Hi timk,
welcome to LitePlacer forum
timk wrote:I have been wondering what the main limiting factor of the machine is in regards to component placement speed
I would argue that for prototyping or low volume manufacturing the CPH is usually not the most important thing but ease of use, reliability and autonomy of the machine are.
If you look at the whole process, a lot of time is spent outside the PnP operation itself:
1. Setting up parts + configuring the machine for a given job
2. Preparing boards and printing or dispensing solder paste
3. Running the PnP job
4. Validating placements and fixing errors if necessary
5. Transfer boards and reflow solder
6. Test boards
You will spend quite some time for 1. as long as you don't have fully automatic feeders and all parts on reels, in tubes or PnP trays. As I use LP mostly for prototypes, I have many components packaged as cut tape. I made magnetic custom 3D-printed strip holders which snap onto a defined grid which made this operation a lot easier for me. Others are working on automatic feeders; both electrical or mechanical. You will need some sort of part organization + holders, especially if you plan to produce many boards. Sticking them to the table using double sided tape is only good for one-off prototypes. While setting up the parts, you have to teach the PnP software the location and rotation (!) of each component type - depending on the number of different component types, this can take a while as well. If you use some clever tray mechanism, you can greatly reduce the time for setup if you run a job repeatedly.
To me, getting proper stencils and printing the solder paste is the best option for 2. If you work with smaller parts or ICs with small pitch, dispensing will never give reliable results - also manual dispensing is error prone and tedious and automatic dispensing is a complex task which does not pay off given the fact that stencils come cheap.
I assume your CPH question mostly relates to 3 - the actual placement operation. As I already pointed out, speed is not that important for me, as long as the machine works autonomously and does not require constant babysitting. I like "fire and forget"; once I start a job and can attend to something different, I do not care if it completes in 15 or 45 minutes... To me it is more important that the result is reliable.
Any PnP machine using steppers and thus open loop drive (as opposed to servos with closed loop control) will loose more and more accuracy the faster you accelerate and move the machine, be it due to lost steps or mass momentum. Depending on the hardware, you will also have some mechanical tolerances (play in linear rails, slack in belts, etc.) which make things worse - again a reason not to max out speed + accell. By the way, acceleration is more important than end speed - as in PnP the movements are usually rather short distance...
But acceleration and movement speeds are not the only thing affecting speed. "Think" time of the control software, e.g. for image processing and movement planning often takes more time. Then there is dwell time for the vacuum system (short delay to make sure vacuum is sufficient to pickup a part reliably), Z-axis movement etc.
LitePlacer software does not support optical inspection of finished boards (after placement) yet - but that is on the wish list. So validation will be a manual task for now. Again, the more reliably the machine worked in 3. the less problems you will have. I'd rather slow down my machine than having more defective boards...
5. mostly depends on your reflow soldering equipment - so I'll leave that up to you - same goes for 6.
LitePlacer works great based on the kit Juha is selling. In addition to that, it is a great platform for makers to mod and enhance
Many people have spent quite some time to increase ease of use, reliability and accuracy of their LitePlacers. I think the hot topics are better camers, custom feeder systems (for cut tapes + tape and reel), reliable part pickup / failed pickup detecion using vacuum pressure sensors, alternate nozzles + auto changer for nozzles right now. There is plenty of information about all these topics on this forum.
Again, I would suggest to look at those things first and worry about CPH later... But if you really wanted to make PnP operation faster, I think the following *might* help:
- Plan your work area well and find smart ways to minimze travel between parts, camera and boards
- Think about constructing or buying + retrofitting automatic feeders
- Get nice cameras with stable USB connection, high framerate and short settle time to speed up computer vision
- Get a decent control PC to have sufficient processing power for computer vision
- If possible, decrease XY size of machine to reduce moving mass
- Use strong vacuum pump, "pneumatic capacitor" and solenoids with larger orrifices so you can reduce vacuum dwell times
- Redesign head to also reduce its mass; you might prepare it for alternate nozzles (e.g. Jukis) and auto nozzle changer
- I think constructing a dual head could signicantly speed up the process, but software currently only supports one head (-> software changes required)
- If you wanted to accelerate and move faster, easier use beefier NEMA23 steppers (more torque) or even closed loop brushless servos (might require alternate controller)
- Reducing slack and friction in mechanics might also help, some people are considering to replace the makerslides by precision linear rails + slides (rather expensive)
- If you did that, you might want to reinforce the mechanical structure also...
Long story short, there is always a tradeoff between speed + precision and cost.
IMHO LitePlacer is great for assembling prototypes and small batches and can be made even better with a few mods. I've been using it for almost a year now and CPH has not been the limiting factor for me so far.
If I wanted to mass-produce something, I would consider outsourcing that job to an assembly house or buy a multi-head, commercial PnP with proper feeders - if money was no concern
Just my two cents... Hope this helps with your decision.
