Final Trim and Assembly gets the robot touch
Michael Larsson, MD of Business Line Automotive OEMs at ABB Robotics, explains how the company’s Dynamic Assembly Pack is addressing the key challenges that have previously held back the use of robots in Final Trim and Assembly applications
Automotive manufacturing has been a leading exponent of robotic automation, and we have become accustomed to seeing robots used in welding and painting car bodies, and installing heavyweight items such as engines and drive train components. The advantages of speed of production, accuracy and repeatability of welding lines and paint deposition, together with avoiding injury for staff through repetitive or arduous tasks, have seen them employed widely in these applications.
However, the area of Final Trim and Assembly (FTA) is one part of the car plant where robots have so far failed to make a major impact. This has mainly been due to the complexity of assembly tasks and speed of FTA production lines, and has resulted in FTA having a much lower level of automation compared to other production areas. In fact, less than five percent of today’s FTA lines benefit from robotic automation.
One of the main challenges in the automation of FTA is the desire by manufacturers to produce many different models and variants of vehicles, such as left and right-hand drive, two- and four-door, on the same assembly line. Add in the installation of cockpit, seats, carpets, and windows, each with a number of different specification options and colours and the complexity grows.
The car body is usually transported to the FTA station on a conveyor, suspended conveyor system, or an automated guided vehicle (AGV). Using robots in FTA applications has also faced the challenge of the inherent vibration of AGVs or conveyors or variations in the speed of the production line.
For successful assembly of components by a robot, for example, accurately hanging a door or bolting a cockpit, the system must be able to accurately follow a moving body. It must be capable of continuously adjusting position and speed of its approach to ensure there is no danger of colliding with the vehicle, which could damage finished paint work. With an average cycle time of assembly tasks of just 60 seconds, the robot must be able to hit the exact spot in order to secure the component to the body or interior.
These factors have made it difficult to accurately align parts with the car body, introducing the need to either slow down or pause production for them to be fitted properly. Inevitably, this increases production times and cuts productivity.
Meeting the movement challenge
ABB has solved the challenges relating to FTA operations, through the development and application of products and technologies. These include its IRB 6700 and IRB 2600 robots, advanced image processing, sensing and the safety-certified SafeMove2 human-machine collaboration software.
The Dynamic Assembly Pack is a new cell solution that makes use of many of these technologies. It allows the robot to work in concert with a moving car body and adapt its own motions precisely to accurately assemble components to it. The cell uses a Universal Video Tracking (UVT) camera that allows the robot to precisely track the position of the car body as it enters the workstation, either on an AGV or conveyor.
As the robot travels parallel to the AGV, the tracking system also synchronizes its speed with that of the AGV. The camera also reports the colour of the body, ensuring that the vehicle model is fitted with appropriate components.
The cell also allows the robot to compensate for any unexpected movements or vibrations – once the car body reaches a pre-defined position, another vision system, the Compliant Vision Guidance (CVG) camera, mounted on the robot arm, scans it for consistent reference points, such as door edges. By taking images at a rate of 30 to 40 frames per second, the CVG camera determines whether the attachment point is where it should be and if any adjustments are needed to ensure that the part being attached is positioned exactly as needed.
One possible issue is that ambient lighting may affect image quality, leading to the risk of inaccurate positioning. To help compensate for this, both cameras incorporate LEDs to provide consistent illumination.
Using robots in FTA applications has faced the challenge of the inherent vibration of AGVs or conveyors or variations in the speed of the production line
Feel the force
Capable though the cameras are, basic physics dictates that they will lose focus as soon as the arm of the robot gets close to the vehicle. It is here that the system switches from a vision-controlled system to one that relies on a mechanical sensor. The ABB Integrated Force Control technology allows the robot to respond to its environment even when the cameras cannot see. In other words, it can sense its way around assembly operations with a precision that can be measured in millimetres. The robot adapts its programmed lane and speed based on feedback from the sensor, which allows it, for example, to hang a door exactly in the hinges provided.
The Force Control sensor is mounted on top of the sixth axis, directly between the robot and the gripping system. This means that the system can accurately measure the force at all times. The sensor also needs to be able to react to changes at any time, for instance, when the robot must slow down because the AGV is running slower. For the system – and hence, the robot – to sense its way through an assembly situation and dock with no more than the necessary force, the optical system and Integrated Force Control must harmonise exactly with one another, a feat achieved through appropriate programming.
The requirements for automated assembly in a continuously moving process are complex. Yet, they can be reduced if car models are created on a common platform, all having the same body and with their points of connection to the grippers always being the same.
For carmakers building completely new manufacturing facilities, this model platform concept allows them to construct an open system, avoiding the need to integrate individual automated processes into existing lines. For Final Trim and Assembly, open systems mean that automated guided vehicles approach individual automated assembly stations as required.
These open systems also require a completely new level of collaboration between human and machine, demanding a high degree of safety. To ensure this, ABB has developed SafeMove2. As a safety-certified solution built from ABB’s software and hardware components, SafeMove2 allows operators to work safely with the robot system at high-speed during high cycle times.
SafeMove2 cuts costs while providing uncompromised safety by making it easy to install an application that needs no enclosure. Like its predecessor, the original SafeMove, SafeMove2 includes many cutting-edge safety functions, including safe speed limits, safe standstill monitoring, safe axis ranges and supervision of position and orientation.
A safe distance between operators and robot is maintained through the use of safety sensors, laser scanners, and light barriers. Sensors in the robot cell report the presence of an operator. The system then automatically reduces the robot’s speed when a worker approaches, allowing the human and the machine to operate side by side. The robot controller allows the robot to operate only in precisely calculated, predetermined spaces, forcing it to come to a complete stop when this invisible boundary is crossed.
If the operator leaves the defined safety area, the system continues carrying out its task at its initial set speed. Up to four robots can be monitored for tool position, tool speed, and tool orientation. With SafeMove2, car manufacturers get a system that minimises the cost of FTA safety enclosures and which can reduce total investment by up to 30%.
Advanced cells able to work in a highly open and adaptable system, working safely yet quickly, are the key to the highly variable needs of FTA, allowing manufacturers to make a range of different models to meet market demands.
Driving towards greater certainty
With the ability to respond quickly to changing conditions, robots are a great way of providing certainty in uncertain times. With today’s vehicle manufacturers facing an unprecedented raft of challenges, from whether to ramp up production of EVs through to coping with falling consumer demand caused by the Covid-19 pandemic, the inherent speed, efficiency and flexibility afforded by robotic automation represents an ideal way of being able to respond to sudden changes in demand. With the needs of the Final trim and Assembly stage now addressed by a robotic solution, automotive companies can finally move towards enjoying the benefits of totally automated production lines.
For more information, visit the ABB website here.
You have to calculate whether spending money on robots makes sense over the longevity of the product, especially as the investment is mainly bespoke to a vehicle – Mofid Elkemiri, LEVC