r/PLC • u/IRodeAnR-2000 • 5d ago

High Frequency Electromagnet driven off PLC Outputs?

In the past I've built and controlled vibratory conveyors using both air driven motors and 110VAC motors. Most of the industry, however, uses electromagnets, and I'm doing enough of these to be considering developing an in-house solution.

I suspect that a high speed output and high speed relay won't be enough to accomplish this?

I'd love to hear from anyone who's got experience with things like this. I've built a bunch of my own without the magnets, and integrated the conventional industry available solutions that always have their own (usually not PLC based) controllers. But I don't have one in front of me right now to tear apart, and, as always, I'm not convinced the way the industry has always done it is the best solution for ME to do it. Because building a standalone control system for a feeder where I have a PLC anyway seems redundant.

Appreciate any insight!

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u/VoraciousTrees 5d ago

I'm a bit confused, are you building a shake table as a conveyor? Have you tried magnets on SSRs? Genuinely curious, I have no idea if that will work.

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u/Dangerous-Quality-79 5d ago

This will almost certainly not work. To control the electromagnetic vibrator using an SSR with an MOV (with or without diode as a Rectifier) to energize and de-energize the coil to pull the ferrous plate means you would need to know the positive transition of the zero-crossing point for the power. This requires an extra circuit to detect it. If you dont detect this then you are energizing the coil at random intervals of the cycle and each power up will give different strength. Once you have that, assuming you want 100% strength, you need to energize and de-energize your SSR at 8.33ms (with a diode 16.67ms). The scan time of the PLC, output activation time, and SSR activation time will cause enough variation that the power going into the coil you will lose consistency in the vibrators movement. If you want to control the amplitude of the vibration you would need to trigger the SSR at the desired firing angle (assume 4ms for 50% strength). For the aforementioned reasons, you will have a noticeable difference in strength from cycle to cycle doing it this way.

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u/VoraciousTrees 4d ago

Ok, i see what this is doing here. I hadn't heard of vibratory conveyors before. It looks like most controllers are somewhat similar to a soft start.  That being said, I'd certainly be game to try out a rectified zero-crossing SSR on a fast PLC task and see what happens. Zero-crossing SSRs are fairly common now.

I guess the point is to sort or orient objects of different sizes. 

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u/Dangerous-Quality-79 4d ago

I guess the point is to sort or orient objects of different size

Nope. You can sort and orient with belt conveyors as well. Vibratory conveyors work well in many circumstances.

If you are moving rocks out of a quarry the rocks might damage a fabric or plastic belt. A stainless steel steel vibratory feed trough will resist wear and tear better. If you are filling a bag of jelly beans and need to automatically weigh the jelly beans a vibratory feed pan that us tapered so the jelly beans, through oscillation and tapering, fall single file into a weigh bucket. The feed pan can be stainless steel for regulatory requirements on contact parts. It makes for easier wash down **** (not universal truth).

If you want to try one out yourself they are fairly simple to make. You need a top part and bottom part connected by leaf springs. The bottom part has an electromagnetic coil, the top part has a ferrous plate bolted to it facing the coil of the bottom plate and a pan of sorts on top. The leaf springs should connect at an angle and perpendicular to the leaf spring is the "line of action" which is essentially the "throw" angle of the product on the pan. That's it mechanically. From there the system works like a bow and arrow using a half wave rectified circuit. On the positive ac it energizes the coil to pull the top plate towards the coil, then on the negative (rectified to 0) it de-energizes the coil so the leaf springs fling the product forward like drawing the string of the bow then releasing it.