Wiring up the Alarm output on Leadshine AM882

**Ricardoco** · 07-01-2013

Originally Posted by Shinobiwan

Thanks Rick,

Have I interpreted it correctly?

Yep I think you have, although on my machines i always make the Estop ring as normaly closed ie you break the loop to Impose a condition, the reason for this is if a wire or connection breaks or the power fails or a component fails it will always break the circuit, showing an alarm condition. so all respective relays are energised giving closed condition for normal. this basicly gives me a circuit that is broken in the event of component failure or activation. the other way would not alarm in the event of a broken wire or failed component.

Remember to check it with the Gurus though..

Rick

**Shinobiwan** · 07-01-2013

OK will hope someone can confirm if this will work. I still have doubts about what I've drawn there. I know just enough to be dangerous!

**m_c** · 07-01-2013

Either way of wiring in the relay would work. Your first diagram switched the high (positive) side, and your second switched the low (negative/gnd) side.

Only thing that threw me was the markings on your relays. Vcc is a supply voltage in electronics, whereas you've used it for the contacts.

Ricardoco is right that e-stop circuits should be fail safe. For the actual e-stop button circuit, the relay should be active when the e-stop circuit is not in stop condition, with the BOB e-stop wires going through a pair of NO (Normally Open) contacts. That way if anything fails, the machine stops.

With the drive alarm function, a truly failsafe method is not possible due to the fact the alarm only activates when there is a fault, so you need to implement a system that relies on relays/wiring working when there is a fault. This isn't quite as big an issue on the alarm funcion, as a failure to stop when a drive faults out isn't as major a safety issue. At worst two axis keep moving, while one sits still.

**Shinobiwan** · 08-01-2013

OK with that sorted I'm also looking to eventually add proximity switches for home positions.

These look a little different since they're powered devices with an output intended for a parallel port input.

Am I right in thinking its possible to only use 1 input on the BOB for 3 switches or does each need its own? Currently I have 1 input with 3 mechanical switches but not sure if that will work here.

**m_c** · 08-01-2013

If they have active (i.e. TTL level) outputs, then they won't like being connected up. Possible work arounds could be some kind of OR gate, or mini relays.

If they have an Open Collector option, then it will be possible to link them up.

**Shinobiwan** · 08-01-2013

Hi m_c, thanks for all the help you've given. Appreciate it.

The sensors are these types:

DC 10-30V 4mm Inductive Green Proximity Sensor Switch 3-wire PNP SN04-P2 | eBay

Sadly no data sheet and the specs are basic at best. I'd say that they're active outputs as I had them test wired this evening and when you tie all the outputs together they do strange things. There's a little led on each to show active, when wired in this manner you have to trip a couple of them in order to get things going. Wired individually they work fine.

Could I place a diode after each output or is this not a case of current flowing back to one another?

**Shinobiwan** · 08-01-2013

I did manage to find a datasheet to these devices, its in Chinese though!

http://www.ic72.com/pdf_file/-/84401.pdf

**m_c** · 09-01-2013

Given that they're NC when not activated, if you want to connect them through a single pin, then you'll need some way to invert the signal.

There are various options, however the one that involves reasonable size components is to use a small relay for each sensor.

However, looking at the specs for those sensors, they are far from ideal, given detection distance is listed as 5mm +/- 10%.
A slot type sensor is far more accurate, such as Optical End / StartStop w. mounts- For CNC, Reprap and laserengraving machine | eBay

**Shinobiwan** · 09-01-2013

Originally Posted by m_c

However, looking at the specs for those sensors, they are far from ideal, given detection distance is listed as 5mm +/- 10%.
A slot type sensor is far more accurate, such as Optical End / StartStop w. mounts- For CNC, Reprap and laserengraving machine | eBay

I was reading the massive thread over on cnczone about the DIY version of these and it depends how you use them as far as accuracy goes. Passing the sensing object very close across the sensor is preferable to bringing the object up to the sensor. That's 20% error in the specs is at a distance of 5mm from the sensing object. The closer the object is to the sensor the more accurate it is. At 1mm they're accurate to 0.05mm or better.

There's video here showing the repeatability of these cheap ebay proximity switches using a dial indicator.

**m_c** · 09-01-2013

For a router, that accuracy is pretty good.
I'm more used to metal work, where 0.05 is borderline acceptible. It's certainly not really good enough for a lathe, as that translates to 0.1mm on the diameter. The sensor I'm using acheives better than 0.01mm accuracy.