Power & Force Limiting Cobots for Dull, Dirty and Dangerous Applications

Collaborative robots, or cobots, is currently one of the most exciting topics in automation. But what do people mean when they say “collaborative robot”? Generally, they are talking about robots which can safely work near and together with humans. The goal of a collaborative robot system is to optimize the use of humans and robots, building on the capabilities of each.

There are four modes of robot collaborative operation defined by the global standard ISO/TS 15066. We discussed these modes in a previous blog, Robot Collaborative Operation.

This post will go more deeply into the most commonly used mode: power & force limiting. Robots in this category include ones made by Universal Robots, as well as FANUC’s green robots and ABB’s Yumi.

What is power & force limiting?

Power & force limiting robots are designed with limited power and force, along with physical features to avoid or reduce injury or damage in case of contact. These robots are generally smaller, slower and less powerful than traditional robots but also more flexible and able to work near or with humans — assuming a risk assessment determines it is safe to do so.

The standards define the creation of a shared or collaborative work space for the robot and human, and define how they may interact in this space. In a power & force limiting application, the robot and operator can be in the shared/collaborative work space at the same time and there may be contact or collision between the operator and the collaborative robot system (which includes the robot, gripper/tool and work piece). Under the proper conditions the features built into the power & force limiting robot allow this close interaction and contact to occur without danger to the operator.

What technologies allow these robots to work closely with humans?

The limiting of the robot’s force can be implemented in several ways. Internal torque/feedback sensors in the joints, external sensors or “skins” and/or elastic joints are some of the methods robot suppliers use to assure low force or low impact. They also design possible contact areas to avoid injury or damage by using rounded edges, padding, large surface areas, etc. to soften contact. Grippers, tools and work pieces also need to be considered and designed to avoid injury or damage to people and equipment.

Peripherally, additional sensors in the robots, grippers, tools, work holders and surrounding work stations are critical parts of high performance robot applications. Connecting these sensors through protocols such as IO-Link and PROFISafe Over IO-Link allows more tightly integrated, better performing, and safer collaborative robot systems.

Where are power & force limiting robots typically applied?

Similar to traditional robots, power & force limiting robots are best applied in applications which are dull, dirty and/or dangerous (the 3 Ds of robotics). They are especially well suited to applications where the danger is ergonomic — repetitive tasks which cause strain on an operator. In many cases, power & force limiting robots are being applied to cooperate closely with people: the robots take on the repetitive tasks, while the humans take on the tasks which require more cognitive skills.

A large number of the customers for power & force limiting robots are small or medium-sized enterprises which can not afford the investment and time to implement a traditional robot, but find that power & force limiting robots fit within their budget and technical capabilities.

What are some of the benefits and drawbacks to power & force limiting robots?

Benefits:

  • Low cost
  • Fast, simple programming and set up; often does not require special knowledge or training
  • Small and lightweight
  • Easy to deploy and redeploy
  • Can be fenceless
  • Low power usage
  • Close human-robot interaction

Drawbacks:

  • Slow
  • Small payload
  • Low force
  • Low precision (not always the case, and improving)

Final Thoughts

Buying a power & force limiting robot does not necessarily mean that fences or other safeguards can be removed; a risk assessment must be completed in order to ensure the application is appropriately safeguarded. The benefits, however, can be significant, especially for smaller firms with limited resources. These firms will find that power & force limiting robots are very good at cost-effectively solving many of their dull, dirty and dangerous applications.

Tom Knauer has more than 25 years of experience in the industrial automation industry, with equipment/solution suppliers including GE Fanuc, Parker Hannifin, Omron STI and Balluff. His roles have included product management, sales, marketing, finance and business strategy; his product experience covers PLCs, CNCs, motion control and safety. Tom's current focus is on developing and growing the Balluff manufacturing & plant engineering and safety businesses in the Americas, working closely with customers, sales, product management and product development. His recent activities include work on current and future safety sensing to support collaborative robots and mobile robots, and device level safety networks combining standard and safety sensors.

Leave a Reply