The project requires a new machine to automate the laser drilling of holes in small plastic parts used in gas detectors for the mining industry. We were contracted to build the automation system and a vision system for the machine that would enable the parts to be automatically inspected, ensuring that the holes had been accurately drilled into them.
The challenge faced was that there were no fewer than eleven different variants of plastic part that needed to be inspected, drilled with holes that varied in diameter from 15um to 50um. The system itself was required to accommodate all the variants — inspecting each one to determine its position, as well as the entry and exit sizes of holes in the plastic. In addition, it needed to be flexible enough to enable an operator to quickly change the tooling of the parts between each of the component runs.
The system incorporated a bowl feeder into which parts of a specific batch type are loaded. A vision guided robotic system then identifies the part and places it onto a fixed position on a walking beam transfer system. A UV laser drilling system then drills hyperboloid- or hour glass-shaped holes into the part, after which the part is moved through three further vision stations where they are inspected. Having done so, parts are transferred over two bins where they are either accepted or rejected.
On the line
Due to the variety of plastic parts to be produced, a system was developed to enable an operator to quickly change the tooling on the machine to accommodate different product runs. To do so, a Mitsubishi PLC — which controls the entire operation of the machine — was programmed to identify a unique barcode associated with each batch of product to be produced.
When the barcode is scanned, tooling setup parameters for a specific type of component that were previously programmed and stored on the PLC are displayed to the user on a touch screen interface. These indicate to the operator what type of tooling should be fitted to both the bowl feeder and the walking beam system. In addition, the PLC can automatically recognize if incorrect sets of tooling are fitted, eliminating the risk of inadvertent human errors. A fully validated tool changeover to accommodate a different plastic part can be accomplished in less than five minutes, resulting in improved uptime and productivity.
Once the correct tooling is fitted to the machine, it is ready to drill and inspect the parts. Before the process commences, the raw plastic components are first loaded into the RNA vibratory bowl feeder which transfers the parts onto a linear conveyor. A six axis robot is then used pick the parts from the conveyor and place them into the first fixture of a walking beam system which in turn uses pneumatic grippers to sequentially transfer each part from the linear conveyor under the first of a series of vision stations.
Prior to laser drilling, it was important to ensure that the robot picked the parts from the linear conveyor and correctly oriented each one before transferring it to the walking beam system. To enable it to do so, Fisher-Smith GenVis software running on a PC was trained to create templates of each of the unique plastic parts by using MVTech’s HALCON shape-based matching algorithm.
The vision system incorporates 3 camera stations, with the ability to inspect each component for position of the hole, entry hole size and exit hole size. Having inspected the part, the walking beam moves it to the end of the walking beam over a pass or reject chute. At this point, all the various pass or fail results acquired from the hole position, entry hole and exit hole cameras at the vision stations have been aggregated by the PLC, which then instructs the walking beam to release the grippers it uses to hold the part, dropping the part into one of the two chutes.
A fully validated changeover to switch from one component to another can be accomplished in less than 5 minutes, resulting in improved uptime and productivity.
Machine building and integration, machine and process control, Robot integration, Bowl Feeding, Vision Inspection, Poka-Yoke design, Project management