Paul Stevens looks at developments in industrial robots.
As European member states' economies start to recover from the recession, manufacturing companies are seeking ways to ramp up production in a flexible way. One option is to use industrial robots, which are now more cost-effective both to purchase and to implement, thanks largely to programming software that is more engineer-friendly.
With robots now being simpler to integrate, there is increasing competition among manufacturers to add functionality so they can offer increasingly sophisticated systems. For example, Maurice Hanley, Fanuc Robotics' sales and marketing manager, says: "Fanuc robots now come with onboard vision so there is no need for engineers to get bogged down in interface and connectivity issues."
For industrial automation the four main types of robot are Cartesian (gantry) robots, Selective Compliant Articulated Robot Arm (Scara) types, anthropomorphic robots that typically have five or six axes, and Delta (parallel kinematic) types. Hanley adds: "Scara still leads in the electronics sector, but the speed of the standard arm has improved to rival that of Scara now. A Cartesian robot more closely matches the motion of a human arm where manual tasks need to be automated."
In a partnership between BAE Systems and the UK MOD, known as Munitions Acquisition - the Supply Solution (Mass), a manufacturing facility has been commissioned for machining artillery shells. The new manufacturing unit removes operators from potentially hazardous areas, occupies one-quarter of the space, requires four fewer operators per shift, enhances product quality and increases available capacity. The system comprises four robotic manufacturing cells capable of independent operation to allow maintenance and retooling to be undertaken without interrupting production. The system is designed to manufacture both 105mm and 155mm shells, with quick changeover routines embodied within the manufacturing processes.
Each of the four Fanuc robots has a gripper to handle the shell either on its outside diameter or on the fuse bore. One cell includes an inspection system into which the robot loads and unloads machined shells. In another cell the robot picks and loads a driving band to a machined groove, which is then press-fitted.
Picking the best
It is not always a simple choice between Cartesian and Scara robots, and some applications can benefit from the use of both, as Ricoh found when it automated the assembly of toner cartridge shutters. Ricoh design engineer Matt Talbot says: "In the past, pick-and-place activity was done by pneumatics or by hand. Our experience was in small assembly jigs, so this project was a big learning curve."
Evershed Robotics suggested using a combination of a Toshiba Machine TH650 Scara robot, a Toshiba Machine Cartesian robot to work with six bowl feeders, and a rotary index table (Fig. 1). This system assembles five components in 7.5 seconds and operates for three shifts per day, six days a week. After the parts are unloaded, they are stacked in trays before being moved to the next stage of the assembly line.
Talbot comments: "The parts are quite delicate, and some of the seals can be easily dislodged, so we need precision. The Scara robot uses sensitive parallel grippers to pick a raw body from a bowl feeder and place it on the table. Then, from the next unit clockwise around the table, it picks up a completed assembly. This assembly is then rotated through 90 degrees so it is in the correct position to be packed and secured. To do that process with pneumatics would have been a nightmare - we have 72 positions on the packing tray!" The packing trays are supported by a Cartesian robot, held by a vacuum attachment, and the 72 pockets in the tray are arranged in an eight-by-nine array (Fig. 2). Talbot adds: "Without the robots and the automation, the cost of doing this job manually would be very high, and the quality of the assembled parts could not be guaranteed."
On a somewhat larger scale, Kuka is playing a key role in developing an innovative automated system for assembling complex aircraft structures in collaboration with Airbus. This system performs a variety of drilling and fastening tasks on the upper and lower wing covers of a lateral wing box demonstration unit being built at the Airbus facility in Filton.
Kuka's collaboration with Airbus is part of the EUR100 million, EC-backed, Advanced Low Cost Aircraft Structures (Alcas) project that aims to identify new composite manufacturing and assembly strategies. One of the project's main objectives is to improve efficiency by using a horizontal wing build philosophy instead of the conventional vertical manual method, which is a time-consuming and labour-intensive process.
Markus Gruber, Kuka's aerospace manager, says: "An effective assembly system was devised that incorporates Kuka's 18-tonne payload Omnimove, a mobile positioning device that provides an alternative to using a crane for manoeuvring the carbon fibre wing covers into the jig.
"The Omnimove is also used to position a pair of platform-mounted Kuka robots for drilling holes in the lower wing cover. The assembly system also includes an identical pair of robots installed on a high-level gantry for the upper wing cover operation" (Fig. 3).
Two of the robots are equipped with an adaptive guidance system for monitoring the accuracy of the drill head position, while the others feature a multi-function end effector that is designed to drill holes ranging in diameter from 6-22mm in materials up to 110mm thick. The design offers a choice of spindle systems for axial and orbital drilling capabilities, as well as other integrated features such as a fastener insertion facility and non-contact optical measurement probe.
The integration of robots within intelligent manufacturing systems is something with which Mitsubishi Electric is also involved. Robot technology from Mitsubishi Electric now allows the economical use of flexible location robots in production environments; even during the movement of the robot arm, the robots react to changes in their environment and adapt their trajectory to suit. Cleverly, the self-positioning of the robot and the pinpointing of other moving objects within the workcell are achieved without the use of an image processing system. Moreover, the sensor-guided real-time control does not require elaborate programming.
A key element of this flexible handling technology for industrial automation is the VRFloor (Virtual Reality Floor) positioning system developed by Robotics Technology Leaders. This utilises passive markers with a constant identity, sensors for registering the marking points, and a control computer for analysing the information. The markers are fitted beneath the floor, and an air cushion provides for smooth motion of the robot both within the workcell and between production stations.
Sensors are fixed on the base of the robot and to other moving objects in the working area such as workpiece carriers. With this set-up it is no longer necessary to align and position workpieces precisely when they are fed into the workcell.
Dr Stefan Riesner, the managing director of Robotics Technology Leaders in Munich, comments: "To be able to make robots and manufacturing stations so flexible, a real-time controller is indispensable." The fast interchange of data between sensors and controller puts the robot in a position to react directly to changes in the work area and to determine its trajectory during movement on the basis of current sensor values. A computer calculates the movement information from the signals and transfers the position data to the robot controller, typically within one to ten milliseconds. For a 15cm curved motion of the robot arm, which takes place in a period of three seconds, for example, 1500 positions must be transferred to the robot controller within a cycle time of two milliseconds.
Riesner concludes: "The reliable self-positioning of the mobile robot dispenses with the need for the often highly time-consuming and expensive programming, which frequently makes it unprofitable to use stationary industrial robots, particularly for small batch sizes, high numbers of variants and quick product changes."
Aside from the developments in industrial robots outlined above, it is worth mentioning the project that Festo unveiled at the 2010 Hanover Fair. The Bionic Handling Assistant is not a saleable product, but Festo's demonstration of a design concept to stimulate dialogue with customers, suppliers and partners. Inspiration for this concept came from elephants' trunks, and the result is said to be a flexible and safe means of moving objects from one position to another. As well as a flexible arm, the Bionic Handling Assistant has a 'wrist' axis with a ball joint, and a gripper with adaptive fingers (Fig. 4).
In the event of a collision with an object - including a human - the Bionic Handling Assistant yields immediately, without modifying its desired overall dynamic behaviour, and then it resumes its operation when the obstruction is removed. Unlike heavy industrial robots, the Bionic Handling Assistant is said to be characterised by an excellent mass-to-payload ratio, provides smooth operating motion with more degrees of freedom, and makes very efficient use of resources.
Nobody would suggest that robots are perfect for every manufacturing operation, as there will always be some for which dedicated special-purpose automation systems are more appropriate, and others for which manual assembly is better suited. However, having made workers redundant during the recession, and faced with competition from low-wage economies, many manufacturers are taking a fresh look at how robotics might help them to meet rising demand.