The right robot for the job

For many small and mid-sized companies, these collaborative robots, or cobots as they are often referred to as, have helped bring the entry point for automation within range, allowing them to finally gain some of the competitive advantages of automation that had previously only been achievable for larger manufacturers. And while cobots can’t offer all the benefits of full industrial automation, they can be an effective stepping stone. Or, indeed, a speed bump.

As with any major business decision, even something that appears to be low-risk and low-cost can become expensive when surprises start to stack up. It’s important for manufacturers to understand the pros and cons of different types of automation in order to make the best long-term decision.

First, let’s look at a comparison of cobots and traditional robots:

Cobots are designed for interaction with a human within a defined collaborative workspace. Cobots typically fulfil repetitive or injury-prone tasks such as machine tending or palletising, while the human worker performs higher-value upstream or downstream manual tasks. Cobots mimic human actions and carry out tasks at similar or slower speeds, with payload and reach that are also similar to a human’s.

Industrial robots are automatically controlled, reprogrammable, multipurpose manipulators that are programmable in three or more axes, and that may be fixed in place or mobile. They can automate an extremely broad range of processes. Multiple robots can be integrated for fully automated production lines that remove human operators entirely from unsafe environments and provide significant ROI for high-volume processes. Improvements in safety technologies are now allowing industrial robots to be used in collaborative operations, providing many of the same benefits as a cobot along with an increase in payload and speed and reduction in cost for traditional automation. New programming interfaces are highly intuitive and simple to use, and all movement is calculated internally for the smoothest and most efficient route.

Misconceptions

Now that we’ve defined both types of automation, it’s important to set the record straight on a few key misconceptions about collaborative robots:

1. Cobots are the only collaborative robots. While vendors are eager to claim the term “collaborative robots,” the robots themselves aren’t collaborative; it’s the application that defines the ability for human and machine to collaborate. Almost any robot is capable of collaborative operation with the appropriate safety mechanisms in place. In February 2016, the technical standard ISO/TS 15066 was published to provide safety guidelines for the use of robots in collaborative applications. The standard explains collaborative techniques and provides force guidelines, maximum allowable robot power and speed, and design criteria for robot and robot tool manufacturers.
2. Cobots can always work without safety caging. Every automated application where humans are present requires a risk assessment, and collaborative applications require a range of safety mechanisms to keep human workers safe. Cobot customers are often unhappily surprised to find that their application requires a safety cage. Other applications require force limiters or reduced robot speed, which also limits the robot’s capabilities and output. Still others use sensors, cameras, or light curtains to sense when a human enters the robot’s workspace, with safety software that stops or slows the robot until the human moves safely out of range and restarts the robot. All of these requirements can add cost and reduce output on what was initially intended to be a low-cost, low-risk cobot investment.
3. Cobots operate faster and are more productive than human workers. Because cobots are intended to work safely alongside humans, they are designed to manage processes at the same or slower speeds than human workers, with about the same throughput. Beyond safety, another reason is the programming approach that most cobots use, in which an operator moves the robot arm in human-like motions and enters way points for each stop or action. The programming is simple, but it incorporates every human jiggle and inefficient motion into the program. Where cobots may increase output over manual processes is by running for longer shifts, but because they’re designed to be collaborative, they typically don’t eliminate the need for human workers in those additional shifts.

Injection Molding

Let’s look at a common application for robotics: injection molding machine tending. In this example, a collaborative robot is used much like a human would be to load or unload an injection molding machine in a repetitive process. The robot takes care of the repetitive part of the operation, leaving the operator to handle the complex part of the operation (in automation terms), such as inspection. The robot’s function is humanoid, even to the point of opening machine doors and pressing the same buttons a human operator would, so speeds and payloads are low.

For a manufacturer of low-volume, highly changeable parts, the cobot can be an ideal automation solution, using a small injection molding machine for low production volumes of a few parts per minute. At a reasonably low cost, the manufacturer gains the advantages of highly repeatable processes and consistent output. And at low speeds, a risk assessment is likely to allow for close collaboration with human workers on upstream or downstream processes without expensive safety guarding. ROI is dependent on how much of a human worker’s processes can be taken on by the cobot. It's not uncommon for a cobot to replace the equivalent of half a worker through a couple of workers.

The challenge for the manufacturer is when production volumes increase for a successful product line, requiring a significant increase in speed and accuracy and potentially interaction with other automated processes, or when high rigidity is required, such as with heavier payloads.

For high-volume production, an industrial robot would be integrated into an injection molding line with an emphasis on productivity and cost-efficiency. A medium-sized 6-axis or Cartesian robot unloads the molding machine to a conveyor or single-axis Cartesian, which passes the part onto a SCARA or 6-axis robot to carry out another function such as quality control or assembly. A fully guarded system would allow significantly higher cycle times of up to 120 parts per minute, for an output of more than 63 million parts per year running three mostly unattended shifts. ROI in this case becomes much more defined, even before taking into account safety, work environment, and quality and consistency of the final product.

Speed bumps

For the manufacturer, it may be that the cobot is an ideal first step towards automated processes. If the risk assessment doesn’t require safety guarding, the initial investment is low and employees gain experience and familiarity with robotic systems. But it’s important to look ahead and watch for speed bumps. The approach must take into account the likelihood of the application growing past the cobot’s abilities. If multiple cobots are required, the cost of the equipment (and the additional human workers) will quickly exceed the cost of an industrial robot, and without the additional advantages of speed and unattended production.