Calculating Servo Positions Automatically

[macgioo2]

Hi People,

I've had a two servos working in tandem for about 2 years now and the company say they are not happy about having to reteach them.

Servo 1 has three positions, teach POS1, POS2 and POS3 are autocalculated.

Servo 2 has two positions, teach POS1, POS2 is auto calculated.

Now, if you don't want to do a manual reteach and your zero point on the encoder can shift during a collision how do you get around it.

Currently, a homing request will home left until the home sensor goes on, then off, then I will home right until the home sensor goes on, then off again and finally stops when it finds zero on the encoder.

If it is currently left of the home sensor, it will home Left until it hits the over travel sensor then move right to home as normal.


Ok so that's the basics out of the way..... so is the only way to teach the new positions if the belt has slipped, to place a sensor at POS1 and slowly move the servo to that position, when it sees the sensor write the new position value into POS1 and auto calculate POS2 and POS3 from there.

Or is there a more clever solution.

Any suggestions are most welcome.
Thanks
Oran

 

[jstolaruk]

Fix the slipping belt?

 

[macgioo2]

Due to bad mechanical design, inconsistent components and a massive lag in cycle time crashes and jams are going to be a fact of life on this thing!

 

[jstolaruk]

Use a hard stop at the end-of-travel, that most likely won't change.

 

[Peter Nachtwey]

Can you use an absolute linear encoder like a MDT SSI rod?

 

[Steve Bailey]

Google "detent clutch" for devices that will decouple the motor from the load upon excess torque and re-engage at the same relative orientation between the motor and the load. With that style of clutch you can replace the belt that slips with a timing belt.

 

[MichaelG]

what hardware are you using?
PLC, servo etc


what you are trying to work out is the distance from your Zero to POS1 if it is the same each time then it should just be a fixed offset

If the value (POS1) changes every time you perform a home routine then fix the home routine so that it is consistent

As your home routine uses the encoder Zero this may cause issues if the belts keep on jumping as the encoder zero will keep moving

Can you just use the falling edge of the home sensor moving right?

 

[Jeebs]

As MichaelG said:
Home should be a fixed point.
Encoder zero will cause issues in your setup.