Making the cups that cheer

Variable speed drives give precise control of the motors of an indexing turntable positioning system and of the automatic teacup-moulding machines that work around it

Teacups are shaped in an automatic machine where the mould can be spun at high speed and raised to meet a die above it. An extruder dispenses a precisely measured piece of clay into the mould and a partial vacuum is applied to hold the clay in place as the mould is raised to meet the die, at which point the mould is spun to form the cup. For quality reasons, it is essential that the spinning starts and stops with maximum acceleration and deceleration.

As the mould stops spinning, the vacuum is released, the die is raised and the turntable indexes to its next position. For the last 10 years the spinning was powered by a fixed speed motor with a mechanical clutch and brake to start and stop the mould. Josiah Wedgwood’s group electrical engineer, Andrew Achtmanis, says it was a work of art to set up the clutch and brake to deliver the required performance; and the set-up would vary during the day. This meant quality control problems and a great deal of maintenance.

The answer was to be found for the 36-station indexing turntable with the IMO Precision Controls’ Jaguar drives that are already widely installed throughout the factory. These drives provide not only the speed control for the spinning mould but by using a Jaguar VXS sensorless vector variable frequency inverter, the means of starting and stopping it suddenly and precisely.

Another VXS inverter would control the motor which powered the die and yet another would control the motor of the indexing positioning system, again to provide precise starting and stopping to ensure that the turntable was always in exactly the right position for spinning the next cup.

The VXS is said to be ideal for this type of application as it is compact, delivers 200% torque at 1Hz and provides extremely fast torque response.

Designed specifically for controlling small electric motors it is available in outputs from 0.4kW through to 4.0kW, and has user programmable I/O with an integral detachable keypad.

IMO Precision Controls Tel: 0181 452 6444