OpenPNP Pick & Place machine. - Page 1
Forum section: electronics / projects

author: Muxr
author_rank: Super Contributor
timestamp: February 16, 2016, 06:32:35 am
content: Been kind of toying with the idea of getting a Pick and Place machine. I have looked at a few used decommissioned large professional PNPs, but I really didn't feel like A.) running proprietary software that I probably couldn't get any support on B.) operating a machine that isn't backed by a community for troubleshooting or configuration help. I am just one guy and I certainly can't afford support contracts with these industrial PNP machine producers, even if I could purchase one of these machines by breaking my bank it is still a lot of money to risk on something that I may not get going.The idea of openPNP open source really appeals to me. Because it's FOSS if I have a need I can fix it myself, and usually there is a vibrant support around these projects, and I can contribute to it as well and more people will most likely get use out of it.I have sort of ignored the DIY scene mainly due to the lack of reliable feeders and having not been impressed with what I saw. But this presentation by Jon Oxer recently has sort of made me do a double take.The base machine build is described here:https://github.com/openpnp/openpnp-openbuilds/wiki/Build-InstructionsHere is a BOM link:https://docs.google.com/spreadsheets/d/1Jt3jb6zsk9aa-5eUBTdAOFm7u1YypV3FqZMti7bdn9s/edit#gid=0All the parts come out to anywhere from $950-$1200. And there is a very vibrant community around the project, so things will likely improve further.Even if I could get it to just place the LEDs and resistors, it would be a huge win over what I am doing today. I've already ordered the nozzles since they are from China, but as time permits I will order the rest of the parts and start working on it.Here is more of the same machine in action:Same type of machine with both nozzles going:There are also examples of folks repurposing the feeders from commercial machines to work with this installation, as well as feeders being developed by the community.I've built a 3D printer before [my Mendel90], so I think I will build me this PNP, let you know how it goes.

author: and101
author_rank: Contributor
timestamp: February 16, 2016, 10:24:22 am
content: If you can afford it get some decent quality linear guides for the rails rather than the usual cheap Chinese bearings that a lot of people use.Something like these guideswill be a lot more accurate and reliable and will allow you to place small parts like TSSOP packages without needing vision. Ball screws will also increase the accuracy. On my machine I used belts for the X and Y axis and lead screws for the pickers but when I build the next machine I am going to use ball screws as belts stretch over time which throws out the accuracy.Commercial feeders will also save a lot of time and stress and make the machine faster and more accurate. Onmy PnP machineI got some panasonic feeders from ebay, I think they cost about £20 each, and use a pneumatic ram on a linear guide to activate the feeders. It makes changing the components easier as you just have to pull out a feeder and replace it instead of messing around trying to feed the tapes into the machine by hand and align everything.

author: Muxr
author_rank: Super Contributor
timestamp: February 16, 2016, 11:11:18 am
content: Quote from: and101 on February 16, 2016, 10:24:22 amThanks for the tips! Once I get the machine to the point of just feeding from the double sided tape I will definitely look into getting the proper feeders, like the ones you mentioned. My original budget was about $5k so I have plenty of room to grow once I am convinced this is the right path.How difficult was adapting the Panasonic feeders to work with the machine? Random Siemens, Fuju and Mydata pop up on ebay at a decent price from time to time, wonder if I could go with a different brand or are the Panasonic ones the easiest to get working?

author: and101
author_rank: Contributor
timestamp: February 16, 2016, 11:20:40 am
content: The Panasonic ones were the only type available on ebay at the time so I went with them. If I was to start again I would use a feeder with a built in motor drive system as it would simplify the design and allow you to activate more than one feeder at the same time. I did find one company that make motorised feeders but they are about £500 each.This blog postshows the modifications that I had to do to make the feeders work. Basically I just shortened them and milled off a few bits of metal on the bottom so they would fit the frame we had designed. Once we figured out what modifications were needed it took less than a day to get all 20 feeders working.I did look at designing our own feeders but the biggest problem would be making every one exactly the same as a difference in size of 0.1mm is enough to throw the small components out of alignment. My milling machine is not accurate enough so we would have had to find a metal machining company who would do the work and I doubt if that would be cheap.

author: Muxr
author_rank: Super Contributor
timestamp: February 16, 2016, 11:23:48 am
content: Quote from: and101 on February 16, 2016, 11:20:40 amAwesome, thank you! I glanced at your blog, looks like it has tons of good information and will definitely read it thoroughly. Will keep an eye on the commercial feeders on ebay.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 16, 2016, 11:34:20 am
content: Quote from: and101 on February 16, 2016, 10:24:22 amYou're always going to need vision for reliable fine pitch stuff as the parts will not be located accurately enough in the tape/tray.These days vision costs so little that there's really no reason not to have it.

author: Muxr
author_rank: Super Contributor
timestamp: February 16, 2016, 11:42:35 am
content: Quote from: mikeselectricstuff on February 16, 2016, 11:34:20 amAbsolutely, I have seen some DIY vision setups leveraging the OpenCV. It's definitely something I will look into.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 16, 2016, 01:07:19 pm
content: And you don't need a fancy camera or lens as the focus distance is fixed and well defined - just move a normal lens away from the sensor to get close focus. AIUI the only slightly tricky bit can be getting multiple USB cameras running on one system.

author: Muxr
author_rank: Super Contributor
timestamp: February 16, 2016, 01:43:00 pm
content: Quote from: mikeselectricstuff on February 16, 2016, 01:07:19 pmGotcha. I will probably end up using something like the rPi to do the visual processing with OpenCV with its CSI camera (the camera is relatively cheap but decent), and just signal the adjustments to the Smoothy main driver board. This way it should be able to do quick 1-2 pic snaps for both parts on the nozzles and defer processing. So that there could be some room for speed optimization, the nozzles can be moving to the position to place the parts, while the Pi is doing visual recognition and calculating adjustments on the captured photos.Might have to have a one time self calibration routine for each type of component, but I am still far from that.

author: Muxr
author_rank: Super Contributor
timestamp: February 16, 2016, 02:06:47 pm
content: For those following along, from my preliminary research OpenCV seems to do well with orientation analysis.https://robospace.wordpress.com/2013/10/09/object-orientation-principal-component-analysis-opencv/

author: and101
author_rank: Contributor
timestamp: February 16, 2016, 03:17:16 pm
content: Quote from: mikeselectricstuff on February 16, 2016, 11:34:20 amOn my PnP machine I made some aluminium inserts for the chip feeder that are the same dimensions as the chip so they always come out of the feeder in the same position. It is not quite as accurate as a camera system but when I am placing TSSOP packages only one in fifty will need nudging and even then it is only out by less than a pad width. With larger packages like SOIC it places them close enough that they rarely need adjusting afterwards. The PCBs always get a visual inspection before cooking so if a chip is slightly off I can correct it.I designed the PnP machine with a camera system but so far I haven't needed to use it and it has placed at least 10,000 boards so far.

author: Muxr
author_rank: Super Contributor
timestamp: February 16, 2016, 03:24:58 pm
content: Quote from: and101 on February 16, 2016, 03:17:16 pmThat's impressive. I might do it [visual correction] eventually for the sake of the adventure and learning experience.

author: H.O
author_rank: Frequent Contributor
timestamp: February 16, 2016, 04:27:58 pm
content: I've been working on a machine for years (on and off of course). NSK and THK linear rails, ballscrews and DC-servos on X/Y, steppers on Z and rotataion.Tried the drag feeder stuff but didn't like where it was heading so I got a bunch (probably not enough but as many as I could afford) FUJI KG mototorized feeders. Couldn't figure out how to make them work so I designed my own control board for them.The machine is not "finished" but at this point I'm pretty much stuck at the software so yeah, an open (as in configurable) software solution (doesn't have to be free, I'd pay $1000 if it did the job) but I don't Think it's going to happen since there's just WAY WAY too many combinations of how the "right" machine should be built and out of what. Motors, drivers, motion controllers, cameras, feeders, vacum sensors, interfaces you name it. I need to send a custom serial command out an RS232 port to advance the correct feeder before pickup.Currentlt I'm fooling around with Mach3 as the motion controller and Roborealm for vision. I can get the two to talk to each other and IF I can get reliable image processing (I don't really grasp the concepts) I could probably make something work(able) but it will be a total hack - as almost all homebrew machine I've seen (and even some comercial ones).

author: and101
author_rank: Contributor
timestamp: February 16, 2016, 05:02:18 pm
content: Quote from: H.O on February 16, 2016, 04:27:58 pmI started off with Mach 3 controlling a SmoothStepper ethernet controller on my PnP machine as I already had experience using it on my mill. One problem I found with using their API is it takes quite a long time to generate the motion path when you give it a row of coordinates so there would be a lag of about half a second before it starts each move. The only way I could make it work without pauses was to generate a single G-Code file for the entire PCB but that meant that I couldn't then check to see if the component feeders were ready before it tried to pick up the parts so it would occasionally overtake the feeders and start hammering chips into the PCB.In the end I found a KFlop motion controller that has a better api and gives a far faster and smoother control of the motors. You can see the speed difference between the two motion controllers on this video..Since making that video I have managed to knock an extra 10 seconds off the build time for that board by tweaking the settings and motor speeds.

author: langwadt
author_rank: Super Contributor
timestamp: February 16, 2016, 05:20:21 pm
content: Quote from: and101 on February 16, 2016, 10:24:22 amwith vision it ought to be possible to calibrate out belt stretch, just stick a reference, something like aruler, on each edge of the table and periodically check the movement

author: and101
author_rank: Contributor
timestamp: February 16, 2016, 05:29:25 pm
content: Quote from: langwadt on February 16, 2016, 05:20:21 pmBut that would mean having to use the camera to place every component. Unless the camera is built into the head that would add quite a bit of extra time to place each part. You are better off designing the machine to be accurate in the first place so you don't have to try and compensate for the problems later on.

author: H.O
author_rank: Frequent Contributor
timestamp: February 16, 2016, 05:43:39 pm
content: QuoteYeah, like I said, using Mach3 would be a total hack but it's still probably the "easiest" way (for me that is) to get the machine going since I'm not that great at "low level" PC programming. I'm not accessing Mach3 from another application via its API, I'm actually running Mach3 using the built in scripting engine, talking to Roborealm and I'm using the LPT-port. I think perhaps the delay you experienced might have been due to the Smoothstepper driver and hardware buffering, perhaps.I've been using Mach3 and its predecessors for 15+ years and done and interfaced all sorts of weird stuff with it but again, at the end of the day it would be a hack, a semi usable one perhaps but still a hack.Am I correct when I say that you ditched Mach3 alltogether and wrote your own software from scratch, using the KFlop API from Dynomotion?I've also considered using the Ioni servo drives (since I have four of them) and they provide a Windows API but then we're back at the low level programming stuff. Did you use the S-curved velocity profile that the KFlop provides or did you use the "normal" ones?

author: langwadt
author_rank: Super Contributor
timestamp: February 16, 2016, 05:52:43 pm
content: Quote from: and101 on February 16, 2016, 05:29:25 pmif the belt stretch is a long term effect I don't see why you would need to use vision for every part, you'd justdo a single check to map steps to actual position as determined by the camera, just like a fiducial checkan accurate machine is obviously better

author: and101
author_rank: Contributor
timestamp: February 16, 2016, 06:02:22 pm
content: Quote from: H.O on February 16, 2016, 05:43:39 pmWe have ditched Mach 3 and now use an application that we wrote in C# to control the KFlop controller through their .NET API.You can see what the software looks like here.I think we are using the normal velocity profile but I am not sure as I worked on the hardware side and my brother worked on the software.

author: Muxr
author_rank: Super Contributor
timestamp: February 16, 2016, 06:03:48 pm
content: Quote from: langwadt on February 16, 2016, 05:52:43 pmTrue (both of you). Some 3D printers do well with this by self calibrating before each print job, it is not a big time cost just once, the belt isn't going to stretch much in a single session. It can be done before each PNP job. But yeah having a rigid ballscrew is obviously better.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 16, 2016, 06:13:20 pm
content: To some extent the fiducial correction on the PCB will also compensate for mechanical error.

author: Koen
author_rank: Frequent Contributor
timestamp: February 16, 2016, 07:07:20 pm
content: Hey, vendors of cheap chinese ballscrews can also offer prismatic rails and wagons. It's often not in their eBay catalog, contact them. It's the right tradeoff between price and repeatability. Prismatic rails from THK, SKF, Hiwin and so on are crazy expensive, even used, for the gain you'll obtain. Especially if you don't have perfect planes and the equipment to align everything perfectly. Nice thing about servos for a milling machine is the nearly-constant torque from 0 to rated-rpm but on the PNP, I'll stick to cheap steppers. There isn't much counteracting force when moving components in air.

author: JuKu
author_rank: Frequent Contributor
timestamp: February 24, 2016, 09:48:53 am
content: I'm the builder of the LitePlacer machine mentioned in the video. I'd like to put in a few comments:- Jon Oxer misunderstood my license terms. :-( It is non-commercial, but the limitation is only for building pick and place machines as a business.mikeselectricstuff: "These days vision costs so little that there's really no reason not to have it."Right. I don't really see how you could build and use a pnp machine without (although and101 has done just that!). Locating the parts is one problem. Another is the PCB itself. The pcb edge cuts are generally not accurate enough for small components, so even if you could get your pcb jig accurately placed, the pcb positioning is an issue. Vision helps greatly here, too. You only need to position the board accurately enough that the vision system finds the alignment marks. In use, vision is very helpful also: it is much easier to get positions with vision than mechanically.H.O: "but at this point I'm pretty much stuck at the software"You could have a look at my system. The software is free and open. It is windows only (so far) and relies on TinyG controller. If you can find a four axis controller with a good feedback from the machine position, you could probably adapt the software easily enough."langwadt": with vision it ought to be possible to calibrate out belt stretch"and101": But that would mean having to use the camera to place every component.´No, it wouldn't. Belt stretch is not a real issue. The belts have built in glass fibre and kevlar enforcements, they don't stretch much at all. When you build the machine, you tight the belts and that's it. I can measure my machine to about 0.02mm (vision helps here!) and I have a um accurate reference. In a year or so, the tight belts I use have stretched nil. In fact, when I checked the movement accuracy, I got a just a bit less movement than I should have, only 99.995% (0.2mm error on 400mm movement) . Either my reference is more accurate than the belt manufactures, or the manufacturer has accounted for some stretch and my belts are not quite as tight as they could be. Anyway, the point is that belts out of the box are very accurate and stay that way.mikeselectricstuff: "To some extent the fiducial correction on the PCB will also compensate for mechanical error."As will visual part recognition. Of course, the better mechanics you have, the better results you get, but having vision, software allowing corrections and careful tuning of the machine and its parameters will get you a long way. My machine is built from affordable parts and put together by non-mechanical experts, so it needs and has some corrections in the software. If you build your own machine, I really recommend putting vision in. That gives you things like- board and component location: You don't need to put those on the board with high precision, it is enough to be precise enough that the vision finds them (that is, you don't need to be precise at all).- accurate homing of the machine. Mechanical switches give you "only" about 0.05mm homing accuracy. Surprisingly good imo, but all the errors add up.- perfectly aligned machine: It is hard to even measure squareness accurately mechanically, and almost impossible for a hobbyist to mechanically square a machine accurately. However, the measurement is trivial with vision, and building a correction for non-squareness to software is even easier.

author: and101
author_rank: Contributor
timestamp: February 24, 2016, 11:36:33 am
content: Quote from: JuKu on February 24, 2016, 09:48:53 amYou can get better accuracy using optical switches. I used some optical break beam sensors which I salvaged from an old laser printer and they seem to be pretty reliable for homing the machine. The main limitation with accuracy is the software delay between the sensor picking up the break in the beam and the code responding to the input and stopping the motor but that can be calculated and compensated for in the software.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 24, 2016, 11:43:12 am
content: If you have a down-looking camera, why do you need accurate homing? - just have an accurate reference point that the camera can spot.

author: and101
author_rank: Contributor
timestamp: February 24, 2016, 11:57:26 am
content: Wouldn't you need a camera with a very high refresh rate? A lot of the cheap Chinese webcams only work at 50Hz or less so by the time the camera has captured the image and the computer has decided whether or not the homing spot is in view the picker head would have already passed the home point.The down-looking camera on my machine only has a refresh rate of about 10Hz with the head mounted LEDs. To get a faster refresh rate I need about 500W of halogen lights around the machine to get enough light into the camera. It works fine for setting up the component positions when building a new board profile but it would have difficulty tracking the location of the picker head accurately when the machine is running at full speed.If you want good continuous accuracy then you would be better off using a linear encoder with a magnetic strip on each axis so the motor driver can keep track of the location and compensate for any missed motor steps on the fly.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 24, 2016, 01:38:03 pm
content: Why would you need fast refresh - you don't have to sight it on the move- just stop in roughly the right area then home in on it. Only needs doing once at startup so no big deal

author: and101
author_rank: Contributor
timestamp: February 24, 2016, 02:05:30 pm
content: That is true, but you are still limited by the resolution of the camera, unless you have a very narrow lens in which case you would need to be fairly close to the correct position in the first place. Without position sensors how would you know where to send the camera to put it close to the home location? If the head gets moved when the machine is switched off then it wouldn't know where to go and would have to scan the full surface of the bed looking for the home mark.Surely a simple optical switch that puts a pin high when the picker head is homed is simpler than using a camera, computer and image recognition software to try and figure out the location of the head?

author: JuKu
author_rank: Frequent Contributor
timestamp: February 24, 2016, 02:33:22 pm
content: Quote from: mikeselectricstuff on February 24, 2016, 11:43:12 amHoming = finding out where the machine is at power up. As I see it, "have an accurate reference point that the camera can spot" is accurate homing. The machine sees the reference point and sets coordinates accordingly.

author: JuKu
author_rank: Frequent Contributor
timestamp: February 24, 2016, 02:39:24 pm
content: Quote from: and101 on February 24, 2016, 02:05:30 pmA machine needs some sensors or switches anyway. When it is powered on, it homes to switches. All CNC machines do this, and in most cases, good mechanical or optical switches give sufficient accuracy. But if there is vision, you can get an additional 10x improvement for free. Resolution of the camera is not a limitation, if you select the camera to fit the mechanics. Vision measures to half a pixel, and one pixel of a camera image is rather small in real life.

author: and101
author_rank: Contributor
timestamp: February 24, 2016, 02:48:06 pm
content: Quote from: JuKu on February 24, 2016, 02:39:24 pmI agree that a camera will improve the homing accuracy, I was just a bit confused by Mikes idea of using a camera to home the machine. Normally you would home first and then use the camera to get a more accurate location.If you can get a good home position to start with using optical sensors and linear encoders then it reduces the need for a camera. Linear encoders will also make sure that the machine doesn't loose position during a build which can happen if you use stepper motors and run them near their limits. Using servos would reduce the problem as they have encoders built in.Ideally you need to home the machine after every board otherwise if anything happens during a build to put the head out of alignment the machine wouldn't be aware of it and would place any further boards in the wrong position.

author: JuKu
author_rank: Frequent Contributor
timestamp: February 24, 2016, 02:52:46 pm
content: Quote from: and101 on February 24, 2016, 11:57:26 amOne more reply: You don't need fast refresh. You only need the video when doing a measurement, and that is not that often. We are talking about DIY machines, not those 10 components per second beasts. If the machine needs to stop for 0.1 second every now and then to get a up-to-date frame from a video stream, no big deal, it has very small impact to overall speed.Besides, depending on camera and its settings, the frame rate doesn't necessarily depend on lights. Some (most?) cameras keep the same rate and just send a dimmer image.And finally, a pnp machine does not miss steps. You can rely on the position you command the machine to go to, there is no need to track the position in real time, provided the controller is giving you feedback telling the control software when it has reached a certain poisition, so you can give it a command for next operation. This is different from a CNC machine that might loose steps, if you are milling hard stuff with too fast feed rates. There is nothing pushing against a pnp machine, it will keep its position during operation. Of course, if you set speeds too high any machine will stall, but that's a catastrophic failure, not a small "lost a step or two" error.

author: JuKu
author_rank: Frequent Contributor
timestamp: February 24, 2016, 02:58:40 pm
content: Quote from: and101 on February 24, 2016, 02:48:06 pmI think all of us mean exactly that, home first and fine tune the position fix with vision. We just didn't say it clearly enough.QuoteBy my experience, steppers in this application either keep their position or stall. If they stall, the position is way off, most of a move didn't happen. The next movement will hit a limit switch and game over.Nothing wrong with servos and good encoders but nothing wrong with steppers, either.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 24, 2016, 03:07:42 pm
content: Quote from: and101 on February 24, 2016, 02:05:30 pmThe comment was about high ccuracy position sensor s- you need a home position swithc but if you have a camera it doesn't need to be accurate.You only need absolute accuracy for feeder positions as board position will come from the fiducials.Quote

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 24, 2016, 03:10:02 pm
content: Quote from: JuKu on February 24, 2016, 02:52:46 pmYes, unlike a CNC, there is effectively no variation in load unless the head crashes into something, so it should be possible to accurately tune speeds so you never lose position.If it did lose steps, you'd find almost immediately when it fails to pick parts from the feeders ,

author: and101
author_rank: Contributor
timestamp: February 24, 2016, 03:15:46 pm
content: One thing I did look at when I was designing my machine was linear motors as they are faster and more accurate than stepper or servo motors plus it would simplify the design as you could have the motor built directly into each axis. Some of the high end pick and place machines use linear motors but I couldn't find anyone who made them at a reasonable price.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 24, 2016, 04:28:51 pm
content: Quote from: and101 on February 24, 2016, 03:15:46 pmThat reminds me - I recently saw theMydataMycronic paste printer - this has what looks like a row of neodymium magnets along each axis - presumably a voice-coil linear actuator - I wonder how hard it would be to homebrew something like that....You can see it in the vids on this pagehttp://www.worthingtonassembly.com/blog/2015/4/9/visit-to-mycronic-to-learn-about-the-my600-jet-printer

author: and101
author_rank: Contributor
timestamp: February 24, 2016, 04:56:47 pm
content: If you look on youtube for "diy linear motor" there seems to be quite a few people who have built them. I suspect that making one accurate enough for a pnp machine would be harder as it would need to be consistent across the full range of travel so you would need magnets that are all identical and placed accurately to a few micrometers.I suppose you could make one that is fairly accurate and then compensate for the errors in software using a lookup table or use a linear encoder to keep track of where the motor head is so you can then move to the rough position and make fine adjustments.

author: C
author_rank: Super Contributor
timestamp: February 24, 2016, 05:36:07 pm
content: I keep seeing versions of use optical to fix the mechanical system.Change it around and use mechanical system to improve the optical system.If the mechanical system is driven by rubber bands what needs to happen in the optical system?If you have a down looking camera on head & a up looking camera on bed you can get the displacement of the down camera and placement head. Here you need something that one camera can see while moving to get this displacement.If you know the offset then you do not look at where the part goes but the reference the camera took that is at the displacement from part position.So this step just created a bunch of position references.Everything just became a video reference to match up with what the camera see's. The mechanical system just needs to get in range of optical correction.The optical system can keep track of what it told the mechanical system for a move and how much it needed to correct the next command to mechanical system.If optical is used you have less need of a great mechanical system.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 24, 2016, 05:53:28 pm
content: Quote from: C on February 24, 2016, 05:36:07 pmThe problem is you can't see the placement position accurately enough as it's covered in solder paste

author: langwadt
author_rank: Super Contributor
timestamp: February 24, 2016, 05:55:51 pm
content: Quote from: and101 on February 24, 2016, 04:56:47 pmyou would have to use a linear encoder in any case, your are never going to get enough resolution using a linear motor as a stepper, you have to use it as a servo and that point it doesn't have to be any more accurate than any other motorbut unless you aiming for ridicules speeds I don't see a linear motor have much advantage compared to a regular dc motor and a belt once you have a linear encoderThose optical encoder and plastic strips used in cheap printers ought to work

author: C
author_rank: Super Contributor
timestamp: February 24, 2016, 07:35:04 pm
content: Quote from: mikeselectricstuff on February 24, 2016, 05:53:28 pmYou are not looking at the placement position with the camera but at the camera offset position from where part goes.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 24, 2016, 07:52:34 pm
content: Quote from: C on February 24, 2016, 07:35:04 pmThink you misunderstood. You can't use camera/optics to correct for bad mechanics as the accuracy depends on getting the right position of the placement relative to the fixed camera (or head in the case of a flying camera), which can only be done mechanically as you can't use vision to detect the placement position due to the solder paste.However if you could come up with a way to accurately measure the position of the tip of the head, you could use that to correct for cheaper mechanics. Laser interferometry perhaps?Though cheap mechanics is also about durability, and even a low-end pick/place could be expected to place millions of parts in its lifetime.

author: C
author_rank: Super Contributor
timestamp: February 24, 2016, 08:22:58 pm
content: mikeselectricstuffThink you misunderstood. Not using mechanics to position parts!NOT looking at part placement position!The Up camera and the Down camera measures the distance between the what the down camera see's and the placement head.The Down camera and placement head are a fixed displacement.Both move the same.The mechanics are just moving from one optical view to a different optical view. The mechanics just needs to get into optical view correction range. With Real bad mechanics system would need to do an optical search.For placement of each part you have a board fiducial that is composed of the traces and other things seen that is not covered by solder paste at that offset( down camera to place head) from the actual part place position.If the new PC board is rotated to much, then the system might need to use the real board fiducials to take new pictures of the part offset fiducial.Denser boards actually helps here.