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miercuri, 27 ianuarie 2016

The Importance of Automation

1.) A brief history of automation


Automation is one of the most important factors in today’s automotive industry. In these times when on-time delivery is key only few high-end manufacturers (Rolls Royce) still prefer to use manual labor in favor of robotic labor. But this would not have been possible, without the contribution of a single person, Henry Ford.
“Henry Ford (July 30, 1863 – April 7, 1947) was an American industrialist, the founder of the Ford Motor Company, and the sponsor of the development of the assembly line technique of mass production. Although Ford did not invent the automobile or the assembly line, he developed and manufactured the first automobile that many middle class Americans could afford. In doing so, Ford converted the automobile from an expensive curiosity into a practical conveyance that would profoundly impact the landscape of the twentieth century. His introduction of the Model T automobile revolutionized transportation and American industry. As the owner of the Ford Motor Company, he became one of the richest and best-known people in the world. He is credited with "Fordism": mass production of inexpensive goods coupled with high wages for workers. Ford had a global vision, with consumerism as the key to peace. His intense commitment to systematically lowering costs resulted in many technical and business innovations, including a franchise system that put dealerships throughout most of North America and in major cities on six continents. Ford left most of his vast wealth to the Ford Foundation and arranged for his family to control the company permanently.”[1]
As the encyclopedia Britannica tells us “the mass-produced automobile is generally and correctly attributed to Henry Ford, but he was not alone in seeing the possibilities in a mass market. Ransom E. Olds made the first major bid for the mass market with a famous curved-dash Oldsmobile buggy in 1901. Although the first Oldsmobile was a popular car, it was too lightly built to withstand rough usage. The same defect applied to Olds’s imitators. Ford, more successful in realizing his dream of “a car for the great multitude,” designed his car first and then considered the problem of producing it cheaply. The car was the so-called Model T, the best-known motor vehicle in history. It was built to be durable for service on the rough American country roads of that period, economical to operate, and easy to maintain and repair. It was first put on the market in 1908, and more than 15 million were built before it was discontinued in 1927.
When the design of the Model T proved successful, Ford and his associates turned to the problem of producing the car in large volume and at a low unit cost. The solution was found in the moving assembly line, a method first tested in assembling magnetos. After more experimentation, in 1913 the Ford Motor Company displayed to the world the complete assembly-line mass production of motor vehicles. The technique consisted of two basic elements: a conveyor system and the limitation of each worker to a single repetitive task. Despite its deceptive simplicity, the technique required elaborate planning and synchronization.
The first Ford assembly line permitted only very minor variations in the basic model, a limitation that was compensated for by the low cost. The price of the Model T touring car dropped from $950 in 1909 to $360 in 1916 and still lower to an incredible $290 in 1926. By that time Ford was producing half of all the motor vehicles in the world. The bulk of the world’s new cars come from the moving assembly line introduced by Ford, but the process is much more refined and elaborated today. The first requisite of this process is an accurately controlled flow of materials into the assembly plants. No company can afford either the money or the space to stockpile the parts and components needed for any extended period of production. Interruption or confusion in the flow of materials quickly stops production. Ford envisioned an organization in which no item was ever at rest from the time the raw material was extracted until the vehicle was completed—a dream that has not yet been realized.
The need for careful control over the flow of materials is an incentive for automobile firms to manufacture their own components, sometimes directly but more often through subsidiaries. Yet complete integration does not exist, nor is it desirable. Tires, batteries, and dashboard instruments are generally procured from outside sources. In addition, and for the same reasons, the largest companies support outside suppliers even for items of in-house manufacture. First, it may be more economical to buy externally than to provide additional internal facilities for the purpose. Second, the supplier firm may have special equipment and capability. Third, the outside supplier provides a check on the costs of the in-house operation. American companies rely more than others on independent suppliers.
Production of a new model also calls for elaborate tooling, and the larger the output, the more highly specialized the tools in which the manufacturer is willing to invest. For example, it is expensive to install a stamping press exclusively to make a single body panel for a single model, but, if the model run reaches several hundred thousand, the cost is amply justified.
The assembly process itself has a quite uniform pattern throughout the world. As a rule, there are two main assembly lines, body and chassis. On the first the body panels are welded together, the doors and windows are installed, and the body is painted and trimmed (with upholstery, interior hardware, and wiring). On the second line the frame has the springs, wheels, steering gear, and power train (engine, transmission, drive shaft, and differential) installed, plus the brakes and exhaust system. The two lines merge at the point at which the car is finished except for minor items and necessary testing and inspection. A variation on this process is “unitized” construction, whereby the body and frame are assembled as a unit. In this system the undercarriage still goes down the chassis line for the power train, front suspension, and rear axle, to be supported on pedestals until they are joined to the unitized body structure. Most passenger vehicles today are manufactured by the unitized method, and most trucks and commercial vehicles still employ a separate frame.
Assembly lines have been elaborately refined by automatic control systems, transfer machines, computer-guided welding robots, and other automated equipment, which have replaced many manual operations when volume is high. Austin Motors in Britain pioneered with its automatic transfer machines in 1950. The first large-scale automated installation in the United States was a Ford Motor Company engine plant that went into production in 1951. A universal form of automatic control has used computers to schedule assembly operations so that a variety of styles can be programmed along the same assembly line. Customers can be offered wide choices in body styles, wheel patterns, and color combinations.” [2]

2.) Robotic manipulation


Robotic manipulation is one process used in many industries across many companies but it has made its mark in the automotive industry, mainly because it is proven that using robotic manipulators to transport, hold and do multiple tasks is a much cheaper way then hiring someone to do the same tasks. The main advantage in this case being that robotic manipulators are able to work 24/7, thus reducing the respective company millions. “The earliest known industrial robot, conforming to the ISO definition was completed by "Bill" Griffith P. Taylor in 1937 and published in Meccano Magazine, March 1938. The crane-like device was built almost entirely using Meccano parts, and powered by a single electric motor. Five axes of movement were possible, including grab and grab rotation. Automation was achieved using punched paper tape to energize solenoids, which would facilitate the movement of the crane's control levers. The robot could stack wooden blocks in pre-programmed patterns. The number of motor revolutions required for each desired movement was first plotted on graph paper. This information was then transferred to the paper tape, which was also driven by the robot's single motor. Chris Shute built a complete replica of the robot in 1997.” [3]
A robotic manipulator has a set of basic parameters that defines it. If one of these are missing the resulting construction cannot be considered a robotic manipulator or industrial robot.
These parameters are:
a.)    Number of axis – two axes for a point on a plane and three to reach any point in space, but for full control more axes are required (yaw, pitch, roll).
b.)    Degrees of freedom – usually number of axis.
c.)    Working envelope – reaching area.
d.)    Kinematics – arrangement of rigid members and joints on the robot.
e.)    Carrying capacity (payload) – how much can the robot lift.
f..)     Speed – how fast can the robot position its arm.
g.)    Acceleration – the acceleration of an axis.
h.)    Accuracy – how closely can the robot arm reach the designated position.
i..)     Repeatability – how well can a robot return to a position.
j..)     Motion control -  for some applications, such as simple pick-and-place assembly, the robot need merely return repeatable to a limited number of pre-taught positions. For more sophisticated applications, such as welding and finishing (spray painting), motion must be continuously controlled to follow a path in space, with controlled orientation and velocity.
k.)    Power source – hydraulic or electric in most cases.
l.l)     Drive – e.g. electric motors connect to joints via gears.
m.) Compliance -  this is a measure of the amount in angle or distance that a robot axis will move when a force is applied to it.
But manufacturing a high performance industrial robot has never been a technical challenge, it has always been a mathematical challenge. All the parameters mentioned above alongside their sub-parameters can be calculated mathematically and this is where the performance of the industrial robot really shows. For example the figure below show hot to graphically represent the rotational motion for a rigid body transformation (which is the basis for industrial robots).



Fig.2.1 – Rotation of a rigid object about a point. The dotted coordinate frame is attached to the rotating rigid body.[4]
Another more complex example are rotations for a rigid body, as shown below.

Fig.2.1 – Tip point trajectory generated by rotation about the ω axis. [4]
        Another issue that depicts the performance of an industrial robot is the minimum time path, which is the most optimum path that a robot need to take from point A to point B, taking into account possible obstacles in its way. This also is more a matter of mathematics than a technological issue. Many case studies have been conducted for this matter and only few of them show real promise. “It is shown that the studied drilling/ spot welding tasks can be described by a performance limited traveling salesman problem (TSP): the manipulator effector acts as the salesman, it starts from one machining point and passes through each point just by once meanwhile it must be full stopped to finish the machining task. Since its high computational complexity, the solution of TSP is always an open problem. Currently, the feasible solutions of TSP can be classified by enumeration method, dynamic programming, branch and bound method, or intelligent optimization method (such as genetic algorithm (GA), simulated annealing (SA), Particle Swarm Optimization (PSO), etc).
In order to simplify the problem, the common path planning strategies for multi points manufacturing assume the transfer path between any two points is straight line, and the problem can be described as a TSP with minimum distance index., it is shown that due to the nonlinear expressions of the manipulator kinodynamics and gravitational torques, it is non-equivalent between the minimum time path and the minimum distance path, even the minimum time path from point i to point j is also different from the point j to point i path. Hence besides the optimization of travelling schedule of the set points, the transfer paths between machining points also need to be optimized to obtain the minimum transfer time.” [5]
Robotic manipulation has always been the basis of any automated assembly line, as manipulators do most of the assembly required to complete a vehicle.

3.) Robotic welding


The use of robotic welding started off in the 1960s in the US auto industry, but it never really took off until the 1980s when it spreaded like wildfire. The main reason is that using robots is a much more productive and precise solution (and also cost-effective in time) then hiring skilled labor to do this type of job. Another reason is that by using robots welding can be done in a much more controlled environment.
“Robot welding is the use of mechanized programmable tools (robots), which completely automate a welding process by both performing the weld and handling the part. Processes such as gas metal arc welding, while often automated, are not necessarily equivalent to robot welding, since a human operator sometimes prepares the materials to be welded. Robot welding is commonly used for resistance spot welding and arc welding in high production applications, such as the automotive industry.
Robot welding is a relatively new application of robotics, even though robots were first introduced into US industry during the 1960s. The use of robots in welding did not take off until the 1980s, when the automotive industry began using robots extensively for spot welding. Since then, both the number of robots used in industry and the number of their applications has grown greatly. In 2005, more than 120,000 robots were in use in North American industry, about half of them for welding. Growth is primarily limited by high equipment costs, and the resulting restriction to high-production applications. In 2014, FANUC America Corp. introduced a low cost arc welding robot to provide small manufacturers with a cost-effective robotic arc welding solution. Robot arc welding has begun growing quickly just recently, and already it commands about 20% of industrial robot applications. The major components of arc welding robots are the manipulator or the mechanical unit and the controller, which acts as the robot's "brain". The manipulator is what makes the robot move, and the design of these systems can be categorized into several common types, such as SCARA and Cartesian coordinate robot, which use different coordinate systems to direct the arms of the machine. The robot may weld a pre-programmed position, be guided by machine vision, or by a combination of the two methods. However, the many benefits of robotic welding have proven to make it a technology that helps many original equipment manufacturers increase accuracy, repeat-ability, and throughput. The technology of signature image processing has been developed since the late 1990s for analyzing electrical data in real time collected from automated, robotic welding, thus enabling the optimization of welds.” [6]

Fig.3.1 – Robotic welding on a vehicle body [7]
Although it has its advantages, robotic welding has one big disadvantage, the sheer volume of programming required to properly make these industrial robots do their job in the most adequate way possible.
One solution for this issue is the use of intuitive teaching, when an industrial robot is following the gestures done by a human specialist, and learning from them. This as one of the biggest breakthroughs that modern technologies can accomplish and it will be properly implemented in the years to come.
One other interesting method is the use of augmented reality in combination with an industrial robot. For example, if we have to make complicate welds on a vehicle to reinforce its structure most robots struggle with this issue because most of the times these welds are done in hard to reach places. But by using augmented reality a human operator can make these weld whilst the computer displays the most adequate welding route for them on a special pair of glasses. This means that while the industrial robot is making the spot welds, a human operator can make the more complicated welds with the help of augmented reality, thus decreasing the manufacturing time, and also the quality of the weld will increase.
“Manual spot welding loses the comparison with automated spot welding, not because of a higher execution time, but due to an inferior quality of welded points, mostly a low repeatability. It is not a human fault. Human welder is compelled to operate without having at disposal the knowledge of significant process features that are known by the robot: exact position of the welding spot, electric parameters to be adopted for every specific point, quality of the welded spot and, based on it, possible need for repetition of a defective weld.
The research shows that, using an augmented reality device, it is possible to display this very data to the human operator, in order to enhance the manual process execution. The adopted device is a tablet mounted on the welding gun. It displays the working area seen by the built-in camera. The image is augmented by the superposition of computer generated images of the welding spots and their properties. The state of the spot (welded or not) and its execution quality (good or defective weld) is transmitted by some graphic features, like point color, size and way of blinking. The paper describes the algorithms used in the development of the program for this application, focusing on the problem of real time localization of the welding gun position. The augmented reality application was actually installed on an experimental station by a welding gun manufacturer and the results of the tests are presented and discussed.” [8]
Some of the most important issues that industrial welding robots come across are:
a.)    Poor wire feeding – there are two causes for wire feeding problems, buildup of debris on the liner or a broken wire feeder, and sometimes another issue might be some kinking wire cables, these result in a poor arc and weld quality.
b.)    Inconsistent or off-location welds – most common issue is the tool center point, the focal point of a tool, in these cases there are a lot of things to reposition in order to fix this issue, sometimes even reconstructing the base on which the robot is placed.
c.)    Poor consumable performance and premature failure - the poor performance or premature failure of consumables—including nozzles, contact tips, retaining heads (or diffusers), and liners—can be caused by a number of issues, including spatter or debris buildup, loose connections, or improper liner installation.
d.)    Premature cable failure - premature power cable failure, on either a through-arm robotic welding system (where the cable feeds through the arm of the robot) or in a standard robotic welding system, can be the result of incorrect programming that results in aggressive movements. It can also occur when using the incorrect power cable length.
e.)    Nozzle cleaning station isn’t operating properly - The most common peripheral added to a robotic system is a nozzle cleaning station or reamer, which, as its name implies, is responsible for cleaning the nozzle (and other front-end consumables). This cleaning occurs during routine pauses in production, and any issues with it typically relate to one of three factors: the position between the reamer and robotic MIG gun nozzle, poor anti-spatter solution coverage, or a dull cutting blade.[9]
All these issues are time consuming problems and let us not forget about route programming issue for the robots and collision avoidance.
Other issues involving robotic welders are travelling times and dimensional variations, one paper in particular deals with these issues in a more impressive way, using mathematics to help the robotic welder determine the optimum solution.
“Complex assembled products as an automotive car body consist of about 300 sheet metal parts joined by up to 4000 spot welds. In the body factory, there are several hundred robots organized into lines of welding stations. The distribution of welds between robots and the welding sequences have a significant influence on both dimensional quality and throughput. Therefore, this paper proposes a novel method for quality and throughput optimization based on a systematic search algorithm which exploits properties of the welding process. It uses approximated lower bounds to speed up the search and to estimate the quality of the solution. The method is successfully tested on reference assemblies, including detailed fixtures, welding robots and guns.”[10]

4.) Robotic painting


One more important automation factor for the automation in the automotive industry is the introduction of a robotic painting system, in which we use robotic arms in controlled environments in order to apply coats of paint to the finished vehicle. Here the main advantage is that by eliminating the human factor we eliminate most cause for low quality paint jobs on vehicles and vehicle parts.
“Robotics in this case can be used in order to calculate the most adequate covering distance and also to apply a more even coat of paint that no human could.
Originally industrial paint robots were large and expensive, but today the price of the robots have come down to the point that general industry can now afford to have the same level of automation that only the big automotive manufacturers could once afford.
The selection of today’s paint robot is much greater varying in size and payload to allow many configurations for painting items of all sizes. The prices vary as well as the new robot market becomes more competitive and the used market continues to expand.
Painting robots are generally equipped with five or six axis, three for the base motions and up to three for applicator orientation. These robots can be used in any explosion hazard Class 1 Division 1 environment.” [11]
One of the most used painting robots in the automotive industry are the Kawasaki Paint Robots, also known as the K Series. With their revolutionary hollow wrist version, they can be fitted with special paint hoses inside the arms, in this way the performance is maximized, overspray minimized and also the risk of contaminating the finished product as at a minimum. “Kawasaki Robotics also offers a control panel to enhance the ease of system building and interfacing with peripheral equipment such as robot traveling unit, workpiece transfer unit, rotation unit, and other devices. The control panel is an intuitive graphical interface that allows users to centrally operate and control all components of the robotic finishing system. K Series Robots can be programmed in two ways, via the robot teach pendant or a computer, and using one of the two Kawasaki's programming methodologies, Block Step or AS Language. The Block Step programming method eliminates time consuming program teaching with auto-path generating software. The powerful AS Language provides ultimate flexibility via any word processor text file and enables the programmer to create advanced logic, manipulate program locations, integrate peripheral components and control the application process.” [12]

Fig.4.1 – Kawasaki K-Series Paint Robot [13]
Paint robots for painting the interior of vehicles have been used in Germany since the 1980s at Mercedes-Benz and BMW.
“A look at the development of robot technology in the last ten years allows a comparison of several key parameters and shows clearly how the versatility of the machines has improved. Electrically driven paint robots, which operate with much higher availability and require less costly maintenance, are now used exclusively. In addition, the painting speed has been increased by about 50 percent, while the dynamic accuracy of the path tracking and the absolute accuracy (referred to the target coordinates) have also improved (Table 1). Absolute accuracy with respect to a given point, for example, has improved from ± 4 mm to ± 1 mm, dynamic accuracy (referred to the path) from ± 25 mm to ± 6 mm.” [14]

Fig.4.2 – Development of robot technology over the last decade [14]
The main advantage of using robotic painter is that they can work in a hazardous environment (in which humans cannot) thus making modern paint stations very productive, mainly because they can also be fitted with a curing oven, in this way the moment the vehicle body comes out of the paint station it is already dried and ready to use.

                                                                       

Fig.4.3 – Typical paint station for painting the interior of car bodies. The displacement of the cabin axis is a way to improve air management in the spray booth [14]


5.) Robotic inspection


In the past the only way parts and other products could be measure were traditional measuring tools like calipers and such, but in today’s automotive industry there is a need for fast and accurate measures. The only way this can be achieved is with the use of robotic inspection tools.
The basis for such tools are the more modern coordinate measuring machines. A coordinate measuring machine (CMM) is a device for measuring the physical geometrical characteristics of an object. This machine may be manually controlled by an operator or it may be computer controlled. Measurements are defined by a probe attached to the third moving axis of this machine. Probes may be mechanical, optical, laser, or white light, amongst others. A machine which takes readings in six degrees of freedom and displays these readings in mathematical form is known as a CMM. The typical 3D "bridge" CMM is composed of three axes, X, Y and Z. These axes are orthogonal to each other in a typical three-dimensional coordinate system. Each axis has a scale system that indicates the location of that axis. The machine reads the input from the touch probe, as directed by the operator or programmer. The machine then uses the X,Y,Z coordinates of each of these points to determine size and position with micrometer precision typically. A coordinate measuring machine (CMM) is also a device used in manufacturing and assembly processes to test a part or assembly against the design intent. By precisely recording the X, Y, and Z coordinates of the target, points are generated which can then be analyzed via regression algorithms for the construction of features. These points are collected by using a probe that is positioned manually by an operator or automatically via Direct Computer Control (DCC). DCC CMMs can be programmed to repeatedly measure identical parts, thus a CMM is a specialized form of industrial robot. [15]

Fig 5.1 – A typical Coordinate Measuring Machine [15]



Other machines that contributed in today’s robotic inspectors are 3D scanners. These devices are used to re-create physical objects in a form recognized by a computer. Basically what a 3D scanner does is triangulate designated points on the object, thus recreating on the computer a 3D scanned surface. A 3D scanner is a device that analyses a real-world object or environment to collect data on its shape and possibly its appearance (e.g. color). The collected data can then be used to construct digital three-dimensional models. Many different technologies can be used to build these 3D-scanning devices; each technology comes with its own limitations, advantages and costs. Many limitations in the kind of objects that can be digitized are still present, for example, optical technologies encounter many difficulties with shiny, mirroring or transparent objects. For example, industrial computed tomography scanning can be used to construct digital 3D models, applying non-destructive testing.
Collected 3D data is useful for a wide variety of applications. These devices are used extensively by the entertainment industry in the production of movies and video games. Other common applications of this technology include industrial design, orthotics and prosthetics, reverse engineering and prototyping, quality control/inspection and documentation of cultural artifacts. [16]

Fig.5.2 – A handheld 3D scanning device [16]
One important test in which the automotive industry is still using human labor for is visual inspection. But now leading scientists in the field of robotics are trying to develop robotic inspector capable of subjecting vehicles to the dreaded “water leak test”. The “water leak test” in an automotive final assembly line is often a significant cost factor due to its labor intensive nature. This is particularly the case for premium car manufacturers as each vehicle is watered and manually inspected for leakage. This paper delivers an approach that optimizes the efficiency and capability of the test process by using a new automated in-line inspection system whereby thermographic images are taken by a lightweight robot system and then processed to locate the leak. Such optimization allows the collaboration of robots and manual labor which in turn enhances the capability of the process station. [17]
Basically in order to perform this test the finished vehicle is places in a controlled environment that simulates rainfall. It sits in different types of rain for about six minutes after which it is visually inspected for leakage.
Overall quality checks for a finished vehicle is about 10% of the time to delivery, but because today most of the inspection processes are done via robots that 10% is slowly but surely decreasing in the years to come.
For example, BMW has an almost completely automated assembly line, it is capable of producing a vehicle from start to finish without human intervention, but in delicate operations that require experience and finesse human intervention is always preferred.

Fig.5.3 – BMW assembly line [18]

6.) Advantages/Disadvantages


As in any manufacturing process, assembly line automation has its advantages but also a few disadvantages.

6.1) Advantages


                If we take into account the time it takes to manufacture an entire vehicle using only manual labor, we can clearly see where the advantages of automated assembly lines come. For example, in 2014 BMW produce 3.5 cars every hour. Using industrial robots, you could create a modern assembly line in which you would need only 2 or 3 engineers supervising the whole process. It is more cost-effective then using manual labor. The quality for most things is better.
            Also by using industrial robots you can combine multiple operations, for example painting and curing on the same station, thus reducing delivery time.
            If we were to summarize all these factors, there are some key points that prove that automation has many more advantages then disadvantages:
a.)     Increased throughput or productivity.
b.)    Improved quality or increased predictability of quality.
c.)     Improved robustness (consistency), of processes or product.
d.)    Increased consistency of output.
e.)     Reduced direct human labor costs and expenses.
f.)      Install automation in operations to reduce cycle time.
g.)    Install automation where a high degree of accuracy is required.
h.)    Replacing human operators in tasks that involve hard physical or monotonous work. Replacing humans in tasks done in dangerous environments (i.e. fire, space, volcanoes, nuclear facilities, underwater, etc.)
i.)      Performing tasks that are beyond human capabilities of size, weight, speed, endurance, etc.
j.)      Economic improvement: Automation may improve in economy of enterprises, society or most of humanity.
k.)    Reduces operation time and work handling time significantly.
l.)      Frees up workers to take on other roles.
m.)  Provides higher level jobs in the development, deployment, maintenance and running of the automated processes.

6.2) Disadvantages


The main disadvantages of automation are:
a.)    Security Threats/Vulnerability: An automated system may have a limited level of intelligence, and is therefore more susceptible to committing errors outside of its immediate scope of knowledge (e.g., it is typically unable to apply the rules of simple logic to general propositions).
b.)    Unpredictable/excessive development costs: The research and development cost of automating a process may exceed the cost saved by the automation itself.
c.)    High initial cost: The automation of a new product or plant typically requires a very large initial investment in comparison with the unit cost of the product, although the cost of automation may be spread among many products and over time.

7.) Conclusions


Automation especially in the automotive industry is proven to be the most cost-effective, productive and time effective method in order to ensure the best most possible results. From automated assembly to automated painting every process controlled via computer.
You can run an entire manufacturing plant 24/7, no need for launch breaks but especially robotic workers do not need a salary nor days off.
Automation is a natural evolution of technology in today’s modern age

8.) References


1.)    Automotive Industry, Wikipedia, https://en.wikipedia.org/wiki/Automotive_industry , 21.01.2016;
2.)    Encyclopedia Britannica http://www.britannica.com/topic/automotive-industry , 21.01.2016;
3.)    Industrial Robots, Wikipedia https://en.wikipedia.org/wiki/Industrial_robot , 20.01.2016;
4.)    Richard M. Murray – “A Mathematical Introduction to Robotic Manipulation”, California Institute of Technology, 1994;
5.)    Qiang Zhang, Ming-Yong Zhao – “Minimum Time Path Planning for Robotic Manipulator in Drilling/Spot Welding Tasks”, Journal of Computational Design and Engineering, Chinese Academy of Sciences, 2015;
6.)    Robotic Welding, Wikipedia, https://en.wikipedia.org/wiki/Robot_welding , 19.01.2016;
8.)    Dario Antonelli, “Enhancing the Quality of Manual Spot Welding through Augmented Reality Assisted Guidance”, Procedia CIRP, Politecnico di Torino, 2015;
9.)    Plant Engineering Website, http://www.plantengineering.com/single-article/identifying-the-causes-and-fixes-for-robotic-welding-troubles/458204525a823b5754b9541fbc69cad4.html, 19.01.2016;
10.)                        Johan S. Carlson, “Minimizing Dimensional Variation and Robot Traveling Time in Welding Stations”, Procedia CIRP, Chalmers Science Park, 2014;
11.)                        Robotic Painter, Wikipedia, https://en.wikipedia.org/wiki/Paint_robot , 18.01.2016;
12.)                        Kawasaki Robotics K-Series website, https://robotics.kawasaki.com/en/products/robots/painting/index.html , 18.01.2016;
13.)                        https://upload.wikimedia.org/wikipedia/commons/6/60/KJ_314.jpg ,18.01.2016;
14.)                        ABB Review Magazine, Paint Robots, 04/1996 Edition;
15.)                        Coordinate Measuring Machine, Wikipedia, https://en.wikipedia.org/wiki/Coordinate-measuring_machine , 22.01.2016;
16.)                        3D Scanner, Wikipedia, https://en.wikipedia.org/wiki/3D_scanner , 22.01.2016;
17.)                        Rainer Muller, “Inspector Robot – A New Collaborative Testing System Designed for the Automotive Final Assembly Line”, Procedia CIRP, ZeMA Center for Mechatronics and Automation, Gewerbepark Eschberger Weg, Geb 9, 66121 Saarbrücken, 2014;

18.)                        BMW Assembly line, http://st.motortrend.com/uploads/sites/5/2014/07/bmw-spartanburg-robotic-welding-line.jpg , 22.01.2016.