A collaborative robot is essentially an industrial robot with additional safety capabilities. These safety features include:
- Safety-rated monitored stop (zero speed limiting)
- Speed and separation monitoring (limiting)
- Power and force limiting (PFL)
The collaborative features listed above are meant to make it easier to interact with or use the robot by allowing for alternate safety solutions to help protect the operator instead of using the time-tested, but restrictive method of hard guarding. An example would be a large palletizing robot system utilizing ESPE (Electro Sensitive Protective Devices), in conjunction with speed and separation monitoring to reduce the robot speed when an operator presence is detected, and to limit the robot range of motion (in lieu of hard guarding around the robot). Another example would be a machine load/unload application where an industrial robot is using the safety-rated monitored stop feature to allow an operator to interact with the robot in the collaborative workspace. The PFL feature allows an operator to work alongside a moving robot with reduced risk of injury in the case of an operator-robot collision. This is done by limiting the power or force transmitted to the operator during either a transient (dynamic) event or in a quasi-static (clamping/crushing) situation.
Major industrial robot brands have supported items one and two of the above capabilities for over a decade. Hand-guiding has also been implemented on industrial robots as an application- level add-on. Power and force limiting have not been supported until recently on industrial robots. From the customer perspective, a collaborative robot can limit its power and force, thereby limiting the injury it can cause an operator who is working in close proximity to the robot.
Additionally, customers perceive these robots to be smaller, slower, lighter, and easier to use (all factors geared toward easy and safe operator interaction). The PFL feature is the one that is actually being used to target new applications that involve the use of robots in unstructured environments driven by flexible plant layouts and frequent human intervention. This intervention may be continuous where a human works alongside the robot, or intermittent where a human may intervene in the robot workspace to recover from errors or take over some tasks, or as a result of operator error.
Human assist is an application area where customers can augment a robot’s precision and load-carrying capacity with human judgement. The handguiding feature of a collaborative robot will be utilized for such applications. Hand-guiding will also be useful in easy recovery from fault conditions as opposed to what’s common today, where a well-trained operator has to jog a robot in three-dimensional space from its faulted position to a safe position using a teach pendant.
In practice, a collaborative robot is only different from a traditional industrial robot because it is power- and force-limiting. For example, these robots are not necessarily any smarter in terms of dealing with unstructured environments or recovering from faults that may occur during complex assembly processes. However, customers do expect collaborative robots to have easy-to-use interfaces that are suited for applications that involve frequent operator interaction, and for a workforce that is not familiar with industrial robots. As such, the intelligent aspects of these robots are mostly in their operator interface, which makes complex robot programming easily accessible to a minimally trained operator. This ease of use allows customers to self-deploy these robots and reprogram them with ease. This reduces overall cost, thereby justifying the return on investment for a low-volume robot user.
There are still significant safety concerns when robots and humans work side-by-side, and these concerns involve the overall system/solution and not just the robot arm. To date, highly trained engineers who are exploring automation possibilities have been the ones who have mostly deployed collaborative robots. Some of these deployments have involved overall solution-risk assessment. As these robots proliferate, their deployment will move from the first adopters to more process-driven plant personnel. As this happens, the safety standards will increasingly require systematic risk assessment before a solution is deployed.