A New Conversion Method to Evaluate the Hazard Potential of Collaborative Robots in Free Collisions

Abstract

With the increasing importance of collaborative robots in industrial manufacturing, their economic efficiency is becoming more and more important. Today, one approach to prevent collaborative robots from injuring humans is to assure that the robot cannot exceed biomechanical limits in the event of an accidental collision or clamping. The ability of the robot to avoid collision forces beyond the limits must be validated with a biofidelic measurement device that mimics the biomechanical behavior of the human. For reliable use, the measurement devices must be attached to a rigid frame. Consequently, the test setup is solely able to simulate the contact dynamics and biomechanical consequences of a clamping contact in which the human body part cannot move. Free collisions that allow the human to move freely reduce the collision forces, but can only be evaluated with such a measurement device. This technical limitation leads to slower robots and thus a loss of productivity. The study presents a method that increases the efficiency of safe collaborative robots by adding a new validation procedure. The presented method incorporates a model-based conversion of measurements that enables safety experts to validate robots in free collisions. Data from experimental tests with a collaborative robot and a biofidelic measurement device show a good fit of the model-based prediction and thus confirm our approach. This new approach has great potential to increase the productivity of collaborative robots, since our method will allow them to move at faster but still safe speeds.

Collision Tests in Human-Robot Collaboration: Experiments on the Influence of Additional Impact Parameters on Safety

“…According to [9], a conversion model for converting the measured impact force of a fixed PFMD to a transient force is under development. Such a model is presented in [15], and it calculates the transient impact force as a product of the force measured using a fixed PFMD F f and a conversion term composed of m H and m R . Through the conversion term, the impact force will be lowered, and m H is considered in the transient impact force, which was initially measured using a fixed PFMD.…”

“…Larger robots, such as the GoFa, show stronger deviations of impact forces at few changes in safety settings (Table 9 fixed PFMD F max 40 N versus F max 70 N). As previously mentioned, the model for converting the measured impact force of a fixed device to a transient impact presented in [15] calculates the transient impact force as a product of the force measured using a fixed device F f multiplied by a conversion term composed of m H and m R . As m H and m R do not change in our tests, from the mathematical perspective, the conversion term should be constant and can be represented as a quotient of F m divided by F f .…”

“…Movable devices are not applicable in collision scenarios that work against gravity. For these situations, a conversion model is presented in [15] that estimates the transient impact forces from the values measured using a fixed PFMD .…”

Experimental Safety Analysis of R-Min, an Underactuated Parallel Robot

“…As mentioned in multiple works [14,35], there exists a linear relationship between the maximum impact force and the velocity of the impact point at the time of impact v i (t c ). In what follows, we show that this linear relation is verified for each of the 18 impact scenarios.…”

Modeling the Contact Force in Constrained Human–Robot Collisions

“…Seriani et al [18] show that compliant mechanisms can be beneficial as they reduce a robot's overall stiffness and thus the maximum force in collisions. Most of the models researched focus on the exchange of kinetic energy between the colliding masses and thus are ideally suited to predict the contact force in unconstrained collisions, where the influence of the motion controller and safety functions can be ignored due to the short contact duration [19].…”