Design and optimization of a signal converter for incremental encoders : A study about maximizing the boundary limits of quadrature pulse conversion

University essay from KTH/Maskinkonstruktion (Inst.)

Author: Anton Dahlqvist; Victor Karlsson; [2016]

Keywords: ;

Abstract: This project was carried out during spring 2016 in collaboration with BOSCH Rexroth, Mellansel, and aimed to investigate the possibility of implementing a converter with the ability to scale incremental pulse resolution and also convert the velocity to a 4-20mA current loop reference. An investigation on how a fault tolerance mechanism could be implemented to increase the dependability of the encoder was done and the out-coming results were implemented. The software and hardware were revised and optimized to facilitate a future encapsulation, and still keep the converter reprogrammable. A background study was performed during 8 continuous weeks to acquire enough knowledge about possible conversion techniques, to nally derive these down to two for further testing. The nal conversion algorithms were multiplication and extrapolation techniques, which would be utilized to scale the pulse signal. The background study also involved writing ecient c code and a general study about fault tolerance. With the information from the background study, two algorithms were implemented on a specially designed hardware platform. Tests were designed from the requirements given from Bosch and these were performed at a test rig with a magnetic ring encoder connected to dSPACE control desk. A converter that met the criteria was designed and implemented. The test results showed that the most successful algorithm implemented was the multiplication algorithm, optimized with adaptive resolution, which decreases the input update rate with increasing speed. Although extrapolation caused more noiseand also a static error on the signal, this is the one leaving most room for future optimizations. Dependability means were implemented which stops the converter from outputting erroneous pulses, and also to reboot the software in case of invalid inputs. Whether this made the converter fail-safe or not is dicult to tell since fail-safe is a vague term and applies di erent for each situation. It was concluded that the implemented fault tolerance mechanism worked though. The software and hardware were designed so reprogramming is possible even though the component is casted. This particular function was not tested since the development board did not provide access to the required pins.

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