Run a stepper from 2 DM542 drive

[BeagleBrainz]

If you disable the drive before switching the switching the STEP & DIR it may help with not generating any spurious steps. Just don't forget to re-enable the drive before kicking off again.

[Doddy]

If you disable the drive before switching the switching the STEP & DIR it may help with not generating any spurious steps. Just don't forget to re-enable the drive before kicking off again.

Not intended to drag this conversation onwards, but for clarity on the behaviour of a stepper driver:

A stepper driver can be described as a finite-state machine. It will present a series of currents to each of the two (e.g.) coils according to the number of micro-steps selected. The following is an extract from the data sheet for the TB6600 - though the principle applies to any stepper driver.



You should be able to see that for a 1/8 micro-step, there's 32 discrete states for the A/B coil currents. Whether you move CW or CCW, you're just stepping either forwards or backwards in the state-machine ("phase", in my original post).

My point?, if using two stepper drivers, each will maintain it's own internal state as its operated. If you swap the outputs from one driver to another - unless there's the random fluke of each driver having the same state, there WILL be a discrete change in the coil currents appropriate to the different phase in the state machine that WILL result in a discrete change in shaft position. There's no mechanism available to synchronise the drivers. Disabling the drivers before switching the STEP/DIR will have no impact on this.

A_Camera's point of switching grounds is valid - or my lazy assumption that you share a common ground.

[BeagleBrainz]

Not intended to drag this conversation onwards, but for clarity on the behaviour of a stepper driver:

A stepper driver can be described as a finite-state machine. It will present a series of currents to each of the two (e.g.) coils according to the number of micro-steps selected. The following is an extract from the data sheet for the TB6600 - though the principle applies to any stepper driver.



You should be able to see that for a 1/8 micro-step, there's 32 discrete states for the A/B coil currents. Whether you move CW or CCW, you're just stepping either forwards or backwards in the state-machine ("phase", in my original post).

My point?, if using two stepper drivers, each will maintain it's own internal state as its operated. If you swap the outputs from one driver to another - unless there's the random fluke of each driver having the same state, there WILL be a discrete change in the coil currents appropriate to the different phase in the state machine that WILL result in a discrete change in shaft position. There's no mechanism available to synchronise the drivers. Disabling the drivers before switching the STEP/DIR will have no impact on this.

A_Camera's point of switching grounds is valid - or my lazy assumption that you share a common ground.

Very good points.

As long as the outputs driving the STEP & DIR are at a logic LOW (assuming common) is ground there should be an issue, but if the outputs are at a logic HI and using a mechanical switch to change over disabling the drive would prevent spurious steps, due to bounce.

All in all a better mechanical design would help.

Actually it would be worthwhile knowing the circuitry that drives the STEP & DIRECTION, before really delving in too deep. Considering that the design requires switching 2 different sources for driving the stepper who knows how the electrical side has been done.

[gabi68]

The fiber laser has a board called DLC2-M4-2D which is a 2 board connected with pins. The top board is a controller for X,Y,Z,A axis (can drive a Z axis, a rotary axis, an XY table and all the combination between). The bottom board is dedicated to run the laser head itself (2 small servo motors connected to 2 mirrors to steer the beam and stop it and start it depending the user design).
The top board is a step and dir controller and is connected to a stepper motor which operates the Z axis
I also have a device (with his own stepper driver) which has a measuring sensor for the focal distance (different lens have different focal distance) and this device needs to use the same stepper motor on the z axis.
This was my question: how can I change the drivers (safely) to use the same motor when I need to use one or the other device?

Thank you
Gabi