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Encoder

Measure incremental position and direction of motor connected to EV3 brick

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Add-On Required: This feature requires the Simulink Support Package for LEGO MINDSTORMS EV3 Hardware add-on.

  • Encoder block

Libraries:
Simulink Support Package for LEGO MINDSTORMS EV3 Hardware

Description

Use the Encoder block to measure the incremental wheel rotation of the motor connected to an EV3 brick in degrees. Every increment in the tick count of the encoder indicates that the motor is rotating clockwise. Every decrement in the tick count of the encoder indicates that the motor is rotating counterclockwise. The total tick count represents the incremental position of the rotating motor.

You can reset the encoder readings from the block using the Reset mode parameter in the block parameters dialog box.

You can use the Motor block with the Encoder block.

During simulations without hardware, this block emits zeros. See Block Produces Zeros or Does Nothing in Simulation.

Ports

Input

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Use this input port to reset the Encoder block tick counter.

When the value of the signal at the input port is 0, the block outputs the total tick count it reads from the encoder. In this case, the block output is the same as in the No reset mode. When the value of the signal at the input port is a nonzero value, the block outputs the number of ticks it reads from the encoder at the at the sample time you set in the Sample time parameter. In this case, the block output is the same as in the Reset at each Sample time mode.

Dependencies

To enable this port, set Reset mode to Reset by external signal.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean

Output

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The block outputs the relative change in the position of the rotating motor in ticks.

Data Types: int32

Parameters

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Select the EV3 brick output port to which the motor is connected. If your Simulink® model contains both the Motor and Encoder blocks, set the EV3 brick output port parameter in both the blocks to the same port.

The block supports three reset modes.

  • No reset — The block outputs the total tick count it reads from the encoder.

  • Reset at each Sample time — The block outputs the number of ticks it reads from the encoder at the sample time you set in the Sample time parameter.

  • Reset by external signal — When you set the parameter to this mode, an input port becomes available. In this mode, when the value of the signal at the input port is 0, the block output is the same as in the No reset mode. When the value of the signal at the input port is a nonzero value, the block output is the same as in the Reset at each sample time mode.

Assume that the encoder wheel that you have connected to your EV3 brick has 90 slots, which means that the encoder tick count is 1 for every 4 degrees of rotation. Assume that the block sample time is 1 second and the tick count at time instant T = 0 is 0. This table shows the tick counts that the block outputs in the three modes.

LegoEV3 reset mode image

  • Between T = 0 and T = 1, assume that the encoder rotates 20 degrees clockwise.

    • No reset — The output is 20/4 = 5

    • Reset at each sample time — Assume that the encoder has rotated 20 degrees at the given sample time, so the output is 20/4 = 5

    • Reset by external signal — Assume that the value of the external signal is 0, so the count is calculated as in the No reset mode, and the output is 20/4 = 5

  • Between T = 1 and T = 2, assume that the encoder rotates 40 degrees clockwise.

    • No reset — In this mode, the block output at any time instant is the sum of the previous count and the current count, so the output is 5+40/4 = 15

    • Reset at each sample time — Assume that the encoder has rotated 40 degrees at the given sample time, so the output is 40/4 = 10

    • Reset by external signal — Assume that the value of the external signal is 0, so the block calculates the count as in the No reset mode, and the output is 5+40/4 = 15

  • Between T = 3 and T = 4, assume that the encoder rotates 20 degrees counterclockwise.

    • No reset — In this mode, the block output at any time instant is the sum of the previous count and the current count, so the output is 30–20/4 = 25

    • Reset at each sample time — Assume that the encoder has rotated 20 degree counterclockwise at the given sample time, so the output is – 20/4 = – 5

    • Reset by external signal — Assume that the value of the external signal is a nonzero value, so the block calculates the count as in the Reset at each sample time mode, and the output is – 20/4 = – 5

Specify the frequency of how often the block reads data from the encoder. Shorter sample times, such as 0.01, may produce unreliable measurements.

Smaller sample times require the processor to complete the same number of instructions in less time, which can cause task overruns.

Version History

Introduced in R2012a

See Also

Topics

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