Inner profile measurement is an important matter in such fields as medicine, dentistry and anthropology as well as
mechanical engineering and industry. Here we propose a measurement method for inner diameter of pipes and/or
holes. The key device in this technique is a ring beam device which consists of a conical mirror and a laser diode.
And the fundamental principle is based on optical sectioning without any contact probe. The optically sectioned
profile of an inner wall of a pipe-like object is analyzed to give the inner profile in addition to the inner diameter.
This optical instrument with a simple and small configuration is now under development for practical uses. In the
hitherto-tried experimental works, the availability of this instrument has been highly evaluated and usability for
practical applications is expected, especially, for measurement and inspection of mechanical components and
elements besides pipes. This ring beam device consisting of a conical mirror and a LD is assembled to form a disklike
light beam sheet. We show measurement result of pipes and holes, and, at the same time, report a compact inner
profile measuring instrument. Both the ring beam device and a miniaturized CCD camera are fabricated in a glass
tube. Availability of this instrument is shown by measuring the inner profiles of various pipes. In response to this
trial, there appeared a strong request that not only the internal but external profiles should be measured
simultaneously. Therefore we propose an improved method for measuring the external profile in addition to the
internal profile. In our arrangement, one pair of concaved conical mirrors is used for the external profile
measurement. In combination with the inner profile measurement technique, simultaneous measurement of the inner
and outer profiles becomes attainable. A measurement result on a bevel gear shows availability of newly proposed
principle. Now we are aiming to realize simultaneous measurement of the internal and external profiles of various
types of pipes and similar objects.