Mechatronics & Timing Belts

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Mechatronics: The Major SubsystemsMAY 12, 2010

In just a couple weeks Ill be starting my new mechanicalengineering job withElectroimpact, a major aerospace toolingand automated machine production supplier (The video above isone of their automated fiber placement machines; it lays downcarbon fiber tows on the mandrel barrel sections of the Boeing 787fuselage). Since I have limited professional experience withCNC/mechatronics system design (beyond teaching simple design-

build-test, kit-based projects to undergrads), I thought it would beappropriate for me to review the major subsystems which comprise

the design space of a mechatronics-based engineering project.

Rather than focusing on the technical details of how to specify,design, and select and/or create individual components for each ofthese systems (which would be a diabolically large and unfeasible

blog post), this write-up will just review the major subsystemsthedesign building blocksof the technology which underpins CNCmachinery & roboticsmechatronics, in the more general sense.This write-up will describe and then illustrate these subsystems

with some specific examples. As an entry-level mechanicalengineer, the field of mechatronics necessarily incorporatesexpertise which is beyond the realm of the knowledge which Ipossess at this point in my career. And, due to the inherent breadthof disciplines required in mechatronics system design, it will bequite a whileif everbefore I could comfortably write up athorough explanation on specifying and designing componentsfor allof these subsystems Some of these subsystems are much

better handled by Electrical Engineers, or engineers with a depth ofexperience in controls engineering.

Nevertheless, this write-up on mechatronics systems which hasbeen written in broad brush strokes is outlined as follows:

Mechatronics Defined
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Prime Moverso Electrically Powered Actuation Linear Movement Electric Actuators Solenoids Shape-Memory Alloys

Rotation Servos Stepper motors

o Mechanically Powered Actuation Linear Movement Pneumatic cylinders Hydraulic cylinders

Rotation Air motors Hydraulic motors Combustion Engine Steam Engine

Motion Hardwareo Rolling-Element Bearings Ball Bearings Roller Bearings Needle Bearings Tapered Roller Bearings Spherical Roller Bearings Thrust Bearings Linear Bearings Linear Guide Blocks & Rails


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Ball Screws & Ball Nutso Plain Bearingso Ball Jointso Leadscrewso Ballscrewso Camso Gears Spur Gears Helical Gears Double Helical Gears Bevel Gears Hypoid Gears Worm Gears Rack & Pinion Gears Epicyclic / Sun & Planet Gears

o Belts & Pulleys; Chain & Sprocketso Springs

Linkages & Structureo Foundationo Frames & Bedplateso Four-Bar Linkages

The End Effector / Tool Control Hardwareo Switcheso Relayso PLCso Power Management Hardware

Control Software


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Sensorso Limit Switcheso Proximity Sensorso Photoelectric Sensorso Rotary Encoderso Machine Visiono Temperature Sensorso Pressure Sensors

References

Mechatronics DefinedMechatronics is defined as a combination of the engineeringdisciplines of mechanical, electronic, computer, control, andsystems design. [1] With the advent of electrically powered primemovers (motors) and then the development of computers, machinescould begin to be controlled much more efficiently with electricityand then accurately and flexibly with computers. Strictlymechanical systems (pre-electric, industrial revolution era

machinery for example) had severe limitations relative to these newtypes of machines. Computer-controlled machinery can generallyoperate much faster, much more efficiently, can be designed tooperate usefully in a wider range of situations, and can operatemuch more independent of human input. The main value drivingthis interdisciplinary field of engineering are these advantages

which mechatronics systems have over their strictly mechanicalforebears.

Prime MoversPrime movers are those elements of a machine which provide themotive force driving the motion of the device.

Electrically Powered ActuationLinear MovementElectric Actuators


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Devices called electric actuators are technically a combination of amotor and gearbox (which provides torque/rotational movement)coupled to an acme thread and ball-screw assembly to transform themotors rotation into extension of the rod (acme thread/ball screws

will be described later in the Motion Hardware section).However,they can be boughtas electrically powered plug-and-

play systems which do provide linear motion.

Solenoids

Solenoidsare an induction-based technology which ejects aferrous pin from the inductor barrel/coil when current is applied tothe coil. I couldnt find a video of a solenoid in action which wasntpart of a valve demonstration, but this video does show the guts of

the valve (the actual solenoid), as well as a particularly dorkylooking fellow in the role of narrator:

Controlling flow in valves is a very common application of thistechnology. I employed these valves in my senior capstone designproject to create a pneumatic t-shirt launcher mounted on a R.C.mobile platform for Michigan State sporting events.

Shape-Memory Alloys

Shape-memory alloys are applied in technology relatively rarely, butthey commonly function as electrically powered actuators whichprovide linear motion. Shape-memory alloys are special metals (orother materials) which, when heated (typically through resistance toelectric current running through them), return to a shape whichthey had prior to being deformed by an external force.Demonstrating that heat (a warm cup of water) can return the

shape memory alloy to its original shape:

In an actual mechatronics application, a spring force opposing thememory allocy can be used to stretch the shape memory alloy, whichachieves machine motion in one direction. A current applied to thealloy causes the alloy to contract, which returns the device to itsoriginal shape or position. A common shape memory materialisNitinol.
http://www.mcmaster.com/#electric-actuators/=70q1xjhttp://www.mcmaster.com/#electric-actuators/=70q1xjhttp://www.mcmaster.com/#electric-actuators/=70q1xjhttp://en.wikipedia.org/wiki/Solenoid#Electromechanical_solenoidshttp://en.wikipedia.org/wiki/Solenoid#Electromechanical_solenoidshttp://en.wikipedia.org/wiki/Nickel_titaniumhttp://en.wikipedia.org/wiki/Nickel_titaniumhttp://en.wikipedia.org/wiki/Nickel_titaniumhttp://en.wikipedia.org/wiki/Nickel_titaniumhttp://en.wikipedia.org/wiki/Solenoid#Electromechanical_solenoidshttp://www.mcmaster.com/#electric-actuators/=70q1xj


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RotationElectric motors are one of the major technologies which makes thefield of mechatronics a viable field worth pursuing. There are manydifferent types and classifications of electric motors, and a thorough

listing of all types of motors would be the subject of another blogpost. However, the two most relevant types of motors with respectto precision mechatronics are listed below.

Servomotors

Servomotorsare one dominant type of motor used inmechatronics. Their electrical design (synchronous, asynchronous,

AC or DC) is not limited to a specific design, but all servomotorsshare the feature of feedback control. This relies on a controller,

which can be a component separate from the motor itself known asthe servo drive, which monitors the state of the motor ormechanical system with a sensor. The controller then compares thissensor reading to a command input. The servo drive then amplifiesthe differential electrical reading to power the motor towards thecommand input value. A commonly used type of sensor is a rotaryencoder (explained in the Sensors section), which measuresrotational position of the motor shaft.

Stepper Motors

A stepper motor on the other handinstead of relying entirely onexternal control hardware and a sensoralso relies on a specificgeometric shape of the rotor and stator. This type of rotor andstator design allows it to be rotated by a specific angle. The statorconsists of several toothed electromagnets placed around theperiphery of a similarly toothed wheel on the rotor. Theelectromagnets are energized sequentially such that torque is

optimally generated based on the current position of theelectromagnet teeth, relative to the position of the teeth on the rotor(a very good animation of stepper motor design is available atthewikipedia articleon the subject). Stepper motors have highstarting torque and, apparently, can be used for more than justaccurate positioning of CNC machines:
http://en.wikipedia.org/wiki/Servo_motorhttp://en.wikipedia.org/wiki/Servo_motorhttp://en.wikipedia.org/wiki/Servo_drivehttp://en.wikipedia.org/wiki/Servo_drivehttp://en.wikipedia.org/wiki/Stepper_motorhttp://en.wikipedia.org/wiki/Stepper_motorhttp://en.wikipedia.org/wiki/Stepper_motorhttp://en.wikipedia.org/wiki/Stepper_motorhttp://en.wikipedia.org/wiki/Servo_drivehttp://en.wikipedia.org/wiki/Servo_motor


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Mechanically Powered ActuationLinear Movement

Pneumatic Cylinders

Pneumatic (compressed air) power is used in mechatronicsapplications requiring the application of a liner force. Compressedair is already such a common thing in factories where impact toolsare used, that it can be a natural extension to use equipment thatruns on compressed air.

You can see in this video that the cylinder is double acting: somecylinders rely on a return spring to draw the cylinder back into placeafter extending it (the latter are called single acting).

Hydraulic Cylinders

Where high powered linear motion is required, hydraulic cylinders(compressed fluid) do the job. Hydraulic cylinders require heavyduty pumps for anything require high throughput, but their powerdensity allows them to perform even the largest of lifting operations:

watch the A heavy weight on stilts video atMammoetswebsiteto get a sense of just how large the loads can be, which can

be lifted by hydraulics.The tensile testing frames I used during my masters thesis to testcarbon fiber composite coupons were hydraulic cylinders, controlled

by feedback control. They could apply peak loads of approximately1,000 lbs at 100 Hz (1oo cycles per second!).

RotationAir Motors

Less common than using compressed air to power pneumatic

cylinders is using compressed air to power anair motor, whichrotates the shaft of a reversed blower type device.

Wind turbines too can be considered a mechatronics system relyingon air to drive the system. Wind turbines themselves are certainlymechatronics machines (being automatically operated, controlled,
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and monitored by a PLC system). I spent about a year and a halfworking on these devices at General Electric.

Hydraulic Motors

Where a supply of compressed fluid exists, or electricity cannot be used,hydraulic motors may make sense, where a torque is required. Hydraulic

motors drive a shaft off of a set of vanes or gears which are propelled by

hydraulic fluid rushing through the motor housing. They supply much

more torque than air motors.

And similar to wind turbines, river dams use much larger turbinesrelying on fluid to drive the mechatronics system / generateelectricity.

Combustion EngineInternal combustion engines which convert expanding combustiongases directly to mechanical work include variations of piston-basedor turbine engines. Obviously, a wide range of power can be derivedfrom combustion enginesfrom small handheld portable generatorsto 600 MW gas turbines at power plants. Modern controls appliedto combustion engines has rendered them mechatronics systems inthemselveseven before considering the possibility of using them todirectly power another mechatronics system.

1,000 Watts of piston power by Honda
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520,000,000 Watts of turbine power by General Electric

Steam Engine

The steam engineeither piston-powered or turbine-basedisanother mechanical source of torque. Steam piston engines werecommon during the industrial revolution but are rare nowadays(However, the floating relic known as the SS Badgera coal-firedcarferry I lived and worked on one summer on Lake Michiganstillrelies on them. We had a breakdown one night and I observed theship engineers swapping a new two-foot diameter piston into thesuffering steam-powered cylinder). Modern steam-poweredsystems burn fossil fuels (coal or gas typically) to generate steam in
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boilers, which is then run through a steam turbine. These are largecomplex systems which are usually attached to generators whoseelectricity is subsequently used to power smaller machines. As withmany combustion engines, steam engines are typically complex

mechatronics systems in their own right.

Motion HardwareMotion hardware are the machine elements which promotesystem motion, and enable it to move in a reliable manner. Theyoften also serve to prevent wear of other components (the linkagesand structure).

Rolling-Element Bearings

Rolling-element bearings come in many forms, but greatly reducefrictional wear at a pivot point by replacing material-on-materialsliding with elements rolling across each other. There are manytypes of rolling element bearings. The images below are takeneither from thewikipedia articleon rolling-element bearings, orfrom theMcMaster-Carr catalog offeringson bearings.

Ball BearingsBall bearings are good for high speed applications and can be made

fairly economically relative to other bearing types. However, thehigh point-load contact with the race can limit the load they are ableto bear. The inner and outer races can tolerate some misalignmentand ball bearings can tolerate axial and radial loads.
http://en.wikipedia.org/wiki/Rolling-element_bearinghttp://en.wikipedia.org/wiki/Rolling-element_bearinghttp://en.wikipedia.org/wiki/Rolling-element_bearinghttp://www.mcmaster.com/#bearings/=71645zhttp://www.mcmaster.com/#bearings/=71645zhttp://www.mcmaster.com/#bearings/=71645zhttp://www.mcmaster.com/#bearings/=71645zhttp://en.wikipedia.org/wiki/Rolling-element_bearing


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Roller BearingsRoller bearings rely on cylindrical rolling elements. Due to the line-contact of the cylindrical rolling element, they can bear a higherload than an equivalently sized ball bearing of similar material.

However, they do not tolerate race misalignment or axial loadingvery well.
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Needle BearingsWhereas roller bearings use rolling elements with a length onlyslightly greater than their diamter, needle bearings rely on elements

whose length greatly exceeds their diameter. This also incrases the

number of elements while permitting the bearing to fit much moreclosely around the shaft.
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Tapered Roller BearingTapered roller bearings rely on conical races and conically shapedrolling elements. Their large contact surface and ability to bear highradial and axial loads are beneficial, but their unique, conically

based geometry makes them more difficult to manufacture thansimple ball bearings. The outer ring, or cup, can be separatedfrom the inner roller cage and race.
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Spherical Roller BearingSpherical roller bearings are designed with rolling elements whoseouter surface is some portion of a sphere, with a race to run tomatch. The primary benefit of these bearings is that they can run

with misalignment of the inner and out race, but they are difficult tomanufacture and run hot because different points along the contactline run at different speeds as the elements rotate, causing wear.
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Thrust BearingsThese bearimgs can have cylindrical, conical, or spherical rollingelements, and can also be bought as turntables. Obviously, theyare designed for where the primary load is axial thrust. Fluid and

magnetic thrust bearings are also available, which do away withrolling elements altogether.
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Linear BearingsLinear bearings are used to promote sliding alongthe axis of a rodas opposed to promoting rotation of the rod withinthe bearing(though linear bearings are available which permit both, if that type

of unique application is what you are dealing with).
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Linear Guide Blocks & Rails

Linear guide blocks and rails are co-engineered, precision-madeunits. The rolling elements in the guide block are designed to fitinto features on the rails with minimal clearance. Due to the factthat the rolling elements ride in grooves on the rails, linear guide

blocks typically can bear more load than simple linear bearings, andcan handle offset loads better than simple linear bearings.

Ball Screws & Ball NutsAnother type of rolling-element bearing which promotes lineartranslation is the ball screw and ball nut. This is a bearing with alarge number of spherical ball bearings that are captive, internal tothe ball nut. The ball nut itself is threaded on a ball screw threaded
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rod, and when the ball screw is rotated, the ball nut translates up ordown the ball screw rod. The ball bearings roll along inside thegrooves in the threaded rod, and are recirculated to begin theprocess again, through a ball passageway that is external to the race.

Ball screws have a much higher efficiency than leadscrews(described later) because they rely on rolling elements, instead offrictional sliding. They are fairly expensive to make, but are great

where precise linear positioning is required.

Plain BearingsAlso known as a sleeve bearings or journal bearings whereloads are not too high, it can be practical and much less expensive toinstall a sleeve bearing to promote sliding (along a shaft) or rotation

(within the bearing). Sleeve bearings come in many types of durableplastic, but also in porous metal which has been impregnated withoil to self-lubricate itself; some even have graphite coresembedded in them to promote lubrication.

Plain linear bearings are also available for promoting linearsliding alonga shaft:
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Plain bearing versions of the guide block format of linear bearingare also available:

Ball JointsBall joints are a type of bearing which captures a spherical metalball in a housing, and allows rotation within a limited range ofmotion. They are not technically rolling-element bearings becausethe sphere slides within the housingit does not roll. There aremany different geometries of ball joints available.
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LeadscrewsLeadscrews (also known as power screws) are used to translaterotational motion into linear translation. Acme leadscrew threadedrod can be purchased and matched to internally threadedcomponents which can be mounted to the device which requireslinear translation.

Acme threaded rod:

Acme threaded nuts and flanges:

Leadscrews can also be bought as a prepackaged devices with aslide table mounted onto a component with internal threading

matched to the leadscrew.
http://en.wikipedia.org/wiki/Power_screwhttp://valuablemechanisms.files.wordpress.com/2010/05/acme-lead-screw-slide.gifhttp://valuablemechanisms.files.wordpress.com/2010/05/acme-nuts-and-flanges.jpghttp://valuablemechanisms.files.wordpress.com/2010/05/acme-threaded-rod.jpghttp://valuablemechanisms.files.wordpress.com/2010/05/acme-lead-screw-slide.gifhttp://valuablemechanisms.files.wordpress.com/2010/05/acme-nuts-and-flanges.jpghttp://valuablemechanisms.files.wordpress.com/2010/05/acme-threaded-rod.jpghttp://valuablemechanisms.files.wordpress.com/2010/05/acme-lead-screw-slide.gifhttp://valuablemechanisms.files.wordpress.com/2010/05/acme-nuts-and-flanges.jpghttp://valuablemechanisms.files.wordpress.com/2010/05/acme-threaded-rod.jpghttp://en.wikipedia.org/wiki/Power_screw


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Leadscrews are commonly used in the x and y axis positioning ofmilling machines, and anywhere else precise positioning is neededand a feasible length of threaded rod can be installed.

CamsCams are mechanical timing elements which are carefully shaped tocause a predicted motion output for a cam-follower that rides on thecam. The most familiar application of cams is in internalcombustion piston-based enginesthey are used to lift the intakeand exhaust valves at known positions of the engine crankshaft,preventing the piston from colliding with the valves. Much morecomplicated motion can be accomplished than just a simple linear

valve lift:

GearsGears transfer rotational motion accurately between two shafts andcan increase/decrease torque while decreasing/increasing shaftrotational speed, respectively. Gearboxes are combinations ofmultiple sets of gears which can achieve higher gear ratios in morereasonably sized and feasibly produced sizes, than if just one gearstage were employed. There are many different types of gears which

allow the engineer to achieve different ends. Again, many of theimages below are from awikipedia articleon gearing.

Spur GearsThis is the typical hob-cut, simple gear external gear. Axes must beparallel for these types of gears since the teeth are parallel to theshaft axis; and they exhibit noise if running in high speedapplications because the teeth do not engage gradually.
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Helical GearsHelical gears, while being more complex to make than spur gears,are much better suited for high-speed applications since the teethengage more gradually than spur gears. Spur gears engageinstantaneously along a line across the whole tooth, but helical gearsengage at a point, develop into a line of contact, then separate at a

single point of contact. This causes less noise / mechanical shock inthe tooth. The tooth shape of a helical gear is a segment of a helix,and their shaft axes can be oriented at any angle, though the contactarea tends to be optimal when the shafts are parallel [2]. Thrust isgenerated along the shaft axis in helical gears, which has to becounteracted with thrust, taper, or spherical bearings.
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Double Helical GearsDouble helicals (also known as herringbone gears) prevent theproblem of axial thrust which is present in helical gears. However,they are even more complex to manufacture.
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Bevel GearsBevel gears consist of two conically profiled gears (in cross-section)

whose hypothetical vertices intersect. Teeth can be straight-cut orspiral-cut (which are analagous in functionality to straight hob-cut

spur gears and helical gears).
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Hypoid GearsSimilar to bevel gears except the shaft axes do not lie in the sameplane.

Worm GearsWorm gears function similar to leadscrews. The worm can alwaysdrive the gear, but they can be designed such that the gear cannot

backdrive the worm.
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Rack and PinionWhen the teeth on the periphery of a helical or straight-cut gear areinstead placed along a single line instead of the circumference of acircle, a rack and pinion is formed. In this way, finite linear

motion can be achieved directly from a rotating gear.
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Epicylic / Sun & Planet GearsGears can be paired to create epicyclic gear sets, in which one ormore of the gear axes rotates during gearing operation. By fixingone or more sets of these axes, different output gear ratios can beobtainedand this is the principle and type of gearing in the modern

automotive gearbox transmission (a great interactive illustration, inwhich various axes can be held fixed by the user, is availablehere).

Belts & Pulleys; Chain & SprocketsBelts & pulleys (and cables) / chain & sprockets transfer force andmotion from one shaft to another, and similar to gears, they canincrease/decrease torque while decreasing/increasing rotationalspeed respectively. Pulleys combined with a non-toothed belt orcable, such as a V-belt, provide a useful method of transferring
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power where an approximate (but not absolute) ratio of input speedto output speed is necessary.

Timing belts are pulleys with teeth features on the belt and pulley,which provide a much more exacting ratio of input-to-outputrotational speed.
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Of course, compound pulleys (a block and tackle arrangement)can be used to magnify mechanical forcetrading off the distance aload is moved for the amount of force applied to it.
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Timing chains and sprockets are more expensive, (can be) noisierthan belting, and require lubrication, but they can transfer morepower within a given space and have a direct and exact ratio ofinput-to-output shaft speed. They also require exacting location of

the shafts.
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Springs

Springs store mechanical energy in the form of strain energy of thespring material. They can supply a linear reactive force or a torquewhen they are deformed from their resting state (either compressedor extended). A typical helical spring for linear tension force:
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Clock springs can supply a reactive torque when deformed fromtheir initial state:
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Leaf springs and recurve bows function on the same basicgeometryapplying a bending moment to a strip of material,applying tension between the two points of the spring elementsattachment. They can also apply a force transverse to a line throughthe mounting points, if deformed from their initial static state. Thisis what provides suspension force in the case of leaf springs, and theforce to launch an arrow in the case of a recurve bow.
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Linkages & StructureThe Linkages &Structure serve as the frame (dynamic or static) orplatform/base upon which all the other elements are installed or

work from. These are often custom designed for unique process

machinery. Basic elements of mechtronics linkage and structureinclude the following categories.
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FoundationSome mechatronics systems are meant to be stationary, but involve

very large forcesjust from the sheer mass of the machine or what itis manipulating, or from dynamic loading from the machinesmotion. This is especially true for process and assembly machineryand the design of the foundation for the machine can be critical toensuring the machine will operate effectivelyappropriatelysupporting and damping out any vibrations. Companies suchasUnisorbspecialize in installation and foundation designspecifically.

Frames & Bedplates

Generally, major mechatronics systems that require a seriousfoundation will also have machine components which could bedescribed as the machine frame in order to do useful work.Frames & bedplates serve as structures which all the other system

components mount to, and serve as the rigid base whichcounteract any forces generated by the prime movers to move theother kinematic elements of the system. A diagram from a GEturbine:

In that illustration, the Main Frame (labeled as number 5), as wellas the bedplate (directly under the Gearbox-13), and the towerserve as the frame to which the dynamic elements are mountedthe rotor assembly, rotor shaft, (internal gears of the) gearbox, andthe generators rotor (Though it should be noted that the machinehead itself can rotate on top of the tower).
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Four-Bar LinkagesA unique machine element which can effect complex machinemotion, while still serving as part of the machine structure is thefour-bar linkage. Four-bars are exploited in robotics, andanywhere a unique but consistently repeatable path is required, or amechanical advantage needs to be derived from a simple assemblyof linkages in series:

Applications are numerous in mechatronics. Aparallelmanipulatoris shown in the video belowvery similar to the ABBFlexpicker featured in anearlier writeupand each of the threearms is a parallelogram of linkages with ball joints at their vertices:

Each of the kinematic parallelograms is a four-bar linkage. A four-bar is also what enables the vise-grip to do such great work for us inthe shop:
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Four-bar linkages can be thought of as a means to do one of threethings. The first is to achieve a unique but repeatable tool path (theposition of elements in the four-bar system are an exercise inadvanced geometry). The second is to increase force input to asystem: by rotating one of the larger linkages in the system, inputforce can be multiplied in the motion of one of the smaller links(this is what vise-grip pliers do). Four-bar linkages can also help

you achieve the opposite process: by manipulating one of theshorter linkages in the system, the output speeds and distancestranslated at a larger linkage in the system can be greatly increasedrelative to the input. Mounting a motor at one of the jointsdrivingone of the linkages to rotateis one way in which a four-bar could beincorporated into a mechatronics system.

The End Effector / ToolThe end effector is the device which carries out the task which themachine is designed to perform. This is typically a custom-designeddevice, and is specific to whatever the mechatronics machine has

been designed to do. In the first video at the very top of this write-
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up, the end effector is the head which contains multiple spools ofcarbon fiber tows, the motors and hardware for paying out the towsand guiding them onto the mandrel, and the shears used to trim thetows. In this robot however, the end effector is a painting head:

In this robot, its a spot welder:

The end effector is specific to whatever the task of interest is.

Control HardwareThere is electronics or controls-related hardware associated withany mechatronics system.

Switches

A switch is typically defined as a component which can interrupt anelectric circuit. It usually also refers to an electromechanical devicethat is manually thrown by an operator. Wide-scale use of switchesto operate mechatronics systems is not common todaygood systemdesign and the use of PLCs and sensors can remove the need for anoperator to approve every step of a machines operation bythrowing a swtich.

Switches can be designed to be thrown by almost any sort ofstimuli the engineer can think of, which then makes the switchthen defined as a sensor (a binary, on-or-off, mechanical statedetector): vibration, turning a key, the orientation of the switch,
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presence of a magnetic field, rotation, presence of a mechanicalstopthe possibilities are numerous. For machinery incorporatingpneumatic and hydraulic power, switches (valves) are available forthese systems as well.

RelaysRelays are a step up in terms of automation, relative to switches.Instead of manually throwing a switch, relays close a circuit when

current is provided to the relay from another circuit. In this way, asensor can close a relay when it detects a certain machine state, andthe closed relay then powers some other device, reacting to the

machine state which triggered the sensor. For example, an opticalswitch monitoring a conveyor belt can detect the presence of apackage and then send a low voltage signal to the relay wired to theconveyor belts motor. When the optical switch detects a package onthe belt, it closes the relay with a low voltage sensor reading; theclosed relay supplies high-power electricity to the motor, which thendrives the conveyor forward.

Electromechanical relays are based on induction: copper windings

energized by the low power circuit drive an iron core out of the coil,which closes or opens the high-power relay contacts.
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Relays do not have to be mechanicalphysically closing a contact;they are available assolid-state devices. Based entirely oncircuitry and with no moving parts, these can be particularly useful

where vibration can risk closing an electromechanical relay whenthe circuit is not actually energized. For high-current applicationsor where frequent switching occurs, heatsinks are required todissipate the power which is consumed during their operation.

Programmable Logic Controller (PLC)Many, if not most, modern mechatronics devices are controlled byprogrammable logic controllers. PLCs are simple computers whichcan continuously monitor multiple inputs, compare these inputs touser defined settings or operator commands, and then commandgovern the behavior of multiple components in the system asoutputsturning them on or off as appropriate. In this way, PLCsare the brain of many mechatronics systems you see today.
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PLCs were designed to replace the increasingly complex controlsystems comprised entirely of huge systems of logic-based relay

circuitry. Modern PLCs commonly have the code which runs themwritten on and debugged on a separate personal computer. Thiscode is then downloaded to the PLC via ethernet or RS-232 cablingand stored on RAM or flash memory. To control high-powereddevices, PLCs often energize relays to close high-power circuits.PLCs need not interact and control their mechatronic systems

according to digital on/off inputs and outputs; analog inputs andoutputs can be incorporated because PLCs can monitor the intensity

of a voltage or current being sent to it (this enables quantifiablemonitoring of things like pressure, temperature, or weight).Additionally, PID control can be implemented to preventovershooting system targets.

Power Management Hardware
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With so many devices requiring different power and voltage levels(sensors, prime movers, end-effector machinery), its common formechatronics systems to need power management hardware. To behonest, I have very little experience with this hardware at this point

in my career, but its worth mentioning that it can be necessary.

Control SoftwareThe software controlling the PLC depends on the PLC which isselected for the job. The logic controllers manufacturer will havetheir own code language for their hardware. For example, Fanuchas its own software for the robots it sells, Ive worked with andtaught the use of Parallax pbasic to students, and Arduinomicrocontrollers have a language that is similar to C++.

The details of coding are a topic way outside the purpose of this blogpost, but logic commands like IF, THEN, ELSE, FOR,WHILE, and COUNT, were some of the common commandsfrom pbasic code. There are analogous commands betweendifferent manufacturers coding languages, and computerprogramming in general. For example, lot of my training as anundergrad in MatLab code writing carried over pretty directly intocoding in pbasic.

SensorsSensors monitor features of the system which the engineer deemsimportant to the behavior of the systemeither with respect tofunction, safety, or preventing system damage. Some commonsensors are presented below.

Limit SwitchThese are mechanical switches with a toggle or button which, when

depressed by an object moving past them, either activate ordeactivate a circuit. These provide true/false information about themachine statushas the machine reached this positionyes or no?They dont provide information about the absolute current position

of the machine beyond whether it has reached the limit defined bythe switch position itself. They are useful in shutting off or slowing


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down machinery which are reaching a position which could bedangerous to an operator, or to damaging the system itself. Limitswitches come in many forms.

Proximity Sensor

Proximity sensors come in various forms. They can detect thepresence of a metal object (through thehall effect), they can detectthe presence of liquidsome liquid level sensors close their circuitthrough the liquid itself. Noncontact liquid level sensors canmeasure the presence of liquid by reflecting ultrasonic waves off thesurface of the liquid. A metal-sensing proximity switch looks likethis:

While working as a mechanical engineering co-op for GE WindEnergy, I saw the switches in this image used as redundant

measures of wind turbine tower rotation In addition to encodermeasurement of yaw motor rotation, these prox switches measuredthe passage of gear teeth on the yaw bearing, relate to the bedplatesmotion.
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Photolelectric SensorsPhotoelectric sensors are another sensor which providesinformation in a yes or no formatthey provide a signal to thecontroller when an object is present or absent, when it interrupts alight beam.

Rotary EncodersMost machine motion is facilitated by torque-providing prime

moverselectric motors, or perhaps engines rotating a shaft. If thisis isnt the case (for example, if hydraulic cylinders are being used),most machine motion can still be measured fairly easily as afunction of rotation, and thusrotary encodersare the devices

which are commonly used to measure the absolute position of amachine. Rotary encoders measure the position of a rotating shaft.Some encoders also have the ability to count the number of

complete revolutions the shaft has turned, which gives the engineer

the ability to know how far the machine has moved from a specifieddatum.

If an encoder is being integrated with a PLC system, an analog todigital converter (ADC) will be required to convert the analog

voltage or current signal to a digital signal that the PLC can readifits not already integrated into the encoder itself. Encoders optically
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measure a pattern etched into or through a surface with a photodetector, the photo detector yields a current/voltage reading, andthis reading is converted to a digital signal. The encoder etchingpattern determines the shaft position which corresponds to the

analog/digital.

It can be observed in the image above that each of the eight, 45-degree arc sections has a unique pattern in it, which then uniquely(in 45-degree increments) determines the position of the shaft.However, encoders are available with more than 10,000 counts per
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revolution! Obviously, very precise positioning can be achieved withencoders. Precision can (typically) be further enhanced bymeasuring motor rotation instead of machine component rotationthis is true because motor rotation speeds are (typically) kicked

down by a gearbox in order to attain speeds which are useful formost machinery.

In the days of yorewhen the computer mouse relied on a trackballinstead of optical surface sensingencoders were what measured themovement of the trackball.

Machine VisionMachine vision is a large topic in itself, but it is like a photoelectric

switch on steroids Instead of measuring the presence or absenceof light on a single sensor, an entire array of pixels on a CCD can bemonitored for the presence or absence of specified light intensitylevels. In this way, objects of interest can be differentiated fromtheir background, and these objects can then be reacted to by thecontroller system thats monitoring them. For example, if you fastforward to 1:50 in the video below, the ABB Flexpicker controlsystem can be seen locating the presence (AND type!) of muffins on

the conveyor belt:Machine vision is a new but rapidly expanding field.

Temperature SensorsTemperature can be measured as an analog signal by a temperaturesensor, converted to a digital signal, and read and reacted to by amicrocontroller. Thermocouples can serve this purpose; infraredthermometers are also available.
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Pressure SensorsSimilar to temperature sensors, pressure transducers can measurepressuremeasured as an analog signal, converted to digital by an

ADC, which is then read and reacted to by a PLC.

There are few limits on how many types of machine conditionscould potentially be read by a sensor of some type, as either a digitalor analog signal.

References[1]http://en.wikipedia.org/wiki/Mechatronics

[2]http://www.roymech.co.uk/Useful_Tables/Drive/Hellical_Gears.html
http://en.wikipedia.org/wiki/Mechatronicshttp://en.wikipedia.org/wiki/Mechatronicshttp://en.wikipedia.org/wiki/Mechatronicshttp://www.roymech.co.uk/Useful_Tables/Drive/Hellical_Gears.htmlhttp://www.roymech.co.uk/Useful_Tables/Drive/Hellical_Gears.htmlhttp://www.roymech.co.uk/Useful_Tables/Drive/Hellical_Gears.htmlhttp://www.roymech.co.uk/Useful_Tables/Drive/Hellical_Gears.htmlhttp://valuablemechanisms.files.wordpress.com/2010/05/pressure-transducer.jpghttp://www.roymech.co.uk/Useful_Tables/Drive/Hellical_Gears.htmlhttp://www.roymech.co.uk/Useful_Tables/Drive/Hellical_Gears.htmlhttp://en.wikipedia.org/wiki/Mechatronics


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TIMING BELT & TIMING BELT PULLEY


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GT2 timing pulleys 20 teeth 6mm width and 10m length belt

Type: GT2 timing pulleys 20 teeth 6mm width and 10m length belt1. 20GT2-6 timin gpulley

Tooth nuber: 20Width: 6mm

Bore: 5mmMaterial: aluminumFlange: doubleHub: oneScrew hole: 2*M3Quantity: 10pcs2.6GT2-10m open timing beltWidth: 6mmMaterial: rubber with glass fibreQuantity: 10m


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Mechatronics & Timing Belts

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