Compact brushless DC motor selected for medical instrument

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Karen Whittaker of maxon motor interviews Pedrum Kamali, of the Royal Surrey County Hospital, to find out more about an interesting application for one of maxon's compact brushless DC motors in a medical instrument.

Compact brushless DC motor selected for medical instrumentHow did you come to the industry?

After completing my BSc in Physics, at the University of Surrey, I completed a self-funded MSc in Medical Physics. I then applied to the NHS Clinical Scientist scheme in 2010 and was successfully awarded a trainee position at the Royal Surrey County Hospital (RSCH) within Medical Physics. Shortly after starting the scheme I was employed as a permanent member of staff. My role as a Diagnostic Imaging Medical Physicist allows me to balance routine duties along with a variety of research and development projects.

How did you start using maxon electric motors?

One of the projects included developing and implementing an in-house built Doppler phantom, which led me to the introduction of maxon motor UK Ltd. The Doppler phantom will be used to test the calibration of blood velocity measurements that ultrasound machines provide. To do this we have created a phantom filled with water, that uses a maxon motor to rotate a blood-like mass at a calibrated velocity, similarly experienced in humans. That way we can use clinical ultrasound scanners to measure the velocity of the calibrated blood-like mass to test the scanner velocity measurement accuracy.

Tell us about your organisation.

My department within the Radiation Protection Service is made up of six physicists, three technologists and three trainee physicists, all working to provide medical physics support to a large region within the UK. The work we cover includes testing and optimising medical imaging systems, such as computed tomography scanners, mammography x-ray units, ultrasound scanners and a large number of other imaging modalities, as well as providing radiation protection advice to a number of medical facilities. Our work covers a number of sites across the country, including NHS and private hospitals, dentists, vets and others, including a hospital in Gibraltar.

Why did you choose maxon motor?

One of the requirements of our project was to use a reliable and robust motor, which had the ability to be programmed and fine-tuned to meet the requirements of published guidance on ultrasound testing. The type of work required for the project, and the equipment we were purchasing, was new territory for us and therefore the technical support, along with the standard of equipment provided, was what attracted us to maxon motor UK Ltd, over their competitors.

How have you found working with maxon?

maxon provided us with a technical support contact who I have spoken to numerous times over the past few years. Each time I have spoken with the technical support team they have been extremely helpful and almost always solved my issues. When this has not been possible alternative support has been offered, including a visit to the head office where I had a free one-to-one which solved our issues.

maxon's support has been second to none.

Without maxon's advice the project would never have taken off. Their support really has helped us troubleshoot and to understand our system more.

Mark Gibbons, a Technical Sales Engineer at maxon motor, comments: "Pedrum contacted me about the issue he was having and I invited him to visit maxon UK, as he confessed not to be an expert with motion control systems and felt he would benefit from some hands-on assistance. We looked into the issue and the problem was diagnosed quickly and a solution provided within an hour.

"The brushless DC motor's speed control needed to curtail the Doppler calibration and would have to be extremely accurate, independent of the load the motor would be under. The supplier's tool to calibrate this instrument was very expensive. An in-house solution would offer the hospital a cost saving, as well as the convenience to calibrate the equipment onsite and not have to send the units away. The motor would need to be controlled via the PC as the hospital wanted to avoid the use of any customised control front end and it would be far more convenient if a PC interface was available.

"The Doppler phantom uses a 22mm brushless DC motor from the maxon EC-max range, which offers good reliability and product longevity. As the constant speed of the phantom is paramount to the calibration of the Doppler instrument a 512-count line driven MR (magneto resistive) encoder was specified for its compactness and direct compatibility with the EPOS motor controller. A gearhead was added to the assembly for two reasons; there was a requirement for very slow speeds that would have proven difficult with a direct drive and the combination would be attached to a belt under tension which would exert an axial load.

"The EPOS positioning motor controllers were selected to provide control via a PC terminal through the on-board USB connection. The EPOS devices have a USB-to-CAN gateway that allows communication to the device without the expense of a CAN interface card on the user's PC. This allows the user to control and monitor the motion of the phantom without the expense of a custom interface or HMI using the native hardware and the free EPOS studio software."

What have been the highlights and lowlights of the current project?

The highlights have been seeing the prototype up and running and knowing we were on the right track. The lowlights of the project was finding out that our phantom was not strong enough to withstand the forces of the motor and seeing it collapse under its own force in the initial stages.

What is the next step for your organisation?

We would like to continue developing our Quality Assurance programme, particularly in the field of ultrasound. This is an area that is less developed, in comparison to x-ray imaging modalities, and therefore provides us with a number of challenges.

How do you see the industry evolving over the next five years?

The NHS faces some tough times over the next five years. Most of our work will be to optimise our systems to make them more cost-effective and time-efficient, whilst trying to maintain clinical quality. To do this we will need to improve our testing methods and identify areas of calibration and development. The use of ultrasound systems is rapidly expanding and therefore our systems of quality assurance will have to focus on catching up with the rapid advancement of imaging technology.

Follow the link for more information about maxon EC-max brushless DC motors.

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