In the development of new and improved types of optical glass, we have applied quality engineering to small-scale evaluation in the laboratory, with the goal of vertical ramp-up in the melting process. Previously, we had optimized each process individually in small-scale experiments, determined the optimal production conditions, and then carried out a large-scale experiment to confirm that these conditions were actually suitable for volume production. A problem that had sometimes delayed the start of volume production in the past was that the small-scale experimental results could not be replicated in the large-scale experiment. To solve this problem, we started by surveying the entire process, selecting the factors to be studied, and studying the optimization of the process as a whole. Next we adjusted the evaluation metrics and noise factors to obtain small-scale evaluation methods that would give results that could be replicated in large-scale experiments. By applying this methodology to many types of glass, we obtained a body of production technology information that turned out to be applicable to many types of optical glass in the same family. The result was that we were able to ramp up volume production of even newly developed types of glass quickly, without performing orthogonal array experiments.

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Given the goal of more efficient parameter design in the drilling of small holes by an electrical discharge machine with an electrode diameter on the order of 0.1 mm, the strategy adopted in this study was to use Taguchi’s T-method(1) to predict the quality characteristic of the output from the input energy waveform. When members with matching rises in their discharge waveforms were taken, the voltage and current peaks both failed to align on the time axis and the predicted and measured amounts of material removed had a low correlation coefficient. When a correction was made to allow for the different discharge durations of the members and align their peak positions(maximum values)on the time axis, with voltage used as the energy characteristic, the correlation coefficient improved from 0.518 7 to 0.749 0. This was considered to indicate that the signal-to-noise ratio had improved because singular value effects had been eliminated by the correction. Nevertheless, adequate predictive accuracy was not obtained in the factor effect diagram of the removed volume, indicating that further work will be needed before predicted values can be used in practical parameter design.

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Many ophthalmic instruments use fixation targets, which are marks at which a subject gazes continuously to hold his or her eyeball or line of sight in a fixed position. In research and development work at Fuji Xerox on optical instruments for use with the eyeball, it became necessary to keep the subject’s line of sight steady for an extended period of time. With existing fixation targets this proved difficult: the targets were hard to recognize and the line of sight tended to wander quickly. In this study quality engineering was used to test quickly new ideas for the design and display of fixation targets by evaluating temporal variations in the subject’s gaze position as a dynamic characteristic. The target design and display method became control factors in experiments using an L12 orthogonal array. In consideration of the varying signal levels and effective divisor in different experiments, the evaluation was carried out with the energetic S/N ratio. This led to the development of a fixation target and display method that improved gaze stability by approximately a factor of two.

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