Assuring the reliability of a control display for medical applications.

System Reliability, Quality, Assurance, Medical Technology

Fig. 1: Control display by Dräger combined with a ventilator (photo: Dräger)

The Dräger Company develops and produces medical devices for various applications. Control displays, such as those used in hospitals to control ventilators and other peripherals, are the subject of the present investigation. At the same time, these assist the staff to display the patient’s vital data or operating parameters of the device, Fig. 1. With regard to further product development in the future, the aim is to first develop and subsequently implement a concept for further assuring reliability.

Definition of reliability targets

The first step in developing the concept was to define the targets to be achieved in respect of reliability with the customer. Dräger aims not to exceed a certain number of returns from the field. Of interest in the investigations are scenarios which lead to a change in perception of the device’s performance. Examples of this are that the sensitivity levels of the control elements or the touch display deteriorate or that the brightness of the LEDs might change.

System and use analysis

As can be seen in Fig. 1, the display to be investigated is made up of various components: touch display, pushbuttons and knobs, ports (e.g. USB), internal electronics, etc. The device also interacts with the peripheral device to be operated (a ventilator in this case) via a data line. A complete systems analysis was carried out for the entire system by first examining each of these main components qualitatively in respect of detailed construction, functionality and possible failure modes. Environmental and load conditions were derived from the conditions of use expected for the display so that it was possible to obtain a detailed picture of any mechanical, thermal, electrical and also chemical loads occurring. 

Based on these findings, a two-pronged investigation strategy was found to be effective. On the one hand, existing FMEA data, developed partly by suppliers, were merged using the established failure modes and effects analysis (FMEA), supplemented as needed and evaluated with the focus on possible failure states in field operation, Fig. 2. An experimental environmental simulation is also carried out to replicate the expected vibration, temperature and climatic loads, Fig. 3. Customized test setups are designed specifically to investigate product functions classified as functionally critical, e.g. the touch user interface, and special verification tests are conducted. The findings regarding possible design weaknesses are to be fed back continuously into the development process in order to achieve the required reliability targets in the field.

Concept for assuring reliability

Based on these findings, we defined a two-pronged investigation strategy that was found to be effective. On the one hand, existing FMEA data inventories, developed partly by suppliers, were merged using the established failure modes and effects analysis (FMEA), supplemented as needed and evaluated with the focus on possible errors in field operation, Fig. 2. An experimental environmental simulation was also carried out to replicate the expected vibration, temperature and climatic loads, Fig. 3. Customized test setups will be designed specifically to investigate product functions classified as functionally critical, e.g. the touch user interface, and special verification tests will be conducted. The findings regarding possible design vulnerabilities are to be fed back continuously into the development process in order to achieve the required reliability targets in the field..

Autor
»Thanks to the LBF’s system-wide, cross-method skills ranging from FMEA to experimental verification, it is possible to develop and also implement reliability concepts for our products according to the “single source principle".« Martin Meyer, Reliability Engineer, Drägerwerk AG & Co. KGaA

Contact