Product category:
Stepper and Servo Drives, Motors, Controls
News Release from: Micromech | Subject: UMac Turbo controller
Edited by the Engineeringtalk Editorial
Team on 27 January 2006
DSP increases robot ability to collect
DNA samples
Combined controller and DSP provides power behind robot helping genomics researchers collect DNA information.
A robot is helping genomics researchers collect more DNA information than they ever could by hand, raising their efforts from the study of a few genes a day to thousands per day With the precision of a micro-surgical tool, the robot can cross a 1.2 by 1.2m area in 0.25s, then move, stop, and drop its cargo in 2.5cm increments at a rate of 25 times per second
All the high-speed deposits are within 1um of their desired locations.
Like a super-automated eye dropper, the machine lifts DNA-rich fluids from a trough, then delivers them to 25 separate glass slides.
This happens in under a second and it repeats the action until thousands or even tens of thousands of drops have been placed.
This ability lets pharmaceutical companies and human genome researchers come closer to mapping human genes and developing drugs to cure diseases from malaria to various cancers.
The system integrates linear motors, non-Cartesian actuators, DSP-based control, full digital control schemes and high-resolution feedback.
Comprising a linear motor-powered gantry robot spanning its x-axis, the gantry robot is built on top of two linear motor stages, one at each end, which serve as the foundation for y-axis motion.
Linear motors enable a high-speed motion with a peak force of about 200N due to the use of an overlapping winding configuration.
With this design there is 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.
But even with the system's low inertia linear motors to achieve the machine's 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 uses an enhanced microprocessor CPU and an 80MHz Motorola 56311 DSP.
DSPs are optimised for fast and repeated mathematical calculations so the pipelined maths capabilities can run repetitive algorithms to handle streams of data.
DSPs do this without using the latest processors and therefore can cut control costs.
Most DSPs provide such applications with a level of servo feedback control that prevents the occurrence of natural instabilities that can occur at slower processing speeds.
In particular, they let a system apply more restoring force in response to position errors without fear of a large overshoot.
In general, the faster the closing of 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 used without positioning problems.
With the processor looking at the system 10 times every millisecond, then a higher restoring force can be applied because the system can always be caught before it overshoots.
Delays are reduced through the integration of fully digital control schemes and direct pulse width modulation.
All the calculations are done by 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; this can be 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 20um sine waves coming out of the analogue sensors are broken into 5nm counts, which account for the system's high resolution.
It is possible the machine could operate faster than it does now, possibly above 30Hz or more.
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