MOTION CONTROL & LINEAR MOTION FEATURE
WHY MOTION CONTROL IS instrumental in medical technology
Motion control equipment provided by Mclennan has been selected for a project dedicated to developing an instrument capable of rapidly diagnosing sepsis, a potentially fatal infection which affects 18 million people per year, at an early stage
S
epsis – a bacterial infection which affects the blood, causing a potentially
fatal whole-body inflammation that injures tissues and organs – affects 18 million people worldwide each year and costs the NHS over £2billion. However, scientists at the University of Liverpool have developed a method of detecting the infection in its early stages, in a move that will help with rapid diagnosis of the condition in order to help combat it. They are now translating this into a point-of-care device. For this, the university has been
working with Mclennan to develop a portable prototype diagnostic device capable of performing a quick test from a small sample of blood.
THE INSTRUMENT IN OPERATION The project was funded by the National Institute for Health Research (NIHR) under the Invention for Innovation (i4i) programme (II-LS-1010-10045) which provides guided progression of innovative medical product prototypes via commercial development; aiming for eventual use in the clinical environment for the benefit of patients in the NHS.
With the sepsis instrument, the blood
sample is loaded into a multi layered disposable disc which is about the size of a CD. The single axis machine carries out high speed controlled ‘spinning’ of this to centrifugally separate the blood plasma and then performs precision indexing to rotate it through one or two revolutions to various positions, where chambers containing biomarked and unmarked ‘control’ plasma samples are presented for microfluidic examination.
TECHNOLOGY To meet the requirements, Mclennan supplied an open loop stepper motor drive - from the control requirements given, it was decided that an intelligent drive with I/O and maths capability could possibly take on most of the machine functions. Applied Motion Products’ (AMP) ST series intelligent microstepping drives met the demands. As the ST series stepper drive essentially
uses the same programming and has similar functionality to AMP’s servo range, it was an easy transition when the instrument was further developed, and servo motor control with high resolution
RAMPING UP THE DESIGN OF LINEAR ACTUATION
When looking for a linear actuator product to fold and unfold the ramps on its wheelchair accessible vehicles, a manufacturer turned to Warner Linear for a solution. The previous actuator needed high levels of force to manually retract in the event of a power failure, so the company wanted a solution that would better suit the application. In addition, however, the limited space available meant a parallel motor design could not be used, so an inline design was needed. To meet demands, Warner worked closely with the customer to design the I-Track actuator - an inline
design with a release clutch and narrow footprint. This requires less than 3kg of force to retract when the motor is disengaged. The I-Track is able to release the actuator’s rod when the power is off, so if there is an unexpected power failure, the ramp can be manually retracted quickly and with minimal effort. In addition, it features an overload protection of the motor in the event that the ramp becomes jammed. Now available to purchase from Warner Linear, the solution has a load capacity of 90kg, superior sealing, and components with enhanced corrosion resistance, the company explains.
Warner Linear T: 02380 733211
www.warnerlinear.com
For the blood testing instrument, Mclennan supplied technology including an open loop stepper motor drive. This is a pre-production model
position feedback was specified. It was, in fact, a deciding factor than the AMP stepper and servo versions were scalable. AMP SV7 series intelligent drives
combine many progressive features for digital servo control, including advanced current control and Ethernet communications, which proved useful for this application. Here, AMP’s ‘Q Programmer’ language proved beneficial. In addition, a simple LCD display and pushbutton panel connected to the drive is used to initiate and run the SV7 program, which includes data registers along with I/O for various functions including interaction with the microfluidic examination process developed by the University. Sample processing is completed automatically with the results displayed on screen. It would be possible to output this information to a PC for further use.
PROTOTYPING THE SOLUTION In the latest prototype version these same components are included in a miniaturised model. If continued, the project would be cost reduced, and for Mclennan it would be unlikely that the AMP SV7 intelligent drive, servomotor and encoder would be selected. However, through the capability to design and supply customised mechatronic solutions, the company may still play a role in the future of the instrument.
Mclennan Servo Supplies T: 08707 700700
www.mclennan.co.uk
/ DESIGNSOLUTIONS DESIGN SOLUTIONS | NOVEMBER 2015 25
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