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Mishandling detection in pick-and-place operations has historically been a good application for pressure sensors. A single pick-and-place nozzle typically uses three valves, one for picking up an object, one for blowing off the component and one to periodically clean the nozzle. The pressure sensor detects the negative pressure increase when the object is picked up. If mishandling occurs, the pressure remains low because the nozzle is open. With shrinking component size and increased mounting density in printed circuit board applications, the use of smaller nozzle diameters and shorter tact times causes a smaller pressure change. As a result, detecting that change is more difficult with a pressure sensor.
In contrast to sensing pressure, flow sensors can detect the true flow through the nozzle. "Detecting the flow through the nozzle can provide a higher sensitivity and faster response than sensing pressure," says Donna Sandfox, product manager, MEMS Sensors, Omron Electronic Components LLC. Positioned very close to the nozzle, a flow sensor provides a high-speed and high-sensitivity response regardless of the nozzle size. To get close enough, the flow sensor needs to be very thin.
Measuring 16.8 × 8 × 36.6 mm, Omron's D6F-03 unidirectional MEMS mass flow sensor addresses this and other flow sensing applications that require a thin sensor. The MEMS device is a thermopile element that converts thermal energy into electrical energy. Capable of measuring mass airflow up to 3 lpm with a ±5 percent full-scale repeatable accuracy, the sensor provides a 1 to 5V dc analog output signal and operates on a supply voltage of 10.8 to 26.4V dc. Consuming just 15 mA maximum, the sensor has a very stable output across the entire scale and operates from 0 to 50C.
In the pick-and-place application, the flow sensors provide nozzle clog and blow detection. Other applications for the thin flow sensor include leak detection, spectroscopy, mass flow controllers, test equipment and fuel cells.
Go with the Flow
Flow sensors detect mishandling in multiple valves in a pick-and-place application.
Submit your ideas for this section to Randy Frank; Design News, 225 Wyman St., Waltham, MA 02451; 480-236-9913;r.frank@ieee.org.
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