Limit Switches - optical / mechanical / proximity

[Johannescnc]

skeptical... seem too cheap to me... or all the others over priced?
but... for the price, it may be worth the risk. but IMO, will it be worth it when they fail?
VALUE?

[KenC]

Definitely affordable, one can afford to have more spares & still better off. I had given ups asking why the Chinese can supply at such price... & accept the reliability set back...
My concern is the range, is 4mm sufficient?

[Gerald D]

4mm is a perfect range. Does that site tell you the diameter and the voltage range? (I couldn't see it at first look)

[Johannescnc]

well my point Ken, was, do we want to spend our time using our machine or working on it...

[KenC]

Gerald, Voltage range 6~36V, 12mm Dia.
They also have some with 2mm range, same V & Dia.

John, from my experience, electronics part will either fail in the first 5min or last the perceived life span lets (just say say 2 years...). Off the shelve price of reputable proxi sensors goes at around US$80~100, at least US$250 saving.... about a days salary of a CEO in a mid size company here.... Changing a sensor won't take more the 2 hours... Under such scenario, I won't mind work on the machine....

[domino11]

He also has a 15mm detection range with a 30MM dia, a 5mm Detection range with 18mm Dia and a 8mm Detection Range with18mm dia. What sesor would be more suited to users who are using the aluminum angle?

[smreish]

Heath,
As Nils and I found out, the Aluminum angle being a non-ferrous material requires a "little" longer sensing distance to work really well. If memory is right, we had the 3-5 mm sense and didn't work as well as the 7-15mm sense.

[domino11]

So the 8mm or 15mm would be a better choice for the aluminum rails. The 8mm seems a little better at 18mm dia versus the 15mm at 30mm dia to work with.

[KenC]

At the price that they are offering, we can experiment with it.
Just place an order for 5 pcs of the 4mm dist dia.12mm sensor, 1 for spare...

[swatkins]

Please let us know how long it take to recieve them Ken Did you order any relays?

[KenC]

No, I can get relays easily from every hardware shop in town.

They normally arrive within 1 week. Anyway, I'm not in the US

[Richards]

If you have trouble sensing aluminum, just replace the 'hole' in the aluminum with a steel bolt, then instead of sensing the absence of metal, you will sense the presence of metal when you hit the 'target'. My Shopbot is setup that way. When I had the 12mm tubular sensors installed, I set them at 3mm (they were rated to 4mm) and everything worked perfectly. Now I use the APS4-12M-E-D from www.AutomationDirect.com, which costs $16.75 each. That flat style is more easily mounted on my machine.

[Gerald D]

Mike, that will prevent us from sensing when the gantry lifts off from the rail.

[PEU]

Originally Posted by KenC

No, I can get relays easily from every hardware shop in town.

They normally arrive within 1 week. Anyway, I'm not in the US

You used the ebay dealer I found? I plan to order from them too, but now that you ordered I'll wait for your review

[KenC]

Pablo, it will take some time for me to install the sensors, as I'd just made dust, my priorities list are as such,
1) setting the axis & spindle square,
2) learning CAM
3) proxi switches....
4) .....
5) .....

BUT I'll report when I get there, that's a promise.

[PEU]

Ken, one more question, do these sensors come with a cable with conector or the cable is attached directly to the sensor?

Thanks!

[smreish]

Pablo,
All the Proxy units I have ordered thus far have the cable as an added item. M12 connection. Check with your supplier - a lot of options are available.

Sean

[riesvantwisk]

Originally Posted by Gerald D

Mike, that will prevent us from sensing when the gantry lifts off from the rail.

Within the Mechmate community, how often does this happen... just wondering.. My machine has micro-switches , so I cannot detect 'lift off (Houston, we have a problem...) '

just wondering if it ever happened...

[smreish]

When I was doing some Crazy prototype cutting of 3D shapes - I would derail at least once a week.

It's funny how well the Gantry wants to lift up when you drive a 12" long / 1/2" diameter roughing bit into the work. Happens everytime I write the tool file and Rhino would reset the ZERO to the center of the object and not TOP of object. You tell Mach to GO TO ZERO and BANG........300 dollar tool bit goes clunk.

So, for me - the derail feature was very necessary.

Sean

[Richards]

Sometimes we have to decide whether a proximity sensor that can't sense aluminum at standard distances is better than adding a target that can be sensed (at standard distances).

The design of the machine expected that you would use ferrous metal that a proximity sensor could easily sense so that you could sense a hole. If you modify the design and use aluminum, then you have to also modify the design. You have three choices:

1. Buy more expensive sensors that can sense aluminum at standard distances.

2. Use a bolt as a target and loose the ability to know that the gantry has raised.

3. Not use any sensors and hope for the best.

It would be better to use ferrous iron for the rails so that you didn't have to compromise; otherwise, I would at least use a target so that you won't smack the end stops.

[Gerald D]

We have seldom lifted the big gantry off the rails, but in the early days the y-car was lifted about once a week.
- forget to switch router on
- electrical interference made router go too deep
- bad programming
- bad restart of a program, forgeting that machine moves in a straight line to the next point (from wherever it happens to be)
- run collet/cutter into a clamp
- run collet against a part of the job while cutting a very deep profile
- run dust foot against a clamp, or x-beam
- cutter went blunt within one meter of cutting (HSS instead of carbide)
- rag lying on rail
- scrap jammed inside cut out hole
- try to plunge a big diam cutter that was not designed to drill
- etc. . . . .

Most of those, and more were part of the learning curve and the number of jumps off the rails are now very much reduced, but they still do happen

[J.R. Hatcher]

Let's talk about the proxy switch and do we need NO or NC. My understanding is we need NO, (as Mike used) in mid air it's open, when it senses the rail it closes, then when it gets to the hole or jumps rail or even if it loses connection it opens again. Please read post 252, 253 in this thread and reply. Thanks

[Gerald D]

Proxy sensors do sense aluminium, albeit at a reduced distance (the gap between proxy and alu rail can be set to less than 1mm). The NO (normally open) type should be used. "Normal" means in free air, without metal nearby.

[smreish]

....and for some reason I now feel that Gerald had a security camera installed in my shop to monitor my progress with that very clear list of things I have done in the past few years!

[timberlinemd]

My thoughts on the proxies are to use the 12mm AC units SI12-AE4 NO with a 4mm range from FactoryMation. I chose to use a low voltage (24v AC) system for the E-Stops, so I have that power on hand. These proxies are two wire and I would wire them in series to one 24v AC relay. When the machine is on the Normaly Open proxies would be closed when in close contact with the rails which would provide the 24v to the relay coil to close the relay switch so that the signal from the G540 would be grounded. If one of the proxies were to open then the 24v would be broken to the relay coil causing the relay switch to open also and the signal would go high to the G540. Does anyone see a problem with this setup?

[smreish]

Steve,
The only noted challenge might be the noise potential on the ground. I tried some Allen Bradley prox units early on in Beta testing and found that the ac freq on the machine ground (from the z axis) caused the steppers to erratically pick up the noise. Even with shielded cable. Thus, I tested the DC units and no noise. I can't say with certainty that the noise was from the ac prox circuit, but it went away when I changed units.

.....ground loop and noise is REALLY hard to iron out. The bugger in my MM's thus far on all of the machines I have built.

Good luck.

[Richards]

Steve,

AC proximity sensors are slow. Those that you specified are rated at 12Hz, which is 83 milliseconds. The DC proximity sensors are rated at 1000Hz, which is one millisecond. The DC proximity sensors operate 83 times faster than the AC sensors.

At the slower speeds, precise positioning might be a problem. At 2-ips (the speed that I use to 'sneak up' on my zero point), an axis would move 0.166 inches during that 83 milliseconds. The DC sensors would see the target within 0.002 inches at that same speed.

[timberlinemd]

Thanks, Sean and Mike! This is great stuff to know. I thought that 'noise' may be a problem, but never even considered hertz speed! I will need to rethink this.

[David Bryant]

Hi all
I have just finished my plan for the proxies (Parts ordered but not tested yet)
I note that my sensor choice for detecting the Al rails has a sense distance Sn of 8mm (For standard steel sensor) this gets derated by X 0.55 or a sense distance for detecting Al at 4-5mm.
So if the sensor is 2-3 mm above the Al rail (6mm thick) it has the ability to detect the steel below the Aluminium!!!!
This could be the difficulty some have had setting up sensors on Al rail (Plus the decrease sensing distance.)

My plan is with holes in the Al and an underlying hole in the steel to ensure prox works by sensing the Al.

I have on order three PNP NO 12mm diam 8mm sense distance for Al rail detection and one 8mm dia NPN NO with 3mm sense distance for the Z axis.

I will follow up on the testing when they arrive.

Cheers
David

[KenC]

Originally Posted by PEU

Ken, one more question, do these sensors come with a cable with conector or the cable is attached directly to the sensor?

Thanks!

I don't know how I left this question unanswered... Better late then never ..
Yes, it came with the cable attached directly to the sensor, no connector in between.