Driving a motor to predefined positions

Hi people!
Before I start puzzling my self I want to hear your ideas driven by your experience! (I know it is not the way of learning but I run out of time here!)
So here is the problem:
I want to control a motor (not a step motor). I want it to move to a specific position on an axe after the fisrt press of a control button and then second a second press to return to the position it started. I have some ideas but I want to hear some more.
Because the motor will be heavelly used I have rejected the idea of using a time counter. Aging of the device will provoke wrong positioning. Of course I can use adaptative methods but it will become very complicated and I don't want to.
That is my small problem for the week. Any good ideas?

Thanks
D.

Hi D,

Is there any gear on this motor?

Hi Ante,
no gear, just a switch: First press moves to predifined location, second press returns to previous position. Motor is running on 220V.
D.

Why type of motor that you're going to control?

Have a look at servo motors. They are good in this sort of applications.
**broken link removed**

Nice url Ian, but not what I want to control. Although it gave me some ideas. The motor is a huge 220V motor that moves on a still axe. In fact it moves the axe back and forward in order to obtain the correct position. The hole system controls the position of a chair. So what I want to do is to set a fixed point on the axe and force thew motor to move to this point by the press of button. That is the easy part . Then I want to move the axe back to the previous position.
One thought is to mark the starting position as 0s (let it be time) then the desired position as Ts, and divide the axe in time steps: 1s represend 5cm, 2s -> 10cm etc. The problem is that the ageing of the motor will alter this division.
The original question is if there is another way to divide the axe and tell the motor : Move 5cm or return to previous position [3cm].

Thanks
D.

Is it a AC induction motor?

Will the positions you wish the motor to stop change with time?

Do you think coupling the shaft to a position encoder will help?

In this case I would suggest so called "absolute encoder" which will give you certain amount of unique readings for each position, for example 65536 per rotation. You may not need this high resolution, so it will be the matter of finding the right encoder.
You can mout t directly n the shaft or through gears or small belt.

You will need something to read the encoder output (PC, PLC, microcontroller..) and control your motor accordingly (maybe small VSD with Start/Stop feature).