preface:Shanghai Lujia Automation Technology Co., LtdAs traditional industrial robots gradually replace monotonous, repetitive, and hazardous work,Research and development transformationintelligenceCollaborative robotsworkstationIt will also gradually penetrate into various industrial fields and work together with people.

1. Collaboration partner

Due to the inability of current robots to complete tasks independently, it is necessary to install appropriate end tools and add necessary external auxiliary facilities to form a robot workstation for normal operation. Therefore, when we talk about collaboration, we are not referring to robots（Robot）Collaboration with humans, but rather robot systems（Robot System）Collaboration between individuals.

Robot system（The concept of Robot System includes:

Industrial robots（Industrial Robot）；

end effector/Tool (End effector (s));

Other sensors, devices, mechanical facilities, and external axes used to support robots in completing tasks.

In any specification related to robot safety, for risk assessment（The description of the Risk Assessment stage, which targets robot systems, requiresCollaborative robotsSpeaking of which, it's the same. For example, if a sharp knife is installed at the end of a collaborative robot for cutting, although the robot is relatively safe, the tools used are very dangerous, making it difficult for a robot system to meet the requirements of human-machine collaboration.

The majority of the safety assessment work for the entire robot system should be carried out by integrators.

It should be emphasized that collaborative robots are not unconditionally safe, and a risk assessment must be conducted before use to determine appropriate protective measuresTaking UR (Universal Robot) as an example, after conducting a compliant risk assessment, only about 80% of cases do not require the use of additional safety measures:

Around 80% of the 6 axis UR robots worldwide operate with no safety guarding after initial risk assessment.

2. Collaboration mode

When we mention human-machine collaboration, the first thing that comes to mind isUR, LBR iiwa, and Sawyer are lightweight robots with slim figures and modern shapes, but in reality, human-machine collaboration is not exclusive to collaborative robots. Traditional robots can also perform collaborative tasks.

Four human-machine collaboration methods have been proposed in descending order of collaboration level（Methods）， namely:

Safety-rated monitored stop(Security level monitoring stopped)

Hand guiding(Manual guidance)

Speed and separation monitoring(Speed and distance monitoring)

Power and force limiting(Power and Force Limitations)

Traditional robots equipped with appropriate safety controllers/Under the security option, collaboration functions of 1-3 can be achieved. For the fourth type, it is generally difficult to achieve.

Safety-rated monitored stop(Security level monitoring stopped)

This is the basic collaboration method, which means that when personnel enter the collaboration area, the robot stops moving and ensures a safe rest, so that the operator can perform certain operations (such as installing workpieces to be processed on the robot, replacing tools used by the robot, etc.); When personnel leave the collaborative area, the robot can automatically resume normal operation（Non-Collaboratively）， See the following figure:

It may seem complicated, but in reality, you only need to pay attention to the two red areas in the above picture, that is When both the operator and the robot are in the collaborative area, the robot must remain stationary.

Hand guiding(Manual guidance)

Manual guidance is a slightly more advanced collaboration method, similar to the current drag and drop teaching. In manual guidance mode, the operator operates through a manually operated device（Hand operated devices transmit motion commands to the robot system. Before the operator is allowed to enter the collaborative area and perform manual guidance tasks, the robot should have been in a safety level monitoring stop state. The operator controls the robot to complete tasks by manually manipulating the guidance device installed at or near the end effector of the robot.

The manual guided operation process is as follows:

The robot enters the collaborative area and triggers a safety level monitoring stop, preparing for manual guidance——Afterwards, the operator is allowed to enter the collaborative area;

When the operator starts using the manual guidance device to control the robot, the safety monitoring stops contact and the operator begins to guide the robot to work;

When the operator releases the manual guidance device, the safety monitoring should be triggered to stop;

When the operator leaves the collaborative area, the robot system can revert back to non collaborative mode.

If the operator enters the collaborative area and the robot system is not ready for manual guidance, a protective stop should be triggered（Protective Stop）。

Speed and separation monitoring(Speed and distance monitoring)

In this mode, both robots and personnel are allowed to appear in the collaborative area, but a safe distance must be maintained between the robots and personnel. When the distance between the two is less than the safe distance, the robot immediately stops. After personnel leave, the robot can automatically resume operation, but still needs to maintain a safe distance. If the robot reduces its movement speed, the safety protection distance can also be correspondingly reduced.

Speed and distance monitoring are applicable to personnel within the collaborative area. If the performance of protective measures is limited by the number of people in the collaborative space, the allowable maximum number of people should be specified in the instructions for use. When the number is exceeded, the protection should be triggered to stop（Protective Stop）。

When the distance between a dangerous component in the robot system and any person is less than the safe distance, the robot system should:

Trigger protection stop;

Trigger safety level functions connected to the robot system (such as shutting down tools that may cause danger);

The methods that robots can use to reduce the risk of violating safety distances include but are not limited to:

Reduce speed and may switch to a safe monitoring stop state;

Choose a path that does not violate the safe distance and continue to move while keeping the speed and distance monitoring functions activated;

When the actual distance reaches or exceeds the safe distance, the robot can return to its normal motion state.

The implementation of this collaborative approach relies on external sensing or detection methods and is limited by cost/The performance limitations are not very common in practical applications.

Power and force limiting(Power and Force Limitations)

（Iiwa can detect collisions or squeezes on the periphery and will not cause harm to the human body due to accidental human intervention during assembly

In the experiment, those with collision detection functionKUKA iiwa， After installing a dagger at the end, it can be safely stopped without causing injury

The three collaboration methods mentioned above are more like passive means in a sense (although strictly speaking, they are not passive), and what truly enables collaborative robots to achieve rapid development is the fourth, more essential, advanced, and safer collaboration function, Restricting the abilities and forces that the robot itself can output to prevent injury events from occurring at the root.

In addition, the above three methods do not allow direct contact between humans and robots（Physical Contact）， In this mode, intentional or unintentional physical contact between the robot system (including workpieces) and the human body is allowed.

In this mode, the possible situations of contact between the operator and the robot system are as follows:

Planned contact is part of the entire application.

Unexpected contact situations may be caused by failure to follow operating procedures, but there is no technical malfunction（technical failure）。

Mode failure leads to contact.

The possible contact between moving robot components and different areas of the human body can be divided into two types:

Quasi-static contact（Quasi-Static Contact）：This situation generally refers to the human body being sandwiched between robots and other components. At this point, the robot system will apply a continuous force to the clamped human body until the state is released.

Transient contact（Transient Contact）：Also known as dynamic impact（Dynamic Impact）， Refers to a situation where the human body is impacted by the moving parts of a robot system, and the human body is not caught or trapped by the robot system, resulting in a short-term actual contact; Transient contact depends on the combination of robot inertia, human inertia, and the relative velocity between the two.

(The former can be seen as transient contact in the above figure, while the latter can be seen as quasi-static contact)

Restricting the power and force output of robots can ensure safe work for humans near the machines without reducing their efficiency or increasing application costs. This is an important function that mainstream collaborative robots should possess.