Campden Instruments Engineering Policy
Engineering, Quality Assurance and Metrology in Production
The following is abridged from a paper written for in-house project planning lead by our Chief Mechanical Engineer.
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.
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.
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.
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.
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.