Collaborative robots , i.e. robots designed for direct interaction with a human, present a promising step in robotic manufacturing. However, their performance is limited by the safety demands of standards . In this article , we measure the forces exerted by two robot arms (UR10e and Kuka LBR iiwa) on an impact measuring device in different positions in the robot workspace andwith various velocities. Based on these measurements, we investigate the Power and Force Limiting regime presented in ISO/TS 15066. Impact forces are in practice hard to calculate analytically as many properties of the robots are not available (e.g., proprietary control algorithms). This motivates the use of simple, yet reasonably accurate, approximations. Our results show that height of the impact location is also an important factor and that an accurate model of the robot can be created from a limited number of impact samples. Previous work predicted impact forces based on other factors (distance, velocity, weight), yet these predictions are less accurate. This would allow a fast estimation of the impact forcesin the robot's workspace and thus make it easier to design a safe human-robot collaboration setup .
The need to guarantee the safety of collaborative robots limits their performance, in particular, their speed and hence cycle time . In this work , we measure the forces exerted by two collaborative manipulators (UR10e and KUKA LBR iiwa) on an impact measuring device . Our contributions are the following: (i) a new data-driven model predicting impact forces from velocity, distance from robot base, and, newly, the height in the workspace; (ii) demonstration that the model can be trained on a limited number of data points; (iii) analysis of the force evolution upon impact. The standard ISO/TS 15066 defines the Power and Force Limiting operation mode and prescribes force thresholds that a moving robot is allowed to exert on human body parts during impact (for the back of the hand, 280 N for transient and 140 N for quasi-static contact), along with a simple formula to obtain maximum allowed speed of the robot in the whole workspace. Applying this to our scenario where the impact has a clamping nature, the allowed end effector speed on the whole robot workspace would be only 0.13 and 0.16 m/s for the UR10e and KUKA LBR iiwa, respectively. Our measurements reveal that if the task is performed for example 0.8 m away and 0.4 m above the robot base, speeds of 0.16 m/s (UR10e) and 0.20 m/s (KUKA LBR iiwa) can be safely operated, staying within the prescribed force limit. Furthermore, the force evolution during impact for the UR10e reveals that clamping never occurs. With the 280 N limit, 0.36 m/s will still be safe with the UR10e. The formulas relating robot mass, velocity, and impact forces from ISO/TS 15066 are insufficient---leading both to significant underestimation and overestimation of velocities/forces, and thus to unnecessarily long cycle times or even dangerous applications .
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Collaborative robots , i.e. robots designed for direct interaction with a human, present a promising step in robotic manufacturing. However, their performance is limited by the safety demands of standards
The need to guarantee the safety of collaborative robots limits their performance, in particular, their speed and hence cycle time
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article
work
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robot arms
collaborative manipulators
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Kuka
KUKA
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in different positions in the robot workspace andwith various velocities. Based on these measurements, we investigate the Power and Force Limiting regime presented in
. Our contributions are the following: (i) a new data-driven model predicting impact forces from velocity, distance from robot base, and, newly, the height in the workspace; (ii) demonstration that the model can be trained on a limited number of data points; (iii) analysis of the force evolution upon impact. The standard
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15066. Impact forces are in practice hard to calculate analytically as many properties of the robots are not available (e.g., proprietary control algorithms). This motivates the use of simple, yet reasonably accurate, approximations. Our results show that height of the impact location is also an important factor and that an accurate model of the robot can be created from a limited number of impact samples. Previous work predicted impact forces based on other factors (distance, velocity, weight), yet these predictions are less accurate. This would allow a fast estimation of the impact forcesin the robot's workspace and thus make it easier to design a safe human-robot collaboration setup
15066 defines the Power and Force Limiting operation mode and prescribes force thresholds that a moving robot is allowed to exert on human body parts during impact (for the back of the hand, 280 N for transient and 140 N for quasi-static contact), along with a simple formula to obtain maximum allowed speed of the robot in the whole workspace. Applying this to our scenario where the impact has a clamping nature, the allowed end effector speed on the whole robot workspace would be only 0.13 and 0.16 m/s for the UR10e and KUKA LBR iiwa, respectively. Our measurements reveal that if the task is performed for example 0.8 m away and 0.4 m above the robot base, speeds of 0.16 m/s (UR10e) and 0.20 m/s (KUKA LBR iiwa) can be safely operated, staying within the prescribed force limit. Furthermore, the force evolution during impact for the UR10e reveals that clamping never occurs. With the 280 N limit, 0.36 m/s will still be safe with the UR10e. The formulas relating robot mass, velocity, and impact forces from ISO/TS 15066 are insufficient---leading both to significant underestimation and overestimation of velocities/forces, and thus to unnecessarily long cycle times or even dangerous applications