Retrofit CNC to this saw with kflop?


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Thread: Retrofit CNC to this saw with kflop?

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    Default Retrofit CNC to this saw with kflop?

    Hello,

    I've got a very old saw for cutting stone. It originally used steel cable with abrasive slurry. Since I've owned it I have converted it to use diamond wire and have the two motors running off of VFD's so I can control the speeds. The main motor that drives the wire is 10hp, the up/down motor is 0.75 hp going through a gear reduction and a winch... resulting in down feeds speeds of 12-36" per HOUR. I'll be adding a second axis (horizontal) soon and plan to use a similar setup to the down feed, 1 to 2 hp motor controlled by a VFD. Sort of like a foam wire saw.

    I'm new to CNC so trying to figure out if what I want to do is doable. Here is what I'd like to do:
    - Have 2 axis control, expandable to a third (rotating table), but even if I don't get the third axis just the two would be great.
    - I'd be happy with tolerances measured in mm... I'm cutting stone not building space craft.

    So my questions are:
    - The VFD that controls the down feed motor has inputs for speed (0-10v or 4-20mA). If I added a magnetic linear encoder that had the magnetic strip the length of the full axis travel, would that allow me to control the speed and positioning? Since I'm not using servo motors I'm fuzzy on this. Is the feedback sensor all that is needed for positioning?
    - Currently my down feed speed is manually set. The main motor that drives the cutting wire is controlled by a VFD, I can output the amp load to a 0-10v analog output... would like to use that as input into the feed speed (PID?)

    FWIW I'm a software developer (mainly C++) so if I have to I think I should be able to do any C programming needed.

    Here's a video of the saw in operation:


    Thanks for any pointers.
    Greg.

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    Community Moderator Al_The_Man's Avatar
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    Default Re: Retrofit CNC to this saw with kflop?

    I assume from watching the video you just need straight point-to-point, non-interpolated positioning, and no fancy varying cut rates during operation?
    If so, a CNC control per-se may be overkill.
    If you obtain VFD's with encoder feedback and put scales such as Newall type for precise motion speed, and place hermetically sealed limit switches that can be set for cut limits, you could also place calibrated potentiometers on a control panel to set before each cut.
    That would be my interpretation on all you would need, unless I am missing something?
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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


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    Default Re: Retrofit CNC to this saw with kflop?

    Hi Al,
    Thanks for the reply. If I understand what you are suggesting, I'd only be able to make straight cuts on each of the two axis, so 90 degree cuts. While that would be a nice start, ideally I'm looking to be able to do more complex cuts.



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    Community Moderator Al_The_Man's Avatar
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    Default Re: Retrofit CNC to this saw with kflop?

    Quote Originally Posted by Greg9504 View Post
    The main motor that drives the wire is 10hp, the up/down motor is 0.75 hp going through a gear reduction and a winch... resulting in down feeds speeds of 12-36" per HOUR. I'll be adding a second axis (horizontal) soon and plan to use a similar setup to the down feed, 1 to 2 hp motor controlled by a VFD. Sort of like a foam wire saw.
    Greg.
    So I am assuming that the VFD's will control the wire speed and if the positioning motors are all around the .75hp then you could fit around the same size gear-reduced servo motors to each axis, Could then the VFD's be sensorless vector with simple manual pot adjust?
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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


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    Gold Member TomKerekes's Avatar
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    Default Re: Retrofit CNC to this saw with kflop?

    Hi Greg,

    Really cool (and big) machine. By adding the linear scales I believe that would work. Of course you would need one for each axis. You could then configure the feedback loop such that the winch speeds would be varied to keep the measured axis position following the trajectory. Simple proportional (P) gain may work. As position error increases speed would increase. Probably a very low frequency low pass filter might be added to smooth out the commanded speed.

    Regards



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    Default Re: Retrofit CNC to this saw with kflop?

    Quote Originally Posted by Al_The_Man View Post
    So I am assuming that the VFD's will control the wire speed and if the positioning motors are all around the .75hp then you could fit around the same size gear-reduced servo motors to each axis, Could then the VFD's be sensorless vector with simple manual pot adjust?
    Al.
    Hi Al,

    I'm hoping to find a solution that allows me to use the existing motors/gearing I have for the axis drives. The 10hp motor that drives the wire is controlled now by a sensorless vector VFD, as is the down feed axis, and I have another VFD and gear motor for the horizontal axis which I'm adding now.



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    Default Re: Retrofit CNC to this saw with kflop?

    Quote Originally Posted by TomKerekes View Post
    Hi Greg,

    Really cool (and big) machine. By adding the linear scales I believe that would work. Of course you would need one for each axis. You could then configure the feedback loop such that the winch speeds would be varied to keep the measured axis position following the trajectory. Simple proportional (P) gain may work. As position error increases speed would increase. Probably a very low frequency low pass filter might be added to smooth out the commanded speed.

    Regards
    OK, that's reassuring. I assume the kflop with kanalog to get differential encoder support is the ideal option. Just one more question, as I've been reading up on encoders I see there are both incremental and absolute. Is it incremental I want?

    Now thinking of using a draw wire encoder for the vertical axis, as it moves up/down via cable and I may have troubles with the mounting of a magnetic strip encoder.



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    Gold Member TomKerekes's Avatar
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    Default Re: Retrofit CNC to this saw with kflop?

    Hi Greg,

    Yes KFLOP+Kanalog will provide the Analog Outputs and the differential encoder inputs.

    KFLOP only supports incremental encoders unless you do something custom. Incremental encoders require a home sequence or some way to set the current position where absolute encoders know where the axes are on power up. If you need to do something like manually zero at the top of the stock anyway I don't see where there would be a big advantage. Maybe if you need to power down mid way through and resume later.

    A draw wire encoder may work. I've never used them. Probably not as accurate but for your application it might be the right choice.

    Regards



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    Community Moderator Al_The_Man's Avatar
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    Default Re: Retrofit CNC to this saw with kflop?

    Quote Originally Posted by Greg9504 View Post
    Now thinking of using a draw wire encoder for the vertical axis, as it moves up/down via cable and I may have troubles with the mounting of a magnetic strip encoder.
    I have used these to synchronize four jacks required to lift box cars, they were quite successful, this is a link to the type I used but not the actual make.
    https://www.posital.com/en/products/...technology.php
    I also think it may be the answer to your project.
    Al.

    CNC, Mechatronics Integration and Custom Machine Design

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


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    Default Re: Retrofit CNC to this saw with kflop?

    OK ebay has been kind to me (I think). I've found a draw wire encoder with IP 65 protection, new and cheap with the following specs. Just looking to confirm this is an acceptable encoder? It's a TTL line driver at 5VDC. Only has 11.53 pulses/mm but again I'm not too concerned with accuracy, hoping that kflop/kanalog is indifferent to this, meaning you give it feedback with less resolution and you get less accurate machining... but there is no minimum resolution needed?

    Thanks again.
    Greg.

    measuring range 3000 mm,
    model P96,
    linearity +/- 0,02% FSO,
    incl. incremental encoder
    power supply 5 VDC,
    TTL, A,B,O and inverted,
    resolution 11,53 pulses/mm,
    protection class IP65

    Retrofit CNC to this saw with kflop?-drawwiresensor_2-jpg
    Retrofit CNC to this saw with kflop?-wds-3000-p96_1-jpg



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    Default Re: Retrofit CNC to this saw with kflop?

    Hi Greg,

    That encoder should be compatible. There is no minimum resolution for KFLOP/Kanalog. But higher resolution helps the servo loop to know the amount of error and the rate the error is changing more precisely.

    Good luck,
    regards



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    Default Re: Retrofit CNC to this saw with kflop?

    OK it's been a year and I've made enough progress to now want to go ahead with this. Last year I did purchase the draw string encoders I linked to above. I've added my second axis (details below if you are really interested). So I just have a few questions about power supplies, cabling, and distance to my differential encoders:

    Power supplies
    - I need 5VDC for Kflop, from wiki an old PC power supply should do the trick.
    - I need 5VDC to power the differential encoders. Should I power the encoders from JP8 pins 13-16(as shown here)? The specs for the encoders say each has <20mA load, so 40mA max for both. The linked doc says max of 100mA, so should be OK. There is a slight catch, see below about distance to encoders.

    Cabling/Distance
    - Any recommendations for cabling from Kanalog to the encoders? Outdoor rated cat6? The distance from where kflop/Kanalog will be and the encoders are ~ 35', and second ~ 50'. Are there problems having the differential encoders mounted that far away from kflop/kanalog?

    That's it for now. Thanks.

    2nd Axis Configuration for those that are interested:
    Despite being a bunch of junkyard material, the horizontal axis seems to work well and moves effortlessly considering the load (tested at 12000lbs on the cart). The horizontal axis uses part of an old automotive lift (Hofmann model Duolift-GE with 6500 lb capacity), the lift uses a 44mm acme screw with 7mm pitch, has a plastic nut. I need to be able to run the axis really slow, 8" to 60" per HOUR. So I picked up a 1/8 hp motor with a 900:1 gear reduction on it. However this means that moving the cart for positioning the stone prior to cutting is slow. I'm using the VFD to over speed the motor to 7200 RPM, which gives me a positioning speed of 4" per minute. Still slow but workable. The gearmotor is rated to 3600 rpm, I only need to run above that for short times.

    Couple of pictures, and video


    Attached Thumbnails Attached Thumbnails Retrofit CNC to this saw with kflop?-sawrailandtrolley_005-jpg   Retrofit CNC to this saw with kflop?-sawrailandtrolley_012-jpg   Retrofit CNC to this saw with kflop?-sawrailandtrolley_013-jpg  


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Retrofit CNC to this saw with kflop?

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