Robotic hybrid sensors - those with multiple types of detection systems – aren’t part of the flexible automation mainstream. However, the use of hybrids, while small, is on the rise. More end users of robotic systems believe hybrid sensors have a role in manufacturing. The devices are especially useful for delivering multiple types of part information in robotic manufacturing processes.
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A hybrid sensor has “multiple sensors and multiple processing techniques to obtain more information than one could achieve from independent sensors,” says John R. Wright, Jr., associate professor of automation and electronics technologies at the University of Pennsylvania, Millersville. Wright uses a simple equation to describe them: “1+1=3.”
And the survey said...
In the fall of 2006, the Robotic Industries Association (RIA, www.roboticsonline.com), Ann Arbor, Mich., the only North American trade association solely dedicated to robotics, worked with Wright to survey its member companies to explore the potential market for hybrid sensors. The data shows that almost 75% of respondents believe that hybrid sensors would be useful in their plants.
The top three points of interest for hybrid sensors are vision, infrared/laser and photoelectric applications, according to the survey. The survey also asked what benefits deploying hybrid sensors would bring. Adding functionality to a robotic work cell and ease of integration topped the list of perceived benefits.
The greatest potential for hybrid sensors is expected to come from giving vision systems supplemental functionality to undertake applications that are problematical for current vision technology. Nearly 75% of those answering the survey say vision has the most potential to be used in a hybrid sensor system. The survey also found that material handling, assembly, welding and machine tending are applications in which hybrid sensors would be most useful.
Why go hybrid?
There are two reasons that you might consider investing in hybrid sensors for your robotic systems.
“Hybrid sensors can do things that traditional two-dimensional cameras can’t. Two-dimensional cameras can take a picture and send the data to the robot,” says Jeffery Noruk, president of Servo-Robot Corp. (www.servorobot.com). “But, two-dimensional cameras can’t operate under all conditions, such as when lighting changes or depth information changes.” These scenarios are where a hybrid sensor with laser and two-dimensional capabilities would come in handy, Noruk claims.
The second motive Noruk offers for investing in hybrid sensors is related to the limitations of standalone laser vision systems. “Laser vision has a small depth of field and can work only in a relatively small envelope. In a larger envelope, we use an ultrasonic sensor to access a part with precision,” he says.
Hybrid sensors are less expensive in the long run because less equipment can accomplish a range of tasks.
“Justifications for investing in hybrid sensors are the cost-per-performance argument, where hybrid sensors might compete with low-end vision systems, and a pure performance argument, where the addition of other sensory perception combined with existing vision systems might add value for complex applications,” explains Wright.
Hybrid sensor apps
Hybrid sensors are useful for a variety of purposes, including material handling applications. “Hybrid sensors used in material-handling applications combine a camera and an ultrasonic sensor. The ultrasonic sensor gets the gripper to a part at a high speed,” Noruk says. “At a certain distance from the part, the laser sensor, which has a smaller range or depth of field, takes over and guides the robot to the precise location.”
Welding is an application where hybrid sensors could be useful. “One end user deployed a laser system for weld seam tracking using a microphone and a Web camera. The laser sensor is used in real-time robot guidance and the microphone was added for audible confirmation that the process sounds right,” Noruk says. “While the robot is in teach mode, end users have seen the advantages of using hybrid sensors for welding applications.”
Hybrid sensors also are beneficial in pick and place, de-palletizing and auto-racking applications when ultrasonic sensors are combined with laser vision (Figure 1). “Hybrid sensors allow manufacturers to perform some material-handling applications that weren’t possible or efficient before,” says Noruk.
Hybrid sensors have a role in material-handling applications. “Hybrid sensors are used for part location with two-dimensional vision fused with three-dimensional position and orientation information,” says Claude Dinsmoor, general manager for controller product development, FANUC Robotics America (www.fanucrobotics.com).