I hacked a hole in the door with a jigsaw, and installed a Perspex window and 16” widescreen monitor.  I suspended the monitor with 3mm x 25mm aluminium strips.

I Started with second hand control cabinets that had been thrown out to scrap at work. The cabinets were full of holes, and some damaged contactors, timers, relays etc. I sifted through several discarded control cabinets over 12 months to scavenge enough working parts for my project. 

 

After the initial paper design, I started to wire it up knowing that as I went I would learn more, and figure out better ways to  make the control system work. It took several weeks of late nights in the shed after work.

Making the electrical cabinet.

Experimenting with layout

Half finished

Finished control cabinet.

I changed the design several times due to my different ideas in how to implement an emergency stop system. I wanted to have one central E-Stop button that could be pushed and perform the following functions.

           -Stop the spindle motor,

           -Stop the coolant pump,

           -freeze all servo drives as quickly and safely as possible,

           -tell the controlling computer to stop executing G-code as quickly as possible.

 

My first attempt at doing this involved using contactors to disconnect the servo motors from the servo controllers. The idea was that this would cut the power source instantly and therefore stop them spinning. DO NOT TRY THIS YOURSELF. I discovered very quickly that this blows up the IRF540N field effect transistors in a Geckodrive 320. The H– bridge is completely smoked by the back-EMF, and is generally a very bad idea.

 

A much better way is to use a relay to pull the “Error /Reset” wire from 5V to 0V DC, this uses the built in stop features of the servo controller, and does not kill the controller.

 

 

I also had to use a 3 second reset pulse to ensure that all of the servo controllers would be reset simultaneously, and that they would all stop if one drive faulted. All of this became too complicated to wire up practically with relay logic, so I purchased an excellent little PLC from a local automation company. The weapon of choice was an “Allen-Bradley Micro logix 1000.” This provided six logic inputs and four relay outputs.

 

I like PLC’s because if your needs change in the future you can change a few lines of programming, where as in a relay logic system, you have to remove bunches of wiring and start again.

PLC Program

Parallel port break out board.

Servo power  overload.

Text Box: 72V Transformer
Text Box: Micrologix PLC
Text Box: Servo controllers

Finished control cabinet from the outside.

Testing to control system before use.

Grae-Tech