Assembly Robotic Cell Research Articles

On-line collision avoidance for collaborative robot manipulators by adjusting off-line generated paths: An industrial use case

Human–robot collision avoidance is a key in collaborative robotics and in the framework of Industry 4.0. It plays an important role for achieving safety criteria while having humans and machines working side-by-side in unstructured and time-varying environment. This study introduces the subject of manipulator’s on-line collision avoidance into a real industrial application implementing typical sensors and a commonly used collaborative industrial manipulator, KUKA iiwa. In the proposed methodology, the human co-worker and the robot are represented by geometric primitives (capsules). The minimum distance and relative velocity between them is calculated, when human/obstacles are nearby the concept of hypothetical repulsion and attraction vectors is used. By coupling this concept with a mathematical representation of robot’s kinematics, a task level control with collision avoidance capability is achieved. Consequently, the off-line generated nominal path of the industrial task is modified on-the-fly so the robot is able to avoid collision with the co-worker safely while being able to fulfill the industrial operation. To guarantee motion continuity when switching between different tasks, the notion of repulsion-vector-reshaping is introduced. Tests on an assembly robotic cell in automotive industry show that the robot moves smoothly and avoids collisions successfully by adjusting the off-line generated nominal paths.

Development and Applications of the SCARA Robot

In the 1980s, when the author worked for Seiko Epson Corporation as a wristwatch production engineer, consumer needs had become so diversified that wristwatches had to be assembled on the same automated assembly line in small lots of about 10,000 pieces per month. Most of the robots available in those days were for processing purposes such as spot welding and were not applicable in practical terms to automated assembly lines for wristwatches in precision, speed, ease of use or cost. The prototype SCARA robot developed by the SCARA Study Group led by Dr. Hiroshi Makino, a professor at the Department of Precision Engineering at Yamanashi University, was found to be the most suitable for automated watch assembly lines. We reviewed assembly work procedures and succeeded in limiting the number of simultaneous control axes to four at a maximum and in cutting assembly costs to 60% of those of conventional processing robots. As the term “selective compliance” suggests, SCARA robots possess all of the functions necessary for stable assembly and for precision and speed. Development team members, including the author, made the most use of previous experience in developing dedicated automated assembly machines for in-house use and succeeded in developing practical SCARA robots by creating a robot language based on workers’ voice. In applications of SCARA robots, this paper introduces just two of many possible examples. One is for oiling work on manual assembly lines and the other is the TAF-M mixed-models wristwatch assembly line. In the oiling work application example, SCARA robots used for infinitesimal oiling work on a manual assembly line for small lots of luxury wristwatches have been found to be very cost-effective and useful for training operators and/or programmers for robots. The TAFM application example represents the assembly line built based on the original Seiko-Epson purpose for introducing SCARA robot development, which consists of both robots and of 52 newly developed “assembly robot cells” where most assembly work should be done. An assembly robot cell includes a SCARA robot, a main conveyor, a multiple-parts feeder, an automatic hand changer, an assembly detection unit, etc. At present, one such assembly line automatically assembles more than 100 models of wristwatches. Use of such automated assembly lines has reduced the human workforce by about 40 workers, cut costs by over 60%, and shortened delivery time by about 50%.

A cooperative multi-agent system for an assembly robotic cell

A multi-agent system architecture is justified here and described for the sake of its application to an assembly robotics testbed. A blackboard-based agent using a GBB/DBB facility for intra (and not inter) agent communication is presented as well as its main functionality. Cooperation between organizers and respondent agents may lead to the use of either negotiation or client/server protocols. Also some cooperative policies and involved knowledge have been studied, classified and implemented in the robotic testbed enabling sophisticated agent behavior both in terms of cooperation and local control. We also describe several scenaria where different cooperative and conflictual situations arise, in order to discuss our system behavior. A real testbed, whose agents are briefly presented, working with real-time constraints has been already implemented and tested at our laboratory.

Calibration of an smt robot assembly cell

AbstractA new calibration method for an assembly robot cell is described. The proposed method is a combination of a model‐free, numerical, relative robot calibration procedure and a procedure for the robot periphery calibration. Two important simplifications based on the study of an assembly process are introduced into the calibration strategy. A robot is calibrated in a task (Cartesian) space. The robot workspace and the number of calibrated degrees of freedom (dof) in the task space are reduced in accordance with the difficulty measure of the task. An automatic measurement system for measuring the relative robot accuracy was developed. An original principle of transforming the robot endpoint approach distance into the one‐dimensional position displacement error is introduced. The accuracy errors of each particular calibrated dof in the task space is measured separately. The error tables are used in a direct robot calibration procedure that is based on the linear interpolation of the discrete position‐error functions. An iterative inverse calibration algorithm used in a particular robot cell is described. An efficient sensor‐based system for an additional simultaneous robot periphery calibration is presented. The implementation of the proposed calibration methodology in the pick‐and‐place robot cell for Surface Mount Technology (SMT) is presented. © 1994 John Wiley & Sons, Inc.