Robots For Automated Cells

Continuous productivity with multiple automated functions

Robots are ideal for automated cells — spindles are consistently fed, so machine utilization is high, while grouping equipment close together means secondary operations can also be automated, and in-process inventory eliminated. Waste is reduced through early detection of quality problems and less floorspace is needed. Robotic cellular manufacturing is a flexible approach that enables cost-effective automated production of low- and medium-volume product families.

Automated cells can take many forms, with one or more robots performing the handling duties that make everything work together smoothly. Sheet metal bending, stamping, part machining, material removal and polishing are just some of the processes that can be arranged as cells, automated with a robot. For example, in a machining business a robot equipped with a double gripper end-effector could lift a casting from an input conveyor, unload the previous part from a lathe, and chuck the next. While the lathe turns the new casting, the robot might take the machined part to a drill, and then to a wash station. Some automated cells even include inspection before placing the part in a bin or on an outfeed conveyor. Machine utilization is maximized because the robot repeats each cycle with complete consistency and without taking breaks.

Robotic cellular manufacturing cuts costs, improves quality and increases capacity, but none of that happens without careful planning. The keys to success are first recognizing the challenges and then developing a plan that meets project goals.

Automated cells differ from conventional cellular manufacturing in two main ways:

  • Equipment layout must suit the automation employed
  • Robot end-effectors must be appropriate for the product or products being produced

Addressing Layout Challenges

When considering automation, robots have strengths and limitations. They are accurate, fast and repeatable, but have restricted reach and payload. Larger robots are always available but need more floorspace. Likewise, robots can be rail-mounted to move between machines, but this takes space and can require a more linear machine layout.

Layout factors to consider for robotic cellular manufacturing include:

  • Requirement for human workers in the cell
  • Machine spacing
  • Target takt time
  • Regripping/re-orientation
  • Robot reach and payload

Human Workers

If people are to work alongside robots (perhaps because some tasks need additional dexterity and/or decision-making), a collaborative robot (cobot) approach may make most sense. Alternatively, if the cell will be operated manually at times and robotically at others, it’s essential to leave open access to machines and workstations.

In hybrid automated cells such as these, consider mounting robots overhead. This keeps the floor open for human workers.

Machine Spacing

Some machine builders provide top access for robots to reach in. Such design facilitates close machine spacing, unless human loading will also be needed. Human-operated cells often work better with a U-shaped layout, so take this into account.

Takt Time

A common goal for cellular manufacturing is one-piece flow. Matching processing times to average demand produces the target cell takt time. Actual processing times at individual operations could be significantly shorter, so consider the need for intermediate storage and the impact on robot sequence timing.

Regripping/Re-Orientation

In automation, robots often need to put a part down and regrip. Consider where such stations will be placed within the cell, especially if it will be human-operated on occasion.

Robot Reach and Payload

Reaching into machines for unloading/loading may require complex arm positioning. As a result, the maximum reach needed may be greater than it appears. Consider also that longer reach robots are larger and heavier, and that reach affects payload.

End-Effectors

The gripper, end-effector or end-of-arm-tooling (EOAT) is part of the robot payload and must be considered as such. End-effectors take many forms and should be appropriate to the product characteristics. In particular, consider how inertial forces will change the effective payload and the potential for a part to come free.

The three main classes of end-effectors are:

  • Impactive
  • Ingressive
  • Astrictive

(A fourth class — contigutive — uses forms of adhesion such as freezing. These are seldom seen in manufacturing.)

Impactive grippers are jaws or claws. Depending on the part being gripped, these can be of two-jaw or three-jaw design and may have parallel or angular movement.

Ingressive grippers push pins or needles into the workpiece. These are often used with textiles and carbon fiber.

Astrictive grippers use suction. This is usually magnetic or vacuum and is widely used for handling flat sheets.

Seek Expert Input

With thought and planning, robotic cellular manufacturing lowers expenses and increases profits. Specialists at Acieta can advise on the best approaches to layout and end-effector selection.

To discuss known automation opportunities or discover new ones:

DISPELLING ROBOTIC MYTHS

Myth:
Automation is for high production jobs.
Truth:
Robots are NOT just for high production any more. Changeovers and small lots become minor concerns when considering that machine efficiency increases by 30% or greater with robotics. Like a CNC machine tool, robots can quickly change over from job to job by utilizing increased program storage, auto gripper changers and vision. The changeover should be the same or less time than changing over one of the CNC machines.