Coupling Design Process - Problem Definition

The first step of any design process is to gather information about the problem. This information is used to place bounds or constraints on the requirements for the design. In coupling design process, one of the main requirements is to reduce the total interface error, which is composed of the following three items:

1. Accuracy - Ability of a single coupling interface to match a position on one interface to a target position on the matching interface. This accuracy is essentially a measurement of the manufacturing quality and specified tolerances of a single matched coupling pair.
2. Interchangability - Ability of multiple coupling interfaces to match a position on a randomly selected male interface to a target position on a randomly selected female interface. This accuracy is essentially a measurement of the manufacturing ability and specified tolerances of a multitude of male and female coupling interfaces.
3. Repeatability - Ability of a coupling interface to return to the same position after multiple cycles of coupling removal and replacement. Repeatability is a complex value incorporating errors from effects that are either too complex or expensive to effectively analyze. Typical causes of non-repeatability include surface friction, environmental variation, preload, geometric design, and other parameters.
   

In order to understand the effect of the total interface error, a error budget analysis should be performed on the entire system. A spreadsheet is a useful tool for performing the error budget, as it allows for quick determination of the sensitivity of the system error to the interface error. Prof. Slocum's Error Gain Spreadsheet shows an example of such a tool for analyzing the combined error caused by a chain of interfaces.

In addition to the error requirements, the following items should be considered during coupling design:

1. Cost
2. Manufacturing capability (tolerances, precision, part sizes, etc)
3. Assembly ability
4. Interface loads - static and Ffatigue
5. Interface size constraints
6. Interface geometric placement constraints due to existing features
7. Thermal effects (sensitivity to thermal changes, thermal barrier between components)
8. Environmental detriments (including corrosive chemicals)
9. Exchangability factors (ergonomics, time to perform exchange, complexity of operations, etc)

After determing all design requirements, priority must be placed on each requirement. This priority is required to assess which coupling would be best suited for implementation.

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