Senior Design Project - Printer Hydration System

[mcenbold]

Hey all,

I am working on a design project and need some help with the electronics since everyone is a mechanical engineer. For the project we are taking a current hydration system in a high speed production printer, and replacing and improving components to reduce system cost and increase functionality. The system logic is currently run by an Allen Bradley MicroLogic 4000 PLC. We want to replace the PLC with something less expensive. We don't need the fluidity that the PLC provides and are considering the BASIC Stamp 2. Could we make this work for our project?

[Phil Pilgrim (PhiPi)]

Welcome to the forum mcenbold! To receive the help you seek, you will have to provide a lot more information about your requirements. For example:

1. What does a printer hydration system do?

2. What do you need to control? What kind of outputs?

3. What kind of feedback does the system provide? What kind of inputs?

4. How fast does the control system need to respond to those inputs?

-Phil

[Mike Green]

I assume that your "printer hydration system" somehow provides moisture for the printing press so the ink dries at the proper rate. As PhiPi asked, what would the Stamp have to control? I assume it's some sort of solenoid controlled valves or something similar. What sort of voltages and currents are involved? What kind of sensors does this system have and what signals do they produce?

[mcenbold]

Great! Thank you for the responses! I will do my best to explain the full problem and answer your questions.

One of Ricoh’s newest improvements is a hydration system for use in their line of high speed production inkjet printers. The company found that after extensive use during the day, the printheads would sit overnight and develop clogs. To remedy this issue Ricoh developed a hydration system that constantly keeps small pads inside the caps wet. The printheads rest on these pads when not in use, allowing them to keep from drying out and clogging. Every day the water in the pads and lines is vacuumed out, along with the glycol left behind by the ink, and the pads are then refilled with water. This is an important process because if the pads dry out, then the glycol in the pads will absorb water from the printheads when they rest on the pads. This causes the ink to dry out and the printheads to clog. The hydration system was a relatively quick fix that has proven to be effective. Ricoh believes however that the system is too expensive and has tasked our team with finding a way to reduce cost. The project is very open ended with possible improvements ranging from finding cheaper materials to design changes in the system.

The current system has an Allen Bradley MircoLogix 1400 PLC, an Allen Bradley MicroLogix 1400 Relay Output Expansion Unit, and and Allen Bradley Panelview C300. The PLC was initially used because there was a lot of potential for the system programming to change.

The Stamp would have to control two large vacuum pumps, 9 solenoids, and receive input from a distance sensor (to determine when the printheads are away from the caps allowing for the cycle to run). The system has three parts to it. When the system starts it vacuums out the lines connected to the caps to remove all water/ink in the lines. It then pumps water back through the lines into the caps to hydrate them, and again purges the lines to clean out excess. This process has to happen once a day to keep the printheads from drying out. The whole process must run in less than 2 minutes, and the time the cycle can run is completely reliant on whether the printheads are in use or not so it does not occur at the same time every day.

This is somewhat difficult to explain without diagrams. Let me know what I can clarify and other questions that need to be answered in order to give you a better idea of whats going on here. Thanks Phil and Mike!

[mcenbold]

This is our our schematic of the system.

[Phil Pilgrim (PhiPi)]

I assume the entire cycle has to run before the printheads return to their home position, right? So how does the system know that it has enough time to complete the purge task before the printheads return? Is there some sort of messaging that goes on with the print job management firmware?

-Phil

[mcenbold]

The system does not know beforehand if there will be enough time to complete the cycle. The hydration process will start and if the printheads start to return before the cycle is complete it will run a quick purge and end the process. It will then have to try again at another time until it can complete one cycle in 24 hours. There is no way to predict how long the printheads will be away because the print job info comes from an external source.

[Mike Green]

It looks like the timing of the events in the hydration cycle is very much in the range that would work for a Stamp (about a millisecond per statement). You will need some kind of driver for the pumps and solenoids depending on the voltages and currents involved. It looks like you have maybe 9 solenoids and 2 pumps to switch on and off and at least one sensor. What sort of signal does the distance sensor put out?

With the times involved, the Stamp should be able to keep track of the times involved even though it doesn't have a built-in clock. You should be able to use a PAUSE statement as an accurate time tick for the 24 hour timeout as well as the shorter times for the various parts of the cycle.

The solenoids could probably be driven by a couple of Darlington arrays if the current levels are low enough (500mA). The pumps may need a relay which would be driven by the Darlington array. There are all sorts of other options once you describe the voltage and currents involved.

Take a look at the EFX-TEK Prop-2 controller which uses a BS2 and includes 2 x 8 Darlington arrays that can handle 24V solenoids or relays. You don't have to use all the Darlington outputs and could attach your sensor(s) to some of the I/O pins.

[mcenbold]

The sensor signal is voltage I believe? I could be completely off there but it uses a laser.

The Prop-2 controller looks pretty good from what I can actually understand about it. I have what might be a dumb question, but this is almost like another language for me... what is the difference between a prop controller and any other type of controller?

[Mike Green]

The Prop-2 controller is designed for use in props (movies / art / etc.) for sequencing of lights, small motors, or solenoids with supply voltages up to 30V so you can use 12V or 24V solenoids and power source. It has a Basic Stamp 2 as the controller and comes with a pair of Darlington transistor arrays for switching up to 1/2A loads to ground (1.2A per array maximum total current). It has 4 of the 16 I/O pins set up so they can easily be used for switch closures with built-in selectable pull up or pull down resistors and these 4 I/O pins can also be used for other functions. You could use 3 pins to interface with an Analog to Digital converter for example.

Other Stamp boards might be optimized for other uses (in terms of built-in functionality).

[mcenbold]

Thank you! This is really helpful information. We are going to do some more work on this and we will most likely have some more questions for you!