatrix.org/ParallelRobotic.htm

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