[david_geng]

I think we are talking about a small PnP machine used for DIY or R&D purpose. So it does not have to be fast but must be cheap and versatile.

Recently I am also planning such a machine for my own using. I was fed up with soldering hundreds of small capcitors manually for just one board. I have got a small X-Y CNC bed without any controller, to which I still need to add Z axis and and a R axis for rotating the head.

I'm going to add one or two webcams as a vision system. There will be a training zone on the bed, so that the aligment between the head and the camera will be done at the run-time.

There will be two types of heads: one for the paste dispensing another for PnP. I'll just discuss the PnP one here.

Basically that head is like a syringe and takes that type of needle for small devices. For a large package like QFP, that needle will pick up a bigger adaptor first. The adaptor is a plastic or rubber nozzle. The head can put the needle into it under the guide of the vision system, and the nozzle will stay with the needle for rest of the operation. To take off the nozzel, put the nozzel on the nozzel tray (a smooth even surface), turn the vaccum on, and the head puts up to get rid of the nozzle, then, turn the vaccum off.

For the feeding, there will be a component area with a variaty of slots and trays. The slots are for the SMD strips, e.g. up to 50 components. The strip is pre-cut and peeled mannually according to how many is needed for this board. For more than 50 piecs, just use a second slot. For a few less than 50 pieces they can be compined. However, there is no need to use strip and slot for just a few pieces, say < 10. There are also square trays, e.g. 20mm x 20mm for loose SMD. Again, the vision system is used to locate the components.

The head is rotatable. The head socket is like a cylinder with teeth on the outside, and a stepper will drive a timing belt to rotate the socket. The head socket may measure 20mm ~ 25mm in diameter and fixed to the Z platform via a ball bearing. The rotating motor is also no the Z platform.

I haven't decided how to put the head on the socket quick and easy, and also compatible with the paste dispenser head.

I know there are a lot for work for it. So it has to be well planned and ideally if people can cooperate on it, e.g. control software, vision software, system interface to a PC, making of the mechincal parts, etc.

ta
David

[nisma]

I think we are talking about a small PnP machine used for DIY or R&D purpose. So it does not have to be fast but must be cheap and versatile.

Recently I am also planning such a machine for my own using. I was fed up with soldering hundreds of small capcitors manually for just one board. I have got a small X-Y CNC bed without any controller, to which I still need to add Z axis and and a R axis for rotating the head.

I'm going to add one or two webcams as a vision system. There will be a training zone on the bed, so that the aligment between the head and the camera will be done at the run-time.

This will not work. It´s better to measure the offset and set it manually.
For the first time, you can use a paper that your have fixed with
tape to the base. Next put the needle on a stamp-pad and now, with
the camera and manual Z control, you can measure the offset. It remains
constant. With the camera, you can now measure the offset accuratly.
You need a led on the X/Y table for the purpose of reference point for
the camera. This allows you to automatically measure the backlash and
other type of meccanical errors, that can be compensate by SW.

There will be two types of heads: one for the paste dispensing another for PnP. I'll just discuss the PnP one here.

Basically that head is like a syringe and takes that type of needle for small devices. For a large package like QFP, that needle will pick up a bigger adaptor first. The adaptor is a plastic or rubber nozzle. The head can put the needle into it under the guide of the vision system, and the nozzle will stay with the needle for rest of the operation. To take off the nozzel, put the -nozzel on the nozzel tray (a smooth even surface), turn the vaccum on, and the head puts up to get rid of the nozzle, then, turn the vaccum off.

Generally, with two nozzles (of different diameter and with different rubber)
you can make all components excepts big electrolyt condensators.
Basically, you have two indipendent Z axis, one for the P&P needle and
the other for the dispenser. This can be one Z axis and two solenoids as
example. Otherwise you don´t be able to dispense and place at the same
time. Maybe you don´t have necessety to do so.
At the same time, you can think of using two needles on the same head,
maybe one fix and the other interchangable, either manually or automatically.
The C Axis can use the same timing belt and motor to drive both axis at
the same time.

For the feeding, there will be a component area with a variaty of slots and trays. The slots are for the SMD strips, e.g. up to 50 components. The strip is pre-cut and peeled mannually according to how many is needed for this board. For more than 50 piecs, just use a second slot. For a few less than 50 pieces they can be compined. However, there is no need to use strip and slot for just a few pieces, say < 10. There are also square trays, e.g. 20mm x 20mm for loose SMD. Again, the vision system is used to locate the components.

The head is rotatable. The head socket is like a cylinder with teeth on the outside, and a stepper will drive a timing belt to rotate the socket. The head socket may measure 20mm ~ 25mm in diameter and fixed to the Z platform via a ball bearing. The rotating motor is also no the Z platform.

I haven't decided how to put the head on the socket quick and easy, and also compatible with the paste dispenser head.

I know there are a lot for work for it. So it has to be well planned and ideally if people can cooperate on it, e.g. control software, vision software, system interface to a PC, making of the mechincal parts, etc.

ta
David

I have written some SW for the linux system in order to control the P&P
including vision recognizion. This implies, that the used webcam
is full supported on linux.

[Eclipze]

Ok... add me to the list of people building a pick'n'place

Been acquiring some gears/motors to start planning the system, and this thread has been very useful to generate some ideas.

For vacuum pickup, the aquarium pump is what I was planning to use. I have see these vacuum tools available...
http://cgi.ebay.com.au/Pick-and-Place-Vacuum-Pens-for-SMT-SMD_W0QQitemZ280039971649QQihZ018QQcategoryZ36327Q QssPageNameZWD2VQQrdZ1QQcmdZViewItem
Which looks like a basic pump with pen.

I plan to use an aquarium pump and for the needles use solder paste syringe needles. They come in a good range of sizes, have flat bottom and you can get them in plastic too. Then use a hand pick'n'place tool to get some cheap silicon heads for the bigger parts.

I have considered a crane system, whereby the base would be at the centre rear of the table and rotate the crane across the board, and then have the head run along a track. Maths would be a complication. I'm keen to have a full XY with static PCB, as it is far more flexible for retrieving parts. In addition, I want to have one XY for the PnP and other for the solder paste dispenser.

I want to have approx 12 tapes at the front, feeding with servos via the tape holes. The idea with the tape plastic is to part it from the tape, rotate it 90 degrees to allow component pickup and then rejoin it with a common roller to the tape.

Using an optical mouse sensor, I'm thinking of using one to correct the datum for the pickup tool... and it's position is right in the path for component pickup. Hence once a component is collected, it passes over the sensor before placement. The head can therefore correct rotation of the part on the fly, or pause to correct it with a simplier software alogorithm determine the flat edge.

The vacuum pick'n'place tool would be operated by a servo for the Z plane, using a spring loaded catilever arrangement. Therefore the head will go down to the component and then the spring would allow the servo to rotate further without placing much more force on the component.

I'd like to consider in the future having a seperate basic XY table to hold the hot air station, or adaptor a heat gun element to have a system that reflows the board. So a pre-heater underneath, and perhaps a temperature sensor on heating element to track/control a soldering temperature profile. Rather a seperate table for this to avoid over complicating the pick'n'place, and its really an additional feature that can wait.

Currently I'm only looking to place the 0805, 1206, SOT23, SOT223 components. These take the longest to place and I find the easiest to hot air solder. I may include an area to hand place components for the pickup head to use. For example, spots for all the common footprints, plus some for SO8,14,16, TSSOPs, diodes, DPAK/D2PAK etc... and have an LCD for prompting the component required. Have a tiny light sensor under each component depot would make the system quite nice to use, particularly if the tape feeders are not up and running at that stage. Ideally I'd put the dremel in the XY head to route out these component depots hahaa..

Only just starting on this project and putting ideas together...

[nisma]

Ok... add me to the list of people building a pick'n'place

Been acquiring some gears/motors to start planning the system, and this thread has been very useful to generate some ideas.

For vacuum pickup, the aquarium pump is what I was planning to use. I have see these vacuum tools available...
http://cgi.ebay.com.au/Pick-and-Place-Vacuum-Pens-for-SMT-SMD_W0QQitemZ280039971649QQihZ018QQcategoryZ36327Q QssPageNameZWD2VQQrdZ1QQcmdZViewItem
Which looks like a basic pump with pen.

I plan to use an aquarium pump and for the needles use solder paste syringe needles. They come in a good range of sizes, have flat bottom and you can get them in plastic too. Then use a hand pick'n'place tool to get some cheap silicon heads for the bigger parts.

The solder past needles don´t do the job. The manual smd pick and place
needle have a small silicon head. This rubber is really important for a
pick and place when only moderate vacuum are available, like a aquarium pump. Further this reduce vibration and allows for some errors on the
Z axis, because the rubber compensate it. You can buy this needle as replacement. Maddel as example sell it for 1.5$ if i remeber correctly.
With two needles of different size, you can make over 94% of all components.

I have considered a crane system, whereby the base would be at the centre rear of the table and rotate the crane across the board, and then have the head run along a track. Maths would be a complication. I'm keen to have a full XY with static PCB, as it is far more flexible for retrieving parts. In addition, I want to have one XY for the PnP and other for the solder paste dispenser.

Can you have enought resolution with a cran system without using
costly gears without backlash.

I want to have approx 12 tapes at the front, feeding with servos via the tape holes. The idea with the tape plastic is to part it from the tape, rotate it 90 degrees to allow component pickup and then rejoin it with a common roller to the tape.

Sorry, i don´t have understand it, maybe my bad english. Can you explain
it again eventually a bit more explitly.

Using an optical mouse sensor, I'm thinking of using one to correct the datum for the pickup tool... and it's position is right in the path for component pickup. Hence once a component is collected, it passes over the sensor before placement. The head can therefore correct rotation of the part on the fly, or pause to correct it with a simplier software alogorithm determine the flat edge.

The vacuum pick'n'place tool would be operated by a servo for the Z plane, using a spring loaded catilever arrangement. Therefore the head will go down to the component and then the spring would allow the servo to rotate further without placing much more force on the component.

I'd like to consider in the future having a seperate basic XY table to hold the hot air station, or adaptor a heat gun element to have a system that reflows the board. So a pre-heater underneath, and perhaps a temperature sensor on heating element to track/control a soldering temperature profile. Rather a seperate table for this to avoid over complicating the pick'n'place, and its really an additional feature that can wait.

Currently I'm only looking to place the 0805, 1206, SOT23, SOT223 components. These take the longest to place and I find the easiest to hot air solder. I may include an area to hand place components for the pickup head to use. For example, spots for all the common footprints, plus some for SO8,14,16, TSSOPs, diodes, DPAK/D2PAK etc... and have an LCD for prompting the component required. Have a tiny light sensor under each component depot would make the system quite nice to use, particularly if the tape feeders are not up and running at that stage. Ideally I'd put the dremel in the XY head to route out these component depots hahaa..

Only just starting on this project and putting ideas together...

For the C rotation, just today i have found a nice system.
Two 12V stepper motor, one for the Z axis and annother for the C axis,
both driven with one ULN2803. The stepper motors should be 12V and
have 1.8 degre step or 200 full steps / rotation. The motor is driven with half
steps.
One plastic bevel gear with a reduction of 2:1 is used to rotate the nozzle
and the component when the Z axis is lifted up completly. The C axis have
some type of friction (antivibration nut as example) that removes the possibility of rotation during the Z axis movements.

[Eclipze]

The solder past needles don´t do the job. The manual smd pick and place
needle have a small silicon head. This rubber is really important for a
pick and place when only moderate vacuum are available, like a aquarium pump. Further this reduce vibration and allows for some errors on the
Z axis, because the rubber compensate it. You can buy this needle as replacement. Maddel as example sell it for 1.5$ if i remeber correctly.
With two needles of different size, you can make over 94% of all components.

I'II have to look into that, thanks. I want to buy one of those hand vacuum pickup tool pen's, which come with 4 silicon nozzles. I don't know how they go with 0805 components... never used one. I did experiement with a syringe, just with the plastic tip, and I could reliably pickup a SO8. Certainly finding someone local for the actual pickup needles and silicon heads is the preferred method.

Only thing I'm not sure on yet is how to create a system for both the suction and then slight blow action to help the component detach. I'm thinking of making some sort of solenoid that will cut off the suction which also result in a pulse of positive pressure.

Can you have enought resolution with a cran system without using
costly gears without backlash.

That was my concern also, and with the concept was looking at motor control strategies that would approach the cooridinants with one direction and deadbeat to the other direction with slight residual pressure to obtain consistent operation. Certainly the mechanical side requires precision to get the needed placement accuracy. I plan to develop a few system 'parts' to test movement speeds, relative accuracies (step resolution) under loads and prove design ideas. Then I'm going to fork out some money and have a machine shop make some of the assembly components accurately.

Sorry, i don´t have understand it, maybe my bad english. Can you explain
it again eventually a bit more explitly.

Certainly... hard to explain without a picture, however...
The idea is to have the tapes on a common axial holder. The tapes are spooled via servos pulling the tape via the tape holes. The pickup head always picks up from the component tape in the same location. At this location, the clear plastic tape cover must not be covering the component, but I don't want to strip is off and have it collect seperately. Rather I want to have it re-joined to the tape. Therefore, the section where the pickup head takes the component the clear tape is peeled to the side (perpendicular to the actual tape) so the pickup tool has clear access. The clear tape is ~20mm further down, the tape rotates back onto the component tape. Both before and after the pickup location there will be a roller to hold the tape down, and also help with the rejoining of the clear tape to the component tape.

For the C rotation, just today i have found a nice system.
Two 12V stepper motor, one for the Z axis and annother for the C axis,
both driven with one ULN2803. The stepper motors should be 12V and
have 1.8 degre step or 200 full steps / rotation. The motor is driven with half
steps.
One plastic bevel gear with a reduction of 2:1 is used to rotate the nozzle
and the component when the Z axis is lifted up completly. The C axis have
some type of friction (antivibration nut as example) that removes the possibility of rotation during the Z axis movements.

The Z axis I'm looking at a servo with catilever operation and spring arrangement to allow excessive travel after the component has been touched. The C axis I have not given much though to yet, however was thinking of another servo. Might not give full rotation however, but also possible to pre-rotate the head prior to component pickup. I do like your approach with a stepper though.


I haven't decided on stepper or DC motors yet. I like the thought of DC motors with optical feedback. They can move faster and with more torque, which can therefore provide greater absolute positioning, faster. So I may use DC motors for the XY. Even if I used steppers, I may still use optical feedback... or at least allow for it in the design.

Thanks for the feedback... this is going to be a fun project

[nisma]

Only thing I'm not sure on yet is how to create a system for both the suction and then slight blow action to help the component detach. I'm thinking of making some sort of solenoid that will cut off the suction which also result in a pulse of positive pressure.

If you limit the components to 603, and slow down the speed,
waiting 500ms-700ms instead of 10ms for releasing the component, you simply can cut-off the suction. For this, you must have a small hole
in order that when the system is off the vacuum don´t remain.
The needle for a siringe (small diameter) is a good starting point.

That was my concern also, and with the concept was looking at motor control strategies that would approach the cooridinants with one direction and deadbeat to the other direction with slight residual pressure to obtain consistent operation. Certainly the mechanical side requires precision to get the needed placement accuracy. I plan to develop a few system 'parts' to test movement speeds, relative accuracies (step resolution) under loads and prove design ideas. Then I'm going to fork out some money and have a machine shop make some of the assembly components accurately.

I have found some cheap linear guide system from igus, dryline serie,
and as such i prefer a ordinary x/y table.

Certainly... hard to explain without a picture, however...
The idea is to have the tapes on a common axial holder. The tapes are spooled via servos pulling the tape via the tape holes. The pickup head always picks up from the component tape in the same location. At this location, the clear plastic tape cover must not be covering the component, but I don't want to strip is off and have it collect seperately. Rather I want to have it re-joined to the tape. Therefore, the section where the pickup head takes the component the clear tape is peeled to the side (perpendicular to the actual tape) so the pickup tool has clear access. The clear tape is ~20mm further down, the tape rotates back onto the component tape. Both before and after the pickup location there will be a roller to hold the tape down, and also help with the rejoining of the clear tape to the component tape.

If you pick off 20 components, this system will work ?

The Z axis I'm looking at a servo with catilever operation and spring arrangement to allow excessive travel after the component has been touched. The C axis I have not given much though to yet, however was thinking of another servo. Might not give full rotation however, but also possible to pre-rotate the head prior to component pickup. I do like your approach with a stepper though.

I have a arrangement with two servos, it works, but ...
When picking up components, you should check the height of the component.
When placing the component, you must release the component above the
solder past, and not overtravel and pressing down the solder past.

I haven't decided on stepper or DC motors yet. I like the thought of DC motors with optical feedback. They can move faster and with more torque, which can therefore provide greater absolute positioning, faster. So I may use DC motors for the XY. Even if I used steppers, I may still use optical feedback... or at least allow for it in the design.

The resolution is greater with stepper motors, and the speed is not a problem.
Generally, the motor must be slow down because the linear guide don´t support the speed.
For the normal gantry table, optical feedback is not needed for component
size 402 and above.

[Eclipze]

If you limit the components to 603, and slow down the speed,
waiting 500ms-700ms instead of 10ms for releasing the component, you simply can cut-off the suction. For this, you must have a small hole
in order that when the system is off the vacuum don&#180;t remain.
The needle for a siringe (small diameter) is a good starting point.

Ahhh... this makes sense, and a wait period hear is quite exceptable to simplify the design. If fact, having the blow function is something that could be considered at a later stage, if I wanted to trim the time down. Thankyou for the tip! You saved me a good hour of procrastination. How small are you talking? 0.3 to 0.7mm? Confused between needle only pickup, or needle with silicon head.

I have found some cheap linear guide system from igus, dryline serie,
and as such i prefer a ordinary x/y table.

cut-paste... equipment to look for
Edit: that stuff is quite expensive. Had a look, and it would offer the linear guide, but not the mechanism for controlled movement. I've been thinking of using a long large guage thread to support the gantry and move it.

If you pick off 20 components, this system will work ?

I'm hoping it will, but will only know by giving it a go. For the start of the reel, there is always plenty of leader tape to use for the slack. Otherwise, I'II just need to sit there and feed it through while running. My concern with this setup is with the reels not being in a cassette, but then again these reels will most likely have the common components anyway.

I have a arrangement with two servos, it works, but ...
When picking up components, you should check the height of the component.
When placing the component, you must release the component above the
solder past, and not overtravel and pressing down the solder past.

I had planned to stamp the component right down on the board. I can see why that would be counterproductive. I always lean towards feedback design, rather than program the height. What about having an infrared switch on the XY head, where the pickup tool lifts the component to standard clearance height which the infrared switch detects has the bottom of the component. Placement is then an offset to this detected component bottom? Or is this just taking it too far?

The resolution is greater with stepper motors, and the speed is not a problem.
Generally, the motor must be slow down because the linear guide don&#180;t support the speed.
For the normal gantry table, optical feedback is not needed for component
size 402 and above.

I don't yet have a feel for the effective gear ratio vs movement for the mechanisms yet, so appreciate such comments. My previous experience with steppers has taught me that torque is lost with speed, hence my interest with DC motors with optical feedback.


I will have to start putting some of these ideas into CAD to get a better perspective on how it is going to come together.

[nisma]

cut-paste... equipment to look for
Edit: that stuff is quite expensive. Had a look, and it would offer the linear guide, but not the mechanism for controlled movement. I've been thinking of using a long large guage thread to support the gantry and move it.

In the past weeks, i have searched for sourcing the parts.
Now, i&#180;m near finished. For some items i still search some cheaper alternatives. The resulting price is 120-170 Euro including the motors and
electronic for the microstepper driver.
For a setup for placing BGA&#180;s or uBGA, two usb cameras are additionally
needed, add maybe 30-40 Euro for it and 160 Euro for a linux controller
with ethernet, 2xusb host and lcd display for standalone operation.

I'm hoping it will, but will only know by giving it a go. For the start of the reel, there is always plenty of leader tape to use for the slack. Otherwise, I'II just need to sit there and feed it through while running. My concern with this setup is with the reels not being in a cassette, but then again these reels will most likely have the common components anyway.

For stripes of reels, i have used a small sugar panel, on that i have designed
some lines in order to align the stripes correctly.
I have fixed one side with a needle, peel off the protection, and fixed the
other end with a second needle. Further i have one mark for the first position,
on that i align the center of the first component. This works great for
small productions. The stripe don&#180;t be necessary of 50 items, but can be
tree or eight components only.

I had planned to stamp the component right down on the board. I can see why that would be counterproductive. I always lean towards feedback design, rather than program the height. What about having an infrared switch on the XY head, where the pickup tool lifts the component to standard clearance height which the infrared switch detects has the bottom of the component. Placement is then an offset to this detected component bottom? Or is this just taking it too far?

This is the way that some machines uses, but it&#180;s only used for verification
of the coded height, because the resolution is poor.
I have used a switch to detect the height of component from the pick-up,
with the servo doing aftertravel, but it&#180;s not very affidable.
So i&#180;m returned to codify the height, and using one switch on the ground plane to measure the height of the
component. For the switch, i have used a piezo operated switch made
from a piezo buzzer.

[Eclipze]

Only just starting to realise how little I know. I have a lot to learn about the mechanisms and mechanical requirements for a CNC before I get to the details for the pick'n'place requirements.

[nisma]

Only just starting to realise how little I know. I have a lot to learn about the mechanisms and mechanical requirements for a CNC before I get to the details for the pick'n'place requirements.

The meccanical requirements for a pick and place is quite different as for
a cnc.
The pick and place has to move a small weight with no lateral forces.
The cnc have to move a big weight and need to be really stable and have
big lateral forces.
Further the move rates for P&P is mt/s, on a cnc it&#180;s mm/s.

Wit drawer linear guides it&#180;s possible to lower the price to 1/2 for the P&P.
If you have two spare 1/8 microstep driver, then it&#180;s possible to make it
under 50$.

[Eclipze]

Good point!

I've had a look at a lot of the designs, and a common theme is to have two smooth rods and a single thread drive down the middle. I had initially though of having two thread drives that were geared together, and therefore driven by a single motor. This is in an effort to reduce the mechanical requirements and also weight. I would still use a solid size for good measure, but I'm planning on a small setup around a foot long.

Given I'm interested in two gantries, this mechanism would most likely benefit from sharing the same rod sliders and seperate centre thread.

Looking at the igus products, I can now see how these guides could be used instead of rods for the y and z axis. There are only two dealer in Australia for igus, one of which is only 10mins away. So early next week I'II be taking a visit to get an idea of what is available and costs. I would really like to find these types of linear slides with a thread already built in. This would be absolutely idea, and would certainly be worth the extra cost!!!

[Eclipze]

I'm having trouble with the combination of Z and C. Ideally, a 1.8 degree stepper motor with a hollow shaft would be perfect. However I'm trying to use a smaller/lightweight 7.5 degree stepper, using a hollow tube mounted on the shaft. The tube is a T-piece, to allow the external vaccum/blow off connection. It does restrict the C to ~180 degrees, but 360 degrees with rotation before pickup.

Trouble is, I want to have the Z spring loaded. Such that I can touch a part and push slightly (to get a good vaccum pickup) and detect when to stop. This would also provide for a height calibration.

I had tried many variations in CAD of how to implement all this. Some using the igus N-rails, others with a fine pitch belt pulleys and more with fine pitch bolts for screw driven. Sometimes the problems result in resolution issues, either two highly gears (5 second traversal) to not enough precision (>0.2mm).

Has anyone got some ideas, suggest parts to try or webstore to look at, or seen a good design I could use as a reference?

[phomann]

I'm having trouble with the combination of Z and C. Ideally, a 1.8 degree stepper motor with a hollow shaft would be perfect. However I'm trying to use a smaller/lightweight 7.5 degree stepper, using a hollow tube mounted on the shaft. The tube is a T-piece, to allow the external vaccum/blow off connection. It does restrict the C to ~180 degrees, but 360 degrees with rotation before pickup.

Trouble is, I want to have the Z spring loaded. Such that I can touch a part and push slightly (to get a good vaccum pickup) and detect when to stop. This would also provide for a height calibration.

I had tried many variations in CAD of how to implement all this. Some using the igus N-rails, others with a fine pitch belt pulleys and more with fine pitch bolts for screw driven. Sometimes the problems result in resolution issues, either two highly gears (5 second traversal) to not enough precision (>0.2mm).

Has anyone got some ideas, suggest parts to try or webstore to look at, or seen a good design I could use as a reference?

What about this;

Your stepper and "pick-up: tube are mounte on a small single linear rail. That giges you your Z movement. then parallel to it is a stepper driven leadscrew. The nut on the leadscrew has a horizontal bar that "raises" the stepper and pick-up tube. The bar could lift by sitting unter the stepper motor mounting flange.

With this arrangement the Z axis is only raised. Gravity is used to lower it, as it rests on the bar.

That way you won't drive it through the PCB. You may need a spring to control the downward pressure.

Cheers,

Peter.

[Eclipze]

Thanks for the reply phomann. This is very close to a design I did try. Part of the problem I had was in resolving the nut fixture, while keeping it aligned. I did use a spring in this arrangement which gave it both the free play to not bind and also the desired cushion for contact with a part. It was certainly easier with a linear bearing like the igus N-27 series and I very much liked the solution. The head arrange was however large and I had trouble figuring out how to hold the top of the screw to minimise movement and pressure on the steppers axis. I tried the thread in between the carraige and the C-axis, however the length became a bit of a problem. Then I tried it above the carraige assembly, however this was getting quite high. I have been trying to create a compact head, in an effort to have three heads (2 PnP, 1 paste).


The variant to this design was to use the igus N-40 series and use a 2.5mm pitch belt running top to bottom to move the carriage. The pulley gears were embedded in the rail, which made for a neat axle holder. Size was still a problem, as was step resolution. I had to use larger pulleys to clear the rail, and then introduce a gear or worm drive. This was a nice solution, though difficult to make it compact.

I have been drawing everything in CAD with great detail to work out the particulars of the design, ensuring the necessary clearances and operating movements.

Reading back through the thread, it has re-kindled my interest in using mini servo motors. I've pulled one apart, and it's easy to remove the rotation restriction. However I will be looking at an alternate hardware driver and an alternative method for feedback.

The approach is to use a igus N-27 rail for the Z-axis, with one servo on top with a long arm, connected to a push rod, which is then connected to the carriage. Not a linear arrangement, but something easily corrected in software. It has the additional advantage of having higher speed mid-stroke, and slower at the extents.

On the carriage, I am going to try another mini-servo to directly drive a T-piece tube (where vacuum connects), then use a solder paste nozzle with silicon pad for pickup. So far, the design looks very compact. I do have to resolve how to get the accurate feedback I want, as well as a spring loaded arrangement for measuring/detecting object collision on the Z-axis.

[Eclipze]

Ok... I back on track. Using servos is a much much better solution to using steppers. They are quite quick too! Moving the distance I need in less than half a second. With some magnetic positional feedback, the solution is so much easier on the mechanics, and far more compact. They are a little noisy though <zheet...zheet........zheet...zheet>.

I am including a spring mechanism, which will allow relief for vertical downward pressure. Electronics will detect this, allowing for automatic height control calibration.

Now the Z-axis is so fast, I may have to re-consider the use of steppers for the X & Y. I have NMEA 1.8 degree bi-polar steppers. Not sure have fast I can rotate these with the necessary torque, however I don't think they will be as accurate and as fast as a good mid-sized DC motor with worm drive to belt arrangement. I don't think the backlash will be much of a problem given I'm looking at a 40 tooth gear (driven by worm gear). It is noisy though driving the worm drive at speed. The worm drive will also be used for an optical sensor, which will give some great position precision.

[ciccio]

Maybe some good idea can be taken from new Madell
pick & place , see
http://cgi.ebay.com/New-Automatic-Ta...ayphotohosting

[Eclipze]

Very nice... thanks for the post.

I'm still working on mine, though it is designed for a much smaller working area and without tape feeders (use tape strips instead). I'd really like to see a close up of their PnP head!

[ciccio]

If you go here
http://espares.assembleon.com
you can find some interesting pictures
Paolo

[Eclipze]

Fantastic site! Some really good diagrams. Now that I've seen them, I realise they aren't that useful afterall. The placement heads on them are quite complex from a hobby perspective. Not something easily designed and manufacturered. I'II certainly be continuing with my current approach.

Good site though... appreciate the link!

I'm actually working on the reflow side of the equation. I've look at the toaster ovens, but just not happy with them. I'm going to try my own design using nichrome wire. Have a cheap multimeter with thermal probe and optical output being feed into a micro, which by next week should be controlling the temperature. I'II will end up with something that can reflow a board following a temperature profile.

[ciccio]

I built a reflow oven based on a very low cost oven
It is in some way similar to Elektor project
It works , I can have good SMD boards
...now I need an inexpensive P&P...
I buyed on ebay
http://cgi.ebay.com/Pick-Place-Rotar...QQcmdZViewItem