Limit switch timing from a cam

There's this...

I know I've seen other brands, but can't think of the names right now.

The traditional way to adjust the timing and dwell of a cam is to use a pair of plate cams sandwiched together by a clamping hub. Here's a photo of a camshaft on a spring winding machine I tooled up. Someone else made the fancy graduated hubs - I doubt anyone ever really looked at the numbers.

If you can get away with a homing routine at startup, a quadrature counter or a cheap PLC and an encoder would also work. If you're sure the shaft will never turn backwards, then the quadrature is unecessary.

I should have mentioned, if it's not obvious, the dwell is adjusted by changing the overlap of the plate cams. The cams are usually identical so you get a 2:1 adjustment in dwell.

Those are stock items, or somebody actually engraved them?

Indeed, some can boast of being the world's largest because they are the world's only manufacturer of certain niche items. Niches are nice.

I cant get that picture to load but google programmable limit switches. They use an rotary encoder connected to a control box which provides the switching.

Wes

Tom, Switches are a non-starter. You will never get the cycle rates you are looking for. I suggest you keep it simple and stick to hall effect sensors, amplifier and a solid state switch. Then drive a mechanical solution like an electrical clutch and brake or a simple dog clutch and latch or if the lever forces are not so high, a simple electrical solenoid. Avoid optical sensors in a contaminated environment, because dirt will get you. Hall effect sensors work in all conditions. Resolve the problem with simple electronics. I would not use pneumatics, as response times are poor and leaks are a pain.. If you use a solid state magnetic solution, be wary of back emf reverse biasing the solid state switch and use a diode of reverse polarity across the coil. Steve

"Steve Lusardi" fired this volley in news:g50bgo$dik$02$ snipped-for-privacy@news.t-online.com:

I'd like to suggest an alternative. Hall Effect sensors work reliably, but they're difficult to use in a mechanism requiring as tight an off-to- on angle of rotation as he requires. They're better for things like sensing rotation speed, or locating a position that's not so critical as Tom requires.

The alternative, and one that works well in millions (yes millions) of consumer machines, that works in hostile, hot, dirty environments; that can sense angles as small as 1/10th degree easily, and can easily be made to have adjustable dwell is: A controlled-reluctance sensor.

Pole width determines positional accuracy. Dwell can be established by distance to the sensed cam or by electronic means.

The cost is a bit more than Hall Effect types, because you'll require more electronics to sense and condition the signal. But it's minimal compared to the advantages they offer.

Just because you have a dirty environment doesn't rule out the use of optical choppers. Proper positioning can keep them clean in most applications. And they're the simplest of all types, providing all the features Tom wants without any complex 'tronix.

LLoyd

The most reliable and accurate way would be to replace the cams with an rotary optical encoder and electronic cam switch. One unit will do both switch operations. Adjustments are all done in software so changing timing is quite simple.

I'm pretty sure they were shop-made. My customer bought the machine to produce a family of parts for a competitor who needed a second source as they transitioned to offshore production. The competitor reconditioned the machine for my customer and made some improvements to it, several of which had the character of those graduated hubs. They had a beautiful toolroom turning out all sorts of lovely overcomplicated little gadgets. It was so pervasive, I came to believe that culture of overcomplication was likely a contributing factor to the plant being closed.