Author Topic: Choosing the right equipment  (Read 1788 times)

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Offline BS235Topic starter

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Choosing the right equipment
« on: October 04, 2016, 05:28:25 PM »
Hello!  I am new to robot building/automation but have some experience.  I have purchased a motor from Maxon Motors and I am currently trying to use their EPOS2 70/10 positioning controller for this project.  I have been advised to use a PLC as the controller does not possess the capability to do what we need.

The project is very basic but it seems difficult to find a controller with a simple way to integrate this. 
The project:
A small car is captured with wheels on a track.  A motor is at one end of the track, and an idle pulley is at the opposite end.  A rubber timing belt makes a loop.. it starts at one end of the car, passes around the motor pulley, back under the car (unattached), around the idle pulley, and then attaches back to the car. This way, when the motor spins left or right, the car travels left or right on the track.  The motor is driven left or right with a joystick. The user will be able to control the speed  and direction with a slider knob and from pressure on the joystick.  The controller should set software limits to keep the car from traveling off either end of the track.  This needs to be done from encoder positions, not from any external sensors.

So.. this is all relatively simple.  The difficult part is this.. Getting the car to stop at the end of the track at the same position, regardless of the speed it is traveling.  This is simple in controllers when commanding a position to travel to, but I cannot find a controller that will allow you to accept a joystick signal (+/- 10v, pwm etc) and still have speed sensitive end limits. 

The answer I was commonly given is to use a microcontroller to develop a lookup table that would constantly monitor the position and trigger a deceleration at the appropriate encoder count.  This would require a lot of R&D and change drastically dependent on payload on the car.  I know that there must be a simple way of doing it and some expert out there knows it. 

The only other challenge is it must incorporate a dual encoder feedback loop.. but the EOPS2 controller already has that integrated. 

If anyone has some solution to drive this system, I would really appreciate the advice!  Thanks!


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