[dmorton]

I'm researching the possibility of building my first CNC machine, but its a bit unusual - its a CNC controlled plastic film welding machine.

The machine needs to be able to control the position of the welding element - and for that I pretty much understand the mechanicals and control system needed. It can all be done with inexpensive Igus slides, stepper motors, and some relatively simple software.

The machine also needs to control the pressure applied to the welding element, and here I am a bit lost. I want to keep everything electric powered, not using air or hydraulic pressure. I have seen "electric actuators" out there, but its not clear if these can be commanded to apply a given force. What is the best way to apply a CNC controlled amount of force over a small travel?

There is also a rotary element to this machine, which needs to apply a constant torque. Essentially I want two powered nip rollers to work against each other so that the plastic film is kept in tension while the welding element operates, and then to work with each other (at a different toques) while the plastic film advances. For this kind of control, we are talking servomotors, correct?

[mike_Kilroy]

yes, servomotors will do what u want but u need a controller that control it the way u want... check out examples of linear servo driven actuators here:

http://www.kollmorgen.com/en-us/misc...r_positioners/

all good servo drives control first the torque (force/thrust) then speed then position and if needed then force. or if application can handle it just go back to force/torque loop only until you hit a switch or force or something.

where are you located? perhaps there is someone near you who would be willing to come explain the options to you in exchange for opportunity to maybe sell u something?