Greetings all; This "jerk" you are discussing seems like the ideal place to have a module similar in nature to one of the limit functions, and which would subject a step change in speed to what I would call in a broadcast waveform analyzing situation as a "sine-squared" function. This could be compared in the mechanical world to the camshaft design that gradually accelerates the opening of an engine valve from zero to some maximum velocity achieved at 50% of the lift, then gently slows the valve to zero velocity at peak lift.
The idealized waveform then would be taking a full cycle of a sine wave, and clipping out the 180 degrees representing the 2 peaks from the lowest swing to the highest swing, but with arbitrary time lengths at the peak of the swings. In our case the lowest peak would be zero velocity, and the highest peak would be the imposed MAXVEL for that motor/joint. Exactly the same considerations apply when slowing or stopping, where the maximum accel is at the 50% of the change point. In the analog domain we used filters, Chebychev's in the cheaper stuff and Butterworths in the fancier lab stuff. These have been made to work using digital processing, facilitated by time gating the result to remove the pre and post ringing inherent in the analog world. The ringing removal would be a rather huge plus for machining operations. But I'm not the math guy that can show how its done. I just know that we got damned good at it in the last 20 years of NTSC broadcasting. One way I might suggest is a tapped delay line, an 8 or more stage shift register, tapped at each register with a simulation of the correct gain for that step, taking maximum gains in the sum stage from those registers in the center of the chain, and very little from those registers at the ends of the chain. One of the best transmitter distortion correctors ever, the Ward, used exactly that technique, using 3 delay lines of about .75 microseconds in series, and a center tapped=0 effect potentiometer to add, or subtract bits of the signal so as to correct to a very high degree, the time distortions associated with a limited bandwidth making maximum use of that allowed bandwidth, and doing it in such a way as to also pre-correct those distortions imposed by the average receiver which did not have the filtering complexity they could have achieved with a full Butterworth setup. That would have raised the shelf price of the average tv by $20 or more back then, so we did it for you. For us, a 16 tap line with the correct fixed gains per tap would help a lot, getting close to the ideal and our only real control input would be the clock speed of the shift register itself. You would get maximum accel when the change has propagated halfway thru the module, with very smooth because they would be smaller steps, accel profiles at the beginning and ends of the velocity change. Shorter, even only a 4 tap setup could be of help and might be worth exploring just for S&G, concept checking to see if I know what I'm going on about. ;-) It might even be worth doing a "digital sine squared" search on google for ideas. Cheers, Gene -- "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> SEMPER UBI SUB UBI!!!! [ Always wear underwater ] A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ Rapidly troubleshoot problems before they affect your business. Most IT organizations don't have a clear picture of how application performance affects their revenue. With AppDynamics, you get 100% visibility into your Java,.NET, & PHP application. Start your 15-day FREE TRIAL of AppDynamics Pro! http://pubads.g.doubleclick.net/gampad/clk?id=84349831&iu=/4140/ostg.clktrk _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
