Faced with a highly competitive marketplace and tight just-in-time production schedules, manufacturers are requiring more functionality from the sensors they use to monitor critical equipment and operations. In high demand are features like quick-disconnects, multiple inputs/outputs, and reduced wiring requirements.
In their sensor preferences, according to Ernie Maddox, product manager at ifm efector inc, Exton, PA, manufacturers are also affected by the need to address major trends in industrial automation, including an overall reduction in costs, smaller machines, smaller parts being fabricated, and higher-speed equipment.
Technology also has had an impact on sensor developments. Advances in miniaturization have been particularly influential. So has the evolution of digital communication and networking, which has enhanced device versatility. Unfortunately, the lack of a common interface for connecting digital sensors to microprocessors and networks has complicated installation, in some cases. This should change if the Smart Transducer Interface standard (IEEE 1451.2) is widely accepted.
Shrinking Sensors
Among the most intriguing new small sensors is a group described as microelectromechanical systems (MEMS). An example is the line of IPS (integrated pressure sensor) products from Motorola, Phoenix, AZ. These silicon pressure sensors combine advanced micromachining techniques, thin film metallization, and bipolar semiconductor processing to provide anaccurate, high-level analog input signal proportional to applied pressure. The shear-stress strain gauge, temperature compensation, plus calibration and signal conditioning circuitry are all integrated onto a monolithic chip. A temperature- and chemical-resistant polyphenyl sulfide SOP (small outline package) protects the unit, allowing direct mounting on pcbs.
Fiber optics increase the versatility of ifm efector's OB photoelectric amplifier.Some of the most dramatic size reductions have been in photoelectrics, enabling positioning in tight spots on complex machines. Since photoelectric response can be affected by dust and dirt collecting on the face, many of today's most sophisticatedunits compensate for declining capabilities and provide an alert when cleaning is required.
The sugar-cube-sized Series 3 photoelectric from Leuze-Lumiflex, Rockaway, NJ, already widely used in Europe on conveyors, can be positioned looking up on roller conveyors to detect oncoming products.On belt conveyors like those preceding wrapping machines, it can be positioned looking down to detect products such as candy bars. Through-beam, retroreflective, and diffuse versions provide scanning ranges of 6 m, 2.5 m, and 300 mm, respectively. A comparatively large optical surface for its size makes the unit "much more reliable against dust and dirt," says Manfred Schneider, sales engineer at Leuze.
When even the smallest sensor is too big, as is the case on assembly machines for products like cellular phones, fiber optic cables connected to photoelectric amplifiers make it possible to snake through equipment, turn right angles, or create a light curtain array to detect small objects. The new OB photoelectric amplifier from ifm efector inc, can meet virtually any requirement for sensing in tight spots by providing a family of 19 cut-to-fit fiber optic cables. These include styles fitted with an integrated lens to lengthen their sensing ranges up to 5 times. An onboard microprocessor automates setup; quick-disconnect cables and mounting hardware simplify installation. A fast 500 Hz switching rate permits use in high-speed applications, while a 1""90 µsec time delay option can compensate for slower PLC scan times.
Fiber optics offer other benefits, as well. "Fiber is immune to noise, so it prevents false triggering from motors and inductive loads," explains Mike Frey, sensor development manager at Omron Electronics, Schaumburg, IL. In addition, fiber optic devices move the amplifier away from the action where space is more available and chances of damage are minimized. Should the fiber be damaged, it is easily and, most likely, inexpensively replaced. The new fiber is then simply connected to the original amplifier.
Get Smart
Perhaps nowhere is the trend toward smarter sensors more apparent than in the development of visual inspectors. The compact Series 600 SmartImage sensor from DVT, Norcross, GA, integrates camera, image acquisition electronics, and computer in a rugged injection-molded, 1.6 x 2.2 x 4 in. case. Compared with earlier models, this unit offers higher resolution (640 x 480 pixels), faster speeds due to an upgrade to a Power PC, as well as Ethernet and fieldbus connectivity."With Ethernet connectivity, the sensor works as a node on the network and becomes a really powerful setup for data transfer in real-time," explains Michael Valverde, director of communications at DVT. Consequently, the unit can deliver data such as quality control inspection results; coordinate information for motion controllers; statistical process control data; and even 2D code verification. "Ethernet is the de facto standard in the office. We believe it will become the standard on the factory floor, as well," he states.
Model WL 12G photoelectric reflex sensor from Sick tolerates dust and other contaminants."Today's sensor technology is driven by the need for smaller and faster sensors with greater resolution and improved repeatability,
As the first sensor capable of analog or digital output, Omron's E3X-DA digital fiber optic amplifier can, for example, check cap color (analog) or cap presence (digital), making it unnecessary to install a new sensor when needs change. The flexibility also is important because
DeviceNet connectivity and multiple diagnostic outputs are offered by a range of presence-sensing devices from Rockwell Automation, Milwaukee, WI, such as the Allen-Bradley RightSight DeviceNet photoelectric.
Tough ENOUGH
Equipment with extremely tight space constraints, such as robot grippers, valves, power clamps, and pick-and-place systems, as well as situations where a particular shape is required, are targets for overmolded sensors from Turck, Plymouth, MN. The injection-molding process creates a housing around the sensor circuit board and coil to produce a completely sealed unit.
A lifespan of months instead of days under the tough conditions arising from machining, the frequent high-pressure washdowns of food and beverage plants, and the grease, salt, and weather exposure of transportation applications, is the goal of the Pile Driver, an inductive proximity sensor from Pepperl+ Fuchs, Twinsburg, OH. Protection is provided by a thick metal sensing face in a seamless stainless steel housing. Dedicated ferrous and nonferrous units offer sensing ranges of 2, 5 and 8 mm.
DeviceNet interface enables the remote monitoring of Banner's Micro-Screen safety light curtain.SAFETY Sensors. For greater personnel safety on the plant floor, Banner Engineering Corp, Minneapolis, MN, offers the Micro-Screen safety light curtain to separate workers from equipment that automatically starts and stops, such as automated drilling stations, robotic workcells, and injection-molding machines. In action, an optoelectronic emitter generates an infrared light screen, which if broken halts the machine in less than 38 msec. The smart feature is a built-in DeviceNet interface. When the system is linked to a DeviceNet network, troubleshooting and status monitoring can be conducted from a central location, reducing downtime and maintenance cost.
Keeping a close ear on the well-being of machinery and warning of impending failure by tracking subtle changes in emitted sound is the function of the Acoustic Machinery Monitor from Horton Industrial Products, Minneapolis, MN. It records and analyzes up to 5 acoustic signatures to monitor machine applications with more than one acoustical phase of operation. The monitor compares real-time filter outputs from 96 bandpass filters with previously stored acoustic signatures, and activates an alarm if the output deviates by more than a preset amount. Noncontact level sensing of liquids and slurries in vessels, stilling wells, and bypass pipes in extreme process conditions is possible with the Micropilot II FMR 230V from Endress+Hauser, Greenwood, IN. Since it uses microwaves, the sensor is unaffected by process temperatures, pressures, vacuum, gas composition, or turbulence.
What's Next?
There's no question sensors have become smarter, However, the lack of compatibility between different networks and devices remains a problem.One possible solution is the widespread acceptance of the recently adopted IEEE 1451.2 standard, Transducer to Microprocessor Communication Protocols and Transducer Electronic Data Sheet (TEDS) Formats. A joint effort by the National Institute of Standards and Technology (NIST) and more than 25 companies, it simplifies the connection of transducers to control systems or networks. Anticipated benefits include reduced sensor development time, as well as lower installation, maintenance, and wiring costs.
On another front, although they are still more expensive than visible or infrared LED photoelectrics, the market for laser units is growing because their more focused light beam offers operation at longer ranges with greater precision. "A laser-based optical measuring device, for example, can measure distance from sensor to target in tenths of a millimeter," reports Leuze's Schneider. Vision sensors also are an area of activity. "The gap between photoelectrics and high-end vision systems is starting to become smaller and smaller," says ifm efector's Maddox.
Look, too, for increased bidirectional communication capability between sensor and computer as bus systems mature and prices come down. In the meantime, manufacturers' requirements will continue to grow, suppliers agree. "Everything is getting smaller, less expensive, and more feature-packed," sums up Frey at Omron."New ICs are being developed, which allow more features to be incorporated," notes Maddox. "In the past, to add features meant increasing the size of the housing because you had to add components," he explains. Considering all the developmental activity, sensor market growth promises to be healthy, with sales estimated at close to $13 billion by 2000, according to a report by NIST.
