Pick and place build, openpnp

[RoGeorge]

Never seen such a request before.

I don't think a logic analyzer will be of any help, let alone an optical one.  Also, there's no need to look at small signals and high amplification, but rather to measure the eye opening with an oscilloscope synced on both raising/falling edges and try to deduce the expected BER (Bit Error Rate).

And if it were to go optical, then better use the optical path for the signals that drive the machine, why bother with optical cables for a debugger?  Are those boards DIY or bought?  What communication protocols are used, and at what speed, what error checking codes are in use, etc.?

Though since the logic analyzer have problems reading the signals to be visualized, same problems will happen to the electronic in charge with all the data communication.  Maybe the motors need chokes to remove part of the noise, maybe there is a ground loop somewhere, or maybe the data boards need better HF filters and cleaner power lines.

Are you familiar with ground loops, and with transmission lines + reflections that happen in a line/wire at any point where there is a change in impedance?  Are the data lines properly matched in impedance and with the proper terminators attached?  Does the communication wires have the proper impedance, as requested by the design?

[pisoiu]

Ok, some clarifications are necessary.
The USB serial interface from openpnp is located on the main board, installed on the machine bench. This board have around 60 analog and digital ports, one CAN interface, one RS485 interface. Ports are connected mainly to relays for feeders, RS485 and some ports are routed to servo controllers and CAN is going to head. On the head, there is another board which control 4 nozzles with steppers for rotation and Z actuation, position sensors and relays for vacuum ejectors. Both boards are based on a Silabs 8051 CPU. There is no signal integrity problem on the machine. USB serial connection is stable, cameras never disconnects. CAN bus is properly terminated, works without errors. Servos as well, there are chokes everywhere, as required by servo controllers installation guide.
The problem is that the board's firmware is work in progress. Everything is written from 0. My problem is not to debug something which is supposed to work. My problem is to write the firmware for the entire machine and I have some glitches in algorythms somewhere, and I cannot find them. Typically, a command received on USB is broken in pieces. Some pieces are for servo controllers, those are sent by main board to the servos. Other pieces are for head board, to actuate nozzles, sent on CAN, and there, head board splits them further into signals for stepper drivers. After those are sent, both main board and head board must be monitored for command completion, in position signals, end of stepper movement, etc.  Sometimes (1 from 1000 placed components typically), this chain fails somewhere and I need to see where, by monitoring all the path from USB serial port to the other end. When I connect logic analyzer to the machine, it needs to be connected to both boards (base and head) to see the sequence of the signals. But I also need to put analyzer's ground on boards and to laptop and thus I create ground loops which destroys the analyzed signal. This is why I need to transport test signals from both boards to analyzer  without electrical connection.
You can see the boards in the picture. They are actually identical hardware but the firmware is differentiating between main board and head board.

[Kjelt]

I had this discussion many times on the cnc forum where they do not connect the shield of the motor or servo cables at both ends to ground. If you don't do this your cable is emc leak for elektromagnetic disturbance.
What you should do (IMO) is follow the NEN guidelines for industrial machine construction and have each and every metal bar/profile/plate seperately hard grounded with a 4mm2 or better 6mm2 copper cable, preferably litze cable for emc but that runs up the bill. Tie all cables to a large copper bar somewhere on the machine and ground hard. Also connect the electronicscabinet to this point as all other cabinets/power supplies.
By doing so you create the same earth potential on every part of the machine and per definition you can not introduce ground loops or perhaps on very high frequencies.
Do not think one moment that a spindle with ball nut and linear rails are a good conductor. Yes you're Fluke will measure it below 0,3ohms resistance on dc level but the grease balls etc are for emc a high resistance.

[pisoiu]

Agree, I never take metallic mechanical components as ground conductors. I will try to connect them with thick wire. I have several shielded ethernet cables between table and head and none of them are using shield as current carrier. I use some twisted pairs for CAN, sensors and one cable is just for power distribution , 4 wires are gnd, 4 are 24V, one gnd wire is twisted with one 24v wire.
I cannot remember now how the servo cables are connected but I can assure you they are installed as in the manufacturer documentation. They are Panasonic Minas A6 series and there is a quite comprehensive documentation available just for this subject of connecting power cables.

[MR]

Hi Pisoiu,

are you measuring the component height in advance or via sensor now?
I think you did some alignment work back then how did that go?

i would also like to add a sensor for measuring the component height on my machine so I don't have to measure the component height manually all the time.

[pisoiu]

Hi,
Last period was a little busy with other (more important) stuff, so the machine had to wait. But it is completed and now I am working at calibration. Unfortunatey I have an ellusive problem regarding Z alignment, somewhere, either the z axis of the top camera or the z axis of the heads are not perfectly perpendicular on the working surface. Because of this I have some problems at picking components, 2 out of 4 heads are picking with errors. Now I am building a device to help me calibrate perpendicularity but it is not completed yet. Same calibration will have to be done with both laser displacement sensors. After that, yes, I do plan to measure component height with displacement sensor, any solution which helps me to avoid doing things manually is good.

LE: the position of the nozzles were marked with indigo on a piece of papers then measured with top camera, the picking position also measured with top camera. However, there is significant error when head goes to pick the component (0603), as it is vizible in the high speed film analysis. Film is upside down because the camera is mounted inverted.
https://youtu.be/9y3F2kAtCw0

[MR]

After that, yes, I do plan to measure component height with displacement sensor, any solution which helps me to avoid doing things manually is good.

I think you have done some work on this in the past, or some experiments no?
Which sensor did sensors did you use for that? And which accuracy did you get?
I don't plan alignment via laser sensor, only height measuring.

[pisoiu]

Yes, I did some tests. They were for validating mechanical and optical problems but so far the sensors are not integrated into the openpnp workflow.
I have a bottom sensor mounted on machine table, maybe I will use that one for checking presence of component in nozzle, measure height of component in nozzle and I have a top sensor mounted on head, that is for component height measurement, mostly for components in trays, cut tapes, etc. For components in pneumatic feeders I don't think it is necessary, they are usually all at the picking level. I also plan to use top sensor in a checking program, after placement is done, to see all the components are on board before soldering.
I have 2 models,  HG-C1050 and HG-C1100, one with +-15mm range and 30 microns repeatability and the other with +-35mm range and 70 microns repeatability. They are made by panasonic.

[Kjelt]

I have 2 models,  HG-C1050 and HG-C1100

Interesting till I saw the price 

[pisoiu]

Yes, they're not cheap. If you go with official distribution channels it's probably worse. On aliexpress they are now at $250 ish. When I purchased mine in 2020 they were at $205.
I remember I had the same issue with my servos (400w high inertia panasonic minas a6). I purchased from Singapore 2 sets of motor+driver+cable at a total of $1000 at the same time when in my country, Panasonic dealer quoted just one motor around 700 eur. Crazy.

[Kjelt]

With Ali it is a lottery. I had $50 digitalpressure sensorswitches from Panasonic that in EU cost $100+ and also $20 SSRs and other stuff from Omron, all fake. They worked but were definitely not from the A brands. I stopped buying A brands from Ali therefore, good to hear you had a legit seller.

[MR]

Yes, they're not cheap. If you go with official distribution channels it's probably worse. On aliexpress they are now at $250 ish. When I purchased mine in 2020 they were at $205.
I remember I had the same issue with my servos (400w high inertia panasonic minas a6). I purchased from Singapore 2 sets of motor+driver+cable at a total of $1000 at the same time when in my country, Panasonic dealer quoted just one motor around 700 eur. Crazy.

You might check them on alibaba rather than aliexpress, I got mine for 160$ back then... while tme stocked them for 300 EUR or something like that.

[pisoiu]

My machine is now somehow finished but not yet operational, there are some calibration and tweaks to be done. But those are on the way.
Currently, the head uses 2 double nozzle assemblies from aliexpress (those everybody know of, with juki tips). Far from perfect and far from my original plan, but it greately sped up the commisioning of the machine.
New heads, which I plan to design from scratch, are left for the coming period, sort of stage 2 of the plan. Initially, few years ago, my plans for the head design were to use a voice coil to actuate Z and a small motor (like those used in cameras) for rotation. I took this path mainly because availability, for me, of such fine mechanical parts is limited.
But now, taking into consideration recent advancements in 3d printing (I already have at my office 3 SLAs), new options may open up. Now I am taking into consideration to find a way to actuate pneumatically both Z and R since I already have compressed air in the system. I am thinking at a closed loop system: actuator, sensor for displacement and a mechanical brake.
Does anybody know if some pick-n-place machine manufacturer uses such techical solution?

[Kjelt]

These p&p heads from the 90s did use pneumatics for the Z placement for parts upto 0402 but the whole idea is that there is some flexibility in the Z movement of the head (springs).
It does give some kick when it hit the board so you should have theboard also able to flex a bit otherwise already placed parts might jump. For rotation they use a small motor with quadrature encoder.
https://www.eevblog.com/forum/projects/tear-down-of-an-assembleonphilips-pp-head/msg1287990/#msg1287990

The more modern machines with precision placement seem to have linear actuators like these:
https://www.eevblog.com/forum/projects/mystery-pp-part-found-need-help-identifying-purpose/msg1398879/#msg1398879

[MR]

Last time I had a look at some Juki machines they use ground ballscrews for the vertical actuator.
Some other machines (also commercial ones) just use a spring loaded belt connected to the linear rail.
And many chinese ones use a stepper to hit down the spring loaded nozzle