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Design Solutions
Programme 4: Systems and Control
This programme aims to introduce students to the following:
To provide a context in which to illustrate systems design from initial functional performance requirements to practical solution
To show how various members of the design team work together
To demonstrate the importance of testing using a variety of approaches such as computer simulation, data logging and prototypes
To describe the process of systems design from a list of functions, through block diagrams, to circuit design and configuration of components compatible with physical mechanical design
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This programme follows a team of designers who are designing a remotely operated vehicle (ROV) for use underwater.
0:00 – Hydrovision, based in Aberdeen, is a company whose core business is based in the offshore oil industry. It specialises in the design and manufacture of sub-sea robotic systems, including ROVs. Since 1989, Hydrovision has produced the 'Hyball'. This is a deep-sea robot that can do what is impossible for divers to achieve. It can work in dangerous conditions such as inside wrecks or in polluted waters, in a depth of up to 300 metres. The 'Hyball', operated by pilots on the surface who direct and programme the machines, allows a remote eye (video) to relay images back to the surface. However, the design is now dated in terms of technology, uses and flexibility. It needs modernising.
2:00 – Chris Tarmey, Chief Executive Officer of Hydrovision, explains that a new type of 'Hyball' is required. It should be easy to use, affordable, portable, carry a range of tools such as sonars, measuring devices, sensors, manipulator packages and be flexible enough to allow the client to add their own tools and accessories.
4:00 – The electrical engineer, Jon Robertson begins with a list of all the functions the remotely operated vehicle, ROV, must be able to perform. He uses block diagrams to work out the relationships and requirements of the sub-sea devices. The processes and purpose of each are explained in terms of input and output devices. The navigation sensor components are the main focus ie compass, gyroscope and depth gauge. He describes how these will have to be mounted onto a printed circuit board (PCB).
6:00 – He explores the possible 3D configurations of the housing for the sensors using 3D computer-aided design (CAD) modelling in order to design the unit and PCB. He builds a 3D computer model of all the components, including the thrusters on to the frame.
7:00 – The PCBs are constructed. Simon Massey, research and development electronic engineer, tests the navigation pod of the ROV, specifically the depth transducer, speed rate gyroscope and the digital compass, by measuring all the outputs to ensure that they are functioning correctly. He checks how well it operates and how well it sends data back to the surface, how it is displayed and used to loop back to operate the output such as the thrusters. Simon describes the system as does John, but refers to the physical components whilst describing and demonstrating his tasks, giving a clear indication of their size and scale.
8:00 – The physical components are assembled as a working prototype for testing.
8:30 – Jon tests the autohead function of the Seaeye Falcon ROV in the test tank. However, there proves to be a problem with the autohead function. The autohead should keep the Seaeye Falcon on course of navigation but seems to thrash about instead.
9:00 – Simon tests each of the data signals collected, explaining how each sensor is testing in turn. He finds the problem does not lie with the subsea pod autoheading. Miles Merckol, software engineer identified it as a fault with the microprocessor surface circuit. This is adjusted and tested again. The software engineer rectifies the faults by changing the values of the computer software programme.
10:00 – The Seaeye Falcon is tested again and the inputs are performing correctly and informing the outputs, so the Falcon ROV can go into production. Workshop assembly is shown briefly.
11:00 – The performance of the design solution is checked against the initial brief. Performance of 50kg thrust for the same weight of ROV, 50kg. A 1:1 power to weight ratio has never been done before. The marketing and sales director, Tom Keane indicates that the response has been fantastic. It is thought to be so much better than its predecessor. With the open frame, the manipulator packages, the sonars, measuring devises, etc. can be added on as needed, and as long as it has a supply of electricity it has 24-hour continuous working capability.
13:00 – End of programme.
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Scotland: National Qualifications: Technological Studies: Intermediate 2 and Higher
Outcome 1
This programme illustrates the analysis of the operation of control systems. The designer uses graphical representation to describe the system, subsystems, closed loop, etc.
Outcome 2
The design involves closed loop analogue, opamps and tests by construction for evaluation
Outcome 3
The sequence and components, software, interfacing devices, etc. involved in the control of the mechatronic system of the ROV is illustrated clearly
Outcome 4
The need for the subsystems which inform the microprocessor which in turn send back input signals eg to thrusters is described. Multiplexing. The testing undertaken demonstrates signal processing and verifying
Electronics
Outcome 1
The design of an electronic system to meet a given specification is touched upon in the components and subsystems, inputs and outputs illustrated in terms of function, intended operation and testing
Outcome 2
The design of a system using operational amplifiers to meet given specifications is described
England: National Curriculum KS4
Knowledge and understanding of systems and control
5- a, i, ii, iii
The concepts of input, process and output and the importance of feedback in controlling systems, including: the design, use and purposes, how feedback is incorporated into the systems and how to analyse the performance of systems
General Curriculum relevance
The programme uses block diagrams, systems and subsystems and closed loops to analyse the functional performance required, as demanded by the brief and specification; it demonstrates the control system of a mechatronic system and evaluation of the control system through various testing. Therefore, it is also suitable for Standard Grade Technological Studies as a general illustration of the practical application of their studies.
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This programme outlines the design stages from evaluating an existing product and devising an initial specification for a new model through to final product, of a remotely operated vehicle (ROV). The design engineers explain how the initial requirements are used to develop a basic block diagram, how the system works in terms of inputs and outputs, configuration of the actual components and then we see the results in practice.
It illustrates the importance of testing, diagnosing faults and overcoming errors.
It describes the process and the people and the various disciplines involved.
The shape and relationship of the various PCBs with each other and the housing design are good demonstrations of the real application in comparison to the theory ie round circuit boards rather than rectangular or square.
Background information on how a digital compass works will be useful for the overall context of this programme and subsequent questions and understanding. For example, the depth sensor is a closed loop system, as is the compass and as is the speed gyroscope, but the distance is decided by the pilot (open loop system) which decides on the arrival point or whether the target has been met. What difference would a global positioning system (GPS) have made? This could be discussed with the class after viewing the programme. The designers could have selected an onboard power supply, but opted for the umbilical cord. This offers the opportunity for discussion of advantages and disadvantages (see suggestions for activities).
The full specification of the resultant design can be found on the Hydrovision company website (see links section). This provides good background for the study of the system the programme summarises. There is also a short mpeg of the ROV in operation, which allows the students to develop an understanding of the function of various components discussed in the programme.
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Before viewing the programme
- Discuss with students what a remotely operated vehicle (ROV) is. List the types of contexts and scenarios these might be used in, eg salmon farming.
- Watch the Hydrovision Seaeye website video of the Falcon in action to familiarise the students with the purpose of the vehicle.
- Ensure the students are aware of inputs, outputs, closed and open loop systems.
- Provide some key questions to structure the students' note-taking, eg note the requirements of the replacement Hyball - what should it be capable of doing?;
note the three sensors which will provide input signals to the surface processor - what is the job of the gyroscope?
After viewing the programme
- Discuss the key stages in the design process as described in the programme.
- Ask the students to list / draw up the required specification as laid out by the chief executive for the replacement to the 'Hyball'.
- Make a list of the subsea inputs and outputs and identify the subsystems described by the electronic engineers. Ensure the students understood the relationship between the subsea and the surface in the system.
- Elicit from the students a description of the function of the autohead.
- Pause on the 3D CAD model of the digital compass and explain that the coils, as sensors, give a direction signal. (One coil is perpendicular and the other is parallel with the earth's magnetic field). The voltage is the same. When movement occurs, there is change in the signal; this input is received by the data logger which responds to match the set programme. Therefore, the autohead will send a signal as an output to the thrusters to change direction.
- Encourage the students to consider what is required to get from to A to B. Make a list of all the information required and where this information could come from, including maps. Encourage students to think of other ways of achieving a navigational control feature, eg GPS (3D data is provided by these), laser guidance, radar, etc.
- Encourage students to think of other ways of achieving a navigational control feature. For example, GPS (3D data is provided by these).
- The umbilical cable in the programme allowed the Seaeye to dive 300 metres.
- Set up a spreadsheet for students to explore the variables and make a best-fit decision for the design of the umbilical cable in terms of length and cross section. Each variable will have impact on the weight, power loss and the cost. The constants are the resistance of copper, and density (for weight). The variables are the length and cross section. Calculations of weight and power loss. Voltage and amp rating of the thrusters could be simplified for calculations, the real specification can be incorporated (see http://www.seaeye.com/products5.html).
- Alternatively set them a calculation with given values and ask them to calculate the resistance per metre of the cable, eg 24V motors for the thrusters, 10amp cable with cross section of 3mm; or calculate the voltage drop along the cable using potential divider theory.
- Ask the students to search the website to find out which attachment accessories and sensor devices are available for the Seaeye Falcon. The various pages in this link provide specifications for each of the main components incorporated in the ROV seaeye and are good for research and further understanding of the design solution, eg the thrusters. www.seaeye.com/products5.html
- Check out the features of the Seaeye and compare with other 2.5kw appliances such as those around the house: eg Domestic kettle: 10kw
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This web page contains links to other websites that are neither controlled nor maintained by Channel 4 Television. Channel 4 Television is not responsible for the content of these sites and does not necessarily endorse the material on them.
www.hydrovision.co.uk/
For an mpeg of the Seaeye Falcon in action: 10.9MB 352 X 288 Mpeg Video. Duration 4 minutes. Best viewed with Windows Media Player.
Seaeye Falcon Features:
- 300 metre depth rating, 16 kilo payload
- Magnetically coupled brushless DC thrusters with velocity feedback loop
- 4 Vectored and 1 vertical thruster
- 50kg thrust with 1:1 power to weight ratio
- Distributed intelligence control system
- Integral system diagnostics
- High resolution colour camera on 180° Tilt Platform
- Variable intensity 150 watts of lighting
- Auto heading, depth, compass and rate gyro
- Portable surface control system with video overlay and daylight readable display
- Low drag umbilical
- Single phase A/C power input - universal 100-270 VAC at 2.5kw
www.seaeye.com/products5.html for details on the thrusters Robot World, virtual robot building tutorials and simulations, research news and profiles of various robot types: www.bbc.co.uk/science/robots
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