Cartesian positioner maps ultrasound fields

Edited by the Engineeringtalk editorial team Sep 14, 2001

Unimatic has helped automate the calibration of tiny medical ultrasound sensors, a process that involves taking up to 100 separate measurements from precise points.

Unimatic has helped automate the calibration of tiny medical ultrasound sensors, a process that involves taking up to 100 separate measurements from precise points within a three-dimensional field.

Performed manually a typical calibration run could easily take several days, but with the new system the task can be completed in 3-4 hours with the scientists only needing to operate in an overview role.

Ultrasound surveys are used in many fields, such as healthcare, medical monitoring, materials testing and environmental studies.

The system was developed in conjunction with Precision Acoustics in Dorchester, which although small is one of the world1s top five companies in the field.

The largest ultrasound sensor it makes is 1mm diameter, and this is huge compared with the smallest in the range 40 microns across (a human hair is 50 microns diameter)! Ninety-seven per cent of production is exported, half to America and a third to the Pacific Rim.

The basic principle upon which the new calibration system works is to move the sensor around the 3D field created by an ultrasound source, taking measurements at peak points.

The accuracy with which the sensor has to be positioned for the most critical measurements is considerable, so Precision Acoustics called on the expert assistance of Unimatic.

The tests are carried out in a tank of water about 1m long and 0.35m square.

The ultrasound source is located at one end of the tank, and the sensor is moved about in X,Y and Z planes by the Unimatic system which is based on Parker1s DIN rail mounting stepper drives and Isel linear actuators.

The stepper drives are intrinsically digital, which helps with the accuracy and repeatability of positioning.

They communicate with a PC running LabView, a specialist software programme developed by National Instruments which is used extensively by the scientific community.

The calibration is carried out as part of Precision Acoustics1 quality assurance procedure, and Unimatic1s automated positioning equipment is proving very popular with the company1s technical staff.

Chief Scientist Andrew Hurrell says: "The time savings we are achieving with the new rig is freeing up highly qualified staff from repetitive (although vital) work.

This takes a big chunk out of our production costs, makes us more efficient and allows us greater time to concentrate on the creative research and development that is essential to maintain our world position." Hurrell is already in discussion with Unimatic about refinements to the system that will add a further dimension to the calibration profiles.

"We are looking at adding a Theta drive to Unimatic1s positioner, so that we can rotate the sensor around on its own axis.

With this fourth movement our calibration will be elevated to truly world class, in some cases approaching the absolute measurements currently only achievable in National Metrology Laboratories.".