woman doing manual inspection
Manual inspection requires the presence of a person, an inspector who performs assessment of the entity under question and passes judgement on it according to some training or previous knowledge. No equipment is required except the naked eye of the trained inspector.
According to research, visual inspection errors typically range from 20% to 30% (Drury & Fox, 1975). Some imperfections can be attributed to human error, while others are due to limitations of space. Certain errors can be reduced through training and practice, but cannot be completely removed.
Inspection process in industries chart
Inspection process. (Source : The Role of Visual Inspection in the 21st Century (See & Drury, 2017)
Table showing factors in inspection performance
Factors influencing Inspection performance
Visual inspection errors in manufacturing take one of two forms — missing an existing defect or incorrectly identifying a defect that does not exist (false positive). Misses tend to occur much more frequently than false alarms (See, 2012). Misses can lead to loss in quality, while false positives can cause unnecessary production costs and overall wastage.
manual inspection drawbacks, slow, ineffective, subjective to inspector
Limitations of manual inspection
Besides, manual inspection suffers from other limitations such as these
There remains the fact that the human eye, while more technologically advanced than any mechanical camera, can also be easily fooled. Consider some of these weaknesses associated with visual inspection:
Optical illusion
An optical illusion where black dots seem to appear and disappear at the intersections of the white lines.
Human Vision alone is undependable — Optical illusions such as those to the left can demonstrate just how unreliable the human eye can be. This does not necessarily mean that manual inspection is totally useless, but that it would be unwise to depend entirely on it.
parallel lines optical illusion
Parallel lines appear to be sloping.
Imprecision of eyesight — The human eye is incapable of making precise measurements, especially on a very tiny scale. Even while comparing two similar objects, the eye might not notice that one is slightly smaller or larger than the other. This concept also applies to characteristics such as surface roughness, size, and any other factor that needs to be measured.
Cost of labour – Manual inspection remains a costly venture due to the appointment of (multiple) trained individuals. Cost-wise, manual inspection operators may be earning a yearly salary of $50,000 to $60,000.
quality inspector salaries from AI glasses
Source: Glassdoor
A new age alternative
Automated Visual inspection can overcome these problems by making the whole procedure of visual inspection independent of any human involvement. Using automated systems typically surpasses the standard of manual inspection.