Marvelous Mechanisms: The Ubiquitous Four Bar Linkage

The four bar linkage is a type of mechanical linkage that is used in many different devices. A few examples are: locking pliers, bicycles, oil well pumps, loaders, internal combustion engines, compressors, and pantographs. In biology we can also find examples of this linkage, as in the human knee joint, where the mechanism allows rotation and keeps the two legs bones attached to each other. It is also present in some fish jaws that evolved to take advantage of the force multiplication that the four bar mechanism can provide.

How It Works

The study of linkages started with Archimedes who applied geometry to the study of the lever, but a full mathematical description had to wait until the late 1800’s, however, due to the complexity of the resulting equations, the study and design of complex linkages was greatly simplified with the advent of the digital computer.

Mechanical linkages in general are a group of bodies connected to each other to manage forces and movement. The bodies, or links, that form the linkage, are connected to each other at points called joints. Perhaps the simplest example is the lever, that consists of a rigid bar that is allowed to pivot about a fulcrum, used to obtain a mechanical advantage: you can raise an object using less force than the weight of the object.

Two levers can be connected to each other to form the four bar linkage. In the figure, the levers are represented by the links a (A-D) and b (B-C).  The points A and B are the fulcrum points.  A third link f (C-D) connects the levers, and the fourth link is the ground or frame g (A-B) where the mechanism is mounted. In the animation below, the input link a (the crank) performs a rotational motion driving the rocker rod b and resulting in a reciprocating motion of the link b (the rocker).

This slider-crank arrangement is the heart of the internal combustion engine, where the expansion of gases against a sliding piston in the cylinder drives the rotation of the crank. In a compressor the opposite happens, the rotation of the crank pushes the piston to compress the gas in the cylinder. Depending on how the mechanism is arranged, it can perform the following tasks:

• convert rotational motion to reciprocating motion, as we just discussed above.
• convert reciprocating motion to rotational motion, as in the bicycle.
• constrain motion, e.g. knee joint and car suspension.
• magnify force, as in the parrotfish jaw.

Some Applications

One interesting application of the four bar linkage is found in locking pliers. The B-C and C-D links are set at an angle close to 180 degrees. When force is applied to the handle, the angle between the links is less than 180 (measured from inside the linkage), and the resulting force in the jaws tries to keep the handle open. When the pliers snap into the locked position that angle becomes less than 180, and the force in the jaws keeps the handle in the locked position.

In a bicycle, the reciprocating motion of the rider´s legs is converted to rotational motion via a four bar mechanism that is formed by the two leg segments, the bicycle frame, and the crank.

As with many other inventions of humankind, we often find that nature has already come up with the same idea via evolution. The parrotfish lives on coral reefs, from which it feeds, and has to grind the coral to get to the polyps inside. For that job, they need a very powerful bite. The parrotfish obtains a mechanical advantage to the muscle force by using a four bar linkage in their jaws! Other species also use the same mechanism, one is the Moray eel, shown in the image, which has the very particular ability to launch its jaws up in the mouth to capture its prey, much like the alien from the film series.

The joints connecting the links in the linkage can be of two types. A hinged joint is called a revolute, and a sliding joint is called a prismatic. Depending on the number of revolute and prismatic joints, the four bar linkage can be of three types:

• Planar quadrilateral linkage formed by four links and four revolute points. This is shown in the animation above.
• Slider-crank linkage, formed by three revolute joints and a prismatic joint.
• Double slider formed by two revolute joints and two prismatic joints. The Scotch yoke and the trammel of Archimedes are examples.

There are a great number of variations for the four bar linkage, and as you can guess, the design process to obtain the forces and movements that we need is not an easy task. An excellent resource for the interested reader is KMODDL (Kinematic Models for Design Digital Library) from Cornell University. Other interesting sites are the 507 mechanical movements, where you can find nice animations, and [thang010146]’s YouTube channel.

We hope to have piqued your curiosity in mechanical things. In these times of ultra fast developments in electronics, looking at the working of mechanisms that were developed centuries ago, but are still present and needed in our everyday lives can be a rewarding experience. We plan to work on more articles featuring interesting mechanisms so please let us know your favorites in the comments below.

Silicon Wafer Transfer Machine Is Beautifully Expensive

There’s nothing more freeing than to be an engineer with no perceptible budget in sight. [BrendaEM] walks us through a teardown of a machine that was designed under just such a lack of constraint. It sat inside of a big box whose job was to take silicon wafers in on one side and spit out integrated circuits on the other.

[BrendaEM] never really divulges how she got her hands on something so expensive that the engineer could specify “tiny optical fiber prisms on the end of a precision sintered metal post” as an interrupt solution for the wafer.  However, we’re glad she did.

The machine features lots of things you would expect; pricey ultra precise motors, silky smooth linear motion systems, etcetera. At one point she turns on a gripper movement, the sound of it moving can be adequately described as poetic.

It also gives an unexpected view into how challenging it is to produce the silicon we rely on daily at the ridiculously affordable price we’ve come to expect. Everything from the ceramic plates and jaws that can handle the heat of the silicon right out of the oven to the obvious cleanliness of even this heavily used unit.

It’s a rare look into an expensive world most of us peasants aren’t invited to. Video after the break.

Battery Powered Fog Machine Just in Time for Halloween

[makendo] needed a portable fog machine for an upcoming project. It seemed like the kind of a thing a liberal application of money on the Internet could fix in no time. But quality fog machines are too expensive, and the cheap machines are just, well, cheap. Stuck between \$800 and quickly broken crap, he decided instead to fashion his own.

Fortunately for him, a recent fad has made it so that a certain segment of the populace absolutely require dramatic clouds of scented drug fog or they get cranky. The market saw an opportunity, cost optimized, and now there are many portable fog machines just waiting to be born in the form of an e-cigarette. However, an e-cigarette needs interaction from a person’s lungs to provide an annoying cloud. So he modeled up a 3D printable case that would blow air into the intake of the e-cigarette. Instead of filling a person’s lungs with a cloud of eye drops and nicotine, it would let out a steady stream of fog.

This device does burn through emitters, because the e-cigarette was not designed for this kind of heavy duty. Even reading the Amazon comments for the \$800 dollar version, this is fairly normal for these things. So now [makendo] is able to produce a nice cloud of smoke whenever he needs and it only set him back around \$40 US dollars.

Hacker Places To Visit: Musée des Arts et Métiers in Paris

The best way to pull off this deception: tell your significant other that you’d want nothing more than a romantic week in Paris. Arrive in Paris, stash your bags, and then take either the number three or eleven Metro. When you get to the station that looks like the inside of a giant steam engine, Arts et Métiers, get out. You’re now ten Euros away from one of the coolest museums a hacker could visit.

A significant portion of modern science’s beginnings is sitting in the Musée, polished and beautiful. Most of them are housed in cabinets so old they’re part of the exhibit. Now, the Henry Ford museum in Detroit Michigan is a monument to industrialization, and cool in its own right, but it leaves some questions unanswered. We’re all spoiled by desktop CNCs, precision measurement tools for pennies, and more. How did we get here? How did they measure a shaft or turn a screw before precision digital micrometers? What did early automation look like? Early construction?

Also did I mention it has Foucault’s Pendulum? You know, the one that finally convinced everyone that the Earth rotated around an axis? No big deal.

The museum has a few permanent exhibits: instruments scientifique, matériaux, construction, communication, énergie, mécanique et transports.

Instruments Scientifiques was one of my favorites. Not only did it include old scientific instruments, it had sections containing some of the original experiments in optics, computation, and more. For example you can see not just one but a few original examples of Pascal’s Pascaline, arguably the first mechanical calculators in the modern era to be used by the layman for every day calculation, signed by Pascal. It’s also worth noting just how incredible the workmanship of these tools are. They’re beautiful.

Matériaux was initially a disappointment as I entered it from the wrong end. For me it started of with a tragically boring and simplistic display on recycling materials designed primarily to torture children on field trips. Luckily it quickly ramped into a fascinating display on materials manufacturing technology. How did we go from hand looms to fully automated Jacquard looms (of which you can see some of the first examples) to our modern day robotic looms? How did ceramic evolve? What was early steelmaking like? It’s very cool and models are all in beautiful condition.

By the time I got to Communication I was reaching the limit of my endurance and also what you can fit into a single day of the museum. It’s a large building. It was packed through many of the early examples of computing, television, and space. There was quite a display of early camera equipment. You could get close enough to some truly massive old computers to smell the still off-gassing phenolics.

Construction held my interest for a long time. It’s not my usual interest, but after living in Paris for a month or so I was absolutely burning with curiosity. How did anyone without a single powered crane or vehicle build so many buildings out of stone? It’s packed for four rooms and two stores from floor to ceiling of beautiful little wood models explaining exactly how.

Énergie was quite cool. It followed the development of steam power for the most part. It started with primitive waterwheels. Moved on to turbines. Then showed the gradual increase in complexity until the the modern day. It had some internal combustion too, but much of that was reserved for the transports section of the museum. It also had some interactive displays to entertain children and Hackaday writers. However they were in desperate need of an oiling and this is by far the most ear-piercingly squeaky exhibit in the whole building.

Mécanique is competing with instruments scientifique as my favorite exhibit. Have you ever wanted to see hundreds of examples of screw machines, old lathes, and the evolution of the milling machine? What about models of the factories that built steam engines or massive wagon wheels. They even had a lathe that belonged to a French king. Apparently he thought metalworking was the way to get in touch with the common people.

Transports was a nice exhibit, but it fell a little short for me since I’d been to the aforementioned Henry Ford museum. However, it covered the history of some of the European automobile manufacturers pretty well. Had a nice section on trains and subways. And even had some models of the ships used in the European Space Agency.

The last exhibit is the museum itself. It’s an historic building. It was originally built as a school for training engineers in 1794 but as the school grew out of it, it slowly transformed into the museum it is today. The architecture is beautiful. It’s adorned in stone and statue like all the French museums. It also has sections cut out in some of the higher storeys of the building so you can see how it was constructed.

Part of its beauty is also related to the school swallowing up the Priory of Saint Martin des Champs (Google translate does a great job if you don’t read French). The Priory is a beautiful old church, founded in 1079. It was home to the last trial by combat the country would see. You can piece together the story between the two pages dedicated to the combatants Jean de Carrouges and Jacques Le Gris.

The final display in the museum is in the church. It holds Foucault’s pendulum, dangling from the center of the sanctuary. If you get there early enough in the day you may get to watch it knock over a peg or two and prove the rotation for yourself.

Rather than the statues of the saints there are statues of the muses of Industrie and Agriculture. The hall is filled with more exhibits. There are cutaway original automobiles. A model of the Statue of Liberty. A catwalk lets you take a high view of the surroundings. It is also beautiful in and of itself. The church is well maintained and painted in the style original to them.

If you find yourself in Paris with a few hours (or days) to spare I highly recommend this museum. Any technical person would be hard pressed to leave uninspired and unawed by the display. It’s good to get a perspective on the past.

Featured Photo CC: Roi Boshi

Grand Theft Auto V Used To Teach Self-Driving AI

For all the complexity involved in driving, it becomes second nature to respond to pedestrians, environmental conditions, even the basic rules of the road. When it comes to AI, teaching machine learning algorithms how to drive in a virtual world makes sense when the real one is packed full of squishy humans and other potential catastrophes. So, why not use the wildly successful virtual world of Grand Theft Auto V to teach machine learning programs to operate a vehicle?

The hard problem with this approach is getting a large enough sample for the machine learning to be viable. The idea is this: the virtual world provides a far more efficient solution to supplying enough data to these programs compared to the time-consuming task of annotating object data from real-world images. In addition to scaling up the amount of data, researchers can manipulate weather, traffic, pedestrians and more to create complex conditions with which to train AI.

It’s pretty easy to teach the “rules of the road” — we do with 16-year-olds all the time. But those earliest drivers have already spent a lifetime observing the real world and watching parents drive. The virtual world inside GTA V is fantastically realistic. Humans are great pattern recognizers and fickle gamers would cry foul at anything that doesn’t analog real life. What we’re left with is a near-perfect source of test cases for machine learning to be applied to the hard part of self-drive: understanding the vastly variable world every vehicle encounters.

A team of researchers from Intel Labs and Darmstadt University in Germany created a program that automatically indexes the virtual world (as seen above), creating useful data for a machine learning program to consume. This isn’t a complete substitute for real-world experience mind you, but the freedom to make a few mistakes before putting an AI behind the wheel of a vehicle has the potential to speed up development of autonomous vehicles. Read the paper the team published Playing for Data: Ground Truth from Video Games.

Hackaday Prize Entry: Coffee Machine Grows In Complexity With No Sign Of Stopping

In Star Trek, there is a race of cyborgs with a drive to slowly assimilate all sentient life. Their aesthetic is not far off from the one [Ronald]’s ever expanding coffee machine is taking on. One has to wonder, what dark purpose would bring the Borg into existence? Where did they start? If [Ronald] doesn’t get a satisfying cup of coffee soon, we may find out.

We covered the first iteration of his brewing machine in 2013. We like to imagine that he’s spent many sleepless, heavily caffeinated days and nights since then to arrive at version 2. This version is a mechanical improvement over his original Rube Goldberg contraption. On top of that, it has improved electronics and code, with a color screen reminiscent of industrial control panels.

He’s also working on something called, “AutoBaristaScript(TM),” which attempts to hold the entire universe of pour-over coffee within its clutches. We don’t know when he’ll stop, but when he does finally create that perfect cup, what’s left of the world will breathe easier. They’ll also drink good coffee.

Editor’s Note: The Borg do not necessarily want to assimilate all sentient life as an end unto itself. The Kazon were deemed unworthy of assimilation (VOY: Mortal Coil). The Borg are driven towards perfection, accomplished by adding technological and biological distinctiveness to their own.

The Mystery Behind the Globs of Epoxy

When Sparkfun visited the factory that makes their multimeters and photographed a mysterious industrial process.

We all know that the little black globs on electronics has a semiconductor of some sort hiding beneath, but the process is one that’s not really explored much in the home shop.  The basic story being that, for various reasons , there is no cheaper way to get a chip on a board than to use the aptly named chip-on-board or COB process. Without the expense of encapsulating  the raw chunk of etched and plated silicon, the semiconductor retailer can sell the chip for pennies. It’s also a great way to accept delivery of custom silicon or place a grouping of chips closely together while maintaining a cheap, reliable, and low-profile package.

As SparkFun reveals, the story begins with a tray of silicon wafers. A person epoxies the wafer with some conductive glue to its place on the board. Surprisingly, alignment isn’t critical. The epoxy dries and then the circuit board is taken to a, “semi-automatic thermosonic wire bonding machine,” and slotted into a fixture at its base. The awesomely named machine needs the operator to find the center of the first two pads to be bonded with wire. Using this information it quickly bonds the pads on the silicon wafer to the  board — a process you’ll find satisfying in the clip below.

The final step is to place the familiar black blob of epoxy over the assembly and bake the board at the temperature the recipe in the datasheet demands. It’s a common manufacturing process that saves more money than coloring a multimeter anything other than yellow.