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Rethinking Chair Comfort

Core 77 - Wed, 2019-09-11 21:04

Years ago, I stumbled into an old storefront in rural Virginia with some friends and encountered one of the thousands of rocking chairs that have been inspired by Sam Maloof. It was a dramatic example of the form with a huge sweeping back and long rockers. But most amazing was the seat itself.

It was a massive chunk of walnut that had been deeply scooped out – perhaps a 2"-deep saddle. And the pommel of the seat was tall – almost 2" high.

One of my friends said, "Do you know how come that's a lady's chair?" The rest of us shrugged.

"Because that seat 'lifts and separates.'"

Underwear jokes aside, the guy was right. Sitting in the chair felt like I was being prepped for a medical exam that few people enjoy. The seat looked gorgeous, but you don't sit on a seat with your eyeballs. So, you have to think hard about the human rump (and other body parts) when designing a chair.

Chair design is a topic that can fill an entire book. We don't have the space for that here, so I'm going to write about how I design the all-wood chairs that I build. Some of my guidelines are at odds with modern rules for chairs, but that's because my chairs aren't entirely modern. I take many cues from ancient chairs.

The seat of a Sam Maloof chair. The saddling is deep, but Maloof left some room for the legs to move. People who copy his work tend to make the saddling deep and without much room to move. Ouch.

Start with the Saddle

One of the most important principles in chair comfort is that "sitting" and "sitting still" are not the same thing. And we rarely sit still.

"One of the major difficulties in the design of seating is that sitting is…viewed as a static activity while, in actuality, it is a rather dynamic one."

— "Human Dimension & Interior Space," by Julius Panero and Martin Zelnik.

This is the problem with deeply saddled seats. We sit in them and they feel amazing at first – they support and cradle the bottom in a pleasant way. The only problem is that we can't often sit still. Here's why. In a typical chair, the sitter's weight is confined to about four square inches of buttocks. The pressure on that small area requires us to shift our weight, even just a little, to remain comfortable.

But a deeply saddled seat doesn't allow us to move much, if at all. So, these sorts of seats become agonizing in short order.

I have yet to see an ancient chair that is sculpted as dramatically as our modern Jell-O moulds with legs. I'm sure they are out there, but they've never been the dominant form. Instead, many old chairs had shallow saddling (maybe 1/4" to 1/2") or even no saddle whatsoever. A shallow saddle gives you some curve but also allows you to reposition yourself with ease. (Oh, and they are easier to make.)

I also suspect that many all-wood chairs would be draped with an animal skin or a small cushion. I've put sheepskins on all my chairs and can attest that even the minor cushioning they provide makes a world of difference in the department of butt comfort. (You'll see this cushion concept again when I sneak it into a discussion of seat height.)

For some reason, some modern chairmakers are masochists and seek to make a chair as comfortable as a La-Z-Boy recliner via the magic of curvy valleys. This strict attitude reminds me of people who insist that a single scrap of sandpaper in a shop is an abomination. Lighten up, Francis, and go fetch a cushion.

Seat Height

How far is the front of the chair from the floor? The typical modern chair height is 18" – that's almost inviolate. Sorry to say, I think that is too high to be a general rule.

Tall seats are punishing for shorter sitters. If their feet cannot rest flat on the floor, the front edge of the seat will constrict blood flow in the thighs and produce agony.

Slightly shorter seats, however, are just fine for tall sitters. Their feet can still sit on the floor and their thighs hover above the seat – allowing blood flow. The only downside to a tall person sitting in a shorter chair is the short chair is a little more difficult to dismount.

(Side note: This is true for a table's height as well. Standard table height is 30". A high table is a pain for a shorter people. But a slightly shorter table [29" or even 28"] is no problem for a tall sitter.)

So, if 18" is too high as an overall rule, what should the height be? The answer is not cut and dried with a custom chair. Here are the questions I ask to calculate the seat height:

1. What is the sitter's "popliteal height?" Some people call this "stool height." It's the distance from the bottom of the foot to the bottom of the thigh of a seated person. It ranges from 14" to 19-3/8" in the general population.

2. What sort of footwear will the sitter use? Work boots, 3"-high heels and moccasins all can change the equation.

3. What is the chair to be used for? If it's for dining or keyboarding, it should be a little higher so it is easy to mount and dismount. If it is for relaxing, it should be lower. How low? Seats can be as low as 12"-13" for lounging. Low seats allow you to stretch your legs – a luxury. Low chairs are harder to get out of – but that's the point.

4. Will there be a cushion or other seat cover? Cushions can add 2" or more to the seat height, so you should subtract that when making the chair's frame.

You might be wondering how to determine the seat height for the general populace instead of for a particular person. When I need to do that, I typically use 16-3/4" or 17" for a dining/working chair. And 15" to 16" for a lounging chair. These are on the low side, but they aren't radically low. Tall people will hardly notice. Short people definitely will, and they'll be grateful.

The seat of this Welsh chair is less than 13" deep. Yet it sits just as well as a chair with a 16"-deep seat. That was a revelation for me.

Seat Depth

A typical seat depth for one of my chairs is 16". Once you get deeper than 17", you risk cutting off the sitter's blood flow behind the knees. Surprisingly, shallow seats work well. I have made seats as shallow as 12" and they sit just fine (unless you have an epic backside or the seat is too high. Having both is a disastrous combination). A shallow and low seat also prevents the blood in your thighs from being constricted.

In general, I don't mess with the seat depth too much. If it's between 14" and 16" I know it will work in most cases. This slight flexibility allows me to build using narrower boards. If I have to glue up my seat from two 7"-wide boards, I'll do that and call the 14"-deep seat done. I won't glue on an additional 2"-wide strip of wood to get to the magic 16" depth.

We're not done with the seat quite yet. But to understand the last bit of seat data, we need to first understand the chair's armrest (sometimes called the "armbow").

Armrest Height

Biometric data suggests the top of the armrest should be about 7" to 10" from the seat, depending on the sitter. I usually shoot for 8" to 9" (or less). People have asked for 10" – this height makes some people shrug their shoulders, and you can feel it in the neck after a while. My rule of thumb is 8" for shorter people and 9" for taller ones.

Backrest & Seat Tilt

The small of the back – sometimes called the "lumbar" region – is where I do a lot of work to make a chair comfortable. If you build a chair that supports the lumbar spine, you will make friends – as well as chairs. The lumbar is about 7" to 9" above the seat. This is why I keep my armbows at 8" as much as I can and add a "doubler" above it (and sometimes below it) to increase the thickness of the armbow so I can support the lumbar.

Chairs that lack lumbar support are fatiguing to me. I squirm to push my lower back against the chair's back, but my shoulders and buttocks prevent it. I guess this is why we have low pillows. Nothing wrong with a pillow.

One of the oft-overlooked aspects of chair design – the seat's tilt – can help the lumbar region get to its destination, which is the armbow in my chairs or a lower slat in ladderback chairs.

Most chairs tilt a little toward the back. A seat that is flat to the floor can feel like you are being thrust forward and out of the seat. Adding some additional tilt can encourage the sitter to slide backward and put their lumbar directly on the armbow.

But how much tilt? I like Welsh chairmaker John Brown's method of using his fingers and a spirit level. Put a level on the seat's pommel so it runs from the front to the back of the chair. Raise the spirit level at the rear of the seat until it indicates it is level. If you can get one finger (plus a little more) under the level at the back, that's a chair that's for dining or other proper things – keyboarding etc. Two fingers and you have a chair that is good for lounging. Three fingers – alcohol consumption. Use that information to cut the legs down to get the tilt you want.

Here is the Irish Gibson chair I finished up in May. The back is angled at 25°. Surprisingly, it sits like a fairly normal side chair.

Back Angle

For me this is where the rules get blurry and surprisingly flexible. Most modern chairs have the chair's back tilted back about 5° to 7° or so. That's fine. But adding a couple degrees can also encourage the body to touch the chair's armbow and doubler.

So, I tend to tilt the back about 9° backward, but I will tilt it a little more at times. And I will continue to play with different angles as I think there are some discoveries to be made. Earlier this year I built a copy of an Irish chair that had its back tilted at 25°. That's about three times as much as normal. As I built the chair I imagined that sitting it would be like visiting the dentist. I was wrong.

It wasn't as different as expected. This chair – called a Gibson, hedge or famine chair – was historically used as a kitchen table chair. Even though it looked more like a chair for sunbathing. Your eyes and expectations can deceive you. So don't believe them, this book or your vicar. Work it out yourself.

The high headrest on this chair is comfortable but looks disproportionate to the chair's other elements.

Lowering the back by a few inches greatly improves the look of the chair without sacrificing comfort.

Headrest Height

How high should the crest (aka headrest or comb) be? That depends. For customers who want to be able to pass out in their chairs I want to have a high comb to cradle the head during unconsciousness (after reading a good novel, of course). So, I measure to the base of their skull. I think these chairs look too tall, but some customers like the anthropomorphic appearance of these chairs.

What I prefer in a chair is to have a crest that supports the shoulder blades without the crest digging into them. This is about 22" above the seat.

But this location can be tricky depending on how beefy the sitter is. Broad-shouldered sitters can feel the ends of a significantly curved crest rail push into their shoulders. Thinner sitters of the same height cannot.

The easy way out is to simply raise the crest rail a couple inches, however this dramatically affects the way the chair looks. I prefer a compact chair. Another way out is to make the crest rail so it doesn't have as pronounced a curve. My crest rail typically has a 10" radius. That's tight, but it keeps me from over-bending my chairs' spindles. The crest can be curved less, such as a 14" or 16" radius (which is OK). Or it can be flat (which fixes one problem but causes another by reducing support for the curve of the shoulder blades).

Here's the good news on the crest rail: You can do it at the end of the construction process and experiment with different crest rails – different curves and stick spacing. Dry-fit a prototype crest rail and see how it feels to your back. Make some changes and see how they feel.

When all else fails with your chair's design, add a sheepskin. Or pillow.

Nuclear Sheep

When I talk about chair comfort with other chairmakers, it's inevitable that someone will say: Ah heck, just put a cushion on it and call it done.

Me, I like sheepskins – a traditional Welsh chair covering. They don't add much bulk to the seat, and they won't make the seat too high. But they do add some cushioning and warmth. (And they give me an excuse to go to IKEA without a disguise.)

So do your best to make your chairs comfortable. But know that it's never a bad idea to become a man (or a woman) of the cloth.

Christopher Schwarz is the editor at Lost Art Press and one of the founders of Crucible Tool. He works from a restored 1896 German barroom in Covington, Ky. You can see his furniture at christophermschwarz.com.

Siemens PLM Becomes Siemens Digital Industries Software

Design News - Wed, 2019-09-11 05:00

At the Siemens Media and Analyst Conference last week, Siemens PLM executives announced Xcelerator – a collection of software, services, and application development tools that can be personalized and adapted for industry-specific needs. The goal is to help companies become digital enterprises. Xcelerator combines Siemens’ software for design, engineering, and manufacturing with an expanded Mendix low-code application development platform.

Siemens Xcelator is a protfolio of softare plartforms that bring together a number of Siemens brands. Many are now merged with the Mendix low-code application generator.

As part of this broadening of industrial software, Siemens PLM Software has changed its name to Siemens Digital Industries Software. The move came from the realization that PLM is just not sufficient to describe the wide range of software tools Siemens now offers.

As well as blending the recently acquired Mendix tools into Siemens PLM software, the Mendix platform has also been expanded. It now includes cloud and application services for digital engineering powered by MindSphere, the company’s cloud-based, open IoT operating system. Since Mendix uses low-code configuration instead of requiring original programming, the platform is designed to help companies go digital by using citizen developers and engineers rather than programmers.

The Ease of Low-Code Development

The standout feature of Mendix – which Siemens acquired last year – is the platform’s low-code development system. Applications can be developed Lego-like rather than requiring substantial original programming. “Everybody is moving in the direction of low code. It’s going into middleware at the minimum. Low code is the next logical step in software. Just like Java was a layer. Now it’s low code to speed productivity and re-use,” Derek Roos, CEO of Mendix, told Design News. “The other benefit low code is that it is abstractive from the technical details. This opens the opportunity for people who are less technical to participate.”

With the advantage of low code application development, companies can automate a wider range of manufacturing tasks. “This is part of the trend of automating what can be automated. Manufacturers can we use the meta data in our platform – which is model driven – and add machine learning,” said Roos. “How much more can we automate? More than we once thought. It’s a mega trend. Everything we’re automating is becoming easier and faster.”

The Further Integration of Siemens Software

As part of the expansion of Siemens Digital Industries Software, the company is blending the software from a number of Siemens brands. Capital software from Mentor has been embedded into NX software so experts across engineering disciplines can create new products collaboratively. Siemens Opcenter solution has been integrated with Valor software, which expands the digital thread from design to manufacturing. The overall goal is continuous quality improvement.

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Siemens also recently integrated multiple automotive validation tools to create the PAVE360, a pre-silicon autonomous validation environment. This open-integration was created to provide rapid innovation and validation of products and operations by creating a more precise digital twin that melds model-based simulations with test data and real performance analytics.

Rob Spiegel has covered automation and control for 19 years, 17 of them for Design News. Other topics he has covered include supply chain technology, alternative energy, and cyber security. For 10 years, he was owner and publisher of the food magazine Chile Pepper.

How to Build a Low-Frequency Theremin With the Evive

Design News - Wed, 2019-09-11 04:00

The maker movement has spawned a variety of electronics prototyping platforms like the Arduino, the Raspberry Pi (RPi), micro:bit, and the Circuit Playground Express (CPX). What all of these platforms have in common is their cost effectiveness, high-performance, and that they provide a low barrier to entry to those looking to get into DIY electronics.

But there is another development device that has entered the educational technology and maker product market called the evive. In this Gadget Freak article, the evive we'll be exploring the evive by building a low-frequency theremin.

What is the evive?

The evive is an all-one electronics and robotics prototyping and technology learning platform. (Image source: Agilo Research Pvt, Ltd.)

The evive was created by Agilo Research Pvt, Ltd, an educational technology hardware startup located in Ahmedabad, Gujarat India. The co-founders Dhrupal Shah, Abhishek Sharma, and Pankaj Kumar Verma, are three enthusiastic entrepreneurs and engineers who dreamt of enabling young minds to innovate and create by providing them with world-class technology and learning resources. The evive originated from this vision and provides a wealth of technology resources within a single prototyping platform.

The evive is a palm-sized prototyping platform (115 x 140 x 32mm) used for learning electronics and robotics through constructionism-based projects. The evive weighs 340 grams, including the rechargeable 5VDC lithium-ion battery.

The evive features are inclusive to a traditional electronics and robotics lab and include: an integrated oscilloscope; a function generator and voltmeter for electrical measurement data visualization; an Integrated H-bridge motor driver; two potentiometers; toggle/momentary pushbutton switches; a thin-film transistor (TFT) display; an adjustable 0-+5VDC power supply; and digital-analog converter (DAC).

On top of the evive’s printed circuit board (PCB) is a mini breadboard, dual in line female header connectors for external electronic circuit prototyping and placement of external shields, and external connectors for XBee and Bluetooth communication modules. The core development board that allows these integrated features to work synchronously is an Arduino Mega 2560 (which is based on the ATmega2560 from Microchip Technology). Technology concepts and projects that can be investigated with evive include: the Internet of Things (IoT) the Industrial Internet of Things (IIoT/Industry 4.0); robotics; predictive maintenance; automation; and electronic controls. With the integrated solderless breadboard, General Purpose Input-Output (GPIO), and analog-digital converter (ADC) female header connectors, a variety of external embedded platforms can be included for building proof-of-concept prototypes.

A Low-Frequency evive Theremin

Now that we've gotten our introductions out of the way, let's explore building a low-frequency theremin using the evive.

The theremin is an electronic musical instrument that generates sounds from hand gestures based on their proximity to the instrument's two antennas. The theremin’s electronic oscillators direct the frequency or audible sound based on the thereminist’s hands' distance within the two antennas. A typical theremin’s variable frequency oscillator is in the range of 257 – 260 KHz. The output frequency range of the evive theremin is below 20Hz. Therefore, the audible sound varies between single clock pulses to a solid-state buzzer. The low frequency theremin’s device construction is based on a simple hybrid design consisting of the evive, a light sensor, and speaker amplifier.

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Device Design (Block Diagram)

The low-frequency theremin is a hybrid design using off-the-shelf electronic components. The design consists of a photocell (light sensor) receiving ambient light levels at pin A12 of the evive -ATmega2560-based microcontroller. The embedded software residing inside of the Arduino microcontroller’s RAM memory will read the varying light level analog values. These analog values will provide varying flashing rates for the LED wired to pin D13 of the microcontroller. The LED flashing audible output sounds will be heard through the littleBits o26 speaker electronic module.

Here's the complete hybrid design of the theremin:

 The low frequency theremin consists of off the shelf electronic components.

Parts List and Device Assembly

The table shown next lists the components for the hand gesture-based control oscillator. Although the table lists specific electronic components for the project, the experienced maker or engineer can use appropriate alternative parts to build the device.

Quantity

Component

Description- Circuit Reference Designator

Supplier

1

evive

Electronic prototyping device

STEMpedia

1

littleBits o26 speaker

Electronic speaker amplifier module

littleBits Electronics

1

littleBits proto

Electrical terminal block

littleBits Electronics

1

Photocell

Light dependent resistor (PC1)

Jameco Electronics

1

4.7 Kilo-ohm (KΩ) resistor:(yellow, violet, red, gold stripes)

A fixed-pulldown resistor (R1)

Jameco Electronics

1

220 ohm (Ω) resistor: (red, red, brown, gold stripes)

A fixed-series current limiting resistor (R2)

Jameco Electronics

1

Light emitting diode (LED) red or alternative color

Audible output visual indicator (LED1)

Jameco Electronics

NA

Electrical jumper wires

NA

Jameco Electronics

The littleBits proto-module: (Image source: littleBits)

The approach behind this design is a physical mashup of different educational technology prototyping and learning platforms. Rapid prototyping using this this mashup method allows makers and engineers to use low- and high-tech development boards and tools to capture specific hardware features.

The design concept challenge of this project is the integration of the evive and the littleBits products to rapidly develop a proof-of-concept audible and visual electronics device. The evive theremin PoC produces low-frequency audible tones based on the physical proximity detection of a hand. The key component to assist in the electrical circuit integration of these different educational technology tools is the use of the littleBits proto module.

Pinout of a typical littleBits bitSnap. 

The littleBits proto-module consist of two three terminal blocks and jumpers mounted on a mini PCB. The mini PCB has two plastic bitSnaps that have metal pins for providing electrical connections to adjacent littleBits electronic modules. The electrical connections include: vcc (+5V power supply), sig (electrical signal), and gnd (electrical ground). To reduce error in building a littleBits gadget or device, small magnets are placed inside and flushed with the bitSnaps front surface.

With the proto-module, electrical integration of the evive to the littleBits speaker can easily be accomplished.

Building the Theremin

1.) Wire the light sensor circuit on the evive prototyping device. The light sensor circuit is wired to the evive using the mini solderless breadboard mounted onto its PCB.

The electrical wiring of the light sensor circuit to the evive.

 

Here is a closer view of the solderless breadboard showing the details of the light sensor circuit electrical wiring of the individual electronic components.

Closeup view of the light sensor circuit electrical wiring on a solderless breadboard.

 

2.) Next, the light sensor circuit is wired to the littleBits o26 speaker using the proto board.

The electronic circuit schematic diagram of the light sensor circuit to the littleBit’s 026 theremin.

 

With the electrical wiring completed, the low frequency theremin should appear as shown:

 

The completely built low frequency theremin.

3.) All that remains in the completing the project is the inclusion of software.

The software is basically an Arduino sketch coded in C++ language for light level detection and flashing the external LED. In addition, the evive’s (TFT) screen displays the varying analog values. With the theremin code uploaded to the evive’s ATmega 2560 microcontroller, the LEDs (external and evive wired) will begin to flash. Adjusting the volume control on the littleBits’ o26 speaker will allow the audible tones to be heard.

You can click here to download the source code as text file.

As an option, a visual stroboscopic effect can be created by adding the littleBits’ LED bargraph. The littleBits bargraph module is electrically and magnetically attached to the 026speaker module.

The littleBits o9 bargraph can be added to provide a stroboscopic -visual effect for the low frequency theremin device.

Additional technical information on the evive can be found on the STEMpedia website.

[All images courtesy Don Wilcher, unless otherwise noted]

Don Wilcher is a passionate teacher of electronics technology and an electrical engineer with 26 years of industrial experience. He’s worked on industrial robotics systems, automotive electronic modules/systems, and embedded wireless controls for small consumer appliances. He’s also a book author, writing DIY project books on electronics and robotics technologies