Newbie Questions re: KFLOP and SnapAmp


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Thread: Questions re: KFLOP and SnapAmp

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    Default Questions re: KFLOP and SnapAmp

    Greetings!

    I am new to CNC and have recently acquired a 10+ year old CNC router table (2ft X 5ft). I will be cutting plywood and aluminum sheet material.
    I am planning a refit of the CNC router as it has good mechanical functionality but old unsupported controls and motors.

    I will be upgrading the system with new control software, controller board, brushed dc servo motors and encoders. My current thinking is as follows:

    Planned Motors: For all three axes - Automation Technology KL23-120-36 brushed servo motors.
    Planned encoders: CUI AMT 102-V
    Motor Driver: G320x or Dynomotion SnapAmp
    Controller Board: PoKeys57CNC or Dynomotion KFLOP
    GCode Software: Mach 3(4?) or KMotionCNC or perhaps both.

    I am trying to understand how these things work and where the closed loop control is taking place in the various possible configurations.



    Option 1: KMotionCNC->KFLOP->Gecko G320x->brushed servo with quadrature encoder

    Case 1.1. Quadrature encoder connected to Gecko G320x. As I understand it, when the encoders are connected to the G320x, the G320x does closed loop control for each step commanded (allowing up to a configured "count following error" before declaring a fault). In this case, is the KFLOP performing path following in open loop mode (ie. no PID control) expecting that the G320x will keep up?

    Case 1.2. Quadrature Encoder connected directly to the KFLOP. Does this work? or does the G320x require encoders connected? If it does work, would it allow the KFLOP to "close the loop" during it's path following operations?


    Option 2: KMotionCNC->KFLOP -> SnapAmp -> brushed servo with quadrature encoder

    Case 2.1. Quadrature encoder connected to SnapAmp. When the encoders are connected to the SnapAmp, does the SnapAmp perform closed loop control for each step commanded (like the GeckoDrive 320x does)?

    Case 2.2. Quadrature Encoder connected directly to the KFLOP (as shown in Dynomotion's "KFLOP+SnapAmp DC Brush Motors with MPG" wiring diagram). Does the KFLOP "close the loop" during it's path generation/following operations or is it operating in a similar way to Case 1.1 above where the Gecko is closing the loop for each step command? Is there any benefit in path following capability by using the SnapAmp versus the G320x?

    Option 3: Mach -> KFLOP ...

    Case 3.1 I understand that Mach is doing the path planning but in open loop mode. In this case what is the advantage of using KFLOP versus PoKey57CNC?

    Thanks very much for help in understanding this.

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  2. #2
    Gold Member TomKerekes's Avatar
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    Default Re: Questions re: KFLOP and SnapAmp

    Hi dchapman,

    Planned encoders: CUI AMT 102-V
    Please see other Threads on noise/jitter issues with these capacitive encoders.

    Option 1: KMotionCNC->KFLOP->Gecko G320x->brushed servo with quadrature encoder.
    Case 1.1. Quadrature encoder connected to Gecko G320x. As I understand it, when the encoders are connected to the G320x, the G320x does closed loop control for each step commanded (allowing up to a configured "count following error" before declaring a fault). In this case, is the KFLOP performing path following in open loop mode (ie. no PID control) expecting that the G320x will keep up?
    Step/Dir to Gecko. Gecko closes the position loop. Open loop from the Controllers perspective. I would not refer to it as "KFLOP performing path following". Rather KFLOP is creating the trajectory.

    Case 1.2. Quadrature Encoder connected directly to the KFLOP. Does this work? or does the G320x require encoders connected? If it does work, would it allow the KFLOP to "close the loop" during it's path following operations?
    This doesn't work. The C320X requires encoder feedback to close the position loop.

    Option 2: KMotionCNC->KFLOP -> SnapAmp -> brushed servo with quadrature encoder

    Case 2.1. Quadrature encoder connected to SnapAmp. When the encoders are connected to the SnapAmp, does the SnapAmp perform closed loop control for each step commanded (like the GeckoDrive 320x does)?
    SnapAmp is simply an IO device for KFLOP. It has differential encoder inputs so the encoder position can be presented to KFLOP and it allows KFLOP to command a Motor Current. Motor Current basically corresponds to motor torque or acceleration.

    Case 2.2. Quadrature Encoder connected directly to the KFLOP (as shown in Dynomotion's "KFLOP+SnapAmp DC Brush Motors with MPG" wiring diagram). Does the KFLOP "close the loop" during it's path generation/following operations or is it operating in a similar way to Case 1.1 above where the Gecko is closing the loop for each step command? Is there any benefit in path following capability by using the SnapAmp versus the G320x?
    Whether the encoder feedback is connected directly to KFLOP or to SnapAmp doesn't make any difference to the functionality. In both cases the position is available to KFLOP to close the loop, plot the response, monitor following errors, and so forth. The difference is that KFLOP has only single ended inputs and SnapAmp has differential inputs. Differential inputs have less noise sensitivity. When you purchase encoders its best to get differential outputs as they can be connected to either differential inputs or single ended inputs.

    In this configuration there is no need for "steps" or to send the commanded position anywhere. KFLOP performs the trajectory and knows the desired position with floating point precision. The advantage with SnapAmp would be this elimination of steps and the ability to tune and verify the system's performance using the KMotion.exe parameters and tools. Another advantage with KFLOP closing the loop is that KFLOP can track encoder position while the Axes are disabled or have faulted. The allows recovery without loss of position and having to re-home the system.

    Option 3: Mach -> KFLOP ...

    Case 3.1 I understand that Mach is doing the path planning but in open loop mode. In this case what is the advantage of using KFLOP versus PoKey57CNC?
    I've heard good things about PoKeys but not familiar with it. KFLOP only supports Mach3 not Mach4. When using Mach3 or Mach4 you will be using the Trajectory Planner in Mach3 or Mach4. We feel the KMotionCNC Trajectory Planner performs better on complex high-performance jobs.

    HTH
    Regards

    TK
    http://dynomotion.com


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    Default Re: Questions re: KFLOP and SnapAmp

    dchapman,
    Don't waste your time with the Pokeys, they take forever to put out fixes that actually work. If you want something that actually works go with the KFLOP. It will support a Mach3 plugin, but do yourself a huge favor just skip Mach3 and go with Dynomotions free KmotionCNC which is rock solid. The KFLOP supports closed loop operation and you can close the loop with servos with encoders and you can also add another closed loop with Linear encoders depending on your needs. KmotionCNC does not go off and do unexpected stuff like often happens on Mach3. I have Mach3, Mach4, and KmotionCNC so trust me I know what I am talking about. Pick the right hardware and get some good servos and you will have a rock solid machine.
    Russ



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    Default Re: Questions re: KFLOP and SnapAmp

    Thanks for the prompt reply, Tom.
    Interesting about the KFLOP/SnapAmp maintaining encoder position during fault conditions. If the PC connection is lost (eg. Windows decides to reboot) how does KmotionCNC and Mach 3 resynchronize with the KFLOP so that a rehome is not needed?



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    Gold Member TomKerekes's Avatar
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    Default Re: Questions re: KFLOP and SnapAmp

    Hi dchapman,
    Interesting about the KFLOP/SnapAmp maintaining encoder position during fault conditions. If the PC connection is lost (eg. Windows decides to reboot) how does KmotionCNC and Mach 3 resynchronize with the KFLOP so that a rehome is not needed?
    Assuming power continues to KFLOP and the encoders it maintains the commanded position and encoder position. When the App starts up the currently command position is read from KFLOP and synchronized to the App.

    Your example isn't really the problematic case. You might be able to assume the Geckos held position while Windows rebooted and the last commanded position is still valid. However if for example the Axes were disabled and manually moved (with or without Windows re-booting) in the case of the Geckos there is no way to determine where the Axes currently are. With feedback to SnapAmp, KFLOP (and any Apps) can track where the Axes physically are even while disabled. They can then be re-enabled and commanded to their current Position with everything again in Sync.

    HTH
    Regards

    TK
    http://dynomotion.com


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    Default Re: Questions re: KFLOP and SnapAmp

    OK. Good information. Thanks.

    Assuming a KFLOP + SnapAmp implementation:

    1. Encoder Type

    I have found this optical encoder with line driver output:
    https://www.digikey.com/product-deta...750-ND/2219462

    Is this compatible with the differential encoder input of the SnapAmp or do you have some other suggestion?

    2. Encoder CPR

    My motors will spin max around 3300RPM. A 500 CPR encoder will provide sufficient resolution for my table (best case +/- .0005in ... there are ball screws on Y and Z axes) and would result in a pulse rate of around 27.5kHz ( 4 X that if the KFLOP is counting edges?). Is this reasonable? Suggestions?

    Home and Limit Switch Inputs

    My plan is to have limit switches on three axes and 3 home switches. (there are none now). For limit switches, the + and - end of each axis will be in series and thus I will need three inputs for these plus I will need three home switch inputs. I would also like to plan for a touch probe tool height setter. All together this would require 7 inputs. My proposal for these inputs is to use 12V, normally closed switches, shielded cabling connected to the SnapAmp opto-oslated inputs. Does this make sense? Suggestions?

    Thanks for the input!



  7. #7
    Gold Member TomKerekes's Avatar
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    Default Re: Questions re: KFLOP and SnapAmp

    Assuming a KFLOP + SnapAmp implementation:

    1. Encoder Type

    I have found this optical encoder with line driver output:
    https://www.digikey.com/product-deta...750-ND/2219462

    Is this compatible with the differential encoder input of the SnapAmp or do you have some other suggestion?
    Yes that looks compatible.

    2. Encoder CPR

    My motors will spin max around 3300RPM. A 500 CPR encoder will provide sufficient resolution for my table (best case +/- .0005in ... there are ball screws on Y and Z axes) and would result in a pulse rate of around 27.5kHz ( 4 X that if the KFLOP is counting edges?). Is this reasonable? Suggestions?
    That sounds correct to me. KFLOP counts edges (quadrature counts) to the count rate would be 110,000 counts/sec well below KFLOP's max count rate of 1,000,000 counts/sec. Normally a servo will hold the error within a few counts. So the encoder resolution should be much higher than the system precision you wish to achieve. I'm not sure how you calculated the 0.0005in or what your requirements are.

    The SnapAmp differential inputs don't have any built in termination resistance. It may work ok without any especially at your relatively slow count rates. But you might want to make previsions for putting 120~200 Ohms across the + - pairs as close to KFLOP as possible.


    Home and Limit Switch Inputs

    My plan is to have limit switches on three axes and 3 home switches. (there are none now). For limit switches, the + and - end of each axis will be in series and thus I will need three inputs for these plus I will need three home switch inputs. I would also like to plan for a touch probe tool height setter. All together this would require 7 inputs. My proposal for these inputs is to use 12V, normally closed switches, shielded cabling connected to the SnapAmp opto-oslated inputs. Does this make sense? Suggestions?
    That sounds reasonable. One issue might be the + and - Limits in series. That makes it difficult to know which way is safe to move when in a limit. The other option is to combine all the + and - ends together. Or combine Home sensors and only home one axis at a time.

    TK
    http://dynomotion.com


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    Default Re: Questions re: KFLOP and SnapAmp

    I would just use 3 home switches and three limit switches. The home switches can be used for limits after homing since you can move as far off the sensor as you want before zeroing your axis. You will also be setting up soft limits so the software can look ahead and prevent obvious crashes.

    Ben

    Sent from my HTC6525LVW using Tapatalk



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    Default Re: Questions re: KFLOP and SnapAmp

    Thanks for the input!



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Questions re: KFLOP and SnapAmp
Questions re: KFLOP and SnapAmp