Advancing Safety Through Advanced Sensing
Sensors for the seemingly mundane activity of ensuring industrial safety are moving forward in sophistication, packaging and watching what needs protecting.
With all the buzz about mobility, cloud computing, big data in manufacturing, Industrial Internet of Things and autonomous operations, let’s not forget some basics regarding the manufacturing floor: safety. That would be the safety of people, machines and processes.
The cost of sensors has plummeted, making their implementation for safety applications a no-brainer. Industrial safety sensors are a requirement from both a regulatory and liability standpoint. It also makes sense (no pun intended) economically: Sensors protect the investments companies make in people and machines on the manufacturing floor. Moreover, callous as it might seem, stopping a machine or an entire production line for an emergency involving people or machines is downright costly. Ergo, safety sensors not only protect and prevent accidents, they also increase productivity.
The universe of safety sensors covers a lot. The photoelectric sensors for safety applications from Pepperl+Fuchs (pepperl-fuchs.com), to mention one vendor, include light scanners (diffuse mode and active infrared), photoelectric sensors (thru-beam, slot and retroreflective sensors), fire protection sensors, passive infrared scanners, radar sensors, laser distance sensors and distance measurement devices, and safety light grids and curtains. Add to that list safety edges, safety mats, anti-collision sensors and both magnetic and ultrasonic sensors. In its report published in March with a very lengthy title, IndustryARC (industryarc.com) points out that “safety switches also encompass an extensive range of products, such as limit switches, hinge switches, non-contact magnetic switches, position switches, door switches, foot switches, interlock switches, emergency stop buttons and rope pull switches.”
Here are some examples of what’s new in just two categories of safety sensors.
Big advances in small packages
Photoelectric sensors sense the difference in light intensity to determine the presence or absence of an object and, in some cases, the distance to that object. These sensors have been a mainstay in safety applications for decades. What’s changed about them is their packaging and electronics. Sensor housings have shrunk from the size of a person’s fist to half the length of one’s pinkie finger. Light sources now include light emitting diodes (LED) producing visible red or invisible infrared light as well as laser light. Laser sensors with a 16.5-foot range are commonplace. Last, as with all electronic devices, photoelectric sensors now come with “smarts,” enough so to quickly calculate distance (position) and light intensity (contrast), thereby improving sensor accuracy.
For example, the microScan3 Core from SICK is a compact safety laser scanner that can detect objects up to 18 feet and within a 275 degree scanning angle. The scanner features SICK’s own safeHDDM (high definition distance measurement) scanning technology, which is based on the time-of-flight measurements of laser pulses; distance is calculated by the delay time from when the sensor transmits a pulse beam and when that beam, reflected by the object being detected, is received. The multi-pulse is around 80,000 pulses in each scan, which is about 160 times more than in conventional scanners. Moreover, the laser pulses are coded by a time delay of a few nanoseconds. Altogether, safeHDDM effectively filters out dust, ambient light, weld sparks, cross talk, and other obstacles to scan accuracy. It can even recognize objects with a remission of 1.8 percent, such as black pants. The scanner includes pushbutton diagnostics, which simplifies setup and troubleshooting, and a multicolored display indicating operating status. The entire unit is in a light metal die-cast housing (read durable).
Semiconductor technology, says Bethany Dunich, content marketing manager for Panasonic Industrial Device Sales Co. Of America (na.industrial.panasonic.com), “allows for the development of thermopile sensors made up of hundreds of thermocouples over several square millimeters. These sensors provide faster response time, are reasonably priced, and are accurate and small.” This is microelectronic systems (MEMS) technology applied to sensing. “By printing thin-film IR absorbers surrounded by free-standing thermal isolation structures,” continues Dunich, “this MEMS-based technology [measures] radiated power to remotely determine an object's temperature.”
One such sensor is the second generation AMG88 Series Grid-EYE Sensor from Panasonic. This device is an uncooled IR sensor with an 8x8 thermopile array in a reflow-compatible surface mount (SMD) package that includes MEMS sensor chip, RF-shielded metal cover, digital ASIC with I2C interface, and 60 degree silicon lens etched out of a silicon wafer (the lens is less than 0.01 inches high)—all in a package measuring 11.6mm x 8mm x 4.3mm, which is, according to Panasonic, about 70 percent smaller than competitive products. Each of the array's 64 pixel sensing elements converts the thermal energy into a proportional output signal. These temperature signals are amplified, converted from analog to digital, referenced against an ambient temperature value and then transmitted to a microprocessor. “The microprocessor maps the temperatures into a complete thermal representation of the entire field of view,” explains Dunich. “From this thermal grid, it is possible to detect moving people as well as the direction they are moving and the presence of motionless people.” Grid-EYE sensors detect objects up to 7 m and have frame rates up to 10 fps.
Ultrasonic sensors also exist on the plant floor. For instance, UC-F77 from Pepperl+Fuchs is about 1.25 inches high and can detect objects up to 31.5 feet away. “It has an extremely small deadband, meaning even objects in close proximity to the sensor are reliably detected,” says Product Manager Carsten Heim. Helping matters is that the sensor’s switch points, output mode, output logic and sound beam width are programmable by buttons on the sensor. The sensor includes automatic synchronization, which allows up to 10 sensors to operate in the same cycle or multiplex mode without external intervention. Continues Heim, “This prevents cross-talk between sensors mounted close [to] each other and ensures the shortest possible response time.” The sensor comes in both thru-hole and surface-mount versions.
Is this all worth it? You betcha! As stated in a SICK brochure entitled “Guide for Safe Machinery”: “Safety is a basic human need.”
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