M1 18 000 Alternative Stopper Block

[dmoore]

Here is an alternative stopper block (not that there is anything wrong with the current versions!). I purchased my 18mm NPN proxy sensors from www.automation-overstock.com for 10$ USD each along with 90 degree 5 meter cables for 5.50$ USD for a grant total of $85.50 (I purchased 5 instead of just 4 for a spare).

I'm particularly happy with the way the proxy pokes right out the top of the Y-car.

See photos below.

[J.R. Hatcher]

David, that's a slick looking system. Nice work

[smreish]

I am SO VERY glad to see the proximities being used on various machines. I know that Gerald's design called for them and weren't full executed in the field until recently with Ed, doug, myself and others. As active limits, they are working well on my machine and dust, etc has not affected them the least. ....and I have a VERT dirty/dusty machine right now :)
Sean

[dmoore]

I am SO VERY glad to see the proximities being used on various machines.

While Gerald doesn't use proxies on his machines, they have saved me a few times on my old machine which didn't respond well to being run into the end of the table. I also like starting up Mach3 and having it ref all and be ready to go. Also, the cost is minimal - you could do 4 proxies with cable for less than $200 USD.

I still think there is room for some improvement in the stopper block - it's a complex part that needs to be exact. I spent more time on stopper blocks than I did on cutting and grinding the rails. It seems there must be a design that uses less parts and allows for built-in adjustment (without the eccentric M1 18 027 T).

[Johannescnc]

How accurate are these proxies?

[dmoore]

How accurate are these proxies?

I guess I would depend on what level of accuracy we are talking about. They are surely accurate enough for the intended function - limit switches and homing. Would you be referring to the ability to re-home after a power outage, skipped step or some other issue and then pickup on the same job where you left off?

Since I went with the mechanical relays to interface the proxies with the breakout board, I would suspect the relays are a greater cause of inaccuracy than the repeatable sensing ability of the proxy.

[javeria]

cant we use transistors(or any other form of electronics ) to switch instead of the mechanical relays?

[dmoore]

cant we use transistors(or any other form of electronics ) to switch instead of the mechanical relays?

You bet we can. There was an attempt to develop a standard control box for the Y-Car for this but it didn't pan out. Here are the details (read the entire thing):

http://www.mechmate.com/forums/showthread.php?t=584

Richards "Mike" did post this complete diagram including Opto-Isolation, though I am unaware of anyone that has built one:

http://www.mechmate.com/forums/showthread.php?p=8710&postcount=37

http://www.mechmate.com/forums/attachment.php?attachmentid=908&d=1202186626.jpg

Using the electronics instead of the relays would be much faster, more power efficient and safer.

[Gerald D]

There is absolutely nothing wrong with using mechanical relays for this application.

When "homing" the gantry, the move speed is slow, controlled, and repeatable. The delays in the switching system (or the distances travelled after the signal is processed) are totally repeatable, even for a relay.

Only one of the proxies needs a method for fine mechanical adjustment, and that is only if one is using the gantry auto-square offered by Mach. Even then, the machanical adjustment is done once only - using something like shims or eccentrics should be quite adequate.

[Johannescnc]

I guess I would depend on what level of accuracy we are talking about. They are surely accurate enough for the intended function - limit switches and homing. Would you be referring to the ability to re-home after a power outage, skipped step or some other issue and then pickup on the same job where you left off?

Since I went with the mechanical relays to interface the proxies with the breakout board, I would suspect the relays are a greater cause of inaccuracy than the repeatable sensing ability of the proxy.

I ask this because of the dificulty of settin up limit switches on my present Machine.... these look very good and simple to implement. accuracy would be to home consistantly...:confused:

[dmoore]

Using the electronics instead of the relays would be much faster, more power efficient and safer.
There is absolutely nothing wrong with using mechanical relays for this application.

I didn't want to imply that there is something wrong with mechanical relays - in fact I've used them with the proxies on my system. I, as it appears you do also, feel that relays are more than adequate for the task at hand on a MechMate. They also have the advantage of being simple to understand and service, universally available and easy to hookup.

I still think it is valid to say they are faster, more efficient and safer. No?

[Greg J]

I used the proximity sensors and was amazed by the low cost and ease of assembly/setup/troubleshooting. I bought the Prox's with the integral LED's. I don't have to open the control cabinet to check status of the relay.

What's the cost of mechanical relays?

As for safety, if a prox. dies, the system "opens" and E-stops. Mechanical items also fail over time.

The mechanical relay is fine for this application, but, the prox. sensor may have a slight advantage when considering cost/installation/troubleshooting.

[dmoore]

The mechanical relay is fine for this application, but, the prox. sensor may have a slight advantage when considering cost/installation/troubleshooting.

Were you able to wire your proxies right into the break out board or do you have the proxies controlling the relays, which control the BOB?

On a side note about cheap proxy sensors... Here are a bunch of discount (USA supplier) 8, 12, 18, 30mm, etc proxies for $10:

http://www.automation-overstock.com/products.asp?cat=16

I highly recommend the 5 meter, right angle cables they sell for about $5.50 also. Read the specs carefully - NPN/PNP/sensing distance.

[Greg J]

I just followed Sean's setup. Prox's wired to relays. Relays wired to BOB.

Also agree on reading the spec's carefully. Lots of differences between sensors.

[smreish]

Greg,
...and it worked?:D

[Greg J]

Sean,

Actually, your design (like the MM) was so eloquent, even someone like myself was able to get it working. :)

Seriously, very nice design and documentation.