Our conveyor travel distance is measured by an inductive proximity sensor counting the conveyor gear wheel teeth. The gear wheel is about 4 inches in diameter. The prox is 24V NPN shielded. We had to replace the prox. Everything works great when we test it right after installing the prox. But always about a day later, the prox reading stays at 1 while the gear wheel turns ONLY IN ONE DIRECTION. 0 and 1 alternates as it is supposed to when the gear turns the other direction. We tried different proxes. We adjust the gap. Adjusted conveyor speed. But as always, the prox works at first and then a day after of running the machine the prox stops working (0 and 1 not changing) always in one direction. The other direction always works.
prox on wheel teeth only one direction
- Thread starter unsaint33
- Start date
AkaHammer
Member
no speed difference
no speed difference in one direction or the other it is the same. when looking at a gear remember(can be tricky some times) you have to see enough of the gear tooth to make the prox. but you also need to be able to see a gap between teeth so setting the distance from teeth can be tricky. The diameter of the prox. will make a big difference also the size and spacing of the teeth, so you want to pay attention to how far from gear you set prox. the diameter of prox makes huge difference the bigger the diameter the more sensing distance but also a larger area it covers so harder to not see teeth. hope this helps.
no speed difference in one direction or the other it is the same. when looking at a gear remember(can be tricky some times) you have to see enough of the gear tooth to make the prox. but you also need to be able to see a gap between teeth so setting the distance from teeth can be tricky. The diameter of the prox. will make a big difference also the size and spacing of the teeth, so you want to pay attention to how far from gear you set prox. the diameter of prox makes huge difference the bigger the diameter the more sensing distance but also a larger area it covers so harder to not see teeth. hope this helps.
Steve Bailey
Lifetime Supporting Member + Moderator
Could there be more vibration in the prox mount when running in direction showing the problem? Or difference in loading that causes the prox mount to deflect more?
Depending on the speed the gear is turning you might want to look at the switching frequency of the prox and make sure its on/off times can handle the input.
On a side note when I have to use a prox to count teeth this way I make a one shot fire when prox is on and another when its off, by combining these it doubles the resolution and in a sense you count the teeth & the valleys.
On a side note when I have to use a prox to count teeth this way I make a one shot fire when prox is on and another when its off, by combining these it doubles the resolution and in a sense you count the teeth & the valleys.
I_Automation
Lifetime Supporting Member
Is this a used gear?
What I have done in similar situations is attach a sprocket to the shaft and have the prox look at the sprocket teeth. If needed I buy a sprocket with an even number of teeth and mill half of them off for a large gap.
What I have done in similar situations is attach a sprocket to the shaft and have the prox look at the sprocket teeth. If needed I buy a sprocket with an even number of teeth and mill half of them off for a large gap.
drbitboy
Lifetime Supporting Member
Since you note that the reliability of the prox system is sensitive to the radial position of the prox sensor, have you considered that there might be some slop (radial movement) in the sprocket, which shifts the relative alignment between the prox and the sprocket?
I_Automation
Lifetime Supporting Member
On drbitboy's line I had one machine that ate the prox watching a gear. It counted teeth of a pinion gear to know the position of the rack it drove.
This line of machine had worked good for years, but the new one kept eating prox's. Actually chewed the front 1/8" off occasionally.
Turns out the latest machine design changed to a vibration dampened motor that was basically a rubber plate between the motor and mount plate. If there was enough backpressure from what was being driven it was enough to push the motor and gear away from the rack into the prox.
This line of machine had worked good for years, but the new one kept eating prox's. Actually chewed the front 1/8" off occasionally.
Turns out the latest machine design changed to a vibration dampened motor that was basically a rubber plate between the motor and mount plate. If there was enough backpressure from what was being driven it was enough to push the motor and gear away from the rack into the prox.
No. The conveyor is driven by 2 way hydraulic valve.
We replaced the prox with exact same size prox that was working for years.
We checked the prox mount and the gear mount. They are tight.
geniusintraining
Lifetime Supporting Member + Moderator
Night shift is changing the prox and putting the old prox back in service, install a camera, just kidding... with everyone else guessing this was the only one left 
Ken Roach
Lifetime Supporting Member + Moderator
Is the chain on the sprocket fully clear of the prox switch; could it be drooping toward the switch in one direction only ?
Is the conveyor under a greater load in the direction where the prox switch stays on ? Is it possible that induced magnetic fields from a VFD are causing the switch to stay on ?
I stopped using proxes on sprockets when one of the operators I trained showed me how hard it was to get his work gloves on over his three remaining fingers. Especially with modern rugged contactless magnetic encoders, the risk and adjustment challenges of a prox on a sprocket just aren't worth the cost savings.
Is the conveyor under a greater load in the direction where the prox switch stays on ? Is it possible that induced magnetic fields from a VFD are causing the switch to stay on ?
I stopped using proxes on sprockets when one of the operators I trained showed me how hard it was to get his work gloves on over his three remaining fingers. Especially with modern rugged contactless magnetic encoders, the risk and adjustment challenges of a prox on a sprocket just aren't worth the cost savings.
We will slow it down and try again. The controller CPU is not programmable. Or at least not by us. In other words, we cannot program in one shot functions.
when we first tested the new prox, we made sure that none of the teeth was touching the prox. maybe after a day of running the machine, the gear moves slightly possibly damaging the prox? We will have to look into that.
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