Collaborative robots are becoming vital for different industries as they boost safety and productivity. As these units share the same workspace with humans, new techniques are needed to maintain safety while increasing productivity. Read on to understand design guidelines for the collaborative robot system.
The core collaborative robot design principles can be outlined as the ability to achieve:
- Secure interaction with fragile assembly equipment and human workers.
- Robotic tasks at a compatible rate with human potential
- Fast and straightforward programming by non-technical workers to manage high-rate production
- Light and compact form factors
- Clean and noise-free operations
- Fewer costs to validate the continued use of robotic labor functions
Design Guidelines for the Collaborative Robot System
The core factor that robotic manufacturers should understand is that the unit shares the same workspace with humans. A designer should ensure the cobot can recognize unpredictable movements and react safely to prevent injuries without compromising its efficiency.
Further, the designer should also bar the robot from applying excess force if contact occurs between humans. That process can make the design process complex. Remember, while safety systems in an industrial robot are not inbuilt. However, collaborative robots come with inbuilt safety systems integrated into their structure. The robot systems control it.
Guidance on possible design challenges is available in international collaborative robot safety standards. These standards have been created with the rapid adoption of robots in the production line. For example, the ISO (International Organization for Standardization) offers guidelines for a TS (technical specifications) and drafting collaborative robots in its 10218 document.
The TS/ISP 15066 specializes in collaborative robot safety while highlighting the importance of a safety-based control system principle in regulating process specifications like force and speed. Worth mentioning is that TS/ISO 15066 depicts a voluntary document but is not a standard. However, it could form a standard foundation in the future.
- General Collaborative Robot Information
TS/ISO 15066 also offers general collaborative robot data that designers can leverage. Such data highlights the importance of conducting a risk assessment for possible dangers in the workspace.
For instance, no robot can be deemed safe if it continues operating at high speed in the presence of an object. Again, the workspace could pose a risk if it contains fixed items that can hinder ample operations between the robot and human workers. The core sections of the TS/ISO 15066 discuss the design of a cobot’s processes, the workspace, and the changeover between a robot’s non-collaborative and collaborative operations.
The document offers comprehensive details to facilitate the implementation of the collaborative operation factors below that create efficient and safe solutions that meet the design goals discussed above.
Safety-Ranked Monitored Stop
A safety-ranked monitored stop is a guaranteed robot stop that occurs automatically when the unit detects human presence in a collaborative workspace. The system ensures that humans and robots don’t move concurrently. It is usually used when the machine moves heavy loads rapidly across the workspace.
Separation and Speed Monitoring
This is among the most relevant collaborative work strategies. It allows the robot and a human operator to move within the same working environment simultaneously by installing sensors in the robot to check how close to the unit the human is. The unit can continue working when there is a big gap between it and humans. However, it does so at a moderate speed and activates the safety ranked monitored stop when the worker is very close.
Before a hand-guided application can begin, a robot must execute a safety-ranked monitored stop. During the operation, humans contact the robot arm directly and can move it using hand controls. This application is used in highly variable tool applications and lift assists.
Force and Power Limiting
Force and power limiting are needed in applications where there might be unintentional or intentional contact between a human and a collaborative robot when both are running in the same collaborative workspace. Contact can be transient or quasi-static. The former involves hitting part of the human’s body where they can retract. The latter consists in gripping a part of a human’s body between a fixed item and a cobot’s manipulator.
Design Safety Challenges
By making modifications to restrict complexity, size, and cost, collaborative robot designers can use existing robotic technology in some systems and still apply the work strategies discussed above. For instance, the safety ranked monitored stop is an endorsed technology for industrial robots that leverages safety barriers to perform an emergency stop if humans get in the working space.
Separation and speed monitoring require new engineering approaches because industrial robots are made to stop immediately humans get into the work area. On the contrary, collaborative robots continue moving even with humans in the same working space but at a reduced speed when humans enter the working area.
The secret to constituting such systems lies in incorporating sensors in the robot’s control systems. The close-loop assessment facilitates rapid motor response to activate speed reduction. Force and power limiting can be the most complex challenge. Designers can learn from industrial robot design because it emphasizes speed and load capacity.
- Continued Research
Research on injury and pain thresholds is still ongoing. However, the existing guidelines recommend reducing clamping dangers by ensuring the robot speed remains 250mm/s, and its force is less than 150N during separation and speed monitoring applications. Transient forces can be twice those specifications but should not be applied for over 500ms.
Additional instructions in the ISO document include:
- Removing crush and pinch points from the robot
- Lowering robot speed once it approached a fixed object allowing it to stop quickly
- Lowering robot mass and inertia
Collaborative robots boost productivity in various workspaces by merging human dexterity with robot power and analytical skills. Designing collaborative robots is an evolving field meaning there is insufficient guidance to rely on. International safety principles for robots are being established.
Suppliers are lining up sensors and electronics with progressive mechanical assemblies to develop new integral components like unique joints that cater to particular demands that collaborative robots have to deal with during daily operations, duties, and interactions.
A new design structure will come in handy to ensure that cobots are safe around workers while maintaining load-handling, precision, and speed benefits.
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