On Thursday 19 September 2019 09:39:41 Curtis Dutton wrote: > I appreciate the help and information. > > One last question before I go out and try this. I found a servo motor > with a serial encoder. What interface board should I use to read that > if I were using an 8i20 to power the servo? > That depends on the format the encoder outputs. And there are several.
The most popular is an open ended protocol whose range is limited only by the limits imposed by the number of valid bits the OS supports. This is commonly call ABX or similar, where there is an electrical phase angle of 90 degrees between the A and B signals, with an additional, 3rd signal of 1 pulse per rev to mark the 0 degree point in the rotation. Such a scheme gives the system enough data the it can know both the actual rotational position of the device, but which direction it is turning, at any time one of the A or B signals changes state. These encoders often come in LVDS, meaning low voltage differential, with at least 8 leads. These work exceptionally well in high noise environments as noise is usually longitudinal, its the difference between the A+ lead and the A- lead that is detected, ditto for B and X. This is very precise, but assumes the homeing switch that indirectly zero's all the counters, is the absolute accurate reference. I find the typical miniature microswitch with a rollor tipped lever, can be repeatable if consistently operated by the machinery to sub .001", and often much smaller errors, like .0002". Spring-dome pushbuttons, also selling for 50 cents or so are even more accurate in terms of repeatability. Contaminate exclusion may be up to the user. There are encoders that output a train of serial data in absolute format, but because it takes a finite amount of time to send it, also have a latency between recording the position, and updating the controling program. So the machine has to slowed considerably as it approaches the stopping point. I'm not a great believer in that, but it has been made to work. There are other ways to do it, often proprietary. Meaning if the company goes under, you have an unsupported device. That bothers me. Your trivia factoid for the day. ;-) > On Thu, Sep 19, 2019 at 9:06 AM Les Newell <les.new...@fastmail.co.uk> > > wrote: > > If you are trying to counterbalance a pure weight this system would > > inevitably end up accelerating into it's travel limits. However if > > the load has some sort of spring component it should be stable. For > > instance if you are trying to counterbalance a load so the force > > feedback is providing most of the force but something else is > > providing a small stabilizing force it should work. > > > > It is difficult to provide better advice without knowing more about > > the application. > > > > Les > > > > On 19/09/2019 13:31, Todd Zuercher wrote: > > > I don't think closing the loop with force feedback would work, If > > > the > > > > motor is applying x amount of force, adding more weight isn't going > > to change the amount of force read by the force feedback device. It > > will just push it down. The feedback will only be reading the force > > applied by the motor to resist the load, not the load itself, so > > changing the load will only cause acceleration. > > > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
