Archive for the ‘Non-HCI’ Category

Shoes for the Shoemaker

Saturday, December 5th, 2009

Design ideas for a more ergonomic computer workstation.

As a senior human factors engineer working in human-computer interface, you would anticipate my computer workstation at home would be the epitome of ergonomics and usability. “Man,” you probably think, “he must have a killer setup.” And I do. It looks like this (click for larger):

Sawed-off door on a file cabinet.

What’s that they say about the shoes of the shoemaker’s children?

Let’s start with the obvious:

  • The desk top is too high. I had to raise my chair so high that my feet dangle. Even then, it only puts my arms at the right height for writing with pen and paper -they’re still not right for using a mouse or keyboard.
  • Computing space interferes with writing space. The massive 21″ CRT monitor necessarily projects out over the space I need for paperwork. Even after sliding the keyboard under the monitor and the mouse off to the side, it’s cramped.
  • Removable media in the CPU is hard to see and reach. Inserting a CD or thumb drive under the card table is awkward.
  • Network components consume valuable desktop space. On the left file cabinet you see a network bridge. It used to be on top of the CPU, but it tended to overheat there. Also, I needed to have it handy for rebooting.
  • Printer is hard to see and reach. With it high up on the top shelf (on the left), loading new toner cartridges is tricky. Also, I have to stand on my toes to read the status lights, and I’m at about the 70th percentile height for males.

Less obvious from the photo:

  • I placed the desk on a wall opposite of a large window (which is causing the flare on the right of the pic), resulting in reflections on the monitor, making it hard to read sometimes. It was the only way to fit everything in the room.
  • That CPU is noisy. Even though it’s more than an arms length away, it’s still a distracting racket.

Computer History

Like many cases of problematic human factors, the cause wasn’t so much poor design as a lack of design. The workstation was cobbled together from whatever furniture I had on hand. Each piece actually worked well for its original intended purpose. However, like assembling an enterprise solution from COTS products from various vendors, its not surprising that the human interfaces don’t fit well together, in this case literally.

That’s okay. This workstation was only temporary until I got a proper setup. However, knowledge of human factors is double-edged. On the one hand, I know a bad setup when I have one. On the other hand, I had a certain performance level I was willing to accept. After I perused various stores and catalogs, it became clear quickly that no available desk would reach that target. By “quickly,” I mean after several years. I was going to have to design and build my own desk, which I was soon ready to do. By “soon,” I mean after several more years.

It would’ve taken even longer, except I started teleworking, which gave the project new urgency, and not just because I was spending more time at my home computer. My employer encourages teleworking, but each employee was required to complete a form (this being the government) certifying that his or her home workstation complies with federal ergonomic standards. Federal ergonomic standards? Sure, my rig complies with federal ergonomic standards the way Bill Clinton complied with his marriage vows. For example, take the requirement that the user must have his or her feet flat on the floor or a footrest. Yeah, I got a footrest. I use the legs of the chair. You can tell where the paint was wearing off.

Bare aluminum showing on painted chair leg.

Design A

Mobile Desktop

As with web pages and windows in software, real estate was a prime constraint. The room was only so large and needed to fit the computer system, the main workstation, a secondary workstation (for my wife, who was using the card table in the setup above), plus a bookshelf, guest bed, and other items. Everything would fit easily if the main workstation used the same space for both computer work and paperwork.

Of course, the desktop needed to be lower, but how low? The optimal height for paperwork is a few inches higher than that for the keyboard and mouse, being about 29 and 25 inches respectively for my own physical dimensions. One obvious solution is to set the desktop height for paperwork and use a keyboard drawer under the desktop for computer work. Such drawers are readily available, but the problem is that they move the user back from the desk. Too often I’ve seen setups with the LCD monitors against the back wall, exploiting their thinness to provide more desktop space, but that places the LCD rather far away. Then there’s a keyboard drawer that effectively makes the monitor even farther away from the user’s eyes. Adding to the squintihood, LCDs tend to have pretty fine pixel pitch -on the order of 100 per inch, so the default font is quite small. Not so good.

If I use a drawer, the monitor should be placed closer for optimal viewing distance, but that interferes with desktop space needed for papers. I could put the monitor on an articulated arm or sliding tracks so I could move the monitor back and forth when necessary, which was something I had done before when I had 9 inches of diagonal, and was happy to have it. However, now I was dealing with a 21-inch 70 lb. behemoth that wasn’t particularly motivated to move anywhere. Even if I wanted to replace the CRT with an LCD, the one I was eyeing would still represent substantial bulk to be sliding around.

A more reasonable approach was to put the paperwork on tracks. The keyboard and mouse would fit in a stationery well under the desktop. A panel of the desktop, papers and all, would slide back into a slot under the monitor to expose the computer controls for use. Here’s a plan view sketch that I made while working on the design (click for labeled pic):

Keyboard and mouse under moving panel.

The Tech Tower

To further make the most of the available space, I sought to minimize the footprint of the computer and network components by stacking them vertically in a tower built into the desk, as shown in this early design sketch (click for labels):

Narrow sloped-face console with small shelf.

Components that I would rarely access, like the motherboard (yeah, right) would be located deep in the tower, while components for removable media would be mounted on the tower’s narrow external face for easy access. Switches mounted on external face would let me power cycle the network components when needed. Burying the motherboard, power supply, hard drives, and their multiple fans deep in the tower would also provide sound insulation, but would require careful attention to heat management. The design called for the “technology tower” to become the CPU’s case. By mounting the CPU chassis “face down,” I could duct air up from the bottom and vent it out the top. With the chassis in that orientation, the removable media components would have to be relocated from the chassis to the tower itself. Taking inspiration from a project I saw on the web (for recent versions, see DeskTopped), the computer components would be literally built into the desk.

Reclined Computer Operation

We all know the proper posture for computer use: sit bolt upright, feet flat on the floor, 90-degree bends at the knees and waist. We all also know that no one sits that way. Walk down a row of cubicles, and you see many users slouching, leaning back in the chairs, legs stretch out in front (alternatively, users hunch forward, perhaps resting their heads on their respective chins -maybe those are the ones with their LCDs back against the wall). I’d often find myself in the reclined slouch. That can’t be good, with the chair providing poor support of the lower back. It also ruins the careful positioning of the keyboard and monitor provided by the computer desk -they end up being too high. But surely it must be more comfortable than the “proper” posture or else users wouldn’t end up that way. I remembered an ergonomics journal article (unfortunately, I can’t find the cite now) that noted these habits and asked why we’re trying to fight against natural human inclinations? Why don’t we design our computer workstations for a reclined posture?

Why indeed? Being a specialist in transportation human factors, I would never design a vehicle interface with a bolt-upright sitting posture. Typically, the operator stations for airliners, locomotives, and motor vehicles (other than motorcycles) all recline their operators by 10 degrees or so. It’s not only more comfortable but it takes a load of stress off the lower back as long as the station is designed to be used that way. In all these vehicle stations, visual attention is primarily directed straight ahead or slightly down, like with a desktop computer workstation. Computer workstations should also be designed for a partially reclined user. (Not so for workstations for paperwork, where visual attention is more sharply down.)

Conflicting Requirements

Put the sliding paperwork panel together with a reclined seating position and there was a problem. Chair height was fixed to that best for paperwork (i.e., feet flat on the floor when sitting upright). So I’d need a foot rest to properly support the legs when leaning back to use the computer, but that wasn’t the problem. Fix seat height meant a fixed eye height when reclined. Eye height determined the monitor height. You want the top of the monitor to be level with the user’s eyes because looking up continuously is straining, while looking down is okay. Put these together with my physical dimensions, and the base of the monitor would have to be below the top of the panel for paperwork, as shown in this contemporary sketch.

CRT on sliped surface dips down to knees.Here’s a clearer image from the final stage of design of the desk with an LCD monitor rather than a CRT:

Monitor surface below desk surface.

That meant I couldn’t slide the paperwork panel under the monitor. I considered other alternatives, such as sliding the panel sideways, but couldn’t figure out a way to make it work.

The whole idea was coming apart for my application. A reclined position also meant my head was further back than usual, which meant the monitor would have to be moved closer, right up to the back edge of the keyboard, seriously encroaching on the paperwork area. The paperwork area could extend further back (I’d roll my chair forward into a cutout to use the keyboard), but that made the entire desk too deep for the room.

Then there was the question of my mechanical building skill, or lack thereof. The sliding desktop mechanism would be quite a challenge to construct, as would the tech tower for the computer. Building the computer into the desk also made repairs difficult. I was learning from experience that (a) computers are increasingly unreliable, and (b) computers were beyond my technical abilities to fix. What would I do if I had to ship the computer out for service? Send the whole desk?

You probably could make the sliding desktop idea work for some applications. Using a not-too-large wall-mounting LCD or two, rather than my clomstrous CRT, you should be able to keep the bottom of the monitor above the top of the desktop. Maybe you could motorize the paperwork panel so that it would not only be ergonomic, but wicked cool. Yeah, and hide the monitors behind a motorized case for office supplies. Click one switch, and zzzzht! Like something out of Thunderbirds!

I personally wasn’t ready to discard my trusty old CRT. I had paid a lot for it back in 1998, and it still worked fine. With a maximum resolution of 1200 by 1600 pixels, it was about as good as a 24-inch LCD and color fidelity was generally superior. I planned to keep it until it broke (which it did, of course, while I as in the midst of finally building the desk designed to accommodate it).

Besides, I had discovered a way to have separate spaces for computer work and paperwork fit into the room, eliminating the need for a variable geometry desk.

Design B

Corner Office

By placing the main and secondary workstations on adjacent walls, I could create a third position in the corner. Normally the corner is difficult to exploit in L-shaped desks, but I saw a setup make good use of it by having a stretch of desktop set at 45 degrees. Here’s an illustration of how the positions would fit in the room.

User modeled on each wall and diagonally in the corner.

(This is literally user-centered design: I put the users in the model, position the computer components accordingly, then designed the desk around them)

The corner position tends to be deep, but that’s an asset for computer work. Sitting semi-reclined with my feet stretch out in front, I’d need the depth. Certainly the CRT needed the depth.

Tech Tower II

Meanwhile the tech tower morphed away from being the computer case to embracing the computer case, making it easier to construct and easier to service the CPU.

Tech tower loaded with computer components.

The CPU sits high in the tech tower, protruding above the desktop to provide room for the UPS and network components below. Access panels in the tower support basic maintenance such as plugging in a peripheral or card, although crawling under the desk to get to the panels feels like climbing into a Jefferies Tube. A hinged lid on the top of the tower allows easy removal of the CPU for major servicing. The only portion of the CPU exposed is the components for removable media, putting them in easy reach and use. Everything else is sheathed in wood to help deaden the sound of the cooling fans.

Final Design

The completed design looks like this (click for labels):

Secondary station, tech tower, computer work position, then paperwork position.

The main workstation is in the center (computer work position) and to the right (paperwork position). The secondary workstation is on the left, separated from the main workstation by the tech tower. Flat-panel legs at the extreme are easy to make and maximize space under the desk.

The desk in operation looks like this (click for larger):

Photo of completed desk.

The material is primarily 3/4 inch oak plywood with a frame of 1×4s and 2×4s. The room’s window is 45-degrees to the side of the monitor, minimizing glare (especially with the new flat screen). The (new) printer is now at a reasonable height (partially in view on the white file cabinet on the far right) for easier use and maintenance.

Paper-Computer Transition

With the paperwork position separated from the computer work position by only 45 degrees, one can move between them easily. To fully capitalize on this, the user should be able to pivot between the positions without banging any shins on a desk leg or other supports. This meant the monitor surface had to extend well under the desktop before coming to a leg. The monitor surface was not only long, but thin -no more the three inches thick so the top would be low enough for the reclined seating position and bottom would be high enough to clear my knees when I reclined. This represented a structural challenge because it had to be strong and stiff enough to hold 70 lbs. of monitor. I had seen that monitor warp three feet of plywood and outright break pine board, so I had some appreciation of the load it imposed. I considered various approaches to creating a metal frame (e.g., steel pipe or Unistrut), until my father, the civil engineer, convinced me a fabricated box girder of plywood would be sufficiently strong and easier to make. Here’s how it looks from the back, with the tech tower hidden for clarity.

End on view of box girder for monitor and keyboard.

The top face of the girder is the surface for the monitor while the bottom is the keyboard/mouse tray. Sidewalls are 1×2 red oak. As events transpired, this all proved overkill since the CRT didn’t live to see the day that it would rest on the new desk. But then, the new LCD monitor I got to replace it was no featherweight at 40 lb, so it wasn’t all a waste.


With the CPU protruding above the top of the desk, the front face of the tech tower below the desk is used as much as possible to hold objects that otherwise would take up valuable desktop surfaces.

Front of tech tower with shelves and phone.

A shallow shelf provides handy storage of CDs and DVDs I’m currently using. (Yes, I’m currently using CDs; going mp3 is something I’ll do some day. By “some day” I mean “some year.”)

The larger curved lower shelf is for laying cameras, GPSs, and whatnot for uploading/downloading with the computer. Interface cables are permanently routed from the back of the CPU to the shelf. The landline phone finds a vertical surface to hang from.

The USB backup drive lives with the network components on a shelf behind sliding Plexiglas doors in the tech tower. The drive has a dedicated USB cable, but I only plug in the drive when backing up, which I can do from sitting at the computer. There’s no point in having backups if they’re going to be blown away by the same lightning strike or malware attack that takes out the hard drive, so I leave an air gap most of the time.

Thermal Management

Airflow into and out of the tech tower remained another challenge. I wanted to filter the intake air because I had experienced processor overheating from dust clogging the heat sink. Besides, I hate dust bunnies in my CPU. To minimize the restriction of airflow, the filter needs a large surface area. To achieve this, I replaced the left side of the CPU case with a removable panel of the tech tower.

Left side of tech tower showing louvered panel.

The panel sandwiches a disposable filter intended for an air conditioning system making the entire side of the CPU into the air intake.

Left panel set aside, showing filter and weatherstripping.

A cardboard bell (not visible) feeds cool air directly to the processor fan.

Hot air is exhausted out the front and back of the CPU by the usual fans, where it is collected in a plenum in the back of the tech tower that also gathers hot air from the network components and UPS.

Ducting of air out front and back of CPU to back of tech tower. Front ducts under CPU.

An extra processor fan draws air out of the plenum, its wiring extended to reach into the CPU to the motherboard so it turns on whenever the computer is on.

Plenum from top. Fan bolted to right wall.

The cowl for the fan is made from keypunch computer cards, showing that they’ve yet to exhaust their usefulness.

The cooling scheme seems to work. So far, I yet to see CPU temps reach 40 C (104 F). With 73 F ambient conditions, the air exiting the tech tower is 87 F, while the air on the network component shelf is 78 F.

But there’s more: heat isn’t just a computer problem -it’s a human factors problem too. With the computer blowing out 80+ F air, the small office can get quite toasty, which is great when teleworking in the winter and the rest of the house is set for 60 during the day, but it can get uncomfortable in the summer. So there’s a 4-inch pipe running behind the monitor that routes the exhaust air towards the window, as shown in this plan view.

Pipe from back of tech tower, around back of monitor, and along right wall.

In summer I fit in a window insert to direct the air outside.

Plywood insert with 4-inch elbow to route exhaust out doors.

Shortly I’ll add some storage trays to the insert to hold odds or ends. By “shortly,” I mean, well, you can guess.

Recycling Bin

With the demise of the CRT, I suddenly had plenty of space behind the monitor. Some of this is used for a long-arm desk lamp, freeing more space for papers. It also allowed a more direct routing of the exhaust air to the window. Even while I was designing the desk around the CRT, I was anticipating its LCD replacement, figuring the desk would out last the CRT (which it did by a negative value). I made some vague plans for using the space behind a LCD for some sort of storage, something I’ll complete in the very near future. Assume geological scales of time.

Then there’s the recycling bin, placed on the desk in the back corner to provide more floor and file space.

In back corner of desk, a wooden box with slot for throwing papers.

(Formerly, recycling went in the “1000 PAC” cardboard box shown in the pic of the old setup above. Not much leg room at the secondary workstation, is there?)

The recycling bin actually was always designed to fit to the back right of the monitor even when the CRT remained, although its self-destruction allowed me to place the bin in easier reach. The bin holds a standard paper shopping bag at a 60 degree angle, as shown in this cross-section from the right side.

Cross-section of bin: angled shelf holds bag.

This way, papers thrown into the slot tend to land in a neat stack, maximizing the capacity of the paper bag. The top is hinged for replacing the bag. I think that qualifies it as a green desk. Maybe I can take a tax deduction on the construction materials.


Input Devices

You wouldn’t expect a usability professional to replace his CRT with anything less than a state-of-the-art big-ass LCD monitor, but you might be surprised by the ordinary keyboard and mouse. Where’s the fancy curved ergonomic keyboard and megabutton mouse?

Take a closer look at the keyboard, and you’ll see something unusual: the keypad is on the left hand side. Originally I planned to accomplish this with a compact keyboard that has no keypad, and combine it with a separate keypad on the left side, but it turns out DSI already makes them that way. The left side keypad has a number of advantages:

  • I can keep my left hand over the keypad and the right hand on the mouse, so I can enter numeric data quickly and combine mouse movements with cursor key movements (e.g., select a field with the mouse and clear it with the Delete key).
  • It makes it easier to center the QWERTY home keys in the middle of the keyboard tray so I don’t put my right wrist in an awkward right-hand angle when touch-typing. I suspect that’ll prevent repetitive motion injury as much as a curved keyboard.
  • It moves the mouse closer to the QWERTY home keys, making for perceptively faster shifts of my right hand between the keyboard and mouse (consistent with Fitts’s Law).
  • It places the Backspace and Enter key within reasonable reach of my right thumb when I’m holding the mouse, allowing one-handed entry in certain cases (e.g., select a checkbox in a dialogue box with the mouse, and select OK by smacking the Enter key).

I’m right handed, so you might expect it would be awkward to use the keypad with my left hand. However, back in high school, I had trained myself to use a calculator with my left hand so I could conduct calculations with the left while writing the results with the right (a personal time-and-motion intervention that proves I was always destine to be a human factors engineer). It helped that my left-hand dexterity was enhanced by years of viola lessons. Your mileage may vary.

As for the mouse, my right hand is plenty busy with left clicking, right clicking, center clicking, and scroll wheeling (and occasional key-smacking). On the other hand, my feet are sitting on the footrest doing nothing other than enjoy the vibrations from the subwoofer (makes music listening a tactile as well as acoustic experience). So I have a Kinesis 3-pedal foot switch, programmed for Back (Alt-Left), Change Windows (Alt-Tab), and Close Window (Alt-F4; yes, that’s dangerous, but it’s great for pop-up ads). The pedal provides a consistent means of interaction whether I’m using the keyboard or mouse, reducing my cognitive workload. I’m thinking of getting a second pedal for the left foot for cut, copy, and paste.

Papers etc.

Two holdovers from my old desk earned their place on the new desk for handling non-digital media. In front of the recycling bin is a wood and Plexiglas “work rack” for displaying papers that need my attention. They would all stack neatly in simple basket serving as physical inbox, but if I don’t see the paper, I forget about it. Spreading all the papers over my desk would use the space I need to work. The work rack provides a more compact way to display the papers. The only issue is that, not unlike a digital inbox, I need to clear it out now and then of items I’m just not getting to despite their visibility (e.g., ideas for what to do with the space behind the monitor).

A desktop shelf, as seen at the secondary workstation, is something I had in grad school that I found very convenient for putting materials in easy reach while sitting at the desk, so it is carried through here, although it better serves my wife than me. This particular shelving unit is salvaged from one that was damaged in shipping. It’ll do for now, but I’ll be building a unit that better matches the desk. Shouldn’t rush it -it’s not something one should do without the proper tools. Right now, I only own hex-type tuits (English and metric). I’ll build the shelf when I get a round tuit.

Building drawers is beyond my skill level, but fortunately I had inherited from my father-in-law an oak veneer file cabinet. After carefully cutting down the base a couple inches, it just slid under the right side of the desk.


The key aesthetic quality I was after was that the desk not grossly offend me. However, living in middle class suburbastan, it also had to not be embarrassing for my wife and me if guests see it (the room includes a spare bed). The layered overhanging theme has a contemporary Frank-Lloyd-Wright-ish look that may appeal to some, but more importantly it effectively hides off-course cuts and misalignments one has to expect from someone with my woodworking skills. The natural wood finished is consistent with other house furnishings and warms the otherwise cool contemporary form. Rounded corners are trendy (thank you Apple), but I think they’ll retain their organic appeal after it falls out of fashion.

Summary Checklist

Problem: Building an ergonomic computer desk for limited space.

Potential Solutions:

  • Consider a sliding panel desktop with a stationery keyboard/mouse well to allow computer work close to the monitor while providing ample paper-work space.
  • Use corner space for the computer work position adjacent to a conventionally dimensioned paperwork position, keeping the space between them clear of any supports for easy transition.
  • Design the computer position for use while partially reclined, providing a foot rest if necessary.
  • Stack technological components in an easy to access well-ventilated tower. Ideally, provide an air filter and means to vent the heat outdoors.
  • Find little ways to save space by using vertical surfaces and the space behind the monitor.