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CAN and CANopen in Medical Systems

by Frank Pastors | Dec 23, 2014

Benefits and current implementation

 

The history of CAN and CANopen in medical technology goes back many years. As early as 1992 the company Philips Medical Systems recognized the advantages of the CAN technology and developed a protocol for use in their medical tables and X-ray systems. This first approach, the CMS protocol, served in the following years as a scaffold for the CAL protocol specified by "CAN in Automation e.V." which ultimately found its fulfillment in today's CANopen protocol. CANopen is a mature and safe communication standard which has a variety of available device profiles, not least for medical devices, and is used by a wide range of equipment manufacturers.

 

CAN und CANopen in der Medizintechnik

What ARE CAN and CANopen ABLE TO DO, others can not?

 

The advantages which result to device manufacturers through the use of a bus system, are easily recognizable considering that modern medical equipment nowadays consist of a number of modules that must be connected to a functioning overall system. Individual system components, such as X-ray generators, patient tables or injectors can – with the use of a standardized bus system – be independently developed, modular connected and controlled from a central point. This saves development costs and enables the universal and scalable deployment of components in different systems. It also reduces the number of cables to a considerable extent.

A decisive advantage of CANopen as the communication protocol is the availability of profiles for a variety of medical devices, which ensures the interoperability of the components in an easy way.

Due to the nature of CAN, CANopen provides a very high error robustness, short waiting and error-recovery times, a robust data transmission, a variety of possibilities for the modularization of systems and networks, plug & play support and standardized system services.

Furthermore, the CAN and CANopen technology already is approved by TÜV Germany and the FDA in the US for use in medical systems, since here a number of approved applications are using this technology.

CAN and CANopen offer a very good price / performance ratio. Due to “slim” software protocol packages only small demands are placed on the microcontroller of each node; in addition the necessary CAN controller is already included in many popular microcontrollers for free.

The actual interconnection can, in most cases, be done without additional components (like e.g. switches) which saves costs too. Nonetheless, even complex topologies can be realized if necessary, through the use of topology components such as bridges and repeaters. Topology components also allow the electrical isolation of individual network sections, as on patient safety or for the change of the transmission medium (optical fiber, Ethernet, Bluetooth, or other serial protocols). Combinations of several sub networks, wireless transmission or interference sensitive communication thereby can be easily implemented.

In addition to the cost advantage and the low demands on performance and memory CAN also has advantages in terms of data security and data integrity within the network, the rapid transmission of high-priority information, and the automatic retransmission of messages in case of transmission errors.

All these features are part of CAN itself, so they do not need to be treated by the protocol or application software.

The performance of CAN and CANopen is more than sufficient for many applications, which makes the use of more expensive Ethernet-based communication solutions unnecessary. Nevertheless, the use of Ethernet-based technologies in medical systems can be useful in certain areas, for example, for transferring large amounts of data (image or video data), which are not time-critical and are typically exchanged by a peer-to-peer connection via TCP/IP between transmitter and receiver.

 

APPLICATIONS OF DATA COMMUNICATION IN MEDICAL

When talking about medical technology, it’s mostly of imaging or invasive systems. And indeed, there is a clear trend to connect the devices of operating rooms, intensive care units or other treatment rooms with each other and thus to be able to use the information globally.

Position data of instruments are determined during an operation via navigation systems, verified by X-ray or ultrasound images and often also correlated with preoperative CT data. When a contrast agent is required this can be infused through an automatic injector at the right time. These concepts of integrated operating rooms are the subject of numerous research projects.

Other areas in medical technology are less obvious, but equally important. So among other pumps are controlled in dialysis devices via CAN. Another peripheral area of medical technology is laboratory automation. Blood and other samples are nowadays hardly examined manually.  Much of it is processed completely automated. This is partly due to the huge quantities and the associated error rate. Thus, the samples are loaded into a holder, the ID read from the test tube, more empty test tubes provided with this ID and the sample split on it. Then the actual test can be performed. The evaluation and the protocol to the respective ID are then created automatically. Communication between the conveyor belts, robots, centrifuges, palletizing etc. is implemented in many cases with CAN and CANopen. The system structure and requirements are often very similar to those from classical automation applications such as pick and place machines. Thus standard components from the industrial sector are generally used.