Stepper - first step

[Jeremy Leach]

Just been thinking ... if you have a bipolar stepper, you don't know the position of the rotor at startup and so you would need to send control signals to cycle through a few steps in one direction before the rotor 'locks in'. Is this correct??

 

[Technical]

Yes, it is normal to have a known calibration point - light sensor/microswitch etc which is moved to after power up. There is no way to power up on an exact known step.

 

[AlainB]

Hi,

I am not 100% sure about that!

When using a CNC program like TurboCNC, at power down, the software will save the current positions of the axles. At power up, the motors will be energized at the same position that they were at power down and the current position loaded in the memory.

I never used that feature but I suppose that if it is available is must be possible to know the exact position of the rotor at startup.

Alain

 

[Technical]

At power up, the motors will be energized at the same position that they were at power down and the current position loaded in the memory.

Assuming no one had nudged the table in between! In theory this is correct, but in practise backlash in the gear system, vibration, people manually moving the mechanism etc. etc. means the only truly reliable system is a known calibration point. This can be as simple as moving to the end stop.

 

[AlainB]

the only truly reliable system is a known calibration point. This can be as simple as moving to the end stop.

I agree with you!

Alain