Building a Delta Printer – Part I: Prerequisites

Introduction and Motivation

A few years ago, 3D-printing caught my attention. When you’re a maker and constantly in need of specialized parts in small batches for your projects, rapid prototyping is a technique that can be extraordinary useful – and once tried out, I’d say your hobbyist life can’t be imagined without it.

A short time reading into the topic passed, and I decided to build a printer on my own. Vincent Grampp from the german reprap-subforum developed the Sparkcube, which is a cartesian printer based on the CoreXY system. I think that this particular approach is very sophisticated and so I ordered the printed parts from his shop and started gathering the remaining components from my own findings or chinese suppliers.

It didn’t take long until I could deposit the first sausages of molten plastic on the printing bed, and some meaningful prints were to follow as well. Somehow though, I never managed to increase the print quality beyond a certain point. These days, I also know why: Being the cheapo that I am, I always chose the money-saving options, and instead of sticking to the BOM, I searched for ways to improvise with stuff that I had lying around. The result was a printer that worked quite good, but not as good as it could. Moreover, I completely lost the motivation to improve the printer as a complete makeover would have been necessary.

A few days ago, 3D-printing recaught my attention. Somehow, I stumbled across a video of a Delta printer in action. This was the point where I knew what was needed to finally have a printer that was fun to operate. The footprint of a Delta is small enough so it can be placed in my student apartment. This is a huge benefit, as I can only operate my old printer whenever I drive home (every couple months).

BOM

My decision fell on the standard Kossel by Johann C. Rocholl. Instead of printed parts, which are prone to fractures when e.g. the screws are tightened a tad to much, I opted for a set of injection molded parts from chinese manufacturer Micromake.

Framing and Structural Parts

  • Set of injection molded Kossel parts, Micromake – 32 €
  • 9x 240mm + 3x 600mm 20x20mm aluminium extrusions, Motedis – 20 €
  • 50+ T-slot nuts, mostly M4 size
  • 6x Carbon rods for mounting the extruder, Micromake – 13€
  • 3x Aluminium effectors, Aliexpress – 15€
  • 5m GT2 Timing Belt, Aliexpress – 4€
  • 3x HIWIN MGN12-H linear guide rail, Aliexpress – 3×22€
  • 6x F623zz flanged bearing, eBay – 7€

Electronics

  • RAMPS 1.4 control board with Arduino MEGA
  • 4x DRV8825 stepper driver
  • 4x NEMA17 stepping motor, 1.8 deg/step
  • 2004 LCD Smart Controller, Micromake – 10€

Additional Parts

  • J-Head MkV Hotend

This bill of materials is by no means complete and more items will be added throughout the build. I am currently waiting for the first components to arrive from the various suppliers. In the next article, you will learn about the assembly of the framing and the main structural parts.

Alex

A thermoelectric cooler controller based on the LTC1923

Many components in a laser cavity such as the pump diode or the gain crystal require careful and stable temperature control. Where water cooling is not feasible, thermoelectric coolers or “Peltier Elements” are the method of choice.

For simple applications, one could drive the Peltier cooler using a MOSFET, whose gate is controlled by a PWM signal. When working with long time constants, e.g. in the order of seconds, this approach might work. But when higher switching frequencies are used, the pulsed signal will lead to a rapid decrease in cooling efficiency and could even damage the device.

Additionally, the required temperature stability demands a sophisticated control loop, often implemented using a PID controller. These kinds of circuits can easily become quite complicated, and therefore a solution in form of an Integrated Circuit can be very convenient.

After a bit of research, my decision fell on the LTC1923 by Linear Technologies. The main reason is that the thermoelectric coolers which I will be using require several amps at a fairly low voltage (2-4V), and other controllers have integrated MOSFETs which are only rated for some hundred milliamps of continuous current. Secondly, the documentation on LT’s website is exemplary, they even provide detailed schematics and board design guidelines.

In a first version, I designed the circuit to be capable of providing higher voltages, so that I can also drive the TEC1270X devices sold on various online marketplaces. Unfortunately, this requires the use of external high-speed gate drivers, as the LTC1923 can’t be powered with more than 5.5V.

I drew the board in EAGLE, closely following the recommended design outlines which can be found in the datasheet. (“Right Click” -> “Open image in new tab” for Hi-Res pictures)

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As can be seen in the schematic, the circuit essentially consists of the following subunits (left to right):

  1. H-Bridge with gate drivers: The two dual N- and P-Channel MOSFETs (IRF7343) are driven by dual high-speed gate drivers (LTC1693) and control the current flow as well as its direction.
  2. LTC1923: This is the main integrated circuit which includes the error amplifier and controls the gate drivers.
  3. LTC2053: An additional Rail-to-Rail Instrumentation Amplifier is used to achieve a higher setpoint stability of up to a theoretical maximum of 0.01°C.
  4. MCP4725: An 12-bit I²C Digital-to-Analog Converter with nonvolatile memory allows us to easily set the temperature setpoint using e.g. a microcontroller.

The temperature feedback is provided by a thermistor which has to be in close thermal contact to the device that is to be cooled/heated. A jumper decides whether the temperature setpoint is controlled via an analog trimmer potentiometer on the board, or via the I²C DAC.

The prototype then went to iteadstudio, who manufactured the board for me. As I chose the cheapest manufacturing options and hadn’t ordered any custom PCBs before, I wasn’t sure how the final board would turn out. When it finally arrived, the result surpassed all my expectations: The green solder mask is applied uniformly, texts on the silkscreen can easily be read and the HASL finish is of high quality. For better solderability, I could as well have chosen an ENIG gold finish, but this option would have cost disproportionately more and soldering problems weren’t observed during assembly.

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Assembly was pretty straightforward, as no excessively fine pitched packages were used. However, it still took about three hours of focused soldering to mount the many small capacitors and resistors.

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A first test verified that the board is operative and no traces are shorted out. I am currently building a simple test stand to monitor the behavior in a real environment, as the component values critical to the feedback loop have to be determined experimentally. Afterwards, I can give a statement about the controller’s actual performance.

> TO BE CONTINUED: FIELD TESTS <

I am planning to design a new version which is intended to work with supply voltages of 2.7V to 5.5V and therefore without additional gate drivers. The layout will fit a 5x5cm area for decreased manufacturing costs.

 

Resources

[1]: Schematic (PDF)

[2]: Top Layer (PDF)

[3]: Bottom Layer (PDF)

B&W TEK BWB-10-OEM 473nm blue Lab-Style DPSS Laser

This week, a new goodie for my laser collection arrived. I always wanted to own a 473nm laser because of the awesome, azure blue light. In comparison to this, the 445nm Nichia Diodes almost look violet.

Despite many of the units, which are apparently pulled from medical equipment, suffer from power and mode fluctuations, mine arrived lasing in a nice TEM00 mode out of the box.

The divergence is not that good, but I guess a bit of realignment should do the trick. As mine arrived without the power supply, I had a bit of fun figuring out the power supply lines on the D-SUB connector.

It turned out that pins 5&9 on the standard DB9-Pinout are connected to VDD, and pins 1,2&6 to GND. Pin 4 is the TTL modulation input, the laser will fire when this pin is pulled high. The driver board must be connected to a 5V supply with a nominal current rating of at least 4A.

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Opening the top cover reveals the guts of this neat CNI-made setup. It consists of (from right to left)

Pump Diode->Collimating Optics->Anamorphic Prism Pair->Focusing Optics->Crystal Assembly

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The crystal assembly is protected by a plastic cover. Removing this allows a look into the resonant cavity. Dominant is the big Lithium triborate (LiB3O5) crystal used for the generation of the second harmonic. The two aluminium parts hold the cavity optics (Output coupler and High reflector), the Nd:YVO4 crystal sits near the black focusing optic in the brazen plate.

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Using feedback from a photodiode, these units were stabilized for 10mW optical output. When I find some more spare time, I will try to realign the cavity and focusing optics and perhaps install a higher powered pump diode. Let’s see if I can push more than 50mW of stable power out of it. 😉

Hello World!

Welcome to my blog!

My name is Alexander and I am a physics student at the University of Heidelberg.

On my blog, you will read about everything DIY and about my current projects. From time to time, I will also post some updates from my studies and university life in general.

Have fun reading through my posts (Yes, there are many to come), and feel free to contact me about anything you want to know. 😉

Cheers!