PDA

View Full Version : proximity switches



rcrabb
07-19-2003, 06:51 PM
will proximity switches make good home and limit swithes?

HuFlungDung
07-19-2003, 07:47 PM
Not in my opinion. They also require quite a bit more riggin' to interface with your computer, because they require a detector brain to decide whether a pulse has been received from the sensor, then to operate a relay to give a maintained contact. You need a maintained contact for the limit and home logic to work properly.

balsaman
07-20-2003, 01:23 AM
Hu is right, kindoff...Most prox switches won't work on the 5 volts from your PC. You would need a relay. Most prox switches I know of have the brain built in so it's just N.O. or N.C. like any limit switch. I wonder though about a prox switches repeatability.

I considered using reed switches, the style that bolt to the side of an aluminum cylinder and detect the location of the piston. The ones I had were 10-30 volts, so they would not work as an input to the PC. (I tried).

ToyMaker
07-20-2003, 10:01 AM
What technology prox switch? capacitive, magnetic, sonar, laser, LED, other?
They all have trade-offs like range, accuracy, precision, and repeatability that affect their use.

robotic regards,

Tom
= = = = =
Its easier to teach a journalist engineering than an engineer to write

rcrabb
07-20-2003, 11:37 AM
I'm not really sure what kind they are. All I know is they are 24 to 240 volt. I'll post a picture if that will help. The reason I'm asking about there use is because I have about 10 of them. I would like to use them just to be a little different than the next guy. I know a simple lever switch would be the simple way to go. I have a 24volt transformer and the relays. I don't want to spend all the time setting them up to find out they don't have very good repeatability.

HuFlungDung
07-20-2003, 12:44 PM
Can you simply hook one up on a test bench and try it? I thought that the object being sensed had to move through the field to be detected, but I'm just guessing. As soon as it stops moving, even if it is close, it is no longer detected.

So far as repeatability for homing, it depends on what procedure you want to use. The best methods do not simply rely on any switch to interrupt a circuit, and that becomes "home". The switch is used to interrupt the circuit, and after that, a search is made for the nearest encoder index pulse, which would be within one whole turn of the screw.

balsaman
07-21-2003, 01:27 AM
Hu,

No, proximity switches detect the proximity of the thing your are trying to sense. It doesn't have to be moving.

I have thought about the index pulse thing, as my encoders do support that. I even saw a circuit on how it's done, but since I am somewhat electronically challenged, I thought I would just stick to the limit swtch for now. maybe later.

Eric