[peteeng]

\r\n \r\n Hi Mactec - OK I have done some more reading and digging. The input shaping functions more like a damper on a car wheel (commonly called a shock absorber) it initially uses an accelerometer to test and calculate the spectral frequency response of the structure. Once this spectral response is known a suitable damping factor can be built into the motor signal, same as you can get different damping ratio motion dampers. You can also get dynamic dampers that have adjustable damping ratios. I suspect that\'s what\'s happening here with the algorithms . In Klipper there are a few damping strategies that can be selected. So its not an active control or an adaptive control. But it is a valid strategy to improve smoothness/decrease jerk same as a automotive wheel motion damper provides.
\n
\nsee convolving - https://en.wikipedia.org/wiki/Convolution
\n
\n\'I assumed that since the accelerometer was mounted permanently on the spindle in the articles I looked at it was actively involved in the motion control. Since then I have found it is only used when recalibration of the system is needed...
\n
\nhttps://all3dp.com/2/klipper-input-s...ply-explained/
\n
\nThe search goes on. I shall use the bigtree/klipper combo on the printer I\'m building to get some experience with this approach.... I have found a local supplier that seems to have good knowledge/ support. So I\'m setting up a question list for them at the moment. Considering the board cost $125AUD and the 8A 60V ( up to eight drivers per board) drivers cost $40AUD each seems its good value compared to mill/router type controllers etc. Peter\r\n \r\n

[peteeng]

\r\n \r\n Hi All - I have been speaking to the local 3D printer place and they have given me ideas. The duet3d drivers have input shaping and have a good CNC "ecology" as they say. D3D can use Marlin or Klipper. More digging to do. Peter
\n
\nDuet 3D\r\n \r\n

[peteeng]

\r\n \r\n more info on shapers - Peter\r\n \r\n

[peteeng]

\r\n \r\n Hi All - Looks like Marlin has had s-curve accel in development , but I think shaping is better. Sorting some accelerometers at the moment. Peter
\n
\nSearch · s-curve · GitHub\r\n \r\n

[peteeng]

\r\n \r\n Hi All - Ard found a good video on damping in another thread from Rexroth. Here\'s a clip for the video showing the feedback loop. The feedback goes into a PID filter and the command signal gets modified depending on the settings. The feedback can be acceleration or position. It can also be sensorless and this would use an input shaper type function. peter
\n
\nhttps://youtu.be/eikPy2vJKyI\r\n \r\n

[deadlykitten]

\r\n \r\n as high cnc\'s have allready their loops, rexroth senzors are add-ons to such machines ( for complementary tasks ), but more likely they are used for less automatized systems
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\r\n \r\n feedback can be acceleration or position \r\n \r\n

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or sound, or pressure ... whatever type of senzor there is
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\njerk control = jerk + control = motion change + control = planer + mcs
\n
\nfor hobby, is a great jump from linear to s acceleration, and this makes one focus only on start and end accelerations
\n
\na high end machine modulates acceleration based on curvature, and may use not only linear and s, multi stage deceleration, so it\'s focus is not only start&end, but continuously; this are functions for die-molds
\n
\n

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\nas stated from begining, the answer is data from feedback loop for example, for that 3d pritner of yours, if you could map the head accel data with position data, you would be able to fine tune it / kindly \r\n \r\n

[peteeng]

\r\n \r\n Hi DK - Indeed that\'s what I shall do. But you don\'t have to map accel with position only correct velocity at known vibration zones. Peter\r\n \r\n

[deadlykitten]

\r\n \r\n hy pete, i was not reffering to changing acceleration, thus not to what to do with recorded data, but, for example, for that 3d printer, as to record data from accelerometer senzor, togheter with axis position, because only accelerometer data alone is hard to interpret - is needed to relate it to something
\n
\nthe loop is reactive upon reading, regardless of what kind of loop is, or what process/machine is there
\n
\nreading data involves sampling averages, that form paterns, and tuning the loop, involves a reaction upon each patern ( there is no clue for the machine that it is actually vibrating, but it can detect an abnormal patern; is it vibration ? who knows )
\n
\nsuch functions are not open to client, being more machine builder specifics, but it can allow some partial control over it
\n
\nis possible to record data from systems without loops, but is not only recording, but also processing, because, like this, a result is created and initial data is deleted ( or large portions of it ), otherwise, with those high frequencies, one would end up with an enormous amount of data
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\nunfortunately, i don\'t know what such tools are there at hobby system
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\r\n \r\n Indeed that\'s what I shall do\r\n \r\n

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i don\'t know what you are after so far, it seems to me that going with S curve capable controllers is a nice step
\n
\nif the controoler does not allow too much acces, you can use some senzors over your construction and \'check\' how is it performing ?!
\n
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\nyour entire idea with \'jerk control\' can be put in a larger area, like stability, or how much to push a system until it deteriorates
\n
\ndefine a method to control, to quantify the \'thing\' you are after; within buget
\n
\nfor example :
\n... there are cases where senzors are used to detect bending, so to avoid cnc machine wear, simply because the closed loop can not detect such a case
\n... or bridge deformation under stress ... or helicopter blades twist ( rexroth - siemens )
\n... or to detect sound, checking versus a baseline, for wear detection
\n
\ni have seen that you focused a lot on jerk, but for expensive cnc\'s, smoothnes is much more than jerk and splines, so to say it; you can define smoothness as long as loop deviation is tolerated
\n
\nsomehow the discusion is a mix, balanced between hobby and profesional systems
\n
\nif i was to decide on control for building a machine with reasonable costs, i would contact all such guys that are into this, so to bring my self to-date fast with what is there; i don\'t know, maybe i am wrong, but my intuittion says that s curve capable hobby controlers is not a new thing / kindly \r\n \r\n

[peteeng]

\r\n \r\n Hi DK - The 3D printer industry have gone well past s-curve velocity profiles and use input shaping to improve machine vibration using electronic damping. For my level of technology and economy input shaping is the one to pick for CNC machines. It provides nearly all of the performance of full active control in a simple implementation. This thread and investigation has covered a lot of territory and there\'s not much more to investigate. My overall comment is that the Maker level CNC tech is far behind the 3D printer tech. Things like Klipper and Marlin are very attractive and the printer hardware is cheaper and better developed then the CNC boards.
\n
\nThe next generation of CNC builders will use Arduinos, 3D printer boards and Klipper etc as they will have been exposed to all of that at school and its straight forward to use and cheaper then CNC stuff. There are several 3D printer retail shops within 2hrs of me, there are no retail desktop router shops anywhere. So the printer market is well developed and will continue to develop as it has the money and customer support to do this. So printers now have input shaping and in the future will have full active control of motion standard. Mach4 does not make a motion controller so they will lose momentum , their machine motion control is decades out of date. UCCNC has the advantage of making their own motion controllers. These need to be integrated and updated to input shaping and then they would be hobby market leaders. There are several people working on CNC style GUIs for Klipper and Marlin , once this happens they are the pick as then there will be no major front end difference but there will be a large performance difference.
\n
\nSo anyone starting to design a machine now I suggest they look at Big Tree Tech control boards and Duet3D boards they offer better tech and better $$$ for the people interested in this sort of thing... Peter\r\n \r\n

[peteeng]

\r\n \r\n a good note on shaping - Peter
\n
\nhttps://github.com/MarlinFirmware/Marlin/pull/24797\r\n \r\n

[peteeng]

\r\n \r\n Summary 12-2022 till 02-2023 "Jerk" control. So there has been a lot of input into this thanks everyone. The outcome has been to find all sorts of approaches to having a machine behave smoother. So I\'ll summaries here:
\n1) Trapezoidal velocity planning is simple and common. Motion is limited either by set Vmax or set Accel max. Unfortunately this strategy has high jerk at its "knee" when velocity changes instantly producing mathematically infinite accel and large inertial forces creating vibrations. Since gcode is feed to the machine in strict time segments we can calculate acceleration as we know Vstart and Vfinish at each segment and we know the segment length. So accel=(V-u)/t this is calculated at each segment so the controller knows when to limit the accel. It also limits velocity. The accel is created by the torque capacity of the motor at any point of time reacting to the inertial load upon it.
\n2) To get rid of the knee "s-curve" velocity profiles are used. These place a bezier curve at the knee to soften the curve. The S does not mean sine or anything special , It just means the curve could look like an S. The length of the curve can be adjusted in some systems. Its an improvement over Trap
\n3) Input shaping - is a damping technique that uses an added inverse signal to cancel the vibration of the system. Firstly the system is excited and measured to determine its major vibration modes. Then an algorithm is selected to run alongside the velocity profile. This dampens the vibrations. This is the same process as a shock absorber on a wheel or noise cancelling headphones use. 3D printing has used it for many years to improve their machine motion. Should be used on CNC more often. Superior to S curve as it includes the actual machine responses vs guessing what that response is
\n4) Active feedback - This takes a signal from an encoder, usually acceleration (can be displacement as well) and uses similar math to the input shaping to reduce vibration by smoothing velocity. This is usually by a PID controller in the loop. This is common in servo systems. It is better then input shaping as it is working with the inertial conditions in real time.
\n
\nFor shaping and active systems to work there has to be co-operation between the machine controller developers and the motion control developers. Since these have been divided tasks in the hobby CNC market "advanced" motion has been impossible. Companies like UNCNC could integrate their Machine control with their motion control and implement shaping. 3D printer controllers are all on one board so can do this easily which they have done. Many printers now have on head accelerometers and its logical to expect that they will implement active systems very soon as shaping has become the norm.
\n
\nThanks again hopefully this has been useful for someone. It has for me and I shall be using a 3D printer board on the next build and implementing input shaping. Probably Marlin controller and Duet3D board. Peter\r\n \r\n

[deadlykitten]

\r\n \r\n ploters operate in controled enviroment, while cnc machines are for hazard conditions
\n
\na controlled enviroment requires only initial calibration, while hazard requires the ability to react to unknown i think this can be seen as the line between a hobby and a profesional system
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\r\n \r\n Q is block compression. best to set it to 0 always. What it does is collapse lines of code within a specified angle of each other, so you get less lines, longer segments and faster motion. sounds fine in theory but in practice you can get very out of square cuts.
\n
\nWhen the cam system creates a spline it will not be initially smooth. It has to be analysed and smoothed. This is what adaptions are they are cycles in which the derivative of the curvature is looked at and then the curve is adjusted until it is to the required smoothness.\r\n \r\n

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there is something to add here; i remebered it when i was away from pc, but forgot when i was posting
\n
\nabout cnc\'s capable of geometry manipulation; a cam system has it\'s own aproximation methods, so adding another aproximation at the cnc is a bit useless
\n
\nfor example, if you wish for 0.5 precision, is nonsense to use cam with 0.4, and cnc with 0.1, is like having to split/balance errors between cam and cnc
\n
\none good method to adress it, is to keep all math inside the cam, and generate a toolpath with a minimal number of elements ( like to avoid a too crowded code, only to put useless stress on the cnc )
\n
\nfor example, if there are only lines, then the cnc should have a larger ( maxxed ) value for roughing, and technical drawing tolerance for finishing
\n
\nthus cam to handle only static, only shape related things, and the cnc to handle only motion related things
\n
\nin practice, a common aproach with splines, is to segment the toolpath way too much ( very very dense code at 3-5um), then cnc it with ~0.01 deviation, thus to be sure that the solid gets recreated almost \'identical\' in reality; this aproach can lead to increased cycle time( even if buffer size is bigger, machine is doing too much math, and advancing too little ); a better aproach, is to filter the toolpath inside the cam, just how the cnc does, so to have a g-code as simple as it could get, but this requires a skilled programmer
\n
\nto meet this demand, more like to meet this situation off too dense codes, the cnc algorithms got even better at being able to ignore useless points, and aproximate only what remains ...
\n
\nso, if cnc has such numerical aproximations, one can dump in it whatever trash code it has; otherwise, achiving short cycle times, requires skills / kindly \r\n \r\n

[JR107]

\r\n \r\n I noticed this thread specifically a while back and wanted to throw some insight into the ezcam/forums.
\r\n
\r\nIt is hard to pinpoint a good response since the initial disscussion/s is a more generalized question & theory of how the large CNC\'s controlled and accounted for jerk. After reading the entire thread, it shifts toward the hobby-oriented side of what is possible. I bring this up because apart from theory, both are somewhat different in the practical implementation of error corrections. It should go without saying, but I\'ll reiterate that when all is said and done, a 60-year-old manual Bridgeport will still give a higher-quality surface finish than a benchtop CNC imported from China. There is only so much customized software + CAD/CAM can fix; you quickly realize the sunk cost fallacy.
\r\n
\r\nThe above is essential when looking at large "commercial" CNC machines. The kinematics behind their base operation is already good enough for 70%+ of their work potential. You would be surprised, because they do not require many advanced adjustments to motion. Any higher percentage value becomes a cost/complexity tradeoff that increases exponentially. 10-15% additional percentage points on that arbitrary value is simply in the form of adequately configured - closed loop; error correction routines. For brevity, I am placing servo motor motion profiles in this category. Pick your poison, as the velocity and its derivatives within the servo profile, can be optimized for different factors. Adding ACTUAL linear encoders on all the axes may yield an additional 5% to the potential accuracy, even within a simple PID loop. Someone reading this will instantly jump to comment, "but my servos already have an encoder with xx-bits or x-million PPR of positional accuracy," or (my favorite), "glass scales are only for GD&T / checking thermal growth," failing to realize that a servo is essentially a DC motor with an encoder stuck on the back; once you figure in torque is applied perpendicular to an axis of rotation: regardless of ballscrews, way type, etc.. roll, yaw, and pitch errors are introduced. As the bed moves further from the servo, the probability of the reported position being exact decreases with simple physics. Speeding up latency on the control network with something like EtherCAT will yield an additional 2-3% of potential.
\r\n
\r\nNow comes the fun part. There is an inherent disconnect between CAM software and commercial CNC controllers. Many (so many it will make your head hurt) mathematical methods exist to optimize motion and tool path planning. All require access to the control loop of the servos. In the first step of tuning the servo profiles, errors along each respective axis are often parameterized and then transformed into a 3-D vector model in joint space. An equation is estimated from this three-dimensional space as an error mapping function. This approach is as "black box" as it gets; low cost and is processed entirely behind the scenes by the central controller. G-code passes through, and the machine passively corrects the errors. *errors as in erroneous values of the derivatives of position, pre-determined by whomever.*
\r\n
\r\nThe next question is how spindle load and feed rate factor into the equation. The most recognized approach is constraining the jerk term as a function of path displacement while still within a servo control loop. This method uses quintic splines to smooth consecutive steps, regardless of the toolpath from the CAM software. Keeping the step size constant (if the base servo profile is configured correctly) allows the spline chord lengths to be recursively updated using the previously known position for the following position. A 10th-order polynomial is solved in real-time. This is all happening within the servo control loop. So instead of move here -> accelerate -> decelerate etc., every consecutive movement is fitted to a spline for smoothing.
\r\n
\r\nWithout direct access to a machine\'s servo controller loop commands, there aren\'t many things to "optimize." Using glass scales along each axis is the easiest way to overcome this pitfall in commercial machines. Because if your linear encoder along any given axis has roughly 5-10x the resolution of the tolerance you are trying to hold, the general philosophy is that the manufacturer\'s controller should have enough sampling bandwidth to adjust the motion profiles for smoothness.
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\r\n
\r\nI tried keeping all of that as non-mathematician-friendly as possible for other readers. Still, I can easily derive almost any significant motion planning optimization algorithm you care to ask about. It all boils down to implementation, and once again, there is a massive disconnect between CAM and Machine. 5-axis also gets interesting since all of the above no longer works.\r\n \r\n

[deadlykitten]

\r\n \r\n

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4) Active feedback - This takes a signal from an encoder, usually acceleration (can be displacement as well) and uses similar math to the input shaping to reduce vibration by smoothing velocity

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he pete that is true for a 3d printer head, going way too fast, and needed to be slowed down ... while most common cnc systems, don\'t sense vibration, for example drilling with a big tool will push the machine to it\'s limits, and reaction loop will simply make it vibrate more and more, and machine won\'t stop unless the overtorque is reached ( if they have overtorque, otherwse, it keeps going ... damage may occur ): this aplies to almost all cnc machines, unless expensive ones ( protected like servtech described; idea is that they have more than the basic loop )
\n
\nso, there is vibration when initial machine is calibrated ( like video you shared with rextorh ), and also from the hazard enviroment ... they are both vibrations, but they are sensed different
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\nthus, reaction is not always to reduce speed ... depends on what the loop is there for
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\r\n \r\n So I think the printer tech has gone past the CNC tech \r\n \r\n

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with printers demand growing, some solutions arrived; new market; as how those may be better than those for an equivalent cnc ?! i can\'t see this through ...
\n
\ni mean, there is like this :
\n... plooters :
\n...... edm : repetitive fast motion; same thing over and over
\n...... wire : slow motion
\n...... routers : fast motion, all over the place
\n...... printers : even faster motion
\n... cnc machine : enviroment bites/fightes back
\n
\ni mean there are some similarities between systems with kind of identical requirement, but still, the range is soo large, so to say that printer tech has gone past cnc tech
\n
\nfor example, high end machines have aditive and laser heads, but if their cnc system would be developed only for those heads, that machine would not be able to cut metal anymore ... it would loose it\'s primalry function
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\r\n \r\n I first got involved in CNC stuff some 35 years ago. I was making some components ... \r\n \r\n

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good memories
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\r\n \r\n My planned printer will have an integrated accelerometer at the head so it would not know if its a printer or a spindle... \r\n \r\n

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i can\'t believe you just said that i read it twice .... indeed, it has no clue; zero clue; zeroooooooo
\n
\nmcs is numbers, algorithms, has it\'s own mind whatever the g-code ( or the input is )
\n
\ni am sure you remebet that page you shared, where they described how to adjust the printer, based on vibration pattern found on the printed part, and mactec said that mostly it will go away if mechanical structure is rigid; indeed, the jerk control, the pure control, has .... how to say it ... does not care much of g-code; and is not jerk control, is called motion control system, mcs ... ( handles also jerk, if you wish )
\n
\nmost programmers focus only on cam & gcode, while the critical things are inside the machine, and they are indeed \'invisible\'; only a few programers actually deal with cnc motion parameters ( need to understand 1st, then the cnc to allow such acces, then they to have tools to acces those ... is not easy, is not common, and is mostly an off-topic, off-limit subject for usual shop guys; is more relevant to machine builders )
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\r\n \r\n time will tell\r\n \r\n

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the idea with the accelerometer, for a fast moving printer ( or heavy cnc machine at high feed), etc, is that it can tell if the system has stabilized so the next move to begin, or there are still vibrations manifesting
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\nin order for the basic cnc to detect inertia, it must occur at a very high value, so to trigger a big reaction in the system ... it can not, while such an accelerometer, being placed on the head, is way closer to the source of vibrations
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\nhow to join accelerometer data into the allready existing system ... i believe this is maybe what you wish for; i don\'t know
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, a 60-year-old manual Bridgeport will still give a higher-quality surface finish than a benchtop CNC imported from China. There is only so much customized software + CAD/CAM can fix;

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hy jr yes, you said it ... indeed, a controlled cnc system is not a guarantee; thus its presence ant the fact that it is working as designed, does not mean that it meets client expectation, so to say
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\nso 1st step is data from feedback loop analysys, but also what is that loop monitoring is also important ...
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\r\n \r\n Someone reading this will instantly jump to comment, "but my servos already have an encoder with xx-bits or x-million PPR of positional accuracy," or (my favorite), "glass scales are only for GD&T / checking thermal growth, ... As the bed moves further from the servo \r\n \r\n

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that is so true; i had the \'honor\' to have to explain to such persons why the new expensive cnc machine dispplaying 0.001 accuracy on screen, is not stable within 0.01 for some dimensions; once you understand such things, life with cnc machines is a bit easiear
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\r\n \r\n There is an inherent disconnect between CAM software and commercial CNC controllers.\r\n \r\n

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please develop on this a bit; for example, what should a cam do more, or what kind of functions would you like to be there ?
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\r\n \r\n This method uses quintic splines to smooth consecutive steps, regardless of the toolpath from the CAM software. Keeping the step size constant (if the base servo profile is configured correctly) allows the spline chord lengths to be recursively updated using the previously known position for the following position. A 10th-order polynomial is solved in real-time. This is all happening within the servo control loop. So instead of move here -> accelerate -> decelerate etc., every consecutive movement is fitted to a spline for smoothing.\r\n \r\n

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there is a big difference between \'move here -> accelerate -> decelerate\' and \'spline smoothing capable machines\'; i mean this spline ones are top tier, and next motion is indeed fitted to an allreadt existing one, high degree poly are there ... yes, that\'s true such spline machines are good as long as the final shape, the object to be machined, is shapy, curvy, otherwise, having splines control active for only lines toolpath, with arches here and there ... there is no reason
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\r\n \r\n 5-axis also gets interesting since all of the above no longer works.\r\n \r\n

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if i may ask, please, what is with 5 axis ?
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\r\n \r\n So I was retrieving real time data directly onto a pc -> attempting to calculate things (5 axis stuff)\r\n \r\n

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please, can you develop ? thank you \r\n \r\n

[peteeng]

\r\n \r\n Hi JR - Thanks for chipping in. The Maker/Hobby and to some extent the commercial suppliers do have an issue with the disconnect as you say of the CAM SW, the machine controller, motor drivers and the motion planner. This is a function of how the industry has developed over the last 40 years as each component was and is still seen as a specialist area. Only the large commercial players have integrated the functions. Contrary to this the 3D printer market promptly integrated all of this onto one board 1) as it makes sense 2) costs less to make one board vs 3 or more and 3) they require the performance as its a developing performance driven/ cost down market vs maker level CNC which is small time slow moving tech. So I think the printer tech has gone past the CNC tech and it will become the defacto stuff we use very soon... I was in an electronics shop the other day and there were some school kids there discussion an arduino project. If they were to build a CNC they would not use Mach4/MC and and motion controller etc. They\'d dive into big tree or similar. ... I\'m helping a guy in Cairo build a router and he\'s the same, very comfortable with 3D printer stuff so is going that way with the control and input shaping. Peter\r\n \r\n

[JR107]

\r\n \r\n A critical thing to note is that as 3D printer motion controllers become more and more advanced, their effectiveness with CNC machining work will diminish. The math involved in control planning additive-based manufacturing differs from subtractive-based, primarily due to loads and tool displacements.
\r\n
\r\nI agree that somewhere in the future, there will be an inflection point where companies realize they can likely produce better parts with a custom machine that can control every last parameter than one purchased due to convenience and distributor relationships.
\r\n
\r\nWorth looking into is Granite Devices and Trinamic. Both companies are working towards more user-defined functionality within motion control. ICAM also gets added to the list, but they are focused on the CAM/post-processing side of things. Supposedly they offer software to build your own post-processing from scratch, though I hesitate to know the cost of that one.
\r\n
\r\nI do a lot of research with LabVIEW, and can vouch that the functionality is there. However, I would not consider that practical in any working industrial environment. If you think AutoDesk nickel and dimes - N.I. is worse.\r\n \r\n

[peteeng]

\r\n \r\n HI JR - This disconnect you mention reminds me of when I first got involved in CNC stuff some 35 years ago. I was making some components in a project via water jet cutting then finish machining. I came across our factory neighbor one day and found he had a CNC mill so I said can you make these? He said yes but he could not program the part as it was complex (complex for then even though it was 2.5 axis work). So I found a programmer but he wanted a CAD file or a point table. CAD programs were really $$$ pro-engineer cost over $30000AUD at the time and the computer was nearly as much. So I sat down and manually calculated to 4 dec places all the inflection points on the part. Took this to the programmer and he charged $250 (a weeks wages for me) for the program on a floppy disc and I took that to the machinist at which point he said what\'s this? So he got a reader installed and off we went. I did a few jobs like this for the machinist after that then bought a wireframe cad and made the front end a bit easier. Now you can download Fusion360 hobby and get 1000x more stuff for free! We have come along way but we still have a long way to go. Technology does not stop. Peter\r\n \r\n

[JR107]

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HI JR - This disconnect you mention reminds me of when I first got involved in CNC stuff some 35 years ago. I was making some components in a project via water jet cutting then finish machining. I came across our factory neighbor one day and found he had a CNC mill so I said can you make these? He said yes but he could not program the part as it was complex (complex for then even though it was 2.5 axis work). So I found a programmer but he wanted a CAD file or a point table. CAD programs were really $$$ pro-engineer cost over $30000AUD at the time and the computer was nearly as much. So I sat down and manually calculated to 4 dec places all the inflection points on the part. Took this to the programmer and he charged $250 (a weeks wages for me) for the program on a floppy disc and I took that to the machinist at which point he said what\'s this? So he got a reader installed and off we went. I did a few jobs like this for the machinist after that then bought a wireframe cad and made the front end a bit easier. Now you can download Fusion360 hobby and get 1000x more stuff for free! We have come along way but we still have a long way to go. Technology does not stop. Peter

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Funny you mention this; quite a few years back I bought an old machine with an Heidenhain controller for the sole purpose of trying to hack it. It was one of the only controllers that I could find with the ability to actively read / write data via rs-232. The internal memory was so small that you could only realistically fetch data via rs-232. The solution was to trick the controller into using the floppy drive read commands from a different data line as the overwrite. So I was retrieving real time data directly onto a pc -> attempting to calculate things (5 axis stuff)-> drip feeding the updated G-code to a virtual machine running DOS -> which then drip fed back to the controller. Making use of some clever if & then commands in the G-code as well as temporary stops allowed a semi working controller. I quickly realized how much of a train wreck the idea was and abandoned the project.\r\n \r\n

[peteeng]

\r\n \r\n Hi JR - Trinamic is already well embedded in printer tech, they particularly were embraced due to their resultant zero motor noise. This is important for printers because they are domestic appliances. I\'ve had a quick look at Granite Devices and will investigate further. I think once printers go active we will be able to tune both ways. My planned printer will have an integrated accelerometer at the head so it would not know if its a printer or a spindle... time will tell...Thanks Peter\r\n \r\n

[peteeng]

\r\n \r\n Hi DK - I think most of what you ask has been covered before in the thread. My aim is to have smoother motion than is available with Mach4 and UCCNC and similar machine controllers. I believe input shaping is a viable and economic way to achieve this at the Maker/Hobby level and indeed the printer controllers have achieved this via integration of the machine controller/motor drivers and motion control. And they will get better whereas the CNC tech has been stagnant for a long time due to the disconnected components (or toolchain as it is called) and their developers and the lack of "push back or forward" from the cnc users to achieve better products. All of the technicalities of how to do it are out there. Peter\r\n \r\n

[peteeng]

\r\n \r\n Hi All - This makes using BTT boards very easy. Will research this a bit more.... Peter
\n
\nBigTreeTech to Release Open-Source Klipper-Based Tablet | All3DP\r\n \r\n

[peteeng]

\r\n \r\n Hi All - I have cleared out a space to rebuild one of my small cnc platforms into a test machine for a high voltage high speed control system. I was to use the BTT stuff but one of my clients uses the Nighthawk controller and so for his 8x4ft machine I was going to go with that, so he would be familiar. So I spoke to the Nighthawk people and they are implementing input shaping plus they are releasing a 6 axis version of their controller. This lines up really well with a couple of future projects. So they are only 1 hours drive away from me so I shall obtain one of their controllers and get familiar.... that\'s very exciting in a way, they seem really focused on maximum product development, great to see. This is also good as their controller is for CNC vs printing so it has the full gcode available. It also supports plasma, laser and printing so many opportunities. And you can run your machine from your phone, wireless! bargain...You can use their one box controller or buy the board only and run high voltage drivers or any driver you like. Many many options... Peter
\n
\nhttps://www.cnc3d.com.au/nighthawkcnc-controller\r\n \r\n

[deadlykitten]

\r\n \r\n hello i was on batteries today, and i remembered this discusion
\n
\ni shared okuma\'s documents for spline\'s, as a general info ... but such things are so \'unique\', that most okuma users that try to use them, may end up with some average machine settings, or give up, or mess up the controller parameters in a way that requires servo retuning by specialized personal, as some parameters are not to be messed up with
\n
\nsome okuma employes may reveal some technical informations, a piece here, another there, but for regular shops, the knowledge is hard to get, as it requires math skills, good understanding of the controller, ways to input logic in the postrocessors, debuging skils, quantify change-effect, etc ... that\'s not a regular combo of skills
\n
\nin short, is a top specialized function, developed from other functions, and it shares parts with other servo tuning functions, and very few persons are into cnc functions good understanding
\n
\nimplementention is different in cnc brands, different extent / kindly \r\n \r\n

[deadlykitten]

\r\n \r\n a little tip : if you wish to cut a curvy shape, but your machine has no special functions, then is needed to break the toolpath in small segments g01s
\n
\nthe smaller the segment, the harder for the cnc to follow, so is up to you to find the breakpoint of your machine for okuma, is 1/7500, thus a 1mm segment can be executed at F7500mm/min max speed
\n
\nsuch a trick allows you to machine within balance, thus at the limit where cnc still delivers; you may go beyond that point as long as your part will look ok, but the cost is cycle time, that will start to increase pretty much
\n
\nanother thing to consider, is that toolpath segments should not be equal, but dependant on curvature and desired tolerance, and implementing this should deliver a much smaller program size, thus the buffer won\'t be overloaded, so again, machine limit will be reached later, as computational time will be able to stay in front of execution
\n
\nthis requires machine behaviour tests, and software logic / kindly \r\n \r\n

[jackjr-123]

\r\n \r\n Hi Peter,
\n
\nI think this is relevant to what you\'re looking for:
\nhttps://www.youtube.com/watch?v=nUdvrO6lsX8\r\n \r\n

[peteeng]

\r\n \r\n Hi Jack - Thks for the link .I understand this at an "in-principle" level. The receding horizon approach I have not seen before. The maths have to be run in loops each loop gets better until a converged answer is achieved at the desired tolerance.
\n
\nThis work attempts to do the calc in real time. This is possible these days but it could be done as an adaptive post process before it gets to the machine. Its a trajectory planner and I\'m tending to think that it has to be coupled with the machine mechanics (maybe the mechanics are more important). No good having a wizz bang jerk free trajectory on a wimpy noodle machine. I\'m setting up a machine with a Nighthawk (NH) controller. The nighthawk people are implementing input shaping so I wait for that. In the mean time I can run Klipper into the NH controller and have a play with input shaping (IS).. When I get IS running I\'ll report here. Thks Peter\r\n \r\n

[jackjr-123]

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This work attempts to do the calc in real time. This is possible these days but it could be done as an adaptive post process before it gets to the machine. Its a trajectory planner and I\'m tending to think that it has to be coupled with the machine mechanics (maybe the mechanics are more important).

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Actually their trajectory planner (it\'s open source, you can check it out) has no realtime requirements. As long as you provide the machine parameters (max velocity, accel and jerk), the trajectory can be computed entirely offline.
\r\n
\r\nI\'m also curious about these input shaping algorithms used in 3D printers, but I fear they are not up to the task for a machine tool where cutting loads are constantly changing. Please keep us posted.\r\n \r\n

[deadlykitten]

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\r\n \r\n their trajectory planner (it\'s open source, you can check it out) has no realtime requirements ... trajectory can be computed entirely offline\r\n \r\n

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a cnc system that does not adapt to inertia caused by part\'s mass change, can be considered to be "offline", or runing in only one dynamic mode; have the algorithms for such, and you can estimate toolpaths at a pc, with pretty acurrate time, without miscelanous like tool changes, magazines, etc
\n
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\r\n \r\n I fear they are not up to the task for a machine tool where cutting loads are constantly changing\r\n \r\n

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basically, that\'s what a diff control is
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\r\n \r\n Once machines have accelerometers on the spindles ... Sophisticated machines have been doing this for some time\r\n \r\n

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another trick is the diff map, for controlers that are to operate at minimal cutting loads, like a high speed finishing, or a cam lathe, so to identify hot position, where motion is a bit out of control
\n
\n

---

\nand in last 2 months, i did such applications :
\n... lathe sinusoisal acceleration rpm, for heavy parts, as basic acceleration is way to agressive
\n... harmonic control for live tools, like to destabilize the rpm, instead of using an endmill with variable flutes / kindly \r\n \r\n

[peteeng]

\r\n \r\n Hi Jack - Here\'s a couple of papers. Shapers are not a compete solution. They "solve" the mechanical vibration side of things in a simple way, they do not improve jerk, they are like a noise cancelling circuit. You have to identify the potential vibrations of the machine and address those with the cancelling circuit. It does not change the trajectory to improve jerk.
\n
\nOnce machines have accelerometers on the spindles (such as printers do) we can feed back the head accels and use jerk algorithms hand in hand with the shaper to solve it even better. Sophisticated machines have been doing this for some time. Peter
\n
\nhttps://www.mdpi.com/1424-8220/22/6/2186\r\n \r\n

[peteeng]

\r\n \r\n Hi All - I have been researching on and off this subject for a while. Been 7 months since I\'ve spoken about jerk here. I have started a collaborative design with a company for a large router (3mx1.5m) and they want to use servo motors and run fast. So I dug out my notes and did a bit more digging on controllers. I found an old note about Dynomotion and started reading their stuff. I also sent a note to Duet3D and started reading their stuff. I found Duets docs and ezcam/forum was like walking through mud. However Dynomotion was clear and happy. Plus Tom from Dyno answered an email even though its Easter... I like Kflop and its now the front runner for the AA machine. Good diagnostic software and jerk control to boot for steppers and servos. Shall know more after reading more. Its also open architecture so maybe able to write an input shaping or active control for it... Have to brush up on C. Peter
\n
\nhttps://www.dynomotion.com\r\n \r\n

[peteeng]

\r\n \r\n Hi All - I didn\'t find this at the beginning would have saved a lot of time ... I\'d be using Kflop by now. So will get one on order and test it very soon. Peter
\n
\nhttps://youtu.be/LdkyiH-v_9A\r\n \r\n

[deadlykitten]

\r\n \r\n hello recently, i talked a lot with shineworld, from rosetta cnc, on different topics; that guy covers a wide range of things
\n
\ntheir controller being shared by different cnc machines configurations, he can simply switch defaults, post-analyze and adapt, then send to the real machine; implement custom functions if needed; very good development, on all sides, and he knows his stuff
\n
\ni was after some abstractizations, related to cad-cam-cnc combo, and he managed to point me towards a good direction
\n
\ni wonder where is mactec ? all the best peteeng \r\n \r\n

[peteeng]

\r\n \r\n Thanks DK - I think I have resolved the jerk issue. Some time ago I looked at Rosetta stuff and yes its impressive but outside the hobby scope/cost area. I\'m sure MC is lurking but there\'s not much meaty stuff on the ezcam/forum at the moment for him. I\'m having fun with structural design and AI, adaptive and generative optimisation design for my two new machines. Looking fwd to using Dynomotion on the upcoming machines... I\'ll have to brush up on my 35 year old C programming.... Peter\r\n \r\n

[deadlykitten]

\r\n \r\n hy pete, nice background
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\r\n \r\n . Seems at the hobby level we are using disjointed systems. Some pro high level systems are longitudinally integrated right through from CAD to the motors.\r\n \r\n

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is not quite that fancy, only that most are kind-of satisfied with what they have
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\r\n \r\n run a simple profile for instance from CAD to Gcode to controller to toolpath (and what those systems are) so I or members can get an idea of how these things really work. \r\n \r\n

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is not needed to consider such a long chain as cad-cam-gcode-cnc-motion_control_system; last 2 are one and the same, while what\'s before them is simply the input
\n
\ng-code is critical to run a machine
\n
\ncad apeared separately, and only some cad softwares are for mechanics, and from them, some have cam as a module, thus they can be used to design whatever product for whatever industry, and by a single addon, they may take that product to futher metal cutting processing ( cam - postprocessor, etc )
\n
\npoint is that cam software evolves to keep up with machine, not the other way arround, so if you understand the machine, it will be easier to use a cam, but if someone only uses a cam, then there is no guarantee that he knows what the machine is doing
\n
\nas an intermediate conclusion, is needed to know how the machine will react when g-code changes to put it simple, if a machine won\'t react as expected, people will start to have questions
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\r\n \r\n Seems there\'s a lot of smoke around some areas.\r\n \r\n

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okey, let\'s talk, let\'s begin with a single linear axis; if it moves too many times back&forth, it may no longer know where it is ?! where am i ? so it needs a reference :
\n... home position
\n... absolut encoder
\n... absolut scale
\nis that simple
\n
\nok, now it knows where it is and is put back to work, back & forth, forever .... so the big management arives, or the cam guy, and says that max speed/feed for that axis is 1000mm/minute, but it seems that it does not travel in reality 1000, but only 400mm/minute, so why ?
\n
\nlet\'s consider that travel is 100mm, so expectations are for 10 travels/minute ( so to reach the brochure spec of 1000mm/min ), while in reality only 4 travels/minute occur
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\nif i may, what is causing the difference between 1000 and 400mm/min ? \r\n \r\n

[deadlykitten]

\r\n \r\n hy pette i saw also some of your replies in another thread, then you started this one
\n
\nseems you are hunting, somehow, the big picture; please, i need to understand better what is behind your words :
\n... what made you to start looking into this ?
\n... why are you so focused on jerk , tangential/smooth movement ? if i may, this is local/simple, while mcs is global
\n
\nsorry for repeating, my advice, is to eliminate from equation cad & cam, and focus only on cnc/mcs, because is better to focus only on one at a time; if you clear your thougths with cnc/mcs, then cad/cam will be clear, not the other way arround; cad/cam is an extension, is not the key, it simply generates input to suit the cnc
\n
\nalso, from cnc/mcs, i proposed that 1 linear axis example, because is simpler to focus on a single axis, rather than all at once
\n
\nokey, now i will try to answer to some texts :
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\r\n \r\n Its a series of point to point moves \r\n \r\n

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not point to point ... is vecinity towards other vecinity; think of a group that croses the street on a crosswalk: some go middle, some go near an edge, others may go diagonally
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\nthere is a tolerance, just like how you would turn a part with diameter 100, and accept as good the 99.8 and also the 100.3
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\r\n \r\n at the Gcode level the machine does not know if its a spline or an arc \r\n \r\n

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this is true only for segmented toolpaths, thus g-code only with G01s; otherwise, it will make a difference between g01 and g02 for example
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\nas for splines, i think you allready know that most cnc\'s dont have a g code for it
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that\'s the nominal, while mcs is cheking that real motion is within tolerance, or else will/should stop the machine
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\r\n \r\n I have started to play with G64 \r\n \r\n

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is this exact stop mode ? \r\n \r\n

[mactec54]

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Hi Mactec - Just trying to clarify what you mean by jerk. I\'ve said this before lay "jerky motion" is machine compliance, rough motion and rough accelerations. Engineering jerk has no physical expression or symptom in terms of motion control. It is only a way to determine the rate of change of acceleration and value or visualise the smoothness of acceleration. Acceleration however creates inertial forces which can contribute to vibration and rough motion.
\r\n
\r\nIHNF I looked at the sinumeric controller and the jerk setting limits jerk it does not "control" jerk. By control I mean the value is shaped or changed like driving a car and using the accelerator pedal. You control the speed via the pedal. If the car is speed limited once you get to that speed you have no control its capped. That\'s how the sinumerik works its a limit setting. This is apparent in the graph with the flat top accel curves. For example the Rosetta controller has rounded top jerk & accel curves, the controller has shaped the acceleration curve to smooth the jerk curve. Peter

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Here is SoftServos from 2016 this covers some of what they can do at their control, there is no other control that comes close to what they have done, because most of their system they have is covered by Patents, I won\'t post the PDF but give you the web link as it has regulations on it\'s use, open the WMX2 Functions PDF
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\r\nhttps://www.bing.com/search?q=SoftSe...ANNTA1&PC=LCTS\r\n \r\n

[deadlykitten]

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The okuma seems to be a blanket override. Can\'t find much on it.

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it\'s mainly closed, even for fellow japanes officials; from early years, some of it\'s achievements are repacked in a cheapar manner/fanuc, then go worldwide
\n
\nbut in the last decade, this gap started to get smaller, as the worlwide competition cathced up, so the genos line appeared
\n
\nonly later i realized that it is "i have no fish" ... ha ha
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I went to Haase to buy a mini mill ... They told me flat out we do not sell to a non business entity or a home user

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there are vendors that sell used machines with guarantee similar to a new one; competitive prices, like for the price of a new cnc, you would get an used similar one with higher specs and a new minimill; it\'s quite of a best deal for a buck
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Feed rate with this control will leave most speechless
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\n... most of their system they have is covered by Patents

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hy mactec, i am pretty sure pete will deliver something to beat it
\n
\nplease, if i may ask, what is your background ? and on what machines type/size does that top cnc goes to ? are you involved in it\'s development ?
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what is adaptive control doing?

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( trying to ) output within a predifined range, like not only not to overshoot position, speed, inertia or cutting force, but keep it inside an user defined domain
\n
\nsome may argue that position is not caused by adaptive, being too basic to debate, while controlling cutting force is definetly adaptive
\n
\nadaptive means output within desired tolerance
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\nit may be live, or trained / kindly \r\n \r\n

[deadlykitten]

\r\n \r\n hello again please, how a cam achieves smoothnes and how a cnc does it ?
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\r\n \r\n We work in continuums because then you can do std mathematical functions to smooth paths, optimise paths \r\n \r\n

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for most machines, nurbs is out of the question, toolpaths are line/arch, and most parts are simple
\n
\nso i ask : is it possible for a normal non-nurbs machine to behave as smooth, or even smoother than one that runs nurbs ? how is smoothness quantified ?
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\r\n \r\n More points does not necessarily mean its "smoother". In fact most of the time more points make it bumpier.\r\n \r\n

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how can i find the right amount of points ?
\nis it the same for feed override 50% and override 350% ?
\nis it possible not to care about the amount of points, and always go for max settings ?
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\r\n \r\n If you look at the logic diagram you wills see the advanced system has feedback loops. These are not in CAD-CAM but on the hardware side. \r\n \r\n

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i have looked over it right when you posted it : please check attached response
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\r\n \r\n S-curve will be smoother then trap not the other way round.\r\n \r\n

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nonono, it will be smoother only if it is being programed so
\n
\nconsidering acceleration/decc ramps, trap/s/combination(thus something in between trap and s may be used)/etc : for max performance, you need to reach an area beyond you can not go futher, then back off a bit; how do you reach it ?
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\nusual factors : rigidity, inertia, cuting forces, material mass : how are those taken into consideration ?
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\r\n \r\n Real time computation means its done while the CNC is working, Post processing is sorting something out before you run the machine.\r\n \r\n

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feedback loop requires post process; no feedback loop means real time
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\nhow much nurbs(or whatever else) is it possible to push inside the machine ? when does a machine capable of post process, no longer be capable to postprocess ? how is this balanced ? kindly \r\n \r\n

[peteeng]

Hi Jack - Here's a couple of papers. Shapers are not a compete solution. They "solve" the mechanical vibration side of things in a simple way, they do not improve jerk, they are like a noise cancelling circuit. You have to identify the potential vibrations of the machine and address those with the cancelling circuit. It does not change the trajectory to improve jerk.

Once machines have accelerometers on the spindles (such as printers do) we can feed back the head accels and use jerk algorithms hand in hand with the shaper to solve it even better. Sophisticated machines have been doing this for some time. Peter

https://www.mdpi.com/1424-8220/22/6/2186