Z-Axis Brake with Clearpath Hard Stop Homing

[grossmsj]

I need advice on how to wire my Z-Axis brake.
I have Clearpath Servos wired via the C86 board with hard enable. When power is on, the Acorn board is powered up and the Servo motors are enabled. The motors slowly march to endstops and hard stop homing is completed. Works great. It all happens before I even have CNC12 running.
I put in a Z-axis brake powered from 24 volts. If I wire 24 volts to both the brake (directly) and the Acorn, the brake releases a split second before servos are engaged and the spindle plunges down. No bueno.
I now have 24 volts wired through Output3 running AxisBrakeRelease. AxisBrakeRelease (as I understand it) requires a motor command to close the output and release the brake. To make this work I have to power up the system with the E-Stop engaged so power won't go to the motors. I can then power up CNC12. Then I have to reach over and release the E-stop followed quickly by hitting Start so the brake releases. This works fine but feels kludgy. I'd like a solution where there is a very short delay between Servo Activation and Z-brake release that doesn't require my intervention. This could be via wiring, some interaction between the DriveOK input, or changes to the PLC.
What would you suggest I do to get the brake/motor timing working right?

[jhnmdahl]

The brake should normally be released any time the axis is powered, i.e., as soon as the controller is powered on and a control signal is sent to the motors, applied again in an E-stop condition, and released again upon subsequent axis movement. The axis doesn't have to move for the brake to be released - edit - it appears the motors are held in place with power and a control signal bringing them to an active state - see below posts

If your Z axis is so heavy that it falls in the split second between brake release and adequate power being provided to your Z axis motor, I can think of a couple options - one, add a delay circuit in the brake release signal, or two, add some mechanical resistance to the Z axis (or use a finer pitch leadscrew, etc.).

[grossmsj]

The brake should normally be released any time the axis is powered

Does it matter if this occurs during hard stop homing? Is the axis 'powered' at this point, as the motion of the motors is independent of Acorn control when the C86 board is powered? I guess the drives are enabled (they have power), but I don't know if this qualifies as 'axis is powered'.
What I see is this: I power up with E-stop pressed in and launch CNC12. When I release the E-stop the motors will move toward home. If don't hit the start button during this moment, two things are observed. I don't hear the 'clink' of the brake release and a few moments later the Z-axis will detect a 'hard stop' (because of the brake) and will stop homing. If I do hit the start button shortly after releasing E-Stop, I hear the clink of brake release and homing will occur normally.
I'm using the hard stop homing macro that is written during configuration. There is nothing there but M26's for each axis.

I'm thinking the most direct way to do this is to put a relay between Drive Okay input and the 24 volts going to the brake. When Drive OK is enabled, the relay will close and power the brake.

[jhnmdahl]

Are you using the program in Centroid's tech bulletin to do hard stop homing? It looks like homing should only start after the first enable signal from the controller after everything is powered up. Centroid's preferred configuration can be found here: https://www.centroidcnc.com/dealersuppo ... ds/319.pdf

It also looks like the Clearpath motors are different from the steppers they emulate in that they need both a power signal and a control signal to become active and hold position. I was able to find a demonstration of this on a system very similar to yours (and to one I'm building) at: at 29:20 or so.

The same video shows his software configuration (although he uses limit switch homing instead of hard stop homing) at about 33 minutes, and this video shows it running on his machine at about 23:30:

I started building a similar system last winter, until spring hit Minnesota and it got set aside. Hopefully someone else a few steps farther along in the project with more experience can chime in too.