Evaluation (Validation and Verification) - Medical Device Design: Innovation from Concept to Market - page 225

Figure 9.13
Typical USB microscope. (Courtesy Staffordshire University)
surface damage, crack propagation, etc., they are a very affordable device ( Figure 9.13 ). All
are able to take still images and some come with the ability to measure dimensions too.
9.3.4.2 Commercial Optical Microscopes
The price of these devices depends on the quality of the lenses and the magnification
achieved. They are still affordable and many have the ability to take still images using
a digital camera ( Figure 9.14 ). These devices are often calibrated and (unlike USB
microscopes) it is possible to take accurate measurements from the images.
9.3.4.3 Profile Projectors
These devices rely on the production of an accurate silhouette of a component. Most have digital
measurement capacity and can magnify an image significantly. They are calibrated devices and
can often measure to an accuracy of 1 μm (1/3000 of a human hair). They are not expensive
(about $3000-5000) and are the mainstay of all commercial quality departments. Many have the
capability for surface evaluation using surface lighting (but not all). However, these devices are
best used for checking for wear of profiles after accelerated life tests ( Figure 9.15 ).
9.3.4.4 Hardness Testing Machines
Often one of the results of accelerated life tests is work-hardening of the component. Hardness
testing machines are invaluable for this type of surface evaluation. However, they are beyond