Sonic boom ahead?
28 Jan 2008
Photoelectric sensors have been the most popular control devices for detecting conveyor-transported packaging items for applications where the target objects are opaque or translucent. Standard systems can, however, prove unreliable in capturing highly transparent packaging, such as modern PET bottles, moving on the line.
Retro-reflective photoelectric sensors do offer the extremely precise adjustment to sense clear objects but they are relatively expensive, complicated and difficult to set-up. Hence some plant and maintenance engineers now see ultrasonics as a more easy-to-apply alternative for detecting high clarity packaging.
Utrasonic sensors use sound waves to sense the position of the target and so are unaffected by the degree of opaqueness of the container. The systems are slower than photocells — operating at the speed of sound within air restricts total output time — though this is not an issue for bottling lines and many filling lines, which have typical line speeds of around four or five items per second.
"With the ultrasonic sensors we have we just set them on the side of the conveyor, look across at the guide rail on the other side, connect the source wire to ground," said Martin Wheatley, MD of sensor supplier Contrinex UK. "The system sends pulses in bursts of five at a frequency of about 190-215 kHz and waits for the slides to come back.
"If anything interrupts it, it knows that there is an object in the way. So colour is irrelevant, clarity is irrelevant, ribbing has absolutely nothing to do with it. You get an absolutely spot-on identification of where the bottle or carton is on the line, ready to fill or put the label on."
Retro-reflective photoelectric sensors do offer the extremely precise adjustment to sense clear objects but they are relatively expensive, complicated and difficult to set-up. Hence some plant and maintenance engineers now see ultrasonics as a more easy-to-apply alternative for detecting high clarity packaging.
Utrasonic sensors use sound waves to sense the position of the target and so are unaffected by the degree of opaqueness of the container. The systems are slower than photocells — operating at the speed of sound within air restricts total output time — though this is not an issue for bottling lines and many filling lines, which have typical line speeds of around four or five items per second.
"With the ultrasonic sensors we have we just set them on the side of the conveyor, look across at the guide rail on the other side, connect the source wire to ground," said Martin Wheatley, MD of sensor supplier Contrinex UK. "The system sends pulses in bursts of five at a frequency of about 190-215 kHz and waits for the slides to come back.
"If anything interrupts it, it knows that there is an object in the way. So colour is irrelevant, clarity is irrelevant, ribbing has absolutely nothing to do with it. You get an absolutely spot-on identification of where the bottle or carton is on the line, ready to fill or put the label on."
