Outpu C - Motor Active

I'm using an AX2850 in a hoist application. I'm utilizing a holding brake which is activated by output C. I'm experiencing a large amount of "chattering" on this ouput during closed loop speed mode and I am wondering how exactly the state of this ouput is determined. My exact situation is as follows:

In open loop mode, when I run the motor slowly up or slowly down (incrementally stepping up the speed,) the output activates fairly close to a "zero" speed and deactivates in the same manner. This works quite well.

In closed loop mode, going up is fine, but when I come down the ouput rapidly switches on and off during steps -1 & -2 and then again around steps -10--13. After that it stays consistently on. When stopping, this behavior occurs when stepping down the speed, but not when the "stop" button is pressed.

Is there a way to tune out this chattering?

Thank-you,

Matt

This should not be happening. We are ware many users who use the controller in close loop with output C releasing the motor brakes whenever power is applied to a motor.

This function is very basic and the output is actviated instantly when the power level to any of the two motors is different than 0

If there is chatter, it may be that there is another even trying to activate output C. This could happen if you change the output via RS232 command, or if you have an input configured to activate the output.

It may also be that you are trying to draw too much current from that output. Disconnect your brake and put a LED to check that the output activates as it should.

There is not a configuration problem. I have not confirmed the LED test, but, unless ouput C's current is in someway tied to the motor current, it shouldn't be a problem. It works in one direction. The key, to me, is the fact that when coming down slowly the motor is always operating in the 4th quadrant.

Things that work:

Up and down, with and without, load in open loop (everything)
Up, with and without load, in closed loop (1st quadrant full amps and no load amps)
Dn, without load, in closed loop (4th quadrant no load amps)

Things that don't work:

Down with a load (4th quadrant full amps.)

The question is, in closed loop mode, what does the drive know, which it doesn't in open loop mode, that is causing it to misinterpret the power output? An encoder is being used for the speed feedback.

It is also interesting that this occurs at two distinct step points. Steps 1-3 and steps 10-12. It is actually fairly stable between those points.

Matt

The output C is enabled whenever the PWM signal on any of the bridge is different than 0. Direction is not used nor is current sensing in that process.

As mentioned, this is a commonly used feature so it is hard to relate to what you are observing but we will run tests on the lab and let you know shortly.

Thank-you for looking into this. If the signal is completely based on the PWM output, then maybe there is a little jitter in the encoder signal or the PID loop is over compensating. I'm working on a better encoder mount and less encoder counts per revolution to see if that eliminates it.

Matt

I have fixed the encoder mount and made sure that the input is clean. It still doesn't work, but it is much more consistent in not working. When going down under load the following occurs: At step 1 the output cycles 3 or 4 times noticably (I can't see in milliseconds) and then stys on. Steps 2-5 are OK. Starting at step 6 and ending at step 13 the output will not stabilize, it constantly goes on and off. As mentioned, this is only in closed loop mode.

Matt

The PID loop is definently the problem. The output of the loop must be being reduced to zero. When I connect a seperate postion / velocity controler I get the exact same problem when I turn on the velocity loop. In position only mode the output is OK but performance is poor. I will need to see if there is anyway to adjust the PID parameters in your controller to eliminte this.

Matt