Vibratory bowl conveyors provide an economical and reliable way of feeding small parts in a given orientation. However, the mechanical parts-orienting channels and guides limit them to handling just one part or a family of similar items. Case in point: In one aerospace application, the task of loading fasteners into a press was suitable for automation with a vibratory bowl feeder plus a pick-and-place robot. The problem was that the 415 parts involved would have required dozens of different feeders.
For a better approach, Rixan Associates Inc., Dayton, Ohio, developed a unique take on the vibratory bowl feeder by using machine vision to replace channels and guides to handle a virtually unlimited number of parts within a certain size range. The new feeder uses the vibratory bowl feeder concept to randomly present the parts in the bowl in any possible orientation. When the vision system views the right part in the right orientation, it stops the feeder and sends the part's location to a robot, which loads the part into the press. The Rixan RFS-1000 flexible vibratory bowl feeder system, which costs about $45,000, provides a 20% productivity improvement and eliminates the need for an operator.
Traditional vibratory bowl feeders use a helical shelf-like inclined ramp winding upwards from the bottom of a bowl to a discharge passageway. The passageway's reciprocating motion pushes the parts up the ramp. Obstructions, cutouts, and other orienting devices are arranged along the passageway to topple off parts that are improperly oriented and allow only properly oriented parts. Vibratory bowl feeders are normally able to handle only a single family of very similar parts. Each different part requires time-consuming adjustments of obstructions and orienting devices. As a result, despite high efficiency and relatively low cost, the vibratory bowl concept is usually not used for applications involving many different parts.
Stephen Harris, Rixan's president, recognized that improvements in the speed and reliability of vision systems make it possible to use a vision sensor to replace channels and guides to deliver a flexible feeder. Harris got the opportunity to validate this concept when he competed for a potential customer processing many high-value aerospace fasteners in a stamping press. Previously, an operator picked parts out of a bin and manually loaded the press with them. The manufacturer wanted to automate this operation because of the potential danger involved in having the operator place his hands into the press. Additionally, the repetitive nature of the task required the operator to take frequent breaks, which limited productivity.
The Rixan concept uses a track on a 24-inch vibratory bowl without the obstructions and cutouts. Every part that reaches the top of the bowl is presented onto a raised semitransparent plenum so the vision system mounted above can easily identify the type of part and its orientation. The robot picks correct parts, while incorrect parts are recycled into the bowl.
Rixan engineers selected a Cognex In-Sight 5401 vision system and a Mitsubishi Electric RV-6SL-S11 robot that have been integrated through a joint development effort between Cognex and Mitsubishi Electric. Mitsubishi Melfa-Vision software incorporates robotic programming software as well as Cognex In-Sight Explorer software to set up both the robot and the vision system simultaneously as an integrated solution.
Melfa-Vision includes standard job programs supporting most common robot applications, enabling novices to easily develop robotic vision applications with up to three robots and seven vision sensors. Rixan engineers picked the Mitsubishi Electric robot for its 6 m/sec speed - and because it has long reach. They selected the Cognex In-Sight 5401 vision system because it provides up to seven times the processing power of other models and acquires up to 60 full 8-bit images per second.
The fastener manufacturer has already purchased three systems and is in the process of programming them to handle its full range of parts. The feeding system is slightly slower than an operator working at full speed but, because the system does not take breaks, it provides an increase of 20% in productivity compared to a human operator. The vision system also eliminates placement errors that can damage the tooling. For more information, visit www.cognex.com and www.rixan.com.