Hero photograph
Grace Beatson with the final prototype of her Mojonnier Shaker
Photo by Otago Polytechnic

Shake it up

Lesley Brook —

An ingenious and practical engineering solution might make life easier for lab workers.

As part of the quality control processes in a dairy factory, the milk powder produced is sampled three times per day and its milk fat tested. This is done by shaking the samples with the testing agents back and forth in Mojonnier test-tubes. The shaking is physically demanding for staff, holding a rack of test-tubes and maintaining the movement for one minute. Complete consistency of movement cannot be maintained for the whole minute and from one staff member to another.

This is the issue which Mechanical Engineering student Grace Beatson focussed on in her final year project, utilising our EPICentre workshop facility. She began by considering how to hold the rack of Mojonnier tubes securely inside the shaker, yet allowing the rack to be moved in and out of the shaker easily. The solution was a ratcheting lid design that would lock in place when pressed down. Under guidance Grace also built the electrical circuitry that would:

  • Rotate the stand of up to eight Mojonnier tubes end on end at 30 rpm;
  • Time the motion for one minute; and
  • Stop the motion with the test-tubes in an upright position for removal.

Grace developed her skills with the water jet cutter to produce steel prototypes with a 3D printed plastic handle. Her final prototype is in stainless steel, with a steel handle 3D printed for her in USA. It has passed initial testing in a dairy factory laboratory.