Assembly in Action: Sensors Overcome Assembly Challenges
Telesis Automation Corp. (Baldwin Park, CA) manufactures assembly, packaging, labeling and inspection machines for the medical, food, cosmetics and electronics industries. Recently, it built a machine for Porex Medical Product Group (Ontario, CA) to assemble Luer-Lok, in-line fittings for use with intravenous tube feeds-at a rate of 240 parts per minute.
Each assembly consists of three components: a hub, a luer and a cap. Assembly takes place on an indexing dial outfitted with 24 nests, which fixture four assemblies each. Parts enter the machine via vibratory bowls and vibrating feed lanes. From there they are positioned in the nests by pick-and-place grippers.
First, each fitting's clear plastic hub is placed in the nest, followed by the luer and the cap. A pair of plunger stations checks each assembly for height to verify that these components have been correctly inserted. A conveyor carries off the finished assemblies for packaging.
In all, the assembly machine incorporates 35 separate sensing stations. It also features adjustable and interchangeable tooling for assembling two lock styles: micro and macro.
In creating the machine, Telesis wanted to use noncontact sensors, as opposed to mechanical switches, to simplify the process. However, because the fittings' hubs and luers are fabricated from clear plastic, this proved to be a challenge. Ultimately, the company went with a set of Allen-Bradley sensors, encoders and other components from Rockwell Automation Inc. (Milwaukee).
At the very start of the process, Telesis wanted to monitor the component part level in the system's feeder bowls. This meant employing a sensor that could not only detect both clear and opaque objects, but also have sufficient background suppression capabilities to prevent sensing the bowl surface.
The latter was an especially tough problem, because standard photoelectric sensors will often pick up reflections from the bowl itself. This causes them to report that the bowl is full, when, in fact, it is not.
To solve the problem, Telesis went with an Allen-Bradley 42EF RightSight background suppression photoelectric, which proved ideal. As an added benefit, this sensor is much more compact than the gravity switches Telesis had used in the past. As a result, by installing the 42EF, Telesis was able to go with noncontact sensing across the system's entire process.
Vibration was also a factor in monitoring the system's feed lanes. "Those caps are jumping vigorously in there," says Telesis President, Jess Leon. "They're not easy to sense." Therefore, the company went with a set of 42FT self-teach, fiber-optic sensors to pinpoint the presence and position of the fitting components. The sensors' self-teach functionality helped compensate for part vibration by determining the optimal sensitivity and hysteresis for the application.
Once the hubs have been placed in their fixtures, a series of Allen-Bradley MiniSight photoelectrics looks across the nest to confirm presence and proper placement of the part. After the luer is inserted and the cap set in place, two "press and check" stations, consisting of four metal plungers fitted with eight 8-millimeter WorldProx inductive proximity sensors, ascertain presence of the cap and correct depth of insertion.
Finally, as the complete assemblies leave the machine, another set of RightSight sensors checks that all finished parts have been ejected in what Telesis calls the "empty nest stage" of the process.
For more on sensing, visit www.ab.com/sensors or eInquiry 7.