Absolute encoders support treatment success in the operating theater

When physicians want to know what is going on inside a patient, they can use a variety of imaging processes to reveal the different tissue types, functions or structures in the body. The mobile C-arm from Ziehm Imaging utilizes advanced X-ray based technologies to guarantee a precise and efficient intraoperative visualization. To ensure a small battery in the movement sensor of a C-arm doesn't become a big problem in the operating theater, the medical technology company from Nuremberg trusts in a customized version of an absolute encoder from SICK.

Ziehm Imaging was founded in Nuremberg in 1972 and is specialized in the development, production and global marketing of C-arms as well as mobile X-ray-based imaging solutions that can be used to optimize clinical procedures. The company's medical devices, named after their characteristic shape, are moved around the patient on the operating table in different directions, angles and distances during an operation without the person being examined noticing anything. The excellent image quality, high level of flexibility, and mobility of C-arms, for example the Ziehm Vision RFD Hybrid Edition, help ensure an optimal treatment outcome in the operating theater. As a result, they are used worldwide in a wide variety of different clinical applications – there are currently more than 22,000 C-arms installed in over 80 countries and the number is growing by about 1,500 more devices annually.

"Our C-arms are not only used in spinal surgery, orthopedics and traumatology but also in vascular surgery and, increasingly often, in the areas of bronchoscopy and oncology, thereby satisfying the most stringent clinical requirements. Hospitals benefit from the low installation costs, the low radiation dose, and the high level of flexibility thanks to the mobility of the C-arms," explains Martin Ringholz from Ziehm Imaging. As the innovation leader's former product manager and now Director Global Marketing for mobile C-arms, he is an expert in mobile intraoperative imaging solutions, and therefore also with the associated technical requirements and day-to-day challenges. Probably the most important of these is avoiding potential failures in the operating theater.

Ensuring reliability in everyday clinical practice

And that's exactly the reason why in 2023 the product manager at Ziehm Imaging chose SICK to be their key supplier for absolute encoders. There had been quality issues with the absolute multiturn encoders they had been using until then or, to be more specific, the availability of a tiny component inside it: a battery. Its task was to maintain an electronic count of the number of revolutions – hence multiturn – even during power outages or when the system was switched off. If the battery fails, no more position values are available. "Since our C-arms can not only be moved by servomotors but also manually if necessary, i.e without the supply of power, the absolute position of the C-arm needs to be provided immediately to the device controller each time the motor is switched on again," explains Martin Ringholz. "The physician expects the full functionality of the C-arm to be available while an operation is in progress since, for example, operations on the heart can be highly critical for the patient's survival. The medical technology therefore needs to perform uncompromisingly and without distracting from the treatment."

The C-arms do indeed operate with the utmost reliability most of the time in normal clinical practice – the battery failures occurred in particular after long periods of non-use of the C-arms, when a replacement encoder was stored for a long time in a spare parts warehouse, or when encoders had to cope with transport or storage in climatically demanding conditions.

Multiturn drives instead of batteries: a customized version of the AFM60 SSI

With the AFM60 SSI absolute encoder, these causes of failure are a thing of the past. The rotary measurement system offers a maximum total resolution of up to 30 bits, a large selection of programmable parameters, good concentricity properties, and a compact housing design. "In particular, however, it uses a rugged mechanical drive for the multiturn counting and operates with the same consistent reliability regardless of periods of non-use and ambient conditions," says Martin Hummel, the responsible product manager at SICK. Martin Ringholz confirms that the high resolution and measurement accuracy are ideal for the demanding application in C-arms: "Thanks to this feature, the surgeon can, for example, use the Ziehm Vision RFD Hybrid Edition C-arm to perform smooth, fluid movements with no shuddering or after-vibrations and position the C-arm accurately for intraoperative imaging. This makes it possible, for example, to already verify the surgery results during the procedure." 

It was not only the functionality of the AFM60 SSI that impressed Ziehm Imaging, but also the possibility of a customer-specific configuration. The "Ziehm Imaging encoder", of which up to four are used per C-arm, was given a connecting cable pre-assembled to a custom length with a Molex plug as well as a customer-specific label specifying the firmware version of the encoder and bearing important product and medical technology related details for identification and traceability. 

Customization means customer satisfaction 

"In actual fact," says Martin Hummel, "customizing is one of our strengths because the ideal customer benefit is often only achieved with application-specific individualization." And the range of customization options is quite impressive: plugs, cable connections, cable lengths, wire and pin assignments, adapter flanges, mounting hole patterns, stator couplings, shafts of different lengths, diameters and designs, electrical interfaces with customer-specific parameterization and communication interface or software – and, of course, combinations of these. "Customer need rather than catalog choices," summarizes the SICK product manager, "almost anything is possible when it comes to individualizing an encoder and ensuring the solution is perfectly tailored to customer requirements, as Ziehm Imaging does."

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