Talk:Microphone stand

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We thank the client for their kind words on our initial findings, including mentions of the "excellent executive summary" and the good descriptions of system function and customer needs. Additionally, we appreciate the constructive comments on some parts of our findings, and have revised our report accordingly. We have also responded to the client's specific questions below:

• Excellent executive summary, although a little more detail on your findings and recommendations would help.

We appreciate the kind words about our summary of the issues. We found the study of this product quite enlightening.

• Good description of customer needs. Is safety also an issue – pinch points?

Pinch points are certainly an issue in this product--it is possible for a user to injure themselves either in between the upper and lower segments, or within the pieces of each segment. To decrease this risk of injury, a possible redesign could incorporate a single piece for each of the upper and lower parts.

• Good description of system function – can you also comment on the four bar linkage AB?

Again, we thank the client for their kind words. The linkage AB serves similarly to a four-bar linkage (although possesses some differences), and allows for adjustment of the height of the microphone while still maintaining its orientation.

• In product use you mention that “in the event that the stand does not stay, the set knobs at the upper and lower joints can be tightened to fix the stand in a position.” Comment more on this. In what situations would the stand not stay in position? Are the knobs used to fix completely so that the stand is immovable, or only to provide sufficient friction to avoid movement without additional human forces?

Through use of the stand, as well as our mechanical analysis, we have concluded that with springs alone, there are a unique number of equilibrium positions. When a position is needed outside of a spring-based equilibrium, the tightening knobs serve to provide additional friction at the joint. This friction is such that movement from the desired position is prevented without rendering the stand immovable under external forces.

• The parts list looks good – is the knurled knob one piece or an assembly? You may want to recheck some of your manufacturing processes – washers are likely stamped, rather than cast, although it’s fine for standard parts to be listed as “purchase”. Threaded rods are similarly typically extruded and threaded, rather than cast.

The knurled knob was found to be a sub-assembly consisting of an external plastic injection molded part and an internal steel extruded part. Additionally, the manufacturing processes for small parts were re-assessed, and they were found mostly to be produced through stamping. The component list in the report has been updated to include these changes.

• Are the lower bars bent only to distinguish from upper bars? If this is the only purpose, it may be possible to reduce costs by avoiding this operation.

The lower bars are bent in order to give way to the internal parts that support the upper-linkage. If not for this reason, the upper and lower bars could be made from the same design.

• Interesting LCA – we agree that the impact is not too high for this product. A sector including “stamped steel parts” might be a better estimate than “iron and steel mills”.

After reviewing the detailed list of sectors, we were unfortunately unable to find one that is concerned specifically with stamping. We do feel that since most of our parts are steel, the "iron and steel mills" sector discussed in the initial report is a relatively close estimate since the steel is produced in forms similar to the final parts' shapes. However, in order to consider more of the environmental effects associated with the manufacturing processes involved in making this product, we performed a brief further investigation into the sector for "turned product and screw, nut and bolt manufacturing", which would represent the large number of small fasteners, such as bolts and washers, and turned rods and spacers that are part of the microphone stand. These findings have been added to the report.

• Interesting FMEA – you are suggesting that testing is performed on the springs to anticipate fatigue failure?

In this microphone stand design, the tension in the springs creates the main counter-moment to support the weight of the microphone, thus making the springs an integral factor in the overall rigidity of the stand. If the springs were to deform or fracture, even though there is only a slight chance of this occurring due to the inclusion of design controls for the spring parameters, the stand would no longer be able to maintain its positional rigidity and may harm the user. Therefore, it is suggested that there be additional testing in order to prevent spring failure.

• In your static analysis, we had some difficulty following: M2 is the moment around point A? This moment should be the component of kx perpendicular to the moment arm at the end of the spring minus the component of kx perpendicular to the moment arm at point B plus the moment caused by the microphone weight. Can you explain where the FA-FB = kx equation comes from? Also what is x_max? The maximum length of the spring under what condition? Labeling all forces and dimensions in the diagrams may help.

We appreciate you taking the time to review our analysis in detail. Indeed, you are correct that the calculation of the moments at joint 2 was confusing. We have revised our analysis to utilize a method of solution that is significantly clearer, particularly at joint 2.

• The conclusions of the numerical analysis are reasonable; however, providing more precise equations to understand the statics would be helpful in supporting a redesign.

Our revised analysis supports our initial conclusions: that there are potentially several equilibrium positions that depend on spring stiffness, initial length, and attachment point along the length of the bar. In considering a redesign, it is our belief that providing variability of spring stiffness or attachment point is of primary interest. Additionally, our market research indicates that this has been undertaken in more recent designs of this product, resulting in improved product function.