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Author Topic: machine safty issue  (Read 2387 times)

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machine safty issue
« on: April 02, 2008, 01:52:10 PM »
reading some of these posts about spontanious machine runs.There needs to be a discussion about a basic hardwire start stop circuit for machine power.I would suggest a start stop button controlled contacter with the soft estop controlling a relay in series with the stop circuit.If someone has a basic circuit diagram they could post go for it Al
Re: machine safty issue
« Reply #1 on: April 02, 2008, 05:01:56 PM »
The mach manuals clearly states that machines are dangerous, it further explains about the charge pump circuit and safety circuit
If implementers decide to go without.... that is their decision

That said I agree a discussion is needed, and here is my particular point:

It is not always best to remove power from drives in a case of emergency.
Rotating parts of the machine with a large mass (think lathe chuck ) take longer to stop if the mains is removed from the inverter drive. In this case removing the “run” signal will stop the chuck faster.
In some cases a special program can be started in the inverter to de-accelerate as fast as possible (either simple Dynamic or DC braking)
A lot of commercial machines simply remove the control signal first and then a few seconds later (after the designed stop time) they remove the power from the drives.
Others are a bit smarter and remove the supply immediately only if they where moving.

The same thing counts for stepper / servo drives if they move the machine parts so fast that mass can continue the movement.

The machinery directive is clear in that each machine function needs to be evaluated separately and as a then whole, what is safe for one machine or function is not for others.

My lathe:
As it has speed both on the chuck and carriage I have decided to interrupt the control directly by the Estop circuit and have a timer circuit take out the suply to both drives a few seconds later

Only the spindle drive has the above treatment on the mill, the power to the axis drives are simply removed (moves to slow)

I found the www a great source of info (Google “machinery directive”) and also reading machine safety component manuals (RS website)

After that use that rare thing called common sense….


 
Re: machine safty issue
« Reply #2 on: April 02, 2008, 06:24:56 PM »
Thanks for the stop lesson.I'll incorporate a contactor with timer for the estop .If a person can assemble one of these I'm sure they could build in safety.Your references should help Al
« Last Edit: April 02, 2008, 06:50:47 PM by asparaguy »