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Revision as of 13:20, 22 September 2007

This page was compiled as a project for the 24-441 Engineering Design Course at Carnegie Mellon University.

Executive summary

Customer needs

This device is primarily a precision positioning mechanism that can move in any direction. It is designed such that it has multiple degrees of freedom to increase the usability for the user. Some of the main users are disc jockeys and radio stations who need a stand for their microphones. This microphone was designed to be a hands-free device and would eliminate the need for the user to have to physically hold the microphone in a particular location.

Another need that is addressed by the product is the small footprint that it has and the overall size of the device. Most radio stations are cluttered and microphones may get lost. The device takes up a small portion of the table and can extend outward in any direction. This device is also easily portable which is beneficial for users who have to move or store equipment around.

This unit is also durable due to material that was used to create it. Bent sheet metal is very strong and the injection molded parts are fairly durable as well. Parts are coupled in pairs for strength and stability.

System function

Force Diagram of the Microphone Stand.

The stand is attached to a surface by a clamp. The 2” rod that protrudes out from the bottom of the stand attaches to the clamp and can swivel 360°. The springs attached to the upper section of the stand create an opposing force to the microphone itself. The spring force creates a moment around point A as shown in Figure 1. This moment counteracts the moment caused by the force created by the microphone. The upper bar linkages can move together respective of point A. They are fixed together by a ¼” bolt and angled plates (point B). As long as the microphone is being adjusted lower than it’s equilibrium position without a microphone as shown in Figure 2, the lower spring does not stretch or compress. Once the upper section moves above the

Product use

Product dissection

The first step in designing an improved product is to fully understand the current product. This includes the purpose, function and structure of the product as a whole, as well as the properties of each of its components. In order to examine the complete functionality of the microphone stand, and to prepare for further design analysis, each component was individually removed and documented in the following table.

Bill of Materials

Part #	Part Name	Qty.	Function	Weight (g)	Material	Manufacturing Process	Photo
01	Knurled knob	1	Friction knob to hold microphone in place	6	Plastic	Injection molding
02	Lock washer (small)	2	Spacer between bolt and surface	0.15	Steel	Casting
03	Headless bolt	1	Holds microphone attachment in place	2	Steel	Casting
04	Microphone attachment	1	Holds microphone by threaded rod	47	Steel	Casting
05	Grasping clamp	2	Clamps microphone attachment in place	13	Steel	Casting
06	Grasping pin	1	Aligns grasping clamps	0.5	Brass	Extrusion
07	Lock washer (large)	1	Spacer between bolt and surface	0.2	Steel	Casting
08	Bolt	4	Holds upper angled plate sub-assembly	2.5	Steel	Casting
09	Angled plate - bent	2	Secures frame to attachment	11	Sheet metal	Stamping/bending
10	Upper spring	2	Counteracts weight of microphone	53	Steel	Wrapped wire extrusion
11	Upper spring attachment	4	Holds spring in place	2	Steel	Casting/turning
12	Threaded rod	2	Holds attachments together	4	Steel	Casting
13	Bar linkage	5	Linkage, houses XLR cable	94	Sheet metal	Extrusion
14	End fitting cap	4	Upper linkage cap, guides XLR cable	(n/a)	Plastic	Injection Molding
15	Lock washer (medium)	2	Spacer between bolt and surface	0.2	Steel	Casting
16	Nut	3	Tightens fixture	0.5	Steel	Casting
17	Headless 1/2-threaded rod	1	Connects lower and upper sections	4	Steel	Casting
18	Spacer (medium)	2	Spacer for central sub-assembly	0.5	Steel	Casting
19	Spacer washer	1	Holds central sub-assembly	0.2	Steel	Casting
20	Washer (medium)	1	Holds central sub-assembly	0.2	Steel	Casting
21	Tightening cap	1	Tightens upper to lower section connection, secures joint angle	3	Plastic	Injection molding
22	Angled plate - flat	2	Base for upper to lower connection	10	Sheet metal	Stamping
23	End fitting cap (flat)	2	Upper linkage cap	(n/a)	Plastic	Injection molding
24	Spacer (large)	3	Spacer for lower sub-assembly	2	Steel	Casting
25	Long 1/4-threaded rod	1	Secures lower sub-assembly	5	Steel	Casting
26	Spacing bolt/rod	1	Spaces and holds lower springs	2	Steel	Turning
27	Lower spring	2	Counteracts weight of microphone	35	Steel	Wrapped wire extrusion
28	Lower spring attachment	2	Holds spring in place	2	Steel	Turning
29	Base bracket	1	Connects frame to mounting section	47	Sheet metal	Stamping/bending
30	White bushing	1	Protects and guides XLR cable	0.5	Plastic	Injection molding
31	XLR cable	1	Carries signal to microphone	50	Various	Electric

Design for 'X'

This microphone stand is a pure mechanical part. Most of the parts are steel with some pieces being made of plastic. This makes the stand very durable and long lasting. Disassembly was possible in approximately 10 minutes. The parts were all re-assembled into the original condition without any trouble.

Design for manufacture

• The bar linkages (5 total) are manufactured by bending sheet metal into the square cross-sections. Although they look similar from a distance, the bottom two linkages have a distinct kink in their line for aesthetics.

• There are two sets of angled plates: one set is bent while one is flat. The process responsible for these parts are stamping and bending.

• Many of the cylindrical parts that either held the springs in place or were spacers seemed to be manufactured by turning. Only the brass cylinder was extruded.

• There are some plastic pieces such as the turning knob and the bushing that appear to be made through injection molding.

• The top springs were of thicker material than that of the lower springs. This was to counterbalance the weight of the microphone at a harder angle. These springs are just normal industrial springs with no special features.

• Other pieces such as washers, bolts, nuts, and clamps were of steel material and cast into their respective shapes. Many of these parts were of different sizes and proportions. For manufacturing purposes, having different sizes might be too costly when one size could work.

Design for assembly

• Although the assembly looked very similar in terms of the links, there were bolts and nuts of different sizes all throughout the assembly. As this affects the price of manufacture, it also makes assembly a bit more complex than it needs to be.

• Reassembling the microphone stand, there were many configurations that would have worked. Pictures had to be used to aid in the reconstruction. There could have been something in the design to force just one configuration.

• Assembly at certain points needed three hands to manage. This also could have been a design consideration as this microphone needs to be taken apart for maintenance. The springs were the hardest to work with so they were put on the last.

Design for usability

• There are two positions where the microphone stays in equilibrium. One angle is about 45 degrees from the vertical and another at about 135 degrees. This seems very limited as the users of the microphone stand are diverse in height and seating positions. Alternative designs should have been implemented to have more adjustments in the microphone position.

• The bottom of the stand has a simple insert-in-slot swivel mechanism so the microphone can be rotated to any degree in that plane with a lock.

• The microphone wire that runs through the brackets to the top is a very good idea as it does not introduce problems of tangling and restriction of rotation and movement.

Design for safety

• One main issue with the stand is that once a microphone is not loaded at the top, the springs snap the arms with such violent force that it could injure the user of the stand. This could be prevented with hydraulics on a more expensive unit.

• All the possible sharp edges on the stand were either filleted or rounded. There were no injuries in the process of disassembling and reassembling the product.

Design for environment

Failure mode and effects analysis

Mechanical analysis