Lab #3 Stepper Position Experiments
Introduction:
After this lab, the user will have gathered basic knowledge on how to control the stepper as a positional device. New features to learn are amount of steps to rotate and stepper homing.
Objectives:
- To control the direction of rotation of a stepper utilizing the SS-ST68 controller.
- To control the speed at which the stepper rotates.
- To control the amount of steps the stepper moves.
- To home the stepper using a home sensor input.
Making it rotate until...
You are already a rotation expert. Controlling speed is easy. And direction, even more! And that is all because the Super Stepper controller takes care of all the intricate details about stepper operation. But what if we want to move the stepper up to a point with predefined precission?
Using the stepper as a rotation device and stopping it by means of a external sensor, which tells the computer to send the stop command, is certainly doable, but of course adds complexity. What if the controller could do it for us? That is why the Super Stepper controller SS-ST68 has a set of commands purposedly design to cover such kind of scenarios!
 |
- Set up your system as you have already learned (power everything up, make sure the serial communication link is open and open a stepper window).
- Press the “Move CW Steps” button on the “Turn CW Speed, Distance” frame.
- Wait a few seconds until the stepper stops.
Lets study what happened. The motor moved at the speed specified under the “Speed” parameter text box. Eventually it stopped. Why? In the “Turn CW Speed, Distance” frame there is a new text box called “Steps”. The box holds the amount of steps the motor has been commanded to run.
Once the amount of steps have been processed, the controller knows and stops the motor. Which is by the way, still powered making it kind of hard to move the shaft. But it will move no more, until a new command arrive, that is.
This feature is very powerful as it gives the user the ability to move something a predetermined distance without having to measure whether the motor has moved there or not. Of course we have to assume that the motor did move, but if the mechanical application is under loaded, the motor should not loose steps. In which case, be certain that the load has moved to the commanded position!
Homing the stepper:
The explained behavior is great and should work flawlessly most of the time. But precisse motion and position is totally useless if the motor is on an unknown position. Let say you want to move the stepper so that a gripper load fetches an item 10 inches away. Where is the gripper? Is it close or far? If you don’t know where the gripper is, how can you specify a distance so that it moves to the proper designated spot?
 |
That is why we need some form of position initialization, or homing. The Super Stepper controller incorporates such feature by the use of a home sensor input. The picture above shows a good example of how to use a position switch as a home sensor.
The controller samples the input and stops the motor as soon as the sensor changes state (asserted low). The home sensor can be a push button, optical sensor, pressure sensor or any other form of signaling that a certain spot has been reached.
- Connect your home sensor to J8. Make sure polarity is observed as polarizing the sensor backwards will yield no positive results.
- Write a 1000 on the “Steps” text box on the “Turn CW Speed, Distance frame”.
- Press the “Move CW Steps” button.
- Before the motor runs the 1000 steps at the specified speed, actuate the sensor. (piece of paper in between the two tabs should do it.)
- The motor should stop immediately after the sensor is tripped.
You have become an expert again! Controlling position has granted you the ability to place objects in a particular spot with an increased level of accuracy and repeteability. Again, let us remind you that direction is something that can be easily controlled with the Super Stepper module. All of our examples have been directed towards the clockwise direction but play a little bit with the same control buttons for the counterclockwise direction and find out how similar the operation is!
Congratulations!!! You have successfully completed the third lab on the Super Stepper Architecture. You are now capable of controlling the position your stepper moves to after receiving position based commands!
Hungry for more? Next topic is controlling the stepper position.
|
|
 |
 |
 |
 |
Last Updated on Jan 10, 2008
 |
 |
 |
 |
Other Avayanic Web Sites