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Re: encoder head pitch
Robert N. Ash
There is a recent article In Motion Control Magazine on encoders MicroE is
the featured product. Good story on some history and the latest offering in high res stuff. Also some good articles on stiffness, ball screws, and harmonic drives. I don't know why I read this stuff (still stuck in manual mode) The low tech salvage encoders I have seen look kinda hard to duplicate though,,, I would also like to try the mouse hack but seems I have been there or tried it but, with no results to show. I have a lot of typewriter motors with encoders on them and plan to try a dos program to implement them. Any comments welcome Robert Ash |
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Re: How do I know if I want Linux
Don Wrote:
I have heard and seen here many messages from the Linux/EMC guru's here,Don... Windows Software can be expensive. Some people are just looking for a cheaper alternative. With Some CNC software costing upwards of $1000 it's easy to see how a 1GB partition on a hard drive to re-boot into linux and run EMC (which is free) is a cheaper alternative. For example: 1GB drive space (free if you have a big disk on your PC) Redhat linux 5.2 $30 with manuls $3 disk only. RT-Linux Free for download EMC Free for download ------------------------------------- Total sofware cost= $30 On the other hand.... install Linux 1Hr X $10 per hour = $10 Figure out install problems 6hr X $10 = $60 Download and Install rt-linux 8hr x $10 = $80 Figure out RT-linux problems 8hr x $10 = $80 Install EMC ( just a guess) 6hr X $10 = $60 Configure EMC (just a guess) 4hr X $10 = $40 ----------------------------------------------------- Total $330 So If your time is valuable ( and you arn't into linux for the fun and education) then I don't see a BIG cost savings. Also You could easily spend a few weeks getting familiar with X windows and other linux stuff. Don't get me wrong... I am a great linux fan. But it is still software and software is full of details no matter who wrote it. Now the idea for a "rtlinux-EMC " ez install CD has merit. it could cut the install time significantly for a person who just wants to use EMC and RT-linux to cut metal. But it will only work if it is focused on the EMC task at hand and is not a general linux install. This means that you would still use your existing Windows OS for all your other functions and only use linux for the machining portion. You must reboot to switch between windows and linux, so it is a pain. But hey PC's are getting cheap too. Look for cheap Pentium 90 Mhz machines at computer shows. A lot of them are being dumped due to Y2K issues. In short it depends on your goals and pocket book. Also if you use your hobbies for education, I can recomend linux as a good way to learn more advanced computer concepts. Hope this helps dave |
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Re: How do I know if I want Linux
Tim Goldstein
If I could get you to come setup my system for $10.00 / hr I just want to
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know when you will start!! Seriously, to me the main issues to look at with using Linux / EMC vs. a DOS / Windows controller product is the features it offers and not so much the price. If I had to bill myself at the rate people pay me to work on their systems and networks I would have about $1000 - $2000 invested into getting the real time kernel set up and EMC running. That is a pretty high price if you are considering just the dollars. If you are just starting to mess with this CNC stuff and want to go the stepper route or Camtronics servo amp based servo route I would suggest you either use DanCAD which is free or DeskNC DOS version which is $60.00. Either one is easy to use. DeskNC allows you to use real g-code and after using both it is my suggestion of where to start. Once you have mastered the basics of getting your machine to make a part with these programs you will be in a much better position to decide if you need more functionality. These programs will handle the basics just fine. As far as EMC / Linux goes, I would only suggest it if you have used one of the DOS / Windows programs and are now wanting to use the more advanced g-codes that the basics don't support. The other reason to look at EMC is if you are going the conventional servo route and need a program that can drive them. In my mind when you consider that EMC is a real time controller and that it supports a wide range of g-code I figure it would cost me at least a couple thousand dollars to get a comparable controller system I feel it was worth the effort to get on the band wagon. I am no Linux / EMC or CNC guru, but that is my 2 cents worth. Tim [Denver, CO] ----- Original Message -----
From: <daveland@...> To: <CAD_CAM_EDM_DRO@...> Sent: Tuesday, June 08, 1999 6:19 PM Subject: Re: [CAD_CAM_EDM_DRO] How do I know if I want Linux From: daveland@...discussion of shop built systems in the above catagories. |
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How do I know if I want Linux
Don Hughes
Gents:
I have read most all the threads that have been coming through about the Linux O/S. Back in the days when I first started with computers it was on the 8086's, and we had to use MS-DOS because that's really all there was to use then. Now, with the development of all the "Windows-Gate" O/S's of the past, present, and who knows what in the future, we all run a variety of Win95, Win NT compatible software for other uses(accounting, Spreadsheets, etc.) than just our CNC machines. My question is, how do I, myself, know and justify the reason that I would want to have Linux on my system with a partition for Linux exclusively to do other tasks? I have heard and seen here many messages from the Linux/EMC guru's here, and with the amount of controller software for Windows systems, I am having a hard time to seek a reason why I would need two O/S's. Can someone please try to explain to me and any others that might be in the same predicament as myself about these decisions. Thanks to all for a great forum here. Regards, Don Hughes Vancouver, BC Canada. |
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Re: Keeping correct.
Ron Ginger
As long as Bill has made a suggestion about replies to the list, Id like
to add one as well. Please be selective in the ammount of an old post you include when you reply. Most mail programs default to inclusing the entire message, but it just takes a couple seconds and a mouse click or two to eliminate all but just enough of the old message to set a context for your reply. Ive seen some replies where someone repeats a whole page, then says 'me too' At the very least please dont include the old tag lines, sine the mailer softwaare is going to add another one anyway. ron |
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Re: encoder head pitch, or, quit your griping.
"Ian W. Wright" <[email protected]
Hi,
Yes, this is the same principle. The point is that with gratings crossed at an angle movement of one relative to the other produces a series of dark bands which move at right angles to the movement. Changing the angle effectively allows you to space these out as much as you like and so it would become practical to make a reading head containing, say, 10 phototransistors equally spaced over 6 inches, then, by arranging it so that the length of this set of sensors corresponds with 9 or 11 dark bands, you get a vernier effect which magnifies the resolution. Ian Bill & Joyce Ammons wrote: Best wishes Ian -- Ian W. Wright LBHI Sheffield Branch Chairman of the British Horological Institute. Bandmaster and Euphonium player of the Hathersage Brass Band. UK. See our homepage at:- or or 'Music is the filling of regular time intervals with harmonious oscillations.' |
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Re: encoder head pitch, NO Griping
David L Anderson
Ian
Wrote: The kind of system I envisage would be easily made on the mechanical side and would consist of a tape with a number of straight black lines running the length of the machine - say ten at any even spacing - and a reading head incorporating another strip of the same kind of stuff and say ten IR phototransistors looking through the crossed gratings via small slits in a metal plate. I think that by choosing the number of lines, the grating angle and the number of phototransistors to give an accurate repeat rate, it should be possible to achieve good resolution by simple means. The grating could proboably be made by dragging a strip of acetate across the cutting adge of a screw tap in a suitable frame. Here is a "work in progress" that I will describe. I have built a small proto-type that is partially functional. It has no readout, Just signals that demonstarte the capability. I shelved the project in 1998 for lack of funds, access to scales or an acurate means to make them, and lack of sufficient CPU power to do the job cost effectivley. It is only a matter of time before silicon speed and prices make this method cheaper than and HEDS1000 solution. Please note that nothing is free in a DRO solution. Displays, power supplies, cabinet ,etc can add up to a few hundred dollars in itself I have been experimenting with a similar idea, Not using moire effect but an array of phototransitors and a course pitch grating (10 gratings to the inch). The photo sensors are in a linear array 2mils per pixel 128 pixels per line 1 line. I consider the sensor spacing etched into the photolithography of sensor as the defraction grating that Ian mentions. The sensor is made by TI (TSL401) and costs about $6. It is unique in that it is analog NOT digital. So instead of just a 1 or 0 in quadtrature, you must read out each pixel's intensity and interpret the results. Consider it as a one line television scanning a set of a set of bands on a moveable scale. As the bands move we get a different pattern of voltages from each of the 128 sensors representing the bar position. We must just scan quickly enough that the fastest motion will not cause us to jump a band, much like a stepper motor "cogs" when we step it to fast (only in reverse). As to potential accuracy, the system might have great potential. The edge of the bar can be found within +/- .005" with very little signal processing. I hooked the output of the sensor to a scope and was able to get this level of accuracy by observing the waveform on the screen. The scale was made on a laser printer using overhead film printed from a cad program. This was glued to a piece of clear plexiglass 1" wide by 11" long to form a "cheap" scale for testing. To get more accuracy I was planning on using the Analog information that is in the voltage on each sensor. This requires more complexity . An A/D converter and led bias circuit for tight control of the light source. The software is much more complex and approaches image processing or DSP in complexity. The problems: 1) The system requires high speed processing to achive even modest feed rates without error. The means (dual) expensive 24 Mhz micro controllers or an FPGA solution Per axis. This Costs a fair amount of development dollars that must be recovered. The processor cost could reach $40 per axis. This is not currently competative with HEDS1000 sensors. With Silicon getting faster though, this cost could drop in half in 18 months.Anyone have an FPGA development system? Let me know!!! 2) The scales need not be fine pitch but must be accurate and have a low coeficient of expansion. Plastic is just to non-unifom in it's thermal expansion characteristics. Glass is fragile. A metal scale is the best choice, but it must be either precision machined or etched. These are not easy operations. This requires acurate machinery, but it could be cheap if done in a reasonable volume. Anyone got a CNC mill that could machine a 1"X36"X3/16" bar of cold rolled with 0.1" wide slots, 1/2" long every 0.1" along its length? If you did it , would it stay straight? Let me know!!! TO BE Continued..... Accuracy, Precision, and the home shop .... [David L Anderson] |
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Re: A sense of humor needs to be restored to these proceedings
[long discussion on making read head snipped] That was pretty good; I'm going to file that someplace where there's a chance I can find it again. I had the read head for my Teledyne/Gurley DRO replaced recently. They used 2 _teeny_ photocells on the PC board. Not really a lot to it. Finally, let me add my voice to those who think that a CD with RT Linux andNot too likely with arbitrary hardware, unfortunately. It might work if you said 'given this video card, any of these network cards, this type of hardrive and CD', but most people wouldn't know the techy details and it's hopeless taking a shopping list to a computer store. Given the range of hardware out there, it's pretty amazing it works as 'painlessly' as it does (note the quotes around that). Heck, I have a machine I'm working on now where Windoze won't even recognize the mouse, serial _or_ PS/2. Probably a hardware glitch, but still a pain ... How about a bundled system including the servo board as an option? It's a lot easier to match up the software if you have the hardware handy and it's the wide range of video cards available that makes configuring X a pain. We end up building PC systems for folks locally (Windows 9x with NT or Linux file servers, depending on what they need). It's more interesting to build Linux systems. -- Paul Amaranth | Rochester MI, USA Aurora Group, Inc. | Software Development paul@... | Unix / C / Tcl-Tk |
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Re: A sense of humor needs to be restored to these proceedings
Jon Elson
Elliot Burke wrote:
In spite of the request to forgo handwaving, that's where I'll begin:Visible red lasers are now available for about $9. By running them below normal rated power, they will last a very long time. They are VASTLY more collimated than LEDs. Detectors are another issue. You can use 2 or 4 detectors. I prefer the 4From a purely electronic/mechanical viewpoint, yes, but from an operational one, a larger spot is less sensitive to a speck of dust or a small defect in the scale grating. The enterprising builder might remove the quadrant detector from a CDTotal GARBAGE! You will be lucky to get registration of .01" over the whole image! There will be all sorts of periodic and some non-periodic errors. These things are made to set type for newspapers, not make measuring scales with .0001" accuracy! People try to make printed circuit boards this way, and are horrified when the two sides don't match up better than .020" or worse over a 12" wide board. These print on mylar film very high contrast stable patterns. The machinesResolution is not accuracy! They are used by Mac zealots, and only understand file formats that arePlain PostScript. Jon |
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Re: encoder head pitch, or, quit your griping.
Jon Elson
"Ian W. Wright" wrote:
From: "Ian W. Wright" <Ian@...>Nope, it doesn't do that. All you get is one wave when the analyzer is moved one grating pitch. (If you had a VERY wide grating, maybe several inches wide, then you could put enough photocells on it to do what you are talking about, but electronic interpolation is easier and cheaper than having glass scales several inches wide. The angle at which theI'm afraid so. The angle of the analyzer does allow you to place your photocells closer or farther apart. But, you'd probably set the spacing of the photocells, and then adjust the analyzer to match. Now, if you want REAL moire' gratings, you use a different spacing grating for the analyzer, and DON'T tilt one with respect to the other, and you get a vernier effect, but it gets real complicated. Yes, but how are you going to make these gratings that have constant spacing, accurate to, say, .001" over 24 or 36", and with no short-term errors worse than this? This is why the scales cost $300 and up. This is actually DARN hard, and requires VERY expensive precision cameras, or laser systems, etc. Jon |
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Re: encoder head pitch, or, quit your griping.
Jon Elson
Elliot Burke wrote:
Mouse electronics count fringes. A serial port mouse sends the positionYes, but the resolution would be awfully low. I suspect many mouse circuits have severe limits on how many counts they can accept per second. Also, losing a few counts here and there is not an issue with a mouse, but losing even one count would be bad news for a DRO. Jon |
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Re: A sense of humor needs to be restored to these proceedings
"Elliot Burke" <elliot@...> writes:
Now on to getting patterns printed on plastic. Forgive me if this is tooA good idea, subject to the proviso that film recorders are not perfectly linear, and that high resolution alone is no guarantee of linearity and absolute accuracy. In my experience most low-end service bureau shop owners don't know the specifications of their machines, just whether or not it is adequate for their application. For precision work I recommend you find a service bureau that does specializes in quality color-separation work and image it at the highest resolution available, preferably 3600 dpi. They are used by Mac zealots, and only understand file formats that areThey all understand PostScript and will accept a PostScript text file for direct download. For a project like this it would be preferable to avoid page layout programs and code the scale directly in PostScript to avoid pixel rounding errors, although if you run it at 3600 dpi the rounding error may not be significant enough to matter. If line width is critical, note that rounding errors can give rise to lines of different width as well as +/- 1 pixel positioning errors. Finally, let me add my voice to those who think that a CD with RT Linux andSince the installation of Linux is very machine dependent, i.e., the set of drivers installed on my machine may differ from the set installed on another machine of different hardware makeup, I suspect it won't be possible, or at least simple, in the near term. Phil Plumbo St. Paul, MN |
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A sense of humor needs to be restored to these proceedings
Elliot Burke
This was intended in a joking fashion. No serious person would suggest that
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any reader of this list is anything other than hardworking and clever. From griping comes invention, as it is an intermediate state after necessity. In spite of the request to forgo handwaving, that's where I'll begin: The light source is the easiest part, but there are some subtlies: the light should be nearly collimated. The simplest way to achieve this is to use a LED with a narrow beam angle. The standard T1 3/4 lamps are 5 mm in diameter and have a beam a bit smaller than that. There are some larger diameters which could be handy. Detectors are another issue. You can use 2 or 4 detectors. I prefer the 4 detector approach, since the electronics then don't have to be as stable. There are some 4 detector packages, for example the UDT SPOT-4DMI and the FIL-S4DG, these have detector sizes of 0.5 mm square and 1.3 mm square, respectively. It is desirable to have the detectors cover as little area as possible, so that the system will be less sensitive to angular misalignment. The enterprising builder might remove the quadrant detector from a CD player. Personally I don't like fussing with surface mount packages. Now on to getting patterns printed on plastic. Forgive me if this is too elementary, but there may be some out there who don't know this trick. The trick is to use the Linotronic (type) film printer at a printing service. These print on mylar film very high contrast stable patterns. The machines have resolutions from between 1200 and 3600 dpi. They are used by Mac zealots, and only understand file formats that are popular in the graphic arts world. My advise is to not try to get them to understand any of your file formats, rather to find out what Mac's like and use that. The programs they typically use are Pagemaker and Photoshot. So if you can make a file in one of those, you're all set. They also read eps files, but I've found that these give poor results- maybe you'll have better results than me. AutoCAD can output eps files, but the linotronic printers don't interpret them accurately. I output files in dxf format and then make a Pagemaker document. This works quite well. You might want to consider how the machines native dot spacing can alias at the spacing you want to use. Tilting the pattern at an angle to the machine axes can reduce the effect of the aliasing. If a few people are interested in making these, let me know and I'll work up a parts list and a graphics file. Mount the LED so it illuminates the detectors. A pattern drawn with line patterns stepped in phase 90 is aligned to the detector. Op amps are used to amplify the signal from the detector, using a transimpedance configuration. The signals from the 0 and 180 are differenced with another op amp, as are the 90 and 270 signals. The outputs from the differential amplifiers are fed to triggers that go to 1 when the output is positive and 0 whent the output is negative. The people on this list can surely think of ways to use the precise patterns that the linotronic machines can generate. You can make scales, half-tone patterns, and my favorite, the business card with microscopic features on it. Finally, let me add my voice to those who think that a CD with RT Linux and EMC on it made as simple as possible to install is a good idea. Like, put in the disk, get a instant machine controller. Is this possible? Elliot Burke Rather than gripe about HP not building what you want, build one yourself.Try to moderate your stridency, eh? Nobody was "griping" that HP |
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Re: LINUX -Beginners Level
Don Hughes
Phil:
I have a .pdf that describes in detail how to install Linux on a PC (part ofWould you please send that.pdf file to me. This way I can have it on file when I get my machine and computer setup. If I decide this is the way I want to go with it. Thanks, Don Hughes pencad@... |
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Re: encoder head pitch, or, quit your griping.
Bill & Joyce Ammons
Ian,
What you described reminds me of a shaft encoder design that utilizes two discs with equal width opaque and transparent sections and the total number of sections for each disc to be different by one opaque section. One disc is stationary and the other is rotated. If the pair is illuminated from one side, interference produces a pattern that is dark at one angle and lighter as you progress across the diameter to the opposite (180 degrees) side. This pattern rotates 360 degrees as one disc is advanced one dark/light increment. So resolution is multiplied by the number of light sensors. For instance, discs with 100 and 99 dark lines and 10 equally spaced sensors looking through the discs, (parallel to the rotation axis), would yield a resolution of 1000 states per revolution. Sorry if this description is not too clear. I'm not that familiar with the terminology. Bill At 09:48 AM 6/8/99 +0100, you wrote: From: "Ian W. Wright" <Ian@...>these discussion of shop built systems in the above catagories.could be adapted to DRO's?Best wishes |
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Re: encoder head pitch, or, quit your griping.
I'm not sure what kind of encoders you r looking for. J & L Industrial supply
sells a DRO for lathes/mills made by mitsutoyo that has very inexpensive scales...I don't know if they will work for what you are trying to do or not...am still trying to get up to speed on what you guys are referring to Good luck, Tracey |
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Re: encoder head pitch, or, quit your griping.
"Ian W. Wright" <[email protected]
Hi,
A number of measuring systems I have seen use the Moire effect - is this a tecnique which might be used to overcome the lack of a suitable pitch grating? As I remember, two gratings are used mounted at a slight angle to each other. this has the effect of producing strong dark bands moving at right angles to the lines of the grating and allowing finer measurement from relatively coarse gratings. The angle at which the gratings are set affects the width of the bands and IIRC a smaller angle increases resolution - or have I got it all wrong? The kind of system I envisage would be easily made on the mechanical side and would consist of a tape with a number of straight black lines running the length of the machine - say ten at any even spacing - and a reading head incorporating another strip of the same kind of stuff and say ten IR phototransistors looking through the crossed gratings via small slits in a metal plate. I think that by choosing the number of lines, the grating angle and the number of phototransistors to give an accurate repeat rate, it should be possible to achieve good resolution by simple means. The grating could proboably be made by dragging a strip of acetate across the cutting adge of a screw tap in a suitable frame. Obviously, the electronics would have to discriminate which of the Phototrannies was dark and interpret this into a measurement but I'm sure this shouldn't be too difficult to achieve. I haven't tried this as I'm working too hard on my CNC mill but I'd be interested to hear your views. Ian Mouse electronics count fringes. A serial port mouse sends the positionBest wishes Ian -- Ian W. Wright LBHI Sheffield Branch Chairman of the British Horological Institute. Bandmaster and Euphonium player of the Hathersage Brass Band. UK. See our homepage at:- or or 'Music is the filling of regular time intervals with harmonious oscillations.' |
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Learner's notes on EMC/Linux
Russell Dunn <[email protected]
Hi Bill |
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