Absolute? So what?
So, we turn on the mains isolator, and then press the ignition switch… The touch screen comes alive and by the time we have walked to the console the display is up. You look for the familiar ‘Home All Axis’ button and then you realize… there isn’t one.
On closer inspection the X, Y, Z readouts have values, this is the position of the machine. The Home buttons have been replaced by Goto Zero buttons. This is the first clue that you will get when you start the PRO series of Unicam machines.
There are many subtle differences to the older CNC systems, besides not having to home the machine.
- Let us consider running a long CNC program which is cutting an alloy mold for producing vacuum-formed plastic containers. While the program is running, load-shedding happens. On a normal machine you would have to re-home the machine… how accurately can your machine home itself, well the Unicam PRO machine will be able to restart and run in exactly the same position as it was, no steps in the mold, absolutely no change in position. The servomotors have a rotary encoder with 16 000 000 counts for one motor rotation, therefore the positional error of the machine will be sub-micron.
- If you fasten a jig to the bed and cut many parts over many days, every part will be exactly the same, the only thing that could change is the wear on the tool.
- You will never crash the tool because you forget to home the machine before doing a tool change.
- The movement of the servo motor is far more accurate than the older step and direction system. This is because the controller sends the motor a position and a time to get to that position, which means that the contour that the motor must achieve is pre-defined. The older systems send a series of pulses which is the same as telling the motor to run at a particular speed. The difference may not be that obvious, but the new system is position-based, and the old system is velocity-based.
- For the same reason, the Absolute system is far less vulnerable to EMF. If it does get a bad command the new system will correct the position on the next command. The older systems will be out of position if they get affected by EMF.
- The gantry will never get out of square because someone bumped the home switch.
Taking the above into consideration, why would you not want an Absolute Servo System?