Although technological advancements have improved sensors since their first use, their purpose ultimately remains constant. "Sensors are called sensors for a reason," says Tony Udelhoven, director, sensors division at Turck (www.turck.com). "They are quite literally the sensory system — the eyes, ears and fingertips — of the machine’s control system that allow the designers to automate machine processes. Sensors have evolved considerably from the first non-contact controls that were developed to replace less-reliable electromechanical switches to accommodate increasingly advanced sensing applications."
And while the application may vary, there’s typically a sensor best-suited for the need. "When navigating automatic guided vehicles (AGVs), highly accurate and dependable sensors like laser scanners and encoders are the basis for attaining the high performance that AGV systems deliver," says Kenneth Palm, product manager, AGV systems, at Danaher Motion (www.danahermotion.com). With software, the information from these sensors is fused to provide a complete navigation solution, he explains.
"In order to control the speed of a vehicle, one needs a speedometer," explains Joseph Vu, applications engineer at Macro Sensors (www.macrosensors.com). "To control a robotic arm, we need a position sensor such as an LVDT to know where it is." With modern digital techniques, the LVDT can reach new heights in terms of temperature stability and accuracy, he says.
"By selecting the right type of sensor, the system designer can expect long-term system performance with continuous feedback," says Greg Montrose, sales manager, American Sensor Technologies (www.astsensors.com).
"Sensors play an ever-increasing role in machine control, especially as these processes become more and more complicated," says Robert Lee, sensors group marketing manager at Omron Electronics (www.omron.com). "For simple presence-absence detection, limit switches, photoelectrics and proximity sensors are more than adequate to fulfill the sensing solution. While photoelectrics are a very cost-effective solution for non-contact detection of targets from a distance, the different variations in photoelectric sensing still remain popular in solving many applications. In applications where the environment may affect the quality of sensing, besides using a limit switch, one may consider using proximity sensors as an alternative." Smart sensors combine the simplicity of photoelectric sensors with the complexity of vision sensors to detect difficult or intricate geometry, he adds.
"Sensors should be a forethought, not an afterthought," says Chris Graber, senior applications engineer, Banner Engineering (www.bannerengineering.com). "Too often, sensors are some of the last components specified during machine design, when in fact the efficiency of the entire machine control system depends upon sensing the product or process. Sensors, including photoelectric, ultrasonic and image, are key components that contribute to higher production throughput, less machine downtime and higher product yields through various error-proofing techniques."
Jim Ashford, president and COO of Omron STI (www. sti.com), agrees, even when it comes to safety sensors. "The best and least expensive way to incorporate safety into a machine is after a complete risk assessment and during the control design phase," he says. "That way, it's built into the machine, rather than being an afterthought."
Sensors are one of the key components to the efficient design of machine control, says Wayne Meyer, Sick industrial sensors product manager at Sick (www.sick.com). "Sensors give feedback about the product location, size, color or presence, using photoelectric, inductive, color, contrast and distance sensors," he explains. "In addition, sensors can be used during machine changeovers to speed up the automated adjustment of a machine. This is done by the remote setting of sensors, remote diagnostic retrieval and even something like a format adjustment drive which combines a motor with encoder to change position of guide rails when performing a changeover from one size product to another."
By including sensors in the machine architecture to provide vital data to the machine control system, real-time control and intervention become a reality, says Cees Links, CEO of Green Peak (www.greenpeak.com). "Wireless sensors can provide easy-to-install alternatives, especially when they have to be mounted on moving parts or in hazardous or hostile environments that would usually require an even more expensive type of cable," he says. "By using sensors equipped with ultra low power transceivers that require no battery replacement or that run on energy harvesting, the maintenance problem of replacing or recharging batteries can also be avoided."
Photoelectric sensors are becoming more and more important in automatic machines, says Carmine Clementelli, product manager, IDEC-Datasensor (www.idec-ds.com). "Sensors have become key factors as they control the machine functioning: object presence control, phase synchronization control and material quality control," says Clementelli. "Moreover, the sensors are fundamental for the productivity and reliability of an automatic machine functioning, for example, in the automatic format change during production without stopping the working cycle or the management of sensor functioning status information using auto-diagnostic functions in more advanced sensors."