On Thu, 2010-11-25 at 08:58 -0700, Cathrine Hribar wrote: ... snip > I looked at those amps and they require an enterface board, I think.
If you already have a breakout board for your steppers, this could work for a PWM servo amp. EMC2 has a software generated PWM signal, but it is pretty slow and has low resolution. It really is only practical for a crude analog signal. It can be used for spindle speed. So, i guess you are right you'll need a hardware signal generator, like the Mesa 7i43P ($80). > The problem is that I am short of money for this hobby and I have to improve > my z axis. the stepper i have on my cnc won't move the z axis with > reliability. By buying step and direction amps i can add one servo and amp, > at > a time and get the benefit of encoder accuracy too, without changing all axis > at once. Am i wrong in thinking that? A servo won't necessarily fix your problem. If a servo were undersized or not working properly, you would get following error alarms, instead of missed steps, the result is basically the same. I would tend to see if your present Z axis could be made to work. The Z stepper slips because the load is greater than the motor torque. So you need to reduce the load or increase the torque. Usually a counter balance or spring can help reduce the Z axis lifting load. Make sure there is no excess friction in the ways. Sometimes, disconnecting the lead screw nut, and moving the axis buy hand, can give you a feel for what might be hanging up. Try to insure the motor is working properly. Is it getting enough power from the motor power supply? Is the step timing correct? Sometimes the motor will lose steps at a resonance point, which might be helped with adding a damper on the motor shaft. You can increase motor torque. Generally, torque is dependent on current and speed on voltage. To increase current one needs to decrease coil resistance, which is hard to do because you would need to rewind the motor. Current can also be increased by increasing the voltage, so you might try increasing the motor power supply voltage up to the maximum voltage of the motor driver (or get a higher voltage driver). This will increase the heat generated in the motor, so add just enough voltage to keep the motor from getting too hot. But, since the motor will need to be replaced if it still slips, you can afford to get it hot enough to fail. Another way to increase torque, sort of, is to go to a finer pitch lead screw, or easier, a reduction pulley system. This will slow the feed rate, so you'll have to balance speed and torque. Also, ball screws require _much_ less input torque for the same output force, so if you have lead screws, consider changing to ball screws. Plus you can get the advantage of double nut preload for zero backlash. There may be other issues I missed. If you can post a description of your machine, power supply, motor driver, motors, lead screw, pulleys, ways, etcetera, it may help reveal more solutions. > I have several computers I can choose from for this system. The high speed > machine u referenced, were u talking about the computer, or an interface card. What I was referring to was the number of steps or pulses it takes for your machine to travel one unit of length. For instance, if your steppers were set up for half stepping and you needed 1000 steps per second for feed rate X, then you change to a fancy micro-stepping drive, at say, 10 micro steps per step, you would need (10 micro-steps/step) x (1000 steps/second) / (2 half-steps/step) = 5000 steps per second, or five times the step rate to get the same axis feed rate. EMC2's software step generator isn't very fast, so the maximum micro-stepping or servo resolution can be limited by the maximum step rate that EMC2 can deliver (20 to 50 kiloHertz is common). Feed rate, resolution, and step or signal rate are tied together. > As u can see, i don't know anything about servo systems. > If there is anyway u can see for me to do what u suggest, without adding > another $100 or more, please let me know! > > Again, happy turkey day! > > Bill Good luck, Bill -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ Increase Visibility of Your 3D Game App & Earn a Chance To Win $500! Tap into the largest installed PC base & get more eyes on your game by optimizing for Intel(R) Graphics Technology. Get started today with the Intel(R) Software Partner Program. Five $500 cash prizes are up for grabs. http://p.sf.net/sfu/intelisp-dev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
