Control at the leading edge

Advanced control is key to achieving unprecedented levels of performance and precision in a range of industries and cutting edge research Controllers from Delta Tau are being used in some of the most leading edge research and development projects in the UK with unprecedented requirements for precision and reproducibility. These include most of the movement mechanics associated with the Diamond Light Source Synchrotron nearing completion on the Harwell Chilton Science Campus, a project to develop bench top sized machines capable of machining to nanometre precisions, robotic test systems for cars, ultrasonic aircraft wing inspection systems and exceptionally accurate machines for diamond cutting and turning. Andy Joslin, managing director of Delta Tau (UK) told us: "We now have a lot more business in the research environment than we ever did before." The most prestigious example in the UK is supplying most of the motion control for beam control and the hexapod specimen carriages for the Diamond Light Source. This £380 million project is a largely X-Ray light source, a trillion times brighter than the average medical X-Ray tube with what will eventually be 48 take off points at which to conduct experiments at the very cutting edges of materials and medical research. Mr Joslin said of the application, "None of the tasks did we consider to be particularly arduous apart from the hexapods, which offer the ability to scan specimens and gather data in real time." There are many hundreds of axes to be controlled in the facility, mostly using stepper motor technology, despite predictions in the industry a few years ago that steppers were not the best technology to go with. Stepper motors, however, are particularly suited to this application because they are much more robust than servo motors and have no sensors that might be damaged in the hot radiation environment. The controllers in this application are VME Turbo Ultralight Motion Controllers connected via fibre optic cables to a macro rack that is in turn connected to the stepper drives and amplifiers and thence to the motors. It is possible to drive up to 32 motors from one controller. The motors are currently being installed on the first four beam lines. A nano machine tool development forms part of the European Union's (EURO)21.5 million, 36- partner, MASMICRO project aimed at developing an integrated production facility for the mass manufacture of miniature and micro components. As part of this, Professor Kai Cheng at Brunel University is leading a project to develop a bench top, 5-axis micro-milling machine for manufacturing miniature and micro components to namometre precisions. Delta Tau has provided a CASE studentship bursary to support the project. At those precisions, Andy Joslin explains: "We would normally have expected to use analogue amplifiers with sinusoidal commutation, but when we commissioned our PWM drives, we obtained considerably better performance." Intended applications for the machine tools include the manufacture of MEMS, optical, medical and mechanical components and dies. Work piece materials include: silicon, glass, polymers, aluminium, non ferrous and ferrous metal alloys up to and including hard steel. An air bearing slide way and rotary table with improved damping capacity has been developed, as has an ultra high speed air bearing spindle and a piezo driven fast tool serve system. It was already proved possible to produce a mirror-like surface with a surface roughness (Ra) of less than 10nm by diamond turning aluminium. But it is not just in research but in routine production that Delta Tau controllers are proving to be crucial to achieving extreme performances. Coborn Engineering in Romford uses the controllers in their latest three axis, 20kW pulsed YAG laser machine for cutting synthetic diamond as well as machines for grinding p- cubic boron nitride tool tips. Diamond turning machines made by Taylor Hobson maintain a sub-10 nanometre finish with sub-100 nanometre accuracy. The machines have oil bearing slides with conventional DC brushed motors, a design about to be upgraded with PWM amplifiers. Midas NDT uses Delta Tau controllers in their ultrasonic inspection systems for composites. The machines work by inserting ultrasonic signals down a jet of water impinging on one side of a structure while read out is through another jet of water impinging on the other side. An obvious application is for the inspection of aircraft wings. A machine now being commissioned in Malaysia has two 6-axis robots, one on each side, both of which have to be tightly synchronised. The controller in this case is a PMAC PCI Ultralight connected by optical fibre to Geo Macro amplifiers on the moving parts of the machine, which is 50m long. In another field of activity, very large format Inca Digital printers require micron accuracy in order to avoid unsightly banding that can otherwise occur between different sections. And working with Anthony Best Dynamics, it has been possible to develop a vehicle steering robot that combines advanced motion control and GPS information to consistently perform repeated manoeuvres such as the elk avoidance test. Tools for the job "One of the technologies we are finding to be particularly successful is the UMAC System in terms of its flexibility and power," Andy Joslin explains. UMAC stands for Universal Motion and Automation Controller and the system offers up to 32 axes of motion control, expandable up to 128 axes. It can come with interfaces to "every kind of feedback device", including sinusoidal encoder/interferometer feedback with 4096x interpolation, SSI, Hiperface, Yaskawa, Mitsubishi encoder inputs, 16-bit resolver to digital converter inputs and MLDT feedback inputs. I/O protocols supported include DeviceNet, Modbus, Profibus, CanOpen, ControlNet and CC Link. The technology is in the process of being further enhanced in the Next Generation Power PMAC and Power UMAC products, which it is claimed, are faster than any other controllers currently available with even more powerful forward and inverse kinematics and lookahead, "C" programmability, enhanced debugging and diagnostics, and Matlab and Simulink connections. Alternatively, PMAC2A-PC/104 controllers for 4- or 8-axis control are suitable for OEM integration. And the company's Geo 'Book' and 'Brick' IGBT based amplifiers are aggressively priced with outputs up to 15A continuous, 30A peak. Delta Tau Pointers *UMAC controllers offer up to 32 axes of motion control, expandable up to 128 axes and can come with interfaces to feedback devices that include: sinusoidal encoder/interferometer feedback with 4096x interpolation, SSI, Hiperface, Yaskawa, Mitsubishi encoder inputs, 16-bit resolver to digital converter inputs and MLDT feedback inputs * The advanced PMAC2A-PC/104 controllers for 4- or 8-axis control are suitable for OEM integration * Geo 'Book' and 'Brick' IGBT based amplifiers are aggressively priced with outputs up to 15A continuous, 30A peak