Post by thread:[EE]: Making linear position sensors

This is an interesting idea... ...has anyone (other than me) actually tried it? Here is what I found: 1. vibration in the cable just kills it. 2. laying the cable on a slide helps until it picks up crap and blocks the sensor. 3. putting it in a tube requires that the tube be retractable I gave up at that point. I've never seen that plastic strip inside a printer, but usually see the insides of laser printers; is that a dot matrix thing? --- James Newton: PICList webmaster/Admin spam_OUTjamesnewtonTakeThisOuTpiclist.com 1-619-652-0593 phone http://www.piclist.com/member/JMN-EFP-786 PIC/PICList FAQ: http://www.piclist.com > {Original Message removed}

We have 2 surface mount machine where I work. On both of them they use an encoder strip that is attached to the machine frame. The moving head has a sensor that rides about .028" from this strip and reads its position from it. This way, since the encoder is a long magnetic strip on the frame, there is always an absolute reference point. {Original Message removed}

James Newton, Host wrote: > This is an interesting idea... > > ...has anyone (other than me) actually tried it? Here is what I found: > > 1. vibration in the cable just kills it. > 2. laying the cable on a slide helps until it picks up crap and blocks the > sensor. > 3. putting it in a tube requires that the tube be retractable > > I gave up at that point. > > I've never seen that plastic strip inside a printer, but usually see the > insides of laser printers; is that a dot matrix thing? > Hi James, Yes it is almost always inkjet specific. I don't think dot matrix printers needed them [not accorate enough] I took a picture of the one in my printer Beware this is a 350kB jpg: <martin.klingensmith.info/printer_optical_encoder.jpg> The 'thing' it goes into on the right is the carriage. -- -- Martin Klingensmith http://infoarchive.net/ http://nnytech.net/ -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Hello, A method used with linear positioning is a grating on the movable table, and fixed optical reader. See this site for the concept: http://www.renishaw.com/client/product/UKEnglish/PRD-856.shtml I have used this method and product for absolute positioning down in the micron measurements. (Observatory Grade Telescopes). If using a sensor, or feeding cables to a moving platform, most commercial machines use a loaded chain type of cable retainer (looks something like a bicycle chain) or an overhead cable with a set of suspension wires or rods (like the bellows support of a commercial laser cutting tool). The object is to support with flexability and no restrictions of movement with minimal loading on the moving platforms. Vern. > James Newton, Host wrote: > > This is an interesting idea... > > > > ...has anyone (other than me) actually tried it? Here is what I found: > > > > 1. vibration in the cable just kills it. > > 2. laying the cable on a slide helps until it picks up crap and blocks the {Quote hidden}> > sensor. > > 3. putting it in a tube requires that the tube be retractable > > > > I gave up at that point. > > > > I've never seen that plastic strip inside a printer, but usually see the > > insides of laser printers; is that a dot matrix thing? > > > > Hi James, > Yes it is almost always inkjet specific. I don't think dot matrix > printers needed them [not accorate enough] > I took a picture of the one in my printer > Beware this is a 350kB jpg: > <http://martin.klingensmith.info/printer_optical_encoder.jpg> > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On 21 Jul 04, at 15:49, Martin Klingensmith wrote: > <martin.klingensmith.info/printer_optical_encoder.jpg Its an HP DeskJet. and I claim my lollypop :.) A simple sensor to use with these strips is to double it over so it acts like a shutter and then use standard LED and Opto Sensor to detect the transition from black to clear ( Moire something effect ). The HP sensor in the head is not, AFIK, readily convertable due to its mechanical construction. for what ever thats worth. atb Mike -- -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Vern Jones <.....soundresKILLspam@spam@FOOTHILL.NET> wrote: > A method used with linear positioning is a grating on the movable table, > and fixed optical reader. > > See this site for the concept: > http://www.renishaw.com/client/product/UKEnglish/PRD-856.shtml > > I have used this method and product for absolute positioning down in the > micron measurements. (Observatory Grade Telescopes). Couldn't you do this in two dimensions using a stationary optical mouse and a suitably patterned card attached to the table? That should give you something like 300-800 ppi resolution. The mouse would face down, and shouldn't get too gunky. The card can be replaced as needed. -- Dave Tweed -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Martin Klingensmith <martinKILLspamNNYTECH.NET> wrote: > Yes it is almost always inkjet specific. I don't think dot matrix > printers needed them [not accorate enough] > I took a picture of the one in my printer > Beware this is a 350kB jpg: > <martin.klingensmith.info/printer_optical_encoder.jpg> > The 'thing' it goes into on the right is the carriage. Some dot-matrix printers used them. For example the original LA300 "DECwriter" had one. It was cool -- you could take the fuse out of the motor drive circuit and move the head back and forth by hand, and it would still put the dots in the exactly correct spots. If you went too fast, the logic would simply stop printing and wait for you to bring the head back to try again. IIRC, my original Centronics printer had such a strip as well. -- Dave Tweed -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > <martin.klingensmith.info/printer_optical_encoder.jpg > Its an HP DeskJet. and I claim my lollypop :.) > > A simple sensor to use with these strips is to double it over so it > acts like a shutter and then use standard LED and Opto Sensor to > detect the transition from black to clear ( Moire something effect ). > The HP sensor in the head is not, AFIK, readily convertable due to > its mechanical construction. > for what ever thats worth. > atb Mike > -- > Well I've actualy interfaced to one of those sensors. The four wires on mine were 5v, gnd, phase A and Phase B. Standard quadrature encoding. Read it with a PIC 16F877 at 4Mhz (port b interrupt on change) -Denny -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Dave Tweed wrote: {Quote hidden}>Vern Jones <.....soundresKILLspam.....FOOTHILL.NET> wrote: > > >>A method used with linear positioning is a grating on the movable table, >>and fixed optical reader. >> >>See this site for the concept: >>www.renishaw.com/client/product/UKEnglish/PRD-856.shtml >> >>I have used this method and product for absolute positioning down in the >>micron measurements. (Observatory Grade Telescopes). >> >> > >Couldn't you do this in two dimensions using a stationary optical mouse >and a suitably patterned card attached to the table? That should give >you something like 300-800 ppi resolution. > >The mouse would face down, and shouldn't get too gunky. The card can >be replaced as needed. > >-- Dave Tweed > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics > > > Now that's a good idea...you could even mount it below the table. Couple of limit switches to zero it. David -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

>>><martin.klingensmith.info/printer_optical_encoder.jpg >> >>Its an HP DeskJet. and I claim my lollypop :.) I'll send you one... >> >>A simple sensor to use with these strips is to double it over so it >>acts like a shutter and then use standard LED and Opto Sensor to >>detect the transition from black to clear ( Moire something effect ). >> The HP sensor in the head is not, AFIK, readily convertable due to >>its mechanical construction. >>for what ever thats worth. >>atb Mike You wouldn't even need to double it over, just have a set of slots the same pitch on the carriage with the detecter looking through them and the strip. Same effect but the strip would stay unmanipulated -- -- Martin Klingensmith http://infoarchive.net/ http://nnytech.net/ -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Since you can get a 6" digital caliper from harbor freight for $18.99 with the computer interface shown in the article on piclist.com, I don't see any reason to make your own unless you need longer distances and have to buy a more expensive caliper. Resolution and accuracy are 1 mil. And yes, the price is correct, though it's on sale. I just found out that a new harbor freight store opened up a few miles from me in May, so I purchased one and verified that it does have the four contacts mentioned in the article. I'm tempted to buy 3 more since they are on sale, but I don't have to to build my own milling machine this year... But I *have* found a new tool store. :-) -Adam James Newton, Host wrote: {Quote hidden}>This is an interesting idea... > >...has anyone (other than me) actually tried it? Here is what I found: > >1. vibration in the cable just kills it. >2. laying the cable on a slide helps until it picks up crap and blocks the >sensor. >3. putting it in a tube requires that the tube be retractable > >I gave up at that point. > >I've never seen that plastic strip inside a printer, but usually see the >insides of laser printers; is that a dot matrix thing? > >--- >James Newton: PICList webmaster/Admin >EraseMEjamesnewtonspam_OUTTakeThisOuTpiclist.com 1-619-652-0593 phone >http://www.piclist.com/member/JMN-EFP-786 >PIC/PICList FAQ: http://www.piclist.com > > > > > >>{Original Message removed}

>IIRC, my original Centronics printer had such a strip as well. The 702 series certainly did, and there was an older model that had one as well. Ah, those were the days, adjust the margin by moving the strip. Change the strip to get different characters per inch. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.