Optical window sensors are utilized where reliable part counting is needed. This type of sensor technology is based on an array of LEDs on one side, opposite an array of phototransistors on the other side. This array covers the whole area of the window’s opening with an evenly as possible distribution of light. The more evenly distributed the light is throughout the window, the higher the resolution.
Optical window sensors are usually assigned a particular term to reveal their specific functionality type. The two typical functionality types for an optical window sensor are either static or dynamic. The differences between the two functionality types are briefly outlined here.
Static functionality looks for unchanging events. In the case for an optical window sensor, static means it detects the percentage of signal blocked by an object present in or passing through the window. Dynamic functionality looks for changing events. In the case for an optical window sensor, dynamic means it detects moving objects in the window and ignores non-moving objects. Still, in either case whether static or dynamic, the sensor detects objects as they pass through the window.
A common follow-up question is: what are the pros and cons for using either functionality over the other? This is a good question, because there are definite benefits and disadvantages to both approaches. A few of these benefits and disadvantages are briefly outlined below.
A couple of benefits of static over dynamic are its ability to:
- Detect long and short objects interchangeably falling through the window without having to adjust pulse stretching
- Detect an object that becomes stuck inside the window
A few benefits of dynamic over static are its ability to:
- Ignore certain objects that are placed in its field of view; for example, the sensor would detect parts falling inside a clear tube, even when the clear tube is placed inside the optical window
- Detect a smaller object – due to looking only for a change in signal rather than a certain percentage in signal drop
- Specify a faster response time – due to the unmodulated LEDs (only the phototransistors are modulated)
Optical window sensors come in a variety of different window openings from 40x80mm to 160x160mm. And usually in dynamic optical windows, one passive side can easily be detached. This allows the window to be used in a u-shaped type configuration, either for added flexibility or to get around an object.
A particular optical window sensor, the UltraFrame series, utilizes dynamic functionality and was specifically designed for the metal stamping industry and has been in this particular industry for several years in a variety of applications.
In the stamping industry invasive lubricants are used and the high velocity of the metal parts bouncing off the sensor surface combine to make detection difficult, particularly in part ejection control applications. To combat these issues, the UltraFrame line was specifically designed so that:
- The sensor is sealed with an oil-resistant epoxy
- The sensor surface is recessed to protect the lenses from the high velocity metal parts flying through and sometimes bouncing off the sensor
- The sensor’s precision optical components provide an object resolution as small as 1mm in diameter for the entirety of the window
- The sensor’s adjustable switching frequency provides the ability to count up to 200 parts per second
For more information on the UltraFrame dynamic optical window sensors, please click here.
