Download Hopkins_sideview_mirror_dimmer_hw4

Robert Hopkins, Marcel Castillo, Cliff Whitman, Michael Vanezis
Assignment#4
Section 1:
For our project we chose the side-view mirror dimmers proposal. Our team met and
decided to split the project into 8 subsystems for more research and to obtain a better overall
understanding of the subjects. Robert will handle the two subsystems “trigonometry in 3dimensions” and “feedback and control.” Marcel will be researching “light detection.” Cliff will
take care of “active/passive matrices” and “smart materials.” In our case, smart materials are
materials that can be changed with light, current, magnetic field, etc. Finally, Michael will be
researching “car computers/regulations and competing systems” and “servo functionality.”
Percentage of
effort toward
assignment
Robert Hopkins
27%
Marcel Castillo
19%
Cliff Whitman
27%
Michael Vanezis
27%
Section 2:
Trigonometry and Geometry in 3-Dimensions
To be able to dim the correct spots on the mirror the team needs to understand just
what the driver is seeing in all of his or her mirrors at any time. The topics involved in making
this calculation are field of view and solid geometry (which just means trigonometry in 3-D).
With a combination of optical tracking and field of view we are hopefully able to darken the
spots on the mirror where bright lights are causing a problem for the driver.
Field of view (FoV) is simply what you are seeing at any given moment in time. For
Humans can see almost 180 degrees in front of us, but more importantly about 120 degrees of
that is in “binocular vision” which allows for depth perception. The project would use 2 optical
trackers to create this depth perception and find the exact placement of a headlight in relation
to the user’s car.
Solid geometry is the study of 3-D shapes. In order to figure out where the lights are
coming from we need to understand and map the 3-D shape that is the driver’s side view mirror
field of view and comprehend its projection onto the 2-D mirror. Once the volume and
dimensions of that field is determined we can place the light sources in this shape and
calculate, with known mirror angles and other factors, whether or not they will be a problem
for the driver.
Feedback and Control
The design is going to have to take into account the fact that driving is a very dynamic
experience, stimuli is constantly around the driver and they are continually adjusting and
making changes. Any good system in a car needs to be able to adapt and accommodate just as
well as the human or they will ultimately be useless. Therefore our system needs to be able to
adjust and change to what is the current and actual field of view of the driver at any point. In
order to do that the system needs to be capable of tracking the head or eyes of the driver in
order to make an accurate prediction of what they are seeing.
The current leading everyday technology for human movement tracking is the “Xbox
Kinect” system made by Microsoft. This is an accessory to the Xbox 360 console that tracks the
full movements of multiple people in a room and uses that movement in real time to play
games and accomplish tasks. It can be modified and the code rewritten to benefit the design
our team already has. A company that had a private tour of Microsoft facilities for the sole
purpose of figuring out how the Kinect works describes its composition as follows, “It’s made of
two main parts: a projector and an IR VGA camera. The former bounces out a laser … across the
entire field of play, which the camera picks up to separate you from your sofa on what’s called
a ‘depth field.’ It’s essentially all the pixels that Kinect gets back as IR noise measured in varying
colour, dependent on how close they are to the system. That way bodies appear a bright shade
of red, green etc, and things further away appear grey.” If adjusted properly, it can be used to
precisely and continuously track the location of the driver’s head and allow the design to adapt
from one user to the next and also not require the user to sit completely still.
Light Detection
In order to cancel out the light from a cars headlight we must be able to detect where
that light is. The simplest way is to use photodiodes. A photodiode is a device that is able to
detect light and the intensity of that light which is proportional to the voltage it emits. The nice
thing about photodiodes is that they act also linear as a function of output power to incident
light. They also require very low voltage to run and a cheap, small, durable, and lightweight.
The Photodiode is a PN junction which is biased to create a depletion region. When light
photons combine with holes they are transported across the diode which is a measurable
current. The higher intensity of the light the more current is generated. Having a the light in a
measureable quantity is a very useful tool and a threshold can be set as to when to activate the
system and the ability to triangulate the source using multiple phodiodes.
Another form of light detection is the photoresistor. A photoresistor is a resistor that
changes with incident light. These are typically made from a semiconductor that reacts with
light and can be controlled by the dopants as to what wavelength of light it will be affected by.
The way it works is a photon excites an electron across the band gap from the valence band to
the conduction band. This means that the electron is able to be conducted out of the resistor
and into the circuit. The resistance of the resistor is therefore lowered and a higher current is
then seen. This type of device would be easy to implement and would need to be used in a
similar way to the Photodiode above.
Smart Materials
Smart materials are certain materials that can change properties due to external stimuli.
We can take advantage of these smart materials to be able to remove the blinding effects of
headlights in side rear view mirrors. A typical mirror is made up of glass with a metallic coating
that reflects light back giving an image. If we can take advantage of a smart material we can
then be selective in the surface that reflects light back. In other words we can use a smart
material to omit the undesired light. One smart material is a magnetostriction material as
described in the paper from UCLA. A magnetostrictive material is able to change shape by the
use of a magnetic field. We could use this material as our reflective surface and choose where
to change the shape of the material by changing the magnetic field behind it. The change is
done at an atomic level and can be thought of as tiny opposing and attracting magnets that
rotate with certain magnetic field. The fields produced behind the material can be easily
controlled by many coils.
Another possible solution to the material acting as the reflective surface is a chromatic
material. A chromatic material is one that changes color due to stimuli. There are a few
options in the form of heat, light and electric current or as they are known thermochromism,
photochromism and electrochromism respectively. Thermotropic materials are used not only in
novelty clothing and jewlry but are seeing an application in window coatings to help reduce the
heat that in brought into the house in summer months to lower energy bills. These coating
described in the “Thermotropic and Thermochromic Polymer Based Materials for Adaptive
Solar Control” paper show that the color of the material changes to block out the sun’s rays as
the air heats up to act as a blind on the outside of the window. This is similar to what we would
like to do but instead we would like to control the heat to where the light beam is perceived by
the driver in the rear view mirror to change the color of the mirror to something less reflective.
A Photochromatic material is one that changes with light which is a great match for the
project. A good example of this is the transitions glasses that change in the sunlight to
sunglasses and then when back indoors return to transparent. The glasses are slow to change
though and work with UV rays not the visible band. The material described in the “Rapid
Photochromic Switching in a Rigid Polymer Matrix Using Living Radical Polymerization” journal
is adjustable and quickly adaptive to light which could simplify the design of the project if the
glass and reflective material were just static and did all they work by the materials they are
made from. The last possible chromatic material, elctrochromitic, is one that changes due to
charge place on the object. This technology is used in privacy glass to change from see through
to frosted or opaque. This technology could be used either for the glass or reflective material
behind it. The current that changes the glass would be generated much like how an LCD TV
works by sending current to particular rows and columns to specify a point on a grid.
Active/Passive Matrix
Active or Passive matrices are two schemes that are implemented in addressing certain
pixels in an LCD display. The first technology developed is the Passive matrix that the pixel
must remain at the state on its own without being driven by circuitry. This type of design is
especially good for ebooks since the pixels are comfortable being at two different states or just
black and white to mimic printed text. This could also be good for our systems since we only
need the material to be reflective or non-reflective. We also aren’t concerned about pixels of
an LCD display but rather pixels of material. An active Matrix is one that actively maintains the
state of the pixel while other pixels are being addressed to avoid mix up this is done through
use of a transistor and capacitor attached to each pixel. A passive system is basically a grid that
gets a positive voltage from a column and a ground from a row to light up the certain pixels
where the two meet completing a circuit. . An active matrix is in most LED screens today and
has a better response time and voltage control. The result of this is a ghosting of an image is
the image is too fast and blurry images do to nearby pixels lighting up.
Servos to Control Internal Mirror Angles
The angle of a car’s side-view mirror is dependent completely on the user who is
operating the automobile. This means that every user is going to have a different setting and
also different preferences as to the location of said mirrors. With that being said, there needs
to
be a way to correctly determine the position of the mirror compared to the vehicle operator so
as to properly operate. Our system is going to use servos to determine and control the
positioning of the side-view mirrors so as to optimize the performance of the side-view mirror
selective dimmers.
The servo in our system is most likely going to utilize DC power since cars today are run
completely on DC power. The DC power would then be used to power and control a stepper
motor. The stepper motor is an electromechanical actuator which converts digital inputs to
analog motion. This device indexes in fixed angular increments when energized in a
programmed manner and its operation consists of discrete angular motions of uniform
magnitude. The step motor is very useful in this application because it works in a step function
method that will work well with determining the angle of the system.
The attached article “A Tutorial on Visual Servo Control” is more geared towards robots
but still carries a lot of similar components that will assist in the side-view mirror selective
dimming system. The specific section of the article to be utilized is Section 4 “Position-Based
Visual Servo Control” The type of position-based control to be used in this system is point-topoint positioning. This will utilize the predicted position of the vehicle operator and adjust the
servos accordingly.
There are several possibilities for determining the position of the vehicle operator. A
low-resolution camera can be used to pinpoint the location of the user’s eyes and adjust the
servos to the correct position. Another option is to calculate the average position of a user’s
eyes based on the seat settings. A proximity sensor can be set-up above the driver’s seat in
order to calculate their height in turn with the positioning of their seat.
These servos will be easy to add to the already existing electrical system of the car.
First, it will use DC power that is already in use by the car itself. Secondly, the car’s CANbus
network is easy to tap into and add connections to in order to help communicate with the rest
of the car’s system. This part will be discussed in the sub-system “Car Computers/Regulations/
Competing Systems.”
Car Computers/Regulations/Competing Systems
The side-view mirror selective dimming system will need to be integrated into the car’s
computer system. This can be easily done due to the Controller Area Network, or CAN, which is
the system of wires and software protocols acting as the connective tissue between a vehicle’s
computers and sensors. The system reduces the amount of wires needed throughout a car
since communication can occur through one system instead of every component having to be
hard wired into the overall system.
The CAN system was developed as a way to efficiently connect to all of the engine
sensors to help a car self-diagnose its issues. This all started in the late 1970s with the National
Highway Traffic Safety Administration and the California Air Resources Board which required a
way to measure and monitor vehicle emissions. This resulted in the On-Board Diagnostics
protocol.
Since there already exists an On-Board Diagnostics protocol it will be a very streamlined
process of implementing the side-view mirror selective dimming system. It will most likely
enumerate with the existing microprocessor that controls the side-view mirrors with maybe a
few added components since it is adding to the complexity of the system. The wiring for the
system will take advantage of multiplexing in the region of the side-view mirrors in order to cut
back on the complexity of wiring up the system.
Another option to be implemented into the system would be something along the lines
of Dr. R. Andrew Hicks who invented a side-view mirror that eliminates blind spots. This glass
design was developed around the middle of last year and can drastically increase the efficiency
of the system. By eliminating blind spots while decreasing the effects of bright lights this system
can drastically increase safety during night driving.
Articles for Reference:
http://www.baldor.com/pdf/manuals/1205-394.pdf
http://eprints.qut.edu.au/50025/1/50025.pdf
http://www.popularmechanics.com/cars/how-to/repair/how-it-works-the-computer-insideyourcar
http://auto.howstuffworks.com/under-the-hood/trends-innovations/car-computer.htm
http://www.sciencedaily.com/releases/2012/06/120607122206.htm
http://aml.seas.ucla.edu/research/areas/magnetostrictive/mag-composites/
Magnetostriction%20and%20Magnetostrictive%20Materials.htm
http://www.mdpi.com/1996-1944/3/12/5143 “Thermotropic and Thermochromic Polymer
Based Materials for Adaptive Solar Control”
http://pubs.acs.org/doi/abs/10.1021/ma052002f “Rapid Photochromic Switching in a Rigid
Polymer Matrix Using Living Radical Polymerization”
http://pubs.acs.org/doi/abs/10.1021/cm902069k “Black to Transmissive Switching in a Pseudo
Three-Electrode Electrochromic Device“
http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=1478049 “A 6 × 6-in 20-lpi
electroluminescent display panel”
http://books.google.com/books?id=N0ys_sSxD60C&pg=PA15#v=onepage&q&f=false “Precision
Nanometrology: Sensors and Measuring Systems for Nanomanufacturing” by Wei Gao
http://www.t3.com/features/exclusive-how-does-microsoft-xbox-kinect-work
http://webeye.ophth.uiowa.edu/eyeforum/tutorials/BINOCULAR-VISION.pdf