Disc Pump Powered Ball Sorter - How it Works

Each year, we challenge ourselves to come up with new and engaging ways of showing off the capability of our unique micropump technology through the creation of marketing demonstrators. Our most recent system - a coloured ball sorter - highlights the incredible response speed and high-precision control of Disc Pump. We caught up with William Deeks, Senior Engineer at TTP Ventus, to discuss how it works.

What was the brief for this demonstrator?
William Deeks: The main objective was to highlight the unique features of the pump whilst ensuring the demonstrator is as eye-catching as possible, given that it needs to compete for attention in busy tradeshow halls and social media news feeds!

How did you come up with the idea?
WD: It came up during a brainstorm. Someone raised the idea of those industrial machines that sort grains of rice based on their colour, using little puffs of air to direct falling grains one way or the other. As the concept developed, it evolved into a hybrid with of a kind-of pinball idea, given that we needed the moving parts to be continuously recycled in order that the demo could run without intervention.

What are the main components of the system and how do they interact?
WD: At the heart of the system is our Disc Pump evaluation kit, consisting of a pump mounted on a drive electronics board. The pump is connected to a ball-launching chute via a tube. Balls are loaded into the chute one at time by a motorised wheel.

Mounted on top of the chute, we have an Adafruit RGB colour sensor, controlled by a Nucleo development board. The Nucleo board detects the presence of a ball, measures the colour (orange, yellow or green) and issues a short pulse to the evaluation kit - the exact length of the pulse depends on the colour of the ball. The evaluation kit drives the pump for the duration of the pulse, creating a puff of air that drives the ball up the chute and out onto an inclined base plate.

Longer pulses send the ball further than shorter pulses. This is where the sorting aspect comes in. The base plate has three target bins, created by dividers - one bin for each colour. The aim is to fire the balls into the matching coloured bin.

To capture attention further, we added addressable LEDs - again controlled by the Nucleo board. These LEDs light up the bin that the system is aiming to fire the ball into. A second strip of LEDs lights up the chute as the ball fires.

The ball ultimately returns down a guide rail, leading to the motorised wheel which loads the ball back into the chute for the process to repeat.

Annotation of TTP Ventus' coloured ball sorter demonstration

Which features of the pump does the demonstrator highlight? Where are these features useful in real-world applications?
WD: Whilst the demo is playful in nature, it actually does highlight some quite incredible features of the pump. The key to sorting reliably is in the steady, repeatable acceleration of the ball. Three features of the pump play into this.

Response speed
The difference in the length of the control pulse used to send a ball into the furthest-away green bin and the nearest yellow bin is only 40 milliseconds. Disc Pump is able to go from a standing start to maximum output in just a few milliseconds - this is because its piezoelectric actuator has very low inertia. By contrast, a conventional pump might take perhaps 300 milliseconds to turn on/off, meaning that this demonstration simply wouldn't be possible without additional equipment, e.g. high-speed valving. A good example of where fast response speed is useful is in Owlstone Medical's ReCIVA, a breathalyser for disease looking to early signs of cancer. Fast response speed enables high-precision breath sampling, which has allowed Owlstone to create a more sensitive detector. You can read more on this product here: ttpventus.com/medical/owlstone-medical

Pulsation-free airflow
Disc Pump moves a tiny quantity of air per cycle, typically in the range of 10s to 100s nanolitres, resulting in negligible pulsation in pressure and flow - this is something we showed off in last year's "Dancing Flow Tube" demonstration. The lack of pulsation means that each ball accelerates smoothly. A practical application of smooth flow is in gas sensing, where pulsation can limit the signal-to-noise ratio (SNR) and the resulting sensitivity of instrumentation. System designers often have to include baffles, accumulators and other damping hardware to reduce pulsation. With Disc Pump, airflow can be delivered directly to the sensor, eliminating the need for damping hardware altogether. See out applications page to learn more on this: ttpventus.com/applications/environmental.

High-precision pressure control
During the control pulse - which lasts only 200 milliseconds or so - the evaluation kit executes a continuous feedback loop to control the pump output to a precise pressure. This means that the balls accelerate consistently every time, which is important to ensure that they travel exactly the intended distance. High precision pressure (or flow) control is interesting for all manner of applications, from air quality monitoring - where flow control is helpful for measuring accurate concentrations of potentially-harmful VOCs - to meniscus pressure control in industrial inkjet printing, where precise pressure control can help to improve print quality.

So how well does it sort? Where there any integration challenges?
WD: Actually, pretty well - better than 95% I'd say. There are one or two things that can trip it up. We've found that static electricity build-up over 4 days use at a show can result in the ball wandering off course. However, a wipe with a damp cloth soon fixes that problem. I think we'd look at a grounded base plate or grounding brush if we built it again. Dust build up is another issue - we designed a transparent cover plate for the demonstrator, but it seemed to detract from observing it somehow, so in the end we ran without it.

What's next?
WD: That's a closely guarded secret (read: we haven't decided yet!). We must have a dozen or so ideas that were discussed initially, from autonomous blimps to miniature light-up water jets. You'll have to wait until November and Compamed 2020 to see!

Disc Pump Evaluation Kit

TTP Ventus’ Disc Pump evaluation kit is a versatile development platform that enables engineers and product designers to quickly evaluate Disc Pump for their application. The kit contains everything necessary to start testing: two pumps, drive electronics, mains power supply, PC software for configuration and control, and all the ancillaries necessary to get up and running. Contact us today to discuss your application and request a quotation.

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