This article is about a project I have started back in January 2018. As for many of my projects, it took longer than anticipated.But now it is working, and the result is looking very good: a DIY automated pick and place machine to place parts on circuit boards. In the age of cheap PCBs, that machine closes the gap for small series of boards which have to be populated in a time consuming way otherwise.

Outline

This DIY machine can populate circuit boards with SMD/SMT parts. If you are wondering, what this is: it is about putting Surface Mounted Devices (SMD) on a Printed Circuit Board (PCB). I gave a talk at the Embedded Computing Conference 2018 on this subject (ECC18 Styger – PickAndPlace mit OpenPnP).

The following videos give an overview about the current state of that machine:

The motivation of building such a machine is that at the university we are populating boards by hand:

Solder gets placed on the boards (stencils are rarely used):

Then parts get placed on the boards

We do have as well vision support for the manual placing:

And finally they run through a reflow oven:

That’s all working fine. The problem is that this all takes a lot of time. Doing it for one board is one thing, but doing it for 10-50 boards takes too much time. Clearly, for mor than 50 or 100 boards, outsourcing is the logical choice. But for a few boards as we usually have to do, outsourcing is not the best option as it is expensive and takes a lot of time too.

What I wanted is a machine to automate the manual placing of components. Such a machine is called a ‘Pick and Place’ machine: it picks parts and places them on a PCB.

DIY Pick & Place Maschine: OpenPnP

When searching for such Pick&Place machines, I stumbled over the OpenPnP project at http://openpnp.org/: A open source community and project which builds such machines. So I thought: why not building one myself too? And here we go :-).

OpenPnP offers a framework to run such a machine. They have guides and tutorials how to build such a machine. And it is up to you how you build it and what features get added. I did not want to build the fastest or the cheapest machine: my goal was to keep the hardware costs below $1000, and that the machine is able to place parts down to the 0402 size.

All the software and BOM are available on GitHub (see links section at the end of this article).

The machine uses 24V stepper motors for X, Y and Z axis. Two smaller stepper motors on the head (C1, C2) can be rotated. Attached to the head is a down-looking camera.

Integrated in the work area are nozzle changers, a bottom camera and different feeders.

Under the base plate all the other electronics (solenoid, pump, USB Hub, feeder and controller board with LCD and power supply.

CAD (KiCAD, Altium, Eagle) data is loaded on a host PC running OpenPnP.

Below are pictures of the machine under construction with some details. I hope this gives you ideas and an inspiration to build your own machine.

Microcontroller

The heart of the machine is the NXP LPC1769 on the Smoothieboard:

It is responsible for all the sensors and drives all the motors. The picture below shows first tests with a stepper motor:

Frame

The frame is constructed with 20×20 and 20×40 standard aluminum extrusion profiles:

The profiles allow an easy construction of the frame.

Rails

The linear rails arrived very well oiled and in good shape.

The rails get attached to the top of the frame:

It has been an iterative process, and many parts first have been built with a laser cutter and plywood. Below is a picture of an early version:

Vacuum Pump

Actuators in the system are 24V. Below is the diaphragm vacuum pump used for the nozzles:

Terminals of the pump:

The pump together with the two high-speed solenoid on a base plate. To reduce noise, the pump has been placed into a box standing on anti-vibration feet:

Below a first test with three stepper motors:

Power Supply

For the 24V 13.4A Power supply I added an on-off switch with integrated fuse holder:

Flyback Diodes

As flyback diodes for the pump and solenoids I used the Vishay BYV27-200-TAP:

Vacuum Valves

I’m using the STNC TM-06 high frequency valve (24VDC) with 1/8″ pipe connectors:

Below how they are connected to the board with the flyback diodes mounted to the connectors:

For example the M813 G-Gode turns it ON (2-1 connected), and M812 turns it OFF (2-3 connected). The image below shows the air flow:

That means the vacuum pump will be on connection 1 and the nozzle on connection 2, with connection 3 used to release the vacuum.

End Stops

The total of 6 end stops are optical ones:

The first (not ideal) way to mount the end stops:

Second version of end stop mounting with 3D printed holder:

3D printing end stop blades:

Mounted end stopper blade:

In a next step lowered the end stop position:

Pick and Place Head

Very first version of the head:

Holder for the pick stepper motor:

Rails for the pick head steppers:

Frame with first pick head:

Pick head with end stops:

Because the X axis was not rigid enough, 3D printed brackets were added:

X-Y-Rail

T-Nuts on X-Y Rail:

Y Steppers

Two stepper motors wired together are driving the Y axis. It works, but I would not recommend that approach: better use a single motor with an extended shaft and coupling.

Laser cutting the motor and pulley brackets:

Of course it was an iterative process, and many design ideas did not end up in the final machine. The good thing with plywood is that it is cheap and is easy to construct with it.

Second Pick Head Design

The second version of the pick head was more compact and easier to attach to the linear rail.

Below the head attached to the X axis:

Below an early version of the head with no cable chains attached:

I used 3D printed parts to attach the heads with the Z axis belt:

The belt is attached to the linear rails using a press-fit connection, and the connector acts as an end stop the same time:

Here with the rails, belt and endstop mounted:

Here the head with the pick heads:

Downlooking Camera

Below an early design of the downlooking camera integrated into the bottom of the head:

First down camera and light tests:

First Camara and LED ring holder:

A plexiglass with a sheet of whiter paper acts as diffuser:

Pick heads with downlooking camera:

Mounted head with first cable chains:

Metal Pick Head

The next iteration oft the pick&place had is a version built with aluminium profiles. The first step was to use aluminium profiles for the head mounts:

Then the head backplane has been built with aluminium profiles:

That way the head was more sturdy than the one made of plywood.

Below with the hollow shaft stepper motors mounted, plus a cable chain for the end stops, LED ring and camera USB cable on the left:

Nozzle Holder

Nozzle Holder, magnet holds the nozzle:

Improved nozzle holder with 1.5 mm space between the plates and acrylic on the top:

Cut Tape Holder

See  3D Printed SMT Cut Tape Holder for more details.

Feeder

The automatic feeder is designed by Simon Huber. The goal was to create a feeder for SMD parts on rolls.

The feeder uses 3D printed parts:

Each feeder uses a NXP K20DX128 (ARM Cortex-M4) as the controller:

One DC motor moves the tape and one DC motor peels the cover:

A tinyK20 (NXP K22FN512, ARM Cortex-M4) receives M-Codes from OpenPnP and passes them to all feeders:

The feeders are in a daisy chain, and the machine has space for up to 16 feeders.

Nozzles

The first nozzle stepper motors did not work well. The M5 screw did not match the stepper motor hollow shaft. The designed adapter had too much wobble and was not usable.

So I had to put aside the nice and small hollow shaft stepper motors. I ordered new (bigger) ones so I can easier attach the nozzle changes and a vacuum tube connector on the back. The new motors had on both sides an M5 screw so I can attach rotation tube adapters and attach easily the nozzle adapter.

Because the motors were bigger, I had to create new motor holders:

Cable Chains

The first cable chains were too small to hold all the tubing and cables, so a new one has been installed.Below the machine with the first (too tiny) cable chains:

Small cable chain attached to the head:

New cable chains arrived:

That larger (40×15 mm) was able to keep all the cables and tubing.

Below with the new chain attached to the head:

Base Plate

The bottom plate with cutouts for the feeders and the bottom camera:

It gets painted with three layers of magnetic paint:

Bottom Camera

Assembling the bottom camera enclosure:

Assembled bottom camera case:

Testing the camera:

Up camera mounted into base plate:

Bottom Vision

With the bottom camera, OpenPnP can move a part over the camera to correct angle and position with the vision system:

It uses a vision pipeline, below with a blur filter applied:

Masking:

getting the part outline:

Getting the contours:

Detecting part position and angle:

OpenPnP includes a loose part feeder: parts can be put into a bin and the vision system can identify it:

PCB Holder

As the top camera has rather small focus area, I need to keep the feeder pick (see “3D Printed SMT Cut Tape Holder“) height and the PCB surface on the same height. For this I have created 3D printed magnetic PCB board holders.

Graphic LCD

Similar as for my laser cutter (see “Upgrading a Laser Cutter with Cohesion3D Mini and LCD“) I added a graphics LCD to the board.

http://smoothieware.org/rrdglcdadapter describes the settings and installation of a graphics LCD on the Smoothieboard.

I decided to order an adapter board from 3DWare:

Below the bottom side of the board:

Below how the adapter board is installed on the board:

Below the display attached to the board and working :-):

Below the (still messy) electronic parts on a base plate:

Added to the display is an emergency stop button. Below the connection to the controller board:

OpenPnP Software

The OpenPnP software runs on the host PC.

The host PC does all the image processing and sends commands to the machine.

Drop Box

For bad parts or to drop parts, OpenPnP can use a dedicated ‘drop area’. for this I created a custom (laser cut) drop box: It uses 3mm red acrylic on the top:

4mm plywood on the bottom with magnets so it sticks to the machine surface:

Plexiglas Brackets

The motor and belt brackets originally were cut out of plywood: here I replaced the 4mm plywood with 5 mm laser-cut plexiglas ones which looks nicer :-):

The machine mounted on a 16mm plywood base plate:

Summary

It has been a fun project, and the machine works well, but still needs some tuning. I plan to add a solder paste dispenser: that way, if no stencil is available, the machine can add the solder paste to the pads on the board. Another thing is to use pressure sensors to monitor the vacuum for each nozzle. And for the motor auto-feeder I would like to update the design. So there is always something to improve. Currently the machine can place around 500-600 parts per hour down to 0402 size. With this and little setup, we can run small board series successfully.

PS: a big “thank you!” to the OpenPnP community: without all their work and contributions, such a project would not have been possible.

Happy Picking 🙂

Links

• Files of my machine on GitHub: https://github.com/ErichStyger/McuOpenPnP_Machine
• Presentation at the Embedded Computing Conference 2018: http://www.swisst.net/files/swisstnet/de/dokumente/ECC/ECC18/Referate/3C2_Styger_HSLU.PDF
• 3D Printed SMT Cut Tape Holder
• Smoothieboard hardware on GitHub: https://github.com/Smoothieware/Smoothieboard
• Smoothieboard configuration options: http://smoothieware.org/configuration-options
• Smoothieboard supported G and M codes: http://smoothieware.org/supported-g-codes
• Smoothieboard extruder: http://smoothieware.github.io/Webif-pack/documentation/web/html/extruder.html
• LinuxCNC G-Code List: http://linuxcnc.org/docs/2.6/html/gcode/gcode.html#_g_code_quick_reference_table_a_id_quick_reference_table_a
• Reprap G-Code List: http://reprap.org/wiki/G-code
• STNC TM-06 24V valve: https://www.robotdigg.com/product/566/High-frequency-Solenoid-Valve-12-or-24VDC
• GLCD Adapter board: https://www.3dware.ch/Adapter-LCD-s-GLCD-f%C3%BCr-Smoothieboard-De.htm