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Engineering, Quality Assurance and
Metrology in Production |
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The following is abridged from a paper written
for in-house project planning lead by our
Chief Mechanical Engineer. For a full version of this article
download the PDF here: |
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Engineering Design
To satisfy the requirements of both user and specimen preservation,
design must encompass many areas such as ergonomics, material
selection and analysis, production techniques, metrology, quality
control and assurance, microprocessor circuitry, software design and
programming. The design procedure must ensure compliance with
international directives and standards for product safety,
Electromagnetic Compliance (EMC), etc. Prototype production units
should be sent to some of the most demanding researchers for
critical review. When designing new products (or upgrading existing
ones) it is essential that the components selected will have a long
production life. Where possible, component selection is made to
incorporate the most up to date technologies. Components
manufactured to our designs are supplied by companies that have been
accredited to internationally recognized quality standards.
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Production and Quality
Assurance Quality
Assurance during product build must be continuous and all stages of
assembly must be carefully monitored to ensure all specifications
are met.
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Metrology
The difference between accuracy and resolution also needs to be
clearly understood – accuracy may be defined as the degree of
correctness while the resolution is the readable limits within which
the measurement can be ascertained using a particular instrument.
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Repeatability of measurement is also a
significant factor to be considered. The instrumentation must be
suitably reliable. Statistical analysis of readings should be
employed to establish the reliability and allow confidence to be
quantified.
When investigating the accuracy of motion of a microtome blade
that is vibrating at frequencies up to 125Hz and to measure that
motion to accuracies in the micron (0.001mm) range, specialized
techniques have to be used as conventional mechanical contact
inspect methods cannot react quickly enough or be relied upon. Thus,
the in-house development of non-contact optical inspection
techniques calibrated to micron accuracy using certificated masters
that are traceable to National Standards is an integral part of the
microtome development project. |
In-House Metrology
Device and Oscilloscope
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Z-Axis
Deflection Statement...
Campden Instruments uses a method of
non-contact metrology on every
Integraslice machine both during production and in final test
before dispatch. This method measures the degree of occlusion of a
photobeam by the oscillating blade.
A statement of ‘x’ microns of z-axis
deflection by itself is not meaningful. A true representation of
performance can only be given in the context of the speed and the
amplitude of oscillation and the condition of the surface being
measured.
- Surface Measure -
The surface of Campden Instruments
Ceramic Blades, Model 7550/1/C,
are first ground and then lapped flat with micron sized diamond
grit.
- Scope of Measurement -
Measurements are taken at three
different amplitudes these being 0.5mm, 1.0mm and 1.5mm and at
each amplitude from 20Hz to the maximum oscillation speed at that
amplitude.
Therefore, our statement on z-axis
deflection is as follows: "With this evaluation, Campden
Instruments is able to guarantee that at all speeds of oscillation
and amplitudes the z-axis deflection is not more than a few microns"
These measurements have shown
Integraslice to be an order of
magnitude improvement on the Vibroslice. Integraslice does not require
regular servicing to maintain its z-axis accuracy. |
