New Machine Build Servo Advice Needed


Page 1 of 2 12 LastLast
Results 1 to 12 of 21

Thread: Servo Advice Needed

  1. #1
    Registered
    Join Date
    Apr 2007
    Location
    usa
    Posts
    10
    Downloads
    0
    Uploads
    0

    Default Servo Advice Needed

    Hello out there,

    First I want to thank everyone one this forum for their contributions. I have spent countless hours reading the innumerable helpful entries.

    I need help in designing the electrical portion of the linear system on a machine I am planning to build.

    The machine is to be a very small milling/engraving machine, eventually to have 5 axis. I will be using this machine to make prototypes in wax, plastic and maybe aluminum or copper as well. The maximum work piece size will be around a 4 inch cube. The XYZ travels will be 5,6,5 inches respectively.

    The configuration of the machine is almost exactly the same as a Hermle 5 axis VMC but with a single sided trunnion arrangement mounted in the back wall instead of across the base as some MORI machines have. The base dimensions are roughly 15x15x18, and will be mineral cast.

    At the moment I plan to make the gantry out of aluminum possibly with the inclusion of some mineral cast to dampen vibrations. The idea is to keep it as light as possible.

    Linear motion will be on tiny little THK RSR9 guides. I have these.

    The ball screws are 2mm lead preloaded, 8mm dia.

    I want to use Linuxcnc(emc2) as a controler and I already have a dedicated motherboard for this purpose. (I have yet to choose the PCI cards etc.)

    I would like to make this machine as accurate and fast as possible. It also needs to be smooth enough to cut very small profiles using very small cutters and drills.

    I have two ideas as to how to drive this machine.

    DRIVE OPTION 1 The first is to use 100w Panasonic Minas S series servos directly coupled to the ball screws. I happen to have the drives for these and I can get the motors, and all the rest of the electrical components for proper setup for $200 each axis.

    I do not yet know if it is possible to use these drives in velocity mode and have a close loop with EMC, but I am still investigating that and which Mesa card combination will suit. Any input is welcome on that subject.

    DRIVE OPTION 2 The second idea was to use Dumb PMW/Dir drives such as AMC BD30A8 to drive some 60W Maxon brush-less motors with a belt reduction of say 2:1. When all is said and done this will probably cost the same, unless the electronics/cards cost is much different. I have none of these components presently.

    I have been reading so many posts my brain is boiling over. I would like to know if anyone has any advice as to which idea to follow.

    Note: This is only concerning the XYZ arrangement for now. The AB rotary axis will be added later.

    At the moment I have considered using some hefty Inland brushed torque motors with some very high count GSI Lumonics encoders. I have these.

    EDIT: I forgon to mention that I have also considered using dual servos on the Y axiz that carries the entire gantry. I have a forth Panasonic drive. I do not know how easy it is to tune two of these together but it seems like there should be a way since i can see there would be a need for it in industry.

    Similar Threads:
    Last edited by geowhat; 08-09-2012 at 04:37 PM.


  2. #2
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    23067
    Downloads
    0
    Uploads
    0

    Default

    Quote Originally Posted by geowhat View Post
    I want to use Linuxcnc(emc2) as a controler and I already have a dedicated motherboard for this purpose. (I have yet to choose the PCI cards etc.)

    DRIVE OPTION 2 The second idea was to use Dumb PMW/Dir drives such as AMC BD30A8 to drive some 60W Maxon brush-less motors with a belt reduction of say 2:1. When all is said and done this will probably cost the same, unless the electronics/cards cost is much different. I have none of these components presently.
    .
    I use A-M-C or Copley controls, there is not a lot of point using intelligent drives if you close the loop in the controller.
    These drive come up on ebay all the time.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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


  3. #3
    Registered
    Join Date
    Apr 2007
    Location
    usa
    Posts
    10
    Downloads
    0
    Uploads
    0

    Default

    Thank you for the reply.

    I thought you would say that. I will sell the Panasonic Drives I have.

    So I am trying to match some motors with the appropriate drives.

    I am wondering if I use drives that do not operate in velocity mode but only in pwm/Dir mode can EMC maintain two loops, one velocity and the other position?

    If I use motors that have a max current rating that is slightly higher than the drive's rating can they still work together?



  4. #4
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    23067
    Downloads
    0
    Uploads
    0

    Default

    You may get away with setting the current limit on the drive, it is rare to run a servo up to continuous torque value.
    I have only used AMC with Galil Motion Cards, and run these in torque mode with just one loop.
    Also AMC recommend torque mode in CNC mode of operation.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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


  5. #5
    Registered
    Join Date
    Apr 2007
    Location
    usa
    Posts
    10
    Downloads
    0
    Uploads
    0

    Default

    More Details:

    Both of these are on ebay

    Amp:
    9 Advanced Motion Control Brushless PWM Servo Amplifier AMC BE12A6E,BLDC Encoder | eBay

    And Motor:
    PITTMAN AMETEK BRUSHLESS DC MOTOR # A0422052NC-HCXX 24VDC 4000RPM NEMA17 | eBay

    Amp specifications:
    http://www.a-m-c.com/download/datasheet/be12a6.pdf

    Motor specifications:
    http://www.pittman-motors.com/Portal...s_dc_motor.pdf

    The motor specifications are a little confusing since the manufacturer specs are different from the ones on the sticker on ebay. Maybe H in the end of the part number means a different winding. In any case I am just wondering if these can be used together if the motor specifications are as they appear on the actual motor. Most of my concern is the max current rating of the motor.

    I like the drives because they will run in encoder-velocity and current mode.

    Last edited by geowhat; 08-10-2012 at 02:38 PM.


  6. #6
    Member
    Join Date
    Jul 2003
    Location
    Holmen, WI
    Posts
    1650
    Downloads
    2
    Uploads
    0

    Default

    those drives are a good deal....

    they seem like they should work together.

    the last letter on the amc drives is just the rev level.

    sam



  7. #7
    Registered
    Join Date
    Apr 2007
    Location
    usa
    Posts
    10
    Downloads
    0
    Uploads
    0

    Default

    My other concern with this combination is whether or not it can run smoothly enough to drive the lead screws (ball) directly at very low speeds allowing me to do intricate work with very small end-mills and drills.

    If not then I will have to add a belt reduction which I would rather not for simplicities sake.



  8. #8
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    23067
    Downloads
    0
    Uploads
    0

    Default

    With servo's your least input increment possible will be the resolution of the encoder.
    Not sure why you would think they will not run smooth, I run BLDC motors with the Galil and they perform perfectly at very low rpm using torque mode.
    Usually a problem with drive under sizing is when operating a large overhauling load and the drive could go into current limit.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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


  9. #9
    Member
    Join Date
    Jul 2003
    Location
    Holmen, WI
    Posts
    1650
    Downloads
    2
    Uploads
    0

    Default

    my gut feeling is that you will want some sort of reduction... The motors are 4000 rpm. Are you going to spin the ball screws at 4000rpm? so figure out what you want.

    force at the table?
    maximum feed?
    lowest resolution?

    As Al said - the encoder resolution is going to be your minimum.. but you can never tune perfectly so it will be something over 1 count..

    sam



  10. #10
    Registered
    Join Date
    Apr 2007
    Location
    usa
    Posts
    10
    Downloads
    0
    Uploads
    0

    Default

    I was not so much worried about smoothness as far as resolution.

    I was worried about cogging type roughness.

    If these motors have the standard 1000 count resolution encoders that I think they do, dividing a 2mm lead divided by 1000 gives me 0.00007" or so for each count. I think that is almost ridiculously good. Even though it will never actually be that good it will be good enough with the expected error in it.

    I do not think that I will ever run the screw at 4000 rpm. That would be like 300ipm. I guess it depends what I am cutting with the 1/8 maximum bit size for the spindle I am planning to use.

    I thought that if I could get away with not using any reduction because the cutting forces and the loads could be driven by the motor directly it would be nice. There would be no fooling around with belts and gears and more parts, just heli-couplers and that's it.

    I hoped that I could simply not make the motor turn at full rpm by not ever telling it to.

    In any case I have not done all the math on the load of the tiny gantry so I am just going with my gut here and exploring possibilities. I still have not finished designing it yet. If I need a reduction I can add some weight to the structure or at least not worry about the weight so much.

    I know, better do the MATH.

    Speaking of that I saw a really nice rundown on calculating loads and such but I can't remember where it was. Does anyone know of one. I would just use a scale and tug on a pile of parts stacked on the linear ways like I have before but this thing is too small to get a good read that way (with the scale I have).



  11. #11
    Community Moderator Al_The_Man's Avatar
    Join Date
    Dec 2003
    Location
    Canada
    Posts
    23067
    Downloads
    0
    Uploads
    0

    Default

    Sizing s/w Electromate Industrial Sales
    Torque increases by the ratio of the reduction and motor to load inertia ratio reduces by the square of the reduction.
    Ideal motor load inertia ratio <10:1.
    A large influence on this is the accel/decel rate.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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


  12. #12
    Registered
    Join Date
    Apr 2007
    Location
    usa
    Posts
    10
    Downloads
    0
    Uploads
    0

    Default

    Well this is a good conversation for me. I am a 40 year old engineering student just about ready to start my second year. I started a little behind in the Math dpt. so in some ways this will be my first engineering year. I spent the first year learning CAD etc. I do have a sort of long background in metal fabrication and manual machining. There was not alot of calculating there accept Trig and measuring. Everything was done by gut and feel. Sooooooo

    If I want to calculate the load inertia what do I use as the radius?

    The ball circle diameter of the screw?

    I am a little confused because I am not trying to spin it, just drag it.



Page 1 of 2 12 LastLast

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
  •  


About CNCzone.com

    We are the largest and most active discussion forum for manufacturing industry. The site is 100% free to join and use, so join today!

Follow us on


Our Brands

Servo Advice Needed

Servo Advice Needed