Parts presentation isn’t always the easiest automation problem to solve, but it can be one of the most important in determining the level of automation you can add to a production line. An effective parts presentation platform can provide enough stock to run an entire overnight shift without operator intervention and can eliminate unnecessary alignment steps that slow cycle time. Not all parts and machining operations are good candidates for continuous parts presentation, so understanding the design obstacles and opportunities that your task presents will help you develop the best method for your automation needs.
PARTS PRESENTATION FOR ROBOTIC SYSTEMS
For some machining operations, automated feeders do all the work. Rolled steel can be flattened for stamping presses and long bars can be advanced through the back of the lathe chuck. Other operations require each part to the presented and oriented individually, such as blanks for a press brake or dovetailed stock for a CNC machine.
The latter cases come with two steps: presentation and alignment. Presentation is the step where the parts are made available for the system to grab. Alignment is the step where inconsistencies in the presentation method are eliminated. A well-designed fixture does both steps at once, assuming the geometry of the parts permits it.
Automated parts presentation also comes with a set of challenges. How do you make the feed continuous? How does the automated system locate the next part? What if the feed system fails and the task continues to run without parts? Let’s address these below.
A continuous feed parts presentation method is one where the next part to be machined is automatically located in a set position for the robot arm to grab. The best way to imagine this fixture is a slide which bars of a set length can roll toward a fence. The operator loads the bars and gravity feeds them to the bottom of the slide where the fence holds them in place. The robot arm reaches only for the part against the fence and gravity advances the next part into its place.
In this scenario, the next part to be grabbed is always presented at one location and the fixture can be continuously refilled from the top or designed to be as long as necessary for the desired production time.
True bin picking solutions are cost prohibitive and can be difficult to program. If you can present an array of parts to your system in a grid or a stack, you can simplify the programming and make it easier to adapt to different parts.
Both grids and stacks have their advantages. Stack picking uses force to find the top of the stack and pulls parts until it reaches the bottom. You can use the “Save Position” node to program the Forge Station to remember where the top of the stack is as it pulls parts, shortening the time needed to find each part. Stack picking is best for flat parts. Grid picking works well when parts cannot evenly sit on top of each other or are too large for a stack. Grid picking uses the “Grid” node to create an array of evenly spaced waypoints based on the corners of the grid. Each time the node executes, it will move to the next part in the grid.
When an operator loads a machine, he can check that the part is oriented correctly and placed firmly against the fences or chuck. The Forge Station can use force motions to check that parts are properly placed, but this assumes that they were properly picked up. If a part is slightly askew in the presentation, that inconsistency may carry through to the placement step.
Gravity trays are an effective way to guarantee that all parts are grabbed consistently before being introduced to the machine. A gravity tray is a platform in which a dropped part will roll or slide into a corner from which it can be picked up. Regardless of how the part is dropped, it slides into the same corner and is therefore always grabbed the same way.
Building alignment into your part presentation or end-of-arm tooling is an efficient way to guarantee consistent part handling. Round parts can be centered in a centric 3-finger gripper and bottomed out against machined fingers. Laser cut or waterjet a part grid to present each part in a precise location. Build a fence into your part stack or slide that you can push the next part against before grabbing it, ensuring that it’s bottomed against that surface. These simple alignment additions cut valuable seconds off your cycle time and make programming and production more consistent.
FEED FAILURES OR BAD PARTS
Not all stock fits the way you want. A bent bar or a large burr could be the difference between a good part and a bad part. And a distracted operator could forget to fill a grid, leaving a CNC machine cutting air. You can program force feedback loops that react to a missing or bad part and notify the operator if something is amiss.
Use a force motion to grab parts from a grid and pause the task if the robot arm doesn’t feel a part where it should be. Check that a part has seated properly in a chuck by moving the robot arm over the top of it. If the part isn’t bottomed out, the arm will collide with it and can either attempt to place it again or put the part in a reject bin.
THE FORGE STATION
Certain part geometries require certain part presentation setups. Others leave room for experimentation. The Forge Station gives you the flexibility to try a variety of solutions until you find the one that fits. With interactive tools that notify operators when parts are low and an interface that encourages new ideas, the Forge Station will never be an obstacle to the automation environment best suited to your task.