robot technology_derby college

BTEC HIGHER NATIONAL DIPLOMA: DERBY COLLEGE

Student: Michael Harvey Identification Number: 491074

HIGHER NATIONAL CERTIFICATE

Robot Technology

Outcome 1:

Analyse an industrial robots key elements and operational

principles

Assessor:

Wayne Seal



Contents Page

Task 1a

Examine in detail the role of powered industrial robots in industry today considering the different configurations of robots and their principle advantages and disadvantages.

Analyse the main configurations of a robot and their principles applications during safe operation.

Task 1b

Analyse the key elements of a robot manipulator and their principles of operation.

Task 2

Describe the main control elements of a robot system and their function.

Task 3

Describe devices and methods used to improve the intelligence of a robot.



HIGHER NATIONAL CERTIFICATE

Robot Technology

Task 1a & 1b:

Analyse the main configurations of a robot and their

principles applications during safe operation.

Assessor:

Wayne Seal



Task 1a – A Brief insight into automation and robotics in industry

Task requirements Examine in detail the role of powered industrial robots in industry today considering the different configurations of robots and their principle advantages and disadvantages. Analyse the main configurations of a robot and their principles applications during safe operation. Introduction What is my definition of a robot? A robot is a re-programmable multi purpose manipulator that moves material, parts, tools or specialised devises in 3 or more axis. A robot is obviously more complicated than my general description but this forms the basis for simple operation of a robot in an industrial environment. Automation and robotics in industry today Robots are increasingly becoming a key component of a modern working industrial manufacturing system. They are relatively cheap and simple to implement compared to very complex modern manufacturing cells which companies invest millions of dollars in today’s quest for lean manufacturing. The term robot is derived from the Czech word “robota” which means forced labour or slave. The first forms of robot were termed “Universal Transfer Devices” these were introduced in the early 1950’s. The first commercial robot was introduced in 1961 in the die casting industry. By today’s standards this robot would have been slow, bulky and very expensive to implement, other limitations of it use would have been;

Very limited movement;

Time consuming to programme, days instead of hours;

Simple contours could not be achieved;

Incremental positioning was almost impossible to achieve; and

Component parts were slow and totally unreliable.



Today things are very different, Industrial robots are now fully programmable multi functional mechanical manipulators designed to move material, parts, tools, or specially designed devices through variable programmed multi axis motions to perform a variety of simple and complicated tasks. An industrial robot system includes not only industrial robots but also any devices and or sensors required for the robot to perform its tasks as well as sequencing or monitoring communication interfaces. Robots in industry are generally used to perform a variety of tasks and operations; these tasks may be.

Unsafe;

Hazardous;

Highly repetitive; and

Too heavy or high for an operator. They have many different industrial functions some of which are detailed below;

Material handling;

Mechanical assembly;

Electrical assembly;

Arc welding;

Machine tool load and unload functions;

Spray painting;

Packing; and even

Medical applications. Most robots are set up for an operation by the teach-and-repeat technique. In this mode, trained operators know as a programmer typically uses a portable control device (teach pendant) to teach the robot its task manually. Robot speeds during this programming phase are usually very slow.



This teach mode instruction phase includes must include the safety considerations necessary to operate the robot properly and use it automatically in conjunction with other peripheral equipment located within the working envelope of the robot. Modern industrial robots of today can be characterised by the following features;

Cheap and simple to implement, although the systems may be expensive and time consuming whilst under development;

Simple, efficient, and reliable in operation within the constraints of the working envelope;

Simple to control, easy to remove redundant tasks and operations;

Easy to safeguard worker safety, by the use of light curtains and interlocks.

Systems require little or no maintenance;

Operate without the intervention of humans; and

Many different configurations and geometrical structures depending on the application / purpose the system has been designed to service.

Task 1a - Configuration and applications of robots

Industrial robots are available commercially in a wide range of sizes, shapes, and configurations. They are designed and fabricated with different design configurations and a different number of axes or degrees of freedom. These factors of a robot's design influence its working envelope (the volume of the working envelope). Diagrams of the different robot design configurations are shown in Figure 1 below.



So what do I mean by the degree of freedom or working envelope? The diagram below details the movement of an articulated arm robot from a side on view and a plan view from above. It shows the maximum envelope as well as the restricted and operating limitation of a modern 5 axis robot used in a typical manufacturing process today.

Figure 2. A typical robotic working envelope

Classifications of robots

Robots can be sorted and classified due to their application and configuration as well as their loading capacity. Some of the main types of robot classification are;

Material handling robots;

Assembly robots;

Welding robots; and

Paint spraying robots. All of the above are classification of robots and not modes of operation or configuration. The configuration of the robot will determine the operational



constraints and limitation of the robot itself. Some of the main robot configurations used today in industry are;

Articulated-arm co-ordinate;

Cartesian co-ordinate;

Polar co-ordinate;

Cylindrical co-ordinate;

Gantry; and

Selective Compliance Assembly Robot Arm (SCARA).

Articulated-arm co-ordinate

The articulated configuration consists of a number of rigid arms connected by rotary joints; movement around the base is also available. This type of robot is sometimes referred to as a jointed arm configuration; this is because it resembles the movement of the human body. The structure of this robot is very flexible but this can create problems as a simple straight line movement requires the use of axis or joints, this make programming the arm somewhat troublesome but some of its advantages are

Cartesian co-ordinate The Cartesian configuration is very simple and provides three linear axes moving at right angles, this is sometimes known as orthogonal. The movement is the same as a conventional milling machine providing x, y, and z-axes.

Very good manoeuvrability;

Can reach over obstacles;

Good access all round;

Good accessibility in restricted tight areas;

Fast due to articulated joints; and

Able to follow complex 3D paths easily;



Polar co-ordinate

The configuration of the spherical or polar co-ordinate robot combines rotation movement in both horizontal and vertical planes with the aid of a in and out extension of the robot arm. This is sometimes known as the gun turret configuration. While this set up can cover and sweep large areas or volumes the access of the arm can hinder its efficiency. Some of the advantages of this configuration are;

Easily controlled and programmed;

Polar co-ordinates are easily understood;

Large payload capability;

Very fast and accurate; and

Able to extend arm in and out for long reach payloads. Cylindrical co-ordinate The cylindrical configuration has the ability to combine both vertical and horizontal linear movement with the rotary axis movement about the vertical plane. Its motion is, as you would expect mainly from sweeping round in a circular pattern some of the advantages of this system are;

The advantages of this configuration are;


Very accurate;

Simple control system;

Accurate at high speed with good payload capacity;

X, Y, Z co-ordinate programming easily understood;

Large payload capacity;

Large area of coverage;

Easy to expand working envelope; and

Structurally simple with very little required maintenance.

Good accuracy;

Simple structure;

Good robust and simple control system;

Good access from the front and side;

Fast operation; and

Easy to programme



Gantry Gantry robotic systems are again a very simple configuration using mainly three axes of movement very similar to rectangular co-ordinate or Cartesian co-ordinate system. The main difference with this configuration is as the name would suggest the framework or structure of the robot are mounted in the Gantry of the place of work i.e. the roof space or above the machine or components that are to be manually handled or moved from workstation to workstation. This system would be well suited to working in a warehouse environment. Some of the advantages of this configuration are; Selective Compliance Assembly Robot Arm (SCARA) Selective Compliance Assembly Robot Arm SCARA for short is a combination of a cylindrical configuration with a jointed link arm. The link arm has several rotary joints which provide movement in the horizontal with vertical plane movement provided by the use of the end of the arm itself. Advantages of this type of robot configuration are;


Co-ordinates are easily understood;

Large payload capability;

Very fast and accurate;

Able to cover a large working area; and

Little maintenance required.

Fast operation;

Very accurate;

Can lift higher payloads due to the configuration of the jointed arm and limited vertical movement; and

Easy to programme with good access and manoeuvrability.



As with any business case for and against the use of a new or emerging technology such as robotics; there are pro’s and con’s which must be fully considered and evaluated. It's important to take time to consider the fact’s and discuss the needs of the process the robot has been tasked with completing.

The following address some of the good and the bad of points that should be considered before opting to use a robot to aid a particular process.

The Advantages of using industrial Robots;

Quality;

Robots have the capacity to dramatically improve a product’s quality. Applications are performed with precision and high repeatability every time. This level of consistency can be hard to achieve any other way especially in a hazardous or dangerous environment.

Production;

With robots, throughput speeds increase, which directly impacts production. Because robots have the ability to work at a constant speed without pausing for breaks, sleep, holidays, they have the potential to produce more than an average employee / worker.

Safety;

Robots increase workplace safety. Operator’s roles are changed to a more supervisory role safeguarded by additional systems such as light curtains and interlocks; this is so they no longer have to perform dangerous applications in hazardous surroundings.

Savings;

Greater worker safety leads to financial savings. There are fewer HS&E concerns for employers. Robots also offer 24 hour performance 7 days a week which saves valuable time and money. Their movements are always exact, so less time is wasted performing unnecessary tasks.

Text referenced from http://www.robots.com/blog.php?tag=112



The Disadvantages of industrial Robots;

Expense;

The initial investment of robots is very high, especially when businesses are limiting their purchases to new robotic equipment and ancillary devices. The cost of automation should be calculated in light of a well defined and structured business plan and never on a whim just to improve production and through put.

Regular maintenance schedules can have a financial toll as well; this must also be factored into the overall cost of the introduction of a robot cell.

Expertise;

Employees will require training in programming and interacting with the new robotic equipment. This normally takes time and is initially a financial drain on the company.

Safety;

Robots may protect workers from some hazards, but in the meantime, their very presence can create other safety problems. These new dangers must be taken into consideration when setting up an automated cell generally by the use of expensive additional systems such as laser light curtains, machine interlocks and operational barriers.

All of these additional safety systems must be fully risk assessed and evaluated during a HS&E audit to ensure all operatives of the equipment are working in a controlled and safe environment.

Task 1b – Drive systems and mechanisms

Task requirements Examine in detail the main drive systems used to power industrial robots and consider the methods in which the power is transmitted into linear and rotary drive. Analyse the key elements of a robot manipulator and their principles of operation.

http://www.robots.com/robotics.php?page=industrial+automation



Components of an industrial Robot

A typical robot used in industry today generally consists of 5 basic components.

Controller

Every robot is connected to a computer controller, which regulates the components of the arm and keeps them working together. The controller also allows the robot to be networked to other systems, so that it may work together with other machines, processes, or robots. Almost all robots are pre-programmed using "teaching" devices or offline software programs. In the future, controllers with artificial intelligence (AI) could allow robots to think on their own, even program themselves. This could make robots more self-reliant and independent.

Arm

The arm is the part of the robot that positions the end-effector and sensors to do their pre-programmed business. Many are built to resemble human arms, and have shoulders, elbows, wrists, even fingers. Each joint is said to give the robot 1 degree of freedom. A simple robot arm with 3 degrees of freedom could move in 3 ways: up and down, left and right, forward and backward. Most working robots today have 6 degrees of freedom to allow them to reach any possible point in space within its work envelope. The human arm has 7.

End-Effector

The end-effector could be thought of as the "hand" on the end of the robotic arm. There are many possible end-effectors including a gripper, a vacuum pump, tweezers, scalpel, blowtorch, welder, spray gun, or just about anything that helps it do its job. Some robots can change end-effectors, and be reprogrammed for a different set of tasks.

Sensor

The sensor sends information, in the form of electronic signals back to the controller. Sensors also give the robot controller information about its surroundings and lets it know the exact position of the arm, or the state of the world around it. One of the more exciting areas of sensor development is occurring in the field of computer vision and object recognition. Robot sensors can detect infrared radiation to "see" in the dark.

And finally; a drive system.



Drive

The links, the sections between the joints are moved into their desired position by the drive system. Typically, a drive is powered by one of the following;

Pneumatic (air);

Hydraulic pressure (oil); and

Electricity.

Illustration referenced from http://www.engineershandbook.com/Components/robots2.htm

Figure 3. A diagram of a typical 6 axis articulated robot used in industry today. Note; The axis numbers start from the base A1 upwards to the A6 wrist axis. The movement of the robot is determined by the drive system used to power the robot. This can any one of three i.e. air, oil or electricity, the chosen drive system would be dependant on the task the robot is performing. An example of this would be a robot

http://www.engineershandbook.com/Components/robots2.htm



carrying heavy payloads with a large working envelope would most certainly use a hydraulic drive system as this would be the most effective. Drive systems used in robotic applications Pneumatic drives Pneumatic drive systems use compressed air as the method to drive the system that operates the robot. Many of the principles of hydraulic systems are the same as using compressed air. Since air is compressible, precise control speeds and position is a little more difficult to achieve, it is also less powerful than the use of hydraulics. However one advantage is that by compressing air is has the ability to absorb shock preventing possible damage to the component being moved or manipulated. Some of the other advantages of using pneumatic systems are;

Simple and reliable;

Plentiful supply in most factories;

Clean and safe i.e. will not explode or catch fire;

No need for large return tanks;

Easily stored and transported; and

Relatively cheap;

Before compressed air can be used for the operation of a robotic system certain conditioning must be carried out to ensure the reliable safe operation of the robot;

Air must be dried to remove moisture which can cause rusting of steel components and bearings;

After the removal of the moisture from the air a very fine oil mist provides lubrication to the system, this is achieved by the use of a filter system;

The filter system is also used to filter out dust particles and foreign objects which can cause wear and therefore damage to the components of the robot.



Hydraulic drives Fluid power systems involve a number of conversion stages in order to finally produce and therefore achieve motion. The hydraulic oil is pressurised by the use of an electric motor driving the hydraulic pump which in turn delivers the oil under pressure. The fluid under pressure is then converted into mechanical power via the use of a series of cylinders and actuators. This method requires the system to be closed due to the high pressures involved any exhausted oil must be redirected back to the hydraulic pump for it to be re circulated. A simple diagram detailing this is shown below.

Diagram referenced from http://claymore.engineer.gvsu.edu/~jackh/books/plcs/html/plcs-700.gif

What is a hydraulic actuator? Hydraulic robot operating systems may drive a rotary type actuator or be used to extend / retract pistons within cylinders. This type of system is known as a linear actuator rather than a rotary actuator. The holes in the hydraulic component that admit the fluid and allow it to be exhausted are called ports; these ports may act as an input or an output for the fluid. By using linear actuators the system could then be powered in both forward and reverse directions.

http://claymore.engineer.gvsu.edu/~jackh/books/plcs/html/plcs-700.gif



Figure 4 – Diagram of a double action hydraulic actuator

Illustration referenced from http://www.resonancepub.com/actuator.htm Rotary actuators The rotary type actuators comprise of a shaft jointed into a rotary vane with two separate ports located around the circumference of the body. Hydraulic fluid is then displaced from one of the ports by the pressurized fluid entering the other. The vane within the body of the actuator rotates in the direction of the input force driving the output shaft. An example of a rotary actuator can be seen below;

Illustration referenced from

http://www.hydraulicspneumatics.com/Content/Site200/ebooks/01_01_2006/63488fig1531gif_00000039412.gif





Electric motors The electric motor is a transducer that converts electrical energy into mechanical energy by the means of an AC or DC power supply. These motors are used as the actuators in many industrial robots used today in many manufacturing applications. The AC and DC motors are able to generate high torque levels from relatively small devices that are easily controlled via the use of a microprocessor or computer. The AC motors is generally the preferred option by today’s robot manufacturer and suppliers. The reason for this being that the AC induction motor can produce the same power output as a DC device but with higher torque and a reduction in the component size. Another plus point is that the motor does not require brushes and is fully enclosed and self cooling thus reducing component maintenance schedules. DC motors are still used for a variety of robot applications. The wrist arm section of many robots use DC motors instead of AC motors because their speed decreases when a higher load is applied. Thus with lighter loads the acceleration of the robot increases dramatically thus enabling the robot to be position very precisely at high speeds. An additional type of electric motor is also used in some robot applications. Stepper motors are used for much cheaper open loop command systems with very light payload. This motor is generally not suitable for heavy payload devices due to the jerky drive and movement often associated with stepper motors. A typical example of an application for the use of stepper motors would be loading flat pack boxes onto a pallet for packaging.

Figure 5 – An example of a simple 2 pole DC motor workings



Figure 6 – An example of a typical AC brushless servo motor Drive mechanisms used in robotic applications The axes movement of robots can be either linear or rotary and in many cases both at the same time. The movement of the axis is usually achieved by the means of a mechanical device converting electrical rotational motion into linear motion or drive. This can be achieved in many ways, some of which are detailed below;

Drive chains;

Gears;

Linkages; and

Toothed pulleys and drive belts. The mechanism’s above are mainly used for very simple robust mechanical devises and are not really suited for today’s advanced and high speed applications; although they have been very useful in the formative years of robot development and manufacture, they are not generally the most practical solution today;



The most commonly used precision robot drive mechanisms currently manufactured are;

Lead screws;

Ball screws; and

Harmonic. So what are they and how do they work? Lead screws A precision machined or ground screw cut shaft rotates driving a nut usually made of phosphorus bronze, which is attached to the driven part. This type of drive would only be used on very simple gantry type machine similar to that used in a CNC machining centre because of the high force and friction involved during its operation. A typical example of a lead screw can be seen below;

Photo referenced from http://www.idamotion.co.uk/images/microslide%20tech%20pic.jpg

http://www.idamotion.co.uk/images/microslide%20tech%20pic.jpg



Ball screws Ball bearings are feed out of a carrier into a precision ground ball screw that reticulates the balls back into the carrier after three or four revolutions of the screw. This system produces a low friction drive due to the fact that the load ids being transmitted at the point of contact i.e. the surface contact point of the ball bearings which is very small. This system also benefits from a very limited amount of backlash which limits the amount of wear to the rotating components. This system is mainly used in articulated robots to convert the rotational motion of the DC to drive the shoulder and arm axis. An example of a ball screw is shown below, note that all surface are precision ground, this type drive mechanism is very expensive to manufacture due to the tight tolerance requirement for the ball bearings to rotate without seizure.

Harmonic drives Harmonic drives are the popular choice for a drive system in robotics today. They are widely used due to the fact they provide a high output torque from the drive motors and also reduce rotational speeds, by doing this they have very little backlash and require virtually no maintenance. Compared to other drive system they are lightweight, compact, more reliable and thus much efficient. The unit also has a very low vibration capability at



very low speeds, this make them ideal for precise manufacturing requirements such as welding or assembly applications. So how does a harmonic drive system work? The harmonic gear allows high reduction ratios with concentric shafts and with very low backlash and vibration. It is based on a very simple construction utilising metals elasto-mechanical property. Harmonic drive transmissions are noted for their ability to reduce backlash in a motion control system. The principle of operation of harmonic gears is through the use of a thin-walled flexible cup with external splines on its lip, placed inside a circular thick-walled rigid ring machined with internal splines. The external flexible spline has two fewer teeth than the internal circular spline. An elliptical cam enclosed in an antifriction ball bearing assembly is mounted inside the flexible cup and forces the flexible cup splines to push deeply into the rigid ring at two opposite points while rotating. The two contact points rotate at a speed governed be the difference in the number of teeth on the two splines. This method basically preloads the teeth, which reduces backlash Harmonic drive applications

Robotics Harmonic Drives offer robot manufacturers many benefits including zero backlash, high positional accuracy, low vibration and a compact design. They can be used in any of the robot axes and their light weight design contributes minimal weight to the robotic arm which increases robot payload capacity.

Machine Tools Harmonic drives allow accurate control of the motions for axis positioning and for tool changing.

Medical Applications using harmonic drives include patient beds, rehabilitation equipment, and MRI / CAT scan gantries.

Military Aerospace The Harmonic Drives are used to accurately rotate and tilt the antennas and arrays. They are also used for driving lunar vehicle motions and positioning aerials and telescopes e.g. Harmonic drives are used in the Hubble Telescope.



Harmonic gear construction

Wave generator;

The wave generator is an oval-shaped cam with a thin ball bearing placed around the outer circumference of the oval cam. The wave generator is mounted onto the motor shaft. Flex spline;

The flex spline is a thin, cup-shaped component made of elastic metal, with teeth formed along the outer circumference of the cup's opening. The gear's output shaft is attached to the bottom of the flex spline. Circular spline;

The circular spline is a rigid internal gear with teeth formed along its inner circumference. These teeth are the same size as those of the flex spline, but the circular spline has two more teeth than the flex spline. The circular spline is attached to the gearbox along its outer circumference

Figure 7 – Simple schematic of a Harmonic drive system used in robot technology

Text and illustration referenced from http://www.roymech.co.uk/Useful_Tables/Drive/Harmonic_Gears.html



BTEC HIGHER NATIONAL DIPLOMA

Robot Technology

Task 2:

Describe the main control elements of a robot system and

their function

Assessor:

Wayne Seal



Task 2 – Robot control systems

Task requirements Describe the main control elements of a robot system and their function. Robot control systems

An open-loop controller, also called a non-feedback controller, is a type of controller which computes its input into a system using only the current state and its model of the system.

A characteristic of the open-loop controller is that it does not use feedback to determine if its input has achieved the desired goal. This means that the system does not observe the output of the processes that it is controlling. Consequently, a true open-loop system can not engage in machine learning and also cannot correct any errors that it could make. It also may not compensate for disturbances in the system.

Open-loop control is useful for well-defined systems where the relationship between input and the resultant state can be modeled by a mathematical formula. For example determining the voltage to be fed to an electric motor that drives a constant load, in order to achieve a desired speed would be a good application of open-loop control. If the load were not predictable, on the other hand, the motor's speed might vary as a function of the load as well as of the voltage, and an open-loop controller would therefore not be sufficient to ensure repeatable control of the velocity.

An example of this is a conveyor system that is required to travel at a constant speed. For a constant voltage, the conveyor will move at a different speed depending on the load on the motor (represented here by the weight of objects on the conveyor). In order for the conveyor to run at a constant speed, the voltage of the motor must be adjusted depending on the load. In this case, a closed-loop control system would be necessary.

An open-loop controller is often used in simple processes because of its simplicity and low-cost, especially in systems where feedback is not critical. A typical example would be a conventional washing machine, for which the length of machine wash time is entirely dependent on the judgment and estimation of the human operator. Generally, to obtain a more accurate or more adaptive control, it is necessary to feed the output of the system back to the inputs of the controller. This type of system is called a closed-loop system.

Referenced from http://en.wikipedia.org/wiki/Control_theory

http://en.wikipedia.org/wiki/Controller_(control_theory)

http://en.wikipedia.org/wiki/State_(controls)

http://en.wikipedia.org/wiki/Mathematical_model

http://en.wikipedia.org/wiki/Feedback

http://en.wikipedia.org/wiki/Machine_learning

http://en.wikipedia.org/wiki/Voltage

http://en.wikipedia.org/wiki/Electric_motor

http://en.wikipedia.org/wiki/Speed

http://en.wikipedia.org/wiki/Washing_machine

http://en.wikipedia.org/wiki/Control_theory



Closed loop system

For the purpose of describing a closed system I am going to use part of an assignment I completed during my first year of my HNC.

A simple example of an open loop system would be the use of an electric furnace.

The furnace operates using an open loop system; the temperature setting will indicate the heating element to deliver energy / power to generate the set furnace temperature, regardless of the actual temperature of the furnace. This open loop cannot regulate the set temperature of the furnace as there is no method of motoring the required and actual temperature of the furnace.

As you can imagine this type of system may not be suitable for all application, for example an operator may wish to heat a component to a set temperature for a period of time before removing it and replacing it with another identical part.

So how would we do this?

We would create a closed loop system to monitor the temperature of the furnace using a thermocouple and then regulate that temperature using a controller which is basically a regulator of the power required to heat the furnace.

This method requires a controller to set temperature is via an automated control loop this is provided by a Eurotherm controller. The controller will automatically control process variables in this case the temperature. The automatic temperature control loop consists of a sensor to measure the temperature; a thermocouple and a controller which is a power regulator. The controller compares the measured temperature with the desired temperature called the “set point” and regulates the output power to make them the same. The difference between the set point and the measured value is called the error signal, this signal is then measured by the controller and the temperature can be raised or lowered. A block diagram of how this system operates can be seen overleaf. In simple terms when the temperature is too high the controller will cut the power to the furnace heating element allowing the temperature to drop to the set point. The temperature is monitored by the internal thermocouple which sends a signal to the controller and the reverse will happen if the thermocouple reading is below the set point. By creating a closed loop system we now have total control of the temperature within the furnace, whilst an open loop system would not.



Control structure

As in my example of a simple furnace, we have already discovered the benefits of having a closed loop control system to enable the operator to have full control of the working environment.

So how is this achieved in industrial robotic systems?

Every robot is connected to a computer controller, which regulates the components of the arm and keeps them working together. The controller also allows the robot to be networked to other systems, so that it may work together with other machines, processes, or robots. Almost all robots are pre-programmed using "teaching" devices or offline software programs.

A typical example of a robot controller system and teach pendant. The teach pendant below is used to both programme the robot and also teach basic commands and simple moves.



The control cabinet generally consists of a central processing unit and various micro chips mechanisms that are able to drive the robot mechanisms, process program commands, receive input signals and send output signals. An example of the function of the control system can be seen below.

Illustration referenced from http://www.eod.gvsu.edu/~jackh/books/integrated/html/integrated.html

Digital to analogue converters (DAC)

For the controller to function correctly and interface with all of the systems required to operate the robot a DAC will be requires. A Digital to Analogue Converter (DAC) allows the feedback from the sensors of the robot such as a transducer which outputs analogue voltages. These analogue voltages must then be converted to a digital signal for the CPU to process via the use of an interface. Interfaces are the electronic devices that convert and process signals to make them compatible. Generally all of the incoming signals, from the external devices or sensors pass through this interface device. An example of a Digital to Analogue Converter (DAC) can be seen overleaf controlling the split furnace voltage signals and then converting them to a digital signal for the Eurotherm PID controller encode.

http://www.eod.gvsu.edu/~jackh/books/integrated/html/integrated.html



Positional sensors The most commonly used positional sensor on articulated robotic systems is the rotary transducer (sensor). This type of sensor has a large number of fine lines evenly spaced radially around a disc which are either reflective or transparent. These interrupt a narrow beam of light transmitted through the disc, or reflect from it. The light sensor transmits light pulses as electrical signals to a counter in the controller; this signal pattern is used as a measure of rotational movement which ids converted into a linear measurement. This type of optical encoder can be connected directly to any robotic arm or joint, or directly mounted on to the shaft of a drive motor for either rotary or linear drive provided by a suitable mechanism. When heavy payloads are used and require a very precise positioning the rotary encoder speed is controlled by a tachogenerator on the motor shaft. By doing this the control system can decelerate the drive mechanism before it reaches the final position required giving a faster and more accurate positioning of the component being loaded. Other commonly used types of positional sensors are;

Linear sensors;

Optical sensors;

Incremental sensors;

Absolute sensors;

Velocity sensors; and

Laser sensors. When considering what type of positional sensor should be used the following should be fully evaluated during the initial specification period of the robotic system.

The environment;

Payload weight;

Drive system;



Heat;

Cold;

Vibration;

The purpose of the robot; and

The manipulator / gripper system. Figure 8 – An example of a rotary transducer used in robotics

Illustration referenced from http://www.ludlsemi.com/Portals/0/JpegImage/Rotary-Encoder-

Illustration.jpg




Robot Technology

Task 3:

Describe devices and methods used to improve the

intelligence of a robot

Assessor:

Wayne Seal



Task 3 – Sensory feedback systems

Task requirements Describe devices and methods used to improve the intelligence of a robot. Machine vision systems Machine vision is concerned with the sensing of vision data and its interpretation by the computer controller. A typical machine vision system consisits of a camera and digitizing equipment, a computer and the necessary ancillary systems that will allow them all to interface and interact correctly. The interface unit is often referred to a preprocessor. The operation of the vision system relies on of three main functions; these functions are;

Function 1 - Sensing and digitizing image data;

Function 2 - Processing of the image and then analyzing the image;

Function 3 - Applying this data into an actual intelligent movement. This area of industrial robotics is currently one the most exciting active fields of research and development costing many millions of pounds every year. While intelligent digitizing vision systems may be the future, they are very difficult to implement and are very expensive to introduce successfully to a manufacturing environment. To be successful when introducing these systems there are four main elements that must be fundamentally present; these are.

1. A source of illumination; 2. A camera source;

3. A computer interface; and

4. Analytical software.



Source of illumination A good suitable lighting source is a must for vision systems for two main reasons. The first being a suitable image must be produced with the minimum amount of light available. In an industrial environment the light available is usually much less than most photographic equipment would require to operate effectively. The ambient lighting condition of factories will most probably incorporate large areas of inconsistent light due to the shadows casts of large machine and the positioning of the windows. Secondly contrast levels are essential for a motion system. The ability to differentiate between the component and the background depends mainly on the level of contrast within the digitized image. Contrast is the difference in the visual properties that makes an object distinguishable from other objects and the background in simple terms the difference between the whitest white and the blackest black. It is therefore essential that the correct light source is selected for the process or application but just as important is the positioning of the light source with regard to the environment the robot is operating. The light source must provide a constant level of contrast to enable the system to differentiate between the subject and the background other wise the system will malfunction on a regular basis. A camera source Vision sensing cameras are basically split into two different types. These are;

1. TV camera tube or Vidicon tube; and 2. Solid state camera or Charged Coupled Devices (CCD).

The CCD devices are most commonly used as they are the more modern technology and are rapidly taking the place of the older Vidicon tubes for most robot applications. This is due to the following;

They cannot be damaged due to the constant exposure to a high intensity light source;

They consume a lot less power than the Vidicon tubes; and

They provide a more consistent blur free image that the Vidicon system It is also worth noting that the lenses can be easily changed on these systems to alter the depth of field for different sized components and fixtures.



A computer interface A computer interface is required to link the output from the camera system to the CPU that will carry out the analysis of the recorded image or data. This interface device may well carry out several important tasks. This will generally be in the form of converting an analogue signal to a digital signal just the same as the DAC within the robot itself. This signal may also require filtering to remove any external noise or distortion. The image itself may need enhancing to improve the contrast between the subject and the background. As you can image all of this data must be processed very quickly otherwise the system would grind to a halt. It is therefore imperative that this system operates very quickly so it most likely to employ state of the art high speed processing chips. Analytical software Once the image has been digitized, it then has to be converted to some sort of meaningful and relevant information. This is usually very complicated and involves the use of mathematical equations and logarithms. As you can imagine the image system is only as good as the software that operates it. These software packages can take many years to perfect and are very expensive to research and develop. This part of the system would generally be supplied by a computer interface company that specialises in vision system and ancillary equipment to meet the needs of the industry today. End effectors (The final component of the system)

The end effector is the last part of the robot furthest from the base which interacts with the environment. In the human arm comparison, the end effector would be the equivalent of the hand.

The robot's task is to deliver the end effector to the desired location so that the End Effector may accomplish its task by either being a tool itself or by holding a tool. There are many different types of end effector available which depend wholly on each application.

Below are some types of end effectors Loop Technology can utilise to provide your robotic solutions:-

Vision For applications that require a vision system for inspection or guidance, the End Effector will be or contain a camera. Many other End Effectors could incorporate a camera to give the operators a view of the robot at all times



Welding Guns Robotic welders have end effectors available for each type of welding (i.e., MIG, TIG, Laser, Resistance, Gas etc). Each end effector will have the welding torch and method of applying the filler material where required.

Grippers There are a few types of grippers and some can be custom designed if the object is a particular shape or structure. Here are the main types of grippers;

General purpose (2 Jaw) Gripper – for applications requiring a high grip force to moment ratio and positive pick and place.

General purpose (3 Jaw) Gripper – for applications requiring a gripper that offers self centring of parts, high grip force to moment ratio and positive pick and place.

High-moment gripper – for applications that apply extreme stress to the gripper (e.g., applying high acceleration to heavy objects or extremely long, precisely positioned jaws).

Long-stroke gripper – for applications requiring longer stroke lengths. Miniature gripper – for applications requiring small stroke lengths. Collet gripper –- for applications requiring precise picking and placing

of uniform cylindrical part

Referenced from http://www.looptechnology.com/robotic-robot-types.asp

An example of a SCARA robot using lever type grippers to locate and move bottles with the aid of a camera vision system.

Illustration referenced from

http://www.intelligentactuator.com/products/rcp2gripper.php

Solid state camera



Bibliography

Derby College HND handout course notes; Industrial Robotics, Technology, Programming and Applications – Groover, Weiss, Nagel and Odrey.

Web site sites used during this assignment

www.google.co.uk. http://www.robots.com/blog.php?tag=112 http://www.engineershandbook.com/Components/robots2.htm http://claymore.engineer.gvsu.edu/~jackh/books/plcs/html/plcs-700.gif http://www.resonancepub.com/actuator.htm http://www.roymech.co.uk/Useful_Tables/Drive/Harmonic_Gears.html http://www.eod.gvsu.edu/~jackh/books/integrated/html/integrated.html http://www.ludlsemi.com/Portals/0/JpegImage/Rotary-Encoder- http://www.engineershandbook.com/Components/robots.htm http://www.robotics.utexas.edu/rrg/learn_more/low_ed/types/industrial.html http://www.learnaboutrobots.com/robotVision.htm http://www.robots.com/kuka.php?robot=kr+6 http://www.intelligentactuator.com/products/rcp2gripper.php

http://www.looptechnology.com/robotic-robot-types.asp

Appendix 1

Additional information - Kuka KR6,15 technical specification

http://www.google.co.uk/

http://www.robots.com/blog.php?tag=112

http://www.engineershandbook.com/Components/robots2.htm

http://claymore.engineer.gvsu.edu/~jackh/books/plcs/html/plcs-700.gif

http://www.resonancepub.com/actuator.htm

http://www.roymech.co.uk/Useful_Tables/Drive/Harmonic_Gears.html

http://www.eod.gvsu.edu/~jackh/books/integrated/html/integrated.html

http://www.engineershandbook.com/Components/robots.htm

http://www.robotics.utexas.edu/rrg/learn_more/low_ed/types/industrial.html

http://www.learnaboutrobots.com/robotVision.htm




Robot Technology

Appendix 1:

Kuka KR5,15 technical specification

Assessor:

Wayne Seal

robot technology_derby college

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