The Challenges of Inspecting Manufactured Parts
Monitoring and controlling any process requires measurement capability, both in process and at final inspection.
Many of today’s flexible automated factories produce parts and assemblies at very high production rates, making 100% inspection challenging. Tactile and other traditional sensing technologies, prevalent in the past, are unable to keep up with modern production rates.
Without 100% inspection, there are no guarantees that defective parts or assemblies aren’t passed on to downstream operations or the end user.
In many cases, high volume quality monitoring and process control measurement data can be implemented by use of 2D or 3D sensing, with 2D being well accepted, and 3D becoming more prevalent as smart, all-in-one, easy-to-use sensors today are priced competitively with 2D.
There are still, however, challenges that must be considered when implementing 3D sensing for inspection of manufactured parts.
Sampling Speed
High volume manufacturing lines can often produce thousands of parts per hour, requiring very high sensor speeds to insure 100% measurement of every part produced.
Sensors must not only acquire data at high speed, but also buffer, align and deterministically deliver pass/fail results without dropping data during processing and communication.
Target Motion
Today's manufacturing and assembly lines use automated parts transfer between multiple operations. Transfer may be incremental (such as a lift and carry mechanism) or continuous (such as a continuously moving conveyor). Selection of a 3D sensor for a specific application depends on the type of transfer at the desired inspection station.
Stationary parts require an area-based sensor, which takes a 3D snapshot of the target at rest, requiring only a trigger signal that the target is in position, ready for measurement.
Continuous motion inspection stations require a laser line-based profiling sensor to take target profile sections at desired increments and then assemble them into a full 3D point cloud representing the part shape. This implementation requires an encoder connected to the conveyor to trigger the sensor profiles at specific positions as the conveyor moves, independent of conveyor speed. In this case, using an all-in-one smart sensor with a built-in encoder input will significantly simplify the integration effort.
Compatibility with Factory Interfaces
All smart sensors inspecting manufactured parts must communicate with external reject handling systems such as a PLC. In addition, measurement information about each part such as status and dimensions of key features are often sent over a factory network for logging.
The complexity of communications interfacing in a factory automation environment can be dramatically simplified by use of a 3D smart sensor that offers built-in standard protocols and flexible string-based transactions.
These built-in protocols include communication support for a range of PLC standards such as Ether/IP and Modbus. Simpler direct I/O such as digital, analog, and serial support higher frequency, time critical messaging.
In cases where inspection is more involved than on-board measurement tools can offer, the best of today’s smart sensors support native drivers to interface to different popular third party processing packages, such as Halcon, Common Vision Blox, HexSight, Matrox and LabVIEW.
