Identification of a Proper Sensor to Determine Solder Wire Length - Page 1
Forum section: electronics / projects

author: t1d
author_rank: Super Contributor
timestamp: November 23, 2016, 04:42:05 am
content: I want to build an automated solder wire dispenser.- The motor will be a stepper.- The controller will likely be a PIC18F4550, in an already developed breakout package.- Every time the solder wire is consumed, the motor is to advance the wire back to the preset distance beyond the “Dispenser Tube”/wire guide.All of the facets of the design are known, except for the sensor method. A sensor will recognize that motion has occurred within the dispensed wire zone and, then, after a delay, for the motion to subside, a sensor (either the first, doing dual duty, or a second) needs to recognize the length of the dispensed wire remaining, so that the amount to be re-dispensed can be calculated. It is this second sensor with which I need your help.The simplest method would be to put a grounding brush on the wire roll and a pad in front of the solder wire, with the pad tied to the controller. This would make a switch, of sorts. When the solder wire reached the pad, the pin tied to the pad would go low, the motor would stop and, then, reverse to a set distance away from the pad, allowing distance to be able to load the iron tip. However, testing of this method proved that the flux within the solder creates a non-conductive coating that prevents the pad from recognizing contact. I tried it, repeatedly.The best means of detection would be something that creates a beam plane and detects interruption anywhere in the beam curtain. This would allow for slight bends in the solder wire.I have considered lots of sensor types… Sonic, Infrared, Capacitive, Inductive, Metal Detectors, etc. The problem that I am having is with the lack of precision of the beam field and the possibility that the wire may not be exactly in the same place. Take an infrared sensor as an example… The wire is not likely to create enough of a shadow to be detected well, particularly when considering ambient light. And, if the wire is slightly bent, it might not be in the proper alignment between the emitter and receiver.So, I am hopeful that you may know of an appropriate sensor, or solution. A drawing is provided for your consideration. I look for to your insights. And, thank you.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 23, 2016, 05:21:08 am
content: If the dispenser tube were a transducer of some kind (piezoelectric, magnetic, etc.) then the resonant frequency would change depending on how much solder is sticking out the end.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 23, 2016, 02:41:53 pm
content: If you are driving a stepper motor then you know how far based on how many pulses you sent to the stepper motor, so I don't see why you would even need an encoder.But the issue doesn't appear to be how much solder you are dispensing, the issue is detecting how much (variable) amount remains after the last soldering activity.Another possibility might be to retract the solder back until a contact at the end of the dispenser tube loses contact, and then you have a known location of the end so you can push out however much is programmed.

author: t1d
author_rank: Super Contributor
timestamp: November 23, 2016, 04:40:41 pm
content: Quote from: Richard Crowley on November 23, 2016, 05:21:08 amHi, Richard,Thank you for helping me. This is a method which had not come to mind. And, I don't know much about it. So, if you would either 1) tell me about it, 2) point me to an educational link, or 3) tell me the proper term to Google, I would really appreciate it.

author: t1d
author_rank: Super Contributor
timestamp: November 23, 2016, 04:42:42 pm
content: Quote from: blueskull on November 23, 2016, 05:28:35 amThanks for joining in, BlueSkull... Please continue to offer ideas!

author: t1d
author_rank: Super Contributor
timestamp: November 23, 2016, 05:05:08 pm
content: Quote from: Richard Crowley on November 23, 2016, 02:41:53 pmThis is the correct understanding of the challenge.Quote from: Richard Crowley on November 23, 2016, 02:41:53 pmMy brother is working on this with me and he had offered this exact idea... Great minds... Your idea is elegant in its simplicity.I looked back at my notes and determined that I had, erroneously, discounted the method, based on it not being able to detect consumption of the solder. The solution to that is to add a second sensor that detects activity within the dispensed wire zone. That is an easier challenge. Once activity is sensed, the wire resets using your brush sensor method. Hmm... I'm feeling pretty good about that... I will have to give it some thought... Thanks, Richard!

author: PointyOintment
author_rank: Frequent Contributor
timestamp: November 24, 2016, 10:26:17 am
content: Going a bit more advanced…Time-domain reflectometry? As long as the dispenser tube and drive wheels aren't conductive (or, if one is, you use that as the contact, maybe), the end of the wire should give a good reflection. You will of course get a reflection from the wire on the spool too, but if you make sure the spool is at a different distance from the TDR contact than the dispensing end, it should be possible to ignore that reflection by range-gating. As the wire runs out and the end on the spool comes off the spool and approaches the TDR, you can ignore it by simply knowing where it is from keeping track of how you move the wire, or looking at which distance increases and which decreases as you move the wire in a known direction. Or you could make a direction-selective TDR using a phased array of contacts (knowing the propagation speed in your wire).Frequency-domain reflectometry? Just as the wire will resonate mechanically at a length-dependent frequency, it will also do so electrically. It will also act as an antenna, though, so be careful to avoid jamming all nearby radio communications as you sweep the frequency. You can exclude the wire on the spool by its greatly different resonant frequency and likely different Q. As the end approaches, you can differentiate it from the end you're pushing out in the same way as with TDR.Both of these techniques should also allow you to estimate how much wire remains, too, as long as there isn't any cross-conduction between turns on the spool (which there almost certainly will be, so I suggest using a weigh-scale instead if you want to achieve that).The flux core, if it's conductive, could preclude using either one of these techniques. And it may or may not be apparent, but I actually know next to nothing about either one.

author: dmills
author_rank: Super Contributor
timestamp: November 24, 2016, 10:32:37 am
content: You have the drive rollers and the dispensing tube, split the dispensing tube into two segments (or place a photo switch at the front of the dispensing tube).Now back the motor up until the solder just clears the sensor (or the two tube segments show open circuit, whatever), then run forward to give the desired amount of tail sticking out the front.73 Dan.

author: t1d
author_rank: Super Contributor
timestamp: November 25, 2016, 03:25:04 am
content: Quote from: dmills on November 24, 2016, 10:32:37 amI like your way of thinking Dan. Thanks for your participation.

author: t1d
author_rank: Super Contributor
timestamp: November 25, 2016, 03:45:05 am
content: I have remembered some of the challenges of the contact sensor method suggested by Richard. The main difficulty is that the solder wire must be reversed to find its end. This would require turning the solder spool, itself, to prevent backlashing the wire. That means a second drive mechanism for the spool. And, the two wheel drive that pulls the wire forward could not be eliminated, because of the possibility of backlash in that direction, too, if there is just a spool motor. This issue is caused by the soft nature of the solder wire.I am reconsidering the contact pad placed in front of the solder wire. The problem is that the flux coats the end of the wire and prevents conduction. I might try using steel wool for the contact pad. Maybe the wool would attain conduction through the side of the solder wire. There is still the matter of having to reverse the wire back from the wool... Hmm...Keep those ideas coming! Thanks!

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 25, 2016, 05:35:21 am
content: Why not leave enough open space between the spool and the drive wheel so that the "blowback" has a place to go momentarily? The supply spool doesn't really need to be actively powered, does it?Why not just a button on the side of the dispenser so that the user can feed as much solder as they like? Hold the button down until you have enough. That way the user could spit out more to reach into tight quarters, or less for fine SMD work, etc, etc.

author: jeremy
author_rank: Super Contributor
timestamp: November 25, 2016, 06:31:29 am
content: One thing to note is that if you yank on the solder, you can probably pretty easily skip some steps with your stepper motor (unless you are using a monster stepper and/or gearbox). A number of precision stepper motors use encoders for this reason; not to control the motor position, but to detect when the motor skips or is being forced. See Oriental Motor's "alphastep" as an example. Also solder can stretch pretty easily in the smaller diameters for some compositions. Both of these will cause accumulating error.As for detecting the solder, perhaps some more information on your application may help narrow things down. Detection using openCV and a webcam should be pretty straight forward, but depending on what it is for, you may be better off with the forwards/backwards buttons as mentioned

author: t1d
author_rank: Super Contributor
timestamp: December 06, 2016, 09:27:17 am
content: Quote from: Richard Crowley on November 25, 2016, 05:35:21 amBecause my hands are busy holding, or doing, other things.Quote from: Richard Crowley on November 25, 2016, 05:35:21 amThis is a stationary unit.I have been considering the reverse/reset method. The solder will have to be used as a conductor for the electrical signal for the controller. This means that a separate electrical device, the soldering iron, is brought into contact with the dispenser circuit. Is this a significant danger?Hey, what about some type of pressure operated switch?.. The type that is actuated by contact from a moving part... It would have to have minimal resistance... Place it in front of the wire path. Reverse the wire away from the switch "button", to allow for the soldering iron to reach the end of the wire, without leaving solder on the button. This method does not require the solder to be part of the live circuit...Jeremy, please tell me about the OpenCV/WebCam method... I know nothing of it.EDIT: That method requires full computing power. Might be possible on a Raspberry Pi, depending on it requirements, but that is considerably more than I had intended to get into... Great technology, though!Thanks to all...

author: jeremy
author_rank: Super Contributor
timestamp: December 06, 2016, 09:45:36 am
content: How about foot pedals

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 06, 2016, 10:04:47 am
content: An electrical sensor will be prone to dirt etc.Optical, maybe, however for presence sensing I'd use an inductive senspr - a small SMD inductor close to the wire path - set it up as an LC resonant circuit with an NPO cap, ping it and measure the ring-down time, which will reduce in the presence of a conductive metal.

author: t1d
author_rank: Super Contributor
timestamp: December 06, 2016, 09:23:08 pm
content: I have designed a switch to sense the length of the wire. The switch will sit in front of the solder wire. An infrared motion sensor detects the activity of loading the iron with solder. The controller advances the wire, until the wire closes the switch. Then, the controller retracts the wire a set distance, leaving a fresh length of solder to use and a space in which to reach in with the soldering iron tip.The switch was made as follows... I cut a square of sheet aluminum. I cut two ribbons on the sides of this square. I rolled these ribbons into two hinge barrels. I ran a piece of solid copper wire through the barrels, to complete the pressure plate. This wire supports the pressure plate and makes connectivity with a wire going to the controller. The back of the plate is covered with tape, to keep the solder wire from making connectivity with the plate. An angle was bent into the plate, to make a counter weight that holds the pressure plate perfectly horizontal, when at rest. Gravity acts as the spring mechanism to return the plate to its neutral position. As the plate is feather light, the solder will have no problem pressing it onto the copper clad. The two plates are wired to the controller. The switch works without energizing the solder wire... Bob's your uncle...The picture gives a better explanation. It is a side view.

author: mikerj
author_rank: Super Contributor
timestamp: December 07, 2016, 03:43:24 pm
content: How does the above system know that you have used some solder, and that it's time to advance it? Just using an IR sensor surely risks that it could start advancing whilst you are still trying to solder?Also the switch looks like it would get in the way an awful lot.

author: KL27x
author_rank: Super Contributor
timestamp: December 07, 2016, 07:24:33 pm
content: Alternative, more organic model. I.e., how a little elf might feed you solder. How you might already feed yourself solder, manually. Just automatically:1. IR detection of iron2. When iron is detected, wait until iron is no longer detected, delay 2 seconds, then feed solder about an inch or so. More than is used in one go.The idea is... you pick up solder with the iron, and nothing happens... You pick up more and nothing happens.... Until you get past the "red line," where IR sensor minimum threshhold is reached. Next time you reach for solder, you have gotten a big, quantum dose of more solder wire. KISS. No runaway solder feed when it gets bent and misses your contact switch. No contact switch in the way.Another KISS method I have given some thought to: A contact switch you press with the iron (perhaps under a small cleaning sponge?). This activates a very slow feed rate that continues for 30 seconds or so, then stop. Maybe just and inch or so fed over 30 seconds, as a starting point from which to tweak from. Press the button as needed. I went so far as to buy a worm gear motor to build this, but never got around to it. The downside to this whole thing is size. Compared to small half pound reel holder with a support rod, which you manually advance one in 10 uses, which you can place anywhere.

author: t1d
author_rank: Super Contributor
timestamp: December 08, 2016, 04:07:36 am
content: Quote from: mikerj on December 07, 2016, 03:43:24 pmHi, Mikerj... The way you asked the question, I think you know the answer... Yes, the IR sensor detects activity (there is the assumption that the activity is caused by using solder) and the controller resets the length of wire. And, your concerns over the sensitivity of an IR sensor are pertinent. This very point is why I have asked for help in identifying a proper sensor.I will try to limit the Phototransistor's field of view, by covering it with a bit of heat shrink to create a bottle-necked collar. And, I have added a trim pot to the circuit to vary the intensity of the IR LED. Only testing will give the answer, as to whether it will work, or not.Quote from: mikerj on December 07, 2016, 03:43:24 pmThe solder seems to be much more rigid than I expected. It has no trouble staying straight and activating the switch at about two inches.The reset procedure is to sense activity, advance the wire, until it activates the switch and retract the wire a known, and sufficient, distance away from the switch, to allow the solder iron tip to easily reach in.Thank you for your contribution. Please continue to help me think it through.

author: t1d
author_rank: Super Contributor
timestamp: December 08, 2016, 04:16:46 am
content: Quote from: KL27x on December 07, 2016, 07:24:33 pmHi, KL27x... This is exactly how I intended to write the code. Great thinking!Quote from: KL27x on December 07, 2016, 07:24:33 pmThat is an interesting approach. I think you should give it a go...Quote from: KL27x on December 07, 2016, 07:24:33 pmThat is a good point. Just giving it a guess, I think it will be about twice the size of a regular holder.

author: t1d
author_rank: Super Contributor
timestamp: December 08, 2016, 04:36:28 am
content: I spent the day designing the controller circuit in Eagle. I also laid out the PCB board. The board has a unique feature; it doubles as the mount to hold the IR Sensor.I am using a Microchip PIC18F14K22, because it is one of their chips that I want to learn about. It is a good thing that I choose this chip, because it has 17 I/O pins and I kept adding features... A speed control pot for the motor, a switch to set the wire length, etc.Coding is the next step. I know very little about coding and I look forward to learning...Here is another diagram of the device, with more detail. It shows top-down and side views. It is not to scale, which makes it look long. The real one should not be so spread out.Thanks to everyone!