LATEST MECHANICAL INVENTION

Robotic device has therapeutic potential for ankles and feet

A soft, wearable device that mimics the muscles, tendons and ligaments of the lower leg could aid in the rehabilitation of patients with ankle-foot disorders.

This is the claim of Yong-Lae Park, an assistant professor of robotics at Carnegie Mellon University. He worked with collaborators at Harvard University, the University of Southern California, MIT and Massachusetts-based BioSensics to develop an active orthotic (artificial support or brace) device using soft plastics and composite materials instead of a rigid exoskeleton.

The soft materials - combined with pneumatic artificial muscles (PAMs), lightweight sensors, and advanced control software - made it possible for the robotic device to achieve natural motions in the ankle.

The researchers reported on the development in the journal Bioinspiration & Biomimetics. In a statement, Park said the same approach could be used to create rehabilitative devices for other joints of the body or create soft exoskeletons that increase the strength of the wearer.

The robotic device would be suitable for aiding people with neuromuscular disorders of the foot and ankle associated with cerebral palsy, amyotrophic lateral sclerosis, multiple sclerosis or stroke. These gait disorders include drop foot, in which the forefoot drops because of weakness or paralysis, and equinus, in which the upward bending motion of the ankle is limited. Conventional passive ankle braces can improve gait, but long-term use can lead to muscle atrophy because of disuse. Active, powered devices can improve function and also help re-educate the neuromuscular system.

‘The limitation of a traditional exoskeleton is that it limits the natural degrees of freedom of the body,’ said Park. The ankle is naturally capable of a complicated three-dimensional motion, but most rigid exoskeletons allow only a single pivot point. The soft orthotic device enabled the researchers to mimic the biological structure of the lower leg. The device’s artificial tendons were attached to four PAMs, which correspond with three muscles in the foreleg and one in the back that control ankle motion. The prototype was capable of generating an ankle range of sagittal motion of 27 degrees, which is sufficient for a normal walking gait.

The soft device, however, is more difficult to control than a rigid exoskeleton. Park said it required more sophisticated sensing to track the position of the ankle and foot, and a more intelligent scheme for controlling foot motion. The device contains sensors made of a touch-sensitive artificial skin, and thin rubber sheets that contain long microchannels filled with a liquid metal alloy. When these rubber sheets are stretched or pressed, the shapes of the microchannels change, which cause changes in the electrical resistance of the alloy. These sensors were positioned on the top and at the side of the ankle.

Park said additional work will be necessary to improve the wearability of the device. This includes artificial muscles that are less bulky than the commercially produced PAMs used in this project.

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Filed Under: Mechanical Engineering, Robotics on Wednesday, February 5, 2014 2 Comments

Types and working of Power Steering

There are 2 types of power steering currently in use. These are integral and linkage booster types. Both are operated by hydraulic pressure produced by an engine driven pump to assist in turning the steering mechanism. The integral power steering is explained below :

Integral Power Steering : figure shows the integral power steering when the vehicle moves in the straight head position. the oil pump is belt driven from the engine crankshaft pulley. It consists of a solid cylinder with 2 grooves cut called valve spool which slides within the valve housing. The housing has three internal grooves is connected to the pump and the other are connected to the reservoir.

 

 

The two additional opening are connected to the two sides of the cylinder fitted with piston. When the valve spool is in the position as shown is figure , the pump delivers the oil in the central part of the housing which flows back to the reservoir by the passage shown by the arrows. In this position, there is no oil pressure in the cylinder and there is no tendency for the position to slide in any direction. There is no steering action and the vehicle moves in the straight-head position.

Figure 2nd shows that when the valve spool is moved towards right side, the direct return supply from the pump to the reservoir is closed. The oil flows into the cylinder by the right side passage and pushes the piston to the left side as shown in the figure. The oil on the left side of the piston flows back to the reservoir through the valve housing under this position. The left side outward movement of the piston rod turns towards left side of the road, the vehicle can be turned to the right side by reversing the steering operation.

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Filed Under: Steering Systems on Monday, February 3, 2014 2 Comments

Different types of Casting Process

1) Investment casting

2) Permanent mold casting

3) Centrifugal casting

4) Continuous casting

5) Sand casting

Investment casting

Investment casting (known as lost-wax casting in art) is a process that has been practiced for thousands of years, with lost wax process being one of the oldest known metal forming techniques. From 5000 years ago, when bees wax formed the pattern, to today’s high technology waxes, refractory materials and specialist alloys, the castings ensure high quality components are produced with the key benefits of accuracy, repeatability, versatility and integrity.

Investment casting derives its name from the fact that the pattern is invested, or surrounded, with a refractory material. The wax patterns require extreme care for they are not strong enough to withstand forces encountered during the mold making. One advantage of investment casting it that the wax can be reused.

The process is suitable for repeatable production of net shape components, from a variety of different metals and high performance alloys. Although generally used for small castings, this process has been used to produce complete aircraft door frames, with steel castings of up to 300 kg and aluminum castings of up to 30 kg. Compared to other casting processes such as die casting or sand casting it can be an expensive process, however the components that can be produced using investment casting can incorporate intricate contours, and in most cases the components are cast near net shape, so requiring little or no rework once cast.

Permanent mold casting

Permanent mold casting (typically for non-ferrous metals) requires a set-up time on the order of weeks to prepare a steel tool, after which production rates of 5-50 pieces/hr-mold are achieved with an upper mass limit of 9 kg per iron alloy item (cf., up to 135 kg for many nonferrous metal parts) and a lower limit of about 0.1 kg. Steel cavities are coated with a refractory wash of acetylene soot before processing to allow easy removal of the workpiece and promote longer tool life. Permanent molds have a limited life before wearing out. Worn molds require either refinishing or replacement. Cast parts from a permanent mold generally show 20% increase in tensile strength and 30% increase in elongation as compared to the products of sand casting.

The only necessary input is the coating applied regularly. Typically, permanent mold casting is used in forming iron, aluminum, magnesium, and copper based alloys. The process is highly automated.

Sub-types of permanent mold casting

1. Gravity Die Casting.

2. Low pressure die casting.(LPDC)

3. High pressure die casting.(PDC)

 

Centrifugal casting

Centrifugal casting is both gravity- and pressure-independent since it creates its own force feed using a temporary sand mold held in a spinning chamber at up to 900 N (90 g). Lead time varies with the application. Semi- and true-centrifugal processing permit 30-50 pieces/hr-mold to be produced, with a practical limit for batch processing of approximately 9000 kg total mass with a typical per-item limit of 2.3-4.5 kg.

Industrially, the centrifugal casting of railway wheels was an early application of the method developed by German industrial company Krupp and this capability enabled the rapid growth of the enterprise.

Continuous casting

Continuous casting is a refinement of the casting process for the continuous, high-volume production of metal sections with a constant cross-section. Molten metal is poured into an open-ended, water-cooled copper mold, which allows a 'skin' of solid metal to form over the still-liquid centre. The strand, as it is now called, is withdrawn from the mold and passed into a chamber of rollers and water sprays; the rollers support the thin skin of the strand while the sprays remove heat from the strand, gradually solidifying the strand from the outside in. After solidification, predetermined lengths of the strand are cut off by either mechanical shears or travelling oxyacetylene torches and transferred to further forming processes, or to a stockpile. Cast sizes can range from strip (a few millimeters thick by about five metres wide) to billets (90 to 160 mm square) to slabs (1.25 m wide by 230 mm thick). Sometimes, the strand may undergo an initial hot rolling process before being cut.

Continuous casting is used due to the lower costs associated with continuous production of a standard product, and also increases the quality of the final product. Metals such as steel, copper and aluminium are continuously cast, with steel being the metal with the greatest tonnages cast using this method.

 

Sand casting

Sand casting is one of the most popular and simplest types of casting that has been used for centuries. Sand casting allows for smaller batches to be made compared to permanent mold casting and a very reasonable cost. Not only does this method allow for manufacturers to create products for a good cost there are other benefits to sand casting such as there are very little size operations. From castings that fit in the palm of your hand to train beds (one casting can create the entire bed for one rail car) it can be done with sand casting. Sand casting also allows for most metals to be cast depending in the the type of sand used for the molds.

Sand casting requires a lead time of days for production at high output rates (1-20 pieces/hr-mold), and is unsurpassed for large-part production. Green (moist) sand has almost no part weight limit, whereas dry sand has a practical part mass limit of 2300-2700 kg. Minimum part weight ranges from 0.075-0.1 kg. The sand is bonded together using clays (as in green sand) or chemical binders, or polymerized oils (such as motor oil.) Sand in most operations can be recycled many times and requires little additional input.

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Filed Under: Casting, Mechanical Industry on Saturday, February 1, 2014 2 Comments

Why Manual Transmission Cars Make a Loud Whirring Noise in Reverse?

Manual transmissions use mostly helical gears, but reverse is a special situation that requires a different type of gear - a spur gear.

The gears that make up the forward gear ratios are all helical gears. The teeth on helical gears are cut at an angle to the face of the gear. When two teeth on a helical gear system engage, the contact starts at one end of the tooth and gradually spreads as the gears rotate, until the two teeth are in full engagement. This gradual engagement makes helical gears operate much more smoothly and quietly than spur gears. Also, because of the angle of the gear teeth, more teeth are in engagement at any one time. This spreads the load out more and reduces stresses.

The only problem with helical gears is that it is hard to slide them in and out of engagement with each other. On a manual transmission the forward gears stay engaged with each other at all times, and collars that are controlled by the shift stick lock different gears to the output shaft (see How Manual Transmissions Work for details). The reverse gear on your manual transmission uses an idler gear (the large spur gear visible at the right side of the picture below), which has to slide into mesh with two other spur gears at the same time in order to reverse the direction of rotation.

Spur gears, which have straight teeth, slide into engagement much more easily than helical gears, so the three gears used for reverse are spur gears>
Each time a gear tooth engages on a spur gear, the teeth collide instead of gently sliding into contact as they do on helical gears. This impact makes a lot of noise and also increases the stresses on the gear teeth. When you hear a loud, whirring noise from your car in reverse, what you are hearing is the sound of the spur gear teeth clacking against one another!

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Filed Under: Automobile Industry, Mechanical Engineering on 5 Comments

10 reasons why Mechanical Engineering is the best

There has always been a debate and discussion among all engineering students about which engineering course is the best? Students always love discussing about the best branch of engineering. Though this is a proven fact and it needs no discussion that mechanical engineering is the best still I will be providing 10 reasons over here which make mechanical engineering The Best among all other branches of engineering.

10 reasons why Mechanical Engineering is the best

1) Evergreen Field: Mechanical engineering is an evergreen field. Applications of mechanical engineering have spread over such a wide spectrum that it has penetrated into almost every industry. Mechanical engineering got its application started right from the birth of this universe and it will continue till the end of this universe.

2) Mother Of All Engineering Disciplines: Yeah it’s mother of all engineering disciplines and you know it! Mechanical engineering links all engineering disciplines together and provides a base for all engineering education.

3) Everything Is Mechanical: Mechanical engineering has its application in all fields of life. May it be medicine, construction, automobile or even software and IT industry. Everything you see around you involves mechanical engineering to some extent.

4) Everlasting Scope: Scope of mechanical engineering is everlasting. Mechanical engineering graduates can find career placements in almost every sector, right from construction sector to steel industry and from automobile to software.

5) Best Job Offers: Mechanical engineers get best job offers after graduation. It’s one of the highest paid jobs all over the world.

6) Social Status: Mechanical engineers are respected in every society. They possess a respectful social status among masses. They are like global ambassadors. Wherever they go, they are treated with respect.

7) Most Interesting: Mechanical engineering involves study of some of the most interesting phenomena of science and engineering. The basic focus during study is on subjects such as thermal engineering, fluid sciences, machine design, industrial engineering and production engineering.

8) Even GOD Loves ME: Ever thought GOD also implemented mechanical engineering in nature? Motion of your body, arms, hands and feet involves mechanical engineering. Your heart pumps blood and it runs through all your veins. This is again application of mechanical engineering. The more you look into nature with the eye of a mechanical engineer, you will find more application of it.

9) Best Lifestyle: Do you need a best lifestyle to live in? Mechanical engineering offers you one of the best lifestyles. It’s like a dream come true.

10) Vast Industry: Mechanical engineering industry is vast. Every industry needs mechanical engineers to run its business smoothly.

Do you have more reasons to say? Don’t forget to comment. Let us see how many reasons we can gather here in comments.

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Filed Under: Mechanical Engineering on 5 Comments

Ultrasonic Welding

Ultrasonic welding is represented as a friction welding method, where oxides and other contaminants present on the material surfaces are broken up and also the components to be welded are brought together under simultaneous pressure. Molecular bonding, just like the conventional cold-press welding, then takes place. Ultrasonic welding is the conversion of high frequency electrical energy into high frequency mechanical energy. In ultrasonic welding spot welds in thin steels are produced by the local application of high frequency vibrating energy to work pieces held together under pressure. The work pieces are clamped together under a moderate static force applied normal to their face and oscillating shear stresses of ultrasonic frequencies (1 KHz to 40 KHz) with a power ranging of 700 to 6000 watts are applied parallel to the interface. The vibrating probe called “a sonotrode” induces lateral vibrations and slip between the surfaces fracturing the brittle oxide layers and softening the asperities because of localized heating. The combined effects of pressure and vibrations cause movement of metal molecule bringing about a sound weld.

The bonding is achieved in solid state without application of external heat, filler rod or high pressure. There is also no need for any thorough cleaning before welding because all contaminants, oxides, moisture etc are removed by the vibrating motion.

Ultrasonic Welding Equipment:

The ultrasonic vibrating unit consists of following main components:

1. Frequency converter,
2. Booster,
3. Horn or sonotrode,
4. Pneumatic Press /Actuator,
5. Ultrasonic power supply, and
6. holding fixture

This converts 50 Hz – 60 Hz line power into high frequency electrical power and a transducer which changes the high frequency electrical power into ultrasonic vibratory motion that is transmitted to the joint. The weld is completed in 0.5 to 1.5 seconds.

Ultrasonic welding of plastics:

Plastics are typically engineered materials consisting of polymers. Polymers are shaped by polymerisation that may be a chemical action during which two or more molecules are combined to make a larger molecule. Polymers are often classified as either thermosets or thermoplastics. Thermosets aren’t appropriate for ultrasonic assembly because they degrade when subjected to intense heat. Thermoplastics on the opposite hand soften when heated and cool when hardened and are thus ideally fitted for ultrasonic assembly.

Materials for Ultrasonic Welding of Plastics:

Most of the thermoplastic materials can be ultrasonic weldable. Teflon with low coefficient of friction and high melting temperature is impossible to weld using this process. 

Welding Temperature Achieved:

Ultrasonic welding produces a localized temperature rise from the combined effects of elastic hysteresis, interfacial slip and plastic deformation. The weld interfaces reach roughly 1/3 the temperatures required to melt the metals. Since the temperature doesn’t reach the melting point of the material, the physical properties of the welded material are preserved. As the ultrasonic welding method is an exothermic reaction, as welding time will increases so does weld temperature.

 

The ultrasonic welding process has the advantage that since no bulk heating of the work pieces is involved and there is no danger of any mechanical or metallurgical bad effects. Although metals have up to 2.5 mm thick have been welded by this process. It is used mostly for welding foils. This process is suitable only for thermoplastics with the exception of thermosetting resins and Teflons. The process can be used on a variety of metals including the refractory metals. Even dissimilar metals can be welded because there is no fusion. The process can also be used on temperature sensitive materials because temperature rise is limited.

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Filed Under: Welding on 1 Comment

2 stroke engines in racing motorcycles

Although two stroke engines have long since been updated with four stroke racing bike engines, two stroke engines provide a lightweight and suitable solution for racing bikes, motocross and dirt bikes.
Earlier on, the two stroke engines in racing bikes were quite popular, but they have since then have been replaced with the four stroke version of the engine.

The two stroke engine was a much simpler design, therefore provided a low cost solution for racing teams.

The two stroke bike engine operates in two strokes, instead of the normal four stroke Otto cycle.
The stages in a two stroke engine are:

1. Power/exhaust stroke: This is the stroke that occurs right after the ignition of the charge, forcing the piston down. After sometime, the top of the piston goes over the exhaust port, with a large amount of the pressurized gases to escape. The downward movement of the piston continues to compress crankcase containing the air, fuel, oil mixture. The top of the piston having passed the transfer port, the charge that is compressed enters the cylinder with any exhaust being forced out.

2. Upon entering the cylinder, the air fuel mixture makes the piston move up, compressing the charge in the cylinder. This results in a vacuum being drawn in the crankcase, with drawing in more air, fuel and oil. The spark plug now ignites the compressed charge, and thereafter the cycle begins again.

The main variations of the two stroke engine types are found in the method of the fuel intake; this depends on the various different types of the cylinder arrangement.

The Reed valve type of configuration delivers power through a wider RPM range than the regular piston and port types, which is generally a suitable arrangement for dirt bikes, as a dirt bike course demands more power over the difficult jump sections.

A rotary inlet valve type of engine configuration has a thin disk attached to the crankshaft, which spins at the crankshaft speed. The fuel-air mixture is made to pass through the disk, with the disk having a section cut, opening if it passes the intake pipe, closing otherwise.

The advantage of the rotary valve arrangement is that it asymmetrically arranges the two stroke mechanism’s intake timing, not possible with piston port type of arrangements.

Cross flow engines are configured to house the transfer ports and exhaust ports on opposing sides, with on top of the piston being the deflector, directing the fresh intake charge on to the upper side of the cylinder.

The residual gas is pushed down the deflector’s other side, out of the exhaust port. The 235 hp 2.6 L V6 crossflow till date has some of the highest output, coming from a low weight engine.

For motocross bikes, such as the 125 SX, bought out in 2007, being ultra light is a key feature. The two stroke engines are competitive, and preferred by racers who do not want to indulge in complicated four stroke machinery.

This bike has a displacement of 124.8cc with bore and stroke 54/54.5, with a TVC power valve.
This 6 gear, premix fuel run two stroke has a front suspension of WP USD 48 mm, with a total weight being about 89.5 kg. Bikes such as this one have a multi-disc hydraulically operated clutch system, with an ignition through a Kokusan digital magneto CDI.

The basic advantage over such two stroke dirt bikes over their four stroke counterparts is that they provide a much more hassle free, yet powerful transmission solutions.

The 250 SX 2007 is a two stroke bike that is powerful enough to give the four stroke category bikes a run for their money. Added to this it is light, making it ideal for motocross racers.

The single cylinder, two stroke engine calls for easy maintenance, and the fantastic suspension, with PDS geometry means that it is a beast on the tough dirt circuit.

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Filed Under: Automobile Engineering on 6 Comments