On Friday 10 March 2017 11:33:05 Jon Elson wrote: > On 03/10/2017 02:22 AM, Chris Albertson wrote: > > I asked about how to characterize a servo motor here, got some good > > answers. Thanks. Turns out I have some capable DC servo motors. > > > > Now one more question: How are people connecting these motors? > > It looks to me that machine kit/LinuxCNC/EMC can read the quadrature > > encoder and product PWM to drive the motor. If so then I'D need a > > dual H-bridge and a power supply. It could also produce a step > > and direction signal and I might use a Gecko 320X controller. > > You really can't generate PWM at reasonable frequency and > time resolution in software. > So, in general, you need a PWM generator in hardware. If > you want to use Machinekit on the Beagle Bone, the PRU is > kind of in-between, and probably will work. Or, Mesa and > Pico Systems (my company) have devices that can generate the > PWM in hardware. > Pico Systems has the Universal PWM Controller, and PWM servo > amplifiers to run most medium-sized servo motors. > See > http://pico-systems.com/osc2.5/catalog/product_info.php?cPath=3&produc >ts_id=19 and > http://pico-systems.com/osc2.5/catalog/product_info.php?cPath=3&produc >ts_id=26 for more info. > As for this latter servo driver, I am using 2 of them, a bit off target for a servo, but they have made truly excellent spindle drivers for 1 horse class dc brushed motors here. Response times, and extra overhead in the power has caused me to insert a limit3 in the signal path to the pwmgen to control the acceleration rates on the TLM (a small lathe) to prevent destruction of drive parts due the the mass of the chuck on TLM. In both cases I am useing hardware pwmgen's with a cycle rate in the 10 kilohertz range, so the control rate is essentially the servo-thread rate. That rate demands faster opto's if opto-isolated breakout boards are used. In the case of TLM they were avoided by feeding the pwm directly to the pwm-servo, but on the G0704, I had to pull and bypass that one opto else the control was extremely non-linear. With it bypassed, control non-linearity is well within tolerance, 5% of the requested speed from 100-2700 revs. In both cases, there is an optical A/B/X encoder on the spindle for speed/velocity feedback, and with a PID stage, speed vs load is very stiff. Thats very close to vfd performance at a quite a few less sheckels.
Highly recommended by grandpa Gene, for motors rated below 160 volt dc drive and less than 20 amps locked rotor. > The original Gecko 320 has some issues with tightness of the > servo loop, ie. with some motors and power supply voltages, > it allows a LOT of slack. I have not tried the 320X to see > if it does better. > > Jon Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Announcing the Oxford Dictionaries API! The API offers world-renowned dictionary content that is easy and intuitive to access. Sign up for an account today to start using our lexical data to power your apps and projects. Get started today and enter our developer competition. http://sdm.link/oxford _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
