Rotating disc drives

Drive unit and hydraulic adjustment of — axial position of Stationary disc rotating disc... 

Hard-disc drive heads are subjected to a heavier use and therefore need a different design in order to prevent wear and extend the useful life of both the disc and the head. Hard-disc drive heads (also known as Winchester heads) make no physical contact with the hard disc. They are designed to fly very close to the disc, supported by the air flow resulting from the disc rotation. Fig. 5.18. The magnetic element in Winchester heads is usually a Mn-Zn ferrite. 

FIGURE 19 A mechanical foam breaker. The motor, drive, and shaft assembly are used to rotate the stack of conical discs at a high speed. The foam enters the spaces between the rotating discs at a and is separated into gas and iiquid by the centrifugal force. The liquid spins into the bioreactor and iiquid-free gas exhausts through the nozzie b. The mechanicai seai d prevents ieakage into and out of the steriie bioreactor. The seai is iubricated by steriie cooiing water c. 

The ability of the spinning disc to operate with very small driving temperature and concentration differences can improve the thermodynamic efficiency of the overall process system. This is clearly the case with the Hickman vapor compression evaporator, and it is also exemplified in the applications described next. In general, the power needed to rotate the spinning disc assembly is a small fraction of that saved by virtue of the establishment of an intensified fluid dynamic environment. 

Fig. 9. Rotating disk. S, Main drive shaft connecting to motor and controller I, inert sleeve, usually constructed from PTFE R, resin disc C, single crystal mounted in resin with disk exposed.

When reading information from a CD, the drive is basically reading a lot of pits and lands (lands are the spaces between the pits) in the disc surface. The pits are etched into the CD at production time. The laser reflects off the CD s surface and onto a sensor. The sensor detects the pattern of pits and lands as the disc rotates and translates them into patterns of Is and Os. This binary information is fed to the computer that is retrieving the data. 

For the following example, the function is not directly obvious from Fig. 7.2.1. A flat disc-shaped rotor, suspended by flexible beams at a central point, is set into horizontal, rotational vibrations by comb drive structures. If a turning movement occurs in the plane of the sensor chip, the rotor responds with a perpendicular tilt due to the conservation of angular momentum by Coriolis forces. The distance of the rotor disc to the substrate is detected capacitively and provides a signal proportional to the yaw rate. As the rotary oscillation periodically changes its direction, the whole structure executes tilt oscillations towards the substrate with the frequency of the drive (Fig. 7.2.14, Fig. 7.2.15). 

Fig. 11. The design consists of an 8-in. diameter rotary valve (Unidev) on which the upper part is fixed (the stator) and the lower part rotates (the rotor). Both rotor and stator are provided with pairs of radial holes. Between the two valve faces is fixed a disc of graphite-loaded PTFE (the progranme disc). The complete valve assembly is compressed together using disc springs with a maximum force of 2 tons. Interconnections between various ports on the stator are used to provide a fixed flow sequence. The lower part of the valve is formed to accommodate twenty coluim loops, retained by cbnipression couplings. The lower mechanism can be rotated in steps equivalent to the distance between each pair of column loops using a reduction gear drive.

The rotational actuation, which is typically provided by a conventional, low-cost spindle motor, also removes the requirement of external, pressure-driven pumps and their associated microfluidic interconnects and chip-to-world interfacing. Moreover, the modular nature of the LoaD platform completely separates the electromechanical driving instrumentation and the conventional optical readout units from the liquid sample and reagents under test the sample and/or reagents are exclusively handled by the microstructured, typically disposable test disc. These features are particularly beneficial for biological applications since the potentially hazardous samples can be processed in an encapsulated system, thus minimizing the risk of crosscontamination and carry-over. 

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