. .
Page 1 of 2 12 LastLast
  1. #1
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 7 Hours Ago Has been a member for 7-8 years. Has a total post count of 1,466. Received thanks 275 times, giving thanks to others 9 times.
    Had a call from a friend earlier - "my CNC mill ain't working!" It's a Bridgeport-style vertical mill, built by Ajax, and by the looks of it, a decent machine in decent, little used, condition. Which is more than can be said for the control system - it's built-in PC still has a floppy disk drive and the whole lot is probably 25 years old. The current fault on it might be as simple as a dirty connector somewhere, or it might be something on a control board which would probably be uneconomic to replace.

    We started kicking around ideas for a refresh of the machine. I believe that it uses DC brushed motors, no plate on them, and I have no idea what's on the back of them. Encoder, tacho feedback, or whatever. I'm trying to get some idea of what to use for the control system and motor sizing so that I can give him a rough budget and estimate of work involved. I have considered leaving the motors and their drivers in place (I believe 10V analogue) but not having any idea what the servo feedback is on these machines and given the reduced choice of control options for analogue, I'm not entirely happy with that. I haven't had the covers off the motor mounts (apparently belt-drive to the feedscrews) to look at mounting arrangements, etc, to get an idea of ease of replacement but that might be easier than grafting a new motion controller on to the existing drive electronics (assuming that that's not where the fault is!)

    I'm happy to give him a few options for the control electronics (UC300+PC, dedicated Chinese controller (SZGH?) are likely options) but not sure about motor sizing for a machine like this, at least to be able to consider ease of replacement and costs. Any back-of-the-envelope guesses? I'm currently thinking something like 1.5KW/6Nm absolute servos with matching drivers (absolute as this machine has a mechanical limit switch and I'm not sure how repeatable homing would be). Table size is about 36x12" and the Z axis drives the quill rather than the table.

    Spindle motor drives the spindle via a variable-speed gearbox so the control system only needs motor on/off control, not speed. He's happy to stick with that.

    Any thoughts or suggestions?

  2. #2
    The Big Mill I've got had the same controller and probably similar type motors and drives. Thou i think the Bridge port size machines used slightly smaller motors.?
    The motors will most likely be badged up Analim but they are actually made by SEM and I'd guess around 3.5Nm -4.5Nm (30-40 IN-LBS) 4000rpm Max voltage 120-140V and will running at 100-120Vdc. Often they will have a voltage rating of around 36v per 1000rpm so 110Vdc will give 3100rpm.
    They could have Resolvers or Encoders with Tacho but most likely Encoders but they will be 5 wire single end encoders and around 1000ppr.

    The drives will be the same Badged Analim but the will most likely be made by Glentek. They will most likely be 200A drives if the larger motors or 160A if the smaller ones.

    The simplest and cheapest solution would be to re-use the DC motor but replace the Resolvers/Tacho with differential encoders and then use DC drives with Step + Dir.
    CNC drive makes 160VDC 35A drives with Step & Dir inputs which will work nicely with UC300. They also have tuning software for the drives.
    If the motors have Single-ended Encoders fitted you can also get a differential line driver from CNCdrive so can use with there DC drives which only accept differential signals.

    Or maybe go with the ET10 from PV Automation and run it on MYCNC and keep it fully closed loop with original drives etc. Though I think you'll buy the drives and UC300 cheaper than the ET10 and does a machine like this really need Fully closed-loop and all the tuning hassles that can come with it and old Analog drives.?

    However, If it was me I'd be fitting Chinese 1.2Kw AC Servos with incremental encoders which will be more than enough for this machine and using something like ET6 or ET7 depending on I/O needs.
    I wouldn't go with a UC300 with AC servos as it's limited to 100Khz so you'll need to electronically gear it in the drive to get the speed you'll require and that means you are wasting the resolution of the encoders which is what gives you the smoothness and accuracy. The UC400 would be a slightly better choice but still, you'll need some electronic gearing to get full rpm out of the motors because quadrature 2500ppr encoders will require 500Khz for full rated 3000rpm of typical AC servo.
    -use common sense, if you lack it, there is no software to help that.

  3. #3
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 7 Hours Ago Has been a member for 7-8 years. Has a total post count of 1,466. Received thanks 275 times, giving thanks to others 9 times.
    Thanks, Dean. That's thrown a few good ideas into the melting pot, and because my mind tends to think "steppers" I had forgotten the pulse rate issue with encoders. There's a few broad decisions to make, like what do we keep/replace, and whether he wants a self-contained control system or PC-driven motion controller. I've only had a quick look at the machine so I need to do a bit more investigation before making too many decisions. I've no idea at the moment how easy it will be to swap motors (mounting arrangements) or change to modern encoders, for instance. We'll see!

  4. #4
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 3 Hours Ago Has been a member for 2-3 years. Has a total post count of 190. Received thanks 29 times, giving thanks to others 5 times.
    When you say "modern encoders", nothing's changed in the meantime. You just need to know if your encoders are single-ended or differential output and which of those your drives require, using a converter if necessary. My SEM motors from the early 80s had Heidenhain encoders with differential outputs that wired directly into the cncdrive DG4S-16035 drives - quick and easy, no messing.

    The main difference between DC drives today and 20 odd years ago is that now they use microcontrollers rather than analogue circuits. So you can throw away the tachogenerator and simply use an encoder. Conversely, an actual resolver would be a PITA that you'd want to replace with an encoder. Resolvers give some measure of absolute position, whereas encoders only tell you how many clicks the motor has moved. Again, my SEM motors had tachos but I simply left them in place, as removing them would have involved additional ballache for no obvious benefit.

  5. #5
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 7 Hours Ago Has been a member for 7-8 years. Has a total post count of 1,466. Received thanks 275 times, giving thanks to others 9 times.
    Thanks again for the comments. My problem is that I understand the theory of the control systems and the various bits that go to make it up, but I have no experience with the actual hardware, even to the level of knowing how interchangeable things like encoders are. Is there some kind of mechanical standard (like NEMA motor casings?) or would this mean adapter plates, spindle couplers, or whatever? This might sound trivial to those who have done this kind of thing but it's a bit of a barrier to entry for someone like me!

    I could leave the servo motors in place, but almost certainly have to replace the encoders. Single-ended, differential - yes, I can cope with that, especially if there are off-the-shelf converters available.

    I could leave the existing servo drivers in place (yes, Dean - I'm pretty sure from the part numbers that these are rebadged Glentek) but then need an analogue motion controller, I believe. As an alternative, are there modern DC brushed motor servo drivers that would take step/dir input? That widens the motion controller choice.

    At the motion controller level, I could use either a self-contained system, complete with display, etc (like the SZGH or Newker or whatever), or a PC with motion controller (PV ET7? Probably not CSMIO-IP/S or A because that means Mach3/4 or the CS Labs equivalent, none of which seem especially desirable), or halfway house with, say, ET7 plus dedicated single-board Linux and display. Are there other likely candidates that I should look at?

    It's really the driver stage onwards that gives me the most uncertainty purely due to lack of experience in replacing driver/encoder/motor "stuff". I've been a stepper and EM806 kind of guy to date...

    My mate has been doing some research of his own but given the fact that he understands even less than I do, we're going to have an interesting conversation soon!

  6. #6
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 3 Hours Ago Has been a member for 2-3 years. Has a total post count of 190. Received thanks 29 times, giving thanks to others 5 times.
    I've got 3 of those cncdrive drives Dean mentioned on my larger machine, If you have a brushed motor with an encoder, these will work and they take a step/dir input. I'm driving mine with a Centroid Acorn but an SZGH would dohttps://www.cncdrive.com/DG4S_16035.html

    They are based in Hungary, so no tax or duties on the way in to the UK.

  7. #7
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 7 Hours Ago Has been a member for 7-8 years. Has a total post count of 1,466. Received thanks 275 times, giving thanks to others 9 times.
    Thanks - given that there is already a suitable DC power supply, that looks like the right kind of thing.

  8. #8
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 3 Hours Ago Has been a member for 2-3 years. Has a total post count of 190. Received thanks 29 times, giving thanks to others 5 times.
    You probably need about 120-140Vdc, so a 100Vac transformer is about right. I used a site transformer (240-120V) and removed some of the secondary winding. You might hope the existing PSU would be OK but is it single phase?

  9. #9
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 7 Hours Ago Has been a member for 7-8 years. Has a total post count of 1,466. Received thanks 275 times, giving thanks to others 9 times.
    Yup, as far as I know the whole machine runs off single-phase (although I need to double-check). The machine was running until recently in its present location, so I have assumed that adequate power is available.

  10. #10
    Muzzer's Avatar
    Lives in Lytham St. Annes, United Kingdom. Last Activity: 3 Hours Ago Has been a member for 2-3 years. Has a total post count of 190. Received thanks 29 times, giving thanks to others 5 times.
    The biggest load is likely to be the spindle which can use a VFD run from single phase. The servos etc don't take much power to begin with. Ideal if it's already single phase but no big deal to change over if it isn't.

Page 1 of 2 12 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Upgrade questions fro beaver mill VBRP Mk2 with Anilam Crusader II controls
    By Breg90 in forum Milling Machines, Builds & Conversions
    Replies: 11
    Last Post: 25-05-2020, 07:08 PM
  2. RFQ: Semi automatic welding system Linear beam control system
    By richway in forum Projects, Jobs & Requests
    Replies: 0
    Last Post: 24-01-2017, 07:54 PM
  3. Replies: 3
    Last Post: 18-05-2014, 02:40 AM
  4. Replies: 0
    Last Post: 06-02-2014, 08:52 PM
  5. drive control system
    By oadamo in forum General Electronics
    Replies: 1
    Last Post: 22-05-2011, 06:30 PM

Bookmarks

Posting Permissions

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