Very High-Resolution Application Solutions with QR12 and LP12 Sine/Cosine Incremental Encoder Output
February 14, 2020
Incremental rotary encoder resolution equals the number of measuring units in one revolution of the shaft, and is measured in PPR (pulses per revolution). Because incremental rotary encoders have A/B outputs, resolution is 4 times the PPR: accounting for 2 edges each on the A channel and B channel.
High-resolution incremental encoders are used in applications where precise control is required, especially in positioning systems with constant velocity control such as robotics.
For applications that require extremely high resolution, OEM equipment designers have historically chosen to incorporate absolute encoders into their designs. Quantum Devices’ QR12 and LP12 sine/cosine encoders are now challenging the perception that absolute encoders are the only high-resolution solution available to the industry.
High resolution rotary encoder advantages
The benefits of QR12 or LP12 sine/cosine signal is the ability to divide the signal period of the analog A sine and B cosine into additional positions. This is accomplished within an associated drive logic to resolve proportional positional states occurring on the analog waveforms.
The QR12 and LP12 sine/cosine option can be used to reliably perform high resolution motion control functions in a wide variety of OEM equipment. The benefit of this approach is a lower cost incremental encoder solution when compared to the traditional absolute encoder.
Interpolation technique plus drive delivers higher resolutions
The chart below illustrates a 4x interpolation of the signal period. The additional positional states on the analog waveforms are marked with circles. In this example, there are 16 points for each signal period. Each of these points is digitized by the electronics, providing 16 quadrature positions for each signal period. This provides a 4x increase in resolution over a fundamental conversion of the analog signals shown.
High-resolution encoder technology demonstration
By using this interpolation technique, a Quantum Devices’ QR12 or LP12 sine/cosine encoder and a drive such as Copley’s Accelnet Plus is able to achieve over 20 million counts per revolution. The QR12 or LP12 sine/cosine encoder outputs up to 1250 sine/cosine fundamental analog signals per revolution with an amplitude of 1-volt peak to peak. When these signals are interpolated with the Accelnet Plus drive you are able to achieve resolutions better than 24 bit per revolution. Copley demonstrates this high-resolution technology pairing in the following product videos.