Young Engineers

What a CD Player Can Teach You About Mechatronics

May 7, 2014

As the field continues to define itself, confusion remains about what mechatronics engineering is and isn’t. Let’s clear some things up.

It’s not the musical group that performed Pump Up The Jam. It’s not our all-Asura clan in Guild Wars 2. While it may help you design giant robots, there is far more to the discipline than glorious, ground-shaking mecha.

Mechatronics, a portmanteau of mechanical and electronics, is a multidisciplinary catch-all for intersection of mechanical engineering, electrical engineering, control systems and computer engineering. The drive for smaller, lighter, cheaper, high-performance devices demands efficient, elegant and maximized solutions. By working towards a synergy between design, control, electronics, software, these goals can be more easily achieved.

The hard drive in your laptop, the anti-lock brakes in your car, and the robots that built your car all would be less performant, more expensive, or just plain impossible without the Mechatronics approach.

Still unclear?  Let’s look at the Compact Disc player from the Mechatronics perspective:

First proposed in 1974, before the advent of personal computers and dirt-cheap digital signal processors, the Compact Disc was remarkably ambitious and forward-looking. While a CD player may seem quaint and disposable today (a point we’ll return to later) its ability to read 44,100 16-bit samples per second in real-time was nearly science fiction in 1974.

Mechatronics: Take One Part Mechanical Engineering …

What a CD Player Can Teach You About Mechatronics The Compact Disc is a 120mm (4.7in) Lexan disc, pressed with bumps (pits) in the surface. The pits and the spaces between them (called lands) form a spiral pattern that begins near the center hole and ends near the physical edge of the disc. A thin aluminum coating provides the reflectivity. Each track of the spiral is 1.5 micrometers in width. Since the disc is read at a constant linear velocity (rather than a constant rotational velocity like a vinyl record) the CDs speed can be anywhere from 200rpm to 500rpm, depending on what part of the disc is currently being played back.

Oh, yeah. Did we mention that a laser reads the information, and that focus is critical?

… Add One Part Control Systems …

What a CD Player Can Teach You About Mechatronics

Credit: Wikimedia Commons

Coordinating the speed of the motor spinning the disk with the position of the actual laser lens would be a challenging enough engineering project, but the CD player must be operational in normal household settings. A music player that skipped every time Uncle Bob shifted in his chair would not be terribly attractive to the consumer. So the lens and tracking mechanism must be able to constantly self-align, quickly, accurately, and cheaply.  In addition, the spiral of pits and lands on a compact disk is never perfectly centered. Although the laser itself can only tolerate 0.2 micrometers of misalignment, the head must be able to deal with up to 0.2mm of sinusoidal wobble. To make this work (and to deliver a product with a reasonable price point) we need a closed loop control system, where information on position and velocity are fed back into the control system .  In other words, the laser assembly must have a certain degree of smarts.

… One Part Computer Engineering …

A consumer audio player must also be forgiving of imperfections in the medium. Part of this is handled in encoding (eight-to-fourteen modulation provides some redundancy by using fourteen physical bits on the disc to encode eight bits of actual data) but other factors must be taken into account.

… Then Materials Science & Design. Stir.

What a CD Player Can Teach You About Mechatronics

Credit: Wikimedia Commons

Numerous other factors informed the design of the optical read laser in the compact disc player. The resonant frequencies of the parts must be considered. Vibration from one component can set others in motion. Materials will behave in less than ideal ways. The compact disc player must deal, not with ideal cases, but with the boots-on-the-ground reality of what is happening in the system as a whole.

Naturally, none of these problems are insurmountable. IBM had been building drum memory and hard disks with closer tolerances for more than 2 decades before the release of the CD player. Unfortunately, these devices were several orders of magnitude more expensive, and performed best in a laboratory setting – and none of them were something you could put in your pocket or would want in your living room.

To bring such digital wizardry to the masses,  a synergy between disciplines was required.  Mechatronics is that synergy. Considering the system as a whole and comprehensively modeling & simulating it is key to “right the first time” designs. Instead of the mechanical engineers designing one aspect, then handing the design off to control systems people, then to software engineers, the Mechatronics approach allows engineers to communicate laterally and in a timely fashion.

The result?  Today one can purchase a drive that will play back and burn a variety of optical disc formats for around $20.

Sound good?  Check out our Mechatronics Career Profile for more information, tweet us, or sound off in the comment section below.