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Computer Science

Accurate Quadrature Encoder Decoding Using Programmable Logic

Profile image of Yassen GorbounovYassen Gorbounov

2016

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5 pages

Abstract

the quadrature encoder (or incremental detector) is amongst the most widely used positional feedback devices for both rotational and linear motion machines. It is well known that in conventional circuits for quadrature signals decoding, an error emerges during the direction change of the sensor movement. In some situations this error can be accumulative but in any case it provokes a position error, that is equal to the resolution (one pulse) of the sensor. A corrective algorithm is proposed here that fully eliminates this type of error. It is an improvement over a previous research of the author which is much simpler and resource saving without compromising the performance of the device. A Xilinx CPLD platform has been chosen for the experiments. The inherent parallelism of programmable logic devices permits a multi-channel CNC machine to be fully served by a single chip. This approach outperforms the capabilities of any conventional microcontroller available on the market.

Key takeaways
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  1. The proposed corrective algorithm eliminates positional errors during quadrature encoder direction changes.
  2. Eight specific erroneous situations can occur during direction reversal of quadrature encoders.
  3. The implementation utilizes a Xilinx CPLD, optimizing resource usage by 17.65% compared to previous designs.
  4. The algorithm ensures error-free operation, crucial for high precision servo drive systems.
  5. Programmable logic devices can support multiple CNC axes, outperforming traditional microcontroller solutions.
Figures (13)
When Dir=1 the direction of the movement is positive and when Dir=0 - it is negative. As can be seen in the figure Figure 4 A conventional direction identification circuit and the emerging error
When Dir=1 the direction of the movement is positive and when Dir=0 - it is negative. As can be seen in the figure Figure 4 A conventional direction identification circuit and the emerging error
There exist many solutions on the market that deal with the decoding of incremental encoders. Some of them are Figure 5 The conventional device block diagram
There exist many solutions on the market that deal with the decoding of incremental encoders. Some of them are Figure 5 The conventional device block diagram
Figure 7 The reverse situations, emerging errors during the positive edge
Figure 7 The reverse situations, emerging errors during the positive edge
Another four happen on positive clock transition which is shown in fig.7. Figure 6 The reverse situations, emerging errors dur- ng the negative edge
Another four happen on positive clock transition which is shown in fig.7. Figure 6 The reverse situations, emerging errors dur- ng the negative edge
Finally, the quadrupled frequency and the correct direc- tion signals are used to drive a multiplexer circuit that out- Figure 10 Corrective and output forming circuit
Finally, the quadrupled frequency and the correct direc- tion signals are used to drive a multiplexer circuit that out- Figure 10 Corrective and output forming circuit
Figure 9 Direction reset circuit Figure 8 Frequency quadrupling and erroneous direction detector circuit
Figure 9 Direction reset circuit Figure 8 Frequency quadrupling and erroneous direction detector circuit
Figure 14 Case Delta - backward-forward transition Figure 13 Case Gamma - forward-backward transition
Figure 14 Case Delta - backward-forward transition Figure 13 Case Gamma - forward-backward transition
Figure 12 Case Beta - backward -forward transition Figure 11 Case Alpha - forward-backward transition
Figure 12 Case Beta - backward -forward transition Figure 11 Case Alpha - forward-backward transition
Figure 15 Case Epsilon - forward-backward transition
Figure 15 Case Epsilon - forward-backward transition
Figure 16 Case Zeta - backward-forward transition
Figure 16 Case Zeta - backward-forward transition
Figure 18 Case Theta - backward-forward transition Figure 17 Case Eta - forward-backward transition
Figure 18 Case Theta - backward-forward transition Figure 17 Case Eta - forward-backward transition

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