Kinds of Maintenance
Consider the availability of skill, tools, and parts inventory and the consequences of random failures. Is your company policy to correct failures by part replacement, by subassembly module replacement, or by complete disposability and complete replacement? Are modules repaired by the factory and returned to a replacement pool? What replacement parts, modules, and supplies should be stocked by the customer?
In your product's maintenance environment will the people be trained? Untrained? Equipped with an inventory of spare parts? Equipped with good maintenance tools? Disciplined and good-willed or undisciplined and malicious? Trained maintenance people employed by your own organization or by distributors for your organization? In this case you can assume that the maintainer is unlikely to do damage, understands the machine, is equipped with special tools, and is capable of rather educated diagnostic thinking. Next there is the class of professional maintainers such as garage mechanics who are more or less trained and more or less well equipped. Third, there is maintenance by the user, who may be highly qualified, as in the case of electronic technicians in research laboratories, or may be highly unqualified, as in the case of users who include the uneducated and unskilled.
Disposability
The use of disposability as a maintenance technique has been increasing for some time. In medical products disposables eliminate the need for sterilization between uses and the handling and reassembly of components into kits. The labor saving in hospitals is substantial. There is a continuing development program in this industry to make instruments in very inexpensive ways to justify their disposal. The single-use hypodermic needle is the most commonly employed example. In both consumer and other maintenance, the use of disposables reduces the skill and cost of maintenance. Your design policy in this matter deserves great consideration.
Accessibility for Maintenance
Accessibility for maintenance is of great value in reducing the cost of maintenance and reducing the irritation of your customers when they have to go through contortions and squinting in order to repair or adjust your product. Accessibility for diagnosis, adjustment, lubrication, and replacement prolongs the life of the product because it makes it easier to maintain and people are thus more likely to do so. It also promotes goodwill from the customer who has to perform the maintenance. However, such maintenance accessibility can conflict with aesthetics, the size of the envelope, and the cost. Here is another opportunity for two-way winners.
As the designer you have the choice of designing for special maintenance tools, which makes your design life easier or working very hard to make maintenance easy.
Built-in Diagnostics
In some modern electronically controlled products it is the practice to design in very complex diagnostics which display to the maintenance person the nature of the fault or the nature of the action required. It is sometimes very desirable to put conspicuous displays of need for supplies such as paper in a duplicating machine so that the user is not tempted to fix a nonexistent fault and thereby create a fault.
Hot-Line Maintenance
The establishment and availability of hot-line operating and maintenance system service permits a degree of complexity in operation and maintenance which might not otherwise be permissible.
How to improve Reliability
A product may be modified in many ways to increase reliability and reduce maintenance. Better components, exclusion of dirt, simplified adjustments, easier access, redesign of parts subject to failure, consideration of both electrical and mechanical components, redundancy of components, reduced operating temperature from better heat-transfer means-the list is endless.
Testing
Testing is essential to expose sources of unreliability. However, you cannot test reliability into a product either in development or in production. Increased reliability comes only from improved design and better manufacturing.
You test to see if the product works at all, to see its performance under different combinations of manufacturing tolerances, to see its performance under different combinations of environmental stress, to determine its operating life, and to see its performance with respect to safety. You test during R&D, and you do partial testing in production to detect defects which may be either initial or "infant mortality."
Planning for Maintenance
As part of your design process you should predict all possible failure modes and decide what to do about each. Aside from designing out the possibility of failure in each mode, you should provide for preventive and/or corrective maintenance for each. For example, a part subject to failure should not be welded or riveted in place.
In electronic circuits part count should be minimized and temperature should be minimized.
You should keep records of your reliability design studies and tests, both for future use and for defense in case of product liability suits.
People Problems
We have considered the reliability of your product and many of the things you can do to make it more reliable. Part of the problem is the reliability of the people, organizations, and procedures involved from initial design through testing, manufacturing, shipment, and use.
The military have elaborate specifications on inspection, shipping, and many other things which affect the final reliability of their purchases. The Food and Drug Administration (FDA) has similar and even more stringent requirements on products it controls.
You should assess the reliability of the people, procedures, and organizations that will be involved with your product and request your management to make changes in anything which you fear may reduce its reliability.
Reliability is a good thing, like motherhood, patriotism, and the flag. However, there are different kinds of reliability needs.
Different Service Requirements for Reliability
In a newspaper printing plant it is permissible that the machinery require careful, skilled, unhurried, preventive maintenance every single day; but for a few hours each day after the press has been turned on it is absolutely essential that no breakdown whatever takes place because the cost of interrupting a newspaper printing run is enormous. A surgical heart-lung machine has similar design rules, but here a failure can cause a death.
A cardiac pacemaker can be maintained by surgical replacement, but if the failure is sudden, it can threaten a life. If the failure is "fail-soft" and gives warning, there is time for surgery before there is a life threat. Battery wear-out is managed by surgical replacement of the entire pacemaker on a time schedule. Therefore the longest-life batteries available are used, and the batteries as well as the remainder of the pacemaker are made under extremely strict quality control.
A different kind of thinking is required in the design of space vehicle hardware, for which maintenance by humans is zero, a small amount can be done by remote control, operation is continual, and the cost of failure of an inexpensive part can be the multimillion-dollar cost of a lost mission.
Designing for reliability and maintenance is not as much fun as designing for function, but it is an equally important part of designing for success.
