The type of robot most appropriate for a given pick-and-place application depends on the speed required, the size of the payload and other factors. For most applications, only one type of robot will be appropriate. But there are many borderline applications where more than one type could be used, and the end user (or his/her system integrator) must prioritize the factors.
One of the most significant developments in pick-and-place robotics has been improvements in servo motor design. Today’s servo motors pack more power into smaller sizes, maintaining or increasing output and payload capacity.
Another development is refinements to motion control software and hardware. Motion control is the essence of robotics. It’s needed to find objects, to guide the robot arm in picking them up and releasing them, and to coordinate with equipment upstream and down.
In the past, operating a robot would have required integration between the robot’s motion controller and the programmable logic controllers (PLCs) that coordinate the robot’s actions with the rest of the line. But the trend has been to combine those functions, as much as possible, into common controllers. This eliminates software coding that would otherwise have been required to coordinate the separate controllers.
Several kinds of robots can be used for upstream pick-and-place:
• Delta-style robots that operate from overhead with three or four long, thin arms that meet at the effector head;
• SCARA (selective compliant articulated robot arm) models, which are fixed-base robots with three vertical-axis (horizontal-motion) rotary arms; and
• Multi-axis articulated robots, which can have up to six axes, with joints that can rotate in any direction.
Choosing among these three kinds of robots depends largely on speed and payload size. (The payload includes the weight of both the product or package and the end-of-arm tooling needed to grip it.) Generally speaking, delta-style robots go twice as fast as SCARA robots, which in turn go twice as fast as six-axis articulated robots. Conversely, six-axis robots can handle the heaviest payloads, followed by SCARA robots and delta-style models.
As with most aspects of packaging, end users want pick-and-place to run as fast as possible. But some applications have practical limitations. Fragile products like baked goods have to be handled gently, which means slowing down.
Other applications have complex pattern requirements. When objects are being deposited in single layers at a time, especially when they’re relatively light, a delta robot arm can work fast. But in case packing or other applications that require extra precision, delta robots may not have the versatility to put the primary packages where they need to go. Articulated robots can work better in such applications, because they can rotate what they’re holding and also because they can pick up entire layers of primary packages and drop them into cases.
Pick-and-place applications are fertile ground for robotic equipment. As technology and other developments make such equipment increasingly viable, end users who pick the right machines will find themselves in a good place. F&BP