Bjoern Matthias

Safety of collaborative industrial robots: Certification possibilities for a collaborative assembly robot concept

Industrial requirements for automation of small parts assembly operations are driving technology into the direction of scalable robotic automation, suitable for operation in shared environments with human workers and exhibiting highest flexibility and ease of use. One of the challenges is developing solutions for personnel safety under these conditions. This paper discusses both the presently viable approaches to risk assessment for collaborative robots and a more detailed future methodology that will be better able to resolve the relevant low-level injury risks.

Optimized task distribution for industrial assembly in mixed human-robot environments - Case study on IO module assembly

Introduction of robots into manual assembly lines to assist human workers or introduction of human into robot-based manufacturing attracts more and more attention in academy and industry. This interest stems from the insight that the integration of robots into manual assembly lines or vice versa may increase productivity by combining the abilities of machines with those of humans. To uphold productivity while respecting safety constraints is the target, and one of the challenges is how to productively distribute tasks among workers and robots. We studied one small-part assembly scenario, namely the assembly of a PLC Input/Output module by an ABB Dual Arm Concept Robot and a human worker. A method is proposed in this paper to optimize the operation/task assignment in the collaborative environment. An exemplary calculation shows that the cycle time can be shortened to increase the productivity. Finally, we show that the developed method can also be generalized and applied to different scenarios in mixed environments.

Structured collaborative behavior of industrial robots in mixed human-robot environments

In mixed human-robot environments safety and productivity are two important factors for the design of robotic collaborative behaviors. The collaborative behavior should be able to uphold productivity as far as possible while respecting safety constraints for varying collaboration modes and evaluation criteria. In this paper, a concept of using a finite state automaton for structuring the collaborative behavior of industrial robots is proposed to systematically handle the following exceptions. Safety and productivity (S&P) exceptions which either interfere with productivity or compromise workers safety are caught by the corresponding exception reaction. The regular production operation after an exception reaction is restored with exception recovery strategies. The state automaton model for an industrial assembly scenario is finally presented to illustrate this concept. A demonstration realizing the example for interaction between an ABB Dual-Arm Concept Robot and a human is discussed.

Collaborative behavior design of industrial robots for multiple human-robot collaboration

Industrial robots are being introduced to assist human workers in performing assembly tasks such as small-parts assembly. A mixed environment is the best choice for certain assembly operations, of which some are better executed by robots and others are better handled by human workers. However, it is a challenge to design the collaborative behavior of robots to maximize productivity respecting to safety constraints while interacting with human workers. This becomes more complex for multiple human-robot collaboration. An approach has been proposed for structuring the collaborative behavior using finite state automata (FSA). In this paper, the approach is extended to deal with multiple human-robot collaboration, by applying the composition rules of FSA. The approach is finally demonstrated in an ABB Dual-Arm Concept Robot working with multiple human workers in an industrial assembly scenario.

Contact force estimation for robotic assembly using motor torques

For tasks in robotic assembly, a basic requirement is the capability of the robotic system to detect contacts with the environment. While this information can readily be obtained from dedicated force-torque sensors, it might either be technically difficult to mount such sensors or too expensive to do so. In this paper, an alternative approach is presented which reconstructs the external forces and torques based on signals that can be obtained without a force sensor, namely motor currents/torques and joint angles. After an automatic offline calibration of the algorithm, the method allows for a lean online implementation. Apart from the theoretical development of the method, its applicability to contact force estimation is demonstrated by measurement results obtained from an ABB Dual-Arm Concept Robot.

Combined pose-wrench and state machine representation for modeling Robotic Assembly Skills

A new Robotic Assembly Skill (RAS) modeling framework is proposed. An assembly skill is a primitive that encapsulates the capabilities to coordinate, control and supervise an elementary robot task. To gain reusability of a primitive in alike robot tasks, the primitives are represented as generic templates that are parametrized for each situation with data from an assembly specification. A skill is represented in two ways, namely as a trajectory describing compliant motions in pose-wrench space and as a finite state machine. This approach comes with the potential to simplify robot programming and to improve robustness in robotic assembly due to inherent quality checking. The approach is implemented on an ABB YuMi robot performing the assembly of a programmable logic controller (PLC) I/O module.

A design metric for safety assessment of industrial robot design suitable for power- and force-limited collaborative operation

This research presents a novel design metric based on maximum power flux density for the assessment of the severity of a transient physical contact between a robot manipulator and a human body region. Such incidental transient contact can occur in the course of a collaborative application of the power- and force-limiting type. The proposed metric is intended for the design and development of the robot manipulator as well as for the design of manufacturing applications. Such safety metric can also aid in controlling the robot’s speeds during manufacturing operations by carrying out rapid risk assessments of impending collisions that could arise due to the proximity to the human co-worker. Furthermore, this study contributes by expressing the physical impact between the robot and the human body region as a linear spring-damper model. The influence of the restitution coefficient and the elasticity of the human tissues on the contact duration and contact area during the collision is analysed. With the demonstrated analysis model, the dependence of the power flux density with respect to the robot’s effective mass, speed, and geometrical and damping coefficients during the human-industrial robot manipulator collision process is investigated.