Cursor

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Contents

The cursor project is an ElN project done at the end of the first semester. It consists in driving a DC motor which moves the cursor chariot with the help of a screw.

Cursor in Action

Components

The system consists of

Power circuit

The chariot DC motor is powered with 12 V. The power circuit contains an H-bridge controlled by digital signals. On the power board, a 5 V regulator generates the proper voltage for powering the FPGA board.

DC motor

The DC motor is controlled by a L6207 H-bridge driver.

Encoder

The angle of the screw can be measured with the help of an incremental encoder module. The model used on the assembly is a AEDB-9140-A12, which has 500 Counts Per Revolution (CPR).

Toplevel Design

There is a Empty and a Demo Toplevel Design. the Empty for the Students to create their own system and the Full is our example.

Specification

The basic specification is the following one:

  • On reset, the cursor moves to the start position given by a Hall sensor close to the DC motor.
  • When pos 1 button is pressed, the cursor has to accelerate towards position 1, advance with full speed, decelerate and stop at position 1, be it from the start position or from position 2.
  • When pos 2 button is pressed, the cursor has to accelerate towards position 2, advance with full speed, decelerate and stop at position 2.

The acceleration and deceleration ramps are a function of the position and not of the time. Indeed, it would be very difficult to know when to start decelerating to reach one of the positions if the deceleration was to be produced by a counter. The slope of the ramp has to be chosen such as the acceleration and deceleration distances are in the order of magnitude of 1 cm.

The positions to reach are:

  • position 1 = 8 cm
  • position 2 = 12 cm

The following figure represents the shape of the speed versus position:

Position Range Diagram
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