Monitoring Stepper Motor Current

Hello,

I am using two stepper motors controlled by two TB6600 stepper drivers (one per motor). These motors are driving a lead screw system. Is there a way to compare stepper motor current continuously to check for spikes in current?

I want to monitor if one screw isn't as clean or has more resistance than the other so I know to grease it or give a warning.

Thanks

Smagby: Hello,

I am using two stepper motors controlled by two TB6600 stepper drivers (one per motor). These motors are driving a lead screw system. Is there a way to compare stepper motor current continuously to check for spikes in current?

I want to monitor if one screw isn't as clean or has more resistance than the other so I know to grease it or give a warning.

Thanks

Your stepper motor current is continuously varying as the motor coils are pulsed to make the motor move. The only time there is a steady current is when the motor is stationary. Where do you think there might be spikes?

Paul

Smagby: I am using two stepper motors controlled by two TB6600 stepper drivers (one per motor). These motors are driving a lead screw system. Is there a way to compare stepper motor current continuously to check for spikes in current?

The stepper driver will be monitoring the current continuously during every single step so it can implement whatever current limit you have selected.

The stepper motor current won't be affected by the load on the motor in the way that current in a DC motor is. If the load gets too great it will just miss steps.

...R

Robin2: The stepper driver will be monitoring the current continuously during every single step so it can implement whatever current limit you have selected.

The stepper motor current won't be affected by the load on the motor in the way that current in a DC motor is. If the load gets too great it will just miss steps.

...R

Is there a way to measure the current?

Thanks

Smagby: Is there a way to measure the current?

Thanks

Since the current is continually changing while the motor is active, and possibly even changing polarity, the only way is to use an oscilloscope.

Paul

Smagby: Is there a way to measure the current?

Even taking account of Reply #4, what would be the point of measuring the current?

...R

I want to monitor if one screw isn’t as clean or has more resistance than the other so I know to grease it or give a warning

Monitoring the current isn’t going to work, but a shaft encoder will tell you if the stepper can’t overcome the load resistance, and misses steps.

A strain gauge on the motor mount is one way to measure the torque that it's producing. That seems like overkill for something that you can observe directly and grease it when you see it needs it. If it's on a Mars rover, then yes, they have all sorts of instrumentation on their motors.

MorganS: If it's on a Mars rover, then yes, they have all sorts of instrumentation on their motors.

One wonders how they keep the grease-monkey alive on Mars ? :)

...R

Smagby: Hello,

I am using two stepper motors controlled by two TB6600 stepper drivers (one per motor). These motors are driving a lead screw system. Is there a way to compare stepper motor current continuously to check for spikes in current?

I want to monitor if one screw isn't as clean or has more resistance than the other so I know to grease it or give a warning.

Thanks

No, monitoring torque isn't possible with a stepper, its hard enough to do stall detection (the chips I've used with stall detection are hopeless at it).

If you want to monitor and control torque you need a servomotor.

Robin2:
Even taking account of Reply #4, what would be the point of measuring the current?

…R

I want to stop the system if something happens on one screw and not the other.

An example would be something getting stuck or have more resistance on screw #2, detect that, and stop the system for repair.

I would use the current readings to compare those as the motor current would spike under more strain.

jremington: Monitoring the current isn't going to work, but a shaft encoder will tell you if the stepper can't overcome the load resistance, and misses steps.

I want to stop the system if something happens on one screw and not the other.

An example would be something getting stuck or have more resistance on screw #2, detect that, and stop the system for repair.

I would use the current readings to compare those as the motor current would spike under more strain.

as the motor current would spike under more strain

It does not. Stepping motors don't work that way.

You are thinking of brushed DC motors.

Smagby: I would use the current readings to compare those as the motor current would spike under more strain.

Do you not bother reading the Replies you get? You have already been told more than once that that is not how they work.

I want to stop the system if something happens on one screw and not the other.

Then you need to put a rotary encoder on each shaft and monitor the rotation of the shaft via the encoders.

And that was also mentioned already, in Reply #6

...R

Robin2:
Do you not bother reading the Replies you get? You have already been told more than once that that is not how they work.

Then you need to put a rotary encoder on each shaft and monitor the rotation of the shaft via the encoders.

And that was also mentioned already, in Reply #6

…R

I apologize. I guess I am a bit confused on why the current does not increase when under strain. Would you have an explanation or article handy?

Thank you very much for the help.

Smagby: I apologize. I guess I am a bit confused on why the current does not increase when under strain.

The explanation is simple. The stepper driver controls the current according the limit you set. It has not no way of knowing what load is on the motor.

The bible is Jones on Stepper Motors

...R

Robin2: The explanation is simple. The stepper driver controls the current according the limit you set. It has not way of knowing what load is on the motor.

The bible is Jones on Stepper Motors

...R

This is great. I will read into this. Again, thank you for being patient with my questions. You were very helpful!

A stepper motor has four wires connected to two coils. Those two coils are like two regular motors. To hold position on a step, they pull against each other. When it is standing still, they are pulling the strongest.