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Targeting tumours: Maxon drive systems contribute to progress in radiation therapy

Targeting tumours: Maxon drive systems contribute to progress in radiation therapy
For medical scientists involved in the development of radiation therapy, a constant challenge has been to maximise the treatment's impact on tumours while minimising damage to healthy tissue. In its HD120 MLC computerised radiation machine, Varian Medical Systems has provided an effective solution, with a little help from 120 Maxon Motor drives, gearheads and encoders.

Also known as a 'high definition multileaf collimator', the machine features 120 individually adjustable tungsten leaves which can be positioned to form an aperture perfectly shaped to direct the radiation in a pattern that exactly matches the shape of the tumour. Furthermore, the radiation can be delivered from different angles to match the contours of the tumour. With this level of control, the radiation intensity can be adjusted to deliver a higher dose to more aggressive areas of the tumour and a lower dose around sensitive healthy tissue.

Varian Medical Systems chose 120 Maxon brushless DC (electronically commutated) motors with diameters of 8, 10 or 13mm to move the leaves. Each is equipped with a fully compatible Maxon planetary gearhead and encoder, which takes the length of the individual drive systems to between 17.0 and 24.6mm. This allows all 120 motors to fit into an area measuring just 40cm by 40cm. Despite their compact design, the motors are remarkably powerful, thanks largely to their high-quality neodymium magnets.

The shape of the aperture, formed by positioning of the leaves, needs to be adjusted quickly and precisely in response to pre-programmed data. With their patented ironless winding, Maxon motors have no magnetic detent, which means their movements can be controlled with great accuracy.

High torque is needed to overcome friction within the system of synchronously adjusting leaves. The performance of the Maxon drive systems ranges between 0.5 and 1.5 Watts, and the nominal torque goes up to 1.61mNm. In fact, matching Maxon gearheads with reduction ratios from 4:1 to 1024:1 can increase their torque to 200mNm. Efficiency and acceleration are also high.

"The properties of our motors and associated components ticked every box in the designers' wish list," says Angelo Guttoriello, CEO of Maxon Motor UK. "Needless to say, they also wanted a long service life and reliable operation.  In applications like theirs, where component failure can cost lives, the reputation of Maxon products for total reliability is highly valued."
 

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