I am a new user of Mach3
now I got a problem

if I want to release on when z axis moving
how can I do?

I thought I can check the "togo" of Z
if the var is not 0
release the brake
else brake up.

the problem is how can I know the "togo" of Z
and if I put this function in macropump, and i hope to add a  timer to delay the Z axis move
how to do?

thx a lot..

Normally the brake would either be controlled internally by your servo drive or if thats not possible you would use an enable signal. In other words when the axis is enabled the brake will be powered and released. If the axis faults or is switched off then the brake will be applied as it loses its signal from the enable.

Hood

I told my customer like what u talk,
but he thought his head is too heavy and hope the brake can help the motor to hold the position..

I told my customer like what u talk,
but he thought his head is too heavy and hope the brake can help the motor to hold the position..

That is no use, he either needs to fit a counter weight or get a bigger motor.

Hood

I still need one way to realize the software function, to solve the problem or to prove his solution fail
Can anyone tell me the way to get the "togo" var of Z-Axis?

I still need one way to realize the software function, to solve the problem or to prove his solution fail
Can anyone tell me the way to get the "togo" var of Z-Axis?

I am wokring on a similar project, but for the A axis. My goal however, is to make the operation tansparent to MACH.

My current thinking is to use a 'position reached' output on a servo drive to activate a brake. That seems promising, but I have not had a chance to develop the idea yet. I am busy with other stuff at the moment, so it may be a while till I revisit this project.

For a rotary axis I can see the point but if this is as in the OP's case for a Z axis then I dont see the point. If the motor is not good enough to hold the axis in position when stationary then it will be no use when it is moving and cutting.
Just my opinion of course.
Hood

I found GetDRO(16002) seem to be use for get "togo" distance
but it didn't work when trying...
does anyone know why?

I agree with Hood, normally when an axis is in position a brake should not be applied on a servo when the motor is active, the drive has to be shut off or disabled while the brake is on, this implies that when the drive is re-enabled, the true position is re-established otherwise a jump can occur if the Z has moved at all
On a Z axis a counterbalance system should be employed.
 A rotary table is often the exception, but the motor still has to be de-activated.

I agree that a counterbalance is a better solution for a typical Z axis, not only to reduce stress on the motor, but to eliminate backlash . . a benefit unique to the Z axis.

On the other hand, I disagree that a drive motor 'must' be deactivated prior to an axis being locked in all cases. I have been doing some research into this question and I find that there are many different applications and each has it's own set of variables to consider. I am wokring with a servo drive that already has a separate set of parameters that are automatically engaged whenever the motor is not moving, so manually disabling the motor *might* be superfluous (too early to tell just yet). I know of several stepper motor drives that automatically reduce power when the motor is not moving, so locking an axis in that situation would do nothing but prevent stress on the motors and potentially prevent lost steps in the case of an extreme force such as occurs during tool chatter while the motor is at reduced power.

Then there is the example of a rotary tool holder where it is evident that the motor is used only for positioning and a positive mechanical lock takes the cutting forces.

Axis locking is an interesting elephant, to be sure.