Evaluation of three optical-encoder-based speed estimation methods for motion control.

Abstract

Three speed estimation methodologies: pulse count, elapsed time, and constant sample-time digital tachometer (CSDT) methods, used with optical incremental encoders, are implemented and compared in a closed-loop system setup using a specialised Analog Devices CM403f DSP. Dedicated hardware for quadrature encoders on the DSP facilitates the implementation of advanced speed estimation methods, such as the CSDT, by minimising the delay resulting from software intervention. The error of each methodology is evaluated theoretically and experimentally. The CSDT has limited error over all its speed range. The error of the elapsed time method increases as the speed increases. On the contrary, the relative error of the pulse count method (which is often substantial) decreases with increased speed. Several filtering techniques can be used to reduce the error of the elapsed time method; here an oversampling technique is implemented with that aim.

Keywords

• closed loop systems
• tachometers
• digital signal processing chips
• signal sampling
• motion control
• velocity control
• digital control
• filtering theory
• optical-encoder-based speed estimation methods
• motion control
• speed estimation methodologies
• constant sample-time digital tachometer methods
• CSDT
• optical incremental encoders
• quadrature encoders
• advanced speed estimation methods
• relative error
• pulse count method
• elapsed time method
• closed-loop system
• elapsed time
• specialised analogue devices CM403f DSP
• filtering techniques
• oversampling technique
• delay minimisation
• software intervention
• error reduction