529,725 active members*
3,753 visitors online*
Register for free
Login
IndustryArena Forum > CNC Electronics > Servo Motors / Drives > ClearPath Servos - Do they lock like a stepper
Results 1 to 17 of 17
  1. #1

    ClearPath Servos - Do they lock like a stepper

    So i've swapped out my steppers for Clearpath Servos. I've run the through 'autotune' and they're and moving fine.

    I've noticed that unlike steppers, when enabled, the servos don't lock hard, I can moved the gantry servo (master and slave) about 1/4" without too much effort. When jogging the gantry, I can see the slave servo move just a little bit after the master has stopped.

    The steppers they replaced locked the gantry in place quite hard and it took some effort to jar it out of the place.

    Is this normal???

  2. #2
    Community Moderator ger21's Avatar
    Join Date
    Mar 2003
    Posts
    35136

    Re: ClearPath Servos - Do they lock like a stepper

    Sounds like the tuning is not quite right.
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  3. #3

    Re: ClearPath Servos - Do they lock like a stepper

    I would agree Gerry!

    The auto tune feature is pretty simple to go through, not sure what I might have screwed up.

  4. #4

    Re: ClearPath Servos - Do they lock like a stepper

    About 14:34 into this video the host shows how hard it is to move the servo. That's what I would expect to see.

    https://www.youtube.com/watch?v=n33fCmUu9A8

    I'll have to try re-tuning in the morning.

  5. #5
    Registered
    Join Date
    Nov 2013
    Posts
    931

    Re: ClearPath Servos - Do they lock like a stepper

    Hi,
    when steppers are energized but idle they are locked, or rather they are at maximum 'holding' torque. They can be dislodged from their position
    but it takes considerable effort.

    A servo when energized but idle occurs when the controller is not issuing position commands, ie the last position command entered is the position the
    controller expects the servo to stop. The servo stops at that position and actively tries to maintain that position. If some external force attempts to
    shift the axis the servo/drive will try to counter that force so that it remains in its commanded (stationary) position.

    Modern AC servos like your Clearpaths have a 'zero window'. It will vary by manufacturer but the same general idea applies.
    My Allen Bradley servo for instance has a 2000 line/rev encoder for 8000 counts/rev. The default 'zero window' is 4 counts wide. That is to
    say the drive will attempt to close the error between the commanded input and the actual position as measured by the encoder until it gets
    to within 4 counts, thereafter it stops trying....in effect saying that within 4 counts is 'good enough'. Note I can program the 'zero window' to what I
    like. It would not make sense to reduce it to zero or one though. That would mean the drive would keep trying to achieve perfect position even when it was
    already very close and would 'buzz' as possibly get warm. On the other hand if I programmed the 'zero window' to 2000 say, to give a wild example, then
    the drive would get to within 1/4 turn of its commanded position and then stop trying.....not especially useful for an axis servo.

    From what you have described I believe your 'zero window' is too wide. What is happening, my guess, is that when you try to deflect the servo when its
    at rest it moves a distance with little or no resistance because the drive deems that it is still 'good enough'. Only when you exceed that 'zero window' does the drive
    start to apply a counter force.

    I think amongst the different downloads I have a manual for Clearpaths. I will take a look...I think you have some programmatic control over the 'zero window'.

    Craig

  6. #6

    Re: ClearPath Servos - Do they lock like a stepper

    I've been running to auto tune on the gantry servo, it had the same problem. Going on a few hours, still doing something, but this is WAY beyond the normal auto tune run time.

  7. #7
    Registered
    Join Date
    Nov 2013
    Posts
    931

    Re: ClearPath Servos - Do they lock like a stepper

    Hi,
    I rather doubt AutoTune sets the 'zero window'. AutoTune is good but there are a lot of things that it does not do.

    Craig

  8. #8
    Registered
    Join Date
    Nov 2013
    Posts
    931

    Re: ClearPath Servos - Do they lock like a stepper

    Hi,

    ASG-POSITION
    ASG-Position mode is typically used as a “move done” signal. In this
    mode, the HLFB output asserts (conducts) when ClearPath is enabled and
    settled within X counts of the target position, for at least Y milliseconds
    (you set X and Y in MSP via the Move Done Criteria dialog).
    This is from the Clearpath manual. It is clear that there is programmatic control over the zero window or as Tecknics call it ASG.

    Craig

  9. #9
    Registered
    Join Date
    Nov 2013
    Posts
    931

    Re: ClearPath Servos - Do they lock like a stepper

    Hi,

    Move Done Criteria
    Move Done status is used to determine when the All Systems Go-Position
    signal should be asserted at the HLFB output. The Move Done Criteria
    consist of two parameters: the “In-Range Window” and the “Verify Time”.
    These parameters are explained in the screen capture, taken from MSP,
    below.
    Move Done Criteria Setup
    How Move Done Works
    Move Done status is achieved when the Move Done criteria are met. In the
    above figure, Move Done occurs when the motor is within +/-10 encoder
    counts of the commanded position (the In-Range Window) for a
    minimum of 10.1 milliseconds (the Verify Time).
    Note: If the encoder leaves the In-Range window during the time
    qualification period, the Move Done timer automatically resets. The timer
    will begin a fresh countdown as soon as the motor comes back in range.
    Because encoder resolution, mechanical systems, and settling
    performance requirements vary by application, you may need to
    15 10 5 0 5 10 15
    Move Direction
    Encoder Scale
    (1 line = 1 count)
    Commanded Position (0) Actual Position (count 5)
    In-Range Window +/- 10 counts
    ENCODER
    from page 67 of the manual.

    Craig

  10. #10
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Posts
    23476

    Re: ClearPath Servos - Do they lock like a stepper

    Servo's should be capable of zero movement under control of the PID loop up to the manuf rated continuous torque level when tuned correctly.
    Al.
    CNC, Mechatronics Integration and Custom Machine Design

    “Logic will get you from A to B. Imagination will take you everywhere.”
    Albert E.

  11. #11
    Quote Originally Posted by joeavaerage View Post
    Hi,



    from page 67 of the manual.

    Craig
    Thanks for looking into this Craig.

    Reading this it appears that this setting just sets the HLFB output signal based on the criteria set.

    But I'll try anything at this point!

  12. #12

    Re: ClearPath Servos - Do they lock like a stepper

    I've played with those settings and don't see any difference. I'm still able to move the servo.

    I'll contact Teknic tomorrow and see if they can provide any assistance.

  13. #13
    Registered
    Join Date
    Apr 2018
    Posts
    18

    Re: ClearPath Servos - Do they lock like a stepper

    Hi everyone,

    I'm an applications engineer for Teknic and I came across this post. I thought it might be helpful to provide some more information regarding ClearPath servos. (Bobmagnuson, you may have spoken with one of our other engineers already and hopefully solved this issue, but I figured I'd post more information in case anyone with the same problem comes across this post in the future.)

    ClearPath motors (and all servo motors) will lock and hold position when energized and enabled. Even though you aren't actively sending steps to the servo, the motor will interpret the lack of new steps as a command to hold the current position. The servo will use as much torque as required (up to the motor's peak torque) to hold position and fight any external forces that are trying to move the motor off its commanded position.

    Depending on how well the motor has been tuned, the motor's disturbance rejection will vary (i.e. how quickly the motor applies torque to counteract a sudden change in outside force such as you suddenly pushing on the mechanics). Greater disturbance rejection results in the mechanics feeling much stiffer. You would not be able to move the motor shaft very far before the motor uses its full peak torque to return to its commanded position. Low disturbance rejection can result in mechanics feeling "spongy". In that case, you'd be able to move the motor shaft farther before the motor uses torque to return to its commanded position.

    In this situation, it sounds like you may have been trying to auto-tune a dual driven gantry. Unfortunately, auto-tune was not designed for these types of axes because there is no way to sync the auto-tune of two motors at the same time. Attempting to tune a dual-driven gantry by means of auto-tune could result in poor tuning since one motor will see the full load of the gantry.

    If you were able to successfully complete auto-tune on a dual gantry, it's likely that the auto-tune did not achieve the proper gains for the system which could be causing the issue you are seeing. There are different, more optimal ways to tune a dual-driven gantry and Teknic would be happy to help you with that. (Here is a link to an application note to get you started: https://www.teknic.com/files/downloa...Motor-Axis.pdf )

    I also wanted to touch on what joeavaerage mentioned. While some other servo motors may have a "zero window" or deadband, ClearPath motors will use full torque to return to the last commanded position (to the encoder count). The Move Done Criteria previously mentioned does not refer to how well the motor holds its position but instead refers to the motor's digital output called "HLFB" or "High Level Feedback". This output can be configured to alert the user/controller when ClearPath has reached its commanded position (this configuration is called "All Systems Go - Position").

    Part of setting up the HLFB involves defining an "in-range" window, which is a number of position counts that the motor can be within to be considered "at target position". Even though the motor is "at target position" from the application's perspective, the motor understands that there is one specific encoder count that it was commanded to, and will still fight within its torque capability to reach and hold that exact position. As long as the motor is properly tuned, the motor will hold the commanded position.

    I hope this information is useful. Please feel free to contact Teknic with any questions or if you need any help with tuning/troubleshooting this situation.

    Best regards,
    Bridgette G.
    Teknic Inc.

  14. #14

    Re: ClearPath Servos - Do they lock like a stepper

    Thanks Bridgette!

    I was seeing the issue on both the Y axis (single servo) and the X axis (dual servos). They had been Auto-tuned per Teknic's recommendations and I was still seeing issues.

    I've been working with Zach on the Teknic support team. We tried a few things and it appears that the Nema 23 Clearpath Servo's may be undersized for what I need.

    I've got a big Nema 34 on order to see if it help resolve the issue.

  15. #15

    Re: ClearPath Servos - Do they lock like a stepper

    Bob,

    Were you bale to find a solution with this? I just installed Teknic servos and am running into the same issue. Thy are actually a little oversized and I have ran Auto tune with various settings but cannot get rid of the spongy feeling. Like yo, at rest I can move the carriage 1/4" each way but if I push gently with force it engages quickly.

    This was part of a change out to Masso controller.

    Any insight you have since would be appreciated.

  16. #16
    Member
    Join Date
    Jan 2005
    Posts
    11544

    Re: ClearPath Servos - Do they lock like a stepper

    Quote Originally Posted by sebastian502 View Post
    Bob,

    Were you bale to find a solution with this? I just installed Teknic servos and am running into the same issue. Thy are actually a little oversized and I have ran Auto tune with various settings but cannot get rid of the spongy feeling. Like yo, at rest I can move the carriage 1/4" each way but if I push gently with force it engages quickly.

    This was part of a change out to Masso controller.

    Any insight you have since would be appreciated.
    One of the main problems with these servos is the cost and that they are only 3 Pole, most servos of the same class are from 6 to 12 Pole with the quality servos being 12 Pole so it does not matter what you do they are not going to hold the position very well, no amount of tuning can solve this problem

    When you look at what is available for the same price and cheaper today these servo's don't stack up to be suitable for CNC machines no matter what the tec. guys say they can't solve these problems
    Mactec54

  17. #17

    Re: ClearPath Servos - Do they lock like a stepper

    Quote Originally Posted by sebastian502 View Post
    Bob,

    Were you bale to find a solution with this? I just installed Teknic servos and am running into the same issue. Thy are actually a little oversized and I have ran Auto tune with various settings but cannot get rid of the spongy feeling. Like yo, at rest I can move the carriage 1/4" each way but if I push gently with force it engages quickly.

    This was part of a change out to Masso controller.

    Any insight you have since would be appreciated.
    Going with the larger servos helped. I also had Teknic remote into my machine and assist with the tuning. It helped quite a bit.

Similar Threads

  1. Saturn 4'x4' My Second Build the first time with Clearpath Servos
    By WhiteWolf in forum FineLine Automation
    Replies: 46
    Last Post: 04-07-2020, 05:58 PM
  2. Can two clearpath servos be used to power one axis?
    By Dangle_kt in forum DIY CNC Router Table Machines
    Replies: 35
    Last Post: 08-02-2017, 03:46 AM
  3. Mach3 motor tuning - ClearPath servos
    By flathead in forum Mach Software (ArtSoft software)
    Replies: 7
    Last Post: 05-18-2017, 01:45 PM
  4. Clearpath Servos for Tormach?
    By GLCarlson in forum Tormach Personal CNC Mill
    Replies: 30
    Last Post: 05-02-2017, 01:31 PM
  5. Some advice and opinion on Clearpath servos
    By KennyPowers in forum Servo Motors / Drives
    Replies: 14
    Last Post: 09-11-2016, 09:22 PM

Tags for this Thread

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •