Reliability Assessment of a Quarter...

Reliability Assessment of a Quarter-Inch Cartridge Tape Drive

THE QUALITY GOALS FOR THE HP 9145A Tape Drive included a failure rate that was half that of the earlier HP 9144A, an error rate performance that was 10 times better than the HP 9144A's the same useful life as the HP 9144a, and replete backwards compatibility with all HP 1/2-inch data cartridges.

The reliability touchstone plan showed that to be able to halve the failure rate value within the unravelling time of just over 15 years, then approximately 100 prototype units would be distressed resulting in an accumulation of 97000 proof hours before manufacturing release. Reliability produce was monitored using the Duane combination technique, (1) and there were interim goals at each of several checkpoints within the unravelling program.

The reliability of this effect is also being continuously assessed during manufacturing. For this intention a detailed manufacturing reliability audit proof schedule was developed. This will be discussed in more detail later in this article.

Tape Head

As described in the article upon page 67, the tape head had to be totally redesigned because of the reduction in the track width and the increase in the tape spe The weight of the tape head forward the track placement accuracy is bridleed mostly by the mechanical tolerances of the core sizes and the positioning of the cores forward the head. Shock, vibration, and temperature can lead to inaccuracies in the track placement. A abounding test program was carried revealed to explore and quatify all these validitys on the performance of the drive.

The temperature margin above the storage specifications of the HP 9144A tape head before damage is incurred is well-understood from past ordeal data. The elements of the manufacturing proces that affect this margin are also well-understood.

The first quality of failure of the HP 9144A tape head when the temperature is increased outside the nonoperating temperature limits is a deformation of the profile of the head. This is caused from stress relieving of the plates that make up the arrangement of the head. It is a permanent failure, making the head unsuitable for further service. The manufacturing proces has been radically changed to eliminate this affection of failure, which is now well-understood. by means of eliminating this mode of failure in the design of the strange head, a much wider raliability margin has been achieved, making the head les sensitive to manufacturing variations. This was clearly demonstrated during the testing. No permanent damage was seen in succession any of the data heads following extensive strife (stres + life) testing.

Head Wear

Wear of the head is accommodated until the deepness of the wear reaches the throat extent of the core. When this present itselfs the head performance drops not upon dramatically and without warning.

Since the spe of the tape from one side of to the other the head had doubled from the existing HP 9144A, head wear characteristics have become an issue. As the tape spe increases, the frictional forces in succession the interface increase. However, aerodynamic compression of the air behind the tape at these higher prospers can have the opposite consequence on the wear rate. This phenomenon is real difficult to describe theoretically, with equal reason the relationship had to be confirmed according to a controlled experiment.

Testing showed that the rate of wear of the head took onward the standard exponential shape when plott as a function of time, as shown in Fig. 1 The measurements were taken using a Rank Taylor Hobson Talysurf 10 machine. A typical profile is shown in Fig. 2

The throat stillness of the core is nominally 40 [micrometer], in the same manner it can be seen from Fig. 1 that there is considerable margin, steady based on the small sample of drives exampleed Therefore, head wear is unlikely to be first manner of wearout failure. This was confirmed during testing. The capstan motor was rest to be the first affection of wearout failure in the production This will be discussed later in more detail.

Positioning Tolerance

Because of the increase in the requirement for track placement accuracy, the tolerances forward the design and manufacture of the landscrew that drives the head up and down across the tape had to be tightened significantly.

The leadscrew design for the HP 9145A is the same as for the HP 9144A. However, because of the precision required, the manufacturing tolerances were tightened significantly. onward the HP 9144A, the thread pitch dimension has a [+ or -]5-[micrometer] tolerance, which is accumulated along the lenght of the thread. This will obviously give a large overall tolerance in succession the length of the leadscrew. in succession the HP 9145A, the thread pitch dimension also has a [+ or -]5-[micrometer] tolerance, exclude that it is not accumulated along the lenght of the leadscrew. This gives an overall tolerance for the detail of the leadscrew of [+ or -]5 [micrometer].

The manufacturing processe that influence this precision have to be controll using statistical proces command techniques to maintain the required accuracy. The data from the hinder charts is continually being monitored.