L6470

[CSu.12]

Hi,

 

I am using L6470 for our stepper motor.

Can I use it as motion tracking? Just like: If I change the target position, it will move to it...

If not, is there any stepper motor drive from ST that can do it?

Thanks,

Christie

[Peter BENSCH]

In principle, you can do this, it just depends on the controlling MCU how exactly this has to be implemented. The L6470 recognises various commands for this, such as Move or Goto, whereby Goto is the shortest way to the target position. However, you then also need feedback, e.g. with an encoder, because a stepper motor can lose steps depending on the load, which results in a permanent offset and must be corrected.

Hope that helps?

Regards
/Peter

[CSu.12]

Hi Peter,

Thank you.

What I want as follows:

The drive is in active move mode, then when I update the target, it will go to target because I want to track the existing pass and make it move as fast as possible.

The existing way takes too much time...

Is there any stepper motor drive from ST can support this?

Thanks,

Christie

[Peter BENSCH]

If I understand you correctly, L6470 can reach your tracked target, just that it happens too slowly, correct?

I assume that you are in high-resolution microstepping mode, in which it will inevitably take longer - if the speed is not changed. However, there is an automatic full-step mode on the L6470 (data sheet, section 6.4):

When motor speed is greater than a programmable full-step speed threshold, the L64701 device switches automatically to Full-step mode (see Figure 7); the driving mode returns to microstepping when motor speed decreases below the full-step speed threshold. The fullstep speed threshold is set through the FS_SPD register.

Regards
/Peter

[CSu.12]

Hi Peter,

I am using it in full step mode and positioning is fine, not slow.

When I get the target position and wait there for next target based on tracking pass...

I want to just update the target, then move to the new target without sending extra command...

 

Thanks,

Christie

[Peter BENSCH]

The L6470 is a stepper motor driver that accepts commands and acts on them. If you want to track and thus specify a new destination, this must be converted into corresponding commands. I am not aware of any stepper motor driver that does this autonomously.

Regards
/Peter

[CSu.12]

Hi Peter,

Thanks.

I am trying to use STEP-Clock mode to do tracking.by using 10Khz step clock(100uS) and works fine.

When I trying use 100KHz, I can see that motor can not move the required steps, but position register shows exact steps moved. Exe: Position register shows 1000 steps, but the real movement of motor is only 100 steps.

Could you tell me why? What is the maximum frequency allowed for STEP-Clock?

Thanks,

Christie

[Peter BENSCH]

Now I'm beginning to understand the background to your question. However, you should take a close look at the parameters of your stepper motor, i.e. both the mechanical and electrical parameters. This includes other parameters, such as details of the moving mass and the motor voltage, which are important for determining the maximum speed.

For stepper motors, a certain number of full steps is specified for a full rotation of the rotor. A very high frequency for the maximum number of full steps that can be controlled could be assumed with around 1000...4000 steps, which together with the number of full steps for one revolution results in the rotor speed that you could achieve. It should also be noted that the torque decreases as the step frequency increases.

As you can see from the register content, the motor driver would certainly be able to work with higher frequencies. The maximum frequency of the step clock cannot be specified in general, but is limited by the physics of the parameters mentioned above.

Regards
/Peter

 

[Peter BENSCH]

I can't answer either of these questions at the moment, but perhaps a friendly community member will find the time.