1. Applied Control Systems Robotics & Robotic Control

2. DC Motors Most common and cheapest Powered with two wires from source
Draws large amounts of current
Cannot be wired straight from a PIC
Does not offer accuracy or speed control

3. Stepper Motors Stepper has many electromagnets
Stepper controlled by sequential turning on and off of
magnets
Each pulse moves another step, providing a step angle
Example shows a step angle of 90°
Poor control with a large angle
Better step angle achieved with the toothed disc

4. Stepper motor operation

5. Stepper motor operation

6. Stepper motor operation

7. Stepper motor operation

8. Stepper Motors 3.6 degree step angle => 100 steps per revolution
25 teeth, 4 step= 1 tooth => 100 steps for 25teeth
Controlled using output Blocks on a PIC
Correct sequence essential
Reverse sequence - reverse motor

9. Servo motors Servo offers smoothest control Rotate to a specific point
Offer good torque and control
Ideal for powering robot arms etc.
However:
Degree of revolution is limited
Not suitable for applications which require
continuous rotation

10. Servo motors
Contain motor, gearbox, driver controller and potentiometer
Three wires - 0v, 5v and PIC signal
Potentiometer connected to gearbox - monitors movement
Provides feedback
If position is distorted - automatic correction
+ 5V

11. Servo motors Operation
Pulse Width Modulation (0.75ms to 2.25ms)
Pulse Width takes servo from 0° to 150° rotation
Continuous stream every 20ms
On programming block, pulse width and output pin
must be set.
Pulse width can also be expressed as a variable

12. Open and Closed Loop Control
All control systems contain three elements:
(i) The control
(ii) Current Amplifiers
(iii) Servo Motors
The control is the Brain - reads instruction
Current amplifier receives orders from brain and sends
required signal to the motor
Signal sent depends on the whether Open or Closed loop
control is used.

13. Open Loop Control For Open Loop Control:
The controller is told where the output device needs to be
Once the controller sends the signal to motor it does not
receive feedback to known if it has reached desired position
Open loop much cheaper than closed loop but less accurate

14. Open Loop Control

15. Closed Loop Control
Provided feedback to the control unit telling it the actual
position of the motor.
This actual position is found using an encoder.
The actual position is compared to the desired.
Position is changed if necessary

16. The Encoder
Encoders give the control unit information as to the actual
position of the motor.
Light shines through a slotted disc, the light sensor counts
the speed and number of breaks in the light.
Allows for the calculation of speed, direction and distance
travelled.

17. Closed Loop Control The desired value is compared to the actual value.
Comparator subtracts actual from desired.
The difference is the error which is fed to the controller
which generates a control action to eliminate the error.