Hello. I’m new to the forum and just getting started with motor controllers with feedback. Please forgive my ignorance as I continue to learn.
My question is about slaving the jrk to a 4046 PLL IC using a cmos chip as the source for the lock. I have a slotted disc (tachometer style) that marks the rotation point of the motor shaft (driven by the jrk) with an audio pulse. I simply want the cmos signal to match up with the pulse on each rotation.
I’ve been through the documentation and I’m not sure if the jrk is capable of doing this. I read in a post from Jan that the Jrk doesn’t do position control on a continuously rotating shaft. Maybe I’m mixing the two concepts up completely. Theoretically (at least in my head it makes sense…), if I lock the two signals together via the PLL it should give me what I’m after. Please correct me if wrong. Can anyone point me in the right direction?
The tachometer feedback is for speed control and not for position control. For position control, you want an analog voltage source as feedback, usually provided by a potentiometer. You can find more information about this in the “Feedback Options” section of the jrk user’s guide
It is not clear what you are trying to do. Could you provide more information about your project and what you are trying to accomplish?
Essentially what I have is a capstan driven tape path (with a DC brushed motor) for high speed stop motion capture using a camera. With the capstan, the motor moves the tape along the path at a constant speed. At marked positions the camera needs to grab a frame capture. The issue I have is due to the lack of phase lock of the camera to the path speed. The images wind up half way through any given frame count by the camera, rendering them unusable. By slaving the speed and position of the tape path to the camera signal via PLL I believe this will fix the problem. Perhaps, however, I need to take a look at servos for the position control instead of trying to do it through motor feedback. Thoughts?
My approach would be to put a rotational encoder on the capstan, which would trigger an exposure at a precisely defined angular position. I think that would be much simpler than to design and build a feedback system to deliver phase locked rotation. The encoder could do double duty to regulate the angular velocity of the capstan as well.
Thanks for your explanation. But I still don’t understand. I think Jim thinks that triggering a shot is immediate. As if you’re using a still camera.
I myself think you’re running a video camera and triggering a capture of the “current frame” when the trigger happens. And that your problem is that if the camera is running at 30fps, it will be taking shots at say 333ms and 366 ms, while the trigger happens at 350ms resulting in a visible error.
I don’t understand what the “tape” has to do with all this.
My apologies. Here’s some clarification. I say tape out of habit as this is an audio reel to reel machine. The tape path has been remachined for the purpose of running and scanning 8mm film. The camera is, indeed, progressive 30p video with offset problems as you mentioned due to the lack of phase lock. With different gauges and frame sizes between super8 and regular 8 film, an encoder on the capstan is not an option. The capstan speed for frame advancement must be proportional to the camera frame rate regardless of the varied lengths between film types. Thus the need for motor control. The position of each frame is accurately marked by the leading edge of the sprocket hole using ir several frames before capture, thus allowing for needed changes. As there is typically extremely little variance between frames, the capstan should cure most of the consistent position issues, but I’d guess that any variance at all will spell big trouble.
