Steed Webzell explores the latest work in robot cell design and layout, discovering simulation technologies are rooted firmly at the heart of best practice.
Gone are the days of marking the reach of robots in chalk on the shop floor to avoid collisions. Today, this vital production engineering function is facilitated at automotive plants by the latest in simulation technologies.
Robot simulation is an essential element of modern and agile auto facilities as it gives manufacturing engineers the ability to visualise and pre-evaluate the performance of robot programs generated off-line. Sean J Murphy, regional sales manager at Fanuc Robotics UK, says three main factors influence cell optimisation: cycle time; path trajectory; and energy consumption.
“Each process can have its own requirement,” says Murphy. “In spot welding it is cycle time, reducing the time taken to travel between points; while applying adhesive to a windscreen requires path trajectory to ensure the material is in the correct position. Meanwhile, energy consumption is a new factor and all Fanuc robots have a facility where the path can be optimised to reduce energy.”
With Fanuc robots, real-time simulations can be prepared by generating a 3D model of the cell and using customer supplied CAD data. This process allows engineers in different countries to work on the same project. Once complete, Fanuc RoboGuide offline program generation and simulation software (with Fanuc real-time clock) has the ability to provide accurate cycle time predictions. The thinking is similar at Comau, which lists integration and cycle time as crucial to cell optimisation. “We place great value on R&D to improve our capabilities in terms of speed, robustness, reliability and precision,” says Arturo Baroncelli, robotics proposal manager at Comau SpA. “As such, issues of quality and productivity are not usually part of the cell layout discussion. Where our customers ask us to intervene is in streamlining the integration process and improving cycle times – using simulation we can predict the actual cycle time to within 10%.”
Comau Robotics and system integrator Comau Body Welding simulate cells together and program the robots offline in order to enhance integration capabilities and reduce installation times. The programming software is then downloaded from the computer directly to the robots so that once in the field, the programming phase is reduced, if not eliminated completely.
Comau is actually able to take the concept of offline simulation and programming one step further, applying it to the company’s patented ‘hollow wrist’ robots which have proved popular in body shop environments. These innovative robots house all of the service cables (power, signals, water and air) inside the forearm and wrist of the robot. Comau says this is not possible with a conventional robot as external cables cannot be simulated.
Taking a holistic view, the primary aim of cell layout simulation is to assess whether all the points in a robot program be reached without risk of collision. Simulation is also used to create motion sequences for the robots, which can be moved around to clarify the execution of the program and system concept.
One such software suite designed for these very tasks is KUKA.Sim Layout from Kuka Robotics. In this, models of cell components can be downloaded from an online library, most of which are parametric in design. For example, it is possible to load a safety fence and adapt its height and width according to requirements. Components can be dragged from the library into the robotic cell and linked with other components by clicking on predefined ‘snap’ points. According to Kawasaki Robotics, safety is one of the principal considerations in any robotic cell design. With this in mind, the company has devised a new intelligent safety system that provides operators with less restrictive and safer access to robot systems. Cubic-S uses dual CPUs that are independent of the robot’s control CPU to monitor speed and position. The monitoring functions of Cubic-S, used with external hardware such as pressure mats or light guards, allow human machine interfaces (HMIs) to be established. Typically, this could allow human intervention for inspection of a component while it is gripped by the powered robot. By restricting the robot’s work space to its programmed operational area, Cubic-S also provides the opportunity to save floor space. Additional in-cell safety equipment can similarly be reduced as the system’s functionality integrates into robot programs to allow the location of peripheral equipment to be considered.
For a glimpse of what robotic cells at auto plants could look like in the future, look no further than the UR10 robot from Universal Robots. Safety fears have always put pay to new ideas requiring humans and robots to inhabit a single production cell but Universal’s lightweight, six-axis UR10 can work alongside personnel and generally requires no safety shielding. How so? Well, the robotic arm deploys patented technology to measure electrical current in its joints and determine force and movement. As soon as an employee comes into contact with the robot arm and a force of at least 150N is exerted, the robot arm stops operating. And there are other benefits. For instance, a simple user interface lets employees with no previous programming experience quickly set up and commence operations. Intuitive programming is facilitated by a graphical user interface combined with a ‘teach’ function that allows the user to simply grab the robot arm and show it how a movement should be performed.
Daimler AG is reported to be one auto company exploring this area, having signed an agreement with Kuka that focuses on safe human-robot co-operation in tasks such as assembly and in-vehicle screw applications.
Direct human-robot interaction makes it possible to employ trendsetting manufacturing concepts, where a lightweight robot acts as a worker’s ‘third hand’. The lightweight robot earmarked for the task was originally developed by the German Aerospace Centre (Deutsches Zentrum für Luft- und Raumfahrt) for use in outer space. Its sensitive motorised grippers give it a delicate touch, which enables it to handle objects gently and perform difficult tasks precisely. The robot can be positioned and set-up to optimally support workers ergonomically. As an example, the lightweight robot takes over and performs tiring tasks such as steps that involve handling items overhead. Working with and handling the robot is said to be straightforward and intuitive, which reduces programming time and increases process efficiency.