Linear motors propel genomic print head at speeds that are a blur to the human eye, lifting DNA-rich fluids from a trough, then delivering them in a flash of motion to 25 separate glass slides
Improbable as it sounds, machines now exist that can place characters within a millionth of a metre of the desired locations.
Clearly this is not an office printer, although it combines the precision of a micro-surgical tool with speeds far faster than those current office usage.
It can cross a 1.2x1.2m work envelope in a quarter of a second, then a 'move, stop, and drop' of its cargo in one-inch increments at a rate of 25 times per second.
Incredibly it makes all of its high-speed deposits within a micron of their desired locations.
Like a super-automated eye dropper the machine lifts DNA-rich fluids from a trough, then delivers them in a flash of motion to 25 separate glass slides.
This all happens in under a second and then it keeps repeating the action until thousands or even tens of thousands of drops have been placed.
The technology enables genomics researchers, whose data requirements could choke a supercomputer, to collect far more information than they could ever gather by hand and, as a result, they expect to advance their efforts from the study of a few genes a day to thousands per day.
The ability to quickly collect so much data enables pharmaceutical companies and human genome researchers to come closer to mapping human genes and developing drugs to cure a host of deadly diseases, ranging from malaria to various cancers.
The system integrates an array of state-of-the-art technologies, including linear motors, non-Cartesian actuators, fast DSP-based (digital signal processor) control, full digital control schemes, and very high-resolution feedback.
Comprising of a linear motor-powered gantry robot spanning its X-axis, the gantry robot is built atop two linear motor stages, one at each end, which serve as the foundation for Y-axis motion.
Using powerful linear motors enable its high-speed motion offering peak force of about 200N due to its use of an 'overlapping winding' configuration that is said to provide more power in a smaller package.
With this clever design about 15% to 20% more copper turns in the flux space and as a result of the overlapping concept, the linear motors are said to be about 20% more efficient that those of competitors.
However even with the system's low inertia linear motors to achieve the machine's extraordinary speeds it required a, tight, highly integrated, DSP-based control system.
The key to the system's control is the Umac Turbo controller from Delta Tau Data Systems.
It employs an enhanced microprocessor CPU and an 80MHz Motorola 56311 DSP, which is said to be inherently better suited to serve the needs of this type of machine than ordinary microcontrollers.
The reason they are said to be more suitable for such applications is that DSPs are optimised for fast and repeated mathematical calculations with the highly pipelined maths capabilities easily run repetitive algorithms designed to handle streams of data.
In addition DSP's accomplish this without the need to employ costly state-of-the-art processors and therefore can cut control costs.
Most importantly DSPs provide such applications with a level of servo feedback control that prevents the occurrence of natural instabilities which can sometimes crop up at slower processing speeds.
In particular, they allow a system to apply greater restoring force in response to position errors without fear of a large overshoot.
In general, the faster closing the loop digitally, the higher the gains can be, the higher the gains, the greater the stiffness of the overall system.
As a result of that stiffness the full speed of the linear motors can be employed without fear of positioning problems.
With the processor looking at the system ten times every millisecond, then a higher restoring force can be applied because the system can always be caught before it overshoots.
Furthermore delays are reduced through the integration of fully digital control schemes and direct pulse width modulation.
Unlike conventional control schemes, which typically pass data back and forth between the controller and the drive the Delta Tau system does all of its calculations in one central processor.
Further reductions in delays are possible by doing as little analogue to digital and digital to analogue conversion as possible.
Such conversions typically cause delays to build up thus affecting control loop performance and are a major problem in a servo loop.
The longer the delay the lower the system gain, and the lower the gain, the slower the reaction to positioning error.
The machine resolution was also improved by using Delta Tau's ACC-51 interpolator accessory card, which accepts the sinusoidal input from the encoders.
It essentially 'chops up' the signal, creating 4096 steps per sine wave cycle and as a result the 20-micron sine waves coming out of the analogue sensors are broken into 5nm counts, which account for the system's unusually high resolution.
The precise servo control achieved due to the intelligent use of linear motors, together with tight control and high servo stiffness have resulted in a machine believed to be the fastest and most accurate in its field.
It is even suggested the machine could operate even faster than it does now, possibly in excess of 30Hz or more.
Micromech Systems is an authorised systems integrator for Delta Tau high level, multi-axis motion control products.
