The Design Of Servo Control Program For CD-ROM

The computer and VCD player can be see in all our life, theoptical disc driver has become a thing indispensably. The floppy driverhas been washed out, because the want to storage and transfer moreinformation in higher speed. The CD-ROM because of its high speed,big capacitance, low price and easy to take, it becomes very popularwith people. But it is limited in using because its speed andcapacitance is lower then the hard driver. So many people work hard tofind a way to advance the speed and the capacitance of the optical disc.This paper summarizes the importance of researching the opticalstorage device. In Japan and Taiwan, the optical storage device isimportant part in their economy. Our government is also want to R&Dthe key technology of the optical storage device.Then I introduce the optical device in the CD driver – the opticalpickup unit (OPU). I take the example of the philips' OPU66.21. ThisOPU is 3D OPU, it can not only move up and down and move throughthe radial of the disc, but also can turn around the radial of the disc.This kinds of OPU is fewer, it isn't wildly used in the commonCD-driver. There are three coil motors, these motors can complete theaction of focus, track seek and track lock. The signal feed back fromthe disc is also send out by it in the form of current. So the OPU isvery important in the CD-driver, the performance of the CD-driver isdependent on it.In the later of the paper, I introduced the information carrier –optical disc. In this text I take CD-ROM for example, the physic sizeof the CD-ROM is introduced in detail. The spec of physic size of theCD-ROM is very strict, because the servo controller of the CD-driveris a very precious system. The optical disc can't be identified if its sizeisn't fix to the standard. I also introduced the position where theinformation is recoded – reflect layer, there are gold, silver, aluminumwith AZO for the reflect layer. At last I introduced the sharp of thetrack.In the next chapter I introduced the structure of the servo controlloop. The servo control loop is composed by SCP (servo controlprocess), MCU, circuit for signal, SLED motor and OPU. SCP is aDSP design for the servo of the CD driver, it executes the controlprogram as well as operation of the high speed signal. The MCU is themain controller of the CD driver. It takes charge of incept thecommand external, setup the SCP, deal the exception in the thread ofthe servo. The signal circuit is used to adjust the peek-peek and offsetof the feedback signal of the servo. SLED motor is a step motor,it isused to move the OPU. I took charge of the circuit debugging. Ichecked the instructions of the SCP, and if its interface to the circuitoutside was working correctly. I used the MCU to generate the signalfor the circuit which is used to adjust the signal to check the functionof it. I worked with other designer to complete the whole circuit.At last I introduced the theory of the servo controller, as well as thecontrol process. There are three parts, Focus, Seek and Track. TheSeek can be divided into two parts, the SLED motor seek and TRACKmotor seek, they work together to complete the seek for the whole disc.The design and debug of the focus program was complete by me andmy partners, my work was make the OPU not lose the position offocus when the OPU is seeking. The seek program was design bymyself, I got the speed of the two motors in deferent power, and thedistance the motors can move. Then I set up the model for seek, andcomplete the seek control. I design the track program when the OPUget the exact track. In these process the program must make sure theOPU not departure the focus position when the OPU stop suddenly.It is also the emphases of the TRACK seek, it requires the speed of theTRACK motor is zero or very slow. It is almost impossible to makethe speed of the TRACK motor to zero, so we do our best to make theTRACK motor move slowly.At the last of the project I built up the whole servo program withmy partners. The servo I designed can focus on the disc faster andsteadier, and the seek time is less than the VCD driver which used thesame OPU. The servo can play the VCD smoothly. What we need todo next step is to make the servo for the DVD, and advance thecapability for the error process.