Group 4 - Computer DVD Drive
The main focus of this product dissection was to fully disassemble a CD-R/RW drive typical of optical drives used today for reading the data on the ubiquitous CD-R. This particular device is intended to fit in the 5.25" drive bay of modern desktop computer towers. The procedure was to incorporate a complete product dissection including careful disassembly, component study, and reassembly. The initial phase consisted of a complete tear-down of the product and photo-documentation. Subassemblies were numbered and placed in separate containers for later identification and ease of reassembly. Each component and subassembly was studied in order to better understand its function within the unit, and how it interacted with other components in order to perform the same overall function. Once inside, the intricacies and capabilities of modern electronics can be fully realized. The product itself is able to load a DVD disc into the tray, read it through the use of a laser, convert the data into a signal readable by the computer in a package not much larger than the disc itself. After documenting a few crucial components in a 3-D CAD program the components were assembled back together. The process was straightforward and easy using only a small screwdriver and basic disassembly skills can completely remove almost all necessary components to study the product. As this was a base-model widely available device, and most certainly not intended for infinite life use, some of the components were not designed to withstand the forces necessary to disassemble it. These include many small plastic pieces and a small rubber belt that was missing upon delivery of the item.
- Computer CD-R/RW Drive
- Manufacturer: HL Data Storage, April 2002
- Designed By: Hitachi-LG Data Storage
- Model Number: GCE-8400B
- Laser Class: 1
- Buffer Size: 8 MB
- Access Time: 110 ms
- Read Speed: 40x
- Write Speed: 40x
- Rewrite Speed: 12x
- Maximum Data Transfer Rate: 6,000 KB/s
- Dimensions: 5.25in (length), .5in (height)
CD drives have become a crucial and effective way of storing and viewing data. Computer drives offer a simple exterior design that houses many well designed components. CD drives have been incorporated into society and have become essential to many situations.
Data is read from a disc using a laser and photosensor, the laser shines onto the disc reading the lands and pits. Pits are small bumps written to the disc; lands are the flat surfaces between the pits. The disc contains the lands and pits in a spiral track, when the spiral is stretched out it measures 3.5 miles in length. Upon a laser shining onto the disc it is either reflected into the photosensor or diverted away from the photosensor, this creates binary code. When the laser is reflected into the photosensor it is deemed a "1", when it is diverted away it is deemed a "0". The type and content of the file is determined by this code.
This drive also has the capability of writing or "burning" data to a CD-R(recordable). A more powerful laser is used to burn the pits and grooves into the blank CD. The CD-R has a data size limit; it cannot be exceeded. Also, once data is burned into the CD-R, it cannot be used again. There is another type writable CD the drive can utilize called a CD-RW(Rewritable), which can be used more than once, but also contains a data size limit. Data can be repeatedly burned onto the disc so long as it does not exceed its limit.
All group members collaborated on the project and each had their own parts to work on.
- Bryan Humes - Group leader, 3D CAD, wikipage, oral presentation
- Brian Maisch - 3D CAD, oral presentation, references
- Eric Klaben - Oral presentation, wikipage
- Winnie Liu - Disassembly
- Fahr-Deen Kadree - Reassembly
The purpose of the CD-R\RW drive can be broken down into 3 main functions. It is used to save data to preserve it for future use. To read or play the file encoded on the disc and this model can also burn data onto a CD-R or CD-RW.
The product was in fair condition, all moving parts functioned; However, the product was missing a pulley belt, therfore, it did not operate properly.
Parts and Materials
Our group estimated our product would contain approximately 20 different parts and 6 different types of materials before disassembly.
|Part Number||Part Name||Quantity of Type||Part Material||Manufacturing Process||Image of Part|
|2||Main Circuit Board||1||FR-4, steel, copper, various||printed circuit board (PCB)|
|3||Sled Motor||1||aluminum, steel, copper wire||stamped, welded|
|4||Red Head Drive Interface||1||plastic||cast|
|6||Red Head Brackets||1||plastic||cast|
|7||Red Head||1||various; metal, glass lens||mass produced||Red Head|
|11||Disc Support||1||aluminum, rubber damping||Stamped|
|13||Spindle Motor||1||steel, aluminum||mass produced|
|16||Emergency Eject Mechanism||1||plastic||cast|
|17||Eject Motor, Volume Control, Headphone Jack||1||FR-4, steel, plastic||printed circuit board, cast|
|18||Internal Frame||1||blank||Injection Molding|
Provides protection to the delicate interior components.
Main Circuit Board:
Relays signals through the system.
This motor provides motion to the red head assembly, moving it at a constant rate as the disc spins.
Red Head Drive Interface:
This interface connects to the red head assembly and fits into grooves located on the sled motor. There are 2 notches on the interface that fit into the grooves, as the sled motor rotates it now moves the red head assembly through this interface.
The metal case is the rest of the exterior that provides protection for the interior components.
Red Head Brackets:
The brackets hold the red head tracks in place. The red head assembly can now move on its tracks.
The red head houses the laser, photosensor, and various lenses. The laser is focused through lenses and onto the disc. The laser is responsible for reading the data from the disc and the photosensor it responsible for recieving the data.
The disc tray holds the disc as it is placed into the drive and ejected from the drive. It is made to fit the standard disc diameter of 120mm or 4.28in.
It moves the height adjustor left to right. During the motion it lowers or raises the lift actuator which in turn lowers or raises the spindle motor support.
Connects to a belt, it ejects and returns the disc tray.
Spindle Motor Support:
This support houses the disc motor when assembled. It contains rubber dampers to provide cushioning for the motor when it moves up and down as a disc is inserted or ejected. It also houses 2 springs that provide support and cushioning.
These are located inbetween the spindle motor support. They provide support and cushioning for the spindle motor.
The spindle motor provides motion to the disc. The motor lowers when the disc is ejected and rises as a disc is inserted, landing in the center of the disc. The motor has grooves carved into the top which grab the disc as it rotates. The motor rotates with speeds from 200-500rpm.
The light actuator is responsible for lowering and raising the spindle motor support. It follows a track provided by the height adjustor.
The height adjustor provides a track for the lift actuator to travel when lowered or raised. It has grooves on top to provide a way to lock it in place or to release it. It is raised and lowered using the grooves located on top of the height adjustor.
Emergency Eject Mechanism:
This mechanism is a way to retrieve your disc if complete failure or a power outage occurs. There is a small hole in the front of the drive, where a small rod or paper clip can be inserted. When inserted far enough it triggers the mechanism to eject the disc tray. The tray is now free and can be pulled out with little effort.
Eject Motor, Volume Control, Headphone Jack:
The eject motor is responsible for ejecting and inserting the disc tray. The volume control is in the form of a wheel, it can be turned either way producing a louder or quieter sound. The headphone jack is a small opening in the front of the drive. A set of headphones can be plugged into the drive to isolate the sound to the headphones.
The internal frame is essentially the chassis of the entire drive. Everything is connected to the internal frame as it provides structure for the drive.
3D CAD Models
|Side View||Angled View||Top View|
The spindle motor is essential to the drive. The spindle motor support which houses the spindle motor lowers with the help of the hieght adjustor and the lift actuator. The lift actuator slides down through the groove in the height adjustor, which in turn lowers the spindle motor. The disc is now able to be inserted into the drive with no obstructions. The spindle motor support is now raised with the help of the same mechanisms. The spindle motor is now in the center of the disc and will spin it when the energy is provided. The spindle motor runs between 200 and 500 rpm depending on the location of the red head on the disc.
|Side View||Angled View||Top View|
The sled motor provides a constant rate of motion for the red head. The sled motor has a series of spiral grooves in which the red head drive interface is connected. The red head drive interface is connected to the red head. As the motor turns the spiral grooves, it provides motion to the drive interface which moves the red head.
|Side View||Angled View||Top View|
The red head contains the laser, lenses, and photo sensors. The laser beam is focused through the lenses to read the lands and pits on the CD. The red head is installed on a set of rods(tracks) and is provided motion from the sled motor.
Assembled in Sequence
|Part Name||3D CAD Diagram|
|Spindle Motor Support|
5 being the hardest
|Tools Required||Picture of Step|
|1||Place adjusting gear and eject pulley in slots on the top of the internal frame||1||Hands||watch video|
|2||Connect height adjustor to eject gear and connect emergency eject mechanism to it||1||Hands||Watch video|
|3||Connect the lift actuator to the internal frame and connect it to height adjustor.||2||Hands||Watch video|
|4||Reassemble the pieces of the spindle motor support. This includes the spindle motor, sled motor, red head, and the read head drive interface. The read head drive interface connects the sled motor to the spindle motor support.||2||Phillips head screw driver||watch video|
|5||Attached the spindle motor support to the bottom of the internal frame and lift actuator with screws.||2||Phillips head screw driver||watch video|
|6||Connect eject motor/ volume control/headphone jack to bottom of the frame, along with the main circuit board. Then connect the different power components to the main circuit board.||3||Phillips head screw driver and Hands||watch video|
|7||The disc tray was slid into place||3||Hands||Watch video|
|8||The bottom plate and metal case were both screwed on to complete the assembly||1||Phillips head screw driver||Watch video|
<embed src="http://www.youtube.com/v/_r_ifyYJfb0&hl=en&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed>
Does it still work?
Our product still does not work after assembly. The product did not operate properly before disassembly nor were we able to connect it to a computer interface to test it.
- Was assembly a mirror process of disassembly?
The reassembly process was not a mirror process of the disassembly. When we first received the product, we did not understand the inner layout or workings of the product. We went slow and were very careful as we disassembled the product; we did not want to damage any components. The different components that made up the system were numbered in the order of their removal during disassembly. This allowed us to see where the different components belonged upon reassembly. In contrast, reassembly was very straightforward. Since we knew where all the pieces went, it was an easy reassembly. Altogether it took less than 40 minutes.
- Reflection on the assembly process.
The reassembly process was verystraight forward. We had carefully documented the disassembly by numbering parts as they were removed from the device and took pictures of each step as we went along. The adjusting gear and eject pulley were the first items to be placed in their slots on the internal frame. After, the eject motor/volume control/headphone jack was snapped into place at the bottom of the frame. Next the height adjustor was placed in the groves in the internal frame. The height adjustor allowed the dvd tray to move up and down during operation. After, the lift actuator was connected to the height adjustor and this in turn was connected to the adjusting gear. The spindle motor support, red head, spindle motor, and sled motor were screwed on to the internal frame. The spindle motor support was then screwed onto the lift actuator. The main circuit board of the drive was snapped in place underneath the internal frame. Once this was completed, the metal cover and bottom plate were screwed on. Finally the disc tray was slid into the reassembled drive to complete the process.
How it Works
The CD-R\RW drive works in a general sense by converting electrical energy into mechanical energy. This mechanical energy is used first to load the disc tray into the chassis, then to spin the disc at a variable angular velocity so as to obtain a constant bit rate. This is due to the angular velocity being greater at the outer edge of the disc than at the inner edge. The device must also simultaneously transfer the rotational motion of the laser motor into a linear path from the innermost edge of the disc to the outer edge while the laser is scanning the disc. This is an interesting mechanism and can be seen below. It utilizes a spiral engraved shaft to transmit motion to a plastic interface component that carries the laser the needed distance, at a predetermined rate. The device then uses several feedback mechanisms and circuitry to convert the laser information which is a measured voltage difference into binary coded data and exports it through the use of a parallel ATA-type communication link. The data can then be processed by software programs intended for the purpose of multi-media type data interpreting.
This animation shows how the disc is read and how the data is interpreted
<embed src="http://static.howstuffworks.com/flash/cd-read.swf" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="440" height="150"></embed>
This animation shows how the laser tracks across the disc and how the motor changes rpm
<embed src="http://static.howstuffworks.com/flash/cd-drive.swf" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="400" height="300"></embed>
A stress/strain model needs to be considered for all moving or load bearing parts. The sled motor in our case is constantly under stress and strain. It has to be able to move the red head assembly numerous amounts of times in its life cycle. The interface that connects the sled motor and red head is also under stress and strain. There is a force placed on it every time it signaled to move the red head. Stress and strain models need to be evaluated to ensure it will meet its physical expectancy when being operated. This could entail both fatigue models and static failure ones, although the product is more likely to fail from fatigue loading than static loads as that is the nature of its operation.
A thermal model is needed to evaluate the amount of heat generated by the drive during operation. This is necessary because the internal components need to be able to perform during this heat and survive the heat output. This is also important for this product because it sits inside of a computer tower, where other vital components lay. Engineers have to develop this model to ensure the longevity and efficiency of the components and safety of the consumer.
Electrical Energy: Electrical energy is transfered to the drive from an ordinary household eletric supply.
Rotational Energy: Rotational enery is transfered when power is supplied to the spindle motor, thus creating rotation.
Thermal Energy: Created by friction due to moving parts, such as the red head and the spindle motor.
Types of Materials
Recommended Design Changes/Improvements
Overall this product was very well designed. The only improvement we could suggest at the time of production is removing the pulley system and replacing it with a set of gears. We suggest this because upon recieving the drive the pulley belt was missing, which would cause the product to malfunction. If this belt was replaced with a set of gears this problem could be averted all together. The drive was very well put together and designed.
The product dissection of the Hitachi CD-R/RW-Drive was successful and informative. Much was learned from examining the various systems of the product and how they interact with one another. Working with a team of engineering students to gain insight into a real world design scenario is essential to the field's future success and growth. We hope this page will serve as both a learning tool and an information resource for any who are interested.
- Elton, M. (2006). How DVD and CD Drives Work. Scribd. Retrieved October 10th, 2008, from http://www.scribd.com/doc/596/How-DVD-and-CD-Drives-Work
- Byte, U. (2008). Compact Disk. USByte. Retrieved October 15th, 2008 from http://www.usbyte.com/common/compact_disk_4.htm
- Sweet, M. (n.d.). How DVD Drives Work. Smart Computing. Retrieved October 20th, from http://www.smartcomputing.com/articles/archive/r0403/08r03/08r03.pdf