Archive for the ‘MECHANICAL’ category

New kit converts earthmovers to full remote control

February 2, 2013

New kit converts earthmovers to full remote control

July 7, 2006 If you’re a remote control enthusiast seeking the ultimate toy, the birthday present wish list will become frightfully expensive by the end of this paragraph. Defence technology specialist QinetiQ has launched a range of Applique Robotic Kits (ARKs) that convert the current in-service military JCB 4CXM or Caterpillar CAT320B families of vehicles into fully integrated remote controlled units for use by the military in hazardous environments. Operators can be up to a kilometre away and don’t even need to directly see the vehicle they are operating, but still have full control of it. By simply flicking a switch, existing vehicles can change between full remote or manual mode, immediately reducing potential dangers to the operators but still enabling it to be fully used for the tasks for which it was designed.

“Plant operators and drivers have often been placed in real danger when working in hazardous environments – for the first time they have a viable alternative,” explained Fiona Lewinton, MD of QinetiQ’s Land Division. “Activities involving military operations, nuclear waste or chemical management, contaminated other hazardous land clearance or activities on unstable land place significant safety risks and safety management issues on operators and companies. QinetiQ’s Appliqué Robotic Kit, once fully integrated on a vehicle, now means that they can fully operate the vehicle at a safe distance.”

New kit converts earthmovers to full remote control

The ARK system is easily transferred between vehicles or simply removed after use, returning the vehicle to its non modified state. Each kit comprises a Portable Command Console (PCC), Vehicle Mounted Control Modules (VCMs) and a host feedback interface and electro-hydraulic system for each specific vehicle. The electro-hydraulic modules are vehicle specific, with all the other components being generic.

Based on QinetiQ’s historical development work for the MOD on vehicles such as the JCB 170, the ARK system provides a robust and reliable solution that meets UK safety critical hardware standards including Safety Integrity Level 2 (SIL2). The remote control capabilities are managed via a COFDM radio solution that provides high quality video and data feedback at relatively low power consumption.

The Portable Command Console (PCC) controls everything from vehicle windscreen wipers to the brakes and bucket but does not impede the driver when the vehicle is operated in manual mode. The PCC operates continuously via an external 24v power supply or for 1.5 hours using batteries. A 128 bit encryption dongle key coupled with a remote e-stop button on the console ensures maximum security and safety to the remote operator.

A 15-inch sunlight readable LCD screen presents a crystal clear display and 20 buttons surround the screen, providing access to the easy to use menu system and its various features. Sensors and auxiliary tools and cameras can also be fitted to provide additional information – dependent on the operational scenario. Selectable camera views, vital vehicle information and vehicle position are all displayed on the console to provide the operator with all the information to run the plant equipment with confidence.

New kit converts earthmovers to full remote control

The vehicle control unit acts as the main router of the system on the vehicle and receives feedback from the vehicle hydraulic module, the vehicle electrical module and the camera modules. The vehicle electrical module links to the host vehicle and provides and receives signals for the host vehicle such as the vehicle engine speed and operator warnings. The vehicle hydraulic module provides the control link to the host vehicle hydraulic system.

In addition to the core ARK systems, QinetiQ is also offering potential customers a range of options that include a kit and sensor fitment service, full in life support and training, a range of add-ons like infra-red and pan-n-tilt camera units plus a spooler/fibre cable unit. A bespoke kit design service for other vehicles is also available.

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MECHATRONICS & MICROPROCESSOR-06ME64 Question papers

January 11, 2013

2007 -Dec.07-Jan.08-ME63

2007 -July-ME63

2008 -Dec.08-Jan.09-ME63

2008 -June.July-ME63

2009 -June.July-06ME64

2010 -May.June-06ME64

2010 -May.June-ME63

some important basics required to study Fluid Mechanics

November 10, 2012
  1. fluid_pr
  2. conmass
  3. integral_equations
  4. non-dimensional-numbers
  5. streamlines

Compressor Types

September 21, 2012

Contents

    • Piston Compressors
    • Screw Compressors
    • Dynamic Compressors
    • Air Treatment
    • Air Lubrication
  • Pressure Regulation

The majority of air compressors work on positive displacement, this means a fixed volume of air is delivered from each rotation of the compressor.

Piston Compressors
Piston compressors are the most common form of compressor for compressing air, some smaller compressors use a single cylinder compressing air in one direction of its stroke, this type of compression method can however cause an uneven air supply, this can be due to pressure being lost through use of the air supply while the piston is moving back drawing in more air. The double-acting construction (shown below) uses both sides of the piston and compresses on both strokes during one revolution, this gives a smoother air supply.

Double Acting Compressor

The above image shows a combined two stage compressor which is fine as it is, however when high pressures are required from a compressor set up like this then the compressed air temperature can rise to over 200°C and motor power needed to drive the compressor rises with this temperature.
So for these higher desired pressures it is far more economical to include a cooling system between each stage, this would then be known as a multistage compressor. These cooling systems are commonly known as intercoolers which work by drawing the hot compressed air over a very large surface area where the heat can dissipate quickly, this cooled air will then enter the second stage compression to be compressed even further by the last piston.

Two-stage compressor
Screw Compressor

Click for Larger Image

Screw compressors

Screw compressors are best suited when only medium pressures are required (<10 bar).
Screw compressors offer a steady flow of air without pulses and fluctuating pressure that can be associated with piston compressors, they also offer a simple system with fewer moving parts which equates to a more reliable system with less maintenance involved.

Screw compressors work on the basis of two intermeshing rotating screws with minimal clearance between each screw fin, they draw in air and squeeze it up along the screw with air getting compressed tighter the further along the screw its drawn until it reaches the discharge port, it is here that it is delivered out of the compressor.

The two intermeshed screws can be synchronised by external timing gears meaning that the screws should remain close but without touching each other. The other version is known as wet rotary screw compression, this is where the first screw is driven by a motor while the second screw isn’t, the second screw is rotated by being in physical contact with the first. This requires oil to be sprayed in with the air to relieve friction and wear; some of this lubricant will make its way into the air system so it is removed by later oil separation units.
Dynamic Compressors

Dynamic compressors are capable of delivering large volumes of air but little pressure (0.5-3bar). These compressors are usually known as blowers and work by drawing air in and throwing it out with the use of rotary fins, these fins rotate at very high speed.

There are 2 main types of dynamic compressor, they are centrifugal and axial.
Centrifugal systems use centrifugal force to hurl air out from the fins, centrifugal systems can generally obtain greater pressures than the axial type compressor.

Axial type compressor use a set of fan blades in line to generate large air flow, pressures from this method aren’t expected to reach much over 0.5bar. The axial compressors are largely used for ventilation and as part of air processing.

Axial Compressor

Axial Compressor

Air Saturation

The air we breathe from our atmosphere contains moisture in the form of water vapour; people often refer the amount of moisture in the air as levels of ‘humidity’. Humidity levels are a percentage of the saturation of air with water.
The maximum amount of water saturation in air varies greatly with temperature; hotter air can hold much more moisture than cold air. Due to the change in air pressure when compressing air its ability to hold moisture is seriously reduced, so some of the moisture content that was previously in the air will simply condense out of it when the air is compressed. This is why drainage systems and dryers are an important part of compressor systems.
If the water was allowed to travel out of the compressor into the pneumatic components that it was powering then this could cause big problems, for example ceasing valves and actuators.

Air Saturation

Relative Humidity = Mass of water vapour present           X 100
Mass of water needed to saturate it

Stages of air treatment

Filters
Compressed air requires filtration and drying before it leaves for pneumatic components, atmospheric air carries many particles of debris and moisture that unless filtered out can block valves or cause increased wear. Compressors usually filter air before its compressed, this is mainly to remove relatively large particles which could damage the compressor. A fine grade filter used after it is compressed helps filter the small particles which could clog or damage the pneumatic components that are used in pneumatic system set ups.

Air dryers
Before air can be used the excess moisture has to be removed, where well dried air isn’t a requirement all that may be needed is a basic intercooler followed by a separator unit; this is where the condensed water collects and is drained off.

Refrigeration units
The dew point can be lowered even further by cooling the air with a refrigeration unit which cools the air even further to around 0°C helping more moisture collect in the separator tank. This cold air is then routed through a separate section of the initial heat exchanger to help cool the warm air which is flowing through from the compressor.
This system of drying is suitable for most systems as air is dried out well.

Deliquescent dryer
Where completely dry air is a necessity then a chemical dryer should be used, the chemicals can remove moisture in two ways.
1) A chemical agent called a desiccant is used, this chemical agent collects water vapour and holds it while it eventually turns itself into a liquid once so much vapour has been collected and runs to the bottom of the unit where it is drained off. This chemical agent needs to be replaced quite regularly.

Absorption dryer
2) Within an absorption dryer a material called silicone dioxide or copper sulphate is used, this process works by attracting moisture to the sharp edges of these granular materials. Once these materials become saturated they are dried by passing heat through them, this process cant be carried out while it is still drying incoming air so they are usually set up with 2 of these moisture collectors which can be swapped over instantly, this allows one collector to collect the moisture while the remaining collector is left to dry itself out.
Oil is often added to the air to lubricate moving parts, the oil is released as a fine mist into well dried air, if the air is poorly dried then the oil will mix with the moisture and become tacky which will cause problems sticking valves ect.

Lubricator for compressed air systems

The oil is drawn up from the oil reservoir due to the way the air flows through the lubricator; a pressure difference between the lower and upper chambers is created as the air is channelled down past the oil mist opening. The screw valve is used to adjust this pressure difference.

Pressure Regulation

Pressure regulation in pneumatics is vital for the correct operation of circuits and for damage prevention to circuit components. As you would imagine all pneumatic components have a maximum operating pressure.

Relief valves
These are basic pressure regulators and are usually used in pneumatic circuits as a backup device should the main pressure controller fail. They work with the use of a ball valve which is under an adjustable amount of pressure to keep the valve shut, once this pressure is exceeded the ball forces the spring back allowing the excess pressure to escape. Care should be taken when employing a pressure relief valve, this is because the valve must have sufficient ability to vent the pressure and flow quickly enough should a fault occur, and should the worst happen the relief valve may have to dump the entire compressor output.
Once a fault has triggered the release mechanism and the pressure has dropped sufficiently then the valve automatically closes and re-seals itself. This type of valve is always ready to release pressure again if needed, however a safety valve must be manually reset once it has cracked to release pressure.

Non-relieving pressure regulators
Non-relieving pressure regulators work by restricting flow rather then venting it should over pressure occur. The regulator restricts flow when the pressure gets too high because the pressure acts on the diaphragm forcing it up against the spring pressure, the diaphragm has what is called a ‘poppet’ attached on the end of it which is drawn up with the diaphragm and restricts the passing air flow.

Non-Relieving Pressure Regulator (Pneumatics)

Relieving pressure regulators
Relieving pressure regulators use a similar diaphragm system to that of the non-relieving regulator. The diaphragm drops if the outlet pressure is too high closing the inlet valve and opening the outlet vent, releasing pressure until it falls back to the preset pressure.

Relieving pressure regulator

Drop Forging – Introduction

September 21, 2012

Contents

    • Introduction

What is drop forging?
Drop forging is a metal shaping process, the metal to be formed is first heated then shaped by forcing it into the contours of a die, this force can be in excess of 2000 tons. The drop forging process can be performed with the material at various temperatures;

  • Hot ForgingDuring hot forging the metals are heated to above their recrystallization temperature. The main benefit of this hot forging is that work hardening is prevented due to the recrystallization of the metal as it begins to cool.
  • Cold ForgingCold Forging is generally performed with metal at room temperature below the the recrystallization temperature. Cold forging typically work hardens the metal.

There are two types of drop forging, open die and closed die.
Open die drop forging requires the operator to position the work piece while it is impacted by the ram. The die attached to the ram is usually flat or of a simple contour, most of the shaping is achieved by the operator physically positioning the work piece before each stroke of the ram. There are also special dies which can be used to cut the metal, form holes or notches. see more

Closed die drop forging comprises of a die on the anvil which resembles a mould, the ram which falls and strikes the top of the metal billet can also be equipped with a die. The heated metal billet is placed on the lower die while the ram drives down forcing the metal to fill the contours of the die blocks. see more

 

Drop Forging Diagram
Diagram of basic drop forging set up

Investment casting

September 21, 2012

Investment casting is one of the oldest known metal forming techniques, dating back over 5’000 years ago when beeswax was used to create the pattern. Beeswax back then didn’t allow the accuracy and intricate shapes we can produce today. Investment castings are used in a huge array of items, golf clubs are investment cast, aeroplanes use investment cast parts as do cars and other motor vehicles.

Creating The Mould

To begin the process wax patterns are made by injecting hot molten wax into an aluminium die, this sets the wax pattern to the exact size and shape of the required part. Many of these wax moulds are attached to a wax sprue which forms a stem linking all of the individual moulds together.
Sprue

Once the sprues are filled with the mould attachments they are dipped into a cleaning bath to ensure the future layers of shell cling to the mould profile correctly. Before the first layer of the shell is added the sprue assembly is dipped into a bath of slurry, this will form the bonding agent to the layer of ceramic powder which is added in either a rainfall sander or a fluidised sand bed, this process gradually builds up a ceramic shell around the moulds and sprue, with progressively coarser layers of ceramic coating being added over several coats until the desired shell thickness is achieved.

After the ceramic thickness is achieved the sprue along with its moulds are oven baked to both harden the ceramic shell and to melt all of the wax from within it, this will include all of the wax moulds and the wax sprue leaving a hollow ceramic shell. The wax moulds once melted leave a perfect void of the desired mould to be cast, the sprue once melted leaves open channels for the liquid metal to flow and fill all of the hollow shell (see image below). The molten metals are poured into the now hollow ceramic shell via the filling cup and left to cool off. Once the metal has cooled sufficiently the ceramic shell is broken up by either being submitted to vibrations or a water jet.

Investment Casting Shell

Advantages

Investment casting offers a number of advantages, the first being the excellent surface finish achievable, although of course the mould itself must first have these finishes. Investment casting leaves no parting or flash lines and the high quality finishes mean that the expense of another machine process to clean up surface finish is rarely required.

High dimensional accuracy is achievable which again can save a big cost on later machining to bring parts within the required tolerances.

Almost any metal can be investment cast and there is very little material waste from the process, any defect parts can usually be melted down and re used.

Investment casting has the potential to create extremely intricate parts; the molten metal will run and fill the mould very neatly, and because the castings mould is broken up to be retrieved there is little constraint to the shape of a casting.

Disadvantages

The creation of a mould can be fairly expensive and time consuming, a lot of labour is also required throughout the rest of the casting process. Occasional defects do occur for example air pockets within the casting.

Bearing Numbers Explained

September 21, 2012

  • (1) Prefix :
  • (2) Basic Number:
  • (3) Suffix

Prefix

K Cage with roller elements
L Removable bearing ring
R Ring with roller set
S Roll body of stainless steel
W Stainless steel deep groove ball bearing

*Note: Each bearing company may create their own prefixes. e.g. E2. = SKF Energy Efficient bearings

Suffix

2 RS Bearing with rubber seal on both sides. RS provides a better seal but more rolling friction than 2Z.
RS Bearing with rubber seal on one side, one side open.
2 Z / ZZ Bearing with a metal seal on both sides.
Z Bearing with a metal seal on one side, one side open.
E Reinforced Design
P2 Highest precision
K Bearing with taper bore

Bearing Numbers

The example at the header shows a 6001 2RS bearing. So what does the 6001 actually mean?
Lets attempt to break it down.

(6)001

This second number relates the bearing series, which reflects the robustness of the bearing. As you go up the scale below from 9 to 4 the inner and outer race thickness will usually increase along with the ball size, this will be to help cope with extra load.

9 Very thin section
0 Extra light
1 Extra light thrust
2 Light
3 Medium
4 Heavy

60(01)

The 3rd and 4th digits of the bearing number relate to the bore size of the bearing, numbers 00 to 03 have a designated bore size depending on the number.

00 10mm
01 12mm
02 15mm
03 17mm

While numbers over 03 simply have a bore size which is 5 times that of the 3rd and 4th digit.

This first number relates to the bearing type, as shown in the table below type 6 is a deep grooved roller bearing.

1 Self-Aligning Ball BearingThis kind of ball bearing has a spherical outer race, allowing the axis of the bearing to “wander around”. This is important because misalignment is one of the big causes of bearing failure. Self Aligning Ball Bearing
2 Barrel and Spherical Roller Bearings
3 Tapered Roller BearingDesigned to take large axial loads as well as radial loads. double row angular contact ball bearing
4 Deep Groove Double-Row Ball BearingDesigned for heavy radial loads. Double-Row Ball Bearing
5 Axial Deep Groove Ball BearingIntended for exclusively axial loads. Thrust Ball Bearing
6 Deep Groove Ball Bearing(Single row)Typical ball bearing. Handles light axial loads as well as radial loads. Single-Row Deep Groove Ball Bearing
7 Single-Row Angular Contact BearingSpecific geometry of angular contact bearing raceways and shoulders creates ball contact angles that support higher axial loads Angular contact ball bearing
8 Axial Cylindrical Roller BearingsAxial cylindrical roller bearings comprise axial cylindrical roller and cage assemblies and shaft and housing locating washers.
The bearings have particularly small axial section height, have high load carrying capacity and high rigidity and can support axial forces in one direction.

 

Axial Cylindrical Roller Bearings