N.K. Boggarpu

Publications (2)1.21 Total impact

• Source

  Available from: ac.uk

  Article: New Learning Algorithm for High-Quality Velocity Measurement and Control When Using Low-Cost Optical Encoders

  N.K. Boggarpu, R.C. Kavanagh
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  ABSTRACT: A new compensation method that can greatly reduce the slit errors (i.e., transition location errors) due to nonidealities in optical incremental encoders caused by manufacturing limitations in the code wheel, optical components, and analog circuitry is presented. An M/T-type constant sample-time digital tachometer (CSDT), which involves pulse-count and high-frequency timer measurement, effectively time-stamps the encoder transitions. Using CSDT-based data, encoder compensation techniques that improve velocity measurement accuracy are presented. These do not require precise knowledge of the shaft velocity, thereby eliminating the need for high-accuracy reference equipment. During the initial learning stage (possibly performed in situ ), slit errors are calculated through pseudoinverse-based solutions of simple approximate linear equations or an iterative method that requires very little memory storage. Subsequent operation of the motion system utilizes adjusted slit positions for more accurate velocity calculation. The performance improvement in velocity measurement is experimentally demonstrated using motor drive systems, each of which includes a field-programmable gate array (FPGA) and a digital signal processor (DSP). Results from open-loop velocity measurement and closed-loop servo control applications are given, with the latter highlighting the resultant reduction in high-frequency motor torque. Slit error reductions in the range of 60%-86% are obtained (typically approximately 80%) with a similar improvement in velocity measurement error.
  IEEE Transactions on Instrumentation and Measurement 04/2010; · 1.21 Impact Factor
• Conference Proceeding: New Learning Algorithm for High-Quality Velocity Measurement from Low-Cost Optical Encoders

  N.K. Boggarpu, R.C. Kavanagh
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  ABSTRACT: A novel compensation method to greatly reduce the slit errors (i.e. code wheel errors) that are caused by non-idealites in optical incremental encoders is proposed in this paper. Manufacturing limitations in the code wheel, optical components and analog circuitry hinder the use of cheaper encoders for high-end applications. To measure the shaft velocity, the M/T-type constant sample-time digital tachometer (CSDT) method, which involves both pulse-count and auxiliary timer measurement, is employed to effectively time-stamp the encoder transitions, thereby removing the quantization error that is often associated with the sampling of digital positions. However, the accuracy of the velocity calculation is usually compromised by encoder errors. This paper presents a two-stage, software solution to the problem. During the initial learning stage (which can be performed in-situ without the use of any expensive, high-accuracy reference equipment), the slit errors are calculated using the information obtained from the CSDT, while subsequent operation of the motion system utilizes adjusted edge positions for velocity calculation. The performance improvement in velocity measurement associated with the learning algorithm is demonstrated using both a simulation model and an experimental implementation that utilizes a three-channel, optical incremental encoder, field-programmable gate array (FPGA) and digital signal processor (DSP).
  Instrumentation and Measurement Technology Conference Proceedings, 2008. IMTC 2008. IEEE; 06/2008