Unison's (www.unisonltd.com) new Uni-vercell machine packs a complete end-to-end loading/end-forming/bending and vision inspection process in the space typically required for a standalone tube-bending machine. It breaks new ground in terms of performance and compactness by exploiting an articulated robot arm to manage all the intervening movements and transfers. The arm eliminates the need for the conventional carriage of a tube-bending machine, and also optimises manufacturing precision because it retains the part for the duration of the process - eliminating a lot of hardware in the process.
The tube-bending and end-forming processes, and general operational control of the cell, are handled by the Powerlink system, based on the NextMove e100 machine controller from Baldor. This controller manages four MicroFlex e100 servo motor drives which control the tube bending head's clamp, pressure die and bend arm axes, plus the actuation of the end forming tool for flaring and/or compressing. In addition to these core functions, the controller manages all of the cell's I/O, plus the link to the front end user interface.
A compact footprint was one of the key design objectives, and Unison believes the simple daisy-chained nature of the high speed Powerlink network reduced the electrical system's size, as well as the wiring and system building tasks, by something in the region of 50% compared with conventional analogue motion control.
Powerlink was also selected as the control platform for a number of technical reasons. For this project, the 100Mbit/s network provides sufficient bandwidth to control each motor's position and torque parameters - control mechanisms that provide ultra-precise control over the bending process and which are not normally possible with a traditional analogue interface.
The network also facilitated easy deployment of all of the local I/O required for the cell's operation. Some I/O resides directly on the controller, while other I/O is located on the distributed servo drives - yet is still controlled in software as if it were local. The cost of this remote I/O was also minimised. As the Powerlink industrial Ethernet standard is compatible with CANopen device profile, readily available CANopen I/O modules can be used with ease.
Another reason behind Unison's choice of industrial Ethernet protocol was system expansion and evolution. The new cell is designed for the repetitive production of mass volume parts such as automotive fuel, water or hydraulic components, and the bill of materials is a major consideration. Their system has no front end user interface; instead, this resides on a laptop that is connected, as required, to the cell's controller, in order to download a production program.
However, Unison also expects the cell concept to appeal to more general metalworking fabrication companies, who manufacture in smaller batches, and for this application it's likely that a local man-machine interface will be required. Using a standard Powerlink gateway device, the cell can easily be connected to a PC or conventional Ethernet network.
Motion control axes can also be added for more complex end-forming, or labelling/marking functions. Most conventional motion controllers handle only a discrete number of axes, but with Powerlink and the Baldor controller, the number of axes and other network-located functions such as I/O is almost unlimited. Such flexibility enables the machine to be adapted for future applications. Unison's lead engineer on the Uni-vercell project, Mike Kay, takes up the story:
"Powerlink hardware reduces the system building complexity, and the software support on Baldor's controller made it particularly easy to develop. For this machine I managed to programme the first iteration in just two weeks, which speaks volumes about the simplicity of the control system and the development tools."
Unison's Uni-vercell delivers remarkable performance. It can fabricate parts to an overall accuracy of 0.1 mm, and while it is optimised for repetitive volume applications, the flexibility of the robot arm allows it to be configured easily for batch production as well. Accuracy and repeatability are assured, because of the system's use of closed-loop electronic control. This drift-free performance also means that the machine can be instantly set up to fabricate parts at the upload of a program, rather than making and scrapping trial parts until the configuration is right.
The cell is designed for continuous use and can easily fabricate thousands of parts a day. With a typical energy consumption of around 1.5kW (measured using an example part with three bends and one end form, including stacking at the end of the process, and 100% inspection), daily electricity running costs are around seven Euros.
The software-controlled nature of the machine delivers many further technical advantages, including much greater control over the bending process. Fine adjustments to torque levels or movement profiles can be made, for example, to optimise bend quality. Complicated shapes that might be difficult to make on a conventional hydraulic unit can also be produced easily, because the machine is able to make intervening adjustments or moves between stages - to avoid a collision for instance. This programmability can equally be exploited to optimise cycle time - by making only the minimum movements required.
Programming the cell for an application can be achieved very rapidly thanks to Unison's powerful front-end software package, Unibend, and the friendly teaching software supplied with the robot. Programming bends and end forms requires only the input of data such as position, angle, rotation and torque, and the machine sets up automatically. All of the intervening movements are programmed by manually positioning the arm and capturing the relevant data. Using these simple techniques, a complete cell program can easily be produced in less than an hour.
The fabrication processes and movement-related operations are also discrete stages of a cell program, allowing modifications such as fine tuning of bending or end-forming, or movement optimisation to be made quickly, and without generating a new program.