Developing on-line testing

The Insitec was installed at a work station on one of the assembly lines, directly beneath the bench to which the grinder is delivered for testing.

To carry out the test the assembly line worker pours fresh coffee beans into the grinder and initiates the test sequence. The grinder starts to work and the resulting ground coffee flows out of the grinding chamber, down towards the analyzer. A venturi aspirates the arriving sample into the measurement zone of the instrument.

One of the parameters measured during laser diffraction particle size analysis is obscuration (or transmission), the amount of light penetrating the sample. Measuring at an appropriate obscuration is essential to obtain reliable particle size data and is therefore one of the issues addressed during method development. In routine operation, obscuration can be used to trigger an analysis. In this set-up the arrival of ground coffee reduces the amount of light seen by the detector, automatically triggering measurement at an appropriate concentration, without any manual intervention. The end of the analysis is marked in an identical manner.

The particle size distribution data for the sample is presented in real-time on the screen towards the back of the workstation. Data presentation has been precisely developed to meet the requirements of the application and particle size data is not the most prominently displayed information although the software does calculate a median particle size for the coffee (Dv50 – the particle size below which 50% of the population by volume lies). The focus of attention for the operator is the green areas of the screen which indicate whether the grinder is giving acceptable performance, and if not, how many turns of the gear wheel are required to correct it.

Figure 2 shows a test result where change is required, in this case a single turn in one direction. A negative sign ahead of the number would indicate a need to turn in the opposite direction. Following any corrective action a second test is carried out.

Refining the analytical solution to this level of simplicity and effectiveness required some initial effort. Key tasks were to establish suitable specifications, for each grinder type manufactured, and the development of a suitable interface.

De'Longhi worked with Malvern application specialists to exploit the full potential of the software that drives the analyzer and enables its integration with other processing equipment. The result is that data is presented in an easy to understand way that minimises the risk of error by the operator.

Testing is now completed in a few seconds and the amount of coffee used is relatively small. Because the grinder is tested with real coffee, small sample size is a distinct advantage that reduces the ongoing cost of testing. Every grinder is tested and each one leaves the testing station with numerical test data verifying performance. This data is linked to the serial number for the grinder, and ultimately the coffee maker, and form part of a matrix of QC test data for the machine, that verifies every aspect of performance.

Although the company no longer relies on the expert eye/feel of the assembly line staff but they are still trained to recognise powders in this way. Today, particle size data enables trainers to teach people to recognise the feel of specific blends and to demonstrate the sensitivity of the solution that the company has developed. Such efforts emphasise to all staff the need to control the particle size of the coffee in a statistically reliable way, and underline company commitment to manufacture of the highest quality products.

Looking further forward, particle size information is also now driving continuing development. At De’Longhi the Insitec systems are in almost constant use as development staff also use the system to gather experimental data to support research. Particle size results also enable assessment of different grinder designs, with, for example, different internals, allowing the company to refine its product offering.