Cursor
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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.
Specification
Function
The basic specification is the following one:
- When restart button is pressed, 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
Circuit
- The DC motor is controlled by three signals
motorOn
,side1
,side2
. Its speed is controlled by a PWM-modulation. - There are two Hall-Senors at the ends of the rail, which detect the presence of the cursor chariot (
sensor1
,sensor2
). - The Encoder Module is used to count the position of the cursor chariot. Its three encoder outputs,
encoderA
,encoderB
andencoderI
, allow to follow the angle of the screw. - Three Buttons are used to control the system:
restart
,go1
andgo2
; an additional button,setPoint
, can be used for optional functionality - The
testOut
pins can be used to output additional information from the system, e.g. for debug or in order to drive the LEDs
The Empty Toplevel Design shows all the signals connected to the FPGA board.
Components
The system consists of
- a chariot assembly
- an FPGA prototyping board
- a control board with 4 buttons and 8 LEDs
- a power board driving the motor
Motor control circuit
The chariot DC motor is powered with 12 V. The power board 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).
Hall sensors
The hall sensor is a switch which is working with the hall effect. If a magnet is close to the sensor, the contact closes. For the projects 2 hall sensors are used to identify the left and right limits of the chariot.
FPGA board
The main board is called FPGA-EBS and is the school's main development board. It features many different interfaces and a Xilinx Spartan xc3s500e FPGA.
For additional information see the FPGA-EBS page.
Buttons and LEDs
The Buttons and Leds board is to be attached to the FPGA board. It has 4 buttons and 8 leds which can be used in the design.
Getting started
In order to start the projects you should do the following:
- Read carefully the specifications above
- Consult the guides for the first steps
Additional Information
Additional informations for collaborators