Utveckling och utvärdering av en funktionssäker pulsgivare : Konkretisering och vidareutveckling av en patenterad lösning vilken ämnas detektera låsta lager

Sammanfattning: An emerging industrial automation has led to higher demands required for construction of encoders to ensure functionality of automated processes. The main purpose of the encoder is to provide data which indicates the condition of a drive system. If the encoder is found to be defective, there is a risk of causing a critical discontinuity in the drive system increasing the risk of causing a dangerous situation. For rotary inductive encoders, ball bearing failure is the main reason for encoder failure. Since the effectiveness of a lubricant decreases over time, continued operation of the encoder will lead to wear increasing frictional torque in the ball bearings. The bearings will eventually lose their ability to rotate resulting in blocked bearings. This thesis has been executed at the request of Leine & Linde with the aim of concretising and further developing a patented conceptual solution initiated by the company. A solution that aims to mechanically register lost rotational ability of the ball bearings in a rotary inductive encoder. As a result, maintenance or replacement of defective ball bearings can be scheduled upon indication of wear rather than after a malfunction has occurred contributing to increased functional safety. This has led to formulation of two research questions:  RQ1: How can a mechanical solution be designed to enable the detection of blocked bearings in a rotary inductive encoder and thereby increase the functional safety of a control system? RQ2: Which aspects should be taken into account when designing industrial rotary encoders with inductive measurement technique on which the functional safety increases?  This study includes two sub-studies which were executed within a period of 20 weeks: 1) theoretical study; 2) empirical study. The theoretical sub-study is based on a literature study of published research articles as well as relevant company documents in functional safety, operational monitoring and control as well as flexible and robust constructions. The empirical study consists of a case study which is based on an exploratory iterative product development process which, after evaluating a patented solution, examined six alternative solutions with regard to established requirements. Empirical data has primarily been collected through Computer-Aided Design (CAD), empirical test observations of 3D-printed functional prototypes as well as a Computer Numerical Control (CNC) produced functional prototype. Additionally, failure effect analyses (FMEA) were executed. All sub-results have been verified through discussions with relevant actors at the case company.  The result of the study has showed a working function including a spring force which, integrated in the case company’s general product architecture, enables an extended distance of 1.5 mm between rotor and stator in case of blocked bearings. The given distance variation, within an inductive encoder, is assumed to produce deviating electromagnetic values which can be registered by connected software. However, functional performance depends on external circumstances where a correct installation and application is assumed. An analysis of theoretical and empirical studies has shown seven factors which are seen to affect functional safety: 1) product architecture; 2) product structure; 3) risk assessment; 4) material & geometry requirements; 5) maintenance & redundancy; 6) product variability; 7) spring application. An essential conclusion of executed study refer to mechanical springs which may be incompatible with functional safety constructions due to risk of fatigue failure. Thus, it is recommended to further investigate whether a solution without a spring is possible.