Bilgisayar Destekli Tasarım Ders Notları

Transcription

ME 521
Computer Aided Design
3. CAD Input Devices
Yrd.Doç.Dr. Ahmet Zafer Şenalp
e‐mail: [email protected]
Makine Mühendisliği Bölümü
Gebze Yüksek Teknoloji Enstitüsü
Hardware of a CAD System
Computer System
Mainframe Computer and Graphics Terminals
Powerful
Inconvenient
High cost
Turn‐key CAD System
Dedicated computer systems for CAD applications, consisting of a super‐
mini computer and several design work stations.
Following the "central control concept"
Inconvenient and not powerful enough for complex 3D modeling.

Workstations & High‐End Personal Computers
Supporting multiple tasks
Supporting network and file‐sharing – convenient
Low costs
Present and trend
Dr. Ahmet Zafer Şenalp
ME 521
GYTE-Makine Mühendisliği Bölümü
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Hardware of a CAD System
Input/Output Devices
Graphical Output
Graphical Input
Computer
(CAD Workstation,
Computer Terminal,
Micro computer)
Alpha Numeric Output
Alpha Numeric Input
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Input Devices
¾Keyboard
¾Tablet/digitizer
¾Mouse
¾Trackball
¾Light pen
¾Touchpad
¾Touchscreen
¾Kontrol dials or knobs
¾Function switches
¾Joystick
¾Voice input
¾3D Data Acquisition Systems
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Conventional keyboards are text only devices. Keyboards are the essential and basic input devices for all computer applications. They are typically employed to create & edit programs or to perform word processing functions.
A typical keyboard is shown in the above figure. It is divided into four different areas
The first area " (A) " is for normal typewriting when entering text strings.
The second one " (B) " is the function key area for simplified handling of common operations. The third area " (C) " is composed by seperate cursor and control keys. This area presents several different configurations depending on the supplier of the keyboard, including arrows, thumbwheels etc The fourth area " (D) " is the numeric keyboard for fast numerical digit input.
Working principals of keyboards are simple. A keyboard has typically two registers whose contents can be read by the computer, one to set a status bit when a key has been struck the other to identify the key by its character code.The value of the status bit is monitored in a continuous repetitive manner. When the user hits a key, the status bit is set and application program is consequently interrupted to clear the status bit, followed by reading the corresponding code of the key character. The loop is repeated every time the user strikes a key.
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Tablet is a computer input device that allows one to hand‐draw images and graphics, similar to the way one draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures. It can also be used to trace an image from a piece of paper which is taped or otherwise secured to the surface. Capturing data in this way, either by tracing or entering the corners of linear poly‐lines or shapes is called digitizing.
A graphics tablet (also called pen pad or digitizer) consists of a flat surface upon which the user may "draw" or trace an image using an attached stylus, a pen‐like drawing apparatus. The image generally does not appear on the tablet itself but, rather, is displayed on the computer monitor. Some tablets however, come as a functioning secondary computer screen that you can interact with directly using the stylus.
Some tablets are intended as a general replacement for a mouse as the primary pointing and navigation device for desktop computers.
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Tablet types:
Some of them use magnetic field to determine x,y coordinates.
Some of them use strain wave.
Acoustic tablets use acoustic methods.
Microphones are placed in x,y,z axis. Pointer will point to the end of a certain frequency ranges. Microphones recieve this sound and x,y,z coordinates are determined according to recieving and formation time of sound. 2 and 3 D applications are avalibale.
Acoustic 3D tablet
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In computing, a mouse is a pointing device that functions
by detecting two‐dimensional motion relative to its
supporting surface. Physically, a mouse consists of an object held under one of the user's hands, with one or
more buttons. It sometimes features other elements, such
as "wheels", which allow the user to perform various
system‐dependent operations, or extra buttons or features
that can add more control or dimensional input. The
mouse's motion typically translates into the motion of a cursor on a display, which allows for fine control of a graphical user interface.
First mousse of the world (1952)
The first computer mouse,
Douglas Engelbart, (1963)
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Operating an opto-mechanical mouse:
1. moving the mouse turns the ball.
2. X and Y rollers grip the ball and transfer movement
3. Optical encoding disks include light holes.
4. Infrared LEDs shine through the disks.
5. Sensors gather light pulses to convert to X and Y
vectors.
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Cable Mouse
In early times of computers mouse work by connecting to serial port. Recently this connection is adopted to PS/2 port. Today, most cable mouse connects to the USB port of a computer mouse. In addition, by means of various adapters, USB ports can be converted to PS / 2 or vice versa.
Cordless Mouse
¾ Infrared mouse: This mouse uses an infrared communication with the computer. System is connected to computer’s serial, PS/2 or USB port, and mouse connects to the system by means of infrared rays. If an object is present between the mouse and the system mouse movements won’t be detected. Today this type of mouse is no longer available in the market.
¾ Radio wave mouse: Different from infrared mouse this mouse use radio wave signals for communication. Coverage areas is generally measured in tens of meters. ¾ Bluetooth mouse: This mouse use Bluetooth cordless technology for communication. Has advantages compared to above two types: Can be used wiyh every device as uses a standard protocol (PC, Apple and even Pocket PC)
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Types according to motion detection methods:
¾ Mechanical mice
Mechanical mice detects motion by means of a ball which can rotate by the mouse movement. This ball is coated by rubber and inside core is metal. As dust can cover the movement ball by passing time maintenance should be performed. Dr. Ahmet Zafer Şenalp
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¾ LEDed Optical Mice
These types of mice enable motion by reflection of the LED emitted. Top version models has 1000‐2000 dpi resolution.
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¾ Laser Optical Mice
These types of mice enable motion by light emitted by laser light source. Bu tür Appropriate choice for those desire high resolution. Resolution can be 3000 dpi and more. If mice are categorized according to motion detection, most expensive is the laser optical mouse.
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9 A trackball is a device which is very similar to a mouse. It consists of an “upside‐down” mouse, in which the ball on the bottom of the mouse has been turned up to the top. As the ball is rolled by the hand of user it moves and the cursor on the screen. It controls the position of the cursor on the screen with the direction of rotation controlling the direction of cursor movement and the distance the cursor travels controlled by the number of revolutions of the ball. Also some functional buttons can be added to the trackball similar to mouse.
The world's first trackball
invented by Tom Cranston,(1952)
9 In CAD applications large balled models are preferred for better precision. Before the invention of touchpad the usage of trackball was common in laptop computers.
9 With the end of 1990’s with the invention of scroll wheel that is used in mice the usage of trackball is decreased. 9 Still used in cartography and similar applications.
Logitech trackman
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¾A Lightpen is an input device which allows interaction with a display from a computer screen.
The lightpens can be used to input data as well as to draw as shown in the figure. The idea behind the lightpen
is the familiarity of an ordinary writing. It is a direct and natural form of input.
¾A light pen can work with any CRT‐based display, but not with LCD screens.
¾A light pen is fairly simple to implement. A light pen works by sensing the sudden small change in brightness of a point on the screen when the electron gun refreshes that spot. By noting exactly where the scanning has reached at that moment, the X,Y position of the pen can be resolved. Dr. Ahmet Zafer Şenalp
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Even invented in 1952 became popular in 1980’s.
First
Light pen
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A touchpad (also trackpad) is a pointing device consisting of specialized surface that can translate the motion and position of a user's fingers to a relative position on screen. They are a common feature of laptop computers and also used as a substitute for a computer mouse where desk space is scarce. Touchpads vary in size but are rarely made larger than 40 square centimeters
Touch pads consist of single plastic mylar
membrane silkscreened with a silver
conductive grid and two resistive strips and works in a similar way with touch screens except the fact that it works on a flat pad. When a key is pressed, two electrical resistances are reflected between a common line and the x and y output lines.
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¾ The touch screen, namely touch‐sensitive‐screen, works by direct user‐interaction with the CRT. A screen overlay is capable of sensing the physical contact of the operator's fingers or any other stylus on the screen.
¾ The screen overlay consists of transparent plates that fit over the screen and can convert the touch of the user, by optical, electrical or acoustical methods, into
digital information consisting of several screen coordinates.
¾ The touch sensitive screen is utilised mainly to choose one out of a set of options presented in the panel. Just like on ATM machines, in industrial process control applications.
¾ It can also be used for drawing some shapes on the screen but since its accuracy is not great compared to other input devices not used for this purpose much. Disadvantages:
± Extended use causes tired arms, ± Smudges on screen, ± Insufficient accuracy for CAD applications based on pixel by pixel drawing. Dr. Ahmet Zafer Şenalp
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Windows 7 supports touchscreen usage
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The dials, which are used as valuators, are graphical devices adequate to input scalar values to application programs. They are rotary potentiometers grouped in special assemblies most commonly used to control rotation or linear movements of objects displayed on a screen. When the user moves the dial, the voltage being output is changed. The translation from voltage to digital information is made by analog‐to‐digital converters. The dials can be programmed to input values into the graphics program. Beside this some dials have a user‐programmable label. The label can indicate the function of the dial. As the functions of the dials change in the program the labels can be changed interactively so the functions of the dials are always clear.
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Buttons and function switches are either toggle or push‐button switches. They may be either continuously closed, continuously open, or momentary‐contact switches. The most common convenient type of function switch incorporates both capabilities. Software controlled lights indicating which switches or buttons are active are usually provided. Buttons and switches are frequently incorporated into other devices. Switches make the on/off settings for input or mode of operations.
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Clasical Joystick: Literally only 1 or 2 button + direction, functions as a control tool
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Second Generation Joystick
Second generation joysticks have more than two buttons and have perfect ergonomic structure, the routing function is analog and detects all kinds of precise orientation and most important is that it is a control device with input output function.
analog controlled nintendo; first 64 then game cube applied
Input output functions: In old times control devices only reflect the choice of the player to the game but by improving technology joysticks are changed and joysticks that response to sense are developed. These respond according to the movement they sense and generally vibration property is presented by game devices such as PlayStation (dual shock) Example: A crash in a car race is responded by the vibration of the joystick.
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The best example to the last generation joysticks: Nintendo wii control device
¾ Cordless control ¾ Input output function
¾ Sensing function: Sensing function enables the player’s the movements to be sensed and converted to the game. Example: In a tennis play the movement of player’s hand is simulated as a movement of tennis racket
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Nintendo wii
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A voice entry system (VDE) consists of a microphone attached to a speech recognition device, which in turn transmits voice command information to a computer. As it can be understood from its name VDE working principal is data entry through voice commands. When user sounds a command, the command is interpreted according to a preprogrammed definition of its meaning.
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3D Data Acquisition Systems
2D Image: (for each pixel: X and Y coordinates and light intensity). The intensity could be gray (8 bits: 0 – 255) or color RGB (24 bits).
3D Range Image/Data from Range Sensing Devices and 3D Camera –
data points defined by their x, y, z coordinates (cloud point data).
• Mechanical probe (measurement and scanning)
• Laser scanning
¾ Triangulation‐based range sensing devices
¾ Time‐of‐flight based range sensing devices
Machine vision based CAD model generation for:
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reverse engineering
machine vision and intelligent robot
vehicle size measurement and traffic monitoring
scanning of 3D object, human body, and art work
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Automotive Design and
CAD Model Generation
Scanning of Clay Model to
Obtain Surface Data
Design Details Using CAD System
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Full Size Foam Model Machined Using a 5‐Axis CNC Mill
from 3D CAD Model
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Scanners with
Mechanical Probe
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CAD Modeling Based on a 3‐D Vision System
• 3D Range Sensors (3D Cameras): 3D Cloud Data Points
– Triangulation‐based: visible laser light,
short range, accurate
– Time‐of‐flight‐based: laser light & micro wave, long range, less accurate
• Processing of 3D Range Data
– 3D Cloud Data Points Cross‐section‐based CAD Model
– Generation of a Complete Description for Objects and Workspace –
Sensor Fusion
• Forming a Surface Model and Carrying out Reverse Engineering
– Cross‐section ‐based CAD Model RP; etc. Dr. Ahmet Zafer Şenalp
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Surface Model GYTE-Makine Mühendisliği Bölümü
CNC Machining; 33
Multiple View Fusion and Model Integration
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Global Model Generation with
Multiple View Fusion
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Automated Vehicle Dimension
Measurement System for Commercial and
Oversize Vehicles
Implemented at BC Ferries Terminal
• Real‐time Vehicle Dimension Measurement
• Complex Vehicle Shapes
• Dimensions Measured at Speeds up to 120 km/hr
• Adverse Weather Conditions
• Height and Width Accuracy: 15 cm
• Length Accuracy: 30 cm
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Automated Real‐time Dimension Measurement of
Moving Vehicles Using Infrared Laser
Rangefinders
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Automated Real‐time Dimension Measurement
of Moving Vehicles Using Infrared Laser
Rangefinders
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Reverse Engineering and Automated CNC Tool
Path Generation for Efficient and High Quality
Sculptured Part Machining
Geometric Modeling Based on 3D Scanning
• Challenges:
– Accuracy/Lighting/Range (Selecting Right 3D Sensing Tech)
– Occlusion (Obstruction)/Multiple View Fusion
– Multiple Level Modeling: Cloud Data Points/Crosssections/
Surfaces/Solid
• Applications:
– Reverse Engineering (e.g. Face Mask)
– Size Measurement (e.g. Moving Vehicle)
– Object Recognition (e.g. Moving Vehicle)
– 3D Log CAD Model Generation
– 3D Sculpture Documentation
– Shoe Making
– Character Modeling in Movies/Computer Games
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