At Arm’s Length
- June 15, 2020
Hang on tight: there’s more to automation than the robot
Should you choose a robot or cobot? Do you need a machine tool interface? How about conveyors, programmable doors or hydraulic and pneumatic workholding? There’s a whole host of things to think about when automating a CNC lathe or machining centre, but one thing that gets overlooked are grippers, also known as end-of-arm tooling.
It’s an easy thing to overlook, but equipping your robot with the equivalent of a human hand isn’t like bolting on a set of top jaws for a three-jaw chuck. There are adapters to consider, as well as the size and weight of the workpiece, the amount of gripping force needed to securely hold it without causing damage. Have you considered whether to use electric or pneumatic activation, the communication between the robot and gripper…the list goes on. Are you ready?
Checking the boxes
Chris Nandor, key account manager for robotics and automation at Schunk Intec Canada, might start this conversation by asking some basic questions and guiding you through the company website, where more than 2,500 standard gripper options are listed. These include everything from parallel and collaborative to centric, angular and magnetic versions, making it possible to manage darned near anything on darned near any brand and model of robot.
Even with all this variety, however, Nandor will tell you that Schunk does a brisk business in the manufacture of custom gripping units. “Determining the best gripper solution has traditionally been done by the integrator, but here in North America, an increasing number of customers are coming to us for help with end-of-arm tooling selection and design,” he says. “Instead of spending a great deal of time designing individual plates and fingers or trying to figure out what size gripper is needed, they’ll ask us to make those calculations, and even produce a custom solution for them if it’s truly needed.”
In all fairness, robots are called upon to handle everything from safety pins to steamroller wheels, and sorting through a few thousand options is a daunting task. Schunk makes it easier with an online product finder that prompts users to select drive type, stroke length and other variables. But that doesn’t necessarily ensure shops will develop a sound gripper strategy. The result? usually an underperforming gripper, or purchasing more grippers than are needed.
Inertia, mass, etc.
To avoid this, Nandor and others recommend that shops—especially those new to robotics—lean on the experts for support. “Part of my initial conversation with a customer is to understand all of the individual aspects of their process and what parts they’ll be automating,” he says. “It might sound like a strange sales strategy, but my goal is to utilize a customers capital in the best way, and this means Schunk’s strategy is to present what we believe is a complete and calculated solution for the application. Nothing more. Nothing less.”
Adrian Kiss, sales support manager at ABB Inc. in Burlington, Ont., outlines several “gotchas” that the inexperienced specifier wouldn’t think to consider, starting with the gripper’s zero-point. “Just as a CNC machine tool has an X-Y-Z coordinate system, so does end-of-arm tooling,” he says. “We call the point at the centre of the flange where it meets the robot its origin, or ‘tool zero.’ Every robot manufacturer offers values such as mass and distance that must be measured from this origin if you’re to achieve maximum performance and robot life.”
Kiss explains that it’s easy enough to determine these values using the CAD software packages once you’ve imported the end-effector’s solid model. These values should then be entered into the robot software so that it can adjust its maximum speed and acceleration based on the combined mass and dimensions of the gripper and its workpiece. These values should be updated with each new job, otherwise the robot might be moving too fast, stressing its internal components and reducing its lifespan, or not fast enough, which hits cycle time and throughput.
“Robots are a little like automobiles in this respect,” he says. “Forty years ago, carmakers didn’t worry so much about fuel efficiency or vehicle weight and used heavy steel parts and powerful engines. Today, cars are lighter and much more efficient, but if you bump into something, you’re more likely to cause damage. Robotic manufacturing has taken a similar path. Robots are lighter than those of a few decades ago, with higher speeds and acceleration. Because of that, users need to tune each setup accordingly to optimize the robot’s performance,” says Kiss.
Despite these gentle cautions and considerations, robots are clearly the way forward for manufacturers of all sizes. Kiss suggests that robot optimization is much faster and easier than it sounds, and as Schunk’s Nandor points out, a shop’s end-of-arm tooling investment can be kept manageable if a little planning is done early on.
Best of all, this can be true even with multiple brands and styles of robot, adds Yarek Niedbala, vice president of sales at Kuka Robotics Canada. “Many of the robots within a given category have the same flange pattern,” he says. “If not, you might need an adapter plate, but that’s not a big deal.”
You’ll also need to look at the robot’s dress package, also known as an energy supply, he adds. “These are the pneumatic and/or electrical lines running from the base of the robot to the end of the arm. Pneumatic and vacuum grippers will obviously need a different dress package than electric ones, while flexible grippers typically need some kind of data cable that communicates various values such as aperture, speed, and grasp force to the gripper. Whatever the case, it’s all very doable.” SMT