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91-468: When over-braking, the Decelostat will detect rapid deceleration of wheel rotation caused by creep in the wheelset , another condition preceding the wheel-slide. Once detected, the system manipulates brake valves to reduce brake pressure. This allows the affected wheels to rotate at the speeds that are more comparable to the speeds of the train to gain the wheel/rail adhesion again. When that happens,

182-489: A linear motor , which can be thought as a rotary electric motor which has been cut and unrolled. Thus, instead of producing a rotational movement, it produces a linear force along their length. Because it generally has lower friction losses than the alternatives, a linear electric actuator can last over a hundred million cycles. Linear motors are divided in 3 basic categories: flat linear motor (classic), U-Channel linear motors and Tubular linear motors. Linear motor technology

273-427: A mechanism that is directly driven by the motions or forces of other parts of the system. An example is the camshafts that drive the intake and exhaust valves in internal combustion engines , driven by the engine itself. Another example is the mechanism that strikes the hours in a traditional grandfather clock or cuckoo clock . A hydraulic actuator typically uses the pressure of a liquid (usually oil) to cause

364-432: A (non-electronic) thermostat contains a strip with two layers of different metals, that will bend when heated. Thermal actuators may also exploit the properties of shape-memory alloys . Some actuators are driven by externally applied magnetic fields . They typically contain parts made of ferromagnetic materials that are strongly attracted to each other when they are magnetized by the external field. An example are

455-414: A ball or a lead screw or planetary roller screw). The main advantages of electromechanical actuators are their relatively good level of accuracy with respect to pneumatics, their possible long lifecycle and the little maintenance effort required (might require grease). It is possible to reach relatively high force, on the order of 100 kN. The main limitation of these actuators are the reachable speed,

546-399: A braking sanding system, the wheel slide protection can get activated repeatedly while braking on a bad rail section because the root cause of wheel-rail adhesion is not addressed. Applying sand to the rail addresses the issue with adhesion to improve the braking performance. Decelostat can be integrated with a braking sanding system to let the two systems work together automatically. An example

637-403: A combination of friction and weight to start a train. The heaviest trains require the highest friction and the heaviest locomotive. The friction can vary a great deal, but it was known on early railways that sand helped, and it is still used today, even on locomotives with modern traction controls. To start the heaviest trains, the locomotive must be as heavy as can be tolerated by the bridges along

728-431: A dump value to release the air in the brake cylinder to the atmosphere. The valve unit may contain multiple valves such that it would close off the protection valve to block off any air from the line from entering the brake cylinder while opening the dump valve. In some models, the reader and controller components may be combined into one unit. For example, a system that uses flywheel to read and detect deceleration beyond

819-404: A heavy train slowly. Slip is the additional speed that the wheel has and creep is the slip level divided by the locomotive speed. These parameters are those that are measured and which go into the creep controller. On an adhesion railway, most locomotives will have a sand containment vessel. Properly dried sand can be dropped onto the rail to improve traction under slippery conditions. The sand

910-430: A linear motion, but is not a linear motor ). Another broad classification of actuators separates them into two types: incremental-drive actuators and continuous-drive actuators. Stepper motors are one type of incremental-drive actuators. Examples of continuous-drive actuators include DC torque motors , induction motors , hydraulic and pneumatic motors , and piston-cylinder drives (rams). An actuator can be just

1001-400: A modern, exceptionally high-speed train at 80 m/s (290 km/h; 180 mph), the minimum radius would be about 2.5 km (1.6 mi). In practice, the minimum radius of turn is much greater than this, as contact between the wheel flanges and rail at high speed could cause significant damage to both. For very high speeds, the minimum adhesion limit again appears appropriate, implying

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1092-574: A new pathway for fabricating low-cost and fast response SMP actuators. The process of receiving external stimuli like heat, moisture, electrical input, light or magnetic field by SMP is referred to as shape memory effect (SME). SMP exhibits some rewarding features such a low density, high strain recovery, biocompatibility, and biodegradability . Photopolymers or light activated polymers (LAP) are another type of SMP that are activated by light stimuli. The LAP actuators can be controlled remotely with instant response and, without any physical contact, only with

1183-442: A normal operation, the wheel will be rotated at the same speeds as the flywheel. In a heavy braking, the wheel will be decelerated at a higher rate than the flywheel, causing the inertia of the flywheel to overrun the rotation of the wheel. In a pneumatic system, this causes a valve to be open and makes the protection and dump values to release air break pressure. In an electro-pneumatic system, this causes an electric circuit to trigger

1274-432: A piston to slide inside a hollow cylindrical tube linear, rotatory or oscillatory motion. In a single acting actuator the fluid pressure is applied to just one side of the piston, so that it applies useful force in only one direction. The opposite motion may be effected by a spring , by gravity, or by other forces present in the system. In a double acting actuator, the return stroke is driven by fluid pressure applied to

1365-404: A radius of turn of about 13 km (8.1 mi). In practice, curved tracks used for high speed travel are superelevated or canted , so that the minimum radius of curvature is closer to 7 km (4.3 mi). During the 19th century, it was widely believed that coupling the drive wheels would compromise performance, and this was avoided on engines intended for express passenger service. With

1456-487: A single drive wheelset, the Hertzian contact stress between the wheel and rail necessitated the largest-diameter wheels that could be accommodated. The weight of locomotives was restricted by the stress on the rail, and sandboxes were required, even under reasonable adhesion conditions. It may be thought that the wheels are kept on the tracks by the flanges. However, close examination of a typical railway wheel reveals that

1547-414: A single step by rapid prototyping methods, such as 3D printing , are utilized to narrow the gap between the design and implementation of soft actuators, making the process faster, less expensive, and simpler. They also enable incorporation of all actuator components into a single structure eliminating the need to use external joints , adhesives , and fasteners . Shape memory polymer (SMP) actuators are

1638-463: A subdivision of transducers. They are devices which transform an input signal (mainly an electrical signal ) into some form of motion. Motors are mostly used when circular motions are needed, but can also be used for linear applications by transforming circular to linear motion with a lead screw or similar mechanism. On the other hand, some actuators are intrinsically linear, such as piezoelectric actuators. Conversion between circular and linear motion

1729-408: A train can proceed around a turn is limited by the radius of turn, the position of the centre of mass of the units, the wheel gauge and whether the track is superelevated , or canted . Toppling will occur when the overturning moment due to the side force ( centrifugal acceleration) is sufficient to cause the inner wheel to begin to lift off the rail. This may result in loss of adhesion – causing

1820-417: Is a pneumatic Decelostat system that uses an actuator to control the braking sanding system. When the flywheel of the Decelostat detects a sharp deceleration of the wheel, the valve that relieves air pressure from the brake cylinder is actuated. At that time, the valve for the braking sanding is also actuated, delivering sand to the rail. Momentarily, the wheel speeds are back in sync with the flywheel, causing

1911-404: Is between 0.35 and 0.5, whilst under extreme conditions it can fall to as low as 0.05. Thus a 100-tonne locomotive could have a tractive effort of 350 kilonewtons, under the ideal conditions (assuming sufficient force can be produced by the engine), falling to 50 kilonewtons under the worst conditions. Steam locomotives suffer particularly badly from adhesion issues because the traction force at

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2002-399: Is caused by friction , with maximum tangential force produced by a driving wheel before slipping given by: F m a x = μ W , {\displaystyle F_{\mathrm {max} }=\mu W,} where μ {\displaystyle \mu } is the coefficient of friction and W {\displaystyle W} is the weight on

2093-582: Is commonly made via a few simple types of mechanism including: In virtual instrumentation , actuators and sensors are the hardware complements of virtual instruments. Performance metrics for actuators include speed, acceleration, and force (alternatively, angular speed, angular acceleration, and torque), as well as energy efficiency and considerations such as mass, volume, operating conditions, and durability, among others. When considering force in actuators for applications, two main metrics should be considered. These two are static and dynamic loads. Static load

2184-495: Is compressed to a film on the track where the wheels make contact. Together with some moisture on the track, which acts as a light adhesive and keeps the applied sand on the track, the wheels "bake" the crushed sand into a more solid layer of sand. Because the sand is applied to the first wheels on the locomotive, the following wheels may run, at least partially and for a limited time, on a layer of sand (sandfilm). While traveling this means that electric locomotives may lose contact with

2275-411: Is converted to rotary motion by some sort of crankshaft mechanism. Since 1960, several actuator technologies have been developed. Electric actuators can be classified in the following groups: An electromechanical actuator (EMA) uses mechanical means to convert the rotational force of an ordinary (rotary) electric motor into a linear movement. The mechanism may be a toothed belt or a screw (either

2366-451: Is known as hunting oscillation . Hunting oscillation was known by the end of the 19th century, although the cause was not fully understood until the 1920s, and measures to eliminate it were not taken until the late 1960s. The maximum speed was limited not by raw power but by a possible instability in the motion. The kinematic description of the motion of tapered treads on the two rails is insufficient to describe hunting well enough to predict

2457-416: Is lowered with contamination, the maximum obtainable under those conditions occurs at greater values of creep. The controllers must respond to different friction conditions along the track. Some of the starting requirements were a challenge for steam locomotive designers – "sanding systems that did not work, controls that were inconvenient to operate, lubrication that spewed oil everywhere, drains that wetted

2548-421: Is most often applied using compressed air via tower, crane, silo or train. When an engine slips, particularly when starting a heavy train, sand applied at the front of the driving wheels greatly aids in tractive effort causing the train to "lift", or to commence the motion intended by the engine driver. Sanding however also has some negative effects. It can cause a "sandfilm", which consists of crushed sand, that

2639-452: Is needed. The driving wheels must turn faster than the locomotive is moving (known as creep control) to generate the maximum coefficient of friction, and the axles must be driven independently with their own controller because different axles will see different conditions. The maximum available friction occurs when the wheels are slipping/creeping. If contamination is unavoidable the wheels must be driven with more creep because, although friction

2730-462: Is reduced when the top of the rail is wet or frosty or contaminated with grease, oil or decomposing leaves which compact into a hard slippery lignin coating. Leaf contamination can be removed by applying " Sandite " (a gel–sand mix) from maintenance trains, using scrubbers and water jets, and can be reduced with long-term management of railside vegetation. Locomotives and trams use sand to improve traction when driving wheels start to slip. Adhesion

2821-399: Is slightly tapered. When the train is in the centre of the track, the region of the wheels in contact with the rail traces out a circle which has the same diameter for both wheels. The velocities of the two wheels are equal, so the train moves in a straight line. If, however, the wheelset is displaced to one side, the diameters of the regions of contact, and hence the tangential velocities of

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2912-533: Is supplied to it in a system (called an actuating system ). The effect is usually produced in a controlled way. An actuator translates such an input signal into the required form of mechanical energy . It is a type of transducer . In simple terms, it is a "mover". An actuator requires a control device (which provides control signal ) and a source of energy . The control signal is relatively low in energy and may be voltage , electric current , pneumatic , or hydraulic fluid pressure , or even human power . In

3003-456: Is the assumption that wheels are round. A glance at the tyres of a parked car will immediately show that this is not true: the region in contact with the road is noticeably flattened, so that the wheel and road conform to each other over a region of contact. If this were not the case, the contact stress of a load being transferred through a line contact would be infinite. Rails and railway wheels are much stiffer than pneumatic tyres and tarmac but

3094-403: Is the best solution in the context of a low load (up to 30Kgs) because it provides the highest level of speed, control and accuracy. In fact, it represents the most desired and versatile technology. Due to the limitations of pneumatics, the current electric actuator technology is a viable solution for specific industry applications and it has been successfully introduced in market segments such as

3185-417: Is the force capability of the actuator while not in motion. Conversely, the dynamic load of the actuator is the force capability while in motion. Speed should be considered primarily at a no-load pace, since the speed will invariably decrease as the load amount increases. The rate the speed will decrease will directly correlate with the amount of force and the initial speed. Actuators are commonly rated using

3276-424: Is the taper of the treads. For a given speed, the longer the wavelength and the lower the inertial forces will be, so the more likely it is that the oscillation will be damped out. Since the wavelength increases with reducing taper, increasing the critical speed requires the taper to be reduced, which implies a large minimum radius of turn. A more complete analysis, taking account of the actual forces acting, yields

3367-408: Is the unit that is attached to the axle journal in order to read speeds or acceleration/deceleration of the wheels. The function of the controller component is to detect the situations, such as a rapid deceleration in excess of the limit, in order to activate the valve unit. The valve unit manipulates air brake to reduce braking cylinder pressure of the affected wheels. This can be done by activating

3458-447: Is used to actuate equipment such as multi-turn valves, or electric-powered construction and excavation equipment. When used to control the flow of fluid through a valve, a brake is typically installed above the motor to prevent the fluid pressure from forcing open the valve. If no brake is installed, the actuator gets activated to reclose the valve, which is slowly forced open again. This sets up an oscillation (open, close, open ...) and

3549-458: Is what most of the actuators are used for. For most actuators they are mechanically durable yet do not have an ability to adapt compared to soft actuators. The soft actuators apply to mainly safety and healthcare for humans which is why they are able to adapt to environments by disassembling their parts. This is why the driven energy behind soft actuators deal with flexible materials like certain polymers and liquids that are harmless The majority of

3640-589: The SR V Schools class , operated with a factor of adhesion below 4 because the traction force at the wheel rim does not fluctuate as much. Other factors affecting the likelihood of wheelslip include wheel size, the sensitivity of the regulator and the skill of the driver. The term all-weather adhesion is usually used in North America , and refers to the adhesion available during traction mode with 99% reliability in all weather conditions. The maximum speed at which

3731-405: The reed switches that may be used as door opening sensors in a building security system. Alternatively, magnetic actuators can use magnetic shape-memory alloys . A soft actuator is made of a flexible material that changes its shape in response to stimuli including mechanical, thermal, magnetic, and electrical. Soft actuators mainly deal with the robotics of humans rather than industry which

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3822-404: The "vehicle velocity". When a wheel rolls freely along the rail the contact patch is in what is known as a "stick" condition. If the wheel is driven or braked the proportion of the contact patch with the "stick" condition gets smaller and a gradually increasing proportion is in what is known as a "slip condition". This diminishing "stick" area and increasing "slip" area supports a gradual increase in

3913-416: The Decelostat to close the valves to resume braking again. At that moment, the sand has already been delivered to the rail, making the braking more effective. A Decelostat system was introduced to the aviation industry in the 1950s to control the wheel braking during the landing. A Decelostat unit was fitted inside the wheel component of the landing gear . In addition to the pneumatic system used on trains,

4004-450: The associated wheels. The generator could be of any type but preferably a permanent-magnet type ( magneto ) which would allow polarities to be reversed when the wheels were turned in the reverse direction. The generator was connected to a controller which contained a series of capacitors and relays in the way that the detection could be done when wheels turned in either direction. When the wheels increased speed of rotation, it would cause

4095-416: The control module to activate the release of the air brake pressure. The release slows down the wheel brake to prevent wheel slipping, and brings the rotations of the wheel and the flywheel back to be in sync again. A well known pneumatic flywheel model is called "3-AP". Modern Decelostat systems are made of an electronic speed sensor that measures the actual speed of the wheel and a controller that calculates

4186-492: The critical speed further. However, in order to achieve the highest speeds without encountering instability, a significant reduction in wheel taper is necessary. For example, taper on Shinkansen wheel treads was reduced to 1:40 (when the Shinkansen first ran) for both stability at high speeds and performance on curves. That said, from the 1980s onwards, the Shinkansen engineers developed an effective taper of 1:16 by tapering

4277-413: The critical speed. It is necessary to deal with the forces involved. There are two features which must be taken into account: The kinematic approximation corresponds to the case which is dominated by contact forces. An analysis of the kinematics of the coning action yields an estimate of the wavelength of the lateral oscillation: where d is the wheel gauge, r is the nominal wheel radius and k

4368-435: The device easier to set up still with durability and a set torque. Rotary motors can be powered by 3 different techniques such as Electric, Fluid, or Manual. However, Fluid powered rotary actuators have 5 sub-sections of actuators such as Scotch Yoke, Vane, Rack-and-Pinion, Helical, and Electrohydraulic. All forms have their own specific design and use allowing the ability to choose multiple angles of degree. Applications for

4459-445: The dump valve. The system would be set to a predetermined amount of deceleration that would trigger the dump, such as at the decelerating rate of 10 mph per second or more. In the 1930s, Westinghouse developed another form of Decelostat using a flywheel of a rotary inertia type. The flywheel module is installed to the axlebox and connected to the wheel by a spring in such way that the flywheel will be rotating along with wheel. In

4550-425: The dynamics of wheelsets and complete rail vehicles, the contact forces can be treated as linearly dependent on the creep ( Joost Jacques Kalker 's linear theory, valid for small creepage) or more advanced theories can be used from frictional contact mechanics . The forces which result in directional stability, propulsion and braking may all be traced to creep. It is present in a single wheelset and will accommodate

4641-411: The electric, hydraulic, and pneumatic sense, it is a form of automation or automatic control . The displacement achieved is commonly linear or rotational, as exemplified by linear motors and rotary motors , respectively. Rotary motion is more natural for small machines making large displacements. By means of a leadscrew , rotary motion can be adapted to function as a linear actuator (which produces

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4732-747: The electronic circuit to control the valves. The system was used in rail cars in the late twenties century as an alternative to pneumatic Decelostat of Westinghouse. Both systems were phased out with introduction of an early speed sensor model of Decelostat. In aviation, Dunlop introduced an antiskid unit called Maxaret in the 1950s using the flywheel concept similar to the Decelostat. By the 1970s, there were various antiskid braking systems used in commercial and military jet airplanes that were more sophisticated and designed to provide maximum braking effort while maintaining full antiskid protection under all weather conditions. National Aeronautics and Space Administration ( NASA ) also employed an antiskid system in each of

4823-566: The existing soft actuators are fabricated using multistep low yield processes such as micro-moulding, solid freeform fabrication, and mask lithography. However, these methods require manual fabrication of devices, post processing/assembly, and lengthy iterations until maturity in the fabrication is achieved. To avoid the tedious and time-consuming aspects of the current fabrication processes, researchers are exploring an appropriate manufacturing approach for effective fabrication of soft actuators. Therefore, special soft systems that can be fabricated in

4914-432: The flywheel was also slightly modified to hook up to the oil-based hydraulic system. The principal of operation was still the same as in the pneumatic version by having the flywheel with a preset amount of optimal braking with deceleration rate without runway skidding. When there was a higher rate of deceleration, such as in runway skidding, the flywheel would push the valve piston , cutting the pressurized oil from reaching

5005-416: The following result for the critical speed of a wheelset: where W is the axle load for the wheelset, a is a shape factor related to the amount of wear on the wheel and rail, C is the moment of inertia of the wheelset perpendicular to the axle, m is the wheelset mass. The result is consistent with the kinematic result in that the critical speed depends inversely on the taper. It also implies that

5096-631: The higher rate of wheel deceleration was still detected. The device was on trials first in the United States and later by the British. Decelostat was also used in some of the U.S. military transport aircraft . In 1954, Popular Science revealed that there was preliminary testing of the Decelostat system to prevent car swirling on a heavy brake by the US car manufacturers in Detroit . However, there

5187-473: The important dimensions and weight they require. The main application of such actuators is mainly seen in health care devices and factory automation. Another approach is an electrohydraulic actuator , where the electric motor remains the prime mover but provides torque to operate a hydraulic accumulator that is then used to transmit actuation force in much the same way that diesel engine/hydraulics are typically used in heavy equipment . Electrical energy

5278-475: The limit can directly send signal to the valve component. In the 1930s, Westinghouse Air Brake Company developed a wheel slip control system, first in an electrical type. The system operated by having a direct-current generator installed at the journal box of the axle. As the wheels moved, the generator would generate the output voltage. The voltage of the generator was then used to measure the acceleration (voltage increased) and deceleration (voltage decreased) of

5369-404: The most similar to our muscles, providing a response to a range of stimuli such as light, electrical, magnetic, heat, pH, and moisture changes. They have some deficiencies including fatigue and high response time that have been improved through the introduction of smart materials and combination of different materials by means of advanced fabrication technology. The advent of 3D printers has made

5460-405: The motor and actuator will eventually become damaged. Electric rotary actuators use a rotary motor to turn the target part over a certain angle. Rotary actuators can have up to a rotation of 360 degrees. This allows it to differ from a linear motor as the linear is bound to a set distance compared to the rotary motor. Rotary motors have the ability to be set at any given degree in a field making

5551-427: The opposite side of the piston. Since liquids are nearly impossible to compress, a hydraulic actuator can exert a large force. The drawback of this approach is its limited acceleration. They respond quickly to input changes, have little inertia, can operate continuously over a relatively large working range, and can hold their position without any significant energy input. A hydraulic actuator can be used to displace

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5642-510: The orbiter's four main landing gear wheels of the Space Shuttle . In automobile, the root of anti-lock braking system (ABS) came from the development of antiskid systems in the aviation industry in the 1950s. The first generation of ABS units for automotive was in the early 1970s. Creep (railway wheels) An adhesion railway relies on adhesion traction to move the train, and is the most widespread and common type of railway in

5733-408: The rack of a rack and pinion mechanism, causing the pinion to turn. This arrangement is used, for example, to operate valves in pipelines and other industrial fluid transport installations. A pneumatic actuator is similar to a hydraulic one but uses a gas (usually air) instead of a liquid. Compared to hydraulic actuators, pneumatic ones are less complicated because they do not need pipes for

5824-429: The rails, and so on.." Others had to wait for modern electric transmissions on diesel and electric locomotives. The frictional force on the rails and the amount of wheel slip drops steadily as the train picks up speed. A driven wheel does not roll freely but turns faster than the corresponding locomotive velocity. The difference between the two is known as the "slip velocity". "Slip" is the "slip velocity" compared to

5915-414: The railway industry as a generic term to refer to wheel slide protection systems during the late twentieth century. However, it was a registered trademark of Westinghouse Air Brake Company from 1943 to 2003, and the trademark was assigned to Wabtec , Westinghouse's successor, in 2004. The main components of the Decelostat system are wheel speed/acceleration reader, controller and valve. The reader component

6006-500: The rate of deceleration to determine whether to reduce the braking to prevent wheel slipping or not. The "E-5" model is an example of such Decelostat systems. It has a 100-tooth gear that is attached to the wheel journal. The sensor measures the wheel speed by counting the gear teeth that are moved past the sensor. A braking sanding system delivers sand on the rail in front of the wheel to improve wheel-to-rail adhesion to prevent wheel slide while braking. When using Decelostat alone without

6097-441: The region where they first come into contact, followed by a region of slippage. The net result is that, during traction, the wheel does not advance as far as would be expected from rolling contact but, during braking, it advances further. This mix of elastic distortion and local slipping is known as "creep" (not to be confused with the creep of materials under constant load). The definition of creep in this context is: In analysing

6188-421: The return and recycling of the working fluid. On the other hand, they still need external infrastructure such as compressors, reservoirs, filters, and air treatment subsystems, which often makes them less convenient that electrical and electromechanical actuators. In the first steam engines and in all steam locomotives , steam pressure is used to drive pneumatic actuators to produce a reciprocating motion, which

6279-405: The rotary actuators are just about endless but, will more than likely be found dealing with mostly hydraulic pressured devices and industries. Rotary actuators are even used in the robotics field when seeing robotic arms in industry lines. Anything you see that deals with motion control systems to perform a task in technology is a good chance to be a rotary actuator. A linear electric actuator uses

6370-458: The route and the track itself. The weight of the locomotive must be shared equally by the wheels that are driven, with no weight transfer as the starting force builds. The wheels must turn with a steady driving force on the very small contact area of about 1 cm between each wheel and the top of the rail. The top of the rail must be dry, with no man-made or weather-related contamination, such as oil or rain. Friction-enhancing sand or an equivalent

6461-467: The same distortion takes place at the region of contact. Typically, the area of contact is elliptical, of the order of 15 mm across. The distortion in the wheel and rail is small and localised but the forces which arise from it are large. In addition to the distortion due to the weight, both wheel and rail distort when braking and accelerating forces are applied and when the vehicle is subjected to side forces. These tangential forces cause distortion in

6552-434: The slight kinematic incompatibility introduced by coupling wheelsets together, without causing gross slippage, as was once feared. Provided the radius of turn is sufficiently great (as should be expected for express passenger services), two or three linked wheelsets should not present a problem. However, 10 drive wheels (5 main wheelsets) are usually associated with heavy freight locomotives. The adhesion railway relies on

6643-418: The system deactivates to allow the brake pressure to be restored to continue braking. The system may reactivate again if it detects another creep. The cycle of activation and deactivation is usually brief but it could take place repeatedly during the braking process. Decelostat was the term used by Westinghouse Air Brake Company when it originally developed the system in the 1930s. The term had then been used by

6734-441: The track-ground, causing the locomotive to create electromagnetic interference and currents through the couplers. In standstill, when the locomotive is parked, track circuits may detect an empty track because the locomotive is electrically isolated from the track. Actuator An actuator is a component of a machine that produces force , torque , or displacement , when an electrical , pneumatic or hydraulic input

6825-420: The traction or braking torque that can be sustained as the force at the wheel rim increases until the whole area is "slip". The "slip" area provides the traction. During the transition from the "all-stick" no-torque to the "all-slip" condition the wheel has had a gradual increase in slip, also known as creep and creepage. High adhesion locomotives control wheel creep to give maximum effort when starting and pulling

6916-428: The train stays on the track, it becomes evident why Victorian locomotive engineers were averse to coupling wheelsets. This simple coning action is possible only with wheelsets where each can have some free motion about its vertical axis. If wheelsets are rigidly coupled together, this motion is restricted, so that coupling the wheels would be expected to introduce sliding, resulting in increased rolling losses. This problem

7007-415: The train to slow, preventing toppling. Alternatively, the inertia may be sufficient to cause the train to continue to move at speed, causing carriages to topple completely. For a wheel gauge of 1.5 m (4.9 ft) with no canting, a centre of gravity height of 3 m (9.8 ft) and a speed of 30 m/s (110 km/h; 67 mph), the minimum radius of curvature is 360 m (1,180 ft). For

7098-399: The tread is burnished but the flange is not—the flanges rarely make contact with the rail and, when they do, most of the contact is sliding. The rubbing of a flange on the track dissipates large amounts of energy, mainly as heat but also including noise and, if sustained, would lead to excessive wheel wear. Centering is actually accomplished through shaping of the wheel. The tread of the wheel

7189-852: The variation of light frequency or intensity. A need for soft, lightweight and biocompatible soft actuators in soft robotics has influenced researchers for devising pneumatic soft actuators because of their intrinsic compliance nature and ability to produce muscle tension. Polymers such as dielectric elastomers (DE), ionic polymer–metal composites (IPMC), ionic electroactive polymers, polyelectrolyte gels, and gel-metal composites are common materials to form 3D layered structures that can be tailored to work as soft actuators. EAP actuators are categorized as 3D printed soft actuators that respond to electrical excitation as deformation in their shape. In engineering , actuators are frequently used as mechanisms to introduce motion , or to clamp an object so as to prevent motion. In electronic engineering, actuators are

7280-434: The voltage from the generator to be higher. The circuit in the Decelostat was configured that when the capacitor was in the charging mode, the unidirectional relay would not be activated. When the wheels were rapidly decelerating, the voltage would be dropped at a high rate causing the capacitor to discharge reversely through the pick-up winding of the corresponding relay. This would cause the relay switch to pick up and activate

7371-468: The watchmaking, semiconductor and pharmaceutical industries (as high as 60% of the applications. The growing interest for this technology, can be explained by the following characteristics: The main disadvantages of linear motors are: An actuator may be driven by heat through the expansion that most solid material exhibit when the temperature increases. This principle is commonly used, for example, to operate electric switches in thermostats . Typically,

7462-464: The weight of the rotating mass should be minimised compared with the weight of the vehicle. The wheel gauge appears in both the numerator and denominator, implying that it has only a second-order effect on the critical speed. The true situation is much more complicated, as the response of the vehicle suspension must be taken into account. Restraining springs, opposing the yaw motion of the wheelset, and similar restraints on bogies , may be used to raise

7553-420: The wheel brakes and release the oil to the return circuit of the hydraulic braking system. This would relief the braking pressure from the landing wheels and allow them to gain speed again to match the flywheel. As the speed of the landing wheels became normal again, the valves were reset to normal mode to start applying the pressurized oil to the wheel brakes. These entire steps may repeat in rapid succession while

7644-507: The wheel rim fluctuates (especially in 2- or most 4-cylinder engines) and, on large locomotives, not all wheels are driven. The "factor of adhesion", being the weight on the driven wheels divided by the theoretical starting tractive effort, was generally designed to have a value of 4 or slightly higher, reflecting a typical wheel–rail friction coefficient of 0.25. A locomotive with a factor of adhesion much lower than 4 would be highly prone to wheelslip, although some 3-cylinder locomotives, such as

7735-431: The wheel with multiple arcs, so that the wheel could work effectively both at high speed as well as at sharper curves. The behaviour of vehicles moving on adhesion railways is determined by the forces arising between two surfaces in contact. This may appear trivially simple from a superficial glance but it becomes extremely complex when studied to the depth necessary to predict useful results. The first error to address

7826-406: The wheel. Usually the force needed to start sliding is greater than that needed to continue sliding. The former is concerned with static friction (also known as " stiction " ) or "limiting friction", whilst the latter is dynamic friction, also called "sliding friction". For steel on steel, the coefficient of friction can be as high as 0.78, under laboratory conditions, but typically on railways it

7917-433: The wheels and rails occurs in the wheel–rail interface or contact patch. The traction force, the braking forces and the centering forces all contribute to stable running. However, running friction increases costs, due to higher fuel consumption and increased maintenance needed to address fatigue damage and wear on rail heads and on the wheel rims and rail movement from traction and braking forces. Traction or friction

8008-470: The wheels at the running surfaces, are different and the wheelset tends to steer back towards the centre. Also, when the train encounters an unbanked turn , the wheelset displaces laterally slightly, so that the outer wheel tread speeds up linearly, and the inner wheel tread slows down, causing the train to turn the corner. Some railway systems employ a flat wheel and track profile, relying on cant alone to reduce or eliminate flange contact. Understanding how

8099-416: The world. Adhesion traction is the friction between the drive wheels and the steel rail. Since the vast majority of railways are adhesion railways, the term adhesion railway is used only when it is necessary to distinguish adhesion railways from railways moved by other means, such as by a stationary engine pulling on a cable attached to the cars or by a pinion meshing with a rack . The friction between

8190-419: Was alleviated to a great extent by ensuring that the diameters of all coupled wheels were very closely matched. With perfect rolling contact between the wheel and rail, this coning behaviour manifests itself as a swaying of the train from side to side. In practice, the swaying is damped out below a critical speed, but is amplified by the forward motion of the train above the critical speed. This lateral swaying

8281-524: Was no public information of the test results. In railway, the Budd Company developed a system in the 1940s to improve the use of the electrical model of Decelostat by giving back the control of the braking to the operator in the event of a short-circuit in the Decelostat controller. The company later developed its own wheel slip protection system called Rolakron . The system used the same flywheel technology to detect rapid rate of deceleration, but used

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