Proximity switch "contact bounce"

[Boyan Silyavski]

You must have been unlucky with that batch/ seller. Yes, there is not a flickering stage normally. Its either on or off. Hysteresis means once you are ON and the back to OFF, like you noted there is a ~0.4mm distance / at least on my switches.

[Neale]

The more I look, the more certain I am that that is the problem. Fortunately I only need to replace three of them - the switches are fine as limits where the lack of hysteresis doesn't matter. But how do you find a seller that has good ones in stock! Maybe not looking for the cheapest would be a good start...

[njhussey]

I bought mine from Farnell, think they were £8 each....but as I wasn't paying for them 😁 decided cost didn't matter therefore to buy from uk...

Sent from my HUAWEI VNS-L31 using Tapatalk

[Clive S]

The more I look, the more certain I am that that is the problem. Fortunately I only need to replace three of them - the switches are fine as limits where the lack of hysteresis doesn't matter. But how do you find a seller that has good ones in stock! Maybe not looking for the cheapest would be a good start...

Neale if you pm me your address I will send you one

[Neale]

Clive - that's a very kind offer but I have just ordered 4 more which should be here by the end of the week. For the moment, I can get by with homing each axis in turn (using the buttons on the Diagnostics page). I home one axis, then jog it a tiny bit away from the home position. Doing each axis in turn like this is a bit of a chore but it does mean that I can continue with testing. Next job is to sort out squaring the gantry and then test my ideas for dual-motor homing using an IP/M which does not support this.

[Neale]

I ordered some new switches, and I also put the controller box in the machine frame where it was supposed to go. That meant that I could connect the star point earth terminal in the control cabinet to the frame. This completely cured all the homing problems I was seeing. Reliable homing, and not a single limit switch trip since. Was this a shielding/noise/ground loop problem? No idea, but I seem to have fixed it. I was testing the proximity switches by connecting them to a bench power supply and just watching the built-in LEDs; in retrospect I'm not sure that this is a valid test and I should probably have connected the switch output to some kind of load (like motion controller input). When the new switches arrived, I tested those and still did not see any hysteresis but again this was "off load" and might not be a valid test. I do see the axis overshoot very slightly and then return slowly to the home position (which is what you would expect) on two of the three axes; it might be happening on the third but the movement is too small to see easily.

I did have a problem with one limit switch apparently triggering as the cable chain containing motor cables moved near its cable but I rerouted the cable and that seems OK now.

I haven't measured resetting accuracy when homing yet. Be interesting to see what these cheap switches can achieve.

[paulus.v]

I had the bouncing problem when the distance between the sensor and the triggering metal was too high and the triggering metal was aluminium. I have the sensor passing by the metal not towards it.
In regard to repeatability, I have one sensor mounted too close to the stepper and the triggering position differs with the position of the stepper rotor, but only by a few hundredths of a millimeter.

[Boyan Silyavski]

When i home with Mach3 i am not in a hurry and use low speeds for not to overshoot much. With the Chinese controller this is not a problem as i can program it to home 5 times, so it checks 5 times where it is, each of them slower. I use 2 times though. First time overshoots, then slowly homes on place.

[cropwell]

An NPN output usually requires a separate pull up resistor

I think that is incorporated in the switch, but the exact switch has not been mentioned, so I cannot be sure.