JUST HOW BIG ARE WE

May 21, 2016


My wife and I went to a party this afternoon—an outdoor party given by a company devoted to fitness.  They wanted to show their appreciation for allowing their clients to beat them up several times each week.  (We even pay for them doing this. Go figure.)  Great party and it made me realize what a marvelous country we live in.  There is room on top of room if you happen to be in the right “neck of the woods”.  We traveled only thirty-five (35) minutes to Jasper Highlands, Tennessee to enjoy the day and say hello to our friends.  The location was on the top of Jasper Mountain.  Take a look.

Looking West

This is looking West from the top of the Highlands.

Looking South

Looking South from the Highlands.

It got me to thinking: Just how big are we in this country?

Together, the forty-eight (48) contiguous states and Washington, D.C. occupy a combined area of 3,119,884.69 square miles (8,080,464.3 km2), which is 1.58% of the total surface area of Earth. Of this area, 2,959,064.44 square miles (7,663,941.7 km2) is land, composing 83.65% of U.S. land area, similar to the area of Australia.  Officially, 160,820.25 square miles (416,522.5 km2) is water area, composing 62.66% of the nation’s total water area.

The contiguous United States would be placed 5th in the list of countries and dependencies by area; the total area of the country, including Alaska and Hawaii, ranks fourth. Brazil is the only country that is larger in total area than the contiguous United States, but smaller than the entire United States, while RussiaCanada and China are the only three countries larger than both. The 2010 census population of this area was 306,675,006, comprising 99.33% of the nation’s population, and a density of 103.639 inhabitants/sq mi (40.015/km2), compared to 87.264/sq mi (33.692/km2) for the nation as a whole.

If we just look at Alaska, we see the following:

According to an October 1998 report by the United States Bureau of Land Management, approximately sixty-five percent (65%) of Alaska is owned and managed by the U.S. federal government as public lands, including a multitude of national forests, national parks, and national wildlife refuges. Of these, the Bureau of Land Management manages 87 million acres (35 million hectares), or 23.8% of the state. The Arctic National Wildlife Refuge is managed by the United States Fish and Wildlife Service. It is the world’s largest wildlife refuge, comprising 16 million acres (6.5 million hectares).

Of the remaining land area, the state of Alaska owns 101 million acres (41 million hectares), its entitlement under the Alaska Statehood Act. A portion of that acreage is occasionally ceded to organized boroughs, under the statutory provisions pertaining to newly formed boroughs. Smaller portions are set aside for rural subdivisions and other homesteading-related opportunities. These are not very popular due to the often remote and roadless locations. The University of Alaska, as a land grant university, also owns substantial acreage which it manages independently.

Another forty-four (44) million acres (18 million hectares) are owned by 12 regional, and scores of local, Native corporations created under the Alaska Native Claims Settlement Act (ANCSA) of 1971. Regional Native corporation Doyon, Limited often promotes itself as the largest private landowner in Alaska in advertisements and other communications. Provisions of ANCSA allowing the corporations’ land holdings to be sold on the open market starting in 1991 were repealed before they could take effect. Effectively, the corporations hold title (including subsurface title in many cases, a privilege denied to individual Alaskans) but cannot sell the land. Individual Native allotments can be and are sold on the open market, however.

Various private interests own the remaining land, totaling about one percent of the state. Alaska is, by a large margin, the state with the smallest percentage of private land ownership when Native corporation holdings are excluded.

To get an idea as to just how big Alaska is, take a look at the map below.

How Big is Alaska

OK, now let’s look at our biggest state within the contiguous United States—Texas.

Texas

Texas is the second largest U.S. state, behind Alaska, with an area of 268,820 square miles (696,200 km2). Though ten percent (10%) larger than France and almost twice as large as Germany or Japan, it ranks only 27th worldwide among country subdivisions by size. If it were still an independent country, Texas would be the 40th largest behind Chile and Zambia.

Now if you really want to talk about the wide open spaces, take a look at the area around Telluride, Colorado.  You would think enough room for the entire nation.

Colorado

Colorado (2)

We are a vast country with something to satisfy every taste. You can travel to Manhattan where the population density puts you right on top of everyone else or Alaska where you nearest neighbor may be twenty miles away.

Advertisements

ENCODERS

May 21, 2016


Once a month a group of guys and I get together for lunch.  Great friends needing to solve the world’s problems.  (Here lately, it’s taken much longer than the one and one-half hours we spend during our meeting.)  One of our friends, call him Joe, just underwent surgery for prostate cancer.  This is called a Prostatectomy and is done every day.  His description of the “event” was fascinating.  To begin with, the surgeon was about twenty (20) feet from the operating table. Yes, that’s correct; the entire surgery was accomplished via robotic systems. OK, why is this procedure more desirable than the “standard” procedure”?   The robotic-assisted approach is less invasive, reduces bleeding and offers large 3-D views of the operating fields. The mechanical arms for the robotic system are controlled by the surgeon and provide greater precision than the human hand.  This allows the surgeon more control when separating nerves and muscles from the prostate. This benefits patients by lowering the risk of side effects, such as erectile dysfunction and incontinence, while also completely removing cancer tissue.  The equipment looks very similar, if not identical to the one given in the JPEG below.  Let’s take a look.

Prostate Surgery and Robotic Systems

As you can see, the electromechanical devices are remarkably sophisticated and represent significant advantages in medical technology.  The equipment you are seeing above is called the “patient side cart”. It looks as follows:

Surgical Side Cart

During a robotic prostatectomy, the patient side cart is positioned next to the operating table.  The system you see above is a da Vinci robotic arm arranged to provide entry points into the human body and prostate.  EndoWrist instruments, and the da Vinci Insite Vision System, are mounted onto the robot’s electromechanical arms representing the surgeon’s left and right hands. They provide the functionality to perform complex tissue manipulation through the entry points, or ports.  EndoWrist instruments include forceps, scissors, electrocautery, scalpels and other surgical tools. If the surgeon needs to change an Endowrist instrument, common during robotic prostatectomy, the instrument is withdrawn from the surgical system using controls at the console. Typically, an operating room nurse standing near the patient physically removes the EndoWrist instruments and replaces them with new instruments.

There are certainly other types of surgery performed today using robotic systems.  Several of these are as follows:

One electromechanical device that helps to make this remarkable procedure possible is called an encoder.  Let’s define an encoder.

An encoder is a sensor of mechanical motion that generates digital signals in response to motion. As an electro-mechanical device, an encoder is able to provide motion control system users with information concerning position, velocity and direction. There are two different types of encoders: linear and rotary. A linear encoder responds to motion along a path, while a rotary encoder responds to rotational motion. An encoder is generally categorized by the means of its output. An incremental encoder generates a train of pulses which can be used to determine position and speed. An absolute encoder generates unique bit configurations to track positions directly.

As you might expect, knowing the exact position of a medical device used during surgery is absolutely critical to the outcome.  The surgeon MUST know the angular position of the device at all times to ensure no errors are made.  Nerves, tendons and muscles must be left intact.  This information is provided by encoders and encoder data systems.

ENCODER TYPES:

Linear and rotary encoders are broken down into two main types: the absolute encoder and the incremental encoder. The construction of these two types of encoders is quite similar; however they differ in physical properties and the interpretation of movement.

Incremental rotary encoders utilize a transparent disk which contains opaque sections that are equally spaced to determine movement. A light emitting diode is used to pass through the glass disk and is detected by a photo detector. This causes the encoder to generate a train of equally spaced pulses as it rotates. The output of incremental rotary encoders is measured in pulses per revolution which is used to keep track of position or determine speed.  This type of encoder is required with the medical system given above.

Absolute encoders utilize stationary mask in between the photodetector and the encoder disk as shown below. The output signal generated from an absolute encoder is in digital bits which correspond to a unique position. The bit configuration is produced by the light which is received by the photodetector when the disk rotates. The light configuration received is translated into gray code. As a result, each position has its own unique bit configuration.

Typical construction for a rotary encoder is given as follows:

Rotary Encoders

Please note the following features:

  • Electrical connection to the right of the encoder body.
  • Encoder shaft that couples to the medical device.
  • Electrical specifications indicating the device is driven by a five (5) volt +/- 5% source.

Encoder Specifics

You can see from the above illustrated parts breakdown that a rotary encoder is quite technical in design.

SYSTEM ACCURACY:

System accuracy is critical, especially during surgery. Let’s look.

An encoder’s performance is typically stated as resolution, rather than accuracy of measurement. The encoder may be able to resolve movement into precise bits very accurately, but the accuracy of each bit is limited by the quality of the machine motion being monitored. For example, if there are deflections of machine elements under load, or if there is a drive screw with 0.1 inch of play, using a 1000 count-per-turn encoder with an output reading to 0.001 inch will not improve the 0.1 inch tolerance on the measurement. The encoder only reports position; it cannot improve on the basic accuracy of the shaft motion from which the position is sensed.  As you can see, the best encoders, hopefully those used in a surgical device, can deliver accuracy to 0.10 inch.  Remarkable accuracy for a robotic device and absolutely necessary.

CONCLUSIONS: 

TECHNOLOGY DELIVERS.  Ours lives are much better served with advancing technology and certainly technology applied to the medical profession. This is the reason engineers and technologists endure the rigor necessary to achieve talents that ultimately will be directed to solving problems and advancing technology you have seen from the post above.

As always, I welcome your comments.  bobjengr@comcast.net

%d bloggers like this: