How does speed physically interact with time?

Human-robot collaboration: This is how humans and machines work together safely

There are basically four different protection principles for human-robot collaboration (HRC) [2].

1. Hand guidance: The robot movement is actively controlled by the employee with suitable equipment.

Comprehensive analyzes of the current situation and the use of innovative technologies for planning and developing new HRC systems in production meet the requirements for quality, ergonomics, product and personal safety. For example, a robot may only move at a monitored speed in accordance with performance level d (PL d). The risk assessment determines the maximum speed in advance. This operating mode is suitable when humans and robots share a workspace, work at the same time and there is physical contact between humans and robots, the so-called collaboration.

2. Speed ​​and distance monitoring: Contact between employees and a moving robot is prevented by the robot.

Direct contact between humans and robots cannot always be prevented and is sometimes even necessary. Tactile sensors that are applied to the robot like an artificial skin [3] can reliably detect contact and stop the robot's movements. The speed of the robot must be reduced as soon as a person approaches. If the minimum distance between the robot and an approaching person is not reached, the robot must stop safely.

3. Safety-related, monitored standstill: The robot stops when the employee enters the shared work area and continues when the employee has left the shared work area.

The latest technologies remove the separation between humans and robots by monitoring the work areas with optical sensor systems, calculating dynamic protection zones and also adapting the speed and direction of movement of the robot depending on the situation. Another technology recognizes the approach of humans to the robot in the close range (capacitive sensors). When people enter the collaboration room, the robot must stop safely. A speed reduction followed by a Category 2 stop with safe monitoring is also possible. This operating mode is suitable for the coexistence of humans and robots. There is no need for a protective fence, but humans and robots do not share a workspace. In addition, this operating mode can also be used for sequential cooperation between humans and robots, in which humans and robots share a workspace, but do not work there at the same time.

4. Power and force limitation: The contact forces between employees and robots are technically limited to a safe level.

The risk of injury when a person collides with a robot depends on many factors, such as force, pressure distribution, body region, collision area, robot speed and robot mass as well as its overtravel. HRCs are light, usually 1 to 30 kilograms, so that the potential collision mass is small, and have soft curves to avoid collision damage [4]. The speed should not be faster than human movements. The maximum speed of the wrist is, for example, around 1.5 meters per second with a load of around 0.5 kilograms). The speed of movement is thus significantly lower than that of robots that work in isolation from humans. Tasks that require torques greater than 15 nanometers (safety value) are only suitable to a limited extent for the HRC because the robot may not be able to reliably differentiate between collision-related and work-related torque [5]. In this operating mode, it is important to ensure a sensory, mechanical and / or electronic limitation of force or pressure in the event of a collision between humans and robots. The force atlas from ISO / TS 15066 [6] and DIN EN ISO 10218-2 should be used. The limit values ​​are determined according to the risk assessment and user information.

These four basic protection principles of the HRC are explained in more detail in the standards DIN EN ISO 10218 "Industrial Robots - Safety Requirements" Part 1 [7] and Part 2 [8].