a mechatronic marvel: the digital camera

Digital Camera K. Craig & M. Nagurka 1

Dr. Kevin Craig & Dr. Mark NagurkaProfessors of Mechanical Engineering

Marquette University

A Mechatronic Marvel:

The Digital Camera


Design News Web Cast

• Web Cast Introduction– Mechatronics and the Digital Camera

• The Digital World & Digital Images• Photography: Analog vs. Digital

– Key Features and Functions– Difference between Film and Digital: Image Sensors

• Digital Camera and Mechatronics: How is Mechatronics Enabling the Digital Camera?

• Autofocus• Image Stabilization


PlantDesign

Plant Dynamics&

Control Structure


A Mechatronic Marvel


Auto Focus

Image Stabilization

Zoom Lens Auto

Exposure

Mechatronics


The Digital World & Digital Images• Before Digital There Was Analog

– Analog refers to phenomena that are characterized by fluctuating, evolving, or continually changing physical quantities, such as force or voltage.


Discrete in

Time

Continuousin

Time Discrete

in Amplitude

D-D

D-C Continuous

in Amplitude

C-D

C-C


– Early electronic technology was built using an important analog device called the vacuum tube. Such tubes, used in nearly every piece of electronics, were used to control the electrical current and voltage in systems such as radios, radar, and very early computers. These vacuum tubes got very hot and burned out regularly.

A vacuum tube,a modern

transistor, andan integrated

circuit

vacuum tube

transistor

integrated circuit


• Birth of the Digital Age– During the middle of the 20th century, mathematicians

and engineers discovered a process for converting physical quantities found in the world (e.g., sound waves, light intensity, forces, voltages, current) to numbers or digits.

– This remarkable, yet simple discovery, was the mathematical foundation that gave birth to the digital age.

– The word digital refers to technology or phenomena that are characterized by numbers. The era was born with the creation of the transistor.

– The digital age is generally thought to have reached full maturity at the time that computers gained widespread use, during the mid-1980s.


– Some advantages to digitizing analog quantities:• Real-time adaptability• Less susceptible to noise or parameter variation

in instrumentation• Large amounts of data can be stored using

compact, high-density data storage methods• Fast data transmission is possible over long

distances without introducing dynamic delays• Digital processing uses low operational voltages• Very high accuracy and speed are possible

through digital processing• Easier to change system through programming

rather than by changing hardware


– In 1945, engineers produced the first digital computer using the readily-available vacuum tubes as the basic digital building blocks. It was called the ENIAC.

ENIACBuilt out of more

than 17,000 vacuum tubes,

weighing 30 tons, and filling a 30-by-

50-foot room.Imagine the heat

produced!


– In 1947, engineers at Bell Labs developed a small, fast, inexpensive digital replacement for the vacuum tube that consumed much less power – the transistor.

– A transistor is a switch – either open or closed – that regulates the voltage or current flow through electrical circuits. It is the basic building block for all digital electronic technology.

– The transistor might be the most important invention of the 20th century.

– The next critical step forward into the digital age was the ability to put many transistors onto a single small part that could be used for increasingly complex tasks.

– Jack Kilby invented the integrated circuit, or IC, in 1958. Nearly all the individual components on an IC are transistors.


The first IC produced by Jack Kilby

A modern IC


– Moore’s Law says that the number of transistors on an IC will double every two years. Equivalently stated, the computing power of ICs doubles every two years. This law is used as one of the strongest principles for predicting the future of technology.


• Digital Images– Seeing is believing! A picture is worth a thousand

words! About half of our brain activity is dedicated to gathering, processing, and storing visual information.

– Digital Imaging is the technique of representing images as a sequence of numbers. Of course, we also need a way to convert the numbers back into the original picture.

– The first step in converting a picture into a series of numbers is to create a grid with a uniform cell size and superimpose it on the picture. Each cell is now one element of a picture. A pixel (contraction of the words picture and element) corresponds to the smallest detail in a picture that one wants to preserve.


The number of pixels in the image determines its pixel count. For example, a 640 x 480 image would have 307,200 pixels, or approximately 307 kilopixels; a 3872 x 2592 image would have

10,036,224 pixels, or approximately a 10 megapixels.


Photography: Analog vs. Digital

A camera is basically a black box with: • a lens (or lenses) to focus the image, • an aperture that determines how bright the light is,• a shutter that determines how long the light enters ,

and• light sensitive film or an image sensor.

To adjust exposure, two different settings can be changed: aperture and shutter speed.


LensShutter Curtain

Focal Plane

Optical Axis

Light from subject (A) reaches focal plane through the lens.

The lens focuses the image.


Camera Focus


lens

Single Lens Reflex (SLR) Camera


Large Aperture

Small Aperture

Diaphragm


Depth of Field

Shallow depth of field


Shutter Speed


CameraTripod


ISO/ASA 100

ISO/ASA 200

ISO/ASA 400

Film Sensitivity


Film vs. Digital Photography• The major difference between traditional film and

digital cameras is how they capture the image.– Instead of film, digital cameras use a solid-state

device (a silicon chip) called an image sensor. On the surface of the image sensor are millions of photosensitive diodes, each capturing a single pixel.

– Two types of image sensors are used:• CCD or Charge-Coupled Device• CMOS or Complementary metal–oxide–

semiconductor


Light Path in a Digital Camera

The heart of all digital cameras is the digital imaging sensor. It is the component that converts the light coming from the subject

being photographed into an electronic signal.

image sensor


• Although the principles of basic photography (aperture, shutter speed, ISO) are the same in a digital camera as in a film camera, the inner workings of a digital camera are quite different.

• Replacing emulsion-based light-sensitive chemical film, the imaging is performed by an image sensor. (CCD or CMOS sensors).

• Each sensor element converts light into a voltage proportional to the brightness which is passed into an analog-to-digital converter (ADC) which translates the sensor image signals into discrete or digital data.


Image Sensor

Sigma DP1 14MP Digital Camera


• The digital output of the ADC is sent to a digital signal processor (DSP) which adjusts contrast and detail, and compresses the image before sending it to the storage medium.

• The brighter the light, the higher the voltage and the brighter the resulting computer pixel. The more elements, the higher the resolution, and the greater the detail that can be captured.


DigitalCamera

Operation


Nikon D3 12.1 Megapixel Full-Frame Optical Sensor


Batteries

Prism for viewfinder

Mirror

CMOS Sensor

Lenses

Electronics

Nikon D3 Cut in Half


Inside the Back of a Digital Camera


Image Sensors


Digital camera light sensors rely on the ability of certain semiconductor materials to convert light

into electrical charge.


RGB Inside the Camera


Digital Noise

ISO 1600; 100% Crop

ISO 200; 100% Crop


Mechatronics & The Digital Camera• Today, Autofocus has all but eliminated fuzzy pictures and is a

must for action shots. The implementations of autofocus are diverse and fall into active and passive categories.

• A sharp image is the photographer’s elusive goal, but even when focus and depth of field are just right, a photographer’s hands are still wiggling. Even on a tripod, a gust of wind or a truck rumbling by is enough to ruin a photo. Camera makers have come up with several ways to stifle vibrations in cameras.

• A Vibration Reduction System must counteract vertical vibration (pitch) and side-to-side vibration (yaw), and every direction in between, and it needs to make the correction within a few milliseconds!


Autofocus• There are approaches to autofocus in a digital camera:

active and passive.• In active autofocus, there are two types found on less

expensive cameras.– The first type is akin to the echo technology of radar

and sonar.– The other is based on the triangulation used in range

finders.• In passive autofocus, the light from the image is used to

focus the camera.• Both the active and passive types require a motor to make

work and that motor is an ultrasonic motor.


• Echo Active Autofocus– When the shutter button is depressed, an infrared light

is emitted towards the subject of the photograph.– The infrared light bounces off the subject and returns to

a detector. The time it took for the light to make the round trip is determined – usually in nanoseconds.

• A microprocessor controls a motor built into the lens housing. The motor rotates to a position that’s been calibrated to focus on an object at the distance determined by the infrared bounce.

• This type of autofocus works with objects not more than 30 feet from the camera.


• Triangulation Active Autofocus– Unlike timing autofocus, which uses the same

transducer to generate and receive bursts of light, triangulation active autofocus works with one device to shine light at the photo’s subject and a second device to receive the light after it bounces off the subject.

• The separate devices allow the autofocus mechanism to make use of the different angles formed by the light’s path to the subject and its path on the return trip.


• Passive Autofocus– Here light passes through the lens of the camera and is

diverted from the image sensor at the back of the camera by a mirror or prism.

– The light falls on a strip of 100-200 photocells, called linear sensors, similar to those that make up the imaging sensor.

• The strip is positioned so that the distance the light travels to it is equal to the distance to the imaging sensor.

• The camera’s processor compares the intensity of the light falling on each photocell to the intensities of the adjacent cells. Adjacent pixels have similar intensities for an out-of-focus image.


• The Motor that Moves The Lens: Ultrasonic Motor– Any autofocusing camera must

have a motor to move the lens elements to bring the subject into focus. Great speed and precision is required and there is so little space! The Ultrasonic Motor meets those requirements!

– The Ultrasonic Motor is built on a phenomenon called the piezoelectric effect. The effect is shown in the diagram for the substance zirconium titanate (PZT), a ceramic lead.


– The next step in creating a piezo motor is to bond PZT to both sides of a flexible member (steel spring metal) and send opposite charges to alternating sections of the beam. The charge on one section makes the beam bow out at the same time the opposite charges going to the sections on either side make them curve inward.


Image Stabilization• Normally, light rays from a scene being photographed pass

through the object lens element at the front of the lens and stay true to the len’s optical axis.

To Subject


• When the lens moves, the beams of light pass through elements of the lens at the wrong points. More importantly, the image sensor moves out of position and the light is smeared across the surface of the sensor, blurring the subject.


• Preventing vibration and movement is virtually impossible. Any system that seeks to reduce blurs caused by camera movement must do something to put the light beams back on the right path before they hit the sensor.

• Electronic Image Stabilization is the one exception to this rule as it corrects the blur with software after it has occurred.

• How Does A Camera Detect Movement?– When the system is active and something jostles the

camera, the movement is detected by two gyro-sensors, which are gyroscopes attached to devices that measure motion. One is used to detect yaw and the other, mounted 90º away from the first, detects pitch.


Simplified Physical Explanationof Gyroscopic Precision

Fdt dG

Mdt dH

=

=


• Vari-Angle Prism System– In a lens using a vari-angle prism (VAP) to correct

movements, gyro-sensors are used to detect the slightest wiggle. The sensors send electronic information to a microprocessor built into the lens.


– The microchip sends an electrical signal to voice coil motors, smaller versions of the motors used to vibrate the cones in speakers. The motors sit at 90º angles to each other on the rim of the vari-prism.


• Piezoelectric Supersonic Linear Actuator Stabilization– The VAP system just discussed attempts to bend the

errant light rays as they pass through the lens so they strike the correct pixels on the image sensor. This is like trying to deflect an arrow on the way to its target.

– An opposite tact is to hold the target and move it wherever the arrow is coming in.


Image SensorVertical (Y-axis) Slider

Horizontal (X-axis) Slider

Y-Axis Actuator

X-Axis Actuator

Microprocessor


Image Sensor stabilization


• Shift Image Stabilizer– This form of image stabilization (IS) is among the most

common. It relies on an IS lens element mounted among other elements that make up the complete lens. This element is like the other lenses that make up the complete lens, except it can change position.

– Gyro-sensors detect vertical and horizontal movement. The len’s microprocessor uses this information to send signals to the voice-coil motors mounted at 90º angles to one another along the edge of the IS lens element.


– The motors slide the element in the direction opposite from the direction the lens moved. If the lens dipped down, the motors push the IS element up. The correction takes 2 thousandths of a second to complete.

– Light now enters and exits the IS element at new angles that deflect the light so it regains its original path to the image sensor. Shift stabilization is most effective for lower frequency movements caused by platform vibration or wind.


Lens-based stabilization


Nikon Vibration Reduction System


Survey Questions• The Digital Camera is one of the ultimate

mechatronic systems ever developed.• Do you work on systems of similar complexity?• How is the integration required for a mechatronic

system such as this implemented in your company?

• How is the control system design done? In an integrated way or as after-thought add-on?

• What skills do you feel you are lacking that you would urge young engineers to focus on?


THANK YOU!

a mechatronic marvel: the digital camera

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